Malaysian Journal of Analytical Sciences Vol 22 No 2 (2018): 270 - 278

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

(Degradasi Metilena Biru Menggunakan Nanopartikel ZnO Sebagai Fotomangkin yang Didopkan dengan Perak Tumbuh di atas Pasir Bersaiz Mikro)

Nur Azmina Mohamed Safian¹*, Roslan Md Nor¹, Hartini Ahmad Rafaie², Siti Fairus Abdul Sani¹, Zurina Osman¹

¹Department of Physics, Faculty of Sciences,

University of Malaya, 50603 Kuala Lumpur, Malaysia

²Unit of Physics, School of Science,

Universiti Teknologi MARA Pahang, Jengka, 26400 Bandar Tun Abdul Razak, Jengka Pahang, Malaysia

*Corresponding author: nurazminasafian@siswa.um.edu.my

Received: 4 December 2016; Accepted: 1 December 2017

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, nanoparticles

Abstrak

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

References

1. Tanaka, K. and Blyholder, G. (1972). Photocatalytic reactions on zinc oxide. III. Hydrogenation of ethylene. The Journal of Physical Chemistry, 76(10): 1394-1397.

2. Yan, Y., Al-Jassim, M. M. and Wei, S. H. (2006). Doping of ZnO by Group-IB elements. Applied physics letters, 89(18): 181912.

3. Ren, C., Yang, B., Wu, M., Xu, J., Fu, Z., Guo, T., Zhao, Y. and Zhu, C. (2010). Synthesis of Ag/ZnO nanorods array with enhanced photocatalytic performance. Journal of Hazardous materials, 182(1): 123-129.

4. Hosseini, S. M., Sarsari, I. A., Kameli, P. and Salamati, H. (2015). Effect of Ag doping on structural, optical, and photocatalytic properties of ZnO nanoparticles. Journal of Alloys and Compounds, 640: 408-415.

5. Karunakaran, C., Rajeswari, V. and Gomathisankar, P. (2011). Combustion synthesis of ZnO and Ag-doped ZnO and their bactericidal and photocatalytic activities. Superlattices and Microstructures, 50(3): 234-241.

6. Amornpitoksuk, P., Suwanboon, S., Sangkanu, S., Sukhoom, A., Muensit, N. and Baltrusaitis, J. (2012). Synthesis, characterization, photocatalytic and antibacterial activities of Ag-doped ZnO powders modified with a diblock copolymer. Powder Technology, 219: 158-164.

7. Tamargo, M. C. (2002). II-VI semiconductor materials and their applications (Vol. 12). CRC Press.

8. Sun, W. C., Yeh, Y. C., Ko, C. T., He, J. H. and Chen, M. J. (2011). Improved characteristics of near-band-edge and deep-level emissions from ZnO nanorod arrays by atomic-layer-deposited Al₂O₃and ZnO shell layers. Nanoscale Research Letters, 6(1): 556.

9. Vanheusden, K., Warren, W. L., Seager, C. H., Tallant, D. R., Voigt, J. A. and Gnade, B. E. (1996). Mechanisms behind green photoluminescence in ZnO phosphor powders. Journal of Applied Physics, 79 (10): 7983-7990.

10. Wu, J. J. and Liu, S. C. (2002). Low-temperature growth of well-aligned ZnO nanorods by chemical vapor deposition. Advanced Materials, 14(3): 215-218.

11. Liu, M., Kitai, A. H. and Mascher, P. (1992). Point defects and luminescence centres in zinc oxide and zinc oxide doped with manganese. Journal of Luminescence, 54(1): 35-42.

12. Wu, X. L., Siu, G. G., Fu, C. L. and Ong, H. C. (2001). Photoluminescence and cathodoluminescence studies of stoichiometric and oxygen-deficient ZnO films. Applied Physics Letters, 78(16): 2285-2287.

13. Djurišić, A. B., Leung, Y. H., Tam, K. H., Hsu, Y. F., Ding, L., Ge, W. K., Zhong, Y. C., Wong, K. S., Chan, W. K., Tam, H. L. and Cheah, K. W. (2007). Defect emissions in ZnO nanostructures. Nanotechnology, 18(9): 095702.

14. Kong, M., Li, Y., Chen, X., Tian, T., Fang, P., Zheng, F. and Zhao, X. (2011). Tuning the relative concentration ratio of bulk defects to surface defects in TiO₂ nanocrystals leads to high photocatalytic efficiency. Journal of the American Chemical Society, 133(41): 16414-16417.