Fabrication of new polypyrrole/silicon nitride hybrid materials for potential applications in electrochemical sensors: Synthesis and characterization

In this research, an efficient fabrication process of conducting polypyrrole (PPy)/silicon nitride (Si₃N₄) hybrid materials were developed in order to be employed as transducers in electrochemical sensors used in various environmental and biomedical applications. The fabrication process was assisted by oxidative polymerization of pyrrole (Py) monomer on the surface of Si/SiO₂/Si₃N₄ substrate in presence of FeCl₃ as oxidant. To improve the adhesion of PPy layer to Si₃N₄ surface, a pyrrole-silane (SPy) was chemically bonded through silanization process onto the Si₃N₄ surface before deposition of PPy layer. After Py polymerization, Si/SiO₂/Si₃N₄-(SPy-PPy) substrate was formed. The influence of SPy concentration and temperature of silanization process on chemical composition and surface morphology of the prepared Si/SiO₂/Si₃N₄-(SPy-PPy) substrates was studied by FTIR and SEM. In addition, the electrical properties of the prepared substrates were characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). It was found that the best silanization reaction conditions to get Si/SiO₂/Si₃N₄-(SPy-PPy) substrate with high PPy adhesion and good electrical conductivity were obtained by using SPy at low concentration (4.3 mM) at 90°C. These promising findings open the way for fabrication of new hybrid materials which can be used as transducers in miniaturized sensing devices for various environmental and biomedical applications.     

Cyclic Voltammetric and Ac Impedance Behavior of TiO2 Electrodes under UV Illumination

Electrochemical behavior of an ITO/TiO₂ electrode both under ultraviolet (UV) illumination and in the dark was investigated using the methods of cyclic voltammetry and ac impedance spectroscopy. A new oxidative peak is observed at 0.15 V when the TiO₂ electrode was illuminated by UV light for a certain time. The peak current and the anodic photocurrent increased with the increase of UV light intensity. It is assumed that the new peak belonging to the oxidation of Ti³⁺, which was formed on the electrode surface during the UV illumination. It is also found that the apparent resistance was decreased but the capacitance was increased when the TiO₂ electrode was illuminated by UV light according to the measurement results of ac impedance. Based on the results in this paper, it was directly proved that Ti³⁺ was actually formed when the electrode was irradiated by UV light.     

Capacitance Polypyrrole‐based Impedimetric Immunosensor for Interleukin‐10 Cytokine Detection

In the present study, we developed a novel label‐free capacitance impedimetric immunosensor based on the immobilization of the human monoclonal antibody anti‐interleukin‐10 (anti‐IL‐10 mAb) onto polypyrrole (PPy)‐modified silicon nitride (Si₃N₄) substrates. The immunosensor was used for the detection of the recombinant interleukin‐10 antigen (rh IL‐10) that may be secreted in patients at the early stage of inflammation. The immunosensor was created by chemical deposition of PPy conducting layer on pyrrole?silane (SPy)‐treated Si/SiO₂/Si₃N₄ substrates (Si/SiO₂/Si₃N₄?SPy), followed by anti‐IL‐10 mAb immobilization through carboxyl‐functionalized diazonium (CMA) protocol and carbodiimide chemistry. The surface characterization and the biofunctionalization steps were characterized by SEM, FTIR and cyclic voltammetry (CV) while the detection process was carried out by using electrochemical impedance spectroscopy (EIS) analyses. The created immunosensor showed two linear fittings (R²=0.999) for the detection of rh IL‐10 within the concentration range from 1–50 pg/mL. It exhibited high sensitivity (0.1128 (pg/mL)^?1) with a very low limit of detection (LOD)=0.347 pg/mL, more particularly, at the low concentration range (1–10 pg/mL). Thus, this developed polypyrrole‐based immunosensor represents a promising strategy for creation of miniaturized label‐free, fast and highly sensitive biosensors for diagnosis of inflammation biomarkers at very low concentrations with reduced cost.     

