Assessment of porous carbon from rice straw residues with potassium ferrate-assisted activation as cationic and anionic dye adsorbents

Agricultural wastes are huge source of organic materials for preparation of active carbon, which can be applied to water treatment by absorbing the dissolved substances. Rice straw (RS) or their pulping byproducts, Kraft black liquor (KBL) and kraft lignin (Lignin-KBL) are used as precursors for the preparation of activated carbons (ACs). The process was carried out with activation assistance of potassium ferrate (K2FeO4). The optimum temperature of activation on RS precursor is 700 °C evaluating by the textural analysis and the liquid phase adsorption models. The prepared activated carbon (RSFAC) under K2FeO4 from RS at this temperature provided highest BET surface area and total pore volume (440.5 m2/g and 0.274 cm3/g). It had excellent adsorption capacities of cationic and anionic dyes and a maximum adsorption capacity of iodine (585.2 mg/g). Applied the optimum activation temperature to pulping by-products (KBL), the result showed AC with BET surface area and total pore volume of 378 m2/g and 0.218 cm3/g, respectively. These results are higher than that obtained from using phosphoric acid activating agent, and at temperature 450 °C (BET surface area and total pore volume were 310.6 m2/g and 0.243 cm3/g). The ferrate activation of RS and lignin-KBL is contributed to the function of iron oxide as an oxidation catalyst, which gave the ACs with mesoporous and microporous. Regarding to the liquid phase adsorption models and kinetics, anionic dye adsorption equilibriums of all RSFACs (Coomassie brilliant blue R-250 CBB) follow the Freundlich model, but the cationic methylene blue dye adsorption equilibriums mostly follow the Langmuir model. Adsorption kinetics of these RSFACs are well-explained in terms of dye kinetic adsorption by the pseudo-second-order model. The procedures for AC preparation from rice straw under K2FeO4 provided a good route to utilize agricultural residues.