Along with the progress of nanoscience and nanotechnology, nanomaterials with attractive structural and functional properties have gained more attention than ever before, especially in the field of electronic sensors. In recent years, the gas sensing devices have made great achievement and also created wide application prospects, which leads to a new wave of research for designing advanced sensing materials. There is no doubt that the characteristics are highly governed by the sensitive layers. For this reason, important advances for the outstanding, novel sensing materials with different dimensional structures including 0D, 1D, 2D, and 3D are reported and summarized systematically. The sensing materials cover noble metals, metal oxide semiconductors, carbon nanomaterials, metal dichalcogenides, g-C3 N4 , MXenes, and complex composites. Discussion is also extended to the relation between sensing performances and their structure, electronic properties, and surface chemistry. In addition, some gas sensing related applications are also highlighted, including environment monitoring, breath analysis, food quality and safety, and flexible wearable electronics, from current situation and the facing challenges to the future research perspectives.

Recent Progress of Nanostructured Sensing Materials from 0D to 3D: Overview of Structure–Property-Application Relationship for Gas Sensors

NO2 is an oxidizing gas, which is considered to be the most dangerous and most toxic gas that should be controlled. Because of the advantages of high sensitivity, selectivity, stability and fast response/recovery speed, the chemical resistance sensor is used as a NO2 gas sensor. This article reviews the NO2 gas sensor based on metal oxides. Firstly, the hazards of NO2 and the major disadvantages of chemiresistive sensors based on metal oxides were discussed. Then, different sensitive materials of chemical resistance sensors were discussed, including metal oxides (MO), conductive polymers and carbon-based materials. Finally, the NO2 gas sensors based on metal oxide (including ZnO, NiO, CuO, SnO2, WO3) were discussed from the aspects of morphology, preparation method, modification, doping and composite. 

Metal Oxide Gas Sensors For Detecting NO2 in Industrial Exhaust Gas: Recent Developments

Metal oxide heterostructures have great potential in gas sensor devices due to the attractive chemical and electronic properties at the heterogeneous interfaces. Herein, a unique heterostructure of NiO nanoprisms/Fe 2 O 3 nanosheets is rationally designed by a solution method for use in n-butanol sensors with superior performances. Mott-Schottky tests reveal that the conductivity of the NiO sensor transforms from p-type to n-type after growing Fe 2 O 3. This conversion of conductivity plays a crucial role in improving the sensor response, which overcomes the low response of p-type metal oxides. The sensor shows good linear response within the concentration range of 0.1–20 ppm n-butanol under operating temperatures (Room Temperature-320 °C). Gas sensing investigations show the sensor based on NiO/Fe 2 O 3 has a response of 4.2–10 ppm n-butanol at an optimal temperature of 200 °C, revealing a 3-time enhancement compared to pure NiO. Meanwhile the NiO/Fe 2 O 3 sensor exhibits a detection limit of 48 ppb, which is much lower than that (296 ppb) of NiO. The proposed structural design in this work provides a new idea for synthesis of high-performance sensing materials for the detection of ppb-level n-butanol. • Fe 2 O 3 nanosheets are grown on NiO nanoprisms by wet-chemical method. • Fe 2 O 3 nanosheets improve the adsorption of reactive oxygen on NiO nanoprisms. • The NiO/Fe 2 O 3 heterostructures exhibit fast response for n-butanol detection. • The NiO/Fe 2 O 3 sensor delivers good selectivity and low detection limit to n-butanol. 

