Structure–reactivity studies on the polymerization and crosslinking behavior of tri(propylene glycol) diacrylate in aqueous solutions

Radiation induced polymerization of tri(propylene glycol) diacrylate (TRPGDA) has been investigated by steady state and pulse radiolysis (PR) techniques. Reactions of TRPGDA with primary species of water radiolysis such as OH radical, ${\text{e}}_{\text{aq}}^{-}$, H atom and oxidizing species like ${\text{N}}_3^{\text{<mglyph src="https://sdfestaticassets-us-east-1.sciencedirectassets.com/shared-assets/16/entities/rad"></mglyph>}}$ are reported. The rate constant values of 2.9 ± 0.19 × 10⁹ dm³ mol⁻¹ s⁻¹ and 1.3 × 10⁹ dm³ mol⁻¹ s⁻¹ were obtained for the reaction of TRPGDA with ${\text{e}}_{\text{aq}}^{-}$ and OH radical, respectively. The spectrum of hydrated electron was found to be pH dependent whereas the spectrum of transient species formed with OH radicals was found to be unaffected with pH variation. The radical anion formed, preferentially undergoes propagation. The OH adduct was found to be an α-carboxyalkyl radical with an absorption maximum at 300 nm. Steady state investigation reveals a significant dependence of the polymerization behavior on the nature of radiolytic species present and on the ambient environment. A very efficient function of TRPGDA as a crosslinker in poly(vinyl alcohol) matrix was demonstrated by the reduction in D_gel value from 1.1 kGy to 0.2 kGy for crosslinking in presence of 1% TRPGDA.     

Effect of wall surface materials on deposition of particles with the aid of negative air ions

This work studied how wall surface materials influence the removal of airborne particles with negative air ions (NAIs) in indoor environments. Five wall surface materials—stainless steel, wood, PVC (polyvinyl chloride), wallpaper and cement paint—were applied to the inner surface of a test chamber. Two monodispersed solid NaCl particle sizes, 300 and 30 nm, were tested. The NAIs in the chamber were generated by negatively electric discharge in the range 3000–5000 ions cm${}^{-3}$. Experiments on the natural decay and application of NAIs were conducted at an air exchange rate of 1 h${}^{-1}$. The decay coefficient, the removal efficiency, the time to halve the concentration ($T_{50}$) and the effective cleaning rate (ECR) were taken into account. The experimental data revealed that NAIs enhanced the removal of both 300 and 30 nm particles for each wall surface material. The decay coefficients of the NAI applications ($k_{\mathrm{a}}$) were 2.9–7.4 and 2.5–4.0 times higher than those of natural decay ($k_{\mathrm{n}}$) for 300 and 30 nm particles, respectively. However, the effect of the wall surfaces on the removal of particles was observed in both natural decay and NAI application experiments. The order of natural decay for 300 and 30 nm particles under different wall surfaces was cement paint $>\mathrm{PVC}\cong \mathrm{wallpaper}\cong \mathrm{wood}>$ stainless steel, as perhaps determined by the roughness of the wall materials. The overall removal efficiencies of 300 and 30 nm particles during 30 min of NAI emission were over 60% and 80%, respectively, in the chamber with wood and PVC wall surfaces. The half concentration times ($T_{50}$) of NAI applications for various wall surfaces were less than 20 min, except for stainless steel and cement paint walls. The ECR demonstrated that the net effects of the NAIs for 300 nm particles followed the order wood (34.6 Lpm) $>$ PVC (33.3 Lpm) $>$ wallpaper (27.0 Lpm) $>$ stainless steel (16.6 Lpm) $>$ cement paint (14.8 Lpm). The ECR for 30 nm particles followed the order wood (41.4 Lpm) $>$ PVC (30.4 Lpm) $\cong$ cement paint (30.3 Lpm) $>$ wallpaper (27.7 Lpm) $>$ stainless steel (20.1 Lpm). The NAI could remove particles from the wood and PVC wall surfaces substantially more effectively than from other wall materials. The various electrical characteristics and roughness of the wall materials may have been responsible for the associated of the various ECRs with the various wall surface materials.     

