Treatment of Direct Blending Dye Wastewater and Recycling of Dye Sludge

Abstract

A new sorbent material, barium sulfate-Direct Blending Yellow D-3RNL hybrid (BSD), was synthesized and characterized by various methods. Both the anionic dyes, Reactive Brilliant Red X-3B and Weak Acid Green GS were hardly adsorbed by the BSD material, while the sorption of Ethyl Violet (EV) and Victoria Blue B were extremely obvious. The sorption of cationic dyes obeyed the Langmuir isotherm model, which depended on the electric charge attraction. The saturation amount of EV adsorbed onto the BSD material approached to 39.36 mg/g. The sorption of EV changed little with pH from 3 to 12 while it increased with increasing levels of electrolyte. A dye wastewater sampled from Jinjiang Chemicals was treated, and the color removal rate was more than the COD removal rate. In addition, the cationic dye-BSD sludge was utilized as a colorant fill-in coating. The light stability and thermal stability of the colorant was measured and exhibited good features. This work provided a simple and eco-friendly method for dye wastewater treatment with recycling of waste.

Full text

Molecules 2012, 17, 2784-2795; doi:10.3390/molecules17032784
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Treatment of Direct Blending Dye Wastewater and Recycling of
Dye Sludge
Xin-Hui Xu, Ming-Li Li * and Yuan Yuan
State Key Laboratory of Pollution Control and Resource Reuse, College of Environmental Science and
Engineering, Tongji University, Shanghai 200092, China; E-Mails: xinfei0105@163.com (X.-H.X.);
Enviklab@tongji.edu.cn (Y.Y.)
* Author to whom correspondence should be addressed; E-Mail: li_mingli@tongji.edu.cn;
Tel./Fax: +86-21-6598-2684.
Received: 30 November 2011; in revised form: 13 February 2012 / Accepted: 29 February 2012 /
Published: 6 March 2012
Abstract: A new sorbent material, barium sulfate-Direct Blending Yellow D-3RNL hybrid
(BSD), was synthesized and characterized by various methods. Both the anionic dyes,
Reactive Brilliant Red X-3B and Weak Acid Green GS were hardly adsorbed by the BSD
material, while the sorption of Ethyl Violet (EV) and Victoria Blue B were extremely
obvious. The sorption of cationic dyes obeyed the Langmuir isotherm model, which
depended on the electric charge attraction. The saturation amount of EV adsorbed onto the
BSD material approached to 39.36 mg/g. The sorption of EV changed little with pH from 3
to 12 while it increased with increasing levels of electrolyte. A dye wastewater sampled
from Jinjiang Chemicals was treated, and the color removal rate was more than the COD
removal rate. In addition, the cationic dye-BSD sludge was utilized as a colorant fill-in
coating. The light stability and thermal stability of the colorant was measured and
exhibited good features. This work provided a simple and eco-friendly method for dye
wastewater treatment with recycling of waste.
Keywords: barium sulfate; direct blending dye; hybrid material; dye wastewater treatment;
reuse of sludge
OPEN ACCESS

Molecules 2012, 17 2785
1. Introduction
A growing population leads to rapid proliferation of industries and their pollution. Over 10,000 dyes
and more than 700,000 tons of dyes are produced every year, and over 5% are discharged into the
aquatic environment [1]. Many dyes are discharged into water as a waste and this causes very serious
pollution as they are difficult to degrade [2,3]. Most dyes contain azo groups or aromatic rings, which
are mutagenic and carcinogenic [4]. In recent years, the Yangtze Delta Area of China has been
suffering from serious dye wastewater pollution, which causes damage to people’s health [5].
Therefore, dye wastewater pollution is a very important issue that needs to be solved.
In recent years physical or chemical treatment processes have been developed to treat dye
wastewater, such as adsorption, biological treatments, electrochemical, flocculation–coagulation,
advanced oxidation processes and membrane separation [6–12]. Some of them have proved effective,
but they are often expensive and complex. An economical and easy solution to the treatment of highly
concentrated dye wastewater is still an important problem faced by the dye industries. Adsorption is
considered to be a simple and effective technology with wide potential applications in dye wastewater
treatment. Many adsorbents for dye removal, such as activated carbon, agricultural by-products, fly
ash, sewage sludge, clays and zeolites have been investigated [13–18]. However, most of the
absorbents have low adsorption capacity, slow adsorption equilibria and are expensive, and the sludge
produced in the treatment is another pollution problem.
The concept of inorganic/organic hybridization is applied extensively in composite materials, which
are used as biomaterials, catalysts, thin-films, photosensitive cells, etc. [19–21]. However, this method
is seldom considered in wastewater pollution control. Recently, Gao’s group have described some
hybrids used in dye wastewater treatment, for example, a Ag(SCN)-tetrabromo/tetrachlorofluorescein
hybrid material [22], calcium oxalate-Bromopyrogallol Red hybrid material [23], and calcium
carbonate-Weak Acidic Pink Red B hybrid material [24]. Zhao and Gao [25] developed a facile
treatment of a dye wastewater mixture by in situ hybridization with growing calcium carbonate.
Oladoja [26] also reported a method similar to Zhao and Gao’s method. This work has developed a
low-cost sorbent by hybridizing Direct Blending Yellow D-3RNL with barium sulfate. As a
conventional dye, D-3RNL (Figure 1), with its eight sulfonic groups, exhibits a good nucleophilicity
with alkaline-earth metals, e.g., Ba2+.
Figure 1. The chemical structure of direct blending yellow D-3RNL.

