Gas sensing properties of tin oxide nanostructures synthesized via a solid-state reaction method

Development of a Toxic Lead Ionic Sensor Using Carboxyl-Functionalized MWCNTs in Real Water Sample Analyses

Functional multiwall carbon nanotubes (f-MWCNTs) are of significant interest due to their dispersion ability in the aqueous phase and potential application in environmental, nanotechnology, and biological fields. Herein, we functionalized MWCNTs by a simple acid treatment under ultra-sonification, which represented a terminal or side-functional improvement for the fabrication of a toxic lead ion sensor. The f-MWCNTs were characterized in detail by XRD, Raman, XPS, BET, UV/vis, FTIR, and FESEM-coupled XEDS techniques. The analytical performance of the f-MWCNTs was studied for the selective detection of toxic lead ions by inductively coupled plasma-optical emission spectrometry (ICP-OES). The selectivity of the f-MWCNTs was evaluated using several metal ions such as Cd²⁺, Co²⁺, Cr³⁺, Cu²⁺, Fe³⁺, Ni²⁺, Pb²⁺, and Zn²⁺ ions. Lastly, the newly designed ionic sensor was successfully employed to selectively detect lead ions in several environmental water samples with reasonable results. This approach introduced a new technique for the selective detection of heavy metal ions using functional carbon nanotubes with ICP-OES for the safety of environmental and healthcare fields on a broad scale.

Template-Free Construction of Tin Oxide Porous Hollow Microspheres for Room-Temperature Gas Sensors

Porous hollow microsphere (PHM) materials represent ideal building blocks for realizing diverse functional applications such as catalysis, energy storage, drug delivery, and chemical sensing. This has stimulated intense efforts to construct metal oxide PHMs for achieving highly sensitive and low-power-consumption semiconductor gas sensors. Conventional methods for constructing PHMs rely on delicate reprogramming of templates and may suffer from the structural collapse issue during the removal of templates. Here, we propose a template-free method for the construction of tin oxide (SnO₂) PHMs via the competition between the solvent evaporation rate and the phase separation dynamics of colloidal SnO₂ quantum wires. The SnO₂ PHMs (typically 3 ± 0.5 μm diameter and approximately 200 nm shell thickness) exhibit desirable structural stability with desirable processing compatibility with various substrates. This enables the realization of NO₂ gas sensors having a superior response and recovery process at room temperature. The superior NO₂-sensing characteristic is attributed to the effective gas adsorption competition on solid surfaces benefiting from efficient diffusion channels, enhancing the interaction of metal oxide solids with gas molecules in terms of the receptor function, transducer function, and utility factor. In addition, the one-step deposition of SnO₂ PHMs directly onto device substrates simplifies the fabrication conditions for semiconductor gas sensors. The desirable structural stability of PHMs combined with the functional diversity of metal oxides may open new opportunities for the design of functional materials and devices.

Characterization of individual barium titanate nanorods and their assessment as building blocks of new circuit architectures

In this work, we report on the integration of individual BaTiO(3) nanorods into simple circuit architectures. Polycrystalline BaTiO(3) nanorods were synthesized by electrophoretic deposition (EPD) of barium titanate sol into aluminium oxide (AAO) templates and subsequent annealing. Transmission electron microscopy (TEM) observations revealed the presence of slabs of hexagonal polymorphs intergrown within cubic grains, resulting from the local reducing atmosphere during the thermal treatment. Electrical measurements performed on individual BaTiO(3) nanorods revealed resistivity values between 10 and 100 Ω cm, which is in good agreement with typical values reported in the past for oxygen-deficient barium titanate films. Consequently the presence of oxygen vacancies in their structure was indirectly validated. Some of these nanorods were tested as proof-of-concept humidity sensors. They showed reproducible responses towards different moisture concentrations, demonstrating that individual BaTiO(3) nanorods may be integrated in complex circuit architectures with functional capacities.

Modular "click" chemistry for electrochemically and photoelectrochemically active molecular interfaces to tin oxide surfaces

We demonstrate the use of "click" chemistry to form electrochemically and photoelectrochemically active molecular interfaces to SnO(2) nanoparticle thin films. By using photochemical grafting to link a short-chain alcohol to the surface followed by conversion to a surface azide group, we enable use of the Cu(I)-catalyzed azide-alkyne [3 + 2] cycloaddition (CuAAC) reaction, a form of "click" chemistry, on metal oxide surfaces. Results are shown with three model compounds to test the surface chemistry and subsequent ability to achieve electrochemical and photoelectrochemical charge transfer. Surface-tethered ferrocene groups exhibit good electron-transfer characteristics with thermal rates estimated at >1000 s(-1). Time-resolved surface photovoltage measurements using a ruthenium terpyridyl coordination compound demonstrate photoelectron charge transfer on time scales of nanoseconds or less, limited by the laser pulse width. The results demonstrate that the CuAAC "click" reaction can be used to form electrochemically and photoelectrochemically active molecular interfaces to SnO(2) and other metal oxide semiconductors.