Photocatalytic Decolorization of Congo Red and Rhodamine B Using ZnO Under UV LED Irradiation

Joti Souripet (Department of Chemistry, Faculty of Science and Technology, Pattimura University, Jl. Ir. M. Putuhena, Ambon 97233, Indonesia)
Hellna Tehubijuluw (Department of Chemistry, Faculty of Science and Technology, Pattimura University, Jl. Ir. M. Putuhena, Ambon 97233, Indonesia)
Catherina Bijang (Department of Chemistry, Faculty of Science and Technology, Pattimura University, Jl. Ir. M. Putuhena, Ambon 97233, Indonesia)
Riki Subagyo (Department of Chemistry, Faculty of Science and Data Analytics, Sepuluh Nopember Institute of Technology, Keputih, Sukolilo, Surabaya 60111, Indonesia)
Dewi Sri (Department of Chemistry, Faculty of Science and Technology, Pattimura University, Jl. Ir. M. Putuhena, Ambon 97233, Indonesia)
Didik Prasetyoko (Department of Chemistry, Faculty of Science and Data Analytics, Sepuluh Nopember Institute of Technology, Keputih, Sukolilo, Surabaya 60111, Indonesia)
Yuly Kusumawati (Department of Chemistry, Faculty of Science and Data Analytics, Sepuluh Nopember Institute of Technology, Keputih, Sukolilo, Surabaya 60111, Indonesia)

Indonesian Journal of Chemistry
Vol 26, No 5 (2026)

Textile wastewater containing synthetic dyes poses persistent environmental challenges due to its toxicity, chemical stability, and resistance to conventional treatment processes. This study evaluates the photocatalytic degradation performance of zinc oxide (ZnO) toward Congo Red (azo dye) and Rhodamine B (xanthene dye) under ultraviolet light-emitting diode (UV LED) irradiation. ZnO was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and field emission scanning electron microscopy (FESEM), confirming the formation of crystalline, phase-pure hexagonal wurtzite ZnO with nanoscale morphology and mesoporous features. The crystallite size estimated using the Scherrer equation ranged from 25.9 to 33.2 nm. Photocatalytic experiments were conducted at different initial dye concentrations (5–20 mg/L) with irradiation times up to 30 min. Under the investigated conditions, Rhodamine B achieved up to 97.2% removal, while Congo Red reached 89.3% removal. Kinetic analysis indicated apparent pseudo-first-order behavior with rate constants of 0.091 and 0.072 min−1 for Rhodamine B and Congo Red, respectively. Control experiments confirmed the essential role of UV LED irradiation in promoting photocatalytic activity. These findings demonstrate that ZnO activated by UV LED irradiation exhibits promising potential for efficient, sustainable, and environmentally friendly dye degradation in wastewater treatment under optimized experimental conditions with significant practical applicability.