Didik Prasetyoko

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.

Mesoporous silica (MS) is an excellent adsorbent for removing methylene blue (MB) in solution. However, the adsorption process only transfers mass from the solution to the MS surface, leading to adsorbent saturation and a disposal issue for solid waste. To address this, zinc (Zn) at 10–30% (w/w) was incorporated onto the MS surface to generate a synergistic photocatalyst-adsorbent for MB removal. Adding Zn species to the surface of MS generates a mixed phase of Zn ₂ SiO ₄ and ZnO, indicating good dispersion of Zn species during impregnation. Consequently, the surface area of MS is reduced due to the utilisation of uncalcined MS during impregnation, thereby inhibiting pore blockage by Zn species. FTIR analysis revealed several essential functional groups, including the internal symmetric vibration of Si-O-Si at 1084 cm ^− 1 and the stretching vibration of Si-OH at 960 cm ^− 1 . SEM imaging uncovered a worm-like microcrystallite. The impregnated MS exhibited the highest surface area, 414.5 m ² /g, among the 30ZnO-Zn ₂ SiO ₄ /MS samples. The highest band gap was observed for 10ZnO-Zn ₂ SiO ₄ /MS, at 4.69 eV. Notably, the structure of MS is retained even after impregnation, indicating good stability. Such features promote efficient MB removal under UV-LED irradiation over the MB concentration range of 50–90 mg·L ^− 1 . 20ZnO-Zn ₂ SiO ₄ /MS demonstrated the highest photocatalytic-adsorption performance with an efficiency of 98% (after 90 min irradiation) using 50 mg·L ^− 1 MB solution at a pH solution of 9 and a dosage of 12.5 mg. The stability test of 20ZnO-Zn ₂ SiO ₄ /MS confirmed that 20ZnO-Zn ₂ SiO ₄ /MS showed a modest stability test of the photocatalytic-adsorption process. This finding provides insight into optimising the generation of an integrated photocatalyst-adsorbent for wastewater removal.