Synthesis and adsorption behavior of Zn₂SiO₄ nanoparticles incorporated with biomass-derived activated carbon as a novel adsorbent in a circular economy framework

Abstract

Efficient utilization of biomass waste as a precursor holds significant implications for both the economy and the environment. In line with the principles of the circular economy, this study introduces a novel adsorbent, Zn₂SiO₄/activated carbon (Zn₂SiO₄/AC), synthesized from spent coffee grounds, tetraethyl orthosilicate (TEOS), and zinc chloride (ZnCl₂) via a one-pot carbonization approach for the efficient removal of crystal violet (CV) from aqueous solutions. The composite exhibited a high surface area (625.54 m²/g) and a well-defined porous structure, facilitating superior adsorption capacity. The synthesis parameters were optimized at a carbonization temperature of 600 °C, a heating time of 3 h, and an SCGs:ZnCl₂:TEOS (w:w:v) ratio of 3:3:3. Experimental results demonstrated that Zn₂SiO₄/AC exhibits a high adsorption capacity for CV, with a maximum adsorption capacity of 163.39 mg/g under optimal conditions (pH 5, adsorbent dosage of 2 g/L, temperature 45 °C, and adsorption time 105 min). Detailed mechanistic studies revealed that the pseudo-second-order kinetic and Freundlich isotherm models best described the adsorption process. FTIR and XRD analyses confirmed the structural integrity of Zn₂SiO₄/AC post-adsorption and identified key interactions such as hydrogen bonding, π-π interactions, coordination bonding, and electrostatic attractions facilitating CV adsorption. Zn₂SiO₄/AC demonstrated excellent reusability, retaining significant adsorption capacity (77.96 mg/g) after five cycles, highlighting its practical potential for wastewater treatment. This study clarifies the formation mechanism of Zn₂SiO₄/AC and its adsorption process, establishing it as an efficient, stable, and reusable adsorbent for dye removal.