Questions tagged [adsorption]
The adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface.
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Is the adsorption of dissolved iodine onto activated carbon physical adsorption or chemical adsorption?
For an experiment, I am looking to see the effect of temperatures from 0–100 °C on the efficacy of activated carbon as an adsorbent. My adsorbate is iodine and I am confused as to whether the ...
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0answers
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How did Zyklon hold and release HCN?
$\ce{HCN}$ is notoriously unstable: It boils at room temperature, and it tends to polymerize when concentrated in unbuffered liquid form. Yet $\ce{HCN}$ was for decades widely used as a fumigant ...
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1answer
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How to quantify the adsorption affinity of gases?
Is there a term/quantity which shows how 'sticky/adsorptive' a molecule is? I am interested in gas adsorption on steel surfaces in our mass spectrometer and would like to estimate which gases have a ...
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1answer
133 views
Hygroscopic Substances and Drying Agents
My book says:
Most of the hygroscopic substances are drying agents
Based on what I read on several websites, I think dehydrating agents also act as drying agents. If so, all dehydrating agents ...
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1answer
124 views
What is 'desorption hysteresis'?
I am currently reading a paper titled "Polystyrene Nanoplastics-Enhanced Contaminant Transport: Role of Irreversible Adsorption in Glassy Polymeric Domain" (link here).
In the paper, the authors ...
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Aren't “lack of specificity” and “nature of adsorbate” contradictory factors in physisorption?
It was mentioned in my course book under "Characteristics of physisorption" that:
Lack of specificity: An adsorbent does not show any preference for a particular gas as the van der Waal's ...
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138 views
Why does physisorption change to chemisorption at high temperatures?
I read in my textbook:
In certain cases, physisorption changes to chemisorption as temperature is increased.
Could anyone explain why it is so? I know the basics of both physisorption and ...
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How to develop a Reactive Force Field (ReaxFF)? (Molecular simulation)
Currently, I am working on CO2 capture on Hydrotalcites as solid adsorbents. I want to run molecular simulations to analyse the behaviour of the material under different temperatures, pressures and ...
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Application of BET to micropore
'application of the BET equation should be restricted to the range where the term n(1 – p/p0) continuously increases with p/p0'see 5.2.2 in the reference
This is one of the criterias IUPAC proposes ...
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1answer
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Calculating surface area from BET results
I have been trying to work out the workings of the BET method and I have come to a standstill.
The surface area of a sample is given by
$$
S_{\text{BET}} = \frac{\nu_{\text{m}}Ns}{V}
$$
where $\...
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In solution preparation for adsorption experiments, why does water need to be added in the flask first before the dye solution?
The procedure in my laboratory manual notes that when preparing solutions of different concentrations of methylene blue in Erlenmeyer flasks, water should go in first before the dye solution.
I ...
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Why does the order of adsorption of hydrated alkali metals on an ion exchange resin decrease down the group?
Why does the order of adsorption of hydrated alkali metals on an ion exchange resin decrease down the group?
I recently did a question on this topic and they say adsorption order is $$\ce{ Li+ > ...
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1answer
91 views
Langmuir method
I have done a biosorption study using a protein as a biosorbent and six different concentrations of $\ce{Pb}$ ions. I need to show the efficiency of the biosorbent, I was told to use the Langmuir ...
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1answer
207 views
“Nitrogen (gas) is physisorbed over iron (metal) at room temperature”: Is this for real? [closed]
My copy (PDF) of Levine's Physical Chemistry (6th ed.), page 570-571, section: "Adsorption of Gases on Solids", states:
Physical adsorption is nonspecific. For example, $\ce{N2}$ will be physically ...
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Pd-catalysed hydrogenation of imines
Hydrogenation of imines to amines by $\ce{H2}$ on $\ce{Pd/C}$ has been used e.g. in the synthesis of Pumiliotoxin. By contrast, carbonyl groups are rarely reduced in this way, which I though was due ...
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1answer
115 views
Is there a direct relationship between the adsorption energy and the catalytic activty
I have seen in several papers, where people correlate adsorption energy with the catalytic activity; the greater the adsorption energy, the greater would be the catalytic activity.
I understand that ...
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2answers
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What is the physical state of the gas adsorbed on a solid adsorbent?
