Green synthesis and characterization of copper oxide and zinc oxide nanoparticles derived from aqueous mangosteen (garcinia mangostana) leaf extract for palm oil mill effluent (pome) treatment

Chan, Yu Bin (2025) Green synthesis and characterization of copper oxide and zinc oxide nanoparticles derived from aqueous mangosteen (garcinia mangostana) leaf extract for palm oil mill effluent (pome) treatment. PhD thesis, UTAR.

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Abstract

Green synthesis of nanomaterials using plant extracts offers a sustainable and eco-friendly alternative to conventional methods. In this study, copper oxide (CuO), zinc oxide (ZnO), and zinc oxide-copper oxide (ZnO-CuO) nanomaterials were successfully synthesized using mangosteen (Garcinia mangostana) leaf extract (MLE). The synthesis process was optimized based on key parameters such as MLE concentration, calcination temperature, and the Zn-to-Cu ratio. The synthesized nanomaterials were characterized using a range of analytical tools to assess their physicochemical properties. The optimized CuO, ZnO and ZnO-CuO nanomaterials were chosen in inhibiting selected bacteria using Broth macrodilution assay and treating palm oil mill effluent (POME) at different conditions under light-emitting diode (LED). In preliminary in vitro antibacterial study, MLE-mediated synthesized CuO nanoparticles (NPs) and ZnO NPs calcinated at 500oC and 0.05 g/mL MLE-mediated synthesized 70ZnO-30CuO nanocomposites (NCs) calcinated at 500oC were chosen due to their small crystalline size. The average particle sizes of the synthesized nanomaterials were 14.31 nm ± 5.368, 29.61 nm ± 12.573 and 23.09 nm ± 10.656 and mostly spherical structure. The ZnO NPs demonstrated the highest antibacterial efficacy with minimum inhibitory concentrations (MIC) of 15.63 μg/mL (Staphylococcus aureus, Bacillus subtilis), 62.50 μg/mL (Escherichia coli), and 125.00 μg/mL (Klebsiella pneumoniae). ZnO-CuO NCs ranked second, with MICs of 62.50 μg/mL, 62.50 μg/mL, 250.00 μg/mL, and 125.00 μg/mL, respectively. CuO NPs were the least effective, showing higher MICs of 250.00 μg/mL, 125.00 μg/mL, 125.00 μg/mL, and 500.00 μg/mL. For POME treatment, ZnO NPs calcinated at 400°C achieved the best performance with COD and AN removal efficiencies at 54.05% ± 0.03 and 38.72% ± 0.00, respectively, using 50 mg of NPs under 120 min of blue LED exposure. In contrast, 150 mg of CuO NPs and ZnO-CuO NCs were required for optimal photodegradation under blue LED for 150 min, achieving COD and AN removal efficiencies of 58.58% ± 0.02 and 38.86% ± 0.01 (CuO NPs) and 59.72% ± 0.02 and 27.80% ± 0.01 (ZnO-CuO NCs), respectively. In conclusion, this study demonstrates the potential of MLE-mediated green synthesis of nanomaterials as a sustainable approach for producing effective photocatalyst and antibacterial agents. ZnO NPs, in particular, exhibit high promise for environmental and biomedical applications. This study introduced a sustainable and environmentally friendly approach to MLE-based nanomaterial synthesis. Additionally, it offered a viable alternative method of bacterial inhibition and a treatment for POME. Moreover, the use of treated POME shown good agricultural development. This study proposed breakthroughs in scientific knowledge of nanomaterial synthesis, antibacterial and photocatalysis mechanisms. This work has a significant contribution to science and society as the results have far-reaching implications for sustainable development, public health and environmental protection – all of which are parallel to the sixth and twelfth sustainable development goals.

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