Ammonia modification of activated carbon derived from biomass via gamma irradiation vs. hydrothermal method for methylene blue removal

Abstract

Local biomass (water hyacinth, “WH” and eucalyptus charcoal, “EU”) were turned to high-quality activated carbon (WHAC and EUAC) for methylene blue adsorbents. The carbonization (at 800°C for 5 hours under an N2 atmosphere) and chemical activation (KOH) were applied for the AC production. Two methods of ammonia modification were used: gamma irradiation and hydrothermal treatment, to improve the adsorption ability of AC. The nitrogen contents of WHAC and EUAC modified by hydrothermal method (3-4%) are slightly higher than that of gamma irradiation (1.5-2.0%). The sequence of methylene blue (MB) adsorption ability of WHAC is the gamma irradiation (587.92 mg/g) > the hydrothermal technique (565.15 mg/g) > unmodified (462.98 mg/g), which is similar to EUAC (552.16 > 541.88 > 453.52 mg/g, respectively). The higher MB adsorption capacity of WHAC may be due to the combination of high surface area and naturally occurring calcium oxide. Gamma irradiation successfully doped nitrogen to the WHAC surface and gives a significantly larger surface area, increasing from 1038.70 m²/g (WHAC unirradiated) to 1765.52 m²/g (WHAC irradiated at 100 kGy) without harmful chemicals, heat, and chemical waste.