Electrospinning Preparation Of ZnO-based Composite Nanofibers And Their Photocatalytic Properties

With the rapid development of industry and high-speed process of urbanization,various environmental problems make people anxious.For example,water pollution caused by organic dyes,and global warming caused by emissions of carbon dioxide and other greenhouse gases in atmosphere are threating to environment and people's health.Therefore,it is urgent to solve the problems of water pollution and global warming.Organic dyes can be effectively removed by photocatalytic degradation of ZnO.N and Mn codoped ZnO nanofibers obtained by electrospinning exhibited improved photocatalytic efficiency within visible light region.The obtained ZnO@ZIF-8 core-shell nanofibers have both adsorption and photocatalytic properties toward Congo red(CR).Hierarchical ZIF-L synthesized by hydrothermal method shows the enhanced CO2 capture capacity.Our work is to develop novel ZnO composite nanofibers by electrospinning and discuss their photocatalytic ability.(1)Zn(CH3COO)2·2H2O was added to PVP nanofibers,CH3COONH4 and Mn(CH3COO)2 were used as nitrogen and manganese source.N and Mn co-doped ZnO nanofibers(N&Mn-ZnO)were obtained by calcining PVP precursor nanofibers at 500 ? for 4 h in air.The optical properties were superior to those of N doped ZnO(N-ZnO)and Mn doped ZnO(Mn-ZnO).Importantly,the doping of Mn can improve the solid solubility of N in ZnO.Subsquently,N&Mn-ZnO nanofibers exhibit 75%of degradation rate of CR under visiable light.Codoping of N and Mn reduce the band gap of ZnO and slow down recombination rate of electrons(e')and holes(h+),and more hydroxyl radical(OH)obtained.Increasement of oxygen vacancies on the surface of ZnO nanofibers improves adsorption capacity towards O2,and leads to degradation enhancement.(2)Continous ZnO nanofibers were synthesized by electrospinning.ZnO nanofiber is not only a templete but also as zinc source to in situ ZIF-8 and obtain ZnO@ZIF-8 core-shell nanofibers.Concentration of dimethyl imidazole and reaction time were crucial for the formation of ZnO@ZIF-8 core-shell nanofibers.Such core-shell nanofibers can be obtained within the dimethyl imidazole concentration of 3-4 mol· L-1.The results showed that the growth rate of ZIF-8 was related to Zn2+ release rate of ZnO in dimethyl imidazole.Subsquently,ZnO@ZIF-8 core-shell nanofibers exhibited 85%of degradation rate of CR in 140 min with hole scavenger(H2O2)after adsorption equilibrium,it showed efficient adsorption and photocatalytic performance.(3)A hierarchical ZIF-L was prepared by hydrothermal method at 125 ? for 1 h.Hierarchical ZIF-L has symmetrical cross shaped morphology and consists of ZIF-L leaves,the length of hierarchical ZIF-L is about 6?m,width of 3 ?m,and thickness of?300 nm.Hydrothermal temperature is crucial for the formation of hierarchial ZIF-L.Such hierarchical ZIF-L has the higher surface area(304 m2·g-1)as compared with that of reported two-dimensional ZIF-L(161 m2·g-1).In addition,time dependent experiment shows the secondary crystal growth of hierarchical ZIF-L.Subsequently,hierarchical ZIF-L exihibited the enhanced CO2 adsorption capacity(1.56 mmol·g-1)as compared with two-dimensional ZIF-L(0.94 mmol·g-1)at 298 K and 1 bar.