Photocatalytic Activity of TiO2, ZnO and Nb2O5 Applied To Degradation of Textile Wastewater
Photocatalytic Activity of TiO2, ZnO and Nb2O5 Applied To Degradation of Textile Wastewater
Photocatalytic Activity of TiO2, ZnO and Nb2O5 Applied To Degradation of Textile Wastewater
A R T I C L E I N F O A B S T R A C T
Article history:
Received 7 December 2015 In this work, photocatalysis was employed in the treatment of textile efuent from industrial laundry
Received in revised form 13 June 2016 jeans using the catalysts TiO2 P25 (commercial), TiO2, ZnO and Nb2O5, under articial UV irradiation. The
Accepted 16 June 2016 parameters investigated were: pH of the solution and catalyst concentration. The photocatalytic activity
Available online 18 June 2016 was evaluated by means of kinetic efciency (rate constant and half life time), thermodynamic
(absorbance reduction at 228, 254, 284, 310, 350, 500 and 660 nm), COD reduction, mineralization in
Keywords: terms of the formation of inorganic ions (NH4+, NO3, NO2, SO42 and Cl) and toxicity reduction
Textile efuent (bioassays using Artemia salina). The photocatalytic degradation of textile efuent at pH 3.0 and catalyst
Photodegradation
concentration of 0.250 g L1 showed the best results, being found 95.91%; 87.35%; 86.95% and 59.18% of
Toxicity
absorbance reduction at 660 nm (lmax) after 300 min of articial irradiation with TiO2 P25, Nb2O5, TiO2
Mineralization
and ZnO, respectively. TiO2 and Nb2O5 were responsible for the reduction of approximately 70 and 66% of
COD and the photocatalytic activity of TiO2 was very close to TiO2 P25. In this sense, Nb2O5 becomes a
promising alternative to replace the commercial TiO2 P25. Bioassays with Artemia salina conrmed the
efcacy of the treatment, indicating that after photodegradation there was an expressive decrease in
efuent toxicity for up to 3 times.
2016 Elsevier B.V. All rights reserved.
1. Introduction highly colored due to the presence of dyes that are not xed to the
ber during the dyeing process. These efuents usually have high
In recent years, the environmental contamination has been pH values, biochemical oxygen demand (BOD), chemical oxygen
identied as one of the greatest problems of modern society, being demand (COD), turbidity and other toxic chemical compounds.
the contamination of natural water sources the biggest one, mainly Furthermore, many textile dyes or by-products present themselves
due to unmeasured population growth and increase of industrial carcinogenic and/or mutagenic effects [3,4].
activity [1]. The conventional technologies currently used to degrade textile
Among the industrial processes that are responsible for efuent are based in the processes of coagulation/occulation
generating large volumes of wastewater stand out the textile [5,6], electrocoagulation [7], adsorption on activated carbon [8,9]
sector. The textile industry consumes a considerable amount of and reverse osmosis/membrane ltration [10,11]. However, these
water during the processes of dyeing and nishing [2,3], as well as techniques are non-destructive, since they only transfer the
a great variety and quantity of chemicals, among them the dyes. organic contaminant into sludge giving rise to a new type of
Textile industries usually generate between 200 and 350 m3 of pollution, which needs further treatment [2,3,12]. In this
wastewater per ton of nished product [3]. Due to those factors, it perspective, advanced oxidation processes (AOPs) employing
is classied as one of the most polluting efuents from all heterogeneous photocatalysis have emerged as potential destruc-
industries [3]. The textile efuents are characterized by being tive technology leading to the total mineralization of most of
organic pollutants without generating solid wastes [1].
Titanium dioxide (TiO2) is one of the most studied catalysts in
* Corresponding author.
photocatalysis due to the high photocatalytic activity, non toxicity
E-mail address: jucgarcia@ibest.com.br (J.C. Garcia). and photostability [13]. Many studies have been reported using
http://dx.doi.org/10.1016/j.jphotochem.2016.06.013
1010-6030/ 2016 Elsevier B.V. All rights reserved.
