Sensitizing effect of bio-based chemicals from urban wastes on the photodegradation of azo-dyes

Article abstract of DOI:10.1016/j.jphotochem.2009.11.020

To promote bio-based products for the industry, six bio-organic substances (cHALi) isolated from yard trimmings (green) and food (humid) urban residues aged under aerobic digestion for 0-60 days were investigated for their potential to perform as sensitizers for azo-dyes photodegradation. Ethylorange (EO) was used as probe molecule at 5mgL^-1 starting concentration and irradiated in a closed Pyrex cell with a Xenon (1500W) lamp and a cut-off filter for wavelengths below 340nm or in a cylindrical photochemical reactor equipped with a 125W medium pressure Hg lamp. The cHALi/EO ratio in the starting EO solution varied in the 0-200 (w/w) range. The % dye abatement was found a function of the irradiation time, of the type of cHALi substance and of the cHALi/EO ratio. The best results were achieved with cHALi isolated after 7 days biomass aerobic digestion. Total dye abatement was achieved within relatively short few hours. A progressive dye mineralization was observed under the same experimental conditions. On the contrary no significant degradation was evident for the cHALi substances within the same irradiation time. Several hydroxylated azo compounds were identified as likely responsible of residual color after total EO abatement. The results, coupled to the previously reported good performance of the same cHALi substances as auxiliaries for textile dyeing, augur well for the development of both efficient and environmentally friendly textile dyeing processes.

Full text of DOI:10.1016/j.jphotochem.2009.11.020

Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 224–231
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Sensitizing effect of bio-based chemicals from urban wastes on the
photodegradation of azo-dyes
Alessandra Bianco Prevota,∗, Debora Fabbria, Edmondo Pramauroa, Claudio Baiocchia,
Claudio Medanaa, Enzo Montonerib, Vittorio Boffab
a Dipartimento di Chimica Analitica, Università di Torino, Via Giuria 5, 10125 Torino, Italy
b Dipartimento di Chimica Generale e Chimica Organica, Università di Torino, C.so Massimo d’Azeglio 48, 10125 Torino, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 21 July 2009
Received in revised form 8 October 2009
Accepted 26 November 2009
Available online 2 December 2009
To promote bio-based products for the industry, six bio-organic substances (cHALi) isolated from yard
trimmings (green) and food (humid) urban residues aged under aerobic digestion for 0–60 days were
investigated for their potential to perform as sensitizers for azo-dyes photodegradation. Ethylorange
(EO) was used as probe molecule at 5 mg L−1 starting concentration and irradiated in a closed Pyrex® cell
with a Xenon (1500 W) lamp and a cut-off filter for wavelengths below 340 nm or in a cylindrical photo-
chemical reactor equipped with a 125 W medium pressure Hg lamp. The cHALi/EO ratio in the starting
EO solution varied in the 0–200 (w/w) range. The % dye abatement was found a function of the irradiation
time, of the type of cHALi substance and of the cHALi/EO ratio. The best results were achieved with cHALi
isolated after 7 days biomass aerobic digestion. Total dye abatement was achieved within relatively short
few hours. A progressive dye mineralization was observed under the same experimental conditions. On
the contrary no significant degradation was evident for the cHALi substances within the same irradia-
tion time. Several hydroxylated azo compounds were identified as likely responsible of residual color
after total EO abatement. The results, coupled to the previously reported good performance of the same
cHALi substances as auxiliaries for textile dyeing, augur well for the development of both efficient and
environmentally friendly textile dyeing processes.
Keywords:
Azo-dye
Photodegradation
Sensitizers
Urban refuses
Dyeing baths
Effluents remediation
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
both the dye adsorption by the fiber and the excess dye removal
from the exhaust dyeing bath, thus improving both the production
In the global frame of waste management and sustainable devel-
opment, urban wastes have been proposed as possible source of
chemicals to recycle for industrial uses at commercial level [1–4].
They look nowadays rather attractive for several reasons. As a result
of the increased production due to population urbanization, urban
wastes are concentrated in confined areas by municipal collection.
