This research employs DFT + U calculations to investigate the impact of doping with Co, Ni, Cu, and Zn on the structural, electronic, optical, and gas sensing characteristics of rutile TiO2. The doping process results in lattice expansion, with optimized lattice constants increasing from 4.630 Å (a) and 2.980 Å (c) in pure TiO2 to as much as 4.681 Å and 3.143 Å in Zn-doped systems. This expansion is explained by the variation in atomic radii between Ti and the doped atoms. A reduction in the bandgap is noted across all doped systems (pure: 3.04 eV; Co: 2.51 eV; Cu: 2.63 eV; Ni: 2.66 eV; Zn: 2.56 eV), which enhances the absorption of visible light and promotes p-type conductivity. The analysis of the PDOS indicates significant hybridization among the Ti-3d, O-2p, and dopant 3d orbitals, as well as magnetic properties in the Co, Ni, and Cu-doped systems. The optical properties, including the dielectric function and absorption spectra, further indicate a redshift in all transition metal (TM) doped systems. The gas sensing evaluation shows enhanced detection of CO and NO, with Zn-doping achieving superior selectivity for CO with an adsorption energy of -0.949 eV, while Ni-doping demonstrates a strong affinity for both CO (-0.726 eV) and NO (-0.639 eV), making it suitable for multi-gas detection. Doped rutile TiO2 systems exhibit enhanced sensitivity, stability, and reusability, positioning them as promising candidates for optoelectronic and gas sensing applications.

Detecting aromatic volatile organic compounds (VOCs) like xylene isomers, especially m-xylene, amidst benzene and toluene remains challenging due to their similar structures, boiling points, and overlapping properties. M-Xylene is particularly challenging to identify due to its low reactivity and polarity, often requiring high temperatures that increase power consumption and reduce sensor lifespan, thereby limiting portable and real-time applications. Thus, herein, Ag-decorated SrTiO3/MXene heterostructures were synthesized and systematically evaluated to elucidate the influence of Ag incorporation on their structural, optical, and gas-sensing properties. Ag-loading preserved the sheet-like architecture of SrTiO3/MXene while inducing notable improvements in microstructure. Structural findings confirmed Ag nanoparticle sizes of similar to 5-25 nm for 1 wt% and similar to 15-45 nm for 2 wt% samples. A significant reduction in defect-related electronic states upon Ag addition was observed. Gas-sensing investigations demonstrated that the 1 wt% Ag-loaded sample exhibited a better response toward m-xylene at 100 degrees C, with a response value of 1.002, a detection limit of 3.1 ppm, and rapid response/recovery times of 15 s/ 25 s, respectively. This enhancement is associated with the increased surface area, stronger catalytic activity, and effective oxygen spillover, which collectively promote the formation of reactive oxygen species and facilitate charge-transfer interactions with m-xylene. Selectivity toward m-xylene was further supported by its electron-rich structure, minimal steric hindrance, and favourable pi-pi interactions compared to other BTX gases. These findings confirmed that the Ag-modified SrTiO3/MXene heterostructure is a capable sensor for low-temperature aromatic VOC detection in complex environments.

Liquefied petroleum gas (LPG) production is imperative as part of the global energy mix, while its timely detection is also vital for the safety of mankind. Thus, herein, Ru-loaded Co3O4/rGO nanocomposites were evaluated for LPG sensing. Structural analyses confirmed the successful loading of Ru nanoparticles (NPs) onto Co3O4/rGO sheets, resulting in the formation of hierarchical nanostructures as observed in the morphology analysis. Among the fabricated sensors, the 1.5 wt% Ru sensor exhibited the highest sensitivity of 12.3 toward 1000 ppm LPG at 75 degrees C, with a rapid response time of 44 sand a recovery time of 218 s. When the sensors were tested toward LPG in the presence of other interfering gases (NO2, CH4, CO, C3H8, C3H6O, CH3OH, C2H5OH, and 90 % RH, the sensor demonstrated superior sensitivity, stability, and selectivity toward LPG at a low temperature of 75 degrees C. Moreover, the sensor demonstrated good humidity tolerance and operational stability, retaining 95 % of the initial response over 30 days. These enhancements are attributed to the catalytic role of Ru and its promotion of charge transfer at the Co3O4/ rGO interface. The findings highlight the potential of Ru-decorated Co3O4/rGO as a promising material for low-temperature LPG detection. Keywords: Co3O4; rGO; Ru; Nanoparticles; LPG; Gas sensing.

