Initial Substrate Temperature Research Articles

Optimization of the asymmetric synthesis of chiral aromatic alcohol using freeze-dried carrots as whole-cell biocatalysts

AbstractAsymmetric reduction of ketones is an important transformation in organic synthesis, because chiral carbinols are useful bioactive compounds. In this study, bioreduction of acetophenone (ACP) for production of enantiomerically pure (S)-1-phenyl-ethanol was investigated and freeze-dried carrots were used as a source of alcohol dehydrogenases (ADHs). However, production of product was investigated systematically using response surface methodology (RSM). Before RSM, the effects of the initial substrate concentration, reaction time, temperature and pH on the bioreduction were studied. The best results for enantiomeric excesses (ee) and conversion (c) were obtained with >99% and 58%, respectively, for the reaction time 48 h, initial substrate concentration 1 m

Enzymatic Synthesis of Rhamnose Containing Chemicals by Reverse Hydrolysis.

Rhamnose containing chemicals (RCCs) are widely occurred in plants and bacteria and are known to possess important bioactivities. However, few of them were available using the enzymatic synthesis method because of the scarcity of the α-L-rhamnosidases with wide acceptor specificity. In this work, an α-L-rhamnosidase from Alternaria sp. L1 was expressed in Pichia pastroris strain GS115. The recombinant enzyme was purified and used to synthesize novel RCCs through reverse hydrolysis in the presence of rhamnose as donor and mannitol, fructose or esculin as acceptors. The effects of initial substrate concentrations, reaction time, and temperature on RCC yields were investigated in detail when using mannitol as the acceptor. The mannitol derivative achieved a maximal yield of 36.1% by incubation of the enzyme with 0.4 M L-rhamnose and 0.2 M mannitol in pH 6.5 buffers at 55°C for 48 h. In identical conditions except for the initial acceptor concentrations, the maximal yields of fructose and esculin derivatives reached 11.9% and 17.9% respectively. The structures of the three derivatives were identified to be α-L-rhamnopyranosyl-(1→6')-D-mannitol, α-L-rhamnopyranosyl-(1→1')-β-D-fructopyranose, and 6,7-dihydroxycoumarin α-L-rhamnopyranosyl-(1→6')-β-D-glucopyranoside by ESI-MS and NMR spectroscopy. The high glycosylation efficiency as well as the broad acceptor specificity of this enzyme makes it a powerful tool for the synthesis of novel rhamnosyl glycosides.

Synthesis and heat treatment of sprayed high-temperature NiAl–Ni3Al coatings by in-flight combustion synthesis (CAFSY)

Combustion-Assisted Flame SpraYing (CAFSY) of intermetallic coatings is a new, cost-efficient and on-site-applicable thermal spraying process for applying Ni–Al intermetallic overlays or bond-coats on metallic substrates for protection at high temperature. This is the synthesis of desired intermetallic phases inflight and in-situ on the substrates during oxy-acetylene thermal spraying, using only low cost base-metal powders. By adjusting the spraying conditions (initial composition, spraying distance, substrate temperature, and flame temperature), excellent Ni–Al-based coatings have been produced on various substrates, including mild steel, stainless steel, and aluminum alloys. In some cases, however, the intermetallic phases formed on the substrates during CAFSY have been found to be metastable or the nickel and aluminum powders have not reacted sufficiently. In such cases, post-spraying heat treatments of the coatings allow the solid-state combustion reactions to proceed to completion in the coating. In many cases, it was found that increasing the temperature and the duration of the heat treatment increased the amount of intermetallic compounds (NiAl, Ni3Al, NiAl3, and Ni2Al3) in the coating up to as much as 90 vol %. In particular, all remaining aluminum reacts completely by forming Ni–Al intermetallics in the coatings. In all cases, porosity of the coatings remains below 3% while adhesion strength increases and reaches 57 MPa. The CAFSY method is a special manifestation of combustion synthesis, along the lines of the well-known SHS method. Without the need for expensive pre-alloyed intermetallic powders, optimization of spraying conditions allows very fast, in-flight reactions between component base metal powders to produce the required coating alloys when they reach the surface of the substrate. The actual mixture of the intermetallic phases of the coatings and their properties can be optimized for any industrial use by controlling spraying conditions and composition of powder mixtures.