In addition, depending on the type of treatment and on composi-
tion, they may provide high yields of a large variety of bio-organic
substances (BOS) fitting a wide range of uses. One very promising
application has been shown in textile dyeing. Several BOS isolated
from green and/or food urban wastes have been demonstrated to
be efficient auxiliaries for dyeing cellulose acetate fabric [4]. For
one BOS, isolated from urban yard trimming wastes, an additional
property has also been reported [3], i.e., the capacity to acceler-
ate the photodegradation of the azo-dye ethylorange (EO). These
results allow predicting a rather unique opportunity for the whole
textile dyeing process, i.e., to use one same substance to optimize
and waste management processes.
Actually the textile industry uses more than three thousand
dyes, and it is estimated that about 15% of the world dyes pro-
duction is lost in the environment during the dyeing process [5,6].
Azo-dyes constitute about 50% of the total dye consumption; their
environmental impact is not only related to color, but also to reduc-
tion producing carcinogenic aromatic amines [7]. This poses the
problem of their removal from industrial wastes or polluted natural
water streams.
Photosensitizing properties have already been reported for BOS
present in natural waters and soil [8–14] or isolated from mix-
tures of yard trimmings and/or sewage sludge undergoing aerobic
biodegradation [15,16]. The photosensitizing properties of these
substances have been studied using mostly phenol molecules or
pesticide substances as probe substrates.
The present work concerns the EO photosensitized degrada-
tion in the presence of six BOS isolated from urban refuses which
hereinafter will be referred to by the abbreviation cHALi, i = 2–7:
cHAL2, cHAL3 and cHAL4 isolated from urban yard trimmings
(green wastes) and cHAL5, cHAL6 and cHAL7 isolated from a 1:1
(w/w) mix of food (humid) and green residues at the start of the aer-
∗
Corresponding author. Tel.: +39 0116707634; fax: +39 0116707615.
E-mail address: alessandra.biancoprevot@unito.it (A. Bianco Prevot).
1010-6030/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2009.11.020

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225
obic digestion process (cHAL2 and cHAL5), and after 7 days (cHAL3
and cHAL6) and 60 days (cHAL4 and cHAL7) aging. Relatively to
previous work performed with cHAL2 only [3], the investigation of
the above six BOS addresses several issues: i.e., assessing chemi-
cal structure and photosensitizing properties as a function of the
nature and treatment type of the product source, and the fate of
photodegraded EO. These issues were rather challenging for sev-
eral reasons. First, it should be considered that the investigated
cHALi substances are new materials of biological origin with quite
complex chemical composition for which several molecular mod-
els have been reported [1,23]. Secondly, the chemical variability
of the urban refuses may prospect a desirable availability of mul-
tiple bioproducts, but also poses a major concern, regarding the
capacity to yield bio-based products with constant performance
specifications. Thirdly, it should be considered that the real cHALi
performance to assist EO photodegradation should be rated on
the basis of fate of both the dye and the photosensitizer. This
requirement, considering the chemical structure complexity of the
latter and the multiplicity of degradation products which might
be expected to arise from both the dye and the photosensitizer,
poses rather demanding analytical problems to face. In particular
we focused our attention on the kinetics of EO degradation and on
the identification of the intermediates formed in the initial degra-
dation steps. High performance liquid chromatography coupled to
high resolution mass spectrometry (HPLC–HRMS) was applied as a
powerful tool.
Finally, the capacity of the cHALi to yield micellar aggregates
[1] in water was also a matter of concern in this work. Indeed, the
presence of aggregates could give rise to EO partitioning between
the bulk water and the more hydrophobic micellar region, and this
could influence the EO photodegradation kinetics and yield [17].
Thus, a study of the molecular aggregation of the cHALi was neces-
sary to define the most suitable experimental concentration range
to be investigated for preliminary evaluation of their photosensi-
tizing properties.
For the above reasons, the issues of this work cannot be
exhaustively dealt with in just one paper. The present manuscript
therefore does not claim to provide specific problem solutions,
but is rather meant as ground for prospecting the potential of
urban refuses to become exploitable source of photosensitizing
bio-substances.
tion of the functional groups was accomplished by potentiometric
titration and by solid-state 13C NMR spectroscopy as previously
reported [1]. The functional groups composition reported as C ratios
relative to total unsaturated and aromatic C (Ct) in Table 1 was cal-
culated from the above NMR signals area ratios, and from the total
C and N microanalytical and acid groups concentration reported
as supporting data in Appendix A under the assumption that the
total N was present as amine or amide N and that all organic C
in the sample was accounted for by the above NMR signals. Sur-
face tension (ꢀ) measurements of aqueous solutions containing
the sample of the investigate substances at variable concentrations
(Cs = 0.005–3 g L−1) were carried out at 25 ◦C and pH 7 with a Kruss
K100 automatic tensiometer and the critical micellar concentration
(cmc) was calculated from ꢀ–Cs plots as previously reported [2].
