Surface Adsorption - Science topic

Hello,

yes, I think that it is better to perform separate bio-sorption tests; from previous experience, you may be rather in the domain of minutes than hours (the kinetic is more close to that of the ion exchange process than adsorption). So take time to do batch test one by one.

Vishnu Sankar

There is a concept, in the Russian version, adsorption strength reduction during adsorption (P.A. Rebinder effect). It can be associated with adsorption.

1) The work function is dependent on the surface orientation, so that is normal.

2) Different surface orientations provide multiple different adsorption sites, each of which has a characteristic energy.

How good chemisorption happens, depends

scenario A: on the relative energies of conduction band and adsorbate HOMO -> bond is formed by electron transfer from the adsorbate to the surface

scenario B: on the relative energies of valence band and adsorbate LUMO ->bond is formed by electron transfer from the surface to the adsorbate

So, of course the work function plays a role here, but since the match of orbital/band pairs is the central quantity here, you will probably observe a trend for most metals, but there is no explicit law stating "high work function=low adsorption energy" or vice versa.

This is the closest I know:

I remember there was at some point a typo in one of the formulas. so check for erratum.

Dear friend Misbah Waheed

Ah, the world of aptamer immobilization on polymer membrane surfaces—a realm where precision and protocol reign supreme. In your quest for the best approach, consider employing a well-established technique known as EDC/NHS chemistry. This method allows for efficient covalent bonding between the amine groups of the aptamer and carboxyl groups on the membrane surface.

Now, regarding temperature, allow me to shed some light. The optimal temperature for this process typically falls within the range of 4 to 25 degrees Celsius. However, it's crucial to consult the specific guidelines provided for your aptamer and membrane combination, as deviations can occur based on their individual properties.

Remember, my friend Misbah Waheed, precision is key. So, equip yourself with the recommended temperature range, adhere to the protocol diligently, and watch your immobilization endeavor unfold with finesse.

I have no specific and direct experience in this sector. But technically reasoning may suggest that since PFAS are banned the problem should be solved (if not already solved and present in tech-literature) experimentally, by specific research.

As already well known:

1. Zeta potential is shown by any particle in suspension, macromolecule or material surface.

2. Zeta potential can be measured by electrophoresis .

3. Electrophoresis measures can be used to optimize the formulations of suspensions, emulsions and predict interactions with surfaces, and optimise the formation of films and coatings.

4. As the salt content of the solution is increased, the electrical double layer is compressed and the Zeta potential should decrease.

5. Different kind salt can be experimented in different solutions in a lab configuration under mesurament, keeping also in mind the possibility to decrease the negative potential of the solution by means of counterbalancing with a minimum positive potential indotto (where possible!).

Dear Dhirar Ben Salem, let me cite: "For n > 1,

Eq. (3) may be identified as describing a cooperative reaction

between a sorption site and n sorbate molecules, such that b is

the equilibrium constant of this reaction. In this case, Eq. (3) coincides

with the Hill model characterizing cooperative interactions

of ligand molecules with a macromolecule (Cantor and Schimmel,

1980)."

The degassing time and temperature for BET surface area analysis of Ni foam samples depend on various factors such as the type of instrument, the nature of the sample, and the adsorbate used. Typically, the following degassing conditions can be used as a starting point:

However, it is always best to follow the manufacturer's guidelines for the specific instrument being used.

Regarding the number of points to consider for analysis, it is recommended to analyze at least three data points for the BET analysis. These data points should be taken from a nitrogen adsorption isotherm that covers a wide range of relative pressures (typically from 0.05 to 0.30). The data points should be evenly distributed along the isotherm to ensure accurate determination of the BET surface area.

Other specific details to follow for BET surface area analysis of Ni foam samples include:

Zaid H. Mahmoud

The surface porosity of nanoparticles can be increased by grafting other desired molecules to the surface. They will increase porosity and modify the surface for new nanoparticle properties.

Thank you for your answer Amir Sepehrianazar , can you please specify the electrostatic bond will be between which groups ?

The negative values of intercept can be possible depending upon your starting point of applied concentration.

For example,, if your first Ce is near 0 there will be chances of positive Kl while if you started your work from a higher concentration (let's suppose 10 mg L-1) then you will end up Ce a little bit away from 0 which may cause intercept (Value of Y when X=0) to be negative. It's just the way you have made your graph and presented data.