Molecules 2012, 17 2786
Barium sulfate is often used as additive in coatings, plastics, and paper to improve their toughness
and impact strength [27,28]. Thus, barium sulfate and D-3RNL were selected for synthesizing a
conjugate–BaSO4 hybrid to treat dye wastewater and the dye-BSD sludge produced during the
treatment process may have the potential to be reused as colorant fill-in coating. Thus, the dye
wastewater and sludge will be treated simultaneously to decrease the discharge of organic pollutants to
the environment.
2. Results and Discussion
2.1. Preparation and Characterization of the Dye Conjugate–BaSO4 Hybrid
The hybridization of D-3RNL into BaSO4 obeyed the Langmuir sorption isotherm when freshly
formed (Figure 2A). The saturation mole number (N) of D-3RNL to BaSO4 was calculated to be 1/64.7
and the binding constant (K) was 1.92 × 105 M−1. The reaction rate (η) of D-3RNL is less than 50%
when the initial mole ratio of D-3RNL to BaSO4 is more than 0.025 (Figure 2B). Referring to the
previous research [24,29] and considering the reaction rate of D-3RNL, the D-3RNL conjugate–BaSO4
hybrid material (BSD) was prepared with the molar ratio for the dosage of Ba2+, SO42− and D-3RNL is
1.5:1:0.025. The material was dried and determined to be C 2.635%, N 0.819% and H 0.516% by
elemental analysis. Thus, the molar ratio of D-3RNL to BaSO4 was calculated to be about 1/124 in
the hybrid.
Figure 2. Effects of D-3RNL on its binding mole number (A) and reaction rate η (B). c0,
and c D-3RNL are the initial and equilibrium molarity, cBaSO4 is the initial molarity of SO42−
and γ is the mole ratio of D-3RNL to BaSO4 in the BSD hybrid.
D-3RNL played an important role in control of the size and morphology of the hybrid. From the
SEM images, the BaSO4-only particles look like pebbles and their surface is smooth (Figure 3a–c).

Molecules 2012, 17 2787
However, the BSD particles look discoidal and have rough surfaces with many small globes embedded
into the particles (Figure 3d–f). Besides, the addition of D-3RNL affected the size of the particles. The
size of the BSD particles was bigger than the BaSO4-only, which would be beneficial for the
sedimentation of the dye-BSD sludge.
Figure 3. SEM images of the materials. a,b,c—BaSO4-only and d,e,f—BaSO4–D3RNL hybrid.
The FTIR spectra (Figure 4) revealed the difference in composition between the BaSO4-only and the
BSD material. It is well-known that BaSO4 has characteristic vibration bands, such as the peaks near
1195, 1119 and 1075 cm−1 corresponding to the sulfate absorption bands [30]. Both curves have the
characteristic vibration bands of sulfate, but compared to unmodified BaSO4 (Figure 4, curve 1),
curve 2 shows that the FTIR spectrum of the BSD material was more complicated. In the FTIR of the
BSD material, all the characteristic bands corresponding to D-3RNL and BaSO4 appear on the right
positions. The characteristic bands of BSD appear at 3440, 1623, 1509, 1413, and 1385 cm−1 due to the
N–H stretching vibrations, the C=C vibration band of benzene ring (1623, 1509 and 1413 cm−1), and
the C-H band of benzene ring (1385 cm−1), which prove the D-3RNL conjugate hybridization with the
growing barium sulfate.
The ζ-potential of the BSD material was measured to be −21.13 mV, while BaSO4-only material had
+1.11 mV of ζ-potential. This means the BSD material would form a negatively electronic aggregate
in aqueous media [24]. From the SEM, FTIR and ζ-potential research, it could be concluded that
D-3RNL was absorbed and occluded in BaSO4 particles during the co-precipitation process. A dye
conjugate–BaSO4 hybrid formed, which was negatively charged due to the sulfonic acid groups (Figure 1).