I am studying surface chemistry in high school I have this doubt and I am unable to find a answer your help is appreciated
I searched for the answer on google I asked my chemistry teacher he said the ...
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Langmuir parameters for fixed bed continous column
I have prepared a model of fixed bed adsorption column in MATLAB. I have to insert Langmuir parameter value there, so how can I calculate them in case of continuous fixed bed column. I have calculated ...
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Equations Used in Isothermal Titration Calorimetry
I have been attempting to understand and derive the formulas used for ITC which can be found here starting on page 310. I am particularly interested in the single set of identical sites. To first ...
3
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1answer
1k views
Freundlich Equation's dimensions
So, we have the Freundlich's Isotherm equation as $\frac{x}{m} = kp^{\frac{1}n}$, where the LHS measures the extent of adsorption with the corresponding pressure $p$ in the RHS with the two constants, ...
3
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1answer
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What is the difference between BET and Langmuir model for calculating the specific surface area?
Brunauer–Emmett–Teller (BET) surface area is measured by specific surface area of the adsorbent. BET surface area is measured by using non-corrosive gases like $\ce{N2}$, $\ce{CO2}$, $\ce{Ar}$ etc. ...
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Can negative adsorption be considered equal to sorption?
In my book it was written sorption is basically when the substance gets uniformly distributed into the bulk of the solid but at the same time its concentration is higher at the surface then in the ...
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1answer
343 views
How does activated carbon trap impurities?
I've tried and I've tried to find an answer to this all over the web, but I can't seem to find an in depth explanation.
To the best of my knowledge, activated carbon has a very microporous structure ...
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Selective sorption of toxins by polymethylsiloxane polyhydrate
Polymethylsiloxane polyhydrate (PMSPH) is used as enterosorbent for a couple of decades (nowadays under the trademark "Enterosgel"), intended for binding in the gastrointestinal tract and excretion of ...
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How to calculate Langmuir and frendulich isotherm constants for linear equations [duplicate]
Can anyone please help me out how to calculate both Langmuir and Frendulich isotherm constants for linear equation. I'm trying to calculate in both the cases, but still I'm confusing how to calculate ...
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1answer
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How does water freeze and crystallize on a cold superhydrophobic surface?
Superhydrophobic surfaces are nano-structured to "repel" liquid water and there has been a lot of work done to understand the microscopics of wetting of these nanostructures.
What I currently am ...
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Why increase in enthalpy leads to increase in entropy? [closed]
Given statement: Enthalpy of adsorption is the strength at which molecule (say $\ce{H2}$) is bound to the adsorbent (say some metal center). For a free $\ce{H2}$ molecule, the entropy contribution is ...
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2answers
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How does physical adsorption of mixed gas occur on solid? (eg I mean how the gas molecules of compete each other for a slot on solid surface)
I am working on sorption phenomenon of gases (including inert gas) on coal seam surface.
For a mixture of 2 gases at a certain pressure, carbon dioxide and methane, for instance, $\ce{CO2}$ is ...
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1answer
373 views
Surface area: what is the difference?
What are the differences between:
van der waals surface area
solvent accessible surface area
topographical polar surface area
What is the significance of these differences, and what are the ...
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1answer
438 views
Interaction between a pencil and rubber (eraser)
Is there a interaction between a graphite pencil and and a eraser. For example, if I drew a line on a piece of paper and then erased that, what interaction is occurring?
Is it a Van der Waals ...
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4answers
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Why does physisorption (physical adsorption) increase with ease of liquefaction?
This is what my textbook says about physisorption
The amount of gas adsorbed by a solid depends on the nature of gas. In general easily liquefiable gases (i.e. with higher critical temperature) ...
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1answer
651 views
Catalysist activation energy - the Brønsted-Evans-Polanyi relation
I have stumbled upon something called the Brønsted-Evans-Polanyi relation in a study about the design of catalysts (for reactions like those in hydrocracking fuel production.)
The relation shows that ...
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1answer
37 views
How to convert the D'Arcy and Watt model from activity to concentration in mol/m^3
The D'Arcy and Watt 1970 model in "Analysis of sorption isotherms of non-homogeneous sorbents" for water adsorption is as follows:
$$W = \frac{KK'a}{1+Ka} + ca + \frac{kk'a}{1-ka},$$
where:
$W$ is ...
