Catalytic Adsorptive Stripping Voltammetric Determination of Cr(VI)

168 Pages·2015·5.79 MB·English

INVESTIGATION ON SUITABILITY
OF ION EXCHANGERS AND SORBENTS FOR TOXIC
SUBSTANCES REMOVAL FROM WATER AND SLUDGE

Zbigniew HUBICKI, Dorota KOŁODYŃSKA, Monika WAWRZKIEWICZ,
Anna WOŁOWICZ and Grzegorz WÓJCIK
DEPARTMENT OF INORGANIC CHEMISTRY

The elimination of toxic and hazardous chemical substances such as chromium
(VI), copper, synthetic dyes from waste effluents is a major concern worldwide.
Among all heavy metals, copper, chromium and zinc ingestion beyond permissible
quantities causes various chronic disorders in human beings. The aim of these
studies was to investigate of sorption mechanism of chromium(VI) , copper ions,
and synthetic dyes from water solution on various type ion exchangers. The
strong base ion exchangers Dowex PSR-2 and Dowex PSR-3 were used for removal
of chromium and synthetic dyes (C.I. Acid Orange 7, C.I. Reactive Black 5, C.I.
Direct Blue 71). The molecular structure of Dowex PSR-2 is presented on Figure 1.

H2
H2C CH C

CH2
C4H9
C4H9 N+
SO42-
C4H9
Fig. 1. Molecular structure of Dowex PSR-2.

The difference between Dowex PSR-2 and Dowex PSR-3 is their skeleton. Dowex
PSR-2 possess gel type skeleton, while Dowex PSR-3 macroporous. Experimental
result showed that the sorption of chromium(VI) anions can be represented
stoichiometrically by the following equations:

(-CH (C H ) N+ ) SO 2- + 2HCrO - ⇌ 2-CH (C H ) N+ HCrO - + SO 2-
2 4 9 3 2 4 4 2 4 9 3 4 4
(-CH (C H ) N+ ) SO 2- + Cr O 2- ⇌ (-CH (C H ) N+ ) Cr O 2- + SO 2-
2 4 9 3 2 4 2 7 2 4 9 3 2 2 7 4
(-CH (C H ) N+ ) SO 2- + CrO 2- ⇌ (-CH (C H ) N+ ) CrO 2- + SO 2-
2 4 9 3 2 4 4 2 4 9 3 2 4 4

The investigations of chromium(III) and(VI) speciation allowed to notice that
chromium(VI) is reduced to chromium(III) ions at pH 1.5. The reduced
chromium(III) ions are not retained by strong base ion exchanger but are transferred
from internal to aqueous solution. Similar observation during sorption of chromium
(VI) ions on strongly basic anion exchanger were reported [1,2].
1
The affinity series of the dyes of increasing molecular weight towards the gel
and macroporous anion exchangers Dowex PSR-2 and Dowex PSR-3 based on the
values of the monolayer sorption capacities determined from the Langmuir model
can be presented as follows:
C.I. Acid Orange 7 > C.I. Reactive Black 5 > C.I. Direct Blue 71
However the dyes sorption on the anion exchangers was influenced not only by the
dye molecules size but also by the resin structure [3]. It seems that the macroporous
anion exchanger Dowex PSR-3 can be a promising sorbent for the acid, reactive
and direct dyes from aqueous solutions because of high values of the monolayer
sorption capacities: 336 mg/g for C.I. Acid Orange 7, 308 mg/g for C.I. Reactive
Black 5 and 81.6 mg/g for C.I. Direct Blue 71.
It was also compared the removal of Cu(II) ions using Dowex M 4195 and
Lewatit® MonoPlus TP 220 from acidic streams. The research was carried out
under different operational conditions. The parameters determined for the sorption
process were correlated with the detailed microscopic characteristics of Dowex M
4195 and Lewatit® MonoPlus TP 220. It was found that the effectiveness of the
Cu(II) sorption of on Dowex M 4195 and Lewatit® MonoPlus TP 220 depends on:
concentration of Cu(II) ions, pH, ion exchanger sample size, phase contact time,
and the presence of chloride and sulfate ions. The Cu(II) sorption process is the
most effective on Lewatit® MonoPlus TP 220, especially for the lower
concentrations of Cu(II) ions. It proceeds according to the mechanism of typical
pseudo second-order reaction, as evidenced by higher values of correlation
coefficients (0.99-1.00). Sorption takes place in the entire volume of the ion
exchangers used, and in the case of Dowex M 4195 especially in the edge part.
Therefore, this process is dependent on the synthesis method of the chelating ion
exchanger. This was confirmed by the optical profiler analysis, which allows
obtaining 3D imaging of any area, numerical analysis of roughness, and plotting
surface profile anywhere in the image of the ion exchanger sample. The most
effective chelating ion exchanger proved to be Lewatit® MonoPlus TP 220. Cu(II)
ions sorption was affected by the presence of sulfate ions in the system. The
monolayer sorption capacity (q ) for Lewatit® MonoPlus TP 220 was found to be
0
50.69 mg/g and 86.44 mg/g in the presence of chloride ions. In the presence of
sulfate ions these values were higher and equal to 56.66 mg/g and 94.20 mg/g,
respectively[4].

