CO2 sensing properties of electro-spun Ca-doped ZnO fibres.

The availability of low-cost, high-performing sensors for carbon dioxide detection in the environment may play a crucial role for reducing CO2 emissions and limiting global warming. In this study, calcium-doped zinc oxide nanofibres with different Ca to Zn loading ratios (1:40 or 1:20) are synthesised via electro-spinning, thoroughly characterised and, for the first time, tested as an active material for the detection of carbon dioxide. The results of their characterisation show that the highly porous fibres consist of interconnected grains of oxide with the hexagonal wurtzite structure of zincite. Depending on the Ca:Zn loading ratio, calcium fully or partly segregates to form calcite on the fibre surface. The high response of the sensor based on the fibres with the highest Ca-doping level can be attributed to the synergy between the fibre morphology and the basicity of Ca-ion sites, which favour the diffusion of the gas molecules within the sensing layer and the CO2 adsorption, respectively.

Structural and antibacterial studies of novel ZnO and ZnxMn(1-x)O nanostructured titanium scaffolds for biomedical applications.

In the biomedical field, the demand for the development of broad-spectrum biomaterials able to inhibit bacterial growth is constantly increasing. Chronic infections represent the most serious and devastating complication related to the use of biomaterials. This is particularly relevant in the orthopaedic field, where infections can lead to implant loosening, arthrodesis, amputations and sometimes death. Antibiotics are the conventional approach for implanted-associated infections, but they have the limitation of increasing antibiotic resistance, a critical worldwide healthcare issue. In this context, the development of anti-infective biomaterials and infection-resistant surfaces can be considered the more effective strategy to prevent the implant colonisation and biofilm formation by bacteria, so reducing the occurrence of implant-associated infections. In the last years, inorganic nanostructures have become extremely appealing for chemical modifications or coatings of Ti surfaces, since they do not generate antibiotic resistance issues and are featured by superior stability, durability, and full compatibility with the sterilization process. In this work, we present a simple, rapid, and cheap chemical nanofunctionalization of titanium (Ti) scaffolds with colloidal ZnO and Mn-doped ZnO nanoparticles (NPs), prepared by a sol-gel method, exhibiting antibacterial activity. ZnO NPs and ZnxMn(1-x)O NPs formation with a size around 10-20nm and band gap values of 3.42 eV and 3.38 eV, respectively, have been displayed by characterization studies. UV-Vis, fluorescence, and Raman investigation suggested that Mn ions acting as dopants in the ZnO lattice. Ti scaffolds have been functionalized through dip coating, obtaining ZnO@Ti and ZnxMn(1-x)O@Ti biomaterials characterized by a continuous nanostructured film. ZnO@Ti and ZnxMn(1-x)O@Ti displayed an enhanced antibacterial activity against both Gram-positive Staphylococcus aureus (S. aureus) and Gram-negative Pseudomonas aeruginosa (P. aeruginosa) bacterial strains, compared to NPs in solution with better performance of ZnxMn(1-x)O@Ti respect to ZnO@Ti. Notably, it has been observed that ZnxMn(1-x)O@Ti scaffolds reach a complete eradication for S. aureus and 90 % of reduction for P. aeruginosa. This can be attributed to Zn2+ and Mn2+ metal ions release (as observed by ICP MS experiments) that is also maintained over time (72 h). To the best of our knowledge, this is the first study reported in the literature describing ZnO and Mn-doped ZnO NPs nanofunctionalized Ti scaffolds with improved antibacterial performance, paving the way for the realization of new hybrid implantable devices through a low-cost process, compatible with the biotechnological industrial chain method.

Electrochemical Sensing of Serotonin by a Modified MnO2-Graphene Electrode.

The development of MnO2-graphene (MnO2-GR) composite by microwave irradiation method and its application as an electrode material for the selective determination of serotonin (SE), popularly known as "happy chemical", is reported. Anchoring MnO2 nanoparticles on graphene, yielded MnO2-GR composite with a large surface area, improved electron transport, high conductivity and numerous channels for rapid diffusion of electrolyte ions. The composite was characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and scanning electron microscopy (SEM) for assessing the actual composition, structure and morphology. The MnO2-GR composite modified glassy carbon electrode (GCE) exhibited an excellent electrochemical activity towards the detection of SE in phosphate buffer saline (PBS) at physiological pH of 7.0. Under optimum conditions, the modified electrode could be applied to the quantification of serotonin by square wave voltammetry over a wide linear range of 0.1 to 800 µM with the lowest detection limit of 10 nM (S/N = 3). The newly fabricated sensor also exhibited attractive features such as good anti-interference ability, high reproducibility and long-term stability.

