Non-modified Sample Research Articles

Effective immobilization of candida cylindracea lipase on surfactant-modified bentonite

Lipase OF from Candida cylindracea was adsorbed onto surfactant-modified Na-bentonite (Bent), and the effects of the surfactants on the catalytic properties of immobilized lipase were studied in detail. The results showed that both the specific activity and enzyme loading of immobilized lipase varied significantly with modified support of different surfactants. The highest specific activity was obtained with Tween20-modified Bent: 11.9-fold higher than the non-modified sample. Upon modification by a single surfactant, two kinds of surfactants were combined to process the modification. It was surprising to find that the enzyme immobilized on CTAB (60%) and TX-100 (40%) co-modified Bent yielded a specific activity recovery of 133.4% indicating that the enzyme might be “activated”. Kinetic analyses for the hydrolysis of p-nitrophenyl palmitate (p-NPP) showed that K m decreased from 5.57 mg mL−1 of free lipase to 3.43 mg·mL−1 and V max increased 1.35-fold higher. The structure, surface morphology, and hydrophobicity of the modified bentonite and immobilize lipase were characterized via X-ray diffraction, Fourier transform-infrared spectroscopy, scanning electron microscopy, and contact angle measurements. We assumed that lipase molecules may be bound to the surface of the carrier, and the surface hydrophobicity and the change of the functional group caused by the modification of surfactant may be the key factor affecting lipase immobilization.

Cerium-modified cryptomelane: an antibacterial activity against Pseudomonas aeruginosa

K-OMS-2 (non-modified sample) and Ce-modified OMS-2 with different Ce-loading amounts were prepared by the refluxed method. The cryptomelane structure and elemental composition of synthesized samples were characterized with X-ray diffraction (XRD) and inductively coupled plasma mass spectrometry (ICP-MS), respectively. ICP-MS analysis revealed ~0.06 – 0.11 of K/Mn molar ratio and the Ce-loading amounts increased from 0 to —11.27 wt.% under increasing Ce-precursor concentration. Antibacterial activity against Pseudomonas aeruginosa was evaluated by the agar well diffusion method. The antibacterial ability against Pseudomonas aeruginosa was not recorded over K-OMS-2 (Ce0; 4.5 wt.% of K; 0 wt.% of Ce) and Ce3 (0.89 wt.% of K; 11.27 wt.% of Ce) samples while Ce2 sample (1.89 wt.% of K; 8.7 wt.% of Ce) showed a comparable antibacterial activity against Pseudomonas aeruginosa with ~12 mm of inhibition-zone diameter. This suggested the potentiality of using metal-modified cryptomelane in acceleration of antimicrobial ability.

Lead dioxide-SDS composites: Design and properties

Abstract The electrodeposition of PbO2 from a sodium dodecyl sulphate-containing medium has been investigated. The presence of sodium dodecyl sulfate in the deposition electrolyte leads to a slight inhibition of the deposition of lead dioxide. It has been found that the morphology and structure of composite materials differs significantly from lead dioxide. With an increase in the additive content in the composite, there is a transition from large-grained deposits to materials with submicron and nano-sized crystals. It is shown that anionic surfactants, sodium dodecyl sulfate in particular, are included in the growing lead dioxide. The changing in deposition conditions (temperature, pH and anodic current density) allows one to control the content of surfactant in the resulting oxide. It is possible to obtain a surfactant-oxide composite with the content of organic substance in the oxide up to 5.4 wt%. The electocatalytic activity of the materials involved was investigated in respect to oxygen evolution reaction and the oxidation of 4-chlorophenol. Oxygen overpotential on PbO2-SDS coatings decreases in comparison to non-modified sample because of a decrease in the degree of filling of oxygen-containing particles on the surface of the electrode, probably due to blocking by sulfate ions. The 4-chlorophenol oxidation rate is significantly increased on PbO2-SDS composites. Thus, already after 90 min of electrolysis on composites, contained 2 and 4.2 wt% SDS, all aromatic intermediates are destroyed, and only aliphatic acids are found in the solution.

