A simple water-soluble phenazine dye for colorimetric/ fluorogenic dual-mode detection and removal of Cu2+ in natural water and plant samples

Article abstract of DOI:10.1016/j.dyepig.2019.107707

Detection and removal of heavy metal ions in a variety of complex water systems using dyes remains a challenge. Here we have developed a rapid, low-cost, on-site water-soluble dye for the colorimetric/fluorogenic detection and removal of copper ions in natural water and plant samples. By comparing with dye molecule AHP, this water-soluble phenazine dye (AHPN) has a high fluorescence quantum yield and excellent coordinated ability with copper ions. AHPN can effectively remove copper ions in various natural water samples due to its strong binding ability with Cu²⁺. Moreover, the test strips also were fabricated and successfully used for real-time detection of Cu²⁺ in water with simple-to-use, low-cost, quick response and provide an obvious effect by naked-eye. All data in this experiment showed that this water-soluble phenazine dye AHPN has excellent effect on the detection and removal of Cu²⁺.

Full text of DOI:10.1016/j.dyepig.2019.107707

Accepted Manuscript
A simple water-soluble phenazine dye for colorimetric/ fluorogenic dual-mode
detection and removal of Cu2+ in natural water and plant samples
Tai-Bao Wei, Bi-Rong Yong, Li-Rong Dang, You-Ming Zhang, Hong Yao, Qi Lin
PII:
S0143-7208(19)30944-1
DOI:
https://doi.org/10.1016/j.dyepig.2019.107707
Article Number: 107707
Reference:
DYPI 107707
To appear in: Dyes and Pigments
Received Date: 26 April 2019
Revised Date: 9 July 2019
Accepted Date: 9 July 2019
Please cite this article as: Wei T-B, Yong B-R, Dang L-R, Zhang Y-M, Yao H, Lin Q, A simple water-
soluble phenazine dye for colorimetric/ fluorogenic dual-mode detection and removal of Cu2+ in natural
water and plant samples, Dyes and Pigments (2019), doi: https://doi.org/10.1016/j.dyepig.2019.107707.
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ACCEPTED MANUSCRIPT
Graphical Abstract
A simple water-soluble phenazine dye for colorimetric/
fluorogenic dual-mode detection and removal of Cu2+ in
natural water and plant samples
a
Tai-Bao Wei , Bi-Rong Yong a, Li-Rong Dang a, You-Ming Zhang a, b, Hong Yao a and
Qi Lin *a
A rapid, low-cost, real-time and water-soluble phenazine dye (AHPN) was
constructed for the colorimetric and fluorogenic detection of copper ions. At the same
time, it shows excellent removal ability of copper ions in natural water samples.
Corresponding authors. Tel.: +86-931-7973120; E-mail: weitaibao@126.com (T. - B. Wei); linqi2004@126.com
(Q. Lin).

ACCEPTED MANUSCRIPT
A simple water-soluble phenazine dye for colorimetric/
fluorogenic dual-mode detection and removal of Cu2+ in natural
water and plant samples
Tai-Bao Wei a, Bi-Rong Yong a, Li-Rong Dang a, You-Ming Zhang a, b, Hong Yao a and Qi Lin *a
a Key Laboratory of Eco-Environment-Related Polymer Materials, Ministry of Education of China, Key
Laboratory of Polymer Materials of Gansu Province,
College of Chemistry and Chemical Engineering, Northwest Normal University, Lanzhou, Gansu,
730070, P. R. China
b College of Chemical and Chemical Engineering, Lanzhou City University, Lanzhou, Gansu, 730070, P.
R. China.
Abstract
Detection and removal of heavy metal ions in a variety of complex water
systems using dyes remains a challenge. Here we have developed a rapid, low-cost,
on-site water-soluble dye for the colorimetric/fluorogenic detection and removal of
copper ions in natural water and plant samples. By comparing with dye molecule AHP,
this water-soluble phenazine dye (AHPN) has a high fluorescence quantum yield and
excellent coordinated ability with copper ions. AHPN can effectively remove copper
ions in various natural water samples due to its strong binding ability with Cu2+.
Moreover, the test strips also were fabricated and successfully used for real-time
Corresponding authors. Tel.: +86-931-7973120; E-mail: weitaibao@126.com (T. - B. Wei); linqi2004@126.com
(Q. Lin).
