Development of low-cost metal oxide pH electrodes based on the polymeric precursor method

In this work, the polymeric precursor method was used to prepare low-cost solid-state sensors for pH determination based on iridium oxide as the main pH sensitive material. The iridium content was reduced with addition of TiO₂, forming the binary system IrO_x–TiO₂, whose electroanalytical properties were evaluated in comparison with a commercial glass pH electrode. The minimum iridium content which gave suitable results was 30 mol%, and the electrode presented Nernstian and fast response in the pH range from 1 to 13, with no hysteresis effect observed. Besides, the electrode showed high selectivity in the presence of alkali ions as Li⁺, Na⁺ or K⁺. The amount of iridium in the prepared electrodes was very small (<0.1 mg), supporting the efficiency of this method on the simple preparation of functional low-cost pH electrodes.     

氧化铱纳米颗粒修饰碳纤维电极用于水果中pH在线检测

pH检测在农业生产、食品加工、环境保护、疾病诊断等领域有着重要意义.电化学法具有响应速度快、灵敏度高和操作简单等优点,是目前最常用的pH检测方法之一.然而,商品化的pH计存在体积大、质子敏感膜易损等问题,仅能在相对稳定的样本溶液环境中工作,并不适用于植入式pH分析.本文将氧化铱纳米颗粒修饰在碳纤维微电极表面,构建了一种...     

Use of iridium oxide films as hydrogen gas evolution cathodes in aqueous media

Hydrous iridium oxide films are highly resistant to reduction under cathodic, hydrogen gas evolution, conditions in aqueous acid or base. Such behavior is not in agreement with simple thermodynamic (Pourbaix) data based on the assumption that the system behaves in a reversible manner. The barrier to reduction is attributed, as discussed earlier for RuO₂, to the involvement of high-energy intermediates (iridium atoms or microclusters of same) which can only be generated at unusually negative overpotential values evidently far into the hydrogen gas evolution region. Thermally prepared IrO₂/Ti electrodes are possible candidates for hydrogen gas evolution cathodes in water electrolysis cells; however, under extended operating conditions, the performance of these cathodes was found to deteriorate due to gradual shedding of the active oxide layer.     

Carbonate‐Melt Oxidized Iridium Wire for pH Sensing

A new approach to the preparation of an iridium oxide film for pH sensing is demonstrated. A thick, uniform and dense ceramic oxide layer was grown on the surface of an iridium wire by oxidizing the wire in a molten alkali metal carbonate at high temperature. The alkali metal ion from the carbonate melt was incorporated into the oxide, resulting in a highly stable oxide compound. After treated in acid solution, the oxide layer became hydrated. SEM, XRD, TGA and element analysis were carried out to characterize the oxide film, and a possible formula of the oxide was computed as Li_0.86IrO_2.34(OH)_0.76?0.39H₂O. The electrode made with this new type of oxide film exhibited good pH sensitivity and stability, even in strong acid/base solutions, or in strong corrosive solution such as hydrofluoric acid. Furthermore, the electrode showed excellent long‐term stability over the test period of two and a half years. In addition, individual electrodes prepared from the same batch exhibited remarkable agreement with respect to potential/pH slopes and apparent standard electrode potentials. The performance of the electrodes depends on the properties of the oxide film, such as composition, hydration state and oxidation state.     

Synthesis of tetra-metal oxide system based pH sensor via branched cathodic electrodeposition on different substrates

In this paper pH sensors based on tetra-metal oxide system (TMOF) film was synthesized by branched cathodic electrodeposition technique. Four different metal oxides mainly IrO₂, RuO₂, SnO₂, and TiO₂ used to form a film, which coated on various substrates such as titanium, steel, tin, and copper. The fabricated pH sensors underwent characterization and evaluation sensing performance. Characterizations results have indicated that titanium and steel substrates outperform alternative metal substrates Tin and copper. Nernstian performance of Steel and Titanium substrate with pH sensitivity ∼59 mV/pH remain the same, as well as tin and copper which are behaved as super-Nernstian with sensitivity ∼65 mV/pH. Fast response time ranged from 1 to 3 s were obtained. Perfect selectivity obtained using Na⁺, K⁺, Li⁺ and Mg²⁺ ions vs. primary one H⁺.     

