Metal oxides and polysaccharides: an efficient hybrid association for materials chemistry

Abstract

Metal oxides and polysaccharides in nature and in laboratories: limits and aims of the review. Part 1: Different ways to associate metal oxides and polysaccharides. Part 2: Controlled growth of metal oxide nanoparticles throughout polysaccharide fibers. Part 3: Biotemplating and bio-replication on the micro- to nanoscale. Part 4: Chemical transformation of polysaccharide fibers by mineralisation. Perspectives and concluding remarks. Biopolymers and inorganic minerals are often associated in nature, and living organisms benefit from these materials with a sophisticated and hierarchical architecture. Inspired by nature, chemists have tried to extend these combinations by associating natural polymers with inorganic materials that do not occur naturally in living organisms. In this review, we propose to focus only on research conducted on the association between polysaccharides and metal oxides. Over the last 10–15 years, substantial research has been focused on finding ways to combine these two types of materials, with the goal of mastering the morphology, porosity, composition and structure of the hybrid materials (metal oxide@polysaccharide) or pure metal oxides obtained after polysaccharide elimination. There are many possibilities for interactions between metal cations and the chemical functionality of the carbohydrate, thus allowing different approaches, as the structure and functionality of the polysaccharide are of major importance. Because of the sophisticated architecture that can be achieved on the one hand, and the potential sustainable use of these biopolymers (a green approach) on the other hand, these material elaboration processes offer a unique way for chemists to prepare functional hybrid materials and metal oxides (e.g. luminescent materials, catalysts, absorbent materials, magnetic composites, anode and photocatalyst materials). To be as comprehensive as possible, this review is limited to some natural polysaccharides. After contextualisation, we successively considered metal oxide growth control by biotemplating, the replication of raw and refined polysaccharide templates, ending with a discussion of the most recent approaches like mineralisation.

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B. Boury

Prof. Bruno BOURY obtained his PhD in 1989 from the Université Montpellier 2 (Dina-Surdin awards) supervised by Pr. Corriu. After a postdoctoral year in Pr. Seyferth's laboratory at MIT, he joined Flamel Technologies Company in Lyon and then UM2 as an assistant professor (1994). After habilitation in 2000, he became full professor by 2004. His research interests focus on the syntheses of inorganic and hybrid materials prepared by high or low temperature processes of specially designed molecular precursors. He is now interested in the integration of natural products in this field or research on greener synthetic processes.

S. Plumejeau

Sandrine PLUMEJEAU is currently a PhD student in hybrid materials and membranes at the Université Montpellier 2 (Institut Européen des Membranes and Institut Charles Gerhardt). She is working on TiO2 from natural fibers to make photocatalytic membranes for water remediation. After receiving a master's degree in energy and sustainable development (CMP@ED^2), her research interests focus on materials for sustainable development.

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Introduction

Biopolymers and metal oxides

Living organisms depend on abiotic factors such as the composition of inorganic solids with which they are in contact, and in turn they contribute to transformation.⁷ At the same time, very early in evolution, inorganic materials were incorporated into structures of living beings such as exoskeletons of diatomaceous organisms, shells or corals,⁸ endoskeletons of sponges, fishes and animals,⁹ macro- or nanoparticles (otoliths of fish and mammals, magnetosomes of magnetotactic bacteria).^4,6,10 However, besides what we learn from nature, chemists can now consider new types of mineral/biomaterial associations with objectives that differ completely from those found in living organisms.

A limited number of minerals are used by living organisms (mainly silicon oxide, carbonates, and some phosphates, oxalates and sulfides), whereas the chemist takes advantage of every opportunity offered by the elements of the periodic table. Contemporary chemists also strive to use all sources of renewable materials and the ultimate goals of chemists when using materials may differ completely from the natural functions of the same materials. Therefore, besides the substantial amount of research focused on the natural interaction between mineral and living processes (upper part of Fig. 2),^8,9,11–14 the field of research with the aim of producing new materials required for energy, health and environmental applications is growing (Fig. 1). In nature, metal oxides are generally not closely associated with polysaccharides but more with proteins, with the latter currently being studied for their involvement in the nucleation and growth of inorganic materials in living organisms.^11,15–18 MO@PS therefore represents a new field of research.

Fig. 1 Example of PS@MO synthesised in laboratories (A, B, C) and found in nature (D, E, F). (A) Titania replica of natural cotton fibers by sol-gel impregnation (Reprinted with permission from ref. 1, Copyright (2003) American Chemical Society). (B) Dispersion of ZnO particles along bacterial cellulose fibers (Reprinted from ref. 2, Copyright (1959), with permission from Elsevier). (C) TiO₂ replica by mineralisation of filter paper with TiCl₄ under anhydrous conditions (Reprinted from ref. 3, Copyright (2013), with permission from Wiley and Sons). (D) Uranium oxide nanoparticles on fungal hyphae (Reprinted from ref. 3, Copyright (2007), with permission from Wiley and Sons). (E) Natural diatomite from a Borownica deposit in Poland (Reprinted from ref. 5, Copyright (2010), with permission from Elsevier). (F) Magnetite nanoparticles in Magnetospirillum magnetotacticum (From ref. 6, Reprinted with permission from AAAS (Copyright 1998)).

Fig. 2 Fields of research involving combinations of different PS and many different metal oxides.

Context and objectives of the review

Plant fossilisation studies and the characterisation of cellulose structures were probably the first investigations related to this field, followed quickly after by the use of soluble polysaccharides in the sol–gel process and the templating of natural fibers and crystals. The interest in MO@PS is the result of knowledge and processes concerning polysaccharides and also the demand for metal oxides, mixed- or doped-metal oxides and even MO@C composites.

MO is high in demand for industrial and high-tech applications, their properties being substantially altered by the porosity, crystallinity, morphology, doping, particle size and, last but not least, their arrangement in hierarchical structures from the macro- to the nano- and micro-scale (for example in the case of TiO₂,^19,20 and other oxides in electrochemical devices²¹ or sensors²²).

On the other hand, polysaccharides are hugely diversified in terms of structure and functionality, and those not requiring purification are among the “greenest” possible materials. Their shaping at the nanoscale has also definitively opened a new area with the production of nanocrystals, nanorods, nanoplatelets, nanofibers or aerogels of various biopolymers.^23–28 Recently, a new type of polysaccharide was introduced in this field, i.e. exopolysaccharides (EPS) produced by microalgae and cyanobacteria for their phototaxis, has been used for photo-patterning and mineral replica.^29,30

Therefore, at the crossroads between these two materials science domains (MO and PS) there are different fields of research: enhancing the conversion of PS into renewable fuels and chemicals, transforming PS into functional carbons, using them as modifiers of the MO surface, combining them into nanocomposites, etc.

Here we assess the usefulness of PS in the MO preparation process to control MO synthesis, in terms of size, morphology, porosity, composition, etc. The interplay between MO and PS is at a different level: in controlling the chemistry leading to MO formation, in MO molding (morphology, size, porosity, etc.), and also in the chemistry that is involved upon PS elimination or transformation.

Limits of the review

We will not consider the following issues, for which the reader is directed to possible references (among others) and that are closely connected to the topic of this review: micro- and nano-casting of wood^31–37 or textiles³⁸ by metal oxide powders, impregnation of wood as precursors of SiC or SiOC,³⁹ PS-to-carbon synthesis,^40–45 PS-to-biofuel and chemical synthesis,⁴⁶ preparation of catalysts,⁴⁷ PS in electro-conductive composites,⁴⁸ MO@PS as a material for biotechnology for enzyme support,⁴⁹ bacteria encapsulation,^50–53 coating of MO nanoparticles by PS or modified-PS (for diagnosis, therapy, catalysis and remediation).^54–56 Interested readers are also referred to the literature on magnetic nanoparticles,^57,58 or metal and metal hydroxides.^27,59–61

To be comprehensive as much as possible, we limited this minireview to a few natural polysaccharides like cellulose, chitosan, chitin, amylose (starch), alginate and carrageenan. Related publications with a broader scope are also recommended.^24,62–68

Part 1: the different ways to associate metal oxides and polysaccharides

In nature, microorganisms can form deposits of nanoparticles of different inorganic compounds, and in some cases of metal oxides or hydroxides of metals such as iron, manganese or uranium, these processes are important for biogeochemical cycles of metals throughout the environment.⁴ Mineralisation processes generally involve proteins, but some of them are glycosylated.^69,70

In laboratories, among the earliest work dealing with associations of cellulose and inorganic materials, one can mention, back in the 1940s, the infiltration of cellulose with inorganic salts to produce a “metallic shadow casting” to improve the contrast of the cellulose in the early age of microscopy.^71,72 The formation of inorganic phases was not pursued at that time. Later, different researchers, focusing on assessing the fossilisation process of wood and algae, performed infiltration and impregnation of these materials to produce their silification.⁷³ Amongst early work on the formation of metal oxides with polysaccharides one can mention the patent of Union Carbide^74,75 by Elliot and Huggins on NaAlO₂–Al₂O₃.⁷⁶

Otherwise, progress in the sol–gel “Chimie douce” and periodic mesoporous silica fields^77,78 has also probably generated ideas. Before the use of glucose as a template in the synthesis of mesoporous silica,^79,80 polysaccharides were first considered as templates that can control the growth of functional MO particles at the nanoscale, as an alternative to the Pechini method: photocatalyst TiO₂ ^81,82 and magnetic Fe₂O₃ nanoparticles prepared with cellulose or alginate,⁸³ superconductor YBaCuO prepared with cellulose^84,85 or luminescent LaMnO₃ prepared with starch.⁶⁰ Sol–gel remains the most suited process to take advantage of PS, but alternative approaches (PVD, ALD, mineralisation) recently paved the way for alternative formation of MO@PS hybrids and templated metal oxides (see Part 3).

Sol–gel is indeed well suited for coating complex shapes, but the use of PS in sol–gel processes goes far beyond this application. It quickly became evident that PS have several advantages during the sol–gel process: (a) they are compatible with many green chemistry principles, (b) PS provides flexible scaffolds/porogens for monolithic nanocomposites and can be easily removed, (c) their hydroxyl groups are reactive in promoting/accelerating polycondensation, or in sequestering cations [Mⁿ⁺] or hydroxylated cations [M(OH)^m+] that can undergo nucleation/growth processes, somewhat similarly to citric acid in Pechini's process, (d) entanglement of PS fibers defines a macro- to nano-cavity that can stabilize nascent MO and control their growth, (e) many simple PS characteristics (MW, solubility, functionality, concentration, etc.) can induce different MO structures and properties.