The influence of processing parameters on the fabrication of Si3N4 wires

Silicon nitride (Si₃N₄) wires have been prepared by means of carbothermal reduction followed by the nitridation (CTRN) of silica gel containing ultrafine decomposed saccharose. The influence of temperature of reaction and mass ratio of carbon to silicon $ \left( \frac{C}{Si} \right) $ on the synthesis of Si₃N₄ wires were studied. The presence of nitrogen gas in the pores of gel at high temperature starts the CTRN reaction leading to the formation of Si₃N₄ wires. The results show that the Si₃N₄ was fully formed with two kinds of morphologies including globular and wire with a width of 100–500 nm and length of several microns at sintering temperature of 1,400 °C by employing the mass ratio of $ \frac{C}{Si} \; = \;0.5 $ . The infrared adsorption of the wires exhibits absorption bands related to the absorption peaks of Si–N bond of Si₃N₄. The thermal analysis results reveal that carbothermal nitridation reaction was completed at temperature of 1,400 °C.     

WS<Subscript>2</Subscript> grafted on silicon and nano-silicon particles etched: a high-performance electrocatalyst for hydrogen evolution reaction

Most of research has been carried out for the development of electrocatalysts for hydrogen evolution reaction (HER), which are high activity and low cost. In this study, a practical, usable, highly active, cheap, and none noble metal catalyst was developed for HER. To this end, tungsten disulfide supported on silicon (WS₂/Si) and on silicon nanoparticles (WS₂/nano-Si) were prepared. To increase the catalytic activity of WS₂/nano-Si, chemical etching was used to prepare WS₂/nano-Si etched. The synthesized electrocatalysts were characterized using Fortier transform infrared spectroscopy, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction methods. To evaluate the electrochemical attributes of WS₂/Si and WS₂/n-Si before and after chemical etching, electrochemical impedance spectroscopy, linear sweep, and cyclic voltammetry were used. The electrochemical measurements indicated an intense activity of the WS₂/nano-Si/etched, through a high density of the current and low overpotential for HER, with a small overpotential of 0.14 V, Tafel slopes as small as 45 mV dec^?1, and large cathodic currents. These results show that through etching process of silicon in HF the quantities of the active sites have been changed and increased considerably.     

The Binary Silicides Eu5Si3 and Yb3Si5 – Synthesis,Crystal Structure,and Chemical Bonding

The binary silicides Eu₅Si₃ and Yb₃Si₅ were prepared from the elements in sealed tantalum tubes and their crystal structures were determined from single crystal X-ray data: I4/mcm, a = 791.88(7) pm, c = 1532.2(2) pm, Z = 4, wR2 = 0.0545, 600 F² values, 16 variables for Eu₅Si₃ (Cr₅B₃-type) and P62m, a = 650.8(2) pm, c = 409.2(1) pm, Z = 1, wR2 = 0.0427, 375 F² values, 12 variables for Yb₃Si₅ (Th₃Pd₅ type). The new silicide Eu₅Si₃ contains isolated silicon atoms and silicon pairs with a Si–Si distance of 242.4 pm. This silicide may be described as a Zintl phase with the formula [5 Eu²⁺]¹⁰⁺[Si]^4–[Si₂]^6–. The silicon atoms in Yb₃Si₅ form a two-dimensional planar network with two-connected and three-connected silicon atoms. According to the Zintl-Klemm concept the formula of homogeneous mixed-valent Yb₃Si₅ may to a first approximation be written as [3 Yb]⁸⁺[2 Si^–]^2–[3 Si^2–]^6–. Magnetic susceptibility investigations of Eu₅Si₃ show Curie-Weiss behaviour above 100 K with a magnetic moment of 7.85(5) μ_B which is close to the free ion value of 7.94 μ_B for Eu²⁺. Chemical bonding in Eu₅Si₃ and Yb₃Si₅ was investigated by semi-empirical band structure calculations using an extended Hückel hamiltonian. The strongest bonding interactions are found for the Si–Si contacts followed by Eu–Si and Yb–Si, respectively. The main bonding characteristics in Eu₅Si₃ are antibonding Si1₂-π* and bonding Eu–Si1 states at the Fermi level. The same holds true for the silicon polyanion in Yb₃Si₅.     