Developing an Iridium Oxide Film Modified Microelectrode for Microscale Measurement of pH

Iridium oxide film modified microelectrode was fabricated by anodic oxidation method onto the tip of an etched iridium wire in diluted sulfuric acid solution by cyclic voltammetry. The iridium oxide film microelectrode exhibited very promising pH sensing performance, with an ideal Nernstian in the tested pH range of 0 to 14. This method for preparing microelectrode allowed accurately control of the deposited amount and the rate of the iridium oxide film growth. The electrodes demonstrated advantages of long lifetime, good selectivity and fast response with a relative time less than 0.2 s for pH changes in a large scale. The microelectrode was not interfered by a wide variety of inorganic ions and organic compounds. Furthermore, the electrodes were successfully applied to the measurement of pH in microscale of apples.     

Highly sensitive and selective amperometric sensors for nanomolar detection of iodate and periodate based on glassy carbon electrode modified with iridium oxide nanoparticles

Iridium oxide nanoparticles are grown on a glassy carbon electrode by electrodepositing method. The electrochemical behavior and electrocatalytic activity of modified electrode towards reduction of iodate and periodate are studied. The reductions of both ions occur at the unusual positive peak potential of 0.7 V vs. reference electrode. The modified electrode is employed successfully for iodate and periodates detection using cyclic voltammetry, hydrodynamic amperometry and flow injection analysis (FIA). In the performed experiments, flow injection amperometric determination of iodate and periodate yielded calibration curves with the following characteristics: linear dynamic range up to 100 and 80 μM, sensitivity of 140.9 and 150.6 nA μM⁻¹ and detection limits of 5 and 36 nM, respectively. The repeatability of the modified electrode for 21 injections of 1.5 μM of iodate solution is 1.5%. The interference effects of NO₂⁻, NO₃⁻, ClO₃⁻, BrO₃⁻, ClO₄⁻, SO₄²⁻, Cu²⁺, Zn²⁺, Mn²⁺, Mg²⁺, Cd²⁺, Ca²⁺, Na⁺, K⁺, NH₄⁺ and K⁺, CH₃COO⁻ and glucose were negligible at the concentration ratio of more than 1000. The obtained attractive analytical performance together with high selectivity and simplicity of the proposed method provide an effective and e novel modified electrode to develop an iodate and periodate sensor. Sensitivity, selectivity, the liner concentration range and the detection limit of the developed sensor are all much better than all known similar sensors in the literature for iodate and periodate determination.     

Diamond like carbon films for enzyme electrodes; characterisation of novel overlying permselective barriers

Diamond like carbon (DLC) coated microporous polycarbonate membranes have been studied for use as novel composite permselective barriers membranes for a glucose enzyme electrode. Permeability coefficients, P, for key electrochemically active interferents across uncoated and DLC coated polycarbonate membranes has been compared. Interferent responses have then been assessed for sensors incorporating such membranes, and their relationship to differing DLC depositions assessed. Membranes with smaller pore sizes (0.03 and 0.01 μm) and extended DLC depositions (up to 7 min coating), while imparting some enhanced selectivity towards glucose, failed to show major discrimination for glucose over interferents as shown by P values: maximum glucose-to-interferent P ratios being 1.36 and 1.25 for ascorbate and urate, respectively. The implications of these findings are discussed.     

