Study On The Photodegradation Of Two Typical VOCs By RGO-TiO₂ Photocatalysts

Volatile organic chemicals?VOCs?are major sources of air pollution.Long-term exposure to VOCs will jeopardize human health.Hence,the elimination of VOCs is an important subject.Titanium dioxide?TiO₂?,a photocatalytic material with high oxidation activity and high stability,may play an effective role in the elimination of VOCs.However,there are some intrinsic shortcomings,including the weak adsorptivity for gaseous pollutants and high recombination rate of e^--h⁺pairs,limit the practical application of TiO₂ in the degradation of gaseous pollutants.Graphene is a material with remarkable electron mobility,large specific surface area and extended?bond.The e^--h⁺separation efficiency and adsorption capacity can be improved by hybridizing graphene with TiO₂.In this work,we synthesized the graphene-TiO₂ nanocomposites with high photocatalytic activity by designing and controlling the structure of the composite.On this base,the composites were applied to the photodegradation of low concentration VOCs.Among the various VOCs,acetaldehyde is a common indoor air pollutant with small mmolecular weight.It exhibits hydrophilicity and strong polarity due to the aldehyde group.While o-xylene is a typical industrial pollutant with large molecular weight.It is a hydrophobic molecule which contains a phenyl ring.So o-xylene and acetaldehyde were chosen to be the representative of the aldehydes and aromatics to explore the different adsorption and degradation mechanism of different VOCs.The detailed research contents and results are as follows:?1?The hybrids of reduced graphene oxidized?rGO?with TiO₂ were synthesized by in-situ method using graphene oxidized?GO?and tetrabutyl orthotitanate.The TiO₂ nucleated on the surface of the rGO sheets.The TiO₂ particles were loaded on the surface of rGO sheets in as-prepared nanocomposites.The XPS spectra indicated that there were Ti-C bonds between rGO sheets and TiO₂,which was essential for the interfacial charge transfer.The pohotogenerated electrons in TiO₂ can transfer to the rGO sheets through the Ti-C bond,decreasing the recombination rate of charge carriers.ESR test proved that rGO promoted the generation of·OH radicals and depressed the formation of·O₂^-radicals at the same time.The chemically bonded nanocomposites exhibited enhanced photocatalytic activity in the degradation of flowing mode gaseous o-xylene.With an optimal rGO loading of 0.5%,the removal efficiency of o-xylene was 47%,exceeding that of P25 by a factor of 1.6.?2?rGO@TiO₂ nanocomposites were prepared by a facile solvothermal treatment using amorphous TiO₂ and GO.The rGO sheets wrapped the TiO₂ particles in as-prepared nanocomposite,which can facilitate the adsorption of VOCs.Two types of volatile organic chemicals?VOCs?,acetaldehyde and o-xylene,were selected to probe the adsorption and photodegradation mechanism of gaseous photocatalysis.The results indicated that the rGO could effectively enhance the photocatalytic activity.The highest photocatalytic activity was achieved when the rGO content was 0.5%.The removal efficiencies of the acetaldehyde and o-xylene at a flow rate of 80 mL·min^-1 were only 30%and 28%when P25 was applied,while the efficiencies were sharply increased to 42%and 54%,respectively,by using 0.5%rGO@TiO₂as the photocatalyst.Notably,the removal efficiency of o-xylene was higher than that of acetaldehyde with identical nanocomposite.This can be ascribe to that the adsorbance of o-xylene was higher than that of acetaldehyde owing to the?-?conjugation between rGO and the benzene ring of o-xylene.Moreover,the radical-scavenger tests revealed the different degradation mechanism between o-xylene and acetaldehyde.The·O₂^-and·OH played similar roles in the photocatalytic degradation process of o-xylene,while·O₂^-was the predominant radical in the degradation of acetaldehyde.The different adsorption and photodegradation properties of the two types of VOCs could propel the target orientation design of photocatalyst.