Effect of Solution pH on the Photo-Oxidation of 4-Chlorophenol by Synthesized Silver-Zinc Oxide Photocatalyst

Nur Syafiqa Hazirah Razali; Hayati Mohamad Mukhair; Kian Mun Lee; Mohd Izham Saiman; Abdul Halim Abdullah

doi:10.22146/ijc.71763

Effect of Solution pH on the Photo-Oxidation of 4-Chlorophenol by Synthesized Silver-Zinc Oxide Photocatalyst

https://doi.org/10.22146/ijc.71763

Nur Syafiqa Hazirah Razali⁽¹⁾, Hayati Mohamad Mukhair⁽²⁾, Kian Mun Lee⁽³⁾, Mohd Izham Saiman⁽⁴⁾, Abdul Halim Abdullah^(5*)

(1) Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43300 UPM Serdang, Selangor Malaysia
(2) Institute of Nanoscience and Nanotechnology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
(3) Nanotechnology and Catalysis Research Centre (NANOCAT), University of Malaya, 50603 Kuala Lumpur, Malaysia
(4) Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43300 UPM Serdang, Selangor Malaysia
(5) Department of Chemistry, Faculty of Science, Universiti Putra Malaysia, 43300 UPM Serdang, Selangor Malaysia; Institute of Nanoscience and Nanotechnology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
(*) Corresponding Author

Abstract

Due to its toxicity, 4-chlorophenol (4CP) must be removed from the wastewater before discharging into open water. In this work, ZnO and Ag-ZnO photocatalysts were prepared via a solvothermal method under mild conditions (150 °C), followed by calcination at 300 °C and then characterized. The addition of Ag resulted in a change of the ZnO morphologies, which exhibited wurtzite structure, from irregular to rod-like shape, lower bandgap energy, and a lower electron-hole recombination rate. The 0.6 Ag-ZnO catalyst showed the highest efficiency in the photooxidation of 4CP under UV irradiation. Molecular 4CP exists in acidic and near-neutral conditions (pH 4 and 6) and is stable towards UV irradiation. Photooxidation of 2.3 × 10^–4 mol/L 4CP by 0.8 g of 0.6% Ag-ZnO resulted in 67% removal of molecular 4CP at pH 6 with a rate constant of 4.0 × 10^–3 min^–1. Under similar conditions, a complete photooxidation of the anionic 4CP was observed at pH 11 with a rate constant of 1.4 × 10^–2 min^–1. The holes and superoxide radicals are the species responsible for molecular 4CP photoooxidation, while hydroxyl radicals are the dominant species for anionic 4CP. The prepared Ag/ZnO photocatalyst exhibit good potential to efficiently oxidize 4CP in both acidic and alkaline conditions.

Keywords

Ag-ZnO; photooxidation; 4-chlorophenol; endocrine disruptor chemicals; photocatalyst

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DOI: https://doi.org/10.22146/ijc.71763