Development and Evaluation of Plant-Mediated Nanocomposite Materials for the Disinfection and Removal of Heavy Metals and Fluoride from Drinking Water
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Date
2025-05
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Addis Ababa University
Abstract
Water pollution remains a critical threat to public health and environmental sustainability, especially in low- and middle-income countries where access to efficient and affordable purification technologies is often limited. Conventional treatment systems frequently fail to effectively remove key contaminants such as pathogenic microorganisms, toxic heavy metals, and excess fluoride from drinking water. This study seeks to address these challenges by developing green-synthesized nanocomposite materials, mediated by coffee husk extract (CHE), for advanced water treatment applications including microbial disinfection and the removal of both cationic (Pb²⁺, Cr(VI)) and anionic (F⁻) pollutants. The specific objectives of this study were to: (1) synthesize CHE-capped ZnO nanoparticles (ZnO NPs) for the disinfection of waterborne pathogens; (2) enhance the properties and antibacterial activity of bare CHE-capped ZnO NPs through the incorporation of CHE-capped Fe₃O₄/PU nanocomposites (NCs); (3) develop a CHE-capped magnetite-based pumice silica nanocomposite (CHE-M/PU/Si-NC) for lead ion adsorption; and (4) incorporate CHE-capped MgO NPs and amine functional groups into the CHE-capped M/PU/Si-NC to improve surface charge for the removal of anionic pollutants. For the plant-mediated synthesis of nanomaterials, coffee husk extract (CHE) was obtained using an ethanol-based solid–liquid extraction method. The study focused on optimizing the synthesis parameters of ZnO nanoparticles (ZnO-NPs) by employing CHE as an effective reducing and capping agent to improve nanoparticle size control and functional performance. The optimization involved key parameters such as temperature, zinc precursor-to-CHE ratio, reaction time, and pH. Moreover, the total phenolic content of indigenous CHE, which is essential for understanding its reducing potential, was evaluated and applied throughout all synthesis procedures. The initial formation of the synthesized nanomaterial was visually indicated by a noticeable color change. This was followed by thorough characterization using ultraviolet–visible (UV–Vis) spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Further analysis of the physicochemical properties of the synthesized materials was carried out using scanning electron microscopy (SEM), zeta potential analysis, dynamic light scattering (DLS), Brunauer–Emmett–Teller (BET) surface area analysis, and thermogravimetric analysis (TGA).The functional performance of the nanocomposites was assessed through antibacterial activity using agar well diffusion assays, heavy metal quantification via atomic absorption spectroscopy (AAS), and fluoride removal efficiency using a fluoride ion-selective electrode. The optimized CHE-ZnO NPs synthesis conditions included a 1:1 zinc precursor-to-extract ratio, pH 10, reaction temperature of 80 °C, and a 1h reaction time. The resulting ZnO nanoparticles exhibited strong antibacterial activity, against S. aureus and E. coli. Their performance was further improved by forming a composite with Fe₃O₄/PU, yielding particles with enhanced colloidal stability (zeta potential −23.8 mV), reduced size (11.2 nm), and broader-spectrum antibacterial efficacy against both S. aureus and E. coli . For heavy metal adsorption, a green-synthesized CHE capped magnetite-pumice-silica nanocomposite (M/PU/Si-NC) was fabricated and tested for lead removal. The material demonstrated a high surface area (313 m²/g), good thermal stability (up to 690 °C), and a strong negative surface charge (−37.7 mV). It achieved 95% lead removal efficiency at 2 g/L dosage and 100 mg/L Pb²⁺ concentration. Adsorption followed the Langmuir isotherm model with a maximum capacity of 150 mg/g and pseudo-second-order kinetics. The CHE-capped M/PU/Si-NC maintained its initial adsorption capacity after five cycles highlighting its reusability. However, its negatively charged surface limited its ability to capture anionic species such as fluoride and Cr (VI). To address this, the material was modified by incorporating magnesium oxide and amine functional groups, resulting in a positively charged surface under acidic conditions. The amine functionalized magnetite-magnesium silica nanocomposite achieved removal efficiencies of 92% for fluoride and 86% for Cr (VI), the material maintained a relatively high removal efficiency even after multiple cycles. The adsorption behaviors for both pollutants conformed to the Langmuir isotherm and pseudo-second-order kinetics, confirming the efficiency and stability of the modified adsorbent. In conclusion, this research successfully demonstrates the potential of plant-mediated nanotechnology for the development of sustainable water purification materials. The synthesized aforementioned nanocomposites effectively addressed key challenges in water treatment by combining disinfection capabilities with the removal of hazardous ions. Their high performance, environmental compatibility, and reusability make them strong candidates for practical implementation in decentralized or resource-constrained communities, offering a scalable solution to global water quality concerns.
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Keywords
phenolic compound, pollutant, drinking water, biogenic-synthesis, Water treatment.