Hazardous o-toluidine mineralization by photocatalytic bismuth doped ZnO slurries

Article abstract of DOI:10.1039/c5cc02620b

Photocatalytic mineralization of o-toluidine in aqueous media under UV/solar irradiation was achieved by bare and bismuth doped zinc oxide nanoparticles. By adopting different analytical approaches a reaction mechanism is proposed, explaining the differences in photodetoxification performances.

Full text of DOI:10.1039/c5cc02620b

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Hazardous o-toluidine mineralization by photocatalytic
bismuth doped ZnO slurries
Cite this: DOI: 10.1039/x0xx00000x
a
a
a
a
a‡
G. Cappelletti, * V. Pifferi, S. Mostoni, L. Falciola, C. Di Bari, F.
a†
a
b
a
Spadavecchia, D. Meroni, E. Davoli and S. Ardizzone
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
www.rsc.org/
Photocatalytic mineralization of
o
-toluidine in aqueous (obtained by impregnation of the commercial one with Bi/Zn molar
ratios in the range 0.01ꢀ0.03) was performed with the aim of
media under UV/solar irradiation was achieved by bare and
bismuth doped zinc oxide nanoparticles. By adopting
different analytical approaches a reaction mechanism is
proposed, explaining the differences in photodetoxification
performances.
photodegrading oꢀtoluidine. This pollutant, an aromatic amine, has
been chosen because of its high toxicity and carcinogenic properties
23,24
for animals and humans
even at low levels of concentration. This
pollutant is present in the environment due to its use in industries as
precursors in the synthesis of azoꢀdyes, in the rubber industry and
pharmaceutical production. The present work is focused on the
Nowadays environmental pollution has become a very diffuse topic comparison between the doped and undoped materials, considering
for scientific research and several articles deal with the development the role of their morphological and structural properties in imposing
of innovative techniques and materials for treatments of both final photodegradation performances. Moreover, the complete
1
wastewaters and polluted air . In this context, photocatalysis has a mineralization of oꢀtoluidine requires an efficient treatment process,
great potential as green technique for the depollution of several because byproducts could be even harmful than the precursor one.
organic and inorganic toxic molecules.
The role of photocatalysis has to be related to the use of Previous works describe the removal of oꢀtoluidine particularly in
Further, a comparison between solar and UV irradiation was made.
2
5
semiconductor materials, especially TiO , which in recent years has the gas phase, as reported for example by An et al. , using films of
2
2
–5
assisted to a great expansion . Zinc oxide has been introduced in TiO under UV irradiation. Only a single study could be found in
2
heterogeneous photocatalytic treatments as an alternative material to literature about the removal of oꢀtoluidine in the liquid phase by zinc
10
TiO , thanks to its similar properties: high photosensitivity, nonꢀ oxide nanopowders , but to the authors best knowledge no
2
toxicity, low cost, competitive photocatalytic activity. In particular, investigations regarding the improvement obtained by the addition of
ZnO presents a band gap of 3.37 eV, with a red shift down to 3.2 eV bismuth or other dopants are present.
6,7
due to agglomeration of nanocrystallites into larger ones . Recently, All the ZnO nanopowders were finely characterized from
along with their traditional application fields (e.g. coatings, morphological (N2 adsorption isotherm, electron microscopy),
cosmetics), ZnO nanopowders have been used as photocatalysts optical (diffuse reflectance spectra) and structural (Xꢀray diffraction)
(
second only to TiO ) for environmental remediation both in points of view. The addition of bismuth provokes a dramatic loss of
2
8–11
nd
2
ꢀ1
aqueous and gas phases . Furthermore, some pioneering papers surface area (Table 1,
demonstrate the possibility to couple ZnO with TiO2
2
column) passing from 12 m g for the
1
2,13
2
ꢀ1
. The best commercial sample to values lower than 2 m g for all the doped
performances for nanosized ZnO can be reached either modifying ones
.
