Sludge Biochar Modified by B-doped and Its Adsorption Behavior and Mechanism of 1,2-DCA in Water

Abstract

Sludge biochar (BC600) and B-doped sludge biochar (BBC600) were prepared with the boric acid doping modified co-pyrolysis method using municipal sludge as precursors, and the materials were structurally characterized by SEM, BET, FTIR, and Zeta potential and static contact angle to investigate the adsorption behavior, mechanism of BC600 and BBC600 on 1,2-DCA in water, and the influencing factors. The results of structural characterization showed that the B element content, specific surface area, and pore volume of biochar increased by 76%, 48%, and 30%, respectively, after the B doping modification; the effect of B doping modification on the surface charge and hydrophobicity of biochar was not significant. The results of adsorption experiments showed that the adsorption of 1,2-DCA by BBC600 was better than that by BC600 due to the larger specific surface area and higher strength of oxygen-containing functional groups of BBC600; the pseudo-first-order kinetic equation could better describe the adsorption of 1,2-DCA by BC600, and the pseudo-second-order kinetic equation could better fit the adsorption of 1,2-DCA by BBC600. The intraparticle diffusion was not the only rate-limiting step affecting the adsorption rate; the biochar material was more dispersed and stable under alkaline conditions, and its oxygen-containing functional groups were deprotonated and had enhanced electron-donating ability, which was beneficial to the adsorption of 1,2-DCA. Humic acid (HA) showed a low concentration-promoting and high concentration-inhibiting effect on the adsorption of 1,2-DCA by BC600, whereas both low and high concentrations of HA showed an inhibitory effect on the adsorption of 1,2-DCA by BBC600. The adsorption of 1,2-DCA by BC600 was inhibited by both low and high concentrations of HA, and HA competed with 1,2-DCA for adsorption; Cl-, SO42-, and NO3- all inhibited the adsorption of 1,2-DCA by biochar, and the degree of inhibition ordered from small to large was Cl-<SO42-<NO3-. The main mechanisms of 1,2-DCA adsorption by biochar were pore filling and π-π interaction.