Paracetamol removal from water using N-doped activated carbon derived from coconut shell: Kinetics, equilibrium, cost analysis, heat contributions, and molecular-level insight

Abstract

Activated carbon (AC) and char derived from coconut shell were modified using urea and KOH to achieve N-doped AC. The effect of activated temperature and gas agent was studied. The series of adsorbents was characterized and it was found that the pore size and surface functional group were developed thoroughly. Paracetamol (PC) removal from aqueous solution was accomplished by adsorption in a batch system at 298 K. The intraparticle diffusion model was suitable to describe the kinetic PC removal from water rather than other models because of a complicated adsorption process in the pore connection of actual materials. The maximum capacity of these adsorbents was in a range of 39.9–357.1 mg/g, promoting them as an alternative adsorbent. Among them, the N-doped AC had the highest surface area (538 m2/g) and the highest PC adsorption capacity. The PC equilibrium uptakes in these samples were not pH-dependent, indicating that the pore size is the most dominant factor than the electrostatic charge of functional group on the solid surface for adsorption, which is evidenced in our simulation results. Furthermore, a Grand Canonical Monte Carlo simulation was used to study equilibrium adsorption. The effect of pore size and functional group type (carboxylic, hydroxyl, carbonyl, quaternary-N, pyrrolic-N, and pyridinic-N) were investigated on PC-water mixtures at 298 K. The heat contributions including fluid-fluid, fluid-solid, and fluid-functional group interactions of each adsorbate were investigated. The maximum capacity was found in the pore size of 0.70 nm, which was the best fit for complete monolayer coverage of PC molecules. The simulation confirmed that N-group types, especially pyridinic-N were more attractive than O-group types for enhanced PC removal. This work provided a new strategy to develop the optimal pore size and functional group type of ACs for high capacity of PC removal from aqueous solution. The estimated costs of production for char, AC, and N-doped AC were about 0.73, 2.63, and 3.83 U.S.$/kg respectively, indicating a highly competitive cost in the market. However, the N-doped AC was the cheapest price in order to remove the same amount of PC from aqueous solution.