Large-scale synthesis of self-assembled ultralong cannonite nanobelt film as a visible-light photocatalyst

Abstract

A high-efficiency cannonite Bi₂O(OH)₂SO₄ nanobelt photocatalyst has been successfully synthesized with sodium dodecyl sulfate (SDS) as both the coordinating agent and sulfur source through hydrolytic reaction based on a facile one-step hydrothermal process. Surface morphology analysis indicates that the products consist of ultralong nanobelts with widths around 30–50 nm, thicknesses of approximately 10 nm and lengths up to hundreds of micrometers. It is worth noting that these single crystalline nanobelts are self-assembled in the form of macroscopic architecture suspended in the solution which could be transferred onto substrates as thin films on a large scale. The as-prepared cannonite nanobelt films exhibit high photocatalytic activity for the degradation of organic dye wastewater such as rhodamine B (RhB), methylene blue, methyl orange and Congo red aqueous solutions under visible-light irradiation and have advantages of easy catalyst separation and recovery over commonly used powder-form catalysts. This new promising photocatalyst shows potential application in the treatment of dye-containing wastewaters.

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1. Introduction

Over the last few decades, since Fujishima and Honda reported the capability of water splitting with a TiO₂-based photocatalyst in 1972, semiconductor-based photocatalysis using visible light or solar energy has attracted tremendous scientific attention as an economic and green technique for solving current energy and environment problems.^1–6 In order to utilize visible light in solar and indoor illumination, developing new kinds of efficient photocatalysts under visible light is desirable and has become one of the most imperative topics in environmental photocatalysis.^7,8

In recent years, given the low price, abundant source on Earth and manifold structural motifs, bismuth-containing nanomaterials with layered structure have received much attention, especially for their relatively high photocatalytic activities under visible light or solar light because of their admirable photo absorption,^9–17 among which Aurivillius-based oxide family composed of alternative stacking of [Bi₂O₂]²⁺ layers and slabs of inorganic atoms or groups are one of the most attractive candidates.^18,19 Unfortunately, as an important monoclinic-prismatic mineral including elements of bismuth, hydrogen, oxygen and sulfur, cannonite materials with intergrowth of [Bi₂O₂]²⁺ layers have been seldom studied intensively before, and only few reports focusing on the synthesis of Bi₂O₃ nanowires from cannonite precursor have been reported.²⁰ In this sense, the monoclinic-phase cannonite with less attention could be worth expecting as potential visible-light-driven photocatalysts because of the similarities in structure with the Aurivillius phase (the presence of [Bi₂O₂]²⁺ layers).^21,22

In this manuscript, we reported a facile one-step hydrothermal method by using surfactant sodium dodecyl sulfate (SDS) as additive for the preparation of cannonite Bi₂O(OH)₂SO₄ macroscopic architecture which was self-assembled by ultralong nanobelts. Interestingly, this macroscopic architecture of Bi₂O(OH)₂SO₄ ultralong nanobelts could be easily transferred and anchored on different substrates like metals, glass and silicon wafer with large scale. The underlying formation mechanism of cannonite nanobelts was proposed. Furthermore, the photocatalytic activity of the as-prepared samples was evaluated towards degradation of rhodamine B (RhB), methylene blue, methyl orange and Congo red under visible-light irradiation for the first time. The results demonstrate that the as-prepared Bi₂O(OH)₂SO₄ nanobelts exhibit high visible-light photocatalytic activity for the degradation of organic dyes. In addition, compared with commonly used powder-form catalysts, the as-prepared Bi₂O(OH)₂SO₄ nanobelt film has advantage of easy catalyst separation and recovery.

2. Experimental section

2.1 Chemicals

All of the chemicals were purchased from Sinopharm Chemical Reagent Co. Ltd, being used without any further purification.

2.2 Sample preparation

A typical procedure for the synthesis of cannonite Bi₂O(OH)₂SO₄ nanobelts was performed as follows. 0.1 g of SDS was dissolved in 40 mL of distilled water. Then 0.1 g of Bi(NO₃)₃·5H₂O was added in the above solution. The mixture was stirred for about twenty minutes and then transferred into a 50 mL Teflon-lined autoclave with a stainless steel shell. The autoclave was heated at 170 °C for 7 h and then cooled to room temperature naturally in air. Afterwards, the resulted precipitate was collected and washed with distilled water and ethanol each for several times. The product was white scarf-like flocculent precipitate suspending in the solution. And this product could be collected in the form of powder after being dried in vacuum at 60 °C for 6 h or in the form of films after being transferred onto different substrates, such as glass, Si wafer, Cu foil and so on, with excellent adhesion.