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detection of Cu2+ in water with simple-to-use, low-cost, quick response and provide
an obvious effect by naked-eye. All data in this experiment showed that this
water-soluble phenazine dye AHPN has excellent effect on the detection and removal
of Cu2+.
Keywords: Water-soluble dye; Colorimetric/Fluorogenic; Detection; Removal; Cu2+.
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1. Introduction
Copper is the third most abundant transition metal in the human body [1]. It is
also a micronutrient for all known life forms, and it has multiple functions ranging
from bone formation and cellular respiration to connective tissue development [2-5].
Low level of Cu2+ in the cells will affect some enzymes activity, while Cu2+ existence
in excess level will cause many diseases such as Wilson disease, Alzheimer disease,
liver cirrhosis, prion-induced diseases and kidney failure [6-10]. High concentrations
of Cu2+ can hamper the self-purification capability of the seas or rivers also can
destroy the biological reprocessing systems in water; its toxicity can accumulate and
non-biodegradable in the food chain, etc [11-16]. Cu2+ pollution has become more and
more serious along with the development of industry. These problems are threatening
the ecosystem and human health and have become a huge concern throughout the
world [11].
Phenazine has a special status in the field of organic chemistry. Mid-19th century,
Perkin tried to synthesize quinine but he got the mauveine (a mixture of substituted
phenazine and other compounds) [17, 18]. This was the first time that humans had
obtained a dyeable substance by chemical method, thus began a new era of artificial
synthesis of dyes [19, 20]. There are also other applications those make phenazines
attractive for modern chemistry [21], spanning from organic electronics to sensors and
pharmaceutical purposes, as well as photoactive materials for dye sensitized solar
cells and for photocatalysis [22-24].
Phenazine derivatives can be used as ion ligands and hydrogen bond receptors
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due to their own structural characteristics (π system with electron deficiency, nitrogen
atom with lone pair of electrons, and three condensed aromatic rings), and facilitate
the cross-interaction of π-π electrons. Because of its large conjugate system, special
optical properties, high fluorescence quantum yield, narrow emission band, large
stokes displacement and the maximum absorption and emission wavelength in the
visible region [25-27]. Therefore, these compounds have great application prospects
in the field of weak interaction in supramolecular chemistry, and they have been
studied for many years as a molecular probe and molecular self-assembly device of
signal response [28, 29]. In recent years, the application of phenazine derivatives are
widely concerned in the field of molecular ion recognition and supramolecular
self-assembly [30-32]. Therefore, it is of great significance to study the optical
properties and sensing behavior of water-soluble phenazine dye.
Although there have been a lot of reports on the detection of copper ion [33-41]
and application of dye [42-46], there are few reports on the detection and removal of
copper ions in real water samples by phenazine dyes [47-48] (Table S1). In this work,
we reported the water-soluble phenazine (AHPN) by colorimetric and fluorogenic
detection and removal of Cu2+. We treated it with NaOH to increase its solubility and
optical properties [49]. At the same time, its application and difference with AHP
optical response are also studied. This water-soluble phenazine dye has a higher
fluorescence quantum yield (Φ up to 0.52) than AHP due to the intramolecular charge
transfer from AHP to AHPN. It can also detect and remove Cu2+ in more complex
natural water systems with low detection limit, quick response, and good
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anti-interference ability. World Health Organization (WHO) and U. S. Environmental
Protection Agency (EPA) had defined the concentration limits (2.0 mg/L and 1.3 mg/L)
of copper in the drinking water [50]. In the three concentrations of solutions prepared
by us, the worst adsorption concentration limits can reach 0.083 mg/L. Moreover, in
order to make it more valuable, a colorimetric strip paper was fabricated. The
fabricated test strip is simple-to-use, low-cost, instant and easily noticeable by
naked-eye detection. This test strip also demonstrated excellent selectivity towards
Cu2+ without interfering with any other ions. These data show that this water-soluble
phenazine dye has a superior detection and high removal capacity for Cu2+. Up to now,
to the best of our knowledge, this is the first report on colorimetric and fluorescent
chemosensor based on water-soluble phenazine dye for the detection and removal of
Cu2+ in complex natural water systems.
