Elsevier

Optics & Laser Technology

Volume 57, April 2014, Pages 181-188
Optics & Laser Technology

Fabrication of iron titanium oxide thin film and its application as opto-electronic humidity and liquefied petroleum gas sensors

https://doi.org/10.1016/j.optlastec.2013.10.007Get rights and content

Highlights

  • Iron titanium oxide nanocomposite was synthesized using sol–gel route.

  • Sensing thin film was deposited on the base of equilateral prism.

  • Crystallite size of iron titanium oxide was found 9 nm.

  • Fabricated opto-electronic humidity sensor shows maximum sensitivity 4.5 μW/%RH.

  • Enhanced sensitivity in comparison to earlier reported LPG sensors.

Abstract

Present paper explores the synthesis, characterization, and opto-electronic humidity as well as liquefied petroleum gas (LPG) sensing applications of iron titanium oxide nanocomposite. Thin film of iron titanium oxide was deposited on an equilateral borosilicate glass prism using sol–gel spin coating process. X-ray diffraction reveals the formation of iron titanium oxide having minimum crystallite size 9 nm. The opto-electronic humidity sensing properties of the fabricated film were investigated at different angles of incidence of the light. It was observed that the intensity of reflected light increased with an increase in relative humidity (%RH) in the range 5–95. The fabricated film shows maximum sensitivity 4.5 μW/%RH, which is quite significant for sensor fabrication purposes. The maximum percentage sensor response for LPG was found 2600 which is many folds more than the earlier reported titania based LPG sensor.

Introduction

The preparation of nanocomposites based on semiconducting oxides is an important goal for improved functional performance in advanced fields such as opto-electronics, sensing and catalysis. Recently mixed metal oxides or binary semiconducting systems have attracted more and more attention for the fabrication of materials showing novel technological applications, which are often superior to those of the component characteristics.

In recent years, humidity sensing is becoming more important, mainly in control systems for industrial processes and human comfort. An extensive diversity of metal oxides and their nanocomposites, ceramics and polymers have been investigated as humidity sensors [1], [2], [3], [4], [5], [6], [7]. These sensors are mainly based on the variation in electrical parameters such as impedance, resistance and capacitance [8], [9], [10]. Additionally, another category of the sensors is also available whose principle is based on variations in optical parameters such as refractive index (r.i.), intensity modulation, frequency shift and wavelength modulation [11], [12], [13], [14]; these are frequently called optical/opto-electronic sensors. Optical sensors have tremendous advantages over their electrical counterpart as they can operate without any interface from nearby electric or magnetic fields.

Titanium dioxide has been extensively used as an environmentally harmonious and clean photo catalyst because of its various merits, such as optical and electronic properties, low cost, high photocatalytic activity, chemical stability and non-toxicity. Titania is an attractive photocatalytic material in the control of toxic pollutants by means of gas–solid or liquid–solid photo catalyzed reactions [15], [16]. However, the main crystallographic form of titania is anatase, which can only absorb light wavelengths shorter than 400 nm and generates the energy band gap of 3.2 eV. In the literature few reports on titania as gas sensor were found but the sensitivity of such kind of sensors is minute. Fe2O3 is another well documented material for the fabrication of sensors [17], [18]. It has a relatively narrow band gap (2.2 eV) with reasonable stability. However, its energy conversion efficiency is quite low, which has been attributed to low optical absorption coefficient and low electron mobility. Nanocomposites of Fe2O3 and TiO2 could be a motivation to develop the better sensors. As it is a well-known material for photo electrodes with visible light response and photo electrochemical stability. Therefore, such type of reports on this system has been observed. Morosin et al. [19] and Ginley and Butler [20] studied single-crystal and polycrystalline FeTiO3, Fe2TiO4 and Fe2TiO5 as the anodes for photo electrolysis of water.

Chemical sensors play a very important role in both environmental protection and human health. The fabrication of metal oxide semiconducting nanomaterials having large surface to volume ratio for gas sensing applications is currently a major hub of nanoscience and nanotechnology. Recently, some composite oxides such as spinel AB2O4 and perovskite ABO3 were found to be more attractive than single-metal oxides for their better selectivity and/or sensitivity to certain gases. In particular, the perovskite iron titanium oxide (FeTiO3), in which the transition metal Fe+++ incorporated into the lattice of the parent structure may be proved a promising material in detecting liquefied petroleum gas. Here we have investigated the opto-electronic humidity and LPG sensing properties of nanostructured iron titanium oxide.

To the best of our knowledge, the liquefied petroleum gas sensing and opto-electronic humidity sensing properties of iron titanium oxide have not been reported as yet. Therefore, the synthesis of iron titanium oxide via sol–gel technology was carried out. The sol–gel technique [21], [22], [23], [24] enables us to obtain oxides in a relatively simple way and at low temperature. The composition and the microstructure may be finely controlled and tailored for specific applications in the sol–gel process [25], [26], [27], [28]. In the present investigation, thin films were easily fabricated through the sol–gel spin coating technique and found that the sensitivity of the fabricated opto-electronic humidity sensor was enhanced by many folds to the earlier reported works [29], [30], [31], [32], [33] and is depicted in Table 1. The comparison of the fabricated LPG sensor with earlier reported LPG sensor may be seen in Table 2 along with the properties of the fabricated sensors which shows that in the present investigation the sensor response was enhanced by many folds [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47], [48]. Thus, present investigation is an advance step towards the fabrication of a robust and trustworthy opto-electronic humidity and LPG sensing device.