2.3. Ethylorange irradiation experiments
A stock 1 g L−1 cHALi aqueous solutions was prepared by taking
up solid cHALi with MilliQ® water at 250–200 (v/w) ratio, stir-
ring 1 h, then adding aliquots 0.2 M NaOH to keep pH in the 8–9
range until the complete solid dissolution occurred. The solution
was finally filtered through a 0.45 ␮m Millex–HA membrane (Mil-
lipore) and brought to the required volume with MilliQ® water.
The stock solution was kept frozen before use. Aliquots of the stock
solution were used to obtain 5 g L−1 EO solutions containing vari-
able amounts of cHALi. The degradation trials were performed by
irradiating 5 mL cHALi–EO aqueous solution in a closed Pyrex®
cell with a Xenon (1500 W) lamp (Solarbox) and a cut-off filter for
wavelengths below 340 nm. Experiments were also performed on
500 mL cHALi–EO aqueous solutions in a cylindrical photochemical
reactor (Helios-Italquartz, Milan), equipped with a 125 W medium
pressure Hg lamp. The system was kept under continuous stirring
in order to avoid the formation of concentration gradient and air
or nitrogen was bubbled to saturate the solutions with the gases.
Cold water circulating in the jacket surrounding the lamp kept the
temperature within the reactor at 20 ◦C; a Pyrex® glass jacket act-
ing as a cut-off filter for wavelengths below 300 nm was employed,
in order to avoid any possible contribution coming from direct dye
photolysis.
2.4. Analyses of the irradiated solutions
The dye abatement was calculated from the starting EO concen-
tration (Co) and the found EO concentration (Cir) after irradiation.
The Cir value was determined by HPLC–DAD–UV–vis (Surveyor,
Thermo Scientific) analysis under the experimental conditions
reported in Appendix A. The analysis of the EO photodegrada-
tion products was performed by HPLC–MS. A Dionex Ultimate
3000 HPLC coupled with a Surveyor PDA UV detector and a LTQ
Orbitrap mass spectrometer (Thermo Scientific) equipped with an
atmospheric pressure interface and an ESI ion source was used;
N2 was used as sheath and auxiliary gas. The source voltage was
set to 3.1 kV. The heated capillary temperature was maintained at
275 ◦C. The main tuning parameters adopted for ESI source were:
capillary voltage −34.00 V, tube lens offset −68.57 V. Mass accu-
racy of recorded ions (versus calculated) was 15 ppm (without
internal calibration). The chromatographic separations were per-
formed on a Phenomenex Synergi C18 column, 150 mm × 2.0 mm,
3 ␮m particle size. Injection volume was 20 ␮L and flow rate
200 ␮L/min. Gradient mobile phase composition was adopted: ace-
tonitrile/ammonium acetate 0.1 mM 5/95 to 100/0 in 30 min. Total
organic carbon (TOC) in the irradiated solutions was also measured,
by means of Shimadzu TOC-5000 analyzer (catalytic oxidation on Pt
at 680 ◦C), which was previously calibrated using potassium phtha-
late standard solutions. Color bleaching in the irradiated solutions
was quantified by means of a double beam CARY 100 SCAN-VARIAN,
2. Materials and methods
2.1. Bioproducts and reagents
Ethylorange, i.e., 4-(4-diethylaminophenylazo)benzene sodium
sulfonate, 69% HNO3 and 98% CH3COONH4 by Fluka, 99% NaOH and
99% KNO3 by Merck, 99% Na2SO4 and 99.7% NaHCO3 by Aldrich,
analytical grade CH3CN by Scharlau and MilliQ® reagent grade
ultrapure water were used throughout this work as received, unless
otherwise indicated. The cHALi (i = 2–7) substances investigated in
this work were obtained from ground green wastes or from 1:1
(w/w) food and green residues mix collected in the province of
Torino, Italy. Once collected and transported in a municipal waste
treatment plant, the chopped green residues, eventually mixed
with the mechanically selected (Ø < 12 mm) humid wastes, were
aged under aerobic conditions for 0–60 days, sieved through a
mechanic grid (Ø < 10 mm) and used for cHALi extraction. The cHALi
isolation was performed as previously reported [2].
