Abstract
Herein, we report an effective, facile, and low-cost route for preparing ZnO hollow microspheres with a controlled number of shells composed of small ZnO nanoparticles. The formation mechanism of multiple-shelled structures was investigated in detail. The number of shells is manipulated by using different diameters of carbonaceous microspheres. The products were characterized by X-ray powder diffraction, scanning electron microscopy, and transmission electron microscopy. The as-prepared ZnO hollow microspheres and ZnO nanoparticles were then used to study the degradation of methyl orange (MO) dye under ultraviolet (UV) light irradiation, and the triple-shelled ZnO hollow microspheres exhibit the best photocatalytic activity. This work is helpful to develop ZnO-based photocatalysts with high photocatalytic performance in addressing environmental protection issues, and it is also anticipated to other multiple-shelled metal oxide hollow microsphere structures.
Highlights
With the sustainable development of industry and society, the contamination of the environment caused by organic pollutants is becoming an overwhelming problem all over the world [1]
ZnO is a semiconductor with a bandgap of 3.37 eV and a large exciton binding energy of 60 meV at room temperature which results in the poor utilization of sunlight, limiting its photocatalytic efficiency
According to the principle of photocatalysis, much research focuses on enhancing the surface areas of semiconductor nanomaterials by developing nanoscaled or porous appearance because a large surface area can achieve stronger light harvesting and provide more active sites at which the photocatalytic reaction occurs, small nanoparticles shorten the distance that electrons and holes migrate from bulk to reaction active sites to lower the possibility of recombination of the photogenerated charges, and the porosity can improve the photon application efficiency [7]
Summary
With the sustainable development of industry and society, the contamination of the environment caused by organic pollutants is becoming an overwhelming problem all over the world [1]. Since the semiconductor-based photochemical electrode reported by Fujishima and Honda in 1972 [2], photoactive nanomaterials as photocatalysts, especially semiconductor nanomaterials, have attracted the most attention to the degradation of organic compounds for the purpose of purifying wastewater This is due to their high photocatalytic activity and excellent chemical and mechanical stability, and it is an easy way to utilize the energy of solar light, abundantly available everywhere in the world [3]. It is of substantial importance to carry out works related to semiconductor photocatalysis Among these wide-bandgap semiconductors used in photoelectrochemical and photocatalytic applications, ZnO plays an important role in degrading various organic pollutants and photodegradation of bacteria due to its high catalytic activity, low cost, and environmental friendliness [4,5,6]. A number of efforts have been attracted to obtain high catalytic activity by manufacturing different ZnO nanostructures, such as nanoneedles [8], nanowires [9,10], nanorods [11,12], nanotetrapods [13], nanoplatelets [14], nanotubes [15,16], nanotowers [17], nanoflowers [18,19,20], and hollow nanospheres [21,22]
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