1. A naked eye colorimetric sensor of Fluoride comprising composition based on Titanium Nanoparticles/ Carbon Quantum dots; said composition comprises Carbon Quantum dots -TiO2NPs-H2PO4-CuSO4-C6H8O6, wherein said composition comprises 30 μL Carbon Quantum dots (1 mgml-1 ), 500 μL TiO2 nanoparticles, 500 μL H2PO4, 500 μL CuSO4 and 1.5 ml C6H8O6, wherein said Titanium Nanoparticles and Carbon Quantum dots are synthesized by green process.

2. The sensor as claimed in claim 1,wherein said Titanium nanoparticle is synthesized by a green process, comprising following steps: a) washing waste flowers with deionized water followed by chopping into fine pieces to obtain a solution; b) heating the solution resulting from step (a) at 80ºC for approximately 30 minutes followed by filtering the supernatant to obtain the flower extract acting as a reducing cum stabilizer agent for synthesis of titanium nanoparticle; c) mixing approximately 10 ml of flowers waste extract obtained from the above step (b) in 20 ml of freshly prepared 0.01 M Ti4Cl solution with continuous stirring at 60 ºC; d) centrifuging the suspension obtained from step ( c) at approximately 10,000 rpm for about 20 min to obtain the pellet of Titanium nanoparticle.

3. The sensor as claimed in claim 2, wherein said pellet was repeatedly washed with millipore water and dried in oven at 100°C.

4. The sensor as claimed in claim 1,wherein said fluorescent Carbon Quantum Dots (CQDs) is synthesized by a green process, comprising following steps: a) washing approximately 10 g of flower waste with distilled water followed by crushing to obtain the fine paste and finally making the volume upto 50 ml with distilled water to obtain a solution; b) heating the solution obtained in step (a) at 80ºC for 2 hr followed by filtering it and centrifuging at 4,500 rpm for 10 min; c) suspending the solution obtained from step (b) with 1 N 5 ml NaOH to obtain CQDs solution followed by storing at 4 ˚C for further use. -16-

5. The sensor as claimed in claim 1, wherein said sensor is highly sensitive to detect the presence of fluoride concentration of as low as 0.057 µM.

6. A method for the detection of unhealthy concentration of fluoride present in a water sample by the calorimetric sensor composition as claimed in claim 1, comprising the steps of: a) Mixing the water sample to be tested with the sensor composition as claimed in claim 1, wherein said composition and water to be tested for the presence of the fluoride ion is in the ratio of 1:1 followed by incubation for the time period of 1 to 2 minutes; b) observing the color change in the solution by the naked eye wherein the color change from yellow to green shows the presence of anion in the water sample.

The following background discussion includes information that may be useful in
understanding the present invention. It is not an admission that any of the information
provided herein is prior art or relevant to the presently claimed invention, or that any
publication specifically or implicitly referenced is prior art.
Fluoride (F) occurs naturally in a soil, air and water and is most commonly found element
in earth crusts. Approximately 200 million people worldwide and 60 million people in
India are facing F contamination problem. Nowadays, nanomaterials have gained much
attention with possible application in fluorescence and colorimetric sensors. Among them,
colorimetric sensors have attracted tremendous attention as are highly sensitive, costeffective and naked eye sensors (Jeong & Kim, 2015). The visible colorimetric sensor
mechanism is based on metal-ligand coordination where it behaves as electronic acceptor
and donor (Sung et al., 2013). CQDs-TiO2 complex solution color changes from green to
black on addition of F ions due to exchange of F ions with hydroxyl ions of the solution.
Till date, the techniques for detection of F at community level are outreach and far away
due to its high cost and complex mechanism. The available methods for detection of F are:
1. Ion- Selective Electrode
2. Spectrofluorimetry
3. Paper based Detector
4. Colorimetric Detection
The limitations/ drawbacks of the existing techniques for detection of F are:
1. Require large amount of water sample.
2. Non-portable
3. Complex procedure
4. Non-feasible
5. High cost
6. Require skilled person for operation
7. Less sensitive and specificity
8. Time taken procedure
-3-
Among all of above techniques, Colorimetric detections prove to be more rapid, easy to
operate, cost-effective, sensitive and highly selective method. Several techniques are
available in the market for detection of F. The portable and effectiveness of the detection
techniques are still not satisfactory and still needs corrections.
