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Green synthesis of Iron nanoparticles using made tea and refused tea for dye removal in wastewater
M.A.A.P.M Athapaththu1, E.A.L Lochana1, V.P Ellepola1 and G.A.A.R Perera2
1Department of Export Agriculture, Faculty of Animal Science and Export Agriculture, Uva Wellassa University of Sri Lanka
2Department of Food Science and Technology, Faculty of Animal Science and Export Agriculture, Uva Wellassa University of Sri Lanka
*Corresponding Author: tea20046@std.uwu.ac.lk , lakmini@uwu.ac.lk
Iron nanoparticles are gaining attention as cost-effective, eco-friendly agents for wastewater treatment. This study develops a sustainable method to synthesize iron-based nanoparticles using aqueous extracts of made tea (commercially processed tea) and refused tea (tea rejected during quality grading) from black and green tea varieties. The research explores utilizing tea industry by-products, especially refused tea, which accounts for 4–6% of Sri Lanka's production, as a valuable resource for environmental remediation. Iron-based nanoparticles were synthesized by reacting tea extracts (10% w/v, pH ~5.5) with 0.10 M FeCl₃ solution in a 1:2 ratio under mechanical stirring at room temperature for 2 hours. Nanoparticles were collected by centrifugation, washed three times with deionized water, and dried at 60°C for 24 hours. Characterization was performed using FTIR, UV-Visible Spectroscopy, XRD, and SEM. FTIR identified polyphenolic functional groups (O-H, C=O, C-O) responsible for iron reduction and stabilization, with Fe–O stretching vibrations at 564-576 cm⁻¹ confirming iron oxide formation. UV-Vis spectra showed strong ultraviolet absorption with a characteristic edge around 390 nm, confirming nanoparticle formation. XRD patterns revealed predominantly amorphous or nanocrystalline structure with a weak, broad reflection at 2θ ≈ 44.7–45.1° indexed to the (110) plane of BCC α-Fe, indicating nanoscale iron presence without distinct crystalline oxide phases. SEM revealed irregular, quasi-spherical particles (30–80 nm) with high agglomeration due to magnetic interactions. Synthesis nanoparticle yield varied by tea type: green made tea (Gunpowder 1) achieved 65.5±1.5%, green refused tea 65.6±3.1%, black made tea (CTC Dust 1) 52.9±2.5%, and black refused tea 39.2±2.9%. Nanoparticles were evaluated for methyl orange removal (50 mg/L, pH 6.5, 120 min, 150 rpm, 25°C). Control experiments with tea extract or FeCl₃ alone showed negligible removal (<5%). Black made tea nanoparticles achieved the highest removal efficiency of 80.5±1.8% (40.3 mg/g), followed by green made tea 75.3±0.9% (37.7 mg/g), green refused tea 70.6±1.3% (35.3 mg/g), and black refused tea 63.8±0.8% (31.9 mg/g). Increasing dosage from 1.0 to 2.0 g/L improved efficiency to 85.7%. The discrepancy between synthesis yield and removal performance indicates that surface chemistry governs adsorption efficiency. The removal mechanism is attributed primarily to adsorption with contributions from electrostatic interactions and surface complexation. This research demonstrates the potential of made tea and refused tea as sustainable precursors for iron-based nanoparticle synthesis, presenting an eco-friendly strategy for tea waste valorization and efficient dye-contaminated wastewater treatment.
Keywords: Black tea; Green synthesis; Green tea; Iron nanoparticles; Methyl orange; Refused tea; Wastewater treatment