Anchoring Fe2O3 nanosheets on NiO nanoprisms to regulate the electronic properties for improved n-butanol detection

Metallic MoS2 (i.e., 1T-MoS2 ) is considered as the most promising precious-metal-free electrocatalyst with outstanding hydrogen evolution reaction (HER) performance in acidic media comparable to Pt. However, sluggish kinematics of HER in alkaline media and its inability for the oxygen evolution reaction (OER), hamper its development as bifunctional catalysts. The instability of 1T-MoS2 further impedes its applications for scaling up, calling an urgent need for simple synthesis to produce stable 1T-MoS2 . In this work, the challenge of 1T-MoS2 synthesis is first addressed using a direct one-step hydrothermal method by adopting ascorbic acid. 1T-MoS2 with flower-like morphology is obtained, and transition metals (Ni, Co, Fe) are simultaneously doped into 1T-MoS2 . Ni-1T-MoS2 achieves an enhanced bifunctional catalytic activity for both HER and OER in alkaline media, where the key role of Ni doping as single atom is proved to be essential for boosting HER/OER activity. Finally, a Ni-1T-MoS2 ||Ni-1T-MoS2 electrolyzer is fabricated, reaching a current density of 10 mA cm-2 at an applied cell voltage of only 1.54 V for overall water splitting.

Direct Synthesis of Stable 1T-MoS2 Doped with Ni Single Atoms for Water Splitting in Alkaline Media.

Synthesis of g-C3N4/Fe3O4/MoS2 composites for efficient hydrogen evolution reaction

High-performance, reproducible and stable gas sensors for aromatic compounds detection is important for the environmental monitoring and public health. In this work, we report a promising metal oxides semiconductor (MOS) gas sensor based on Cr-doped NiO nanoparticles (NPs) as the sensing materials for ppb-level detection of benzyl mercaptan. The prepared sensor with 25 at% Cr-doped NiO NPs showed the best performance with the gas response Rg/Ra value of 10.6 towards 100 ppb benzyl mercaptan. In addition, the sensor exhibited significantly high selectivity to benzyl mercaptan against typical interfering VOCs gases including aniline, benzene, trimethylbenzene, xylene, toluene, ethanol, acetone, carbon monoxide, ammonia and nitrogen dioxide. Moreover, the sensor showed remarkable stability after repetitive measurements for ten months. The superior performance of Cr-doped NiO NPs can be ascribed to the electron transfer among Ni O Cr bond, defective oxygen and chemical adsorption oxygen after Cr doping, which are beneficial for the gas adsorption and reaction on the surface of the sensing materials.

Cr-doped NiO nanoparticles as selective and stable gas sensor for ppb-level detection of benzyl mercaptan

Owing to unique alkyne-rich structure, graphdiyne (GDY) has been proven to be a superb support for anchoring metal catalysts. Herein we demonstrate a new role of GDY as the wettability modifier for enhanced hydrogenation catalysis. After loading a certain amount GDY nanospheres, silica mesoporous channels become superaerophilic, which allows gaseous H2 to be directly stored inside, thus significantly increasing H2 concentration around Pd nanoparticles (NPs). At the same time, GDY nanospheres also alter the electronic structure of Pd NPs via the strong d-π interaction. Combining with these two roles of GDY together, the hydrogenation of benzaldehyde could proceed under ambient H2 pressure in water, with an impressive enhancement of 4.3-folds comparing to unmodified Pd/mSiO2 catalyst. This study demonstrates a new role of GDY in constructing wettability matched catalysts for gas-liquid-solid tri-phase reactions.

Graphdiyne Nanospheres as a Wettability and Electron Modifier for Enhanced Hydrogenation Catalysis.

