Effective adsorption of crystal violet onto magnetic nanoparticles decorated bacteria: Kinetic and site energy distribution analysis

The discharge of crystal violet wastewater will cause extremely serious harm to the natural environment and human health, due to its certain toxicity and carcinogenicity. The adsorption characteristics and mechanism of crystal violet on magnetic nanoparticles decorated bacteria (Fe3O4 @bacteria) were investigated especially the adsorption kinetic, equilibrium, mass transfer mechanism, and site energy distribution analysis. With the initial concentration of crystal violet 40 mg/L, pH= 4, the addition of 0.003 g Fe3O4 @bacteria, after adsorption for 2 h under 25 °C, the static maximum adsorption capacity of crystal violet was up to 114.8 mg/g, which was 2.07 times that of Fe3O4 under the same conditions. Fe3O4 @bacteria could be recycled more than 6 times, also exhibited a 76.2% reduction in COD for actual dyeing wastewater. The adsorption data fitted well with the Temkin isotherm model, Elovich kinetic, and pseudo-second-order kinetic models. As for the mass transfer mechanism of the adsorption process, the IPD model was more suitable to describe the mass transfer process of the crystal violet adsorption by Fe3O4 @bacteria, while the intraparticle diffusion is not the only mechanism controlling the adsorption process. The adsorption process is spontaneous and exothermic according to the thermodynamics study. Based on the analysis of site energy distribution, the biosorbent had a heterogeneous surface and most of the crystal violet sorption occurred on the sites with energy over 13.0 kJ/mol, which supported that crystal violet sorption was physical-chemical sorption. Therefore, the magnetic nanoparticles decorated bacteria can serve as promising adsorbents to eliminate the organic dye pollutants caused by textile industry.