Metal oxide semiconductor (MOS) gas sensors possess extensive applications due to their high sensitivity, low cost, and simplicity To boost their excellent sensing performance and meet the growing demand for applications, a series of strategies have been developed, such as the surface morphology engineering and function manipulation Recently, the controlled morphology with exposed high-energy facets and the facet-dependent sensing properties have attracted much attention Because of its abundant unsaturated active sites, the crystal planes with high surface energy usually serve as promising platform for gas sensing After a lot of survey of literature, the authors provide a review of recent efforts on engineering crystal structures with exposed high-energy facets of MOS nanomaterials and their improved gas-sensitive performance, emphasis on six kinds of common gas-sensitive MOS including ZnO, SnO2, TiO2, α-Fe2O3, NiO and Cu2O Also, the relationship between dangling bonds density and gas-sensing properties has been systematically discussed and used as one significant factor to evaluate superior sensing surface of MOS According to the research and calculation, surface engineering by selectively exposing high-energy facets provides an effective way to obtain MOS gas-sensitive materials with superior performance The understanding of the facet-dependent properties of MOS will assist in and guide the fabrication of more excellent gas sensors in the future

An overview: Facet-dependent metal oxide semiconductor gas sensors

The alarming rise of indoor pollution and the need to combat the associated negative effects have promoted increasing attention in modernizing the chemical sensing technologies by newly designed materials with rich and tunable functionalities at atomic or molecular levels. With the appealing physical, chemical, optical, and electronic properties for various potential applications, the state-of-art gas-sensing nanomaterials and their future perspectives are well-documented and summarized in this paper. Specifically, the key performance attributes are addressed in detail such as the sensitivity, selectivity, reversibility, operating temperature, response time, and detection limit. As such, this review provides both critical insights in exploring and understanding various gas sensing nanomaterials and points out limitations and opportunities for further developments, such as morphology control, doping and surface alteration, atomic-scale characterization, and applications in different fields. Finally, the challenges and outlooks are discussed on the basis of the current developments.

Functional gas sensing nanomaterials: A panoramic view

Chemiresistive gas sensors with low power consumption, fast response, and reliable fabrication process for a specific target gas have been now created for many applications. They require both sensitive nanomaterials and an efficient substrate chip for heating and electrical addressing. Herein, a near room working temperature and fast response triethylamine (TEA) gas sensor has been fabricated successfully by designing gold (Au)-loaded ZnO/SnO2 core-shell nanorods. ZnO nanorods grew directly on Al2O3 flat electrodes with a cost-effective hydrothermal process. By employing pulsed laser deposition (PLD) and DC-sputtering methods, the construction of Au nanoparticle-loaded ZnO/SnO2 core/shell nanorod heterostructure is highly controllable and reproducible. In comparison with pristine ZnO, SnO2, and Au-loaded ZnO, SnO2 sensors, Au-ZnO/SnO2 nanorod sensors exhibit a remarkably high and fast response to TEA gas at working temperatures as low as 40 °C. The enhanced sensing property of the Au-ZnO/SnO2 sensor is also discussed with the semiconductor depletion layer model introduced by Au-SnO2 Schottky contact and ZnO/SnO2 N-N heterojunction.

Near Room Temperature, Fast-Response, and Highly Sensitive Triethylamine Sensor Assembled with Au-Loaded ZnO/SnO2 Core–Shell Nanorods on Flat Alumina Substrates

Chemi-resistive sensors based on hybrid functional materials are promising candidates for gas sensing with high responsivity, good selectivity, fast response/recovery, great stability/repeatability, room-working temperature, low cost, and easy-to-fabricate, for versatile applications. This progress report reviews the advantages and advances of these sensing structures compared with the single constituent, according to five main sensing forms: manipulating/constructing heterojunctions, catalytic reaction, charge transfer, charge carrier transport, molecular binding/sieving, and their combinations. Promises and challenges of the advances of each form are presented and discussed. Critical thinking and ideas regarding the orientation of the development of hybrid material-based gas sensor in the future are discussed.

/pdf/gas-sensors-based-on-chemi-resistive-hybrid-functional-i76a6c6prl.pdf

Gas Sensors Based on Chemi-Resistive Hybrid Functional Nanomaterials

The increase of surface area and the functionalization of catalyst are crucial to development of high-performance semiconductor metal oxide (SMO) based chemiresistive gas sensors. Herein, nanoscale catalyst loaded Co3O4 hollow nanocages (HNCs) by using metal–organic framework (MOF) templates have been developed as a new sensing platform. Nanoscale Pd nanoparticles (NPs) were easily loaded on the cavity of Co based zeolite imidazole framework (ZIF-67). The porous structure of ZIF-67 can restrict the size of Pd NPs (2–3 nm) and separate Pd NPs from each other. Subsequently, the calcination of Pd loaded ZIF-67 produced the catalytic PdO NPs functionalized Co3O4 HNCs (PdO–Co3O4 HNCs). The ultrasmall PdO NPs (3–4 nm) are well-distributed in the wall of Co3O4 HNCs, the unique structure of which can provide high surface area and high catalytic activity. As a result, the PdO–Co3O4 HNCs exhibited improved acetone sensing response (Rgas/Rair = 2.51–5 ppm) compared to PdO–Co3O4 powders (Rgas/Rair = 1.98), Co3O4 HNCs...

