Physical-chemistry at the cross-road of advanced oxide materials

Oxide-based materials have been largely studied for their catalytic, electronic or adsorbent properties. Since the early '60s, when oxides and metals dispersed on oxides used for catalysis and sensing were mostly studied, the interest of the scientific community has been extended to other technological applications such as abatement of pollutants, energy production, biotechnology and nanomedicine.

A number of research groups and scientists contributed to the rich and stimulating scientific domain of the physical–chemical understanding of bulk, surface, and interfacial features of oxide-based materials, and among them we would like to mention Prof. Salvatore Coluccia, Prof. Edoardo Garrone and Prof. Giovanna Ghiotti, to whom this themed issue is dedicated on the occasion of their retirement at the end of 2012. Their early work in the Physical Chemistry group of the University of Torino (Prof. Garrone then moved in the late '90s to the Polytechnic of Torino) was specifically focussed on spectroscopic studies (IR, diffuse reflectance UV-vis-NIR, and photoluminescence) of surface species and reactive centres of oxides (primarily MgO and SiO₂) monitored by molecular probes (CO, H₂, NO, etc…). However, they extended their interests through the years to a very broad range of materials using multi-technique approaches, including computational modelling.

This themed issue was inspired by the scientific career of these colleagues, characterized by the pursuit of the development, through the elucidation of structure–function relationships, of new functional oxide-based materials with expected tailored smart properties and, in parallel, of the achievement of fundamental knowledge by using sophisticated tools of characterization.

Indeed, the papers in this issue can be considered as significant present day examples of advances along these two scientific pathways, of course exhibiting significant interconnections. On one hand the reader especially interested in the possibility to push further the frontier of the development of new (in terms of composition, morphology, texture) oxide-based materials will find contributions to these fields dealing with:

− in silico fabrication and characterization of oxide nanotubes (El-Kelany et al. “The electronic structure of MgO nanotubes. An ab initio quantum mechanical investigation”, DOI: 10.1039/c3cp50979f);

− theoretical explanation of the hot points of graphene oxide chemistry, and suggestion of reliable models of both chemically produced and chemically reduced graphene oxides (Sheka and Popova, “Molecular theory of graphene oxide”, DOI: 10.1039/c3cp00032j);

− in depth solid-state NMR characterization of the molecular structure of periodic mesoporous organosilicates (Grüning et al. “Molecular-level characterization of the structure and the surface chemistry of periodic mesoporous organosilicates using DNP-surface enhanced NMR spectroscopy”, DOI: 10.1039/c3cp00026e);

− hierarchical macroporous–mesoporous catalytic materials with an efficient transport of reactants to the catalytically active sites (Kamegawa et al. “Preparation of aluminium-containing mesoporous silica with hierarchical macroporous architecture and its enhanced catalytic activities”, DOI: 10.1039/c3cp51022k);

− design and fabrication of specific active sites in zeotypes materials for targeted catalysed transformations (Potter et al., “Investigating site-specific interactions and probing their role in modifying the acid-strength in framework architectures”, DOI: 10.1039/c3cp51182k);

− the possible exploitation of carefully designed heteropolyacids supported photocatalysts (Marcì et al., “Keggin heteropolyacid H₃PW₁₂O₄₀ supported on different oxides for catalytic and photo-assisted propene hydration”, DOI: 10.1039/c3cp51142a);

− novel organic surfactants to template the synthesis of mesoporous silicas with tuned particle morphology, pore size, and pore ordering (Yuen et al., “A Flexible, Bolaamphiphilic Template for Mesoporous Silicas”, DOI: 10.1039/c3cp51546j);

− metal ions grafted on oxides catalysts for the substitution of present day unsustainable technologies (Tiozzo et al., “Niobium–silica catalysts for the selective epoxidation of cyclic alkenes: the generation of the active site by grafting niobocene dichloride”, DOI: 10.1039/c3cp51570b).

