Enhanced Acetone Gas Sensing behavior of n-ZnO/p-NiO Nanostructures
G. Kavitha[1],*, K. Thanigai Arul2,#, P. Babu1
Supplementary Materials_JMSE-D-03238.doc
Introduction
Synthesis of precisely controlled nanostructures using simple low-cost method is an important topic of interest due to wide range of applications. In most of the chemical methods of nanofabrication, growth of nanostructure starts with the deposition or precipitation of a seed nanoparticle by agglomeration of atoms. As a result, size and shape of the nanostructure are primarily determined by such nucleation processes. Thermodynamically, the nanostructure grows in shape and size which minimizes the free energy and it grows in a direction by maximizing the energy release rate and thereby having maximum non-equilibrium force component in that particular direction. One important aspect that can affect the shape of the nanostructure is the reaction kinetics of the process. Nanostructures in the form of core-shell like nanotubes, nanorods, nanowires, nanocubes, nanosprings, nanodisks, and dendrites have been grown by researchers in the recent years. Spindle shaped nanostructures grow in an environment of medium reactant concentration which promotes an isotropic growth in three dimensions. Nanostructures in elongated shapes and rods are formed at higher reactant concentrations.
TCMOS like mixed metal-oxidenanostructuresformedbythecombination ofp-andn-typesemiconductorsplayaveryimportantrole fortheiruniquephysicalandchemicalpropertieswhicharecompletelydifferentfromtheirindividualmetaloxides. Then-typesemiconductorzincoxide(ZnO)havingawide directband-gap(3.37eV)andlargeexcitonbindingenergy (60meV),providespotentialapplicationsinvariousfields suchassensors,transparentcoatingforsolar-cells,light-emitting diodes,optoelectronic,laserdevices,piezoelectricdevices,catalysis,UVprotection,cosmetics,paintsandpharmaceuticals. Whilenano-structurednickeloxide(NiO),whichisap-typesemiconductorwithastablewideband gap(3.6–4.0 eV),gotextensiveuseindrugdelivery,battery cathodes,photoelectrodes,adsorbents,photocatalysts,electrochemicalcapacitors,electrochromicwindowsandmagnetic materials. Duetothebuild-upofaninnerelectric field atthep–n junction interfaces thenanocrystallineZnO–NiOmixed metaloxidehassuperiorfunctionalperformancesincomparisontotheconsequentsingle-phasemetaloxides. Itisalsofound that ZnOandNiOeasilyformp–n heterojunctionandcreateanelectricalbarrierbetweencrystal grainswhichshowgoodsensitivitytoH2S, acetone, and various chemical gas. In ZnO or NiO semiconductor fast recombination of photogenerated electron–hole pairs occur which is suppressed in ZnO–NiO mixed metal oxide by improving the efficiency of net charge transfer in the reaction process. Thus, it exhibits excellent photocatalytic activity for degradation of methyl orange and in sensing gas for detection of acetone. They are also used as more efficient photocatalysts for the hydrogen production under visible light. The physicochemical properties of the mixed metal oxide nano particles significantly depend on surface area, pore morphology, particle size, porematrix-interface, porosity and the synthetic methods used for their preparation.
Growth mechanism of NZO (p-NiO/n-ZnO) nanoparticles and sensor reaction between the synthesized core-shell nanoparticles
Fig. 1. Growth mechanism and sensor reaction between the synthesized core-shell nanoparticles
EDS Analysis
The EDS spectra of the hybrid materials. The required information has been given in the revised version as well as in this section. However, the elemental mapping for the nanocomposite will be taken near future, due to the lack of analytical instrument facilities we are unable to provide the information at this stage and the revised version.
Fig. 2 EDX analysis of hybrid nanostructures of NZO (p-NiO/n-ZnO)
Respectively, the constitutional elemental composition was identified Ni, Zn, O and the total compositions ~ 100% from the nanocomposites. Particle size of the NCs in the uniform nanocrystal shaped core-shell was approximately 95 nm. The morphology of nanocomposite was both hexagonal and spherical in nature. The inter planar distance (0.234 nm) of ZnO was confirmed from lattice fringe (Fig.2d). The corresponding FE-SEM surface morphology images and their compositional elemental EDX spectra were given supplementary materials. The observed HR-TEM surface morphological images particles crystalline sizes and the calculated X-ray diffraction pattern average particle crystallite sizes were almost similar for the core-shell hybrid nanostructures.
Sensor set-up
The present sensor study of hybrid nanostructures of NZO (p-NiO/n-ZnO) the dynamic response-recovery of sample ZnO/NiO-700 nanocomposite against the various concentration of acetone at 300 C, the sensor was responded linearly with the raise in concentration of acetone. After fresh air exposure, response quickly attained to initial value which indicates good reliability of the materials and reproducibility. Response and recovery time were the basic parameter of gas sensor. For 500 ppm, acetone of ZnO/NiO-700 showed response time around 13 s and recovery time 18 s (Fig. 3b). Sensitivity, selectivity and recovery time of the gas exhibit from the core-shell like crystalline structure of hybrid NZO nanocomposite (p-NiO/n-ZnO) TCMOs materials archived very quick response and short recovery time.
A typical view of sensor electric circuit
1
: *; #; ; (Prof. G. Kavitha)