Abstract
Biochar can be fabricated from waste biomass via thermochemical conversion. Here we investigated the production of activated biochar from cow manure via three different approaches, i.e., hydrochar-impregnation (HAC), impregnated biomass pyrolysis (PAC) and one-pot hydrothermal carbonization (HOC). The surface area of HAC, HOC and PAC increased from 81.00, 307.06 and 333.03 m2/g to 637.75, 791.20 and 841.91 m2/g, respectively, with the increased addition ratio of ZnCl2 to biomass/ biochar (0.5:1~4:1). HOC had significantly superior performance in the surface area, porosity and aromatization degree to HAC, whereas it had similar porosity and surface functional groups, but slightly different surface morphology to PAC.
Specifically, HOC and PAC were characterized with higher amounts of surface functional groups including carboxyl –COOH and phenolic –OH, whereas HAC was detected with more C–O bond. HOC gained a highest degree of aromatization with a maximum sorption capacity of 102.72 mg phenol/g, which was in between HAC (42.12 mg/g) and PAC (125.70 mg/g). The study on phenol sorption revealed that not only surface functional groups but also porosity played critical roles in pollutant sorption.
The well-fitted PSO kinetic model further verified that the sorption using HOC and PAC was involved with chemical and physical processes, whereas the sorption using HAC was accompanied with higher chemisorption and lower physical sorption due to its ample surface groups but poor porosity. In addition, energy analysis revealed that HOC is a simple-operation and energy-effective process to prepare activated biochar in comparison to HAC and PAC.