Universal Piezo-Photocatalytic Wastewater Treatment on Realistic Pollutant Feedstocks by Bi₄TaO₈Cl: Origin of High Efficiency and Adjustable Synergy

Abstract

Clean water is a fundamental human right but millions struggle for it daily. Herein, we demonstrate a new piezophotocatalyst with immense structural diversity for universal wastewater decontamination. Single-crystalline Bi 4 TaO 8 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.

Review of Piezocatalysis and Piezo-Assisted Photocatalysis in Environmental Engineering

“…When piezo potential is presented, the material rods push electrons and holes to the interface of the material and electrolyte and lifts the valence band to increase the oxidation potential. Similar bandbending models were proposed by Banoo et al [95] and Li et al [96] − production [95]. The same results were obtained by Li et al, in that piezo-triggered band bending initiated not only the single-component material but also the composite, e.g., BiOCl/NaNbO 3 [96].…”

Harvesting Vibration Energy to Produce Hydrogen Peroxide with Bi3TiNbO9 Nanosheets through a Water Oxidation Dominated Dual-Channel Pathway

“…As shown in Figure e, with the increase of ultrasonic power, the hydrogen peroxide production rate increased continuously. This phenomenon can be explained by piezoelectric charge density: Q p = d 33 T where d 33 is the piezoelectric coefficient of piezocatalysts and T is stress intensity . With the increase of ultrasonic power, the cavitation effect can be enhanced to apply stronger stress T, which induces more charge carriers, and finally the catalytic efficiency is enhanced.…”

“…where d 33 is the piezoelectric coefficient of piezocatalysts and T is stress intensity. 45 With the increase of ultrasonic power, the cavitation effect can be enhanced to apply stronger stress T, which induces more charge carriers, and finally the catalytic efficiency is enhanced.…”

Double-Layered Sillen–Aurivillius Perovskite Oxybromide Sr2Bi3Nb2O11Br as a Fatigue-Free Piezocatalyst with Ultrahigh Hydrogen Evolution Performance

“…To measure the piezopotential on the nanoplate surface, a piezoelectric potential map (Figure e,f) was generated by scanning a Kelvin probe force microscopy (KPFM) cantilever over the nanoplate, revealing a surface potential of 410 mV. The work function (φ) was determined using the equation , φ tip − φ sample = V CPD / e where V CPD is the contact potential difference between the tip and the nanoplate, φ tip and φ sample represent the work functions of the tip and sample, respectively, and e is the elementary charge. The work function of the nanoplate was estimated as 4.47 eV, with highly oriented pyrolytic graphite (HOPG, φ = 4.66 eV), serving as a reference for calibrating φ tip , which is superior to n = 1, Bi 4 TaO 8 Cl to suggest facile charge transfer during catalysis …”

“…The corresponding phase-angle–voltage hysteresis plot (Figure d) shows a 180° shift under the reversal of the DC bias and confirms the retained polarization switching within the nanoplate. The open-circuit potential ( V p ) was also calculated to find out the magnitude of band bending by following the equation V p = W 3 T 3 d 33 e o e r where W 3 is the thickness of the nanoplate, T 3 is the applied pressure, d 33 is the piezoelectric coefficient, e o is the permittivity of free space, and e r is the relative permittivity. Here, the thickness of the nanoplate and the piezoelectric coefficient are ∼70 nm and 105 pm/V, respectively, while e r has been considered as 150 .…”