2.3 Characterization

X-ray diffraction (XRD) was performed on a RigakuD/Max2500V/PC X-ray diffractometer system (Japan) with CuKα radiation source (λ = 0.154178 nm) operating at 40 kV and 200 mA and a scan rate of 1° min⁻¹ from 2θ = 10° to 70°. Field emission scanning electron microscopy (FESEM) images were taken using a Hitachi SU8020 field emission scanning electron microscope operated at an acceleration voltage of 5 kV. Transmission electron microscopy (TEM), high resolution TEM (HRTEM) images, selective area electron diffraction (SAED) and energy dispersive X-ray spectroscopy (EDS) were taken on JEOL JEM-2100F field emission transmission electron microscope operating at 200 kV. UV-Vis diffuse reflectance spectra were collected on a Shimadzu UV 2550 recording spectrophotometer, which was equipped with an integrating sphere and using BaSO₄ as reference.

2.4 Photocatalytic activity test

The photocatalytic activities of the cannonite nanobelt sample were evaluated by the degradation of RhB, methylene blue, methyl orange and Congo red in aqueous solutions under visible light irradiation at a distance of 10 cm. The photocatalytic system for catalytic reactions include an interior illuminated 500 W Xe lamp, a UV cutoff filter (λ > 400 nm) and circulating water cold trap system. For the convenience of test, the photocatalytic reactions were carried out in a quartz cuvette. Here, to check the photocatalytic activity of the cannonite film, the transferred film on glass substrate (2.5 cm × 0.8 cm, with 2.8–3.2 mg of Bi₂O(OH)₂SO₄, the mass of transferred film was obtained through removing glass substrate weight from the total weight of the film with glass substrate) was vertically immersed in 3 mL of dye aqueous solution with an initial concentration of 1 ppm and faced to the light source. Before being irradiated, the system was placed in dark for several hours to reach the adsorption–desorption equilibrium. Every other 60 min since being irradiated, the photocatalyst was removed from the cuvette and the concentration of residual dye solution was determined by detecting its characteristic emission wavelength on a Shimadzu UV-2550 recording spectrophotometer. Shortly after that, the photocatalyst was immersed in the dye solution again for further photocatalytic reaction. Every measuring process took less than 2 min. In addition, for complementary data, to check the photocatalytic activity of powder-form catalyst, 0.1 g of cannonite nanobelt powder and commercial TiO₂ (P25) powder catalyst were dispersed in 100 mL of RhB aqueous solution with initial concentration of 5 ppm, and then magnetically stirred in the dark for several hours to reach adsorption–desorption equilibrium. At intervals of every 30 min, 3 mL of the dispersion was drawn from the system. After removal of the catalyst by centrifugation, residual RhB concentration was determined by detecting the characteristic absorption peak intensity on a UV-visible spectrometer.

3. Results and discussion

3.1 Characterization of the cannonite nanobelts

In our synthesis, the cannonite product was prepared through hydrolytic reaction under a facile one-step hydrothermal process with SDS as an additive. X-ray diffraction (XRD) was used to investigate the phase structure and purity of the obtained sample. Fig. 1 shows the XRD pattern of the as-prepared sample hydrothermally synthesized for 7 h. All of the diffraction peaks could be readily indexed as a monoclinic phase of cannonite Bi₂O(OH)₂SO₄, with lattice constants of a = 7.700 Å, b = 13.833 Å and c = 5.696 Å, which is found to match well with the standard diffraction pattern (JCPDS card no. 76-1102). Moreover, the sharp and narrow diffraction peaks suggest that the Bi₂O(OH)₂SO₄ product possesses good crystallinity. Furthermore, from the XRD pattern, it is observed that the intensity of (040) plane is much higher than the standard value and those of other planes, indicating the preferred crystallographic orientation of the product.²³

Fig. 1 XRD pattern of the as-prepared nanobelt sample with standard XRD pattern of Bi₂O(OH)₂SO₄.