10 R.P. Souza et al. / Journal of Photochemistry and Photobiology A: Chemistry 329 (2016) 917
TiO2 as a catalyst for treating wastewater of textile industry Corporation 68820) in an apparatus containing a monochromator
[4,5,1417]. Zinc oxide (ZnO) is also presented as one of the most (Oriel Instruments 77250), a high sensitivity capacitive micro-
extensively investigated photocatalysts and has relatively high phone (Bruel and Kjaer) and a lock-in amplier (EG and G5110). The
catalyst efciency, low cost, non toxic and chemical stability. light beam was modulated with a mechanical modulator (Stanford
Studies report that the ZnO degraded efciently textile dyes Research Systems SR540). The photoacoustic spectrum was
[12,1820]. obtained on modulation frequency of 21 Hz at wavelength from
The application of niobium pentoxide (Nb2O5) as catalyst for the 200 to 800 nm. The band gap energies were determined by using
photodegradation of dyes in the textile industry has been few Eq. (1):
reported in the literature [2123]. Nb2O5 exhibits a semiconduc-
hC 1240
tivity similar to that of TiO2 and therefore presents itself as a Eg 1
promising photocatalyst to replace TiO2 and even ZnO, since Brazil
l l
holds 90% of world reserves of niobium. Nb2O5 as well as TiO2, Where Eg is the band gap energy (eV), which was obtained by
presents good chemical stability, non toxicity and commercial plotting (Abs E (eV))m vs E (eV) using the direct method, i.e., m = 2
availability [24]. However, widespread use of TiO2 has become [1,28].
uneconomical for water treatment operations on large scale [12]
mainly due to the need of UV radiation, reactor design and 2.3. Textile efuent and characterization
additional separation steps requirement [25]. Thereby interest has
been drawn towards the search for suitable alternatives to TiO2. Samples of textile efuent were collected in an industrial
The aim of this work was to study the articial photocatalytic laundry, located in the northwest of Parana State, Brazil, directly
degradation of textile efuent from industrial laundry jeans from the stabilization/equalization pond. The physicochemical
through evaluation of the photocatalytic activity of TiO2, ZnO characterization of textile efuent was performed according to the
and Nb2O5 catalysts with favorable particle size for the separation following parameters: biochemical oxygen demand (BOD), chem-
as an alternative to commercial TiO2 P25, contributing for a ical oxygen demand (COD), chloride, ammonia, nitrite, nitrate,
sustainable development and economically viable for industrial sulfate, pH, temperature, turbidity and UVVis spectrophotometry.
application, keeping the photocatalytic activity similar to com- The analytical determinations were performed in accordance with
mercial TiO2 P25. standard methods [29].
Table 1
Characterization of the catalysts.
Catalyst SBETa (m2 g1) Vpb (102 cm3 g1) Vmc (102 cm3 g1) dpd (nm) Ege (eV) l (nm) pHzpc
Ti-500 11.40 5.95 0.29 10.44 3.30 376 6.93
TiO2-P25 60.55 8.07 1.77 5.97 3.12 397 6.12
Zn-500 7.42 1.61 0.14 4.33 3.24 383 8.30
Nb-500 134.30 12.40 3.28 1.85 3.27 379 4.79
a
BET surface area calculated from the linear part of the BET plot (P/P0 = 0.050.35).
b
Total pore volume, taken from the volume of N2 adsorbed at P/P0 = 0.99.
c
Micropore volume, calculated by t-method.
d
Average pore diameter.
e
Band gap energy obtained by photoacoustic spectroscopy.