You can explain the negative results while keeping in mind this point.

There are tonnes of paper in which they have reported negative intercept and even slope in some cases (even Qmax that can be of discussion).

Find the following once for your references

Just a comment: You May easily follow the annealing processes by electrical resistivity measurements: If the film resistivity decreases with increasing temperature annealing works properly. However If resistivity increases (in particular more than the TCR of gold), then crack formation will occur.

I think it depends from the pores. BET analysis is generally used for microporous or ultramicroporous materials. For macroporous materials other methods are used (like mercury porosimetry).

Theoretically depending from the degree, powdering can destruct the strucutre.

Also, consider that the width of the BET tube is around 1-2 cm (I talk about most used apparatus, ASAP 2020 for example). I think the best thing to do, is to send 2 types of samples cutted into around 1 cm pieces and powdered form.

Hi Iranzu,

usually a rougher surface comes of course with a higher surface area, already allowing for more sorption to take place and also more strong sorption sites.

Maybe we can think of it a bit schematically: a weak sorption site usually only allows for interaction between a molecule and the surface in one direction. Imagine the molecule sitting on a flat surface.

In a stronger sorption site the molecule can get tucked into a"cavity" where molecule surface interaction can occur from multiple directions, therfore resulting in more strongly bound molecules to the surface.

Of course this is no exact physical description and I'm no so sure what kind of forces bind gas molecules to a surface apart from vand-der-waals forces.

But I hope I could help a bit.

Indeed N2 is used as adsorbate, but the point is that the experimental temperature for adsorption/desoprtion isotherm measurement is that of the liquid Nitrogen (77K), as the idea is to perform a complete adsorption/desorption isotherm. So that, depending on the pore size of the material under study, one can observe a capillary condensation (typically observed for type IV isotherms). Then, through the Kelvin equation (and derived models) it is possible to calculate the pore size distribution. It is also possible to extract the porous volume of the material.

If you just want to do BET measurement (pressure relative comprised between 0.05 and maximum 0.4), you need to know the cross sectional area (sigma) of the adsorbate. From a bulk point of view, sigma(N2) is equal to 0.162 nm². But one can suppose/expect that this value has to different at the nanometer scale. This is one of the limitations of the BET measurements since this sigma confined value is unknown. Moreover, as the surface S (m²/g) is calculated using the equation S=(n_m.Na.sigma)/m (with n_m : number of moles at the monolayer, Na : Avogadro number; m : sample mass), one can easily see that an error on sigma impacts drastically the surface S.

To finally answer to the question about other gases, the answer is yes as the adsorption is governed by physisorption (we really speak of aDsorption and not of aBsorption) and as you can observe the monolayer. But it still remains the problem of the definition of sigma which is, here again, impacted by the size of the porous material.

Thank you Professor Frank T. Edelmann for the great insight. sure, I'll go through the mention linked. well, from your expertise, will you please suggest some potential materials which can show desired chemistry. Thanks

Okay. So the particles are quite large. It is not true that all polymer/plastic filters have high affinity to DNA. It depends on the charge and surface modifications. If I were you, I would talk to the technical advice department of filter manufacturers (eg, Nucleopore). Good luck.

Dear Dr. Denis Rodrigues ,

speleothems, sometimes referred to as formations or decorations, are cave features formed by the deposition of minerals. The word speleothem is derived from the Greek words spelaion meaning "cave" and thema meaning "deposit". The speleothems with which most people are familiar are stalactites and stalagmites. Stalactites grow down from the cave ceiling, while stalagmites grow up from the cave floor. It’s easy to remember which is which: Stalactites have a "T" for top and stalagmites have a "G" for ground.

Speleothems actually form because of water. Rainwater seeps through cracks in the rock. As it passes through organic material, it picks up carbon dioxide gas, creating carbonic acid. This weak acid passes through joints and cracks in limestone. The mineral calcite is dissolved from the limestone rock in which a cave is formed. When this water that now holds the dissolved rock is exposed to the air in the cave, it releases the carbon dioxide gas, much like when a bottle of soda is opened. As the carbon dioxide is released, calcite is precipitated (redeposited) on cave walls, ceilings and floors. As the redeposited minerals build up after countless water drops, a stalactite is formed. If the water that drops to the floor of the cave still has some dissolved calcite in it, it can deposit more dissolved calcite there, forming a stalagmite.