Molecules 2012, 17 2788
Figure 4. FTIR of BaSO4 (1), BaSO4–D3RNL hybrid (2), D3RNL (3).
2.2. Sorption Selectivity
In order to investigate the sorption selectivity and capacity of the BSD material, the two cationic
dyes e.g., EV (a) and VBB (b), and two anionic dyes e.g., RBRX-3B (c) and WAGGS (d) were tested.
From the photos in Figure 5, the color removal of EV (a) and VBB (b) were extremely obvious and the
sediment turned green for VBB and brown for EV.
Figure 5. Photos illustrating color change of dye solutions and their structures: EV (a),
VBB (b), RBRX-3B (c), WAGGS (d). All the dyes were added 200 μmol/L. All liquids
were settled for 10 min. 1 Dye-only. 2 treated with 0.18% BaSO4-only, 3 treated with
0.18% BSD material.

Molecules 2012, 17 2789
The BSD material had little effect to both the anionic dyes. The BaSO4-only material didn’t show
any obvious removal of any of the dyes. The sorption selectivity clarified that the interaction of
cationic dye with the material was mainly due to the charge attraction. The cationic dyes are positively
charged (Figure 5a,b) and they could be quickly absorbed to the BSD hybrid. On the contrary, the
anionic dyes were excluded by the BSD hybrid due to their negative charges (Figure 5c,d). Thus, the
color didn’t change much.
2.3. Sorption Isotherm
A cationic dye e.g., EV was selected to investigate the sorption performance and isotherm. Figure 6a
shows the sorption isotherm of EV onto the BSD material. The sorption amount of EV increased with
increase of the initial concentration of EV (CL0) and then approached saturation when CL0 was more
than 150 μmol/L. The sorption of EV fits the Langmuir isotherms model, which indicated the
monolayer sorption. The saturation molar number (N) of EV was calculated to be 2.45 mol EV/mol
D-3RNL, i.e., 39.36 mg EV/g (the BSD material) and the sorption constant (K) was calculated to be
1.51 ×106 M−1. Therefore, the sorption of cationic dye was sufficient and stable on the BSD material.
This will be beneficial for the reuse of dye sludge.
Figure 6. (a) Effect of EV (CL0). 1- change of the mole ratio (γ) of EV onto BSD (0.18%)
and 2- plots γ−1 vs. CL−1; (b) Effect of time: variation of the mole ratio (γ) of EV onto BSD
(0.18%), CL = 150 μmol/L, pH = 7; (c) Effects of pH (column) and electrolyte (curve):
variation of mole ratio (γ) of EV onto BSD (0.18%), CL = 150 μmol/L.
The sorption of EV was almost complete in 5 min (Figure 6b) while it took over 30 min onto
activated carbon [24]. The pH from 3 to 12 hardly affected on the sorption resulting from the relatively

Molecules 2012, 17 2790
stable performance of the BSD material (Figure 6c). The electrolyte concentration had an obvious
effect on the sorption (Figure 6c2). The γ of cationic dye increased with increased electrolyte, which is
beneficial for treatment of a concentrated salt dye wastewater.
2.4. Treatment of Dye Wastewater
With increasing public awareness of environmental protection, the recycling and reuse of waste has
long been studied in order to reduce the emission of pollutants and treatment costs [31,32]. The BSD
material was prepared with the D-3RNL dye wastewater discharged from dye plant instead of the
reagent, and it was applied as the sorbent to treat cationic dye wastewater. Figure 7 shows the colority
and COD decrease with increase of the sorbent. The colority of the dye wastewater decreased to 2,000
from 43,000 and COD to 800 mg/L from 5,400 mg/L when 4% of the sorbent was added. The COD
removal rate was less than the colority removal rate. It indicated that not all the organic matters had
been captured by the BSD material, e.g. small uncharged organic molecules. The colority and COD
decreased obviously when the sorbent was less than 3%. The BSD material was suggested treating the
high concentration dye wastewater.
Figure 7. Changes of colority/COD and their removal rate (1, 2) in the cationic dye
wastewater when treated with the BSD material added from 1% to 6%.
2.5. Recycling of the Dye Sludge
As is well known, barium sulfate is often used as additive filler in coatings, so the dye-contaminated
sludge produced from the wastewater treatment could be tried as color filler for coatings (Figure 8a).
As an example, a colored coating was prepared by adding the above sludge into a mixture of
waterborne epoxy coating and curing agent, and then was brushed onto the glass. The colored sludge

