Yes, FTIR and then NMR...

Other than XPS, you can go with the FTIR as in most of the manuscripts that I have encountered they have used FTIR.

XPS, FTIR, Boehm's titration (acidic and basic oxygen functional groups), TPD or TPD-MS. (TPD means temperature programmed desorption and MS is mass spectroscopy). FTIR is more successful for highly functionalized carbon surfaces. Better to use a combination of analytical techniques as one technique complement the other .

SEM andTEM are also useful methods to know the morphorlogy characteristics.

Dear Antonio, beside FTIR, TEM, titration method also use for determination carboxyl, carbonyl, and other functional groups on the surface of ACs qualitatively as well as quantitatively.

you can get more idea from my two publications given below.

1) Microwave treated activated carbon from industrial waste lignin for endosulfan adsorption. Journal of Chemical Technology & Biotechnology 03/2011; 86(8):1074 - 1080.

2) Preparation and characterizations of microwave assisted activated carbons from industrial waste lignin for Cu(II) sorption. Chemical Engineering Journal 01/2011; 168:1103-1111.

Dear Antonio the most primary and fastest characterization method is FT-IR. Furthermore, i agree with Lijo that NMR is a more specific method to investigate the functionalities.

Advice the paper above

http://www.sciencedirect.com/science/article/pii/S0927024809003390

We have had good success using a gas-phase titration technique that only addresses surface functionalities that exclusively react with the gas phase. Gas-phase molecules only "see" or interact with surface funcitonalities whereas FTIR penetrates the solid sample up to a thickness comparable with its wavelength. What we propose is a gas-solid reaction rate experiment that usually necessitates a few mg of the material, depending on its BET surface. Here are three key references for your perusal:

- The use of heterogeneous chemistry for the characterization of functional groups at the Gas – Particle interface of soot and TiO2 nanoparticles, A. Setyan, J.-J. Sauvain and M. J. Rossi, Phys. Chem. Chem. Phys. 2009, 11, 6205-6217, doi:10.1039/b902509j .

- Characterization of surface functional groups present on ambient fine and ultrafine aerosol particles by means of heterogeneous titration reactions, A. Setyan, J.-J. Sauvain, M. Riediker, M. Guillemin and M. J. Rossi, J. Aerosol Sci. 2009, 40, 534-548, doi:10.1016/j.jaerosci.2009.01.008 .

- Probing functional groups at the gas-aerosol interface using heterogeneous titration reactions: A tool for predicting aerosol health effects? A. Setyan, J.-J. Sauvain, M. Guillemin, M. Riediker, B. Demirdjian and M. J. Rossi, CHEMPHYSCHEM 2010, 11, 3823-3835; doi: 10.1002/cphc.201000490 .

Good luck with your assignment.

FTIR is the simplest method for characterization of surface functionalities.

As mentioned above FTIR gives you an overview of surface functionality. Boehm's titration method can give you the quantitative estimation of acidic and basic sites present on carbon surfaces.

Thanks everyone!

FTIR and XPS are the more suitable techniques to investigate the surface functionali. They are give very well information about functional groups on the surface of the chars/activated carbon.

HATR-FTIR will provide you interesting information.

Chemical composition of surface functionality is best estimated by FTIR, XPS, solid state MNR, TPD and chemical analysis. Some examples can be found here:

[1] Puziy AM, Poddubnaya OI, Socha RP, Gurgul J, Wiśniewski M. XPS and NMR studies of phosphoric acid activated carbons. Carbon 2008;46:2113–23.

[2] Puziy AM, Poddubnaya OI, Ziatdinov AM. On the chemical structure of phosphorus compounds in phosphoric acid-activated carbon. Appl Surf Sci 2006;252:8036–8.

[3] Puziy AM, Poddubnaya OI, Martínez-Alonso A, Suárez-García F, Tascón JMD. Synthetic carbons activated with phosphoric acid I. Surface chemistry and ion binding properties. Carbon 2002;40:1493–505.

If you are interested in pK of surface groups the best technique is potentiometric titration:

[1] Puziy AM, Poddubnaya OI, Ritter JA, Ebner AD, Holland CE. Elucidation of the ion binding mechanism in heterogeneous carbon-composite adsorbents. Carbon 2001;39:2313–24.

[2] Puziy AM, Poddubnaya OI, Gawdzik B, Sobiesiak M, Tsyba MM. Functionalization of carbon and silica gel by phosphoric acid. Adsorpt Sci Technol 2007;25:531–42.