References:
[1] G. Wójcik, Z. Hubicki, P. Rusek, Przemysł Chemiczny, 90 (2011) 2153.
[2] G. Wójcik, Z. Hubicki, P. Rusek, Przemysł Chemiczny, 92 (2013) 82.
[3] M. Wawrzkiewicz, Industrial Engineering & Chemistry Research, 51 (2012)
8069.
[4] D. Kołodyńska, W. Sofińska-Chmiel, E. Mendyk, Z. Hubicki, Separation
Science and Technology, 49 (2014) 2003.

2
LUMINESCENCE SPECTRA OF URANIUM ON CLAY

Agnieszka GŁADYSZ-PŁASKA, Marek MAJDAN
DEPARTMENT OF INORGANIC CHEMISTRY

Understanding of radionuclide (including uranium ions) migration behaviour is
very important for safety assessment of nuclear waste disposal in geological
formations. Thus, knowledge of the chemical species of U(VI) formed with
different constituents of the geosphere (soil, water) is an important step for
modelling of uranium ions transport. Indeed, it is necessary to have methods at the
disposal that can not only perform ultratrace analysis of single species but can also
characterize complexes present at low levels in solution. Time-resolved laser-
induced fluorescence is a very sensitive and selective method for actinide and
lanthanide analysis which has been largely used in various fields of the nuclear fuel
cycle (geology, reprocessing, waste storage, medical, environment), mainly for
uranium ultratrace analysis or process control.
The time-resolved laser-induced fluorescence spectroscopy (TRLFS), applied
as a method to study of the kind of U(VI) surface complexes on clays, provides the
information about both the lifetime and spectral characteristics of the adsorbed
species, which allows to point out the number of different species and their spectral
identity. The lifetimes of U(VI) fluorescence species were determined from the bi-
exponential fit analysis of the obtained data indicating at least two surface species.
The TRLFS measurements of uranium(VI) species yield the information about the
position of the fluorescence emission bands and the fluorescence lifetimes. The
fluorescence lifetime varies depending on the number of neighbouring water
molecules surrounding uranium(VI) ion. The TRLFS spectra of the sorbed U(VI)
surface species on clays at pH 6.5 indicate at least two surface species with two
different fluorescence lifetimes, i.e., one short- and one long- lived species. The
shorter fluorescence lifetimes indicate more water molecules in the coordination
sphere of the respective adsorbed U(VI) surface species , since the water molecules
quench the fluorescence [1-5]. Taking this fact into account, it can be assumed that
U(VI) ions form two surface species on clay (sepiolite, bentonite and red clay)
which differ in the amount of water molecules in their coordination sphere.
Comparison of the mean values of the respective fluorescence lifetimes obtained for
different clays (bentonite, sepiolite, red clay) with uranium allows to conclude that
they are significantly shorter for the bentonite samples (U-bentonite: τ1=1100 ns
and τ2=9740 ns; U-PO4-bentonite: τ1=1350 ns and τ2=69870 ns; U-red clay:
τ1=1260 ns and τ2 =26400 ns; U-PO4-red clay: τ1 =6530 ns and τ2 =27550 ns).
The shorter fluorescence lifetimes of U-clay indicate more water molecules in the
coordination environment of the respective adsorbed U(VI) surface species. We
conclude that the surface species with the shorter fluorescence lifetime are the
bidentate mononuclear inner-sphere surface complexes in which U(VI) is bound to
two reactive hydroxyl groups.
3
25000
Legend
red clay
20000
U-red clay
y
tisn U-PO4-red clay
e
tn15000
i
10000
5000
0
450 500 550 600 650
Wavelength, nm

Fig. 1. Emission spectra of red clay samples.