Four main different approaches can be tentatively classified as follows:

(1) the use of dissolved PS in homogeneous solution or as hydrogels into which a metal oxide precursor is introduced. Therefore, the polysaccharide is expected to control the chemistry and growth of the nanoparticles (situation A in Fig. 3);

Fig. 3 A general overview of the different approaches in which PS is introduced as a biotemplate for the preparation of MO@PS, the latter being an intermediate leading, after PS removal, to MO. Alternatively pyrolysis under an inert atmosphere leads to the MO@C composite.

(2) PS is used as an insoluble template onto which a more or less dense layer of metal oxides is formed/deposited. Here the PS fibers are considered as a mold for the preparation of hollow or porous oxide structures (situation B in Fig. 3);

(3) the reaction and therefore the chemical transformation of the fibers with a metal-containing reagent. In contrast to the two previous approaches, here the polysaccharide is a template and an O-source for oxide formation (situation C in Fig. 3);

(4) the impregnation of polysaccharide fibers by ready-made MO nanoparticles as a filler (situation D in Fig. 3). This is frequently carried out for the treatment of textiles, packaging, papers, etc. This is a whole world in itself and is beyond the scope of this review; see, for example, pre-formed silicalite nanoparticles mixed in starch gel,^86,87 or preformed luminescent particles LaVO₄:Ln³⁺ nanorods in cellulose gels,⁸⁸ or preformed silica nanoparticles for the preparation of chitosan-silica for separation membranes,⁸⁹ or chitin/TiO₂ needles for tissue engineering scaffolds.⁹⁰

This classification does not account for all situations, thus there is no clear limit between a deposit of some nanoparticles distributed along the fibers and complete coverage of these fibers by these nanoparticles. In addition, it is sometimes difficult to distinguish between PS “truly dissolved”, fibers that form a gel (more or less solvated and concentrated) and “totally insoluble” fibers. This question is becoming even more complicated because of two advances: new nano-sized polysaccharides (nanocrystals, nanofibers, aerogels) and new media in which fibers are “dissolved”, e.g. NaOH/urea,⁹¹ DMSO/TBAF,⁹² or ionic liquids.^93,94 Regarding this, there is growing interest in the preparation of hybrid PS/MO by electro-spinning of blends, e.g. ZnO–SnO₂@Cellulose acetate⁹⁵ and SiO₂@Chitin.⁹⁶

The last step of the process is calcination to remove the PS template at generally 500–600 °C. Combustion of their organic scaffold likely forms dispersed oxides in conditions under which sintering is not favored. To remove the PS, other means have been explored: dissolution in complex media, or enzyme treatment like in the case of dextran removed by dextranase.⁹⁷ Ionic liquids could be alternatives that remain to be explored with this purpose.⁹³ This makes possible the recycling of the PS, but so far, this has not been reported yet, probably due to no economical interest with regard to the cheapness of PS and the cost of such recycling.

Thermal oxidation of PS is considered as globally benign or with low impact by itself on MO. However, all PS do not behave equally, for example thermal decomposition of alginate is sensitive to cations with the formation of metal oxalate,⁹⁸ and differs from chitosan, chitin,^99,100 or cellulose.¹⁰¹ This situation could be affected by at least two factors, i.e. MO (as a crust, nanoparticles or free ions) and PS-induced nano-sizing. Much attention should be paid to this step and could lead to “element-doping” with PS.

Consequently, the next section (Part 2) is devoted to a range of combinations dealing with soluble and jellified polysaccharides. Data clearly identifying replication of insoluble natural or refined polysaccharide fibers are presented in Part 3, while Part 4 concerns mineralisation through chemical reactions of PS.

Part 2: controlled growth of metal oxide nanoparticles throughout polysaccharide fibers

This approach, schematically depicted in Fig. 4, takes advantage of the functionality of polysaccharides to control hydrolysis/polycondensation and nucleation growth processes – it is sometimes called “in situ precipitation”. It benefits from the fact that polysaccharides are able to absorb metal cations.^102–105 This absorption may occur through different modes: complexation, solvation, M–OH⋯HO–PS H-bonding and also depends on the PS functionality, and the experimental procedure (pH and concentration) (illustration in Fig. 5).

Fig. 4 The general pathway for the control of the growth of MO nanoparticles in the presence of PS.

Fig. 5 Schematic representation of the possible interaction between functions of polysaccharide units and metal-containing species.

It has long been recognized that “a distinguishing feature of polysaccharides is that they sharply accelerate the kinetics of sol–gel processes.… Such acceleration is attributed to a catalytic effect of polysaccharides on the silica synthesis.”¹⁰⁶ Various studies have shown the formation of metal–cellulose complexes, e.g. Fe(III)–cellulose,¹⁰⁷ Cu(II)–cellulose,¹⁰⁸ Zn(II)–cellulose,¹⁰⁹ Pb(II) and Cd(II),¹¹⁰ or Cr(III) and Al(III).¹¹¹ This could improve or introduce properties of the cellulose (mechanical, absorbent, anti-microbial and -fungal, UV self-cleaning, dissolution), but could also be detrimental to its stability.¹¹² These authors highlighted the important role of both the pH and the residual carboxylic group of the cellulose.

In this context, the effect of the type of PS on MO nanoparticles is an important question. For example, in pioneering work on the preparation of maghemite with polysaccharides, it was observed that “starch and guluronic-rich alginate retains large amounts of iron … compared to chitosan”.¹¹³

More recently, the structure and functionality of the polysaccharide were found to not only modify the microstructure and morphology of TiO₂, but they also induced a different phase, with rutile being obtained using β-cyclodextrin and chitosan, anatase being obtained using starch.¹¹⁴ Comparisons of this type are unfortunately still rare. The possibility of combining two PS is also limited to very few examples (see the case of improved chemical and mechanical stability of Fe₃O₄ particles⁵⁵). Other processes like ALD are less commonly used. In that case, the PS reactivity seems to be less involved since the metal oxide nanoparticles are formed before their contact with PS, but their anchoring depends on the functionality of the surface.^115,116

The resulting MO@Cellulose composite is sometimes the targeted material, but generally the metal oxide is targeted and recovered after calcination, unfortunately more seldomly a MO@C is sought by a pyrolytic treatment such as LiFePO₄/C,¹¹⁷ or TiO₂@C (shown in Fig. 6).¹¹⁸

Fig. 6 SEM (A) and TEM (B) images of an example of a MO@C composite obtained by pyrolytic treatment of the corresponding hybrid MO@PS. (A) LiFePO₄@C from filter paper after impregnation with (LiNO₃/FeSO₄) and pyrolysis under Ar + H₂ (Reprinted from ref. 117, Copyright (2013), with permission from Elsevier). (B) TiO₂@C from ashless filter paper impregnated with TTB and pyrolysis under N₂ (Reprinted from ref. 118, Copyright (2010), with permission from Wiley and Sons).

Otherwise, a diverse range of metal oxides and supports have been explored for application or fundamental purposes. In the best cases, metal oxide nanoparticles with a ∅ < 50 nm are homogeneously dispersed along the fibers inside the micro- or nanofiber entanglement. Although the metal oxide structure has an effect, the most common morphology is round-shape, which is not the most attractive, but in some rare cases PS like cellulose allows the formation of unusual morphologies such as TiO₂ cubes¹¹⁹ or flowers.¹²⁰ Recently, cellulose in an ionic liquid was used as a new medium for metal oxide formation, showing a pronounced effect on the morphology and size when compared to aqueous processes (e.g. Na_0.5K_0.5NbO₃ ¹²¹). The solvent effect on sol–gel chemistry is well-known; this is the first example of a PS-IL medium that combines the properties of PS and ILs.

MONP@Cellulose . (See Table 1: MO@Cellulose devoted to metal oxides and Table 2: Mixed-MO@Cellulose devoted to mixed metal oxides in ESI.†) Cellulose is the most popular polysaccharide. It is found in organisms ranging from bacteria to animals, forming a polymeric chain made of β(1→4) linked D-glucose units.

The preparation of Fe₂O₃/Fe₃O₄,^125,126 or YBaCuO^84,85 with cellulose is among the first studies on this topic and examples of MONP@Cellulose before calcination are presented in Fig. 7. No benchmark has been established in this area concerning the type of cellulose, but cellulose pulp (or purified) is frequently used and bacterial cellulose is now increasingly popular as a nano-sized PS.

Fig. 7 SEM images of examples of different metal oxide nanoparticles assembled with or produced from cellulose-type PS (A) Fe₃O₄@BNC (from Acetobacter xylinum) (Reprinted from ref. 122, Copyright (2011), with permission from Elsevier); (B) BiVO₄@Cellulose (from Eucalyptus globulus wood cellulose fibers) (Reprinted from ref. 123, Copyright (2005), with permission from Elsevier); and (C) ZnO@Cellulose layer (from filter paper).¹²⁴

The use of cellulose avoids having to rely on a catalyst in many cases. Besides this common observation and the effectiveness of using cellulose in conjunction with sol–gel, there are two other issues that have been less discussed and need more studies. The first concerns the effect of cellulose degradation on calcination, which is an important point for some applications. For example, in the case of phosphor, some residual carbon can be present depending on the type of cellulose and the temperature, with an impact on the luminescence.^127,128

The second point is the potentially reducing behavior of cellulose, depending on the temperature and atmosphere. Indeed, cellulose is clearly recognized as being a reducing agent in the formation of metal nanoparticles like Pt,¹²⁹ Au,⁶¹ or Ag¹³⁰ and when metal cations with high oxidation potential are involved in the effective reduction of hydroxyl groups, e.g. see the case of Mn(VII),^131,132 leading possibly to aldehyde and carboxylic functions, or C–C bond cleavage.

MONP@Alginate . (See Table 3: MO@Alginate in ESI.†) Alginate is extracted from brown seaweed and consists of mannuronic and guluronic acid residues randomly sequenced along the polysaccharide chain; it is also used in many ways for different materials.^133,134 Examples of MO prepared with alginates are shown in Fig. 8. It is generally recognized that the buckled polyguluronate segments of alginate strongly bind [Mⁿ⁺] multivalent metal cations, preferentially to Na⁺, to form microcrystalline arrays through a mechanism known as the ‘egg-box’ model.¹³⁵

Fig. 8 SEM images of examples of different metal oxide nanoparticles assembled with or produced from alginate-type PS. (A) La_0.67Sr_0.33MnO₃ with sodium alginate¹⁴⁰ and (B) CuO after calcination of Cu-alginate aerogel from sodium alginate (Reprinted from ref. 138, Copyright (2007), with permission from Elsevier).

Prior works targeted the formation of paramagnetic beads of alginate by reaction with iron salt for the potential preparation of biotechnology materials,^113,136,137 extended now to many other oxides. Basically alginates like chitosan are frequently processed as true solutions or after jellification by the addition of multivalent cations. An important novelty in the process concerns the use of supercritical CO₂ drying of the gel after metal oxide formation. These conditions preserve the shape and high specific surface area of the material before calcination.

