Page 5 of 21
RSC Advances
DOI: 10.1039/C4RA12612B
55
Use of urea incorporates nitrogen into the oxygen lattice
confirmed by FTꢀIR and XPS. Band gap value is tuned from 2.82
to 3.20 eV by varying the fuel ratios. Photocatalytic activity
study indicates that nanocrystalline ordered N – doped ZnSb O
+
VB
ꢀ
N ꢀ doped ZnSb O + hν
h
+ e
Scheme (1)
CB ꢀꢀꢀꢀꢀ
2
6
+
VB
+
•
h
+ H O
H + OH
2
2
6
5
can effectively degrade RhB than disordered nanocrystalline and
ꢀ
•
ꢀ
e
+ O2
O2
60 ordered microcrystalline phase. The former generates more
amounts of hydroxyl radicals in aqueous solution in presence of
UV light. This work demonstrates that nanocrystalline N ꢀ doped
CB
•
ꢀ
•
RhB + O + OH
CO + H O + Mineral acids
2 2
2
•
ZnSb
O phases perform as better photocatalysts than the well
2 6
Determination of OH radical by Photoluminescence Spectra
known photocatalyst ZnSb O and are more promising materials
2
6
1
1
2
2
3
0
5
0
5
0
Most of the photocatalytic dye degradation process involves the 65 for photocatalytic applications.
reaction of holes with surface adsorbed water and hydroxyl
•
groups to produce reactive OH, hydroxyl radicals which are
Acknowledgements
mainly responsible for photodegradation. In order to estimate the
rate of formation of active OH hydroxyl radicals under UV light
irradiation, we employed terephthalic acid method in which
terephthalic acid (TA) readily reacts with OH radicals to produce
•
Authors thank VIT University for financial support and
encouragement. Dr.V.Thangadurai, Department of Chemistry,
University of Calgary, Canada is acknowledged for discussion.
•
highly fluorescent 2ꢀhydroxyterephthalic acid (TAOH), Fig.11(a)
which emits fluorescence around 426 nm on excitation at 312
70
Notes and references
5
4ꢀ56
a
nm absorption band.
Hence, by monitoring the fluorescence
Centre for Excellence in Nano Materials, Materials Chemistry
intensity of TAOH with irradiation time, we can estimate the
concentration of hydroxyl radicals. After UV irradiation, TA
suspension along with photocatalyst (microcrystalline ZnSb O ,
Division, School of Advanced Sciences, VIT University, Vellore - 632 014,
India. *Corresponding author: E-mail: rvijayaraghavan@vit.ac.in,
Tel: +91 0416 220 2460.
†Electronic Supplementary Information (ESI) available: See
DOI: 10.1039/b000000x/
2
6
75
nanocrystalline ordered and disordered N – doped ZnSb O )
2
6
shows increase in PL intensity with time indicating increasing
•
concentration of active OH radical species Fig.11 (b). It clearly
confirms that the efficiency of degradation of ZnSb O and Nꢀ
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2
6
doped ZnSb O correlates with the amounts of active
2
6
•
photogenerated OH hydroxyl radicals ESI (Table S5†) and it is
the highest for ordered nanocrystalline phase which exhibits the
maximum efficiency and fast kinetic for RhB degradation. The
3
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4
•
concentration of OH radicals linearly increases with increasing
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8
9
9
5
0
5
irradiation time ESI (Fig.S5 †) as expected and is maximum for
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6
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7
2
3
4
4
5
5
0
5
0
Total organic carbon (TOC) measurements
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9
. J. Jang and S.J Kim. Jpn. J. Appl. Phys., 2012, 51, 10NE23ꢀ1−
0NE23ꢀ4.
2
6
1
content with irradiation time reveals degradation (or)
mineralization by the photocatalyst. Mineralization is more rapid
for Nꢀdoped phases than for ZnSb O . RhB photodegradation
1
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2
6
occurs via two steps, first based on Nꢀdemethylation and then the
breaking of conjugated chromophores in RhB. RhB is converted
to smaller organic species and finally is mineralized to inorganic
1
2. A. Jamal, M.M. Rahman, S. B. Khan, M. Faisal , K. Akhtar, M. A.
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2
2
2
Stability of photocatalyst
1
8
The stability of nanocrystalline ordered Nꢀdoped ZnSb O6
2
05 15. S. Matsushima, T.Tanizaki, H.Nakamura, M.Nonaka and M.Arai,
photocatalyst was evaluated for four runs under the same
experimental conditions. The catalyst did not exhibit any
significant loss of activity between four cycles ESI (Fig. S6†)
revealing the good stability of the photocatalyst and hence, could
be recycled for photocatalytic degradation of dyes.
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Conclusion
2
Our work illustrates the application of combustion synthesis for
nanocrystalline antimonates in single phasic form in one step.
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