Studies on the Development of Adsorbents From Bituminous Coal by Acid Activation at Low Temperatures for the Removal of Phenol From Wastewater

In this study, bituminous coal was activated with sulfuric acid (H 2 SO 4 ) under relatively low temperatures (30°C–60°C), yielding an adsorbent material referred to as chemically activated carbon (CAC). Additionally, another adsorbent material, referred to as physically activated carbon (PAC), was prepared from the same coal through steam activation at 800°C. The physicochemical properties of both adsorbents were examined using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT‐IR) and Brunauer–Emmett–Teller (BET) analysis. The results showed that H 2 SO 4 activation at low temperature did not markedly increase surface area but significantly changed pore structures and surface functional groups. Although CAC exhibited a lower surface area than PAC, its phenol adsorption performance was notably high. In batch adsorption experiments, the removal efficiencies of bituminous coal, CAC and PAC were 7%, 80.3%, and 99.2%, respectively. FT‐IR analysis indicated that hydrogen bonds between phenol molecules and surface functional groups were effective in the adsorption. Kinetic studies revealed that phenol adsorption onto CAC followed a pseudo‐second‐order kinetic model, implying that adsorption rate is controlled by chemical interaction between phenol molecules and active sites on the CAC surface, rather than mass transfer or diffusion. Moreover, CAC was reusable and maintained over 88% phenol removal efficiency up to the third cycle. Overall, low temperature acid activation procedure can be considered an energy‐efficient method for developing an adsorbent that provides high phenol removal from bituminous coal and can be a practical alternative to conventional high temperature steam activation. However, further optimization is required to match the performance of physical activation.