High UV and Sunlight Photocatalytic Performance of Porous ZnO Nanostructures Synthesized by a Facile and Fast Microwave Hydrothermal Method

Abstract

The degradation of organic pollutants in wastewaters assisted by oxide semiconductor nanostructures has been the focus of many research groups over the last decades, along with the synthesis of these nanomaterials by simple, eco-friendly, fast, and cost-effective processes. In this work, porous zinc oxide (ZnO) nanostructures were successfully synthesized via a microwave hydrothermal process. A layered zinc hydroxide carbonate (LZHC) precursor was obtained after 15 min of synthesis and submitted to different calcination temperatures to convert it into porous ZnO nanostructures. The influence of the calcination temperature (300, 500, and 700 °C) on the morphological, structural, and optical properties of the ZnO nanostructureswas investigated. All ZnO samples were tested as photocatalysts in the degradation of rhodamine B (RhB) under UV irradiation and natural sunlight. All samples showed enhanced photocatalytic activity under both light sources, with RhB being practically degraded within 60 min in both situations. The porous ZnO obtained at 700 °C showed the greatest photocatalytic activity due to its high crystallinity, with a degradation rate of 0.091 and 0.084 min−1 for UV light and sunlight, respectively. These results are a very important step towards the use of oxide semiconductors in the degradation of water pollutants mediated by natural sunlight.

UV-Responsive Screen-Printed Porous ZnO Nanostructures on Office Paper for Sustainable and Foldable Electronics

“…As reported in our previous work [67], porous ZnO nanostructures were synthesized through a facile and fast hydrothermal method assisted by microwave irradiation, followed by a washing step to remove remnants of reagents from the synthesis and a calcination step in a furnace to thermally convert the resulting LZHC precursor into ZnO. As demonstrated in that work [67], a calcination process at 700 • C yields porous ZnO nanostructures with high crystallinity and larger pore size when compared to lower calcination temperatures, while ensuring a complete conversion of LZHC into ZnO. Therefore, this calcination temperature was selected to prepare the ZnO nanostructures in this work.…”

“…Following the procedure reported in our previous work [67], porous ZnO nanostructures were synthesized by hydrothermal method assisted by microwave irradiation. Briefly, 0.05 M of zinc nitrate hexahydrate (Zn(NO 3 ) 2 •6H 2 O, 98% from Sigma-Aldrich, St. Louis, MO, USA) was first dissolved in deionized water, followed by the addition of urea (CH 4 N 2 O, 99.0-100.5% from Sigma-Aldrich, St. Louis, MO, USA) to the aqueous solution in a molar ratio of zinc to urea of 1:5.…”

“…These parameters were determined to be 8.2 ± 1.0 and 22.0 ± 2.3 s for t rise and t fall , respectively. The promising results obtained for the produced ZnO UV sensors can be attributed to the enhanced adsorption capacity for oxygen-rich molecules on the surface of the porous ZnO nanostructures due to their large specific surface area as well as the improvement of electron transport properties in ZnO as a result of both its high crystallinity [67] and plane contacts between the porous nanoplates [63]. Overall, the resistance of the sensing layer is strongly affected by the inter-nanostructure barrier at the contacts, meaning that the photoresponse of the sensor is mainly determined by the contacts between the ZnO nanostructures.…”

Sunlight Photocatalytic Performance of ZnO Nanoparticles Synthesized by Green Chemistry Using Different Botanical Extracts and Zinc Acetate as a Precursor

“…From the data in Figure 9 , plots of ln( C 0 / C x ) versus sunlight exposure time were constructed ( Figure 10 ) to evaluate the efficiency of the photocatalytic process through the rate constant k of the process. This constant is given by the pseudo-first-order kinetic reaction (Equation (1)), valid for millimolar pollutant concentrations [ 35 ]. where C 0 is the initial methylene blue concentration, C x is the residual dye concentration in solution after a certain time, k is the rate constant (min −1 ), and t is the exposure time (min).…”

“…From the data in Figure 9, plots of ln(C 0 /C x ) versus sunlight exposure time were constructed (Figure 10) to evaluate the efficiency of the photocatalytic process through the rate constant k of the process. This constant is given by the pseudo-first-order kinetic reaction (Equation ( 1)), valid for millimolar pollutant concentrations [35].…”