| Energy shortage and environmental pollution have become the major problem for sustainable economic development of the world. In recent years, the semiconductor-based photocatalysis technology, due to its high efficiency, low cost, convenient, has become an efficient green technology to solve environmental problems and energy crisis. However, Ti O2 in a pure state has large band gap(3.2 e V) and high recombination of photo-generated electron/hole pair, and Ag3PO4 also has the drawbacks of poor resistant photocorrosion, which limit their industrial application and commercialization. Therefore, it is very significant for developing new and efficient composite photocatalyst. Thus, this study focus on modification, semiconductors coupling, preparation of novel composite photocatalytic materials, its structural characterization, photocatalytic reaction mechanism, formation mechanism of interface on photocatalysts, and so on. And the main contents are as follows:1. Preparation of Ti O2-based composite photocatalysts and enhanced photocatlytic activity.(1) Enhanced photocatlytic activity of Ti O2 modified with different layered metal sulfide(LMS= Mo S2, WS2 and Sn S2). A simple liquid-exfoliation method was employed to obtain Mo S2, WS2 and Sn S2 nano-sheets with mono- or few-layer. Using these nano-sheets as sensitizers, Ti Cl4 as Ti resource, the Ti O2/Mo S2, Ti O2/WS2 and Ti O2/Sn S2 composites were synthesized by liquid-exfoliation and ethanol-thermal method. The results showed that photocatalytic activity of Ti O2 nano-particles was significantly enhanced by LMS when the molar ratio of LMS and Ti O2 were 0.8:50,0.2:50 and 0.1:50, respectively. And the influences of superoxide radicals(?O2-), hydroxyl radicals(?OH), photo-generated electron(e-) and hole(h+) for photocatalytic reaction were investigated by adding the free radical trapping agents. Further, the coupling formation of Ti O2 and metal sulfides at the interface of composite photocatalyst was investigated by density functional theory(DFT) method in a molecular cluster level(2) Enhanced photocatalytic activities of Ti O2/Mo S2@zeolite photocatalysts. The photocatalytic tests results indicated that the supported photocatalyst exhibited enhanced photocatalytic activities for methyl orange(MO) degradation when loading of Ti O2/Mo S2 was 42.3wt%, dosage of photocatalyst was 0.8 g/L and p H value was 2. The photocatalytic mechanism was tentatively analyzed through two kinds of electron-transfer modes.(3) Enhanced photocatalytic activities of Ti O2 modified with LMS/g-C3N4 hybrids. First, the graphite-like carbon nitride(g-C3N4) was obtained by a simple calcination mixture of dicyandiamide and thiocarbamide. And then Mo S2/g-C3N4, WS2/g-C3N4 and Sn S2/g-C3N4 hybrids were synthesized using g-C3N4 as co-complex. The combination route of liquid-exfoliation and ethanol-thermal method were employed to synthesize Ti O2/LMS/g-C3N4 composite photocatalyst using LMS/g-C3N4 as co-catalyst. The enhanced photocatalytic activities of Ti O2/LMS/g-C3N4 photocatalysts were emerged when the mass ratio of Mo S2-g-C3N4, WS2-g-C3N4 and Sn S2-g-C3N4 were 0.15:1.0, 0.1:1.0 and 0.15:1.0, respectively. The DFT method was employed for predicting the possible structure of the composite photocatalysts, and the formation mechanism of the interface between Ti O2 and LMS/g-C3N4 hybrids was analyzed.(4) Enhanced photocatalytic activities of Ti O2 modified with LMS/RGO hybrids. The ethanol-thermal method was conducted to fabricate the Mo S2/RGO, WS2/RGO and Sn S2/RGO hybrid composite using RGO as co-complex. Subsequently, Ti O2 was modified by LMS/RGO hybrids using ethanol-thermal method. The obtained ternary composites Ti O2/LMS/RGO exhibited higher photocatalytic activity for the degradation of Rh B when mass ratio of Mo S2-RGO, WS2-RGO and Sn S2-RGO were 2.5:2.5, 2.0:2.5 and 3.0:2.5, respectively. The synergistic effect of RGO and LMS can significantly enhance the photocatalytic activity of Ti O2 through reducing carrier recombination, enhancing the transfer rate of carriers and increasing the reactive sites on the catalyst surface. In addition, calculation of the as-prepared composite photocatalysts was carried out by using Gaussian09 program at the density functional B3 LYP level using the LANL2 DZ basis set. And the formation mechanism of the interface between Ti O2 and LMS/RGO hybrids was analyzed.2. Preparation of Ag3PO4-based composite photocatalysts and enhanced photocatlytic activity.(1) Enhanced photocatalytic activities of Ag3PO4 modified with LMS/g-C3N4 hybrids. First, the Mo S2/g-C3N4 and WS2/g-C3N4 hybrids were fabricated by a solvothermal method using g-C3N4 as co-complex, in which in situ growth and solvothermal method were used for decorating Ag3PO4 on the surface of Mo S2/g-C3N4 and WS2/g-C3N4 hybrids, respectively. The obtained composite photocatalysts exhibited high photocatalytic activities when the mass fraction of LMS/g-C3N4 was 30wt% in the composites, and the holes(h+) in the valence band of Ag3PO4 with high oxidation potential could completely degrade the organic pollutant into small molecules. In addition, Ag3PO4, g-C3N4, Mo S2, WS2 with good visible-light catalytic activity could make full use of sunlight. And the Z-scheme type electronic structure formed between LMS and Ag3PO4 was conducive to the separation of photogenerated electron-hole pairs of Ag3PO4. The structure of the composite photocatalysts was calculated by DFT method to investigate the formation mechanism at the interface of Ag3PO4 and Mo S2/g-C3N4 or WS2/g-C3N4 hybrids.(2) Enhanced photocatalytic activities of Ag3PO4 modified with LMS/RGO hybrids. Mo S2/RGO and WS2/RGO(LMS/RGO) hybrids were firstly fabricated by using liquid-exfoliation method, respectively, and then using the LMS/RGO hybrid as co-catalyst, ethanol-thermal method was employed for fabricating Ag3PO4/LMS/RGO composites. The Ag3PO4/LMS/RGO photocatalysts showed high photocatalytic activities when the mass ratio of Mo S2-RGO and WS2-RGO were all 3.0:2.5, which were much higher than that of Ti O2/LMS/RGO photocatalysts. This was attributed to: 1) Ag3PO4 with unique band structure has strong photocatalytic oxidation for the degradation of organic pollutant; 2) the synergetic effect of RGO and LMS was beneficial to reduce the carrier recombination, enhance transfer rate of carrier at the interface, and increase the reactive sites and carrier lifetime, resulting to the effective utilization of the photons. Subsequently, photocatalytic mechanism of the composite photocatalyst was analyzed by radicals capture experiment. The possible structures were predicted by DFT method, and formation mechanisms of Ag3PO4/LMS/RGO composites were also analyzed. |
PDF Full Text Request