A Water-Stable Luminescent ZnII Metal-Organic Framework as Chemosensor for High-Efficiency Detection of CrVI-Anions (Cr2O72? and CrO42?) in Aqueous Solution

Article abstract of DOI:10.1002/chem.201705328

A new luminescent Zn^II-MOF with 1D triangular channels along the b axis, namely NUM-5, has been successfully assembled and well characterized, which features good stability, especially in aqueous solution. Interestingly, this compound exhibits

Full text of DOI:10.1002/chem.201705328

A Journal of
Accepted Article
Title: A Water-Stable Luminescent Zn(II) Metal-Organic Framework
as Chemosensor for High-Efficiency Detection of CrVI-Anions
(Cr2O72- and CrO42-) in Aqueous Solution
Authors: Tong-Liang Hu, Zhao-Quan Yao, Guang-Yu Li, Jian Xu, and
Xian-He Bu
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To be cited as: Chem. Eur. J. 10.1002/chem.201705328
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A Water-Stable Luminescent Zn(II) Metal-Organic Framework as
Chemosensor for High-Efficiency Detection of CrVI-Anions
2-
2-
(Cr2O7 and CrO4 ) in Aqueous Solution
Zhao-Quan Yao,†[a] Guang-Yu Li,†[a] Jian Xu,[a] Tong-Liang Hu,*[a,b] and Xian-He Bu*[a,b,c]
Abstract:
A
new luminescent Zn(II)-MOF with 1D triangular
time-consuming, high cost, hardly portable and require trained
personnel. Therefore, developing a new convenient, reliable and
inexpensive method for the detection of CrVI contaminants is
urgently needed.
channels along the b axis, namely NUM-5, has been successfully
assembled and well characterized, which features good stability,
especially in aqueous solution. Interestingly, this compound exhibits
a fast, sensitive and selective luminescence quenching response
towards CrVI (Cr2O72-/CrO42-) in aqueous solution. The detection
It is well established that optical sensing is a simple, real-time
and cost-effective detection method,[9-14] thereby promising for
the detection of CrVI. As a new class of optical materials,
luminescent metal-organic frameworks (LMOFs) have recently
attracted immense interests because of their specific
photophysical properties, easily tailorable structures and
permanent porosity.[15-23] All these fascinating properties endow
them with potential applications in chemosensors,[24-28] photonic
devices,[29-33] and optoelectronic technologies.[34-36] Importantly,
the reported LMOF-based sensors display advantages in quick
response time,[37] excellent sensitivity and selectivity,[38] etc.
2-
2-
limits towards Cr2O7 and CrO4 ions are estimated to be 0.7 and
0.3 ppm, respectively, which are among the lowest detection limits
reported for the MOF-based fluorescent probes that can
2-
2-
simultaneously detect Cr2O7 and CrO4 in aqueous environment.
The possible detection mechanism has been discussed in detail.
Moreover, it can be easily regenerated after detection experiments,
indicative of excellent recyclability. All these results suggest NUM-5
to be a highly selective and recyclable luminescent sensing material
for the quantitative detection of CrVI-anions in aqueous solution.
Therefore, they are a good candidate for detecting CrVI (Cr2O7
2-
/CrO42-) in aqueous solution.[39,40] In this regard, some LMOF
probes for CrVI (Cr2O72-/CrO42-) have been reported recently;
however, the lack of water stability and recyclability impedes
their applications in practice.[41] Thus, the development of a new
LMOF for sensing CrVI (Cr2O72-/CrO42-) in aqueous solution with
high sensitivity, selectivity and excellent recyclability is extremely
beneficial.