Syntheses and properties of sila-functional oligosiloxanes: Synthesis, structure, and spectra of linear and cyclic isocyanato(methyl)oligosiloxanes

Synthesis, structure, and spectra of novel linear and cyclic isocyanato(methyl)oligosiloxanes with the silicon number up to eight were investigated. The linear and cyclic oligosiloxanes were synthesized selectively in good or appreciable yields by vapor phase and liquid phase hydrolysis, respectively. They were isolated as liquids by distillation under reduced pressure except for cyclic tetrasiloxane and pentasiloxane which were provided as solids. The cyclic trisiloxane was obtained as amixture of isomers as confirmed by nuclear magnetic resonance (NMR) spectra. The X-ray analysis of cyclic tetra- and pentasiloxane obtainedrevealed that they have cis-trans-cis andpropeller-like structure, respectively. The infrared (IR) spectra of cyclic siloxanes showed a sharp peak due to ν_Si?O?Si and a remarkable shift fromthe tri- to the tetrasiloxane while peak broadening and almost no shift were observed for the higher homologues. On the other hand, the sharp peak for linear disiloxanes became broad and split into two peaks for the higher homologues, while the peak at low wavenumber shifted even lower as the siloxane linkages increased, yet no corresponding shift is observed for thepeak at higher wavenumber. In the ²⁹Si NMR spectra of linearoligosiloxanes, the signals appeared separately at low and high fields in narrow regions, which are ascribed to the terminal silicon atom and the silicon associatedwith the silylmethyl groups, respectively. These regions hardly changed, regardless of the length of siloxane linkage. Similar trends were observed in the ¹H and ¹³C NMR spectra.     

Electrochemical characterization of PANI-Nafion membranes and their electrocatalytic activity

PANI-Nafion^® membranes were prepared by a chemical method in which the faces of a commercial Nafion membrane were contacted with two acid solutions containing an oxidant (Fe³⁺) and aniline respectively. They were then characterized by a variety of electrochemical techniques (cyclic voltammetry, chronoamperometry, ac impedance). PANI was stored mostly in the vicinity of the Nafion face exposed to the oxidant. When this face was contacted with Hg and the other with electrolyte solutions, typical electrochemical responses of PANI were detected. Electrocatalytic reduction of O₂ and oxidation of N₂H₄ were achieved on PANI-Nafion electrodes and found to be only slightly slowed down with respect to ordinary PANI film electrodes, at variance with a fast process such as Fe³⁺ reduction, the rate of which was severely limited by diffusion through the membrane.     

Effect of different conductive additives on charge/discharge properties of LiCoPO<Subscript>4</Subscript>/Li batteries

Single-phase LiCoPO₄ nanoparticles were synthesized by solid-state reaction method and subsequent high-energy ball milling. The electrochemical properties of LiCoPO₄/Li batteries were analyzed by ac impedance experiments, cyclic voltammetry (CV), and charge/discharge tests. The structural and morphological performance of LiCoPO₄ nanoparticles was investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM). The XRD result demonstrated that LiCoPO₄ nanoparticles had an orthorhombic olivine-type structure with a space group of Pmnb. Different conductive additives including acetylene black and carbon black (SP270) were used to fabricate electrodes. The morphologies of the electrodes and different conductive additives were observed by field emission-scanning electron microscopy (FE-SEM). LiCoPO₄/Li battery with acetylene black showed the best electrochemical properties, and exhibited a discharge plateau at around 4.7 V with an initial discharge capacity of 110 mAh g⁻¹ at a discharge current density of 0.05 mA cm⁻² at 25 °C.     