5000
Legend
0
y 4000 delay 5 us
tisn delay 10 us
etni 3000 ddeellaayy 1250 uuss
delay 25 us
2000
1000
0
500 550 600 650
Wavelength, nm
Fig. 2. Time-resolved laser-induced phosphorescence spectra of U-PO4-clay sample.

References:
[1] J.I. Domingo, Reprod. Toxicol., 15 (2001) 603.
[2] N.D. Priest, Lancet, 357/27 (2001) 244.
[3] K.G. Orloff, K. Mistry, P. Charp, S. Metcalf, R. Marino, T. Shelly, E. Melaro,
A.M. Donohoe, R. Jones, Environ. Res., 94 (2004) 319.
[4] C. Thiebault, M. Carriere, B. Gouget, Abstr. Toxicol. Lett., 172S (2007) S1-
S240, S57.
[5] M. Majdan, S. Pikus, A. Gajowisk, D. Sternik, E. Zięba, J. Hazard. Mater., 184
(2010) 662.

4
ADSORPTION OF PHOSPHATE(V) ON BENTONITE

Agnieszka GŁADYSZ-PŁASKA, Marek MAJDAN
DEPARTMENT OF INORGANIC CHEMISTRY

Phosphate is contained in the sewage of houses and factories and its
concentration in lakes and seas rapidly increased because of the use of organic
detergent. The presence of phosphate in wastewaters provides an additional nutrient
in the near static water bodies. As a result, an excessive growth of photosynthetic
aquatic micro- and macro-organisms is encouraged in such water bodies which
ultimately become a major cause for the eutrophication of such receiving waters [1,
2]. Therefore wastes containing phosphate must meet the discharge limits for
phosphates as 0.5–1.0 mg/l P. In order to meet effluent quality standards, the
removal of phosphate from wastewaters prior to discharge into natural waters is
required. In wastewater-treatment technology, various techniques have been used
for phosphate removal. Among these, chemical, biological and physical methods
have been successfully applied (reverse osmosis, electrodialysis, contact filtration
and adsorption). Adsorption is one of the techniques, which is comparatively more
useful and economical for phosphate removal. Phosphate is an important nutrient
element in soil. Phosphate in soil may affect the chemical reactions of metals on
mineral surfaces. Recent studies indicated that phosphate minerals, such as apatite,
could sequester heavy metals, metalloids and radionuclide through adsorption
and/or the formation of secondary PO 3- precipitates, which remained stable under a
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wide range of geochemical conditions. Therefore, it is necessary to examine the
influence of phosphate on the reactions of heavy metals on the surface of soil
minerals. Phosphate has been intensively investigated as the coligand and was
usually reported to have a positive effect on the heavy metal adsorption [1-4].
The aim of the investigation was to determine the suitability of the bentonite
for removal of phosphate and uranyl ions from aqueous solutions. Various
parameters, including initial ions concentration, operating temperature, and solution
pH, have been investigated in batch kinetic experiments and desorption studies. All
the experimental results have been analysed by applying adsorption isotherms and
batch kinetic models. The bentonite saturated by hexadecyltrimethylammonium
bromide was used as an organoclay. The initial and the equilibrium concentrations
of ions in the aqueous phase were determined by spectrophotometric method [5].
The bentonite is an effective sorbent for removing uranium(VI) with
phosphate(V) ions from aqueous solution. The kinetics of adsorption follows the
pseudo-second-order model, indicating that the adsorption was controlled by
chemisorption process which was found to be endothermic and spontaneous.
Sorption isotherms of U(VI) and P(V) ions on bentonite in the presence of
phosphate are given in Fig. 1. There is an evident improvement in U(VI) and P(V)
sorption in the bicomponent system compared with the monocomponent systems. It
seems, however, that P(V) peaks refer to the same complex independent of the pH.
5
Their position is located at initial solution c = 0.0005 mol/dm3. The U(VI) peak has
0
changed its position from c = 0.0006 to 0.0008 mol/dm3.
0

Legend
U(VI)
P(V)
6x10-4 6x10-4 6x10-4
g
/lom 4x10-4 4x10-4 4x10-4
c, s 2x10-4 2x10-4 2x10-4
0 0 0
0x10 0x10 0x10
-4 -3 0 -4 -4 -3
5x10 1x10 0x10 5x10 5x10 1x10
3
c ,mol/dm
0

Fig. 1. The sorption isotherms of U(VI) ions on bentonite in the presence of phosphate ions
(A – a monocomponent system, U(VI) alone; B – a monocomponent system, P(V) alone; C
– a bicomponent system, U(VI) + P(V); In all systems, 0.1 mol/dm3 acetate buffer was used
at pH 5.4).