The development of fluoride selective sensors is of potential practical importance and
would offer an attractive low-cost/disposable alternative to the widely used solid-state
LaF3 ion-selective electrode, especially for mass production (e.g., via screen printing) of
planar sensor arrays and single-use devices. Highly selective fluoride sensors are useful
for the determination of fluoride levels in municipal/potable water and for monitoring
oregano fluorophosphates, especially those belonging to a class of highly toxic
neurotoxins that are commonly used as chemical warfare agents. Enzymatic and metal ion
catalyzed degradations of these species liberate fluoride ion, which could be detected
quickly using a suitable fluoride ion-selective sensor. To date, very few colorimetric
selective sensors have been developed for fluoride ions. Surface optical sensors developed
for fluoride ion, based on fluorescence or absorbance/reflectance measurements, suffer
from low selectivity and a high detection limit. For example, fluoride sensors based on
physical immobilization of dyes (e.g., zirconium–calcein blue and alizarine) at the distal
end of bifurcated optical fiber showed a high fluoride detection limit (e.g., 2.6 × 10−5 M),
long response times, and poor fluoride selectivity over common anions such as sulfate,
phosphate and acetate, chloride, bromide, iodide. Further, the conventionally existing
selective sensor suffers with high cost. Thus, there is a need of a simple, efficient and cost
effective fluoride sensor. There is also a need of sensor/s which is prepared through green
method without using hazardous chemicals.
Object/s of the present Invention
The primary object of the present of the present invention is to overcome the limitation of
prior art.
Another object of the present invention is to provide a colorimetric selective fluoride
sensor.
Yet another object of the present invention is to provide a green and cost effective way of
developing sensor.
Yet another objective of the present invention is to provide easy, green and cost-effective
Nanoparticles (NPs) useful for sensor development using temple flower waste.
-4-
Yet another objective of the present invention is the development of fluorescent Carbon
Quantum Dots (CQDs) using temple flower waste.
Yet another objective of the present invention is to provide a process for colorimetric
detection of Fluoride (F) using green and cost-effective solution.
Yet another object of the present invention is to provide cost effective and efficient
selective sensing of fluoride ion.
Summary of the Invention:
In an aspect of the present invention, there is provided a naked eye colorimetric sensor of
Fluoride comprising composition based on Titanium Nanoparticles/ Carbon Quantum
dots comprising Carbon Quantum dots -TiO2NPs-H2PO4-CuSO4-C6H8O6, wherein said
composition comprises 30 μL Carbon Quantum dots (1 mgml-1), 500 μL TiO2
nanoparticles, 500 μL H2PO4, 500 μL CuSO4 and 1.5 ml C6H8O6, wherein said
Titanium Nanoparticles and Carbon Quantum dots are synthesized by green process.
In another aspect, the Titanium nanoparticle is synthesized by a green process, comprising
following steps:
a) washing waste flowers with deionized water followed by chopping into fine
pieces to obtain a solution;
b) heating the solution resulting from step (a) at 80ºC for approximately 30
minutes followed by filtering the supernatant to obtain the flower extract acting
as a reducing cum stabilizer agent for synthesis of titanium nanoparticle;
c) mixing approximately 10 ml of flowers waste extract obtained from the above
step (b) in 20 ml of freshly prepared 0.01 M Ti4Cl solution with continuous
stirring at 60 ºC;
d) centrifuging the suspension obtained from step ( c) at approximately 10,000
rpm for about 20 min to obtain the pellet of Titanium nanoparticle.
In another aspect, the Carbon Quantum Dots (CQDs) is synthesized by a green process,
comprising following steps:
a) washing approximately 10 g of flower waste with distilled water followed by
crushing to obtain the fine paste and finally making the volume upto 50 ml
with distilled water to obtain a solution;
-5-
b) heating the solution obtained in step (a) at 80ºC for 2 hr followed by filtering it
and centrifuging at 4,500 rpm for 10 min;
c) suspending the solution obtained from step (b) with 1 N 5 ml NaOH to obtain
CQDs solution followed by storing at 4 ˚C for further use.
