scholarly journals Study on the Adsorption Kinetics of Acid Red 3B on Expanded Graphite

2008 ◽  
Vol 5 (4) ◽  
pp. 802-809 ◽  
Author(s):  
Xiu-yan Pang ◽  
Fei Gong
Keyword(s):  
Activation Energy ◽  
Adsorption Kinetics ◽  
Adsorption Process ◽  
Expanded Graphite ◽  
Chemical Oxidation ◽  
Adsorption Rate ◽  
Order Kinetic ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Expanded graphite (EG) is a kind of important adsorbent for organic compound such as oil and dyes. We have investigated the adsorption kinetics characteristics of this adsorbent for dye. EG was prepared with 50 mesh crude graphite through chemical oxidation intercalation of potassium permanganate and vitriol, and dye of acid red 3B was used as model sorbate. We have studied the adsorption kinetic models and rate-limiting step of the process. Adsorption rate and activation energy of the adsorption process were calculated. Kinetic studies show that the kinetic data are well described by the pseudo second-order kinetic model. The equilibrium adsorbance increases with the increase of the initial acid red 3B concentration. Initial adsorption rate increases with the increase of the initial dye concentration and temperature. Adsorption process of acid red 3B on EG has small activation energy. Internal diffusion appears to be the rate-limiting step for the adsorption process.

scholarly journals ADSORPTION KINETICS OF Pb(II), Cd(II) AND Cr(III) ON ADSORBENT PRODUCED BY PROTECTED-CROSSLINKING OF HUMIC ACID-CHITOSAN

2010 ◽  
Vol 10 (1) ◽  
pp. 80-87
Author(s):  
Dewi Umaningrum ◽  
Uripto Trisno Santoso ◽  
Radna Nurmasari ◽  
Rahmat Yunus
Keyword(s):  
Humic Acid ◽  
Adsorption Kinetics ◽  
Metal Ion ◽  
Second Order ◽  
Adsorption Rate ◽  
Ion Concentration ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting ◽  
Kinetics Of

Study on adsorption kinetics of of Pb(II), Cd(II) and Cr(III) on adsorbent which was produced by protected-crosslinking of humic acid-chitosan has been done. The Langmuir-Hinshelwood, pseudo first- and second-order kinetics models were used to describe the kinetic data, and the rate constants of adsorption were also evaluated. The experimental data fitted well the second-order kinetics model, indicating that the chemical sorption is the rate-limiting step, instead of mass transfer. The initial metal ion concentration significantly affects the adsorption rate. An increase in initial metal ion concentration results in the decrease in adsorption rate of the metals.   Keywords: kinetics, adsorption, crosslinking, humic acid, chitosan

scholarly journals Single Molecular Catalysis Identifying Activation Energy of Intermediate Product and Rate-Limiting Step in Plasmonic Photocatalysis

2019 ◽  
Author(s):  
Di Li
Keyword(s):  
Activation Energy ◽  
High Performance ◽  
Variable Temperature ◽  
Chemical Conversion ◽  
Catalytic Performance ◽  
Localized Surface Plasmon ◽  
Spatiotemporal Resolution ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Plasmon mediated photocatalysis provides a novel strategy for harvesting solar energy. Identification of rate determining step and its activation energy in plasmon mediated photocatalysis plays critical roles for understanding the contribution of hot carriers that facilitates rational designing catalysts with integrated high photo-chemical conversion efficiency and catalytic performance. However, it remains a challenge due to a lack of research tools with spatiotemporal resolution that capable of capturing intermediates. In this work, we used a single molecular fluorescence approach to investigate a localized surface plasmon resonance (LSPR) enhanced photocatalytic reaction with sub-turnover resolution. By introducing variable temperature as an independent parameter in plasmonic photocatalysis, the activation energies of tandem reaction steps, including intermediate generation, product generation and product dissociation, were clearly differentiated, and intermediates generation was found to be the rate-limiting step. Remarkably, the cause of plasmon enhanced catalysis performance was found to be its ability of lowering the activation energy of intermediates generation. This study gives new insight into the photo-chemical energy conversion pathways in plasmon enhanced photocatalysis and sheds light on designing high performance plasmonic catalysts.

scholarly journals Single Molecular Catalysis Identifying Activation Energy of Intermediate Product and Rate-Limiting Step in Plasmonic Photocatalysis

