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.     

Structure Elucidation of Complex Endotaxially Intergrown Lanthanum Barium Oxonitridosilicate Oxides by Combination of Microfocused Synchrotron Radiation and Transmission Electron Microscopy

Single-crystalline domains in intergrown microcrystalline material of the new compounds Ba_22.5+xLa_55−x[Si₁₂₉N_240−xO_x]O₃:Ce³⁺ and Ba_25.5+xLa_77−x[Si₁₇₀N_312−xO_9+x]O₄:Ce³⁺ were identified by transmission electron microscopy (TEM). Precise diffraction data from these domains were collected with microfocused synchrotron radiation so that crystal structure elucidation of the complex disordered networks became possible. They are composed of two different interconnected slabs of which one is similar in both compounds, which explains their notorious intergrowth. The distribution of Ba and La is indicated by the analysis of bond-valence sums and by comparison with isostructural Sr_28.5+xLa_75−x[Si₁₇₀N_312−xO_9+x]O₄. Ce³⁺ doping leads to yellow luminescence. This is a showcase that highlights the discovery and accurate characterization of new compounds relevant for luminescence applications from heterogeneous microcrystalline samples by exploiting the capability of the combination of TEM and diffraction using the latest focusing techniques for synchrotron radiation.     

Nature of the transient species formed during pulse radiolysis of thioacetamide in aqueous solutions

Thioacetamide (TA) is an organic compound having thioamide group similar to that in thiourea derivatives. Its reactions with e_aq⁻, H-atom and OH radicals were studied using the pulse radiolysis technique at various pHs and the kinetic and spectral characteristics of the transient species were determined. The initial adduct formed by the reaction of TA with OH radicals at pH 7 does not absorb light in the 300–600 nm region but reacts with the parent compound to give a transient species with an absorption maximum around 400 nm. At pH 0, the reaction of OH radicals with TA directly gives a similar transient species with absorption maximum at 400 nm. Transient species formed by H-atom reaction with TA and pH 0 has no absorption in the 300–600 nm region but at higher acidity a new transient species is formed which has absorption maximum at 400 nm. This transient absorption observed in the case of both OH and H atom reaction with TA is ascribed to the formation of a resonance stabilized radical similar to that obtained in the case of thiourea derivatives. The species produced by electron reaction viz. electron adduct was found to be a strong reductant and could reduce MV²⁺ with a high rate constant. H₂S was produced as a stable product in the reaction of e_aq⁻ and its G-value was determined to be about 0.8.     

Charged Si9 Clusters in Neat Solids and the Detection of [H2Si9]2− in Solution: A Combined NMR,Raman, Mass Spectrometric,and Quantum Chemical Investigation

Polyanionic silicon clusters are provided by the Zintl phases K₄Si₄, comprising [Si₄]⁴⁻ units, and K₁₂Si₁₇, consisting of [Si₄]⁴⁻ and [Si₉]⁴⁻ clusters. A combination of solid‐state MAS‐NMR, solution NMR, and Raman spectroscopy, electrospray ionization mass spectrometry, and quantum‐chemical investigations was used to investigate four‐ and nine‐atomic silicon Zintl clusters in neat solids and solution. The results were compared to ²⁹Si isotope‐enriched samples. ²⁹Si‐MAS NMR and Raman shifts of the phase‐pure solids K₄Si₄ and K₁₂Si₁₇ were interpreted by quantum‐chemical calculations. Extraction of [Si₉]⁴⁻ clusters from K₁₂Si₁₇ with liquid ammonia/222crypt and their transfer to pyridine yields in a red solid containing Si₉ clusters. This compound was characterized by elemental and EDX analyses and ²⁹Si‐MAS NMR and Raman spectroscopy. Charged Si₉ clusters were detected by ²⁹Si NMR in solution. ²⁹Si and ¹H NMR spectra reveal the presence of the [H₂Si₉]²⁻ cluster anion in solution.     

