Microwave assisted ZnCl2 conversion of noodle waste into activated carbon/ZnO composite: A circular approach to food waste utilization for crystal violet dye removal

In this study, microwave induced ZnCl2 activation was utilized to produce high surface area activated carbon (AC) from a readily available and sustainable precursor, namely food waste in the form of leftover noodles (LN). The resulting activated carbon composite is referred to as LNAC/ZnO. By using food waste as the starting material, this research contributes to waste valorization and promotes the sustainable utilization of resources from food waste, which addresses the environmental challenges of food waste disposal by offering an eco-friendly solution. Analytical methods such as XRD, N-2 adsorption/absorption isotherms, IR, pH(pzc), and SEM-EDX were employed to characterize the structure and physicochemical properties of LNAC/ZnO. The elimination of organic dyes like crystal violet (CV) was studied by estimation of the CV adsorption efficiency by LNAC/ZnO. With the use of the response surface approach, the role of key adsorption parameters was investigated (A: LNAC/ZnO dosage (0.02-0.12 g/100 mL), B: pH (4-10), and C: duration (30-480 min)). The kinetic data were satisfactorily described by the pseudo-second-order model, and the CV adsorption isotherm profile matches the Freundlich model. The adsorption capacity of CV by LNAC/ZnO was 79.8 mg/g. The adsorption of CV by the LNAC/ZnO composite involves electrostatic forces, pi-pi stacking, pore filling, and H-bonding. Thus, the conversion of LN to LNAC/ZnO can potentially serve as an effective composite adsorbent for purifying wastewater containing cationic dyes and other chemical species.