Synthesis And SOTs Application Of Ultra-low Content Metal/CdS And CdLa₂S₄ Photocatalysts

At present,the rapidly increasing energy demand and the severe situation of environmental protection have aroused the widespread concern of researchers.It is urgent to find and utilize clean and sustainable energy sources and technologies.Photocatalytic technology,as an effective way to utilize solar energy,achieve energy conversion and storage,and environmental governance,has made the huge progress in these areas in the past few decades,but many problems still exist,such as low charge separation efficiency,poor photocatalytic selectivity and indistinct catalytic mechanism.One effective way to solve the above problem is to develop the semiconductor photocatalyst with novel structure reasonably;on the other hand,because the noble metal nanoparticles such as Pt NPs,Au NPs,Au¹³@Pt NPs and so on have good size,optical and conductive properties,they are often reasonably combined with semiconductor photocatalysts in photocatalysis and electrocatalysis.Biological and energy storage and conversion and other fields will have broad prospects.Through rational consideration of the research frontiers,evelopment trend and practical problems in photocatalytic techniques,this thesis mainly focuses on the design and synthesis of new photocatalysts,discussion on mechanism of photocatalytic reaction of aromatic compounds.1.A series of Pt NPs-CdS NRs photocatalysts with different contents of Pt were prepared by solvothermal deposition of 3-4 nm PtNPs on hexagonal CdS nanorods.The photocatalysts were characterized in detail.It was found that under visible light irradiation,Pt NPs-CdS NRs photocatalysts exhibited better photocatalytic activity for selective oxidation of aromatic alcohols to aldehydes and aniline for selective reduction（SR）than pure CdS NRs.When the Pt content was 0.03 wt.%,the conversion rates of p-MBA and NB were 92.7%and 94.8%,respectively,and p-MBAD was obtained.The recoveries of aniline（AL）were 80.5%and 36.0%,respectively,about 2 times that of pure CdS NPs.In this composite photocatalyst,the loading of Pt is much lower than the reported content（usually in the range of 0.5-2 wt.%）,and plays a very important role in improving the activity of the photocatalyst.In addition,we also discussed the photocatalytic reaction mechanism of conversion of aromatic alcohol to aromatic aldehyde and nitrobenzene to aniline in the reaction system.2.Two Au NPs-CdS NRs photocatalytic materials were prepared by a simple solvothermal method.Selective oxidation of aromatic alcohols and reduction of nitroaromatic hydrocarbons in the same system were used to evaluate their photocatalytic properties.The results show that the two kinds of Au NPs have obvious plasmon resonance effect and can improve the photocatalytic performance of CdS NRs.The activity of Au5 NPs-CdS NRs with ultra-low content of Au5（0.0028 wt.%）was increased twice compared to that of single CdS NRs,The synergistic mechanism of selective photocatalytic oxidation of aromatic alcohols and selective photocatalytic reduction of nitroaromatic hydrocarbons over Au NPs-CdS NRs photocatalysts was also proposed.3.A simple solvothermal method was proposed to prepare high quality three-dimensional Au’3@Pt NPs-CdS NRs(Au¹³@Pt modified CdS nanorods).TEM exhibited that Au¹³@Pt core-shell nanoparticles were dispersed onto the surface of CdS NRs.The core-shell Au¹³@Pt exhibited largely improved CdS photocatalytic activity and stability on the photocatalytic selective oxidation（SO）of aromatic alcohols to aldehydes and selective reduction（SR）of nitroarenes to anilines under visible light irradiation（X>420 nm）.Through a series of optimization experiments,it was found that the optimum loading amount of Au¹³@Pt NPs was extremely low（0.00115 wt.%）,but the photocatalytic activity of Au¹³@Pt NPs-CdS NRs was 2 times that of pure CdS NRs.The result proved the superiority of the core-shell metal nanomaterials.On the basis of this,the mechanism of the coupling reaction system was proposed.It also provides an important reference for the design and application of other core-shell metal photocatalysts in the coupling reaction system.4.A novel visible-light-photocatalytic process was successfully developed to couple the selective oxidation（SO）of aromatic alcohols to aldehydes and selective reduction（SR）of nitroarenes to anilines on a bare ternary chalcogenide CdLa₂S₄ photocatalyst in N₂ atmosphere.The photocatalyst showed a high stability and a good generality for the selective conversions due to the well-matched band structure and the high separation efficiency of photoinduced electrons（e^-）and holes（h⁺）.For p-substituted aromatic alcohols,the selectivities to the corresponding aldehydes are as high as ca.90%.The electro-donating substituent in the para position benefits the SO reactions,which are triggered by h⁺ via a successive deprotonation;while for p-substituted nitroarenes,the SR to the corresponding anilines is vulnerable to the steric hindrance of the groups and the selectivities are lower than that of the SO conversions.H⁺ deprotonated in the SO of aromatic alcohols is indispensable for the SR of nitroarenes as they are achieved by a H⁺-coupled six e-reduction process,which leads to the low conversion efficiencies.The half conversions not only be coupled by the photoinducea e-and h⁺,but also collaborate with each other through H⁺.Our results clearly demonstrate the emerging concept of a coupled reaction system for sunlight-driven synthesis of fine chemicals and reveal the underlying mechanism.