Functional group analysis and adsorption efficiency of untreated and treated spent coffee grounds in crystal violet removal

This study investigates the potential of untreated and thermally treated spent coffee grounds (SCG) as low-cost biosorbents for the removal of crystal violet (CV) dye from aqueous solutions. Structural characterization using Fourier-transform infrared spectroscopy (FTIR) revealed functional groups such as hydroxyl, carbonyl, and aromatic groups involved in the adsorption process. Batch adsorption experiments were conducted at various SCG dosages (2–20 g/L) to determine percent removal and adsorption capacity for both untreated and treated SCG. Findings showed that untreated SCG performed slightly better than treated SCG, achieving a maximum CV of 99.7% removal and 231.0 mg/g adsorption capacity, whereas treated SCG consistently showed around 92% removal and 230.7 mg/g adsorption capacity. FTIR analysis suggested that while thermal treatment intensified certain functional groups, it may also reduce porosity and active site accessibility, negatively impacting adsorption performance. These findings highlight the promise of SCG as an eco-friendly and cost-effective adsorbent for dye-contaminated wastewater treatment.