Effect of defects in TiO2 nanoplates with exposed {001} facets on the gas sensing properties

Recent Advancements in TiO2 Nanostructures: Sustainable Synthesis and Gas Sensing

The search for sustainable technology-driven advancements in material synthesis is a new norm, which ensures a low impact on the environment, production cost, and workers' health. In this context, non-toxic, non-hazardous, and low-cost materials and their synthesis methods are integrated to compete with existing physical and chemical methods. From this perspective, titanium oxide (TiO₂) is one of the fascinating materials because of its non-toxicity, biocompatibility, and potential of growing by sustainable methods. Accordingly, TiO₂ is extensively used in gas-sensing devices. Yet, many TiO₂ nanostructures are still synthesized with a lack of mindfulness of environmental impact and sustainable methods, which results in a serious burden on practical commercialization. This review provides a general outline of the advantages and disadvantages of conventional and sustainable methods of TiO₂ preparation. Additionally, a detailed discussion on sustainable growth methods for green synthesis is included. Furthermore, gas-sensing applications and approaches to improve the key functionality of sensors, including response time, recovery time, repeatability, and stability, are discussed in detail in the latter parts of the review. At the end, a concluding discussion is included to provide guidelines for the selection of sustainable synthesis methods and techniques to improve the gas-sensing properties of TiO₂.

Experimental and density functional study of the light-assisted gas-sensing performance of a TiO2-CoFe2O4 heterojunction

Toluene gas as a solvent is widely present in industrial production and indoor decoration, and can seriously harm human health even at low concentrations. Furthermore, toluene can be used as a typical biomarker for disease diagnosis. Therefore, the detection of toluene gas is very important. Herein, a hydrothermal method was used to successfully prepare a TiO₂-CoFe₂O₄ heterostructure for detecting toluene gas. The ultraviolet (UV)-visible diffuse reflectance spectra and photoluminescence spectra showed that the bandgap of the heterojunction was considerably shorter than those of pure TiO₂ and CoFe₂O₄, and the recombination of electron-hole pairs was inhibited. At the same time, the response value of the TiO₂-CoFe₂O₄ heterojunction was 10.5 for 20 ppm toluene at 219 °C, which was much better than those of pure TiO₂ and CoFe₂O₄. Moreover, its response value further increased under UV irradiation. In addition, density functional theory (DFT) was innovatively employed in this study to explain in detail how the heterojunction and UV irradiation can improve gas sensitivity through the calculation of the material energy band, adsorption energy, etc. This work provides a good reference for the preparation of high-efficiency and high-sensitivity gas sensors.

Modification of Liquid Separation Membranes Using Multidimensional Nanomaterials: Revealing the Roles of Dimension Based on Classical Titanium Dioxide

Membrane technology has become increasingly popular and important for separation processes in industries, as well as for desalination and wastewater treatment. Over the last decade, the merger of nanotechnology and membrane technology in the development of nanocomposite membranes has emerged as a rapidly expanding research area. The key motivation driving the development of nanocomposite membranes is the pursuit of high-performance liquid separation membranes that can address the bottlenecks of conventionally used polymeric membranes. Nanostructured materials in the form of zero to three-dimensions exhibit unique dimension-dependent morphology and topology that have triggered considerable attention in various fields. While the surface hydrophilicity, antibacterial, and photocatalytic properties of TiO2 are particularly attractive for liquid separation membranes, the geometry-dependent properties of the nanocomposite membrane can be further fine-tuned by selecting the nanostructures with the right dimension. This review aims to provide an overview and comments on the state-of-the-art modifications of liquid separation membrane using TiO2 as a classical example of multidimensional nanomaterials. The performances of TiO2-incorporated nanocomposite membranes are discussed with attention placed on the special features rendered by their structures and dimensions. The innovations and breakthroughs made in the synthesis and modifications of structure-controlled TiO2 and its composites have enabled fascinating and advantageous properties for the development of high-performance nanocomposite membranes for liquid separation.

