H2SO4-treated Malaysian low rank coal for methylene blue dye decolourization and cod reduction: Optimization of adsorption and mechanism study

Abstract In this research, sulfuric acid (H2SO4, SA) treated Malaysian low rank namely Merit Kapit coal (MKC) for developing acidic-rich group adsorbent for decolourization and chemical oxygen demand (COD) reduction of cationic dye (Methylene blue dye; MB) from aqueous environment. The physicochemical properties of the sulfuric acid-treated Merit Kapit coal (SAMKC) such as morphological aspect, material crystallinity, surface area, surface functional groups, and elemental composition were investigated. The effect of the key adsorption parameters such as A: SAMKC dose, B: solution pH, C: temperature, and D: contact time on decolourization and chemical oxygen demand (COD) reduction of MB dye were statistically optimized using Box–Behnken design. The adsorption isotherm at equilibrium was well-described by the Freundlich model. The optimum BBD output for MB decolourization (78.5%) and COD reduction (63.3%) were recorded at 0.1 g SAMKC dose, solution pH 10, temperature 40 °C, and contact time 37.5 min. At these optimum conditions, the best SAMKC adsorption capacity (421.1 mg/g) for MB dye was recorded at 40 °C. Varity of possible interactions (electrostatic, π–π, and H-bonding) were the main reason for capturing MB dye molecules on the surface of SAMKC. The findings of this work show the feasibility MKC to be a promising precursor for the producing an effective adsorbent with potential application for cationic dye removal from aqueous environment.