A Theoretical and Experimental Study of Carbonized Lignin from Alfa Fibers as a Clay-Based Adsorbent

Abstract

In the current work, a novel carbonaceous composite was successfully synthesized via pyrolysis utilizing lignin extracted from Raw Stipa Tenacissima fibers, locally referred to as Alfa fibers, combined with clay. This composite material was developed with the aim of enhancing the removal efficiency of anionic dyes from wastewater, particularly methyl orange (MO), which is commonly used in the textile industry and known for its persistence in aquatic environments. A comprehensive physicochemical characterization of the adsorbent was conducted to know its surface and structural properties. Zeta potential analysis provided insight into the surface charge behavior, The Brunauer–Emmett–Teller method revealed a significant increase in specific surface area postcarbonization, which correlates with improved adsorption performance. The successful incorporation of carbon on the clay surface was further confirmed by EDX mapping, indicating a uniform and stable distribution of carbonaceous matter throughout the composite matrix. The adsorption performance of the material was evaluated through batch adsorption experiments. Key operational parameters such as adsorbent dosage, contact time, initial dye concentration, temperature, and pH were optimized to identify the conditions leading to maximum removal efficiency. Kinetic modeling indicated that the adsorption behavior closely followed the pseudo-first-order model, suggesting that the process is governed by physisorption mechanisms. A remarkable improvement in adsorption capacity was observed upon carbonization, with the composite exhibiting a maximum equilibrium adsorption capacity (Q_e) of 228.58 mg/g, compared to 110.07 mg/g for pristine clay. To gain molecular-level insights into the adsorption mechanism, density functional theory calculations and Monte Carlo simulations were employed. These theoretical investigations revealed stronger binding affinities of MO molecules on the composite surface, primarily driven by electrostatic interactions and hydrogen bonding between the dye molecules and the surface functional groups introduced during carbonization.