Investigation On The Mg_xFe_yZr_1-x-yO₂ Solid Superacid Coated TiO₂ Nanotubes/PVDF Ultrafiltration Membrane

Nowadays,the shortage of freshwater resources is becoming serious problem all over the world,and the reverse osmosis?RO?membrane desalination technology is one of the main methods to solve the problem.However,RO membrane requires for a strict standard on the quality of feedwater.Therefore,to reach the standards of the RO membrane,ultrafiltration?UF?membranes are utilized to pretreat the seawater to ensure the operation of the ROsystem.In this paper,to improve the anti-fouling and other intergated properties of polyvinylidene fluoride?PVDF?ultrafiltration membranes,porousMg_xFe_yZr_1-x-yO₂solidsuperacidcoatedTiO₂nanotubes?MSMFZr-TiNs?was first designed and synthesized,and then was emdedded into PVDF membrane to form MSMFZr-TiNs/PVDF ultrafiltration membrane with micro-reaction sites?MRLs?.Some parameters such as the structure of the membrane and the mechanism and effect of interaction between the particles and the polymeron the seawater cleaning were investigated.The study has a good theoretical significance and application prospects.In this paper,titanium dioxide nanotubes were synthesized by hydrothermal method,and then MSMFZr-TiNs particles were prepared through the process of coating,etching and acidification.The preparation conditions of MSMFZr-TiNs and MSMFZr-TiNs/PVDF ultrafiltration membranes were discussed and optimized.The structures of MSMFZr-TiNs/PVDF ultrafiltration membranes were characterized by SEM,TEM and other methods.The properties of the polymer were investigated after doping Mg and Fe to clarify the interaction between particles and polymers.The MSMFZr-TiNs/PVDF ultrafiltration membranes were tested for seawater treatment under different pressures,and the permeation flux and the quality of permeation were studied.The changes of permeate flux and its quality were examined under physical cleaning,chemical cleaning,and long-term runningexperiment.The performance of MSMFZr-TiNs/PVDF ultrafiltration membrane was investigated by treating oily seawater,and compared with that of acidified Y_xFe_yZr_1-x-yO₂ solid superacid coated TiO₂ nanotubes/PVDF membrane.XRD and FT-IR tests showed that Mg and Fe were doped into ZrO₂ solid superacid,which stabilized the tetragonal phase and made its acidity reach a value of-16.83.The MRLs formed by the MSMFZr-TiNs particlesinPVDF membrane can degrade or inhibit the formation of organic and inorganic contaminants on the membrane surface and inside the channels,thereby improving the anti-fouling property of ultrafiltration membrane.In addition,the MSMFZr-TiNs/PVDF ultrafiltration membranes with MRLsshowed degradation?decompostion?rates of10.52%and 12.48%for 15 mg/L methyl orange and 50 mg/L Fe₂O₃,respectively,confirming the effect of MRLs.The hydrogen-bonding interaction between MSMFZr-TiNs particles and polymers further improved the tensile strength,water contact angle and other properties of the membrane.The seawater quality after pretreatment with MSMFZr-TiNs/PVDF ultrafiltration membranes was as follows:turbidity:0.05 NTU,COD:18.4 mg/L,solid suspended solids:2.1 mg/L,which met the stardand of RO membranes.After long-term running and cleaning experiments,it was found that MSMFZr-TiNs/PVDF membrane has good anti-fouling property and maintains high permeate flux.With comparison,the integrated properities of MSMFZr-TiNs/PVDF ultrafiltration membranes are superior to that of SYFZr-TiNs/PVDF membranes.Therefore,MSMFZr-TiNs/PVDF ultrafiltration membrane can effectively pretreat seawater to meet the stardand of RO membrane,and thus has good application potential in seawater desalination.