In some cases, “no memory of the fibrillar structure of the polysaccharide can be observed in the morphology and organization of oxide crystals”,¹³⁸ but in the preparation of YBa₂Cu₄O₈ “there is more evidence of the effect of either the polyguluronate/polymannuronate ratio or the counter cation (ammonium/sodium) on metal oxide formation.”^139,140 Again, the nature of the oxide is critical in the ability to control its morphology from the PS. Interestingly, the chemical reactivity of alginate seems to be involved at two levels: first the carboxylate would act as a reducing agent, as proposed in the well-known citrate method (Pechini's method), and secondly the decomposition polymer products help prevent significant mass transport and sintering to leave sponge-like material.^27,141

MONP@Chitosan and chitin . (See Table 4: MO@Chitosan or chitin in ESI.†) Chitosan is an abundant polysaccharide obtained by deacetylation of chitin, a naturally occurring polysaccharide found in fungi and the exoskeleton of insects and crustaceans, already used for many applications (food, cosmetics, biomedical and pharmaceutical applications¹⁴²).

In early work, chitosan was mixed with ready-made Fe₃O₄ nanoparticles to produce a polyelectrolytic support for cell separation processes.¹⁴³ Earlier, SiO₂@Chitosan was targeted as artificial skin due to the high oxygen permeability of such a “membrane”,^144,145 but recent work focuses on TiO₂ as MO (example shown in Fig. 9A). Alternatively, and more frequently, chitosan is engaged as alcogel beads in which a precursor of the metal oxide diffuses from an alcoholic solution to give rise to MO coated chitosan hybrid microspheres. Similar to alginate, before calcination and biotemplate elimination, a key step of the process is the supercritical drying with CO₂, which can prevent the collapse of the opened structure of the alcogel.¹⁴⁶ Alternatively, chitosan can be associated with a solvothermal process.¹⁴⁷

Fig. 9 SEM images of different metal oxide nanoparticles assembled with different PS (A) TiO₂@Chitosan (20% acetylation) (Reprinted from ref. 157, Copyright (2010), with permission from Elsevier); (B) TiO₂ after calcination of the TiO₂@Agarose composite (Reprinted with permission from ref. 158, Copyright (2006) American Chemical Society); and (C) YBa₂Cu₃O₇@Dextran (Reprinted with permission from ref. 159, Copyright (2007) American Chemical Society).

The NH₂ group of the chitosan structure, a distinctive feature of this polysaccharide, is important for understanding its reactivity and chemistry. This group has been identified as one of the key components in the formation of the fibrous structure of oxides.^146,148 Based on IR-data of SiO₂@Chitosan, the Si–O⁻⋯⁺H₂N– interaction is evidenced,¹⁴⁹ along with high hydrogen bonding.¹⁵⁰ The presence of the –NH₂ group suggests that it could be possible to N-dope some oxides prepared with chitosan and after calcination – a situation that has not yet been reported, suggesting the loss of this element upon calcination.¹⁴⁷

In a limited number of cases, the presence of chitosan was postulated to orient the morphology of the recovered metal oxide, e.g. in the case of YBa₂Cu₄O₈ nanowires,¹⁵¹ in contrast to round-shaped nanoparticles obtained in the absence of chitosan, a key result showing the effect of PS and promoting their uses.

Chitin has been less used for MONP formation than for replication (see the next section). However, colloidal solution of chitin crystals can be combined with the sol–gel process, thus giving rise to nanocomposites and porous oxides like SiO₂ and TiO₂.^96,152

MONP@Starch . (See Table 5: MO@Starch, MO@Dextran, MO@Carrageenan, MO@Agarose in ESI.†) Starch is produced by green plants, D-glucose sequences of D-glucose units lead to a spiral structure in linear amylose and in a highly branched structure in amylopectin. Easy to dissolve in water it is routinely combined with cellulose in the preparation of paper and nanocomposites.¹⁵³

Due to its solubility, starch was tested as a “structure directing agent” or a “porogen”, offering the advantages to be easily removed with water, see for example for the preparation of Ni–BaCe_0.9Y_0.1O_2.95 cermet fuel cell electrodes.¹⁵⁴ Early studies used starch for the preparation of oxide Sr-doped LaMnO₃ and Sr-doped La(Fe,Co)O₃. The purpose is clearly to use starch as an alternative to citric acids in the Pechini method.⁶⁰ It was found that starch plays an important role in the formation of homogeneously dispersed nanoparticles, while also having a marked impact on the crystal phase.¹¹⁴ Indeed, aqueous Ti³⁺ solutions lead to anatase with starch, while rutile is obtained with cyclodextrin or chitosan. Although very attractive, the interpretation of such data needs investigations to promote the use of PS.

In the case of ZnO, starch layers were found to be efficient for growing uniformly oriented nanorods, which is evidence of the strong interaction of the initial cluster oxide with the surface of such PS.¹²⁴ Other studies support the assumption that nucleation and initial crystal growth occur through starch/[Metal] species, but show that it is possible to control the morphology and avoid nanorod formation.¹⁵⁵

Starch was also combined with readymade nanoparticles (silicalite for macroporous sponge-like monoliths with meso-/macroporosity⁸⁶), especially as coating to ensure their biocompatibility (SPION superparamagnetic iron oxide nanoparticles¹⁵⁶).

MONP@Carrageenan . Carrageenans are linear sulphated polysaccharides that are extracted from red edible seaweeds, and this family has at least 10 different chemical structures depending on the number and position of the –OSO₃⁻ group (α, β, γ, ι, κ, λ, μ, δ, θ, etc.). The number of studies is limited but, interestingly, it was reported that the presence of carrageenan limits the growth of metal oxide particles in the case of Fe₂O₃ and that the type of carrageenan plays an important role, “with ι-carrageenan nanoparticles showing higher average sizes than κ- and λ-carrageenan.”¹⁶⁰ These different behaviours are probably related to the number of charges (–OSO₃⁻) per monomer unit, a key parameter for understanding the [Fe³⁺]/carrageenan interaction by charge neutralization between sulphate groups and hydrolyzed oxyhydroxide iron species.¹⁶¹ Overall, carrageenan chains crosslink via metal cations, and in turn create a protective layer around iron oxide particles, thus producing a self-assembled nanoreactor for hydrolysis and condensation of oxyhydroxide iron species.

MONP@Agarose. Agarose is generally extracted from cell walls of certain algae species with essentially galactose subunits. The alcoholic gel is used as a reaction medium for the formation of metal oxides by hydrolysis/polycondensation of metal alkoxides absorbed in the gel, and also as a soluble porogen (see an example in Fig. 9B). As in the case of other gels, the impregnation process parameters (mineral/organic ratio, number of cycles, temperature, etc.) are crucial in the diffusion of titanium precursors into templates and the maintenance of a porous structure in the resulting titania beads. This could explain the differences observed with respect to previously published findings. Interestingly, the reducing ability of agarose towards Au salt was combined with its porogen properties to generate the Au@TiO₂ catalyst,¹⁶² an approach that should be generalized to other PS for the preparation of the new composite MONP@C@M'O.

MONP@Dextran is a branched polymer of dextrose (glucose) of very high molecular weight excreted by lactic-acid bacteria, with the best-known being Leuconostoc mesenteroides and Streptococcus mutans. The use of this polymer for metal oxide preparation is limited but, interestingly, in the case of YBa₂Cu₃O₇, the use of dextran is reported to lead to a uniform crystal size and morphology and a macroporous structure (Fig. 9C). With the same PS, calcination of a freeze-dried metal oxide–dextran aqueous mixture leads to foamy porous open structures that are easy to calcine with less sintering.

Part 3: templating of polysaccharide fibers

Bio-replication, which differs from biomorphism,¹⁶³ is the direct replication of a structure found in an organism. This is a very general approach to the synthesis of materials that is implemented to take advantage of hierarchical micro- and nanostructures produced by living organisms (schematically depicted in Fig. 10).^{12,39,64,164–169} The initial aim was to demonstrate the possibility of precisely molding “raw” natural structures with MO. This is still relevant when taking advantage of cheap raw materials via the shortest possible loop, and when preparing metal oxides with complex morphologies and hierarchical architectures (see different examples in Fig. 11). Several examples have been reported from the coarse- to the nano-scale: eggshell membranes,¹⁷⁰ human hairs,^171,172 silk fibers,¹⁷³ pollen,^174,175 diatoms,¹⁷⁶ bacteria,^87,177,178 viruses,¹⁷⁹ protein cages,^180,181 and collagen.¹⁸²

Fig. 10 General pathway for metal oxide preparation by impregnation/deposition with PS, leading to hybrids M_xO_y@PS and then M_xO_y or M_xO_y@C materials upon thermal treatment.

Fig. 11 SEM images of the replication of polysaccharide fibers with metal oxides deposited by sol–gel or ALD techniques. (A) MoO₃@Cellulose (commercial paper) after calcination at 500 °C (Reprinted from ref. 198, Copyright (2008), with permission from Wiley and Sons); (B) TiO₂ hollow fibers after calcination of TiO₂@Cellulose (woven cotton);¹⁸⁹ (C) MnO₂@Cellulose from lens paper before calcination (Reprinted with permission from ref. 199, Copyright (2011) American Chemical Society); (D) ZnO@Cellulose from filter paper before calcination (Reprinted from ref. 200, Copyright (2011), with permission from Wiley); (E) SiO₂ nanotubes after calcination of SiO₂@Cellulose from filter paper (Reprinted with permission from ref. 201, Copyright (2011) American Chemical Society); (F) Fe₃O₄@Cellulose from bacterial cellulose of G. xylinum (Reprinted from ref. 202, Copyright (2011), with permission from Elsevier); (G) TiO₂ after calcination of TiO₂@Cellulose from natural cotton;¹ (H) V₂O₅@Cellulose from bacterial G. xylinum before calcination (Reprinted from ref. 203, Copyright (2013), with permission from Springer); and (I) Al₂O₃ replicas after calcination of Al₂O₃@butterfly wing by ALD (Reprinted with permission from ref. 201, Copyright (2006) American Chemical Society).

In such replication processes, only the outermost part of the surface of the PS is supposed to be involved in the chemical processes. This can be assumed to occur in the same manner as the process involved in the controlled growth of MONP above: by complexation/solvation of cation or hydroxycation species through the organic function of the biotemplate (carboxylate, hydroxyl, amine and amide groups, etc.). In the case of ZnO, for example, it was found that “cellulosic fibers act as hydrophilic substrates for the heterogeneous nucleation of ZnO”;¹⁸³ and this surface can be pre-seeded with metal salt.^184,185

The inner part of the fibers is probably not involved in these nucleation and seeding processes. Calcination is generally used to isolate the inorganic replica but pyrolysis could be of interest in the preparation of MO@C composites. “Biotemplating” or “bioreplicas” are therefore appropriate, in contrast to “mineralisation”, “petrifaction” or “fossilization”, which should be limited to effective chemical transformations of the template in its massive part.

