Hydroxylation And MnO_x Modification Of Reduced Graphene Oxide/Titanium Oxide Hybrids

As one of the most promising and potential photocatalysts,TiO2-based catalysts have played an important role in field of pollution treatment,environmental protection,hydrogen production and solar energy utilization.Due to its excellent electronical conduction and surface chemical properties,graphene as an ideal supporter can improve the adsorbablity and photocatalytic activity of TiO2-based catalysts.It is conductive to obtain the composite catalysts with better performances and good application prospects.However,using traditional methods to synthesize graphene/TiO2 based photocatalysts is difficult to solve the aggregation of graphene and poor compatibility that limit the stability and catalytic activity of hybrids.Graphene oxide has good dispersion performance and strong chemical activity,but its rich defects decrease graphene's physical performances significantly.It needs to be further reduced that increases the technology difficulty and synthesis cost.Microwave heating can shorten the reaction periods,speed up the reaction rate,improve the production efficiency and reduce the energy consumption,which shows great superiority in synthesis of nanomaterials.Therefore,we used ultraviolet irradiation and microwave-assisted H2O2 oxidation technology to reduce graphene oxide and improve the surface hydrolation of TiO2 nanoparticles in situ.It can obtain the graphene/TiO2 hybrids with strong binding interface,wide spectral response range,strong absorbablity and high activity.Based on this,MnOx is further used to modify and build the ternary heterojunction to obtain the effctive and energy-storing visible photocatalyst.Through the comprehensive characterizations on microstructure and property,we find out the optimal preparation technology,and discuss the synthesis and enhancement mechanism.In this report,the ultraviolet excitation-microwave radiation method(UV-WM)not only can realize the green and rapid synthesis of graphene-based composites in an energy-saving and low-cost way,but also induce the high-level hydrolation and in-situ reduction of graphene oxide.Especially,it improves the light absorption and photocatalytic efficiency,and realizes the catalytic and antibacterial activity under no light irradiation eventualy.This study may support an important theoretical guidance and broad prospect for industrial application.The mian findings were exhibited as follows.(1)Using Tetrabutyl titanate,acetate/nitric acid,graphene oxide,H2O2 as raw materials,water-ethanol mixture as a solvent,polyacrylic acid and CTAB as the organic electrolyte,the highly-hydroxylated TiO2/reduced graphene oxide hybrids(OH-rGO/TiO2)were synthesized by the UV-WM method.The structure,morphology and photoabsorption of as-prepared samples were characterized using XRD,TG-DTA,FTIR,Raman,PL,SEM,TEM,XPS and ESR.The photocatalytic activity,durability,antibacterial activity and its mechanism of OH-rGO/TiO2 were systematically studied.The results showed that the surface hydroxylation decreased the crystallinity and size of TiO2,induced many defects on the surface,such as Ti3+,0 vanacy and Ti-OH,and narrowed significantly the band-gap width of TiO2 with its spectral absorption edge shifting to 620 nm and enhanced activity up to 50%of TiO2.Under the light irradiation,hydroxylation proceeded spontaneously and graphene oxide was further reduced in situ,which supported a sustainable adsorablity and high UV-Vis catalytic activity.The good compatibility and synergism of adsorption and catalysis gave OH-rGO/TiO2 hybrids a strong durability for rhodamine B(RhB).In addition,it exhibited a good activity in wide-range and high-concentration organic dyes between 4.89 to 195.6 ppm.(2)Using Tetrabutyl titanate,manganese acetate,acetate/nitric acid,H2O2,graphene oxide as raw materials,water-ethanol mixture as solvent,polyacrylic acid and CTAB as the organic electrolyte,rGO/TiO2-MnOx heterojunction composites were synthesized by a UV-WM method.The structure,morphology and their photoabsorption of samples were characterized by XRD,TG-DTA,SEM,TEM,EDS-mapping,FTIR,Raman,PL and XPS.The photocatalytic,electrochemical and antibacterial activity were systematically investigated,and the enhancement mechanism of MnOx modification was analyzed as well.Results showed that the OH active points on TiO2 benefited for MnOx quantum dots to distribute on rGO/TiO2 hybrids.MnOx modification narrowed the band gap of rGO/TiO2 from 2.79 eV to 2.25 eV.It caused the formation of stacking-fault energy level in rGO/TiO2-MnOx hybrids that reduced the recombination of electron-hole pairs.In this report,the procedure of low manganese load and graphene usage about 6 ml with pH-2.83 made the rGO/TiO2-MnOx with best photocatalytic activity for RhB and methyl orange(MO),where 99.7%of RhB can be degraded within 30 minutes and MO can be completely decomposed in double times.The photocatalytic activity of OH-rGO/TiO2 hybrids was enhanced to about 20%after impoting MnOx.The synthetics showed good recycle activity for the deterioration of RhB and MO.Besides,rGO/TiO2-MnOx hybrids possessed strong antibacterial activity against Escherichia coli and Staphylococcus aureus with the minimal inhibitory concentration(MIC)to 15.62?g/mL and 31.25 ?g/mL,respectively.The antibacterial effect of OH-rGO/TiO2 hybrids was enhanced about 3 times by adding MnOx quantum dots.MnOx dots modification improved the specific capacitance and decreased the impedance of rGO/TiO2 hybrids to some extent,which was conductive to trap and store the photoexcited electrons.It enhanced the surface activity of TiO2 prolonging the conduction life of photoelectrons,which made it possible to reach the catalysis and antibacterial without light irradiation eventually.