Optimization of malachite green removal in water using carbonized wild sugarcane (Saccharum spontaneum L.) as an adsorbent

Abstract

The widespread release of synthetic dyes into aquatic environments has raised critical environmental and public health concerns due to their persistence, toxicity, and resistance to biodegradation. Among these dyes, malachite green (MG) is of particular concern because of its carcinogenic, mutagenic, and teratogenic effects, as well as its widespread use in aquaculture and textile industries. Existing treatment methods, such as coagulation, membrane filtration, and photocatalysis, suffer from high operational costs, secondary waste generation, or limited scalability. Adsorption remains a promising alternative, especially when low-cost, sustainable adsorbents derived from agricultural waste are used. This study explores the potential of carbonized wild sugarcane (Saccharum spontaneum L.), an underutilized lignocellulosic biomass, as a sustainable adsorbent for MG removal from aqueous solutions. Two forms were investigated: untreated (CWSC-U) and acid-treated (CWSC-A). Fourier Transform Infrared (FTIR) spectroscopy confirmed the successful surface modification, showing the removal of native functional groups during carbonization and the reintroduction of oxygen-containing groups after acid treatment. CWSC-U exhibits a fibrous and fragmented carbon structure with hierarchical porosity, whereas CWSC-A displays a more intricate and well-developed porous network. Elemental analysis reveals that CWSC-A possesses a markedly higher carbon concentration and a lower content of inorganic impurities. Batch adsorption experiments evaluated the effects of initial dye concentration, adsorbent dosage, pH, and temperature. Analysis of Variance (ANOVA) identified acid treatment as the most influential factor in improving MG removal, followed by adsorbent dosage, pH, and temperature, with notable interaction effects among variables. CWSC-A demonstrated significantly higher adsorption capacity and stability across a broad pH and temperature range, outperforming CWSC-U, which showed greater sensitivity to operating conditions. This enhanced performance was attributed to CWSC-A’s enriched surface functionality, enabling stronger physisorptive and chemisorptive interactions, in contrast to the primarily physisorptive behavior of CWSC-U. Optimization identified optimal conditions (30 mg/L MG, 8.0 g/L adsorbent dosage, pH 3, 60 °C), under which CWSC-A achieved a validated removal efficiency of 94.90 %, compared to 74.36 % for CWSC-U. Thermodynamic analysis indicated more spontaneous and energetically favorable adsorption on CWSC-A. Post-adsorption FTIR further supported the distinct mechanisms, with CWSC-A involving specific functional group interactions. When benchmarked against other biomass-derived adsorbents, CWSC-A exhibited competitive or superior performance. Overall, acid treatment significantly enhances the adsorption efficiency and versatility of carbonized wild sugarcane, establishing CWSC-A as a promising, low-cost, and eco-friendly material for dye-contaminated wastewater remediation.