1
4
the strategy of synthesis or doping the material with different
species, including transition metals (Mn, Cu) but also rare earth
XRD
S
BET
<d>
(nm)
EDX Bi/Zn
Atomic %
Band Gap
(eV)
Sample
2
-1
15,16
(
m g )
elements (La, Er)
. Also bismuth has been tested as dopant,
proving its ability to shift the adsorption edge of ZnO (reducing the
band gap of the material) to lower energy, exploiting solar light and
ZnO
12
64
91
ꢀ
3.14
2.97
ZnO_0.01Bi
< 2
0.017
17–19
modifying the separation rate of photoinduced charge carriers
.
ZnO_0.02Bi
ZnO_0.03Bi
< 2
< 2
93
98
0.038
0.052
2.93
2.94
Bismuth is a great alternative to noble metals since it is cheaper,
nonꢀtoxic and environmentally friendly material; besides, it is also
able to favour trapping of photoꢀgenerated electrons, reducing the
20–22
Table 1. Surface area, crystallite size by XRD, Bi/Zn atomic ratio by EDX
measurements and band gap values
rate of recombination processes between electrons and holes
.
.
In the present paper a study on both bare (a commercial oxide
available by Sigma Aldrich) and bismuth doped ZnO nanopowders
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All the samples show Xꢀray diffraction peaks that can be indexed (Fig. S6). In all cases production of 2ꢀhydroxybenzaldehyde
to hexagonal wurztite structural ZnO (Figure S1), and match well (OHꢀBzH m/z 123, at 5.0 min RT, Fig. 2b,e and at 4.4 min RT,
with standard hexagonal ZnO (a = 3.249 Å and c = 5.205 Å, Fig. S5d) is evident. For Biꢀdoped samples this compound was
JCPDS Card No. 005ꢀ0664). A segregate Bi O phase (bismite) is already present after 3 hours, whereas for bare ZnO this
2
3
appreciable by increasing the amount of dopant species. The degradation product appears only after 6 hours. Moreover, only
sharp and narrow diffraction peaks (Fig. S1) reveal that all the in the case of Biꢀdoped ZnO nanoparticles, ꢀnitrotoluene (NO2ꢀ
o
rd
crystallites are not extremely small (Table 1, 3 column). Tol, m/z 138) formation is observed after 3 hours (Fig. 2c),
Particularly, Z_comm shows high crystalline and ordered ZnO while, under these experimental conditions, it was undetectable
10
nanocrystals with a pseudoꢀhexagonal shape (Fig. S2a, TEM after 6 hours (Fig. 2f).
image); the Biꢀdoped nanopowders are more packed and
disordered forming compact agglomerates in which Biꢀenriched
wires are evidenced (Fig. S2b). Nevertheless, EDX maps show an
homogeneous bismuth distribution all over the impregnated
powders (Fig. S3d, STEM/EDX); besides the amount of dopant
(
Table 1, 4th column) is always comparable to the starting
concentration. Further, STEM/EDX line profile (Fig. S3e,h) of
ZnO_0.01Bi shows a higher Biꢀenrichment on the edges, which
seems to indicate a Bi loading instead of lattice doping.
Figure 1. % disappearance and mineralization of oꢀtoluidine (25 ppm) by
doped and bare ZnO.
All the samples were tested for
oꢀtoluidine photocatalytic
detoxification in slurry under UV irradiation (Jelosil HG 500 W,
ꢀ
2
λ = 280ꢀ400 nm, effective power density 57 mWcm ). Figure 1
shows the % disappearance (obtained by voltammetry, Figure S4)
and the relative mineralization (obtained by Total Organic
+
Figure 2. Extracted [M+H] ion chromatograms for ZnO_0.01Bi sample after
hours and at the end of photoreaction: (a,d) oꢀtoluidine, 108 m/z; (b,e) 2ꢀ
hydroxybenzaldehyde (OHꢀBzH), 123 m/z; (c,f) oꢀnitrotoluene (NO ꢀTol),
38 m/z.
