Influence of Tectonically Deformed Coal-Based Activated Carbon and Its Surface Modification on Methane Adsorption

A series of coal-based activated carbons (CACs) were synthesized from mylonitized fat coal, a type of tectonically deformed coal (TDC) and symbiotic primary structural coal (PSC), followed by oxidative modification. The pore structure, surface oxygen-containing functional groups, and their influence on methane adsorption by CAC as the simplified coal model were investigated by using low-temperature nitrogen adsorption, Fourier transform infrared spectroscopy, Boehm titration, and X-ray photoelectron spectroscopy. The results showed that tectonic deformation fostered smaller pores, particularly ultramicropores in TDC, dominating methane adsorption. Acid-modified TDC-based activated carbons (ACs) showed higher pore parameters and oxygen-containing functional groups than those of PSC-based ACs. Nitric acid introduced abundant carboxyl groups concurrently increasing the pore volume and specific surface area (SSA), while sulfuric acid-ammonium persulfate treatment resulted in increased lactone groups and a partial collapse/blockage of nanopores. Methane adsorption experiments confirmed the importance of micropores and revealed a significant decrease in capacity owing to increased oxygen-containing functional groups as the primary role, with pore wall corrosion playing a secondary role. Thus, the study highlights the surface effects of TDC on methane adsorption and the potential for producing high-performance methane storage materials from China's tectonic coal resources.