Supporting Information
Highly efficient Photodegradation of Organic Pollutants Assisted
by Sonoluminescence
Anna V. Volkova 1, Silke Nemeth 2, Ekaterina V. Skorb 3, Daria V. Andreeva*2
Analysis of degradation products
UV-vis spectra evaluation
The UV-vis spectra of the sonicated dye - photocatalyst mixtures demonstrated the
hypsochromic shift of the DB71 absorbance maximum to 560 - 575 nm with sonication time.
The shift of max on the spectra depends on the degradation time and the pretreatment of the
photocatalyst. In presence of 0.2 g L-1 stirred titania particles the shift of max value from 584
nm to 565 nm was observed in 60 min of sonication. At the 0.5 g L-1 titania the shift of max was
registered in 40-min sonication. At 1.0 g L-1 titania - in 25 min. The max was at 570 nm and
575 nm, correspondingly. In presence of the pre-sonicated titania max shifts immediately to 575
nm. In this case max did not depend on the catalyst concentration. After longer sonication time
max shifts to 570 - 565 nm. This slight shift can be caused by formation of colored intermediates
due to hydroxylation of aromatic rings of DB71. As pre-sonication of the catalyst aqueous
suspension along with particle dispersion might activate the surface of the catalyst due to ROS,
eCB, hVB+ formation pretreatment step can lead to dye decomposition even before beginning of
the degradation process.
RP-HPLC and HPLC-MC analysis
In order to explore the DB71 degradation process and control of the appearance of intermediate
products the RP-HPLC analysis for some samples at different sonication times, dye and catalyst
concentrations was performed. Only one peak at retention time 15.1 min was detected for DB71
before degradation. This peak diminishes and then disappears under particular conditions with
the degradation time due to dye decomposition. Also, we observed an appearance of new peaks
corresponding to intermediates production. For instance, the sonicated mixture at DB71
concentration 5×10-5 M and catalyst content 1g L-1 (Figure S1A) after 15 min contains along
with parent dye at least four new compounds. The peak at 9.6 min was detected as phenol. After
60 min at the complete declaration of the sonicated dispersion there is no peak corresponding
to DB71 (Figure S1B) and eleven peaks responsible for formed intermediates. The peak 1 (6.5
min) and peak 2 (7.6 min) were detected as hydroquinone and pyrocatechol, correspondingly.
Other used standards were not determined as DB71 decomposition products. For all studied
dye-titania dispersions the percentage in comparison to other products and concentration of
intermediates at 9.6 min (phenol) and 10.7 min increase with sonication time. We confirmed
that complete decoloration of solution doesn’t mean complete mineralization requiring longer
sonication time.
The HPLC-MS analysis of degradation products confirmed higher susceptibility of azo bond
than aromatic rings to ROS attack. The obtained data demonstrate the number of intermediates
for every sample after 40 min sonication and the some molecular ions giving the most intensive
peaks are represented in Table S1. It is seen that these ions can contain only one naphthalene
or benzene ring according to their molecular weights. The most intensive peaks were detected
for m/z ([M-H]+) 149 and 186. The m/z 149 is a characteristic mass for ion of phthalic anhydride
that possibly can be formed during sonodegradation of DB71.
The m/z 186 is obviously correspond to various products because the compounds with the same
molecular weight have different retention times and mass spectra. According to analysis of the
obtained results all these products contain most likely only one benzene ring and some of them
can be isomers of phthalates because the most abundant ion m/z 149 is present in their mass
spectra. The molecular ion weight m/z 183 is possibly corresponding to 3-hydroxyphthalicacid.
27.5
mV
Detector A:Ex:270nm,Em:310nm
A
25.0
22.5
20.0
17.5
15.0
12.5
10.0
7.5
5.0
4
2.5
0.0
-2.5
-5.0
-7.5
-10.0
0.0
2.5
5.0
7.5
10.0
12.5
15.0
17.5
min
mV
Detector A:Ex:270nm,Em:310nm
B
5
500
400
300
4
200
2.5
5.0
7.5
10.0
15.0
11
10
8
7
12.5
9
0
0.0
6
2
1
3
100
17.5
20.0
22.5
min
Figure S1. RP-HPLC chromatograms with flourometric detection for samples at [DB71] =
5×10-5 M, [TiO2] = 1 g L-1 and various sonication times: A – 15 min, B – 60 min (sample 1).
Table S1. Molecular ions [M-H]+ of some DB71 degradation products detected by HPLCMS.
Sample 1
DB71] = 5×10-5 M [TiO2] =
1 g L-1
60 min
retention
m/z
time, min
9.3
186
20.7
149
Sample 2
[DB71] = 2.5×10-5 M
[TiO2] = 0.5 g L-1
60 min
retention
m/z
time, min
10.8
186
13.5
225
19.2
235
20.7
149
Characterization of TiO2 particles
Sample 3
[DB71] = 5×10-5 M [TiO2]
= 0.5 g L-1
40 min
retention
m/z
time, min
2
195
10.1
186
19.2
235
20.7
149
Sample 4
[DB71] = 1×10-4 M [TiO2]
= 0.5 g L-1
40 min
retention
m/z
time, min
8
183
10.1
186
12.6
235
20.7
149
The morphology and the size of the titania particles were characterized by transmission (TEM, Zeiss
EM922 Omega, EFTEM operating at 200 kV), scanning (SEM, LEO 1530 FE-SEM, Zeiss) electron
microscopy, and dynamic light scattering (DLS, Zetasizer Nano ZS, Malvern Instruments). The
powder X-ray diffraction (PXRD) patterns were collected in the θ-θ mode using a Stoe STADI P Xray transmission diffractometer: Cu-anode, K 1-irradiation, room temperature, 2θ =5-90°. The
surface area was measured by the BET (Brunauer-Emmett-Teller) method using krypton at 77 K on a
vacuum gas sorption Autosorb-1 and Autosorb Degasser apparatus (Quantachrom).
All the peaks in the XRD pattern of synthesized TiO2 correspond to the anatase phase (Figure S2).
Intensity (a.u.)
anatase
10
20
30
40
50
60
70
80
90
2 °)
Figure S2. XRD pattern of the TiO2 particles.
BET-specific surface area was determined as 255 m2 g-1. SEM and TEM images demonstrate (Figure
S3) spindle-shaped titania particles with average sizes 6 - 10 nm wide and 15 - 20 nm long. According
to DLS data the average size of majority of the particles calculated on the assumption their spherical
shape is 15 nm (Figure S4) that corresponds to SEM and TEM data.
6 nm
A
B
20 nm
50 nm
Figure S3. SEM (A) and TEM (B) images of the TiO2 particles.
Number (%)
15.3 (90.5%)
38.3 (9.5%)
Size (d, nm)
Figure S4. Size distribution by number of the TiO2 particles
50 nm