Charged Si9 Clusters in Neat Solids and the Detection of [H2Si9]2− in Solution: A Combined NMR,Raman, Mass Spectrometric,and Quantum Chemical Investigation

Polyanionic silicon clusters are provided by the Zintl phases K₄Si₄, comprising [Si₄]⁴⁻ units, and K₁₂Si₁₇, consisting of [Si₄]⁴⁻ and [Si₉]⁴⁻ clusters. A combination of solid‐state MAS‐NMR, solution NMR, and Raman spectroscopy, electrospray ionization mass spectrometry, and quantum‐chemical investigations was used to investigate four‐ and nine‐atomic silicon Zintl clusters in neat solids and solution. The results were compared to ²⁹Si isotope‐enriched samples. ²⁹Si‐MAS NMR and Raman shifts of the phase‐pure solids K₄Si₄ and K₁₂Si₁₇ were interpreted by quantum‐chemical calculations. Extraction of [Si₉]⁴⁻ clusters from K₁₂Si₁₇ with liquid ammonia/222crypt and their transfer to pyridine yields in a red solid containing Si₉ clusters. This compound was characterized by elemental and EDX analyses and ²⁹Si‐MAS NMR and Raman spectroscopy. Charged Si₉ clusters were detected by ²⁹Si NMR in solution. ²⁹Si and ¹H NMR spectra reveal the presence of the [H₂Si₉]²⁻ cluster anion in solution.     

电泳法研究改性硅灰石的表面性质

本工作用测定水合金属氧化物等电点的方法,作为评定在硅灰石表面镁的包膜技术,为硅灰石的一物多用提供了新的途径;亦为在硅灰石表面包覆其他金属氧化物找到了一种新的方法。 本工作还研究了影响镁包覆的几种因素,结果表明,在硅灰石表面镁包膜的最佳条件为:pH=10,氢氧化镁溶胶的浓度为0.1mol·1~(-1),平衡时间为1小时,液固质量比为10以上。     

A spontaneous solid-state NO donor to fight antibiotic resistant bacteria

This study substantiates the chemical origin of a free-radical-driven antibacterial effect at the surface of biomedical silicon nitride (Si₃N₄) in comparison with the long-known effect of oxygen reduction by oxidized TiO₂ at the surface of biomedical titanium alloys. Similar to the antibacterial effect exerted by reactive oxygen species (ROS; i.e., superoxide anions, hydroxyl radicals, singlet oxygen, and hydrogen peroxide) from TiO₂, reactive nitrogen species (RNS), such as nitrous oxide (N₂O), nitric oxide (NO), and peroxynitrite (^?OONO) in Si₃N₄, severely affect bacterial metabolism and lead to their lysis. However, in vitro experiment with gram-positive Staphylococcus epidermidis (S. epidermidis, henceforth) revealed that ROS and RNS promoted different mechanisms of lysis. Fluorescence microscopy of NO radicals and in situ time-lapse Raman spectroscopy revealed different metabolic responses of living bacteria in contact with different substrates. After 48 h, the DNA of bacteria showed complete destruction on Si₃N₄, while carbohydrates of the peptidoglycan membrane induced bacterial degradation on Ti-alloy substrates. Different spectroscopic fingerprints for bacterial lysis documented the distinct effects of RNS and ROS. Spontaneously activated in aqueous environment, the RNS chemistry of Si₃N₄ proved much more effective in counteracting bacterial proliferation as compared to ROS formed on TiO₂, which requires external energy (photocatalytic activation) to enhance effectiveness. Independent of surface topography, the antibacterial effect observed on Si₃N₄ substrates is due to its unique kinetics ultimately producing NO and represents a new intriguing avenue to fight bacterial resistance to conventional antibiotics.     

