Hybrid 3D structures of ZnO nanoflowers and PdO nanoparticles as a highly selective methanol sensor

Abstract

The present study concerns the enhancement of methanol selectivity of three dimensional (3D) nanoflowers (NFs) of ZnO by dispersing nickel oxide (NiO) and palladium oxide (PdO) nanoparticles on the surface of the nanoflowers to form localized hybrid nano-junctions. The nanoflowers were fabricated through a liquid phase deposition technique and the modification was achieved by addition of NiCl and PdCl2 solutions. In addition to the detailed structural (like X-ray diffraction (XRD), electron dispersive spectroscopy (EDS), X-ray mapping, XPS) and morphological characterization (by field emission scanning electron microscopy (FESEM)), the existence of different defect states (viz. oxygen vacancy) was also confirmed by photoluminescence (PL) spectroscopy. The sensing properties of the pristine and metal oxide nanoparticle (NiO/PdO)-ZnO NF hybrid sensor structures, towards different alcohol vapors (methanol, ethanol, 2-propanol) were investigated in the concentration range of 0.5-700 ppm at 100-350 °C. Methanol selectivity study against other interfering species, viz. ethanol, 2-propanol, acetone, benzene, xylene and toluene was also investigated. It was found that the PdO-ZnO NF hybrid system offered enhanced selectivity towards methanol at low temperature (150 °C) compared to the NiO-ZnO NF and pristine ZnO NF counterparts. The underlying mechanism for such improvement has been discussed with respective energy band diagram and preferential dissociation of target species on such 3D hybrid structures. The corresponding improvement in transient characteristics has also been co-related with the proposed model.

Construction of novel hybrid PdO–ZnO p–n heterojunction nanostructures as a high-response sensor for acetaldehyde gas

“…Since the work function of PdO (7.9 eV) is higher than the work function of ZnO (5.3 eV), the electrons in the ZnO conduction band will transfer to that of PdO, while the holes will transfer towards ZnO, until the Fermi level (E f ) of the system is equalized. 30,45 Thus, the PdO/ZnO p-n heterojunction will generate a wider depletion layer, and thus energy band bending at the interface of the PdO@ZnO p-n heterojunction NSs sensor (as shown in Fig. 8(a)).…”

“…29 However, Pd metal is often prone to oxidation during high-temperature treatments, forming PdO which is a p-type MO. 30 Recent studies have utilized Pd and PdO NPs for many VOC sensing applications. 31 Hence, it would be interesting to study the gas sensing properties of the combination of PdO and ZnO, in order to design a p-n heterojunction NSs in a novel way.…”

Atomic layer deposited TiO2 ultrathin layer on Ag_ZnO nanorods for stable and efficient photocatalytic degradation of RhB

“…In addition, as reported in literature, ZnO nanomaterials can be easily obtained with 0-3 D morphologies: nanoparticles [10], nanorods [11], nanoflakes [12], and nanoflowers [13,14], among which the anisotropic structure of ZnO nanorods can facilitate the electron transportation [15]. Besides, ZnO is easier to crystallize on different supports (e.g., stainless steel mesh) with low-temperature methods [16][17][18][19].…”

Enhanced gas selectivity induced by surface active oxygen in SnO/SnO2 heterojunction structures at different temperatures

“…Although a high temperature can accelerate the reaction rate, it also leads to the activation and breaking of bonds, so the optimal temperature of the chemical adsorption-desorption equilibrium position will change with different chemical groups. 12,[33][34][35][36][37]…”

“…Traditionally, selectivity has been improved using various nanostructures and/or composites consisting of two metal oxides to form heterojunction structures. 5,[8][9][10][11][12] These heterojunction structures, such as NiO/ZnO, 13 CuO/ZnO, 14 NiO/ SnO 2 (ref. 15) and a-Fe 2 O 3 /NiO, 16 can largely overcome the shortcomings of selectivity, because they provide synergistic effects between the two components.…”