Zinc Oxide Nanostructures Synthesized by a Simple Hot Water Treatment Method for Photocatalytic Degradation of Organic Pollutants in Water
TL;DR: In this article, the synthesis of ZnO nanostructures by a simple hot water treatment (HWT) method and the photocatalytic activity of the hence produced nanostructure is demonstrated.
Abstract: The use of zinc oxide (ZnO) nanostructures as a photocatalyst for the degradation of organic pollutants in water has received significant attention over the recent years However, synthesis methods for producing ZnO nanostructures are generally costly, complicated, and hazardous to the environment In this work, we demonstrate the synthesis of ZnO nanostructures by a simple hot water treatment (HWT) method and the photocatalytic activity of the hence produced nanostructures HWT is a one-step, low-cost, eco-friendly, and scalable nanostructure growth method By HWT, various metal-oxide nanostructures can be produced simply by the interaction of metals with hot water without the need for any chemical additives in the solution Growth of metal-oxide nanostructures by HWT involves the formation of metal-oxides and their release from the surface of the metal into water, the migration of the metal-oxides in water, and their re-deposition at a different part of the metallic surface, which initiates the growth of nanostructures In this study, we used zinc powder and plates for producing the ZnO nanostructures by HWT in DI water at 75°C Scanning electron microscopy and X-ray diffraction were utilized to verify the formation of ZnO nanostructures Zinc plates produced a suspension of ZnO nanostructures in water, while on the other hand, zinc powder resulted in ZnO nanostructures grown on the powder surface as well as standalone ZnO nanostructures also mixed in water We used these nanostructures + water suspensions for our photocatalytic degradation studies Methylene blue (MB) was used as a model organic pollutant We mixed the ZnO nanostructure suspension with MB and exposed it to UV light The degradation of MB was observed by measuring its absorbance values using a UV-Visible spectrophotometer over a period of 4 hours We observed a 20% decrease in the concentration of MB in 4 hours when nanostructured Zn/ZnO powder suspension was used, and a 30% decrease was achieved when ZnO nanostructure-only suspension produced from zinc plates was used MB alone was also exposed to UV light for the same period as a control experiment, and we did not observe any significant decrease in its concentration These results indicate that the hot water treatment method presents a very simple, cost-effective, scalable, and eco–friendly alternative for the synthesis of ZnO nanostructures for photocatalytic water treatment applications
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TL;DR: In this article , Zhao et al. introduced a simple and chemical additive-free nanostructure synthesis method called hot water treatment (HWT) to produce immobilized ZnO nanostructures on Zn surfaces.
Abstract: Photocatalysis with zinc oxide (ZnO) nanostructures has received significant attention as an alternative method for microbial disinfection in water. However, most ZnO nanostructure synthesis methods are expensive, non-scalable, and use toxic chemicals. Besides that, ZnO photocatalysts are often synthesized in nanopowder form that are suspended in water. Nanostructures suspended in water have various disadvantages such as tendency to agglomerate and difficulty of recovery and reuse. Here we introduce a simple and chemical additive-free nanostructure synthesis method called hot water treatment (HWT) to produce immobilized ZnO nanostructures on Zn surfaces. In this study, Zn plates were immersed in DI water at 75 °C for different durations, which resulted in the formation of ZnO nanostructures of different lengths and diameters. Reduction in E. coli growth was observed on HWT ZnO nanostructured surfaces that were irradiated with UV light, which is believed due to the photocatalytic activity of the HWT ZnO nanostructures. Graphical abstract
TL;DR: In this article , an in situ growth and UV photocatalytic effect of ZnO nanostructures on a Zn plate immersed in methylene blue (MB) at room temperature was discussed.
Abstract: Nanostructures of zinc oxide (ZnO) are considered promising photocatalysts for the degradation of organic pollutants in water. This work discusses an in situ growth and UV photocatalytic effect of ZnO nanostructures on a Zn plate immersed in methylene blue (MB) at room temperature. First, the Zn surfaces were pretreated via sandblasting to introduce a micro-scale roughness. Then, the Zn plates were immersed in MB and exposed to UV light, to observe ZnO nanostructure growth and photocatalytic degradation of MB. Scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and UV-Vis diffuse reflectance spectroscopy were used to characterize the Zn surfaces. We observed the growth of stoichiometric and crystalline ZnO with a nano-leaf morphology and an estimated bandgap of 3.08 eV. The photocatalytic degradation of MB was also observed in the presence of the ZnO nanostructures and UV light. The average percentage degradation was 76% in 4 h, and the degradation rate constant was 0.3535 h−1. The experimental results suggest that room temperature growth of ZnO nanostructures (on Zn surfaces) in organic dye solutions is possible. Furthermore, the nanostructured surface can be used simultaneously for the photocatalytic degradation of the organic dye.
