POME-derived Ag/TiO2-based ternary nanocomposites for oxytetracycline degradation under visible light and membrane integration
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Universiti Malaysia Sarawak
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The rise of emerging pollutants demands efficient and sustainable water treatment technologies. Ag/TiO2-driven photocatalysis is a viable solution due to its durable visiblelight activity and antimicrobial properties, yet stability, recovery, and overall synthesis sustainability remain major challenges that hinder its practical application. Therefore, the need to develop a green, durable, and easily recoverable Ag/TiO2-based photocatalyst is crucial to advance photocatalysis as an eco-friendly solution for the treatment of complex pollutants. To overcome these drawbacks, this study explored the green synthesis of Ag/TiO₂-based ternary nanocomposites using palm oil mill effluent (POME) as a natural reducing and stabilizing agent. Two ternary photocatalysts, Ag/Bi₂MoO₆/TiO₂ (ABMOT) and Ag/g-C₃N₄/TiO₂ (AGCNT), were synthesized via a microwave-assisted method and extensively characterized by Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffractometry (XRD), Scanning Electron Microscopy with Energy-Dispersive X-ray (SEM-EDX), and UV-Visible Diffuse Reflectance Spectroscopy (UV-Vis DRS). Their photocatalytic activities were evaluated against oxytetracycline hydrochloride (OTC). Under visible-light irradiation, ABMOT achieved 97.2% OTC degradation at an optimal dosage of 0.6 g/L, while AGCNT reached 81.3% under the same conditions. ABMOT demonstrated stronger dark-adsorption capacity and greater tolerance to increasing pollutant concentrations than AGCNT, indicating better surface affinity and active-site accessibility. Regardless, both nanocomposites showed good stability over four consecutive recycling cycles, indicating superior stability and reusability potential. Additionally, both nanocomposites further demonstrated antibacterial activity against Escherichia coli and Staphylococcus aureus, confirming their multifunctional potential. To address the limitation of powder recovery in slurry photocatalysis, both nanocomposites were immobilized in polyacrylonitrile (PAN) membranes via the phase-inversion method. Structural and surface analyses confirmed successful integration, with nanocomposite-loaded membranes exhibiting enhanced hydrophilicity and porosity. Permeation studies revealed that AGCNT@PAN (2 wt%) achieved the highest pure water flux (170.94 L·m⁻²·h⁻¹) and rejection rate (90.34%) compared to bare PAN membranes with 149.51 L·m⁻²·h⁻¹ pure water flux and 44.88 % rejection rate. Consequently, ABMOT@PAN also showed improvements. Overall, this study demonstrates a novel, eco-friendly approach for synthesizing multifunctional photocatalysts by valorizing agro-industrial waste. These findings provide valuable insights into advancing green nanotechnology for sustainable water treatment applications.