2.2. Chemical and physical characterization of cHALi substances
C,H,N microanalytical data were obtained with a C. Erba
(Rodano, Milan, Italy) NA-2100 elemental analyzer. The determina-

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Table 1
Ratios for aliphatic C (Cal), methoxy C (OMe), amine C (NC), O-alkyl C (OR), diO-alkyl C (ROCOR), aromatic and/or olefinic C (C C) excluding PhO, phenol (PhOH), phenyl
ether (PhOX, X = R, Ar), carboxylic acid C (COOH) amide C (CON) and keto C, relative to the sum (Ct) of C C, PhOH and PhOX C.
Cal
OMe
NC
OR
ROCOR
C
C
PhOH
PhOX
COOH
CON
C O
cHAL2
cHAL3
cHAL4
cHAL5
cHAL6
cHAL7
3.05
2.54
2.25
4.90
4.50
2.96
0.13
0.20
0.15
0.23
0.00
0.08
0.33
0.22
0.26
0.50
0.56
0.43
0.84
0.78
0.71
1.12
0.90
0.68
0.26
0.27
0.26
0.21
0.66
0.16
0.64
0.70
0.69
0.68
0.61
0.72
0.12
0.19
0.22
0.29
0.39
0.17
0.24
0.11
0.09
0.03
0.00
0.11
0.37
0.34
0.35
0.55
0.49
0.43
0.07
0.14
0.07
0.07
0.05
0.09
0.18
0.20
0.12
0.30
0.19
0.24
UV–vis spectrophotometer by measuring the absorbance at 467 nm
where the EO irradiated solution exhibits the maximum absorptiv-
ity. The absorbance was then corrected for the cHALi contribution.
3.2. Irradiation experiments and % dye abatement
Based on the cmc data, the upper limit of 1 g L−1 cHALi concen-
tration was established in order to avoid or limit the presence of
cHALi aggregates and their potential effect on EO photodegrada-
tion kinetics and yield [17]. A preliminary ranking of the isolated
cHALi substances has been considered on the basis of their sen-
sitizing effect on the photodegradation of EO. The experiments
were performed irradiating the samples in closed cells for 5 h.
3. Results and discussion
3.1. Chemical nature of cHALi and molecular association in
solution
Sample solutions were prepared by dissolving EO at 5 mg L−1
,
The chemical composition of the investigated cHALi substances
is reported in Table 1. It appears that on basis of the Cal, OR, NC
and COOH parameters the chemical nature of the cHALi substances
is significantly affected by both the type and aging of the sourcing
biomass waste. Specifically, the substances isolated from food and
green residues mix (cHAL5–7) seem to have higher Cal, NC and
COOH content relatively to aromatic C than those isolated from
sole green residues (cHAL2–4). This result suggest that the cHAL5–7
substances have a higher content of residual fatty acid and protein
moieties formed by the microbial degradation of the starting bio-
organic matter. Also, for each group of substances, it seems that
increasing the aging time of the sourcing waste causes a decrease
of the Cal, OR and COOH relative C ratio. These changes may be
consistent with the relatively higher sensitivity of aliphatic C to
microbial degradation which has been already reported for other
cases [1]. The data confirm the variability of chemical composition
on the substances source which has already been observed also for
other similar BOS [1,18,19] present in soil, water and city refuses
from other locations.
