Study On The Method And Performance Of High-efficiency Adsorption And Degradation Of Low Concentration Gaseous Toluene Under High Humidity Condition

It’s a research topic of great practical significance that the development of a purification technology that effectively treats indoor air under high humidity conditions,the preparation of environmentally-friendly purification materials,and the improvement of indoor air quality.For many years,as a green purification method with great development potential,nano-photocatalytic oxidation technology can effectively treat gaseous pollutants,which has been confirmed by more and more people in the industry.However,scientific research has found that high humidity conditions can inhibit the development of photocatalytic technology and block the progress of photocatalytic reaction.Direct application of photocatalytic oxidation technology not only makes pollutants degraded more slowly,but deactivates the photocatalyst under high humidity conditions.Therefore,photocatalytic oxidation technology can’t be applied to indoor air purification directly under high humidity.Carbon materials such as graphene and carbon nanotubes can not only adsorb indoor VOCs,but also be acted as good carriers for photocatalyst TiO₂ to apply in high humidity environment.It’s of great significance for improving indoor air quality that combining photocatalytic technology with adsorption technology can make use of binary synergy to form a combined purification technology.The adsorption photocatalytic materials were designed in this thesis include TiO_2-x/rGO and CNT-TiO₂ composite materials.The reduction of Al powder can regulate the hydrophilicity and hydrophobicity of the rGO surface to make the surface humidity of the photocatalytic composite material moderate,which facilitates the photocatalytic reaction.Organic pollutants are adsorbed on the surface of the catalyst first,and then degraded by TiO₂ with its photodegradation effect.Since the indoor VOCs concentration is too low to be degraded easily,we take the measure of adsorption first and then degradation.What’s more,the use of TiO₂ with carbon nanotubes in series cavity-like core-shell structure is more conducive to the diffusion of low-concentration VOCs.Therefore,it is of practical significance to carry out a comprehensive and systematic theoretical and experimental research,which is also the purpose of this article.At the same time,in order to fit the actual situation of low-concentration indoor VOCs better,we use low-concentration gas-phase toluene as a simulated indoor pollutant,and monitor the humidity change in the reaction chamber by a hygrometer.Finally,we solved the problems of difficult enrichment of low-concentration VOCs and easy deactivation of photocatalysts under high humidity conditions through the adsorption and photocatalytic performance of materials prepared by a series of research institutes.The study found that:（1）The reduction of Al powder can regulated the hydrophilicity and hydrophobicity of the surface of rGO,which can be conducive to the progress of the photocatalytic reaction.（2）The rate of direct photocatalytic degradation is low（the reaction of TiO₂ photocatalytic degradation of toluene is a first-order reaction）,so we adopt a reaction mode of adsorption first and then degradation.Organic pollutants are adsorbed on the surface of the catalyst first,and then TiO₂ exerts its photodegradation effect to degrade toxic pollutants.（3）By further selecting TiO₂ with a carbon nanotube series cavity-like core-shell structure,it is more conducive to the diffusion of low-concentration VOCs.The research work in this thesis has accumulated rich data for the application of photocatalytic technology in indoor air treatment,and it has important reference significance for the treatment of air pollutants under high humidity conditions.The main contents of the thesis include:（1）Efficient toluene（g）adsorption on graphene oxide reduced by Al powder under high humidity conditionWe compared and analyzed the adsorption performance of Al-rGO and H₂-rGO on toluene under different humidity and different concentrations using two methods of reducing GO with aluminum powder and hydrogen.The study found that the change of humidity has a great impact on the adsorption performance of two adsorption materials.Meanwhile,we compared the adsorption test between reduced activated carbon and reduced graphene oxide by hydrogenation reduction.Combined with XRD,Raman,FESEM,BET and other characterization methods,we described the structure-activity relationships of several adsorbent materials.The findings showed that the adsorption effect of Al-rGO is slightly better than H₂-rGO under high humidity and low concentration of toluene（g）.While the adsorption effect of hydrogenated activated carbon is the best,because the response to light is weaker than rGO,it is not conducive to subsequent photocatalysis.Comprehensively considering,the reduction of GO for 3 hours at 660^oC is the optimal adsorption condition,which can regulate the hydrophilicity of rGO surface well.The maximum adsorption capacity of Al-rGO reached 5.72 mg·g^-1 under the initial toluene concentration of 20mg·m^-3 and 80%RH,which makes a good purification effect on the indoor gas environment.（2）Photocatalytic degradation of gaseous toluene under high humidity condition by TiO_2-x/RGO composites prepared by one-step reductionWe have successfully synthesised the adsorption-photocatalytic nanocomposite with oxygen vacancies using aluminum powder as a reducing agent to reduce graphene oxide and titanium dioxide simultaneously.FESEM,XRD,FT-IR,UV-vis spetra and other means were used to prove that TiO₂ nanoparticles were evenly distributed on the rGO surface.Through a series of experiments,it was found that the best matching ratio of TiO₂ and rGO is 10 wt%,and the materials at this ratio have the best adsorption and photocatalytic activity under 80%RH and the initial toluene concentration of 20 mg·m^-3,which is of great significance to human daily life and physical health.（3）Photocatalytic degradation of gaseous toluene by carbon nanotubes in series with cavity-like core-shell spherical TiO₂ composites under high humidity conditionIn order to achieve good diffusion of toluene molecules in the gas phase,we planned to synthesize carbon nanotubes in tandem cavity-like core-shell spherical TiO₂ composites.The microwave method was used to synthesize carbon nanotubes in series solid spherical TiO₂ composites with different alcohol solvent systems,and then the chloroplast-like s-CNT-TiO₂ was changed from solid to cavity structure by the alcoholic method.XRD,FESEM,TEM and other characterizations showed the successfully synthesis of chloroplast-like s-CNT-TiO₂ and that different alcohol solvents will lead to the production of CNT-TiO₂ with different structures,while the k-CNT-TiO₂ with cavity-like core-shell structure has a good adsorption and photocatalytic degradation performance under 80%RH and the condition of 20mg·m^-3.Experiments showed that the material can rapidly enrich and continuously degrade toluene（g）,and has a broader application prospect.