3
2
Carbon, TOC analyses) of oꢀtoluidine as a function of reaction
1
time for both bare and Biꢀdoped samples. It is worth noting that
notwithstanding the lower disappearance efficiency of the doped
samples with respect to the bare one, the Biꢀdoped materials
seem to have similar mineralization performances. Moreover, in
the case of ZnO_0.01Bi a slight increase of mineralization
occurs. Even if the pure ZnO allows to reach the higher
Thus, on the basis of the identified byproducts, different
photodegradation pathways are proposed in the following scheme
(
Figure 3). Apart from the two paths (pathways 1,2, Figure 3)
1
0,25
already described in the recent literature
for commercial zinc
oxide, in the case of Bi doped samples a further reaction
mechanism (pathway 3, Figure 3) could be proposed to
corroborate the best mineralization performances (see Figure 1).
percentage of disappearance for the
of byproducts is formed with respect to the sample ZnO_0.01Bi;
instead, using the latter sample almost all the disappeared
toluidine is converted to carbon dioxide, with more benefits from
an environmental point of view. Thus, the gap between
oꢀtoluidine, a major quantity
o
ꢀ
In this case (pathway 3) oꢀtoluidine can be oxidized to NO ꢀtol
2
and successively the elimination of NO group occurs; then a ring
2
o
ꢀ
opening step yields to complete mineralization. Differently, both
toluidine removal and its final mineralization suggests the
occurrence of a complex kinetic pattern. So a more complete
picture of the possible byproducts can be drawn by exploiting
LC/MS analyses.
pathways
ꢀhydroxybenzaldehyde which, according to the literature
a difficult step to overcome for the following oxidation.
In the case of the undoped powders the formation of the dimer
justifies the high degree of ꢀtoluidine disappearance not
followed by its mineralization. Actually, from the
1
and
2
require
the
formation
of
, is
2
7,28
2
HPLCꢀMS chromatograms of degradation products are shown in
Fig. 2. Ions are formed by electrospray ionization (ESI) and
o
+
29
appear as protonated ions, [M+H] . Results show that, using both
electrochemical point of view, the dimer is undetectable
bare and doped ZnO,
oꢀtoluidine (m/z 108, 5.5 min RT, Figure
because the NH electroactive group is substituted with a double
2
2
a,d and 4.8 min retention time (RT) Figure S5a,c) is partially
N=N.
degraded. In the case of bare ZnO sample, a new peak, at 5.33
min retention time (Figure S5c) is observed. A possible structure
assignment is a dimer product, through a azo N=N bond, as
In order to explain the improvement in mineralization of
ZnO_0.01Bi, transient time constant (τ) values have been
ꢀ
+
30,31
evaluated to assess the e /h recombination rate
under UV
is
2
6
already reported in literature . High resolution experiments,
performed on a LTQ XL Orbitrap MS mass spectrometer
irradiation; for the doped ZnO_0.01Bi sample (Fig. S7)
τ
slightly better (7 ± 1 s) than that of the commercial one (4 ± 1 s),
evidencing a better charge separation efficiency, justifying the
photocatalytic results.
(
Thermo Fisher), operated at 50.00 resolution, seem to confirm
this hypothesis with a < 3 ppm mass accuracy assignment error
2
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DOI: 10.1039/C5CC02620B
towards the sought pathway 3, completely eliminating noxious
intermediates.
We thank Dr. Marcello Marelli from CNRꢀISTM/ISTeM for
TEM measurement.
Notes and references
a
Dipartimento di Chimica, Università degli Studi di Milano, via Golgi
1
9, 20133, Milano, Italy, Fax: +390250314228; Tel: +390250314228;
eꢀmail: giuseppe.cappelletti@unimi.it.
b
IRCCS Istituto di Ricerche Farmacologiche "Mario Negri", Via La
Masa 19, 20156, Milano, Italy.
‡
Present Address: Istituto de Catalisis y Petroleoquimica, Consejo
Superior de Investigaciones Cientificas, C/ Marie Curie 2, L10, 28049
Madrid, Spain.
