The effect of polypyrrole-bound anthraquinonedisulphonate dianion on cathodic reduction of oxygen

Functionalized polypyrrole (PPy) films were prepared by incorporation of anthraquinonedisulphonate (AQDS) as doping anion during the electropolymerization of pyrrole (Py) monomer at a glassy carbon electrode from aqueous solution. The electrochemical behavior of the PPy-bound AQDS modified electrode and cathodic reduction of oxygen on the resulting polymer film were studied. An obvious surface redox reaction corresponding to AQ/H₂AQ was observed and the dependence of this reaction on the solution pH was also illustrated. The electrocatalytic ability of the PPy-bound AQDS modified electrode was demonstrated by the electroreduction of oxygen at the optimized pH of 6.3 in a phosphate buffer. The reduced AQDS (H₂AQ) is responsible for the extraordinary catalytic activity to the oxygen reduction reaction. The PPy layers not only act as an electron mediator, but also facilitate the stability of the modified electrode. It was found that the catalytic reaction occurred in the presence of the bound AQDS and O₂ is in agreement with an electrochemical–chemical (EC) mechanism. The kinetic parameters of oxygen reduction were determined using Koutecky–Levich equation and Tafel polarization technique.     

Carboxymethyl chitosan-graft-phosphatidylethanolamine: Amphiphilic matrices for controlled drug delivery

Modified carboxymethyl chitosan (CMC) containing phosphatidylethanolamine (PEA) groups were synthesized by a 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)-mediated coupling reaction. The structure of the modified CMC exhibiting an amphiphilic character was analysed by FT-IR and ¹H NMR. CMC-g-PEA beads were prepared with sodium tripolyphosphate (TPP) by ionic-crosslinking. The beads sizes were in range from 800 to 1200 μm and encapsulation efficiencies of drug were more than 68%. The morphologies of CMC-g-PEA beads were examined with scanning electron microscopy (SEM). The release experiments were performed using ketoprofen as an hydrophobic model drug. The drug dissolution kinetics showed longer release times for CMC-g-PEA beads: 20 h (at pH 1.4) and 45 h (at pH 7.4). The amount of the drug release was much higher in acidic solution than in basic solution due to the swelling properties of the matrix at acidic pH. These results suggest that modified CMC with PEA may become a potential delivery system to control the release of hydrophobic drugs.     

超硬高韧微米颗粒聚晶金刚石块材的超高压制备

以微米级金刚石微粉为初始材料,利用自主研发的二级6-8型超高压大腔体装置,不添加黏结剂,在15 GPa左右条件下制备了超硬、高韧的厘米级块体聚晶金刚石,聚晶块体由高压硬化所致的、具有纳米亚结构的微米级金刚石颗粒组成。该材料的维氏硬度与单晶金刚石的最高维氏硬度（~120 GPa）相当,断裂韧性（18.7 MPa·m1/2）可媲美高性能硬质合金。      

Processing of high-performance Co doped Y2O3 as a single-phase electrolyte for low temperature solid oxide fuel cell (LT-SOFC)

The high-performance single-phase semiconductor materials with higher ionic conductivity have drawn substantial attention in fuel cell applications. Semiconductor materials play a key role to enhance ionic conductivity subsequently promoting low temperature solid oxide fuel cell (LT-SOFC) research. Herein, we proposed a semiconductor Co doped Y₂O₃ (YCO) samples with different molar ratios, which may easily access the high ionic conductivity and electrochemical performances at low operating temperatures. The resulting fabricated fuel cell 10% Co doped Y₂O₃ (YCO-10) device exhibits high ionic conductivity of ∼0.16 S cm⁻¹ and a feasible peak power density of 856 mW cm⁻² along with 1.09 OCV at 530 °C under H₂/air conditions. The electrochemical impedance spectroscopy (EIS) reveals that YCO-10 electrolyte based SOFC device delivers the least ohmic resistance of 0.11–0.16 Ω cm² at 530-450 °C. Electrode polarization resistance of the constructed fuel cell device noticed from 0.59 Ω cm² to 0.28 Ω cm² in H₂/air environment at different elevated temperatures (450 °C to 530 °C). This work suggests that YCO-10 can be a promising alternative electrolyte, owing to its high fuel cell performance and enhanced ionic conductivity for LT-SOFC.     

