*1.2.1 Key properties*

The summarized **Table 2** shows the physical and mechanical properties of sintered titania, while the optical properties of titania are provided in **Table 3**.

## *1.2.2 Photo catalytic properties*

Titania used a photosensitizer for photovoltaic cells and when used as an solid state coating electrode in photo-electrolysis cells, can improve the efficiency of electrolytic splitting of water into hydrogen and oxygen.

In 1972, Fujishima and Honda discovered the photocatalytic water division in TiO2 electrodes. This incident developed the foundations of a new era inheterogeneity. photo-catalysis. Titania is a promising photocatalyst chemical. Two different crystal


**85**

impurities and bacteria in the air.

• Hydrothermal synthesis

are described below:

**Table 2.**

**Table 3.**

*Titania optical properties.*

• Sol-gel method

• Aerosol methods

**1.3 Synthesis methods of nanomaterials**

• Low temperature combustion methods

*Design and Growth of Metal Oxide Film as Liquefied Petroleum Gas Sensors*

Density 4 g cm<sup>−</sup><sup>3</sup> Porosity 0% Compressive strength 680 MPa Poisson's ratio 0.27 Shear modulus 90 GPa Modulus of elasticity 230 GPa Resistivity (25°C) 1012 ohm cm Resistivity (700°C) 2.5 × 104

Dielectric constant (1 MHz) 4 Thermal expansion (RT-1000°C) 9 × 10<sup>−</sup><sup>6</sup> Melting point (°C) 1843°C Boiling point (°C) 2972°C

**Phase Refractive index Density (g cm<sup>−</sup><sup>3</sup>**

ohm cm

**) Crystal structure**

structures of TiO2, rutile and anatase, are normally used in photo-catalysis activity. Photo-catalysis is a photon energy (from the UV in sunlight) used to the medium (catalyst) to support chemical reaction to continue. TiO2 is a semiconductor in which, the valence band is filled with electrons. Since the band gap of TiO2 is 3.20 eV and can use only UV light below 400 nm, numerous efforts have been made to sensitize larger band gap semiconductors or to use slight band gap semiconductors that can absorb visible light. Photon or UV light which is below the wavelength of violet (400 nm) has a high destructive energy. When the photon is familiarized to titania, it becomes unstable thus the electron escapes. This electron can break chemical bond since it has a high energy. This reaction can be very useful to decompose organic material,

Anatase 2.49 3.84 Tetragonal Rutile 2.903 4.26 Tetragonal Brookite 4.123 Orthorhombic

Synthesis methods play very important part of research to control the size and surface area of nanomaterials. There is numerous synthesis methods, some of them

*DOI: http://dx.doi.org/10.5772/intechopen.82082*

*Typical physical and mechanical properties of titania.*

**Table 1.** *Chemical composition.* *Design and Growth of Metal Oxide Film as Liquefied Petroleum Gas Sensors DOI: http://dx.doi.org/10.5772/intechopen.82082*


#### **Table 2.**

*Gas Sensors*

**Figure 3.**

and thermodynamic stage steadiness relied upon the underlying molecule sizes of anatase appeared in **Figure 3**. In the temperature range 973–1073 K only one phase change from anatase to rutile occurred. Both sizes of anatase and rutile particles increased with increasing temperature, but the growth rate was different. Rutile had a much higher growth rate than anatase. The rate of development of the anatase has been stabilized at 800°C. The rutile particles, after nucleation, have grown rapidly, where the size of the anatase particles has remained virtually unchanged with the decrease of the initial particle size, the temperature of start the diminished transition [6]. The diminished warm steadiness in better nanoparticles was fundamentally because of the lessened enactment vitality as a size related surface

The chemical composition of Ti and O in TiO2 is as given in **Table 1**.

electrolytic splitting of water into hydrogen and oxygen.

The summarized **Table 2** shows the physical and mechanical properties of sintered titania, while the optical properties of titania are provided in **Table 3**.

Titania used a photosensitizer for photovoltaic cells and when used as an solid state coating electrode in photo-electrolysis cells, can improve the efficiency of

In 1972, Fujishima and Honda discovered the photocatalytic water division in TiO2 electrodes. This incident developed the foundations of a new era inheterogeneity. photo-catalysis. Titania is a promising photocatalyst chemical. Two different crystal

**Element Content (%)** Titanium 59.93 Oxygen 40.55

enthalpy and stress vitality expanded.

*The schematic diagram of growth of nanoparticles.*

**1.2 Properties of TiO2**

*1.2.1 Key properties*

*1.2.2 Photo catalytic properties*

**84**

**Table 1.**

*Chemical composition.*

*Typical physical and mechanical properties of titania.*


#### **Table 3.**

*Titania optical properties.*

structures of TiO2, rutile and anatase, are normally used in photo-catalysis activity. Photo-catalysis is a photon energy (from the UV in sunlight) used to the medium (catalyst) to support chemical reaction to continue. TiO2 is a semiconductor in which, the valence band is filled with electrons. Since the band gap of TiO2 is 3.20 eV and can use only UV light below 400 nm, numerous efforts have been made to sensitize larger band gap semiconductors or to use slight band gap semiconductors that can absorb visible light. Photon or UV light which is below the wavelength of violet (400 nm) has a high destructive energy. When the photon is familiarized to titania, it becomes unstable thus the electron escapes. This electron can break chemical bond since it has a high energy. This reaction can be very useful to decompose organic material, impurities and bacteria in the air.

