Investigation On PVDF Membrane Embedded By Charged Porous SiO₂ Coated Al_xFe_yZr_1-x-yO₂ Solid Superacid And Its Performance

Reverse osmosis（RO）membrane desalination technology can effectively mitigate the growing freshwater resources shortage in human survival and sustainable development process.In order to meet the requirements of high performance,long life and low power consumption of RO membrane,the key points are how to effectively pretreat seawater to make it reach the feed water quality standards of RO membrane and reduce its salt content.Therefore,to achieve the above objectives,studying and designing small-scale functional materials to modify PVDF ultrafiltration membrane and using the obtained composite membrane for seawater desalination pretreatment are of great theoretical significance and have a broad application prospect.This paper prepared charged porous SiO₂ coated Al_xFe_yZr_1-x-yO₂ solid superacid（CS-SAFZr）founctional particle through the hydrolysis,precipitation and sulfation of ZrOCl₂·8H₂O,Al（NO₃）₃·9H₂O and Fe（NO₃）₃·9H₂O and the hydrolysis,calcination and sulfonation of CTAB and TEOS.The structure and performance of the obtained CS-SAFZr were measured.Then CS-SAFZr was embedded into PVDF membrane to prepare CS-SAFZr/PVDF composite membrane with anti-fouling and partial desalination properties,the structure and performance of CS-SAFZr/PVDF composite membrane were measured.CS-SAFZr/PVDF composite membrane was applied to pretreat seawater in trans-membrane operation pressure of 0.15 MPa,the fluxes and permeate water quality were measured.Moreover,the change of anti-fouling and partial desalination properties of CS-SAFZr/PVDF composite membrane were investigated under long time working conditions.The power consumption saved for RO membrane device through partial desalination of CS-SAFZr/PVDF composite membrane in the low trans-membrane operation pressure was calculated.Finally,particle image velocimetry（PIV）was used to investigate the fluid velocity field on PVDF membrane and CS-SAFZr/PVDF composite membrane surface and how CS-SAFZr influences the fluid flow on PVDF membrane surface.The results show that the diameter of CS-SAFZr is around 80 nm,the acidity is-16.197 and the ion exchange capacity（IEC）is 0.98 mmol/g.The suitable embedding amount is m（CS-SAFZr）:m（PVDF）=30:100（g:g）,the IEC of CS-SAFZr/PVDF composite membrane is 0.042 mmol/g.After the seawater was treated by CS-SAFZr/PVDF composite membrane,the permeate water qualities are:suspended solid:1.8 mg/L,turbidity:0.07 NTU,COD:23.7 mg/L,conductivity:35.8 ms/cm,which reach the feed water quality standards of RO membrane.Meanwhile,the conductivity of seawater decreased 13.20%,which saves 134.78 W effective power consumption for RO membrane device.CS-SAFZr/PVDF composite membrane shows favorable anti-fouling and stable desalination properties under long time working conditions.Furthermore,embedding CS-SAFZr can reduce the thickness of velocity boundary layer and increase the membrane shearing force to some extent,which improves the fluid flow on PVDF membrane surface and promote membrane separation process.The above studies show that CS-SAFZr/PVDF composite membrane with favorable anti-fouling and partial desalination properties can effectively lower the power consumption of RO membrane device and has a wide application prospect in seawater pretreatment.