Enhanced Gas-Sensing Performance of GO/TiO2 Composite by Photocatalysis

Abstract

Few studies have investigated the gas-sensing properties of graphene oxide/titanium dioxide (GO/TiO2) composite combined with photocatalytic effect. Room temperature gas-sensing properties of the GO/TiO2 composite were investigated towards various reducing gases. The composite sensor showed an enhanced gas response and a faster recovery time than a pure GO sensor due to the synergistic effect of the hybridization, such as creation of a hetero-junction at the interface and modulation of charge carrier density. However, the issue of long-term stability at room temperature still remains unsolved even after construction of a composite structure. To address this issue, the surface and hetero-junction of the GO/TiO2 composite were engineered via a UV process. A photocatalytic effect of TiO2 induced the reduction of the GO phase in the composite solution. The comparison of gas-sensing properties before and after the UV process clearly showed the transition from n-type to p-type gas-sensing behavior toward reducing gases. This transition revealed that the dominant sensing material is GO, and TiO2 enhanced the gas reaction by providing more reactive sites. With a UV-treated composite sensor, the function of identifying target gas was maintained over a one-month period, showing strong resistance to humidity.

Special Issue “Advanced Nanomaterials Based Gas Sensors”

“…The improvement of the sensor sensitivity with the inclusion of SnO 2 is attributed to the increase in adsorption sites for the gas molecules created by the metal oxide nanoparticles. The same conclusion is derived for the composite formed by graphene oxide and titanium oxide in [11]. In this case, the mixture of graphene oxide diluted in ethanol with the TiO 2 nanoparticles was dropped onto a flexible polyimide substrate with platinum electrodes.…”

State of the Art in Alcohol Sensing with 2D Materials

“…A homogenous solution GO with TiO 2 nanoparticles was prepared in ethanol by sonicating for 2 h. A thin film of the nanocomposite was then prepared by drop casting 10 mg of the solution over a clean layer of polyimide. The composite sensor offered an enhanced normalised gas response for methanol, ethanol, and ammonia compared to pure GO layer; however, these nano-complexes suffer from short lifetime, and to deal with this issue, UV treatment of the sensor was performed that increased the lifetime of the detector up to 1 month and improved its resistance against water [ 202 ]. The UV-treated sample coloured differently, and this treatment also affected the behaviour of the sensor in a way that reduced the sensitivity of the sensor to different gasses and produced a higher response (normalised gas response) for ethanol than methanol.…”

“…1D TiO 2 nanobelts and Ag–TiO 2 nanobelts were used to formulate an ethanol sensor; the response time and the sensitivity for different concentrations of ethanol from 5 to 500 ppm were tested, and they were weak below 300 ppm [ 281 ]. On the other hand, a sensor developed from 2D TiO 2 offers much better sensitivity (100 ppm), yet the 1D sensors seem to work better in terms of selectivity [ 202 ]. Choi et al conducted a systematic study using four different morphologies of Co 3 O 4 as gas sensors [ 283 ].…”

Insights in the Application of Stoichiometric and Non-Stoichiometric Titanium Oxides for the Design of Sensors for the Determination of Gases and VOCs (TiO2−x and TinO2n−1 vs. TiO2)

“…Among them, many different TiO 2 -based heterostructures were investigated: (i) V 2 O 5 /TiO 2 for chemi-resistive ozone sensors [45], TiO 2 /perovskite heterojunctions for CO gas [46], (ii) TiO 2 / (graphene-carbon)-based toluene VOC sensor operating at room temperature [47], (iii) TiO 2 /SnO 2 for CO and NO 2 [48,49], (iv) TiO 2−x /TiO 2 -structure-based 'self-heated' sensor for various reducing gases and VOCs [1]. Improved gas-sensing performance of TiO 2 by graphene oxide (GO) was demonstrated by Lee et al [50] (Figure 2a,b), this effect was achieved by UV radiation. The authors claimed that n-n junction had been formed and proposed the band diagram of the GO/TiO 2 , which represent an energetic levels at the hetero-junction.…”

“…Therefore, advanced sensing properties can be established by small-grain-based structures [17]. SnO 2 is characterized by high charge-carrier mobility, which is critically important for the resistivity measurement-based gas and VOC sensors [50,61]. In addition, SnO 2 is chemically stabile, cheap and forms gas-and VOC-sensing layers, therefore, even in pristine form it is used in various gas and VOC sensors [62].…”