High-performance NO2 sensors based on spontaneously functionalized hexagonal boron nitride nanosheets via chemical exfoliation

Fiber Optic Sensor Coated with Multiple Layers of Hexagonal Boron Nitride Nanosheets (BNNS) for the Detection of Volatile Organic Compounds

Nowadays, volatile organic compound (VOC) detection is imperative to ensure environmental safety in industry and indoor environments, as well as to monitor human health in medical diagnosis. Gas sensors with the best sensor response, selectivity, and stability are in high demand. Simultaneously, the advancement of nanotechnology facilitates novel nanomaterial-based gas sensors with superior sensor characteristics and low power consumption. Recently, boron nitride, a 2D material, has emerged as an excellent candidate for gas sensing and demonstrated exceptional sensing characteristics for new-generation gas sensing devices. Herein, ultrathin porous boron nitride nanosheets (BNNSs) with large lateral sizes were synthesized using a facile synthesis approach, and their material characteristics were investigated utilizing a variety of analytical techniques, including X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. A BNNS-coated cladding-modified fiber optic sensor (FOS) probe was prepared and employed for VOC (ammonia, ethanol, and acetone) sensing across concentrations varying from 0 to 300 ppm. The BNNSs-coated FOS demonstrated better selectivity toward 300 ppm ammonia, and specifically annealed BNNSs displayed a maximum sensor response of 55% along with a response/recovery times of 15 s/34 s compared to its counterparts. The superior ammonia sensing performances could be attributed to the formation of ultrathin nanosheets and a porous surface with slit-like features in hexagonal boron nitride.

Nanostructured SnO2 Thin Films Based on a Convenient Chemical Deposition for Sensitive Detection of Ethanol

A specific matrix sensor that can operate at low temperatures and has a high sensing response is crucial for monitoring flammable VOC gases. In this study, a nanostructured SnO2 thin film was successfully produced using a suitable chemical deposition method, and its sensing properties were comprehensively analyzed. The SEM images revealed that the thin film of the nanostructured SnO2 is made up of two different sizes of broccoli-like structure nanoparticles. The sensor, which is based on this unique micronano structure, demonstrated a high sensing response (44), low operating temperature (200 °C), and fast response time (6s). Additionally, the nanostructured sensor exhibited excellent resistance to humidity interference and long-term stability. Moreover, DFT is employed to evaluate the electronic properties and to systematically explain the gas sensing mechanism of the nanostructured sensor based on the SnO2 thin film.

2D nanomaterials for realization of flexible and wearable gas sensors: A review

Gas sensors are extensively employed for monitoring and detection of hazardous gases and vapors. Many of them are produced on rigid substrates, but flexible and wearable gas sensors are needed for intriguing usage including the internet of things (IoT) and medical devices. The materials with the greatest potential for the fabrication of flexible and wearable gas sensing devices are two-dimensional (2D) semiconducting nanomaterials, which consist of graphene and its substitutes, transition metal dichalcogenides, and MXenes. These types of materials have good mechanical flexibility, high charge carrier mobility, a large area of surface, an abundance of defects and dangling bonds, and, in certain instances adequate transparency and ease of synthesis. In this review, we have addressed the different 2D nonmaterial properties for gas sensing in the context of fabrication of flexible/wearable gas sensors. We have discussed the sensing performance of flexible/wearable gas sensors in various forms such as pristine, composite and noble metal decorated. We believe that content of this review paper is greatly useful for the researchers working in the research area of fabrication of flexible/wearable gas sensors.

Tunability of electronic and thermoelectric properties of hexagonal boron nitride with carbon impurities under magnetic field: Tight binding investigation

Utilizing the Kubo-Greenwood formula, Tight Binding calculations were employed to examine the electronic and thermoelectric properties of hexagonal boron nitride (h-BN) with carbon impurity instead of boron, nitrogen and pairs boron-nitrogen. The electronic properties of the pristine monolayer BN are markedly impacted by the introduction of carbon dopants and its band gap reduction is directly correlated with the concentration of carbon impurities. The electronic properties of doped h-BN are influenced by the presence of a magnetic field, leading to subband separation and band gap narrowing, independent of the impurity types. The thermal conductivity and magnetic susceptibility of the CBN-doped monolayer BN structure are higher than those of the BC and NC doped h-BN structures and for all structures, their properties have a strong dependence on the magnetic field. The Lorenz Number for all structures has peak at the TM temperature which shifts to a lower temperature as the impurity concentration decreases.