2. Experimental section
2.1.1 Synthesis of dye molecule AHP
Diluted hydrochloric acid (6 mol/L) was added slowly to O-phenylenediamine
(5.40 g, 50 mmol) in round-bottom flask (500 mL). The resulting solution was stirred
at room temperature until the o-phenylenediamine completely dissolved. 53.0 g
FeCl3·6H2O was dissolved in distilled water (75 mL) and trickled slowly into the
round-bottom flask with a constant pressure funnel. With the addition of FeCl3·6H2O,
a red solid gradually formed. Produced mixture was stirred for 24 hours, then
removed and filtered, the red solid was washed with 6mol/L diluted hydrochloric acid
for 3 to 5 times. Put red solid in hot distilled water at 100℃ and added 75 ml NaOH
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(2 mol/L) into it, then a yellow solid is formed immediately. Continue to stir for 30 to
35 minutes and let it stand for 12hrs, after the suction filtration has tan solid was
produced which was 2,3-diaminophenazine (Yield: 41.5%). An orange precipitate was
formed gradually after the addition of hydrochloric acid to the filtrate drop by drop.
Then, adjust the appropriate pH (pH=4~5) for precipitate and washed with distilled
water. The obtained orange-red solid after drying was 2-amino-3-hydroxyphenazine
(AHP). The reaction mechanism and synthesis route of AHP were showed in Scheme
S1. Yield: 52.7%. m.p > 300°C; 1H NMR (DMSO-d6, 600 MHz) δ: 11.33 (s, 1H), 7.94
(dd, J = 17.8, 7.7 Hz, 2H), 7.60 (m, 2H), 7.15 (s, 1H), 6.92 (s, 1H), 6.25 (s, 2H)
[51-52].
2.1.2 Synthesis of dye molecule AHPN
The 2-amino-3-hydroxyphenazine (AHP) (0.4221 g, 2 mmol) was added to 20
ml of EtOH and stirred for 10 minutes in a magnetic stirrer until completely dissolved.
Then, NaOH (0.08 g, 2 mmol) was added and brown precipitate was formed
immediately. Stirring was continued to complete the precipitation, and filtered off the
precipitate. Washed the precipitate with ethanol for 3 times and then dried it in oven
(60°C). AHPN is a brown solid, it has a good solubility in distilled water. Yield: 98%.
m.p > 300°C; 1H NMR (DMSO-d6, 600 MHz) δ: 7.63 (d, J = 8.2 Hz, 2H), 7.57 (s, 1H),
7.28-7.24 (m, 2H), 7.17 (m, 1H), 6.51 (s, 1H), 6.07 (s, 1H); 13C NMR (DMSO-d6, 150
MHz), δ/ppm: 166.44, 150.61, 146.03, 143.58, 140.45, 138.82, 127.55, 126.88,
125.11, 123.42, 100.96, 98.27; IR: (KBr, cm-1) v: 3445 (NH2), 3049 (ArH), 1538
(C=C), 1447 (C=C), 1222 (C–O); ESI/MS: m/z calcd for C12H8N3NaO (M+) 233.0565,
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found 233.0585 (Fig. S1 to Fig. S5). The synthetic route and structures of AHP and
dye molecular AHPN are showed in Scheme 1.
2.2 Characterizations
2.2.1 General procedure for UV-vis experiments
All the UV-vis experiments were carried out in fresh double distilled water on a
Shimadzu UV-2550 spectrometer. Any changes in the UV-vis spectra of the
synthesized compound were recorded on addition of perchlorate salts while keeping
the ligand concentration constant (2.0 × 10-5 M) in all experiments. Perchlorate salt of
cations (Fe3+, Hg2+, Ag+, Ca2+, Cu2+, Co2+, Ni2+, Cd2+, Pb2+, Zn2+, Cr3+, Mg2+ and Fe2+)
were prepared with 4.0 × 10-4 M throughout all UV-vis experiments.
2.2.2 General procedure for fluorescence spectra experiments
All the fluorescence spectroscopy was carried out in fresh double distilled water
on a Shimadzu RF-5301 spectrometer. Any changes in the fluorescence spectra of the
synthesized compound were recorded on addition of perchlorate salts while keeping
the ligand concentration constant (2.0 × 10-5 M) in all experiments. Perchlorate salt of
ions (Fe3+, Hg2+, Ag+, Ca2+, Cu2+, Co2+, Ni2+, Cd2+, Pb2+, Zn2+, Cr3+, Mg2+ and Fe2+)
were prepared with 4.0 × 10-4 M throughout all fluorescence experiments.
