Effects of preparation process parameters of rice husk carbon on adsorption performance

Rice husk carbon was prepared by hydrothermal method from rice husk, and used to adsorb methylene blue from printing and dyeing wastewater. Rice husk carbon was characterized by X-ray diffraction(XRD), Scanning Electron Microscope(SEM), Thermo Gravimetric(TG), Fourier Transform Infrared Spectrometer(FT-IR), and the effects of hydrothermal temperature and hydrothermal time, respectively, on the physicochemical properties and adsorption properties of methylene blue in rice husk carbon were investigated. The results showed that hydrothermal temperature was the important factor to affect the adsorption performance of rice husk carbon. In this study, when the hydrothermal time was 4 h and the hydrothermal temperature was 180-220 ℃, the removal rate of methylene blue in rice husk carbon was more than 90% and the adsorption capacity of rice husk carbon to methylene blue was more than 6.27 mg/g. Among them, the hydrothermal temperature was 200 °C and the hydrothermal time was 8 h(RH-200-8), the structure of rice husk carbon was intact and the yield of rice husk carbon was 65.20%. Besides, the removal rate and adsorption capacity of methylene blue in rice husk carbon were 93.04% and 6.62mg /g in the same condition, respectively. The phenomenon was due to the cellulose was not completely decomposed, the pore structure of rice husk carbon was better and the pore diameter of rice husk carbon was moderate when the hydrothermal temperature was 180-220 °C. In addition, the structure of rice husk carbon was conducted to the methylene blue molecule diffusion and adsorption, and rice husk carbon has more oxygen-containing functional groups with more adsorption active points, so the adsorption performance of rice husk carbon on methylene blue was better. When the hydrothermal temperature was greater than 220 °C, with the increase of hydrothermal temperature, the cellulose would be accelerated decomposition, the oxygen-enriched functional groups were decomposed quickly, the adsorption activity points of rice husk carbon were reduced, the rice husk carbon structure was also changed and the specific surface area was increased, but most probable pore sizes of rice husk carbon were decreased, the phenomenon was not conducted to the methylene blue molecule diffusion in rice husk carbon, so the removal rate and adsorption ability of methylene blue in rice husk carbon decreased. The experiment of rice husk carbon(RH-200-8) regeneration and recycling showed that the removal rate of methylene blue in rice husk carbon decreased slightly with the number of rice husk carbon regeneration increased, and the maximum methylene blue removal rate of RH-220-8-3(Rice husk charcoal use 3rd) reached 82.20% (10 h). © 2020, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.