Optimizing thermoelectric performance of carbon-doped h-BN monolayers through tuning carrier concentrations and magnetic field

The thermoelectric properties of carbon-doped monolayer hexagonal boron nitride (h-BN) are studied using a tight-binding model employing Green function approach and the Kubo formalism. Accurate tight-binding parameters are obtained to achieve excellent fitting with Density Functional Theory results for doped h-BN structures with impurity type and concentration. The influence of carbon doping on the electronic properties, electrical conductivity, and heat capacity of h-BN is studied, especially under an applied magnetic field. Electronic properties are significantly altered by doping type, concentration, and magnetic field due to subband splitting, merging of adjacent subbands, and band gap reduction. These modifications influence the number, location, and magnitude of DOS peaks, generating extra peaks inside the band gap region. Heat capacity displays pronounced dependence on both magnetic field and impurity concentration, exhibiting higher intensity at lower dopant levels. Electrical conductivity is increased by double carbon doping compared to single doping, but is reduced at high magnetic fields because of high carrier scattering. The electronic figure of merit ZT increases with lower impurity concentration and is higher for CB versus CN doping at a given field strength. The power factor can be improved by increasing magnetic field and decreasing doping concentration. In summary, controlling doping and magnetic field demonstrates the ability to effectively engineer the thermoelectric properties of monolayer h-BN.

Covalent Triazine Framework C6N6 as an Electrochemical Sensor for Hydrogen-Containing Industrial Pollutants. A DFT Study

Industrial pollutants pose a serious threat to ecosystems. Hence, there is a need to search for new efficient sensor materials for the detection of pollutants. In the current study, we explored the electrochemical sensing potential of a C₆N₆ sheet for H-containing industrial pollutants (HCN, H₂S, NH₃ and PH₃) through DFT simulations. The adsorption of industrial pollutants over C₆N₆ occurs through physisorption, with adsorption energies ranging from -9.36 kcal/mol to -16.46 kcal/mol. The non-covalent interactions of analyte@C₆N₆ complexes are quantified by symmetry adapted perturbation theory (SAPT0), quantum theory of atoms in molecules (QTAIM) and non-covalent interaction (NCI) analyses. SAPT0 analyses show that electrostatic and dispersion forces play a dominant role in the stabilization of analytes over C₆N₆ sheets. Similarly, NCI and QTAIM analyses also verified the results of SAPT0 and interaction energy analyses. The electronic properties of analyte@C₆N₆ complexes are investigated by electron density difference (EDD), natural bond orbital analyses (NBO) and frontier molecular orbital analyses (FMO). Charge is transferred from the C₆N₆ sheet to HCN, H₂S, NH₃ and PH₃. The highest exchange of charge is noted for H₂S (-0.026 e^-). The results of FMO analyses show that the interaction of all analytes results in changes in the E_H-L gap of the C₆N₆ sheet. However, the highest decrease in the E_H-L gap (2.58 eV) is observed for the NH₃@C₆N₆ complex among all studied analyte@C₆N₆ complexes. The orbital density pattern shows that the HOMO density is completely concentrated on NH₃, while the LUMO density is centred on the C₆N₆ surface. Such a type of electronic transition results in a significant change in the E_H-L gap. Thus, it is concluded that C₆N₆ is highly selective towards NH₃ compared to the other studied analytes.

Zr-Doped h-BN Monolayer: A High-Sensitivity Atmospheric Pollutant-Monitoring Sensor

In the post-epidemic era, industrial production has gradually recovered, and the attendant air pollution problem has attracted much attention. In this study, the Zr-doped h-BN monolayer (Zr-BN) is proposed as a new gas sensor for air pollution. Based on density functional theory (DFT), we calculated and compared the adsorption energies (Eads), geometric parameters, the shortest distance between gas and substrate (dsub/gas), density of states (DOS), electron localization function (ELF), charge density difference (CDD), band structure, band gap energy change rate (ΔEg), and sensitivity (S) of Zr-BN adsorption systems (SO2F2, SOF2, SO2, NO, and CO2 adsorption systems). The results show that Zr-BN had strong adsorption and high sensitivity to the above-mentioned polluted gases, and the sensitivity was in the order of SOF2 > SO2F2 > CO2 > SO2 > NO. Therefore, this study provides a theoretical basis for the preparation of Zr-BN gas sensors and provides new ideas and methods for the development of other gas sensors.

Defect-enhanced electrochemical property of h-BN for Pb2+ detection

A new strategy has been developed for the determination of trace lead ions (Pb²⁺) based on hexagonal boron nitride (h-BN) laden with point defect. The defect-laden boron nitride (D-BN) was synthesized by a thermal polymerization route, in which melamine borate was used as a precursor. The defect microstructure was confirmed by photoluminescence (PL) and x-ray diffraction (XRD) techniques. As compared with h-BN, the D-BN-modified glassy carbon electrode (GCE) showed an enhanced electrochemical response towards Pb²⁺ peaking at - 0.551 V (vs. SCE), which was evidenced by linear sweep anodic stripping voltammetry (LSASV) results. The point defect plays a pivotal role in the electrocatalytic reaction process, which can mediate the electronic structure and surface properties of h-BN. Accordingly, the sensor presented a low detection limit of 0.15 μg/L towards Pb²⁺ and a wide linear response concentration range from 0.5 to 400 μg/L (correlation coefficient = 0.995). In view of its superior selectivity, stability, and reproducibility, the proposed method was applied for Pb²⁺ determination in real samples and exhibited satisfactory results. This work provides insight for the construction of electrochemical sensor with high-performance by engineering defects of modifying materials. Defect-loaden h-BN exhibited enhanced electrocatalytic redox reaction towards lead ions and thus a novel Pb²⁺ sensor with high performances was constructed.

