Fabrication And Anti-fouling Performance Of Carboxylated Nanodiamonds–Polyvinylidene Fluoride Ultrafiltration Membranes

Polyvinylidene fluoride?PVDF?membranes has been extensively used for ultrafiltration recently due to their excellent thermal stability and high rejection towards proteins,bacteria and other large molecules.However,the hydrophobic nature of PVDF makes such membranes susceptible to organic pollutants,causing undesirable permeation flux decline thus greatly shortens their lifespan.Therefore,extensive efforts have been devoted to improve the surface hydrophilicity and minimize fouling of PVDF membranes.Among these strategies,blending nanoparticles into the polymeric bulk brings an effective solution to enhance hydrophilicity and antifouling property.In this study,different amount of the carboxylated nanodiamonds?CND?were embedded into PVDF membranes during phase inversion.The prepared membranes were characterized by scanning electron microscope?SEM?,atomic force microscopy?AFM?and water contact angle analysis.Furthermore,the pure water flux,Bovine serum albumin?BSA?filtration performance and antifouling behaviors of the membranes were also investigated.Compared with the pristine PVDF membrane,CNDs blended membranes had better hydrophilicity,larger porosities and surface pore sizes due to the incorporation of hydrophilic carboxyl groups.The PVDF-CND 1%membrane showed the highest permeability and best antifouling performance.In particular,its ratio of irreversible fouling to the total fouling ratio(R_ir/R_t)was lower to 21%while the R_ir/R_t of its counterpart?pristine PVDF membrane?was calculated as 85%.This study further investigated the synergetic effects of CNDs and commercial titanium dioxide?TiO₂?on permeability,self-cleaning and photocatalytic activity of PVDF-CND/TiO₂composite membranes.The PVDF-CND,PVDF-TiO₂ and PVDF membranes were set as controls.The prepared membranes were characterized by series of aforementioned analysis and tests for their filtration performance.Results showed that the PVDF-CND/TiO₂,PVDF-CND and PVDF-TiO₂ membranes had excellent permeability and BSA rejection.The CND-involved membranes had superior anti-fouling performance.Additionally,both dynamic filtration and static degradation results showed that CNDs could effectively improve the photodegradation performance of the TiO₂ membrane,rendering the catalytic membrane with better self-cleaning properties.The MO decoloration efficiency of PVDF-CND/TiO₂ membrane?82%?was higher than that of PVDF-TiO₂ membrane?74%?,which can be explained that CNDs help separating the TiO2 photogenerated charges during the catalytic reaction process.these results indicated the superior self-cleaning property of PVDF-CND/TiO₂ membrane under solar irradiation.This study for the first time demonstrates that CND are excellent additives in developing antifouling membranes,and further benefits for developing photocatalytic self-cleaning property by introducing TiO₂ in the process of membranes formation.This study may open up a new avenue to the next generation of high-performance membranes.