The Zintl Phase Eu2Si

The Zintl phase Eu₂Si was synthesized from elemental europium and silicon in a sealed tantalum tube in a high‐frequency furnace at 1270 K and subsequent annealing at 970 K. Investigation of the sample by X‐ray powder and single crystal techniques revealed: Co₂Si (anti‐PbCl₂) type, space group Pnma, a = 783.0(1), b = 504.71(9), c = 937.8(1) pm, wR2 = 0.1193, 459 F² values and 20 variables. The structure contains two europium and one silicon site. ¹⁵¹Eu Mössbauer spectroscopic data show a single signal at an isomer shift of −9.63(3) mm/s, compatible with divalent europium. Within the Zintl concept electron counting can be written as (2Eu²⁺)⁴⁺Si⁴⁻, in agreement with the absence of Si‐Si bonding. Each silicon atom has nine europium neighbors in the form of a tri‐capped trigonal prism. The silicon coordinations of the Zintl phases Eu₂Si, Eu₅Si₃, EuSi, and EuSi₂ are compared.     

Effect of fullerene coating on silicon thin film anodes for lithium rechargeable batteries

To improve the electrochemical performances of Si thin film anodes for lithium rechargeable batteries, fullerene thin films are prepared by plasma-assisted evaporation methods to be used as coating materials. Analyses via Raman and X-ray photoelectron spectroscopy indicate that amorphous polymeric films originated from fullerene are formed on the surface of the silicon thin film. The electrochemical performance of these fullerene-coated silicon thin film as an anode material for rechargeable lithium batteries has been investigated by cyclic voltammetry, charge/discharge tests, and electrochemical impedance spectroscopy. The fullerene-coated Si thin films demonstrated a high specific capacity of above 3,000 mAh g⁻¹ as well as good capacity retention for 40 cycles. In comparison with bare silicon anodes, the fullerene-coated silicon thin film showed superior and stable cycle performance which can be attributed to the fullerene coating layer which enhances the Li-ion kinetic property at the electrode/electrolyte interface.     

Impedance study on the correlation between phase transition and electrochemical degradation of Si-based materials

In order to explain the relationship between physical change and electrochemical degradation of Co–Co₃O₄ coated Si, impedance spectroscopy on Co–Co₃O₄ coated Si was conducted at various states during charge or discharge. Nyquist plots during Li⁺ insertion (charge) showed a unique behavior that below 70 mV vs. Li/Li⁺, the more Li⁺’s were inserted into the electrode, the larger its comprehensive resistance was getting. During Li⁺ extraction (discharge), electrode resistance was decreased after going through 0.43 V vs Li/Li⁺. When these data were fitted with the ordinary equivalent circuit which is composed of electrolyte resistance, charge transfer resistance and contact resistance, there was an abrupt augmentation of charge transfer resistance below 70 mV vs. Li/Li⁺ during charge, whereas there was its drastic diminishment between 0.2 and 0.5 V vs. Li/Li⁺ during discharge. Because these potential regions are each related to amorphous Li_xSi-to-Li₁₅Si₄ transition and vice versa, it could be shown that the formation and decomposition of Li₁₅Si₄ is responsible for the electrochemical degradation of Co–Co₃O₄ coated Si.     

OH functionalized Multi-Walled Carbon Nanotube modified electrode as electrochemical sensor for the detection of Aceclofenac

ABSTRACT

The rapid electrochemical determination of Aceclofenac (ACF) has been employed by cyclic voltammetry (CV), differential pulse voltammetry (DPV) using developed OH-functionalised multiwalled carbon nanotube carbon paste electrode (OH-MWCNT/CPE). Modified electrode was characterised by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), X-ray diffraction spectroscopy (XRD), electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The ACF exhibits two oxidation peaks at +0.4 V, +0.66 V and one reduction peak at +0.3 V. The active surface area of the bare carbon paste electrode (BCPE) and modified electrode have been characterised by using K₃[Fe(CN)₆] solution containing 0.1 M KCl. In DPV mode, variation of ACF gave the limit of detection (LOD = 3s/m) 0.246 μM over the concentration range 1.0 to 190.0 μM (R² = 0.9994). The developed electrode has good stability, reproducibility and could be successfully validated for the detection of ACF in pharmaceutical samples and biological fluids.     

