High performance acetone sensor based on γ-Fe2O3/Al-ZnO nanocomposites.

Ternary nanocomposites made of γ-iron oxide and aluminum-doped zinc oxide (γ-Fe2O3/Al-ZnO NCs), with different metal oxides ratio (0%-100%) were prepared through a solvothermal sol-gel process. The synthesized materials were characterized by x-ray diffraction, UV-vis spectroscopy, photoluminescence (PL), scanning electron microscope and BET analysis. Characterization results demonstrated that the ternary γ-Fe2O3/Al-ZnO NCs are mainly constituted by γ-Fe2O3 and Al-ZnO individual phases, while structural and physical properties like surface area, pore size, optical band gap, PL and electrical conductivity were deeply affected by the composition of nanocomposite. The synthesized γ-Fe2O3/Al-ZnO NCs were employed to prepare conductometric gas sensors, then their sensing performances toward acetone were also investigated. Results revealed enhanced sensing performance of nanocomposites than both pure γ-Fe2O3 and Al-ZnO phases. In particular, the γ-Fe2O3(33%)/Al-ZnO based gas sensor showed the best sensing properties, like a high response of R air/R gas = 29, a short response time of 3 s, in addition to an improved selectivity toward acetone versus ethanol at an operating temperature of 200 °C. Overall, ternary γ-Fe2O3/Al-ZnO NCs appear to be promising for the development of conductometric acetone sensors.

A comparison of the ethanol sensing properties of α-iron oxide nanostructures prepared via the sol-gel and electrospinning techniques.

Haematite (α-Fe2O3) nanostructures were synthesized via a Pechini sol-gel method (PSG) and an electrospinning (ES) technique. Their texture and morphology were investigated by scanning and transmission electron microscopy. α-Fe2O3 nanoparticles were obtained by the PSG method, whereas fibrous structures consisting of interconnected particles were synthesized through the ES technique. The crystallinity of the α-Fe2O3 nanostructures was also studied by means of x-ray diffraction and Raman spectroscopy. Gas-sensing devices were fabricated by printing the synthesized samples on ceramic substrates provided with interdigitated Pt electrodes. The sensors were tested towards low concentrations of ethanol in air in the temperature range (200-400 °C). The results show that the α-Fe2O3 nanostructures exhibit somewhat different gas-sensing properties and, interestingly, their sensing behaviour is strongly temperature-dependent. The availability of active sites for oxygen chemisorption and the diffusion of the analyte gas within the sensing layer structure are hypothesized to be the key factors responsible for the different sensing behaviour observed.

Investigations on the effect of gamma-ray irradiation on the gas sensing properties of SnO2 nanoparticles.

In recent years, SnO2 nanoparticles (NPs) have been subjected to various modifications in order to improve their performance in sensing and other applications. Here, we report the synthesis of SnO2 NPs by microwave irradiation, and subsequent exposure to gamma (γ) radiation at different doses (0-150 kGy) to induce desirable physico-chemical properties. The irradiated samples were characterized by x-ray powder diffraction (XRD), transmission electron microscopy (TEM and HR-TEM), and photoluminescence (PL) to evaluate the effect of γ-ray irradiation on their morphology and microstructure. The results revealed that the bulk crystal structure remained unchanged after irradiation, while the existence of defects and a damaged over-layer have been confirmed by PL and HR-TEM respectively. The influence of γ-irradiation on the electrical and CO sensing characteristics was also investigated in the temperature range between 150 and 400 °C. γ-irradiated SnO2 NP based resistive sensors showed better CO sensing characteristics (i.e. higher response and lower working temperature) compared to non-irradiated SnO2. Upon optimizing the γ-ray dose irradiation level and working temperature, a ten-fold enhancement in the response to CO has been achieved (R/R 0 = 12 to 50 ppm of CO in air) in 50 kGy irradiated SnO2 NP based sensors operating at 150 °C. A possible mechanism for the enhanced sensing performance of γ-irradiated SnO2 NPs has been proposed.

A novel disposable electrochemical sensor for determination of carbamazepine based on Fe doped SnO2 nanoparticles modified screen-printed carbon electrode.

An effective strategy to fabricate a novel disposable screen printing carbon electrode modified by iron doped tin dioxide nanoparticles for carbamazepine (CBZ) detection has been developed. Fe-SnO2 (Fe=0 to 5 wt.%) NPs were synthesized by a simple microwave irradiation method and assessed for their structural and morphological changes due to Fe doping into SnO2 matrix by X-ray diffraction and scanning and transmission electron microscopy. The electrochemical behaviour of carbamazepine at the Fe-SnO2 modified screen printed carbon electrode (SPCE) was investigated by cyclic voltammetry and square wave voltammetry. Electron transfer coefficient α (0.63) and electron transfer rate constant ks (0.69 s(-1)) values of the 5 wt.% Fe-SnO2 modified SPCE indicate that the diffusion controlled process takes place on the electrode surface. The fabricated sensor displayed a good electrooxidation response towards the detection of CBZ at a lower oxidation potential of 0.8 V in phosphate buffer solution at pH7.0. Under the optimal conditions, the sensor showed fast and sensitive current response to CBZ over a wide linear range of 0.5-100 µM with a low detection limit of 92 nM. Furthermore, the practical application of the modified electrode has been investigated by the determination of CBZ in pharmaceutical products using standard addition method.