Detection of glucose in the growth media of Ulva lactuca using a Ni-Cu/TiO2/Ti self-assembly nanostructure sensor under the influence of crude oil

Pollution of the marine environment by crude oil is considered as a significant problem. Interestingly, the existence of algae in the marine ecosystem contributes significantly to maintaining the equilibrium of marine life and, consequently, has the ability to alert the ecosystem to the pollution by using their waterborne molecules including the photosynthetic products. The main aim of this work is to develop an electrochemical sensor (EC) for the detection of the concentration of glucose found in the growth media of Ulva sp. as a photosynthetic product or decomposed substance under polluted conditions. A Ni-Cu/TiO2/Ti array electrode was fabricated, where highly-ordered self-organized nanocrystalline TiO2 was prepared via anodization and annealing processes on a Ti substrate and Ni-Cu alloy nanoparticles were electrodeposited by linear sweep voltammetry. The chemical composition, structure and morphology characterization were carried out by high-resolution scanning electron microscopy and energy dispersive X-ray spectroscopy analyses. The ideal non-enzymatic sensor with large and constant sensitivity (402 μA mM−1 cm−2) and low detection limit (495 μM) was successfully employed to detect glucose excreted by Ulva lactuca under oil pollution under alkaline condition. The present study succeeded to combine between the ecological role of algae and electrochemical sensors to be used collectively as an indicator of the oil spillage into the seawater. Keywords: Non-enzymatic glucose sensor, Nutrient, Ni-Cu/TiO2/Ti, Algae, Ulva lactuc

Cathodic activation of titanium-supported gold nanoparticles: An efficient and stable electrocatalyst for the hydrogen evolution reaction

As-polished titanium (Ti) substrates decorated with dispersed gold nanoparticles (Au NPs/Ti) of various sizes and densities were prepared here to effectively catalyze hydrogen evolution reaction (HER) in 0.5 M H2SO4. These materials were synthesized adopting a facile one-step wet chemical method without using reducing agents, stabilizers, or any chemical pre-treatment, where Ti acts as both the reducing agent and support. This was achieved via soaking the Ti substrates for 30 min in a gold precursor bath as a function of temperature (5 -65 degrees C). Morphological characterizations of the synthesized Au NPs/Ti catalysts indicated a size decrease and density increase of loaded Au NPs with the rise of temperature. Cathodic polarization measurements revealed that the catalyst loaded with the highest density of Au NPs exhibited the best HER activity with onset potential (E-HER), exchange current density (j(o)), and Tafel slope (beta(c)) of -44 mV (RHE), 6.0 x 10(-3) mA cm(-2), and 40 mV decade(-1), respectively. This activity has markedly increased upon cathodic activation (cathodic pre-polarization treatment at -2 V (SCE) for 12 h) that yielded a Ti substrate with a porous-like network structure decorated with highly dispersed Au NPs. In addition, a catalytically active TiH2 phase was formed (as evidenced from XRD and XPS) on such a porous substrate. Such cathodically pre-treated catalyst recorded HER electrochemical parameters of -18 mV (RHE), 0.117 mA cm(-2), and 38 mV decade(-1), thus approaching the commercial Pt/C catalyst (E-HER: 0.0 mV, j(o) : 0.78 mA cm(-2), and beta(c): 31 mV dec(-1)). The stability of the best catalyst was assessed employing cyclic polarization and chronoamperometry measurements. It exhibited a good stability with improved activity during stability testing. Copyright (C) 2016, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.As-polished titanium (Ti) substrates decorated with dispersed gold nanoparticles (Au NPs/Ti) of various sizes and densities were prepared here to effectively catalyze hydrogen evolution reaction (HER) in 0.5&nbsp;M&nbsp;H2SO4. These materials were synthesized adopting a facile one-step wet chemical method without using reducing agents, stabilizers, or any chemical pre-treatment, where Ti acts as both the reducing agent and support. This was achieved&nbsp;via&nbsp;soaking the Ti substrates for 30&nbsp;min in a gold precursor bath as a function of temperature (5&ndash;65&nbsp;&deg;C). Morphological characterizations of the synthesized Au NPs/Ti catalysts indicated a size decrease and density increase of loaded Au NPs with the rise of temperature. Cathodic polarization measurements revealed that the catalyst loaded with the highest density of Au NPs exhibited the best HER activity with onset potential (EHER), exchange current density (jo), and Tafel slope (&beta;c) of &minus;44&nbsp;mV (RHE), 6.0&nbsp;&times;&nbsp;10&minus;3&nbsp;mA&nbsp;cm&minus;2, and 40&nbsp;mV&nbsp;decade&minus;1, respectively. This activity has markedly increased upon cathodic activation (cathodic pre-polarization treatment at &minus;2&nbsp;V (SCE) for 12&nbsp;h) that yielded a Ti substrate with a porous-like network structure decorated with highly dispersed Au NPs. In addition, a catalytically active TiH2phase was formed (as evidenced from XRD and XPS) on such a porous substrate. Such cathodically pre-treated catalyst recorded HER electrochemical parameters of &minus;18&nbsp;mV (RHE), 0.117&nbsp;mA&nbsp;cm&minus;2, and 38&nbsp;mV&nbsp;decade&minus;1, thus approaching the commercial Pt/C catalyst (EHER: 0.0&nbsp;mV,&nbsp;jo: 0.78&nbsp;mA&nbsp;cm&minus;2, and&nbsp;&beta;c: 31&nbsp;mV&nbsp;dec&minus;1). The stability of the best catalyst was assessed employing cyclic polarization and chronoamperometry measurements. It exhibited a good stability with improved activity during stability testing.</p