7-甲基鸟苷在玻碳电极上的伏安行为研究

研究了修饰核苷7-甲基鸟苷(7-Methylguanosine)的电化学行为及测定方法.在pH 1.98的B-R缓冲液中,用循环伏安法(CV),线性扫描伏安法(LSV)、微分脉冲伏安法(DPV)等现代电化学技术研究7-甲基鸟苷在玻碳电极(GCE)上的伏安行为.实验表明,7-甲基鸟苷在 1.036 V(vs.SCE)电位处产生一个阳极氧化峰,峰电流与7-甲基鸟苷的浓度在5.0×10-5-2.0×10-6mol/L范围内呈良好的线性关系,最低检测限(D=2σ/K)为4.1×10-7mol/L.并用恒电位库仑电解法等方法对其氧化机理进行了较为详细的探讨,得到了可能的电极反应机理:7-甲基鸟苷在玻碳电极上的电极反应是属于失1质子和2电子的不可逆的氧化反应.     

铬掺杂的锂离子电池正极材料LiVPO4F的制备以及电化学行为的研究

采用高温固相法2步合成了掺Cr的锂离子电池正极材料LiV_1-xCr_xPO₄F(x=0，0.01，0.03，0.05，0.07)，XRD测试表明LiV_1-xCr_xPO₄F属三斜晶系。通过恒电流充放电，循环伏安和交流阻抗实验表明：掺Cr后LiVPO₄F正极材料更有利于锂离子的嵌入和嵌出，材料的放电容量和循环性能进一步提高，例如，铬掺杂的LiVPO₄F样品在室温、0.2 C倍率下充放电，循环50周后容量在110 mAh·g^-1以上。文中还讨论了充放电容量随掺Cr量的关系，n_Cr含量为0.03的LiV_1-xCr_xPO₄F有着较高的放电平台和良好的循环稳定性。     

Photoelectrochemistry of silicon in HF solution

Photoelectrochemical, photoelectrocatalytic, and electrochemical processes of silicon anodic oxidation and hydrogen evolution in aqueous HF solution are discussed in terms of thermodynamic stability of Si, oxides SiO, SiO₂, and Si surface hydrides. It is shown that photoelectrochemical oxidation of n-type low-resistivity silicon to SiO₂ is catalyzed by Si $^{+}$ photo-hole formation, whereas in the case of p-type Si, the feasibility of this reaction is predetermined by p-type conductivity. It is suggested that anodic oxidation of Si goes through the stage of SiO oxide formation and its subsequent oxidation to SiO₂. Such mechanism accounts for chemical inertness of Si phase in HF solutions as well as for selective, anisotropic, and isotropic etching of Si within E ranges from $-0.5$ to 0.35 V, $0.35-0.8~V,$ and $E > 0.8$ V, respectively. Hydrogen evolution reaction on Si surface proceeds at very large overpotential ( $\geq 0.5$ V) through the stage of surface Si hydride formation: $\mathrm {Si + H_{2}O + e^{-} \rightarrow (SiH)_{surf} + OH^{-}}$ (the rate determining step) and $\mathrm {(SiH)_{surf} + H_{2}O + e^{-} \rightarrow Si + H_{2} + OH^{-}}$ . Illumination-related effects of surface reactions relevant to selective and anisotropic etching and nano/micro-structuring of Si surface are discussed.     

