Design And Properties Of Niobate-based Compound Semiconductor Materials

With the rapid development of industry,the increasingly serious environmental pollution has become the key problem that restricts the further healthy development of human society and economy,among which water pollution is particularly prominent.Photocatalytic technology is considered as one of the most promising treatment methods because of its advantages of low cost,no secondary pollution,high efficiency and stability.In recent years,niobate semiconductor materials have attracted extensive attention due to their unique electronic structure and good photochemical stability.Focusing on the preparation and synthesis of new niobate composite photocatalytic materials,this paper further improves the photocatalytic performance of niobate composite materials by broadening the photoresponse range of the materials,promoting the carrier migration efficiency and improving the photochemical stability of the materials,and studies the charge transfer mechanism and pollutant degradation mechanism of the composite materials in the photocatalytic process.The main research contents are as follows:(1)SnNb₂O₆/MgIn₂S₄(SNO/MIS)heterojunction photocatalytic material was synthesized by a simple in-situ growth method.In the experiment of degradation of tetracycline hydrochloride(TC)and reduction of hexavalent chromium(Cr(VI))under visible light irradiation,the apparent rate constant of TC degradation by the best sample SNO/MIS-2 is 30.3times that of SNO and 3.4 times that of MIS.The apparent rate constant of Cr(VI)reduction is498.6 times that of SNO and 2.5 times that of MIS.Experiments show that the construction of heterojunction can effectively inhibit the photo-corrosion of MIS,thus improving the stability of materials in cyclical use.(2)Direct Z-scheme Bi₃NbO₇/BiOCl composite photocatalytic materials were fabricated via a facile hydrothermal method.The composite samples demonstrated excellent photocatalytic performance of degrading ciprofloxacin(CIP)and reducing hexavalent chromium(Cr(VI)).The apparent rate constant of photocatalytic degradation of CIP by the best sample BNO/BiOCl-2 is 3.8 times that of BNO and 5.7 times that of BiOCl.The apparent rate constant of photocatalytic reduction(Cr(VI))is 33.2 times that of BNO and 17.6 times that of BiOCl.The superior activity was chiefly ascribed to the Z-scheme heterojunction formed between Bi₃NbO₇ and BiOCl,which effectively promoted the efficiency of carrier separation and migration.(3)Bi₃NbO₇/AgI(BNO/AgI)heterojunction photocatalysts were fabricated by a simple hydrothermal method and in-situ deposition method.The apparent rate constant of ciprofloxacin(CIP)degradation by composite materials under visible light irradiation is 9.2times that of pure BNO and 23.3 times that of pure AgI.Through a series of experiments and characterization results,it is proved that Ag⁺was partially reduced to Ag⁰ at the initial stage of photocatalytic reaction,and metallic Ag can act as the charge transfer channel of Z-scheme heterojunction,thus achieving the transformation from BNO/AgI II heterojunction to BNO/Ag/AgI Z-scheme heterojunction,and the absorption of visible light was further expanded through SPR effect.In addition,BNO/AgI composites showed excellent photocorrosion resistance and cyclic stability in four photocatalytic cycling tests.