Two-dimensional inorganic nanosheets: production and utility in the development of novel electrochemical (bio)sensors and gas-sensing applications

This review (with 178 references) focuses on inorganic layered materials (ILMs) and the use of their two-dimensional nanosheets in the development of novel electrochemical (bio)sensors, analytical devices, and gas-phase sensing applications. The text is organized in three main sections including the presentation of the most important families of ILMs, a comprehensive outline of various "bottom-up", "top-down," and hydro(solvo)thermal methods that have been used for the production of ILM nanosheets, and finally an evaluative survey on their utility for the determination of analytes with interest in different sectors of contemporary analysis. Critical discussion on the effect of the production method on their electronic properties, the suitability of each nanomaterial in different sensing technologies along with an assessment of the performance of the (bio)sensors and devices that have been proposed within the last 5 years, is enclosed. The perspectives of further improving the utility of 2D inorganic nanosheets in sensing applications, in real-world samples, are also discussed.

Two-dimensional metal organic frameworks for biomedical applications

Two-dimensional (2D) metal organic frameworks (MOFs), are an emerging class of layered nanomaterials with well-defined structure and modular composition. The unique pore structure, high flexibility, tunability, and ability to introduce desired functionality within the structural framework, have led to potential use of MOFs in biomedical applications. This article critically reviews the application of 2D MOFs for therapeutic delivery, tissue engineering, bioimaging, and biosensing. Further, discussion on the challenges and strategies in next generation of 2D MOFs are also included. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

The Properties and Preparation Methods of Different Boron Nitride Nanostructures and Applications of Related Nanocomposites

Due to special non-metallic polar bond between the III group (with certain metallic properties) element boron (B) and the V group element nitrogen (N), boron nitride (BN) has unique physical and chemical properties such as strong high-temperature resistance, oxidation resistance, heat conduction, electrical insulation and neutron absorption. Its unique lamellar, reticular and tubular morphologies and physicochemical properties make it attractive in the fields of adsorption, catalysis, hydrogen storage, thermal conduction, insulation, dielectric substrate of electronic devices, radiation protection, polymer composites, medicine, etc. Therefore, the synthesis and properties of BN derived materials become the main research hotspots of low-dimensional nanomaterials. This paper reviews the synthetic methods, overall properties, and applications of BN nanostructures and nanocomposites. In addition, challenges and prospect of this kind of materials are discussed.

Structural and electronic properties of c-BN (111) surface with hydrogen/fluorine functionalization and nitrogen-based small-molecule adsorption

Using first-principles density functional theory calculations, we systematically investigate the structural and electrical properties of pure, hydrogen (H) and fluorine (F) functionalized polar (111) cubic boron nitride (c-BN) surface. In the absence of surface functionalization, the reconstructed B-terminated surface is energetically preferable. The hydrogenation is favorable for stabilizing N- and B-terminated surfaces, while the fluorination leads to the stable unreconstructed B-terminated structure due to strong site preference of F atoms. The reconstructed c-BN surface has magnetic characteristic, and the spin density distributions are mainly localized around the interlayer weak B-B bonds. The unreconstructed structures are nonmagnetic. Meantime, the adsorption behavior of nitric oxide (NO) and ammonia (NH₃) molecules are investigated on the reconstructed c-BN surface. It is found that the adsorption of NO has a considerable effect on the energy levels near the Fermi level, while the energy levels of NH₃ are located at the deep energy level below the Fermi level. Our theoretical results are helpful for understanding experimental phenomenon in practical applications and designing novel c-BN based molecule sensors.

Comparative Study on the Effect of Protonation Control for Resistive Gas Sensor Based on Close-Packed Polypyrrole Nanoparticles

Conducting polymers are often used as sensor electrodes due to their conjugated chain structure, which leads to high sensitivity and rapid response at room temperature. Numerous studies have been conducted on the structures of conducting polymer nanomaterials to increase the active surface area for the target materials. However, studies on the control of the chemical state of conducting polymer chains and the modification of the sensing signal transfer with these changes have not been reported. In this work, polypyrrole nanoparticles (PPyNPs), where is PPy is a conducting polymer, are applied as a sensor transducer to analyze the chemical sensing ability of the electrode. In particular, the protonation of PPy is adjusted by chemical methods to modify the transfer sensing signals with changes in the polymer chain structure. The PPyNPs that were modified at pH 1 exhibit high sensitivity to the target analyte (down to 1 ppb of NH3) with short response and recovery times of less than 20 s and 50 s, respectively, at 25 °C.

A comprehensive experimental and theoretical study on BN nanosheets for the adsorption of pharmaceutical drugs

BN nanosheets were explored as proficient adsorbents for pharmaceutical drugs owing to high adsorption capacity and favorable interactions.