Surface engineering of pineapple leaf fiber-derived cellulose via tannic acid functionalization for superior Cu ²⁺ adsorption

Tannic acid (TA) is a special polyphenol compound extracted from various plants. Due to its ability to create various coordination interactions, such as ionic, hydrogen, hydrophobic, and π–π interactions, tannic acid enhances the adsorption capacity of heavy metal ions. This study investigated a bioadsorbent by functionalizing the surface structure of pineapple fiber-derived cellulose with TA to enhance the adsorption efficiency of Cu2+ ions in water. Functionalized cellulose by TA was morphologically characterized by scanning electron microscopy (SEM), quantitatively by energy-dispersive X-ray spectroscopy (EDX), and detected functional groups by analytical Fourier transform infrared spectroscopy (FTIR). Batch adsorption experiments conducted under varying pH and time conditions clarified that TA modification significantly improved both Cu2+ adsorption and removal. The evaluation results indicated that the Langmuir and Freundlich kinetic models yielded higher coefficients of determination (R2; 0.9801 vs. 0.9709) and lower χ2 (0.0404 vs. 0.0595), with a maximum adsorption capacity (qmax) of 4.47 mg/g. The Thomas model demonstrates a strong correlation between experimental and theoretical findings in describing the system’s mass transfer kinetics with (R2) of 0.9999 and a χ2 value of 0.00002. These findings suggest that TA-modified cellulose is an effective and environmentally friendly candidate for treating wastewater contaminated with heavy metals.