## **1.3 Synthesis methods of nanomaterials**

Synthesis methods play very important part of research to control the size and surface area of nanomaterials. There is numerous synthesis methods, some of them are described below:


### *1.3.1 Hydrothermal synthesis*

The hydrothermal synthesis is a process which uses single heterogeneous phase reactions in aqueous medium at higher temperature and pressure to crystallize and produce ceramic materials hydrated directly from the solutions [7]. This synthesis offers a low temperature direct route to the oxide powder with a small size distribution that prevents the passage of calcination. The hydrothermal reaction mechanism monitors a liquid nucleation model. Normally, in the hydrothermal process temperature falls between the boiling point of the water and the critical temperature (Tc = 374°C), while the pressure is higher than 100 kPa. The product is washed with deionized water to remove ions from the solvent and other impurities. After drying in the air, very well dispersed ceramic nanoparticles are obtained.

## *1.3.2 Sol-gel method*

First, a solution of the appropriate precursors (metal salts of organic metal compounds) is formed, followed by conversion into homogeneous oxide (gel) after hydrolysis and condensation [8]. The drying and subsequent calcination of the gel produce an oxide product. Usually, for the preparation of multicomponent oxides, the alkoxides are mixed in alcohol. The components for which alkoxides are not available are introduced as salts, such as acetates. The hydrolysis is carried out at a controlled temperature, pH and alkoxide concentration, addition of water and alcohol.

### *1.3.3 Aerosol method*

This method is also defined as a gas phase method. It is considered to be convenient and convenient in the large-scale industrial production of multicomponent materials [9]. Aerosols are suspensions of small solid or liquid particles in a gas. There are two ways of preparing ultrafine particles by aerosol processes. The first concerns the generation of a supersaturated vapor from a reagent followed by a homogeneous nucleation (conversion of gas into particles). The second concerns the generation of liquid droplets, which are subjected to a heat treatment in solid particles (conversion of liquid into particles). The latter is used to prepare multicomponent materials.

Spray drying and spray pyrolysis are the most common methods for converting liquid into solid. A metal precursor (sol) solution is produced, followed by drop atomization, which are conducted to an oven. Therefore, spray drying can be a suitable process for consolidating the nanoparticles into submicronic spherical granules that can be compacted into microscopic shapes.

#### *1.3.4 Low temperature combustion method*

The low-temperature combustion synthesis technique (LCS, for its acronym in English) has proven to be an innovative, extremely easy path, which saves time and saves energy for the synthesis of ultrafine powders [10–13]. This is based on the gelling and subsequent combustion of an aqueous solution containing salts of the desired metals and some organic fuels, which provides a voluminous and fluffy product with a large surface area. As starting materials, oxidizing metals salts, such as metal nitrates and a combination agent (fuel), such as citric acid, polycyclic acid or urea are used. Citrate acid is used more widely, since it does not function only as a reducing/fueling agent, but also as a chelating agent.

**87**

*Design and Growth of Metal Oxide Film as Liquefied Petroleum Gas Sensors*

the sensor close to where measurements are to be made.

the receiver [14].Using this principle, one can distinguish between.

In physical sensors a chemical reaction does not take place in the receiver and the signal is the result of a physical process, such as mass, absorbance, refractive index, temperature or conductivity change. Chemical sensors are based on chemical reactions between the analyte molecules and the receptor. Biochemical sensors are a subclass of chemical sensors, in which the reaction is biochemical. Typical examples of such sensors are microbial potentiometric sensors or immune sensors. It is not always possible to discriminate between physical and chemical sensors. A good example is a gas sensor, in which the signal is the result of gas adsorption.

Gas loss is a major concern in residential, commercial and gas transportation vehicles. One of the precautionary measures to avoid the danger associated with gas leaks is to install a gas leak detector in vulnerable locations. The purpose of this document is to present the design of an automatic economic alarm system, capable of detecting liquefied petroleum gas leaks in different locations. In particular, the

A gas sensor is a device that produces an electrical signal in response to a chemical interaction with the vapors because the information obtained from this process is advantageous. Gas sensors have generated extensive applications in both domestic and industrial environments. However, despite its value, there are many difficulties in making a reliable sensor before it can be used safely. Ideally, gas sensors should exhibit a high sensitivity to steam that are designed to detect. Furthermore, the sensor should produce only an electrical response when exposed to the gas of interest. The sensors must also have stable and reproducible electrical signals to reduce the time required for calibration. There are other practical concerns, such as minimizing size, weight and energy consumption, as well as the ability to position

According to the definition of gas sensor, provided by the International Union of Pure and Applied Chemistry (IUPAC), "a chemical sensor is a device that transforms chemical information, ranging from the concentration of a specific component of the sample to the analysis of the composition total, in an analytically useful signal. The above chemical information can derive from a chemical reaction of the analyte or from a physical property of the system under examination" [14]. Normally, chemical sensors consist of two main parts, a receiver and a transducer. A sensor is an instrument that responds to a physical stimulus (such as heat, light, sound, pressure, magnetism or movement). Collects and measures data related to some properties of a phenomenon, object or material. Sensors are an important part for any measurement and automation application. The sensor is responsible for converting a certain type of physical phenomenon into an amount that can be measured by a data acquisition system (DAQ ). The receiver transforms the chemical information into a form of energy, which can be measured by the transducer. The transducer converts this energy into a useful analytical signal, typically electric. Chemical sensors are classified in different ways. One of the classifications uses the operating principle of

*DOI: http://dx.doi.org/10.5772/intechopen.82082*

**1.4 Introduction to gas sensor**

*1.4.1 Gas sensor technology*

1.Physical sensors,

2.Chemical sensors, and

3.Biochemical sensors.