Development of a versatile rotating ring-disc electrode for in situ pH measurements

There are some electrocatalytic reactions in which the key parameter explaining their behavior is a local change in pH. Therefore, it is of utter importance to develop an electrode that could quantify this parameter in situ, but also be customizable to be used in different systems. The purpose of this work is to build a versatile rotating ring/disc electrode (RRDE) with IrO_x deposited on a glass tube as a ring and any kind of material as disc. As the IrO_x is sensitive to pH variation, the reactions promoted on the disc can trigger proportional pH shifts on the ring. In such assembly, the IrO_x ring presents a fast response time even during the pH transients due to the small thickness of the ring (approximately 10 μm), which enables the detection of interfacial pH changes. The ring electrode was tested toward the interfacial pH shift observed during the electrolytic reduction of water on the disc and also characterized by acid–base titration to determine the response time. As the main conclusions, fast response and durable RRDE were obtained, and this assembly could be used to revisit many electrocatalytic reactions in order to test the importance of local pH on the process.     

ITO-free transparent conductive films based on carbon nanomaterials with metal grid for liquid crystal displays

Carbon nanomaterials with metal grids were used as transparent conductive electrodes for liquid crystal displays (LCDs) to develop an indium tin oxide (ITO)-free device. We prepared LCDs with CNTs and graphene electrodes; however, the working voltage of the device with the CNT electrodes was high. The device with graphene electrodes had good performance, but not as good as devices with ITO electrodes. To improve the device performance, we applied a metal grid to the carbon nanomaterial to create low sheet-resistance transparent electrodes. The device with the graphene and metal grid transparent electrodes had a threshold voltage as low as 0.23 V/µm, which is similar to that of typical LCDs with ITO electrodes. The results show that a hybrid transparent conductive film with graphene and metal grid could be an alternative to ITO for developing ITO-free LCDs.     

Diamond like carbon coated films for enzyme electrodes; characterization of biocompatibility and substrate diffusion limiting properties

The biocompatibility and substrate diffusion limiting properties for a range of diamond like carbon (DLC) coated microporous polycarbonate and DLC coated dialysis (haemodialysis) membranes have been studied. This characterisation builds upon previous findings where DLC coated membranes imparted enhanced enzyme electrode performance. In this study electrode linear ranges have been extended from 10 mM glucose for a 0.01 μm pore size membrane to 160 mM. These findings correlated with the duration of DLC deposition and associated reductions in permeability for glucose. Permeability coefficient ratios for both microporous and dialysis membranes were also found to be important with low glucose/O₂ permeability ratios imparting extensions in glucose linear response range. DLC coated membranes employed within enzyme electrodes have also been shown to exhibit enhanced haemocompatibility as determined by both sensitivity change and surface deposition of blood components examined by scanning electron microscopy. Correlations are made between the reduced losses in sensor response to biofouling/ working electrode passivation processes, and extended linear ranges that DLC coated membranes may impart to enzyme electrode performance. Particular reference is made to the determination of glucose levels within whole blood.     

Development of an Electrochemical Biosensor for the Rapid Detection of Saxitoxin Based on Air Stable Lipid Films with Incorporated Anti‐STX Using Graphene Electrodes

A miniaturized potentiometric saxitoxin sensor on graphene nanosheets with incorporated lipid films and Anti‐STX, the natural saxitoxin receptor, immobilized on the stabilized lipid films is described in the present paper. An adequate selectivity for detection over a wide range of toxin concentrations, fast response time of ca. 5–20 min, and detection limit of 1 nM have been achieved. The proposed sensor is easy to construct and exhibits good reproducibility, reusability, selectivity, long shelf life and high sensitivity of ca. 60 mV/decade of toxin concentration. The method was implemented and evaluated in lake water and shellfish samples. This novel ultrathin film technology is currently adapted to the rapid detection of other toxins that could be used in bioterrorism.     

Development of an Electrochemical Biosensor for the Rapid Detection of Cholera Toxin Based on Air Stable Lipid Films with Incorporated Ganglioside GM1 Using Graphene Electrodes

The present work describes a miniaturized potentiometric cholera toxin sensor on graphene nanosheets with incorporated lipid films. Ganglioside GM1, the natural cholera toxin receptor, immobilized on the stabilized lipid films, provided adequate selectivity for detection over a wide range of toxin concentrations, fast response time of ca. 5 min, and detection limit of 1 nM. The proposed sensor is easy to construct and exhibits good reproducibility, reusability, selectivity, long shelf life and high sensitivity of ca. 60 mV/decade of toxin concentration. The method was implemented and validated in lake water samples. This novel ultrathin film technology is currently adapted to the rapid detection of other toxins that could be used in bioterrorism.     

