Photoenhancement of Gas-Solid Reactions by Surface Excitation

1983 ◽  
Vol 29 ◽  
Author(s):  
Carol I. H. Ashby
Keyword(s):  
Thermal Effects ◽  
Kinetic Studies ◽  
Wavelength Dependence ◽  
Reaction Rates ◽  
Thermal Reaction ◽  
Subsequent Formation ◽  
Rate Limiting Step ◽  
Surface Excitation ◽  
Rate Limiting ◽  
Reactive Excited State

ABSTRACTUltraviolet irradiation of the surface of graphite leads to the enhancement of the reaction of graphite with hydrogen to form methane under conditions where photo-induced thermal effects are negligible. Wavelength dependence of the photoenhancement correlates with excitation of the π-valence to π-conduction transition of graphite centered at 260 nm. Subsequent formation of some reactive excited state species leads to enhanced reaction rates. Likely candidates for such reactive species have been identified by comparative kinetic studies of the thermal and the photoenhanced reactions. For example, at low temperatures (< 500 K), the rate-limiting step of the thermal reaction is addition of H to surface CH3 groups, and the observed photoenhancement can be explained by activation of these CH3 groups.

Removal of Mg from spring water using natural clinoptilolite

Clay Minerals ◽  
2012 ◽  
Vol 47 (1) ◽  
pp. 81-92 ◽  
Author(s):  
S. Tomić ◽  
N. Rajić ◽  
J. Hrenović ◽  
D. Povrenović
Keyword(s):  
Ion Exchange ◽  
Kinetic Studies ◽  
Spring Water ◽  
Zeolite A ◽  
Zeolitic Tuff ◽  
Rate Limiting Step ◽  
Intra Particle Diffusion ◽  
Pseudo Second Order ◽  
Natural Clinoptilolite ◽  
Rate Limiting

AbstractNatural zeolitic tuff from Brus (Serbia) consisting mostly of clinoptilolite (about 90%) has been investigated for the reduction of the Mg concentration in spring water. The sorption capacity of the zeolite is relatively low (about 2.5 mg Mg g-1for the initial concentration of 100 mg Mg dm-3). The zeolitic tuff removes Mg from water solutions by ion exchange, which has been demonstrated by energy dispersive X-ray analysis (EDS). The extent of ion exchange was influenced by the pH and the initial Mg concentration. Kinetic studies revealed that Lagergen's pseudo-second order model was followed. Intra-particle diffusion of Mg2+influenced the ion exchange, but it is not the rate-limiting step. Rather than having to dispose of the Mg-loaded (waste) zeolite, a possible application was tested. Addition to a wastewater with a low concentration of Mg showed that it could successfully make up for the lack of Mg micronutrient and, accordingly, enabled the growth of phosphate-accumulating bacteriaA. Junii, increasing the amount of phosphate removed from the wastewater.

scholarly journals Spectroelectrochemical study of water oxidation on nickel and iron oxyhydroxide electrocatalysts

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Laia Francàs ◽  
Sacha Corby ◽  
Shababa Selim ◽  
Dongho Lee ◽  
Camilo A. Mesa ◽  
...  
Keyword(s):  
Water Oxidation ◽  
Reactive Intermediates ◽  
Reaction Rates ◽  
Iron Oxyhydroxide ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Earth Abundant ◽  
Fe Oxyhydroxides ◽  
Rate Limiting ◽  
Kinetics Of

AbstractNi/Fe oxyhydroxides are the best performing Earth-abundant electrocatalysts for water oxidation. However, the origin of their remarkable performance is not well understood. Herein, we employ spectroelectrochemical techniques to analyse the kinetics of water oxidation on a series of Ni/Fe oxyhydroxide films: FeOOH, FeOOHNiOOH, and Ni(Fe)OOH (5% Fe). The concentrations and reaction rates of the oxidised states accumulated during catalysis are determined. Ni(Fe)OOH is found to exhibit the fastest reaction kinetics but accumulates fewer states, resulting in a similar performance to FeOOHNiOOH. The later catalytic onset in FeOOH is attributed to an anodic shift in the accumulation of oxidised states. Rate law analyses reveal that the rate limiting step for each catalyst involves the accumulation of four oxidised states, Ni-centred for Ni(Fe)OOH but Fe-centred for FeOOH and FeOOHNiOOH. We conclude by highlighting the importance of equilibria between these accumulated species and reactive intermediates in determining the activity of these materials.