Studies on the Potential of Nonmodified and Metal Oxide-Modified Coal Fly Ash Zeolites For Adsorption of Heavy Metals and Catalytic Degradation of Organics for Waste Water Recovery

A nanocrystalline zeolite of Na-X type (CFAZ) was synthesized by ultrasonic-assisted double stage fusion-hydrothermal alkaline conversion of lignite coal fly ash. Modified CFAZ with magnetic nanoparticles (MNP-CFAZ) was obtained by adding presynthesized magnetic nanoparticles between the synthesis stages. CFAZs loaded by particles of copper (Cu-CFAZ) and cobalt (Co-CFAZ) oxides were prepared by postsynthesis modification of the parent CFAZ, applying a wet impregnation technique. The parent and modified CFAZs were examined for their phase composition by X-ray diffraction, morphology by scanning electron microscopy, and surface characteristics by N2 physisorption. Comparative studies have been carried out on the adsorption capacity of the starting CFAZ and its derivatives with respect to Cd2+- and Pb2+-ions from aqueous solutions. Adsorption isotherms of Cd2+-ions on the studied samples were plotted and described by the adsorption equations of Langmuir, Freundlich, Langmuir–Freundlich, and Temkin. The best correlation between the experimental and model isotherms for the parent and modified CFAZ was found with the Langmuir linear model, assuming a monolayer adsorption mechanism. Parent and modified CFAZs were also studied as catalysts for heterogeneous thermal Fenton oxidation of methylene blue. At 90 °C, the higher catalytic activity exhibits the nonmodified sample, but with the decrease in temperature to 60 °C, the modified samples are more effective catalysts.

Study of hydrogen storage properties of oxygen modified Ti- based AB2 type metal hydride alloy

A multi component AB2 type hydrogen storage intermetallic alloy (A = Ti0.85Zr0.15, B2 = Mn1.22Ni0.22Cr0.2V0.3Fe0.06; was investigated in this work. The intermetallic specified above was modified by oxygen to yield the composition AB2O0.05. The oxygen was introduced by adding TiO2 to the charge, with corresponding decrease of the Ti amount, followed by arc melting and annealing at the same conditions as for the oxygen free AB2-type alloy. The addition of oxygen to the alloy did not change much the PCT properties; the only difference was that the plateau pressure for the oxygen-modified alloy increased slightly. Both alloys have shown to be excellent candidates for H2 storage, particularly for utility vehicles, due to their relatively high reversible H2 storage capacity (1.6 wt%) and low plateau pressure at room temperature (<5 bar). The addition of oxygen improved hydrogen absorption kinetics in the AB2 alloy allowing it to immediately absorb H2 without activation while for the non-modified sample an incubation period (30 min) was observed at the same conditions.

Influence of rare earth on the microstructure and mechanical properties of Al–Zn alloy

This paper discusses the influence of Vietnam rare earth (RE) with the composition of 69.4% Ce and 30.5% La (modification content of 4% and 6%) on the microstructure and mechanical properties of Al–5Zn–3.5Mg–1.2Cu alloy when the temperature modification is changed at [Formula: see text] in 150, 200, 250 s. By optical microscopy, the results showed that the microstructure of the modified sample is finer than the nonmodified sample. By the SEM and EDS analysis, at the grain boundaries of this alloy, [Formula: see text] and/or [Formula: see text] intermetallic phases appeared. The modified elements (La, Ce) in RE and aluminum were formed in the intermetallic [Formula: see text] and [Formula: see text] phases, which prevents the development of the dendritic [Formula: see text] phase. The result showed Al–5Zn–3.5Mg–1.2Cu alloy modified with 4% RE in 150 s which is the most optimal result, the grain size is [Formula: see text] and the hardness is 107 HB.