Achieving highly sensitive and selective gas detection at low temperatures remains a key challenge for advanced sensing technologies. In this study, we introduce a Dy- and Ag-loaded Co3O4/In2O3 p-n heterostructure that offers outstanding gas-sensing capabilities by leveraging defect control, catalytic activation, and interfacial charge engineering. Comprehensive morphological, structural, and optical characterizations confirmed the successful loading of Dy and Ag within the Co3O4/In2O3 surface, leading to improved surface defects, active surface area, and accessible adsorption sites. Structural analyses confirmed the loading of Dy and Ag, and the formation of Co3O4/In2O3. Ag-loaded Co3O4/In2O3 exhibited a higher-energy photoluminescence (PL) emission peak (∼3.0 eV) due to band-edge and shallow defect recombination enhanced by Ag, whereas the Dy-loaded Co3O4/In2O3 showed a lower-energy emission (∼2.45 eV) arising from Dy3+ intra-4f transitions. This Dy- and Ag-loaded heterostructure also exhibited a narrower band gap due to defect states and interfacial effects, thereby facilitating better charge excitation. From the gas sensing perspective, the 0.5 wt% Ag-loaded sensor demonstrated a superior sensitivity and selectivity towards m-xylene compared to its counterparts. While the 0.5 wt% Dy-loaded sensor showed a rapid response time of 5 s towards m-xylene. Such higher performance and rapid response could be due to the Dy addition, which generated numerous oxygen vacancies and defect states, greatly increasing surface chemisorption and reactivity, while Ag nanoparticles served as catalytic hotspots, accelerating gas adsorption and dissociation through spillover effects and Schottky barriers. A detailed discussion on the sensing mechanism is also provided.

Detecting hazardous gases like methane (CH4) and nitric oxide (NO) under real-world conditions is a significant challenge for gas sensors. Herein, pure and (0.5-2 wt%) Ag-decorated CeO2-CuO nanorods were prepared using a hydrothermal approach and tested as dual-gas sensors for NO and CH4, with controlled relative humidity (RH). The crystal structures, optical properties, surface adsorption states, and chemical states of the materials were probed using various analytical techniques. The sensors were tested at different temperatures for multiple gases, including benzene, acetone, xylene, carbon monoxide, and CH4. At 175 degrees C, a 2 wt% Ag-decorated CeO2-CuO nanorods demonstrated a superior response and selectivity towards 10,000 ppm CH4gas. In comparison, at 200 degrees C, the 0.5 wt% Ag-decorated CeO2-CuO nanorods showed a remarkable selectivity towards a trace level of (5-100 ppb) NO gas. The sensor showed a notable p-n transition in its electrical response based on the gas and humidity levels. However, an opposite response emerged under humid conditions (RH >50 %), indicating a switch to n-type conductivity. This shift is due to humidity-driven surface hydroxylation, electron donation from Ag nanoparticles, and charge effects at the CeO2-CuO interface. Water molecules on the surface change band bending and increase electron accumulation, promoting n-type behaviour. The sensing mechanism associated with humidity-controlled conduction reversal is discussed in detail