Substrate preheating and structural properties of power plasma sprayed hydroxyapatite coatings

The aim of the present study was to investigate the influence of substrate preheating on the structural properties of hydroxyapatite coatings (HACs) deposited by using the high power (52kW) laminar plasma jet. The deposition experiments were performed within the 20–200°C temperature range at different stand-off distances. The structural properties in the thickness direction and at the surface of the HACs were investigated by using the micro-Raman spectroscopy, scanning electron microscopy coupled with energy dispersive spectrometry, and X-ray powder diffractometry. The deposition without the preheating of the substrate produced HACs with crystallinity gradient in the thickness direction. At the stand-off distance of 80mm, the preheating of the substrate at 200°C practically eliminated the crystallinity gradient. At distances from the coating/substrate interface shorter than ~100µm, the increase of crystallinity with the preheating of the substrate was dominantly attributed to the recrystallization of hydroxyl-rich ACP into HA. At longer distances and higher initial substrate temperatures (>100°C), the crystallinity changes were negligible, whereas the recrystallization of hydroxyl-deficient ACP into oxyapatite (OA) was also possible. The X-ray diffractometry indicated the deposition conditions under which a minimum residual stress was achieved. The results of the present study strongly suggested the relation between the ACP→HA recrystallization process and the bonding strength of the HACs.

Phenol oxidation by air using a Co (II) Salen complex catalyst supported on nanoporous materials: synthesis, characterization and kinetic analysis

Cobalt (II) Salen complex catalysts were synthesized and immobilized through covalent bonds on synthetic silica (SBA-15) and commercial supports, including silica (SiO2), alumina (Al2O3) and granular activated carbon (C). Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV–vis), diffuse reflectance ultraviolet-visible spectroscopy (DR–UV–vis) and X-ray diffraction (XRD) were used to characterize and follow the synthesis of the cobalt (II) Salen complex The UV–vis absorption spectra confirmed the formation of the Salen ligand and its coordination with the Co (II). FTIR spectra showed the incorporation of the Co Salen complex and its anchoring to the support was confirmed by DR–UV–vis. The catalytic activity was evaluated measuring the oxidation of phenol by air in a buffer solution using micellar electrokinetic chromatography (MEKC). The effects of support, initial substrate concentration, pH, oxidant (O2 vs H2O2) and temperature were investigated. The best catalytic performance was obtained when the Co Salen complex was immobilized on SBA-15 (Co Salen/SBA-15). Conversely, the results suggest that the activated carbon promoted the irreversible adsorption of the substrate. The Co Salen support was also characterized by scanning electron microscopy (SEM) to elucidate the morphology. Elemental analysis using energy dispersive X-ray spectroscopy (EDX) exhibited better Co Salen dispersion on the SiO2 and SBA-15 supports. The cobalt loading calculated from atomic absorption spectroscopy (AAS) was 0.22, 0.20, 0.14 and 0.09mmol/g for the Co Salen supported on SiO2, SBA-15, Al2O3 and C, respectively. A specific surface area of 736.13m2/g and a nanoporosity of 3.62nm were obtained for SBA-15 using N2 physisorption analysis; this high specific surface area is characteristic of SBA-15 and plays a critical role in the reported activity. According to these results and the corresponding data analysis, the catalyst promoted the oxidation of phenol with a reversible first-order kinetic reaction in air, as observed from the data obtained at 3 different temperatures (25, 38 and 50°C). These results enabled the calculation of activation energy values of 63 and 57kJ/mol. In addition, the Co Salen/SBA-15 showed very good selectivity toward the production of catechol, which is one of the most important precursors in the chemical industry.

