Adsorption of Methylene Blue, Copper, and Cadmium Onto Activated Carbon Prepared from Hydrothermal Carbonization of Teak (Tectona grandis) Sawdust

Due to the concurrent industrialization and population growth in recent years, Vietnam and other developing countries have been facing increasing problems of environmental pollution, such as water contamination with dyes and heavy metals. Among the methods for removing contaminants, adsorption is regarded as a relatively low-cost and effective means. In this regard, development of carbonaceous adsorbents via a more straightforward, greener, and robust way is essential. Here, activated carbon (AC) samples synthesized from teak sawdust through hydrothermal carbonization and chemical activation were investigated for the adsorption of methylene blue (MB), Cd(II), and Cu(II). The sawdust was carbonized by a hydrothermal process and then activated using the activating agents K₂CO₃ or ZnCl₂ in various weight ratios. The carbonaceous adsorbents were characterized by SEM, S_BET analyzer, FTIR, XPS, and Boehm titration method. Characterization results show that AC samples possessed high S_BET and rich oxygen-containing functional groups. The maximum adsorption capacities obtained for MB, Cd(II), and Cu(II) were 516 mg/g, 166 mg/g, and 159 mg/g, respectively. The amount of oxygen-containing functional groups is regarded as an important factor in determining the adsorptive amounts. Electrostatic force was found to be the primary adsorption mechanism for the contaminants tested. The complexation reaction is a vital adsorption mechanism for Cu²⁺. Other mechanisms are less important in the adsorption of MB and Cd²⁺. The high adsorption capacity of AC for MB, Cu, and Cd suggests that hydrothermal carbonization followed by chemical activation process has the potential application to produce efficient adsorbents used in the wastewater treatment process.