Adsorption-remove effect of p-nitrophenol in water by peanut shell biochar at different pyrolysis temperatures

Biomass carbon is produced from wood or other agricultural and forestry wastes by high temperature pyrolysis under low oxygen or oxygen-limited conditions. It has high carbon content and porosity, large specific surface area and good adsorption performance. In addition, the preparation process is simple and the materials are widely available. Peanut is an important oil crop in China, thus peanut shell is a kind of agricultural waste with a large output. The comprehensive utilization value of peanut shell has been widely concerned. Therefore, biomass carbon has received extensive attention in soil remediation, sewage and waste gas treatment. The adsorption of p-nitrophenol (PNP) by biochars (BC400, BC500, BC600) prepared from pyrolysis of peanut shells at different temperature (400, 500, 600 ℃) was investigated by batch adsorption experiments. The amount of biomass charcoal produced at different temperature conditions decreased from 28.83% at 400 ℃ to 19.40% at 600 ℃. The pyrolysis reaction of biomass charcoal at 400-500 ℃ was more severe than that at 500-600 ℃, and the mass loss ratio was decreased from 42.3% to 31.1%; The ash and volatile matter increased significantly with the increase of pyrolysis temperature, while the water content showed a slow downward trend. The ash on the surface of biochar was removed by hydrochloric acid washing. Combined with the element analysis, scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR) analysis method, pyrolysis temperature showed a pronounced effect on properties of biochar, so effecting its adsorption characteristics on PNP. The deoxidation and dehydrogenation reaction of peanut shells in the process of pyrolysis and carbonization increased with the increase of temperature, and the degree of carbonization increased with the increase of temperature. At the same time, the ratio of biomass carbon H/C, O/C, (O+N)/C gradually decreased, reflecting that the oxygen-containing functional groups in biomass carbon decreased with the increasing temperature. The biomass carbon with more complete aromatic structure had stronger hydrophobicity and lower polarity, which was beneficial to increase the adsorption capacity of biomass carbon for organic matter. Results showed that the output of biochar was decreased with rise of temperature, but the carbon content gradually increased, reflecting that the functional groups containing oxygen in the biochar decreased with the rise of temperature. The higher temperature of pyrolysis was, the more stability of the biochar structure. Adsorption isotherm conformed with the Freundlich model, linear fitting was very good, R2 was between 0.954-0.991. Contrasting pseudo secondary dynamics model, the Elovich model and the diffusion model in particle adsorption behavior, the results showed that the pseudo secondary adsorption dynamics model fitting effect was best, R2 was between 0.981-0.999, equilibrium adsorption amount increased with the rise of the biochar preparation temperature (BC600> BC500>BC400). BC600 adsorption capacity was 34.48 mg/g, that was 2.25 times of the BC400. With NaOH as desorbent, the desorption efficiency of PNP was the highest at 68.21% when the concentration of NaOH was 1.0 mg/L. It can be seen that the regeneration of biomass carbon had certain feasibility. Therefore, the preparation of high temperature peanut shells biochar can be used as a good functional material for PNP removal. Peanut shell biomass carbon has broad development prospects in the field of sewage treatment. © 2019, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.