Preparation Of Attapulgite/Carbon Nitride Based Composites And Their Photocatalytic Properties

Water pollution caused by organic matter,heavy metals,and pathogens has been a major threat to human existence.Among these water contaminants,Cr（Ⅵ）is a poisonous and mutagenic substance,hazardous to the environment and humans,and difficult to remove from water.On the other hand,Cr（Ⅲ）is far less toxic than Cr（Ⅵ）,and its removal from water by physical and chemical methods is relatively easier.Therefore,the conversion of Cr（Ⅵ）to Cr（Ⅲ）is often considered an effective method for wastewater treatment and environmental remediation.Modern water treatment techniques include adsorption,biodegradation,and photocatalytic technology.Among these,the photocatalytic degradation method has recently been very popular as a cost-effective,environmentally friendly,and sustainable technology.Carbon nitride（PCN）as a photocatalyst,has been widely investigated because of its narrow band gap of 2.7 eV,non-toxicity and low cost.However,the disadvantages of PCN are also obvious,such as high complexation rate of photogenerated carriers,low specific surface area and low quantum yield.To overcome these drawbacks,many methods have been tried,such as narrow bandgap semiconductor coupling,doping with metal/nonmetal elements and clay mineral coupling.Attapulgite（ATP）,a magnesium silicate with a rod-like morphology and many active sites on its surface,has been widely used to form functionalized composites for the adsorption of many pollutants,such as heavy metals,phenols and dyes in wastewater.When ATP is embedded in PCN,it not only serves to prevent PCN coalescence and increase the specific surface area of PCN,but also increases the active sites of PCN.This thesis focuses on the preparation of high-performance attapulgite/carbon nitride based photocatalysts by chemical precipitation and hydrothermal reaction methods using albite/carbon nitride as the substrate material.The research contents and experimental results of this thesis are as follows:1.This paper presents the synthesis of Ag@PDA/M-ATP/PCN photocatalysts for the removal of heavy metals and organic dyes via the in-situ reduction method.According to the photoluminescence（PL）spectra,time-resolved fluorescence spectra,UV–vis absorption spectra,transient photocurrent response spectra,and the EIS results,the composite of M-ATP,PDA coating,and single-atom Ag doping further promotes the separation of the photogenerated carriers,reduces the band-gap,improves the photocatalytic performance,and promotes the synergistic effect of charge separation and transfer to enhance the photocatalytic performance.The catalysts prepared by this composite strategy exhibit high charge separation efficiency,higher catalytic efficiency,and better stability than the conventional single-method modified polymeric carbon nitride catalysts.2.The CuInZnS supported attapulgite/polymer carbon nitride composite photocatalyst were successfully prepared by the hydrothermal method.The complexation of CuInZnS with M-ATP/PCN effectively increased the specific surface area,promoted the separation of photogenerated carriers,reduced the band-gap,and improved the catalytic efficiency.The prepared samples with the mass ratio of CuInZnS to M-ATP/PCN of 5:1 showed excellent photocatalytic activity for Cr（Ⅵ）reduction and H₂O₂ production with excellent photocatalytic activity,and the reduction of Cr（Ⅵ）by the catalyst was greater than 99.3%after 40 min of visible light irradiation.Meanwhile,under light（λ>420 nm）and air atmosphere conditions,the heterogeneous structure can produce 372.63 mol L^-1 H₂O₂after 30 minutes of reaction.Active radical scavenging and electron spin resonance experiments revealed that the main active radicals for the reduction of Cr（Ⅵ）are electrons and superoxide radicals.This work will facilitate the development of novel composite photocatalyst for the photocatalytic reduction of Cr（Ⅵ）and H₂O₂ generation catalysts.3.In this work,CdZnS@CQDs/M-ATP/PCN heterostructures,which function as Z-scheme photocatalysts,have been successfully prepared by the hydrothermal method.Significantly improved photocatalytic performance was exhibited by CdZnS@CQDs-1/M-ATP/PCN-1 after its optimization toward the reduction of Cr（Ⅵ）and the production of H₂O₂ under visible light irradiation.The synergistic formation of heterojunctions as well as a Z-scheme photocatalytic system,after coupling of M-ATP/PCN-1 with CdZnS and a moderate addition of CQDs,effectively enhanced the photocatalytic activities of the composites.The results revealed that the CdZnS@CQDs/M-ATP/PCN catalysts contain more active centers and suitable energy band structures,which enable them to produce more·and·.Additionally,they also absorb visible light strongly,which effectively improves the photocatalytic activity.Specifically,greater than 97.6%,reduction of Cr（Ⅵ）by CdZnS@CQDs-1/M-ATP/PCN-1 catalyst was achieved along,with the production of 719.32μmol L^-1 H₂O₂.A non-precious metal-based Z-scheme photocatalytic system with a very high potential for sustainable remediation of the environment and water purification has been developed.