Graphitic carbon nitride (g-C3N4)-assisted materials for the detection and remediation of hazardous gases and VOCs

Graphitic carbon nitride (g-C3N4)-based materials are attracting attention for their unique properties, such as low-cost, chemical stability, facile synthesis, adjustable electronic structure, and optical properties. These facilitate the use of g-C3N4 to design better photocatalytic and sensing materials. Environmental pollution by hazardous gases and volatile organic compounds (VOCs) can be monitored and controlled using eco-friendly g-C3N4- photocatalysts. Firstly, this review introduces the structure, optical and electronic properties of C3N4 and C3N4 assisted materials, followed by various synthesis strategies. In continuation, binary and ternary nanocomposites of C3N4 with metal oxides, sulfides, noble metals, and graphene are elaborated. g-C3N4/metal oxide composites exhibited better charge separation that leads to enhancement in photocatalytic properties. g-C3N4/noble metal composites possess higher photocatalytic activities due to the surface plasmon effects of metals. Ternary composites by the presence of dual heterojunctions improve properties of g-C3N4 for enhanced photocatalytic application. In the later part, we have summarised the application of g-C3N4 and its assisted materials for sensing toxic gases and VOCs and decontaminating NOx and VOCs by photocatalysis. Composites of g-C3N4 with metal and metal oxide give comparatively better results. This review is expected to bring a new sketch for developing g-C3N4-based photocatalysts and sensors with practical applications.

High-Performance N-Butanol Gas Sensor Based on Iron-Doped Metal-Organic Framework-Derived Nickel Oxide and DFT Study

In this study, a straightforward two-step hydrothermal process was used to synthesize Fe-doped NiO nanomaterials. A number of characterization approaches were employed to explore the structure and morphology of the synthesized Fe-doped NiO. The as-prepared samples were multi-layered flower-like structures formed by nanoparticles, according to scanning electron microscopy and transmission electron microscopy studies. The findings of the study on gas sensing performance showed that the response of the 1.5 at % Fe-NiO sensor was nearly 100 times greater than that of the pure NiO sensor, and the lower limit of detection was greatly decreased (50 ppb). The 1.5 at % Fe-NiO sensor exhibited superior sensing performance for n-butanol. The incorporation of an appropriate amount of Fe into the NiO lattice modified the carrier concentration, which is the primary cause of the increased sensor performance of an appropriate amount of Fe-doped NiO. In addition, the density functional theory calculation method based on the first-principles theory was used to study the adsorption performance and electronic behavior of pure NiO and 1.5 at % Fe-NiO for n-butanol. The calculated results were consistent with the experimental results.

High Sensing Performance Toward Acetone Vapor Using TiO2 Flower-Like Nanomaterials

For real-application gas sensors, high performances (response, selectivity, response/recovery time and stability) are demanded. An effective strategy is applying nanomaterials in gas sensors. In this study, the anatase TiO₂ flower-like nanomaterials (FLNMs) are prepared through a one-step hydrothermal method which exhibit high-performance toward acetone vapor. TiO₂ FLNMs sensors property are characterized at optimal working temperature of 330 °C with selectivity (acetone), response (S = 33.72 toward 250 ppm acetone), linear dependence (R² = 0.9913), response/recovery time (46/24 s toward 250 ppm acetone) and long-term stability (30 days). These demonstrate that TiO₂ FLNMs get a high performance for acetone sensor. Moreover, the limit of detection of acetone is 0.65 ppm which is lower than that of exhaled air for diabetes (0.8 ppm), indicating that TiO₂ FLNMs gas sensor gets potential application in medical diagnosis.

Highly Sensing and Selective Performance Based on Bi-Doped Porous ZnSnO3 Nanospheres for Detection of n-Butanol

In this study, pure zinc stannate (ZnSnO₃) and bismuth (Bi)-doped ZnSnO₃ composites (Bi-ZnSnO₃) were synthesized via the in situ precipitation method, and their microstructures, morphologies, chemical components, sizes, and specific surface areas were characterized, followed by testing their gas sensing properties. The results revealed that Bi-ZnSnO₃ showed superior gas sensing properties to n-butanol gas, with an optimal operating temperature of 300 °C, which was 50 °C lower than that of pure ZnSnO₃. At this temperature, moreover, the sensitivity of Bi-ZnSnO₃ to n-butanol gas at the concentration of 100 ppm reached as high as 1450.65, which was 35.57 times that (41.01) of ammonia gas, 2.93 times that (495.09) of acetone gas, 6.02 times that (241.05) of methanol gas, 2.54 times that (571.48) of formaldehyde gas, and 2.98 times that (486.58) of ethanol gas. Bi-ZnSnO₃ had a highly repeatable performance. The total proportion of oxygen vacancies and chemi-adsorbed oxygen in Bi-ZnSnO₃ (4 wt%) was 27.72% to 32.68% higher than that of pure ZnSnO₃. Therefore, Bi-ZnSnO₃ has considerable potential in detecting n-butanol gas by virtue of its excellent gas-sensing properties.

