Utilizing phytochemical-rich spent coffee ground extract for eco-friendly ZnO electrochemical synthesis: Assessing photocatalytic efficacy in 2,4-dichlorophenol degradation

• Published in: Separation and purification technology 2025-02, Vol.354, p.129208, Article 129208
• Main Authors: Mutalib, Aunie Afifah Abdul, Jaafar, Nur Farhana, Miskam, Mazidatulakmam, Ratvijitvech, Thanchanok, Holilah, Holilah, Torlaema, Tasnim Aisya Mahmuelee
• Format: Article
• Language: English
• Subjects: Electro-generation; Green synthesis; Photodegradation; Plant extract; Reducing agent; Wastewater treatment
• ISSN: 1383-5866
• DOI: 10.1016/j.seppur.2024.129208

[Display omitted] •First report of ZnO electrochemical synthesis using SCG extract.•Higher SCG extract phytochemicals reduced particle size and boosted ZnO’s photocatalytic capacity.•Green ZnO synthesis matched the photocatalytic activity of solvent-based ZnO.•SCG-mediated ZnO degraded 92.6 % of 2,4-dichlorophenol in 480 min under visible light. The study explores an alternative electrolyte derived from spent coffee ground (SCG) extract for electrochemical synthesis of zinc oxide (ZnO), aiming to address limitations associated with toxic electrolytes. Three extraction methods specifically, facile, microwave-assisted, and ultrasonic-assisted, were employed to prepare SCG extracts, resulting in ZnO-F, ZnO-MW, and ZnO-UAE, respectively. An organic solvent-mediated catalyst, ZnO-DMF, was synthesized using N, N-dimethylformamide, and served as a comparison. All catalysts were characterized via FTIR, SEM, XRD, BET, PSA, XPS and UV-DRS. The photocatalytic activity was evaluated under visible light through 2,4-dichlorophenol (2,4-DCP) degradation. The facile extraction method yielded the most phytochemical-rich SCG extract, leading to the highest catalytic activity of ZnO-F (92.6 %), followed by ZnO-MW (89.2 %) and ZnO-UAE (83.4 %). Notably, ZnO-DMF exhibited similar degradation efficiency (92 %) to ZnO-F. The ZnO-F’s smaller particle size distribution (Dv [90] = 186 µm) and smaller band gap energy (Eg, 3.18 eV) accredited to phytochemicals involvement during electrosynthesis, compensated its poor crystallinity (relative to ZnO-DMF) hence resulting in equivalent photocatalytic capacity with the organic solvent-mediated ZnO. Further optimization using ZnO-F identified pH 3, 30 ppm of 2,4-DCP, and 0.01 g of catalyst loading as the optimal conditions. The reusability test revealed that ZnO-F can be reused for a maximum of 3 cycles with 80 % degradation at the final cycle. Kinetic and scavenger studies revealed a pseudo-first-order degradation mechanism and photogenerated holes as the main species influencing 2,4-DCP degradation, respectively. This investigation accentuates the potential of SCG extract as a green electrolyte for eco-friendly ZnO synthesis with promising photocatalytic applications.