Cobalt Chromate Nanoparticles\nEmbedded in a Poly(vinylidene\nfluoride) Membrane for the Piezocatalytic Wastewater Remediation

Herein, we first report an eco-friendly and easily retrievable\npiezo-responsive membrane fabricated by encapsulating chemically synthesized\ncobalt chromate quantum dots (CCOQDs) at varying concentrations (0%,\n10%, and 20%) in poly(vinylidene fluoride) (PVDF) using a facile solution-casting\nmethod. The membrane with 10% CCOQDs (PCCO 10) exhibited a high β-phase\nfraction (75.93%), a significant dielectric constant (56.22) and a\nnotable piezo-coefficient (<i>d</i><sub>33</sub>= 65.1 pC/N),\ndemonstrating strong piezocatalytic activity. It effectively generated\nreactive oxygen species (ROS), which reacted with dye solutions, leading\nto 98.7% congo red (CR), 89.9% methylene blue (MB), and 87% mixed\n(1:1 of CR and MB) dye degradation within 50 min of soft ultrasonic\nstimulation, primarily due to •OH radicals, as confirmed by\nscavenger and trapping experiments. Additionally, the membrane removed\n81.98% of total organic carbon (TOC) in 75 min. Optimization with\nan alkaline pH solution, 60 W ultrasonic power, and 1 ppm dye concentration\nenhanced its catalytic efficiency, selectivity, and stability. Real-world\ntesting on drinking and wastewater showed degradation efficiencies\nof 94.65% and 98.31%, highlighting its versatility for industrial\nand household applications. The flexible PCCO 10 membrane also demonstrated\nexcellent reusability (97.2% efficiency after four cycles) and maintained\nstructural integrity under low-frequency stimulation, such as centrifugation,\nvortexing, and stirring, confirming its strong piezocatalytic activity\nin CR degradation. Furthermore, degradation products were identified\nby the LC-MS technique. Also, a pot study established that these degradation\nmolecules have no phytotoxic effects on neem (Azadirachta\nindica) plants. Hence, this multifunctional free-standing\nmembrane holds promising potential as an alternative for sustainable\nwastewater treatment.