INTRODUCTION:

Metal Oxides:

Metal oxides play a very important role in many areas of chemistry, physical and materials science [1-8]. Metal oxides are formed as a consequence of co-ordination tendency of metal ions so that oxide ions form co-ordination sphere around metal ions and give rise to close packed structure. The different physical, magnetic, optical and chemical properties of metal oxides are of great interest to chemists because these are extremely sensitive to change in composition and structure. Different metal/mixed metal oxides have been synthesized and further studied for their applications in diverse field [9-26] Extensive studies of this relationship leads to a better understanding of the chemical bond in crystal. The metal oxides are attracting special attention of scientists due to their easy mode of formation and multifunctional behavior. The transition metals and their compounds are used as catalysts is chemical industry and in battery industries. Besides, these compounds can be used in formation of interstitial compounds and alloy formation.

The transition metals have the special properties of formation of coloured compounds and show magnetic properties. Metals of d-block elements are used for many industrial applications. They behave as catalysts, super conducting materials, sensors, ceramics, phosphors, crystalline lasers etc. Besides these they are excellent photoactive materials and work as photosensitizer. Mixed metal oxide (MMO) electrodes are devices with useful properties for chemical electrolysis. Metal/Mixed metal oxides have wide applications as catalyst because of their high surface area and reactive sites. Number of scientists and academicians are using metal/mixed metal oxides as catalyst in various organic reactions.

