Study On Preparation And Properties Of Ag-based Photocatalysts

In recent years,semiconductor photocatalysis technology has attracted much attention because of its great research value and application prospects in solving water pollution problems.Among photocatalytic materials,silver-based semiconductor materials have attracted extensive attention of researchers because of their simple synthesis process,response to the visible light and excellent photocatalytic effect.However,the cyclic and photocatalytic properties of silver-based semiconductor materials limit the application requirements.To solve this problem,three silver-based composite photocatalytic systems of AgCl/AgIO₄,AgCl/Ag₂SO₃ and Ag₂WO₄/WS₂ were constructed in this work.The friendship of microstructure and photocatalytic performance was discussed and the separation mechanism of photogenerated electron-hole pairs in photocatalytic degradation process was studied.The synergistic mechanism of photocatalysis was also explored.It mainly includes the following aspects:?1?Preparation and properties of AgCl/AgIO₄ composite photocatalysts.A novel AgCl/AgIO₄ composite was fabricated via an in-suit synthetic method.The structure,morphology and optical properties were characterized by X-ray diffraction?XRD?,transmission electron microscopy?TEM?,ultraviolet-visible diffuse reflectance spectroscopy?UV-Vis DRS?,electrochemical impedance spectroscopy?EIS?and X-ray photoelectron spectroscopy?XPS?,respectively.Moreover,rhodamine B dilute solution was used to characterize the photocatalytic activities of the as-prepared composites under the visible light irradiation.Experimental results show that the photocatalytic activity of the as-prepared hybrids is first increased and then decreased with increasing the contents of AgIO₄.When the molar ratio of AgCl to AgIO₄ is 1:5,in 30 min,the as-prepared composites exhibit the highest photocatalytic activity and possesse 96.3%of degradation efficiency.That is increased by 71.5 and 27.9%compared with AgCl and AgIO₄,respectively.Moreover,AgCl is linked with AgIO₄via chemical bound rather than physical contact at the interfaces of these two semiconductors.In addition,a possible photocatalytic degradation mechanism for the as-prepared hybrids has also been presented.The holes and superoxide radicals play the dominant role during the process of photocatalytic degradation.?2?Preparation and properties of AgCl/Ag₂SO₃ composite photocatalysts.A novel highly active AgCl/Ag2SO3 composite photocatalyst was fabricated via an in-suit composite method,and the relationship between the structure and photocatalytic performance was also discussed.Experimental results exhibit that the degradation rate of the as-obtained samples is firstly increased and then decreased with increasing the amount of Ag₂SO₃ under the visible light irradiation.When the mass ratio of AgCl to Ag2SO3 is 1:2,it displays the highest degradation rate of99.2%for rhodamine B in 30 min,which is obviously higher than 46.1 and 60.5%of pure AgCl and Ag₂SO₃,respectively.Similar results could be found in degradation of methyl orange.It has the maximum of 97.4%in 90 min,which is higher than 55.2and 48.7%of pure AgCl and Ag2SO3,respectively.Moreover,the as-prepared hybrids possess the enhanced separation and transfer of photo-generated electron-hole pairs compared to the pure samples.In addition,the holes and superoxide radicals play the dominant role and the hydroxyl radicals play the secondary role during the process of photocatalytic degradation.?3?Preparation and properties of Ag₂WO₄/WS₂ heterojunction photocatalyst.Ag₂WO₄/WS₂ heterojunction photocatalysts have been successfully fabricated by a simple deposition method.Furthermore,the photocatalytic properties of Ag₂WO₄/WS₂ photocatalysts with different WS₂ dosages were studied,and the photocatalytic mechanism was explored.Experimental results show that the wrinkled WS₂ nanosheets can improve the light absorption,photocatalytic activity and recyclability of Ag2WO4 under the visible and near-infrared light irradiation.The degradation efficiency of the as-obtained Ag₂WO₄/WS₂ hybrids show first increased and then decreased with increasing the usage of WS₂ nanosheets.When the amount of WS₂ is 15 wt%,in 120 min,it reaches the maximum of 97.8%,which is much higher than 17.8%of pure Ag₂WO₄.Moreover,after three cycles of the degradation,the as-prepared hybrids still possess 94.4%of the degradation efficiency.Moreover,superoxide radicals and hydroxyl radicals play a major role during the process of photocatalytic degradation reaction.The enhanced photocatalytic activity can be ascribed to the formation of heterojunction at the interface of Ag₂WO₄ and WS₂.