NH3 Sensor Based on 3D Hierarchical Flower-Shaped n-ZnO/p-NiO Heterostructures Yields Outstanding Sensing Capabilities at ppb Level

Abstract

Hierarchical three-dimensional (3D) flower-like n-ZnO/p-NiO heterostructures with various ZnxNiy molar ratios (Zn5Ni1, Zn2Ni1, Zn1Ni1, Zn1Ni2 and Zn1Ni5) were synthesized by a facile hydrothermal method. Their crystal phase, surface morphology, elemental composition and chemical state were comprehensively investigated by XRD, SEM, EDS, TEM and XPS techniques. Gas sensing measurements were conducted on all the as-developed ZnxNiy-based sensors toward ammonia (NH3) detection under various working temperatures from 160 to 340 °C. In particular, the as-prepared Zn1Ni2 sensor exhibited superior NH3 sensing performance under optimum working temperature (280 °C) including high response (25 toward 100 ppm), fast response/recovery time (16 s/7 s), low detection limit (50 ppb), good selectivity and long-term stability. The enhanced NH3 sensing capabilities of Zn1Ni2 sensor could be attributed to both the specific hierarchical structure which facilitates the adsorption of NH3 molecules and produces much more contact sites, and the improved gas response characteristics of p-n heterojunctions. The obtained results clear demonstrated that the optimum n-ZnO/p-NiO heterostructure is indeed very promising sensing material toward NH3 detection for different applications.

Nanoscale Heterostructured Materials Based on Metal Oxides for a Chemiresistive Gas Sensor

“…The presence of heterojunctions causes the ambient resistance in air of the hybrid material to be higher compared to the pristine form. This is due to the formation of an extended depletion region because of the combined effect of two phenomena: (a) surface adsorption of oxygen species by capturing an electron from the conduction band and (b) p-n heterojunction formation upon recombination of the electron and hole due to transfer of the electron from material with a low work function to that having a high work function. − This inevitably reduces the charge conduction channel leading to high sensor resistance. Upward band banding can be observed on the n-side due to the electron depletion layer and the p-side exhibits downward band bending due to the depletion of holes (Figure a).…”

ZnO/NiO heterostructure-based microsensors used in formaldehyde detection at room temperature: Influence of the sensor operating voltage

“…On the other hand, nickel oxide (NiO), which is a p-type semiconductor [ 17 ], can be used in sensor applications, solar cells, electrochromic devices [ 18 , 19 ] and can easily form heterojunctions with ZnO. The combination of NiO and ZnO oxides has been previously described in the literature and used successfully for various gas detection applications [ 20 – 23 ].…”

“…Creating ZnO-n/NiO-p heterojunctions is a simple and effective way to improve gas detection properties, which increases sensor response and decreases recovery time, to develop applications for gas sensors [ 20 , 21 ]. References [ 21 – 23 ] describe NiO-ZnO combinations as efficient materials used for the development of gas sensors at low working temperatures.…”

All‐Inorganic CsPbBr3/Cs4PbBr6 Perovskite/ZnO for Detection of NO with Enhanced Response and Low‐Work Temperature

“…[11] The reported results demonstrated that it was an effective method to form heterostructures by coupling with other semiconductors because heterostructures between two materials resulted in enhancement of carrier separation, thereby further achieving a decrease of the work temperature and improvement of the sensitivity. [12] For example, ZnO was compounded with the Co 3 O 4 nanostructures, the work temperature was decreased from 240°C to 180°C and the response was increased over 26 times to 100 ppm acetone. [10] The responses of RdRh hollow nanocube/ZnO and RdRh solid nanocube/ZnO composites were 9.5 times and 5.5 times higher than the bare ZnO toward 1 ppm H 2 S. [13] Recently, a new sensing material, halide perovskite, was applied to gas sensor for the first time in 2017 and showed good gas-sensing performances, [14] which has been widely investigated as an emerging optoelectronics material in solar cells, [15] absorbers, [16] photodetectors, [17] light-emitting diodes [18] and so on.…”