10.1039/c4cy00238e
Synthesis, acid properties and catalysis by niobium oxide nanostructured materials
Dichloromethane and acetonitrile were purified with a LC Technology Solutions Inc. SPBT-1 Bench-Top Solvent Purification System. Compound 1 was synthesized according to literature procedures.9 NbCl5 and Nb(OEt)5 used in the preparation of T-I and T-II were purchased from Sigma-Aldrich and used as received. Commercial Nb2O5 (Puratronic(r), 99.9985%) was purchased from Alfa Aesar and used as received. Pluronic (P123) and dodecylamine 98% were used as structure-directing agents and were purchased from Sigma-Aldrich. Milli-Q water (resistivity 18.2 MΩ cm-1 at 25 degC; 0.22 μm filter) was used in all preparations and reactions requiring aqueous conditions. 
Synthesis of the Nb2O5 materials discussed within this contribution have been adapted from previously reported procedures. The methods used are briefly described in the following paragraphs:
5 g of NbCl5 (18.5 mmol) were dissolved in 99% ethanol (10 mL) under constant stirring. To this solution NH4OH (1 M) was slowly added to the aforementioned solution until a white precipitate was observed. The precipitate was then separated from the solution by centrifugation (3000 rpm), washed four times using Milli-Q water and dried at 120 degC for 24 hours. 
5 g of NbCl5 (18.5 mmol) were dissolved in 200 mL Milli-Q water. Immediately after addition, the yellow powder became white. After stirring for 3 h at room temperature, the white precipitate was centrifuged (3000 rpm) and washed four times with Milli-Q water until the filtrate was at neutral pH. The obtained solid was dried at 120 degC for 24 hours. 
1.5 g of P-123 were dispersed in 11 mL of Milli-Q water and 45 mL of HCl (2 M) at 40 degC. 5 g of Nb(OEt)5 (15.7 mmol) was added to solution under stirring. The resulting mixture was kept at 40 degC for 24 hours and then precipitated in a Teflon-lined autoclave at 100 degC for 48 hours. The obtained solid was filtered, washed with Milli-Q water and dried in air at room temperature. Excess surfactant was removed by Soxhlet extraction first by washing with 1% HCl in 95% EtOH (300 mL) and then with 95% EtOH only (120 mL). The final, template-free mesoporous Nb2O5*nH2O was dried in the oven at 120 degC for 18 hours. A mixture of Nb(OEt)5 (3.25 g, 10.3 mmol) and dodecylamine (0.57 g, 3.1 mmol) was heated until a homogeneous solution was obtained. Subsequent addition of 65.4 mL of Milli-Q water with manual stirring resulted in the formation of a gel-like precipitate. Further addition of 27.6 μL (0.3 mmol) concentrated HCl afforded a white precipitate. The reaction mixture was allowed to stand overnight, sealed and heated at 40 degC for 30 hours, 60-65 degC for 66 hours, 80 degC for 48 hours, and 95-100 degC for 5 days. The solid was then cooled down, collected by filtration and dried at 95-100 degC for 2 hours, 120 degC for 48 hours, and 140 degC for 48 hours. The white solid was then washed four times to remove the presence of excess surfactant. Each washing cycle was conducted for 24 hours under vigorous stirring followed by Buchner filtration. 645 mg (3.4 mmol) of p-toluenesulfonic acid in 13 mL of ether were added to 100 mL of MeOH for the first wash. For the second wash, 65 mg (0.3 mmol) of p-toluenesulfonic acid in 3 mL of ether were added to 100 mL of MeOH. Third and fourth washings were done using MeOH (100 mL) only. The final, template-free mesoporous Nb2O5*nH2O was dried into the oven at 120 degC for 24 hours.
Nb2O5
99.9985%
%
Pluronic (P123) and dodecylamine
used as structure-directing agents
98%
%
Milli-Q water
resistivity
18.2 MΩ cm-1
MΩ cm-1
Milli-Q water
filter
0.22 μm
μm
Milli-Q water
resistivity 18.2 MΩ cm-1
25 degC
degC
NbCl5
dissolved
5 g
g
NbCl5
18.5 mmol
mmol
ethanol
99%
%
ethanol
10 mL
mL
NH4OH
added
1 M
M
precipitate
dried
120 degC
degC
precipitate
centrifugation
3000 rpm
rpm
precipitate
dried
24 hours
hours
precipitate
washed
four times
times
NbCl5
dissolved
5 g
g
NbCl5
18.5 mmol
mmol
Milli-Q water
200 mL
mL
white precipitate
stirring
3 h
h
white precipitate
centrifuged
3000 rpm
rpm
white precipitate
washed
four times
times
obtained solid
dried
120 degC
degC
obtained solid
dried
24 hours
hours
P-123
dispersed
1.5 g
g
Milli-Q water
11 mL
mL
HCl
45 mL
mL
HCl
2 M
M
1.5 g of P-123
dispersed
40 degC
degC
Nb(OEt)5
added
5 g
g
Nb(OEt)5
added
15.7 mmol
mmol
resulting mixture
kept
40 degC
degC
resulting mixture
kept
24 hours
hours
resulting mixture
precipitated
100 degC
degC
resulting mixture
precipitated
48 hours
hours
HCl
1%
%
EtOH
95%
%
EtOH
300 mL
mL
EtOH
95%
%
EtOH
120 mL
mL
template-free mesoporous Nb2O5*nH2O
dried
120 degC
degC
mesoporous Nb2O5*nH2O
dried
18 hours
hours
mixture
Nb(OEt)5
3.25 g
g
mixture
Nb(OEt)5
10.3 mmol
mmol
mixture
dodecylamine
0.57 g
g
mixture
dodecylamine
3.1 mmol
mmol
Milli-Q water
addition
65.4 mL
mL
HCl
addition
27.6 μL
μL
concentrated HCl
addition
0.3 mmol
mmol
reaction mixture
heated
40 degC for 30 hours, 60-65 degC for 66 hours, 80 degC for 48 hours, and 95-100 degC
degC
reaction mixture
heated
30 hours, 60-65 degC for 66 hours, 80 degC for 48 hours
hours
reaction mixture
heated
5 days
days
solid
dried
95-100 degC for 2 hours, 120 degC for 48 hours, and 140 degC
degC
solid
dried
2 hours, 120 degC for 48 hours, and 140 degC for 48 hours
hours
white solid
washed
four times
times
Each washing cycle
vigorous stirring
24 hours
hours
p-toluenesulfonic acid
added
645 mg
mg
p-toluenesulfonic acid
added
3.4 mmol
mmol
ether
added
13 mL
mL
MeOH
100 mL
mL
p-toluenesulfonic acid
added
65 mg
mg
p-toluenesulfonic acid
0.3 mmol
mmol
ether
added
3 mL
mL
MeOH
100 mL
mL
MeOH
washings
100 mL
mL
template-free mesoporous Nb2O5*nH2O
dried
120 degC
degC
template-free mesoporous Nb2O5*nH2O
dried
24 hours
hours