Spectroscopic reflectometry as in‐operando method for thickness determination of anodic oxide films on titanium

The present work focuses on the development of an in‐operando technique based on the visible spectroscopic reflectometry (VSR) for simultaneous determination of the oxide film formation during anodizing. The establishment of the VSR as in‐operando technique requires an extensive validation by comparative in‐situ but non‐operando thickness measurements under aqueous conditions. The investigations were carried out on anodic oxide films on pure titanium. The authors demonstrate the VSR as a simple and robust method for measurement under electrolyte covering. Additionally, an empirical correction algorithm extends the limitation of the visible reflectometry in thin film thickness. Reliable film thickness values can be measured down to ≥5 nm. The in‐operando mode yields additional information about the film growth time resolved. Copyright © 2013 John Wiley & Sons, Ltd.     

Biofouling studies on nanoparticle-based metal oxide coatings on glass coupons exposed to marine environment

Titania, niobia and silica coatings, derived from their respective nanoparticle dispersions or sols and fabricated on soda lime glass substrates were subjected to field testing in marine environment for antimacrofouling applications for marine optical instruments. Settlement and enumeration of macrofouling organisms like barnacles, hydroides and oysters on these nanoparticle-based metal oxide coatings subjected to different heat treatments up to 400 °C were periodically monitored for a period of 15 days. The differences observed in the antifouling behaviour between the coated and uncoated substrates are discussed based on the solar ultraviolet light induced photocatalytic activities as well as hydrophilicities of the coatings in case of titania and niobia coatings and the inherent hydrophilicity in the case of silica coating. The effect of heat treatment on the photocatalytic activity of the coatings is also discussed.     

Influence of substrate nature on the growth of copper oxide thin films

Cu thin films were deposited on Si(111), glass, and quartz substrates by magnetron sputtering. X‐ray diffraction, SEM, and photoemission electron microscope studies were carried out to characterize the films. An influence of the nature of substrate on the Cu₂O and CuO phases formed was observed. Copper silicide formation in case of silicon substrates aided in formation of Cu₂O rather than CuO unlike glass and quartz substrates. Formation of nanocrystallites was observed by SEM and X‐ray diffraction. Copyright © 2016 John Wiley & Sons, Ltd.     

Disposable amperometric sensor for neurotransmitters based on screen-printed electrodes modified with a thin iridium oxide film.

Potential cycling in the range from -0.2 to +1.2 V is used for the electrodeposition of hydrous iridium oxide films onto a screen-printed electrode from a saturated solution of alkaline iridium(III) solution. The iridium oxide redox couple shows a stable and obvious reversible redox, with the formal potential being pH dependent in the range 1-14. The properties, stability and electrochemical properties of iridium oxide films were investigated by cyclic voltammetry. A modified electrode showed excellent catalytic activity toward the oxidation of neurotransmitters (catecholamines) over a wide pH range (2-8). The electrocatalytic behavior is further exploited as a sensitive detection scheme for adrenaline and dopamine by hydrodynamic amperometry. Under the optimized conditions, the calibration curves are linear in the concentration range 0.1-70 and 0.1-15 microM for dopamine and adrenaline determination, respectively. The detection limit and sensitivity are 30 nM and 30 nA/microM for adrenaline and 15 nM and 80 nA/microM for dopamine. Finally, the analytical performance of the modified electrode was demonstrated for the elimination of interference by uric acid in catecholamines determination when present in a 1000-fold concentration excess.     