Hierarchical metal-phenolic-polyplex assembly toward superwetting membrane for high-flux and antifouling oil-water separation

Superwetting membranes have emerged as promising materials for the efficient treatment of oily wastewater. Typically, superwetting membranes can be developed by ingeniously chemical modification and topographical structuration of microporous membranes. Herein, we report the hierarchical assembly of metal-phenolic-polyplex coating to manipulate membrane surface superwettability by integrating metal-phenolic (Fe^III-tannic acid (TA)) assembly with polyplex (tannic acid-polyethylenimine (PEI)) assembly. The proposed Fe-TA-PEI coating can be deposited on microporous membrane via simply dipping into Fe^III-TA-PEI co-assembly solution. Based on the catechol chemistry, the coordination complexation of Fe^III and TA develops metal-phenolic networks to provide hydrophilic chemistries, and the electrostatic complexation of TA and PEI generates nanoconjugates to impart hierarchical architectures. Benefiting from the synergy of hydrophilic chemistries and hierarchical architectures, the resulting PVDF/Fe-TA-PEI membrane exhibits excellent superhydrophilicity (～0°), underwater superoleophobicity (～150°) and superior anti-oil-adhesion capability. The superhydrophilicity of PVDF/Fe-TA-PEI membrane greatly promotes membrane permeability, featuring water fluxes up to 5860 L m^?2 h^?1. The underwater superoleophobicity of PVDF/Fe-TA-PEI membrane promises potential flux (3393 L m^?2 h^?1), high separation efficiency (99.3%) and desirable antifouling capability for oil-in-water emulsion separation. Thus, we highlight the reported hierarchical metal-phenolic-polyplex assembly as a straightforward and effective strategy that enables the synchronous modulation of surface chemistry and topography toward superwetting membranes for promising high-flux and antifouling oil-water separation.     

A Naphthalene-Like Si1010− Unit in the Novel ∞2[Si2030−] Planar Anion of Sr13Mg2Si20

Two interpenetrating ² _∞ [Si ₂₀ ³⁰⁻ ] polyanions with naphthalene-like Si₁₀¹⁰⁻ building blocks (see picture) characterize the“nonclassical” Zintl phase Sr₁₃Mg₂Si₂₀, which is formed from the elements at 1230–1240 K. The ecliptical stacking of the Si₁₀¹⁰⁻ units leads to one-dimensional conductivity along the stacking direction.     

Study of Surface Modification of Nanosize Si3N4 with Macromolecular Coupling Agent LMPB-g-GMA in Different Solvents

A new macromolecular coupling agent, low-molecular-weight polybutadiene liquid rubber (LMPB)-glycidyl methacrylate (GMA), was synthesized using solution polymerization initiated by benzoyl peroxide (BPO). The molecular structure was confirmed by FTIR and NMR. This macromolecular LMPB-GMA was used for surface modification of silicon nitride (Si₃N₄) nanopowder in n-heptane, chloroform, ethyl acetate, and DMF, respectively. LMPB-GMA and modified nano-Si₃N₄ were systematically investigated by FTIR, NMR, TGA, and TEM. The results showed that LMPB-GMA bonded and formed an organic coating layer onto the surface of nanosized Si₃N₄ particles. The polarity of the solvents plays an important role in this process. Strong or weak polar both affect the results. The dosage loading of LMPB-GMA is 12 wt% of nanosized Si₃N₄. Nanosized Si₃N₄ modified in ethyl acetate has better dispersibility and stability than that modified in n-heptane or DMF. TEM pictures also reveal that modified nano-Si₃N₄ possesses good dispersibility.     

