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A surface acoustic wave (SAW) H 2 S gas sensor based on CuO-TiO 2 p-n heterojunction film was designed and fabricated. The sensor exhibits high sensitivity to H 2 S due to the significant current response of CuO-TiO 2 film to H 2 S gas and the appropriate work point of SAW sensor based on CuO-TiO 2 composite film. The linearity change for sensor frequency shift is strongly associated with the location of work point when the H 2 S concentration increases from 1 to 300 ppm. In addition, the porosity of CuO-TiO 2 film is beneficial to the efficient adsorption for H 2 S, leading to the higher frequency shift of the sensor. The SAW sensor also shows good selectivity and stability to H 2 S with stable frequency shift under different humidity levels. • A H 2 S gas sensor is designed and fabricated using CuO-TiO 2 composite film. • The establishment of CuO-TiO 2 p-n junction significantly enhances the sensitivity of SAW sensor to H 2 S. • The linearity variation of frequency shift is closely related to the position of work point at different H 2 S concentrations. • The key sensing mechanism of SAW sensor based on CuO-TiO 2 film is electric loading. • The SAW sensor shows fast response in high humidity level, and good gas selectivity and repeatability. [ABSTRACT FROM AUTHOR]

Surface acoustic wave (SAW) technology has been widely used in the field of harmful gas detection, but there remain a lot of challenges, such as long response/recovery time as well as poor selectivity and repeatability. Herein, we activate graphene oxide (GO) using MXene with excellent adsorption capacity (MXene/GO) to realize efficient NO 2 gas detection. The SAW sensor assembled with the multilayered MXene/GO composite showcases an enhanced gas sensing performance to the NO 2 gas (1–200 ppm) enabling high sensitivity (Δf = 260 Hz/ppm), fast response/recovery time, excellent selectivity, and good repeatability at room temperature. The enhanced high sensitivity and selectivity detection of NO 2 gas is attributed to the large pore size, hydrophilicity, and abundant surface functional groups of the multilayered MXene/GO composite. This elaborate design is expected to propel the development of next-generation acoustic gas phase sensors. [Display omitted] • The MXene is investigated in surface acoustic wave sensors for the first time and filles the material gap. • The facile synthetic method for the MXene/GO composite is expected to realize rapid and large-scale synthesis of sensitive layers for surface acoustic wave sensors. • The working mechanism of MXene-based sensitive layers is proposed and the factors to influence sensing performance are also considered. • The excellent sensing performance of MXene/GO-based surface acoustic wave sensors is obtained under different conditions. • A novel MXene/GO composite is proposed for the first time to evaluate its working mechanism and sensing performance in SAW gas sensors. [ABSTRACT FROM AUTHOR]

• The sensor can detect H 2 S gas with a concentration as low as 0.5 ppm. • The frequency shift of sensor is derived from the change of mass loading on films. • The responses became much faster and stronger with the increase of RH. Surface acoustic wave (SAW) sensors based on sol–gel processed porous and nanoparticulate CuO films were explored for H 2 S detection operated at room temperature. The SAW sensor showed a negative frequency shift when exposed to H 2 S gas, due to the mass loading effect on the sensitive CuO film. It has a high sensitivity of H 2 S, a detection limit of 500 ppb and a good selectivity to H 2 S gas compared with H 2 , C 2 H 5 OH, acetone, NH 3 , CO, NO, NO 2 gases. Relative humidity (RH) was identified to have a critical influence on the sensing performance of the sensor. The responses became much faster and stronger with the increase of RH. The significant enhancement in the sensing performance is attributed to that the chemical reaction between H 2 S and CuO is hindered and the physical adsorption of CuO to H 2 S is enhanced. [ABSTRACT FROM AUTHOR]

• CuO in mesoporous film can selectively adsorb and react with H 2 S gas molecules. • The adsorbed H 2 S changes both the film's mass and conductivity. • The SAW sensor has better performance because of the mass sensitive mechanism. • The SAW sensor can precisely detect H 2 S gas ranging from 5 ppb to100 ppm. Surface acoustic wave and chemiresistor based gas sensors integrated with a sensing layer of sol-gel CuO-Al 2 O 3 composite film were fabricated and their performance and mechanisms for H 2 S sensing were characterized and compared. In the composite film, CuO nanoparticles provide active sites for adsorption and reaction of H 2 S molecules while Al 2 O 3 nanoparticles help to form a uniform and mesoporous film structure, both of which enhance the sensitivity of the sensors by providing numerous active CuO surfaces. Through the comparative studies, the SAW based H 2 S sensor operated at room temperature showed a lower detection limit, higher sensitivity, better linearity and good selectivity to H 2 S gas with its concentration ranging from 5 ppb to 100 ppm, compared with those of the chemiresistor sensor, which are mainly attributed to the effective mass sensing properties of the SAW sensor, because a minor change in the mass of the film caused by adsorbed H 2 S molecules would lead to a significant and monotonous change of the resonant frequency of the SAW devices. [ABSTRACT FROM AUTHOR]