Non-thermal plasma and BiPO4 induced degradation of aqueous crystal violet

Abstract

Abstract Degradation of crystal violet (CV) in aqueous solution by non-thermal plasma combined with BiPO4 was investigated. BiPO4 was synthesized by the hydro-thermal method and characterized by X-ray diffraction, X-ray fluorescence, scanning electron microscopy and Brunauer-Emmett-Teller surface area. With the addition of BiPO4 in the non-thermal plasma system, a 28% enhancement in the CV degradation rate was observed compared with the single non-thermal plasma system. The effects of discharge power, initial concentration of CV, initial pH and air flow rate on the degradation of CV were reported. The degradation of CV by non-thermal plasma and BiPO4 followed pseudo-first-order reaction kinetics. The concentrations of generated H2O2, O3 and OH in the non-thermal plasma combined with the BiPO4 system increased with increasing discharge time, which eventually achieved 0.43 mg/L, 1.52 mg/L and 5.2 × 10−6 mol/L in CV solution, respectively. In the non-thermal plasma combined with the BiPO4 system, the absorbance of the aqueous solution at 584 nm declined from 0.63 to 0.02, the pH values of the aqueous CV solution decreased from 3.55 to 2.93, and the conductivity of the CV aqueous solution steadily increased from 102 to 203. Good stability of the synthetic BiPO4 was demonstrated. Gas chromatography–mass spectrometry was used to determine the degradation intermediates of CV, and the degradation pathway of CV was proposed according to the detected intermediates, which were produced mainly by conjugated structure destruction, demethylation, hydroxylation, carboxylation and the ring-opening reactions. The acute toxicity of the treated CV solution on luminescent bacteria exhibited a stably declining trend with increasing discharge time.