†
Present Address: Eni S.p.A ꢀ Refining & Marketing Division, San
Donato Milanese Research Center, Via F. Maritano 26, Iꢀ20097 San
Donato Milanese (MI), Italy.
Electronic Supplementary Information (ESI) available: Impregnation
method. Morphological and structural characterizations. Degradation
experiments.
Oxidation
intermediate
products.
Photocurrent
measurements. Optical properties. See DOI: 10.1039/c000000x/
1
A. R. Ribeiro, O. C. Nunes, M. F. R. Pereira and A. M. T. Silva,
Environ. Int., 2015, 75, 33–51.
C.ꢀS. Kuo, C.ꢀF. Lin and P.ꢀK. A. Hong, Water Res., 2015, 74, 1–9.
M. A. Rauf, M. A. Meetani and S. Hisaindee, Desalination, 2011, 276,
Figure 3. Three main proposed mechanisms for the photocatalytic
removal of ꢀtoluidine in aqueous media.
o
2
3
1
3–27.
%
Disappearance
% Mineralization
(TOC)
4
5
6
S. Ardizzone, G. Cappelletti, D. Meroni and F. Spadavecchia, Chem.
Commun. (Camb)., 2011, 47, 2640–2642.
G. Cappelletti, S. Ardizzone, C. L. Bianchi, S. Gialanella, A. Naldoni, C.
Pirola and V. Ragaini, Nanoscale Res. Lett., 2009, 4, 97–105.
J. I. Pankove, Optical processes in semiconductors, PrenticeꢀHall, New
York, Dover., 1975.
Sample
ZnO
ZnO_0.01Bi
(LSV)
UV
74
26
Solar
UV
Solar
56
31
23
6
29
21
7
8
R. Udayabhaskar and B. Karthikeyan, J. Appl. Phys., 2014, 116, 094310.
M. Pudukudy and Z. Yaakob, Superlattices Microstruct., 2013, 63, 47–
Table 2. Comparison of photocatalytic performances of commercial and
ZnO_0.01Bi in terms of percentage of removal/ mineralization passing from
UV to solar light at the end of the photocatalytic treatment (360 min).
5
7.
N. Sobana and M. Swaminathan, Sep. Purif. Technol., 2007, 56, 101–
07.
9
1
Besides, interesting results are also obtained by substituting UV 10 V. Pifferi, G. Cappelletti, S. Ardizzone, L. Falciola, C. Di Bari, F.
Spadavecchia, D. Meroni, A. Carrà, G. Cerrato, S. Morandi and E.
Davoli, Appl. Catal. B Environ., 2014.
light with solar radiation source (Lot oriel, effective power
density: 1 mWcm λ = 280ꢀ400 nm; 14 mWcm λ = 400ꢀ800
nm). Table 2 reports both the disappearance and mineralization
percentages of the oꢀtoluidine in the case of commercial ZnO and
ZnO_0.01Bi (the best sample under UV). The presence of the
bismuth dopant limits the expected lowering of both degradation
ꢀ2
ꢀ2
1
1
1
2
V. Pifferi, G. Cappelletti, C. Di Bari, D. Meroni, F. Spadavecchia and L.
Falciola, Electrochim. Acta, 2014, 146, 403–410.
G. Marci, V. Augugliaro, M. J. LopezꢀMunoz, C. Martin, L. Palmisano,
V. Rives, M. Schiavello, R. J. D. Tilley and A. M. Venezia, J. Phys.
Chem. B, 2001, 105, 1026–1032.
and mineralization with respect to the undoped sample passing 13 G. Marci, V. Augugliaro, J. Lo, L. Palmisano, V. Rives, M. Schiavello,
from higher to lower irradiation energy. Notwithstanding the not
yet optimized photocatalytic performances of the doped sample
R. J. D. Tilley and A. M. Venezia, J. Phys. Chem. B, 2001, 105, 1033–
040.
R. Saravanan, V. K. Gupta, V. Narayanan and A. Stephen, J. Mol. Liq.,
013, 181, 133–141.
