PHOTOCATALYTIC DEGRADATION OF METHYLENE BLUE WITH SILVER DOPED ZnO NANOPARTICLES GROWN ON MICROSCOPIC SAND PARTICLES

Abstract

Pure and Ag doped ZnO nanoparticles were synthesized on microscopic sand particles by sol-gel method. Silver nitrate was used as the doping precursor, Ag doping levels of 1.3 to 7.7 of Ag/Zn ratios were obtained based on energy dispersive X-ray spectroscopy analysis. X-ray diffraction results show that a ZnO (101) peak of Ag doped samples are shifted towards lower degree which around 0.17 o compared to pure ZnO NPs, indicating the existence of doping in the Ag doped samples. The pure and Ag doped ZnO samples were used as photocatalysts in the degradation of methylene blue under UV irradiation. Photodegradation efficiency based on the pseudo-first kinetics model gave measured values of the photodegradation rate, k of 8. 9, 11.8, 12.7, 14.8 and 17.4 x 10 -3 min -1 for pure, 1.3, 1.6, 1.7 and 2.4 of Ag/Zn ratios, respectively. At higher doping levels of 3.3 and 7.7 of Ag/Zn ratios, the k values receded to 12.7 and 12.0 x 10 -3 min -1 , respectively. The increasing trend on k values can be due to the doping defect levels which trapped the recombining electrons, thus lengthening the lifetime of the electron hole pairs. Keywords: photocatalysis, Ag doped ZnO, nanoparticlesAbstrak Nanopartikel ZnO tulen dan nanopartikel ZnO yang didopkan dengan perak (Ag) telah disintesiskan di atas pasir bersaiz mikro menggunakan kaedah sol-gel. Argentum nitrat digunakan sebagai sumber Ag, dapatan tahap pendopan adalah 1.3 sehingga 7.7 nisbah Ag kepada Zn (Ag/Zn). Berdasarkan keputusan spektroskopi sinar-X, terdapat peralihan kedudukan puncak ZnO (101) sebanyak 0.17 o jika dibandingkan antara ZnO tulen dan sampel ZnO yang didopkan dengan Ag. Ini menunjukkan berlaku pendopan di dalam sampel nanopartikel ZnO yang didopkan dengan Ag. Semua sampel diuji sebagai fotomangkin di dalam degradasi metilena biru di bawah sinar UV. Kecekapan degradasi dikira menggunakan model kinetik pseudo-pertama dan memberikan nilai kadar degradasi, k iaitu masing-masing 8.9, 11.8, 12.7, 14.8 dan 17.4 x 10 -3 min -1 untuk sampel ZnO tulen, 1.3, 1.6, 1.7 dan 2.4 untuk nisbah Ag/Zn. Pada tahap pendopan yang tinggi iaitu 3.3 dan 7.7 Ag/Zn, nilai k berkurangan kepada 12.7 dan 12.0 x 10 -3 min -1 . Peningkatan nilai k adalah disebabkan oleh kesan pendopan di mana elektron terperangkap untuk pergabungan semula dan memangjangkan jangka hayat pasangan elektron dan lubang.Kata kunci: fotomangkin, perak didopkan ZnO, nanopartikel ISSN -2506 Nur Azmina et al: PHOTOCATALYTIC DEGRADATION OF METHYLENE BLUE WITH SILVER DOPED ZnO NANOPARTICLES GROWN ON MICROSCOPIC SAND PARTICLES 271Introduction Since 1972, the capability of ZnO in the degradation of wastewater has been studied [1]. Due to its remarkable features which has wide band gap (3.37 eV) at room temperature and high exciton binding energy of approximately 60 meV has made ZnO as a perfect candidate in photocatalyst application. To achieve high photocatalytic degradation efficiency of wastewater, ZnO photocatalyst must offer large specific surface area and a high efficiency for segregation photogenerated electro...