following parameters: pH of solution, catalyst concentration and 2.4.4. Ecotoxicity Artemia salina
photocatalytic activity among the oxides. The catalysts investigat- Ecotoxicity bioassays with Artemia salina were performed based
ed were: Ti-500; Zn-500; Nb-500 and TiO2-P25. The photolysis on the methodology proposed by Garcia et al. [31]. Cysts of Artemia
(no catalyst) was also evaluated. All suspensions were kept salina were incubated in synthetic seawater (23 g L1 NaCl in
under magnetic stirring for 30 min in the dark in order to obtain water) for about 24 h at 25 C with continuous illumination and
the adsorption-desorption equilibrium, and then subjected to aeration. After the cysts had hatched, 611units of alive
irradiation. The temperature was maintained around 25 C and the crustaceans were selected and added to 1 mL of 23 g L1 NaCl
pH of the samples monitored at the end of the reaction. The mixed with 0, 0.3, 0.7, 1.0, 1.5 and 2.0 mL of samples. For each
duration of photoreactions were 300 min with 5.0 mL aliquots dilution of tested efuent, the mortality average value was
withdrawing in intervals of 50 min. The solutions were ltered in calculated and toxicity curves were constructed (mortality vs.
vacuum qualitative lter paper to separate the catalyst, and then efuent dilution), wherein the lethal concentration (LC50) was
analyzed. calculated by linear t of toxicity curves using the Origin 8.0
program.
2.4.2.1. Effect of pH. The evaluation of the pH effect was performed
using 350.0 mL of textile efuent, starting with catalyst 3. Results and discussion
concentration of 0.250 g L1 and irradiation time of 300 min,
based on studies reported by Garcia et al. [30]. The pH was adjusted 3.1. Catalysts characterization
to 2.0; 3.0; 4.0; 5.0 and 6.0 by the addition of HCl and NaOH
0.10 mol L1. The natural pH of textile efuent was also studied. Textural analysis results are shown in Table 1. Ti-500 showed
higher specic surface area than Zn-500, whose specic surface
2.4.2.2. Effect of catalyst concentration. Once the ideal pH have area was 7.42 m2 g1, close to reported by Velmurugan et al. [32].
been found, the following catalyst concentrations were evaluated: The specic area obtained for TiO2-P25 was 60.55 m2 g1 close to
0.175; 0.250; 0.500 and 0.750 g L1. The catalyst was dispersed by found by other authors [25,33,34]. Nb-500 showed high specic
magnetic stirring in 350 mL of textile efuent and irradiated for area, total pore and micropore volume. Garca-Sancho et al. [35]
300 min. synthesized Nb2O5 obtaining similar specic area and pore volume
values. Assessing the average pore diameter, it was observed that
2.4.3. Photocatalytic activity all catalysts presented mesoporosity (250 nm), except Nb-500
The photocatalytic activity of the oxides was evaluated in terms that presented micropores (<2 nm).
of thermodynamic efciency by absorbance decrease at wave- Fig. 2 shows the XRD patterns of the catalysts using the JCPDS
length associated with simple aromatic compounds (228, 254 and database [26]. For Ti-500 catalyst just anatase phase was identied
284 nm), conjugated aromatic compounds (310 and 350 nm), and and the peaks are in agreement with the literature results [28,36].
compounds that absorb in visible region (500 nm) [30]. The TiO2-P25 showed peaks corresponding to anatase and rutile
percentage of absorbance reduction was calculated by means of phases. The peak of the crystal plane (101) for the anatase phase
Eq. (2): appeared at 2u equal to 25.37 and the crystal plane (110) for the
Abso Abs
%Abs Reduction x100 2
Abso
Where: Abso = initial absorbance and Abs = nal absorbance (after
photocatalysis).
The kinetic efciency was evaluated by determining the rate
constant and half life time. The data obtained for the photo-
degradation of textile efuent were adjusted to rst order kinetics
Langmuir-Hinshelwood. The efciency of photodegradation was
also evaluated in terms of mineralization (formation of inorganic
ions: NH4+, NO3, NO2, SO42 and Cl) and COD reduction
percentage from Eq. (3):
COD0 CODf
%COD reduction x100 3
COD0
Where: CODo = concentration (mgO2 L1) of in natura sample
(untreated) and CODf = concentration (mgO2 L1) of sample treated
by photocatalysis. Fig. 2. XRD patterns of the catalysts: (a) Ti-500; (b) TiO2-P25; (c) Zn-500 e (d) Nb-
500. Peaks: (A) anatase e (R) rutile.
12 R.P. Souza et al. / Journal of Photochemistry and Photobiology A: Chemistry 329 (2016) 917
Table 2
Physico-chemical characterization of textile efuent from jeans industrial laundry.