2.2.3 General procedure for 1H–NMR experiments
For 1H NMR titrations, two stock solutions were prepared in DMSO-d6. Aliquots
of the two solutions were mixed directly in NMR tubes. Cu2+ was prepared with 0.01
mol/L in 1H NMR titrations experiments.
2.2.4 Adsorption experiment
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The concentration of AHPN and Cu2+ with 1Õ10-4 M, 1Õ10-5 M and 1Õ10-6 M
were prepared respectively. Added different concentrations of Cu2+ and let the
solution stand still for 10 minutes. Then, separating the precipitate, the supernatant
was assessed by inductively coupled plasma (ICP) analysis.
2.2.5 General procedure for test papers experiments
For Cu2+ test papers, the commercial source of paper was bought from the
Hangzhou Xinhua Paper Industry Co., Ltd. Test strips were prepared by immersing
filter papers into fresh double distilled water of AHPN. The test strips containing the
chemosensor AHPN were utilized to detect Cu2+.
3. Results and Discussion
3.1 Effect of pH
The pH was adjusted by adding HCl and NaOH dropwise to the AHP, and the
fluorescence intensity of the solution at different pH values was measured (pH from 2
to 13). pH-Dependent fluorescence responses of AHP (2 × 10-5 M) in distilled water
upon excitation at 450 nm was characterized in Figure 2. We can see it clearly, The
pH is from 2 to 5, the fluorescence intensity showed a downward trend, the pH is
from 6 to 13, and the fluorescence intensity is continuously increased.
Figure 1
In this context, we synthesized the sodium salts (AHPN) of AHP. The
absorbance and fluorescence intensity of AHP and AHPN (2×10-5 M) in distilled
water was characterized in Fig. S6 and Fig. S7. We can clearly observe that the
intensity of AHPN is the highest among them in both the emission spectrum and the
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UV-vis absorption spectrum. The water-solubility of AHP and AHPN in water were
calculated by the Lambert-Beer law. The AHP corresponding maximum
concentration in ultraviolet titration experiment is 2×10-5 M, the AHPN
corresponding maximum concentration in ultraviolet titration experiment is 2×10-4 M,
so, AHPN has the best solubility in pure water (Fig. S8 and Fig. S9). The emission
quantum yield (Φ1) of the AHP was calculated by 0.26 but AHPN can be up to 0.52
(Φ2) (in Supporting Information). Therefore, it is more significant to study the
recognition performance of AHPN. But in order to compare the difference in the
recognition performance of metal ions between AHP and AHPN, the recognition
performance of AHP with metal ions also be performed in supporting information
(Fig. S10 to Fig. S16).
3.1. UV–vis and fluorescence spectra study
Then, we carefully investigated the influence of metal ions on AHPN in distilled
water. The addition and diffusion of water solutions of various metal ions, including
Fe3+, Hg2+, Ag+, Ca2+, Cu2+, Co2+, Ni2+, Cd2+, Pb2+, Zn2+, Cr3+, Mg2+ and Fe2+ were
prepared with 4.0 × 10-4 M in distilled water. As shown in inset of Figure 2, when
adding 5 equiv. of Cu2+ and other metal ions into AHPN, the color of AHPN quickly
changed from bright yellow to blood red under naked eye (within 3s). Before the
addition of metal ions, AHPN solution in distilled water showed two bands at 258 and
440ꢀnm in UV-vis spectroscopy, respectively. By the addition of 5.0 equiv. of metal
ions to a solution of AHPN, only Cu2+ induced the formation of new obvious
absorption bands at 260 and 443 nm. Meanwhile, a dramatically decrease of the
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absorbance from 0.64 (a.u.) to 0.36 (a.u.) of AHPN in UV-vis spectroscopy, while
other metal ions produced slight spectral responses.
Figure 2
In order to validate the selectivity of sensor AHPN, the UV-vis absorption
spectra competitive complexation of AHPN was studied in Fig. S17. The results show
that AHPN has strong anti-interference ability to detect Cu2+, and other cations have
no or weak influence in UV-vis absorption spectrum response.
