Thermal treatment approach in immobilizing silver nanoparticles into polyvinylidene fluoride membranes for biofouling mitigation during water treatment / Nur Diyana Aqilah Kamarudin

Nur Diyana Aqilah , Kamarudin (2022) Thermal treatment approach in immobilizing silver nanoparticles into polyvinylidene fluoride membranes for biofouling mitigation during water treatment / Nur Diyana Aqilah Kamarudin. PhD thesis, Universiti Malaya.

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Abstract

Impregnation of the noble metal, silver nanoparticles (AgNPs) as a disinfectant into the polymeric membrane is one of the empirical modification methods for producing safe drinking water. However, the dispersion and immobilization of AgNPs during membrane fabrication and application are least discussed despite numerous leaching phenomena reported. Moreover, the synthesis method and parameter are crucial factors in determining nanoparticles formation and nucleation process. Additionally, analysis of membrane fouling despite the mitigation approach is vital for an explicit understanding of fouling occurrence. This study presents the effects of precursor concentration and synthesis temperature on AgNPs formation in two distinctive methods. Silver nanoparticles type 1 (AgNPs-1) and type 2 (AgNPs-2) were prepared and incorporated into polyvinylidene fluoride (PVDF) ultrafiltration membranes with the presence of thermal treatment. The effect of thermal treatment was studied at temperatures 25, 40, and 55°C which significantly influenced the physicochemical characteristics of the PVDF membranes. During filtration using lake water as feed, flux decay rate (FDR), and fouling recovery ratio (FRR) analysis of clean and fouled membranes have implied membrane fouling phenomena. Alternatively, the AgNPs incorporated in PVDF membranes were utilized for surface-enhanced Raman spectroscopy (SERS) as an unconventional approach of built-in surface enhance substrate whilst thermogravimetric analysis (TGA) was employed to quantify foulant as an approach to evaluate the performance of AgNPs. The results have shown a significant variation of AgNPs-1 and AgNPs-2 synthesized with different synthesis parameters for both methods. With respect to particles size determined using a particle size analyzer, the best synthesis condition for AgNPs-1 was at 25°C using 0.255 g AgNO3 while on the other hand the best synthesis condition for AgNPs-2 was at 75°C using 0.03 mol/L AgNO3. Membranes incorporated with selected AgNPs-1 and AgNPs-2, fabricated at the highest temperature portrayed improved mechanical properties and pure water flux. PVDF/PVP/AgNPs-2 membrane released the smallest amount of Ag (3.81%) while PVDF/PVP/AgNPs-1 cast at 40°C released the largest amount of Ag (42.34%) during the phase inversion at fabrication. Notably, no Ag leaching was found in all membranes during the dead-end filtration at 0.5 bar. Membranes with AgNPs-1 and AgNPs-2 showed remarkable bactericidal performance towards E. coli with a percentage reduction of 90.38% and 80.77%, respectively. Thus, membranes with AgNPs fabricated at 55°C offered better mechanical properties of the enhanced permeability and excellent stability of AgNPs immobilization which signified the thermal treatment approach. Remarkably, small significant peaks representing biofoulant presence were obtained from normal Raman while total foulant weight indicated reductions of 82.69% and 75.86% with the presence of AgNPs-1 and AgNPs-2, respectively. Hence, the unconventional approach in fouling analysis for AgNPs in PVDF membrane has potentially been earmarked for surface enhancement in normal Raman analysis while foulant quantification provided a profound understanding of fouling occurrences on the membrane which contributes to the development of the fouling mitigation approach.

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