Abstract
ZnO nanoparticles (NPs) have been synthesized on porous silica microparticles, namely sand microparticles using the sol–gel technique. The ZnO NPs grown on the multifaceted surface of porous silica microparticles were applied as photocatalyst for the degradation of methylene blue (MB) in aqueous solution. The enhanced rate constant observed was due to two reasons. Firstly, the multifaceted surface of the sand substrate provided fixed space for growth space which prevented agglomeration of the ZnO NPs photocatalyst, thus maintaining a large surface area. Secondly, the presence of nanopores on the sand surface provided adsorption sites for MB molecules to be in the vicinity of the photocatalyst. The photocatalytic activity was significantly enhanced where photodegradation efficiency of supported ZnO NPs reached 71.7% compared to 48.2% for unsupported ZnO NPs under UV light irradiation within 150 min. The values of k increased from 4.3 × 10−3 min−1 to 8.6 × 10−3 min−1 for unsupported and supported ZnO NPs, respectively.
Highlights
Nanomaterials possess unique and beneficial chemical, physical and mechanical properties which can be used for a wide variety of applications
We present the results of a study on the use of porous silica microparticles, namely sand microparticles as substrates for the growth of ZnO nanoparticles (NPs)
Crystallite size based on estimations using the Scherrer equation showed slightly bigger crystallites of ZnO NPs grown on sand compared to unsupported ZnO NPs
Summary
Nanomaterials possess unique and beneficial chemical, physical and mechanical properties which can be used for a wide variety of applications. The percentage of surface atoms are high, resulting in enhanced particle reactivity (Gilbert et al 2004; Roduner, 2006) This causes nanoparticles to adhere among themselves and to other materials, including container walls. Good adhesion of the ZnO NPs during the growth process is facilitated, due to the presence of nanosized pores, pits and lines at the surface of the sand. The cleaned sand microparticles were seeded with a very thin ZnO layer This is achieved by three cycles of soaking in a 0.005 M zinc acetate solution and annealing at 300 °C. Sand microparticles deposited with ZnO NPs were extracted from the solution by sieving to remove loose ZnO NPs before being annealed at 300 °C for 2 h. Photodegradation experiments using supported ZnO NPs without irradiation and sand under UV as well as without UV were performed
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