ABSTRACT For single-atom catalysts (SACs), the catalyst supports are not only anchors for single atoms, but also modulators for geometric and electronic structures, which determine their catalytic performance. Selecting an appropriate support to prepare SACs with uniform coordination environments is critical for achieving optimal performance and clarifying the relationship between the structure and the property of SACs. Approaching such a goal is still a significant challenge. Taking advantage of the strong d-π interaction between Cu atoms and diacetylenic in a graphdiyne (GDY) support, we present an efficient and simple strategy for fabricating Cu single atoms anchored on GDY (Cu1/GDY) with uniform Cu1-C4 single sites under mild conditions. The Cu atomic structure was confirmed by combining synchrotron radiation X-ray absorption spectroscopy, X-ray photoelectron spectroscopy and density functional theory (DFT) calculations. The as-prepared Cu1/GDY exhibits much higher activity than state-of-the-art SACs in direct benzene oxidation to phenol with H2O2 reaction, with turnover frequency values of 251 h−1 at room temperature and 1889 h−1 at 60°C, respectively. Furthermore, even with a high benzene conversion of 86%, high phenol selectivity (96%) is maintained, which can be ascribed to the hydrophobic and oleophyllic surface nature of Cu1/GDY for benzene adsorption and phenol desorption. Both experiments and DFT calculations indicate that Cu1-C4 single sites are more effective at activating H2O2 to form Cu=O bonds, which are important active intermediates for benzene oxidation to phenol.

Uniform single atomic Cu1-C4 sites anchored in graphdiyne for hydroxylation of benzene to phenol

Owing to unique alkyne-rich structure, graphdiyne (GDY) has been proven to be a superb support for anchoring metal catalysts. Herein we demonstrate a new role of GDY as the wettability modifier for enhanced hydrogenation catalysis. After loading a certain amount GDY nanospheres, silica mesoporous channels become superaerophilic, which allows gaseous H2 to be directly stored inside, thus significantly increasing H2 concentration around Pd nanoparticles (NPs). At the same time, GDY nanospheres also alter the electronic structure of Pd NPs via the strong d-π interaction. Combining with these two roles of GDY together, the hydrogenation of benzaldehyde could proceed under ambient H2 pressure in water, with an impressive enhancement of 4.3-folds comparing to unmodified Pd/mSiO2 catalyst. This study demonstrates a new role of GDY in constructing wettability matched catalysts for gas-liquid-solid tri-phase reactions. 

Graphdiyne Nanospheres as a Wettability and Electron Modifier for Enhanced Hydrogenation Catalysis

1T-phase molybdenum disulphide (MoS2) is considered to be one of the most promising candidates to substitute noble metals in the hydrogen evolution reaction (HER). Fabricating single layer 1T-phase MoS2 with abundant sulfur vacancies as well as good stability to further enhance catalytic performance remains a challenge. Herein, we develop an efficient in situ TMA cation ((CH3)4N+) intercalation method to produce 1T-phase MoS2. The obtained MoS2 nanosheets comprise about 81% 1T-phase and abundant sulfur vacancies (>12%), as verified by aberration-corrected high-angle annular dark field scanning transmission electron microscopy (AC-HAADF-STEM), X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), etc. In addition, the surface of as-prepared ST-MoS2 is negatively charged, making it very stable in aqueous solution. The as-prepared ST-MoS2 exhibits excellent electrochemical HER performance with a low over-potential and a small Tafel slope as well as superior cycling stability. Furthermore, it is an excellent co-catalyst when coupled with CdS nanowires to form a CdS/ST-MoS2 heterojunction photocatalyst for the HER under visible light irradiation. It achieves a maximum H2 production rate and apparent quantum efficiency (AQE) of approximately 1187 μmol mg−1 h−1 and 73.4%, respectively, which are significantly higher than those of reported CdS/MoS2 photocatalysts.

Jia Yu

Papers

Cr-doped NiO nanoparticles as selective and stable gas sensor for ppb-level detection of benzyl mercaptan

Graphdiyne Nanospheres as a Wettability and Electron Modifier for Enhanced Hydrogenation Catalysis.

Uniform single atomic Cu1-C4 sites anchored in graphdiyne for hydroxylation of benzene to phenol

Graphdiyne Nanospheres as a Wettability and Electron Modifier for Enhanced Hydrogenation Catalysis

Direct synthesis of 1T-phase MoS2 nanosheets with abundant sulfur-vacancies through (CH3)4N+ cation-intercalation for the hydrogen evolution reaction