In other aspect, there is provided a method for the detection of unhealthy concentration of
fluoride present in a water sample by the calorimetric sensor composition as described
above, comprising the steps of:
a) Mixing the water sample to be tested with the sensor composition as claimed in
claim 1, wherein said composition and water to be tested for the presence of the
fluoride ion is in the ratio of 1:1 followed by incubation for the time period of 1
to 2 minutes;
b) observing the color change in the solution by the naked eye wherein the color
change from yellow to green shows the presence of anion in the water sample.
Brief Description of the Drawings:
To further clarify advantages and features of the present invention, a more particular
description of the invention will be rendered by reference to specific embodiments thereof,
which is illustrated in the appended drawings. It is appreciated that these drawings depict
only typical embodiments of the invention and are therefore not to be considered limiting
of its scope. The invention will be described and explained with additional specificity and
detail with the accompanying drawings in which:
Figure 1: illustrates the (a) FESEM of TiO2 NPs, b) EDX spectrum of TiO2 NPs, (c)
Photograph of as-prepared CQDs solution upon irradiation with 365 nm UV light, and (d)
EDX spectrum of CQDs
Figure 2: illustrates the (a) XRD patterns of TiO2 NPs, and (b) XRD patterns of CQDs.
Figure 3: illustrates the 3 (a) Emission spectra at progressively increasing excitation
wavelengths from 325 nm to 450 nm and excitation spectrum of the CQDs solution, and
(b) Zeta Potential of TiO2 NPs.
Figure 4: illustrates the (i) Color change in CQDs-TiO2 complex solution after addition of
F ions (a) CQDs-TiO2 complex solution, (b) 2-4 ppm, (c) 4-7 ppm, (d) 7 ppm and above,
and (ii) Change in color of CQDs-TiO2 complex solution after addition of anion solutions
(a) F ions, (b) Cl ions, (c) Br ions, (d) I ions and (e) HPO4 ions.
-6-
Figure 5: illustrates (a) Change in absorbance of CQDs-TiO2 complex solution upon
addition of F and other anionic solutions, and (b) Values of (A550/300) of CQDs-TiO2
complex solution upon addition of 100 ppm F and other 100 anions. Error bars represent
standard deviations based on three independent measurements
Figure 6: illustrates the (a) UV-vis spectra of CQDs-TiO2 complex solution in presence of
increasing F ions concentration, and (b) absorbance dependence of F ions.
Figure 7: illustrates schematic representation of possible mechanism for F ion sensing
through developed colorimetric sensor.
Figure 7: illustrates that no color changes when Group A and Group B composition was
used for testing fluoride presence in the water sample.
Detailed description of the present invention:
In the present document, the word "exemplary" is used herein to mean "serving as an
example, instance, or illustration." Any embodiment or implementation of the present
subject matter described herein as "exemplary" is not necessarily to be construed as
preferred or advantageous over other embodiments.
While the disclosure is susceptible to various modifications and alternative forms, specific
embodiment thereof has been shown by way of example in the drawings and will be
described in detail below. It should be understood, however that it is not intended to limit
the disclosure to the specific forms disclosed, but on the contrary, the disclosure is to
cover all modifications, equivalents, and alternative falling within the spirit and the scope
of the disclosure.
The terms “comprises”, “comprising”, “includes”, or any other variations thereof, are
intended to cover a non-exclusive inclusion, such that a setup, device or method that
comprises a list of components or steps does not include only those components or steps
but may include other components or steps not expressly listed or inherent to such setup or
device or method. In other words, one or more elements in a system or apparatus
proceeded by “comprises... a” does not, without more constraints, preclude the existence
of other elements or additional elements in the system or method.
This invention relates to colorimetric detection of Fluoride (F). The present invention
involves the synthesis of green and cost-effective Nanoparticles (NPs) and Carbon
Quantum Dot (CQDs) by utilizing the temple flower waste.
-7-
The present invention involves the development of an easy, green and simple method to
synthesize colorimetric process which can detects F ions over other anions in drinking
water.
The detection limit of the process is found to be very low as 1.09 ppm or 0.057 µM.
The proposed novel process of the present invention comprises of CQDs-TiO2NPs-H2PO4-
CuSO4-C6H8O6, (CTPC) which is innovative and economical. The developed process can be
utilized for the easy detection of F ions as it gives distinct color change above 2 ppm-8
ppm from green to black. Selectivity of developed process with other anions such as Cl-
,
Br-
, Iand HPO4
-2 has been done and no spectral response was observed.
