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Nanostructured metal oxide semiconductors have emerged as promising nanoscale photocatalysts due to their excellent photosensitivity, chemical stability, non-toxicity, and biocompatibility. Enhancing the photocatalytic activity of metal oxide is critical in improving their efficiency in radical ion production upon optical exposure for various applications. Therefore, this review paper provides an in-depth analysis of the photocatalytic activity of nanostructured metal oxides, including the photocatalytic mechanism, factors affecting the photocatalytic efficiency, and approaches taken to boost the photocatalytic performance through structure or material modifications. This paper also highlights an overview of the recent applications and discusses the recent advancement of ZnO-based nanocomposite as a promising photocatalytic material for environmental remediation, energy conversion, and biomedical applications., (© 2024 IOP Publishing Ltd.)

Defect engineering has been the most promising strategy to modulate the surface microstructure and electronic structure of the metal oxides, which will govern the efficiency of a given oxide for the applications in heterogeneous catalysis, energy storage and conversion fields, and gas sensing. This review summarizes recent research advances on understanding the role of oxygen vacancies of the metal oxides in gas sensing. First, different strategies for oxygen vacancy productions are summarized and compared. Then, the proper characterization techniques for oxygen vacancy are introduced. Importantly, the structure‐activity relationships between vacancy engineering and gas sensing ability are further illustrated coupling the experimental results and theoretical studies. Finally, the key challenges and prospects regarding defect engineering in gas sensing are highlighted. [ABSTRACT FROM AUTHOR]

Defect engineering has been the most promising strategy to modulate the surface microstructure and electronic structure of the metal oxides, which will govern the efficiency of a given oxide for the applications in heterogeneous catalysis, energy storage and conversion fields, and gas sensing. This review summarizes recent research advances on understanding the role of oxygen vacancies of the metal oxides in gas sensing. First, different strategies for oxygen vacancy productions are summarized and compared. Then, the proper characterization techniques for oxygen vacancy are introduced. Importantly, the structure‐activity relationships between vacancy engineering and gas sensing ability are further illustrated coupling the experimental results and theoretical studies. Finally, the key challenges and prospects regarding defect engineering in gas sensing are highlighted. [ABSTRACT FROM AUTHOR]

The effect of reduced graphene oxide (rGO) and carbon nanotubes (CNTs) on the gas-sensing performance of ZnO hexagonal nanoparticles, forming CNTs/rGO/ZnO composite has been studied. Samples were obtained by a precipitation route, then characterized by a high resolution transmission electron microscope (HRTEM), x-ray diffraction (XRD), differential thermal analysis (DTA), thermogravimetric analysis, Raman spectroscopy, Brunauer–Emmett–Teller surface area (BET), and Barrett–Joyner–Halenda (BJH) pore size measurements. The XRD measurements as well as HRTEM confirmed the formation of the hexagonal ZnO nanoparticles over rGO and CNTs. The gas-sensing performance of the synthesized composite are tested toward ammonia gas. Results revealed that, the prepared composite showed good response to ammonia vapor at room temperature with fast response and recovery time. The combined effect of rGO and CNTs played a vital role in enhancing the sensing behavior of an ammonia gas sensor. The obtained sensor was integrated in a simple comparator electronic circuit. The proposed CNTs/rGO/ZnO sensor might give promise for a portable and room temperature ammonia gas sensor. [ABSTRACT FROM AUTHOR]

Abstract: The development of inorganic solid-state nanostructured solar cells over the last years has been reviewed with respect to concepts and materials. Major attention has been paid to solar cells with extremely thin absorber, solar cells with ultra-thin nano-composite absorber and solar cells with quantum dot absorber layers. The focus has been set to structured transparent electron conductors and absorber materials prepared by mainly low-temperature and wet chemical deposition methods. The great potential of inorganic solid-state nanostructured solar cells is discussed. [Copyright &y& Elsevier]

