Synthesis And Hydrogen Gas Sensing Property Research Of TiO₂ Based On Tillandsia Template

Tillandsia is an aerial epiphytic bromeliad. It is a soilless-rootless plant and lives on trees or other hosts. Tillandsia has the ability to absorb water and nutrients directly from the atmosphere and their hosts through precipitation and dry deposition. Due to the above characterization, this plant is denominated as air plant. There are many reports about applying this plant as biomonitors in different areas.Tillandsia morphology, specific surface area, water wettability and gas sensitivity were investigated. The structure of the surface of the plant and also the inner part of Tillandsia were studied. The specific surface area of the plant was measured in different conditions to find out the abundance of the active sites and the influence of trichomes on the value of the specific surface area. The gas response of the plant after exposing to H2 as a target gas was also reported.Water wettability of the leaves of the plant was considered in different parts of the plant such as top, middle and bottom of the leaves in the presence and absence of trichomes. For better understanding, the water wettability of another two leaves was compared with Tillandsia to find out the difference between them.Lots of methods have been applied to accelerate the gas response of the synthesized samples such as doping and coating some noble metals on the sensor surface. The sensing response of the sensors depends on different parameters such as preparation method, processing condition, crystallization degree, temperature, particle size and so on. To further explore the sensing property and the parameters which affect the gas response, the current study focuses on the relationship between the processing condition and the influence of this condition on the gas sensitivity of the synthesized samples.Ti O2 samples were synthesized via the simple technology of hydrothermal method. A variety of different Ti O2 samples were prepared by changing processing condition such as reaction time and precursor volumes. The influence of the reaction time, tetrabutyl Titanate volume and ethanol volume on the morphology, structure, specific surface area and gas sensitivity of the samples were evaluated. The particle size of the samples was measured by BET method. Low temperature was initially used to synthesize samples. According to the results, all the prepared samples under low temperature exhibit amorphous structure with poor crystallinity.The gas sensing studies on different sample prepared under low temperature have shown that the sample which obtained under the same concentration of ethanol and tetrabutyl titanate and heated at 180°C for 6h(TA3) exhibits the highest value of gas response to hydrogen. The sensitivity of the prepared sample was significantly higher than P25. Furthermore, the synthesized sample prepared at lower temperature than P25.Then the sample which showed the best gas sensitivity was synthesized under elevated temperature to investigate the effect of high temperature on the property of the samples. Other parameters such as reaction time and the precursor volume were kept constant and the temperature varied from 250°C to 400°C. Regarding to the results the sample which obtained at 350°C(TD3) showed the higher sensitivity in comparison with the sample which prepared under low temperature. Although the prepared samples under high temperature present good crystallization, the gas sensitivity just showed a little increased. It can be concluded that the crystallinity of the sample is not the main reason which affect the gas sensitivity.The samples based on multi walled carbon nanotube and Tillandsia have been synthesized to evaluate the influence of the substrates in the sensing property of the samples. These samples prepared by hydrothermal method under low temperature(180°C) due to the importance of using low energy. Ti O2 particles coated directly on the surface of the substrates and the concentration of both substrates varied from 0.3 g to 0.9 g. Due to results the sensitivity of the synthesized samples greatly affected by the concentration of the substrates. Both groups of the samples present the highest gas response when they obtained under 0.6 g substrates. It can be concluded that under this concentration the Ti O2 particles display the uniform distribution with the appropriate thickness which accelerate the electron migration from bulk to the surface and increase the gas sensitivity of the sample.It is noteworthy to mention that the sample which obtained by o.6g Tillandsia(TF2) not only exhibits higher gas response than the samples which prepared by 0.3 g(TF1) and 0.9 g(TF3) Tillandsia, but also shows higher value of gas sensitivity than the samples which prepared base on CNT. This response is more than two times higher than the samples consist of CNT. The results confirm that the high gas sensitivity of the samples based on Tillandsia comes from the best dispersion and the uniform distribution of the Ti O2 particles due to the unique structure of the Tillandsia.