scholarly journals Kinetic studies of formate dehydrogenase

1970 ◽  
Vol 120 (4) ◽  
pp. 763-769 ◽  
Author(s):  
D. Peacock ◽  
D. Boulter
Keyword(s):  
Carbon Dioxide ◽  
Formate Dehydrogenase ◽  
Kinetic Studies ◽  
Kinetic Mechanism ◽  
Product Inhibition ◽  
Reverse Reaction ◽  
Enzyme Form ◽  
Rate Limiting Step ◽  
Measurable Rate ◽  
Rate Limiting

1. The kinetic mechanism of formate dehydrogenase is a sequential pathway. 2. The binding of the substrates proceeds in an obligatory order, NAD+ binding first, followed by formate. 3. It seems most likely that the interconversion of the central ternary complex is extremely rapid, and that the rate-limiting step is the formation or possible isomerization of the enzyme–coenzyme complexes. 4. The secondary plots of the inhibitions with HCO3− and NO3− are non-linear, which suggests that more than one molecule of each species is able to bind to the same enzyme form. 5. The rate of the reverse reaction with carbon dioxide at pH6.0 is 20 times that with bicarbonate at pH8.0, although no product inhibition could be detected with carbon dioxide. The low rate of the reverse reaction precluded any steady-state analysis as the enzyme concentrations needed to obtain a measurable rate are of the same order as the Km values for NAD+ and NADH.

EQUILIBRIUM AND KINETIC STUDIES OF THE ADSORPTION OF 2,4-D AND PICLORAM ON HUMIC ACID

1973 ◽  
Vol 53 (4) ◽  
pp. 429-434 ◽  
Author(s):  
S. U. KHAN
Keyword(s):  
Humic Acid ◽  
Adsorption Process ◽  
Initial Period ◽  
Kinetic Studies ◽  
Time Intervals ◽  
Rate Limiting Step ◽  
Equilibrium Data ◽  
Dichlorophenoxy Acetic Acid ◽  
Rate Limiting ◽  
Physical Type

Equilibrium and kinetic studies of the adsorption of 2,4-D (2,4-dichlorophenoxy acetic acid) and picloram (4-amino-3,5,6-trichloropicolinic acid) on a humic acid have been made. The equilibrium data followed the Freundlich-type isotherm. Rate constants, activation energies, heats of activation, and entropies of activation were calculated for the adsorption of the two herbicides on humic acid. The rate data indicated a physical type of adsorption. In the overall adsorption process the rate-limiting step for the initial period was shown to be the diffusion of the herbicide molecules to the surface of humic acid. However, the rate-limiting process at longer time intervals was interpreted to be intraparticle diffusion of the herbicide molecules into the interior of the humic acid particles.

scholarly journals Preparation and Kinetic Studies of Cross-Linked Chitosan Beads Using Dual Crosslinkers of Tripolyphosphate and Epichlorohydrin for Adsorption of Methyl Orange

