Zinc oxide (ZnO) is a multifunctional material due to its exceptional physicochemical properties and broad usefulness. The special properties resulting from the reduction of the material size from the macro scale to the nano scale has made the application of ZnO nanomaterials (ZnO NMs) more popular in numerous consumer products. In recent years, particular attention has been drawn to the development of various methods of ZnO NMs synthesis, which above all meet the requirements of the green chemistry approach. The application of the microwave heating technology when obtaining ZnO NMs enables the development of new methods of syntheses, which are characterised by, among others, the possibility to control the properties, repeatability, reproducibility, short synthesis duration, low price, purity, and fulfilment of the eco-friendly approach criterion. The dynamic development of materials engineering is the reason why it is necessary to obtain ZnO NMs with strictly defined properties. The present review aims to discuss the state of the art regarding the microwave synthesis of undoped and doped ZnO NMs. The first part of the review presents the properties of ZnO and new applications of ZnO NMs. Subsequently, the properties of microwave heating are discussed and compared with conventional heating and areas of application are presented. The final part of the paper presents reactants, parameters of processes, and the morphology of products, with a division of the microwave synthesis of ZnO NMs into three primary groups, namely hydrothermal, solvothermal, and hybrid methods.

A Review of Microwave Synthesis of Zinc Oxide Nanomaterials: Reactants, Process Parameters and Morphologies

Fabrication of ZnO–TiO2 nanohybrids for rapid sunlight driven photodegradation of textile dyes and antibiotic residue molecules

Pure anatase-phase titanium dioxide films stable up to high temperatures were successfully fabricated by the mist chemical vapor deposition method. A post-annealing treatment of the synthesized films was carried out in oxygen atmosphere in the temperature range from 600 to 1100 °C and no anatase to rutile transformation was observed up to 1000 °C. Based on the grazing incidence X-ray diffraction data, the average crystallite size of the titanium dioxide films increased gradually with increasing annealing temperature. The structural analysis revealed that the high thermal stability of the anatase phase can be attributed to the small crystallite size and a sheet-like grain structure. An incomplete anatase to rutile transformation was observed after annealing at 1100 °C.

https://www.mdpi.com/2079-4991/10/5/911/pdf

High Temperature Stable Anatase Phase Titanium Dioxide Films Synthesized by Mist Chemical Vapor Deposition.

In this study, a mist chemical vapor deposition method was applied to create a coating of titanium dioxide particles in order to fabricate ZnO/TiO2 core–shell nanostructures. The thin layers of titanium dioxide on the zinc oxide nanorods were uniform and confirmed as pure anatase phase. The morphological, structural, optical and photoluminescence properties of the ZnO/TiO2 core–shell structures were influenced by coating time. For instance, the crystallinity of the titanium dioxide increased in accordance with an increase in the duration of the coating time. Additionally, the thickness of the titanium dioxide layer gradually increased with the coating time, resulting in an increased surface area. The transmittance of the arrayed ZnO/TiO2 core–shell structures was 65% after 15 min of coating. The obtained ZnO/TiO2 core–shell nanostructures demonstrated high potentiality to serve as photoanodes for application in dye-sensitized solar cells.

https://www.mdpi.com/2079-4991/9/9/1339/pdf

TiO2 Coated ZnO Nanorods by Mist Chemical Vapor Deposition for Application as Photoanodes for Dye-Sensitized Solar Cells.

Doping of titanium dioxide with p-block elements is typically described as an efficient pathway for the enhancement of photocatalytic activity However, the properties of the doped titania films depend greatly on the production method, source of doping, type of substrate, etc The present work describes the use of pulsed direct current (pDC) magnetron sputtering for the deposition of carbon-doped titania coatings, using CO2 as the source of carbon; ratios of O2/CO2 were varied through variations of CO2 flow rates and oxygen flow control setpoints Additionally, undoped Titanium dioxide (TiO2) coatings were prepared under identical deposition conditions for comparison purposes Coatings were post-deposition annealed at 873 K and analysed with scanning electron microscopy (SEM), X-ray diffreaction (XRD), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) The photocatalytic properties of the thin films were evaluated under ultraviolet (UV) and visible light irradiation using methylene blue and stearic acid decomposition tests Photoinduced hydrophilicity was assessed through measurements of the water contact angle under UV and visible light irradiation It was found that, though C-doping resulted in improved dye degradation compared to undoped TiO2, the UV-induced photoactivity of Carbon-doped (C-doped) photocatalysts was lower for both model pollutants used

Deposition of Visible Light-Active C-Doped Titania Films via Magnetron Sputtering Using CO₂ as a Source of Carbon.

In this research, pure anatase phase titanium dioxide thin films were successfully fabricated for the first time using the mist chemical vapor deposition method, and optional values for deposition temperature and concentration of titanium tetraisopropoxide were established. It was found that the crystallinity of the titanium dioxide film was significantly improved by increasing the deposition temperature. The best crystallinity of titanium dioxide film was obtained at 400 °C. It was confirmed that pure anatase phase titanium dioxide films could be obtained using different concentrations of titanium tetraisopropoxide. The lower concentration of titanium tetraisopropoxide produced better crystallinity in the resultant titanium dioxide film. The morphologies of the titanium dioxide thin films were also significantly influenced by the concentration of titanium tetraisopropoxide in the precursor solution.

https://www.mdpi.com/2079-4991/8/10/827/pdf

Pure Anatase Phase Titanium Dioxide Films Prepared by Mist Chemical Vapor Deposition

Well-arrayed zinc oxide nanorods applied as photoelectrodes for dye-sensitized solar cells were synthesized on an aluminum-doped zinc oxide substrate by the multi-annealing method. In order to improve the chemical stability and surface-to-volume ratio of photoanodes in dye-sensitized solar cells, the synthesized zinc oxide nanorods were coated with pure anatase phase titanium dioxide film using a novel mist chemical vapor deposition method. The effects of the titanium dioxide film on the morphological, structural, optical, and photovoltaic properties of zinc oxide–titanium dioxide core–shell nanorods were investigated. It was found that the diameter and surface-to-volume ratio of zinc oxide nanorods were significantly increased by coating them with titanium dioxide thin film. The power conversion efficiency of dye-sensitized solar cells was improved from 1.31% to 2.68% by coating titanium dioxide film onto the surface of zinc oxide nanorods.

https://www.mdpi.com/2079-4991/10/8/1598/pdf

Qiang Zhang

Papers

High Temperature Stable Anatase Phase Titanium Dioxide Films Synthesized by Mist Chemical Vapor Deposition.

TiO2 Coated ZnO Nanorods by Mist Chemical Vapor Deposition for Application as Photoanodes for Dye-Sensitized Solar Cells.

Pure Anatase Phase Titanium Dioxide Films Prepared by Mist Chemical Vapor Deposition

Titanium Dioxide-Coated Zinc Oxide Nanorods as an Efficient Photoelectrode in Dye-Sensitized Solar Cells.

Effect of Substrates on Structural Properties of Pure Anatase Phase Titanium Dioxide Thin Films Prepared by Mist Chemical Vapor Deposition