2019 ◽  
Author(s):  
Di Li
Keyword(s):  
Activation Energy ◽  
High Performance ◽  
Variable Temperature ◽  
Chemical Conversion ◽  
Catalytic Performance ◽  
Localized Surface Plasmon ◽  
Spatiotemporal Resolution ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Plasmon mediated photocatalysis provides a novel strategy for harvesting solar energy. Identification of rate determining step and its activation energy in plasmon mediated photocatalysis plays critical roles for understanding the contribution of hot carriers that facilitates rational designing catalysts with integrated high photo-chemical conversion efficiency and catalytic performance. However, it remains a challenge due to a lack of research tools with spatiotemporal resolution that capable of capturing intermediates. In this work, we used a single molecular fluorescence approach to investigate a localized surface plasmon resonance (LSPR) enhanced photocatalytic reaction with sub-turnover resolution. By introducing variable temperature as an independent parameter in plasmonic photocatalysis, the activation energies of tandem reaction steps, including intermediate generation, product generation and product dissociation, were clearly differentiated, and intermediates generation was found to be the rate-limiting step. Remarkably, the cause of plasmon enhanced catalysis performance was found to be its ability of lowering the activation energy of intermediates generation. This study gives new insight into the photo-chemical energy conversion pathways in plasmon enhanced photocatalysis and sheds light on designing high performance plasmonic catalysts.

Single-Molecular Catalysis Identifying Activation Energy of the Intermediate Product and Rate-Limiting Step in Plasmonic Photocatalysis

Nano Letters ◽  
2020 ◽  
Vol 20 (4) ◽  
pp. 2507-2513 ◽  
Author(s):  
Wei Li ◽  
Junjian Miao ◽  
Tianhuan Peng ◽  
Hui Lv ◽  
Jun-Gang Wang ◽  
...  
Keyword(s):  
Activation Energy ◽  
Intermediate Product ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Molecular Catalysis ◽  
Rate Limiting

THE FORMATION OF CELLULOSE MICROFIBRILS BY ACETOBACTER XYLINUM IN AGAR SURFACES

1961 ◽  
Vol 7 (3) ◽  
pp. 383-387 ◽  
Author(s):  
B. Millman ◽  
J. Ross Colvin
Keyword(s):  
Activation Energy ◽  
Cell Membrane ◽  
Characteristic Feature ◽  
Acetobacter Xylinum ◽  
Cellulose Microfibrils ◽  
High Polymer ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Liquid Suspensions ◽  
Rate Limiting

The formation of extracellular cellulose microfibrils by Acetobacter xylinum on agar surfaces is remote from the cell membrane and does not involve an intermediate, amorphous high polymer, in agreement with conclusions from studies of liquid suspensions. Growth of individual microfibrils is at the tip(s) only and the rate of extension (0.2 μ per bacterial cell per minute at 34 °C) is comparable with that in liquid medium. The rate of nucleation of new microfibrils is about 40 per 103 bacteria per minute at 34 °C. Both rates are constant after an induction period of about 30 seconds. Newly nucleated microfibrils could be identified unequivocally down to a length of 0.5 μ. A characteristic feature of growth of cellulose on agar surfaces is the formation of bundles of microfibrils with their axes roughly parallel. The results suggest that the rate-limiting step in the formation of these microfibrils has an activation energy of about 15 kc.

scholarly journals Removal of copper from an electroplating industrial effluent using the native and modified spirogyra

2018 ◽  
Vol 78 (1) ◽  
pp. 147-155 ◽  
Author(s):  
Nimra Ilyas ◽  
Sadia Ilyas ◽  
Sajjad-ur-Rahman ◽  
Sidra Yousaf ◽  
Aqsa Zia ◽  
...  
Keyword(s):  
Industrial Effluent ◽  
Order Kinetic ◽  
Sorption Data ◽  
Freundlich Model ◽  
First Order ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Intra Particle Diffusion ◽  
Pseudo Second Order ◽  
Rate Limiting

Abstract In the present study, biosorption behavior of a green filamentous alga, spirogyra in its native and modified states was investigated for copper removal from an electroplating industrial effluent. For this, the effluent containing 194 mg·L−1 Cu2+ in sulfate medium was contacted with both forms of spirogyra, under the parametric variations of effluent pH, adsorbent dosage, contact time, and sorption temperature. The study revealed spirogyra as a prominent candidate for removing contaminant metal cation; however, at the same condition, biosorption capacity of modified biomass in gel form was higher than the native spirogyra. At the optimized condition with 6 g sorbent dosage treated to 100 mL effluent for 30 min at pH 6.0 and temperature 20 °C, the maximum 82.8% and 96.4% copper could be adsorbed by the native and modified spirogyra, respectively. The batch sorption data using native biomass followed pseudo-first-order kinetic; exhibiting the multilayer sorption mechanism via surface diffusion could be defined by the Freundlich model. In contrast, the sulfuric acid treated modified spirogyra followed pseudo-second-order kinetics and intra particle diffusion as the rate-limiting step.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting
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