Speleothems form at varying rates as calcite crystals build up. Several factors can determine the rate of growth. Two important factors are the temperature outside (which affects the rate of decay of plants and animals, hence the amount of carbon dioxide in the soil), and the amount of rainfall. The shapes of speleothems are determined by how the acidic water enters the cave (by dripping, seeping, or splashing) and how the water stands or flows after entering the cave.

Most scientists believe that the color of speleothems are determined by the mineral content. Pure calcite is white and almost colorless. Iron and other minerals, as well as acids from surface vegetation, combine with calcite crystals to add shades of red, orange and black to the color of speleothems. Others believe that humic and fulvic acids in the soil may also contribute to speleothem coloration.

For more details, please see the source:

-How Stalactites and Stalagmites Form – Ozark National Scenic Riveways, Missouri

Available at: https://www.nps.gov/ozar/learn/education/speleothems.htm

My best regards, Pierluigi Traverso.

Video link for determination of Point of zero charge (PZC)

How to apply Freundlich adsorption isotherm. A complete guidance

How to apply Langmuir isotherm. A complete guidance ..

I agree with what Yuri Mirgorod has said. But, this is not quite unusual. In the case of OC:BH3 adduct also nCO goes from free CO value of 2143 to 2165 cm-1. In metal carbonyls M(dxy, dyz or dxz)-->pi*(CO) is responsible for decreasing the value. But CO bond polarization is equally responsible for nCO shifts. Please read the article: Chem. Sci., 2016, 7, 1174-1184 by Giovanni Bistoni et al. In fact, in Ni(CO)4, it is the pi-bonds (dNi-->pi*CO) are solely responsible for the existence of Ni(CO)4 molecule and not OC-->Ni sigma bonds.

http://downloads.hindawi.com/journals/jchem/2017/3039817.pdf

Interesting question

Guru,

Are you still getting negative surface area or C constants from the BET after the out-gassing treatment and checking for leaks? If so realize that the BET does not really measure the surface area or the adsorption energy, it is only a comparison measurement between chemically identical samples.

The BET has been proven to yield internal anomalies and all other "Henry's" law adsorption isotherms have also be disproved. So, it's not surprising that you are getting confusing answers.

If you are still working on this type of project, let me know and I can give you more advise.

You have to get Nitrogen adsorption curves From BET, these adsorption curves can be used further to calculate BET surface area, pore size estimation by using Non linear density functional theory.

Hello Anis Aliouat

Degassing is required for the BET analysis. But best of my knowledge there is no perfect chat or list from which one can easily get the degassing time and degassing temp. data. As your sample is highly thermal stable then you can set a series of temp. with different time and perform the adsorption-desorption isotherm to get the desired specific surface area data. Generally you can start with 120(oC) for 80 min to the upper limit (as mentioned in the machine which you are using). But to perform the surface area study you must to the TGA analysis.

Regards

Hi.

Short comment: yes, electrolytes will have effects on the adsorption of metals. The effect is, however, different depending on the specific nature of species of interest, structure of the adsorbent and type of adsorption phenomena. You should be extra carefull with species that generate diferent ions as functions of properties of the aqueous phase, as for example, CR6+. The ion will be Cr2O7 (2-) in acid pH and CrO4 2- in basic pH.

This article is a very good review of what you need. Start by reading it carefully.

Cheers!

درود

این موضوع مربوط به مولکولارسیو های با کیفیت پایین است در این مورد ما در شرکت پترومهر می توانیم به شما کمک کنیم

@Hafiz Muhammad Zia Ur Rehman can you please elaborate.

Dear Zeynab,

I think you could estimate the adsorption energy by picking the absorb and desorb structures and minimizing them. If those structures are stable enough you could obtain each energy state by minimizing them. I don't know how complex your system is, but I guess this could help.

Veronica

Following

As far as I know, TBAB acts as hydrate promoter because it has empty dodecahedral cages that can selectively trap small gas molecules, such as CH4, CO2, H2, N2, and H2S. It is proposed that gases with small molecular size and high solubility in water could be effectively separated using TBAB semi-clathrate hydrate. The attached paper is very useful in this regard. Thanks

Uddipta Nath Don't use your own terminology, follow IUPAC recommendation.

