Study On Photocatalytic Degradation Of VOCs By Surface Modification Of TiO₂

Indoor air quality has a very significant impact on people’s health.Since people spend most of their time indoors,indoor air quality has been paid more and more attention.Volatile organic compounds（VOCs）are the main components of indoor air pollution.So far,there have been many ways to degrade VOCs.Photocatalytic oxidation has become a research hotspot in the past 20 years because of its high removal efficiency,low energy consumption and environmental friendness.However,there are still a series of problems in the process of removing VOCs by photocatalytic method.VOCs gas is difficult to adsorption;adsorption materials for VOCs adsorption capacity is limited;low catalyst efficiency;easy to produce secondary pollution is the most common problem.The researchers proposed improved methods,such as exposing the crystal face easily adsorbed by VOCs,modifying the groups easily adsorbed by VOCs,promoting charge separation,and enhancing oxidation.In the photocatalytic method,TiO₂ has become one of the most attractive semiconductor materials for the degradation of organic pollutants due to its advantages of high chemical stability,low cost and strong oxidation capacity.However,TiO₂ also has disadvantages such as large band gap width, absorption of ultraviolet light only,easy recombination of electron and hole,and difficult separation and recovery of catalyst,which make it difficult to be widely used in practical life.Various approaches have been taken to overcome these deficiencies,including precious metal modification,multiple modification,surface area increase,doping modification,semiconductor recombination,and photosensitization to promote light absorption and separation of optical carriers,and thus to promote the generation of active free radical species.This paper focuses on metal loading and manufacturing defects to promote the separation of photogenerated charge,thus improving the efficiency of photocatalytic degradation of VOCs and reducing secondary pollution.The research content is divided into the following three parts:（1）We prepared mesoporous single crystal TiO₂ by calcining the precursor solution of dual titanium source in different proportions,and used ethanol as sacrificial agent to create oxygen defects.Then,the binding effect with oxygen vacancy was strengthened by metal loading.It is found that lamellar TiO₂ can be synthesized by adjusting the roasting temperature.This kind of morphology and structure is more conducive to the adsorption of toluene gas.Through activity test,it was found that the synergistic effect of oxygen vacancy and metal increased the activity of commercial P25 by several times.（2）Commercial P25 was selected as the catalyst,F ions were doped onto the P25catalyst by mechanical stirring method,and the loaded sample was labeled as P25-F.Then the oxygen vacancy was manufactured.The catalyst P25-F was irradiated under UV lamp for 30 minutes in an oxygen-free condition,and the labeled sample was called P25-F-V_o.However,the oxygen vacancy synthesized by this method is not stable and can not be exposed to air.In our experiment,it was pleasantly found that the catalyst doped with F ion could make the oxygen vacancy exist stably in the air,and the activity was greatly improved,and the stable existence of oxygen vacancy was proved by XPS,EPR and other characterization methods.（3）Using palladium nanocrystals as seeds and formaldehyde as a relatively mild reductant,by controlling the ratio of Pd precursors to seeds,we obtained homogeneous polyhedra,such as truncated cube,vertical aspectate,truncated octahedron,and octahedron.In this part of work,we want to explore whether different crystal faces of Pd have different influences on the photocatalytic degradation of VOCs.We used the lamellar multilayer porous TiO₂ prepared in the first part of the work as the carrier to load the Pd metal exposed to different crystal faces in the hole or surface.Through experiments,it was found that different crystal faces had different degradation effects,among which the octahedral Pd had the strongest activity, indicating that the crystal face Pd{111}had the strongest activity...