either alone or in the presence of 100 mg L−1 cHALi (i = 2–7). Under
these conditions, the neat EO solution exhibited a negligible 1.8%
dye abatement, whereas rather high dye abatement rates were
observed in the presence of cHALi (Fig. 1), with the cHAL5–7
substances isolated from the mix of green and food residues per-
forming better than the cHAL2–4 substances isolated from sole
green residues. This fact seems to point out a significant mate-
rial source effect on the catalytic performance of the above cHALi
substances for EO photodegradation. Moreover for each group of
substances isolated from the same type of source waste a peak
effect seems to be reached with the substances isolated from 7
days aged source materials, i.e., cHAL3 and cHAL6. The effect of the
source material aging is not as straightforward. Analogously to our
findings, two recent papers have reported on the photosensitizing
properties of BOS isolated from mixtures of yard trimmings, sewage
sludge, and/or animal manure and grapes residues, which were
collected after composting for 0–130 days [15,20]. The photode-
grading activity of such substances appeared to increase between
0 and 70 days composting and to remain quite constant for the next
further 60 days. Searching for possible structure–property relation-
ships, our data show a trend for % dye abatement to increase with
the relative phenol content in Table 1. The linear regression anal-
ysis performed over all data points, excluding the one for cHAL7
that was clearly deviating from the general trend, yields a regres-
The apparent critical micellar concentration (cmc) values for the
investigated substances (see Appendix A) were 0.73–0.77 g L−1 for
cHAL2–4 and 0.98–1.01 g L−1 for cHAL5–7. These appeared there-
fore relatively constant within each group of substances obtained
from the same source material, but changing significantly from one
group to the other (i.e., from cHAL2–4 to cHAL5–7).
Fig. 1. Dye abatement (%) of 5 mg L−1 EO solution in the presence of 100 mg L−1
cHALi after 5 h irradiation in Solarbox.
Fig. 2. Dye % abatement versus cHALi (i = 3 or 6)/EO (w/w) ratio after 3 h irradiation
of 5 mg L−1 EO solutions in Solarbox.

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227
Fig. 3. Dye % abatement and ln(Cir/Co) (Cir and Co = concentrations at time t > 0
and t = 0 respectively) versus irradiation time in Solarbox for 5 mg L−1 starting EO
solutions at 75 (w/w) cHALi (i = 3 or 6)/EO ratio.
sion coefficient of 0.95 and the empirical equation DA = 23.2 + 106
PhOH/Ct, with DA = % dye abatement. Consistently with previous
work [20] phenol functional groups are likely to have an active role
in the photosensitizing process, although other chemical structural
factors may also contribute to the cHALi performance. Regardless
of this empirical relationship, to verify the effect of the source
composition on the photosensitizing power of BOS, successive
experiments were performed with two cHALi selected from each
group based on their % dye abatement rather than on the phenol
content: i.e., cHAL3 and cHAL6, which showed the highest % dye
abatement within the products isolated from sole green wastes and
from the mix of green and humid refuses respectively.
Fig. 2 reports the results of experiments performed by irra-
diating for 3 h solutions containing 5 g L−1 EO in the presence
of 125–1000 mg L−1 cHAL3 or cHAL6. The results indicate that
cHAL6 performs significantly better than cHAL3 and that, for both
substances, the measured degradation yield increases with the
cHALi/EO (w/w) ratio, reaching nearly 100% at about 130 cHAL6/EO
(w/w) ratio.
Fig. 4. Color (open symbols) and dye (solid symbols) % abatement versus irradia-
tion time in closed cells operating with 5 mg L−1 starting EO solutions at 75 (w/w)
cHAL3/EO (lower plots) or cHAL6/EO (upper plots).
Fig. 3 reports the results of EO photodegradation experiments at
75 (w/w) cHALi (i = 3 or 6)/EO ratio as a function of irradiation time.
It may be observed that even at this low cHALi/EO ratio, nearly total
dye abatement is still reached within reasonably short 4 h time.
The data well fit in a first-order kinetic law as clearly shown by the
ln(Cir/Co)–time plot. The higher performance of cHAL6 relatively
to cHAL3 is confirmed throughout the investigated time range.
Analogous kinetics profiles were obtained using the photochem-
ical reactor; in comparison with the results obtained in Solarbox, a
slower abatement rate was observed. This difference is most likely
due to the different geometries and light source intensities present
in the two systems.
nitrogen bubbling in order to evaluate the effect of the atmosphere
on the degradation process. The results (reported in the Appendix
A) show a relevantly lower dye abatement rate in the presence of
pure N2 compared to air, as demonstrated by the calculated first-
order kinetic constants in Table 2. This fact suggests a possible
reaction mechanism involving reactive oxygenated species (ROS)
as already proposed for BOS present in soil and terrestrial waters
[13,21]. Analogously to the mechanism proposed for humic sub-
stances, the light absorption by cHALi may produce excited triplet
states that can in turn react with organic substrate by two main
mechanism: hydrogen-transfer and energy-transfer. The former
one could be proposed in our case; the presence of dissolved oxy-
gen should favor indeed the dye degradation since the generated
hydrogen atom can be transferred to the dissolved oxygen with the
Other experiments were performed with solutions containing
5 mg L−1 EO and 75 (w/w) cHALi (i = 3 or 6)/EO ratio which were
irradiated in the photochemical reactor under continuous air or
formation of various ROS such as •OH, 1O2, •O2 and H2O2 which
−
also contribute to the dye degradation. Experiments in the presence
of scavengers for 1O2, •OH would add useful information. These
offered scope for future research and were not included herewith,
since the specific investigation of the photodegradation mechanism
was beyond the scope of the present work.
