Synthesis of activated carbon from cotton plant by-products in Vietnam to remove methylene blue and congo red

Activated carbon from cottonwood was synthesized by microwave-assisted method with activator NaOH. Activated carbon from cottonwood has a rough surface like coral, an amorphous structure with surface functional groups such as O–H, C–H, C=C, and C–O. The surface area and pore size were recorded at 395.48 m2 g−1 and 2.35 nm. The adsorption capacity of activated carbon from cottonwood was evaluated on two groups of anion dyes (congo red) and cation dye (methylene blue) to evaluate the influencing factors and predict the adsorption process. The best adsorption conditions were recorded for methylene blue (time: 30 min, temperature: 30 °C, pH: 10, activated carbon from cottonwood of 1 g L−1, methylene blue of 80 mg L−1, and adsorption capacity of 30.875 mg g−1) and congo red (time: 150 min, temperature: 60 °C, pH: 2, activated carbon from cottonwood of 2 g L−1, congo red of 100 mg L−1, and adsorption capacity of 45.97 mg g−1), respectively. The adsorption process was consistent with the Bangham kinetic and Dubinin–Radushkevich (D–R) isotherm model. The process of evaluating reusability shows that activated carbon from cottonwood can be reused 4 times.