Tuning the Fermi Level and the Kinetics of Surface States of TiO₂ Nanorods by Means of Ammonia Treatments

Ammonia-induced reduction treatment of titanium dioxide rutile nanorods has been performed, where the treatment triggered a synergistic surface modification of titania electrodes that enhanced its overall photoelectrochemical performance, besides introducing a new absorption band in the 420–480 nm range. A physical model has been proposed to reveal the role of each fundamental interfacial property on the observed behavior. On the one hand, by tuning the Fermi level position, charge separation was optimized by adjusting the depletion region width to maximize the potential drop inside titanium dioxide and also filling the surface states, which in turn decreased electron–hole recombination. On the other hand, by increasing the density of surface holes traps (identified as surface hydroxyl groups), the average hole lifetime was extended, depicting a more efficient hole transfer to electrolyte species. The proposed model could serve as a rationale for controlled interfacial adjustment of nanostructured photoelectrodes tailoring them for the required application

Highly Specific and Wide Range NO₂ Sensor with Color Readout

We present a simple and inexpensive method to implement a Griess-Saltzman-type reaction that combines the advantages of the liquid phase method (high specificity and fast response time) with the benefits of a solid implementation (easy to handle). We demonstrate that the measurements can be carried out using conventional RGB sensors; circumventing all the limitations around the measurement of the samples with spectrometers. We also present a method to optimize the measurement protocol and target a specific range of NO₂ concentrations. We demonstrate that it is possible to measure the concentration of NO₂ from 50 ppb to 300 ppm with high specificity and without modifying the Griess-Saltzman reagent

Band Engineered Epitaxial 3D GaN-InGaN Core–Shell Rod Arrays as an Advanced Photoanode for Visible-Light-Driven Water Splitting

3D single-crystalline, well-aligned GaN-InGaN rod arrays are fabricated by selective area growth (SAG) metal–organic vapor phase epitaxy (MOVPE) for visible-light water splitting. Epitaxial InGaN layer grows successfully on 3D GaN rods to minimize defects within the GaN-InGaN heterojunctions. The indium concentration (In ∼ 0.30 ± 0.04) is rather homogeneous in InGaN shells along the radial and longitudinal directions. The growing strategy allows us to tune the band gap of the InGaN layer in order to match the visible absorption with the solar spectrum as well as to align the semiconductor bands close to the water redox potentials to achieve high efficiency. The relation between structure, surface, and photoelectrochemical property of GaN-InGaN is explored by transmission electron microscopy (TEM), electron energy loss spectroscopy (EELS), Auger electron spectroscopy (AES), current–voltage, and open circuit potential (OCP) measurements. The epitaxial GaN-InGaN interface, pseudomorphic InGaN thin films, homogeneous and suitable indium concentration and defined surface orientation are properties demanded for systematic study and efficient photoanodes based on III-nitride heterojunctions