Removal Of Common Organic Pollutants From Water By Combining Seperation With Catalytic Oxidation Of Carbon Nanocomposite Membranes

In order to reduce the potential threat of micropollutants to water ecology,various carbon nanomaterials,including graphene oxide(GO),reduced graphene oxide(rGO)and multiwalled carbon nanotubes(CNT)etc.,were loaded on the surface of nylon microfiltration membrane to build up a micro-interface reaction platform using ultrasound-assisted filtration method in this study.With introducing persulfate(PS)as the oxidant,the combined adsorptive filtration with catalytic oxidation was achieved in the same process.Firstly,the effects of rGO reduction degree and CNT surficial function groups on the carbon layer structure,permeability performance and removal efficiency of fulvic acid(FA)with small molecule were investigated in both constant-pressure and constant-flux filtration.Moreover,the removal of sulfamethoxazole(SMX)at a low concentration level by PS oxidation,membrane filtration and catalytic oxidation of membrane interface were studied with constant-flux continuous and circulating filtration,with the condition optimization of rGO reduction degree,PS dosage and solution pH etc.In the end,an advanced water treatment method was offered according to the reaction mechanism of the membrane interface-catalytic oxidation system.The results showed that the precise control of carbon-to-oxygen atomic ratio(C/O≈3)on the surface of composite membrane could be achieved by partial reducing oxygen-containing groups on GO sheets with hydrothermal method,which were characterized using scanning electron microscopy(SEM),atomic force microscopy(AFM),and X-ray photoelectron spectroscopy(XPS)etc.A comparable FA removal was observed with the composite membranes dominated by rGO and cross-linked with CNT(the mass ratio of rGO to CNT of 2:1)to GO/CNT ones,while the former showed a better permeability performance,as the evidences of larger water flux J and lower specific filtration resistance r_c.However,the higher reduction degree of rGO would weaken the adsorptive filtration for FA.Although the surface hydrophilicity of composite membrane with hydroxylated or aminated CNT,the rGO layer composited with origin CNT showed the optimum structural stability.When the rGO/CNT composite membranes were employed,the SMX removal efficiency of catalytic oxidation was obviously larger than the additive results of PS oxidation and membrane filtration.At the higher reduction degree of rGO,the stronger catalytic oxidation was obtained with a weaker adsorptive filtration for SMX.Under neutral pH condition,the catalytic oxidation of composite membrane with the surface C/O ratio around 3 presented the most efficient SMX removal and destroyed its molecule effectively.In addition,the SMX removal was improved by increasing PS dosage significantly,and it could be operated at the lower filtration pressure.According to pseudo second order dynamics,the equilibrium absorption capacity of composite membrane for SMX was proportion to PS dosage,and it is that the strong self-cleaning function of catalytic oxidation causing a stable SMX removal in membrane filtration.After the long-term operation,the oxygen content of rGO/CNT composite membrane was increased obviously,which would lead to the deterioration of its permeability and catalytic performance.Thus,it was necessary to treating carbon layer by hydrothermal reduction for the regeneration in practice.Based on the results mentioned above,a novel process for removing organic micro-pollutants with the function of in-situ membrane regeneration was established.It would promote the application of carbon nanomaterials and advanced treatment processes in the field of water pollution control.