The morphologies of the as-prepared samples were investigated by FESEM, TEM and HRTEM (Fig. 2). From the low-magnification FESEM image in Fig. 2a, one can see that ultralong uniform one-dimensional nanostructures with lengths up to hundreds of micrometers could be prepared in a large scale. High magnification FESEM and TEM images (Fig. 2b and c) further reveal that these one-dimensional nanostructures are actually nanobelts with widths about 30–50 nm. Fig. 2d clearly shows the waving and twisting shape of a single belt and the thickness of the nanobelt is approximately 10 nm. The well-developed nanobelt structures are also confirmed by a high magnification TEM image. Fig. 2e shows a typical HRTEM image of a single Bi₂O(OH)₂SO₄ nanobelt, and the clear lattice fringes indicate its high crystallinity. The spacing of 0.29 nm and 0.97 nm between adjacent layer planes corresponds to Bi–O layers and SO₄²⁻ layers along [100] direction.^22,24 This indicates that the growth of the nanobelts is along the direction of Bi–O layer. The single crystal nature of the nanobelts is also confirmed by the selective area electron diffraction (SAED) pattern illustrated in the inset of Fig. 2d. The bright dots in the pattern indicate its good single crystallinity of the nanobelts. However, the nanobelts are highly sensitive to electron beam irradiation. After a certain time of intensive electron beam exposure, the Bi₂O(OH)₂SO₄ nanobelts are transformed into small granular particles, which is similar to other photo-sensitive Bi-containing catalytic compounds.^25,26

Fig. 2 Representative FESEM images (a and b), low magnification TEM images of the as-prepared nanobelts (c) and of a single twisting nanobelt (d), and high-magnification image of nanobelt (e). Inset in (d) is the corresponding SAED pattern of the nanobelt.

Energy dispersive X-ray spectroscopy (EDS) for elemental mapping is a useful technique for elemental composition analysis and distribution identification. Fig. S1 (ESI†), shows the STEM-EDS elemental mapping of the as-prepared crystalline Bi₂O(OH)₂SO₄ nanobelts. As illustrated in Fig. S1,† the distributions of Bi (Fig. S1b†), O (Fig. S1c†), and S (Fig. S1d†) elements have similar contours with the nanobelts in Fig. S1a† verifying the uniform and homogeneous existence of Bi, O, and S elements in the nanobelts. In other words, the distributions of O and S overlap well with that of Bi and all resemble the STEM image.

In order to elucidate the surface compositions and chemical states of Bi, O, and S presented in the nanobelt sample, surface analysis was performed using X-ray photoelectron spectroscopy (XPS) for the nanobelts. A typical XPS survey spectrum of the sample is presented in Fig. S2.† The wide scan spectra collected from nanobelt sample confirms the presence of Bi, O and S as well as C, while no other impurities are found in the samples. The peak positions of different atoms were determined by internally referencing the carbon at a binding energy of 284.8 eV. As shown in the high-resolution XPS spectrum in Fig. 3a, the C1s peak located at a binding energy of ca. 284.8 eV is attributed to the signal from contaminant carbon.²⁷ Fig. 3b presents the high-resolution O 1s spectrum which could be deconvoluted into three peaks. The peak located at 531.0 eV is attributed to lattice oxygen and other two peaks located at 529.7 eV and 533.0 eV can be assigned to the oxygen attached to the Bi–O bond and hydroxyl groups (OH⁻), respectively.²⁸ As the binding energy of S 2p core level is located at 160–165 eV, which overlaps with Bi 4f binding energy, thus S 2s core level is performed to characterize the S element. As shown in Fig. 3c, the S 2s peak is located at 231.9 eV which is consistent with the reported result.²⁹ Fig. 3d displays two strong symmetrical characteristic spin–orbit splittings of Bi 4f peaks at 159.4 eV and 164.3 eV, which is in accordance with the Bi 4f_7/2 and Bi 4f_5/2 signals induced by Bi³⁺ ions in the cannonite sample.³⁰

Fig. 3 High resolution C1s core level (a), O1s core level (b), S2s core level (c) and Bi4f core level (d) XPS spectra of the as-prepared nanobelts.

