Barin, Özlem; Ajjaq, Ahmad; Çağırtekin, Ali Orkun; Karaduman Er, Irmak; Yıldırım, Memet Ali; Ateş, Aytunç; Acar, Selim

Although hydrogen is a non-poisonous gas that can dissipate quickly once is released, it causes suffocation at high concentrations and is very risky on some occasions if not suitably handled. In this study, an effective approach was suggested for developing and tuning hydrogen gas sensors, where the crucial effect of nucleation layers and chemical stabilizing agents on the morphology of hydrothermally-assisted growth and its gas sensing performance was demonstrated. For this purpose, ZnO seed layers were separately synthesized by different solution-based chemical processes based on the successive ionic layer adsorption and reaction, spin, and dip coating techniques followed by a hydrothermal treatment under the same conditions. X-ray diffraction measurements revealed that all the synthesized samples have a similar pure hexagonal wurtzite structure with a big difference in the degree of textural orientation along the c-axis of ZnO. Optical transmittances, forbidden bandgap energies, and Urbach energies of the produced samples were influenced to a great extent by the coating techniques and the chemical solutions used. Aside from that, the morphology of the synthesized samples and their overall thicknesses together with the available oxygen vacancies detected by X-ray photoelectron spectroscopy changed considerably. The change in structure and morphology have influenced the wettability of the synthesized samples. They have also greatly influenced the gas sensing performance of the sensors in terms of optimal working temperature, sensitivity, and response/recovery periods. The hydrogen gas detection mechanism of the fabricated sensors and the logic behind the change that occurred in gas sensing performance based on morphology are discussed.

Ozdokur, K. Volkan; Demir, Bilal; Atman, Ece; Tatli, Alper Yalin; Yilmaz, Buket; Demirkol, Dilek Odaci; Kocak, Suleyman; Timur, Suna; Ertas, F. Nil

Transition metal oxides provide low cost alternatives to noble metals due to their unique electrocatalytic and electrochromic properties and display strong interactions with noble metal nanoparticles. Present study describes the use of mixed molybdenum and manganese oxide film electrode enriched with platinum nanoparticles to enhance the catalytic performance in the oxygen reduction reaction (ORR). The mixed oxide film, denominated as GCE/MnOx-MoOx/Pt, was co-deposited by pulsed potential deposition technique and then, it was used as an immobilization matrix for the intact bacterial cells. The resulted whole cell biosensor has served as a sensing platform for ethanol detection by monitoring of oxygen consumption as a result of the bacterial metabolism in the presence of the substrate. Following the optimization experiments, GCE/MnOx-MoOx/Pt/Gluconobacter oxydans biofilm was applied to investigate the analytical characteristics and response time to ethanol as well as operational stability and substrate specificity for other carbon sources. The linear range was found as 0.075–5.0 mM with a response time of 63 s and the developed method was applied to the ethanol determination in alcoholic drinks. Satisfactory recovery figures were obtained in comparison to the standard method.

Yokuş, Özlem Aktaş; Kardaş, Faruk; Akyildirim, Onur; Eren, Tanju; Atar, Necip; Yola, Mehmet Lütfi

In this report, a novel voltammetric sensor based on polyoxometalate (H3PW12O40, POM) functionalized reduced graphene oxide (rGO) modified glassy carbon electrode (GCE) was presented for simultaneous determination of l-tyrosine (l-Tyr) and l-tryptophan (l-Trp). The nanocomposites were characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The electrochemical determination of l-Tyr and l-Trp has been studied using square wave voltammetry (SWV) on GCE modified with POM-rGO composite (POM-rGO/GCE). The developed method was also applied successfully for the simultaneous determination of l-Tyr and l-Trp in spiked serum sample and the linearity range of l-Tyr and l-Trp was 1.0 × 10-11 - 1.0 × 10-9 M with the detection limit of 2.0 × 10-12 M.