Sensors:
Metal / Mixed metal oxides have wide application as sensors some of them have been described here. Suri et al. [27] synthesized gas and humidity sensors based on iron oxide polypyrole nanocomposites Iron – oxide sensor nanocomposites of iron oxide and polypyrrole were prepared by simultaneous gelation and polymerization process. The composites in the pellet from were used for humidity and gas sensing investigations. Gas sensing was performed for CO₂ N₂ and CH₄ gases at varying pressures. The sensors showed a linear relationship between sensitivity and pressures for all the gases studied. The sensors showed highest sensitivity to CO₂ gas. Tongpool et al. [28] synthesized sol gel processed iron oxide silica nanocomposite films as room temperature humidity sensors. Iron oxide- silica nanocomposite films have been fabricated using sol-gel process and spin coating technique. Iron oxide and silica were segregated. As Si content in the films increase, the films were more compact. The iron oxide films calcined at 400⁰C were hematite but in the presence of silica, iron oxide is composed of hematite and magnetite. Neri et al. [29] studied role of the Au oxidation state in the Co sensing mechanism of Au/iron oxide based gas sensors. A study on the CO sensing mechanism of sensors based on Au-doped/ iron oxide thick films is reported. Thick films were prepared from coprecipitated powders of Au/Fe₂O₃ calcined at temperatures between 100 and 400⁰C.A detailed micro structural characterization by XRD, TEM and XPS has shown that nanometer sized gold particles with gold in a positive oxidation state are predominant after calcination of the powders at 100⁰C. The anomalous response observed over the film annealed at the lowest temperature has been related to the participation of Au (III) ions in the CO sensing mechanism. Sanchez et al. [30] studied novel optical NO₂- Selective sensor based on Phthalocyaninato – iron (H) incorporated into a nanostructured matrix.A novel highly optical NO₂-selective complexing agent. In order to solubilize the iron phthalocyanine and to obtain the monomer species, a N-donor ligand was used as a solvent. The effect of the type and concentration of the N-donor ligand, and the influence of the iron phthalocyanine concentration were investigated as well as the effect of the composition and the morphological characteristics of the nanostructured material. P.Althainz et al. [31] The influence of the response of iron oxide gas sensors. Microgranular layers of iron oxide have been prepared by the deposition of dried aerosol droplets of iron oxalate and subsequent decomposition to investigate the gas sensing properties of this special morphology. For comparison, compact iron-oxide films have been prepared by sputtering of iron and successive oxidation. Several different granular gas detectors have been produced consisting of spherical particles with sizes between 0.2 and 1.2 mm in narrow size distributions. The compact films exhibit a pronounced sensitivity increase with molecular weight of the vapour. In contrast, the granular layers detect all gases with similar sensitivities and react faster than the compact layers. Neri et al. [32] studied of wake influence in co response on gold – doped iron oxide sensors. A temperature programmed desorption (TPD) study of the water and CO- interaction with the surface of gold doped iron oxide sensors is presented. TPD data has shown that CO does not adsorb in the absence of water. The adsorption of CO occurs when water is present as coadsorbate, through the formation of a surface formate intermediate. TP reaction of CO with oxygen in both dry and wet air has shown that water also promotes CO oxidation, likely via the same formate intermediate. The effect of water on the CO sensing of Au/Fe₂O₃ sensors was also investment. Chakraborty et al. [33] selective detection of methane and butane by temperature modulation in iron doped tin oxide sensors. In the present study it is possible to develop sensors based on iron doped tin dioxide, which can detect both methane and butane (present in CNG and LPG, respectively) at a temperature at 350⁰C. However, the same sensors can selectively detect butane at a temperature of 425⁰C. The incorporation of palladium as a catalyst in Fe-doped SnO₂ sensors removes the typical selectivity, and the temperature of the maximum response coincide for methane and butane. Neri et al. [34] studied humidity sensing properties of Li-iron oxide based thin films. Li-doped iron oxide thin films deposited on a porous ceramic substrate by a liquid-phase method (LPD) were investigated as humidity sensors. Large variations in the resistance, up to about 4-5 order of magnitude, were observed by changing the relative humidity (RH) between 10 and 90%. The role of Li on the response to water vapour of iron oxide thin films is discussed. Retting et al. [35] studied a-Iron oxide an intrinsically semiconducting oxide material for direct thermoelectric oxygen sensors. Intrinsically semiconducting oxide materials offer the possibility for highly sensitive direct thermoelectric gas sensors. Intrinsic a-Fe₂O₃ has been chosen as a well suited candidate for direct thermoelectric gas sensors. The used temperature modulation technique combined with a regression analysis allowed a determination of the measured thermopower within 6.4 s and the possibility for self-diagonstics. These presented results shows a possible realization of fast, accurate, highly sensitive direct thermoelectric gas sensors. Comini et al. [36] studied influence of Iron addition on ethanol and CO sensing properties of tin oxide prepared with the RGTO technique. Effects of iron introduction in RGTO prepared tin oxide gas sensors are presented. The films were deposited by sputtering from a tin target with the introduction of an adjustable number or iron inset. Iron content was varied in the range 0-7%. The thin films are investigated by the volt-amperometric technique for electrical and gas-sensing properties. The response of the sensors is stable and reproducible at all operating temperatures tested (200-500⁰C) during 3 months of operation. Cantalini et al. [37] worked on niobium – doped aFe₂O₃ semiconductor ceramics sensors for the measurement of nitric oxide gases. The NO, NO₂ and NOx gas-sensitivity properties of Nb-doped α-Fe₂O₃ sintered compacts have been studied in the 0–100 ppm gas concentration and 150–300 °C temperature ranges, by d.c. and a.c. techniques. Sensors have been prepared by suspending a 130 m² g⁻¹ α-Fe₂O₃ powder in a standard Nb solution in order to yield Nb/Fe atomic percentages between 0.5 and 20 at.