Molecules 2012, 17 2791
was found to be dispersed in the coating without sediment and in Figure 8a it shows uniform color.
The plate-shaped product was immersed in acidic (1 mol/L HCl, Figure 8b1) and basic (1 mol/L
NaOH, Figure 8b2) media. No color substance was found to release after 24 h immersion. The color of
the coating filled with the sludge exhibited a small change with ΔE values (total color change values)
of 3.1 and 4.2 for acidic and basic media immersion, suggesting that the two media have little
influence on the coating. In order to investigate the color stability of sludge, its light stability and
thermal stability have been studied. From Figure 8c, the ΔE increased with an increase in heating time
and UV irradiation time. The ΔE was less than 5 after heating for 12 h (Figure 8c1), and less than 4
after UV irradiation for 12 h (Figure 8c2). The dye-contaminated sludge was proved to be light and
thermally stable in the waterborne epoxy coating. Thus, the dye-contaminated sludge has the potential
to be used as colorant for some coatings. Compared to incineration or landfill, the dye sludge can be
recycled and the secondary pollution could be reduced.
Figure 8. Photos (a,b) illustrating the color change of the colored coating. (a) the colored
coating; (b) the colored coating immersing in acidic (1) and basic (2) aqueous media; (c)
ΔE change with time, curve 1- heated at 100 °C and 2- irradiated with a UV light at 1000 W.
3. Experimental
3.1. Apparatus and Materials
A Model S4100 photodiode array spectrometer (Scinco, Korea) was used to determine the colority
and concentration of color compounds and the suspended substance liquids. A Model TG16-WS
centrifuger (Hunan Xiangyi Instruments, China) was used to separate the hybrid materials from liquid.
A Model Quanta 200 FEG scanning electronic microscope (SEM, FEI Co., USA) was used to measure
the size and shape of the materials. Infrared (IR) spectra of the hybrid in KBr pellets were obtained,
using an Equinoxss/hyperion 2000 infrared spectrometer system (BRUKER Co., Germany). A Model
Vario EL III elemental analyzer was used to analyze the elemental composition of the materials. A
Model 5B-1 programmable digestion system (Lanzhou, China) and a Model PORS-15V portable

