Chitosan-modified spent coffee waste extract as a sustainable adsorbent for enhanced dye wastewater treatment

Reactive dyes are persistent and chemically stable contaminants that pose environmental and potential health risks, particularly due to the formation of toxic degradation products. In this study, chitosan was functionalized with a green modifying agent derived from spent coffee waste extract (SCWE) to enhance its adsorption performance toward reactive red 4 (RR4) dye. The chitosan–SCWE adsorbent was prepared using a simple impregnation method and characterized by Fourier transform infrared spectroscopy (FTIR), field-emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), and point of zero charge (pHpzc) analysis, which confirmed successful surface functionalization and modification of the surface chemistry. Batch adsorption experiments showed that chitosan–SCWE achieved a maximum adsorption capacity of 129.84 mg g−1 under optimal conditions, namely pH 2, a contact time of 120 min, ambient temperature (27°C), and a low adsorbent dosage (0.01 g). The adsorption equilibrium data were well described by the Langmuir isotherm model, indicating monolayer adsorption on a homogeneous surface, while kinetic analysis followed a pseudo-second-order model, suggesting that chemisorption dominated the adsorption process. Thermodynamic analysis further confirmed that the adsorption of RR4 onto chitosan–SCWE was spontaneous and exothermic. Overall, the high adsorption capacity achieved confirms that SCWE functionalization effectively enhances the surface properties and adsorption efficiency of chitosan, demonstrating the viability of SCW-derived extracts as sustainable green modifiers for advanced dye wastewater treatment applications.

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