This study presents an examination of the development of high-performance Co-doped SnO2 nanocolloidal thin films, which are designed for the highly sensitive and selective detection of NH3. By integrating precise sol-gel synthesis with first-principles Density Functional Theory (DFT), we elucidate the importance of defect engineering in modulating gas surface interactions. The XRD analysis confirmed the tetragonal rutile phase of SnO2, revealing that the 2% Co-doped SnO2 exhibits a significantly reduced crystallite size of 4.88 nm. Furthermore, XPS and PL characterization indicated an increase in surface Ov and OC, while UV-vis results demonstrated band gap narrowing due to doping. The DFT calculations suggested that 2% Co-doping introduces mid-gap 3d states, which enhance electronic sensitization. In comparison to the relatively inert pristine SnO2, the 2% Co-doped variant shows a remarkable 153.54% increase in conductivity upon NH3 adsorption, achieving a selectivity ratio of 31.0 relative to H2. Additionally, kinetic analysis revealed that the addition of Co improves sensor reversibility by lowering the NH3 desorption barrier. The combination of reduced crystallite size, defect-rich surface chemistry, and optimized electronic pathways positions 2% Co-doped SnO2 as an outstanding candidate for highly sensitive NH3 detection.

This research employs DFT + U calculations to investigate the impact of doping with Co, Ni, Cu, and Zn on the structural, electronic, optical, and gas sensing characteristics of rutile TiO 2 .

This work presents a detailed DFT + U investigation of the electronic, optical, and gas-sensing properties of rutile and anatase TiO2, emphasizing the influence of oxygen vacancies. An optimized Hubbard U parameter was employed to accurately describe localized Ti-3d states, enabling reliable benchmarks for the bulk electronic and optical behavior of both polymorphs. Formation-energy analyses show that oxygen vacancies are more thermodynamically favorable in r-TiO2 (-4.37 eV) than in a-TiO2(-2.89 eV) under Ti-rich, O-poor conditions, reflecting the higher reducibility of the rutile phase. Gas-sensing evaluations of the a-TiO2 (001) and r-TiO2 (110) facets reveal strong facet-dependent selectivity: r-TiO2 (110) exhibits exceptional sensitivity towards NO (log S approximate to 18), while vacancy-engineered a-TiO2 (001) shows enhanced responsiveness to H2. The study clarifies the common mismatch between adsorption energy and sensing performance, demonstrating that sensing signals are predominantly controlled by orbital hybridization rather than adsorption strength alone. Although introducing a single surface oxygen vacancy significantly boosts sensitivity, reaching conductivity up to 7.53 S/m it also generates deep defect states that slow molecular desorption, revealing a kinetic trade-off. Overall, this work establishes a robust DFT + U framework for designing TiO2-based gas sensors with tunable sensitivity, improved selectivity, and optimized electronic kinetics.

The detection of hazardous volatile aromatic compounds (VOCs), such as toluene, remains a critical challenge in environmental, industrial, and household monitoring for human health protection. Herein, SrTiO3 and SrTiO3/ MXene heterostructures were synthesized using a simple hydrothermal approach, while the Ti3C2Tx (MXene) was synthesized following the LiF-HCl etching method. Their structural, optical, and gas-sensing properties were thoroughly examined. The SrTiO3 showed a wide band gap of 3.20 eV, while the MXene and SrTiO3/MXene heterostructure displayed narrower and intermediate band gaps of 0.93 eV and 2.82 eV, respectively. Photoluminescence results demonstrated higher emission intensity in the heterostructure, indicating increased surface defects and oxygen vacancies that served as active sites for gas adsorption. Gas-sensing analyses revealed that SrTiO3/MXene significantly outperformed individual components in detecting 100 ppm toluene vapors at 50 degrees C. This enhanced response is due to the combined effects of defect-driven oxygen adsorption and efficient charge transport via Ti3C2Tx layers, promoting stronger molecular interactions and faster electron exchange. This work demonstrates the potential of SrTiO3/MXene heterostructures as a possible candidate for the reliable detection of aromatic VOCs.