PS fibers are replicated through a sol–gel process, but a few exceptions are reported with other techniques, leading to a thick MO deposit of 20 to several nm, covering the template, and made of round shaped and aggregated nanoparticles of ∅ < 50 nm. Besides the many different supports highlighted in the table, different “modified cellulose” supports have also been used, e.g. cellulose acetate.^186–188

TiO ₂ -Cellulose. (See Table 6 Biotemplating of cellulosic fibers for TiO₂@Cellulose for TiO₂ formation in ESI.†) Cellulose fibers are the most popular biotemplates here because of their insolubility, which render them more appropriate for bio-replication than for nanoparticle growth control. Otherwise, the most frequently targeted oxide is TiO₂ due to the numerous potential applications of this oxide: sensors for hydrogen, oxygen, humidity, glucose and hydrogen peroxide, anodes for electrochemical devices, and photocatalysts for oxidation and reduction. In pioneering studies, TiO₂ micro- or nanotubes were already targeted with cotton fibers as the template.^189,190

MO replication is achieved mainly by the impregnation or suction/filtration technique using a sol of TiO₂-precursors, the experimental details being one of the knowhow of the authors. An alternative to this process is hydrolysis/condensation of the MO precursor by exposure to air or moisture once it has been absorbed by the cellulose fibers.^191,192 The third possibility involves the ALD process, which can be combined with multi-oxide formation and for which the presence of the hydroxyl group at the cellulose surface seems to “simplify nucleation of water-based ALD processes”.¹⁹³

Calcination (generally at 500 °C) is used to remove the template but the possibility of removing the cellulose by urea/NaOH treatment has also been reported.¹⁹⁴ Generally, anatase is the common phase but rutile has been reported in one case, using flame calcination after impregnation, although it was recognized that “the cellulose template plays key role not only in obtaining the nanotubular structures, but also in achieving smaller particle sizes”.¹⁹⁵ Exceptionally, cellulose is also considered as a source of carbon that could lead to a C@TiO₂ nanocomposite (anatase + rutile),¹⁹⁶ this could be further developed if considering the new materials required for energy and catalysis.

Besides relatively refined cellulosic materials, raw materials directly collected from nature, essentially plant parts, were biotemplated. In these cases, besides the cellulose-rich part of the body (skin, leave seeds, pith, etc.), other biopolymers or salts can be present and interfere in the process. Despite or because of this, some interesting and effective properties have been reported, giving rise to a direct and greener process, mainly for the potential preparation of photocatalysts (see Table 7 Biotemplating of plants for TiO₂@Plant and TiO₂ formation in ESI†).

M _x O _y -Cellulose. (See Table 8 Biotemplating of Cellulose for MO@Cellulose and MO formation in ESI.†) Sol–gel processing is the most commonly used, note that chemical modification of cellulose can be performed to enhance the formation of, for example, SiO₂ around fibers.¹⁹⁷ The ALD technique is attractive, it provides a possibility to adjust the thickness of the metal oxide layer by increasing or decreasing the number of cycles, more precise than sol–gel processing.

M _x O _y @PS and M _x O _y @modified-PS or M _x O _y @raw material . Cellulose is a kind of benchmark to test bio-replication, therefore other polysaccharides are less reported also because some are soluble in water.

Chitin, more than chitosan, is often used due to its abundance in chitinized exoskeletons. Butterfly wings have been templated by different oxides: SiO₂ (CVD),²⁰⁵ Al₂O₃ (ALD),²⁰⁴ TiO₂ (impregnation),²⁰⁶ TiO₂ (ALD),²⁰⁷ Sn–TiO₂ (sol–gel),²⁰⁸ SnO₂ (sol–gel),²⁰⁹ ZnO (sol–gel),^210,211 BaTiO₃ (LbL),²¹² TiO₂ and SiO₂ (sol–gel).²¹³ Other chitin biotemplates have also been tested like beetle cuticles in weevil and longhorn families, and used for the production of inorganic photonic structures by a sol–gel biotemplating method.²¹⁴ Besides arthropods, chitin is also found in marine organisms and biotemplating of a macroporous β-chitin sponge-like monolith of cuttlebone was performed by acidic demineralisation after impregnation with sodium silicate, which provided good replication control.²¹⁵ The objective in all cases is to take advantage of the unique hierarchical structure of the biotemplate, especially for photonic materials, since hierarchical porosity is beneficial for catalysis or electrodes. The ALD process was used to deposit Al₂O₃ on spines of sea mouse (Aphrodita aculeata) made of chitin and proteins.²¹⁶

Chitosan flakes have recently been reported as insoluble biotemplates for the preparation of bulk and mesoporous silica. Here again, the role of the amino group is a key for understanding the role of the biotemplate.²¹⁷

At that point, the wood structure replication can be mentioned, but because the template is a raw mixture of non-purified biopolymers, it will not be detailed. Since the early work of Drum et al. on the silicification of betula wood by an aqueous solution of silicate,²¹⁸ many other wood/MO couples have been investigated, leading to the preparation of MO with complex and hierarchical structures: pine wood (templating Al₂O₃, TiO₂ and ZrO₂;²¹⁹ NiO;²²⁰ SrAl₂O₄:Eu²⁺;²²¹ Fe₂O₃;²²² SiO₂;²²³ Y–ZrO₂;²²⁴ to SiOC²²⁵); fir wood (templating ZnO;²²⁶ TiO₂;²²⁷ Mn₃O₄ and Mn₂O₃;²²⁸ Fe₂O₃;^222,229 and Cr₂O₃ ²³⁰); cedar, cypress and judas wood (to TiO₂ ²²⁷); paulownia (templating Fe₂O₃;^222,229 Cr₂O₃;²³⁰ Mn₃O₄ and Mn₂O₃²²⁸) and lauan wood (templating Fe₂O₃ ²²²), poplar wood (templating SiO₂ ²²³); cedar wood (templating TiO₂ ²³¹ and zeolite²³²); spruce wood (templating SiO₂;^233,234 to Ce_0.5Zr_0.5O₂ ³¹); and bamboo (templating zeolite²³²).

M _x O _y -PS through hard templates. Another approach related to the MO@PS topic is the use of micrometer size granules of PS for nano-casting. Microspheres of starch infiltrated with TiO₂ sol in supercritical CO₂ lead to the formation of mesoporous–macroporous anatase (2 nm to 5 μm).²³⁵ In a different approach, starch granules were first converted into carbonaceous material by a solvothermal process,²³⁶ and then used as sacrificial templates for the preparation of ZnO microspheres after impregnation with zinc(II) acetate.^237,238 This approach was initially pioneered with glucose as a precursor for carbonaceous dots used, for example, for the production of metal and mixed metal oxides.^239–245 With the development of carbon dots, this approach could be fruitfully further enhanced to associate these dots with MO.

Part 4: chemical reaction of biopolymers with metal oxide precursors

In the studies mentioned above, cellulose was exclusively considered as a template and its reactivity was generally not considered, except for the outermost layer. But in other domains, biotemplates have often been considered as a C-provider for the production of carbides, such as SiC^246–249 or²⁵⁰ B₄C,^251,252 TiC,^253,254 C-doped TiO₂,^147,255 C-doped SiO₂,²⁵⁶ or as a reducing agent for the preparation of metal particles,¹²⁹ and recently metal fibers.²⁵⁷ However, biotemplates are very seldom considered as an O-source functioning as both a template and reagent, e.g. gas/solid metathesis between TiF₄ and SiO₂-based diatoms.²⁵⁸

Polysaccharides are indeed highly reactive materials with a high oxygen content, thus making them promising O-providers. In the past, alcohols and ethers have been used in the preparation of metal oxides by the so-called non-hydrolytic sol–gel process.^259,260Fig. 12 schematically illustrates such a general route where polysaccharides are considered as both templates and reagents.

Fig. 12 General scheme of the polysaccharide mineralisation process leading to hybrid M_xO_y@PS and then to either M_xO_y or M_xO_y@C materials.

An ALD-type process has been developed and is based, in the case of the formation of TiO₂, on the reaction for TTIP with-and-on dried nanofibers of nanocellulose aerogels (Fig. 13). Considering the temperature used in the process, i.e. 190 °C at pressures of 1–5 kPa for 2 h, different reactions can occur: with cellulose hydroxyl groups to produce the alcohol of the MO precursor, thermal decomposition of titanium isopropoxide, and reactions with traces of water.^261–263

Fig. 13 SEM images of ZnO@NCA (A, B); TiO₂@NCA (C) and Al₂O₃@NCA (D) obtained reactive ALD with nanocellulose aerogel (Reprinted with permission from ref. 262, Copyright (2011) American Chemical Society).

Recently, we have reported a mineralisation, under strictly anhydrous conditions similar to non-hydrolytic sol–gel processes. TiO₂ can be obtained by the reaction between TiCl₄ as the titanium-source and a cellulosic material like Ferula communis piths or cotton wool acting as the oxygen source.²⁶⁴ This is a one-pot metathetic liquid/solid reaction.

The most important difference from other approaches is that, under mild conditions (<80 °C), mineralisation leads to the formation of nanoparticles with a non-round shape, i.e. nanorod-like structures assembled in needle³ (Fig. 14) or lacework formation,²⁶⁵ a situation that has never been reported in sol–gel biotemplating processes. In addition, this approach can be combined with pre-impregnation of the cellulose and is efficient on aerogel of nanocellulose.

Fig. 14 SEM (A, B, C) and TEM (D) picture of TiO₂@ filter paper obtained by mineralization of filter paper by TiCl₄ under anhydrous conditions at 80 °C.³

Perspectives and concluding remarks

Green, dark green, pale green… How is this Green Chemistry? Answers to this question can be given in relation to the basic principles of “green chemistry”, and by comparison with other methods that aim to control the synthesis of metal oxides.

In terms of maximizing the amount of raw material with no (or limited) environmental impact and toxicity, PS and water are certainly appropriate chemicals, the use of MO precursors cannot be avoided by any process. PS is an ideal sustainable substance, although some of them require purification or extraction like for nanocrystals and nanofibers. Anyway, the use of PS is certainly “greener” than that of surfactants and additives issued from petrochemical industry, and generally used for the same purpose.

In terms of by products, the chemicals produced by the process are usually alcohols (produced by the hydrolysis of the MO precursor) and CO₂ during calcination (plus traces of S and N containing chemicals in some cases), the latter two compounds exhibiting no particular toxicity and being easily mastered by the chemist. However, to limit contamination by metals and maximize the incorporation of all materials used in the process, special attention must be paid to the presence of clusters and metal oxide nanoparticles in the final solution after the filtration step.