One-dimensional In2O3nanorods as sensing material for ppb-level n-butanol detection

Effectively and quantificationally detecting hazardous gas n-butanol is very significant in daily life, which can bring about a safe living condition for humans. In this study, the one-dimensional In₂O₃nanorods were successfully synthesized via hydrothermal route and post-heat treatment. Noticeably, one-dimensional nanorods structures were obtained and the products presented a superior growth orientation along with (222) plane. Additionally, systematical gas-sensing measurements of the sensor made from In₂O₃nanorods towards hazardous n-butanol gas were conducted. Results exhibited that the fabricated sensor showed excellent n-butanol sensing properties, with aspects to a superior response value of 342.20 with concentration 100 ppm at 240 °C, remarkable selectivity, fast response/recovery times (77.5/34.2 s) and good stability. More interestingly, the detection limit of sensor as low as 500 ppb and a good linearity relationship between response values and n-butanol concentrations was presented. Gas-sensitive properties of this sensor are better than previously reported in n-butanol detection. All results demonstrate that one-dimensional In₂O₃nanorod is a promising sensor material to practical applications in effectively detecting n-butanol gas.

Synthesis of ZnO Hollow Microspheres and Analysis of Their Gas Sensing Properties for n-Butanol

ZnO hollow microspheres with a diameter of approximately 1.4 μm were successfully synthesized by a facile one-step chemical precipitation method using trisodium citrate dihydrate as a morphology control agent. The ZnO hollow microspheres consisted of nanoplates and had good dispersibility. Control experiments revealed that trisodium citrate dihydrate played an important role in regulating the morphologies of ZnO products. The morphology of the ZnO product evolved from nanowires to hollow microspheres with the addition of trisodium citrate dihydrate. The sensor response of ZnO hollow microspheres toward 100 ppm n-butanol reached 86.6 at the optimum operating temperature of 340 °C, which was approximately three times higher than that of ZnO nanowires. In addition, the ZnO hollow microspheres also displayed good selectivity and long-term work stability toward n-butanol. The excellent gas sensing performance of ZnO hollow microspheres may be ascribed to the unique hollow sphere structure with high exposed polar crystal surface.

Nanoparticles Assembled CdIn2O4 Spheres with High Sensing Properties towards n-Butanol

Cd/In-glycerate spheres are synthesized through a simple solvothermal method. After thermal treatment, these Cd/In-glycerates can be converted into CdIn2O4 spheres. Many characterization methods were performed to reveal the microstructure and morphology of the CdIn2O4. It was found that pure CdIn2O4 phase was obtained for the Cd/In starting materials at ratios of 1:1.6. The CdIn2O4 spheres are composed by a large number of nanoparticles subunits. The CdIn2O4 sphere-based sensor exhibited a low detection limit (1 ppm), high response (81.20 to 500 ppm n-butanol), fast response (4 s) and recovery (10 s) time, good selectivity, excellent repeatability, and stability at 280 °C. Our findings highlight the possibility to develop a novel gas sensor based on CdIn2O4 for application in n-butanol detection with high performance.

Recent progress and perspectives of gas sensors based on vertically oriented ZnO nanomaterials

Vertically oriented zinc oxide (ZnO) nanomaterials, such as nanorods (NRs), nanowires (NWs), nanotubes (NTs), nanoneedles (NNs), and nanosheets (NSs), are highly ordered architectures that provide remarkable properties for sensors. Furthermore, these nanostructures have fascinating features, including high surface-area-to-volume ratios, high charge carrier concentrations, and many surface-active sites. These features make vertically oriented ZnO nanomaterials exciting candidates for gas sensor fabrication. The development of efficient methods for the production of vertically oriented nanomaterial electrode surfaces has resulted in improved stability, high reproducibility, and gas sensing performance. Moving beyond conventional fabrication processes that include binders and nanomaterial deposition steps has been crucial, as the materials from these processes suffer from poor stability, low reproducibility, and marginal sensing performance. In this feature article, we comprehensively describe vertically oriented ZnO nanomaterials for gas sensing applications. The uses of such nanomaterials for gas sensor fabrication are discussed in the context of ease of growth, stability on an electrode surface, growth reproducibility, and enhancements in device efficiency as a result of their unique and advantageous features. In addition, we summarize applications of gas sensors for a variety of toxic and volatile organic compound (VOC) gases, and we discuss future directions of the vertically oriented ZnO nanomaterials.