%. Sintering has been performed at 800 °C for 2 h. The 20% doped material shows a gas sensitivity (S), defined as R_G/R_A, where R_A and R_G are the electrical resistances in air and in the sample gas, respectively, as high as 36 at 100 ppm NO₂ and 200 °C working temperature. An electrical equivalent circuit including a constant phase element (CPE), which can simulate the electrical response of the sensor in the 0–100 ppm NO₂ gas concentration range, is also presented. Baratto et al. [38] studied iron doped indium oxide by modified RGTO deposition for ozone sensing nanostructured thin films based on indium oxide have been prepared by a modified rheotaxial growth and thermal oxidation (RGTO) deposition technique. The layers were additivated with 8–30% iron in order to stabilize the microstructure and to enhance the sensing properties toward ozone. The electrical test of the sensing layers indicated high sensitivity to ozone together with a relatively low cross-sensitivity to interfering gases. Belle et al. [39] studied the size dependent gas sensing properties of Spinel iron oxide nanoparticles. Spinel iron oxide nanoparticles of sizes from 12 to 60nm have been prepared via a hydrothermal synthesizes. The electrical and gas sensing properties were characterized by impedance spectroscopy using multielectrode substrates. The materials exhibit good sensor responses towards NH₃ with low cross sensitivities towards H₂and NO at 250⁰C. A linearly increasing sensor response towards NH₃ and H₂ with decreasing particle size was found. Tesfamichael et al. [40] worked on thin film deposition and characterization of pure and iron doped electron beam evaporated tungsten oxide gas sensors. Pure tungsten oxide (WO₃) and iron-doped (10 at.%) tungsten oxide (WO₃:Fe) nanostructured thin films were prepared using a dual crucible electron beam evaporation (EBE) technique. The films were deposited at room temperature under high vacuum onto glass as well as alumina substrates and post-heat treated at 300 °C for 1 h. The heat treated films were investigated for gas sensing applications using noise spectroscopy. It was found that doping of Fe to WO₃ produced gas selectivity but reduced gas sensitivity as compared to the WO₃ sensor. Wang et al. [41].Synthesized iron-doped vanadium tin oxide nanocrystallites for CO gas sensing Iron-doped vanadium–tin oxide nanoparticles have been synthesized by a hydrolysis and co-precipitation method from iron(II) acetate, vanadium(III) acetylacetonate and tin tetrachloride. Based on sensitivity measurements in a semiconductor CO gas sensor, the iron doping resulted in a shift of the maximum sensitivity toward the lower temperature side. A correlation between the surface state and sensor performance is proposed. Brezoi et al. [42] studied phase evolution included by polypyrrole in iron oxide- polypyrrole nanocomposite. Nanocomposite of polypyrrole and iron oxide were prepared using simultaneous gelation and polymerization processes. Varied amounts of pyrrole were added to a solution containing in Fe (III) salt as precursor and 2-metoxy ethanol as solvent. The properties of nano composities formed by combining conducting polymers and oxides nano particles are strongly dependent on concentration of polymer and have brought out more fields of applications such as smart windows, toners in photocopying, conductive paints, drug delivery, recharge able batteries. These nanocomposites were used for humidity and gas sensors. Biswal et al. [43] studied pure and Pt-loaded gamma iron oxide as sensor for detection of sub ppm level of acetone. In this study, pure and Pt-loaded nanocrystalline γ-Fe₂O₃ have been prepared by precipitation using ultrasonic irradiation. The synthesized powders were characterized by X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), differential thermal analysis (DTA), transmission electron micrograph (TEM), selected area electron diffraction (SAED), scanning electron microscope (SEM) and energy dispersive X-ray (EDX). Gunjakar et al. [44] studied chemical deposition of nano crystalline nickel oxide from urea containing bath and its use in liquefied petroleum gas sensor. Nanocrystalline nickel oxide (NiO) was deposited onto glass substrates using a chemical deposition method from a bath containing nickel (Ni²⁺) ions and urea at 363 K. The chemically deposited nickel oxide films were effectively used as a liquefied petroleum gas (LPG) sensor and the maximum response of 36.5% was recorded on exposure to 0.3 vol% of LPG at 698. Banno et al. [45] worked on selective nitrogen dioxide sensor based on nickel copper oxide mixed with rare earths scandium – doped nickel copper oxide bulk, which consists of Ni_0.8Cu_0.2O, CuO, Sc₂O₃, and Sc₂Cu₂O₅, responds only to NO₂(50 – 500 ppm) among NOx gases. Thin films of the oxide are prepared by a magnetron sputtering method, and their NOx- sensing characteristics are studied. The disappearance of crystalline Sc₂Cu₂O₅ in the film might affect the sensing performance for NOx. Hotovy et al. [46] studied on preparation of nickel oxide thin films for gas sensors applications. Nickel oxide (NiO) thin films were prepared by dc reactive magnetron sputtering from a nickel metal target in an ArO₂ mixed atmosphere in two sputtering modes. The oxygen content in the gas mixture varied from 15% to 45%. The films prepared in the oxide-sputtering mode were amorphous while the films in metal-sputtering mode exhibited polycrystalline (fcc) NiO phase, found that good NiO stoichiometric films are obtainable with a polycrystalline (fee) structure at 40% oxygen content in the metal-sputtering mode. Jan Hrfac et al. [47] Nitric oxide sensor based on carbon fiber covered with nickel porphyrin layer deposited using optimized electro polymerization procedure. Electropolymerization regime of meso-tetrakis (3-methoxy-4-hydroxyphenyl) porphyrin is optimized to yield films possessing both electrocatalytical and permselective properties towards nitric oxide oxidation. The sensor composed of electrochemically oxideized carbon fiber, covered solely with nickel porphyrin derivative layer electropolymerized. Nafion coating can further enhance selectivity propeteis as well as aids to the stability of the sensors responses.Fei, Cao, et al. [48] Highly sensitive non enzymatic glucose sensor, based on electrosum copper oxide doped nickel oxide composite micro fibers. An improved non enzymatic glucose sensor based on copper oxide-doped nickel oxide composite microfibers (CuO-NiO-MFs) modified flurone tin oxide (FTO) electrode was prepared by electrospinning and calcination technologies without using any immobilization. Its application for detecting glucose concentration of human serum sample showed good agreement with the results obtained from automatic biochemical analyzer.Cao et al. [49] studied nickel oxide micro fibers immobilized onto electrode by electrospining and calcination for non enzymatic glucose sensor and effect of calcinations temperature on the performance. Nickel oxide microfibers (NiO-MFs) were directly immobilized into the surface of fluorine tin oxide (FTO) electrode by electrospinning and calcinations without using any immobilization matrix for nonenzymatic glucose sensor which is among the best values reported in literature. Additionally, excellent selectivity and stability have also been obtained. Pontie et al. [50] Improvement in the performance of a nickel complex – based electro chemically sensor for the detection of nitric oxide in solution.The electroformation of the tetrasulfonated nickel phthaolocyanine (NiTSPc) film in alkaline solution onto carbon fiber microelectrode is investigated in order to improve the electrochemical detection of nitric oxide (NO) in solution. The phthalocyanine film formed by cyclic voltammetry gives a modified microelectrode with a good sensitivity to NO, higher than the obtained one with nickel phthalocyanine and/or prophyrin deposited by controlled potential electrolysis. Bedioui et al. [51] Elaboration and use of nickel planar macrocyclic complex based sensors for the direct electrochemical measurement of nitric oxide in biological media. We described here the electrochemical detection of nitric oxide, NO, in biological systems by using chemically modified ultramicro carbon electrodes. In