In terms of energy, one may argue of the necessity to remove the PS by thermal treatment (although elimination could be done with enzyme or IL extraction in some cases). But firstly, the syntheses of MO require generally a thermal treatment to improve the crystallinity of MO, the temperatures are generally equivalent or even higher than the one required for the elimination of the PS. Secondly, when the thermal treatment is performed under an inert atmosphere, it leads to the carbon phase provided by the PS, a situation that cannot be attained when using surfactants or additives, and that allows, in one step, the formation of MO@C composites. Finally, most of the oxides thus synthesized are required by green chemistry, especially in the catalytic and photocatalysis processes. Therefore, it is among the greenest approaches to the synthesis of materials expected in Green Chemistry.

Over the last two decades, there has been a significant increase in the development of approaches and in research on the use of PS for MO preparation. This is certainly only the beginning of the story considering the importance of polysaccharides as potential materials and reagents, and of metal oxides as functional materials for chemical applications and devices. Of course, the development of chemistry around the nano-sizing and chemical modification of PS is a major issue for the development of this domain, as mentioned above. At the end of this review, we propose to keep in mind five important issues.

First, a precise rationalisation of the effect of the polysaccharide on the formation of the oxide is not possible at present because of the tremendous diversity of processing parameters and the complexity of PS structures. This is further hampered by the lack of a precise description and analyses of what happens during nanoparticle growth or replication. The descriptions of the experimental procedures should always be accurate and detailed. Comparison of different PS engaged under the same conditions would greatly help to understand and rationalise their specificity and interest in these processes.

Secondly, the decomposition/elimination of biopolymers leading to the oxide is an important step requiring greater consideration: for instance, nano-sizing of PS and MO coatings may modify the thermal behaviour of PS, which is an important point with respect to the formation of C-doped MO or C@MO composites.

Thirdly, the reactivity of PS, beyond its role as a template, opens new avenues in terms of the transfer of elements to the targeted MO and of redox reaction before or during thermal treatment for the formation of other composites (M@C, M@MO@C, etc.). Examples of the synthesis of metal nanoparticles,^{130,266–269} or metal oxides (magnetite,²⁷⁰ hausmannite¹³¹) are useful tools in such perspective.

The use of PS is usually to control MO properties including porosity. With the exception of some water-soluble PS (alginates), the results in this area are not very remarkable, especially compared to the results obtained with surfactants. However, the availability of new forms of PS (nanocrystals, nanofibers) offers hope for progress in this area.

Finally, in addition to other advances in PS processing, the latter could be modified by chemical reaction or simply by adsorption of chemicals inside fibers. This offers numerous combinations for the potential preparation of complex MO@PS multifunctional composites.

From a general point of view, the sum of these results shows the diversity and richness of this synthetic pathway to MO, using abundant natural polymers, and which can also lead to the formation of composite and nanocomposite MO@C. Although today we lack a fine and precise understanding of the specific character of each PS, it is already possible today to take advantage of them to access materials of high demand in new technologies and devices.

Abbreviation

PS	Polysaccharide
MO	Metal oxide
MMO	Mixed metal oxide
NP	Nanoparticle
TTIP	Ti(O^iPr)4
TTB	Ti(OBu)4
iMM&SC	Mastering morphology and size control
SSA	Specific surface area
PVD	Plasma vapour deposition
ALD	Atomic layer deposition
A@B	For mixed material like composite or core shell materials, the A@B is used which means that A is quantitatively the minor phase and B the major phase, for example TiO2@C is mostly carbon covered or mixed with TiO2.

Acknowledgements

The authors thank the Institut Charles Gerhardt, Pôle Balard and LabEx cheMISyst for financial support.

