[Ifeffit] Cadmium K-edge
Alan Du
duji0003 at ntu.edu.sg
Tue Jan 11 19:50:51 CST 2011
Hi Bhoopesh,
I agree that high energy sites will be occupied by Cd first. Upon
saturation, the cations will move to low energy sites. That being said, the
Cd loading in Sample 1 was higher than Sample 2. The higher amplitude in
Sample 1 FTmag could be due to presence of more Cd loading.
I have not try Cd-Na presuming low Z would have weak scattering effect. I
should try fitting that.
I will need to go back to Athena to look into the k-range for FT (originally
2:10 Å-1 for both samples). After doing some comparison, S2 k-space data
beyond 9 Å-1 seems to be unreliable to me now.
Anyway, I greatly appreciate your advice. Thank you.
Alan
On 11 January 2011 00:57, Bhoopesh Mishra <bhoopeshm at gmail.com> wrote:
> Hi Alan,
> Looking at the real part of FT, I am convinced that O atom will
> justify for peaks at 1.8 and 2.3 A in sample 1. One of the possibilities for
> sample 2 to be different is, it has higher ss2 for Cd-O (as can be seen from
> lower amplitude of first peak). If Cd loading in sample 1 is lower than
> sample 2, then it makes sense to me that Cd is bound to higher affinity (and
> less disordered) sites on Sodium Titanate nanotube in the sample1. As the Cd
> loading increases, Cd starts going to lower affinity albeit more disordered
> sites, making Cd-O bonding more disordered than sample 1.
>
> Other possibilities include coexistence of O and Na in the first shell
> of sample 2, which might be interfering destructively and dampening the peak
> at 2.3 A). Have you tried that scenario? It might not be trivial to
> distinguish O bonding with high ss2 from O and Na in the first shell. But
> you can try that out by splitting the first shell at two different
> distances with smaller ss2 values.
> It is not obvious to me that your data supports 2nd shell Cd-Ti
> interaction. In the fit you described, your E_not2 and ss_2 are very
> high. The amp_2 is highly correlated with ss_2, and amp_2 value is close to
> its error bar. Put together, these two parameters makes me suspicious of
> your 2nd shell fit. Your Chi data does not necessarily show clear Cd-Ti
> interaction either. In my opinion Cd-Ti interaction would result in high
> amplitude of oscillation in chi (and correspondingly strong peak in FT).
> However, things can behave differently in case of nanomaterials and you
> might have some contribution of Ti in your spectra. If this is a significant
> part of your manuscript, you will have to convince the reviewers.
>
>
> Good Luck,
> Bhoopesh
>
> On Sun, Jan 9, 2011 at 11:43 PM, Alan Du <duji0003 at ntu.edu.sg> wrote:
>
>> Hi Bhoopesh and Scott,
>>
>> I should have given a description of my project. Yes Scott, the work is to
>> investigate the binding mechanisms of aqueous cadmium onto sodium titanate
>> nanotubes. Spectrum of Sample 1 and 2 obtained from merging 9 scans and 4
>> scans, respectively.
>>
>> A quick check in Athena and, indeed, the white line of Samples are higher
>> than CdO. I'm not sure the reason behind it though. It is likely that
>> cadmium binds to the surface of substrate rather than inside the bulk. The
>> lack of distinct peaks after 1.8 Å means that there are not many scatters
>> around the absorber?
>>
>> Bhoopesh, as requested, I have attached the real part of FT (
>> http://img585.imageshack.us/i/ftreal.jpg/). I haven't got a chance to
>> interpret them.
>>
>> From preliminary fitting of Sample 1, the major and minor peaks at 1.8 and
>> 2.3 Å could be described by a Cd-O path (CdO). This interests me because
>> Sample 2 does not have a peak at 2.3 Å, meaning there is another single
>> scattering path for Sample 2?.
>>
>> The peaks at 3 Å were fitted with Cd-Ti path (CdTiO3). No multiple
>> scattering paths used. The best fit goes something like this:
>>
>>
>> ****************************************************************************
>> Independent points = 13.166992187
>> Number of variables = 8.000000000
>> Chi-square = 1534.709946959
>> Reduced Chi-square = 297.021921317
>> R-factor = 0.000128095
>> Measurement uncertainty (k) = 0.000060423
>> Measurement uncertainty (R) = 0.004455442
>> Number of data sets = 1.000000000
>>
>> Guess parameters +/- uncertainties (initial guess):
>> amp = 0.9242390 +/- 0.0509920 (1.0000)
>> enot = 1.3950420 +/- 0.5425380 (0.0000)
>> delr = -0.0872060 +/- 0.0051060 (0.0000)
>> ss = 0.0113250 +/- 0.0008480 (0.0030)
>> amp_2 = 0.2441320 +/- 0.1905250 (1.0000)
>> enot_2 = 22.5261260 +/- 4.5990590 (0.0000)
>> delr_2 = 0.2510860 +/- 0.0719080 (0.0000)
>> ss_2 = 0.0274690 +/- 0.0128040 (0.0030)
>>
>> Correlations between variables:
>> amp_2 and ss_2 --> 0.9342
>> enot_2 and delr_2 --> 0.9133
>> amp and ss --> 0.8865
>> enot and delr --> 0.8632
>> amp_2 and delr_2 --> 0.3040
>> delr_2 and ss_2 --> 0.2888
>> All other correlations are below 0.25
>>
>> k-range = 2.000 - 9.000
>> dk = 1.000
>> k-window = hanning
>> k-weight = 3
>> R-range = 1.000 - 4.000
>> dR = 0.000
>> R-window = hanning
>> fitting space = R
>> background function = none
>> phase correction = none
>>
>>
>> R-factor for this data set = 0.00270
>>
>>
>> ***********************************************************************************
>>
>> The above enot_2 is on the high side. I am not entirely familiar with the
>> parameters yet. Are there other parameters I should worry about?
>>
>>
>> Cheers,
>>
>> Alan J. DU
>> Nanyang Technological University, Singapore
>>
>>
>
--
Alan J. DU
Research Student
Nanyang Technological University, Singapore
School of Civil & Environmental Engineering
Blk N1, N1-B4b-04, 50 Nanyang Avenue, Singapore 639798
Mobile: +65 9621 6991
Fax: +65 6861 5254
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