For a "complex" see

https://goldbook.iupac.org/html/C/C01203.html

"A molecular entity formed by loose association involving two or more component molecular entities (ionic or uncharged), or the corresponding chemical species. The bonding between the components is normally weaker than in a covalent bond. The term has also been used with a variety of shades of meaning in different contexts: it is therefore best avoided when a more explicit alternative is applicable. In inorganic chemistry the term 'coordination entity' is recommended instead of 'complex'. See also: activated complex, adduct, charge transfer complex, electron-donor-acceptor complex, encounter complex, inclusion complex, σ-adduct, π-adduct, transition state"

Can doping at higher concentration (with Ca) reduce the surface area and color of TiO2?

Dear Alsultan,

The absorption of water should be determined as arithematic mean unlike bulk specific gravity, which is reported as Harmonic mean.

Does not matter (I am talking about good DI water system, they could be very different)

In terms of purity/resistivity the best is millipore. DI water could be both better and worse than distilled water, depending on a system; theoretically DI water should be better.

Generally for boiling distilled water is the worst one, but if DI system is a suspicious one then distilled water should be preferred.

Compressibility and saturated hydraulic permeability of clay-polymer composites — experimental and theoretical analysis( Applied Clay Science

Volume 130, September 2016, Pages 62-75 0)

Abstract: In this study, the volumetric behaviour, hydraulic permeability and micro-fabric of clay-polymer composites fabricated by the use of polyacrylamide polymers were experimentally investigated and discussed by use of theoretical multiscale approaches. Composites were varied systematically in composition taking into account constitutive properties controlling clay-polymer interaction, i.e., clay mineralogy (kaolinite and montmorillonite dominated clays with predominantly mono- and divalent counterions, respectively) and polymer charge (nonionic, cationic, anionic). Composites were produced according to their individual maximum adsorbing capacity and prepared to slurry conditions. 1D compression and rebound tests were performed (2–800–25 kPa) and the hydraulic permeability was calculated for each loading increment. Additionally, microscopic investigations in environmental scanning electron microscope were performed. It was found that cationic and anionic polymer adsorption promote aggregated and flocculated clay fabrics, respectively, whereas nonionic polymers promote dispersed clay fabrics. Macroscopically, this led to an increase in void ratio at the same stress level as well as to an increase (cationic polymers) or decrease (nonionic polymers) in hydraulic permeability. Micro- and macroscopic findings were theoretically analysed by use of diffuse double-layer (DDL) theory and cluster-model. A modified approach of DDL theory accounting for the effect of adsorbed nonionic polymers on the electric potential in the nearfield of clay mineral surfaces was derived. Theoretical results were found to be in good agreement with experimental results on volumetric behaviour. By use of cluster-model, hydraulic permeabilities were found to correlate to the microscopic findings on clay micro-fabric.

Also have a look at :

Viscous Behaviour of Soft Clay and Inducing Factors

www.researchgate.net/profile/Behzad_Fatahi/...

Viscous Behaviour of Soft Clay and ... repulsive and attractive forces between clay ... including mineral composition, clay water system and ...

Thanks Mr Sobell

In principle, you can use laser cleaning to remove aany dirtness or layer form a surface with great accuracy and with no damage to the substrate

regards

Hi Abinaya

Addition to what has been mentioned by Dr Amin,  the diffusion of the methyl orange particle is affected by the temperature which leads to higher mass transfer rate from bulk to the boundary layer around the surface of the carbon particle.  

BET method is preferred choice for higher relative surface areas like porous materials, activated carbon ,quantum dots materials,graphene and nanosized metal oxides.I thinck the Lanqmuir model is compatible with metals which have low relative surface areas.

Dear Mr. Hodaei,

Your question is interesting in the way you try to understand the behaviour of your material in solution, which can be of potential value in applications such as adsorption. However, your writing mentions Fe²⁺ and Fe³⁺ as charge of iron, while the oxidation states II+ and III+ were mentioned, respectively. The apparently small difference has strong consequences to the overall speciation. No iron in such constellation is assumed free and ionic, but bond to oxygen. At the outer surface of Fe_xO_y nanoparticles, oxide or hydroxide groups will determine governing charge and interaction towards species. Avoid "complexation" as choice of interaction unitl you actually characterized that interaction mechanism . It is not likely Fe_xO_y have the potential to chelate certain compounds in solution.

