Efficiently flexo-catalysis driven by bending vibration in amorphous non-piezoelectric nano-SiO2 for water purification

All dielectric materials exhibit flexco-electricity, which can spontaneously induce these positive and negative charges when being applied strain gradients, and can further react with the hydroxide and the dissolved O₂ in water solution to respectively generate the •OH and •O₂^- radicals with strong oxidizing ability, yielding to the realization of flexo-catalysis in theory. Though flexo-catalysis is potential for many practical applications, such as the mechanically-driven dye decomposition, so far it is rarely reported. SiO₂ is a naturally occurring mineral resource widely dispersed across the earth's geological layers and is a good and low-cost flexo-catalyst candidate to decompose organic dye molecules of wastewater. In this study, it has found that the amorphous non-piezoelectric SiO₂ nanopowder exhibits excellent flexo-catalytic performance with about 94.5 % Rhodamine B (RhB) dye decomposition ratio within 60 min of vibration excitation. The corresponding flexo-catalytic reaction rate is ∼0.05121 min⁻¹. In addition, these influence factors on flexo-catalysis including the initial dye solution's concentration and the types of the organic dye, are also investigated to obtain the optimization conditions for future practical applications of the amorphous non-piezoelectric nano-SiO₂ flexo-catalyst. After 3 cycle experiments, the decomposition ratios of RhB dye can respectively reach 94.5 %, 93 %, and 90.9 %, indicating that the SiO₂ nanopowder has high recyclability and good stability. The SiO₂ dielectric materials, being naturally and widely distributed on the earth, with the advantages of lost-cost, environment-friendly, and highly-efficient flexo-catalysis, is a potential candidate to harvest the environmental mechanical vibration energy for developing the mechanically-driven environmental water remediation treatment technology in future.