Recent Advances in Sensing Materials Targeting Clinical Volatile Organic Compound (VOC) Biomarkers: A Review

In general, volatile organic compounds (VOCs) have a high vapor pressure at room temperature (RT). It has been reported that all humans generate unique VOC profiles in their exhaled breath which can be utilized as biomarkers to diagnose disease conditions. The VOCs available in exhaled human breath are the products of metabolic activity in the body and, therefore, any changes in its control level can be utilized to diagnose specific diseases. More than 1000 VOCs have been identified in exhaled human breath along with the respiratory droplets which provide rich information on overall health conditions. This provides great potential as a biomarker for a disease that can be sampled non-invasively from exhaled breath with breath biopsy. However, it is still a great challenge to develop a quick responsive, highly selective, and sensitive VOC-sensing system. The VOC sensors are usually coated with various sensing materials to achieve target-specific detection and real-time monitoring of the VOC molecules in the exhaled breath. These VOC-sensing materials have been the subject of huge interest and extensive research has been done in developing various sensing tools based on electrochemical, chemoresistive, and optical methods. The target-sensitive material with excellent sensing performance and capturing of the VOC molecules can be achieved by optimizing the materials, methods, and its thickness. This review paper extensively provides a detailed literature survey on various non-biological VOC-sensing materials including metal oxides, polymers, composites, and other novel materials. Furthermore, this review provides the associated limitations of each material and a summary table comparing the performance of various sensing materials to give a better insight to the readers.

Anticorrosion Protection of TiO₂ Nanofilm on the Surface of Carbon Steel

Carbon steel (CS) is the preferred base material for construction in various industries due to its low cost; however, industrial equipment failure caused by carbon steel corrosion can lead to several environmental risks and safety hazards, thus limiting its application scenarios. Enhancing the corrosion resistance of carbon steel and reducing the maintenance cost of carbon steel substrate have become a hot topic of current research. Therefore, in this study, a zinc oxide/polyaniline-titanium dioxide composite film (ZnO/PAni-TiO₂) with long-lasting photogenerated cathodic protection was constructed based on the photoelectric conversion properties of TiO₂. This new TiO₂ composite film, which can avoid photogenerated electron-hole complexation, significantly enhanced the photoelectric conversion efficiency of TiO₂, thereby decreasing the anodic corrosion current density of low carbon steel and enhancing the cathodic protection of carbon steel. Hence, it is expected to provide a new direction for the preparation of corrosion-resistant TiO₂-laminated carbon steel nanofilms.

Application of candle soot CNPs-TiO2-PVP composite in the detection of volatile organic compounds with aldehyde, amine and ketone functional groups by resistance and impedance responses

We have fabricated a solid-state gas sensor using a composite sensor layer made up of three different sensing materials namely; candle soot Carbon nanoparticles, Titanium dioxide and Poly (vinyl) pyrrolidone (PVP). The study was carried out to study the sensor’s response towards butyraldehyde, diethylamine and isobutyrophenone vapour at room temperature. The sensor was prepared by mixing candle soot CNPs, TiO2 and PVP in dimethylformamide using the ratio (2:1:3) respectively. The sensing materials were characterised using Brunauer–Emmett–Teller (BET), x-ray diffraction (XRD), Transmission and Scanning Electron Microscopy (TEM, SEM). The sensor’s response was measured by injecting a volume of 1 to 5 μl of each liquid analyte in a round-bottomed glass and an LCR metre was used to measure the ∆R and ∆Z responses. In both parameters, the sensor responded well to the different analytes, the response of the sensor linearly increases as the analyte vapour concentration increases. The sensors were discovered to exhibit more sensitivity of 0.07 Ω ppm−1 towards diethylamine in ∆R response and it was more sensitive towards isobutyrophenone in ∆Z response giving a sensitivity of 0.14 Ω ppm−1 while Butyraldehyde had the fastest response time of 145 s and Diethylamine had the fasted recovery time 130 s.