Cobalt Chromate Nanoparticles Embedded in a Poly(vinylidene fluoride) Membrane for the Piezocatalytic Wastewater Remediation

Herein, we first report an eco-friendly and easily retrievable piezo-responsive membrane fabricated by encapsulating chemically synthesized cobalt chromate quantum dots (CCOQDs) at varying concentrations (0%, 10%, and 20%) in poly(vinylidene fluoride) (PVDF) using a facile solution-casting method. The membrane with 10% CCOQDs (PCCO 10) exhibited a high β-phase fraction (75.93%), a significant dielectric constant (56.22) and a notable piezo-coefficient ( d 33 = 65.1 pC/N), demonstrating strong piezocatalytic activity. It effectively generated reactive oxygen species (ROS), which reacted with dye solutions, leading to 98.7% congo red (CR), 89.9% methylene blue (MB), and 87% mixed (1:1 of CR and MB) dye degradation within 50 min of soft ultrasonic stimulation, primarily due to •OH radicals, as confirmed by scavenger and trapping experiments. Additionally, the membrane removed 81.98% of total organic carbon (TOC) in 75 min. Optimization with an alkaline pH solution, 60 W ultrasonic power, and 1 ppm dye concentration enhanced its catalytic efficiency, selectivity, and stability. Real-world testing on drinking and wastewater showed degradation efficiencies of 94.65% and 98.31%, highlighting its versatility for industrial and household applications. The flexible PCCO 10 membrane also demonstrated excellent reusability (97.2% efficiency after four cycles) and maintained structural integrity under low-frequency stimulation, such as centrifugation, vortexing, and stirring, confirming its strong piezocatalytic activity in CR degradation. Furthermore, degradation products were identified by the LC-MS technique. Also, a pot study established that these degradation molecules have no phytotoxic effects on neem ( Azadirachta indica ) plants. Hence, this multifunctional free-standing membrane holds promising potential as an alternative for sustainable wastewater treatment.