Questions tagged [adsorption]
The adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface.
84
questions
2
votes
0answers
44 views
How to obtain the linear form of Redlich Peterson isotherm model by algebraic transformation or any other ways? [closed]
The Redlich Peterson isotherm model is known as:
$$
\begin{aligned}
q_e=\frac{AC_e}{1+BC^g_e}
\end{aligned}
$$
Is there any way to obtain the linear form of this equation by algebraic transformation ...
2
votes
0answers
9 views
hydrodynamic thickness of polymer vs. concentration of electrolyte?
I've measured the hydrodynamic thickness of a NaPSS layer on polystyrene latex and plotted it against the concentration of the supporting electrolyte, NaCl.
My graph shows a general decrease in ...
1
vote
1answer
83 views
Why Freundlich adsorption isotherms fails at high pressure conditions?
Experimentally it was determined that extent of gas adsorption varies directly with pressure, and then it directly varies with pressure raised to the power 1/n until saturation pressure Ps is reached. ...
0
votes
1answer
29 views
Is activated charcoal an air purifier?
It's well known that activated charcoal is an adsorbent and due to very big surface area per unit of mass it can adsorb a lot of particles.
Let's take as an example for my question this product on ...
1
vote
0answers
134 views
Order of reaction in adsorption process
(1) $\ce{PH3(g) <=>[W]PH3(adsorption)->[W]P(s) + 3/2 H2(g)}$
The decomposition of phosphine on tungsten surface at low pressure is a pseudo first order reaction. This is because the rate of ...
1
vote
2answers
467 views
Dangers of using activated carbon past its lifespan
Activated carbon (AC) is one of the most widely used media for water filtration. It's effective at removing chlorine taste and odor, and it's recognized as being safe.
However, most activated carbon ...
6
votes
1answer
111 views
Why does Freundlich adsorption isotherm not have a term for surface area?
Why does Freundlich adsorption isotherm not have a term for surface area?
The formula given by Freundlich adsorption isotherm:
$$ \frac{x}{m}= k P ^{1/n}$$
Where $x$ is the mass of gas adsorbed ...
1
vote
0answers
16 views
Is it possible to reduce the desorption temperature of an adsorption/desorption reaction by changing (decreasing) the pressure?
I am studying about zeolite/water adsorption beds and need to see if there is a way to tune the desorption temperature. Ideally, I need to reduce the desorption temperature. Is it possible to do this ...
-1
votes
1answer
550 views
What are molecular species?
I am a highschooler learning about adsorption for the first time.My school textbook says--
"The accumulation of molecular species at the surface rather than
in the bulk of a solid or liquid is ...
0
votes
0answers
41 views
Preparation of Copper (II) Sulfate Pentahydrate Solution
how would you make a solution of Copper (II) Sulfate Pentahydrate to achieve 150, 200, 250 and 300 mgL−1 concentration of copper? I do not have the anhydrous version of the solute. Also, when I ...
1
vote
2answers
112 views
Why enthalpy of adsorption is negative?
I have already read Is adsorption exothermic, and if so, why? but it didn't answered my query.
To illustrate, let's take a hypothetical vacuum space. In that space, there is a solid and a gas, the ...
3
votes
2answers
111 views
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 ...
2
votes
0answers
83 views
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 ...
0
votes
1answer
34 views
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 ...
0
votes
1answer
1k 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 ...
2
votes
1answer
279 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 ...
-1
votes
1answer
245 views
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 ...
2
votes
0answers
314 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 ...
2
votes
0answers
204 views
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 ...
1
vote
0answers
30 views
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 ...
5
votes
1answer
75 views
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 $\...
3
votes
0answers
223 views
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+ > ...
0
votes
1answer
110 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 ...
1
vote
1answer
632 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 ...
4
votes
0answers
51 views
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 ...
1
vote
2answers
248 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 ...
1
vote
2answers
253 views
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 ...
2
votes
0answers
44 views
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 ...
2
votes
0answers
58 views
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 ...
2
votes
1answer
2k 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
votes
2answers
5k views
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. ...
1
vote
0answers
87 views
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 ...
6
votes
1answer
511 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 ...
5
votes
0answers
962 views
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 ...
4
votes
1answer
125 views
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 ...
2
votes
0answers
2k views
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 ...
0
votes
2answers
119 views
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 ...
0
votes
1answer
620 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 ...
7
votes
1answer
671 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 ...
3
votes
4answers
4k views
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) ...
8
votes
1answer
1k 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 ...
1
vote
1answer
48 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},$$
where:
$W$ is ...
0
votes
1answer
202 views
What is a typical monolayer formation time for liquid phase adsorbate on a solid surface?
Let's say a solid is submerged in a solution of species with functional groups and a self-assembled monolayer is forming. What are the typical time scales for the formation of a continuous monolayer? (...
0
votes
0answers
74 views
Diffused Layer ion in Electrix Double Layer
When KI is added to AgNO3 soln, so AgNO3 is in excess, collidal particle is AgI:Ag+ with diffused layer of I-, Why is the diffused layer not of NO3- when the anion in excess is NO3-?
If we had KI in ...
4
votes
0answers
417 views
Difference between neutral and basic activated alumina
Sigma Aldrich sells two different types of activated alumina for column chromatography: neutral and basic.
Apparently basic alumina is more active and better at adsorbing anions.
Why is this the ...
8
votes
1answer
4k views
Plotting a Langmuir adsorption isotherm
We have,
$$\theta = \frac{Kp_\mathrm a}{1+Kp_\mathrm a}$$
where, the fractional coverage $\theta$ is defined as the number of sites occupied by adsorbate $A$ over the total number of sites. $p_\...
1
vote
2answers
117 views
Overall equilibrium expression for competitive equilibria
I have a case where I have two reactions that depend on a common reactant. The reactions can be written as:
I) $\ce{A + B <=> AB}$
II) $\ce{A + C <=> AC}$
We can thus write equilibrium ...
3
votes
1answer
7k views
Effect of pressure on adsorption of a gas
I am currently studying about the basic terms of surface chemistry, and am facing some conceptual doubt regarding the following:
What effect does pressure have on the adsorption of a gas (adsorbate) ...
2
votes
1answer
668 views
Is it possible for the forward and reverse reactions to have different reaction orders?
For example, in the case of non-dissociative adsorption, the rate of the forward process is given by
$$\frac{\mathrm{d}\theta}{\mathrm{d}t} = kCN(1−\theta)$$
where $C$ is the concentration, $N$ is ...
2
votes
2answers
298 views
Why does the BET equation take into consideration a multimolecular-layer, even though it deals with chemisorption?
I came across the Brunauer-Emmet-Teller (BET) equation recently, and one thing that I found strange was an implicit reference to the formation of molecular multi-layer.
In the BET equation
$$
\begin{...