[3] Puziy AM, Poddubnaya OI, Zaitsev VN, Konoplitska OP. Modeling of heavy metal ion binding by phosphoric acid activated carbon. Appl Surf Sci 2004;221:421–9.

Regards,

Alexander

FT IR definitely gives a preliminary information about the char. The information supported by solid state NMR, XPS would give a detailed structural information regarding the various functional groups and the different environments of the groups as well as the percentage of carbon,etc. Further Boehm's titration as well as Zpc values would give insight into acidic and basic sites of the char

FTIR should serve the purpose of identifying the surface functionalities. sample preparations should be given careful attention to avoid unnecessary peaks due to moisture take up especially for oxygen containing surface functions. Even quantitative estimation of functionalities can be performed by using FTIR.

Hi sandip, what's the sample prep as for FTIR? Also, is it possible to get quantitative estimation of N? As long as I know XPS allows doing that.

Well, its difficult to write everything here. Can you please send your specific requirements to me on [email protected] so that I will be able to send you the details.

depending on the concn of N it ca be determined by, CHN microanalysis, XPS, kjeldahl's method, SEM-EDAX, difficult to use FTIR

TPD can provide useful information without requiring special equipment (just an electric furnace and IR or MS detector)

Boehm titration can provide useful information abot oxigen functional groups without requiring special equipment (just a titrator)

The Boehm titration works on the principle that oxygen groups on carbon surfaces have different acidities and can be neutralized by bases of different strengths. Sodium hydroxide (NaOH) is the strongest base generally used, and is assumed to neutralize all Brønsted acids (including phenols, lactonic groups and carboxylic acids), while sodium carbonate (Na2CO3) neutralizes carboxylic and lactonic groups (e.g. lactone and lactol rings) and sodium bicarbonate (NaHCO3) neutralizes carboxylic acids. The difference between the uptake of the bases can be used to identify and quantify the types of oxygen surface groups present on a carbon sample.

The most straightforward is a precise FTIR measurement, which gives you a picture about functional groups. However NMR, XPS and other techniques are useful too, but they are more expensive. Titration is also good for characterization, however it gives only general information about basic and acidic functional groups.

Good luck

MIlan

Although FTIR is almodt suggested, i think that might be wrong because if you analyze carbon as such (without any pretreatment) you see water and CO2 -and then hydroxyl- coming from air. Then this technique is valide if you heat at least at 150-200C your sample prior the measurment. But this temperature may initialize some rearrangements on the surface, depending on which carbon you re going to measure... I suggest thata Raman is better than FTIR. But you have to choose the right lasere power otherwise you get fluorescence . If IRemember weel, should be the green one.XPS is still good. But again:the pretreatment could not give you the exact composition.

To all my dear colleagues using traditional methods such as Raman, FTIR, XPS, solid state NMR, TPD and the like, etc. etc. etc. All these "classical" methods have the flaw that the penetration depth of the probing radiation is larger than the thickness of the interface which, for practical reasons, comprises up to two or three formal monolayers. Therefore you are probing the interface as well as the subsurface which is useful, but does not answer the posed question as to the properties of the INTERFACE! In my view the best is to let gas molecules "talk" to the Interface because they for sure only interact with the interface of a solid substrate, by definition. I have outlined a possible approach in my previous answer.

so, in case I'd opt for FTIR, a simple pre-drying could be ok as sample prep for my samples (chars/activated carbons)?

Oxygen, carbon and nitrogen surface functionalities.

FTIR of carbons might work (given Michel Rossi's correct statement about surface versus subsurface, using probe molecules, of which there are many, might be a good idea). However, FTIR of carbons can be a problem as the carbon can absorb very strongly so the quality of the spectrum may be poor. NMR will give you information, but not just of the surface (unless you use probe molecules again - see e.g. S J Tavener and V Budarin for 19F probing of surfaces). If you have EPSRC funding, then Durham University offers a very good free service - might be worth talking to them before you send a sample. And 2 techniques are definitely much better than one. TGIR is a nice way of checking how thermally stable your sample is / how much you can heat it before bits fall off (and what the bits are). Raman can work too, although its a bit outside my area of expertise, and seems tricky to get right unless you have a fair bit of experience. Dont forget wet chemistry too - titrations can be very helpful, especially alongside other techniques

If you opt for FT-IR, which is a very easy, economic and fast technique to analyze surfaces, I suggest to you to use a mix in form of KBr disk to have better resolution.

You can also develop a simple test of temperature profile; you can control the heating temperature (measuring with a thermocouple) of your carbon and to prepare immediately the KBr disk and to record the FT-IR spectra at different temperatures, where you can observe how bands disappear or intensity loss or shifted and with references of the functional groups that you are interested you can write a good analysis and discuss. Good luck!