In order to further explore fluorogenic sensing abilities of AHPN in distilled
water, a series of fluorescence spectral was examined. In Figure 3, the free sensor
AHPN showed a dramatically fluorescence at 555 nm. When various metal ions were
added, only the addition of Cu2+ could significantly reduce the fluorescence intensity
(from 133 a.u. to 51 a.u.). Moreover, only the addition of Cu2+ can quench the
fluorescence of AHPN under irradiation with a UV lamp at 365 nm. We know that
from competitive experiments, other metal ions have no or negligible effect on
emissions of AHPN, but due to Fe3+ and Cu2+ are paramagnetic ions, there is some
interference with each other. This idea was also proved by adding Fe2+. As can be seen
in Fig. S18, the addition of Fe2+ also has certain interference with Cu2+, so this is
confirmed.
Figure 3
To further examine the recognition behavior of the AHPN with Cu2+, UV-vis
spectrum and fluorescence titration experiment of AHPN also were studied in
distilled water (Fig. S19 to Fig. S22). The detection limit of the UV-vis spectral and
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fluorescence change is calculated on the basis of 3δ/S method is 7.6×10-6 M and
2.2×10-7 M, respectively. The pH-dependent ultraviolet-visible and fluorescence
spectrum experiments of AHPN and AHPN+Cu2+ using the buffer solution were
tested in Fig. S23 and Fig. S24. Through experiments, we found that pH has no or
only slight effect on AHPN for detection of Cu2+ in ultraviolet and fluorescence
spectrum.
3.4. The naked-eye detection limit of AHPN
In addition, in order to investigate the naked-eye detection ability of AHPN in
distilled water, we also tasted the naked-eye detection limit of AHPN. As shown in
Fig. S25, the naked eye detection concentration of AHPN in visible light is 1 × 10-6
M. The naked-eye detection limit of AHPN under irradiation with the UV lamp also
been tasted in Fig. S26. As can be seen from the figure, the detection concentration is
also 1 × 10-6 M.
3.3. The binding mechanisms of AHPN
To further understand the nature of the stimuli-response mechanism between
AHPN with Cu2+, The 1H NMR titration, IR, XRD, Mass spectra, Job’s plot and SEM
was carefully investigated [53-59]. The 1H NMR titration experiments were
performed in DMSO-d6 with AHPN (0.05mol/L) in the existence of Cu2+ (0.01
mol/L), and the spectral details are shown in Figure 4. The addition of Cu2+ to AHPN
in DMSO-d6 solution directed a downfield shift of the signal of the hydrogen atoms in
the phenazine rings (Ha, Hb, Hc, Hd) and amino proton −NH2 (H1 and H2). Upon
addition of Cu2+ to AHPN, the Ha protons were shifted from 7.62 to 7.71 ppm, Hb
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protons were shifted from 7.57 to 7.65 ppm, Hc protons were shifted from 7.26 to
7.33 ppm, Hd protons were shifted from 7.17 to 7.26 ppm, H1 protons were shifted
from 6.50 to 6.62 ppm and H2 protons were shifted from 6.07 to 6.27 ppm,
respectively. The above results indicate that the AHPN coordinates with Cu2+. The
Job’s plot and mass spectral data revealed that the complex was formed between
AHPN and Cu2+ in 1:1 stoichiometry (Fig. S27), the mass spectral also confirmed the
formation of AHPN and Cu in Fig. S5.
Figure 4
The IR spectrum of AHPN and AHPN-Cu can elucidate the binding mode in
Fig. S28. The IR spectra of AHPN, the stretching vibration absorption peaks of −NH2
appeared at 3345 and 3480 cm-1, −C−O appeared at 1088 cm-1, respectively. However,
when AHPN coordinated with Cu2+, the stretching vibration absorption peaks of
imidazole −NH2 intensity decreases, whereas the stretching vibration absorption
peaks of −C−O intensity increased, which indicated that AHPN complex with Cu2+
via N−Cu−O coordination bond.
Based on the above results, we propose that the reaction mechanism and binding
model of dye molecule AHPN with Cu2+ in Figure 5. To get further insight into the
morphological features of the AHPN and AHPN-Cu, the XRD and SEM studies were
carried out. In Fig. S29, there have two X-ray diffraction peaks at 7.3° and 12.1° in
AHPN, which shows a distinct monomer. But this obvious diffraction peak
disappeared is due to the formation of mixed ligand complexes with Cu2+. A peak at
17.5°, it showed the typical NH-π distance is 2.56Å, in curve of AHPN-Cu, this peak
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gets weaker. It indicates that NH-π in AHPN gets weaker after combination with Cu2+.