2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Akhmad Sabarudin ◽  
Armeida D. R. Madjid
Keyword(s):  
Methyl Orange ◽  
Bulk Diffusion ◽  
Kinetic Studies ◽  
Hydroxyl Group ◽  
High Concentration ◽  
Chitosan Beads ◽  
Kinetics Of Adsorption ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Preparation of cross-linked chitosan beads using dual crosslinkers of tripolyphosphate (TPP) and epichlorohydrin (ECH) for the adsorption and kinetic studies of methyl orange (MO) had been carried out. FTIR spectra showed that TPP could act as the protecting agent of the NH2 group of chitosan and ECH reacted with the primary hydroxyl group of chitosan. Various concentrations of TPP, ECH, and immersing time in the TPP solution for bead formation were studied. The effect of pH and kinetics of adsorption were investigated to define the mechanism of adsorption and rate-limiting step. As a result, pH 3, 10% (w/v) TPP, 5% (v/v) ECH, and 12 h immersing time in TPP were selected as the optimum conditions for preparing the beads as indicated by the highest adsorption amount of MO. The cross-linked chitosan beads’ adsorption capacity for MO under optimum condition was found to be 79.55 mg/g with the adsorption rate constant (k) of 1.29 × 10−3/min. Furthermore, it was found that a low concentration of ECH could maintain the stability of chitosan in acidic conditions, whereas the concentration of TPP and immersing time controlled pore size and morphology of chitosan beads. The mechanism of adsorption of MO was controlled by the pore and rigidity of cross-linked chitosan beads. Bulk diffusion acted as a rate-limiting step, and a high concentration of MO inhibited diffusion and adsorption itself.

scholarly journals Oxidation of Cytochrome 605 Is the Rate-Limiting Step when Ferrimicrobium acidiphilum Respires Aerobically on Soluble Iron

2020 ◽  
Vol 86 (22) ◽  
Author(s):  
Robert C. Blake ◽  
Jessie J. Guidry ◽  
Micah D. Anthony ◽  
Bhupal Ban ◽  
Kayla A. Smith ◽  
...  
Keyword(s):  
Kinetic Studies ◽  
Ferrous Ions ◽  
Gram Positive ◽  
Oxidase Gene ◽  
Physiological Conditions ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Intact Organism ◽  
Rate Limiting

ABSTRACT Proteins that oxidize extracellular substrates in Gram-positive bacteria are poorly understood. Ferrimicrobium acidiphilum is an actinobacterium that respires aerobically on extracellular ferrous ions at pH 1.5. In situ absorbance measurements were conducted on turbid suspensions of intact Fm. acidiphilum using an integrating cavity absorption meter designed for that purpose. Initial velocity kinetic studies monitored the appearance of product ferric ions in the presence of catalytic quantities of cells. Cell-catalyzed iron oxidation obeyed the Michaelis-Menten equation with Km and Vmax values of 71 μM and 0.29 fmol/min/cell, respectively. Limited-turnover kinetic studies were conducted with higher concentrations of cells to detect and monitor changes in the absorbance properties of cellular redox proteins when the cells were exposed to limited quantities of soluble reduced iron. A single a-type cytochrome with reduced absorbance peaks at 448 and 605 nm was the only redox-active chromophore that was visible as the cells respired aerobically on iron. The reduced cytochrome 605 exhibited mathematical and correlational properties that were consistent with the hypothesis that oxidation of the cytochrome constituted the rate-limiting step in the aerobic respiratory process, with a turnover number of 35 ± 2 s−1. Genomic and proteomic analyses showed that Fm. acidiphilum could and did express only two a-type heme copper terminal oxidases. Cytochrome 605 was associated with the terminal oxidase gene that is located between nucleotides 31,090 and 33,039, inclusive, in the annotated circular genome of this bacterium. IMPORTANCE The identities and functions of proteins involved in aerobic respiration on extracellular ferrous ions at acidic pH are poorly understood in the four phyla of Gram-positive eukaryotes and archaea where such activities occur. In situ absorbance measurements were conducted on Fm. acidiphilum as it respired on extracellular iron using an integrating cavity absorption meter that permitted accurate optical measurements in turbid suspensions of the intact bacterium under physiological conditions. The significance of these measurements is that they permitted a direct spectrophotometric examination of the extents and rates of biological electron transfer events in situ under noninvasive physiological conditions without disrupting the complexity of the live cellular environment. One thing is certain: one way to understand how a protein functions in an intact organism is to actually observe that protein as it functions in the intact organism. This paper provides an example of just such an observation.

scholarly journals Application of Functionalized DVB-co-GMA Polymeric Microspheres in the Enhanced Sorption Process of Hazardous Dyes from Dyeing Baths

