ZnO/Zn(OH)2 nanoparticles and self-cleaning coatings for the photocatalytic degradation of organic pollutants

Abstract

Zinc oxide (ZnO) nanostructures have emerged as efficient heterogeneous photocatalysts for the degradation of organic pollutants in aqueous solutions and industrial wastewaters. In this work, a simple and effective method is reported for the synthesis of zinc oxide/zinc hydroxide (ZnO/Zn(OH)2) hybrid nanoparticles using a mineral acid to enhance the photocatalytic activity of ZnO. Infrared spectroscopy reveals the presence of hydroxyl groups in ZnO/Zn(OH)2 nanoparticles. X-ray diffraction shows the formation of hexagonal wurtzite ZnO nanoparticles, which retain their wurtzite structure after acid treatment but additional diffractions for Zn(OH)2 are also recorded. The optical bandgap of resulting ZnO and ZnO/Zn(OH)2 nanoparticles is reduced to 3.05 and 3.08 eV, respectively. In the initial photocatalysis experiments, ZnO/Zn(OH)2 nanoparticles exhibit 3.5-times improved degradation and removal of sunset yellow dye, a model organic pollutant, from deionized water compared to pristine ZnO nanoparticles. Hence, for further studies, ZnO/Zn(OH)2 coatings are fabricated on glass slides with a uniform surface morphology as shown by the atomic force microscopy. The time-dependent UV-visible spectroscopy reveals the photocatalytic degradation of sunset yellow over the surface of ZnO/Zn(OH)2 coatings. The degradation reaction follows the pseudofirst-order mechanism with a rate constant of 2.9 × 10–2 min−1. The recyclability and stability experiments reveal the retention of appreciable photocatalytic activity of ZnO/Zn(OH)2 coatings (with >92% degradation efficiency after six successive cycles). The results are compared with recent examples from the pertinent literature. The surface hydroxyl groups on ZnO/Zn(OH)2 nanoparticles and bandgap lowering enhance the anchoring of dye molecules and electron transfer reactions.

Green Synthesis of Zn(OH)2/ZnO-Based Bionanocomposite using Pomegranate Peels and Its Application in the Degradation of Bacterial Biofilm

“…It was noted that band gaps corresponding to the three edges observed in the UV-Vis spectrum with values of 2.80 eV, 3.44 eV, and 4.46 eV were calculated from the Tauc plot. These observations were in good agreement with studies reported by Ekennia et al [42] and Faheem et al [26]. These authors reported 2.72-4.37eV band gap in the case of biogenic ZnO nanostructures synthesized using Euphorbia sanguinea as the reducing agent.…”

“…Faheem et al recently reported a chemical method for producing ZnO/Zn(OH) 2 NPs via surface protonation of pre-synthesized ZnO NPs. Furthermore, when compared to bare ZnO NPs, ZnO/Zn(OH) 2 demonstrated a 3.5-fold improvement in photocatalytic efficiency for the degradation and removal of sunset yellow dye [26]. Furthermore, such ZnO/Zn(OH) 2 nanostructures can be used as a hard template to prepare a wide range of nanomaterials with diverse physicochemical properties, such as high specific surface area, crystallinity, and mesoporosity, thus exhibiting improved catalytic efficiency [27].…”

Optimizing the structural and photocatalytic performance of Ag‐decorated ZnO/Zn(OH)2 nanoparticles for RhB degradation

“…The optical band gap values of the obtained structures as a result of the aging of 2 and 6 h were found to be 3.59 and 2.89 eV for ZnO phase and 5.32 and 5.20 eV for Zn(OH) 2 phase, respectively. Band gap values of different solution‐aged samples in the UV–vis diffuse reflectance spectra of ZnO/Zn(OH) 2 composite NPs in Figure 5A are corresponded to Zn(OH) 2 phase, which is in good agreement in the literature 28 . As the solution aged, the band gap of the samples decreased.…”

Enhanced photocatalytic activity in ZnO nanoparticles developed using novel Lepidagathis ananthapuramensis leaf extract

“…From the XRD results, it is clearly observed that the crystallite size decreases and the concentration of Zn(OH) 2 increases as the LA extract concentrations are increased. Firstly, the presence of Zn(OH) 2 can introduce an impurity level below the conduction band, which can act as scavengers of charge carriers enhancing the recombination time, 66 thus reducing the band gap. Moreover, the presence of surface hydroxyl group, facilitate the formation of non-covalent bond with the dye molecules.…”