The effect of Ag-loading on the liquefied petroleum gas (LPG) sensing properties of 80 wt% Co3O4 loaded onto rGO (Co3O4/rGO) nanocomposite was investigated. Co3O4/rGO nanocomposite was synthesized using the hydrothermal method, followed by Ag nanoparticles decorated on the surface using the precipitation method. The presence of Ag nanoparticles was confirmed by energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The Ag-loading significantly increased the sensitivity and selectivity towards LPG at low temperatures. The 0.5 wt% Ag-loaded sensor demonstrated a highly selective, and stable LPG sensing response with an exceptional sensitivity (0.016 ppm-1) and a low detection limit of 0.053 ppm (53 ppb) at 100 degrees C. The principles underlying the gas sensing capabilities were thoroughly discussed. Ag-loading onto the Co3O4/rGO sensor's surface was responsible for the sensor's notable improvement in LPG detection. The synergetic combination of Co3O4 and rGO at the p-p nanoscale heterojunction improved gas adsorption. Thus, the sensor surface developed numerous active sites, significantly aiding in the chemisorption of more LPG molecules due to the spillover effect and increasing sensitivity.

Indium sulfide (In2S3) is an intriguing semiconductor and has been extensively utilized as a UV photodetector application. In this study, we report the fabrication of gadolinium (Gd)-doped In2S3 thin films prepared via the nebulised spray pyrolysis technique (NSP). Gd doping enhances the absorption capacity of the host material. The X-ray diffraction (XRD) analysis confirms a cubic β-In2S3 phase, polycrystalline structure. Ultraviolet-visible (UV-Vis) spectroscopy reveals an enhanced UV absorption coefficient in doped films. Photoluminescence (PL) and X-ray photoelectron spectroscopy (XPS) analysis indicate the presence of oxygen (Vo), sulfide (Vs) and indium (VIn) vacancies. Under 365 nm UV illumination, the In2S3:Gd(1%) exhibits outstanding photodetector performance with a responsivity of 35.2×10−2 A W−1, an external quantum efficiency (ηext) of 82.1%, and a detectivity of 33.8×1010 Jones. The device also shows excellent operational stability over 25 cycles, along with fast rise and decay times of 0.53 and 0.50 s, respectively. This remarkable performance is ascribed to the synergistic electro-trapping effect arising from the optimum concentration of defects (Vs and Vo) and which suppresses recombination by prolonging carrier lifetime. Additionally, improved crystallinity, facilitate charge transport by reducing the carrier scattering. This research work paves way for further doping strategies for improving the performance of In2S3 -based photodetectors, beyond the current state-of-the-art.

The aim of this study is to develop and characterize garnet-type Ca2YZr2Al3O12:Eu3+ red-emitting phosphors, obtained through a traditional high-temperature solid-state reaction. They exhibit exceptional luminescence performance under near-UV excitation, a property that has not been widely explored in white light-emitting diode (WLED) applications. The use of the Ca2YZr2Al3O12 garnet structure as a host for Eu3+ doping is novel and contributes to expanding the range of garnet-based red phosphors. The optimized sample (x = 0.48 mol fraction) exhibited chromaticity coordinates of (0.635, 0.365), a good photoluminescence quantum yield (PLQY) of 60 %, and a high color purity of 92.94 %, surpassing many conventional red phosphors. The phosphors exhibit a broad and intense excitation band around 393 nm, making them highly compatible with near-UV chips used in WLED systems. This addresses a key challenge in phosphor-converted WLED technology. The study reveals efficient energy transfer mechanisms and intense red emissions across multiple Eu3+ transitions, with emission peaking at 609 nm-a wavelength ideal for enhancing the red component in WLEDs. Additionally, the results suggested the presence of Zr.Y and V''' abnormal thermal quenching behaviour. This work introduces a new, efficient red phosphor material specifically designed for n-UV-excited tricolor WLEDs, offering improvements in color rendering and thermal stability that are essential for next-generation solid-state lighting.

