School of Engineering and Science - Jacobs University

Absorbance
0.05
1
2
1600 1400 1200 1000
Wavenumber, cm -1
Fig. 4-8. FTIR spectra of the cinchonidine modified Pt nanoclusters (1, sample D) and
free cinchonidine (2), intensity of that spectrum is decreased for better presentation.
The spectra measured in transmission mode with KBr pressed pellet.
The 3-9 cm -1 blue and red shifts in the wavenumber of the corresponding peaks in the
spectra of free and adsorbed modifier clearly indicate on the fact that cinchonidine is
adsorbed on the Pt cluster. The quality of shown spectra increases significantly with
absence of a support due of the mentioned background contribution and because of
higher cinchonidine concentration of surface of Pt for B and D samples with respect to
modified conventional Pt/Al 2 O 3 . However, despite of the fact that not all peaks in the
spectrum of cinchonidine modified conventional Pt/Al 2 O 3 (Fig. 4-6) are resolved well
(due to the alumina background effect) and some corresponding peaks from
cinchonidine modified Pt nanoclusters (Fig. 4-7, 4-8) presence in the Fig. 4-6 as
shoulders, it is possible to conclude, that the spectra of adsorbed cinchonidine on all
three samples have no principal difference. And only difference is in quality of the
spectra. Through comparison of all three spectra is also possible to conclude that the
cinchonidine molecule is still on the Pt surface and did not decompose after samples
preparation, that is especially important to note for B and D sample. Since the spectrum
quality of B type of nanosized sample is better that the quality of modified conventional
Pt/Al 2 O 3 and D sample, this spectrum had been chosen for further detailed analysis,
where as brief analysis of two left spectra can be found below in this chapter (sample
B) and in the chapter 5 (cinchonidine modified conventional Pt/Al 2 O 3 ).
The DRIFT spectrum of sample B (Fig. 4-7) has many peaks and shoulders, thus it
gives difficulties to find corresponding peaks in the spectrum of free cinchonidine
unambiguously for all of them. This is due to the adsorption selection rule [179] by
which intensities of some vibration bonds of adsorbed molecules are changed. That is
why only some of the peaks and shoulders (which are well separated and/or with high
intensity) were chosen for further analysis, they are summarized in Table 4-3. Some of
the peaks from Table 4-3 could be easily assigned to the ‘flat’ or/and ‘tilted’ orientation
mode of cinchonidine by using data from the works of Ferri [76] and Zaera [77].
However, not all vibrations from Table 4-3 could be correlated with prior work due to
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