This process is particularly helpful for places in India, where there fluoride is more than
1.5 ppm in groundwater. The developed CQDs-TiO2 based colorimetric detection process
is portable, selective and sensitive for F ion detection.
The senor provided by the present invention overcomes the following existing problems:
1. Easy and cost effective process
2. Eco-friendly
3. Low detection limit
4. High Selectivity and Sensitivity
5. Portable
6. Simple procedure
In an aspect of the Invention, there is provided a naked eye colorimetric sensor of Fluoride
comprising composition based on Titanium Nanoparticles/ Carbon Quantum dots
comprising Carbon Quantum dots -TiO2NPs-H2PO4-CuSO4-C6H8O6, wherein said
composition comprises 30 μL Carbon Quantum dots (1 mgml-1
), 500 μL TiO2
nanoparticles, 500 μL H2PO4, 500 μL CuSO4 and 1.5 ml C6H8O6, wherein said Titanium
Nanoparticles and Carbon Quantum dots are synthesized by green process.
In an aspect of the Invention, there is provided green synthesis of TiO2 NPs and CQDs
utilizing the temple flower waste.
In an embodiment, the Titanium nanoparticle is synthesized by a green process,
comprising following steps:
a) washing waste flowers with deionized water followed by chopping into fine
pieces to obtain a solution;
b) heating the solution resulting from step (a) at 80ºC for approximately 30
minutes followed by filtering the supernatant to obtain the flower extract acting
as a reducing cum stabilizer agent for synthesis of titanium nanoparticle;
-8-
c) mixing approximately 10 ml of flowers waste extract obtained from the above
step (b) in 20 ml of freshly prepared 0.01 M Ti4Cl solution with continuous
stirring at 60 ºC;
d) centrifuging the suspension obtained from step ( c) at approximately 10,000
rpm for about 20 min to obtain the pellet of Titanium nanoparticle.
In an embodiment, the pellet was repeatedly washed with millipore water and dried in
oven at 100°C.
In an aspect, the fluorescent Carbon Quantum Dots (CQDs) is synthesized by a green
process, comprising following steps:
a) washing approximately 10 g of flower waste with distilled water followed by
crushing to obtain the fine paste and finally making the volume upto 50 ml
with distilled water to obtain a solution;
b) heating the solution obtained in step (a) at 80ºC for 2 hr followed by filtering it
and centrifuging at 4,500 rpm for 10 min;
c) suspending the solution obtained from step (b) with 1 N 5 ml NaOH to obtain
CQDs solution followed by storing at 4˚C for further use.
In an embodiment, the sensor is highly sensitive to detect the presence of fluoride
concentration of as low as 0.057 µM.
In an aspect of the Invention, there is provided a method for the detection of unhealthy
concentration of fluoride present in a water sample by the calorimetric sensor composition
as described above. In an embodiment, the method comprises steps of:
a) Mixing the water sample to be tested with the sensor composition as claimed in
claim 1, wherein said composition and water to be tested for the presence of the
fluoride ion is in the ratio of 1:1 followed by incubation for the time period of 1
to 2 minutes;
b) observing the color change in the solution by the naked eye wherein the color
change from yellow to green shows the presence of anion in the water sample.
In an embodiment, the preparation of waste flowers extract comprises following steps:
Waste flowers were choosen for the synthesis of TiO2 NPs because of its abundant and
easy availability as a waste after decoration and worship at temples. NPs were synthesised
by green method. Firstly, waste flowers were washed with deionized water and chopped
-9-
into fine pieces. 20 g flower waste was taken into an Erlenmeyer flask containing 60 ml of
Milli-Q water. Next, solution was heated to 80 ºC for 30 min and then supernatant was
filtered with Whatmann No. 1 paper to get flower extract and stored at 4 ºC for further use.
The obtained filtrate was utilized as a reducing and stabilizer agent for NPs synthesis.