A peak at 22.2°, the distance is 2.04 Å, that the Cu-O bond’s distance. At 24.7°, d=
1.80 Å, it’s the Cu-N distances in the AHPN-Cu complex. Two sharp diffraction
peaks at 26.9˚ and 28˚ observed of AHPN, in the powder the XRD of AHPN-Cu,
these peaks did not disappear but moved to 25.0˚ and 25.5˚. This phenomenon shows
that the AHPN coordinated with Cu2+ did not destroyed the π−π stacking between
molecular of AHPN. In addition, the morphological features of AHPN and
AHPN-Cu were studied using SEM, which showed an irregular rod-like structure
before cooperating with Cu2+. After the addition of Cu2+, AHPN and Cu2+ coordinate
with metal-coordination, leading to the destruction of hydrogen bonds in AHPN
molecules, and weaken NH-π and π-π stacking interactions, so the original structure
collapses into a laminar structure (Fig. S30).
Figure 5
3.7. Computational study
The optimized structure of AHPN-Cu and the HOMO–LUMO energy gaps for
AHPN and AHPN-Cu were performed by DFT calculations. The proposed binding
mechanism is verified by calculating the optimized structure of AHPN and
AHPN-Cu (Fig. S31). The Frontline orbital energy map of AHPN and AHPN-Cu
was showed in Figure 6. The HOMO–LUMO energy differences (ED) for AHPN and
AHPN-Cu were found to be 0.04568 eV and 0.04365 eV respectively (The DFT
calculations data of AHPN and AHPN-Cu were showed in Table S2 and Table S3).
This indicates that the energy of AHP is transferred after the addition of Cu2+, and the
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energy of AHPN-Cu is lower, and the fluorescence quenching occurs after the
addition of Cu2+. We speculate that it may be due to the presence of PET process.
Figure 6
3.6. Adsorption capacity of the AHPN
Adsorption capacity of the AHPN for Cu2+ in pure water was assessed
inductively coupled plasma (ICP) analysis.
To test the suitability in practical applications, we also evaluated the performance
of AHPN in the applicable removal of Cu2+ (Figure 7). The dye AHPN exhibited
excellent solubility in pure water. When the concentration of the AHPN and Cu2+
were both 1×10-4 M, 1×10-5 M and 1×10-6 M respectively, Cu2+ were added to the host
solution, the solution first changed from bright yellow to blood red. After 10 minutes,
the red solution gradually became colorless with the formation of reddish-brown
precipitation. The supernatant was tested by ICP, and it was found that Cu2+ was not
detected in the supernatant at the concentrations of 1×10-4 M and 1×10-5 M. When the
concentration is 1×10-6 M, Cu2+ is 0.083 mg/L in supernatant. The Cu2+ removal
efficiency was displayed up to 76% (Table S4).
Figure 7
3.6. Application in real samples and plant samples
Meanwhile, the AHPN also was further subjected to natural water examples and
paper strip test. Generally, the application of dye molecular detect and remove Cu2+ in
natural water samples presents a unique set of challenges, which requires detailed
studies of dye molecular performance in the environmental milieu. Next, we tested the
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responding ability of AHPN to Cu2+ in several natural water samples (River water,
lake water and snow water). As shown in Fig. S32, the fluorescence quenching of
AHPN also produced the red-brown precipitate in each samples. These results clearly
show that AHPN can detect Cu2+ in the solutions with a much more complicated
composition. At the same time, as an application in plant samples, we took fresh aloe
vera, peeled off a layer of skin, soaked it in AHPN solution, and then took it out and
added Cu2+ (4×10-3 mol/L) onto the surface. We found that AHPN can completely
enter the pulp of aloe vera before the addition of Cu2+. After the addition of Cu2+, the
pulp’s surface of aloe vera changed to blood red immediately. However, this blood red
does not penetrate into the pulp inside, and will form a flocculation on the surface
(Fig. S33). This phenomenon indicates that AHPN can be used to detect Cu2+ in
plants.
