Preparation Of Walnut Shell-based Hydrothermal Biochar And Its Adsorption Of Basic Dyes

The preparation of carbon materials by waste biomass not only provides a new way for recycling use, reducing environmental pollution, but also meets the huge demand of functional carbon materials. The hydrothermal carbonization process to produce biochar is getting more attention due to its without drying, low energy consumption, less secondary pollution and better property.In this paper, walnut shell which abundant in northeast of China was used as the raw biomass for hydrochar. The preparation parameters were investigated, then modified the hydrochar by nitric acid, several ways were used to characterize the optimal hydrochar and modified-char. The results indicated that:(1)The optimal hydrothermal carbonization conditions were reaction temperature of 240℃, reaction time of 4 h, loading level of 81%, the weight ratio to deionized water of 10%. The hydrothermal carbonization occured carbon-rich, dehydration, decarboxylation process, and the hemicellulose was completely decomposed and cellulose was partly decomposed, some oxygen containing functional groups were produced. The aromaticity, specific surface area and pore content of hydrochar were significantly increased,however the polarity was decreased. Adding hydrochar dosing quantity and prolong the adsorption time can improve the dye removal rate, the adsorption process were fitting the second-order kinetics model and the Langmuir thermodynamic model.(2)The modification by nitric acid can greatly improve the hydrochar’s adsorption of dye, the optimal modified conditions were nitric acid concentration of 6 mol/L, the modification time of 15 min. The specific surface area and pore content were decreased by nitric acid modification, but the oxygen containing functional groups on the surface was greatly increased, this made the dye adsorption performance improved significantly. Adding carbon dosing quantity and prolong the adsorption time can improve the dye removal rate, the adsorption process were fitting the second-order kinetics model and the Langmuir thermodynamic model.