Sucrose-Mediated Fast Synthesis of Zinc Oxide Nanoparticles for the Photocatalytic Degradation of Organic Pollutants in Water

We report a facile method for the synthesis of zinc oxide nanoparticles (nZnOs) by rapidly heating a paste of zinc nitrate and sucrose on the hot plate at 500 °C. The transmission electron microscopy images revealed the spherical shape of the nZnO with an average size of 35 nm. The band gap and the specific surface area of the nZnO were measured to be about 3.32 eV and 80.11 m²/g, respectively. The nZnO was utilized for the photocatalytic degradation of methyl orange (MO) and methylene blue (MB) in water under the ultraviolet (UV-B) light and sunlight irradiation. Photocatalysis was performed in two types of water matrices, viz., the deionized water and the simulated fresh drinking water. Almost a complete degradation of MO and MB was obtained within 30 min of UV-B light irradiation. Under sunlight irradiation, more than 95% of the MO solution underwent degradation within 30 min. The photocatalytic stability of the nZnO was examined for five cycles, and a similar activity was found throughout the cycles. The photocatalytic generation of the hydroxyl radical (^•OH) was confirmed by the terephthalic acid photoluminescence tests. Moreover, the synthesis methodology was validated by triplicating the nZnO synthesis. Every time, the nZnO demonstrated a similar photocatalytic activity, which confirmed the robustness of the synthesis procedure.

Mulberry-like heterostructure (Fe–O–Ti): a novel sensing material for ethanol gas sensors

The gas sensors have been widely used in various fields, to protect the safety of life and property. A novel heterostructure of Fe–O–Ti nanoparticles is fabricated by hydrothermal and wet chemical deposition methods. The Fe–O–Ti nanoparticles with a large number of pores possess high surface area, which is in favour of high-performance gas sensors. Compared with pure Fe₂O₃ and TiO₂, the Fe–O–Ti composite exhibits obviously enhanced sensing characteristics, such as faster response–recovery time (T_res = 6 s, T_rec = 48 s), higher sensing response (response = 35.6) and better selectivity. The results show that the special morphology and large specific surface area of mulberry-like Fe–O–Ti heterostructures provided a large contact area for gas reactions.

The gas sensors have been widely used in various fields, to protect the safety of life and property.

Aliovalent Fe(iii)-doped NiO microspheres for enhanced butanol gas sensing properties

Fe-Doped NiO multi-shelled microspheres have been synthesized via a facile hydrothermal reaction.

Visible-light-mediated dehydrogenative cross-coupling between terminal alkynes and aldehydes by employing a supramolecular polymeric ensemble of PBI derivative

A supramolecular polymer of PBI derivative and ZnO NPs exhibits remarkable efficiency in direct dehydrogenative cross-coupling reaction for the synthesis of ynones under photocatalytic conditions.

TiO2 nanoparticles functionalized by Pd nanoparticles for gas-sensing application with enhanced butane response performances

Pd functionalized TiO₂ nanoparticles were synthesized by a facile hydrothermal method. The structure, morphology, surface chemical states and surface area were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N₂ adsorption-desorption isotherms, respectively. The as-synthesized pure and Pd functionalized TiO₂ nanoparticles were used to fabricate indirect-heating gas sensor, and the gas-sensing characteristics towards butane were investigated. At the optimum temperature, the sensors possess good response, selectivity, response/recovery, repeatability as well as long-term stability. Especially for the high response, the response of 7.5 mol% Pd functionalized TiO₂ nanoparticles based sensor reaches 33.93 towards 3000 ppm butane, which is about 9 times higher than that of pure TiO₂ nanoparticles. The response and recovery time are 13 and 8 s, respectively. Those values demonstrate the potential of using as-synthesized Pd functionalized TiO₂ nanoparticles as butane gas detection, particularly in the dynamic monitoring. Apart from these, a possible mechanism related to the enhanced sensing performance is also investigated.

Two-dimensional SnS nanoflakes: synthesis and application to acetone and alcohol sensors

SnS nanoflakes were synthesized using a solid state reaction method at 600 °C and their gas sensing properties were investigated.

Ag-Functionalized macro-/mesoporous AZO synthesized by solution combustion for VOCs gas sensing application

The aim of this paper is to develop easily manufactured and highly sensitive gas sensors for VOCs (volatile organic compounds) detection.

Reduced graphene oxide/ZnO nanocomposite for application in chemical gas sensors

Coupling of graphene-based materials with metal oxide nanostructures is an effective way to obtain composites with improved gas sensing properties.

The xylene sensing performance of WO3 decorated anatase TiO2 nanoparticles as a sensing material for a gas sensor at a low operating temperature

Here, the pristine and WO₃ decorated TiO₂ nanoparticles were synthesized by a one-step hydrothermal without the use of a surfactant or template, and used to fabricate gas sensors.

A CuO–ZnO nanostructured p–n junction sensor for enhanced N-butanol detection

Herein, a novel CuO–ZnO nanostructured p–n junction composite is prepared via the hydrothermal method.