References:
[1] J.I. Domingo, Reprod. Toxicol., 15 (2001) 603.
[2] N.D. Priest, Lancet, 357/27 (2001) 244.
[3] K.G. Orloff, K. Mistry, P. Charp, S. Metcalf, R. Marino, T. Shelly, E. Melaro,
A.M. Donohoe, R. Jones, Environ. Res., 94 (2004) 319.
[4] C. Thiebault, M. Carriere, B. Gouget, Abstr. Toxicol. Lett. 172S (2007) S1-
S240, S57.
[5] M. Majdan, S. Pikus, A. Gajowiak, D. Sternik, E. Zięba, J. Hazard. Mater., 184
(2010) 662.

6
FLUORESCENCE QUENCHING PROCESS OF PORPHYRIN
SYSTEMS AS A RESULT OF INTERACTIONS WITH
BIOLOGICALLY ACTIVE COMPOUNDS

Magdalena MAKARSKA-BIAŁOKOZ
DEPARTMENT OF INORGANIC CHEMISTRY

Distinctive spectroscopic properties of the porphyrin systems, namely their
ability to electron transfer, as well as high intensity of absorption and fluorescence,
predestine this class of substances to play a role of sensors in processes with the
participation of different biologically important molecules.
Many examples of the specific interactions between water-soluble porphyrins
and biologically active aromatic compounds (caffeine, nucleic bases, nucleosides
and nucleotides, guanine, theophylline, theobromine, xanthine, uric acid) were
monitored before with use of UV-VIS and emission spectroscopy techniques [1-5].
The illustration of such interactions is a π-stacked complex formed between guanine
(2-amino-6-hydroxypurine), a bicyclic nucleic base involved strongly in human
metabolism, and a cationic water-soluble porphyrin (5,10,15,20-tetrakis[4-
(trimethylammonio) phenyl]-21H,23H-porphine tetra-p-tosylate (H TTMePP). The
2
fluorescence quenching effect observed during interactions porphyrin-guanine
points at the fractional accessibility of the fluorophore for the quencher. The
association and fluorescence quenching constants, calculated applying the equation
based on Bjerrum function modified by Beck, and the Lehrer equation, respectively,
are of the order of magnitude of 105 mol-1. The fluorescence lifetimes and the
quantum yields of the porphyrin monoanion form were established as well. For all
calculations the non-linear curve-fitting procedure based on Marquardt–Levenberg
algorithm from Sigma Plot (version 9.0, Jandel Corp.) database program, modified
for the particular systems, was employed.
The results demonstrate that guanine can interact with H TTMePP at basic pH
2
and through formation of stacking complexes (1:1) is able to quench its ability to
emission. The porphyrin examined exists predominantly in the form of monoanion.
The H TTMePP monoanion lifetime is shorter (2 ns) comparing to the lifetime of
2
the free-base porphyrin (9.2 ns). Both forms of the porphyrin, H P and HP-, are
2
fluorescent, but display different quantum yields. The value of Φ is higher for the
F
free-base porphyrin (0.125) than for its monoanion form and decreases drastically
during interacting with guanine. The process of quenching is static (Fig. 1), as
evidenced by the formation of π-stacked complexes, the decrease of the
fluorescence intensity and quantum yield of H TTMePP, as well as its inalterable
2
fluorescence lifetime.
The obtained results can become a support to the idea of a fluorescent
chemosensor of guanine, potentially useful for monitoring of guanine traces in
aqueous environment, studies of the diseases associated with uric acid
overproduction or for other biological and medical purposes.

7
Fig. 1 Reductive electron transfer from guanine (G) to H TTMePP (P) [3].
2

References:
[1] M. Makarska-Bialokoz, J. Fluoresc., 22 (2012) 1521.
[2] M. Makarska-Bialokoz, Cent. Eur. J. Chem., 11 (2013) 1360.
[3] M. Makarska-Bialokoz, J. Lumin., 147 (2014) 27.
[4] M. Makarska-Bialokoz, J. Mol. Struct., doi: 10.1016/j.molstruc.2014.10.032.
[5] M. Makarska-Bialokoz, P. Borowski, J. Lumin., doi: 10.1016/
j.jlumin.2014.12.005
8
UTILIZATION OF CUPFERRON IN STUDY OF NEW
PROCEDURES OF GALLIUM DETERMINATION USING
ADSORPTIVE STRIPPING VOLTAMMETRY