Notes and references

1. J. Huang and T. Kunitake, J. Am. Chem. Soc., 2003, 125, 11834–11835.
2. S. Chen, B. Zhou, W. Hu, W. Zhang, N. Yin and H. Wang, Carbohydr. Polym., 2013, 92, 1953–1959.
3. R. G. Nair, S. K. Samdarshi and B. Boury, Eur. J. Inorg. Chem., 2013, 5303–5310.
4. M. Fomina, J. M. Charnock, S. Hillier, R. Alvarez and G. M. Gadd, Environ. Microbiol., 2007, 9, 1696–1710.
5. M. Sprynskyy, I. Kovalchuk and B. a. Buszewski, J. Hazard. Mater., 2010, 181, 700–707.
6. R. E. Dunin-Borkowski, M. R. McCartney, R. B. Frankel, D. A. Bazylinski, M. Posfai and P. R. Buseck, Science, 1998, 282, 1868–1870.
7. G. M. Gadd, Microbiology, 2010, 156, 609–643.
8. L. Addadi, D. Joester, F. Nudelman and S. Weiner, Chem. – Eur. J., 2006, 12, 980–987.
9. C. E. Killian and F. H. Wilt, Chem. Rev., 2008, 108, 4463–4474.
10. D. Faivre and D. Schüler, Chem. Rev., 2008, 108, 4875–4898.
11. A. M. Belcher, X. H. Wu, R. J. Christensen, P. K. Hansma, G. D. Stucky and D. E. Morse, Nature, 1996, 381, 56–58.
12. H. Cölfen, in Biomineralization II Mineralization Using Synthetic Polymers and Templates, Springer-Verlag, Berlin, 2007, pp. 1–77.
13. E. Bäeuerlein, Handbook of Biomineralization: Biomimetic and bioinspired chemistry, Wiley-VCH, 2007.
14. P. Calvert and P. Rieke, Chem. Mater., 1996, 8, 1715–1727.
15. J. Aizenberg, L. Addadi, S. Weiner and G. Lambert, Adv. Mater., 1996, 8, 222–226.
16. R. L. Brutchey and D. E. Morse, Chem. Rev., 2008, 108, 4915–4934.
17. M. B. Dickerson, K. H. Sandhage and R. R. Naik, Chem. Rev., 2008, 108, 4935–4978.
18. S. V. Patwardhan, Chem. Commun., 2011, 47, 7567–7582.
19. X. Chen and S. S. Mao, Chem. Rev., 2007, 107, 2891–2959.
20. A. Kubacka, M. Fernandez-Garcia and G. Colon, Chem. Rev., 2011, 112, 1555–1614.
21. X. Zhao, B. M. Sanchez, P. J. Dobson and P. S. Grant, Nanoscale, 2011, 3, 839–855.
22. Y.-F. Sun, S.-B. Liu, F.-L. Meng, J.-Y. Liu, Z. Jin, L.-T. Kong and J.-H. Liu, Sensors, 2012, 12, 2610–2631.
23. P. Tingaut, T. Zimmermann and G. Sebe, J. Mater. Chem., 2012, 22, 20105–20111.
24. N. Lin, J. Huang and A. Dufresne, Nanoscale, 2012, 4, 3274–3294.
25. S. Elazzouzi-Hafraoui, J.-L. Putaux and L. Heux, J. Chem. Phys., 2009, 113, 11069–11075.
26. S. Elazzouzi-Hafraoui, Y. Nishiyama, J.-L. Putaux, L. Heux, F. Dubreuil and C. Rochas, Biomacromolecules, 2008, 9, 57–65.
27. S. Sarkar, E. Guibal, F. Quignard and A. K. SenGupta, J. Nanopart. Res., 2012, 14, 1–24.
28. D. Klemm, F. Kramer, S. Moritz, T. Lindström, M. Ankerfors, D. Gray and A. Dorris, Angew. Chem., Int. Ed., 2011, 50, 5438–5466.
29. S. Geresh and S. Arad, Bioresour. Technol., 1991, 38, 195–201.
30. C. Zollfrank, P. Cromme, M. Rauch, H. Scheel, M. H. Kostova, K. Gutbrod, S. Gruber and D. V. Opdenbosch, in Bioinspired, Biomimetic and Nanobiomaterials, 2012, pp. 13–25.
31. A. S. Deshpande, I. Burgert and O. Paris, Small, 2006, 2, 994–998.
32. F. Graziola, F. Girardi, R. Di Maggio, E. Callone, E. Miorin, M. Negri, K. Müller and S. Gross, Prog. Org. Coat., 2012, 74, 479–490.
33. H. Budunoglu, A. Yildirim, M. O. Guler and M. Bayindir, ACS Appl. Mater. Interfaces, 2011, 3, 539–545.
34. S. Wang, R. Mahlberg, S. Jaemsae, J. Nikkola, J. Mannila, A.-C. Ritschkoff and J. Peltonen, Prog. Org. Coat., 2011, 71, 274–282.
35. S. Saha, D. Kocaefe, D. Sarkar, Y. Boluk and A. Pichette, J. Coat. Technol. Res., 2011, 8, 183–190.
36. M. Petrič, Rev. Adhes. Adhes., 2013, 1, 216–247.
37. T. Valdés-Soli and A. B. Fuertes, Mater. Res. Bull., 2006, 41, 2187–2197.
38. T. Nypelö and O. J. Rojas, Am. Ceram. Soc. Bull., 2012, 91, 28–31.
39. M. Singh, J. Martínez-Fernández and A. R. de Arellano-López, Curr. Opin. Solid State Mater. Sci., 2003, 7, 247–254.
40. Z.-G. Zhao, Z.-F. Liu and M. Miyauchi, Chem. Commun., 2010, 46, 3321–3323.
41. L. Zhao, X. Chen, X. Wang, Y. Zhang, W. Wei, Y. Sun, M. Antonietti and M.-M. Titirici, Adv. Mater., 2010, 22, 3317–3321.
42. M.-M. Titirici, M. Antonietti and N. Baccile, Green Chem., 2008, 10, 1204–1212.
43. A. Kruse, A. Funke and M.-M. Titirici, Curr. Opin. Chem. Biol., 2013, 17, 515–521.
44. B. Hu, K. Wang, L. Wu, S.-H. Yu, M. Antonietti and M.-M. Titirici, Adv. Mater., 2010, 22, 813–828.
45. N. Baccile, G. Laurent, C. Coelho, F. Babonneau, L. Zhao and M.-M. Titirici, J. Phys. Chem. C, 2011, 115, 8976–8982.
46. A. Corma, S. Iborra and A. Velty, Chem. Rev., 2007, 107, 2411–2502.
47. A. l. P. Rauter, N. M. Xavier, S. D. Lucas, M. Santos and H. Derek, in Advances in Carbohydrate Chemistry and Biochemistry, Academic Press, 2010, pp. 29–99.
48. Z. Shi, G. O. Phillips and G. Yang, Nanoscale, 2013, 5, 3194–3201.
49. Y. Ohmori and Y. Kurokawa, J. Biotechnol., 1994, 33, 205–209.
50. T. Coradin, N. Nassif and J. Livage, Appl. Microbiol. Biotechnol., 2003, 61, 429–434.
51. M. Perullini, M. Amoura, M. Jobbagy, C. Roux, J. Livage, T. Coradin and S. A. Bilmes, J. Mater. Chem., 2011, 21, 8026–8031.
52. E. Callone, R. Campostrini, G. Carturan, A. Cavazza and R. Guzzon, J. Mater. Chem., 2008, 18, 4839–4848.
53. T. Coradin and J. Livage, J. Sol-Gel Sci. Technol., 2003, 26, 1165–1168.
54. A. M. G. C. Dias, A. Hussain, A. S. Marcos and A. C. A. Roque, Biotechnol. Adv., 2011, 29, 142–155.
55. Z. Liu, H. Wang, C. Liu, Y. Jiang, G. Yu, X. Mu and X. Wang, Chem. Commun., 2012, 48, 7350–7352.
56. J. Wu and M. J. Sailor, Adv. Funct. Mater., 2009, 19, 733–741.
57. S. Liu, D. Tao and L. Zhang, Powder Technol., 2012, 217, 502–509.
58. S. Laurent, D. Forge, M. Port, A. Roch, C. Robic, L. Vander Elst and R. N. Muller, Chem. Rev., 2008, 108, 2064–2110.
59. S. Padalkar, J. R. Capadona, S. J. Rowan, C. Weder, Y.-H. Won, L. A. Stanciu and R. J. Moon, Langmuir, 2010, 26, 8497–8502.
60. L.-W. Tai, H. U. Anderson and P. A. Lessing, J. Am. Ceram. Soc., 1992, 75, 3490–3494.
61. Z. Li, A. Friedrich and A. Taubert, J. Mater. Chem., 2008, 18, 1008–1014.
62. J. Li, Y. Gu and J. Huang, in Nanostructured Biomaterials, Springer, Berlin, Heidelberg, 2010, pp. 133–164.
63. Z. Schnepp, Angew. Chem., Int. Ed., 2013, 52, 1096–1108.
64. R. A. Caruso and M. Antonietti, Chem. Mater., 2001, 13, 3272–3282.
65. I. Ichinose and T. Kunitake, Chem. Rec., 2002, 2, 339–351.
66. S. Lou, X. Guo, T. Fan and D. Zhang, Energy Environ. Sci., 2012, 5, 9195–9216.
67. C. Aimé and T. Coradin, J. Polym. Sci., Part B: Polym. Phys., 2012, 50, 669–680.
68. R. J. Martin-Palma and A. Lakhtakia, Int. J. Smart Nano Mater., 2012, 4, 83–90.
69. F. Marin, P. Narayanappa and S. Motreuil, in Molecular Biomineralization, Springer, Berlin, Heidelberg, 2011, pp. 353–395.
70. C. Pavat, I. Zanella-Cléon, M. Becchi, D. Medakovic, G. Luquet, N. Guichard, G. Alcaraz, J.-L. Dommergues, A. Serpentini, J.-M. Lebel and F. Marin, Comp. Biochem. Physiol., Part B: Biochem. Mol. Biol., 2012, 161, 303–314.
71. W. G. Kinsinger and C. W. Hock, Ind. Eng. Chem. Res., 1948, 40, 1711–1716.
72. C. W. Hock and H. Mark, in Cellulose, ed. E. Ott, Interscience Publishers Inc., New York, 1946, p. 346.
73. C. C. Walters, L. Margulis and E. S. Barghoorn, Precambrian Res., 1977, 5, 241–248.
74. B. H. Hamling, U.S. Pat., 1973, 3,736,160.
75. B. H. Hamling, U.S. Pat., 1968, 3,385,915.
76. A. G. Elliot and R. A. Huggins, J. Am. Ceram. Soc., 1975, 58, 497–500.
77. T. Yanagisawa, T. Shimizu, K. Kuroda and C. Kato, Bull. Chem. Soc. Jpn., 1990, 63, 988–992.
78. J. S. Beck, J. C. Vartuli, W. J. Roth, M. E. Leonowicz, C. T. Kresge, K. D. Schmitt, C. T. W. Chu, D. H. Olson and E. W. Sheppard, J. Am. Chem. Soc., 1992, 114, 10834–10843.
79. Y. Wei, D. Jin, T. Ding, W.-H. Shih, X. Liu, S. Z. D. Cheng and Q. Fu, Adv. Mater., 1998, 10, 313–316.
80. Y. Wei, J. Xu, H. Dong, J. H. Dong, K. Qiu and S. A. Jansen-Varnum, Chem. Mater., 1999, 11, 2023–2029.
81. J. H. Jean and T. A. Ring, Colloids Surf., 1988, 29, 273–291.
82. J. H. Jean and T. A. Ring, Am. Ceram. Soc. Bull., 1986, 65, 1574–1577.
83. E. Kroll, F. M. Winnik and R. F. Ziolo, Chem. Mater., 1996, 8, 1594–1596.
84. T. Itoh, M. Uzawa and H. Uchikawa, J. Mater. Sci. Lett., 1988, 7, 130–132.
85. T. Itoh and H. Uchikawa, J. Mater. Sci. Lett., 1988, 7, 693–694.
86. B. Zhang, S. A. Davis and S. Mann, Chem. Mater., 2002, 14, 1369–1375.
87. B. Zhang, S. A. Davis, N. H. Mendelson and S. Mann, Chem. Commun., 2000, 781–782.
88. Q. Wang, Z. Zhang, Y. Zheng, W. Cai and Y. Yu, CrystEngComm, 2012, 14, 4786–4793.
89. Y.-L. Liu, C.-Y. Hsu, Y.-H. Su and J.-Y. Lai, Biomacromolecules, 2004, 6, 368–373.
90. R. Jayakumar, R. Ramachandran, V. V. Divyarani, K. P. Chennazhi, H. Tamura and S. V. Nair, Int. J. Biol. Macromol., 2011, 48, 336–344.
91. T. Bechtold, A. P. Manian, H. B. Oztürk, U. Paul, B. Siroka, J. Siroky, H. Soliman, L. T. T. Vo and H. Vu-Manh, Carbohydr. Polym., 2013, 93, 316–323.