the first part of the paper, the different steps involved in the electrochemical preparation and characterization of the nickel – based sensor are described. Cao et al. [52]. Highly sensitive nonenzymatic glucose sensor based on electrospun copper oxide doped nickel oxide composite microfibers. An improved nonenzymatic glucose sensor based on copper oxide- doped nickel oxide composite microfibers (CuO-NiO-MFs) modified fluorine tin oxide (FTO) electrode was prepared by electrospinning and calcination technologies without using any immobilization. The nonenzymatic glucose sensors that have been reported in the literature. Additionally, its application for detecting glucose concentration of human serum sample showed good agreement with the results obtained from automatic biochemical analyzer. Ho et al. [53] Chemiresistor type No gas sensor based on nickel phthalocyanine thin films .The sensing characteristics of nickel phthalocyanine (NiPc) thin films for use in a chemiresistor type nitric oxide gas sensor are discussed. The gas- sensing properties, including current transient, sensitivity, response time, and aging, are studied. A kinetic model proposed in the literature for sensing NO₂ with lead phthalocyanine (PbPc) thin films, in which adsorption involves displacement of surface adsorbed O₂ from a range of heterogeneous sites, can be used to explain our experimental results. For a lower concentration range, between 5 and 50 ppm NO, the sensitivity lies between 0.41 and 0.42, while for a higher concentration range, between 50 and 500 ppm, the sensitivity decreases to about 0.17 to 0.19.C.V. Reddy et al. [54] studied semiconducting gas sensor for chlorine based on inverse spinel nickel ferrite. Nickle ferrite, a p-type semi conducting oxide with an inverse spinel structure has been used as a gas sensor to selectively detect chlorine in air. This compound was prepared by two different routes namely, the citrate and co-precipitation method and sensor properties of the resulting compounds from both the methods were compared. X-ray diffraction was used to confirm the structure. The sensitivity to chlorine has been compared with that of other inferring gases. A probable explanation has been proposed to explain the selective sensitivity to oxidizing gases like chlorine. Noh et al. [55] studied electrical properties of nickel oxide thin films for flow sensor application In this work, NiO thin films, with thermal sensitivity superior to Pt and Ni thin films, were formed thorough annealing of Ni films deposited by a r.f. magnetron sputtering. The annealing was carried out in the temperature range of 300-500⁰C under atmospheric condition because of their high resistively and very linear TCR, Ni oxide thin films are superior to pure NI and Pt thin films for flow and temperature sensor applications. Salini et al. [56] studied highly sensitive sensor for picomolar detection of insulin at physiological psH, using GC electrode modified with guanine and electro deposited nickel oxide nano particles. The electro chemical behavior of insulin at glassy carbon (GC) electrode. The modified electrode was applied for insulin detection using cyclic voltammetry of hydrodynamic amperometry techniques. It is promising for for the monitoring of insulin in chromatographic effluents. Mu et al. [57] studied nano nickel Oxide modified non – enzymatic glucose sensors with enhanced sensitivity through an electro chemical process strategy at high potential. Development of fast and sensitive sensors for glucose determination is important in food industry, clinic diagnostics, biotechnology and many other areas. in these years, considerable attention has been paid to develop non-enzymatic electrodes to solve the disadvantages of the enzyme modified electrodes, such as instability, high cost, complicated immobilization procedure and critical operating situation et.al. The non-enzymatic sensors response quickly to glucose and the response time is less than 5’s, demonstrating excellent electroatlytical activity and assay performance the proposed non-enzymatic sensors can be used for the assay of glucose in real sample.Scandium – doped nickel copper oxide bulk, which consists of Ni_0.8Cu_o.2O, CuO, Sc₂O₃, and Sc₂C_u2O₅, responds only to NO₂ (50-500ppm) among NOx gases. Thin films of the oxide are prepared by an r.f. magnetron sputtering method, and their NOx- sensing characteristics are studied. The disappearance of crystalline Sc₂Cu₂O₅ in the film might affect the sensing performance for NOx. D. Barreca et al. [58] worked on supported copper oxide nano systems synthesized by chemical vapor deposition (CVD) on Al₂O₃ substrates and characterized by means of glancing incidence X-ray diffraction (GIXRD), secondary ion mass spectrometry (SIMS) and field emission scanning electron microscopy (FESEM). The obtained results revealed good responses even at moderate operating temperatures, with characteristics directly dependent on the system composition and nano – organization. Yang et al. [59] worked on copper oxide nano particles sensors for hydrogen cyanide detection.Uprecedented selectivity and sensitivity. CuO nano particles were synthesized in a facile way, and characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photo electron spectroscopy, and thermo gravimetry. Using these CuO nano particles, CuO functionalized QCM resonators were fabricated and explored for HCN sensing. The current results would provide an exciting alternative to fast, sensitive and selective detection of trace HCN, which would be of particular benefit in the area of public security and environmental application. Wei et al. [60] a novel hydrogen sulfide room temperature sensor based on copper nanoluster functionalized tin oxide thin films. A novel room temperature solid state senor for the detection of hydrogen sulfide is described. The sensor was fabricated by first depositing a thin film of tin oxide on to a glass substrate followed by surface functionalizing with monolayer protected copper nano clusters (MPCs) capped with different capping agents prepared as per the brust synthesis. The response time for all the samples is smaller than 2 min. Wang et al. [61] studied low temperature H₂O sensor based on copper oxide/ tin dioxide thick film. nano structured tin dioxide (SnO₂) powders were prepared by a sol-gel dialytic process and the doping of CuO on it was completed by a deposition precipitation method. The thick film sensors were fabricated from the CuO/ SnO₂ polycrystalline powders. Sensing behavior of the sensor was investigated with various gases including CO, H₂, NH₃ hexane, acetone, ethanol, methanol and H₂S in air. It might have promising applications in the future.Saumya et al. [62] studied flectropun pallodium (IV) doped copper oxide composite Nanofibers for non emetic glucose sensor. Pd (IV) doped CO oxide composite nanofibers (PCNFs) have been successfully fabricated via electrospinning and then employed to construct an amperometric non-enzymatic glucose sensor. These results indicate that PCNFs are promising candidates for amperometric non enzymatic glucose detection. Tudorache et al. [63] prepared humidity sensor applicative material based on copper-zinc-tungsten spinel ferrite the effect of partially substitution of iron with tungsten on the properties of copper-zinc spinel ferrite for humidity sensors application was presented. The electric properties of the Cu_0.5Zn_0.5W_0.3Fe_1.7O₄ spinel