J. C. Sin, S. M. Lam, K. T. Lee and A. R. Mohamed, Ceram. Int., 2014,
0, 5431–5440.
1
1
1
1
4
5
6
(
Table 2), the removal of the oꢀtoluidine molecule almost
2
corresponds to the final mineralization, proving that only small
amounts of noxious byproducts are present at the end of the
reaction (after 6h, Figure 2).
4
R. Zamiri, A. F. Lemos, A. Reblo, H. A. Ahangar and J. M. F. Ferreira,
Ceram. Int., 2014, 40, 523–529.
th
Table 1 (5 column) reports the bandꢀgap values obtained by
32
Kubelka–Munk method by elaboration of DR curves in terms of 17 S. Balachandran and M. Swaminathan, J. Phys. Chem. C, 2012, 116,
relative transformed reflectance vs. the photon energy (Figure
S8). The lowering of the bang gap for the doped samples
confirms the shift of the absorption edge towards the visible
region, guaranteeing the best mineralization under solar light.
26306–26312.
1
1
2
8
9
0
V. L. Chandraboss, L. Natanapatham, B. Karthikeyan, J.
Kamalakkannan, S. Prabha and S. Senthilvelan, Mater. Res. Bull., 2013,
4
8, 3707–3712.
A. Senthilraja, B. Subash, P. Dhatshanamurthi, M. Swaminathan and M.
Shanthi, Spectrochim. Acta Part A Mol. Biomol. Spectrosc., 2015, 138,
The present investigation has paved the way for tailoring new
zinc oxide materials doped with bismuth for the degradation of
toxic emerging pollutants with enhanced performances. Further
3
1–37.
S. Sajjad, S. A K. Leghari, F. Chen and J. Zhang, Chem. - A Eur. J.,
2010, 16, 13795–13804.
studies are required to enhance the surface area of the doped 21 Z. Bian, J. Zhu, S. Wang, Y. Cao, X. Qian and H. Li, J. Phys. Chem. C,
2
008, 112, 6258–6262.
nanoparticles, increasing the pollutants adsorption, and
concomitantly to design new materials capable of addressing
2
2
D. Meroni, V. Pifferi, B. Sironi, G. Cappelletti, L. Falciola, G. Cerrato
and S. Ardizzone, J. Nanoparticle Res., 2012, 14, 1086.
This journal is © The Royal Society of Chemistry 2012
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2
2
2
2
2
2
2
3
3
4
5
6
7
8
9
0
K. Gaber, U. A. Harréus, C. Matthias, N. H. Kleinsasser and E. Richter,
Toxicology, 2007, 229, 157–164.
L. Lüersen, T. Wellner, H. M. Koch, J. Angerer, H. Drexler and G.
Korinth, Arch. Toxicol., 2006, 80, 644–646.
T. An, L. Sun, G. Li and S. Wan, J. Mol. Catal. A Chem., 2010, 333,
1
28–135.
Y. Takeda, S. Okumura and S. Minakata, Angew. Chemie - Int. Ed.,
012, 51, 7804–7808.
2
F. J. Benitez, J. Beltran−Heredia, T. Gonzalez and F. Real, J. Environ.
Sci. Heal. Part A Environ. Sci. Eng. Toxicol., 1997, 32, 2599–2612.
S. Ardizzone, C. L. Bianchi, G. Cappelletti, A. Naldoni and C. Pirola,
Environ. Sci. Technol., 2008, 42, 6671–6676.
L. Falciola, V. Pifferi and E. Mascheroni, Electroanalysis, 2012, 24,
7
67–775.
R. Dholam, N. Patel, A. Santini and A. Miotello, Int. J. Hydrogen
Energy, 2010, 35, 9581–9590.
3
3
1
2
D. Tafalla, J. Electrochem. Soc., 1990, 137, 1810.
D. Meroni, S. Ardizzone, G. Cappelletti, C. Oliva, M. Ceotto, D.
Poelman and H. Poelman, Catal. Today, 2011, 161, 169–174.
4
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