Adsorption of Orange G on Activated Porous Carbon Derived from Coal Tar Pitch: Experimental and DFT Study

A coal tar pitch-based porous carbon adsorbent (CPA) was synthesized through a straightforward method involving the heating of a mixture of KOH and coal tar pitch (CTP). This CPA exhibited a high surface area of 1811.2 m 2 g –1 and a large pore volume of 0.94 cm 3 g –1 when prepared with a CTP to KOH mass ratio of 1:4 at 800 °C. Parameters such as the heating temperature and activator dose were optimized to enhance the adsorption efficiency. The prepared CPA was extensively characterized by SEM, XRD, FTIR, and BET measurements. Notably, CPA presented a distinct adsorption performance for Orange G (OG), achieving a maximum adsorption capability of 449.7 mg g –1 . Kinetic studies indicated that the adsorption process followed the pseudo-second-order model, while the adsorption isotherm data demonstrated that both chemical and physical interactions favored OG adsorption. Thermodynamic analysis revealed that the adsorption of OG on CPA was spontaneous and exothermic and increased the entropy. Density functional theory (DFT) calculations provided insights into the adsorption mechanism, highlighting electrostatic interactions, hydrogen bonds, and π–π interactions as the dominant processes governing OG adsorption onto the adsorbent.