ferrites heat-treated at different temperatures and humidity conditions were characterized and analyzed. As an application of the material the characteristics of a resistive and capacitive humidity sensors were analyzed using Cu_0.5Zn _0.50.3Fe_1.7O₄ ferrite as active material. Mukherjee et al. [64] Synthesised and studied process induced improvement on the gas sensing characteristics of nano-crystalline magnesium zinc ferrite particles. The gas sensing performances of the ferrite based sensors can be improved by modifying their surfaces to volume ratio, grain size, morphology and meso-porous nature. Synthesis of phase pure ferrites with desired micro-structural features at lower calcinations temperature remains a challenging task. In order to improve their gas sensing performance, they have investigated the (synthesis) process induced modifications of the phase and micro-structural features of wet chemical synthesized ferrite sensing elements. These structural and micro-structural features are found to have significant influence on the gas sensing performances of Mg_0.5Zn_0.5Fe₂O₄ particles prepared using two different wet chemical routes. Mukherjee et al. [65] studied promising methane-sensing characteristics of hydrothermal synthesized magnesium zinc ferrite hollow sphere. The promising methane-sensing characteristics (i.e. per cent response, response and recovery time) identified for Mg _0.5Zn_0.5F₂O₄ hollow sphere-based sensing elements are attractive for developing chemoresistive-type non-conventional complex oxide-based combustible gas sensors.Mukherjee et al. [66] studied Reducing gas sensing behavior of nano-crystalline magnesium–zinc ferrite powders as an effective alternative of simple binary oxides, cubic spinel oxides are considered to be attractive to make sensitive and stable gas sensor, selective to a specific gas and on the investigation of the gas sensing characteristics of cubic spinel based nano-crystalline magnesium zinc ferrite powders. The conductance transients during response and recovery processes have been modeled using Langmuir adsorption isotherm and activation energies for gas adsorption and desorption processes have been estimated from the respective thermally activated kinetic processes. Sutka et al. [67] studied on gas sensing properties of Zn-doped p-type nickel ferrite. For characterization of gas sensor material, synthesized by sol–gel auto combustion method, X-ray diffraction (XRD), scanning electron microscopy (SEM), DC resistance and impedance spectroscopy (IS) measurements were employed. The response change of Zn doped nickel ferrite is related to the interruption of hole hopping between nickel ions. This was improved by change of conductivity type with temperature and gas exposure. Rezlescu et al. [68] studied semiconducting gas sensor for acetone based on the fine grained nickel ferrite .The sensitivity to some reducing gases (acetone, ethanol, methane and liquefied petroleum gas—LPG) of calcia doped nickel ferrite (NiFe₂O₄ + 1%CaO) and cobalt and manganese doped nickel ferrite, Ni _0.99Co_0.01MnxFe ₂−xO _4−δ (x = 0.01 and 0.02), was investigated. The samples were prepared by self combustion method. The gas sensitivity largely depends on the composition, temperature and the test gas species. The ferrite compounds doped with Co and Mn are selective to detect reducing gases at low operating temperature. The mixed ferrite with Ni_0.99Co_0.01Mn_0.02Fe _1.98O_4−δ composition is sensitive and selective to acetone gas. Reddy et al. [69] studied on semiconducting gas sensor for chlorine based on inverse spinel nickel ferrite is a p-type semiconducting oxide with an inverse spinel structure has been used as a gas sensor to selectively detect chlorine in air. The sensitivity to chlorine has been compared with that of other interfering gases. A probable explanation has been proposed to explain the selective sensitivity to oxidising gases like chlorine. Darshane et al. [70] studied on nanostructured nickel ferrite a liquid petroleum gas sensor. The present investigation deal with the synthesis of nanostructured nickel ferrite (NiFe₂O₄) and their liquid petroleum gas-sensing characteristics. The results suggest possibility of utilization of the nanostructured nickel ferrite, without addition of any precious metal ion, as the LPG detector. Galindo et al. [71] studied catalytic properties of nickel ferrites for oxidation of glucose, β-nicotiamide adenine dinucleotide (NADH) and nickel ferrite nanoparticles (NiFe₂O₄) were synthesized by electrochemical method and used as catalyst for direct oxidation of glucose, NADH and methanol. Characterization of these nanoparticles was carried out by X-ray diffraction, Mössbauer spectroscopy, and colloidal properties such as hydrodynamic radius and Zeta potential. Lokhande et al. [72] worked on magnetic studies on one-step chemically synthesized nickel ferrite thin films. Nickel ferrite thin films were synthesized at room temperature using one-step electrodeposition solution processing. Reaction kinetics was also proposed. An effect of air baking on the structural, surface morphological and magnetic properties was investigated. Petrila [73] studied on humidity sensor applicative material based on copper-zinc-tungsten spinel ferrite .The effect of partially substitution of iron with tungsten on the properties of copper-zinc spinel ferrite for humidity sensors application was presented.The electric properties of the Cu_0.5Zn_0.5W_0.3Fe_1.7O₄ spinel ferrites heat-treated at different temperatures and humidity conditions were characterized and analyzed. As an application of the material the characteristics of a resistive and capacitive humidity sensors were analyzed using Cu_0.5Zn_0.5W_0.3Fe_1.7O₄ferrite as active material. Singh et al. [74] worked on synthesis of nanorods and mixed shaped copper ferrite and their applications as liquefied petroleum gas sensor .The preparation and characterization of nanorods and mixed shaped (nanospheres/nanocubes) copper ferrite for liquefied petroleum gas (LPG) sensing at room temperature. The structural, surface morphological, optical, electrical as well as LPG sensing properties of the copper ferrite were investigated. Single phase spinel structure of the CuFe₂O₄ was confirmed by XRD data. The role of PEG in the synthesis for obtaining nanospheres/ nanocubes has also been demonstrated. Khandekar et al. [75] worked on liquefied petroleum gas sensing performance of cerium doped copper ferrite. The gas sensing properties of sintered samples were studied towards different reducing gases such as liquefied petroleum gas (LPG), acetone, ethanol and ammonia. The sample with 4% cerium doped CuFe₂O₄(Ce₄) showed the maximum gas sensitivity (86%) towards LPG with fast response time of 5 s and good recovery time of 68 s. Singh et al.[76] Investigated the effects of surface morphologies on response of LPG sensor based on nanostructured copper ferrite system. Gas sensing properties shows the spinel CuFe₂O₄synthesized in 1:1 molar ratio exhibit best response to LPG adsorption/resistance measurement. Thus resistance based LPG sensor is found robust, cheap and may be applied for kitchens and industrial applications. WO₃ based NPs have been used as gas sensors by . WO₃ layers with controllable porosity and nanostructure were successfully deposited on commercial sensor platforms, and basic measurements to characterize their performance as gas sensors gave promising results.

