Porous Carbon Adsorbents for Highly Efficient Adsorption of Malachite Green Dye From Aqueous Solutions: Kinetics, Isotherms, and Mechanism of Adsorption

A number of new micro-mesoporous carbon materials (FHU100N, FHU100K, FHU70N30K, FHU50N50K and FHU20N80K) based on a mixture of furfural, hydroquinone, and urotropine have been synthesized by the alkaline activation method using a combination of activating agents (KOH and NaOH). The influence of the porous structure of the synthesized adsorbents has been studied with particular attention to the pore size distribution, in particular, to the pore volume in which MG can be adsorbed most efficiently from aqueous solutions. Subsequently, among the tested carbons, the FHU100N has excellent porosity (total pore volume, micropore volume and mesopore volume: 1.136, 0.632 and 0.504 cm³ /g, respectively) with the highest surface area (2575 m² /g). The adsorption capacity of FHU100N (1300 mg/g) for malachite green (MG) was superior to other micro mesoporous carbons (500–918 mg/g). The results obtained showed that the key contribution to the adsorption of the MG dye is made by pores ranging in size from 2 to 3.5 nm. The FHU100N adsorbent, which showed the highest MG adsorption activity, was characterized by nitrogen adsorption, FTIR, Raman spectroscopy, and XRD techniques. To understand the adsorption mechanisms on the obtained material, detailed mathematical analysis of experimental sorption data was carried out using the existing kinetic (pseudo-first order and pseudo-second order) models and diffusion (Weber-Morris and Boyd) models, along with adsorption equilibrium isotherms (Langmuir, Freundlich, Temkin, Dubinin-Radushkevich).

Graphical Abstract