Preparation of rice husk hydrochar as an atrazine adsorbent: Optimization, characterization, and adsorption mechanisms

This study aims to develop rice husk hydrochar as an alternative adsorbent for application in atrazine removal. Hydrochar was obtained by microwave-assisted hydrothermal carbonization under different conditions: temperature (150 – 200°C), residence time (20 – 60 min), and liquid to solid ratio (5:1 – 15:1 mL g -1 ). Surface activation of hydrochar was conducted using various concentrations of KOH and H 2 O 2 . The results indicated that hydrochar prepared at higher temperatures, lower liquid to solid ratios, and longer residence times had significantly higher atrazine adsorption capacities. Atrazine adsorption by pristine and activated hydrochars could be best fitted to the pseudo-second-order and Freundlich models. The adsorption capacity of KOH-activated hydrochar was the highest (4.06 mg g -1 ), which is even greater than that of biochar with higher surface areas. The results of FTIR and XPS demonstrated that activated rice husk hydrochars contained abundant oxygen functional groups, which played a dominant role in atrazine adsorption via hydrogen-bonding interaction. • Increase temperature, time and solid loading improved adsorption capacity of hydrochar. • KOH and H 2 O 2 activation increased oxygen functional groups on hydrochar surfaces. • Abundant oxygen functional groups compensated for the low surface area of hydrochar. • Hydrogen-bonding played a dominant role in atrazine adsorption by hydrochar.