ZnO nanofibers were facilely deposited on indium tin oxide (ITO) substrate by a simple electrodeposition method. The nature and morphology of the ZnO nanofibers were characterized with X-ray diffraction (XRD) and scanning electron microscopy (SEM). Bt exploring the electrochemical characteristics of ZnO nanofibers, it was found out that ZnO nanofibers modified ITO (ZnO/ITO) exhibited great catalytic capability for the oxidation of hydrazine and nitrite by enhancing their oxidation currents and lowering their overpotentials. For ZnO/ITO, the linear calibration plots for hydrazine and NO ^– ₂ were obtained over the range of 1∼1000 μM and 3∼300 μM with detection limits of 0.1 μM and 0.7 μM, respectively. In addition, satisfactory results were obtained by applying ZnO/ITO in the determination of hydrazine and NO^– ₂ in real samples with standard addition method.

REFERENCES:

1. C. Noguera, Physics and Chemistry at Oxide Surfaces; Cambridge University Press: Cambridge, U.K, 1996.

2. V. S. Jaswal, A. K. Arora, Integrated Research Advances’, 3(1) 21-22, 2016

3. H.H. Kung, Transition Metal, Oxides: Surfaces Chemistry and Catalysis; Elsevier; Amsterdam, 1989

4. V.E. Henrich, P.A.Cox, The Surface Chemistry of Metal Oxides, Cambridge University Press; Cambridge UK, 1994

5. A.F. Wells, Structural Inorganic Chemistry 6^th ed; Oxford University Press; New York, 1987.

6. A. K. Arora, V.S. Jaswal, K. Singh, R. Singh,” Int. J. Chem. Sci.: 14(4), 2016, 3215-3227.

7. J.A. Rodriguez, M.G. Fernandez, Synthesis, Properties and Applications of Oxide Nanoparticles Whiley : New Jersey 2007

