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Questions tagged [adsorption]

The adhesion of atoms, ions, or molecules from a gas, liquid, or dissolved solid to a surface.

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20 views

How rate of absorption remains same throughout the process?

While reading surface chemistry, I got Rate of adsorption is high at begining and then decreases till equilibrium is attained . On the other hand , rate of absorption remains same throughout the ...
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1answer
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Adsorption on solids - homogeneous/heterogeneous surface definition

How could we define homogeneous and heterogeneous surfaces (rigorously)? It is among my exam questions (but I could not find any definition in my textbook or on the internet). I would say the ...
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Why is there preferential adsorption of a common ion during preparation of colloids by peptization?

There was a similar question asked here on Chem SE, but the answer was not very satisfactory to me, so I am asking a fresh question. Peptization is the process of creating a colloid from a precipitate ...
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A physical meaning of the Danckwerts boundary condition in terms of concentration profile (adsorption)

Can someone please explain to me in a simplified way, what exactly does a well-recognized Danckwerts boundary condition do to the concentration profile of adsorption phenomena? I just cannot find a ...
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Units conversion of Henry coefficient in adsorption on solids [closed]

In a database of solid microporous materials I have the Henry coefficient in units of $\pu{mol kg^{-1} Pa^{-1}}.$ How to convert to $\pu{Pa^{-1}}?$ I tried to multiply by the molar mass of the sorbate ...
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1answer
96 views

Why is the IUPAC definition of adsorption so different from other definitions?

NB: This question has been edited. Originally, some of the confusion was caused by me not knowing that condensed phase could refer to solid phases as well. This has been removed, but the confusion ...
2
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1answer
28 views

Is there a practical re-use value gained by grinding up activated carbon that is spent/saturated?

I want to buy bulk activated carbon for use in a DIY air-filtration set-up, like this, to improve air quality in my bedroom. From what I understand, the relatively larger sizes of carbon media on the ...
2
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1answer
84 views

Why does chemisorption decrease with increasing temperatures?

Why is it that chemisorption decreases with higher temperatures? The explanations I found online were quite vague and one of them cited Le Chatelier's principle, but I thought chemisorption is an ...
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0answers
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Porous materials: Is the expression of a mean free path $\overline{\ell}$ of the gas molecule valid for a binary mixtures?

Suppose that I have a binary gas mixture at low pressure. Can I calculate the mean free path $\overline{\ell}$ of the gas molecule in a pores of solid material by substituting a molecular weight of a ...
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Dynamic viscosity of gas mixture (appropriate estimation)

What estimation of the dynamic viscosity $\eta = f(T)$ $([\eta] = \pu{Pa·s})$ of the gas mixture components would you recommend during adsorption at a low temperature, approx. $\pu{293 K}$ to $\pu{333 ...
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1answer
203 views

Finding the Freundlich adsorption isotherm from the graph of log(x/m) v/s log(p)

The following problem was asked in JEE Mains 2020 (Sept 2, Shift 1), The mass of gas adsorbed, $x$, per unit mass of adsorbate, $m$, was measured at various pressures, $p$. A graph between $\log\frac ...
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Adsorption of Cu2+ using banana peels for pH 2,2.5,3,3.5,4

so basically I did my experiment which is the title. This is my procedure and results: Make 0.05M CuSO4 pipette 50ml CuSO4 change to respective pH values using HCl Add 2g of oven-dried banana peels ...
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1answer
43 views

How is the hydration state of a chemical related to its adsorption of water?

I am trying to understand adsorption and hydration states better, and I was thinking about the different hydration states of calcium sulfate - anhydrous ($\ce{CaSO4}$), hemihydrate ($\ce{CaSO4*1/2H2O}$...
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37 views

Column Dispersive Mass Balance analytical / numerical solution

Is there any analytical solution for the most common expression of column mass balance: $\dfrac{\partial C}{\partial t} + \left(\dfrac{1+\varepsilon}{\varepsilon}\right)\dfrac{\partial q} {\partial t} ...
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Energy and impurities balance for adsorption with a fixed bed (with description)?

Do you have any suggestion where to look for a source of information about energy and impurities (component) balance for adsorption of mixture CO2/H2O in fixed bed? I have looked into many articles /...
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1answer
623 views

Why are van der Waals' forces between gas molecules strong near its critical temperature?

My textbook says …easily liquefiable gases i.e. with higher critical temperatures are readily adsorbed as van der Waals' forces are stronger near the critical temperatures. What I do understand is ...
2
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2answers
479 views

What is negative adsorption? [closed]

In adsorption, the concentration of adsorbate is greater on the surface. So, how is it possible that the solvent will be more on the surface and the solute (adsorbate) in the bulk… or does solute not ...
2
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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 ...
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0answers
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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 ...
3
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2answers
2k 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. ...
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1answer
128 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 ...
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552 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 ...
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2answers
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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
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1answer
197 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 ...
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2answers
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What are molecular species?

I am in high school 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 ...
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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 ...
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2answers
479 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
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2answers
161 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
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0answers
173 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 ...
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1answer
40 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 ...
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1answer
2k 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
503 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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1answer
335 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 ...
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437 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
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240 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 ...
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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
177 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 $\...
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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
139 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
1k 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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2answers
342 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
278 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 ...
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49 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 ...
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64 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 ...
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2answers
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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, ...
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2answers
9k 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. ...
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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
564 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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1k 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 ...