Monitoring the Changes of Chemical Properties of Rice Straw-Derived Biochars Modified by Different Oxidizing Agents and Their Adsorptive Performance for Organics

Biochar derived from agricultural biomass waste is increasingly recognized as a multifunctional material for various applications according to its characteristics. In this study, rice straw-derived biochars were produced at different temperatures (550, 650, 750 degrees C), then they were modified by using different oxidizing agents, including KOH, HNO3, H2SO4, H2O2, and KMnO4. The influence of carbonization temperature and the oxidizing agent's nature on the surface chemistry was investigated. Fourier transform infrared (FTIR) analysis detected lactone, carbonyl, quinone or conjugated quinone, carboxyl-carbonate structure, and alcohol groups in most of the oxidized samples. Modified biochars have low pH values compared with their parent biochars. This is due to the fact that most treatments of biochar increase the acidic functional groups on the surface. Modified biochars presented greater capacities for adsorption of organic species of different molecular sizes such as iodine, phenol, and methylene blue from solutions. Such behavior proves that the most important surface properties of these biochars affecting their solution adsorption behavior are their acidity/alkalinity and hydrophilicity.