Microwave-induced H₂SO₄ activation of activated carbon derived from rice agricultural wastes for sorption of methylene blue from aqueous solution

Activated carbon derived from the rice straw was used for the rapid removal and fast adsorption of methylene blue (MB) from the solvent phase of the aqueous solution. The developed adsorbent was characterized using various analytical techniques such as scanning electron microscopy and FTIR. The effect of various influential parameters including solution pH, adsorbent dosage, contact time, initial adsorbate concentration, stirring speed, and temperature on MB removal were well investigated and optimized. The experimental optimized data showed that a maximum amount of MB ions can be removed at contact time 25 min, dye ion concentration 40 mg/L, and pH of 7. The obtained results of the isotherm study revealed that adsorption data was in good agreement with Langmuir isotherm model (with R² value of 0.988 and maximum adsorption capacity of 62.5 mg/g at initial pH of 7 and temperature of 298 K). The negative values of ΔG° and the positive values of ΔH° (22.73 kJ/mol) and ΔS° (104 J/mol K) showed that the adsorption process was a spontaneous physical adsorption process i.e. endothermic and entropy driven.