Guangzhong Xie

Preparation, Characterization and Comparative NH3-sensing Characteristic Studies of PANI/inorganic Oxides Nanocomposite Thin Films

Polyaniline (PANI), polyaniline/titanium dioxide (PANI/TiO2), polyaniline/tin oxide (PANI/SnO2) and polyaline/indium oxide (PANI/In2O3) thin films were developed by using an in-situ self-assembly method at ∼10°C. Chemical structure, optical property and morphology of all the thin films were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, UV-Vis absorption spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). NH3 gas-sensing properties of PANI and PA nanocomposite thin films were examined at ambient temperature. The results showed that all the sensors composed of PANI nanocomposite thin films had faster response/recovery rate with better reproducibility selectivity and long-term stability to NH3 than PANI thin film sensor, and PANI/TiO2 nanocomposite thin film sensor showed optimum NH3 gas-sensing characteristics. The effect of humidity on the responses of all the sensors was also investigated.

Self-assembly of TiO2/polypyrrole nanocomposite ultrathin films and application for an NH3 gas sensor

TiO2/polypyrrole (PPy) nanocomposite ultrathin films for NH3 gas detection were fabricated by the in situ self-assembly technique. The films were characterized by UV–Vis absorption, FT–IR spectroscopy, and atomic force microscopy (AFM). The electrical properties of TiO2/PPy ultrathin film NH3 gas sensors, such as sensitivity, selectivity, reproducibility, and stability were investigated at room temperature in air as well as in N2. The results showed that the optimum gas-sensing characteristics of TiO2/PPy ultrathin film were obtained in the presence of 0.1 wt% colloidal TiO2 for 20-min deposition. Compared with pure PPy thin-film sensors, the TiO2/PPy film gas sensor has a shorter response/recovery time. It was also found that both humidity and temperature had an effect on the operation of the TiO2/PPy film gas sensor at low NH3 concentrations.

Ammonia gas sensors based on poly (3-hexylthiophene)-molybdenum disulfide film transistors

In this work, in order to enhance the recovery performance of organic thin film transistors (OTFTs) ammonia (NH3) sensors, poly (3-hexylthiophene) (P3HT) and molybdenum disulfide (MoS2) were combined as sensitive materials. Different sensitive film structures as active layers of OTFTs, i.e., P3HT-MoS2 composite film, P3HT/MoS2 bilayer film and MoS2/P3HT bilayer film were fabricated by spray technology. OTFT gas sensors based on P3HT-MoS2 composite film showed a shorter recovery time than others when the ammonia concentration changed from 4 to 20 ppm. Specifically, x-ray diffraction (XRD), Raman and UV-visible absorption were employed to explore the interface properties between P3HT and single-layer MoS2. Through the complementary characterization, a mechanism based on charge transfer is proposed to explain the physical originality of these OTFT gas sensors: closer interlayer d-spacing and better π-π stacking of the P3HT chains in composite film have ensured a short recovery time of OTFT gas sensors. Moreover, sensing mechanisms of OTFTs were further studied by comparing the device performance in the presence of nitrogen or dry air as a carrier gas. This work not only strengthens the fundamental understanding of the sensing mechanism, but provides a promising approach to optimizing the OTFT gas sensors.

The Fabrication and Optimization of Thin-Film Transistors Based on Poly(3-Hexylthiophene) Films for Nitrogen Dioxide Detection

Poly(3-hexylthiophene) (P3HT) films were used as active layers in bottom contact organic thin-film transistor (OTFT) gas sensors to detect nitrogen dioxide (NO2). The films with different thicknesses were deposited on the devices to measure current-voltage characteristics and to test the gas sensing properties of the OTFT devices. All prepared OTFTs exhibited p-type semiconductor behaviors. The effect of film thickness on the electronic characteristics of OTFTs was investigated, and the OTFT gas sensor with the thinnest film presented best electronic characteristics. The OTFT gas sensors with thinner P3HT film showed smaller baseline drift, higher response to NO2 gas of a certain concentration, and larger sensitivity enhancement. The sensitivity increased from 0.038 to 0.11 ppm-1 (up to 190%) with the decrease in film thickness from 600 to 200 nm. The absorption of NO2 changed the surface doping level, and thereby perturbed the charge transport properties of the devices, which made OTFT gas sensors with thinner film more sensitive. Compared with the response curves and repeatability curves of all devices, the response of the OTFT gas sensor with the thickest film was not precise owing to the baseline drift. The selectivity was also investigated. The results demonstrated that the response to NO2 was improved due to the film thickness optimization. Moreover, the sensing mechanism was analyzed as well.

Reduced graphene oxide–polyethylene oxide hybrid films for toluene sensing at room temperature

A reduced graphene oxide (RGO)–polyethylene oxide (PEO) hybrid film was constructed with composite and bilayer film structures for effective ambient toluene detection. The morphology and chemical properties of the fabricated RGO–PEO hybrid materials were characterized by SEM, and Raman and FTIR spectroscopies, respectively. Sensitive properties of real-time response, sensitivity, repeatability and selectivity to toluene vapor were studied as well at room temperature. The experimental data show that the gas sensors based on composite film have a higher sensitivity than the ones based on bilayer film and pure RGO film at toluene concentrations from 80 ppm to 140 ppm. In addition, the effect of PEO volume fraction and humidity on the sensing performance was also studied. The sensor with a PEO volume fraction of 50% has a better sensitivity and faster response/recovery than others. With respect to selectivity, the gas response of the prepared sensors to toluene was at least 2-fold higher than those to other vapor species, including acetone, ethanol, hydrogen, water and formaldehyde. Furthermore, the sensing mechanism of the fabricated sensors was investigated by comparing the device performance in the presence of dry air or nitrogen as carrier gas.