Numerical analysis of pileup process in metal microdroplet deposition manufacture

A systematic numerical investigation of the transient transport phenomena during the pileup of molten metal droplets on the substrate is carried out in this paper. The prevailing physical mechanisms of the pileup process, including the bulk liquid, capillarity effects at the liquid–solid interface, heat transfer, and solidification, are identified and quantified numerically. Droplet diameters are from 100 μm to 320 μm, the impact velocities are 1–3 m/s, and the maximum flattening velocity is up to 1.5 times than the impact velocity. These conditions correspond to Re = O(100), We = O(1). The initial substrate temperature is 350 K. The initial droplet temperature of aluminum alloy molten droplets is 960 K. The numerical models are validated with experiments. The comparison between the numerical simulations and the experimental findings shows a good agreement. The effects of impacting velocity and relative distances between two successive molten droplets on the end-shapes of the impact regime are examined in order to describe the pileup process. This understanding is essential to implement effective process control in metal microdroplet deposition manufacture.

Numerical Investigation of Pileup Process in Metal Microdroplet Deposition Manufacture

This paper presents a systematic numerical investigation of the transient transport phenomenon during the pileup of molten metal droplets on the substrate. The physical mechanisms of the pileup process, including the bulk liquid, capillarity effects at the liquid-solid interface, heat transfer, and solidification, are identified and quantified numerically. The droplet diameter is 100 μm, and the impact velocities are 1–3 m/s. These conditions correspond to Re = O(100), We = O(1). The initial substrate temperature is 350 K. The initial droplet temperature of aluminum alloy molten droplets is 960 K. The numerical models are validated with experiments. The comparison between numerical simulations and experimental findings shows a good agreement. The effects of impacting velocity and relative distances between two successive molten droplets on the end-shapes of impact regime are examined. This investigation is essential to implement effective process control in metal microdroplet deposition manufacture.

The effects of initial substrate concentration, C/N ratio, and temperature on solid-state anaerobic digestion from composting rice straw

This study investigated the possibilities of improving the biogasification from solid-state anaerobic digestion (SS-AD) of composting rice straw (RS) based on the optimized digestion temperature, initial substrate concentration (ISC) and C/N ratio. RS compounds, such as lignin, cellulose, and hemicellulose, were significantly degraded after composting. A significant interactive effect of temperature, ISC and C/N ratio was found on the biogasification of SS-AD of composting RS, and a maximum biogas production was achieved at 35.6°C, with a 20% ISC and a C/N ratio of 29.6:1. The verification experiment confirmed the optimization results. High-throughput sequencing analysis indicated that microbial communities in the SS-AD mainly consist of Methanobacteria, Bacteroidia, Clostridia, Betaproteobacteria, and Gammaproteobacteria. A dominant Methanobacteria was shifted from Methanobacterium to Methanoculleus during the SS-AD process. This study provides novel information about the interdependent effects and microbial behavior of AD.

Sagging of evaporating droplets of colloidal suspensions on inclined substrates.

A droplet of a colloidal suspension placed on an inclined substrate may sag under the action of gravity. Solvent evaporation raises the concentration of the colloidal particles, and the resulting viscosity changes may influence the sag of the droplet. To investigate this phenomenon, we have developed a mathematical model for perfectly wetting droplets based on lubrication theory and the rapid-vertical-diffusion approximation. Precursor films are assumed to be present, the colloidal particles are taken to be hard spheres, and particle and liquid dynamics are coupled through a concentration-dependent viscosity and diffusivity. Evaporation is assumed to be limited by how rapidly solvent molecules can transfer from the liquid to the vapor phase. The resulting one-dimensional system of nonlinear partial differential equations describing the evolution of the droplet height and particle concentration is solved numerically for a range of initial particle concentrations and substrate temperatures. The solutions reveal that the interaction between evaporation and non-Newtonian suspension rheology gives rise to several distinct regimes of droplet shapes and particle concentration distributions. The results provide insight into how evaporation and suspension rheology can be tuned to minimize sagging as well as the well-known coffee-ring effect, an outcome which is important for industrial coating processes.