8. M.G. Fernandez, A.A. Martinzes, J.C. Hanson, J.A. Rodriguez, Chem. Rev. 104 (2004) 4063.

9. A. K. Arora , Ritu, S. Devi, Current trends in biotechnology and chemical research. Vol 2, (1) 52 -56, 2012.

10. Q. Chen, C.D. Hills, M. Yuan, H. Liv and M. Tyrer, Journal of Hazardous Materials, 153 (2008) 775-783

11. J.M. Sun, X.H. Zhao and J.C. Huang, Chemosphere, 58 (2005) 1003-1010.

12. A. K. Arora, Ritu, P. Kumar, Asian Journal of chemistry_,vol 25, no13 (2013)7283-7386.

13. W. Turbeville and N. Yap, Catalysis Today, 116 (2006) 519-52.

14. A. K. Arora and Ritu, Int. J. Chem. Sci.: 11(3), 2013, 1335-1341.

15. M.E Mahmoud, M.M. Osman, O.S. Hafez, A.H. Hegazi and E. Elmelegy, Desalination, 251 (2010) 123-130.

16. A. K. Arora and Ritu, Int. J. Chem. 11(3) ( 2013) 1342-1352.

17. A. K. Arora and Ritu, Int. J. Chem. Sci.: 11(3),( 2013) 1353-1362.

18. A. K. Arora and Ritu, Res. J. Chem. Sci., Vol. 3(8), August (2013) 18-28

19. A. K. Arora, M. Sharma, V. S. Jaswal, P. Kumar, Journal of Nanotechnology, 2014, Article ID 474909, 7 pages.

20. V. S. Jaswal, A. K. Arora J. Singh, M. Kinger, V. D. Gupta, Oriental Journal of Chemistry, 30(2),(2014) 559-566.

21. A. K. Arora, S. Devi, V. S. Jaswal, J. Singh, M. Kinger, V. D. Gupta, Oriental Journal of Chemistry, 30(04) (2014)1671-1679.

22. A. K. Arora and Kamaluddin, Colloid and surfaces A: Physicochemical and Engineering Aspects 298(3) (2007) 186-191.

23. A. K. Arora, V. Tomar, Aarti, K.T. Venkateswararao and Kamaluddin, International Journal of Astrobiology 6(4) (2007) 267 – 271.

24. A. K. Arora and Kamaluddin, Astrobiology, 9(2) (2009)165-171.

25. A. K. Arora and Kamaluddin, adsorption science and technology, vol 29 (1), 2011).39-46..

26. A.K. Arora, V.S. Jaswal, K. Singh, R. Singh. Oriental Journal of Chemistry, 30(04) (2016) 1671-1679

27. K. Suri, S. Annapoorni, A.K. Sarkar and R.P. Tandon, Sensors and Actuators B: Chemical, 81 (2002) 277-282

28. R. Tongpool and S. Jindasuwan, Sensors and Actuators B: Chemical, 106(2005) 523-528

29. G. Neri, A. Bonavita, C. Milone and S. Galvagno, Sensors and Actuators B: Chemical, 93 (2003) 402-408

30. J.F.F. Sanchez, T. Nezel, R. Steiger and U.E.S. Keller, Sensors and Actuators B: Chemical, 113 (2006) 630-638

31. P. Althainz; L. Schuy, J. Goschick and H.J. Ache, Sensors and Actuators B: Chemical, 25(1995) 448-450

32. G. Neri, A Bonavita, G. Rizzo, S. Galvagno, N. Donato and L.S. Caputi, Sensors and Actuators B: Clinical 101 (2004) 90-96

33. S. Chakraborty, A. Sen and H.S. Maiti, Sensors and Actuators B: Chemical, 115 (2006) 610-613

34. G. Neri,A. Bonavita, S. Galvagno, C. Pall, S. Patane and A. Arena, Sensors and ActuatorsB: Chemical 73 (2001) 89-94

35. F. Retting and R. Moos, Sensors andActuators B: Chemical, 145 (2010) 685-690

36. E. Comini, A. Vomiero, G. Faglia, G.D. Mea and G. Sberveglieri, Sensors and Actuators B: Chemical, 115 (2006) 561-566

37. C. Cantalini, H.T. Sun, M. Faccio, G. Ferri and M. Pelino, Sensors and Actuators: B:Chemical, 25 (1995) 673-677

38. C. Baratto, M. Ferroni, G. Fagliaant G. Sberveglieri Sensors and Actuators B: Chemical, 118 (2006) 221-225

39. C.J. Belle, A. Bonamin, U. Simon, J.S. Salazar, M. Pauly, S.B. Colin and G. Pourroy ,Sensors and Actuators B:Chemical 160 (2011) 942-950