Synthesis and characterization of end-functionalized solution polymerized styrene-butadiene rubber and study the impact of silica dispersion improvement on the wear behavior of the composite

Two end-functionalized solution polymerized styrene-butadiene rubber was synthesized through anionic polymerization for using in formulation of well-dispersed silica compounds with study the wear behavior of the vulcanizates. Polymerization and functionalization were analyzed and confirmed via FT-IR, GPC, and NMR analyses. Novel functionalization, using an amine-containing agent, improved the distribution of silica. With the fine dispersion of silica, the wear rate dropped; the correlations between vulcanizate abrasion resistance, hardness, tear strength, glass transition temperature, and the SEM micrographs of the worn surface were studied. The abrasive stick-slip process was the primary wear mechanism and pattern spacing was the least for amino-modified vulcanizates. Lower reinforcement caused deep grooves, scratches, and pits in the non-modified sample. The amino-functionalized samples had desirable SEM characteristics, low hardness, more dispersed silica with fewer agglomerates and higher tear strength, confirming the higher interaction of silica particles and rubber chains.

INFLUENCE OF RARE-EARTH ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF HIGH MANGANESE STEEL UNDER IMPACT LOAD

In this paper, the influence of rare earth (RE) on the microstructure and mechanical properties of austenitic high manganese steel (HMnS) Mn15Cr2V were investigated. The results showed that the microstructure, hardness and impact strength of RE modification sample is finer and better than non-modified sample. Under the effect of impact load, the hardness and the depth of the work-hardening layer of the modified steel was higher than that of the non-modified steel, thereby, the value of microhardness in the surface of the modified sample was 420 HV while it was only 395 HV in the non-modified sample. The value of the impact strength of the modified sample was up to 132 J/cm2 compared to the non-modified sample is only 115 J/cm2. Moreover, after impact load, the austenite nanoparticles had been found out on the surface of this steel, this is the cause of the increasing of mechanical properties in this steel.

Conjugated Electron Donor⁻Acceptor Hybrid Polymeric Carbon Nitride as a Photocatalyst for CO2 Reduction.

This work incorporates a variety of conjugated donor-acceptor (DA) co-monomers such as 2,6-diaminopurine (DP) into the structure of a polymeric carbon nitride (PCN) backbone using a unique nanostructure co-polymerization strategy and examines its photocatalytic activity performance in the field of photocatalytic CO2 reduction to CO and H2 under visible light irradiation. The as-synthesized samples were successfully analyzed using different characterization methods to explain their electronic and optical properties, crystal phase, microstructure, and their morphology that influenced the performance due to the interactions between the PCN and the DPco-monomer. Based on the density functional theory (DFT) calculation result, pure PCN and CNU-DP15.0 trimers (interpreted as incorporation of the co-monomer at two different positions) were extensively evaluated and exhibited remarkable structural optimization without the inclusion of any symmetry constraints (the non-modified sample derived from urea, named as CNU), and their optical and electronic properties were also manipulated to control occupation of their respective highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). Also, co-polymerization of the donor–acceptor 2,6-diamino-purine co-monomer with PCN influenced the chemical affinities, polarities, and acid–base functions of the PCN, remarkably enhancing the photocatalytic activity for the production of CO and H2 from CO2 by 15.02-fold compared than that of the parental CNU, while also improving the selectivity.

Gold Doping in PtCu3/HSAC Nanoparticles and Their Morphological, Structural, and Compositional Changes during Oxygen Reduction Reaction Electrochemical Cycling

AbstractPt‐based nanoparticles supported on high‐surface‐area carbon (HSAC) show very good properties as catalysts in polymer electrolyte membrane fuel cells (PEMFC). In many cases, however, the initial high activity of such catalysts rapidly drops as caused by various detrimental phenomena occurring in a typical electrochemical environment. In this work, a detailed study of a highly active system composed of PtCu3/HSAC nanoparticles with partially ordered structure and Pt skin with the addition of Au is performed. By using aberration‐corrected scanning transmission electron microscopy, the effects of adding small amounts of gold compared to the nonmodified sample are followed through the different stages of an electrochemical cycling degradation protocol. Various morphological changes such as faceting, reshaping, and thickening of the Pt skin are investigated for both sets of samples on the atomic level. Interesting features such as well‐defined shapes and surface defects are observed after degradation. However, the most important differences in terms of durability seem related to particle porosity. Finally, the experimental morphological observations are successfully reproduced by dealloying simulation with kinetic Monte Carlo modeling.

