TiO₂ Based Nanostructured Photocatalysts For Enhanced Photocatalytic Formaldehyde Degradation

Photocatalytic oxidation technology has a wide applicable prospect in pollutants degradation with the advantages of photocatalytic oxidation of pollutants,without secondary pollutants,low cost and friendliness to environment and human body.TiO₂,as a representative of indirect band gap semiconductor photocatalyst,has found a wide application in water pollutant purification and gaseous pollutant degradation.However,TiO₂can only be excited by near ultraviolet ray due to its wide energy gap.Its high electron-hole recombination rate inhibits the photoinduced carriers participating the reaction.What’s more,TiO₂nanomaterials have potential threaten to human body in the treatment of gaseous pollutants when they enter the air with the airflow.Hence,realization of enhanced photocatalytic performance and fixation of TiO₂are the key to apply in gaseous pollutant degradation and achieve industrial production.The purpose of this study is anchoring TiO₂nanostructured catalyst onto micron carbon cloth and modifying its photocatalytic degradation of formaldehyde under visible light irradiation to expand the application.The dissertation includes three parts:Firstly,TiO₂nanoarrays were constructed on carbon cloth by a seed-assisted hydrothermal method.Heterojunction was formed by loading Ni O particles on the surface of the array to form a point-rod structure.The experiments showed that certain amount of loading Ni O particles could greatly improve the photocatalytic degradation performance of formaldehyde under visible light,while excessive loading of Ni O particles may hinder the light absorption.The optimal degradation efficiency of TN05reached 94%under visible light with wavelength of 420 nm,more than twice that of pure TiO₂.The cycle degradation measurements demonstrated that the catalyst remained 90%eliminate rate.The free radical capture study indicated that the catalyst can generate superoxide radical under visible light.After loading Ni O particles,the absorption of visible light with wavelength between 450 nm and 550 nm is significantly enhanced.The improved visible light utilization efficiency is attributed to the surface plasmon resonance effect by attaching Ni O nanoparticles onto the surface of TiO₂nanoarray,forming Ni-O-Ti bond.Secondly,TiO₂doped with rare earth elements into and deposited with precious metals promoted the surface electron migration and enhanced the catalytic performance.By hydrothermal method,the Y³⁺ions were doped into the TiO₂lattice by mixing different amount of Y（NO₃）₃into the hydrothermal solution.Then Pt particles were loaded onto the surface of the array.The results showed that the degradation rate of formaldede at 420 nm was increased by more than 30%compared with that of pure TiO₂samples with Y element doping.In the process of loading Pt nanoparticles,Pt⁰and Pt²⁺ions appeared on the surface of the nanoarrays.The presence of Pt⁰makes the catalyst have the ability of thermal catalytic decomposition of formaldehyde under dark conditions.With the power of visible light increased,it was found that the catalytic degradation efficiency of the catalyst could reach 100%under the synergistic photo-thermal action.After several cycle tests,the degradation efficiency remain unchanged.The doping of Y element and the loading Pt metal particles increased the concentration of O vacancy,attributing to the enhanced photocatalytic degradation of formaldehyde.Thirdlyt,the lanthanide rare earth element Ce was doped in TiO₂by a hydrothermal method,and Pt nanoparticles were loaded on the surface of the array subsequently.The experimental results showed that a trace amount of Ce doping lead the photocatalytic degradation efficiency of the sample at 420 nm visible light reached96%,nearly twice of TiO₂sample of 56%.After cycle degradation measurement,the removal efficiency kept over 90%.With the Pt noble metal nanoparticles loaded on the surface,the catalyst had the ability to decompose formaldehyde without light irradiation at room temperature.ESR data verified that a small amount of Ce doping significantly enhanced the O vacancy in the catalyst,and the presence of appropriate O vacancy can provide active sites for the photocatalytic reaction.ESR data found that the concentration of O vacancy decreased significantly after the samples loaded with Pt nanoparticles,indicating that Pt nanoparticles mainly occupied the O vacancy in the TiO₂surface during the process,and Pt⁰particles may activate the adsorbed O.In summary,TiO₂nanoarray-based photocatalysts with efficient photocatalytic activity were successfully prepared on carbon cloth by constructing semiconductor heterojunction,element doping and loading precious metal.This study may provide a new pathway to design the filter of air purification equipment for removing formaldehyde.