Study Of The Highly Enhanced Visible Light Photocatalytic Mechanism Of Agx Composites

Recently, semiconductor photocatalytic technology as a branch of greenchemistry, attracted increasingly interest because it provides a promising pathway forsolving environmental problems and energy conversion. However, the traditionalphotocatalyst, for example TiO2, has two disadvantages of weak visible light adsotptionability and easy recombination of photogengerated charge carriers. In order to solve theseproblems, it is highly desirable to develop novel photocatalysts that can yield highreactivity under visible light. In this paper, to design and preparation ofAgX/semiconductor composites materials with high photocatalytic activity and steabilityfor degradation of organic pollouants were studied. The main research contents and resultsof this thesis are divided three parts:(1) Novel Ag/AgBr/g-C3N4composite photocatalysts were constructed viadeposition-precipitation method and extensively characterized by X-ray diffraction (XRD),scanning electron microscopy (SEM), high-resolution transmission electron microscopy(HRTEM), and UV-vis diffuse reflectance spectroscopy (DRS). Under visible light (λ>420nm), Ag/AgBr/g-C3N4composite photocatalysts displayed much higher photocatalyticactivities than those of Ag/AgBr and g-C3N4for degradation of methyl orange (MO).50%Ag/AgBr/g-C3N4presented the best photocatalytic performance, which was mainlyattributed to the synergistic effects of AgBr/g-C3N4interface and the in situ metallic Agnanoparticles for efficiently separating electron-hole pairs. Furthermore, Ag/AgBr/g-C3N4remained good photocatalytic activity through5times of cycle experiments. Additionally,the radical scavengers experiment indicated that O2was the main reactive species for theMO degradation under visible light.(2) Novel Ag/AgI/BiOI composites were controllably synthesized via a facileion-exchange followed by photoreduction strategy by using hierarchical BiOI microfloweras substrate. The as-prepared Ag/AgI/BiOI composites were studied by X-ray powderdiffractometer (XRD), scanning electron microscopy (SEM), high-resolution transmissionelectron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS),Brunauer-Emmett-Teller (BET) surface area analyzer and UV-vis diffuse reflectancespectroscopy (DRS). Under visible light (λ>420nm), Ag/AgI/BiOI displayed highly enhanced photocatalytic activities for degradation of methyl orange (MO) compared to thepure BiOI and AgI, and the contents of AgI in Ag/AgI/BiOI influence the photocatalyticactivities of the composites. The highly photocatalytic activity of Ag/AgI/BiOI was mainlyascribed to the highly efficient separation of electrons and holes through the Z-schemepattern in the Ag/AgI/BiOI ternary system.(3) The binary Ag/BiOI and ternary Ag/AgI/BiOI composites were controllablysynthesized via the same facile photoreduction strategy through adjusting the silver ionsconcentration by using two-dimension hierarchical BiOI as substrate. Under visible light(λ>420nm), the photocatalytic activuties of BiOI, Ag/BiOI and Ag/AgI/BiOI were studiedby degradation of rhodamine B. The results show that the photocatalytic activity followedthis order Ag/AgI/BiOI>Ag/BiOI>BiOI, simlier with the results of the photocurrentintensity among BiOI, Ag/BiOI and Ag/AgI/BiOI. A novel Z-scheme pattern forAg/AgI/BiOI was applied for highly efficient separation of electron-hole pairs incomparison with an Ag co-catalyst model for Ag/BiOI. It provides a generalized way toobtain highly efficient Ag/BiOX (X=Cl, Br, I) and Ag/AgX/BiOX (X=Cl, Br, I)photocatalysts using photoreduction strategy.