Photocatalytic-Adsorptive Abatement of Tetracycline Using a Green Synthesis of ZnO-NPs/Cassava Peel-Activated Carbon: Machine Learning Optimization
No Thumbnail Available
Date
2026-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa University
Abstract
The widespread prevalence and ecotoxicological risks posed by the antibiotic tetracycline (TC) in aqueous environments present significant challenges to conventional wastewater treatment plants. This dissertation comprehensively explores the design, characterization, and application of novel, eco-friendly composite materials for eliminating TC from aqueous streams. This research focuses on the sustainable fabrication of a highly efficient material, combining green-synthesized zinc oxide nanoparticles (ZnO-NPs) with low-cost, biomass-derived activated carbon (AC), to leverage the synergistic mechanisms of simultaneous adsorption and photocatalysis.
The study was conducted in three progressive phases. First, a green, sustainable protocol was developed to synthesize ZnO-NPs using Citrus bergamia leaf extract as a reducing and capping agent. Concurrently, highly active AC was prepared from cassava peels via chemical activation using ZnCl2. Second, the preparation parameters for both components, including impregnation ratios, carbonization temperatures, and dwell times, were systematically controlled and individually optimized for TC removal using Response Surface Methodology (RSM) coupled with Artificial Neural Networks (ANN). Third, the final composite (AC/ZnO-NPs) was fabricated by impregnating the green-synthesized nanoparticles onto the cassava peel-based carbon matrix. The structural, optical, and morphological properties of all materials were systematically characterized using Fourier-Transform Infrared Spectroscopy (FT-IR), Ultraviolet-Visible Spectroscopy (UV-Vis), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). Subsequently, the composite's treatment performance was optimized using a Box-Behnken Design (BBD) under UV/vis irradiation.
Characterization of the green-synthesized ZnO-NPs confirmed a hexagonal wurtzite structure with an average crystallite size of 13.94 nm, a specific surface area of 371 m²/g, and a band gap of 3.15 eV. The cassava peel-derived AC exhibited a highly microporous architecture, an extensive surface area of 1250 m²/g, and an average particle size of approximately 104 nm. In single-component optimization trials, the AC achieved a 97.2% TC removal efficiency under RSM/ANN-optimized conditions (pH 7.49, contact time of 74.15 min, and dosage of 0.059 g/L). Meanwhile, the ZnO-NPs achieved 92.1% TC degradation and 69.47% Total Organic Carbon (TOC) removal under optimized photocatalytic parameters (pH 5.64, irradiation time of 118.96 min, and catalyst dose of 1.49 g/L). For both individual systems, equilibrium and kinetic profiles were accurately modeled by the Langmuir isotherm and pseudo-second-order kinetics, respectively. For the combined AC/ZnO-NPs composite, RSM-BBD optimization established optimal operational parameters: an AC to ZnO-NPs mass ratio of 3.64:1, a composite dosage of 0.747 g/L, and an initial TC concentration of 5.99 mg/L. Under these specific conditions, the composite achieved a superior TC removal efficiency of 99.83% due to the localized synergy of adsorption and photocatalysis. The predictive quadratic model proved highly accurate, displaying a robust coefficient of determination (R2 = 0.9988) and high statistical significance (p < 0.0001).
This dissertation has demonstrated the efficacy of a sustainable, cost-effective, and highly efficient composite material for the abatement of pharmaceutical contaminants in water. By anchoring highly efficient, green-synthesized photocatalytic nanoparticles onto a high-surface-area biomass adsorbent, this research provides a scalable, eco-friendly configuration with substantial potential for integration into advanced industrial water and wastewater treatment systems
Description
Keywords
Green Synthesis · Photocatalysis · Citrus Bergamia · Tetracycline · Emerging pollutant