Synthesis and characterization of a high near infrared reflectance yellow pigment SbxWO3 (x ≤ 0.14)

In this work, a novel yellow near-infrared (NIR) reflective pigment based on the formula of Sb_xWO₃ was developed by high temperature solid-state method at 700–900 °C. The formation of Sb_xWO₃ was confirmed by XRD analysis, and the synthesized pigments are orthorhombic phase with high near infrared reflectivity (84.69%–87.28%). The acid/alkali resistance studies reveal that the color difference ΔE * of the pigments before and after soaking was less than 5, and the as prepared pigments are chemically stable under the atrocious weather. In addition, the synthetic pigments are bright yellowish green (L* = 92.1–92.9, a* = -4.9–4.1, b* = 35.0–37.0). In the heat insulation performance test, the indoor temperature with the Sb_xWO₃ heat insulation coating is 3.1 °C lower than that without heat insulation coating. In summary, the as prepared Sb_xWO₃ pigment has the advantages of high solar reflectivity and less toxic elements, making this new environmentally friendly energy-saving yellow pigment used as a colorant for building exterior coating formulations to reduce heat accumulation and cooling energy consumption.     

Effect of polystyrene addition on properties of porous Si3N4 ceramics fabricated by digital light processing

Porous Si₃N₄ ceramics with high strength and high transmittance have been widely used in the field of defense and military. Additive manufacturing (AM) technology is one of the effective means to fabricate porous Si₃N₄ ceramics. Nevertheless, it is difficult to prepare porous Si₃N₄ ceramics by using digital light processing (DLP) because of the large refractive index difference between Si₃N₄ powders and photosensitive resin. In this study, the effects of the amount of polystyrene (PS) powders on the properties of Si₃N₄ ceramic slurries and sintered ceramics were systematically discussed. The addition of PS reduced the overall refractive index of powders and increased the average particle size of powders, thus improving the cure depth of Si₃N₄ ceramic slurries from 11.0 ± 2.0 μm to 55.7 ± 1.8 μm. With the increase of PS content, the shrinkage and porosity of Si₃N₄ ceramics gradually increased, and the bulk density and flexural strength showed the opposite trend. The slurry with low viscosity (2.38 Pa٠s at a shear rate of 30 s⁻¹) and high cure depth (51.2 ± 4.6 μm) was obtained when the content of PS was 15 wt%, which met the thickness requirements for printing. The total porosity of Si₃N₄ ceramics reached the maximum values at 28.21 ± 2.58%. The addition of PS solved the problem of low cure depth of slurries, and PS as a pore-forming agent could help Si₃N₄ ceramics form porous structure. This research provides valuable insights into the fabrication of non-oxide ceramics with high refractive index using DLP technology.     

Room temperature NH3 gas sensor based on PMMA/RGO/ZnO nanocomposite films fabricated by in-situ solution polymerization

Effective detection of ammonia gas is of great importance due to its detrimental effects on human health, environment, and ecosystem. High-performance composite gas sensors are vital in accomplishing this goal. Herein, we investigate the performance of an ammonia (NH₃) gas sensor fabricated via dip-coating the silver interdigitated electrode for PMMA/RGO/ZnO (PRZ) nanocomposite solution with acetone as a solvent. The PRZ ternary nanocomposite was synthesized using the in-situ solution polymerization method and the resistive properties of the films assembled on the interdigitated electrode were analyzed, with respect to the fixed and varying ammonia gas concentrations, using LCR meter. When the sensor is operated in the controlled chamber containing ammonia gas at room temperature, the sensor responds rapidly to ammonia with a fast recovery of 13.02 s at a gas concentration of 350 ppm. The PRZ sensor exhibits high sensing percentage response (527%), excellent repeatability (four times), high sensitivity at low concentrations (less than 10 ppm), swift response and recovery times (1.94 s/13.02 s), and long-term stability (up to 90 days) with fluctuation of 3.2%, which signifies PRZ composite as a potential material for ammonia gas sensor. Aspects such as simplicity of the synthesis process and fabrication, excellent sensing performance, as well as fast response-recovery time at a particular gas concentration are noteworthy in this study. These features can be utilized for the detection of ammonia gas in chemical and biological fields.     

