Degradation Performance To Toluene Of 3D Monolith TiO₂-based Photocatalyst

With the increasing number of diseases caused by indoor air pollution,toluene has attracted much attention as one of the most prominent and representative indoor volatile organic pollutants（VOCs）.Photocatalytic technology is currently an ideal“green”technology for purifying VOCs,but it still faces many challenges.For example,semiconductor photocatalysts generally have problems such as low photogenerated carrier recombination efficiency and low utilization of sunlight.And in February 2020,TiO₂ nanoparticles were classified in the second category of suspected carcinogens by the European Chemicals Agency（ECHA）.Therefore,this paper proposes the idea of constructing a three-dimensional porous monolithic photocatalyst to improve the gas-solid mass transfer efficiency and recovery rate;alleviating the pervasive challenges of semiconductor materials by introducing photocatalytic promoters or modifying metal-organic frameworks（MOFs）;in addition,by improving the production method,the following problems are solved:（1）the traditional photocatalyst active components are not firmly combined with the carrier,（2）long-term operation leads to deactivation,（3）the VOCs gas and molecules that promote the photocatalytic reaction cannot enter catalyst,resulting in a decrease in catalytic activity.The following three parts of the study were carried out.（1）Regarding the issue above,this paper proposes the concept of 3D layered TiO₂-based inorganic aerogels with high TiO₂content.,high mechanical strength and good adsorption capacity were prepared by freeze-drying.By introducing metal Pt,the electron-hole pair separation efficiency of the semiconductor is improved,and the removal effect of pollutants is improved.Three-dimensional layered TiO₂-based inorganic aerogels had a high specific surface area of 498.442 m²/g,and lipophilicity,which improved the mass-transfer efficiency for the gas–solid reaction.And the three-dimensional layered TiO₂-based inorganic aerogel still has good toluene removal efficiency under simulated sunlight and high relative humidity environment.It is proved that the H₂O molecule is an important participant in the generation of active radicals such as OH during the photocatalytic reaction,and it also provides a new idea for the catalytic purification of VOCs in high-humidity areas.（2）In order to solve the problem that the light cannot be irradiated into the photocatalyst,which leads to the reduction of catalytic activity.In this paper,melamine foam is used as carrier and ascorbic acid is used as reducing agent,the TiO₂ nanofibers were fixed on the surface and inside of the melamine foam through the hydrogen bonding force generated during the reduction of graphene oxide,3D monolith TiO₂foams with stable mechanical properties,porous structure and high specific surface area were obtained.Then,the three-dimensional monolith TiO₂ foam was modified with a metal-organic framework material HKUST-1 with good adsorption capacity for toluene,resulting in a wider light absorption range,lipophilicity,and higher photogenerated carrier separation efficiency.The three-dimensional monolith TiO₂ foam modified by HKUST-1 was applied to a self-built simulated indoor environment,and the removal ability of toluene was evaluated by using simulated sunlight and ultraviolet disinfection lamps as light sources,respectively.The research results show that the three-dimensional monolith TiO₂ foam modified by HKUST-1 has a good toluene removal effect under both light sources,which is beneficial to broaden the practical application scenarios of TiO₂-based photocatalysts.（3）Based on the problem that the powder TiO₂-based photocatalyst and the carrier are not firmly supported.In this thesis,a three-dimensional monolith TiO₂/Cu₂O heterojunction foam was synthesized by combining the n-type semiconductor TiO₂ with the p-type semiconductor Cu₂O using the sacrificial template method and the in-situ loading method using copper foam as the substrate.The three-dimensional monolith TiO₂/Cu₂O heterojunction foam was applied to a self-built simulated indoor environment to explore the removal efficiency of toluene under simulated sunlight and UV disinfection lamps,respectively.The results show that the three-dimensional monolith TiO₂/Cu₂O heterojunction foam can remove toluene under both simulated sunlight and UV disinfection lamps.This is mainly due to the p-n junction formed by the three-dimensional monolith TiO₂/Cu₂O heterojunction foam and its three-dimensional,open internal structure,which is beneficial to improve the gas-solid mass transfer efficiency.In addition,the n-type semiconductor TiO₂ and p-type semiconductor Cu₂O have excellent photoresponse to ultraviolet light and visible light,respectively,enabling the three-dimensional monolith TiO₂/Cu₂O heterojunction foam with a photoresponse range from ultraviolet to visible light.It is confirmed that a method similar to in-situ loading of semiconductor photocatalysts on metal foams to prepare monolithic catalysts is feasible,which also provides new research ideas and directions for the application of photocatalytic technology in indoor VOCs degradation.