scholarly journals A molecular switch based on the manipulation of 1,3-dichlorobenzene on Ge(001) between two adsorption sites by inelastic tunneling electrons

2015 ◽  
Vol 17 (43) ◽  
pp. 28830-28836 ◽  
Author(s):  
A. Wykrota ◽  
M. Bazarnik ◽  
R. Czajka ◽  
K. Morgenstern
Keyword(s):  
Electronic Excitation ◽  
Molecular Switch ◽  
Specific Adsorption ◽  
Adsorption Sites ◽  
Inelastic Tunneling

A molecular switch between two specific adsorption sites of meta-dichlorobenzene on Ge(001) is initiated by the electronic excitation of the molecule.

scholarly journals Specific adsorption sites and conditions derived by thermal decomposition of activated carbons and adsorbed carbamazepine

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Daniel Dittmann ◽  
Paul Eisentraut ◽  
Caroline Goedecke ◽  
Yosri Wiesner ◽  
Martin Jekel ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Activated Carbon ◽  
Activated Carbons ◽  
Evolved Gas Analysis ◽  
Gas Analysis ◽  
Specific Adsorption ◽  
Adsorption Mechanisms ◽  
Adsorption Sites ◽  
Adsorption Processes ◽  
Inorganic Constituents

AbstractThe adsorption of organic micropollutants onto activated carbon is a favourable solution for the treatment of drinking water and wastewater. However, these adsorption processes are not sufficiently understood to allow for the appropriate prediction of removal processes. In this study, thermogravimetric analysis, alongside evolved gas analysis, is proposed for the characterisation of micropollutants adsorbed on activated carbon. Varying amounts of carbamazepine were adsorbed onto three different activated carbons, which were subsequently dried, and their thermal decomposition mechanisms examined. The discovery of 55 different pyrolysis products allowed differentiations to be made between specific adsorption sites and conditions. However, the same adsorption mechanisms were found for all samples, which were enhanced by inorganic constituents and oxygen containing surface groups. Furthermore, increasing the loadings led to the evolution of more hydrated decomposition products, whilst parts of the carbamazepine molecules were also integrated into the carbon structure. It was also found that the chemical composition, especially the degree of dehydration of the activated carbon, plays an important role in the adsorption of carbamazepine. Hence, it is thought that the adsorption sites may have a higher adsorption energy for specific adsorbates, when the activated carbon can then potentially increase its degree of graphitisation.

Surface texture and specific adsorption sites of sol–gel synthesized anatase TiO2 nanoparticles

2010 ◽  
Vol 45 (10) ◽  
pp. 1470-1475 ◽  
Author(s):  
Mohamed I. Zaki ◽  
Gamal A.H. Mekhemer ◽  
Nasr E. Fouad ◽  
Tushar C. Jagadale ◽  
Satishchandra B. Ogale
Keyword(s):  
Tio2 Nanoparticles ◽  
Surface Texture ◽  
Sol Gel ◽  
Anatase Tio2 ◽  
Specific Adsorption ◽  
Adsorption Sites

scholarly journals Copper adsorption in tropical oxisols

2003 ◽  
Vol 46 (4) ◽  
pp. 529-536 ◽  
Author(s):  
Maria Lucia Azevedo Silveira ◽  
Luís Reynaldo Ferracciú Alleoni
Keyword(s):  
Organic Matter ◽  
Copper Surface ◽  
Specific Adsorption ◽  
Copper Adsorption ◽  
Aluminum Oxides ◽  
Adsorption Sites ◽  
Surface Samples ◽  
Positive Balance ◽  
Brazilian Soils ◽  
Iron And Aluminum Oxides

Cu adsorption, at concentrations between 0 to 800 mg L-1, was evaluated in surface and subsurface samples of three Brazilian soils: a heavy clayey-textured Rhodic Hapludalf (RH), a heavy clayey-textured Anionic ''Rhodic'' Acrudox (RA) and a medium-textured Anionic ''Xanthic'' Acrudox (XA). After adsorption, two consecutive extractions were performed to the samples which received 100 mg L-1 copper. Surface samples adsorbed higher amounts of Cu than the subsurface, and exhibited lower Cu removed after the extractions, reinforcing the influence of the organic matter in the reactions. Cu adsorption was significant in the subsurface horizons of the Oxisols, despite the positive balance of charge, demonstrating the existence of mechanisms for specific adsorption, mainly related to the predominance of iron and aluminum oxides in the mineral fractions. In these samples, Cu was easily removed from the adsorption sites. RH demonstrated a higher capacity for the Cu adsorption in both horizons.

scholarly journals Specific Adsorption of Heavy Metals in Soils: Individual and Competitive Experiments

Agronomy ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 1113
Author(s):  
Claudia Campillo-Cora ◽  
Manuel Conde-Cid ◽  
Manuel Arias-Estévez ◽  
David Fernández-Calviño ◽  
Flora Alonso-Vega
Keyword(s):  
Heavy Metals ◽  
Soil Solution ◽  
Solid Phase ◽  
Clay Content ◽  
Important Variable ◽  
Exchange Capacity ◽  
Specific Adsorption ◽  
Acidic Soils ◽  
Adsorption Sites ◽  
The Individual