Table 2
First-order kinetic constant (kobs) values for the photodegradation of EO in the
presence of cHAL3 and cHAL6 calculated from the data reported in Fig. 3 and in
Fig. 1S of the Appendix A.
Experimental conditions
kobs, min−1
cHAL3
cHAL6
3.3. Analyses of irradiated solutions
Solarbox
Photochemical reactor in air
Photochemical reactor in N2
0.45
0.09
0.03
0.59
0.13
0.08
In addition to the analysis of residual EO to determine the
% dye abatement reported above, other analyses for TOC, color

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Table 3
Products from EO photodegradation identified in cHALi (i = 3 or 6)/EO 7.5 (w/w) ratio
solutions after 1–2 h irradiation in Solarbox.
EA
m/z
tR (min)a
304.0747
17.5
Fig. 5. Products relative abundance versus retention time (min) and associated m/z
values for HPLC-ESI–HRMS analysis of EO solution irradiated for 1 h in the presence
of cHAL3 under the experimental conditions reported in Table 3.
abatement and EO intermediates identification were performed in
the attempt to trace the fate of the photodegraded dye. The TOC
measurements were designed in order to distinguish organic C
contributed by EO and its degradation products from the cHALi con-
tribution. Thus, parallel irradiation experiments were performed
for the EO–cHALi solutions and also for solutions containing cHALi
and no EO. The results showed no significant TOC depletion in the
solutions containing cHALi only. On the contrary, in the EO–cHALi
solutions, a progressive TOC depletion versus irradiation time was
observed, which was therefore assigned to the dye disappearance.
The TOC analyses in the EO–cHALi solutions where no dye was
detected after irradiation were consistent with 60% dye mineral-
ization.
320.0694
320.0945
16.5
12.0b
12.9c
Fig. 4 reports the results of the analyses for color bleaching eval-
uated by monitoring the solution absorbance at the wavelength
corresponding to the maximum of EO absorbance in the visible
region (ꢁ = 467 nm), next to the data for % dye abatement as a func-
tion of time for the solutions containing 5 mg L−1 starting EO at
75 (w/w) cHAL3/EO or cHAL6/EO irradiated in closed cells. It may
be observed that the color abatement increases parallel to the dye
abatement, but it is always less than expected on basis of the dye
abatement. Consistently with the TOC analyses, at nearly 100% dye
abatement residual color is still observed, suggesting the forma-
tion of dye degradation products retaining chromophore groups.
These products were therefore the likely source of the organic C left
over from the dye photodegradation. On the basis of these results
we further investigated the composition of the irradiated solutions
searching for possible dye degradation intermediates. Our primary
attention was devoted to sulfonated degradation products. These
compounds, being highly soluble and mobile in the aqueous envi-
ronmental compartments, could extend the potential pollution risk
to larger areas.
348.1006
13.3
16.0
17.9
20.3
a
Multiple retention time values for the same m/z ratio assigned to the presence
of isomers differing for the position of the OH functional group in the aromatic ring.
Due to the hydrophilic nature of the above sulfonated com-
b
pounds the HPLC–MSn technique was chosen as
a suitable
Assigned to compound I.
c
Assigned to compound II.
analytical approach. Liquid chromatography appears the best tech-
nique for direct analysis of polar compounds, requiring neither
derivatization nor complex extraction procedures. This separation
technique, coupled with the LTQ Orbitrap [22] high resolution mass
spectrometry (HRMS), affords powerful diagnostic identification

A. Bianco Prevot et al. / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 224–231
229
Fig. 6. ESI–HRMS spectra for product A in Fig. 5.
and characterization of degradation products as already proven
in metabolomic approach for the identification of transformation
products of small molecules [23].
