We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

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Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

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High-performance gas sensors prepared using p-type oxide semiconductors such as NiO, CuO, Cr2O3, Co3O4, and Mn3O4 were reviewed. The ionized adsorption of oxygen on p-type oxide semiconductors leads to the formation of hole-accumulation layers (HALs), and conduction occurs mainly along the near-surface HAL. Thus, the chemoresistive variations of undoped p-type oxide semiconductors are lower than those induced at the electron-depletion layers of n-type oxide semiconductors. However, highly sensitive and selective p-type oxide-semiconductor-based gas sensors can be designed either by controlling the carrier concentration through aliovalent doping or by promoting the sensing reaction of a specific gas through doping/loading the sensor material with oxide or noble metal catalysts. The junction between p- and n-type oxide semiconductors fabricated with different contact configurations can provide new strategies for designing gas sensors. p-Type oxide semiconductors with distinctive surface reactivity and oxygen adsorption are also advantageous for enhancing gas selectivity, decreasing the humidity dependence of sensor signals to negligible levels, and improving recovery speed. Accordingly, p-type oxide semiconductors are excellent materials not only for fabricating highly sensitive and selective gas sensors but also valuable additives that provide new functionality in gas sensors, which will enable the development of high-performance gas sensors.

Highly sensitive and selective gas sensors using p-type oxide semiconductors: Overview

(1976). Nuclear Tracks in Solids (Principles and Applications) Nuclear Technology: Vol. 30, No. 1, pp. 91-92.

Nuclear Tracks in Solids (Principles and Applications)

Detection of hazardous volatile organic compounds (VOCs) by metal oxide nanostructures-based gas sensors: A review

Graphene/zinc oxide (ZnO) nanocomposite was prepared by in situ reduction of zinc acetate ((CH3COO)2Zn·2H2O) and graphene oxide (GO) during refluxing. For the structural, morphological and elemental analysis, the synthesized samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDX) and Fourier transform infrared spectroscopy (FTIR). Hydrogen sensing properties of synthesized graphene/ZnO nanocomposite have been reported in this paper. For gas sensing properties, thick films of synthesized nanocomposite powder were fabricated on alumina substrate. Sensing results revealed that sensor based on 1.2 wt% graphene/ZnO composite exhibits best sensing response towards 200 ppm of hydrogen gas at an optimum operable temperature of 150 °C among the prepared samples with varying concentrations. Inclusion of graphene into ZnO significantly reduced the optimum operable temperature and increased the sensing response of graphene/ZnO composite towards hydrogen gas. Reported results are based on the change in electrical conductivity of synthesized nanocomposites due to superior electronic conductivity of graphene and the interaction between p-type graphene and n-type zinc oxide.

Hydrogen sensor based on graphene/ZnO nanocomposite

A novel route for the synthesis of polyaniline nanofibers in the presence of varying amounts of zinc oxide has been reported in this paper. The homogeneous PANI nanofibers were prepared through template approach, in which the ZnO nanoparticles were used as template. Structural, optical and morphological analysis of synthesized nanofibers was carried out using X-ray diffraction, UV–vis, IR spectroscopy and FESEM techniques. The thick films of the synthesized polyaniline powder were deposited on alumina substrate and their sensing response to ammonia gas was investigated. Optimum sensing response was achieved with PANI nanofibers synthesized in the presence of 30 wt% ZnO powder. The sensing response of fabricated sensor was proportional to the ammonia gas concentration and exhibited excellent selectivity toward ammonia gas.

ZnO assisted polyaniline nanofibers and its application as ammonia gas sensor

Comparative study on gas sensing properties of rare earth (Tb, Dy and Er) doped ZnO sensor

In the present work, impact of Er3+ doping on the response and selectivity of SnO2 based gas sensor has been investigated in detail. X-ray diffraction (XRD) results confirmed formation of a tetragonal rutile structure of undoped and erbium doped SnO2 nanoparticles. It has been observed that specific surface area of nanoparticles has increased with increase in dopant concentration. The oxidation states and presence of erbium in SnO2 lattice has been confirmed by X-ray photoelectron spectroscopy (XPS). Photoluminescence (PL) analysis revealed that concentration of oxygen vacancies increases with increase in dopant incorporation. It has been observed that 3% Er-doped SnO2 sensor exhibited enhanced sensor response and temperature dependent selectivity towards ethanol and hydrogen at 240 and 360 ℃ respectively. The enhanced sensor response of the fabricated sensor has been ascribed to large surface area, enormous oxygen vacancies and elevated surface basicity of doped nanoparticles used. The tunable dual selectivity of 3% doped sensor towards ethanol and hydrogen makes it a perfect candidate for ethanol-hydrogen sensing for ethanol steam reforming systems combined to fuel cells.

Highly sensitive gas sensor based on Er-doped SnO2 nanostructures and its temperature dependent selectivity towards hydrogen and ethanol

A sensitive and selective acetone sensor based on Gd doped WO3/reduced graphene oxide, a novel nanocomposite, has been reported in this paper. To begin with, pure and Gd-doped (2, 4, 6 and 8 mol%) WO3 nanostructures exhibiting nanoplate type morphology were synthesized using a room temperature simple acid precipitation method without use of any template or surfactant. The gas sensing measurements were performed on pure and Gd doped WO3 nanostructures to select the optimum operating temperature and dopant concentration. The sensor with optimized doping of 6 mol% Gd has been found to be quite selective to acetone and ethanol vapours while operating at optimum temperature of 350 °C. Further improvement in sensitivity, selectivity and lowering of operable temperature has been achieved by incorporation of reduced graphene oxide (RGO) into 6 mol% Gd doped WO3 nanostructures. The novel material thus developed has exhibited significant improvement in sensing response and became selective to acetone at markedly reduced optimum operable temperature to 200 °C. The achieved sensor characteristics could be attributed to change in electrical conductivity of RGO based nanocomposite due to superior electronic conductivity of RGO sheets and the interaction between n-type WO3 and p-type RGO.

Ravi Chand Singh

Papers

Hydrogen sensor based on graphene/ZnO nanocomposite

ZnO assisted polyaniline nanofibers and its application as ammonia gas sensor

Comparative study on gas sensing properties of rare earth (Tb, Dy and Er) doped ZnO sensor

Highly sensitive gas sensor based on Er-doped SnO2 nanostructures and its temperature dependent selectivity towards hydrogen and ethanol

Sensitive and selective acetone sensor based on Gd doped WO3/reduced graphene oxide nanocomposite