Molecules 2012, 17 2792
chemical oxygen demand (COD) analyzer (Pgeneral Co., China) were coupled for determination of
COD in wastewater. A Model/WSC-Y colorimeter (BOIF, China) was used to determine the color
factors (L, a and b) of color coating. The following solutions were prepared by dissolving in deionized
water: Direct Blending Yellow D-3RNL (C.I. 161,Tongluo Chemicals Co., Ltd (Suzhou, China),
45%), Victoria Blue B (VBB, C.I. 44045,Aladdin Co., 80%), Ethyl Violet (EV, C.I. 42600,Aladdin
Co., 90%), Reactive Brilliant Red X-3B (RBRX-3B, C.I.18200,Shuang Hong Chemicals Co., Ltd
(JinHua, China), 75%), Weak Acid Green GS (WAGGS, C.I.61570,Aladdin Co., 95%), Na2SO4
(0.02 mol/L, AR, Aladdin Co.) and BaCl2 (0.02 mol/L, AR, Aladdin Co.). A cationic dye wastewater
was sampled from Jinjiang Chemicals (Hangzhou, China) and its colority determined to be 43,000
(yellow) and COD 5400 mg/L. The waterborne epoxy coating and curing agent (CV-600) was
purchased from Fulang Chemicals Co., Ltd (Shanghai, China).
3.2. Preparation and Characterization of the Dye Conjugate–BaSO4 Hybrid
Direct Blending Yellow D-3RNL (100 mL, 2 mmol/L) was mixed with sodium sulfate (400 mL,
0.02 mol/L) and mixed thoroughly, then barium chloride (600 mL, 0.02 mol/L) was added slowly
under stirring. After 30 min, the suspending substance product was precipitated and washed with deionized
water (1,500 mL) three times. Finally, approximately 18% (W/V) product aqueous liquid was prepared
with deionized water. The surface electricity of the suspending sorbent in liquid was measured by
a ζ-potential detecting-device. The elemental analysis, SEM and FTIR of the BSD material powders
were measured.
3.3 Sorption of Dyes
Four dyes (200 μmol/L), RBRX-3B, WAGGS, EV, and VBB were prepared for investigating the
sorption selectivity, performance, and mechanism of the BSD material. The concentration of dyes was
determined by spectrophotometry.
3.4. Treatment of Dye Wastewater
The cationic dye wastewater sampled from Jinjiang Chemicals (colority 43,000 times and COD
5400 mg/L) was mixed thoroughly with the BSD suspending substance liquid. After 30 min, the
colority of supernatant was determined by spectrophotometry. The unit of “times” means that the
dilution times when the wastewater was diluted until the absorbance is lower than 0.005, which has the
same absorbance with distilled water. The COD was determined by the COD analyzer. Thus, the
colority removal rate of dye wastewater and the removal rate of COD were calculated.
3.5. Reusing Dye-Contaminated Sludge as Colorants
The dye-BSD sludge formed above was separated from the treated wastewater and then
concentrated. 10 mL (75%, W/V) of the concentrated sludge was mixed together with 100 g of
waterborne epoxy coating and 30 g curing agent. After mixing thoroughly, it was brushed on glasses
(60 mm × 60 mm × 3 mm) and dried at room temperature for 7 days. Then, the glass brushed with
colored coating was immersed in 1 mol/L HCl aqueous solution and 1 mol/L NaOH aqueous solution

Molecules 2012, 17 2793
for 24 h, respectively, where both the solutions were 30 mL in volume. In order to investigate light
stability and thermal stability of the colored coating, the prepared samples was irradiated by an
ultraviolet lamp (1,000 W) for 12 h and heated at 100 °C for 12 h, respectively. The release amount of
colored substances and the color change of the samples were observed before and after irradiation,
heating and immersing. The L, a, and b values of color were determined according to the CIE-lab
standard and the change in color, expressed as ΔE, was calculated. During measuring of the L, a and b
values, a couple of sheets of white printing paper were placed below the colored paint samples. The
ΔE was calculated by the following equation [33]:
2
10
2
10
2
10 )L(L)b(b)a(aΔE
where L0, a0 and b0 was the initial color values of the colored coating; L1, a1 and b1 was the color
values after irradiation, heating, and immersing.
In the CIELAB color system, the absolute magnitude of color change between two conditions is
given by ΔE. A ΔE value of one unit is approximately equivalent to a color difference that is just
visually perceptible to 50% of observers under controllable conditions. Value of ΔE from 2 to 3
represents the color difference that is slightly perceptible, and more than 3.3 is visually perceptible to
50% of observers [34]. ΔE more than 7 shows a marked color difference [35].
4. Conclusions
A novel sorbent was prepared by immobilizing D-3RNL into growing BaSO4, and the sorption of
EV was investigated. The sorption of the cationic dye caused by the charge attraction fits the Langmuir
isotherm model. The effects of pH, electrolyte, and sorption time were investigated and the sorption is
fast, affected only a little by pH and favorable for a high salt dye wastewater. The BSD material was
used to treat a cationic wastewater with satisfactory results. The dye-BSD sludge was filled in a
waterborne epoxy coating. The color of the colored paint was stable when immersed in acidic and
basic media and changed little when irradiated by a UV lamp. This work provided an eco-friendly and
facile method for treatment of dye wastewaters.
Acknowledgements
We thank the Foundation of State Key Laboratory of Pollution Control and Resource Reuse (Tongji
University), China (No.PCRRK11003) for financially supporting this work.
References and Notes
1. Gong, R.M.; Li, M.; Yang, C.; Sun, Y.Z.; Chen, J. Removal of cationic dyes from aqueous
solution by adsorption on peanut hull. J. Hazard. Mater. 2005, 121, 247–250.
2. Forgacs, E.; Cserhati, T.; Oros, G. Removal of synthetic dyes from wastewaters: A review.
Environ. Int. 2004, 30, 953–971.
3. Rai, H.S.; Bhattacharyya, M.S.; Singh, J.; Bansal, T.K.; Vats, P.; Banerjee, U.C. Removal of dyes
from the effluent of textile and dyestuff manufacturing industry: a review of emerging techniques
with reference to biological treatment. Crit. Rev. Env. Sci. Tec. 2005, 35, 219–238.