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TL;DR: In this paper, the photo-degradation mechanisms of persistent organic pollutants (POPs) and the recent progress in ZnO nanostructured fabrication methods including doping, heterojunction and modification techniques as well as improvements of ZnOs as a photocatalyst are reviewed.
Abstract: Persistent organic pollutants (POPs) are carbon-based chemical substances that are resistant to environmental degradation and may not be completely removed through treatment processes. Their persistence can contribute to adverse health impacts on wild-life and human beings. Thus, the solar photocatalysis process has received increasing attention due to its great potential as a green and eco-friendly process for the elimination of POPs to increase the security of clean water. In this context, ZnO nanostructures have been shown to be prominent photocatalyst candidates to be used in photodegradation owing to the facts that they are low-cost, non-toxic and more efficient in the absorption across a large fraction of the solar spectrum compared to TiO 2 . There are several aspects, however, need to be taken into consideration for further development. The purpose of this paper is to review the photo-degradation mechanisms of POPs and the recent progress in ZnO nanostructured fabrication methods including doping, heterojunction and modification techniques as well as improvements of ZnO as a photocatalyst. The second objective of this review is to evaluate the immobilization of photocatalyst and suspension systems while looking into their future challenges and prospects.
1,551 citations
TL;DR: A simple approach based on tailoring the surface charge of nanoparticles, NPs, during the preparation to boost the electrostatic attraction between NPs and the organic pollutant was investigated and showed pH-dependent behavior.
Abstract: Herein, a simple approach based on tailoring the surface charge of nanoparticles, NPs, during the preparation to boost the electrostatic attraction between NPs and the organic pollutant was investigated. In this study, chargeable titania nanoparticles (TiΟ2 NPs) were synthesized via a hydrothermal route under different pH conditions (pH = 1.6, 7.0 and 10). The prepared TiΟ2 NPs were fully characterized via various techniques including; transmission electron microscopy (TEM), X-ray diffraction (XRD), N2 adsorption/desorption, X-ray photoelectron spectroscopy (XPS), Ultraviolet–visible spectroscopy (UV-Vis) and dynamic light scattering (DLS). The influence of the preparation pH on the particle size, surface area and band gap was investigated and showed pH-dependent behavior. The results revealed that upon increasing the pH value, the particle size decreases and lead to larger surface area with less particles agglomeration. Additionally, the effect of pH on the surface charge was monitored by XPS to determine the amount of hydroxyl groups on the TiO2 NPs surface. Furthermore, the photocatalytic activity of the prepared TiΟ2 NPs towards methylene blue (MB) photodegradation was manifested. The variation in the preparation pH affected the point of zero charge (pHPZC) of TiO2 NPs, subsequently, different photocatalytic activities based on electrostatic interactions were observed. The optimum efficiency obtained was 97% at a degradation rate of 0.018 min−1 using TiO2 NPs prepared at pH 10.
310 citations
TL;DR: In this article, an overview of antiviral effects of a wide range of photocatalysts, including TiO2-based, metal-containing, and metal-free, is presented.
168 citations
TL;DR: In this article, the authors show that a given TiO 2 sample may not be simultaneously optimal for photocatalytically driving the reduction of Cr(VI) and the oxidation of MB.
Abstract: Using hexavalent chromium (Cr(VI)) and methylene blue (MB) as model sub- strates, we discuss three aspects of TiO 2 -based heterogeneous photocatalysis. We show first that a given TiO 2 sample may not be simultaneously optimal for photocatalytically driving the reduction of Cr(VI) and the oxidation of MB. We further show that a TiO 2 sample that strongly adsorbs either of these substrates in the dark is not optimal as a photocatalyst. The other two aspects concern circumventing the rather poor surface catalytic properties and vis- ible light photoresponse of TiO 2 , respectively. Strategies revolving around the visible light photoexcitation of the substrate itself and metal-modification of the TiO 2 surface, are described as possible solutions.
105 citations
TL;DR: In this article, a new method to synthesize ZnO nanorods on zinc spheres to form a core-shell structure was presented, which can find applications in nanoelectronics, nanophotonics and nanomedicine.
82 citations