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1answer
133 views
What is a typical monolayer formation time for liquid phase adsorbate on a solid surface?
Let's say a solid is submerged in a solution of species with functional groups and a self-assembled monolayer is forming. What are the typical time scales for the formation of a continuous monolayer? (...
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Diffused Layer ion in Electrix Double Layer
When KI is added to AgNO3 soln, so AgNO3 is in excess, collidal particle is AgI:Ag+ with diffused layer of I-, Why is the diffused layer not of NO3- when the anion in excess is NO3-?
If we had KI in ...
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Difference between neutral and basic activated alumina
Sigma Aldrich sells two different types of activated alumina for column chromatography: neutral and basic.
Apparently basic alumina is more active and better at adsorbing anions.
Why is this the ...
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1answer
2k views
Plotting a Langmuir adsorption isotherm
We have,
$$\theta = \frac{Kp_\mathrm a}{1+Kp_\mathrm a}$$
where, the fractional coverage $\theta$ is defined as the number of sites occupied by adsorbate $A$ over the total number of sites. $p_\...
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2answers
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Overall equilibrium expression for competitive equilibria
I have a case where I have two reactions that depend on a common reactant. The reactions can be written as:
I) $\ce{A + B <=> AB}$
II) $\ce{A + C <=> AC}$
We can thus write equilibrium ...
3
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1answer
5k views
Effect of pressure on adsorption of a gas
I am currently studying about the basic terms of surface chemistry, and am facing some conceptual doubt regarding the following:
What effect does pressure have on the adsorption of a gas (adsorbate) ...
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1answer
365 views
Is it possible for the forward and reverse reactions to have different reaction orders?
For example, in the case of non-dissociative adsorption, the rate of the forward process is given by
$$\frac{\mathrm{d}\theta}{\mathrm{d}t} = kCN(1−\theta)$$
where $C$ is the concentration, $N$ is ...
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2answers
209 views
Why does the BET equation take into consideration a multimolecular-layer, even though it deals with chemisorption?
I came across the Brunauer-Emmet-Teller (BET) equation recently, and one thing that I found strange was an implicit reference to the formation of molecular multi-layer.
In the BET equation
$$
\begin{...
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1answer
610 views
Reaction mechanism in fluoride adsorption to aluminum oxide
Despite a fair amount of research (excluding non-open access journals, to which I have not got access), I cannot seem to find an explanation of the process that takes place when $\ce{F^-}$ adsorbs to ...
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1answer
227 views
Counterions in adsorption of ions
When an ion is adsorbed from an aqueous solution onto a solid, what happens to its counterion? Obviously, the solution does not become charged - does this mean that it too is adsorbed?
(Example: $
\...
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Why does chemisorption increase with rise in temperature, even though it is an exothermic process?
Chemisorption is exothermic process, but still it increases with increase in temperature. Why?
I know that there needs to be a minimum activation energy to be achieved in order to initiate ...
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2answers
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How does adsorption work?
I would like to know how adsorption works particularly between a gas and a solid. I know that there is an attraction of intermolecular forces between the gas molecules and the solid surface molecules. ...
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118 views
Adsorption of nitrate ion
Can someone help me in understanding the chemistry of nitrate ion. For example to which functional groups in soil or on charcoal particles present in soil a nitrate ion can make bonding? Normally ...
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1answer
66 views
In terms of remediation, what is sequestration?
I am reading about use of zero valent iron in remediation of heavy metals.
Is sequestration just a broader term for sorption?
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3answers
1k views
Is the rate of desorption dependent on pressure?
While I was learning about Langmuir's adsorption isotherm in my chemistry class, my teacher talked about the situation when the rate of adsorption and desorption will become equal. However, he ...
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0answers
52 views
Type of adsorption in catalysis
why type of adsorption takes place during catalysis? It can't be physisorption because it involves formation of chemical bond. It shouldn't be chemisorption too because it is characterised by ...
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1answer
5k views
Is adsorption exothermic, and if so, why?
Why is adsorption exothermic?
The explanation given in my textbook is:
For a process to be spontaneous, the thermodynamic requirement is that, at constant temperature and pressure, $\Delta G &...