To further realize the practical application, the AHPN was prepared as a test
paper to evaluate its capability of detecting Cu2+ in water. In the experiment, the test
papers were initially immersed in 2×10-4 M concentration of AHPN solution. After
that, the test papers were added with Cu2+. The color of the AHPN-based test papers
rapidly changes from yellow to blood red in visible light. The fluorescence was
quenched rapidly under irradiation with the UV lamp at 365 nm. And the minimum
concentration of Cu2+ detected by this test strip in the naked eye was 1×10-6 M
(Fig.
S34). The solubility of AHPN coated on the surface of the test paper was also tested.
We coated the AHPN on the strips and drip distilled water onto the surface of the test
paper strips, it can see that the AHPN dissolved on the surface of the test paper strips
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as it dripped distilled water. What's more, when the solid of AHPN was completely
dissolved on the test paper, washing the test paper strip with distilled water repeatedly
found that the dye had completely colored the test paper strip and did not fade (Fig.
S35).
4. Conclusion
In summary, we reported a water-soluble dye based on phenazine for
high-performance, dual-mode detection and removal of Cu2+ in water. This phenazine
dye is simple and low-cost to synthesize. Moreover, as an application material, it not
only can detect Cu2+ with quick response and high selectivity, but also can remove
Cu2+ with rapid and high adsorption capacity in natural water samples. The test strips
based on the AHPN also were fabricated and used to convenient detection of Cu2+ in
water. Based on all the above studies we suggest that the water-soluble dye AHPN
has great potential in the treatment of Cu2+ pollution in toxicology or environmental
sciences.
Conflicts of interest
The authors declare no competing financial interests
Funding
This work was supported by the National Natural Science Foundation of China
(Nos. 21662031; 21661028; 21574104), the Program for Changjiang Scholars and
Innovative Research Team in University of Ministry of Education of China (IRT
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15R56).
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Figure & Scheme captions
Scheme 1. The synthesis route and structures of dye molecular AHP and AHPN.
Figure 1. pH-Dependent fluorescence responses of AHP (2 × 10−5 M) in distilled
water upon excitation at 450 nm (pH from 2 to 13) λmax-em=558 nm
.
Figure 2. Absorbance spectra change of AHPN (20 µM) and upon the addition of
various metal ions (4.0 × 10–3 M) in water. Inset: Photographs of samples show that
the change in color of the solution of sensor AHPN after addition of Cu2+ and other
metal ions (5 equiv.) in water under irradiation with visible light.
Figure 3. Fluorescence changes of AHPN (20 µM) upon addition of Cu2+ and other
different perchlorate salts of metal ions (4.0 × 10–3 M) in water (excitation wavelength
= 450 nm). Inset: Photographs of samples show that the change in color of the
solution of sensor AHPN after addition of Cu2+ and other metal ions (5 equiv.) in
water under irradiation with a UV lamp at 365 nm.
1
Figure 4. Partial H NMR titration spectra (400 MHz) of 0.05 mol/L AHPN with
various equivalents of Cu2+ in DMSO–d6 solution (0, 0.1, 0.3, 0.5, 1.0 and 2.0 equiv).
Figure 5. Proposed binding model of dye molecule AHPN with Cu2+.
Figure 6. The HOMO–LUMO energy gaps for AHPN (left) and AHPN-Cu (right).
Figure 7. Photographs of AHPN and added Cu2+ in fresh double distilled water under
natural light and irradiation with the UV lamp at 365 nm (from top to bottom).

ACCEPTED MANUSCRIPT
Scheme 1. The synthesis route and structures of dye molecular AHP and AHPN.
Figure 1. pH-Dependent fluorescence responses of AHP (2 × 10−5 M) in distilled
water upon excitation at 450 nm (pH from 2 to 13) λmax-em=558 nm
.

ACCEPTED MANUSCRIPT
Figure 2. Absorbance spectra change of AHPN (20 µM) and upon the addition of
various metal ions (4.0 × 10–3 M) in water. Inset: Photographs of samples show that
the change in color of the solution of sensor AHPN after addition of Cu2+ and other
metal ions (5 equiv.) in water under irradiation with visible light.
Figure 3. Fluorescence changes of AHPN (20 µM) upon addition of Cu2+ and other
different perchlorate salts of metal ions (4.0 × 10–3 M) in water (excitation wavelength
= 450 nm). Inset: Photographs of samples show that the change in color of the
solution of sensor AHPN after addition of Cu2+ and other metal ions (5 equiv.) in
water under irradiation with a UV lamp at 365 nm.