Universal Piezo-Photocatalytic Wastewater Treatment on Realistic Pollutant Feedstocks by Bi<sub>4</sub>TaO<sub>8</sub>Cl: Origin of High Efficiency and Adjustable Synergy
Maqsuma Banoo, Jaspreet Kaur, Arjun Kumar Sah, Raj Sekhar Roy, Monika Bhakar, Bramhaiah Kommula, Goutam Sheet, Ujjal K. Gautam
Abstract
Cl nanoplates with exposed piezoelectric facets exhibit visible-light response, piezoelectric behavior with coercive voltages of ±5 V yielding 0.35% crystal deformation, and pressure-induced band-bending of >2.5 eV. Using five common contaminants of textile and pharmaceutical industries, we show that the nanoplates can mineralize them in all piezocatalytic, photocatalytic, and piezo-photocatalytic approaches with efficiencies higher than most catalysts developed for just one contaminant. Their efficiencies for feedstocks differing over 2 orders of magnitude in concentrations, the highest to date, are also demonstrated to simulate real-life situations. These extensive studies established that combining piezocatalytic and photocatalytic approaches can lead to a tremendous synergy exceeding >45%. The origin of synergy has been illustrated for the first time using band-bending models and improved charge transfer from valence and conduction band electronic surfaces. We further quantified synergy across reactants, concentrations, and ultrasonic frequency and power to demonstrate their versatility and unpredictability. Finally, seven parameters that contribute to synergy but create unpredictability have been identified for the rational design of piezo-photocatalysts for wastewater treatment.