| Recently, semiconductor-assisted photodegradation of organic wastewater as an eco-friendly technology has received special attention in the application of the solution of the energy and environmental problems. However, most of powder photocatalyst together easily, and is difficult to be removed from the solution. Besides, it has a small surface area and low absorbability with organic pollutants, which is not beneficial for the photocatalytic reaction. If immobilization of photocatalytic nanoparticles onto suitable carrier material, that can enrich the organic substances by adsorption and enhance the photocatalytic performance. In addition, this composite photocatalyst can be easily recovered from aqueous suspensions for reemployment. Bentonite is a phyllosilicate mineral and is easy to exfoliate because of low charge density of its main layer, and there is a larger space degree of freedom of exfoliated bentonite nanosheet. When exfoliated bentonite nanosheets mixed with other substances, the use of the binding force between inorganic layer and insertosome, can generate some new functional materials that is difficult to obtain through direct intercalation method. Herein, we assembled g-C3N4 and Ag3PO4 on exfoliated bentonite nanosheets to synthesize EB/Ag3PO4, EB/g-C3N4 and EB/g-C3N4/Ag3PO4 composites for improving the photocatalytic activities of visible light-responsive supported photocatalysts. The morphology, structure and composition of supported photocatalysts were characterized by X-ray diffraction, Transmission electron microscopy, Fourier transform infrared spectroscopy, UV-Vis diffuse reflection spectroscopy and the Brunauer, Emmett, and Teller(BET) method. The photocatalytic performance of supported photocatalysts was evaluated by the photo-degradation of rhodamine B(RhB) in water under visible light. The structure-function relationship between the structure and photocatalytic activity of supported photocatalysts was discussed. Main results of this paper were as follows:(1) Lamellar exfoliation by intercalation decomposition method and solution dispersion method, as the result, with solution dispersion method, the peeling effect was better than that with intercalation decomposition method. According to the XRD pattern of exfoliated bentonite, the(001) characteristic peaks of montmorillonite were wide and weak obviously, which suggested that the structures of bentonite clay were partially destroyed. The TEM images of the exfoliated bentonite by solution dispersion method shown layered structure of natural bentonite had been stripped into ultrathin sheets.(2) With exfoliated bentonite as the support, EB/Ag3PO4 and EB/g-C3N4 were synthetised. It can be seen that EB/Ag3PO4 and EB/g-C3N4 exhibited enlarged surface area and stronger light absorption ability than pure Ag3PO4 and g-C3N4, respectively. EB-Ag3PO4-3 and 0.3-EB/g-C3N4 exhibited the highest photocatalytic activity for the decolorization of RhB. EB/Ag3PO4 and EB/g-C3N4 displayed higher photocatalytic activity than that of pure Ag3PO4 and g-C3N4, respectively. After 21 min, pure Ag3PO4 could degrade RhB by only 82%, EB-Ag3PO4-3 of RhB degradation rate increased to 85%. After 150 min, pure g-C3N4 could degrade RhB by 78%, but 0.3-EB/g-C3N4 could degrade RhB by 92% after 120 min. The improved photoactivity of EB/Ag3PO4 and EB/g-C3N4 is mainly attributed to the electrostatic interaction between Ag3PO4(g-C3N4) and negatively charged exfoliated bentonite, this lead to the efficient separation rate of photoinduced electron-hole pairs.(3) Novel visible-light-driven heterojunction photocatalysts(EB/g-C3N4/Ag3PO4) composed by exfoliated bentonite, g-C3N4 and Ag3PO4 was synthesized. The characterizations shown the surface area and light absorption ability of EB/g-C3N4/Ag3PO4 were improved, and exfoliated bentonite combined well with g-C3N4. Under visible light irradiation, EB/g-C3N4/Ag3PO4 with 20 % weight ratios of Ag3PO4 exhibited the highest photocatalytic activity for the decolorization of RhB. The kinetic constant of RhB degradation with the EB/g-C3N4/Ag3PO4-20%(k = 0.0658 min-1) was about 1.8-folds higher than that of pure Ag3PO4(k = 0.0356 min-1), 7.5-folds higher than that of pure g-C3N4(k = 0.0088 min-1), and 5.4-folds higher than that of EB/g-C3N4(k = 0.0121 min-1). After three successive degradation of RhB, the photocatalytic activity of the EB/g-C3N4/Ag3PO4-20% could degrade more than 90% of RhB after 60 min. The bulk heterojunction can be easily obtained in g-C3N4 and Ag3PO4, which promote the separation efficiency of the photoinduced electron-hole pairs and thus enhance the photocatalytic activity and structural stability of EB/g-C3N4/Ag3PO4. |
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