Low temperature nanocrystalline TiO2–Fe2O3 mixed oxide by a particulate sol–gel route: Physical and sensing characteristics
Graphical abstract
Highlights
► Nanostructured TiO2–Fe2O3 gas sensor was prepared by a new aqueous sol–gel route. ► The sensor exhibited a remarkable response towards low concentrations of CO. ► It also showed fast response and recovery times at low temperature of 150 °C.
Introduction
Transition metal oxide films have found wide applications as gas sensors [1], catalysts [2] and in optical electronics [3]. TiO2 and Fe2O3 are common single metal oxide semiconductors used as gas sensors since their electric conductivity changes when exposed to gases such as trimethylamine, ethanol, oxygen (O2), hydrogen (H2), carbon monoxide (CO) and petrol vapors [4], [5], [6], [7], [8], [9], [10], [11]. Recently, many efforts have been aimed to improve the gas sensing performance by improvements in selectivity, sensitivity and durability. In order to improve these properties, microstructure control by preparing porous, high specific surface area films and doping with hetero components (such as Sn, V, Cr, W, Co, Cu, Fe, Nb, Ta, Ga and Mo) are known to be effective, because active sites for particular gas species can be produced [1], [12], [13], [14], [15]. Another method to improve gas sensing performance of metal oxide semiconductors is to employ binary metal oxide semiconductors. This novel alternative has the potential to form tailored film morphologies, which facilitates gas-film interaction by altering atomic ratio of each element. Furthermore, it is possible to increase the current single metal oxide surface-to-volume ratio and to fabricate stable nano-sized grain morphologies for high performance gas sensing thin films [16].
Sensing properties of binary oxides based on TiO2 such as TiO2–MoO3 [16], TiO2–WO3 [17], TiO2–Cr2O3 [18] TiO2–V2O5 [14] and TiO2–CeO2 [19] reported previously. Binary oxides based on Fe2O3 such as Fe2O3–SnO2 [9], [20], Fe2O3–CeO2 [21], Fe2O3–ZrO2 [9] and Fe2O3–TiO2 [10] for sensing applications have also been studied before. The major disadvantage of TiO2-based gas sensors is their high power consumption which is required to operate the sensors at the required elevated temperature (>400 °C) [22], [23]. In contrast, Fe2O3-based gas sensors usually operate at lower temperatures (e.g., 100 °C) [9], [20]. Therefore, the empirical exploration of mixing TiO2 and Fe2O3 may lead to new gas sensing properties or may simply lead to a material composed of characteristics similar to TiO2 and Fe2O3. Dai [10] studied sensing properties of TiO2–Fe2O3 thin films, deposited by plasma enhanced chemical vapour deposition (PECVD) technique, towards trimethylamine. Tan et al. [9] investigated sensing characteristics of Fe2O3–TiO2 material, prepared by high-energy ball milling process, towards ethanol and oxygen gases.
Binary metal oxides can be obtained by different deposition techniques. Among chemical routes, sol–gel techniques offer important advantages due to low cost synthetic route, excellent compositional control, high homogeneity at the molecular level, feasibility of producing thin films on large and complex shapes and, the most significant one, low crystallisation temperature. TiO2–Fe2O3 mixed oxides prepared by various sol–gel processes have been reported in the literature. For example, Gupta and Ghosh [24] synthesized iron(III)–titanium(IV) oxide powder by slow injection of TiCl4 into hot (60 °C) FeCl3 solution. They studied kinetics behaviour of the material for arsenic removal. Mora et al. [25], Celik et al. [26], Neri et al. [27] and Pal et al. [28] prepared TiO2–Fe2O3 mixed oxides by polymeric sol–gel process, although these were intended for photocatalytic application. Nanostructured iron oxide–titania aerogel was prepared by sol–gel polymerization of iron acetylacetonate and titanium butoxide for photocatalytic application by Wang and Ro [29]. Balek et al. [30] studied thermal behaviour of Fe2O3–TiO2 mesoporous gels, synthesized by polymeric sol–gel method, using tetrabutyl orthotitanate and iron(III) nitrate as precursors and polyethylene glycol (PEG600) as additive. Long and Yang [31] synthesized Fe2O3–TiO2 powder by polymeric sol–gel process from iron nitrate or sulphate and titanium butoxide precursors for selective catalytic oxidation of ammonia to nitrogen. Magnetic characteristics of TiO2–Fe2O3 powder, synthesized by polymeric sol–gel technique, were studied by Kundu et al. [32].
