Preparation And Application Of Photocatalytic Self-Cleaning TiO₂-CNF Nanofiber Composite Membrane

Photocatalysis is an environmental benign technology,however,the difficulties in recycling,easy aggregation,and low activity of powdered photocatalysts have limited its further development and application.It was found that the integration of membrane separation technology and photocatalytic degradation system can offer possible opportunity to reduce the membrane fouling significantly and enhance the degradation of micro-pollutants in wastewater.Meanwhile,the problem of recycling photocatalysts could also be solved.Therefore,coupled photocatalysis-membrane separation has become a cutting-edge technology for wastewater treatment.Therefore,hydrophilic nanocellulose（CNF）was selected as the nano-scaled-substrate and titanium oxide sulfate was used as the titanium source,while TiO₂nanoparticles were created by in-situ growth on the surface of CNF.The resultant integrated TiO₂-CNF nanocomposite was employed as a photocatalysis for bovine serum albumin（BSA）degradation.The particle size and content of TiO₂,as well as the distribution on CNF,were controlled by changing the conditions of reaction time,temperature,titanium source,and CNF concentration,respectively.The TiO₂-CNF composite was deposited onto electrospun polyacrylonitrile（PAN）membranes by coating and composite ultrafiltration membranes（In-situ growth membrane）with high flux,anti-fouling,and self-cleaning capability,as well as photocatalytic activity were obtained.Moreover,ultrafiltration membranes fabricated with pure CNF and the blend of commercial TiO₂and CNF were achieved and used in controlling experiments.The structure,morphology,and surface nature of the membranes were characterized using SEM,EDS,water contact angle,and various methods.It was found that the addition of TiO₂was beneficial in improving the hydrophilicity and the distribution uniformity of the membranes.The long-term filtration performance of the TiO₂-CNF nanocomposite membrane against natural pollutants such as humic acid and BSA was demonstrated.The results showed that In-situ growth membrane could maintain a higher retention ratio,while the permeation flux of the membrane was 2～3 times higher than that of the Co-blended membrane due to the addition of TiO₂which promotes the formation of water channels in the composite membrane.However,the TiO₂-CNF composite prepared by blending method causes the catalyst to aggregate and increases the defects of the membrane,resulting in a decrease in the retention ratio of the Co-blended membrane.After three cycles of filtration and decomposition,the In-situ growth membrane can still maintain a retention rate of BSA of more than 87%and a flux recovery rate（FRR）of more than 84%,while the retention rate of the blended membrane is only 75%and the FRR is 74.7%.Meanwhile,the mechanism of In-situ growth membrane with improved filtration efficiency and anti-fouling properties was investigated.The self-cleaning ability of In-situ growth membrane through photocatalysis was also demonstrated.This work provides a technical and theoretical support for the practical application of photocatalytic composite ultrafiltration membranes in wastewater treatment.