The partitioning between the soil solid phase and the soil solution determines the mobility of pollutants like heavy metals. If nonspecific sorption takes place, the reactions are easily reversible and heavy metals are released to soil solution increasing the probability of leaching through soil profile. Mobility and leaching are also favoured if other metals are in the system and competition for specific adsorption sites takes place. In this study, desorption equilibrium experiments were conducted after adsorption ones. The specific adsorption was evaluated through the amounts of the still adsorbed Cu, Pb, Cr, Ni and Zn after desorption experiments in ten different soils. In addition, competition adsorption and desorption binary experiments were conducted for evaluating the metal competition in three of the soils. Pb and Cu are the metals adsorbed and retained in higher amounts in all the studied soils. In slightly neutral soils, Cr is retained in lesser amounts while in acidic soils Zn is the metal less retained. Results showed that despite the high and variable amounts of organic matter in the soils, soil pH is the most important variable in neutral soils. In acidic soils, soil properties different than pH play important roles and specific sorption of Pb is related to the cationic exchange capacity of the soils while that of Zn to the clay content. Instead, the release of Cu during desorption experiments is probably due to the more soluble organic fraction of the soils. The individual retention of Cu, Zn, Ni and Pb is higher than when they are in competition, except if Cr is present. In this case, the amount of those four metals and that of Cr increased. Therefore, the presence of Cr together with cationic heavy metals favoured the adsorption of those metals in multi-metal polluted areas. Specific adsorption is also important during competition as soil affinities increase during competition experiments.

Unusual behavior of MgFe2O4 during regeneration: desorption versus specific adsorption

2019 ◽  
Vol 80 (4) ◽  
pp. 654-658 ◽  
Author(s):  
A. I. Ivanets ◽  
V. G. Prozorovich ◽  
M. Yu. Roshchina ◽  
V. Srivastava ◽  
M. Sillanpää
Keyword(s):  
High Efficiency ◽  
Theory And Practice ◽  
Specific Adsorption ◽  
Main Process ◽  
Adsorption Efficiency ◽  
Practical Application ◽  
Unusual Behavior ◽  
Adsorption Sites ◽  
Regeneration Efficiency ◽  
Mb Adsorption

Abstract The reusability of spent adsorbents is the most important characteristic for their practical application. The process of MgFe2O4 regeneration after methylene blue (MB) adsorption was studied. The effect of the nature (HCl, HNO3, and MgCl2) and the concentration (10−3–10−1 M) of regeneration agents was established. All the regeneration agents at 10−3 and 10−2 M had high efficiency and adsorption capacity recovery reached 80–90%, whereas for 10−1 M concentration the adsorption efficiency was in the range of 4.5–36.2%. It was shown that the concentration of desorbed MB was much less than what had been previously adsorbed and did not correlate with regeneration efficiency. The unusual behavior of MgFe2O4 during regeneration could be due to different mechanisms of regeneration by OH3+ and Mg2+ ions: (i) for acidic regeneration the main process was the non-specific adsorption of OH3+ ions in a diffusion layer and the substitution of adsorbed MB due to electrostatic forces; (ii) in the case of Mg2+ as a regeneration agent, there was specific adsorption due to the completion of a crystal lattice of MgFe2O4 nanoparticles by Mg2+ ions (according to the rules of Fayans-Pannet) with the formation of new Mg-OH adsorption sites and the super-equivalent adsorption of Mg2+ ions (according to DLVO (Derjaguin, Landau, Verwey, and Overbeek) theory) accompanied by a recharge of the MgFe2O4 surface. These phenomena of MgFe2O4 regeneration using Mg2+ ions must be taken into account in the theory and practice of adsorption.

scholarly journals The role of Ag+, Ca2+, Pb2+ and Al3+ adions in the SERS turn-on effect of anionic analytes

2019 ◽  
Vol 10 ◽  
pp. 2338-2345 ◽  
Author(s):  
Stefania D Iancu ◽  
Andrei Stefancu ◽  
Vlad Moisoiu ◽  
Loredana F Leopold ◽  
Nicolae Leopold
Keyword(s):  
Active Sites ◽  
Specific Adsorption ◽  
Chemical Mechanism ◽  
Silver Surface ◽  
Adsorption Sites ◽  
Turn On ◽  
Surface Enhanced Raman ◽  
A Charge ◽  
Citrate Capping

In our recent studies we highlighted the role of adsorbed ions (adions) in turning on the surface-enhanced Raman scattering (SERS) effect in a specific mode for anionic and cationic analytes. In this work, we emphasize the role of Ag+, Ca2+, Pb2+ and Al3+ adions in the specific adsorption of anionic analytes such as the citrate capping agent and three organic acids. Our results suggest an adion-specific adsorption mechanism: the adsorption of anionic analytes is facilitated by positively charged adions such as Ag+, Ca2+, Pb2+ or Al3+, which provide adsorption sites specific for the anionic analytes. The turn-on of the SERS effect is explained in the context of the chemical mechanism of SERS. The adions form SERS-active sites on the silver surface enabling a charge transfer between the adsorbate and the silver surface. High-intensity SERS spectra of uric acid, salicylic acid and fumaric acid could be recorded at a concentration of 50 µM only after activation of the colloidal silver nanoparticles by Ca2+, Pb2+ or Al3+ (50 µM). The chemisorption of the three anionic species to the silver surface occurs competitively and is enhanced with the anions of higher affinities to the silver surface as indicated by the SERS spectra of corresponding mixed solutions.

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