Nano Sized ZnO: An Efficient Catalyst for Degradation of Rhodamine B dye in Aqueous Medium

Muhammad Saeed, Government College University Faisalabad Pakistan, E-mail: dur Raoof, Government College University Faisalabad Pakistan, E-mail:

Overview

Nanotechnology is an emerging interdisciplinary technology which has prospered in electronics, aerospace, mechanics and materials science in the past decade. Due to wide range of applications, the nano materials have gained the top rank in various fields of science and technology. Apart from the other nano materials, nano sized metal oxide particles represent an important category of nano materials due to their efficient biological properties, high chemical and physical stability, non-toxicity, environment friendly, etc. Nano sized zinc oxide is a special material due to its unusual characteristics and wide range of applications. ZnO semiconductor can act as efficient catalyst, which can induce redox-processes due to the electronic transitions between filled valence band and an empty conduction band. With these aforesaid properties, it has been realized that the ZnO NPs could be a promising heterogeneous catalyst for the complete mineralization of organic dyes and toxic chemicals in aqueous medium. The aim of present studies is to synthesize and characterize nano sized ZnO, to study the degradation of rhodamine dyes on nano sized ZnO, to optimize the conditions for the degradation reaction of rhodamine B dye. Effect of key operating parameters like temperature, agitation speed, initial dye concentration, contact time and catalyst dose for the degradation of rhodamine B were investigated systematically.

Methods

ZnO NPs were prepared by reaction of zinc acetate dihydrate and sodium hydroxide in distilled water. The prepared ZnO NPs were characterized by XRD, FTIR, SEM TGA and surface area analysis. ZnO NPs were employed as catalyst for oxidative degradation of rhodamine B dye with molecular oxygen in aqueous medium. The effects of various parameters like time, temperature, initial concentration of dye, speed of agitation and catalyst dose on degradation experiments were investigated.

Results

XRD spectrum is dominated with peaks at 2θ value of 31.85°, 34.5°, 36.3°, 47.75°, 56.75°, 63.1°and 68.2° corresponding to the (100), (200), (101), (102), (110), (103) and (112) planes of the hexagonal wurtzite structure of ZnO respectively in accordance with JCPDS No. 89-1397. TGA analysis revealed that prepared catalyst is stable over a wide range of temperature. It was found that catalysts reatins it activity for degradation of rhodamine B dye in aqueous medium. It was recorded that 13.8% of 8 ppm rhodamine B dye decayed in 10 minutes at 303 K and increased to 17.2% and 20.6% at 313 K and 323 K. Similarly 46% dye was degraded after 60 minutes at 303K which was increased to 51.7% and 58.6 % at 313 K and 323 K. Ultimately rhodamine B dye was completely degraded to inorganic products including nitrates, carbon dioxide and water; however some intermediate compounds were also detected with HPLC. Oxidative degradation reaction followed Eley–Rideal mechanism. According to Eley–Rideal mechanism the gaseous reactant, oxygen adsorbs at the surface of catalyst while rhodamine B dye reacts in fluid phase. Adsorbed oxygen transform to reactive radicals through the formation of electron-hole pair between conduction and valence band of zinc oxide catalyst. These active radicals mineralized the dye into water and carbon dioxide.

Conclusions

Nano sized zinc oxide particles were prepared by precipitation methods with zinc acetate and sodium hydroxide. The physiochemical properties of the prepared catalyst were investigated by XRD, FTIR, SEM and TGA analyses. The prepared ZnO NPs were employed as successful catalyst for degradation of rhodamine B dye in aqueous medium. Rhodamine B dye was completely degraded to inorganic products like water and carbon dioxide through a number of intermediate species.

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