Molecules 2012, 17 2794
4. Vanhulle, S.; Trovaslet, M.; Enaud, E.; Lucas, M.; Taghavi, S.; van der Lelie, D.; van Aken, B.;
Foret, M.; Onderwater, R.C.A.; Wesenberg, D.; et al. Decolorization, cytotoxicity, and
genotoxicity reduction during a combined ozonation/fungal treatment of dye-contaminated
wastewater. Environ. Sci. Technol. 2008, 42, 584–589.
5. Yang, M.; Yu, J.W.; Li, Z.L.; Guo, Z.H.; Burch, M.; Lin, T.F. Taihu lake not to blame for Wuxi’s
woes. Science 2008, 319, 158.
6. Hadi, M.; Samarghandi, M.R.; McKay, G. Simplified fixed bed design models for the adsorption
of acid dyes on novel pine cone derived activated carbon. Water Air Soil Poll. 2011, 218,
197–212.
7. Auxilio, A.R.; Andrews, P.C.; Junk, P.C.; Spiccia, V. Adsorption and intercalation of Acid Blue 9
on Mg–Al layered double hydroxides of variable metal composition. Polyhedron 2007, 26,
3479–3490.
8. Arslan-Alaton, I.; Gursoy, B.H.; Schmidt, J.E. Advanced oxidation of acid and reactive dyes:
Effect of Fenton treatment on aerobic, anoxic and anaerobic processes. Dyes Pigments 2008, 78,
117–130.
9. Sarioglu, M.; Bisgin, T. Removal of Maxilon Yellow GL in a mixed methanogenic anaerobic
culture. Dyes Pigments 2007, 75, 544–549.
10. Rivera, M.; Pazos, M.; Sanroman, M.A. Improvement of dye electrochemical treatment by
combination with ultrasound technique. J. Chem. Technol. Biotechnol. 2009, 84, 1118–1124.
11. Moghaddam, S.S.; Moghaddam, M.R.A.; Arami, M. Response surface optimization of acid red
119 dye from simulated wastewater using Al based waterworks sludge and polyaluminium
chloride as coagulant. J. Environ. Manag. 2011, 92, 1284–1291.
12. Zahrim, A.Y.; Tizaoui, C.; Hilal, N. Coagulation with polymers for nanofiltration pre-treatment of
highly concentrated dyes: A review. Desalination 2011, 266, 1–16.
13. Lillo-Rodenas, M.A.; Marco-Lozar, J.P.; Cazorla-Amoros, D.; Linares-Solano, A. Activated
carbons prepared by pyrolysis of mixtures of carbon precursor/alkaline hydroxide. J. Anal. Appl. Pyrol.
2007, 80, 166–174.
14. Phan, N.H.; Rio, S.; Faur, C.; Coq, L.L.; Cloirec, P.L.; Nguyen, T.H. Production of fibrous
activated carbons from natural cellulose (jute, coconut) fibers for water treatment applications.
Carbon 2006, 44, 2569–2577.
15. Mohan, D.; Singh, K.P.; Singh, G.; Kumar, K. Removal of dyes from wastewater using flyash, a
low-cost adsorbent. Ind. Eng. Chem. Res. 2002, 41, 3688–3695.
16. Meshko, V.; Markovska, L.; Mincheva, M.; Rodrigues, A.E. Adsorption of basic dyes on granular
acivated carbon and natural zeolite. Water Res. 2001, 35, 3357–3366.
17. Seredych, M.; Bandosz, T.J. Removal of cationic and ionic dyes on industrial-municipal sludge
based composite adsorbents. Ind. Eng. Chem. Res. 2007, 46, 1786–1793.
18. Gurses, A.; Karaca, S.; Dogar, C.; Bayrak, R.; Açıkyıldız, M.; Yalçın, M. Determination of
adsorptive properties of clay/water system: Methylene blue sorption. J. Colloid Interf. Sci. 2004,
269, 310–314.
19. Takahashi, Y.; Kasai, H.; Nakanishi, H.; Suzuki, T.M. Test strips for heavy-metal ions fabricated
from nanosized dye compounds. Angew. Chem. Int. Ed. Engl. 2006, 45, 913–916.