High removal rate of cross-linked SU-8 resist using hydrogen radicals generated by tungsten hot-wire catalyzer

This paper discusses the removal of chemically amplified negative-tone i-line resist SU-8 using hydrogen radicals generated by the catalytic decomposition of H2 molecules in H2/N2 mixed gas (H2:N2=10:90vol.%) using a tungsten hot-wire catalyzer. SU-8 resists with exposure doses from 7 to 280mJ/cm2 were removed by hydrogen radicals, although the SU-8 removal rate was independent of the exposure dose. The SU-8 removal rate increased with both substrate and catalyzer temperature, in addition to a decrease in the distance between the catalyzer and substrate. A high removal rate for cross-linked SU-8 with an exposure dose of 14mJ/cm2 of approximately 4μm/min was achieved with a catalyzer to substrate distance of 20mm, and catalyzer and initial substrate temperatures of 2400 and 165°C, respectively.

Comparative Assessment of Factors Involved in Acetoin Synthesis by Bacillus subtilis 168.

Acetoin is widely used as flavor agent and serves as a precursor for chemical synthesis. Here we focused on identifying the best physiological conditions (initial substrate concentrations, pH, temperature, and agitation) for enhanced acetoin accumulation by Bacillus subtilis 168. The optimal physiological conditions support maximum acetoin accumulation by minimizing byproduct (acetate and butanediol) synthesis and a maximum of 75% enhancement in acetoin yield could be achieved. Additionally, the effect of change in ALS (acetolactate synthase) and ALDC (acetolactate decarboxylase) activities was evaluated on acetoin accumulation. Increasing ALS and ALDC enzyme activities led to efficient utilization of pyruvate towards acetoin accumulation and about 80% enhancement in acetoin accumulation was observed.

Effect of Initial Substrate Concentrations and Temperature on the Oscillatory Behavior of Phloroglucinol-Based Belousov–Zhabotinsky Reaction

Abstract The present study introduces the use of phloroglucinol (1,3,5-trihydroxybenzene) as organic substrate in BZ reaction for the first time. This work has been carried out to assess the influence of initial reagent concentrations on the behavior of phloroglucinol–bromate–ferroin-based BZ reaction in a stirred batch reactor. The oscillations are followed by observing the change in redox potential. Different oscillatory parameters like induction time (tin), time period (tp), amplitude (A), frequency (v), and number of oscillations (N) show different changes with respect to changes in the initial concentrations of organic substrate, bromate and sulfuric acid, and these observations have been explained on the basis of FKN mechanism. The behavior of the aforesaid system in different aqueous acid media has been reported and it is found that sulfuric acid is the best medium for studying the system as it shows a wide oscillatory window compared to that of nitric acid. In phosphoric and perchloric acids the system does not show any oscillatory behavior. Activation parameters of the reaction have been derived by studying the reaction over a temperature range of 15 to 40 ± 0.1 °C. The effect of different catalysts on the oscillatory behavior has been studied and it is found that the system gives good oscillatory behavior with ferroin and Ce(III) whereas a poor response is seen when Mn(II) and Ce(IV) are used as catalysts.

Enhancing xylanases production by a new Amazon Forest strain of Aspergillus oryzae using solid-state fermentation under controlled operation conditions

Bioprocess studies towards improving the production of xylanases are of great value due to the importance of these enzymes on several industrial applications. This work evaluates the effects of operational conditions on xylanase production by a new strain of Aspergillus oryzae (P6B2) isolated from the Amazon Rain Forest. The fungus was cultivated under solid-state fermentation (SSF) using an instrumented lab-scale bioreactor equipped with an on-line automated monitoring and control system. The effects of initial substrate moisture content and temperature on xylanase production were evaluated and compared to static conditions. It was outstanding the positive effect on xylanase production by SSF cultivations under controlled conditions of forced over static aeration conditions. The conditions selected for further characterization resulted in the highest production of xylanase (2830.7IU/g), which was achieved using an initial substrate moisture content of 80%, at 28°C with an air flow rate of 20mL/min and an inlet air humidity of 80%. Results of respirometric analysis showed good agreement with enzyme production, suggesting that these data could be very useful for optimization and scale-up studies.

