Pyrolyzed coal base high surface area and mesoporous activated carbon for methyl violet 2B dye removal: Optimization of preparation conditions and adsorption key parameters

Abstract

Herein, a low-grade Malaysian coal namely Merit Karpit coal (MRTKC) was transformed into high surface area mesoporous activated carbon (MRTKC-AC) via pyrolysis-assisted ZnCl2 activation. A numerical optimization approach rooted in the Box-Behnken design (BBD) was employed to determine the best operational conditions such as A: dosage of MRTKC-AC (ranging from 0.02 to 0.1 g/100 mL), B: the pH of the solution (varying from 4 to 10), and C: the contact time (ranging from 5 to 25 min). A notable surface area of 1229.1 m2/g and a distinctive mesoporous structure with an average pore diameter of 2.9 nm was achieved at optimum impregnation ratio (1 MRTKC: 2 ZnCl2), heating temperature 500 °C, and residence time 60 min. Moreover, the application of MRTKC-AC was evaluated through the removal of methyl violet (MV) from the aqueous environment. The comprehensive equilibrium and kinetic adsorption analyses showed that the adsorption of MV by MRTKC-AC matched closely to the Langmuir isotherm model, while the kinetic behavior was suitably described by the pseudo-second order model. Thus, the maximum adsorption capacity (qmax) for MV dye onto MRTKC-AC was ascertained to be a substantial 238.6 mg/g. The MV dye adsorption mechanism onto MRTKC-AC surface indicates various dye–adsorbent interactions: electrostatic attraction, p–p interaction, and H-bonding. This work shows that Malaysian low-rank coal is an economical precursor for producing low-cost and efficient mesoporous activated carbon with substantive surface area.