Room-Temperature Wet Chemical Synthesis of Au NPs/TiH 2 /Nanocarved Ti Self-Supported Electrocatalysts for Highly Efficient H 2 Generation

International audienc

Room-Temperature Wet Chemical Synthesis of Au NPs/TiH₂/Nanocarved Ti Self-Supported Electrocatalysts for Highly Efficient H₂ Generation

Self-supported electrocatalysts are a new class of materials exhibiting high catalytic performance for various electrochemical processes and can be directly equipped in energy conversion devices. We present here, for the first time, sparse Au NPs self-supported on etched Ti (nanocarved Ti substrate self-supported with TiH₂) as promising catalysts for the electrochemical generation of hydrogen (H₂) in KOH solutions. Cleaned, as-polished Ti substrates were etched in highly concentrated sulfuric acid solutions without and with 0.1 M NH₄F at room temperature for 15 min. These two etching processes yielded a thin layer of TiH₂ (the corrosion product of the etching process) self-supported on nanocarved Ti substrates with different morphologies. While F^–-free etching process led to formation of parallel channels (average width: 200 nm), where each channel consists of an array of rounded cavities (average width: 150 nm), etching in the presence of F^– yielded Ti surface carved with nanogrooves (average width: 100 nm) in parallel orientation. Au NPs were then grown <i>in situ</i> (self-supported) on such etched surfaces via immersion in a standard gold solution at room temperature without using stabilizers or reducing agents, producing Au NPs/TiH₂/nanostructured Ti catalysts. These materials were characterized by scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), grazing incidence X-ray diffraction (GIXRD), and X-ray photoelectron spectroscopy (XPS). GIXRD confirmed the formation of Au₂Ti phase, thus referring to strong chemical interaction between the supported Au NPs and the substrate surface (also evidenced from XPS) as well as a titanium hydride phase of chemical composition TiH₂. Electrochemical measurements in 0.1 M KOH solution revealed outstanding hydrogen evolution reaction (HER) electrocatalytic activity for our synthesized catalysts, with Au NPs/TiH₂/nanogrooved Ti catalyst being the best one among them. It exhibited fast kinetics for the HER with onset potentials as low as −22 mV vs. RHE, high exchange current density of 0.7 mA cm^–2, and a Tafel slope of 113 mV dec^–1. These HER electrochemical kinetic parameters are very close to those measured here for a commercial Pt/C catalyst (onset potential: −20 mV, Tafel slope: 110 mV dec^–1, and exchange current density: 0.75 mA cm^–2). The high catalytic activity of these materials was attributed to the catalytic impacts of both TiH₂ phase and self-supported Au NPs (active sites for the catalytic reduction of water to H₂), in addition to their nanostructured features which provide a large-surface area for the HER