Dechlorination of chlorinated compounds by Trametes versicolor ATCC 200801 crude laccase and quantitative structure-activity relationship of toxicity

Chlorinated compounds constitute an important class of xenobiotics. Crude laccase was produced using Trametes versicolor ATCC (200801) in potato dextrose broth, with wheat bran as an inducing medium, and its ability to dechlorinate eight compounds was determined. The compounds were 2-chlorophenol, 4-chlorophenol, 2,4-dichlorophenol, 2,6-dichlorophenol, 2,4,5-trichlorophenol, 2,4,6-trichlorophenol, heptachlor and pentachlorophenol. A range of parameters for the dechlorination of some compounds was tested, including incubation period, pH, initial substrate concentration, temperature, and enzyme quantity. The oxygen consumption was determined during each dechlorination process, under pre-determined optimum conditions. The changes in chemical structure of the compounds were also determined, by using FTIR analysis, following dechlorination of test chlorophenolics. Strong interactions were found to lead to the reactivity of hydroxyl groups in some cases and chlorine atoms were released from the benzene ring. The changes in compound toxicity were monitored before and after enzymatic treatment, using Microtox. Quantitative structure-activity relationships for the toxicity of the chlorinated compounds were developed. Consequently, the toxic activity of the test compounds was controlled by electrophilic index and electronic properties.

Comparison of a new immobilized Fe3+ catalyst with homogeneous Fe3+–H2O2 system for degradation of 2,4‐dinitrophenol

AbstractBACKGROUND: Heterogeneous Fenton catalysts have been used to treat various organic pollutants in an aqueous environment. The present study has investigated the degradation of 2,4‐dinitrophenol (2,4‐DNP), a priority pollutant generated by such industries as pharmaceuticals, pesticides, pigments and dyes. Degradation of 2,4‐DNP (100 mg L−1) was studied using Fe3+ loaded on Al2O3 as a heterogeneous catalyst in the presence of H2O2, and the efficiency compared with the homogeneous Fe3+/H2O2 based Fenton‐like process. The effect of different parameters for both processes, such as catalyst loading, H2O2 concentration, initial solution pH, initial substrate concentration and temperature were investigated and the optimum operating conditions determined.RESULTS: Under optimal operating conditions of the homogeneous system ([Fe3+] 125 mg L−1; [H2O2] 250 mg L−1; pH 3; room temperature), 92.5% degradation was achieved in 35 min for an initial 2,4‐DNP concentration of 100 mg L−1. In the case of immobilized Fe (Fe3+–Al2O3 catalyst), degradation improved to 98.7% under the condition 10 wt% [Fe3+–Al2O3] 1 g L−1 catalyst loading; [H2O2] 250 mg L−1; pH 3; at room temperature for the same duration.CONCLUSIONS: This study demonstrated the stability and reusability of the prepared heterogeneous catalyst. This process is a viable technique for treatment of aqueous solutions containing contaminants. Copyright © 2012 Society of Chemical Industry

Marangoni Flows in Polymer Solution Droplets Drying on Heating Surfaces

The effect on substrate temperature on the fluid dynamics in a polymer solution droplet evaporating on a substrate is investigated experimentally and numerically. It is found from the experiments that fluid velocities in the droplets increase with increasing initial substrate temperature and with decreasing initial solute concentration. A mathematical model, which takes thermal and solutal Marangoni effects into account, are numerically solved using a finite element method. The calculated fluid velocities agree with the experiment. Both experiments and calculations show that, though thermal Marangoni forces dominate the fluid dynamics, solute Marangoni forces should never be neglected. The calculations predict that solute Marangoni effects are more emphasized with decreasing contact angle.

Sonophotocatalytic degradation of Rhodamine B using a novel reactor geometry: Effect of operating conditions

