Low temperature preparation of oxygen-deficient tin dioxide nanocrystals and a role of oxygen vacancy in photocatalytic activity improvement

SnO2/Au Microelectromechanical Systems Modified by Oxygen Vacancies for Enhanced Sensing of Dioctyl Phthalate

Dioctyl phthalate (DOP) serves as a characteristic gas utilized in early electrical fire detection, its detection offers promising prospects for the prevention of electrical fires. In this study, we employed a modified photodeposition method to prepare Tin dioxide (SnO2) materials co-modified with Au and oxygen vacancies. Subsequently, microelectromechanical systems (MEMS) gas sensor for DOP detection were fabricated, utilizing 0.5 %Au/SnO2-I as the sensing material. Characterization results reveal the presence of abundant oxygen vacancies in 0.5 %Au/SnO2-I. The synergistic interplay of Au and oxygen vacancies resulted in a remarkable response of 9.98 to 20 ppm of DOP at operational temperature of 250 °C. This represents a significant 96 % enhancement in comparison to the response value of 4.50 exhibited by pure SnO2 at 300 °C. Notably, this gas sensor boasts low power consumption and demonstrates a quick response in the detection of overheating polyvinyl chloride (PVC) cables under simulated conditions.

A Comprehensive Review on the Boosted Effects of Anion Vacancy in the Heterogeneous Photocatalytic Degradation, Part II: Focus on Oxygen Vacancy

Environmental problems, including the increasingly polluted water and the energy crisis, have led to a need to propose novel strategies/methodologies to contribute to sustainable progress and enhance human well-being. For these goals, heterogeneous semiconducting-based photocatalysis is introduced as a green, eco-friendly, cost-effective, and effective strategy. The introduction of anion vacancies in semiconductors has been well-known as an effective strategy for considerably enhancing the photocatalytic activity of such photocatalytic systems, giving them the advantages of promoting light harvesting, facilitating photogenerated electron-hole pair separation, optimizing the electronic structure, and enhancing the yield of reactive radicals. This Review will introduce the effects of anion vacancy-dominated photodegradation systems. Then, their mechanism will illustrate how an anion vacancy changes the photodegradation pathway to enhance the degradation efficiency toward pollutants and the overall photocatalytic performance. Specifically, the vacancy defect types and the methods of tailoring vacancies will be briefly illustrated, and this part of the Review will focus on the oxygen vacancy (OV) and its recent advances. The challenges and development issues for engineered vacancy defects in photocatalysts will also be discussed for practical applications and to provide a promising research direction. Finally, some prospects for this emerging field will be proposed and suggested. All permission numbers for adopted figures from the literature are summarized in a separate file for the Editor.

Synergistic Effect of Oxygen Vacancy-Rich SnO2 and AgCl in the Augmentation of Sustained Oxygen Reduction Reaction

Developing a stable and methanol-tolerant electrocatalyst for a sustained oxygen reduction reaction (ORR) is of great importance for advancing direct methanol fuel cell applications. The silver-based electrocatalysts are particularly interesting among the promising non-Pt-based electrocatalysts for ORR. Herein, we report a single-step synthesis of a composite of AgCl and SnO2 with oxygen vacancy (AgCl-SnO2(VO)), which exhibits sustained and selective catalytic activity for the ORR along with excellent durability. Hydrothermal synthesis generates oxygen vacancies within the material and facilitates a strong interaction between AgCl and SnO2(VO), which effectively augments the ORR activity and the long-term stability of the composite. The composite exhibits remarkable methanol tolerance, as evidenced by a meager shift of only 0.002 V in the half-wave potential. Furthermore, the composite demonstrates excellent durability, with no noticeable changes in onset and half-wave potential even after 2500 cycles. The cost-effectiveness, durability, and ORR selectivity of this composite hold great promise toward contributing to the advancement of clean energy technology.

Preparation of CuS/PbS/ZnO Heterojunction Photocatalyst for Application in Hydrogen Production

A hexagonal wurtzite ZnO photocatalyst was prepared via a precipitation method. CuS nanoparticles (NPs) and PbS quantum dots (QDs) were loaded onto ZnO via a hydrothermal method to obtain a CuS/PbS/ZnO heterojunction photocatalyst. The CuS/PbS/ZnO photocatalyst obtained via the abovementioned method has significant absorption capabilities in the ultraviolet to near-infrared spectral regions, and effectively reduced the recombination of electron–hole pairs during a photocatalytic reaction. Electron microscope images showed that in the CuS/PbS/ZnO photocatalyst prepared at 130 °C, the particle size of the PbS QDs was approximately 5.5–5.7 nm, and the bandgap determined from the Tauc plot was 0.84 eV; this catalyst demonstrated the best water splitting effect. Furthermore, after adding a 0.25 M mixed solution of Na2S and Na2SO3 as the sacrificial reagent in photocatalysis for 5 h, the hydrogen production efficiency from water splitting reached 6654 μmol g−1 h−1.

