Preparation And Photocatalytic Performance Of Cobalt Aluminum Layered Metal Double Hydroxides And Their Composites

Layered bimetallic hydroxides（LDH）,which are also known as hydrotalcite-like layered compounds,possess a unique two-dimensional metal structure consisting of a host layer with a positive charge and exchangeable interlayer anions.In this thesis,a rose-like CoAl-LDH was synthesized using the urea method.Initially,a binary Z-type heterojunction was formed by incorporating transition metal phosphides（Cu₃P）to create a Cu₃P/CoAl-LDH composite.The resulting composite was further modified by adding noble metal Au nanoparticles,and then compounded with metal oxides SnO₂ to create a ternary composite material,SnO₂@（Au/CoAl）,which synergistically enhances the visible light photocatalytic effect.The photocatalytic performance of this composite material was evaluated using simulated sunlight to degrade the organic dye methylene blue（MB）and tetracycline hydrochloride（TC）antibiotic solution,and the photocatalytic mechanism was proposed.By using density functional theory（DFT）calculation,intermediate detection,and toxicity prediction,the photodegradation pathway and related mechanism of MB and TC were clarified.（1）CoAl-LDH was synthesized using the urea method,wherein it was heated in an oil bath at 100℃and stirred continuously for 48 hours.To create a novel Cu₃P/CoAl heterojunction with a Z-type optical carrier transfer mechanism,Cu₃P nanoparticles were anchored onto CoAl-LDH nanosheets via electrostatic assembly.During MB photodegradation driven by simulated sunlight,the 25%Cu₃P/CoAl heterojunction exhibited a photodegradation activity that was 6.8 times higher than that of the monomer CoAl-LDH and 4.9 times higher than that of the monomer Cu₃P.Both experimental and theoretical results indicate that the enhanced photoactivity of Cu₃P/CoAl heterojunctions is due to the effective separation of optical carriers brought about by the Z-type carrier transfer mechanism.The main active species was determined to be·O^2-radical through capture experiments and EPR testing.Furthermore,the work function of the sample was calculated via DFT calculation,intermediate products were detected,and toxicity prediction was conducted.Based on the results,the photodegradation pathway of MB was proposed and the toxicity evaluation of the intermediate was performed.（2）The photocatalytic performance of CoAl-LDH nanosheets was improved by modifying them with Au nanoparticles using ultraviolet irradiation.Among the samples tested under simulated sunlight irradiation,1%Au/CoAl demonstrated the best performance.SnO₂ nanoparticles were synthesized through a hydrothermal method,and binary composite samples were prepared using the electrostatic assembly technique.of these,8%SnO₂/CoAl exhibited the highest photocatalytic activity.Finally,a ternary composite of 8%SnO₂@（1%Au/CoAl）was produced by combining the optimal 1%Au/CoAl with SnO₂.The degradation rate of TC at a concentration of 20 mg/L in 50minutes was 99.8%.The enhanced performance can be attributed to the ability of Au nanoparticles to extend the semiconductor absorption spectrum and the Localized Surface Plasmon Resonance（LSPR）effect.The LSPR effect causes electrons on the surface of Au to transition to a more stable plasma state due to vibrations,and then these hot electrons transition to the conduction band of the semiconductor and participate in the photocatalytic reaction together with electrons in the conduction band.The combination of two n-type semiconductors,SnO₂ and CoAl,forms a Z-type heterojunction,which accelerates the separation efficiency of photogenerated carriers and inhibits the recombination of electrons and holes within the semiconductor,thereby improving photocatalytic performance.