Environmental and energy problems have drawn much attention owing to rapid population growth and accelerated economic development For instance, photocatalysis, "a green technology", plays an important role in solar-energy conversion owing to its potential to solve energy and environmental problems Recently, many efforts have been devoted to improving visible-light photocatalytic activity by using titanium dioxide as a photocatalyst as a result of its wide range of applications in the energy and environment fields However, fast charge recombination and an absorption edge in the UV range limit the photocatalytic efficiency of TiO2 under visible-light irradiation Many investigations have been undertaken to overcome the limitations of TiO2 and, therefore, to enhance its photocatalytic activity under visible light The present literature review focuses on different strategies used to promote the separation efficiency of electron-hole pairs and to shift the absorption edge of TiO2 to the visible region Current synthesis techniques used to elaborate several nanostructures of TiO2 -based materials, recent progress in enhancing visible photocatalytic activity, and different photocatalysis applications will be discussed On the basis of the studies reported in the literature, we believe that this review will help in the development of new strategies to improve the visible-light photocatalytic performance of TiO2 -based materials further

/pdf/recent-progress-on-titanium-dioxide-nanomaterials-for-na4kqaofux.pdf

Recent Progress on Titanium Dioxide Nanomaterials for Photocatalytic Applications.

Reducing soluble U(VI) to insoluble U(IV) is an ideal strategy to collect/remove uranium in water. In this work, a new way is reported to achieve this reduction through a photocorrosion-related photocatalysis process of SnO2/CdCO3/CdS (SCC) under visible light irradiation. The mechanism is systematically studied and discussed through a variety of characterization methods, such as X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Mott-Schottky test, etc. The matching of energy band ensures the separation of photoelectrons and holes, which results in the decrease of charges’ recombination rate and the enhancement of photoreduction activity. The reduction process can be efficiently performed in the ternary complex of SCC in that the photo-generated holes are consumed by oxidization of S2− to S0 on CdS in SCC. Furthermore, uranium extraction could be achieved by SCC without any protective gases or electronic sacrificial agent, which shows great advantages in applications of U(VI) collection/removal.

Highly efficient removal of U(VI) by the photoreduction of SnO2/CdCO3/CdS nanocomposite under visible light irradiation

ZnO is an important material which has been widely applied in photodetector, catalyst, gas sensor, field emitter, etc. Yet, its inability to absorb visible light, poor charge transport, and low conductivity limit the application of these devices. Recently, it was discovered that introduction of defects such as oxygen and zinc vacancies into ZnO can effectively improve the existing properties or lead to new and unexpected yet highly desirable characteristics. Herein, we present a systematic review on the available approaches to synthesize oxygen- and/or zinc-deficient ZnO with emphasis on their chemical, structural, and electrical particularities. Furthermore, applications of defective ZnO in various nanoscale devices are discussed in terms of their functionality, reliability, and performance. Finally, we summarize major challenges and offer perspectives for further research in this field. We hope that this review would make a valuable contribution to broaden the knowledge of defective ZnO.

Defect engineering of ZnO: Review on oxygen and zinc vacancies

The structural, magnetic, and optical properties of the pristine and Gd-doped ZnO nanorods (NRs), prepared by facile thermal decomposition, have been studied using a combination of experimental and density functional theory (DFT) with Hubbard U correction approaches. The XRD patterns demonstrate the single-phase wurtzite structure of the pristine and doped ZnO. The rod-like shape of the nanoparticles has been examined by FESEM and TEM techniques. Elemental compositions of the pure and doped samples were identified by EDX measurement. Due to the Burstein–Moss shift, the optical band gaps of the doped samples have been widened compared to pristine ZnO. The PL spectra show the presence of complex defects. Room temperature magnetic properties have been measured using VSM and revealed the coexistence of paramagnetic and weak ferromagnetic ordering in Gd3+ doped ZnO-NRs. The magnetic moment was increased upon addition of more Gd ions into the ZnO host lattice. The DFT+U calculations confirm that the presence of vacancy-complexes has a significant effect on the structural, electronic, and magnetic properties of a pristine ZnO system.

/pdf/unraveling-the-effect-of-gd-doping-on-the-structural-optical-lwgvgio90m.pdf

Unraveling the effect of Gd doping on the structural, optical, and magnetic properties of ZnO based diluted magnetic semiconductor nanorods

Nanolaminates are of great interest for their unique properties such as high dielectric constants and advanced mechanical, electrical, and optical properties. Here we report on the tuning of optical and structural properties of Al2O3/ZnO nanolaminates designed by atomic layer deposition (ALD). Structural properties of nanolaminates were studied by SEM, GIXRD, and AFM. Optical characterization was performed by transmittance and photoluminescence (PL) spectroscopy. Complex study of monolayer properties was performed by ellipsometry. Optical constants for Al2O3 and ZnO monolayer were calculated. The band gap of ZnO single layers and the excitonic PL peak position were shifted to the UV region related to quantum confinement effects. No peaks in the UV region were observed in nanolaminates with 2 nm ZnO single layer thickness due to fully depleted region in small crystalline grains (<2 nm). The improved room temperature photoluminescence of nanolaminates makes them prominent materials for optical biosensors ap...

Tuning Optical Properties of Al2O3/ZnO Nanolaminates Synthesized by Atomic Layer Deposition

A study of transmittance and photoluminescence spectra on the growth of oxygen-rich ultra-thin ZnO films prepared by atomic layer deposition is reported. The structural transition from an amorphous to a polycrystalline state is observed upon increasing the thickness. The unusual behavior of the energy gap with thickness reflected by optical properties is attributed to the improvement of the crystalline structure resulting from a decreasing concentration of point defects at the growth of grains. The spectra of UV and visible photoluminescence emissions correspond to transitions near the band-edge and defect-related transitions. Additional emissions were observed from band-tail states near the edge. A high oxygen ratio and variable optical properties could be attractive for an application of atomic layer deposition (ALD) deposited ultrathin ZnO films in optical sensors and biosensors.

https://hal.umontpellier.fr/hal-01688689/document

Evolution of microstructure and related optical properties of ZnO grown by atomic layer deposition

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Evolution of microstructure and related optical properties of ZnO grown by atomic layer deposition