Synthesis of New Lithium Ionic Conductor Thio-LISICON—Lithium Silicon Sulfides System

The new lithium ionic conductors, thio-LISICON (LIthium SuperIonic CONductor), were found in the ternary Li₂S-SiS₂-Al₂S₃ and Li₂S-SiS₂-P₂S₅ systems. Their structures of new materials, Li_4+xSi_1−xAl_xS₄ and Li_4−xSi_1−xP_xS₄ were determined by X-ray Rietveld analysis, and the electric and electrochemical properties were studied by electronic conductivity, ac conductivity and cyclic voltammogram measurements. The structure of the host material, Li₄SiS₄ is related to the γ-Li₃PO₄-type structure, and when the Li⁺ interstitials or Li⁺ vacancies were created by the partial substitutions of Al³⁺ or P⁵⁺ for Si⁴⁺, large increases in conductivity occur. The solid solution member x=0.6 in Li_4−xSi_1−xP_xS₄ showed high conductivity of 6.4×10^-4 S cm⁻¹ at 27°C with negligible electronic conductivity. The new solid solution, Li_4−xSi_1−xP_xS₄, also has high electrochemical stability up to ∼5 V vs Li at room temperature. All-solid-state lithium cells were investigated using the Li_3.4Si_0.4P_0.6S₄ electrolyte, LiCoO₂ cathode and In anode.     

Electrochemical Capacitive K+ EMIS Chemical Sensor Based on the Dibromoaza[7]helicene as an Ionophore for Potassium Ions Detection

A K⁺‐sensitive capacitive electrolyte‐membrane‐insulator‐semiconductor (EMIS) based on a novel dibromoaza[7]helicene ionophore has been developed. An ion‐sensitive membrane based on polyvinylchloride (PVC) doped with the ionophore was deposited on the Si₃N₄/SiO₂/Si‐p/Cu‐Al transducer. The properties of the K⁺‐EMIS chemical sensor were investigated by electrochemical impedance spectroscopy (EIS). All the developed devices upon being tested have shown good sensitivity and linearity responses within the range 10^?6 M to 10^?1 M of potassium activity, with good selectivity over a wide variety of other cations (Na⁺, Li⁺, Cu²⁺, Ca²⁺, and Mg²⁺). To our knowledge, this is the first time that a capacitive field‐effect sensor has been fabricated using helicene as a carrier for K⁺‐detection, combined with the structure: Si₃N₄/SiO₂/Si‐p/Cu‐Al as a transducer.     

从SiCl4合成多孔硅/碳复合材料及储锂性能研究

以Li13Si4和SiCl4为原料,通过简单的机械球磨法合成多孔硅/碳复合材料,通过控制Li13Si4颗粒的尺寸可以有效调节产物的比表面积。分别研究了包覆碳含量、多孔硅/Super P(导电碳)比表面积以及极片活性物质负载量对多孔硅/碳复合材料电化学性能的影响。结果表明:多孔硅/Super P比表面积为100.9 m2·g-1,化学气相沉积(CVD)包覆碳含量为25.3wt%(约6 nm厚)的复合材料具有最高的电化学活性,在300 mA·g-1的电流密度下,循环可逆比容量达到1 900 mAh·g-1,50次循环后容量仅衰减7.6%。     

从SiCl4合成多孔硅/碳复合材料及储锂性能研究

以Li₁₃Si₄和SiCl₄为原料,通过简单的机械球磨法合成多孔硅/碳复合材料,通过控制Li₁₃Si₄颗粒的尺寸可以有效调节产物的比表面积。分别研究了包覆碳含量、多孔硅/SuperP(导电碳)比表面积以及极片活性物质负载量对多孔硅/碳复合材料电化学性能的影响。结果表明:多孔硅/SuperP比表面积为100.9m₂·g^-1,化学气相沉积(CVD)包覆碳含量为25.3wt%(约6nm厚)的复合材料具有最高的电化学活性,在300mA·g^-1的电流密度下,循环可逆比容量达到1900mAh·g^-1,50次循环后容量仅衰减7.6%。