Results and discussion 1 Modulated synthesis of Ni-UiO66
Modulated synthesis and characterization of Ni-UiO66
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3. Results and discussion 3.1 Modulated synthesis of Ni-UiO66
Conventional solvothermal method was used for modulated synthesis of Ni-UiO66 with the variant concentration of modulator were 5, 10 and 20 eq. After all reactants were
dissolved in 45 ml DMF, the mixture was sealed and heated at 140
o
C for 6h. The mixture seemed two layer and its colour were bluish while heating process and then turned back to
green after cooling. It was shown at Figure 1. The greenish and bluish color occurred due to the effect of adding ion Ni
2+
. The solid was collected by centrifuge or filtration. The amounts of samples was shown in Figure 2. The graph at Figure 2 shows that the greater the modulator
is added, the heavier the mass produced. Competition reaction between ligand BDC with modulator, acetic acid occurs during the process of solvothermal. As described in the
previous research that the carboxylate groups on the ligand acts as a bridge between clusters because BDC has carboxylic acid groups on both ends, but acetic acid has only one carboxylic
acid group at the end. Thus, the polymerization process stalled when the metal reacts with acetic acid. The ends of the polymerization process is what causes the increased crystallinity
Tsuruoka, 2009.
a b
Figure 1. The mixture of Ni-UiO66 at: a room temperature and b 140
o
C.
Figure 2. Mass products of Ni-UiO66 obtained from modulated synthesis.
The increasing crystallinity due to the adding of modulator were shown at XRD Pattern at Figure 3. The third outcome solids Ni-UiO66 with variations modulator having XRD pattern
similar to the XRD pattern of Ni-UiO66 and UiO-66 Cavka 2009. XRD patterns of three samples had a peak at 7.6 with the highest intensity, followed by a peak of 8.6, 10.3, 20.6,
and 30.5 which have a lower intensity. The addition of modulator does not change the structure UiO66. It was seen in XRD pattern that there no addition or reduction peak.
Intensity at 2 , 7.6 increased significantly. Can be observed from the XRD results that the larger modulator acetic acid were added increasingly sharp characteristic peaks generated.
Ni-UiO66 Mod20 has the highest peak intensity. XRD analysis results consistent with the
D. Iflakhah, R. Ediati
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results argued by Tsuruoka 2009. The competition reaction between ligand BDC and acetic acid ligands to the metal lead to a decrease the speed of crystal formation, thereby reducing
the formation of intergrown crystals, the crystals become more crystalline. Based on the Scherrer equation, particle size of Ni-UiO66 and Ni-UiO66 Mod 20 are 38 nm and 35 nm. In
another research, particle size of UiO-66 is 63 nm Abid, 2012, respectively, which suggests that addition of modulator could result reduced the particle size.
Figure 3. Pattern of XRD.
Ni-UiO66 Ni-UiO66 Mod10
Figure 4. The Image of SEM.
The particle size of Ni-UiO66 obtained from modulated synthesis and morphology crystal can be shown at SEM Image at Figure 4. It is seen that particle size of Ni-UiO66 was
similar with cubic shape at about 70 nm but the particle size of Ni-UiO66 obtained from modulated synthesis was reduced, which confirm the results from XRD analysis. Addition of
acetic acid as modulator in synthesis solution will increase in BDC and metal solubility. Secondly, the metal ion will not aggregate to form larger crystals.
Figure 5 shows spectra of H
2
BDC and Ni-UiO66 with and without modulator. Carboxylate groups on H
2
BDC can be demonstrated by the presence of absorption broad
Modulated synthesis and characterization of Ni-UiO66
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bands in the 3200-2500 cm
-1
which is the stretching area of OH from carboxylate groups, absorption bands in the 1730-1700 cm
-1
which is the stretching area of C = O and the absorption band in the 1320- 1210 cm
-1
which is the stretching area of CO. In addition, at 1600-1465 cm
-1
region, absorption appears bands stretching and the region 800-711 cm
-1
appears bending characteristic absorption band of benzene rings.
Figure 5. FTIR spectra.
Spectra FTIR of Ni-UiO-66 with the addition of modulator has similarities with the spectra FTIR of Ni-UiO66 without modulator. suggesting the similar surface functionality.
Absorption band at 3400 cm
-1
is an OH group stretching region, occurred due to intercrystalline water and physisorbed water. The existence of absorption band of carboxylic
groups missing in the 3200-2500, 1200, and 900 cm
-1
indicating the formation of a new bond between the carboxylic groups with cluster Zr
6
O
6
where ligand BDC is a bridge between clusters Zr
6
O
6
. Absorption bands at 680 and 470 cm
-1
indicates the formation of clusters of Zr and absorption bands 447-470 cm
-1
region is an area stretching 3-OH. Valenzano et al.,
2011. Significant differences between solids Ni-UiO66 with and without the modulator shown in the absorption band in the 1700 and 1400 cm
-1
which is the absorption of the CO group of carboxylic acid groups. At Ni-UiO66 Mod5 intensity absorption band in the 1700 and
1400 cm
-1
was higher than the Ni-UiO66. The larger the modulator is added, the higher the intensity of absorption.
Thermal stability analysis of Ni-UiO66 Mod20 was conducted using a TGA. Weight loss profiles and weight loss rate are presented in Figure 6. It is clear that three-stage weight loss
occurred on Ni-UiO66 Mod20. The first weight loss appearing before 50-100
o
C, 9,32 is due to the evaporation of surface adsorbed water on Ni-UiO66 Mod20. The second weight loss
at 120-200
o
C, 18,76 is attributed to the decomposition of DMF, which was not exchanged by chloroform. The third stage of weight loss at 470-580
o
C, 28,06 is ascribed to the decomposition of Ni-UiO66 Mod20 to ZrO
2
. Compared with Ni-UiO66 exhibited less weight loss rate in the first and third stages, suggesting more thermal stability of Ni-UiO66 Mod20.
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Figure 6. TGA profile.