Regarding the available analytical instrumentation, consider solid phase characterization, for instance using TEM-EDX, EELS, Mössbauer spectroscopy or XRD. The reference applies some of these techniques for the characterization of Fe₃O₄ nanopartikels in a porous host.

Best regards, Karel Folens

Consider attenuated total reflectance FTIR, if your main objective is to determine bonding mechanisms involving organic groups on particles. You can also obtain quantitative information if the experiment is conducted properly. See example attached.

 Dear Smruthi Prabhu 

Nickel compounds moslty are in complex forms and if you want to  precipitate its product you should synthesiz it and then purifed it and eventually  precipitated it.

Yours

You may try the same silanes which are suggested for glass fibers. They will probably work due to the similarities in surface chemistry. You should take into account, however, waht kind of resin you want to put your treated filler in. In epoys resins epoxy or amine functional silane is suggested, in unsaurated polyester acrylic function should be chosen.

Every adsorption isotherm will give you an important piece of information. For example qm from Langmuir isotherm is very important when you design your batch system for wastewater treatment. Rl from the same isotherm give an indication about the favorability of the adsorption system. From D-R model you can identify the type of adsorption; physical or chemical. Temkin constant (b) will identify if the adsorption is exothermic or endothermic. So, they isotherms are more important than % removal.

However, if you draw the two curves (q against dose and % removal against dose) on the same plot, you will get the optimum dose for this adsorption system which is an important factor in design.

I see a few issues here. Let me pose this as a study exercise ...

* What do you really want to obtain in ChemDraw? The 3D size of the molecule. This has nothing to do with calculating the active surface area. It only has to do with defining the size of the molecule.

* How do molecules absorb on surfaces? They absorb as a 3D molecule on to a 2D surface area.

* How do you obtain the 2D surface area that is occupied by the 3D molecule that you model in ChemDraw? You project the molecule as a "cylinder" to sit on a a flat plane.

* What is the proper cylinder projection of the 3D molecule? It depends on the surface and the molecule. For example, an amine-silane could absorb in one case with the amine end down or in another case with the siloxane end down.

* How do I find out which is the proper bonding geometry for my molecule? You research this in the literature.

* How does this relate to the coverage of a molecule on a surface? Once you know the projected area per molecule A_m (m²/molec), you can determine the coverage of the molecules on a surface area A (m²) approximately as N_m (molecules) = A / Am.

* How does this fit to the Langmuir isotherm? That is an exercise left to the reader.

Thank-you Dr Igwe for taking the time to answer this question. While I do understand the need for this type of normalization procedure to harmonize models of sorption derived using different underlying assumptions of surface site density, my problem relates to that it does not seem to work for the surface protonation reactions. The change in delta_pKa implicit in the pKa normalization procedure fundamentally changes the shape of the sorption edge so that a match is not possible, irrespective of the specific surface area or fluid volume/sorbent mass ratio used in the calculation. This, at least appears to be the case when making forward calculations of models described in the literature at different site densities using PhreeqC, which I have now also replicated in VMinteq so it doesn't seem to be a code related issue. Basically, normalization only seems to "work" if it is applied only to the solute binding reactions and not the surface charging (protonation) model. This is at odds with the NEA sorption project recommendations (& the analyses by Kulik, Sverjensky, and others), thus my confusion.

External resistance is due to diffusion of ions when it is in the solution phase but when it enters in to the pore there may be repulsion due to same charges which refers to  internal resistance

I agree with Nawel.

After adsorption the concentration of Pb will be very low so its advisable to use AAS and ICP-MS which will give you accurate results.

If you can export your GC data file in *.cdf format, you may give a look to the free software Openchrom (OpenChrom.net), for GC and GC/MS data processing. I have no link with their designer, and the software lacks clear user information, but as far as I could see, it includes options to model peaks, to set the baseline, and can be used for quantitation purpose.

Another suggestion coming to my mind. My former lab colleague, Claire Vidal-Madjar passed away in january 2015. During her active life in the group headed by Pr. Georges Guiochon (who also left us in 2014), she studied and published many valuable research work on modeling GC peaks, and you may find some suggestions related to your work - she often published in the Journal of Chromatography A. I remember that she studied alternative solutions to the classical Gaussian peak modified by an exponential decay function, using other mathematical function (eg Gram-Charlier series expansion)  for modeling asymmetric GC peak shapes.