Section snippets

Material preparation

All chemical reagents used for the preparation of α-Fe2O3 and TiO2 were of AR grade. Nanostructured TiO2 and α-Fe2O3 were synthesized separately using chemical routes. Titania precursor was prepared by sol–gel method using titanium tetrachloride. Twenty-five milliliters of TiCl4 solution was added drop wise into 125 ml of ice-water under vigorous stirring to obtain a diluted TiCl4 solution. Further 20 g of citric acid was added into the above solution which produces a clear transparent solution.

Surface morphological analysis

Surface morphology of the sensing film was investigated using scanning electron microscope (SEM, LEO-0430, Cambridge). Fig. 3(a) shows a SEM image of the as prepared composite film at 300 nm scale and 23 KX magnifications which exhibits that the grains are almost homogeneously distributed. SEM image of the film annealed at 450 °C shown by Fig. 3(b) reveals that the film is more porous in comparison to Fig. 3(a). The surface consists of a number of active sites which are responsible for the

Optical humidity sensing properties

Fig. 7(a) shows the variations in the reflected intensity Ir (µW) of iron titanium oxide thin film with %RH for different angles of incidence θi=47, 50, 53 and 56°, respectively. Curve I for θi=47° exhibits that the sensor is most sensitive in low humidity region i.e. 5–40%RH. In initial state of the absorption process of the water vapor, the intensity decreases rapidly and sensor showed quick response to the detection of moisture, and the average sensitivity was found 5 µW/%RH for θi=47°. In

Conclusions

Iron titanium oxide was successfully synthesized by sol–gel method and the thin film was fabricated using spin coating process. The synthesized material was characterized for their structural, optical, thermal and surface morphological properties. From SEM micrographs we observed that the film is porous having uniform distribution of grains. XRD analysis reveals a rhombohedral crystal structure with the minimum crystallite size as 9 nm. The film was investigated with the exposition of liquefied

Acknowledgments

Corresponding author is thankful to Department of Science and Technology, India for financial support in the form of FAST-TRACK Project (SR/FTP/PS-21/2009).

References (48)

  • Satyendra Singh et al.

    A comparative study on surface morphological investigations of ferric oxide for LPG and opto- electronic humidity sensors

    Appl Surf Sci

    (2012)
  • B.C. Yadav et al.

    Nanocrystalline SnO2–TiO2 thin film deposited on base of equilateral prism as an opto-electronic humidity sensor

    Opt Laser Technol

    (2012)
  • B.C. Yadav et al.

    Nanonails structured ferric oxide thick film as room temperature liquefied petroleum gas (LPG) sensor

    App Surf Sci

    (2011)
  • Satyendra Singh et al.

    Synthesis of nanorods and mixed shaped copper ferrite and their applications as liquefied petroleum gas sensor

    Appl Surf Sci

    (2011)
  • Sujatha Singh et al.

    Highly sensitive and pulse-like response toward ethanol of Nb doped TiO2 nanorods based gas sensors

    Sens Actuators B

    (2012)
  • A.M. More et al.

    Liquefied petroleum gas (LPG) sensor properties of interconnected web-like structured sprayed TiO2 films

    Sens Actuators B

    (2008)
  • S.S. Joshi et al.

    Fabrication of n-CdTe/p-polyaniline heterojunction-based room temperature LPG sensor

    Sens Actuators B

    (2008)
  • R.B. Kamble et al.

    Nanocrystalline nickel ferrite thick film as an efficient gas sensor at room temperature

    Sens Actuators B

    (2008)
  • Yan-Li Liu et al.

    Ethanol gas sensing properties of nano-crystalline cadmium stannate thick films doped with Pt

    Analyt Chim Acta

    (2004)
  • D.S. Dhawale et al.

    Room temperature liquefied petroleum gas (LPG) sensor based on p-polyaniline/n-TiO2 heterojunction

    Sens Actuators B

    (2008)
  • Satyendra Singh et al.

    Fabrication of nanobeads structured perovskite type neodymium iron oxide film: its structural, optical, electrical and LPG sensing investigations

    Sens Actuators B

    (2013)
  • Satyendra Singh et al.

    Experimental investigations on liquefied petroleum gas sensing of Cd(NO3)2·(AAM)4·2H2O and Cds/polyacrylamide synthesized via frontal polymerization

    Sens Actuators B

    (2011)
  • B.C. Yadav et al.

    Nanocrystalline zinc titanate synthesized via physicochemical route and its application as liquefied petroleum gas sensor

    Sens Actuators B

    (2013)
  • Z. Chen et al.

    Humidity sensors: a review of materials and mechanism

    Sens Lett

    (2005)
  • Cited by (25)

    • Synthesis of transition metal titanium oxide (MTiO<inf>x</inf>, M = Mn, Fe, Cu) and its application in furazolidone electrochemical sensor

      2022, Journal of Industrial and Engineering Chemistry
      Citation Excerpt :

      The crystal structure of titanium cannot support the sensors effectively and in the same way, the iron oxide will possess low ion mobility. So the combination of these two materials would be an innovation in the development of the sensor [48]. It is also known as functional inorganic materials with an extensive range of applications in gas sensors [49], metal-air barriers [50], high-performance catalysts [51], and solid oxide fuels (SOFC) [52].

    • Optimization and modeling of Zn<inf>2</inf>SnO<inf>4</inf> sensitivity as gas sensor for detection benzene in the air by using the response surface methodology

      2021, Journal of Saudi Chemical Society
      Citation Excerpt :

      This feature also applies to other metal oxides. for example, When the two TiO2 and Fe2O3 sensors are used in combination with the new FeTiO3 structure to detect LPG, it is much more effective and has higher sensitivity compared to the single state of both metal oxides [14]. Therefore, most sensor applications have led to the fabrication of mixed metal oxides.

    View all citing articles on Scopus
    View full text