Synthesis of stoichiometric Y2Si2O7 powders by sonohydrolysis-assisted sol–gel route

Stoichiometric compounds Y₂Si₂O₇ were synthesised by an intensified sonohydrolysis–condensation reaction using hydrate yttrium nitrate and tetraethyl orthosilicate as starting materials. The resulting powders were characterized by means of thermo gravimetric–differential thermal analysis, high temperature X-ray diffraction, electron probe microanalysis, scanning electron microscopy, laser scattering particle size analyzer, N₂ adsorption–desorption isotherms measurements and specific surface area analysis. We found that the phase formation and texture were very dependent on the sol–gel process parameters such as starting compounds, catalyst, water content, molar ratios of Y³⁺/Si⁴⁺ and other experiment conditions. The combined effects of polyethylene glycol and acetic acid on the prepared powders have been discussed. The investigation on thermal stability of the obtained disilicate is also presented for potential high temperature membrane or thermal barrier/environmental barrier coating application.     

Diverse Reactivity of bis(Silylene) and bis(Germylene) [LE−EL (E=Si and Ge: L=PhC(NtBu)2)] in the Oxidative Activation of C−F Bond: Si−Si Bond is Retained While the Ge−Ge Bond Is Cleaved

Herein we report the reactions of 3,4,5,6-tetrafluoroterephthalonitrile ( 1 ) with bis(silylene) and bis(germylene) LE−EL [E=Si ( 2 ) and Ge( 3 ): L=PhC(N^tBu)₂)]. The reaction of LSi−SiL (L=PhC(N^tBu)₂) ( 2 ) with two equivalents of 1 resulted in an unprecedented oxidative addition of a C−F bond of 1 leading to disilicon(III) fluoride {L(4-C₈F₃N)FSi−SiF(4-C₈F₃N)L}( 4 ), wherein the Si−Si single bond was retained. In contrast, the reaction of LGe−GeL (L=PhC(N^tBu)₂) ( 3 ) with one equivalent of 1 resulted in the oxidative cleavage of Ge−Ge bond leading to L(4-C₈F₃N₂)Ge ( 5 ) and LGeF ( 6 ). All three compounds ( 4 – 6 ) were characterized by NMR spectroscopy, EI-MS spectrometry, and elemental analysis. X-ray single-crystal structure determination of compound 4 unequivocally established that the Si^III−Si^III bond remains uncleaved.     

Preparation and properties of Ni–Co–P/nano‐sized Si3N4 electroless composite coatings

Ni–Co–P/nano‐sized Si₃N₄ composite coating was successfully fabricated on aluminum alloys by electroless plating in this work. The surface and cross‐sectional morphologies, composition, microstructure, microhardness, friction and wear behavior of deposits were investigated with SEM, EDS, XRD, Vickers hardness and high‐speed reciprocating friction, respectively. It was found that a Ni–Co–P/nano‐sized Si₃N₄ composite coating on aluminum alloy substrate is uniform and compact. The existence of nano‐sized Si₃N₄ particles in the Ni–Co–P alloy matrix causes a rougher surface with a granular appearance, and increases the microhardness but decreases the friction coefficients and wear rate of electroless coatings. Meanwhile, the effects of heat treatment at 200, 300, 400 and 500 °C for 1 h on the hardness and tribological properties were researched. It is revealed that both of the microhardness and tribological properties of Ni–Co–P coatings and Ni–Co–P/Si₃N₄ composite coatings increase with the increase of heating temperature in the range of 200–400 °C, but show different behavior for the two coatings after annealing at 500 °C. Copyright © 2011 John Wiley & Sons, Ltd.     

Sliding friction and wear behaviors of plasma sprayed aluminum–bronze coating in artificial seawater

The friction and wear behaviors of plasma sprayed aluminum–bronze (CuAl) coating sliding against silicon nitride (Si₃N₄) in artificial seawater were investigated and compared with those in pure water and dry sliding. The morphologies of the worn surfaces were analyzed by three‐dimensional non‐contact surface mapping and scanning electron microscopy. Moreover, chemical states of the tribochemical products of CuAl/Si₃N₄ in seawater were characterized by X‐ray photoelectron spectroscopy. Results show that the plasma sprayed CuAl coating possessed a specific wear rate (in order of 10^?7 mm³/Nm) in seawater more than 600 times smaller than that in dry sliding due to the great alleviation in abrasion wear and splats delamination. Besides, the CuAl/Si₃N₄ had a friction coefficient of 0.06 in seawater, significantly lower and more stable than those in pure water and dry sliding. The tribochemical products of CuAl/Si₃N₄ in seawater, which were proved to be silica, alumina, and their hydrates, transformed into a loosened wear‐debris layer under the coagulation effect of the seawater and dominated the excellent lubrication state in artificial seawater. Copyright © 2014 John Wiley & Sons, Ltd.     

