|
|
 | | From: | Ellezeebubbly | | Subject: | transmission FTIR v. reflectance FTIR | | Date: | 11 Jan 2005 10:45:26 -0800 |
|
|
 | Dear Group,
I am new to this group, but this site was recommended by a carbon
research association. I was hoping someone here might be able to give
me a concise explanation of the difference between transmission FTIR
and reflectance FTIR. I am preparing to do some FTIR research on
activated carbon, and I'm having some difficulty with information
overload. I went to the library to find literature on the subject, and
it all seemed very confusing.
Thank you for your help. Any insight into the problem would be much
appreciated.
Ellen
|
|
| | From: | Uncle Al | | Subject: | Re: transmission FTIR v. reflectance FTIR | | Date: | Wed, 12 Jan 2005 17:20:36 -0800 |
|
|
| Ellezeebubbly wrote:
>
> Hi Uncle Al, thanks for you reply. I am looking to characterize
> functional groups on the surface (exterior surface, since the interior
> surfaces are opaque unless doing an ATR-FTIR, which I don't have access
> to). I do have access to a transmission FTIR (straightforward) and a
> diffuse reflectance FTIR (trickier). I am not sure what you mean by
> bulk v. surface, since I assume that the spectrum will produce an
> "average" surface, i.e. the peaks will be qualitative over the domain
> but with no indication of position on the surface.
If you grind it up as finished sample the new surface is the old
interior. Grind it up before playing. Activated charcoal is
remarkably finely dispersed anyway. The only way to effectively hold
it all back is with a moist Celite pad or a membrane filter.
> The assumption is
> that any reactive functional groups reside on the edges, and the basal
> planes will be flat surfaces unadorned by functional groups.
The goodies can intercalcate as well as edge-adsorb. This is
epecially true for Lewis acids.
Activated charcoal is not well-ordered graphene. That is the whole
point of activated charcoal. Do a powder x-ray. Do you get spots or
rings? Compare with powdered crystalline graphite or HOPG. You'll
get lattice spacings either way. For that matter, is there any
graphene in there at all? Do NOT take a magic angle C-13 NMR, at
least until you talk with a knowledgeable operator. Don't spin a
conductor in a magnetic field.
> My
> particles are large with respect to the beam wavelength, but the person
> who owns the equipment seems to think that I should be able to get
> usable data anyway. It would be nice to have smaller particles, but I
> don't know how I can further grind the powdered material without risk
> of adding a lot of contamination.
If it works it was a good idea. If it fails, try reflectance. IR is
not all spiffy with high molar absorbances and narrow linewidths.
X-ray fluorescence surface stuff will do element maps but it is
disappointing for functionalty. Getting fancy is expensive to run.
> I have a hydraulic press to use, but the "setting" disks that are
> available are quite pitted. I was hoping a stainless steel flat
> surface would give me sufficient smoothness.
Sure. Steel is cheap. So is end milling and polishing. A polished
hardened tool steel die face is better, even as in insert. Stainless
steel is weak metal.
> The project is actually pretty interesting from the standpoint of
> sorption of small inorganic anions in activated carbon.
> I'd welcome further discussion. :o)
Start with "what is activated carbon?" Every source gives a different
nanostructure and decoration, and a different BET area. Know what
you've got before you wonder about what you get.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
|
|
| | From: | Uncle Al | | Subject: | Re: transmission FTIR v. reflectance FTIR | | Date: | Tue, 11 Jan 2005 12:48:55 -0800 |
|
|
| Ellezeebubbly wrote:
>
> Dear Group,
>
> I am new to this group, but this site was recommended by a carbon
> research association. I was hoping someone here might be able to give
> me a concise explanation of the difference between transmission FTIR
> and reflectance FTIR. I am preparing to do some FTIR research on
> activated carbon, and I'm having some difficulty with information
> overload. I went to the library to find literature on the subject, and
> it all seemed very confusing.
>
> Thank you for your help. Any insight into the problem would be much
> appreciated.
Do you care about the bulk or about the surface? What defines bulk
vs. surface in your carbon samples? Do you have micronized dust or
centimeter chunks? Grinding up chunks does not necessarily give you a
representative sample - certainly not after adsorption.
You cannot do transmission IR if the sample does not transmit. You
can also have severe problems with scattering including informal
creation of a Klaus filter. That will be fun unless you are the poor
bastard at the bench.
Reflectance IR requires a sample that reflects (not bad given the long
wavelengths). Sample geometry and beam direction can be tricky.
Press a finely powdered sample against glass to template a "smooth"
surface if you need specular reflection thereafter. Remove the glass.
Attenuated total reflectance IR will work with the probe, prism, or
fiber thrust into dog crap. It is only sensitive to a wavelength
above the probe's surface. The sampling depth thererore changes with
wavelength. You might need a lot of interface area to get a good net
signal.
The first duty of a competent engineer is to determine the real
problem. A competent chemist isn't going to listen to management in
the first place.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
|
|
| | From: | Ellezeebubbly | | Subject: | Re: transmission FTIR v. reflectance FTIR | | Date: | 12 Jan 2005 14:15:04 -0800 |
|
|
| Hi Uncle Al, thanks for you reply. I am looking to characterize
functional groups on the surface (exterior surface, since the interior
surfaces are opaque unless doing an ATR-FTIR, which I don't have access
to). I do have access to a transmission FTIR (straightforward) and a
diffuse reflectance FTIR (trickier). I am not sure what you mean by
bulk v. surface, since I assume that the spectrum will produce an
"average" surface, i.e. the peaks will be qualitative over the domain
but with no indication of position on the surface. The assumption is
that any reactive functional groups reside on the edges, and the basal
planes will be flat surfaces unadorned by functional groups. My
particles are large with respect to the beam wavelength, but the person
who owns the equipment seems to think that I should be able to get
usable data anyway. It would be nice to have smaller particles, but I
don't know how I can further grind the powdered material without risk
of adding a lot of contamination.
I have a hydraulic press to use, but the "setting" disks that are
available are quite pitted. I was hoping a stainless steel flat
surface would give me sufficient smoothness.
The project is actually pretty interesting from the standpoint of
sorption of small inorganic anions in activated carbon.
I'd welcome further discussion. :o)
Ellen.
|
|
|