In an embodiment, the synthesis of TiO2 NPs comprises following steps:
For TiO2 NPs synthesis, titanium (IV) chloride (Ti4Cl) solution of 0.01M was freshly
prepared for reduction process. Then, 10 ml of flowers waste extracted was added in 20 ml
of 0.01 M Ti4Cl solution with continuous stirring at 60 ºC. Complete reduction of Ti4Cl to
Ti+
ions was confirmed by the color change to brown. Further, the suspension was
centrifuged at 10,000 rpm for 20 min; the obtained pellet was repeatedly washed with
millipore water and dried in oven at 100°C.
In an embodiment, the synthesis of CQDs comprises following steps:
CQDs were also synthesised by using a green route. Briefly, 10 g of flower waste was
taken and washed thoroughly with distilled water. Then, flower waste properly crushed in
mortar pestle to get fine paste and the volume was make upto 50 ml with distilled water.
This mixture was heated at 80 ºC for 2 hr and filtered with Whatmann No. 1 paper to get
brown colored solution. The solution was then centrifuged at 4,500 rpm for 10 min and
was taken by decantation. The obtained solution was then refluxed at 80 ºC for 2 hr and
allowed to cool. Then, centrifuge for 10 min at 4,500 rpm and obtained solution was
suspended with 1 N 5 ml NaOH. The obtained CQDs solution was then observed under
UV light for fluorescence and stored at 4 ˚C for further use. Finally, CQDs were
characterized through UV-visible spectrophotometer, Energy dispersive X-ray analysis
(EDX), X-ray diffraction (XRD) and fluorescence spectrophotometer.
The mechanism of naked eye colorimetric detector for F is described in Reaction. a and b.
In the reactions, first the Titanium (IV) oxide acts as an oxidising agent because Titanium
is more stable in +2 oxidation state rather than +4 oxidation state. So it oxidised the
hydroxyl group (–OH) into carboxyl group C= O.
Reaction (a)
-10-
Reaction (b)
In the second step the carboxylic groups undergo nucleophilic substitution reaction with
Dihydrogen phosphate ion and form an inorganic ester.
The inorganic ester having charge on oxygen atom acts as a ligand and form a complex
with Cu2+ ion and ascorbic acid.
This complex of Cu2+ ion having d9
electronic configuration show color in its solid state as
well as in aqueous state, this is because of absorption of light radiations in visible region
which cause d-d transition of electron from t2g orbital to eg orbital and show
complementary color.
Further there is nucleophilic substitution reaction by the nucleophilic Fion. This
nucleophile replaces the –OH group. F being a most electronegative atom changes the
color, by changing the crystal field splitting of d-orbital of Cu2+ metal ion. The potential
mechanism is shown by schematic representation in Fig.8.
The sensor provided by the present invention has following advantages as compared to the
conventional technologies:
Available techniques(F detection) TiO2NPs / CQDs based detector
Large amount of water samples required Require small amount of water sample
Energy requirement No energy requirement
High cost Cost effective
Complex process/ procedure Simple procedure
Non-portable Portable
Less sensitive High sensitive
-11-
The Invention is further described with the help of non-limiting example:
Example 1:
Instrumentation
The surface morphology of TiO2 NPs was acquired by FESEM (MIRA 3 TESCAN).
Elemental composition of TiO2 NPs and CQDs was identified by EDX attached with the
FESEM. Crystalline structure and purity of both were characterized using an XRD (Bruker
D8 Discover X-Ray diffractometer). The surface charge of TiO2 NPs was obtained by the
zeta (ζ) potential. The isoelectric point of NPs was acquired by titrating the ζ-potential
over the pH range of 2-9. A fluorescence spectrum of CQDs was measured on
PerkinElmer LS 45 spectrophotometer.
Example 2:
Development of F ion detector
For the F ion sensing, TiO2 NPs based colorimetric sensor was developed. Briefly, a stock
solution of F (100 mgL-1
) was prepared by addition of 0.0221 g NaF to 100 ml double
distilled water. Colorimetric detection of F ions was done to identify the selectivity and
low concentration limit of detector. For the detection, 300 μL of different concentrations
of F ion (2 ppm, 4 ppm, and 6 ppm and above) was added in 500 μL CQDs-TiO2 complex
solution (CQDs-TiO2 NPs-H2PO4-CuSO4-C6H8O6) to identify the lowest naked eye
detection limit. Selectivity tests for F ions were carried with some other anions. Firstly,
CQDs-TiO2 complex solution was prepared with composition of 30 μL CQDs (1 mgml-1
),
500 μL TiO2NPs, 500 μL H2PO4, 500 μL CuSO4 and 1.5 ml C6H8O6 (1.5 g in 50 ml
distilled water for all) till solution color become green color. Then, 500 μL of CQDs-TiO2
complex solution was mixed with 300 μL of different concentrations of F ions. After
incubation for 5 min, color of solution changes from green to black and observed by naked
eye. All selectivity tests were carried out with some other anions such as chloride (Cl-
),
phosphate (P-
), bromide (Br-
) and iodide (I-
) (100 ppm). UV-vis spectrum was also
recorded for different F ion concentrations.
