That is a really good question. Characterizing porous materials via spectroscopic methods you have to assume that the outer surface is the same as the internal (I know this is a far stretch). In my graduate work I had to characterize chromatographic materials and this was always an issue. The methods I used were surface specific such as X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry.

On method that can be used is to look at pore volume/pore size of before and after surface modification via BET surface area measurement. Differences in size can suggest a change of the surface.

Additionally, I know with chromatographic materials they'll do a burn test looking at the amount of carbon after surface modification to look at the amount of surface bound moieties. They use a calculation that involve the amount of carbon evolved and the surface area of the material. If the molecule you are wanting to attach to the surface has a heteroatom, i.e., sulfur or nitrogen, you could do a burn test to determine if the molecule reacted with the surface.

Let me know if this makes sense.

I agree with David. I also use DSIM (further info is here http://www.nrel.gov/pv/measurements/dynamic_secondary_ion.html) to look at the profile of specific fragments, which correlate with the interest elements, as a function of film depth.

I did XPS analysis, but since the material is porous particle, it is difficult to get the whole view of pore. I mean we just got analysis of surface, but material has an interconnected pore structure. How can I assume the outer surface is the same as inner one. It is because when we got the SEM images we realized there are some blockages of pores. That means we may not go down to all pores because of the blockages of pores. And the modifying agents want to bond to the outer surface because it's the first place for surface modification reaction to take place. That's why I need to find another direct or indirect way to address what happened in the pores.

Also, David, I tried what you have listed, but still nothing.

Hung, XPS, dynamic secondary ion and time-of-flight secondary ion mass spectrometer, they are all more or less same. I have already done XPS, so the other methods will not make any difference.

Thank you both for suggestions.

Polymerization can occur during the surface modification because of the modifying agent. That was the reason for blocking the pore. Another thing could be the modification time. The longer the time is, the higher the possibility of polymerization, thus blocking, is. So, I think i may need to reduce time. Also, I already did vacuum and ultrasonication.

Thanks.

It will affect the performance of modified material. Thanks.

Maybe measurement of adsorption can be helpful. Depends on the system. Let say if you have hydrophobized a hydrophilic system water vapor adsorption should tell you if all pores are hydrophobized. Accordingly you may do adsorption studies with marker molecules adsorbing/not adsorbing to unmodified surface or modified surface.

I had to address the same question in one of my publications (http://www.sciencedirect.com/science/article/pii/S0021967311014026) where I was functionalizing porous graphitic carbon and I needed to demonstrate that the surface was really functionalized via spectroscopic methods. During that study we did not have a suitable FTIR system to measure surface functionalization of graphite (eg photoacoustic IR). I demonstrated that the surface was modified using XPS, however, the question was whether the modification was homogeneous or not. This is where BET surface area measurements were needed. To show that the surface was modified with a thin layer of reactant and that the pores where not clogged a before and after BET measurement was preformed. This measurements before and after functionalization were similar enough to assume that the particles where homogeneously reacted.

Dear Ozkan,

you might want to tell us the characteristic sizes of your particles and pores in those, so we could figure out the best suitable technique for you. Of course, conventional XPS is not a best option for you, since XPS is a pretty averaging technique (so the resultant spectrum would be averaged over the surface of your X-ray beam size on the sample), and if there are several pores/characteristic inhomogeneous features in the beam footprint on the surface, which I suggest is the case, you'll get averaging. The other thing is that it is extremely surface sensitive, which has already been discussed. However, If your particles are around tens to hundreds of micrometer size, and the pores are, let's say, .1-10 um, I'd suggest you use Low-energy electron microscopy (LEEM), or even better its photoelectron spectroscopy augmented version (SPELEEM). This would combine microscopy with micrometer-size photoelectron spectrscopy, allowing very precise elemental and chemical state mapping of the surface. You might try to google LEEM/SPELEEM to get more information. The other option for you would in my guess be a combination of tomographic techniques (like X-ray microtomography), with some kind of spectroscopy/spectromicroscopy. But again, it is hard to make guesses without knowing the object, since the modern experimental techniques are getting more and more object-specific.

Regards

Nikolay