We report on the detection of acetone at low concentrations using a W18O49-based gas sensor operating at room temperature (RT). W18O49 was synthesized using the solvothermal method, yielding nanoparticles along with sparsely separated nanorods. The intrinsic properties (i.e., crystal structure, morphology, and defect states) of the W18O49 were examined. While operating at RT, the W18O49-based gas sensor demonstrated superior behavior to acetone among eight (8) other tested gases (ethanol, methanol, m-xylene, p-xylene, o-xylene, benzene, CO, and NO2). The sensor was exposed to a minimal concentration of 0.08 ppm acetone, resulting in a response (Ra/Rg) of 1.04. At 1.8 ppm, the response was 1.49, respectively. The repeatability measurements at 1.8 ppm revealed that the sensor could output a constant response over multiple cycles, with a standard deviation in the spread of the data of 0.1 ppm. Relative humidity (RH) measurements indicated that the sensor performed optimally in humid conditions, suggesting that humidity acted as a catalyzing agent. The sensor displayed the best responses to acetone at lower concentrations than the other gases. The underlying data was then used for Principal Component Analysis (PCA) analysis and the k-Nearest Neighbor (kNN) algorithm. The PCA plot of the sensor responses clearly showed well-separated clusters for the tested gases, indicating that the W18O49-based sensor produced distinct response patterns suitable for data-driven classification. Then, the PCA-kNN classification algorithm achieved a recognition accuracy of 93%, confirming the sensor system's excellent ability to differentiate acetone from other VOCs, even at trace levels. This highlights the benefit of combining nanostructured W18O49 sensing materials with Machine-Learning tools for reliable VOC detection in complex environments. Density Functional Theory analysis was then performed to understand the affinity of the sensor towards acetone compared to the other gases tested. Finally, a proposed sensing mechanism was discussed in detail.

In this study, a “waste-to-wealth” strategy is presented in which palladium (Pd) ions are recovered from wastewater and repurposed to fabricate a highly efficient photocatalyst for hydrogen production. The synthesis involves the in situ oxidative polymerisation of m-phenylenediamine (mPD) monomer within MIL-101(Cr) to form a PmPD/MIL-101(Cr) composite. The composite showed good ability to recover Pd from wastewater to make a Pd-loaded ternary material (Pd@PmPD/MIL-101(Cr)) and its reduced form (Pd(0)@PmPD/MIL-101(Cr). Analysis of the FTIR spectra of the ternary composite showed broadening of the N–H stretching and increased intensities of C–O, and C = O vibrations. Incorporation of Pd(0) markedly reduced the HOMO–LUMO energy gap relative to the Pd@PmPD/MIL-101(Cr) composite. Under visible-light irradiation, the Pd(0)@PmPD/MIL-101(Cr) photocatalyst achieved a hydrogen evolution rate of 3264.4 µmol g⁻¹ min⁻¹, significantly outperforming its individual components. The material also exhibited excellent photostability, as demonstrated by chronoamperometric measurements. Furthermore, electrochemical impedance spectroscopy conducted under illuminated condition revealed a reduced semicircle diameter. The photocatalyst maintained high recyclability and structural stability over multiple cycles. Overall, these findings underscore the potential of waste-derived resources as sustainable and effective precursors for the development of high-performance photocatalysts for hydrogen production.