Introduction
Chromium, especially hexavalent chromium, is one of most
common toxic heavy metal pollutants present in water. Very
dangerously, it causes permanent damage to human health and
living environment, even at a low concentration.[1-4] Thus, World
Health Organization (WHO) guidelines limit CrVI (Cr2O72-/CrO4
to 50 µg L-1 in groundwater.[5] Up to now, the prevailing detection
of CrVI (Cr2O72-/CrO42-) is mainly based on instrumental methods,
including atomic absorption spectroscopy, ICP-MS and
electrochemical analysis.[6-8] However, these methods are often
On the basis of above discussions, we herein employ
luminescent 9,10-bis(4-pyridyl)anthracene ligand and 4,4’-
oxybis(benzoic acid) as organic linkers with Zn2+ ion to fabricate
a new LMOF, {[Zn3(bpanth)(oba)3]·2DMF}n (bpanth = 9,10-bis(4-
pyridyl)anthracene, H2oba = 4,4’-oxybis(benzoic acid), denoted
as NUM-5, the structure of which can be viewed as a three-
dimensional (3D) network with one-dimensional (1D) triangular
channels. Remarkably, NUM-5 could maintain the crystallinity in
several common solvents, especially in aqueous solution,
providing the prerequisite for water-phase detection. In addition,
NUM-5 is highly fluorescent and exhibits selective and sensitive
2-
)
[a]
Z.-Q. Yao, G.-Y. Li, Dr. J. Xu, Prof. T.-L. Hu, Prof. X.-H. Bu
School of Materials Science and Engineering
National Institute for Advanced Materials
Tianjin Key Laboratory of Metal and Molecule-Based Material
Chemistry
quenching response towards CrVI (Cr2O72-/CrO42-) in aqueous
2-
solution, with a detection limit as low as 0.7 ppm for Cr2O7
,
Nankai University
while 0.3 ppm for CrO42-. Furthermore, this compound can also
be easily and quickly regenerated, indicative of excellent
recyclability.
Tianjin 300350 (P. R. China)
E-mail: tlhu@nankai.edu.cn
buxh@nankai.edu.cn
Prof. T.-L. Hu, Prof. X.-H. Bu
[b]
Key Laboratory of Advanced Energy Materials Chemistry (Ministry
of Education)
Collaborative Innovation Center of Chemical Science and
Engineering (Tianjin)
Tianjin 300071 (P. R. China)
Prof. X.-H. Bu
College of Chemistry
Results and Discussion
Structural analysis
[c]
[†]
Nankai University
Tianjin 300071 (P. R. China)
These authors contributed equally.
Single-crystal analysis reveals that NUM-5 crystallizes in
monoclinic system with space group C2/c. The asymmetric unit
contains two Zn2+ cations (Zn1 and Zn2) in different coordination
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.2017xxxxx.
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environments, one bpanth ligand, three oba2- ligands and two
synthesized NUM-5 matches well with the simulated result from
free DMF molecules (Figure S3). As shown in Figures 1a and 1b, single-crystal data, indicating the phase purity (Figure S5). On
Zn1 is octahedrally coordinated by six carboxylate oxygen atoms
from six individual oba2- ligands; Zn2 is five-coordinated by four
oxygen atoms from three oba2- ligands and one nitrogen atom
from bpanth ligand, showing a tetragonal-pyramidal geometry.
One Zn1 and two Zn2 ions form a unique tri-nuclear node as the
secondary building unit (Figure 1c), Zn3O12N2, which is further
connected with six oba2- ligands in different directions to
generate a 3D network with 1D rhombic channels. In these
channels, each Zn2 ion provides a coordination site to anchor
bpanth ligand that has excellent luminescent property,
generating a 3D framework with 1D triangular channels running
along the b axis (Figure1e). We speculate that the specific
bpanth ligands decorated with anthracene group in the channels
play a role in the recognition process. In addition, PLATON
analysis shows that the effective free volume of NUM-5 is 34.6%
of the crystal volume (2559.6 Å3 out of the 7394.0 Å3 unit cell
volume) after squeezing DMF guest molecules.[42] From the
topological viewpoint, when simplifying the tri-nuclear Zn as an
8-connected node (Figure 1d), the single 3D framework of NUM-
5 can then be viewed as an 8-connected ttd net with the point
symbol of {412.58.67.7} (Figure 1f).
the other hand, in order to explore its solvent stability, we
immersed the fresh sample of NUM-5 in several common
solvents (CH3CN, EtOH, AcOEt, THF, H2O, CHCl3, MeOH, DMF,
DMAC, acetone) for 24 h and found that all the PXRD patterns
matched well with that of the as-synthesized sample, indicating
that this compound has good resistance against a wide range of
solvents (Figure 2a). More strikingly, NUM-5 could maintain the
single crystallinity in water for 1 week, even in pH =3 to pH = 11
aqueous solution for 1 day, as revealed by the PXRD patterns in
Figure 2b. These results indicate that the sample is also intact in
acid aqueous solutions. Evidently, such an excellent solvent
stability of NUM-5 makes it more feasible in practical
applications.