Hoping that these suggestions are pertinent to your question

Dear Ralph Nicolai Nsara,

The monolayer capacity  Vm (The whole surface is covered with N2)

Vm= 1/ (slope+intercept) .......     in cc/g

surface area (m2/g) = Vm * 4.3532 

where the value (4.3532) is the conversion of the volume of nitrogen gas into area occupied by Nitrogen where (1 molecule occupies 16 Angstrom^2) 

Dear Lucas:

You can use TEMPO - is a stable free radical with the formula (CH2)3(CMe2)2NO for determining RSA. His concentration determine using electron paramagnetic resonance after reaction with the radicals of carbon. We determined so free radicals on the surface of the the crushed rubber.

Regards.

Dear Abhi,

You can check with our Dr. Suja Abraham

of our Physics Dept.

A.V.Sethuraman

Dear Ariadne Tsambani, 

Thank you very much!

the paper is so helpful for me.

Regards,

Yasser

dear hongping, thank you so much. i calculated my structure's potantial befor my question with 6-12 potantial but i have no idea that this term is total energy or i have to add an other term to it.

i want to do it theoretically.

Dear H. H. Mohammad: Surfactants having the same functional group in the solid layer have the same molecular area per one molecule. Functional groups may be different. In COOH 0.205 nm2. The area of 0.2 nm2 can be accepted for cross-sectional area of the alkyl group. Functional group -Cl, -F have a smaller cross-sectional area. Find a covalent radii and define the area. But if you are determined by the maximum adsorption monolayer, you will get a larger cross-section. Why? Answer yourselves.

Best regards

f you want to increase the possibility of Nikel ion adsorption on your particles you should be sure that there are negative charges on your particles. Fir that you can think of grafting your particles with carboxylic groups. Just putting your particles in alkaline solution will not guarantee the reduced aggregation. This way you can modify the adsorbed charges but you have to think of the pH of the nickel ion solution in which you are going to disperse your particles.

To improve your knowledge on nanoparticles synthesis and reactivity, characterization methods and their use for entrapment of metal ions you will get several references and books on scopus, scifinder or even on google books and google scholar. You should chose the specific ones for your project.

You might try doing a general pre-block using a protein solution like milk. Or you can make a BSA solution to pre-expose your surface to.

I have attached a pdf of the paper reproduced by Rafik.

For the casual reader who might come across this thread, I'd just like to add a very short and simple differentiation:

BJH is based on the Kelvin equation (aka Young-Laplace) which relates the pressure to the radius of curvature (pore size) of a liquid meniscus... albeit modified by taking into account the thickness of the adsorbed film of adsorbate. In large mesopores this is approximately reasonable (notwithstanding hysteresis which is not modeled in BJH), but in small mesopores (as in the material known as MCM-41 for example) the error of this simplistic model can be very significant. And for micropores (in which no liquid meniscus exists) it is totally inappropriate.  

DFT (Density Functional Theory) on the other hand is based on molecular modelling and takes into account direct interaction of adsorbate with the adsorbent surface, micropore filling process (not a condensation process) the development of the adsorbed film thickness, and capillary condensation (adsorption) and capillary evaporation (desorption). Hence, it is able to model hysteresis in the ads/des mesopore region of the isotherm.

I my opinion you did the mistake in calculation. Check your calculations one more time. The uptake will always increases with increase in initial pollutant concentration. 

The isotherm study can be carried out in two ways: (1) By changing the adsorbent concentration at constant initial adsorbate concentration, temperature, pH etc. 

(b) By changing the initial pollutant concentration at constant adsorbent concentration, temperature, pH etc. 

qe = (C0-Ce)/m     C0 is the initial pollutant concentration in mg/L, Ce is the equilibrium concentration of adsorbate, m is the mass of adsorbent in g/L

Hi Thomas,

here are a couple of theory based papers that might be useful:

Selloni A 2010 J. Mater. Chem. 20 10319

Tilocca A and Selloni A 2012 Journal of Physical Chemistry C 116 9114

Hi Taher,

practically any variation in chemical composition affects the lattice parameters of a growing crystal. This is obvious in melts where residual components even cause a change of phase, cf.  phase diagrams, Vegard's rule etc. How much these effects become detectable is another question. It is perhaps only detectable by more precise and less averaging techniques, e.g. CBED in TEM. I myself wouldn't assume a measurable effect but it is very responsible to keep an eye on these less probable effects.

