Study On Adsorption And Degradation Performance Of Graphene/TiO₂ Photocatalyst Towards Acetaldehyde And Ethylene

In recent years,air pollution control has gradually received great attention,especially the removal of volatile organic compounds?VOCs?.VOCs include aldehydes,benzenes,olefins,and alkanes,which pose serious health hazards to human health.Besides,VOCs can react with substances such as NO_X and SO₂ in the air to accelerate the formation of secondary aerosols and cause severe environment problems.Studies have shown that TiO₂ is a highly efficient photocatalyst that can effectively remove VOCs.However,TiO₂ has some intrinsic problems including that electrons and holes are easily to recombine and the utilization rate of light energy is low.Moreover,in the gas phase environment,the adsorption capacity of TiO₂ for organic molecules is weak,which limits its wide application in the field of air pollution control.As a typical two-dimensional material,graphene has good electrical conductivity,high Fermi level and large specific surface area.Studies have shown that the combination of graphene and TiO₂ can effectively improve the photocatalytic degradation ability.Nitrogen-doped graphene has many unique properties compared to graphene.The lone pair of electrons introduced by the nitrogen atoms can improve the conductivity of graphene.Besides,the heterogeneous nitrogen atoms can enhance the oxygen reduction activity of graphene,which is beneficial to the transfer of electrons and the formation of superoxide radicals.In addition,the nitrogen atoms can bring about uneven distribution of the surface charge of the graphene,causing a change in the polarity of the surface.According to these properties,the combination of nitrogen-doped graphene and TiO₂ is beneficial to enhance the adsorption and degradation properties of materials towards organic molecules.In this work,graphene and nitrogen-doped graphene were combined with TiO₂.Acetaldehyde and ethylene were used as representatives of aldehydes and olefins.The adsorption and degradation properties of?nitrogen doped?graphene/titanium dioxide composites for these two kinds of VOCs were studied and the mechanism was analyzed.The specific research contents of this paper are as follows:?1?The combination of graphene and titanium dioxide was achieved by a heat treatment method.The morphology and structure of the composites were characterized by TEM,XRD and Raman.The photoelectric properties of the materials were tested by PL spectrum,UV-Vis absorption spectrum and photocurrent respondence.Adsorption and degradation properties of the catalyst towards acetaldehyde was further detected by gas chromatography.It was found that TiO₂ nanoparticles were prone to agglomerating during the preparation process.However,due to the affinity of graphene towards organic molecules,the adsorption capacity of the composites to acetaldehyde is greatly improved compared with pure TiO₂.Photocurrent test revealed that graphene can effectively promote the separation of electrons and holes.Besides,graphene can also inhibit the deactivation of the catalyst.The degradation experiment proved that the degradation ability towards acetaldehyde can be greatly improved by compounding with graphene and the composite with mass fraction of 1%reached the best degradation performance;?2?Nitrogen-doped graphene/TiO₂?N-GR/TiO₂?composites were prepared by heat treatment.The structure,photoelectric properties and adsorption as well as degradation properties of the composites were investigated.The XPS test showed that the nitrogen atoms were doped into the graphene lattice and mainly existed in the form of graphite nitrogen and pyrrole nitrogen.Graphene interacted with titanium dioxide through the C-O-Ti bond,which facilitated the transfer of electrons between the interfaces.Electron spin resonance testing showed that nitrogen-doped graphene can effectively increase the yield of superoxide radicals and hydroxyl radicals,thereby improving the photocatalytic activity of the materials.In this work,acetaldehyde and ethylene molecules were selected as target pollutants.The adsorption capacity of the materials for the two kinds of gas was studied.The flowing phase gas adsorption method and the isothermal program desorption method were combined to compare adsorption capacity of the pure TiO₂,GR/TiO₂ and N-GR/TiO₂.It was found that nitrogen-doped graphene can significantly improve the adsorption capacity of the catalyst for polar acetaldehyde,but for non-polar molecules of ethylene,the adsorption capacity was not improved compared to GR/TiO₂.The results of further photodegradation performance tests were consistent with the adsorption properties of the materials.Subsequent experiments further controlled the reaction atmosphere by mixing acetaldehyde and ethylene with dry oxygen or humid nitrogen,respectively,in order to control the formation of superoxide radicals and hydroxyl radicals.The study found that superoxide radicals play a major role in the degradation of acetaldehyde,while the contribution of hydroxyl radicals is greater during the degradation of ethylene.This study provides a new idea for the mechanism of gas phase photocatalytic degradation and selective adsorption degradation.