2.0 548
100 (b)
(a)
438
Absorbance (u.a.)
60
1.0
580
40 406
312
0.5
20
300
0.0 0
250 300 350 400 450 500 550 600 650 700 750 800 200 300 400 500 600 700 800
Wavelength (nm) Wavelength (nm)
10
(c)
Absorbance (u.a.) 6
0
300 400 500 600 700 800
Wavelength (nm)
Fig. 5. (a) UVvis absorption spectrum of the in natura textile efuent (b) Emission spectrum of the mercury lamp (without bulb); (c) absorption spectrum of the
photochemical reactor (borosilicate glass).
Fig. 6. Absorbance reduction (%) as a function of pH for the textile efuent treated by photocatalysis with: (a) Ti-500; (b) TiO2-P25; (c) Zn-500; (d) Nb-500, and xed
concentration 0.250 g L1. Wavelengths studied: (&) 228 nm; (&) 254 nm; (*) 284 nm; () 310 nm; (~) 350 nm; (D) 500 nm and (^) 660 nm.
14 R.P. Souza et al. / Journal of Photochemistry and Photobiology A: Chemistry 329 (2016) 917
Fig. 8. (a) Effect of catalyst concentration on the degradation rate constant (k) of the textile efuent at 660 nm: (&) Ti-500; (*) Zn-500; (~) Nb-500 and (!) TiO2-P25 and (b)
percentages of COD reduction as a function of catalyst concentration: ( ) Ti-500; ( ) Zn-500; ( ) Nb-500 and ( )TiO2-P25, with xed pH 3.0.
R.P. Souza et al. / Journal of Photochemistry and Photobiology A: Chemistry 329 (2016) 917 15
Fig. 9. (a) Percentages of absorbance reduction at 660 nm (lmax) as a function of irradiation time and (b) percentages of COD reduction of catalysts: (&) Ti-500; (&) Zn-500;
(*) Nb-500; () TiO2-P25 and (~) Photolysis, at pH 3.0 and catalyst concentration of 0.250 g L1 after 300 min of irradiation.
Table 3
Percentages of absorbance reduction, rate constants of pseudo rst order (k), half life time (t1/2) and linear regressions (R) for the textile efuent treated by photocatalysis
under articial irradiation.
l (nm)
Catalyst 228 254 284 310 350 500 660
Ti-500 % 60.31 2.48a 62.42 2.77a 68.63 3.24a 71.59 2.27a 74.57 1.54a 77.47 2.11a 84.50 2.46a
k (min1) 0.0029 0.0035 0.0042 0.0044 0.0048 0.0053 0.0066
t1/2 (min) 239 198 165 157 144 130 105
R 0.9150 0.9502 0.9567 0.9626 0.9937 0.9883 0.9908
Zn-500 % 43.19 3.73b 45.46 3.91b 46.32 2.84b 47.75 2.84b 51.69 4.45b 64.61 5.30b 67.82 5.64b
k (min1) 0.0014 0.0016 0.0017 0.0018 0.0019 0.0023 0.0024
t1/2 (min) 495 433 407 385 364 301 288
R 0.9028 0.9345 0.9717 0.9616 0.9634 0.9224 0.9375
Nb-500 % 62.17 3.82a 66.20 3.75a 70.79 2.56a 75.57 3.40a 78.56 2.13a 81.80 2.44a 86.02 1.33a
k (min1) 0.0033 0.0035 0.0037 0.0045 0.0049 0.0052 0.0059
t1/2 (min) 210 198 187 154 141 133 117
R 0.9158 0.8973 0.9001 0.9145 0.9548 0.9698 0.9687
TiO2-P25 % 76.58 3.72c 80.40 3.79c 83.76 3.96c 85.26 3.02c 88.70 1.84c 93.54 2.44c 96.78 0.87c
k (min1) 0.0031 0.0048 0.0050 0.0059 0.0064 0.0074 0.0079
t1/2 (min) 223 144 138 117 108 93 87
R 0.9724 0.9490 0.9499 0.9340 0.9506 0.9326 0.9548
Photolysis % 8.03 3.87d 8.35 4.03d 9.25 3.89d 10.16 2.88d 11.18 3.45d 12.83 2.78d 13.63 3.65d
k (min1) 0.00070 0.00072 0.00075 0.00077 0.00080 0.00085 0.00090
t1/2 (min) 990 963 924 900 866 815 770