40. T. Tesfamichael, M. Arita, T Bostromand J. Bell, Thin Solid Films, 518(2010) 4791-4797

41. C.T. Wang,D. L. Lai and M.T. Chen, Materials Letters, 64, 1 (2010) 65-67

42. D.V. Brezoi and R.M. Ion, Sensors and Actuators B: Chemical, 109, 1 (2005) 171-175

43. R.C. Biswal, Sensors and Actuators B: Chemical, 157 (2011) 183-188

44. J.L. Gunjakar, A.M. More and C.D. Lokhande, Sensors and Actuators B:Chemical, 131 (2008) 356-361

45. S. Banno, N. Imanaka and G. Adachi, Sensors and Actuators B: Chemical, 25 (1995) 619-622

46. I. Hotovy, J. Huran, L. Spiess, S. Hascik and V. Rehacek, Sensors and Actuators B: Chemical, 57 (1999) 147-152

47. J. Hrbac, C. Gregor, M. Machova, J. Kralova, T. Bystron, M. Ciz, and A. Lojek, Bioelectro Chemistry, 71 (2007) 46-53

48. F.Cao,S. Guo, H.MA, G.Yang, S. Yang and J. Gong, Talanta, 86 (2011) 214-220

49. F. Cao, S. Guo, H.M.A, D. Shan, S. Yang and J. Gong, Biosensors, and Bioelectronics, 26 (2011) 2756-2760

50. M. Pontie H Lecture and F. Bedioui, Sensors and Actuators B: Chemical, 56 (1999) 1-5

51. F. Bedioui, S. Trevin, J. Dvynkc, F. Lantoine, A. Brunet and M.A. Devynck, Sensors and Actuators B: Chemical , 123 (1997) 205-212

52. F. Cao, S. Guo, H.M.A., G. Yang, S. Yang, and J. Gong, Talanta,86 (2011)214-220

53. K.C. Ho and Y.H. Tsou, Sensors andActuators B: Chemical,77 (2001) 253-259

54. C.V.G. Reddy, S.V. Manorama and V.J. Rao, Sensors and Actuators B: Chemical, 55(1999) 90-95

55. S.Noh, E. Lee J. Seo and M. Mehregany, Sensors and Actuators A: Physical, 125 (2006) 363-366

56. A. Salini, A. Noorbakhash, E. Sharifi and A. Semnani, Biosensors and Bioelectronics, 24(2008) 792-798

57. Y. Mu, D. Jia, Y. He, Y. Miao and H.L. Wu, Biosensors and Bioelectronics, 26 (2011) 2948-2952

58. D. Barreca, E. Comini, A Gasparotto, C. Maccato, C. Sada, G. Sberveglieri, and E. Tondello, Sensors and Actuators B: Chemical, 141 (2009) 270-275

59. M. Yang, J. He, X Hu, C. Yan, Z. Chang, Y. Zhao and G. Zuo, Sensors and Actuators B: Chemical, 155 (2011) 692-698

60. H.Wei, H. Sun, S. Wang, G. Chen, Y. Hou, H. Guo and X. Ma, J. of Natural gas Chemistry, 19 (2010) 393-396

61. W. Wang, Z. Li, W. Zheng, J. Yang, H. Zhang and C. Wang, Electrochemistry Communications, 11 (2009) 1811-1814

62. W. Wang, V. Saumya, K.P. Prathish and T.P. Rao, Talanta, 85 (2011) 1056-1062

63. F. Tudorache and I. Petrila, Material Letters, In Press.

64. K. Mukherjee and S.B. Majumda, Sensors and Actuators B:Chemical , 162 (2012) 229-236

65. K. Mukherjee and S.B. Majumda, Scripta Materialia, 67 (2012) 617-620

66. K. Mukherjee and S.B. Majumda, Talanta ,81 (2010) 1826-1832

67. A. Sutka , G. Mezinskis ,A. Lusis and M. Stingaciu, Sensors and Actuators B:Chemical 171-172 (2012) 354-360

68. N. Rezlescu and P.D. Popa, Sensors and Actuators B:Chemical 114 (2006)427-432

69. C.V. Gopal Reddy, S.V. Monorama and V.J. Rao, Sensors and Actuators B:Chemical ,55(1999) 90-95

70. S. Darshane ,S.S. Suryavanshi and I.S. Mulla, Ceramics International ,35(2009) 1793-1797

71. G.Galino and S.Gutierrez ,Jounal of alloys and compounds, In Press

72. C.D. Lokhande ,S.S. Kulkarni ,R.S. Mane, O.S. Joo and S.H. Han , Ceramics International,37 (2011)3357-3360

73. I. Pertila and F. Tudorache ,Material Letters, In Press

74. S. Singh ,B.C. Yadav ,R. Prakash ,B. Bajaj and J.R. Lee, Applied Surface Science,257 (2011) 10763-10770

75. M.S. Khandekar, N.L. Taral, J.Y. Patil ,F.I. Shaikh ,I.S. Mulla and S.S. Suryavanshi ,Ceramics International ,39 (2013) 5901-5907

76. S. Singh ,B.C. Yadav ,V.D. Gupta and P.K. Diwedi ,Material Research Bulletin , 47 (2012) 3538-3547

Received on 12.09.2017 Modified on 08.01.2018

Asian J. Research Chem. 2018; 11(2):497-504.

DOI: 10.5958/0974-4150.2018.00089.5