Solar photocatalytic generation of hydrogen under ultraviolet-visible light irradiation on (CdS/ZnS)/Ag<Subscript>2</Subscript>S + (RuO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript>) photocatalysts

In order to efficiently use the UV-vis light in the photocatalytic reaction, a novel (CdS/ZnS)/Ag₂S + RuO₂/TiO₂ was synthesized by chemical coprecipitation and metal ion implantation. The composition and structure of this composite were characterized by BET, UV-vis spectroscopy, SEM, XRD and EDX. This composite exhibited much higher photocatalytic activity for the generation of hydrogen (H₂).     

Nanosilver/hyperbranched polyester (HBPE): synthesis, characterization, and antibacterial activity

HBPE of different generations were synthesized using 4-hydroxybenzoic acid and 2,2′,2″-nitrilotriethanol via the A₂ + B₃ method. The reaction was carried out in a dry nitrogen atmosphere using p-toluene sulfonic acid (p-TSA) as an acid catalyst. The chosen molar ratios of 2,2′,2″-nitrilotriethanol to 4-hydroxybenzoic acid were 1:3, 1:6, and 1:21 for the G₁, G₂, and G₅ generations, respectively. The G₅ stage of HBPE was further coupled with acrylic acid to modify the terminal hydroxyl groups. The resulting products were analyzed using ¹H NMR, ¹³C NMR, FTIR spectroscopy, and GPC. Silver nanoparticles were prepared by a reductive technique using HBPEs of the G₅ generation as the matrix. XRD and TEM analysis indicated the formation of highly spherical and stable nanosilver in the HBPE. The antibacterial activity of the nanosilver/HBPE was evaluated against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) bacteria.     

Oxidation Behavior of NBD 200 Silicon Nitride Ceramics

The oxidation behavior of NBD 200 Si₃N₄ containing 1 wt% MgO sintering aid was investigated in oxygen at 900°-1300°C. The oxide growth followed a parabolic rate law with an apparent activation energy of 260 kJ/mol. The oxide layers were enriched with sodium and magnesium because of outward diffusion of intergranular Na⁺ and Mg²⁺ cations in the ceramics. The 2-4 orders of magnitude higher oxidation rate for NBD 200 Si₃N₄ than for other Si₃N₄ ceramics with a similar amount of MgO could be attributed to the presence of sodium. The oxidation process was most likely rate limited by grain-boundary diffusion of Mg²⁺.     

Synthesis and kinetics of ascorbic acid initiated graft copolymerized delignified cellulosic fiber

Graft copolymerization of delignified Grewia optiva fiber with methyl methacrylate (MMA) as vinyl monomer was attempted using ascorbic acid/H₂O₂ as redox initiator. Different reaction conditions affecting the grafting percentage (P_g) were optimized to get the maximum P_g (32.56%) of MMA onto delignified Grewia optiva fibers. Grafted and ungrafted fibers were subsequently subjected to evaluation of physico‐chemical properties such as swelling behavior and acid and alkali resistance. The rate expression for the grafting reaction (R_g = k [ASC]^0.12 [H₂O₂]^0.53 [MMA]^0.05) was evaluated and a suitable mechanism for grafting was suggested. The overall activation energy of the copolymerization reaction was found as 11.97 kJ mol^?1 at temperature range 25–65°C. Further, morphological and structural analysis of raw, delignified, and grafted Grewia optiva‐g‐poly(MMA) were studied by using Fourier‐transform Infrared spectroscopy, scanning electron microscopy, X‐ray diffraction, and thermogravimetric analysis.The tensile properties of grafted and ungrafted fiber samples were also reported. POLYM. ENG. SCI., 55:474–484, 2015. © 2014 Society of Plastics Engineers     

Microstructural studies of PMMA impregnated mortars

Studies on cement concrete microstructures are carried out to explain experimentally observed phenomenon and for modeling of concrete at the macroscopic level. In this article, the preparation of polymer impregnated mortar (PIC) is carried out by partially or fully replacing the pores in the cement mortars (OPC) by PMMA. The effect of this polymer impregnation on density and morphology of the cement matrix is studied. The microstructural changes in the mortar, on exposure of these specimens to hydrochloric acid and sea water for 7 and 28 days, are also investigated in this article. The above studies indicated that the polymer addition decreased the voids in the mortar thereby preventing leaching of water soluble salts present in the OPC. It was observed that the polymer also prevented the external chemical media from permeating into the cement matrix and undergoing interactions with it. It is concluded that the durability and chemical resistance properties of the PIC are better compared with OPC. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Studying nucleation and growth kinetics of alite hydration using μic

This paper investigates the applicability of nucleation and growth mechanisms to the hydration of alite. Various possible mechanisms of nucleation and growth were simulated using the recently-developed microstructural modelling platform μic. Comparison with the Avrami equation and the boundary nucleation model demonstrate the limitations of these equations. Experimental measurements of the rates of hydration of alite powders with different particle size distributions were then simulated with a boundary nucleation and growth model in μic. The results show that while the nucleation and growth of C–S–H having bulk densities in the currently accepted range can explain the acceleration during the first few hours of hydration, it cannot explain the later deceleration. It was also found that the resistance to flow of ions offered by the layer of hydrates forming over the surface of the alite particles (diffusion control) cannot explain the deceleration. The deceleration could be reproduced when C–S–H was assumed to be loosely packed in the beginning with its density of packing increasing with hydration. It is proposed that during the early hours of hydration a loosely-packed C–S–H fills a large fraction of the microstructure and the further development of its microstructure occurs due to an increase in its packing.     

Mechanical properties and durability of PMMA impregnated mortar

Polymer impregnated concrete (PIC) is known to exhibit better strength and durability characteristics than the other classes of polymer cement composites. In the work described herein the monomer was impregnated into cement mortar and polymerized by two methods — the conventional thermal method and using microwaves. The mechanical properties and durability characteristics of the samples and on exposure to chemical environments were then evaluated. The above studies revealed that the strengths of PIC specimens were almost 2–3 times better than those of conventional cement mortars. The chemical resistance was also found to be superior even on prolonged exposure to the chemical media. This may be attributed to the protective layer formed by the polymer on the cement mortar, which prevents the external chemical media from interacting with the cement particles. The properties of the PIC specimens prepared by both methods have also been compared and discussed in this paper.     

Biotransformation of alkylglycerols in plant cell cultures: Production of platelet activating factor and other biologically active ether lipids

Plant cells in culture are capable of incorporating exogenous 1-O-alkyl-sn-glycerols into various neutral and ionic ether lipids. 1-O-Alkyl-2-acyl-sn-glycerol-3-phosphocholines, the major class of compounds thus formed, are used for the preparation of platelet activating factor (PAF) in high yields. Similarly, the prochiral 2-O-alkyl-sn-glycerols are transformed to chiral 2-O-alkyl glycerophospholipids from which compounds can be obtained that exhibit antiviral activity in plant and animal cells. Reaction of 1-O-alkyl-2-acyl-sn-glycerol-3-phosphocholines with phospholipase D in the presence of ethanolamine leads to 1-O-alkyl-2-acyl-sn-glycerol-3-phosphoethanolamines, which serve as starting material, for the preparation of 1-O-alkyl-2-acyl-sn-glycero-3-phospho-(N-acyl)ethanolamines, compounds known to have antitumor activity. Based on a paper presented at the Third International Conference on Platelet-Activating Factor and Structurally Related Alkyl Ether Lipids, Tokyo, Japan, May 1989. Dedicated to Professor Morris Kates, Ottawa, on the occasion of his retirement.