Facile synthesis of novel 3D nanoflower-like CuxO/multilayer graphene composites for room temperature NOx gas sensor application

Abstract

3D nanoflower-like CuxO/multilayer graphene composites (CuMGCs) have been successfully synthesized as a new type of room temperature NOx gas sensor. Firstly, the expanded graphite (EG) was activated by KOH and many moderate functional groups were generated; secondly, Cu(CH3COO)2 and CTAB underwent full infusion into the interlayers of activated EG (aEG) by means of a vacuum-assisted technique and then reacted with the functional groups of aEG accompanied by the exfoliation of aEG via reflux. Eventually, the 3D nanoflower consisting of 5-9 nm CuxO nanoparticles homogeneously grow in situ on aEG. The KOH activation of EG plays a key role in the uniform formation of CuMGCs. When being used as gas sensors for detection of NOx, the CuMGCs achieved a higher response at room temperature than that of the corresponding CuxO. In detail, the CuMGCs show a higher NOx gas sensing performance with low detection limit of 97 ppb, high gas response of 95.1% and short response time of 9.6 s to 97.0 ppm NOx at room temperature. Meanwhile, the CuMGC sensor presents a favorable linearity, good selectivity and stability. The enhancement of the sensing response is mainly attributed to the improved conductivity of the CuMGCs. A series of Mott-Schottky and EIS measurements demonstrated that the CuMGCs have much higher donor densities than CuxO and can easily capture and migrate electrons from the conduction band, resulting in the enhancement of electrical conductivity.

Enhanced NOx Gas Sensing Properties of Ordered Mesoporous WO3/ZnO Prepared by Electroless Plating

“…The oxygen molecules capture the electrons from conduction band of the semiconductor to form a series of oxygen species (O 2 − , O 2− , and O − ). The specific adsorption reaction process can be explained as follows…”

Graphene-based hybrids for chemiresistive gas sensors

“…Some nanocomposites of 2D graphene with large-sized 3D metal-oxide nanostructures have been synthesized, and showed a relatively lower sensitivity than the hybrids of graphene with 0D and 1D nanostructures because the large-sized 3D structures hindered the interaction between metal oxide and RGO, so resulted in reduction of the contact area [84][85][86]. Yang et al [87] synthesized a hybrid of graphene of small size with 3D nanoflower-like Cu x O consisting of NPs of ~5-9 nm, which might also contact graphene. Compared with bare Cu x O, the 3D nanoflower-like Cu x O/graphene hybrids displayed markedly enhanced sensitivity, which may be ascribed to the following two factors:  the enhancement of conductivity caused by graphene with high carrier mobility and the Schottky contact at the interface of Cu x O and graphene;  the effective gas diffusion of slit pores between the parallel layers of graphene braced by the 3D flower-like Cu x O nanostructures; the slit pores acted as channels for gas diffusion, and thus provided more active sites for the reaction of NO x with surface-adsorbed oxygen ions.…”

Facile Synthesis of Hierarchical CuO Microspheres and their Gas Sensing Properties for NOx at Room Temperature

“…[37] A 99.6 % alumina substrate (7 Â 5 Â 0.38 mm) with two interdigitated Au electrodes on its top surface was used. Each Au electrode geometry consisted of 50 pairs of fingers interleaved with each other, the distance between two fingers was 50 mm.…”