Molecules ◽  
2020 ◽  
Vol 25 (22) ◽  
pp. 5247
Author(s):  
Monika Wawrzkiewicz ◽  
Beata Podkościelna ◽  
Przemysław Podkościelny
Keyword(s):  
Dye Adsorption ◽  
Freundlich Isotherm ◽  
Kinetic Studies ◽  
Sorption Process ◽  
Polymeric Microspheres ◽  
Rate Limiting Step ◽  
Rate Limiting ◽  
Intensive Development ◽  
Acid Violet ◽  
Huge Challenge

Intensive development of many industries, including textile, paper, plastic or food, generate huge amounts of wastewaters containing not only toxic dyes but also harmful auxiliaries such as salts, acid, bases, surfactants, oxidants, heavy metal ions. The search for effective pollutant adsorbents is a huge challenge for scientists. Synthesis of divinylbenzene copolymer with glycidyl methacrylate functionalized with triethylenetetramine (DVB-co-GMA-TETA) resin was performed and the obtained microspheres were evaluated as a potential adsorbent for acid dye removal from dyeing effluents. The sorption capacities were equal to 142.4 mg/g for C.I. Acid Green 16 (AG16), 172 mg/g for C.I. Acid Violet 1 (AV1) and 216.3 mg/g for C.I. Acid Red 18 (AR18). Non-linear fitting of the Freundlich isotherm to experimental data was confirmed rather than the Langmuir, Temkin and Dubinin-Radushkevich. The kinetic studies revealed that intraparticle diffusion is the rate-limiting step during dye adsorption. Auxiliaries such as Na2SO4 (5–25 g/L), CH3COOH (0.25–1.5 g/L) and anionic surfactant (0.1–0.5 g/L) present in the dyeing baths enhance the dye adsorption by the resin in most cases. Regeneration of DVB-co-GMA-TETA is possible using 1 M NaCl-50% v/v CH3OH.

Study of Adsorption of Cu2+ and Ni2+ from Aqueous Solutions Using β-Cyclodextrin Modified Zeolites

2014 ◽  
Vol 955-959 ◽  
pp. 3509-3513
Author(s):  
Xiao Hong Li ◽  
Xue Kui Hao
Keyword(s):  
Contact Time ◽  
Physical Adsorption ◽  
Kinetic Studies ◽  
Order Model ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Adsorption Processes ◽  
Pseudo Second Order ◽  
Modified Zeolites ◽  
Rate Limiting

Adsorption of Cu2+ and Ni2+ from aqueous solution on CCDMZ was investigated. The adsorption capacity of Cu2+ and Ni2+ on CCDMZ was found to have a much higher enhance than that of NZ and to be obviously influenced by contact time, initial concentration and pH. The kinetic studies showed that the adsorption processes of Cu2+ and Ni2+ on CCDMZ were complex, including chemical adsorption and physical adsorption. The adsorption followed the pseudo-second-order model, which suggested that the rate-limiting step might be mainly chemisorption.

THE Δ5-3β-HYDROXYSTEROID DEHYDROGENASE OF BOVINE ADRENAL MICROSOMES

1969 ◽  
Vol 43 (4) ◽  
pp. 599-608 ◽  
Author(s):  
A. M. NEVILLE ◽  
J. C. ORR ◽  
L. L. ENGEL
Keyword(s):  
Dehydrogenase Activity ◽  
Kinetic Studies ◽  
Hydroxysteroid Dehydrogenase ◽  
Acetone Powder ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Michaelis Constants ◽  
Rate Limiting

SUMMARY The Δ5-3β-hydroxysteroid dehydrogenase activity of an acetone powder of bovine adrenal microsomes has been studied using 3β-hydroxyandrost-5-en-17-one and 3β-hydroxypregn-5-en-20-one as substrates. The products were separated, identified and quantitated by gas—liquid chromatographymass spectrometry. The Michaelis constants for both steroid substrates and for NAD have been derived and are of the order of 10−6 m. Although kinetic studies indicate the existence of a single Δ5-3β-hydroxysteroid dehydrogenase, the possibility of a non-enzymic rate-limiting step common to both steroid substrates and to NAD must be entertained.

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