Development of miniaturized pH biosensors based on electrosynthesized polymer films

A new type of pH biosensor was developed for biological applications. This biosensor was fabricated using silicon microsystem technology and consists in two platinum microelectrodes. The first microelectrode was coated by an electrosynthesized polymer and acted as the pH sensitive electrode when the second one was coated by a silver layer and was used as the reference electrode. Then, this potentiometric pH miniaturized biosensor based on electrosynthesized polypyrrole or electrosynthesized linear polyethylenimine films was tested. The potentiometric responses appeared reversible and linear to pH changes in the range from pH 4 to 9. More, the responses were fast (less than 1 min for all sensors), they were stable in time since PPy/PEI films were stable during more than 30 days, and no interference was observed. The influence of the polymer thickness was also studied.     

Toward a quantitative description of the anodic oxide films on aluminum

A method to quantify the composition of anodic oxide films on aluminum using Infrared Spectroscopic Ellipsometry (IRSE) is proposed. It consists of obtaining the absorption coefficient of the film as a function of wavelength. Using values of the absorption coefficients for the pure components of the film, the percentages (mole or wt%) of each component in the sample can be calculated.The method is demonstrated in a study of the structure of the oxide film on electropolished aluminum and the anodically formed barrier layer film. Both surface oxides were found to be initially a form of amorphous Al₂O₃. While the barrier film is essentially free of water as prepared, the film on electropolished aluminum contained about 25 wt% water. Hydration of both types of films by immersion in boiling water results in the formation of pseudoboehmite (AlOOH). The technique may have more general applicability to the quantitative determination of the composition of corrosion films and other surface layers on metals.     

金红石型氧化钛负载的铱在催化分解N_2O推进剂反应中的应用（英文）

氧化亚氮(N_2O)是一种性能独特优越的新型绿色推进剂,分解后可以生成高温富氧燃气,实现自增压式多种模式推进,是小卫星推进系统理想的推进剂选择,因而具有广阔的应用前景.在标准状态下,N_2O热分解反应活化能为250 k J/mol,致使其非催化热分解温度高达600 ℃,显然小卫星的能源系统无法满足,必须采取催化分解的手段,改变反应路径、降低反应活化能,使N_2O能够在较低的温度下分解.有关N_2O分解催化剂的报道很多,如纯相或复合氧化物、金属交换分子筛和负载贵金属等,但是这些催化剂仍然存在活性较低等问题,难以满足N_2O推进系统的应用需求.氧化钛是光催化和金催化常用的催化剂,经还原后能够形成氧缺陷,可以为涉氧反应提供电子,而N_2O分解会产生大量氧,氧脱附是其速率控制步骤,因而以氧化钛为载体,有望促进氧脱附及N_2O分解.与此同时,氧化铱具有较高的N_2O分解活性,而且与金红石型氧化钛晶格相似,相似的晶格参数可能会促进其在氧化钛表面的分散,进一步提高N_2O分解性能.基于此,本文以金红石氧化钛(r-TiO_2)为载体,采用匀相沉积沉淀法制备了不同载量的金红石氧化钛负载铱催化剂(Ir/r-TiO_2),并制备了锐钛矿型氧化钛、混合晶相P25和γ-Al_2O_3负载铱催化剂作为对比.通过活性测试我们发现,Ir/r-TiO_2催化剂显示了非常优异的N_2O分解活性,N_2O转化率明显高于参比催化剂,在250℃就能够开始分解,在300 ℃可以分解完全,而且当Ir含量降低到0.1%时,催化剂仍然保持与2 wt%Ir/γ-Al_2O_3相当的催化活性.随后我们采取多种表征手段对Ir/r-TiO_2的活性本质和N_2O分解机理进行了探究.首先利用BET、HAADF-STEM和XRD对催化剂的基本物性进行了测试,发现Ir/r-TiO_2具有较低的比表面积,但金属铱在金红石氧化钛表面表现出较高的分散度,平均粒径仅为1.25 nm.采用H-2-TPR和O 1s XPS考察了催化剂的电子特性和还原特性,发现Ir/r-TiO_2催化剂上高分散的Ir与氧的结合能较弱,易于还原,有助于N_2O的分解和生成氧的脱附.进一步采用原位N_2O-DRIFT对N_2O分解过程进行了研究,发现了桥式过氧物种,并据此提出了N_2O在Ir/r-TiO_2催化剂上的分解机理.