Mieczysław KOROLCZUK, Małgorzata GRABARCZYK, Iwona RUTYNA
DEPARTMENT OF ANALYTICAL CHEMISTRY
AND INSTRUMENTAL ANALYSIS

Since the 1970s gallium has attracted considerable interest, mainly in
electronics, the most common applications for gallium being advanced
semiconductors for microwave transceivers, DVD`s, laser diodes in compact discs
and other electronic devices. Gallium and its compounds are also used in the
production of low-melting alloys and as a specialized mirror coating in high-
temperature thermometers. As a result, in the year 2000 gallium consumption in the
United States reached nearly 40 metric tons and it is expected to increase even more
in the 21st century as scientists continue to find new applications for the metal. As a
result, the level of this element in the environment is gradually increasing. Because
gallium compounds are considered to be potential health hazards and Toxic
Substance Control Acta test submissions indicate that they may be carcinogenic, so
there is a need for reliable methods of their determination in trace concentration in
different environmental samples, especially in water because of its vital importance.
Stripping voltammetry has been widely used as a powerful tool for trace metal
analysis in water samples because of a lot of benefits: the method is cheap,
relatively simple and quick, characterized by possible field portability and most of
all high sensitivity. In order to obtain the low detection limit voltammetry with
adsorptive pre-concentration of a complex of the determined metal is much superior
to other methods. In this work, a new voltammetric strategy for sensitive and
selective determination of gallium using cupferron as a complexing agent was
proposed.

The procedure consists of three main steps:
• simultaneous deaeration of the sample by purging with nitrogen and formation of
Ga(III)-cupferron complex within 4 min.
• adsorption of Ga(III)-cupferron complex on the HMDE electrode within 30 s at
-0.4 V
• recording the differential pulse voltammogram by the electrochemical reduction of
Ga(III)- cupferron complex while the potential was scanned from -0.4 V to -1.2 V

Optimisation of the procedure
The formation of the complexes, their stability, and the potentials of reduction
are strongly dependent upon the pH value of the solution. Thus, the influence of pH
of the acetate buffer used as a supporting electrolyte on the gallium voltammetric
9
signal in the proposed procedure was examined. The maximum current of peak was
observed at pH = 3, for lower and higher of pH value the peak slightly decreases.
In the view of fact that the accumulation potential and time have a significant
influence on the sensitivity of the method, these parameters were precisely
examined in the proposed work. The peak current slightly increased with the
changing potential from -0.7 to -0.4 V. At the potential above -0.4 V the peak firstly
slightly decreased and next, at the potential of 0.1 V, it abruptly falls. Therefore the
potential of -0.4 V was selected as an optimal accumulation potential in the
proposed method. The effect of adsorptive accumulation time on the peak current
was examined over the range from 0 to 300 s using standard measuring conditions.
The peak current was found to increase linearly with accumulation time up to 120 s.
To choose the optimal concentration of cupferron used as a complexing agent
for Ga(III), the effect of their concentration on the peak current was studied. The
peak current increased upon increasing the cupferron concentration to 5 × 10-5 mol
L-1 and after that it was constant.

Analytical characterization
The calibration graph for Ga(III) for an accumulation time of 30 s was linear in
the range from 5 × 10-10 to 5 × 10-7 mol L-1 with the linear correlation coefficient r =
0.998. The relative standard deviation from five determinations of Ga(III) at a
concentration of 2 × 10-9 mol L-1 was 4.1 %. The detection limit estimated from 3
times the standard deviation of low Ga(III) concentration and accumulation time of
30 s was about 1.3 × 10-10 mol L-1.

Analytical application
In order to examine the performance of the new proposed procedure, it was
applied for the determination of trace amounts of gallium in natural water samples,
such as river water (Bystrzyca) and stagnant water (Lake Zemborzyce) collected
from eastern areas of Poland. No Ga(III) was detected in concentrations above the
detection limit, so recovery studies of Ga(III) were carried out of them, after the
addition of a controlled aliquot of standard solution. Samples were spiked 2 × 10-8
and 5 × 10-8 mol L-1 of Ga(III) and analysed with the standard addition method
based on three repetitions of analysis. The obtained recoveries were in the range
from 98.4 to 101.2 % with relative standard deviation between 3.5 and 3.9 % and in
the range from 96.2 to 98.5 % with relative standard deviation between 3.4 and 4.1
%, for Bystrzyca river water and Lake Zemborzyce water, respectively.

10