Molecules 2012, 17 2795
20. Xu, C.S.; Kim, H.; Yang, H.; Hayden, C.C. Multiparameter Fluorescence Spectroscopy of Single
Quantum Dot−Dye FRET Hybrids. J. Am. Chem. Soc. 2007, 129, 11008–11009.
21. Hou, K.; Song, Q.; Nie, D.; Li, F.; Bian, Z.; Liu, L.; Xu, L.; Huang, C. Synthesis of Amphiphilic
Dye-Self-Assembled Mesostructured Powder Silica with Enhanced Emission for Directional
Random Laser. Chem. Mater. 2008, 20, 3814–3820.
22. Wang, H.Y.; Ma, L.M.; Li, T.; Zhang, Y.L.; Gao, H.W. Synthesis of Ag(SCN)/tetrabromo-
tetrachlorofluorescein inclusion material and application to synthetic dye. Colloids Surface. A
2009, 333, 126–132.
23. Wang, H.Y.; Gao, H.W. Preparation of calcium oxalate—bromopyrogallol red inclusion sorbent
and application to treatment of cationic dye and heavy metal wastewaters. Environ. Sci. Pollut. Res.
2009, 16, 339–347.
24. Zhao, D.H.; Gao, H.W. Turning calcium carbonate into a cost-effective wastewater-sorbing
material by occluding waste dye. Environ. Sci. Pollut. Res. 2010, 17, 95–107.
25. Zhao, D.H.; Zhang, Y.L.; Wei, Y.P.; Gao, H.W. Facile Eco-friendly Treatment of Dye
Wastewater Mixture by In-situ Hybridization with Growing Calcium Carbonate. J. Mater. Chem.
2009, 19, 7239–7244.
26. Oladoja, N.A.; Raji, I.O.; Olaseni, S.E.; Onimisi, T.D. In situ hybridization of waste dyes into
growing particles of calcium derivatives synthesized from a Gastropod shell (Achatina Achatina).
Chem. Eng. J. 2011, 171, 941–950.
27. Tan, S.; Tinc, T. Flammability and mechanical properties of Al(OH)3 and BaSO4 filled
polypropylene. J. Appl. Polym. Sci. 2010, 118, 3034–3040.
28. Wei, Y.P.; Wei, D.Q.; Gao, H.W. Treatment of Dye Wastewater by in-situ Hybridization with
Mg-Al Layered Double Hydroxides and Reuse of Dye Sludge. Chem. Eng. J. 2011, 172, 872–878.
29. Lin, J.; Gao, H.W. SDBS@BaSO4: An efficient wastewater-sorbing material. J. Mater. Chem.
2009, 19, 3598–3601.
30. Gupta, A.; Singh, P.; Shivakumara, C. Synthesis of BaSO4 nanoparticles by precipitation method
using sodium hexametaphosphate as a stabilizer. Solid. State. Commun. 2010, 150, 386–388.
31. Tal, A. Seeking sustainability: Israel’s evolving water management strategy. Science 2006, 313,
1081–1084.
32. Liu, W.Z.; Huang, F.; Liao, Y.Q.; Zhang, J.; Ren, G.Q.; Zhuang, Z.Y.; Zhen, J.S.; Lin, Z.; Wang, C.
Treatment of CrVI-containing Mg(OH)2 nanowaste. Angew. Chem. Int. Ed. Engl. 2008, 47, 5619–5622.
33. Commission Internationale d’Eclairage (CIE). Colorimetry; CIE Pub No.15.2. 2nd ed.; Central
Bureau of the CIE: Vienna, Austria, 1986; p. 33.
34. Faltermeier, A.; Behr, M.; Mussig, D. Esthetic brackets: The influence of filler level on color
stability. Am. J. Orthod. Dentofac. 2007, 132, e13–e16.
35. Doray, P.; Wang, X.; Powers, J.; Burgess, J. Accelerated aging affects color stability of
provisional restorative materials. Int. J. Prosthodont. 1996, 6, 183–188.
Sample Availability: Samples of the compounds are available from the authors.
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