tion in the presence of cHAL6. The electrospray ion source (ESI)
and the high resolution (HRMS) allowed by the LTQ Orbitrap mass
spectrometer used in this work (see Section 2) allow to distinguish
well between isomers having exactly the same m/z value, i.e., prod-
ucts A–D with 348.1006 m/z, and products differing for rather small
mass values, i.e., compound G with exactly 320.0694 m/z value
and compounds E and F with exactly 320.0945 m/z values. Fur-
ther structural assignments for products having exactly the same
m/z value may be obtained from the analysis of the fragmentation
pattern of the isolated neat compounds. Figs. 6–9 report the MS2
spectra and the corresponding fragmentation pattern of the single
A–D products isolated by HPLC. The structures, reported in each fig-
ure next to the parent peak with 348.1006 m/z, were assigned on
the following basis. For compounds A–C the presence of the ion at
In the present work several products were identified in the
cHALi (i = 3 or 6)/EO 7.5 (w/w) ratio solutions after 1–2 h irradiation
in Solarbox, as listed in Table 3 reporting HPLC retention times (tR),
mass to charge (m/z) ratios and chemical structures. Fig. 5 reports
the digital reconstruction of a typical HPLC profile obtained after
EO irradiation in the presence of cHAL3 by extracting from the total
ionic current the m/z 348, 320 and 304 signals. It may be observed
that several peaks corresponding to several chemically different
products are found having the same 348 (peaks A–D) or 320 (peaks
E–G) m/z, whereas only one product (peak H) having 304 m/z is
obtained. Analogous results were collected for EO photodegrada-
Fig. 7. ESI–HRMS spectra for product B in Fig. 5.

230
A. Bianco Prevot et al. / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 224–231
Fig. 8. ESI–HRMS spectra for product C in Fig. 5.
m/z = 156 (Figs. 6–8)−is compatible with the OH attack on the ring
not bearing the SO3 group. For compound A (Fig. 6), the struc-
ture attributed to the fragment at m/z = 262 is possible only if the
ring hydroxylation took place in meta position with respect to the
azo group. For compound B (Fig. 7) the species having m/z = 239,
260, 288 and 303 can arise only from the isomer bearing the OH
group in the ethyl chain. The structure of compound C with the
OH in ortho to the azo group is suggested by the presence of the
ion at m/z = 171 (Fig. 8), presumably formed from the hydrazo form
present in an azo-hydrazo tautomery. For compound D (Fig. 8) the
absence of the phenylsulfonic radical (m/z 156) and the presence
of the fragment at m/z 172, corresponding to the hydroxyphenyl-
sulfonic radical, allow one to suppose the introduction of the OH
group in the sulfonated ring.
The formation of different isomers differing for the position of
the OH groups can be easily explained taking into account that
radical reactions are usually not selective.
The key role of HRMS appeared for the structure assessment in
the case of intermediates having m/z = 320 (Fig. 5). For the com-
pound with 16.5 min tR, an exact m/z value of 320.0694 was found,
whereas for the compounds with 12.0 and 12.9 min tR the exact m/z
value was 320.0945. Based on these data two degradation paths
could be hypothesized: the attack on the alkyl chain and the con-
temporary ring hydroxylation or the cleavage of the azo group. In
the latter case no further data are available in order to propose
formulaI rather than II(Table3). Thepresenceofintermediates con-
taining not N, such as I and/or II, indirectly confirms the formation
of molecular nitrogen proposed in the literature as a possible expla-
Fig. 9. ESI–HRMS spectra for product D in Fig. 5.

A. Bianco Prevot et al. / Journal of Photochemistry and Photobiology A: Chemistry 209 (2010) 224–231
231
nation for the lack in the nitrogen mass balance, often evidenced in
Appendix A. Supplementary data
oxidative processes [24].
The chemical structures in Table 3 may suggest that the main
reactions taking place at the photolysis onset were the hydroxy-
lation of both aliphatic and aromatic C combined with cleavage
of alkyl chains and azo groups, followed by some fragments
rearrangement. Similar findings are reported [25] for the pho-
todegradation of EO in the presence of TiO2 where the •OH radical
attack is considered the main process step.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jphotochem.2009.11.020.
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This work was partially carried out with Regione Piemonte Cipe
2006 funds.
Financial support from MIUR (Rome) is gratefully acknowl-
edged.