Figure 1. a)-b) Coordination environment of Zn2+ (Zn1 and Zn2) in NUM-5. c)
Secondary building unit of tri-nuclear Zn3 cluster. d) Tri-nuclear Zn3 cluster
viewed as an 8-connected node. e) Perspective view of 3D coordination
framework of NUM-5 along the b-axis (the bpanth ligands and oba2- ligands
are highlighted in yellow and green, respectively). f) ttd topology network of
NUM-5.
Stability characterization of NUM-5
In order to inspect the thermal stability of NUM-5,
thermogravimetric analysis (TGA) and powder X-ray diffraction
(PXRD) were then carried out. The TGA analysis of the freshly
prepared NUM-5 reveals a weight loss of 12.4% from 87 to 200
˚C, corresponding to the loss of free DMF molecules in channels
(calculated value of 10.1%) and the framework was not
collapsed until 350 ˚C (Figure S6). The PXRD pattern of the as-
Figure 2. a) PXRD patterns of NUM-5 immersed in different solvents for 24 h.
b) PXRD patterns of NUM-5 immersed in aqueous solutions (pH = 2-12) for 1
d and in water at pH = 7 for 3 days (red) and 1 week (green) at room
temperature.
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Luminescent properties and detection of CrVI
In order to explore the sensing property of NUM-5 towards
CrVI, we separately added several sodium salt aqueous solutions
(F-, Cl-, Br-, I-, OAc-, NO3 , SO42-, ClO4 , MoO42-, WO42-, CrO4
,
-
-
2-
Next, we investigated the solid-state luminescent properties of
NUM-5 at room temperature. As shown in Figure S7, under UV
light (365 nm) irradiation, NUM-5 exhibits bright cyan light
emission with the maximum around 460 nm, which red-shifts
about 10 nm relative to that of the bpanth ligand. Thus, the
luminescence of NUM-5 should originate from intra-ligand
emission and the observed slight emission shift is due to the
interaction between the organic linkers and d10 metal ions.[17]
Furthermore, NUM-5 also exhibits much stronger emission
compared to bpanth ligand in aqueous solution due to the better
disperse efficiency (Figure S8). Considering the excellent
luminescent property as well as the good stability in aqueous
solution, employing NUM-5 as a fluorescent sensor for detecting
CrVI in aqueous solution seems to be feasible and promising.
Cr2O72-) with the concentration of 2.5 × 10-3 mol L-1 to the
aqueous suspension of NUM-5. As shown in Figure 3a, only the
2-
2-
additions of CrO4 and Cr2O7 led to significant turn-off
quenching with the quenching percentage being 98.3% and
99.3%, respectively. In contrast, the other anions displayed
slight or no discernible effect under the same conditions.
Beneficially, the fluorescence quenching of NUM-5 in response
2-
2
to the presence of CrO4 or Cr2O7 could be observed by the
naked eyes under UV light (Figure 3b), even when the
concentration of CrVI (Cr2O72-/CrO42-) is as low as 1 × 10-5 mol L-1
(Figure S9). Thus, all these results suggest NUM-5 to be a
qualified fluorescent sensor highly selective to CrVI (Cr2O7
/CrO42-) among other common anions.
2-
Figure 3. a) Anions (2.5 × 10-3 mol L-1) selectivity of NUM-5 in aqueous solution. b) Fluorescence color changes of NUM-5 aqueous solution (3 mg/10 mL, 10 mL)
2-
2-
before and after adding Cr2O7 or CrO4 (2.5 × 10-3 mol L-1) under 365 nm UV light. c)-d) Fluorescence quenching effect of NUM-5 towards different
concentrations of Cr2O72- or CrO42- (0-2.5 mM) in aqueous solution (λex = 390 nm). e)-f) Stern-Volmer plot of I0/I vs. the concentration of Cr2O72- or CrO42- in NUM-5
aqueous solution (Inset figure: enlarged view of a selected area).
