Study on the Effectiveness of H₂SO₄ Activated Coffee Grounds and Imperata cylindrica Bioadsorbents for Methylene Blue Adsorption

Abstract

Textile wastewater with methylene blue dye causes serious environmental issues because of its toxicity, persistence, and negative effects on aquatic life. Using agricultural waste as bioadsorbents provides a sustainable and low-cost way to remove dye from wastewater. The goal of this study was to assess how effective H₂SO₄-activated bioadsorbents made from coffee grounds and Imperata cylindrica are for methylene blue adsorption in batch systems. We prepared the bioadsorbents by carbonizing them at 450°C, followed by chemical activation with 2 M sulfuric acid. We characterized them using FTIR and SEM to study functional groups and surface shape. We conducted batch adsorption experiments by changing the adsorbent mass (0.15–0.3 g), contact time (30–120 minutes), and methylene blue concentration (10–100 mg/L). Langmuir and Freundlich isotherm models were used to evaluate the adsorption behavior. The results showed that activated coffee grounds and Imperata cylindrica had improved porosity and changes in functional groups after activation. The best adsorption conditions were found with an adsorbent mass of 0.3 g, a contact time of 120 minutes, and a methylene blue concentration of 10 mg/L, reaching an adsorption efficiency of up to 97.498%. The adsorption process fit the Langmuir isotherm model better, with maximum adsorption capacities of 42.735 mg/g for coffee grounds and 13.210 mg/g for Imperata cylindrica. These findings suggest that coffee grounds and Imperata cylindrica are promising, cost-effective bioadsorbents for removing methylene blue in textile wastewater treatment.