So far, no significant work has been reported on preparation of TiO2–Fe2O3 thin films by particulate sol–gel process for gas sensing application. Therefore, in the present work a straightforward particulate sol–gel route for improvement of TiO2 sensing performance by adding Fe2O3, in the form of TiO2–Fe2O3 binary oxide film is reported. This process can be defined as an environmentally friendly processing as it uses an aqueous solution. One of the advantages of the present method is using an alternative to alkoxide (i.e., iron(III) chloride) as an iron source to produce a low cost product. Besides controlling the phase structure, composition homogeneity, crystallite size, monodispersity and microstructure, the cost of the product is also an important concern. Therefore, starting with a low cost precursor such as iron(III) chloride may reduce the total cost of production. Since the pores in particulate sol–gel processes are much larger than that found in polymeric sol–gel route, the capillary stress and therefore the shrinkage decrease during heat treatment. Therefore, it is possible to produce crack-free thin films with high surface area.
Section snippets
Preparation of TiO2–Fe2O3 sol
Titanium(IV) tetraisopropoxide (TTIP) with a normal purity of 97% (Aldrich, UK) and iron(III) chloride (FeCl3) with a normal purity of 98% (Aldrich, UK) were used as titanium and iron precursors, respectively. Analytical grade hydrochloric acid (HCl, 37%, Fisher, UK) was used as a catalyst for the peptisation and deionised water was used as a dispersing media. Hydroxypropyl cellulose (HPC) with an average molecular weight of 100,000 g/mol )Aldrich, UK( was used as a polymeric fugitive agent
Particle sizes and charges
Fig. 1 shows the mean size of the particles for prepared sol. It can be observed that it had a narrow particle size distribution around 20.5 nm. The particle size of the TiO2 sol reported in our previous study was around 18 nm [37]. Therefore, no significant increase in the mean size of the particles was observed for TiO2–Fe2O3 sol, which confirms that stability of the sol is maintained when a solution of iron chloride is added into TiO2 sol.
The zeta potential of the particles is shown in Fig. 2.
Conclusions
Nanostructured TiO2–Fe2O3 thin films and powders were successfully prepared via a new particulate sol–gel route for gas sensing application. The sol was stable over 3 months, since the constant zeta potential was measured during this period, being 45 mV at pH=2. Moreover, a narrow particle size distribution around 20.5 nm was observed for prepared sol. Based on XRD analysis, the average crystallite size of the powder was calculated around 6.0 nm at 300 °C and reached to 6.8 nm after annealing at 700
References (47)
- et al.
Sensors and Actuators B: Chemical
(1999) - et al.
Applied Catalysis A: General
(2004) - et al.
Journal of Photochemistry and Photobiology A: Chemistry
(2001) - et al.
Journal of Thin Solid Films
(2003) - et al.
Sensors and Actuators B: Chemical
(2000) - et al.
Sensors and Actuators B: Chemical
(2004) - et al.
Sensors and Actuators B: Chemical
(1998) - et al.
Sensors and Actuators B: Chemical
(1994) - et al.
