2D SnSe2 nanoflakes decorated with 1D ZnO nanowires for ppb-level NO2 detection at room temperature.

The detection of air pollutant nitrogen dioxide (NO2) is of great importance arising from its great harm to the ecological environment and human health. However, the detection range of most NO2 sensors is ppm-level, and it is still challenging to achieve lower concentration (ppb-level) NO2 detection. Herein, 2D tin diselenide nanoflakes decorated with 1D zinc oxide nanowires (SnSe2/ZnO) heterojunctions were first reported by facile hydrothermal and ultra-sonication methods. The response of the fabricated SnSe2/ZnO sensor enhances 3.41 times on average compared with that of pure SnSe2 sensor to 50-150 ppb NO2 with a high detection sensitivity (22.57 ppm-1) at room temperature. In addition, the SnSe2/ZnO sensor has complete recovery, negligible cross-sensitivity, and small relative standard deviation (6.98%) during the 1 month sensing test, which can meet the requirements for NO2 detection in environmental monitoring. The enhanced NO2 sensing performance can be attributed to the n-n heterojunction constructed between SnSe2 and ZnO. The as-prepared sensor based on SnSe2/ZnO hybrid significantly promotes the development of the low detection limit of the NO2 sensor at room temperature.

Facile hydrothermal synthesis of Ti3C2Tx-TiO2 nanocomposites for gaseous volatile organic compounds detection at room temperature.

The gaseous volatile organic compounds (VOCs) sensors with high-selectivity and low-power consumption have been expected for practical applications in environmental monitoring and disease diagnosis. Herein, we demonstrate a room-temperature VOCs gas sensor with enhanced performance based on Ti3C2Tx-TiO2 nanocomposites. The Ti3C2Tx-TiO2 nanocomposites with regular morphology are successfully synthesized via a facile one-step hydrothermal synthesis strategy by using Ti3C2Tx itself as titanium source. Attributed to the formation of interfacial heterojunctions and the modulation of carrier density, the Ti3C2Tx-TiO2 sensor exhibits about 1.5-12.6 times enhanced responses for the detection of various VOCs at room temperature than pure MXene sensor. Moreover, the nanocomposite sensor has better response to hexanal, both an air pollutant and a typical lung cancer biomarker. The gas response of the Ti3C2Tx-TiO2 sensor towards 10 ppm hexanal is about 3.4%. The hexanal gas sensing results display that the nanocomposite sensor maintains a high signal-to-noise ratio and the lower detection limit to hexanal gas is as low as 217 ppb. Due to the low power consumption and easy fabrication process, the Ti3C2Tx-TiO2 nanocomposite sensor is promising for application in IoT environmental monitoring as well as real-time health monitoring.

Hollow Cu2O nanospheres loaded with MoS2/reduced graphene oxide nanosheets for ppb-level NO2 detection at room temperature.

Low energy consumption, high sensing response and high selectivity are the important indexes of metal oxide semiconductor (MOS) gas sensors applied in many application fields. However, the high working temperature and poor selectivity of MOS sensors severely restrict their scope of application in the Internet of Things (IoT). Herein, ternary MoS2-rGO-Cu2O (MG-Cu) composites with boosting ppb-level NO2 sensing characteristics are synthesized by combining hydrothermal method and soft-template method. The optimal proportion of MoS2, rGO and Cu2O is systematically explored. The SEM and TEM analyses confirm the hollow Cu2O is anchored on the surface of MG. The gas sensing tests illustrate that optimum composite sensor exhibits highest response to 500 ppb NO2 at room temperature, which is 11 and 5 times higher compared to pure MoS2 and binary MG15, respectively. Besides, it displays excellent selectivity and superior stability. The synergy of shell-structure with abundant mesoporous, heterojunction construction and enhanced conductivity lead to the enhanced sensing performance of ternary sensor.

Enhanced ammonia sensing performance based on MXene-Ti3C2Tx multilayer nanoflakes functionalized by tungsten trioxide nanoparticles.

Low-power consumption and high sensitivity are highly desirable for a vast range of NH3 sensing applications. As a new type of two-dimension (2D) material, Ti3C2Tx is extensively studied for room temperature NH3 sensors recently. However, the Ti3C2Tx MXene based gas sensors suffer mainly from low sensitivity. Herein, we report a sensitive Ti3C2Tx/WO3 composite resistive sensor for NH3 detection. The Ti3C2Tx/WO3 composite consisting of WO3 nanoparticles anchored on Ti3C2Tx nanoflakes were synthesized successfully with a facile ultra-sonication technique. The composite sensor with optimized components exhibits a high sensitivity of 22.3% for 1 ppm NH3 at room temperature, which is 15.4 times higher than the pure Ti3C2Tx sensor. Furthermore, the composite sensor has excellent reproducibility, good long-term stability, and high selectivity to NH3. The relative humidity influence on NH3 gas sensing properties of the sensors was systematically studied. This research provides an efficient route for the preparation of novel MXene-based sensitive materials for high-performance NH3 sensors.