Process Optimization for Preparation of Hydrochar with Abundant Surface Functional Groups and Promising Adsorption Capacity

Abstract

The study attempted to optimize the synthesis process of hydrochar from bamboo utilizing hydrothermal carbonization (HTC). The process conditions were optimized to maximize the amount of Acid Oxygen Functional Groups (AOFG) for better adsorption capacity, and the yield of hydrochar for better economic feasibility. The hydrochar obtained was subjected to Methylene Blue (MB) adsorption capacity, to assess its potential as lowcost adsorbent for wastewater treatment. Among the process parameters, temperature was found to significantly influence the AOFG amount and the yield, the optimum conditions were found to be a temperature of 180 °C, duration of 24 h and pH of 5, with AOFG amount of 1108 μmol/g and carbon yield of 52.45%. Although with low surface area, the hydrochar had a maximum MB adsorption capacity of 91.74 mg/g. The adsorption kinetic followed the pseudo second-order kinetic model, while the adsorption isotherm resembled Langmuir isotherm model. The experimental results established quantitative relationship between the process conditions and the AOFG amount and yield of bamboo based hydrochar, which also suggested a pragmatic way to enhance the adsorption capacity of hydrochar as low-cost adsorbent by maximizing the surface functional groups under mild hydrothermal carbonization conditions.