In this work, the decoloration of azo dye in aqueous solution by an ultrasound-assisted photocatalytic oxidation (US/UV/TiO 2) process was addressed. Rhodamine B (RhB) (basic violet 10), as the model compound, was decolorized completely within a few minutes in the US/UV/TiO 2 system. A more remarkable synergistic effect was observed on the RhB decolorization by US/UV/TiO 2 process, at low ultrasound frequency, than that observed in the case of individual process such as sonolytic (US), photolytic (UV) or photocatalytic oxidation (UV/TiO 2). The effects of various operating conditions such as initial dye concentration, TiO 2 concentration, hydrogen peroxide (H 2O 2) concentration, ultrasound power and temperature were investigated. In addition, the effects of the presence of radical scavenger tert-butyl-alcohol and the carbon tetrachloride (CCl 4) on the decolorization rate were also studied. Sonophotocatalytic decolorization of RhB was strongly influenced by the initial substrate concentration, acoustic power, temperature and catalyst concentration. It was also found that the dye decolorization was enhanced with increasing CCl 4 concentrations due to the formation of oxidant chlorine species. RhB decolorization increased slightly with increasing the H 2O 2 concentration, with an optimum level reached at H 2O 2 concentration of 1 mmol/L. The rate of dye decolorization was inhibited by the presence of low concentration of tert-butyl-alcohol. If the sonophotocatalysis is carried out in the presence of high tert-butyl-alcohol concentration, a very little RhB decolorization occurs. At low ultrasound frequency, the results indicated that total chemical oxygen demand (COD) removal was obtained in the tested RhB solutions when applying US/UV/TiO 2 system, signifying its great potential for the treatment of wastewaters contaminated with Rhodamine B.

Removal of Polymer for Nano-imprint Lithography using Atomic Hydrogen Generated by the Hot-wire Catalyzer

We investigated the removal characteristics of an ultraviolet (UV) curable polymer for UV nano-imprint lithography (NIL) using atomic hydrogen, which was generated by the catalytic decomposition of H2 molecules in H2/N2 mixed gas (H2:N2=10:90vol.%) using a tungsten hot-wire catalyzer. The cured polymers were removed by atomic hydrogen without a residual layer. The removal rate of the polymer increased with rising catalyzer temperature. It was assumed that both enhanced reactivity between atomic hydrogen and polymer by the substrate temperature increase due to radiation heat of the catalyzer and increased atomic hydrogen concentration occurred as a result of the rise in catalyzer temperature. When the distance between the catalyzer and the substrate was 100mm, the catalyzer temperature was 2400°C, and the initial substrate temperature was room temperature, the removal rate of polymers was 0.17μm/min independent of exposure dose to the polymer. The removal rate of polymers was comparable to the removal rate of general i-line positive-tone novolak resist. The polymer adhering to the micro-asperity portion of the mold was removed without leaving a residual layer by grazing-incidence atomic hydrogen.

Nickel–lithium oxide alloy transparent conducting films deposited by spray pyrolysis technique

In this research, nickel oxide (NiO) transparent semiconducting films are prepared by spray pyrolysis technique on glass substrates. The effect of Ni concentration in initial solution and substrate temperature on the structural, electrical, thermoelectrical, optical and photoconductivity properties of NiO thin films are studied. The results of investigations show that optimum Ni concentration and suitable substrate temperature for preparation of basic undoped NiO thin films with p-type conductivity and high optical transparency is 0.1 M and 450 °C, respectively. Then, by using these optimized deposition parameters, nickel–lithium oxide ((Li:Ni)O x ) alloy films are prepared. The XRD structural analysis indicate the formation of the cubic structure of NiO and (Li:Ni)O x alloy films. Also, in high Li doping levels, Ni 2O 3 and NiCl 2 phases are observed. The electrical measurements show that the resistance of the films decreases with increasing Li level up to 50 at%. For these films, the optical band gap and carrier concentration are obtained to be 3.6 eV and 10 15–10 18 cm −3, respectively.

Weak temperature dependence of stress relaxation in as-deposited polycrystalline gold films

During deposition of polycrystalline gold thin films, a compressive stress develops that reversibly changes during interruptions of growth. One model for this mechanism posits that this reversible stress change is related to adatom diffusion into and out of grain boundaries and recent work has established a relationship between the reversible stress and grain size. In the current study, the dependencies of the relaxation of the compressive stress during growth interruptions on the initial stress and substrate temperature have been studied. Stress was measured in situ during growth and during interruptions in growth. The stress relaxation over a fixed time was found to be proportional to the stress when growth was terminated and the effect of temperature was found to be very weak. These results suggest that grain-boundary diffusion is not a factor in the stress relaxation.