Preparation of Polymeric PVDF-HFP membrane blended with AG-ZnS/MWCNTS Nanocomposite for treatment of natural organic matter from water samples

Abstract

Natural organic matter in water sources poses significant challenges to water treatment and purification processes. Humic acid (HA) and bovine serum albumin (BSA) can interact with disinfectants such as chlorine, leading to harmful disinfection by-products (DBPs) that impact human health. Removing these persistent pollutants is essential to ensure water safety and quality. Traditional treatment methods often struggle to achieve efficient removal, highlighting the need for improved innovative removal technologies. This study investigated the photocatalytic degradation of humic acid using Ag-ZnS nanoparticles at different Ag loadings (synthesised by chemical reduction and photo-deposition methods). The nanoparticles were characterised by powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), scanning electron microscope (SEM), energy dispersive X-ray (EDX) spectroscopy, ultraviolet-visible (UV/Vis) spectroscopy and Brunauer-Emmet Teller (BET). The incorporation of Ag into ZnS lowered the band gap of ZnS; potentially increasing the photocatalytic degradation of the Ag-ZnS. The most effective photocatalytic activity was observed using the 1.5 wt.% Ag-ZnS sample prepared using the chemical reduction method. The sample achieved 90% photocatalytic degradation of humic acid at pH, nanomaterial dosage, contact time, and initial HA concentration of 2, 0.5 g/L, 60 min, and 10 ppm, respectively. The 1.5 wt.% Ag-ZnS sample prepared using the chemical reduction method fitted the Langmuir-Hinshelwood (L-H) kinetic model with k = 0.0136 min-1, indicating that the photocatalytic degradation reaction occurs through a surface-controlled mechanism, where the reaction rate is influenced by the adsorption of reactants on the material’s surface. The 1.5 wt.% Ag-ZnS synthesised by the chemical reduction method exhibited better removal efficiency and was further used in the synthesis of the PVDF-HFP nanocomposite membranes for the photocatalytic degradation of HA and BSA. The characterisation and photodegradation studies of the PVDF-HFP followed the same procedure as the Ag-ZnS nanoparticles. The optimum conditions for the removal of humic acid were a pH of 2, an adsorbent dosage of 1 g/L, an initial concentration of 10 ppm, and a contact time of 30 min. The L-H kinetics indicated a rapid reaction rate of k = 0.121min-1 and 98% degradation efficiency of HA by the 1.5 wt.% Ag-ZnSvi MWCNT/PVDF-HFP. The photocatalytic degradation of BSA showed the optimum pH, adsorbent dosage, initial concentration, and contact time of 4, 1 g/L, 10 ppm, and 120 min, respectively. Reusability studies confirmed that the 1.5 wt.% Ag-ZnSMWCNT/ PVDF-HFP composite showed a 3% loss after recycled four times. The nanocomposite membrane showed increased HA removal efficiency with an increase in NaCl ionic concentration compared to KNO3. Thus, the 1.5 wt.% Ag-Z PVDF-HFP composite membrane shows great photodegradation capabilitiesm for the humic acid and the bovine serum albumin.