Nanoscale PdO Catalyst Functionalized Co3O4 Hollow Nanocages Using MOF Templates for Selective Detection of Acetone Molecules in Exhaled Breath

Porous and single crystalline ZnO nanosheets, which were synthesized by annealing hydrozincite Zn5(CO3)2(OH)6 nanoplates produced with a water/ethylene glycol solvothermal method, are used as building blocks to construct functional Pd–ZnO nanoarchitectures together with Pd nanoparticles based on a self-assembly approach. Chemical sensing performances of the ZnO nanosheets were investigated carefully before and after their surface modification with Pd nanoparticles. It was found that the chemical sensors made with porous ZnO nanosheets exhibit high selectivity and quick response for detecting acetone, because of the 2D ZnO nanocrystals exposed in (100) facets at high percentage. The performances of the acetone sensors can be further improved dramatically, after the surfaces of ZnO nanosheets are modified with Pd nanoparticles. Novel acetone sensors with enhanced response, selectivity and stability have been fabricated successfully by using nanoarchitectures consisting of ZnO nanosheets and Pd nanoparticles.

Highly enhanced acetone sensing performances of porous and single crystalline ZnO nanosheets: high percentage of exposed (100) facets working together with surface modification with Pd nanoparticles.

Co3O4 nanometer material for supercapacitor and preparation method thereof

The invention provides a method for solid phase reaction one-step preparation of a reduced graphene oxide/palladium composite nanometer electrocatalyst. The method comprises that a metal palladium salt, graphene oxide and a solid reducer as raw materials are subjected to grinding or ball milling so that the raw materials undergo a solid-state chemical reaction to produce the reduced graphene oxide/palladium composite nanometer electrocatalyst through one-step reduction. According to different reaction substances, a reaction temperature is a range of normal temperature to 300 DEG C and reaction time is in a range of 10 minutes to 2 weeks. The method is simple and controllable, utilizes cheap and easily available raw materials, realizes large-scale preparation under eco-friendly conditions and can be industrialized easily. The reduced graphene oxide/palladium composite nanometer electrocatalyst has good effects of electrocatalysis of methanol and ethanol electrochemical oxidation and has a wide application prospect in the field of fuel cell electrocatalysis.

Method for solid phase reaction one-step preparation of reduced graphene oxide/palladium composite nanometer electrocatalyst

The invention discloses a preparation method of a Pd-nanoparticle-modified porous ZnO nanosheet gas-sensitive material, which comprises the following steps: mixing and grinding porous monocrystalline ZnO nanosheets and Pd nanoparticles, wherein the weight of the Pd nanoparticles accounts for 0.3-0.8% of the total weight of the porous monocrystalline ZnO nanosheets and Pd nanoparticles; and calcining at 550-650 DEG C for 1-2 hours to obtain the Pd-nanoparticle-modified porous ZnO nanosheet gas-sensitive material. The Pd-nanoparticle-modified porous ZnO nanosheet gas-sensitive material has high sensitivity: the sensitivity for 100ppm acetone gas is up to 70, the sensitivity for 500ppm acetone gas is up to 222, and the sensitivity for 10ppm acetone gas is up to 8 or so. The operating temperature is low: the optimum temperature of the ZnO nanosheet composite material modified by the Pd nanoparticles is 340 DEG C, and is greatly lowered as compared with 420 DEG C of the single ZnO nanosheets. The selectivity is high: the gas sensor is less sensitive to some common organic solvents, such as ethanol, methanol, benzene, toluene and the like, than acetone.

Preparation method of Pd-nanoparticle-modified porous ZnO nanosheet gas-sensitive material and gas sensor

The invention discloses a preparation method for zinc oxide super crystalline materials. The preparation method comprises the following steps: zinc nitrate is used as a raw material and a mixture of normal butanol and water is used as a solvent, zinc nitrate and the mixture are put in a high pressure reactor at the temperature of 50-120 DEC to react for 1-20 hours, the zinc oxide super crystalline materials are directly obtained. The preparation method is characterized in that products don't need to be calcined, self-assembly zinc oxide super crystals with a high degree of crystallinity can be directly obtained, and in addition, the zinc oxide super crystalline materials are uniform in size; meanwhile, the structures of the zinc oxide super crystalline materials change with the different amount of the surfactant AOT added in the reacting system, so that fusiform, dumbbell-shaped, cauliflower-shaped, double-sphere-shaped super crystals and the like can be obtained. According to the invention, the preparation method is simple, efficient and easy to realize industrialization; platy double-sphere-shaped super crystalline materials show bipolar specific blue light emission phenomena due to the special surface structures of the platy double-sphere-shaped super crystalline materials, and the zinc oxide super materials are expected to be used for the design of novel optoelectronic devices.

Zhang Aiqin

Papers

Highly enhanced acetone sensing performances of porous and single crystalline ZnO nanosheets: high percentage of exposed (100) facets working together with surface modification with Pd nanoparticles.

Co3O4 nanometer material for supercapacitor and preparation method thereof

Method for solid phase reaction one-step preparation of reduced graphene oxide/palladium composite nanometer electrocatalyst

Preparation method of Pd-nanoparticle-modified porous ZnO nanosheet gas-sensitive material and gas sensor

Preparation method for zinc oxide super crystalline material