Effects of temperature on rice husk silica ash additive for fouling mitigation by polysulfone–RHS ash mixed-matrix composite membranes

It has been found that the preparation of green silica based on agricultural crops preserves environmental sustainability. In this study, rice husk silica (RHS) ash was prepared by burning rice husk (RH) at different temperatures (400 and 1200 °C). Both types of green RHS ash additives were blended with polysulfone dope, after which membranes were fabricated via phase inversion. The RHS ash that was synthesised at 400 °C (RHS400) had an amorphous structure with strong hydrophilic properties, while the composite membrane containing 3 wt% of RHS400 (A3 membrane) achieved the optimum properties of a dense top, an extended sub-layer of continuous smaller finger-like pores and a bottom layer of macrovoids. A satisfactory mean surface roughness, average pore size (1.90 ± 9.50 × 10⁻² µm), porosity (40.66 ± 2.03%) and tensile strength (3.27 ± 0.16 MPa) were also obtained. The contact angle (52.5° ± 3.6°) further proved that this membrane was hydrophilic. The elemental and thermal analyses confirmed the presence of Si and O, which correlated with the 12% residual that was contributed by the silica inside the membrane. The optimum properties of the A3 membrane were an increased PWF (154.04 ± 7.70 L m⁻² h⁻¹) with the highest rejection of HA (96.00 ± 4.80%) and a fouling mitigation with the lowest internal resistance (6.79 ± 0.34 × 10¹² m⁻¹).