Thanks everyone.

However, still as for FTIR, which are the most suitable analysis settings (resolution, wavenumber/cm range, No. of scans, etc.) in order to better identify oxygen and nitrogen groups onto chars/activated carbons?

Also, is it supposed to substract the background (KBr baseline)?

KBr FT-IR spectra is invisible.

Hi, well known for this purpose is Boehm's titration /well described in literature/. Besides that you may try XPS (C1s) or TPD /sometimes may help if used properly/.

Jacek

Easy and economic method is FT-IR.

Try grazing angle FTIR, as it lengthens optical path. We find it works reasonably well for surface modified nanosilica.

FTIR shows sufficiently the functional groups

How do you usually interpret the resulting spectra? I mean, how am I supposed to identify the absorbance peaks? Should I "manually" match the experimental absorbance bands with those known by literature for the different functional groups or I can use a software?

Yes, Can do both. What I've done is purchase a model compound most closely matching the material you are testing. Usually, the compounds are simple. If the functional environment is complex, you might use two or more model compounds to elucidate.

FTIR and Raman are the best techniques for identifying surface functional groups on an activated carbon structure. The techniques are complementary to each other. Both these techniques require small quantities of sample and are non destructive to the sample. On the other hand you can try to digest the sample and measure any inorganic entities that are present using ICP-OES or ICP-MS

Yes, but FTIR technique is more suitable for this purpose due to it is easy and inexpensive.

FTIR is the most suitable techniques to determine surface functionality of activated carbons.

XRD is also suitable method to predict the surface functionalities

There is not only a technique providing the best information about the surface chemistry of activated carbons or chars. By constrast, the information coming from several techniques allows to make a very reliable picture of the surface functional groups and structures. Among these techniques, probably FT-IR spectroscopy is the most appropriate in order to identifity the surface functional groups, specially by analyzing the so-called finger print region. However, the FT-IR spectra usually show overlapping bands which make very difficult to identify the functionalities and, in addition, the technique does not provide any information about the concentration of such functionalities. Probably, the best technique to determine the concentration of each surface functional group and structures would be TPD. Although it is very tedious, another method providing valuable information about the concentration of surface functional groups in activated carbons is the Boehm's method. Finally, as stated previously by other colleagues, XPS also seems to be a very good option in order to identify and quantify the different surface groups and structures. Probably, the greatest advantages of this technique are its sensitivity, selectivity and simplicity of operation. Nevertheless, it has a very important drawback concerning the deconvolution and assigment of the peaks in the spectra, which usually requires a great experience and long training of the researcher. In addition, MNR has also been used in order to identifiy the surface functionalities. In brief, the identification of surface chemistry in activated carbons usually requires the combination of several techniques to obtain reliable and realistic information.

On the other hand, I don't agree with the statement that XRD allows identifying the functional groups on activated carbon surface. In fact, such a technique only is able to identify amorphous or crystalline inorganic phases. However, as it is well-known, the functionalities on activated carbon surface are essentially atomic groupings covalent-bonded to the edge of the graphene sheets in the activated carbon structure. Therefore, this technique does not fit for such an identificative purpose. Conversely, XRD may accurately determine inorganic compounds present in the activated carbon matrix, such as silica or metal oxides. 

What about CaO or Ca(OH)2? Which technique would be best to identify these?

FTIR is another choice besides XPS, if you can prepare a good sample for measurement (or using DRIFTS or ATR instead of transmission).

For more info on this, you can check the classical paper of Figueiredo (Modification of the surface chemistry of activated carbons) below.

http://paginas.fe.up.pt/lcm/nano_fct/BioMateriais_Papers/Carbon_37_1999_1379.pdf

They are many techniques that you can use to investigate the surface functionalities of materials surface, for instance, you can use FT-IR, XRD, SEM and AFM.

FTIR, XPS, NMR can give reliable information on surface groups. TPD is also used for charaterization of surface groups, however the model of thermal degradation should be known. For characterization of ionizable surface groups Boehm titration is used. However the method is rough and gives amount of several types of groups. More detailed is potentiometric titration with further calculation of proton affinity distribution. For details see Puziy AM, Poddubnaya OI, Ritter JA, Ebner AD, Holland CE. Elucidation of the ion binding mechanism in heterogeneous carbon-composite adsorbents. Carbon 2001;39:2313–24.

HATR-FTIR (infrared spectroscopy using a reflectance mode)