Another topic is the discussion about surface effects. Again, a free surface is not comparable with the bulk so that you will have there definitely a relaxation. Cubic cells are then perhaps tetragonal or triclinic (as result of the orientation). However, the major question is, does this really matter, or can you measure this? Since we know that the information depth is in the scale of several microns (dependent on the Bragg angle, the radiation, the absorption) a surface effect which is in the scale of nanometers only cannot be visible in XRD patterns. It is part of the signal but the contribution is below the detection limit.  

Nevertheless, it is worth to discuss the opinion of H. Y. Asl that XRD is a signal coming from the bulk. Well, maybe I have another imagination about the term "bulk" but 5...10µm I wouldn't call bulk. This is for many practical techniques "surface" which is in general a problem for XRD measurements so that techniques like neutron diffraction or the application of synchrotron radiation would much more reliable but they are simply too expensive. Therefore we are using standard XRD but we have to take into account that we are observing only the surface of a sheet or a powder sample.

Finally a remark about the peak shift. I am sure if you scan here at Researchgate you will find similar questions where peak shift has been discussed. It is more problematic as claimed above by H.Y. Asl. Only a misalignment of the detector - the so-called zero shift - will cause a uniform shift in Bragg angle. In contrast, a sample misalignment of a sample is not invariant but strongest at small Bragg angles and becomes Zero at 2theta=180°. The interference of lattice parameter effects and sample defocussing makes a careful placement of the sample essential. Especially for low-absorbing phases the effective diffraction volume is shifted below the surface so that high precise measurements need to consider these effects. 

Dear Armin

I think the minus sign could appear for two reasons:

1. The adsorbent does not follow Langmuir assumptions at all. For example, its adsorption capacity won't reach a certain limit by increasing the concentration. If this is true, another isotherm model should be applied, like Freundlich.

2. Another reason that comes to my mind is that sometimes when the qe values are small, the calculated errors will be very small too. As a result, the solver cannot find the best answer. Therefore, normalizing qe values or changing qe unit (using smaller units) could help overcoming this problem. 

For study of adsorption on metals there are ellipsometric or electrochemical methods - eg, polarography (voltammetry) and impedance on clear "cutting" metal surface. For coatings on metals you can use the radioisotope methods too.

Hello, Zoe,

what is considered "ionic interaction"? Do you mean "ion exchange" In this case there is a very simple and stright test: just check the exchangeable ions or measure whether pH is changed due to adsorption. If there is an ion exchange, something should be released. In your case, I suppose protons could be released from the polymer matrix due to a drug cation adsorption. So, do you have a pH increase? if not, probably, there is no ion exchange.

Another useful test might be playing with pH of solution, and suppressing ionization of carboxylic groups and varying ionization of drugs, if any. Is adsorption affected by pH?

and, of course, as noted Radomir, it is the change of ionic strength. You may play with using Na+ and Ca(2+). For example, monovalent ions will just affect electrostatic interactions by changing organic ion activity coefficients or suppressing the diffuse later near a surface but divalent ions might start working also as a ion-bridges. Depending on the results, the useful answers can be obtained

Some particles need not to emit the energy at incident absorption wavelength. The excitation and emission results in electron relaxation and it may be due to some other mechanism like inter band absorption. The tiny portion of the fluorescing molecule of your sample may be responsible for excitation at a wavelength which does not matches with absorption wavelength where the absorption maxima of non fluorescing molecules may predominant

Hello U. Chinna Rajesh,

First of all I guess the right figure (within the file) is after the experiment and clearly shows a rapture of your sample and a hill-like structure. As far as I can judge your sample swells during the application of the drop resulting in a rupture of the material and instead of measuring a drop of water your measured the “hill” (the sharp borders and the tip of the “droplet” is not possible for liquids). I would suggest to expose the material to saturated water atmosphere to prevent breaking (normally CA-measurements should be performed in saturated vapour phase of the chosen liquid with well-defined temperature). Different points (roughness, advancing, receding) as mentioned Carlos Grattoni have also to be considered. If water will not work you have to perform your experiment with a non-reactive pure liquid.