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We also carried out the titration experiments to further assess
the sensing ability of NUM-5 against CrVI (Cr2O72-/CrO42-). As
shown in Figures 3c and 3d, the emission intensity of NUM-5 in
aqueous solution gradually decreased with the increasing
However, chemosensors feasible in practical applications
require not only high sensitivity and selectivity, but also good
anti-interference ability, recyclability and response rate. For
NUM-5, the fluorescence intensity was acutely quenched in the
concentration of Cr2O7 (or CrO42-) from 0 to 2.5 × 10-3 mol L-1.
presence of CrO4 or Cr2O72-, while no obvious change was
2-
2-
When the concentration of CrVI approached 2.5 × 10-3 mol L-1,
the fluorescence signal of NUM-5 was almost completely
quenched. The quenching degree can be quantitatively
evaluated by Ksv. (i.e., quenching effect constant) using the
Stern-Volmer equation: I0/I = 1 + Ksv[G]. Herein, I0 and I are the
fluorescence intensities of NUM-5 before and after adding CrVI
(Cr2O72-/CrO42-), while [G] represents the corresponding
concentration. Figures 3e and 3f show that the ratio I0/I
increases in direct proportion to increasing concentration of
observed when the competitive anions (F-, Cl-, Br-, I-, OAc-, NO3 ,
-
-
SO42-, ClO4 , MoO42-, WO42-) were added into the solution
(Figures 4a and 4b). Furthermore, the quenching degree of
NUM-5 was almost not decreased during five consecutive cycles,
2-
for either CrO4 or Cr2O72-(Figures 4c and 4d), and the PXRD
patterns illustrate that the structure of NUM-5 was well
maintained (Figure S11). More strikingly, after adding CrVI
(Cr2O72-/CrO42-) ions (2.5 × 10-3 mol L-1), the fluorescence
intensity of NUM-5 quenched immediately and reached to
minimum in 30s, which indicates the fast response rate (Figure
2-
either Cr2O7 or CrO42-, with the Ksv values calculated to be 9.4
× 104 M (R2 = 0.997) and 1.24 × 105 M (R2 = 0.997), respectively. S12). Consequently, these results support that NUM-5 has good
2-
2-
In addition, the detection limits of Cr2O7 and CrO4 are about
0.7 ppm and 0.3 ppm, respectively (Figure S10), based on the
well-established formula.[43] It is noteworthy that in the light of
literatures, there have been only a small number of MOF-based
anti-interference ability, recyclability and fast response rate, thus
promising for sensing CrVI anions in real environments.
2-
2-
Mechanism for sensing CrVI
fluorescent probes that can detect Cr2O7 and CrO4 ions
simultaneously in aqueous solution,[45,47] compared to which
NUM-5 possesses the lowest detection limit that is very close to
the standard established by WHO.[44-46] In conclusion, the above-
demonstrated results strongly suggest that NUM-5 qualifies as a
chemosensor for CrVI (Cr2O72-/CrO42-) in aqueous solution with
high sensitivity.
In order to explore the possible mechanism of the fluorescent
quenching of NUM-5 induced by CrVI (Cr2O72-/CrO42-), PXRD
experiments were first carried out. The patterns in Figure S11
confirmed that the sample of NUM-5 maintained the crystallinity
after titration and cyclic experiments. Hence, the fluorescence
Figure 4. a)-b) Fluorescence spectra of NUM-5 dispersed in aqueous solutions upon addition of 1 × 10-2 mol L-1 selected anions (red) and subsequent addition of
Cr2O72- or CrO42- ion (black). c)-d) Recyclability of NUM-5 for Cr2O72- or CrO42- detection in aqueous solution.
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intensity reduction was not due to the decomposition of
crystalline structures.[41] Then, we examined the filtrate of NUM-
5 with CrVI (Cr2O72-/CrO42-) in titration experiments by ICP
analysis and solid-state fluorescence spectra measurement. The
ability. Moreover, NUM-5 can be simply regenerated, indicating
its excellent recyclability. Further detailed analyses reveal that
the fluorescence quenching response of NUM-5 actually
originates from the synergistic effect of competitive absorption
and resonance energy transfer from MOF to CrVI. Notably, the
detection limits of NUM-5 for sensing CrVI can reach 0.7 and 0.3
ppm, for Cr2O72- and CrO42-, respectively. All the results suggest
that NUM-5, as an efficient fluorescent probe, holds promise in
the practical application for sensing CrVI (Cr2O72-/CrO42-) in
aqueous solution.
