Effects of nitrogen functional groups and pore structure on high-affinity dye adsorption by plasma-treated activated carbon pellets

Abstract

Expanding dye use elevates ecological risks by increasing dye-contaminated wastewater discharge. Cationic dyes resist removal owing to high stability and toxicity, but activated carbon adsorption remains an efficient and economical treatment. In this study, we examine methylene blue (MB) removal using activated carbon prepared from petroleum pitch through KOH activation, followed by nitrogen plasma treatment for 5, 10, 15, and 30 min. To characterize the surface chemistry and porosity of the nitrogen-functionalized carbon, we employed elemental analysis (EA), X-ray photoelectron spectroscopy (XPS), and N2 adsorption-desorption (Brunauer-Emmett-Teller, BET) measurements. Batch adsorption tests were conducted at MB concentrations of 100, 200, 300, 400, and 500 mg L-& sup1;. The nitrogen plasma treatment increased the surface nitrogen content (from 0.44% to 1.94% depending on the treatment conditions) and enhanced MB adsorption performance. Equilibrium data were fitted using the Langmuir and Freundlich isotherm models; the Freundlich model showed a better correlation, indicating multilayer adsorption on a heterogeneous surface and suggesting that plasma-introduced nitrogen sites provided additional adsorption sites.