92. A. Ostlund, D. Lundberg, L. Nordstierna, K. Holmberg and M. Nydén, Biomacromolecules, 2009, 10, 2401–2407.
93. A. Brandt, J. Grasvik, J. P. Hallett and T. Welton, Green Chem., 2013, 15, 550–583.
94. S. Sen, J. D. Martin and D. S. Argyropoulos, ACS Sustainable Chem. Eng., 2013, 1, 858–870.
95. R. Liu, Y. Huang, A. Xiao and H. Liu, J. Alloys Compd., 2010, 503, 103–110.
96. B. Alonso and E. Belamie, Angew. Chem., Int. Ed., 2010, 49, 8201–8204.
97. Y.-Y. Kim, K. Hore, S. R. Hall and D. Walsh, Small, 2009, 5, 913–918.
98. K. S. Khairou, J. Therm. Anal. Calorim., 2002, 69, 583–588.
99. Y. S. Nam, W. H. Park, D. Ihm and S. M. Hudson, Carbohydr. Polym., 2010, 80, 291–295.
100. M. J. Zohuriaan and F. Shokrolahi, Polym. Test., 2004, 23, 575–579.
101. A. L. Sullivan and R. Ball, Atmos. Environ., 2012, 47, 133–141.
102. P. Sipos, T. G. S. Pierre, E. Tombacz and J. Webb, J. Inorg. Biochem., 1995, 58, 129–138.
103. Y. Ogiwara and H. Kubota, J. Polym. Sci., Part A: Polym. Chem., 1969, 7, 2087–2095.
104. P. Chan, W. Chuaanusorn, M. Nesterova, P. Sipos, T. Stpierre, J. Ward and J. Webb, Aust. J. Chem., 1995, 48, 783–792.
105. E. M. Coe, R. D. Bereman and W. T. Monte, J. Inorg. Biochem., 1995, 60, 149–153.
106. Y. A. Shchipunov and T. y. Y. Karpenko, Langmuir, 2004, 20, 3882–3887.
107. A. Kongdee and T. Bechtold, Carbohydr. Polym., 2004, 56, 47–53.
108. H. E. Emam, A. P. Manian, B. Siroka and T. Bechtold, Carbohydr. Polym., 2012, 90, 1345–1352.
109. Q. Xu and L.-F. Chen, J. Appl. Polym. Sci., 1999, 71, 1441–1446.
110. L. V. A. Gurgel, K. O. Junior, R. Gil Pereira de Freitas and L. F. Gil, Bioresour. Technol., 2008, 99, 3077–3083.
111. N. K. Yurkshtovich, N. V. Golub, F. N. Kaputskii, T. L. Yurkshtovich and R. I. Kosterova, Russ. J. Appl. Chem., 2004, 77, 471–475.
112. A. Potthast, U. Henniges and G. Banik, Cellulose, 2008, 15, 849–859.
113. F. Llanes, C. Diaz, H. Ryan and R. H. Marchessault, Int. J. Polym. Mater. Polym. Biomater., 2002, 51, 537–545.
114. S.-J. Bao, C. Lei, M.-W. Xu, C.-J. Cai, C.-J. Cheng and C. M. Li, CrystEngComm, 2013, 15, 4694–4699.
115. E. Rauwel, G. Clavel, M.-G. Willinger, P. Rauwel and N. Pinna, Angew. Chem., Int. Ed., 2008, 47, 3592–3595.
116. E. Rauwel, M.-G. Willinger, F. Ducroquet, P. Rauwel, I. Matko, D. Kiselev and N. Pinna, J. Phys. Chem. C, 2008, 112, 12754–12759.
117. D. Jugovic, M. Mitric, M. Milovic, B. Jokic, M. Vukomanovic, D. Suvorov and D. Uskokovic, Powder Technol., 2013, 246, 539–544.
118. X. Liu, Y. Gu and J. Huang, Chem. – Eur. J., 2010, 16, 7730–7740.
119. Y. Zhou, E.-Y. Ding and W.-D. Li, Mater. Lett., 2007, 61, 5050–5052.
120. X. Peng and E. Ding, Micro Nano Lett., 2011, 998–1001.
121. D. C. Green, S. Glatzel, A. M. Collins, A. J. Patil and S. R. Hall, Adv. Mater., 2012, 24, 5767–5772.
122. W. Zhang, S. Chen, W. Hu, B. Zhou, Z. Yang, N. Yin and H. Wang, Carbohydr. Polym., 2011, 86, 1760–1767.
123. M. A. B. Barata, M. C. Neves, C. Pascoal Neto and T. Trindade, Dyes Pigm., 2005, 65, 125–127.
124. Z. Ibupoto, K. Khun, M. Eriksson, M. AlSalhi, M. Atif, A. Ansari and M. Willander, Materials, 2013, 6, 3584–3597.
125. R. H. Marchessault, S. Ricard and P. Rioux, Carbohydr. Res., 1992, 224, 133–139.
126. L. Raymond, J. F. Revol, R. H. Marchessault and D. H. Ryan, Polymer, 1995, 36, 5035–5043.
127. Y. Young-Hoon, K. Kab-Young and P. Un-Kyu, Ceram. Int., 2012, 38, 1599–1603.
128. Y. H. Song, M. O. Kim, M. K. Jung, K. Senthil, T. Masaki, K. Toda and D. H. Yoon, Mater. Lett., 2012, 77, 121–124.
129. L. Johnson, W. Thielemans and D. A. Walsh, Green Chem., 2011, 13, 1686–1693.
130. T. Mochochoko, O. S. Oluwafemi, D. N. Jumbam and S. P. Songca, Carbohydr. Polym., 2013, 98, 290–294.
131. J. Yin, F. Gao, Y. Wu, J. Wang and Q. Lu, CrystEngComm, 2010, 12, 3401–3403.
132. W. Jiang, K. Zhang, L. Wei, D. Yu, J. Wei and Y. Chen, Nanoscale, 2013, 5, 11108–11117.
133. M. Robitzer, L. David, C. Rochas, F. D. Renzo and F. Quignard, Langmuir, 2008, 24, 12547–12552.
134. F. Quignard, F. Renzo and E. Guibal, Carbohydr. Sustainable Dev. I, 2010, 294, 165–197.
135. G. T. Grant, E. R. Morris, D. A. Rees, P. J. C. Smith and D. Thom, FEBS Lett., 1973, 32, 195–198.
136. N. M. Pope, R. C. Alsop, Y.-A. Chang and A. K. Smith, J. Biomed. Mater. Res., 1994, 28, 449–457.
137. T. Hamaya, T. Takizawa, H. Hidaka and K. Horikoshi, J. Chem. Eng. Jpn., 1993, 26, 223–224.
138. R. Horga, F. Di Renzo and F. Quignard, Appl. Catal., A, 2007, 325, 251–255.
139. Z. A. C. Schnepp, S. C. Wimbush, S. Mann and S. R. Hall, Adv. Mater., 2008, 20, 1782–1786.
140. Z. Schnepp, S. C. Wimbush, S. Mann and S. R. Hall, CrystEngComm, 2010, 12, 1410–1415.
141. Z. Schnepp, S. R. Hall, M. J. Hollamby and S. Mann, Green Chem., 2011, 13, 272–275.
142. M. Rinaudo, Prog. Polym. Sci., 2006, 31, 603–632.
143. H. Honda, A. Kawabe, M. Shinkai and T. Kobayashi, J. Ferment. Bioeng., 1998, 86, 191–196.
144. T. Suzuki and Y. Mizushima, J. Ferment. Bioeng., 1997, 84, 128–132.
145. Y. Mizushima, J. Non-Cryst. Solids, 1992, 144, 305–307.
146. A. El Kadib and M. Bousmina, Chem. – Eur. J., 2012, 18, 8264–8277.
147. J. Matos, P. Atienzar, H. Garcia and J. C. Hernandez-Garrido, Carbon, 2013, 53, 169–181.
148. X. Guan, J. Du, X. Meng, Y. Sun, B. Sun and Q. Hu, J. Hazard. Mater., 2012, 215–216, 1–16.
149. S. S. Rashidova, D. S. Shakarova, O. N. Ruzimuradov, D. T. Satubaldieva, S. V. Zalyalieva, O. A. Shpigun, V. P. Varlamov and B. D. Kabulov, J. Chromatogr. B: Anal. Technol. Biomed. Life Sci., 2004, 800, 49–53.
150. J.-T. Yeh, C.-L. Chen and K.-S. Huang, Mater. Lett., 2007, 61, 1292–1295.
151. S. R. Hall, Adv. Mater., 2006, 18, 487–490.
152. A. Sachse, V. Hulea, K. L. Kostov, N. Marcotte, M. Y. Boltoeva, E. Belamie and B. Alonso, Chem. Commun., 2012, 48, 10648–10650.
153. F. Xie, E. Pollet, P. J. Halley and L. Averous, Prog. Polym. Sci., 2013, 38, 1590–1628.
154. G. Taillades, P. Batocchi, A. Essoumhi, M. Taillades, D. J. Jones and J. Rozière, Microporous Mesoporous Mater., 2011, 145, 26–31.
155. A. Taubert and G. Wegner, J. Mater. Chem., 2002, 12, 805–807.
156. D. K. Kim, M. Mikhaylova, F. H. Wang, J. Kehr, B. Bjelke, Y. Zhang, T. Tsakalakos and M. Muhammed, Chem. Mater., 2003, 15, 4343–4351.
157. A. El Kadib, K. Molvinger, M. Bousmina and D. Brunel, J. Catal., 2010, 273, 147–155.
158. J. F. Zhou, M. F. Zhou and R. A. Caruso, Langmuir, 2006, 22, 3332–3336.
159. D. Walsh, S. C. Wimbush and S. R. Hall, Chem. Mater., 2007, 19, 647–649.
160. A. L. Daniel-da-Silva, T. Trindade, B. J. Goodfellow, B. F. O. Costa, R. N. Correia and A. M. Gil, Biomacromolecules, 2007, 8, 2350–2357.
161. F. Jones, H. Cölfen and M. Antonietti, Colloid Polym. Sci., 2000, 278, 491–501.
162. X. Wang, D. R. G. Mitchell, K. Prince, A. J. Atanacio and R. A. Caruso, Chem. Mater., 2008, 20, 3917–3926.
163. M. Kellermeier, H. Cölfen and J. M. García-Ruiz, Eur. J. Inorg. Chem., 2012, 2012, 5123–5144.
164. E. Dujardin and S. Mann, Adv. Mater., 2004, 16, 1125–1129.
165. W. Shenton, T. Douglas, M. Young, G. Stubbs and S. Mann, Adv. Mater., 1999, 11, 253–256.
166. S. A. Davis, M. Breulmann, K. H. Rhodes, B. Zhang and S. Mann, Chem. Mater., 2001, 13, 3218–3226.
167. Y. Shin and G. J. Exarhos, in The Nanoscience and Technology of Renewable Biomaterials, John Wiley & Sons, Ltd, 2009, pp. 315–335.
168. J. Huang and Y. Gu, Curr. Opin. Colloid Interface Sci., 2011, 16, 470–481.
169. Y. Kurokawa and K. Hanaya, Carbohydr. Polym., 1995, 27, 313–320.
170. D. Yang, L. Qi and J. Ma, Adv. Mater., 2002, 14, 1543–1546.
171. S. Liu and J. He, J. Am. Chem. Soc., 2005, 88, 3513–3514.
172. K. Kim, Biomacromolecules, 2003, 4, 908.
173. E. L. Mayes, F. Vollrath and S. Mann, Adv. Mater., 1998, 10, 801–805.
174. S. R. Hall, V. M. Swinerd, F. N. Newby, A. M. Collins and S. Mann, Chem. Mater., 2006, 18, 598–600.
175. W. Brandon Goodwin, I. J. Gomez, Y. Fang, J. C. Meredith and K. H. Sandhage, Chem. Mater., 2013, 25, 4529–4536.
176. M. W. Anderson, S. M. Holmes, N. Hanif and C. S. Cundy, Angew. Chem., Int. Ed., 2000, 39, 2707–2710.
177. S. A. Davis, S. L. Burkett, N. H. Mendelson and S. Mann, Nature, 1997, 385, 420–423.
178. S. Chia, J. Urano, F. Tamanoi, B. Dunn and J. I. Zink, J. Am. Chem. Soc., 2000, 122, 6488–6489.
179. D. J. Evans, J. Mater. Chem., 2008, 18, 3746–3754.
180. T. Douglas, E. Strable, D. Willits, A. Aitouchen, M. Libera and M. Young, Adv. Mater., 2002, 14, 415–418.
181. M. Uchida, M. T. Klem, M. Allen, P. Suci, M. Flenniken, E. Gillitzer, Z. Varpness, L. O. Liepold, M. Young and T. Douglas, Adv. Mater., 2007, 19, 1025–1042.
182. Y. Ono, Y. Kanekiyo, K. Inoue, J. Hojo, M. Nango and S. Shinkai, Chem. Lett., 1999, 28, 475–476.
183. G. Gonçalves, P. A. A. P. Marques, C. P. Neto, T. Trindade, M. Peres and T. Monteiro, Cryst. Growth Des., 2009, 9, 386–390.