On The Nature of FeIV=Oaq in Aqueous Media: A DFT analysis

Fe^IV=O_aq is a key intermediate in many advanced oxidation processes and probably in biological systems. It is usually referred to as Fe^IV=O²⁺. The pKa's of Fe^IV=O_aq as derived by DFT are: pKa1=2.37 M06 L/6-311++G(d,p) (SDD for Fe) and pKa2=7.79 M06 L/6-311++G(d,p) (SDD for Fe). This means that in neutral solutions, Fe^IV=O_aq is a mixture of (H₂O)₄(OH)Fe^IV=O⁺ and (H₂O)₂(OH)₂Fe^IV=O. The oxidation potential of Fe^IV=O_aq in an acidic solution, E⁰{(H₂O)₅Fe^IV=O²⁺/Fe^III(H₂O)₆³⁺, pH 0.0} is calculated with and without a second solvation sphere and the recommended value is between 2.86 V (B3LYP/Def2-TZVP, with a second solvation sphere) and 2.23 V (M06 L/Def2-TZVP without a second solvation sphere). This means that Fe^IV=O_aq is the strongest oxidizing agent formed in systems involving Fe^VIO₄²⁻ even in neutral media.     

On nanocomposite fabrication: using rheology to characterize filler/polymer interactions in epoxy-based nanocomposites

The interactions that occur between an amorphous silicon nitride (Si₃N₄) nanofiller and an epoxy matrix are examined, as revealed by rheological changes in a diglycidyl ether of bisphenol-A (DGEBA)-based epoxy resin prior to curing and thermal analysis, scanning electron microscopy, and dielectric spectroscopy of the resulting amine-cured systems. The results show that isothermally heating the as-received Si₃N₄ in DGEBA at 100 °C leads to increases in the viscosity of the mixture. Analysis of rheological data obtained from unfilled, as-received Si₃N₄-filled, and calcined Si₃N₄-filled epoxy systems leads us to interpret this increase in viscosity as arising from reactions between epoxide groups of the DGEBA and nanoparticle surface groups, notably involving surface amines, which are stimulated by the elevated temperature. The extent of this filler/resin reaction depends on the material processing protocol used, particularly prior calcination of the Si₃N₄ and the temperature and duration of nanoparticle/DGEBA mixing. Glass transition temperature data show that cured samples prepared using different methods have significantly different glass transition temperatures, which is a consequence of the epoxide/amine stoichiometric imbalances that result from prior reactions between the Si₃N₄ and the DGEBA. Consistent behavior was observed in the dielectric response. These results demonstrate that ultimate macroscopic properties of Si₃N₄/epoxy nanocomposites are critically affected by details of the processing protocol. Furthermore, we infer that, by using controlled prior calcination of the Si₃N₄, it is may be possible to vary the initial surface chemistry of the nanoparticles so as to adjust their reactivity with epoxy-containing moieties. Here, this is exemplified using only two somewhat extreme thermal treatments and a bifunctional DGEBA-type compound but, we suggest, that the concept may be extended to many other mono- and polyfunctional epoxy-containing compounds in order to generate a wide range of different grafted nanoparticle systems. This strategy may provide a versatile means of adjusting the surface chemistry of inorganic nitride nanoparticles, in order to tailor their surface chemistry and thereby modify resulting nanocomposite properties.     