Selective hydrogenation of cinnamaldehyde catalyzed by palladium nanoparticles immobilized on ionic liquids modified-silica gel

In this paper, preparations of supported Pd catalysts by immobilization of Pd(OAc)₂ on silica gel that was modified by N-3-(-3-triethoxysilylepropyl)-3-methylimidazolium based ionic liquids ([(TESP)MIm][X], X = Cl⁻, ${\text{NO}}_3^{-}$, ${\text{BF}}_4^{-}$, and ${\text{PF}}_6^{-}$), and together with their catalytic applications for hydrogenation of cinnamaldehyde, were investigated. Depending on the ionic liquid involved, palladium can exist in the form as either palladium carbene complex (X = Cl⁻) or palladium nanoparticles with size less than 10 nm ($\text{X}={\text{NO}}_3^{-}$, ${\text{BF}}_4^{-}$, and ${\text{PF}}_6^{-}$), which, in turn, lead to different catalytic activities in respect to hydrogenation of cinnamaldehyde. Supported Pd nanoparticles were demonstrated to be high active and reusable catalysts for selective hydrogenation of cinnamaldehyde to hydrocinnamaldehyde, due to the stabilization effect of ionic liquids. Keeping the yield of product as 100%, they can be reused for nine times with neither Pd leaching nor activity loss, and offer the value of TON as high as nearly 500,000.     

The effect of Co doping on the magnetic and magnetocaloric properties of Pr0.7Ca0.3Mn1−xCoxO3 manganites

In this work, we report the effect of low amount of cobalt doping at the Mn-site on the magnetic and magnetocaloric properties of Pr_0.7Ca_0.3Mn_1−xCo_xO₃ (0≤x≤0.1) powder samples. Our samples, elaborated using the solid–solid reaction method at high temperature, are single phase and crystallize in the orthorhombic system with Pnma space group. While the parent compound Pr_0.7Ca_0.3MnO₃ exhibits a charge order state at low temperature, the substituted samples with low amount of cobalt exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. The Curie temperature T_C increases with Co content from 105 K for x=0 to 116 K for x=0.1. The maximum values of the magnetic entropy change $\left|\mathrm{\Delta }{S}_{\mathrm{M}}^{\max }\right|$ are found to be 0.8 J/kg K, 2.2 J/kg K, 3.1 J/kg K and 3.2 J/kg K in a magnetic field change of 5 T for x=0, 0.02, 0.05 and 0.1 respectively. The maximum value of the relative cooling power RCP is found to be 378.2 J/kg in the Pr_0.7Ca_0.3Mn_0.95Co_0.05O₃ at 5 T. This value of RCP is about 92% of that obtained in gadolinium metal, known as one of the most important materials for magnetic refrigeration, at the same magnetic field change of 5 T.     

High-Q microwave dielectric properties of Li(Zn0.95Co0.05)1.5SiO4 ceramics for LTCC applications

This study investigated the effects of Li₂O-MgO-ZnO₂-B₂O₃-SiO₂ (LMZBS) glass on the microstructure, sintering behaviour and microwave dielectric properties of Li(Zn_0.95Co_0.05)_1.5SiO₄ ceramics. Li(Zn_0.95Co_0.05)_1.5SiO₄ powders were synthesised by a traditional solid-state route and added with different amounts of LMZBS glass (0–4 wt%) to decrease the sintering temperature of the ceramics to approximately 900 °C. The XRD patterns showed that no chemical reactions occurred between the Li(Zn_0.95Co_0.05)_1.5SiO₄ ceramics and the LMZBS glass within the doping range. The SEM images indicated that the sample added with 1.5 wt% glass and sintered at 900 °C exhibited a compact and uniform microstructure. In particular, the microwave dielectric properties of the products were related to LMZBS glass content and sintering temperature. The sample with 1.5 wt% LMZBS glass exhibited excellent microwave dielectric properties, namely, ${\epsilon }_r$=6.12, $Q\times f$=83,600 GHz and ${\tau }_f=-39.1\mathrm{ppm}/\mathrm{℃}.$