Dual-layer hollow fiber (DLHF) nanocomposite membrane prepared by co-extrusion technique allows a uniform distribution of nanoparticles within the membrane outer layer to enhance the membrane performance. The effects of spinning parameters especially the air gap on the physico-chemical properties of ZrO₂-TiO₂ nanoparticles incorporated PVDF DLHF membranes for oily wastewater treatment have been investigated in this study. The zeta potential of the nanoparticles was measured to be around –16.5 mV. FESEM–EDX verified the uniform distribution of Ti, Zr, and O elements throughout the nanoparticle sample and the TEM images showed an average nanoparticles grain size of ~12 nm. Meanwhile, the size distribution intensity was around 716 nm. A lower air gap was found to suppress the macrovoid growth which resulted in the formation of thin outer layer incorporated with nanoparticles. The improvement in the separation performance of PVDF DLHF membranes embedded with ZrO₂-TiO₂ nanoparticles by about 5.7% in comparison to the neat membrane disclosed that the incorporation of ZrO₂-TiO₂ nanoparticles make them potentially useful for oily wastewater treatment.

In this study, pure TiO₂, ZrO₂, and hybrid ZrO₂–TiO₂ photocatalysts were synthesized through solgel process and calcined at three different temperatures. The synthesized photocatalysts were characterized using powder X-ray diffraction (PXRD), field-emission scanning electron microscopy (FESEM), Brunauer–Emmet–Teller (BET), ultraviolet–visible (UV–Vis) spectrometer, and photoluminescence (PL) spectrometer. The PXRD patterns show that the rutile phase of TiO₂ was suppressed through co-doping with ZrO₂ and produced small crystallite size. The hybrid photocatalysts with small crystallite size recorded the highest surface area of 114.7 m²/g compared to pure TiO₂ and ZrO₂ photocatalysts as confirmed by BET analysis. Irregular size and shape was observed in the hybrid photocatalysts compared to spherical shape and size in TiO₂ and flaky shape in ZrO₂ as shown by the FESEM images. The optical properties of the photocatalysts investigated using UV–Vis spectroscopy showed a decrease in band gap energy of pure TiO₂ through linear extrapolation from the Tauc’s plot despite the slightly higher band gap energy of the hybrid photocatalysts. However, PL analysis showed that doping of ZrO₂ into TiO₂ increased the separation efficiency of the electron–hole pairs and enhanced the photocatalytic activity. The phenol degradation of the hybrid ZrO₂–TiO₂ photocatalysts was higher compared to those of the pure TiO₂ and ZrO₂.