Efficient Oxygen Vacancy Defect Engineering for Enhancing Visible-Light Photocatalytic Performance over SnO2-x Ultrafine Nanocrystals

Regardless of its good electron-transfer ability and chemical stability, pure Zn₂SnO₄ (ZSO) still has intrinsic deficiencies of a narrow spectral response region, poor absorption ability, and high photo-activated carrier recombination rate. Aiming to overcome the deficiencies above-mentioned, we designed a facile hydrothermal route for etching ZSO nanoparticles in a dilute acetic acid solution, through which efficient oxygen vacancy defect engineering was accomplished and SnO_2-x nanocrystals were obtained with an ultrafine particle size. In comparison with the untreated ZSO nanoparticles, the specific surface area of SnO_2-x nanocrystals was substantially enlarged, subsequently leading to the notable augmentation of active sites for the photo-degradation reaction. Aside from the above, it is worth noting that SnO_2-x nanocrystals were endowed with a broad spectral response, enhancing light absorption capacity and the photo-activated carrier transfer rate with the aid of oxygen vacancy defect engineering. Accordingly, SnO_2-x nanocrystals exhibited significantly enhanced photoactivity toward the degradation of the organic dye rhodamine B (RhB), which could be imputed to the synergistic effect of increasing active sites, intensified visible-light harvesting, and the separation rate of the photo-activated charge carrier caused by the oxygen vacancy defect engineering. In addition, these findings will inspire us to open up a novel pathway to design and prepare oxide compound photocatalysts modified by oxygen vacancy defects in pursuing excellent visible-light photoactivity.

Optical and photocatalytic properties of a ZnO@C core/shell sphere with rich oxygen vacancies

We develop a novel method to prepare an oxygen-deficient ZnO@C core/shell based on a traditional hydrothermal reaction, and investigate the role of the carbon core and oxygen vacancies in the photocatalytic activity and photoluminescence processes.

One-pot hydrothermal synthesis and characterization of magnetic nanocomposite of titania-deposited copper ferrite/ferrite oxide for photocatalytic decomposition of methylene blue dye

The pure titania (TiO2) and the heterogeneous ternary magnetic nanocomposite of copper ferrite/ferrite oxide (CuFe2O4/Fe2O3) deposited by titanium dioxide (TiO2) were fabricated using a facile one-pot hydrothermal synthesis for the photocatalytic decomposition of methylene blue (MB) dye, under visible light. The nanocomposite was encoded as TCF in this work, where T stands for TiO2, C for CuFe2O4 and F for Fe2O3. Various techniques such as powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy, diffuse reflectance spectroscopy, nitrogen physisorption, and vibrational sample magnetometry (VSM) were used to characterize the prepared samples. The PXRD data showed that the samples had pure anatase structure and the average crystal size of anatase TiO2 in the pure titania and ternary nanocomposite were calculated 147 Å and 135 Å, respectively. The nitrogen physisorption analysis data showed that the pore diameter was increased from 10.6 nm in pure titania to 16.0 nm in TCF. The pore volume was also increased from 0.316 in titania to 0.383 cm3/g in TCF sample. It also increased the typical magnitude of the mesopores’ diameter and volume per weight but it reduced the specific surface area of the samples. The VSM analysis of the ternary nanocomposite showed a considerable magnetic property of the sample (1.99 emu/g), qualifying it as a paramagnetic material. The photocatalytic decomposition efficiency of MB reached 77% and 68% in the presence of pure titania and TCF ternary nanocomposite, after 240-min exposure by the visible light. Active species trapping experiments showed that the major active species responsible for the photodecomposition of MB in the presence of TCF are $${\text{O}}_{2}^{ \cdot - }$$O2·- radicals and holes (h+).

Influence of Surface Defects and Size on Photochemical Properties of SnO₂ Nanoparticles

We report the successful synthesis of surface defective small size (SS) SnO₂ nanoparticles (NPs) by adopting a low temperature surfactant free solution method. The structural properties of the NPs were analyzed using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and transmission electron microscopy (TEM). The presence of surface defects, especially oxygen vacancies, in the sample were characterized using micro-Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and photoluminescence emission. The Brunauer–Emmet–Teller (BET) nitrogen adsorption–desorption isotherms demonstrated the superior textural properties (high surface area and uniform pore size) of SS SnO₂ compared to large size (LS) SnO₂. A comparable study was drawn between SS SnO₂ and LS SnO₂ NPs and a significant decrease in the concentration of surface defects was observed for the LS sample. The results showed that surface defects significantly depend upon the size of the NPs. The surface defects formed within the band gap energy level of SnO₂ significantly participated in the recombination process of photogenerated charge carriers, improving photochemical properties. Moreover, the SS SnO₂ showed superior photoelectrochemical (PEC) and photocatalytic activities compared to the LS SnO₂. The presence of a comparatively large number of surface defects due to its high surface area may enhance the photochemical activity by reducing the recombination rate of the photogenerated charges.