Abstract: Electrochemically deposited biocompatible zirconia (ZrO2) film on gold coated glass electrodes has been utilized for the fabrication of urea biosensor. The prepared ZrO2 films and bioelectrodes have been characterized using Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and electrochemical techniques, respectively. The urea biosensor, fabricated by immobilizing mixed enzyme [urease (Urs) and glutamate dehydrogenase (GLDH)] on this nanobiomaterial, shows linearity up to 40mgdL−1 of analyte (urea) and sensitivity of 0.071μA/(mMcm−2) with stability up to 4months when stored at 4°C. The low value of Michaelis–Menten constant (K m ) estimated using Hans plot as 0.5mM indicates enhancement in the affinity and/or activity of enzyme attached to this nanostructured biocompatible matrix. [Copyright &y& Elsevier]

Abstract: We present an excellent detection of carbon monoxide (CO) gas using Al-doped ZnO nanostructured thin films deposited on self-assembled Au nanodots (ZnO/Au thin films). We formed the self-assembled Au nanodots by annealing a thin Au layer with a thickness of 2nm at a moderate temperature of 500°C prior to the growth of the main ZnO layer via the sputtering method. We observed an enhancement of CO gas sensing response in the ZnO/Au gas sensors by the insertion of a thin Au nucleation layer, especially showing a high maximum sensitivity to CO at 250°C and a low CO detection limit of 5ppm in dry air. In addition, the ZnO/Au thin film CO gas sensors displayed fast response and recovery behaviors. The observed improvement in gas sensing properties is mainly attributed to the effective formation of ZnO nanostructured morphology having a high specific surface-reaction area via self-assembled Au nanodots. These results along with a simple fabrication process demonstrate that the ZnO thin films deposited on self-assembled Au nanodots are very promising for low-cost and high-performance CO gas sensors. [ABSTRACT FROM AUTHOR]

In this paper a transport equation is derived which describes the behaviour of the nanostructured metal oxide films in a photoelectrochemical cell. It is shown that a detailed analysis of the charge compensation mechanism necessarily leads to a transport equation with characteristics similar to but logically distinct from the pure diffusion equation. The studied phenomenon was named ambipolar diffusion in the early 1950s. It takes into account the fact that the diffusion processes of ions and electrons occur at different speeds. A weak electric field therefore couples the processes together to preserve charge neutrality. The electric field in turn affects the transport resulting in a deviation from purely diffusive behaviour. However, this has not been widely recognised in the literature for nanostructured semiconductor films until very recently. In this paper a detailed analysis is presented. It is based on the assumption that the current density is solenoidal. It is shown that application of the ambipolar diffusion model to a photoelectrochemical cell based on a nanostructured metal oxide film leads to an additional term in the transport equation, rather than only a new diffusion coefficient as in earlier work. It is also shown that the boundary conditions interact closely with the equation to form a transport model. [Copyright &y& Elsevier]

Volatile organic compounds (VOCs) are among the most abundant air pollutants. Their high concentrations can adversely affect the human body, and therefore, early detection of VOCs is of outmost importance. Among the different VOCs, in this review paper we have focused our attention to the monitoring of acetaldehyde by chemiresistive gas sensors fabricated from nanostructured semiconducting metal oxides. These sensors can not only provide a high sensing signal for detection of acetaldehyde but also high thermal and mechanical stability along with a low price. This review paper is divided into three major sections. First, we will introduce acetaldehyde as an important VOC and the importance of its detection. Then, the fundamentals of chemiresistive gas sensors will be briefly presented, and in the last section, a survey of the literature on acetaldehyde gas sensors will be presented. The working mechanism of acetaldehyde sensors, their structures, and configurations are reviewed. Finally, the future development outlook and potential applications are discussed, giving a complete panoramic view for researchers working and interested in acetaldehyde detection for different purposes in many fundamental and applicative fields. [ABSTRACT FROM AUTHOR]