Preparation Of ZnO/SiO₂ Hierarchical Nanofibrous Membranes For Removal Of Small Molecular Contaminants From Water

With the rapid development of modern industry,textile dyestuff manufacturing industry has grown rapidly in China.Beyond people's expectation,the arbitrary discharge of dye wastewater has also caused serious water pollution following the rapid development of industry.Hence,how to remove dyes in water has become the focus of attention.In recent years,the adsorption method has become an effective means of removing dyes in water due to its advantages including simple operation,low cost,low energy consumption,and high efficiency etc.Nanofibers prepared by electrospinning have many merits such as high porosity,elongated structure,increased surface area,easy functionalization of the surface and easy recycling,which make them have great potential in adsorption.In this thesis,tetraethyl orthosilicate(TEOS),polyvinyl alcohol(PVA)and anhydrous oxalic acid were used as raw materials to prepare the precursor solution,and the nanofiber adsorbent with hierarchical structure was prepared by combining electrospinning and hydrothermal method.The goal of optimizing the morphology and performance of nanofibers was achieved by continuously adjusting the process conditions in the preparation process.The adsorption isotherm and adsorption kinetics in the adsorption process were discussed in depth,and the adsorption performance of nanofiber membranes on dyes was explored and the potential application of small molecular weight organic pollutants in catalytic water was explored.(1)Firstly,TEOS,PVA and anhydrous oxalic acid were used to prepare the precursor solution,and PVA/Si O₂ nanofiber membranes were prepared by electrospinning method.Then,PVA was removed by calcination at 800?to obtain pure Si O₂.Finally,after acidification and grafting of seed crystals,the hydrothermal method was combined to produce Zn O/Si O₂ nanofiber membranes with different morphologies and multi-level micro-nano structures,which were used for efficient removal of Congo red.The adsorption performance of the nanofiber membranes was investigated by static adsorption experiment.The experimental results showed that the adsorption process of Congo red for the two kinds of nanofiber membranes with different morphology was in accordance with the Langmuir isothermal adsorption model.And the maximum adsorption capacity was estimated to be 30 mg/g and 95 mg/g,respectively.In addition,the adsorption kinetics of the two different morphologies of nanofiber membranes conformed to the pseudo-second-order kinetic model.By comparing the adsorption capacity of Congo red on nanofiber membranes with two morphologies,we found that hierarchical Zn O/Si O₂ nanofiber membranes have better adsorption performance,so they were taken as the object of subsequent research.Combined with the adsorption experiments,the adsorption mechanism of Zn O/Si O₂ nanofiber membranes was electrostatic adsorption.Therefore,Zn O/Si O₂ nanofiber membrane can be used to effectively remove Congo red dye from water.(2)Cu O-Zn O/Si O₂ nanofiber membrane with hierarchical structure were prepared by doping Cu O into Zn O nanosheets.The experimental results revealed that the adsorption of congo red by Cu O-Zn O/Si O₂ nanofiber membrane was in line with the Langmuir isotherm adsorption model,and the adsorption amount of congo red by Cu O-Zn O/Si O₂ nanofiber membrane was estimated to be 141.84 mg/g.In addition,the adsorption kinetics of Cu O-Zn O/Si O₂ nanofiber membranes conformed to the pseudo-second-order kinetic model.It turned out that the whole adsorption process reached equilibrium after 120 min.At the same time,the addition of Cu O made the nanofiber membrane had excellent catalytic degradation performance for 4-nitrophenol.Only in90s,the degradation rate of 4-nitrophenol was up to 96%,which corresponded to the change of the color of the solution from light yellow to colorless and transparent.The degradation rate of 4-nitrophenol could be estimated with a pseudo-first-order kinetic model and-ln(C/C₀)had a linear relationship with time t.The apparent catalytic degradation rate constant(K_app)of Cu O-Zn O/Si O₂nanofiber membrane for 4-nitrophenol is 0.03511 s^-1,which is at a higher level than that in related literatures.