Electrical-Conductive/Insulating Bi-Functional Layers for Stable Zn Metal Anode

Zinc-ion batteries are regarded as an extremely promising candidate for large-scale energy storage equipment due to the inexpensive ingredients and high safety. However, dendrite growth and side reactions occur in the Zn anode, which lead to exceedingly low coulombic efficiency (CE) and poor cycling stability. In this work, we propose a strategy of a conductive/insulating bi-functional coating layer (CIBL) for stable Zn metal anodes. Porous Ag nanowires (NWs) coating as a conductive layer effectively reduces the nuclear barrier and contains Zn²⁺ deposition in a certain space. Polyimide (PI) coatings as insulating layer implement a shunting effect on Zn²⁺, which could reduce the differential concentration on the Zn surface and induce uniform deposition of Zn²⁺. Therefore, the CIBL−Zn//CIBL−Zn battery achieves stable plating/stripping of over 1300 h at 1 mA cm⁻². The CE of CIBL−Zn//CIBL−Zn battery maintains at 99.2 % even after 1000 cycles. Moreover, the CIBL−Zn//V₂O₅ battery exhibits a capacity of nearly 289.2 mA h g⁻¹ at 5 A g⁻¹ after 3000 cycles and no sign of capacity degradation is found, which further demonstrate the feasibility of this strategy in practical application.     

Making Use of the Direct Process Residue: Synthesis of Bifunctional Monosilanes

The industrial production of monosilanes Me_nSiCl_4−n (n=1–3) through the Müller–Rochow Direct Process generates disilanes Me_nSi₂Cl_6−n (n=2–6) as unwanted byproducts (“Direct Process Residue”, DPR) by the thousands of tons annually, large quantities of which are usually disposed of by incineration. Herein we report a surprisingly facile and highly effective protocol for conversion of the DPR: hydrogenation with complex metal hydrides followed by Si−Si bond cleavage with HCl/ether solutions gives (mostly bifunctional) monosilanes in excellent yields. Competing side reactions are efficiently suppressed by the appropriate choice of reaction conditions.     

Si6C18: A bispentalene derivative with two planar tetracoordinate carbons

Here we show that substituting the ten protons in the dianion of a bispentalene derivative (C₁₈H₁₀²⁻) by six Si²⁺ dications produces a minimum energy structure with two planar tetracoordinate carbons (ptC). In Si₆C₁₈, the ptCs are embedded in the terminal C₅ pentagonal rings and participate in a three-center, two-electron (3c-2e) Si-ptC-Si σ-bond. Our exploration of the potential energy surface identifies a triphenylene derivative as the putative global minimum. Nevertheless, robustness to Born–Oppenheimer molecular dynamics (BOMD) simulations at 900 and 1500 K supports bispentalene derivative kinetic stability. Chemical bonding analysis reveals ten delocalized π-bonds, which, according to Hückel's 4n + 2 π-electron rule, would classify it as an aromatic system. Magnetically induced current density analysis reveals the presence of intense local paratropic currents and a weakly global diatropic current, the latter agreeing with the possible global aromatic character of this specie.     

Substitutional disorder in Sr2−yEuyB2−2xSi2+3xAl2−xN8+x (x≃ 0.12, y≃ 0.10)

A novel nitride, Sr_2−yEu_yB_2−2xSi_2+3xAl_2−xN_8+x (x≃ 0.12, y≃ 0.10) (distrontium europium diboron disilicon dialuminium octanitride), with the space group P2c, was synthesized from Sr₃N₂, EuN, Si₃N₄, AlN and BN under nitrogen gas pressure. The structure consists of a host framework with Sr/Eu atoms accommodated in the cavities. The host framework is constructed by the linkage of MN₄ tetrahedra (M = Si, Al) and BN₃ triangles, and contains substitutional disorder described by the alternative occupation of B₂ or Si₂N on the (0, 0, z) axis. The B₂:Si₂N ratio contained in an entire crystal is about 9:1.