CuO Coated Ceramic Hollow Fiber Membrane With In-situ Peroxymonosulfate Activation For Removal Of Organic Pollutants In Water

With the development of industry and the wide application of new technologies,more and more emerging organic pollutants enter water bodies,which threatening the ecological environment and human health.However,conventional microfiltration/ultrafiltration membrane separation technology in water treatment is difficult to effectively remove the refractory organic pollutants.Peroxymonosulfate(PMS)activation is a new advanced oxidation technology that can effectively degrade organic pollutants in water.Therefore,the combination of membrane filtration technology and PMS advanced oxidation can achieve the dual functions of filtration and pollutants removal.Ceramic hollow fiber membrane is a kind of membrane material suitable for coupling with advanced oxidation technology because of its high filling density,small floor space and excellent oxidation resistance.Nonetheless,ceramic hollow fiber membrane is prone to fracture during transportation,loading and use due to its low flexural strength,and higher sintering temperature is required in the preparation process,which results in higher preparation cost.In this study,a ceramic hollow fiber membrane with rationally strong flexural strength at low sintering temperature via a combined phase-inversion and liquid-phase sintering technique was fabricated.Then,the copper oxide(CuO)coated ceramic hollow fiber membranes were prepared via phase-inversion and dip-coating methods,with the expectation to incorporate both the functions of PMS activation and membrane filtration in one process.The catalytic membrane with in-situ PMS activation can not only improves the removal of emerging pollutants in water,but also effectively alleviates membrane pollution,and avoids the problem of loss and recovery of powder catalyst used in water treatment process.The results of the current research are summarized as follows:Aiming at the problem of low bending strength of ceramic hollow fiber membrane,aluminum oxide(Al₂O₃)ceramic hollow fiber membrane was prepared by dry/wet spinning phase conversion method,and CuO and titanium oxide(TiO₂)as composite sintering additives were added into the suspension,so as to reduce sintering temperature and improve the bending strength of ceramic hollow fiber membrane.The effect of CuO contents on the microstructure and properties of the ceramic hollow fiber membrane was systematically investigated.The results show that the presence of CuO significantly enhanced the flexural strength of ceramic hollow fiber membrane due to the appearance of the liquid phase of CuO-TiO₂ during sintering process.The 3 wt%CuO doped ceramic hollow fiber membrane sintered at 1250? for 2 h displayed a maximum flexural strength,which was more than 3 times higher than that of control membrane without CuO addition.Such liquid-phase sintering has a strong promoting effect on the grain growth and densification of the ceramic hollow fiber membrane.However,when the CuO content was higher than 6 wt%,more defects will be formed on the membrane during the sintering process and the flexural strength will be decreased correspondingly.The optimized ceramic hollow fiber membrane showed good corrosion resistance,but CuO in the membrane body cannot exhibit obvious PMS activation performance due to the influence of high temperature and the production of eutectic with TiO₂.In order to prepare the catalytic ceramic hollow fiber membrane with efficient PMS activation function,the catalyst with highly effective PMS activation should be prepared first.CuO catalyst was synthesized by a novel one-step calcination route using polyethylene glycol(PEG)as nonionic polymeric structure directing agent.This method can realize the stability of catalyst samples,a large scale of production,and because of the addition of PEG,the immersion solution has a certain viscosity,which is more conducive to the preparation of catalytic ceramic hollow fiber membrane with CuO coated through sintering.The morphological and physicochemical properties of the CuO were characterized and the catalytic activity for degradation of bisphenol A(BPA)was evaluated.The results show that the CuO has a larger specific area,which is conducive to the full exposure of the active point of the catalyst,thus producing a lot of active species,leading to the efficient degradation of BPA.The mechanism of BPA degradation by CuO/PMS system was studied in-depth,and it indicated that singlet oxygen(¹O₂)was the main active species.Furthermore,the effects of experimental parameters on the degradation of BPA in two coupling modes were analyzed and compared.The results indicate that the coupling mode of in-situ PMS activated catalytic hollow fiber membrane is more stable and efficient,and exhibits less effect by HA in water,showing the advantages of in-situ PMS activated catalytic ceramic hollow fiber membrane.The effects of sintering temperature and coating times on the basic properties(pore diameter,porosity,flux,retention rate,etc.)of CuO coated ceramic hollow fiber membrane prepared by dip-coating-sintering method were investigated.The catalytic performance of CuO coated ceramic hollow fiber membrane for PMS activation was evaluated and the effects of preparation conditions and experimental parameters on the degradation efficiency of BPA were investigated.The mechanism of in-situ activation of PMS by CuO coated ceramic hollow fiber membrane for removing organic pollutant in water was studied.CuO coated ceramic hollow fiber membrane not only improved the membrane retention performance,but also activated PMS to achieve efficient degradation of BPA in water.The removal efficiency of BPA could reach above 96%.The reason is that when raw water passing through the membrane,almost all PMS is activated by the CuO coating layer in a very short time to produce a large number of active species involving in the degradation of BPA.The effect of typical parameters in surface water on the degradation of BPA in the system was investigated.The degradation products of BPA in the system were analyzed,and the possible degradation paths were deduced.Further,the water purification and anti-fouling performance of CuO coated ceramic hollow fiber membrane with in-situ PMS activation were investigated by taking Songhua River water as the actual water.The results show that the system can effectively enhance the removal of DOC,UV₂₅₄ and fluorescent compounds,and significantly reduce the membrane fouling of CuO coated ceramic hollow fiber membrane in the actual water filtration process,suggesting that it is a promising membrane water treatment technology in the future.