Accurate detection of nitric oxide (NO) at parts-per-billion (ppb) levels is critical due to its adverse effects on human health, even at trace concentrations. This study presents the design and evaluation of Co3O4-loaded NiTiO3 nanostructures for ultra-low concentration NO sensing. The nanostructures were synthesized via microwave-assisted hydrothermal method, yielding a hierarchical architecture of Co3O4 nanoflowers uniformly distributed on NiTiO3 rods. The optimized 2 wt% Co3O4/NiTiO3 sensor displayed high sensitivity to NO in the 5-100 ppb range, at an optimal operating temperature of 200 degrees C, with a low detection limit (LoD) of similar to 0.22 ppb, and rapid response/recovery times. The sensor displayed a remarkable stability over 90 days with only similar to 15 % deviation in response and demonstrated robust performance under humid conditions (10-75 % RH). NiTiO3 serves as a chemically stable backbone of the sensor, offering a high-resistance baseline and abundant active sites for oxygen adsorption. Co3O4 modification significantly enhanced gas response by forming p-n heterojunctions, reducing resistance, and facilitating charge transfer. Additionally, mixed valence Co2+/Co3+ and Ti3+/Ti4+, along with increased oxygen vacancy concentration, significantly improved surface catalytic activity. These structural and electronic features synergistically promoted efficient NO oxidation, contributing to superior sensing performance.

Antimony selenosulfide [Sb 2 (S,Se) 3 ] is a scientifically interesting, and technologically promising photovoltaic (PV) material for the next generation of solar cells.

We report on the fabrication of NiO-CeO2 nanosheet-assembled hierarchical structures loaded with various weight percentages of Pt for selective detection of low concentrations of benzene vapour at low functional temperatures. Surface analyses showed that the nanomaterials are made of nanosheet-assembled hierarchical structures. Meanwhile, the structural X-ray photoelectron spectroscopy analyses confirmed the loading of Pt on the surface of NiO-CeO2 heterostructures. The sensing findings showed that the 1.0 wt.% Pt-loaded NiO-CeO2 sensor showed more sensitivity to benzene, amongst other target analytes. The sensor demonstrated a superior response of 2.7 to 2 ppm benzene, a sensitivity of 0.87 ppm-1, and a minimal detection limit of 0.07 ppm at a functional temperature of 100 degrees C. The sensor was very stable to benzene in the presence of 40-70 % relative humidity. Increasing the temperature, both the response and sensitivity reduced, while the detection limit increased, showing that 100 degrees C is an optimal temperature. The improved sensing characteristics were associated with higher surface defects and surface area, as well as the loading of Pt, which acted as a catalyst for benzene adsorption. The smaller optical band gap offered extra adsorption sites for benzene to capture electrons in the conduction band easily. The strong catalytic effect of Pt significantly enriched the sensitivity of chemical and electronic sensitization. The sensing mechanism linked to the benzene detection induced by the loading of Pt was discussed in detail.

The quantification of the exact temperature with precision is fundamentally vital for scientific exploration and industrial production. As a result, the accuracy of regular thermometers is currently questionable for measuring the temperature at sub-micrometric spatial resolution. Hence, there is a high demand for advanced non-contact thermometer sensors, which aid in the alternative fabrication of luminescence thermometry to monitor the temperature with precision accuracy. Therefore, the current review article focuses on the recent advances in luminescence thermometry, also known as optical thermometry, and its applications in biomedical imaging and intracellular temperature sensing. The review will also provide a detailed discussion concerning spectroscopic approaches for temperature read-out, and different materials utilized in this field, including organic compounds, quantum dots, metal nanoclusters-based, upconverting nanoparticles, dye-doped nanoparticles, and luminescence thermometry based on rare-earths. Furthermore, covered is the synthesis of rare earth elements and post-transition metals-based near-infrared thermometric phosphors. Nonetheless, more research is required to completely comprehend the properties and realize the potential applications of these materials. To create high-performing thermometers with desired properties and thermometric parameters, it is crucial to have a deep understanding of the material parameters that affect the thermometric performance of the phosphor. This includes understanding the role of these parameters that relate to sensitivity. Furthermore, the temperature sensitivity also depends on the synthesis and size of the material for thermometry applications. As a result, more efforts are needed to improve the current synthesis methods that offer the nanoparticles because they have poor luminescence and a very low photoluminescence quantum yield. Lastly, we discuss notable factors influencing the sensitivity of optical thermometers and their future directions.