Physicochemical properties of pine-derived bio-chars modified by metal oxides and their performance in the removal of NO

Pine-derived bio-chars have been prepared at different temperatures with and without KOH chemical activation. Three metal oxides (V2O5, MnO and CuO) were loaded on this chars by incipient-wetness impregnation method respectively. Pine wood pellets were characterized by thermogravimetric, and pine-chars samples were characterized by SEM-EDS, XRD, N2 physisorption and FTIR. Activity test for the selective catalytic reduction of NO with NH3 was also carried out in dry simulated flue gas at fixed temperature 160 °C. The results show that pretreatment with KOH and carbonization at 600 °C seems to be the best method for pine-chars preparation. Active metal oxides are well distributed on the surface of carbon support and are partly reduced by carbon during preparation. The mesopores disappear in V- and Mn-containing samples, and V-addition could decrease the amount of micropores as well. At the fixed temperature 160 °C, the active metal oxides have an order of CuO > V2O5 >> MnOx >> Non-modified sample on the NO reduction activity. Pine-chars modified by CuO seems to be the best option in this research.

Effect of electric pulse modification on mircostructure and properties of Ni-rich Al-Si piston alloy

In order to improve the properties of Ni-rich (2.5wt.%) Al-Si piston alloy, electric pulse modification was applied in fabricating the Ni-rich Al-Si piston alloy in this study. The effect of electric pulse modification on the mechanical properties of the Ni-rich Al-Si piston alloy was studied using optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), microhardness measurement and tensile strength testing. The results showed that the microstructures of Ni-rich Al-Si piston alloy treated by electric pulse modification were refined, the solid solubility of Cu, Ni, Si, etc. in cr-AI matrix was improved, and furthermore, the microhardness and high-temperature tensile strength were increased by 9.41% and 17.5%, respectively. The distribution of second phases was also more uniform compared with that of a non-modified sample.

Photocatalytic reduction of CO2 by graphitic carbon nitride polymers derived from urea and barbituric acid

Conjugated carbon nitride nanosheets modified with barbituric acid (BA) were synthesized by a facile one-pot chemical condensation of urea. The obtained BA-modified carbon nitride samples were termed as CNU-BAX and were fully characterized by XRD, FTIR, XPS, NMR, EPR, FESEM, TEM, DRS, PL, BET and photocurrent measurements. The performance of the developed carbon nitride based semiconductors was investigated by applying them as polymeric photocatalysts for the reduction of CO2 under visible light illumination. Results revealed that the copolymerization of urea with BA co-monomer strongly alternated the physical and chemical properties of carbon nitride polymer by improving optical absorption and creating surface molecular heterojunction that promoted charge separation, and consequently the enhanced photocatalytic performance was achieved. Various reaction parameters were investigated and optimized for the reaction system, and we found that under the optimal reaction condition, the best sample (CNU-BA0.03) could effectively photocatalyze the CO2-to-CO conversion reaction with 15-fold-enhanced catalytic activity, compared to the non-modified sample derived from urea (named as CNU). Other typical comonomers were also selected to polymerize with urea to study the beneficial effect of copolymerization on the development of efficient carbon nitride based nanostructures for CO2 photoreduction.