3D printing Si3N4-bonded SiC refractories fabricated using colloidal films-containing slurries based on non-spherical SiC and Si powders

Stable slurries for Si₃N₄-bonded SiC refractories for direct ink writing (DIW) were successfully prepared from a mixture of non-spherical silicon carbide (SiC) and silicon (Si) powders with an average particle size of D₅₀ = 41.98 μm. The rheological properties and printability of slurries prepared using polyvinyl alcohol (PVA; 4–16 wt %) or hydroxypropyl methylcellulose (HPMC, 0.5–2 wt.%) were investigated with the effect of sintering temperature on the mechanical performance, phase, and microstructure of Si₃N₄-bonded SiC refractory products. The results indicated that slurries prepared with the HPMC solution showed better printability than those prepared with the PVA solution because colloidal films formed by HPMC in slurries play a role in encasing particles, preventing solid−liquid separation and contributing to plasticity and lubrication, which guarantees the smooth extrusion and homogeneity of slurries. The successful printing of SiC–Si slurries is not only related to proper viscosity, yield value, and shear thinning characteristics but it is also crucial for maintaining the homogeneity of slurries under extrusion pressure. Optimal SiC–Si slurries containing 52 vol % SiC–Si and 1.5 wt% HPMC exhibited proper viscosity, shear thinning, and homogeneity characteristics during printing. The obtained specimens achieved the best printing performance with height and section retention rates of 98.7% and 97.6%, respectively. When sintered at 1450 °C, Si₃N₄ fibres grow further and reach a diameter of 342.5 nm, the nitriding rate is 92.43%, the fibres tend to form a full network structure, and the mechanical properties of Si₃N₄-bonded SiC products are the best.     

Anti-acid corrosion mechanism of yttrium oxide doped barium borosilicate glass

Designing glass with excellent acid resistance is a prerequisite for developing high-performance terminal electrode pastes. Herein, we fabricated Y₂O₃ doped BaO–B₂O₃–SiO₂ glass with excellent anti-sulfuric acid corrosion properties. The anti-corrosion mechanism of glass in acid environment was investigated by spectra and microstructure analysis. The passivating gel layer with a porous structure was formed on the glass surface during the corrosion process. The average pore diameter of the porous gel could be reduced by increasing the content of Y₂O₃. The smaller pore size of the porous gel would considerably increase the collision frequency between solvent molecules and the pore wall, which could effectively inhibit the ion migration in the gel layer, reduce the corrosion rate, and improve the acid resistance of the glass. This study contributes to the understanding of the corrosion mechanism of the glass and provides theoretical guidance for rationally designing anti-acid corrosion glass for terminal electrode pastes.     

Synthesis of few-layered Ti3C2Tx/ WO3 nanorods foam composite material for NO2 gas sensing at low temperature

The few-layered Ti₃C₂T_x/WO₃ nanorods foam composite material was synthesized by electrostatic self-assembly and bidirectional freeze-drying technologies. The phase structure and microstructure of synthesized samples was characterized by XRD, FESEM, TEM and their gas sensing properties estimated via a self-designed equipment with four test channels. The results demonstrate WO₃ nanorods were successfully anchored on the surface and between layers of few-layered Ti₃C₂T_x MXene by electrostatic self-assembly strategy and the composite material simultaneously has a low-density foam morphology by means of bidirectional freeze-drying processes. There exists a typical heterostructure at the interfaces owing to the inseparable contact between the few-layered Ti₃C₂T_x MXene and WO₃ nanorods. Compared with the original WO₃ nanorods, the few-layered Ti₃C₂T_x/WO₃ nanorods foam composite material displays excellent gas sensing properties for NO₂ detection at low temperature, in particular the optimal value of gas sensing response (R_g/R_a) reaches to 89.46 toward 20 ppm NO₂ at 200 °C. The gas sensing mechanism was also discussed. The increase of gas sensitivity is attributed to a fact that during the reaction process of gas sensing, the excellent conductivity of the few-layered Ti₃C₂T_x MXene provided faster transport channels of free carriers, and the heterojunctions formed by few-layered Ti₃C₂T_x MXene and WO₃ nanorods enhanced the carriers separation efficiency. Meanwhile, the low-density layered structure of few-layered Ti₃C₂T_x/WO₃ nanorods foam composite material provides convenient diffusion paths for gas molecules to the surface of WO₃ nanorods.