Anthropogenic sources of organic pollutants in water systems pose a health danger even at low concentrations. Due to organic pollutant’s recalcitrance, standard water treatment methods are ineffective. Photocatalysis is a method currently being investigated to treat such contaminants, but single-component photocatalysts are constrained by low visible light absorption, catalytic efficiency, low quantum yield, low conductivity, photocorrosion, and fast electron-hole (e^--h⁺) recombination rate. These limitations can be overcome by combining the two oxides to execute multi-tasks at a time. The formation of α-MoO₃/ZnO reduces costs and time while increasing efficiency in dye wastewater treatment. Incorporating carbon into α-MoO₃/ZnO hybrid materials is therefore an efficient strategy to boost their photocatalytic activity by enhancing their visible light activity, reducing photogenerated e^--h⁺ recombination, and broadening the photocatalytic dye degradation light spectrum range. The formation of carbon-α-MoO₃/ZnO is responsible for the high photocatalytic activity in degrading MB under visible light irradiation. Furthermore, the immobilization of hybrid catalysts on Polyvinylidene fluoride (PVDF) polymeric membranes contributes to a more straightforward solution for solid-liquid separation.

This study looked at the synthesis and physicochemical properties of MoO₃, ZnO, and their hybrid-based photocatalysts, namely α-MoO₃/ZnO, MWCNT-MoO₃/ZnO, GT-MoO₃/ZnO, and GL-MoO₃/ZnO prepared hydrothermally and the immobilization of α-MoO₃/ZnO, MWCNT-MoO₃/ZnO, GT-MoO₃/ZnO, and GL-MoO₃/ZnO onto PVDF polymeric material via the phase inversion method. The bandgap energy and e^--h⁺ separation potential of the materials was validated using UV-vis diffuse reflectance spectroscopy (UV-vis DRS) and photoluminescence (PL) spectroscopy. The UV-vis DRS results confirmed the bandgap energy of MoO₃ (2.83 eV), ZnO (3.14 eV), α-MoO₃/ZnO (2.8 eV), and MWCNT-MoO₃/ZnO (2.6 eV). The structure and surface morphology of the samples were validated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray (EDX). The XRD results revealed the presence of a stable α-MoO₃/ZnO-based hybrid photocatalyst at 650 °C. The morphologies from the FESEM image show a decrease in crystallite size from 36 nm to 16 nm. The EDX spectra confirm the presence of prepared samples in the absence of any impurities. The surface area (m²/g) and porosity were determined using the Braeuer-Emmett-Teller (BET) method. The powdered photocatalyst exhibited mainly mesoporous in nature with BET surface area ranged from 3.3 m²/g to 87.4 m²/g. The specific surface area of MZ-MWCNT was approximately 87.362 m²/g, which is greater than that of MZ-GT and α-MoO₃ (76.378 m²/g and 3.3 m²/g, respectively). The introduction of carbon materials were shown to change the physicochemical properties of α-MoO₃/ZnO particles by lowering the bandgap energy, reducing particle and pore diameters, and increasing specific surface area and pore volume.

The hybrid films’ surface roughness and hydrophilicity were measured using atomic force microscopy (AFM) Water Contact Analysis (WCA). PVDF film alone has lower hydrophilicity and surface roughness than hybrid films. The impact of operating parameters of the powdered and film photocatalysts on Methylene Blue (MB) dye degradation under visible light irradiation was investigated. Catalyst loading, solution pH, MB concentration, number of films, radical scavenger, and recyclability studies have been prioritized. The degradation of MB showed that α-MoO₃/ZnO/MWCNT is the superior photocatalyst that effectively degrade 99% MB within 70 minutes under visible light irradiation, followed by α-MoO₃/ZnO (98%, 100 minutes) and α-MoO₃ (97%, 150 minutes). The enhanced photocatalytic activities were attributed to effective e^--h⁺ separation. For the hybrid film photocatalysts α-MoO₃/ZnO/PVDF exhibits photocatalytic activity of 98% for 200 minutes, and PVDF/MWCNT-MoO₃/ZnO exhibits 86% degradation for 120 minutes. The degradation percentage decreased as the initial concentration of MB (10-20 mg/L) increased but increased as the photocatalyst dose and number of films increased. The superoxide radical (.O^2-) and hydroxyl radical (OH.) were the dominant reactive species for the degradation of MB under visible light irradiation. The best catalyst and film can be reused up to five times without any kind of chemical treatment and without losing their stability or effectiveness.

Table 1: Degradation efficiency of MB at different experimental conditions.

*Abstract of the thesis (PhD) by Yusuf Ibrahim.

For further information, please contact:

Abdul Halim bin Abdullah, PhD

halim@upm.edu.my

Date of Input: 30/04/2025 | Updated: 02/05/2025 | roslina_ar