A comprehensive study of ultra-high molecular weight polyethylene modified by α-tocopherol after exposure to extremely high temperatures

The processes occurring in friction of samples of ultra-high molecular weight polyethylene (UHMWPE) obtained by pressing at 190 °C from discrete UHMWPE particles modified by α-tocopherol (α-T) were studied using X-ray photoelectron spectroscopy, thermogravimetry, thermomechanical analysis, investigation of the oxygen uptake kinetics, and determination of the inhibitory activity. Pressing results in the isolation of α-T on the sample surface, its oxidative destruction, and inhibition of UHMWPE oxidation. After tribological tests, the atomic content of oxygen in the surface layer of the modified sample remains at the initial level, while that in the non-modified UHMWPE sample increases by 50%.

Studies of water and ice in hydrophilic and hydrophobic mesoporous silicas: pore characterisation and phase transformations

A study has been made as a function of temperature of the phase transformation of water and ice in two samples of mesoporous silica gel with pore diameters of approximately 50 A. One sample was modified by coating with a layer of trimethylchlorosilane, giving a predominantly hydrophobic internal surface, whereas the unmodified sample has a hydrophilic interface. The pore structure was characterised by nitrogen gas adsorption and NMR cryoporometry and the melting/freezing behaviour of water and ice in the pores was studied by DSC and neutron diffraction for cooling and heating cycles, covering a range of 200 to 300 K. Measurements were made for several filling-factors in the range 0.2 to 0.9. The results show a systematic difference in the form of ice created in each of the samples. The non-modified sample gives similar results to previous studies with hydrophilic silicas, exhibiting a defective form of cubic ice superimposed on a more disordered pattern that changes with temperature and has been characterised as 'plastic' ice [Liu et al., 2006, Webber et al., 2007]. The modified sample has similar general features but displays important variability in the ice transformation features, particularly for the case of the low filling-factor (f = 0.2). The results exhibit a complex temperature-dependent variation of the crystalline and disordered components that are substantially altered for the different filling-factors.

Chemical Modification of Cysteine Residues Is a Misleading Indicator of Their Status as Active Site Residues in the Vitamin K-dependent γ-Glutamyl Carboxylation Reaction

The enzymatic activity of the vitamin K-dependent proteins requires the post-translational conversion of specific glutamic acids to gamma-carboxy-glutamic acid by the integral membrane enzyme, gamma-glutamyl carboxylase. Whether or not cysteine residues are important for carboxylase activity has been the subject of a number of studies. In the present study we used carboxylase with point mutations at cysteines, chemical modification, and mass spectrometry to examine this question. Mutation of any of the free cysteine residues to alanine or serine had little effect on carboxylase activity, although C343A mutant carboxylase had only 38% activity compared with that of wild type. In contrast, treatment with either thiol-reactive reagent 4-acetamido-4'-maleimidylstilbene-2,2'-disulfonic acid, disodium salt, or sodium tetrathionate, caused complete loss of activity. We identified the residues modified, using matrix-assisted laser desorption/ionization time of flight mass spectrometry, as Cys(323) and Cys(343). According to our results, these residues are on the cytoplasmic side of the microsomal membrane, whereas catalytic residues are expected to be on the lumenal side of the membrane. Carboxylase was partially protected from chemical modification by factor IXs propeptide. Although all mutant carboxylases bound propeptide with normal affinity, chemical modification caused a >100-fold decrease in carboxylase affinity for the consensus propeptide. We conclude that cysteine residues are not directly involved in carboxylase catalysis, but chemical modification of Cys(323) and Cys(343) may disrupt the three-dimensional structure, resulting in inactivation.

Surface Modification of ALC by Low Temperature Plasma Treatment

A hydrophobic surface layer of sub-millimeter was obtained by low temperature DC plasma treatment of a porous building material (ALC) for a few minutes in a CHF3 atmosphere. The present modified surface layer of ALC showed, (a) the repellency against water droprets for a 20-40 minutes and (b) the reduction in water vapor adsorption quite less than a nonmodified sample.