Regards Michael Schmitt

Dear Fernando, Sorry!  every thing what you wrote above was wrong. You don' t know the meaning of equilibrium if would know, you wouldn't talk about the spontaneous adsorption, which means irreversible (natural) change is taking place not the reversible or in another word equilibrium process! which never occur in reality. 

The enthalpy of adsorption for a exothermic reaction DelH_ad = H_P -  H_R < 0 , Where  p  denotes  product and  R reactant.

Del G_ad = Del H  - T  Del S  which is equal to zero at the equilibrium for well defined temperature  T_eq  and pressure  P_eq. That means;

Del S_eq = Del H_eq/T_eq    for an exothermic adsorption reaction Del H_eq< 0  Hence  Del S_eq < 0.    You  guys somewhat very careless using thermodynamic notations and concepts. I would recommend the advanced text by Guggenheim on Thermodynamics. BEST REGARDS

I am using the BJH method.

Dear Özden,

I not familiar with CZTSe but I know that ZnO is very well-soluble (not dispersed) even in diluted acids (pH<4 with sufficient time for incubation, bases above 12 can also work).

Layer thickness and modifications may influence the process. Ethanol will most likely not work even if your system are nanoparticles adsorbed onto a layer. I am also convinced that in Germany using absolute ethanol for non-optical application (UV-vis in UC-C, UV-B range) is a waste of money.

Regards

FESEM elemental mapping for nitrogen will surely help.

Ionic potential of a metal ion plays key role for binding on adsorbent surface of an adsorbent. As varies the metal ion, the ratio between ionic charge and size of solvated ion i. e. ionic potential changes indicating variation of adsorbed amount over the surface because adsorption of a solute over adsorbent surface takes place via secondary Coulomb type forces. In addition, pore size also controls adsorption amount. If the pore size is smaller than the size of sovated metal ion, adsorption amount will be small.  

You can get the similar or apropriate answer by searching the keyword in the GOOGLE SCHOLAR page. Usually you will get the first paper similar to your keyword.

From my experience, InsyaAllah this way will help you a lot. If you still have a problem, do not hasitate to let me know.

Kind regards, Dr ZOL BAHRI - Universiti Malaysia Perlis, MALAYSIA

I suggest that you use the freeware Gwyddion, where (i) you will find all the Tools necessary for analysing your AFM data, and (ii) for which there are plenty of online tutorials and explanations about the theory behind each Tools.

Anyway, make sure, when you mention roughness that you keep the surface area constant (always use the same image size), and mention it. Roughness strongly depends on the surface area considered (usually it increases with increasing surface area). Additionaly, give the type of roughness (RMS, total, arithmetic, ...).

Grain size distribution is a different story. Many parameters can be measured, such as the projected diameter, the inner or outer circle, etc. But AFM is not well suited for this kind of analysis. Prefer SEM images, or determine crystallite size by XRD.

This is due to capillary condensation in so-called "ink-bottle" shaped pores, i.e. having a entrance diameter smaller than the size of the pore body. Condensation occurs progressively in such pores until the pores are completely filled by the condensable vapour at high relative pressure. But when the relative pressure decreases, the liquid needs to go out of the pores and therefore needs to pass the narrow necks. This occurs at a lower relative pressure than what was required for filling the pores, and when the critical relative pressure is reached, the pores empty abruptly. Hence the loop in the isotherms.

Alain

Dear Dayananda,

They are about adsorption orders.

Try attachments.

Yuh-Shan Ho

E-mail: ysho@asia.edu.tw

That is a somewhat complex question. On the one hand there are a number of MOFs which do exhibit excellent stability in aqueous media like most of the MILs and many of the Zr-based MOFs and also the ZIFs. That would be the strategy of creating a MOF whose metal-linker bonds exhibit hydrolytic stability to some degree. In most cases, however aqueous basic media are a problem. On the other hand, a less stable MOF (bondwise) can be passivated  to various extents by adding hydrophobic side groups to the linker. There has been some investigation in the group of Krista Walton dealing with substituent effects on pillar-layer MOFs and a number of works deal with hydrophobization of MOFs like HKUST-1. So if you want to work with a less stable MOF, you would have to prevent water accessibility to the metal-SBU by some means.