Piezoelectric Field Assisted Photocatalytic Reduction Of Chromium Hexavalent Based On MoS₂ Nanoflowers

With the development of industrialization,the extensive discharge of various industrial wastewater containing chromium has caused severe water pollution issues,posing a threat to human health.The use of clean energy technology to treat chromium-containing wastewater has attracted widespread attention.The more mature methods for treating chromium-containing wastewater include chemical precipitation,ion exchange,electrochemistry,adsorption,and so on,but these methods all have the risk of causing secondary pollution.In recent years,the photocatalytic effect of MoS₂ nanostructures has been recognized for its potential to treat chromium-containing wastewater in a green,effective,and sustainable way.In particular,MoS₂ nanostructures can absorb,convert,and utilize solar energy to reduce harmful hexavalent chromium ions(Cr⁶⁺)to harmless trivalent chromium ions(Cr³⁺),thereby reducing environmental hazards.However,the narrow bandgap of few-layer MoS₂ nanostructures results in a high hole-electron recombination rate,leading to low efficiency in photocatalytic degradation of chromium-containing wastewater.In this study,a novel method has been proposed for photocatalytic reduction of Cr⁶⁺by combining the characteristics of piezoelectricity in MoS₂ nanostructures.Specifically,it involves the use of a piezoelectric field to assist in the photocatalysis of MoS₂ nanoflower.First,MoS₂ nanoflowers were synthesized by hydrothermal method.Through the characterization of structure and morphology,it was found that the size of MoS₂nanoflowers synthesized under acidic conditions could reach 200 nm,with fewer layers,larger specific surface area,stronger visible light absorption,higher piezoelectricity,and higher photocatalytic activity compared to those synthesized under neutral conditions.The photocatalytic reduction performance of MoS₂ nanoflowers under different ultrasonic power fields was tested,and the results showed that the photocatalytic Cr⁶⁺reduction efficiency increased with the enhancement of the piezoelectric field.Under 80 W ultrasonic power,the photocatalytic Cr⁶⁺reduction rate of MoS₂ nanoflowers increased from 32.7%to 84.9%,with high stability.The piezoelectric-photocatalytic coupling mechanism was analyzed,revealing that the promotion effect was achieved by the piezoelectric field generated by MoS₂ under ultrasonic conditions to facilitate the dissociation of photogenerated excitons.This study firstly proposed the use of a piezoelectric field to assist in photocatalytic effect for treating chromium-containing wastewater.Finally,this study demonstrated the potential to further optimize the performance of MoS₂ piezoelectric photocatalysis for treating chromium-containing wastewater from both material systems and application conditions by surface modification of MoS₂ nanoflowers with silver nanoparticles and using water jet impact force instead of ultrasonic driving force.This study provides a novel,efficient,and sustainable method for treating harmful chemical substances in wastewater using photocatalysis.