3.2 Formation mechanism of the cannonite nanobelts

To reveal the growth process and understand the morphological evolution of the Bi₂O(OH)₂SO₄ nanobelts, time-dependent experiments were carried out and the resulting products collected at different stages were analyzed by SEM, as shown in Fig. 4. Before hydrothermal reaction, a large number of irregular nanoparticles with sizes around 200–500 nm are produced due to the nucleation process (Fig. 4a). After being hydrothermally treated for 0.5 h, the nanoparticles grow bigger and turn to microstructures about 1–2 μm (Fig. 4b) due to the ripening of previous nanocrystals. Notably, the surfaces and edges become thinner sheet-like structures, which mean their tendency to change into two-dimensional (2D) structures. Moreover, XRD patterns of the samples prepared at 0 h and 0.5 h could be both indexed as bismuth oxido nitrate Bi₆(NO₃)₄(OH)₂O₆·H₂O (JCPDS card no. 28-0654), as shown in Fig. S3.† Up to 1 h, the sample mainly consists of thin nanosheets (Fig. 4c), which is perhaps because that the highly anisotropic internal layered structure of cannonite would guide to form 2D morphologies such as sheet-like/plate-like morphologies.³¹ Importantly, it is clearly shown that 1D belt-like nanostructure also exists in the sample, indicating its tendency to 1D structure. As the reaction time is further prolonged to 1.5 h, due to coordination control of the surfactant groups, the sample exists all in 1D nanostructures (Fig. 4d). Ultimately, after 7 h of orientating growth, 1D ultralong twisting and intertwining cannonite nanobelts were obtained via the facile hydrothermal reaction, accompanying with morphology and composition evolution.

Fig. 4 FESEM images of the samples prepared at different time: (a) 0 h, (b) 0.5 h, (c) 1 h, (d) 1.5 h.

As a widely used anionic alkyl sulfate surfactant with a hydrophobic alkyl chain and a hydrophilic head group, SDS could strongly adsorb on crystal surfaces and alter their surface properties and growth behavior, and thus could serve as soft template to orient the growth of nanomaterials.³² As the reaction proceeds, SDS undergoes hydrolysis and releases SO₄²⁻ ions especially in acidic environment,^33,34 followed by the reaction with bismuth oxido nitrate generated from the hydrolysis of the reactant bismuth (III) nitrate pentahydrate [Bi(NO₃)₃·5H₂O]. For more accurate verification, Ba²⁺ ions were utilized to confirm the released SO₄²⁻ ions in the reacted solution. As shown in Fig. S4,† the white precipitate of BaSO₄ obtained from mixing the reacted solution for Bi₂O(OH)₂SO₄ nanobelts with BaCl₂ aqueous solution indicated the existence of free SO₄²⁻ ions in the reacted solution. Therefore, the formation reaction under the hydrothermal conditions could be described as follows:

6Bi(NO₃)₃ + 8H₂O → Bi₆(NO₃)₄(OH)₂O₆ + 14H⁺ + 14NO₃⁻ (a)

C₁₂H₂₅OSO₂ONa + H₂O → C₁₂H₂₅OH + SO₄²⁻ + Na⁺ + H⁺ (b)

Bi₆(NO₃)₄(OH)₂O₆ + 4H₂O + 3SO₄²⁻ → 3Bi₂O(OH)₂SO₄ + 4NO₃⁻ + 2H⁺ (c)

Based on the above reaction mechanism, the additive SDS played an important role in adjusting the nucleation and orienting the growth of Bi₂O(OH)₂SO₄ nanobelts, and it also performed as sulfur source during the growth process. To examine the influence of SDS in the formation of this novel ultralong nanobelt film, a comparison test in the absence of SDS was conducted with other conditions unchanged. As shown in Fig. S5,† only irregular microparticles were observed. Furthermore, another comparative experiment was performed with Na₂SO₄ as additive instead of SDS (equal amount of SO₄²⁻ group), and the sample was composed of a majority of non-uniform nanosheets with thickness about 10 nm and a minority of nanobelts as well (Fig. S6†). This supports the inference that the presence of SDS triggers the phase and morphology formation of the ultralong cannonite nanobelts.

3.3 Characterization of the cannonite nanobelt film

Interestingly, by means of hydrothermal synthesis, the product was white scarf-like flocculent precipitate suspending in the solution and could be collected in the form of powder via facile collecting as well as in the form of thin film via transferring onto substrates. The scarf-like flocculent precipitate can be easily transferred and anchored on different substrates. The morphologies of the transferred film on Si substrate are displayed in Fig. 5. As revealed in the top view FESEM image (Fig. 5a), the film has uniform good coverage on the surface of Si substrate with large area. The cross-sectional FESEM image in Fig. 5b shows that the thickness of the nanobelt film is around 3 μm. In addition, as shown in the optical image (inset of Fig. 5b), the as-prepared scarf-like flocculent product could be transferred onto various substrates such as glass, Si substrates and Cu foil in a large scale (over 1.5 cm × 1.5 cm²) and with good adhesion, which would not come off from the substrates even immersed in solution for more than one month. In a word, the synthesis of this novel nanobelt film and its simple film transferring process could lay directly basis for fundamental devices in many technique applications.³⁵

Fig. 5 Top view (a) and cross-sectional view (b) FESEM images of the as-prepared nanobelt film transferred on Si substrate. Inset in (b) is an optical image of the nanobelt film transferred on glass, Si wafer and Cu foil.