Tailoring the structural and microstructural properties of nanosized tantalum oxide for high temperature electrochemical gas sensors.

Ta2O5 nanopowders to be used as sensing electrodes in high temperature electrochemical gas sensors for hydrocarbons detection were synthesized using a sol-gel method and their structural and microstructural properties were investigated. The as-synthesized powders were heated at different temperatures in the range 250-1000 degrees C and characterized by TG-DTA, XRD, SEM, TEM and FT-IR. This investigation allowed to identify the correct thermal treatments to achieve the microstructural, textural and functional stability of materials working at high temperature, preserving their nano-metric grain size. Planar sensors fabricated by using Ta2O5 powders treated at 750 degrees C showed promising results for the selective detection of propylene at high temperature (700 degrees C). The good stability of the sensing response after gas exposure at high temperature was correlated to the stable microstructure the electrodes. Thus, Ta2O5 powders seems good candidate as sensing electrode for sensors for automotive exhausts monitoring.

A highly sensitive oxygen sensor operating at room temperature based on platinum-doped In2O3 nanocrystals.

Semiconducting In2O3 nanocrystals, synthesised via a nonaqueous sol-gel method and doped with 1 wt% of platinum, have shown to possess a unique high sensitivity to oxygen at room temperature (RT). Consequently, a Pt/In2O3-based oxygen sensor for room temperature operation has been developed showing higher performance compared to the state-of-the-art devices.

Synthesis, Characterization and Gas Sensing Properties of Ag@α-Fe2O3 Core-Shell Nanocomposites.

Ag@α-Fe2O3 nanocomposite having a core-shell structure was synthesized by a two-step reduction-sol gel approach, including Ag nanoparticles synthesis by sodium borohydride as the reducing agent in a first step and the subsequent mixing with a Fe+3 sol for α-Fe2O3 coating. The synthesized Ag@α-Fe2O3 nanocomposite has been characterized by various techniques, such as SEM, TEM and UV-Vis spectroscopy. The electrical and gas sensing properties of the synthesized composite towards low concentrations of ethanol have been evaluated. The Ag@α-Fe2O3 nanocomposite showed better sensing characteristics than the pure α-Fe2O3. The peculiar hierarchical nano-architecture and the chemical and electronic sensitization effect of Ag nanoparticles in Ag@α-Fe2O3 sensors were postulated to play a key role in modulating gas-sensing properties in comparison to pristine α-Fe2O3 sensors.

The controlled deposition of metal oxides onto carbon nanotubes by atomic layer deposition: examples and a case study on the application of V2O4 coated nanotubes in gas sensing.

A new atomic layer deposition (ALD) process was applied for the uniform coating of carbon nanotubes with a number of transition-metal oxide thin films (vanadium, titanium, and hafnium oxide). The presented approach is adapted from non-aqueous sol-gel chemistry and utilizes metal alkoxides and carboxylic acids as precursors. It allows the coating of the inner and outer surface of the tubes with a highly conformal film of controllable thickness and hence, the production of high surface area hybrid materials. The morphology and the chemical composition as well as the high purity of the films are evidenced through a combination of electron microscopic and electron-energy-loss spectrometric techniques. Furthermore, in order to highlight a possible application of the obtained hybrids, the electrical and sensing properties of resistive gas sensors based on hybrid vanadium oxide-coated carbon nanotubes (V2O4-CNTs) are reported and the effect of thermal treatment on the gas sensing properties is studied.

Vanadium oxide sensing layer grown on carbon nanotubes by a new atomic layer deposition process.

A new atomic layer deposition (ALD) process was applied for the homogeneous coating of carbon nanotubes with vanadium oxide. It permits the coating of the inner and outer surface with a highly conformal film of controllable thickness and, hence, the production of high surface area hybrid materials at a so far unprecedented quality. The ALD-coated tubes are used as active component in gas-sensing devices. They show electric responses that are directly related to the peculiar structure, i.e., the p-n heterojunction formed between the support and the film.