2-
results show that only a little amount of Cr2O7 (CrO42-) ions in
solution can be immobilized into the channels of NUM-5 (Table
S3) and this part of CrVI (Cr2O72-/CrO42-) has little quenching
effect to the fluorescence intensity of NUM-5 (Figure S13).
Therefore, in this system, the adsorption amount of target anions
is also not the determining factor for the observed fluorescence
quenching behavior.[48] The luminescence lifetimes of NUM-5
before and after being immersed in CrVI (Cr2O72-/CrO4
)
2-
aqueous solutions are same, which indicated that there was no
coordination effect between CrVI ions and NUM-5 (Figure S14).
Notably, as shown by Figure S15, the UV/Vis absorption bands
Experimental Section
Materials and Methods: All the reagents and solvents for the synthesis
were purchased from commercial sources and used as received, except
for 9,10-bis(4-pyridyl)anthracene ligand, which was synthesized by using
a previous procedure.[52] All solvents were analytical grade and without
further purification. 1H NMR spectrum was recorded on a Mercury Vx-300
spectrometer at 300 MHz in CDCl3. Mass spectrum was tested on an
Agilent 6520 Q-TOF LC/MS in CH2Cl2. Elemental analysis (C, H and N)
was performed on a vario EL CUBE. IR spectrum was measured on a
FTS6000 (Bio-rad) FT-IR spectrometer using KBr pellets in the 4000-400
cm-1 range. Thermogravimetric analysis (TGA) was carried out on a
Rigaku standard TG-DTA analyzer with a heating rate of 10 ˚C·min-1, with
an empty Al2O3 crucible used as a reference. The room-temperature
powder X-ray diffraction (PXRD) patterns were recorded on a Rigaku
D/Max-2500 diffractometer at 60 kV, 300 mA with a Cu-target tube and a
graphite monochromator. All fluorescent measurements were performed
on a Varian Cary Eclipse fluorescence spectrometer equipped with a
plotter unit.
of NUM-5 and CrVI anions (Cr2O72-/CrO42-) strongly overlapped,
far exceeding other tested anions. Thus, the CrVI (Cr2O72-/CrO4
)
2-
ions in aqueous solution compete and hinder the absorption of
excitation energy, accounting for the selective fluorescence
quenching response of NUM-5.[49,50] Apart from this, it is evident
that the broad absorption bands of CrVI (Cr2O72-/CrO42-) from 250
to 525 nm also cover a large part of the emission band of NUM-
5 (400-650 nm), while in the same wavelength range no overlap
between the emission band of NUM-5 and the absorption bands
of other anions was observed (Figure S16). Thus, the resonance
energy transfer from the MOF (NUM-5) to the analyte (CrVI)
might take place and lead to the fluorescence quenching.[45]
Based on these pieces of evidence, we suggest that both
competitive absorption and resonance energy transfer are
responsible for the fluorescence quenching response of NUM-5
to CrVI anions (Figure 5), as reported in other previous
studies.[40,50,51]
Crystal Structure Determination: X-ray single-crystal diffraction data
for NUM-5 was collected on a Rigaku SCX-mini diffractometer at 293(2)
K with Mo-Ka radiation (λ = 0.71073 Å) in ω scan mode. The program
SAINT[53] was used for the integration of the diffraction profiles. All the
structures were solved by direct methods using the SHELXS program of
the SHELXTL package and refined by full-matrix least-squares methods
with SHELXL (semiempirical absorption corrections were applied using
the SADABS program).[54] Metal atoms were located from the E-maps
and other non-hydrogen atoms were located from the successive
difference Fourier syntheses and refined with anisotropic thermal
parameters on F2. Hydrogen atoms of the ligands were generated
theoretically on the specific atoms and refined isotropically with fixed
thermal factors. Hydrogen atoms of the DMF molecules were added by
difference Fourier maps and refined with constraints. Detailed
crystallographic data is summarized in Table S1. The selected bond
lengths and angles are given in Table S2. CCDC 1482730 contain the
supplementary crystallographic data for this paper. The data can be
obtained free of charge from The Cambridge Crystallographic Data
Centre.
Figure 5. The possible quenching mechanism for detecting CrVI by NUM-5.