184. H. Wang, A. Zakirov, S. U. Yuldashev, J. Lee, D. Fu and T. Kang, Mater. Lett., 2011, 65, 1316–1318.
185. S. V. Costa, A. S. Gonçalves, M. A. Zaguete, T. Mazon and A. F. Nogueira, Chem. Commun., 2013, 49, 8096–8098.
186. R. A. Caruso and J. H. Schattka, Adv. Mater., 2000, 12, 1921–1923.
187. J. Zeng, R. Li, S. Liu and L. Zhang, ACS Appl. Mater. Interfaces, 2011, 3, 2074–2079.
188. T. Kimura, Phys. Chem. Chem. Phys., 2013, 15, 15056–15061.
189. H. Imai, M. Matsuta, K. Shimizu, H. Hirashima and N. Negishi, J. Mater. Chem., 2000, 10, 2005–2006.
190. K. Shimizu, H. Imai, H. Hirashima and K. Tsukuma, Thin Solid Films, 1999, 351, 220–224.
191. P. Rodriguez, L. Reinert, M. Comet, J. Kighelman and H. Fuzellier, J. Chem. Phys., 2007, 106, 102–108.
192. A. B. Shishmakov, Y. V. Mikushina, O. V. Koryakova, M. S. Valova and L. A. Petrov, Russ. J. Appl. Chem., 2012, 85, 1514–1518.
193. J. S. Jur, W. J. Sweet, C. J. Oldham and G. N. Parsons, Adv. Funct. Mater., 2011, 21, 1993–2002.
194. Y. Gu and J. Huang, J. Mater. Chem., 2009, 19, 3764–3770.
195. J. Zhao, Y. Gu and J. Huang, Chem. Commun., 2011, 47, 10551–10553.
196. Y. Luo, X. Liu and J. Huang, J. Nanosci. Nanotechnol., 2013, 13, 582–588.
197. C. Zollfrank, H. Scheel and P. Greil, Adv. Mater., 2007, 19, 984–987.
198. L. Jia, K. Fung-luen and D. H. L. Ng, J. Am. Ceram. Soc., 2008, 91, 1350–1353.
199. L. Zhou, J. He, J. Zhang, Z. He, Y. Hu, C. Zhang and H. He, J. Phys. Chem. C, 2011, 115, 16873–16878.
200. M. Estruga, I. Gonzalez-Valls, C. Domingo, M. Lira-Cantu and J. A. Ayllón, Eur. J. Inorg. Chem., 2011, 2011, 821–825.
201. Y. Zhang, X. Liu and J. Huang, ACS Appl. Mater. Interfaces, 2011, 3, 3272–3275.
202. H. Zhu, S. Jia, T. Wan, Y. Jia, H. Yang, J. Li, L. Yan and C. Zhong, Carbohydr. Polym., 2011, 86, 1558–1564.
203. J. Gutierrez, S. M. Fernandes, I. Mondragon and A. Tercjak, Cellulose, 2013, 20, 1301–1311.
204. J. Huang, W. Wang and Z. L. Wang, Nano Lett., 2006, 6, 2325–2331.
205. G. Cook, P. L. Timms and C. Göltner-Spickermann, Angew. Chem., Int. Ed., 2003, 42, 557–559.
206. W. Zhang, D. Zhang, T. Fan, J. Gu, J. Ding, H. Wang, Q. Guo and H. Ogawa, Chem. Mater., 2008, 21, 33–40.
207. D. P. Gaillot, O. Deparis, V. Welch, B. K. Wagner, J. P. Vigneron and C. J. Summers, Phys. Rev. E: Stat. Phys., Plasmas, Fluids, Relat. Interdiscip. Top., 2008, 78, 031922.
208. M. R. Weatherspoon, Y. Cai, M. Crne, M. Srinivasarao and K. H. Sandhage, Angew. Chem., Int. Ed., 2008, 47, 7921–7923.
209. F. Song, H. Su, J. Han, D. Zhang and Z. Chen, Nanotechnology, 2009, 20, 495502.
210. W. Zhang, D. Zhang, T. Fan, J. Ding, Q. Guo and H. Ogawa, Microporous Mesoporous Mater., 2006, 92, 227–233.
211. W. Zhang, D. Zhang, T. Fan, J. Ding, J. Gu, Q. Guo and H. Ogawa, Mater. Sci. Eng., C, 2009, 29, 92–96.
212. J. P. Vernon, Y. Fang, Y. Cai and K. H. Sandhage, Angew. Chem., Int. Ed., 2010, 49, 7765–7768.
213. C. Mille, E. C. Tyrode and R. W. Corkery, RSC Adv., 2013, 3, 3109–3117.
214. J. W. Galusha, L. R. Richey, M. R. Jorgensen, J. S. Gardner and M. H. Bartl, J. Mater. Chem., 2010, 20, 1277–1284.
215. W. Ogasawara, W. Shenton, S. A. Davis and S. Mann, Chem. Mater., 2000, 12, 2835–2837.
216. F. Mumm, M. Kemell, M. Leskelä and P. Sikorski, Bioinspir. Biomim., 2010, 5, 026005.
217. V. Puchol, J. El Haskouri, J. Latorre, C. Guillem, A. Beltran, D. Beltran and P. Amoros, Chem. Commun., 2009, 2694–2696.
218. R. W. Drum, Science, 1968, 161, 175–176.
219. J. Cao, C. R. Rambo and H. Sieber, Ceram. Int., 2004, 30, 1967–1970.
220. Z. Liu, T. Fan and D. Zhang, J. Am. Ceram. Soc., 2006, 89, 662–665.
221. M. H. Kostova, C. Zollfrank, M. Batentschuk, F. Goetz-Neunhoeffer, A. Winnacker and P. Greil, Adv. Funct. Mater., 2009, 19, 599–603.
222. Z. Liu, T. Fan, W. Zhang and D. Zhang, Microporous Mesoporous Mater., 2005, 85, 82–88.
223. Y. Shin, J. Liu, J. H. Chang, Z. Nie and G. J. Exarhos, Adv. Mater., 2001, 13, 728–732.
224. C. R. Rambo, J. Cao and H. Sieber, Mater. Chem. Phys., 2004, 87, 345–352.
225. C. Zollfrank, R. Kladny, H. Sieber and P. Greil, J. Eur. Ceram. Soc., 2004, 24, 479–487.
226. Z. Liu, T. Fan, J. Ding, D. Zhang, Q. Guo and H. Ogawa, Ceram. Int., 2008, 34, 69–74.
227. T. Ota, M. Imaeda, H. Takase, M. Kobayashi, N. Kinoshita, T. Hirashita, H. Miyazaki and Y. Hikichi, J. Am. Ceram. Soc., 2000, 83, 1521–1523.
228. X. Li, T. Fan, Z. Liu, J. Ding, Q. Guo and D. Zhang, J. Eur. Ceram. Soc., 2006, 26, 3657–3664.
229. Z. Liu, T. Fan, J. Gu, D. Zhang, X. Gong, Q. Guo and J. Xu, Mater. Trans., 2007, 48, 878.
230. T. Fan, X. Li, Z. Liu, J. Gu, D. Zhang and Q. Guo, J. Am. Ceram. Soc., 2006, 89, 3511–3515.
231. S. Zhu, D. Zhang, Z. Chen, G. Zhou, H. Jiang and J. Li, J. Nanopart. Res., 2010, 12, 2445–2456.
232. A. Dong, Y. Wang, Y. Tang, N. Ren, Y. Zhang, Y. Yue and Z. Gao, Adv. Mater., 2002, 14, 926–929.
233. G. Fritz-Popovski, D. Van Opdenbosch, C. Zollfrank, B. Aichmayer and O. Paris, Adv. Funct. Mater., 2013, 23, 1265–1272.
234. D. Van Opdenbosch, G. Fritz-Popovski, O. Paris and C. Zollfrank, J. Mater. Res., 2011, 26, 1193–1202.
235. T. Lin-Qi, N. Wei, Z. Hong-Ying, X. Qun and J. Jian-Xia, BioResources, 2009, 4, 38–48.
236. M. Zheng, Y. Liu, Y. Xiao, Y. Zhu, Q. Guan, D. Yuan and J. Zhang, J. Phys. Chem. C, 2009, 113, 8455–8459.
237. G. Patrinoiu, J. M. Caldera-Moreno, D. C. Culita, R. Birjega, R. Ene and O. Carp, J. Solid State Chem., 2013, 202, 291–299.
238. G. Patrinoiu, M. Tudose, J. M. Caldera-Moreno, R. Birjega, P. Budrugeac, R. Ene and O. Carp, J. Solid State Chem., 2012, 186, 17–22.
239. J. Zhang, S. Wang, Y. Wang, M. Xu, H. Xia, S. Zhang, W. Huang, X. Guo and S. Wu, Sens. Actuators, B, 2009, 139, 411–417.
240. X. Sun and Y. Li, Angew. Chem., Int. Ed., 2004, 43, 597–601.
241. J. Yu and X. Yu, Environ. Sci. Technol., 2008, 42, 4902–4907.
242. J. Yu, X. Yu, B. Huang, X. Zhang and Y. Dai, Cryst. Growth Des., 2009, 9, 1474–1480.
243. Q. Wang, H. Li, L. Chen and X. Huang, Carbon, 2001, 39, 2211–2214.
244. X. Lai, J. Li, B. A. Korgel, Z. Dong, Z. Li, F. Su, J. Du and D. Wang, Angew. Chem., Int. Ed., 2011, 50, 2738–2741.
245. X. Sun, J. Liu and Y. Li, Chem. – Eur. J., 2006, 12, 2039–2047.
246. L. Wen, Y. Ma, B. Dai, Y. Zhou, J. Liu and C. Pei, Mater. Res. Bull., 2013, 48, 687–690.
247. Y. Shin and G. Exarhos, Cellulose, 2007, 14, 269–279.
248. A. T. Harris and A. R. Maddocks, Mater. Sci. Technol., 2010, 26, 375–378.
249. T. L. Church, S. Fallani, J. Liu, M. Zhao and A. T. Harris, Catal. Today, 2012, 190, 98–106.
250. Y. Shin, C. Wang, W. D. Samuels and G. J. Exarhos, Mater. Lett., 2007, 61, 2814–2817.
251. X. Tao, L. Dong, X. Wang, W. Zhang, B. J. Nelson and X. Li, Adv. Mater., 2010, 22, 2055–2059.
252. J. Du, Q. Li, Y. Xia, X. Cheng, Y. Gan, H. Huang, W. Zhang and X. Tao, J. Alloys Compd., 2013, 581, 128–132.
253. Y. Shin, X. S. Li, C. Wang, J. R. Coleman and G. J. Exarhos, Adv. Mater., 2004, 16, 1212–1215.
254. Y. Gotoh, K. Fujimura, M. Koike, Y. Ohkoshi, M. Nagura, K. Akamatsu and S. Deki, Mater. Res. Bull., 2001, 36, 2263–2275.
255. H. Haiping, W. Yuxia and T. Honggao, J. Phys.: Condens. Matter, 2002, 14, 11867.
256. W. Ren, Z. Ai, F. Jia, L. Zhang, X. Fan and Z. Zou, Appl. Catal., B, 2007, 69, 138–144.
257. Y. Gu, D. Jia and J. Huang, CrystEngComm, 2013, 15, 8924–8928.
258. R. R. Unocic, F. M. Zalar, P. M. Sarosi, Y. Cai and K. H. Sandhage, Chem. Commun., 2004, 796–797.
259. A. Vioux, Chem. Mater., 1997, 9, 2292–2299.
260. M. Niederberger and N. Pinna, Metal Oxide Nanoparticles in organic solvent, Spinger-Verlag, London, 2007.
261. M. Kettunen, R. J. Silvennoinen, N. Houbenov, A. Nykänen, J. Ruokolainen, J. Sainio, V. Pore, M. Kemell, M. Ankerfors, T. Lindström, M. Ritala, R. H. A. Ras and O. Ikkala, Adv. Funct. Mater., 2011, 21, 510–517.
262. J. T. Korhonen, P. Hiekkataipale, J. Malm, M. Karppinen, O. Ikkala and R. H. A. Ras, ACS Nano, 2011, 5, 1967–1974.
263. J. T. Korhonen, M. Kettunen, R. H. A. Ras and O. Ikkala, ACS Appl. Mater. Interfaces, 2011, 3, 1813–1816.
264. B. Boury, R. G. Nair, S. K. Samdarshi, T. Makiabadi and P. H. Mutin, New J. Chem., 2012, 36, 2196–2200.
265. B. Boury and S. Plumejeau, un-published results, 2014.
266. K. Benaissi, L. Johnson, D. A. Walsh and W. Thielemans, Green Chem., 2010, 12, 220–222.
267. M. Wu, S. Kuga and Y. Huang, Langmuir, 2008, 24, 10494–10497.
268. X. Wu, C. Lu, W. Zhang, G. Yuan, R. Xiong and X. Zhang, J. Mater. Chem. A, 2013, 1, 8645–8652.
269. R. Xiong, C. Lu, W. Zhang, Z. Zhou and X. Zhang, Carbohydr. Polym., 2013, 95, 214–219.
270. J. L. T. Hage, R. D. Schuiling and S. P. Vriend, Can. Metall. Q., 1999, 38, 267–276.

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c4gc00957f

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