On the other hand, in another ensemble of papers, new physical–chemical insights mainly based on investigations of solid–molecules interactions are presented, aimed at understanding in depth some relevant features of oxide-based materials, such as:

− structure–property relationships of zeolite nanocrystal with an innovative morphology: detailed description of the nature and localization of the hydroxyl groups and surfaces species by the use of probe molecules (Bleken et al., “Probing the surface of nanosheet H-ZSM-5 with FTIR spectroscopy”, DOI: 10.1039/c3cp51280k);

− role of surfaces in promoting the formation of “high energy bonds”: amino acids adsorbed on non-porous silica (Lambert et al., “A comparative study of the catalysis of peptide bond formation by oxide surfaces”, DOI: 10.1039/c3cp51282g);

− nature and accessibility of external and internal surfaces of hydrophilic and hydrophobic alumino-silicate nanotubes (Bonelli et al., “Surface properties of alumino-silicate single-walled nanotubes of the imogolite type”, DOI: 10.1039/c3cp51508g);

− surface topography of nanoparticles at the unit-cell level (Deiana et al., “Surface features of TiO₂ nanoparticles: combination modes of adsorbed CO probe the stepping of (101) facets”, DOI: 10.1039/c3cp51524a);

− defects-related surface chemistry (Vindigni et al., “Effect of Ceria Structural Properties on Catalytic Activity of Au/CeO₂ Catalysts for WGS Reaction, DOI: 10.1039/c3cp51198g);

− complexity of the physical–chemical interplay among co-adsorbed molecules (Morandi et al., “Effect of water and ammonia on surface species formed during NO_x storage-reduction cycles over Pt–K/Al₂O₃ and Pt–Ba/Al₂O₃ catalysts, DOI: 10.1039/c3cp51195b);

− intermolecular and host–guest interactions in nanocomposites (Conterosito et al., “Structural characterization and thermal and chemical stability of bioactive molecule/hydrotalcite (LDH) nanocomposites”, DOI: 10.1039/c3cp51235e);

− structural and energetic aspects ruling the adsorption behaviour of pollutant molecules in zeolites (Sacchetto et al., “The interactions of methyl tert-butyl ether on high silica zeolites: a combined experimental and computational study”, DOI: 10.1039/c3cp51684a);

− molecular events occurring during the disaggregation of lamellar materials (Martins de Souza e Silva et al., “Novel insights on magadiite disaggregation: a multitechnique study on thermal stability”, DOI: 10.1039/c3cp51491a);

− identification of surface reactive sites on heterogeneous surfaces (Crocellà et al., “On the adsorption/reaction of acetone on pure and sulfate-modified zirconias”, DOI: 10.1039/c3cp50990g);

The themed issue is enriched by two perspective articles which enlighten selected areas of heterogeneous catalysis involving oxides in the context of clean technology, green chemistry and sustainability. Sir J. M. Thomas (“Oxidic materials: an endless frontier”, DOI: 10.1039/c3cp52182f) reports on some examples of reactions, effected under benign conditions, by the use of single-site heterogeneous oxidic catalysts (SSHCS). A brief survey is also given of strategies that are required for the design of better oxidic photocatalysts for the conversion of visible light to H₂ and O₂. The topic of the development of oxide materials for solar energy conversion technologies, including water splitting and photofuel cells, is also covered by the perspective article of the Prof. M. Anpo group (Horiuchi et al. “Recent advances in visible-light-responsive photocatalysts for hydrogen production and solar energy conversion – from semiconducting TiO₂ to MOF/PCP photocatalysts”, DOI: 10.1039/c3cp51427g).

The third perspective article authored by Costantino et al. (“Coupling physical chemical techniques with hydrotalcite-like compounds to exploit their structural features and new multifunctional hybrids with luminescent properties”, DOI: 10.1039/c3cp51581h) deals with recent advances in the application of physical–chemical techniques for the study of hydrotalcite-like compounds (HTlc) and for the design and synthesis, using intercalation chemistry routes, of new hybrid luminescent materials.

Finally, we would like to express our sincere gratitude to the contributors to this PCCP themed issue. The relevance of physical chemistry studies for understanding the properties of oxide materials and for their exploitation in several technological applications has been enlightened by the high quality papers collected here. All contributors helped to effectively illustrate different topics in the field of oxide materials research which is, in all of its facets, so deeply connected to the life's work of Profs. Salvatore Coluccia, Edoardo Garrone and Giovanna Ghiotti. We are also indebted to the staff of PCCP for their very effective assistance.

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