3.4 Optical property and band gap of the cannonite nanobelts

Optical absorption is a key factor controlling the photocatalytic ability of a photocatalyst.³⁶ It is well known that the UV-vis absorbance edge is relevant to the energy band of semiconductors, depending on their electronic structure feature.^37–39 To estimate the band gap of the prepared photocatalyst, the UV-visible diffuse reflectance spectra of the prepared cannonite nanobelt sample is measured by using a UV-visible spectrometer. Fig. 6a shows the typical UV-visible diffuse reflectance spectra of the as-prepared nanobelt sample, from which one can see that it has absorbance in the range of both UV and visible light regions. The band gap energy could be calculated according to the following formula:^40,41

α(hν) = A(hν − E_g)^n/2

where α, h, ν, E_g, and A are the absorption coefficient, Plank constant, light frequency, band gap energy, and a constant, respectively. Among them, n depends on the characteristics of the transition in a semiconductor, i.e., direct inter-band transition (n = 1) or indirect inter-band transition (n = 4). For cannonite Bi₂O(OH)₂SO₄, which is an indirect-band gap transition material, the value of n is 4. From the diffused reflectance spectra, the Kubelka–Munk function can be used instead of α for estimating the optical absorption edge energy.⁴⁰ Therefore, the band gap energy (E_g value) of Bi₂O(OH)₂SO₄ can be estimated from the plot of (αhν)^1/2 vs. photon energy (hν), as shown in Fig. 6b. The intercept of the tangent to the X axis would give a good approximation of the band gap energy for the nanobelt sample. Thus, by extrapolating the straight portion of (αhν)^1/2 − (hν) plot to the α = 0 point, the estimated band gap energy is calculated to be 3.02 eV. Impressively, demonstrated from Fig. 6a, the as-prepared nanobelts have absorbance both in the UV and visible regions. It shows indirect inter-band transition and direct electron transition at lower energy level and higher energy level, respectively, and is thus responsive to both UV and visible-light. This indicates that the nanobelts have a relatively suitable band gap for photocatalytic decomposition of organic contaminants under visible-light irradiation.

Fig. 6 UV-visible diffuse reflectance spectrum (a) and plot of (αhν)^1/2 vs. photon energy (hν) (b) of the as-prepared nanobelt sample.

3.5 Photocatalytic activity of the cannonite nanobelt film

Photocatalytic activities of transferred cannonite nanobelt film on glass substrate were mainly evaluated by the degradation of RhB dye solution under visible-light irradiation. The temporal UV-Vis spectral changes of RhB aqueous solution during the dark adsorption process are shown in Fig. S7.† The main absorbance of RhB decreased gradually with time and finally could achieve adsorption equilibrium after about 4 h under dark condition (Fig. S7†). To eliminate the adsorption effect on the photocatalytic system, photocatalysis of nanobelt film was conducted under visible-light irradiation (λ > 400 nm) after 4 h adsorption in the dark condition.

As we expected, the photocatalytic tests indicate that our nanobelt film is a good photocatalysts on degradation of dye solution. The photodegradation process of dye wastewater was recorded by temporal evolution of the UV-vis spectra. The temporal UV-vis spectral evolution of RhB aqueous solution under photo irradiation is shown in Fig. 7a. The main absorbance decreased clearly with irradiation time, and almost completely disappeared after 7 h, accompanying with color fading from pink to final transparent solution (Fig. S8†). The absorption peaks at 554 nm corresponding to RhB diminished gradually with a slight absorption band shift to shorter wavelengths as the exposure time was extended. Finally, no new absorption bands show in either the UV or visible regions, implying the step-by-step deethylation of RhB during the photodegradation process.¹⁶ The photocatalytic performance of nanobelt film towards RhB dye solution was determined by the degradation efficiency (Fig. 7b). As shown in Fig. 7b, the blank test demonstrated that RhB degradation was extremely slow without photocatalyst under visible light illumination. In a prolonged period in dark, the amount of RhB adsorption (1 − C/C₀) (C/C₀, C is the concentration of RhB at irradiation time t, C₀ is the concentration of dye after the establishment of adsorption–desorption equilibrium) on the cannonite nanobelt sample was ca. 30% of the initial RhB solution. In contrast, it is obviously seen that the photodegradation efficiency of RhB by nanobelt film reached ca. 92% at 7 h, exhibiting great photocatalytic activity towards RhB.

