Synthesis And Photocatalytic Performance Of In-containing Layered Double Hydroxides Based Photocatalysts

In recent years, considerable efforts have been placed on the design and fabrication of novel and visible-light-active photocatalysts in the field of solar energy conversion and environmental purification. The composite photocatalysts show higher photocatalytic efficiencies than pure TiO2 and ZnO. In this work, novel composite photocatalysts with visible light response were designed and synthesed by regulating band structure. The NiZnln ternary layered double hydroxides (LDHs) were prepared by introducing Ni and In elements in order to increase valence band location and decrease conduction band location. ZnFe2O4/In2O3/ZnO ternary heteronanostructure system was obtained by coupling broad band gap ZnO with narrow band gap ZnFe2O4 and In2O3 semiconductor. The as-prepared NiZnln-LDHs and ZnFe2O4/In2O3/ZnO composites were characterized by XRD, SEM, TEM, N2 adsorption-desorption isotherm, XPS, UV-vis DRS, PL and EPR.For NiZnIn-LDHs composites, the results showed that the composites were composed of major NiZnIn-LDHs and trace In(OH)3 phases. Strong absorption peaks appeared in the visible light region of UV-vis diffuse reflectance spectra due to the incorporation of Ni and In into materials. The ternary composite had the lowest PL intensity compared to the other binary LDHs, indicating that the coexistence of three ions promotes charge separation. NiZnln LDHs with the Ni/Zn/In molar ratio of 2/1/1 had the highest photocatalytic activity for the degradation of malachite green under visible light irradiation, which was attributed to the proper band gap, fast charge transfer and large specific surface area. LDHs materials possessed abundant surface hydroxyl groups that can accept photogenerated holes to suppress the recombination of electron-hole pairs. In addition, the oxo-bridged bimetallic M-O-M linkages accelerate the photogenerated charge transfer and enhance the photocatalytic efficiency.For ZnFe2O4/In2O3/ZnO composites, the results revealed the composites consisted of ZnO, In2O3 and ZnFe2O4 phases, displyed the existence of nano-heterojunction, visible light strong absorption, and lowest PL intensity. When heterojunction was formed, electrons can migrate from the conduction band (CB) of ZnFe2O4 to the CB of In2O3 and then to ZnO through the interfacial potential gradient. ZnFe2O4/In2O3/ZnO composites with the Zn/In/Fe molar ratio of 3/0.3/0.7 had the highest photocatalytic activity for the degradation of methylene blue under visible light irradiation, because the heterostructure can give rise to the visible-light response, as well as reducing the recombination opportunities of the photogenerated electron-hole pairs.The two types of photocatalysts exhibit good stability and universality. This work provides promising alternatives for developing visible-light responsive ternary systems for dye degradation.