Synthesis of Bpanth Ligand:[52,55-56] 9,10-Dibromoanthracene (2.00 g,
5.95 mmol), 4-pyridylboronic acid (2.40 g, 17.80 mmol), and K2CO3
(11.60 g, 35.50 mmol) were added to a mixture of dry PhMe/DMF (300
mL, v:v = 1:1), which had been degassed with Ar for 15 min. Next,
Pd(PPh3)4 (0.68 g, 0.59 mmol) was added to the reaction mixture and the
solution was heated to 130 ˚C under Ar for 48 h. Then, the reaction
mixture was cooled to room temperature and the palladium catalyst was
filtered off using Celite. The organic phase was concentrated under
vacuum and then dissolved in CH2Cl2 followed by extracting with H2O
three times. Concentrated HCl was added dropwise (pH = 2-3) to the
Conclusions
In summary, a new luminescent Zn(II)-MOF (NUM-5) based on
anthracene-contained ligand has been rationally constructed.
The results of fluorescence titration, anti-interference, and cyclic
experiments indicate that this compound can be used as an
excellent probe for sensing CrVI (Cr2O72-/CrO42-) in aqueous
solution with high sensitivity, selectivity and anti-interference
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organic layer, which caused the desired product to precipitate from
solution. The precipitate was collected by filtration and then dissolved in
H2O. Finally, NaOH (aq., 10 M) was added dropwise to the water layer
until the pH was ~ 8-9, which resulted in precipitation of pure product.
Yield: 1.4g (70%). Data for bpanth: MS: m/z (%): 333.1387 [M+H]+ 1H
NMR (300MHz, CDCl3): δ=8.87 (d, J=6.0 Hz, 4H; ArH), 7.61 (m, 4H, ArH),
7.44 (d, J=6.0 Hz,4H;ArH), 7.40 ppm (m, 4H, ArH). MS and 1H NMR
spectra of bpanth were shown in Figure S1 and Figure S2, respectively.
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Synthesis of NUM-5: Zn(NO3)2·6H2O (30.00 mg, 0.10 mmol), bpanth
(16.60 mg, 0.05 mmol), and 4,4’-oxybis(benzoic acid) (H2oba) (16.60 mg,
0.10 mmol) were dissolved in 3 mL N,N’-dimethylformamide (DMF), and
stirred for 30 min. The resulting solution was then sealed, and heated to
100 ˚C and kept for 3d. After cooling down to room temperature, orange
chrysanthemum petal-shaped crystals were obtained (yield ca. 53.8 %,
based on bpanth). EA Calcd (%) for C72H54Zn3N4O17: C 59.12, H 3.77, N
3.88; Found: C 58.83, H 3.68, N 3.68. FT-IR (cm-1, KBr): 3321w, 3065s,
2932s, 1923m, 1662s, 1606vs, 1562vs, 1500s, 1409vs, 1302m, 1163vs,
1099s, 1017m, 877vs, 777vs, 701m, 658s, 532m.
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Fluorescence Titration Experiments: Fluorescence titrations were
performed on a Varian Cary Eclipse fluorescence spectrometer using a 1
cm path length quartz fluorescence cell. Titrations were carried out by
placing the aqueous suspensions of NUM-5 (3 mg/10 mL) into the 4 mL
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cuvette and adding increasing amounts of CrVI (Cr2O7 or CrO42-) (0-2.5
2-
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× 10-3 mol L-1) using a microsyringe. The aqueous suspensions of NUM-5
was excited at 390 nm, and the emission spectra were recorded in the
range 400-650 nm. After each addition, an equilibration time of 8-10 min
was allowed before the fluorescence intensity was recorded. Statistical
analysis of the data was carried out using Origin 8.0.
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A novel luminescent Zn(II)-MOF,
(NUM-5) has been successfully
assembled and investigated as a
regenerable luminescent sensor with
excellent sensitivity, selectivity and
fast luminescence quenching
response to CrVI-anions in aqueous
solution. The experiments exhibit
NUM-5 can be a great candidate for
quantitatively detecting CrVI-anions in
aqueous solution.
Zhao-Quan Yao,† Guang-Yu Li,† Jian
Xu, Tong-Liang Hu,* and Xian-He Bu*
Page No. – Page No.
A Water-Stable Luminescent Zn(II)
Metal-Organic Framework as
Chemosensor for High-Efficiency
Detection of CrVI-Anions (Cr2O72- and
CrO42-) in Aqueous Solution
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