R 0.9532 0.9678 0.9688 0.9702 0.9768 0.9789 0.9812
are more difcult to be broken. Rodrigues et al. [42] reported that devising an appropriate photocatalyst immobilization strategy to
the compounds with high electron density, which absorb at higher provide a cost-effective solidliquid separation [44]. The differen-
wavelengths, are more susceptible to rapid attack by photo- tial of this work is the particle size presented by Ti-500 and Nb-
generated radicals, therefore are degraded at a higher speed. 500, which can be easily separated from the solution using a simple
The greater thermodynamic and kinetic efciency was found ltration system with common lter paper, thus contributing to
for TiO2-P25, because of their relatively high surface area and the sustainable development and economically viable for industrial
thinner particle size of its particles. In addition, TiO2-P25 showed application, maintaining the photocatalytic activity similar to TiO2-
lower bang gap energy, absorbing more effectively the energy P25. There was a lower efciency both thermodynamic and
supplied by the lamp. However, the Ti-500 and Nb-500 catalysts kinetics for Zn-500 (Table 3), indicating low photocatalytic activity,
also proved to be efcient, which showed absorbance and COD which can be associated with the low surface area and the greater
reductions close to that obtained for TiO2-P25. pore diameter. Moreover, ZnO can often suffer photocorrosion
TiO2-P25 is largely used commercially and was used as a when subjected to UV radiation, reducing its photocatalytic
positive control in this work, because it is known that it shows high activity [32,45].
photocatalytic activity. However, commercial TiO2 P25 is presented
as nanoparticles, making it difcult to industrial use, since 3.4.1. Mineralization
separation and reuse becomes impractical for large-scale appli- The results demonstrated that the textile efuent was
cations, requiring additional investment with separation steps or successfully degraded in 300 min of articial irradiation, proven
16 R.P. Souza et al. / Journal of Photochemistry and Photobiology A: Chemistry 329 (2016) 917
Table 4
Final concentration of mineralized ions at the end of 300 min of articial irradiation of the textile efuent at pH 3.0 and catalyst concentration of 0.250 g L1.*
Catalyst NH4+ (mg L1) NO2 (mg L1) NO3 (mg L1) SO42 (mg L1) Cl (mg L1)
in natura 2.39 0.07 0.066 0.003 1.46 0.13 42.07 0.07 287.5 27.5
Ti-500 5.98 0.27a 0.164 0.016a 3.99 0.44a 85.87 0.37a 687.5 12.5a
TiO2-P25 6.88 1.00a,c 0.205 0.008b 4.43 0.44a,c 139.62 0.15b 825.0 25.0b
Zn-500 6.56 0.18b 0.156 0.008a 3.76 0.66b 132.76 0.07c 712.5 12.5a
Nb-500 7.78 0.09a,c 0.173 0.008a,b 3.88 0.11a,c 103.34 0.59d 837.5 12.5b
*
Results expressed as means standard deviations of the triplicate. Different letters in the same column imply values statistically different (P < 0.05) by Tukey test
(ACTION, 2013).
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