Fig. 7 (a) Temporal UV-vis spectral evolutions of RhB solution in the presence of nanobelt film as a function of visible-light irradiation time (2.8–3.2 mg of film catalyst), (b) photocatalytic activities of nanobelt film with RhB solution, (c) photocatalytic activities of nanobelt powders and P25 powders with RhB solution respectively (0.1 g of powder catalysts each), (d) comparison of photocatalysis kinetics of RhB solution on as-prepared nanobelt film, nanobelt powder and P25 powder samples. (C₀ and C are the initial concentration of RhB after the establishment of adsorption–desorption equilibrium and the concentration of RhB at irradiation time t, respectively.)

In addition, photocatalytic activities of powder-form catalysts including cannonite nanobelt powder and commercial TiO₂ (P25) powder catalysts, were also evaluated under visible-light irradiation. The photodegradation efficiencies of RhB mediated by different powder-form catalysts under identical conditions are displayed in Fig. 7c. The cannonite nanobelt powder exhibits enhancement in photocatalytic activity compared with the film catalyst, with degradation efficiency of RhB as high as 94% in 90 min. While P25 powder shows relatively lower activity, only reaching 45% even after 120 min. Moreover, the photocatalytic experimental data also affords a linear pattern by fitting with a pseudo-first-order kinetics model, as shown in Fig. 7d. The pseudo-first-order rate constants (k) reflect the rate of degradation of RhB solution over different forms of photocatalysts under visible light. The reaction rate constant is ca. 2.06 h⁻¹ for the nanobelt powder photocatalyst, 4.8 times and 5.8 times of that for P25 powder and the nanobelt film photocatalyst, respectively. As we know, for powder catalysts, P25 is a common photocatalyst driven by UV irradiation, therefore, its photocatalytic activity is not as good as nanobelt powder under visible-light irradiation. The nanobelt film on substrates has lower reaction rate constant in comparison with powder-form photocatalyst due to its reduced contact area with the dye molecules and limited mass diffusion in RhB solution. However, the film-form photocatalyst on substrates has the advantages of easy catalyst separation and recovery, as well as stable structure, thus shows potential application in the treatment of dye-containing wastewaters.⁴²

Furthermore, as revealed by the temporal UV-vis spectral evolutions for methylene blue, methyl orange and Congo red dye solutions (Fig. S9†), the as-prepared nanobelt film also exhibited high photocatalytic performance towards these organic dye solutions, which suggests that cannonite nanobelt structure is a promising photocatalyst for degrading organic pollutants under visible light irradiation.

4. Conclusions

In summary, we have demonstrated that crystalline cannonite Bi₂O(OH)₂SO₄ nanobelts can be fabricated via a simple hydrolysis reaction controlled by hydrothermal method. The additive SDS played an important role in orienting the growth of nanobelts, which performs as both sulfur source and coordinating agent through the nanobelt growth process, and thus significantly influences the phase and morphology of the final nanobelts. Notably, the novel macroscopic product is essentially self-assembled by ultralong nanobelts with widths around 30–50 nm, thicknesses of approximate 10 nm and lengths up to hundreds of micrometers. Moreover, the macroscopic product could be easily transferred and anchored on various substrates to form thin film material in a large scale with excellent adhesion. Photocatalytic experiments first reveal that the transferred cannonite nanobelt film exhibits high visible-light photocatalytic activity for the degradation of various organic pollutants such as RhB, methylene blue, methyl orange and Congo red. This work not only demonstrates a new and facile route for the fabrication of Bi₂O(OH)₂SO₄ nanobelts, but also provides a new promising photocatalyst for the degradation of dye wastewater for environmental remediation.

Acknowledgements

This work has been supported by the National Natural Science Foundation of China (NSFC Grants 20976033, 21176054 and 21271058), the Fundamental Research Funds for the Central Universities (2010HGZY0012) and the Education Department of Anhui Provincial Government (TD200702).

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Footnote

† Electronic supplementary information (ESI) available. See DOI: 10.1039/c4ra10916c

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