Ceramics International
(2004) Sensors and Actuators B: Chemical
(1998)
Sensors and Actuators B: Chemical
Sensors and Actuators B: Chemical
Sensors and Actuators B: Chemical
Sensors and Actuators B: Chemical
Sensors and Actuators B: Chemical
Sensors and Actuators B: Chemical
Sensors and Actuators B: Chemical
Sensors and Actuators B: Chemical
Sensors and Actuators B: Chemical
Applied Surface Science
Sensors and Actuators B: Chemical
Sensors and Actuators B: Chemical
Sensors and Actuators B: Chemical
Cited by (21)
Synergistic effects of α-Fe<inf>2</inf>O<inf>3</inf>-TiO<inf>2</inf> and Na<inf>2</inf>S<inf>2</inf>O<inf>8</inf> on the performance of a non-thermal plasma reactor as a novel catalytic oxidation process for dimethyl phthalate degradation
2020, Separation and Purification TechnologyCitation Excerpt :It is apparent that the deposition of α-Fe2O3 on the anatase phase of TiO2 did not significantly change the surface morphology of TiO2 which is in accordance with Lee et al. (2017) study [57]. Comparing the FESEM images of the present study with Mohammadi and Fray's (2012) study can illustrate that the present synthesized nanocomposite has less aggregation and more pores where are beneficial for photocatalytic activity [58]. The observed particles sizes are in the range of 31–39.1, 15.7–31.6, and 43.4–56.5 nm for TiO2, α-Fe2O3, and α-Fe2O3-TiO2, respectively.
Cobalt oxide doped hematite as a petrol vapor sensor
2020, Materials Chemistry and PhysicsCitation Excerpt :Pristine iron oxide has been used for Acetone [1], Carbon Monoxide [2], Nitrogen Dioxide [3], H2S [4], Ethanol [5], and LPG [6] sensing. WO3 [7], CuO [8], TiO2 [9], SnO2 [10], Sb2O3 [11], ZnO [12], ZrO2 [13], In2O3 [14] and CdO [15] have also been tested as a dopant with iron oxide (α-Fe2O3) as a base material for toxic gas detection. Cobalt Oxide is a well-known p-type semiconductor.
Fe-TiOx nanoparticles on pineapple peel: Synthesis, characterization and As(V) sorption
2018, Environmental Nanotechnology, Monitoring and ManagementCitation Excerpt :The absorption bands of the hydroxyl and carboxyl groups are related to the presence of water, alcohols, phenols, carboxylic acids and polysaccharides such as cellulose, hemi-cellulose and lignin (Xu et al., 2013; Barnette et al., 2012; Sena-Neto et al., 2013; Hameed et al., 2009; Akar and Celik, 2011; Saleh, 2015). On the other hand, the characteristic adsorption bands 590 cm−1 corresponding at the link Fe-O and at 545 cm−1 in the Ti-O groups are located in the spectrum (Aliahmad and Moghaddam, 2013, Jabeen et al., 2013; Mohammadi and Fray, 2012 and Hernández-Enríquez et al., 2008). After the As sorption (Fig. 3b) an important change is observed in four bands located at 1371 cm−1, 900 cm−1, 590 cm−1 and 545 cm−1, these vibration modes increased slightly due to the interaction of functional groups with As(V) species.
Template-assisted hydrothermally synthesized iron-titanium binary oxides and their application as catalysts for ethyl acetate oxidation
2016, Applied Catalysis A: GeneralCitation Excerpt :Formation of ilmenite, pseudorutile, pseudobrookite or mixture of hematite and TiO2 with mutual solubility depending on the Fe/Ti ratio and the calcination temperature used has been reported in [8,9,16,27][8,9,16,20,27,and refs. therein]. The effect of titania doping on the phase transformation of anatase to rutile has also been a matter of controversial discussion in refs. [4,6,10,13,20,27–29]. The incorporation of iron species into titania was carried out by several methods, e.g. co-precipitation, microemulsion procedures, combustion, sol-gel, hydrothermal/solvothermal, chemical synthesis, plasma pyrolysis etc. [1,6,11][1,6,11 and refs therein], but up to now the controlled synthesis of materials with well defined structure, morphology, texture and dispersion by a simple and reproducible method is still a challenge.
Sol–gel synthesis of TiO<inf>2</inf>-Fe<inf>2</inf>O<inf>3</inf> systems: Effects of Fe<inf>2</inf>O<inf>3</inf> content and their photocatalytic properties
2016, Journal of Industrial and Engineering Chemistry
- 1
Postal address: Department of Materials Science & Engineering, Sharif University of Technology, Azadi Ave., Tehran, Iran.