Enhanced Formaldehyde-Sensing Performances of Mixed Polyethyleneimine-Multiwalled Carbon Nanotubes Composite Films on Quartz Crystal Microbalance

The development of a robust, reproducible, cheap, and low-power gas sensor for monitoring the low-level concentration of formaldehyde is in urgent demand. In this paper, mixed polyethyleneimine (PEI)-multiwalled carbon nanotubes (MWCNTs) nanocomposite thin film was coated on a quartz crystal microbalance (QCM) using a facile spraying process for formaldehyde detection at room temperature. The effects of spraying loads and ratios of PEI to MWCNTs on sensing properties were investigated. The hydrogen-bonding interaction between PEI and MWCNTs was proved by the X-ray photoelectron spectrometer (XPS) characterization, and the formaldehyde-sensing characteristics results revealed that the PEI-MWCNTs nanocomposite film sensor exhibited superior sensing properties than the pure PEI film sensor, with linear response characteristics, fast response, low detection limit (0.6ppm), good reproducibility and selectivity to formaldehyde within 6 ppm. A sensing mechanism model was introduced to understand the chemical reaction between formaldehyde gas molecules and amine functional groups of PEI along with the ultraviolet-visible absorption spectra analysis. This paper shows the great potential for developing sensitive and fast-response formaldehyde gas sensor with a simple spraying fabrication method.

Wind energy harvesting and self-powered flow rate sensor enabled by contact electrification

We have developed a free-standing-mode based triboelectric nanogenerator (F-TENG) that consists of indium tin oxide (ITO) foils and a polytetrafluoroethylene (PTFE) thin film. By utilizing the wind-induced resonance vibration of a PTFE film between two ITO electrodes, the F-TENG delivers an open-circuit voltage up to 37 V and a short-circuit current of 6.2 μA, which can be used as a sustainable power source to simultaneously and continuously light up tens of light emitting diodes (LEDs) and charge capacitors. Moreover, uniform division of the electrode into several parallel units efficiently suppresses the inner counteracting effect of undulating film and leads to an enhancement of output current by 95%. The F-TENG holds prominent durability and an excellent linear relationship between output current and flow rate, revealing its feasibility as a self-powered sensor for detecting wind speed. This work demonstrates potential applications of the triboelectric generator in gas flow harvesters, self-powered air navigation, self-powered gas sensors and wind vector sensors.

Layer-by-layer assembly carbon nanotubes thin film based gas sensors for ammonia detection

Single walled carbon nanotubes (SWNTs) were deposited on interdigital electrode (IDE) devices and quartz crystal microbalance (QCM) devices through layer-by-layer self-assembly method to fabricate resistance sensitive and mass sensitive gas sensors, respectively. Their ammonia gas-sensitive characteristics were detected at different temperature. It is revealed that the SWNTs based mass sensitive gas sensor has good sensing properties at room temperature. However, the SWNTs based resistance sensitive gas sensor has irreversible response for ammonia gas. When the temperature increases, the noise of SWNTs based mass sensitive gas sensor increases and the gas sensitive characteristic decreases. Meanwhile, the humidity effect is also discussed. It is important to optimize gas sensor by making it work at an appropriate external environment.

Novel Piezoelectric DDVP Sensor Based on Self‐Assembly Method

Abstract A novel piezoelectric sensor was fabricated by depositing the films of polyvinyl pyrrolindone (PVP) and PVP with butyl cholinesterase (BuChE) (BuChE‐PVP), respectively, on the surface of quartz crystal microbalance (QCM) using self‐assembly method. The sensitive films were characterized with online examination and XPS technique. The obtained sensors were applied to measure o,o‐dimethyl‐o‐2,2‐dichlorovinyl phosphate (DDVP) pesticide concentration. It shows that BuChE‐PVP sensor has higher sensitivity than PVP sensor. There is a linear relationship between the shift of frequency and the concentration of DDVP in a range from 4.25 to 21.25 ppm. This highly sensitive sensor has also been shown to determine DDVP concentration in several samples, and the relative standard error is less than 3%. It also shows that CO, NO2, H2S, and SO2 with 10 times the concentration of DDVP have no interference with DDVP detection in the tested concentration range.

An Artificial Olfactory System Based on Gas Sensor Array and Back-Propagation Neural Network

An artificial olfactory system is constructed to determine the individual gas concentrations of gas mixture (CO and H2) with high accuracy. And a Back-Propagation (BP) neural network algorism has been designed using MATLAB neural network toolbox. And an effective study to enhance the parameters of the neural network, including pre-processing techniques and early stopping method is presented in this paper. It is showed that the method of BP artificial neural improves the selectivity and sensitivity of semiconductor gas sensor, and is valuable to engineering application.