Example 3:
Selectivity Study
The selectivity of the F ion detector was investigated by checking its absorption maxima
on interaction with other anions such Cl-
, P-
, Brand I-
. To confirm the precision and
recovery of the detector, each set of experiments was carried out in triplicate. Similar
results were obtained within the maximum error of 2−3%.
-12-
Example 4:
Characterization of TiO2 NPs and CQDs
The surface morphology of synthesized TiO2 NPs was analyzed through FESEM (Figure
1a). TiO2 NPs showed dense agglomeration of particles and are irregular in shape
(Anandgaonker et al.2014). TiO2 NPs elemental composition was obtained through EDX
elemental mapping and showed the presence of Ti (17.1%) and O (18.1%) (Fig.1b). EDX
elemental spectrum confirmed the presence of Ti element in the sample. CQDs solution
shows light–brown color under the normal light and emitted blue luminescence on
exposure with 365 nm UV irradiation as shown in Fig. 1c. CQDs sample EDX analysis
showed the presence of C (94.7%), O (3.5%), Na (0.2%) and Cl (0.3%) (Fig.1d).
Fig. 2 illustrates the XRD pattern of TiO2 NPs and CQDs; intense diffraction peaks of
TiO2 NPs at 25.33˚, 27.50˚, 37.88˚, 48.13˚ and of CQDs at 30.10˚ were observed (Bling
Xin et al. 2012; Baruah et al. 2014). The XRD patterns indicate the crystalline nature of
both and their average crystalline size can be determined using through Debye-Scherrer
equation. Debye-Scherrer equation is shown as:
D= kλ/ βhkl cosθhkl

(1)
Where D is the crystallite size, λ is the X-ray wavelength of radiation for Cu Kα (0.154
nm), βhkl is the full-width at half maximum (FWHM), k is Scherrer constant (0.9) and θhkl
is the diffraction angle. The average crystallite size of TiO2 NPs was 32.72 nm and CQDs
was 4.94 nm. The XRD peaks of TiO2 NPs were observed as similar to JCPDS No.84-
1285. CQDs synthesized through waste material exhibits photoluminescence properties
and its strong photoluminescence and optical properties were confirmed (Fig.3a).
Maximum emission was observed at 457 nm when excited at 350 nm (Baruah et al. 2014).
Example 5:
ζ-Potential and isoelectric point (IEP)
The surface charge of the TiO2 NPs plays an important role on their mobility and
suspension stability in drinking water. The extents of surface potential decide the level of
the electrostatic repulsion between particles. The ζ-potential of TiO2 NPs is positive when
pH is lower than the isoelectric point (IEP) of 6.4 and shows positive surface charges over
a broad range of pH (2 to 6) (Junna Xu et al. 2013).
-13-
Example 6:
Detection of F ions
For practical application visual inspection of colorimetric detector is essential as it should
be capable to detect and provide immediate color change response to F ions. The potential
application of CQDs-TiO2 complex solution based colorimetric detector can be validated
by selectivity mechanism of the detector. This can be accomplish by examining the color
response of CQDs-TiO2 complex solution upon addition of F and other anions such as Cl-
,
Br-
, Iand HPO4
-2
. As shown in Fig. 4a, distinct color change was observed from green to
black upon addition of different F concentrations (2 ppm-8 ppm).
Notable color change is observed on addition of 2 ppm F solution in CQDs-TiO2 complex
solution from green to grey. Then, color become more distinct as shown in result by
addition of 3 ppm, 4ppm, 5 ppm and above F solution to mixture from grey to black,
respectively. Hence, CQDs-TiO2 complex solution become notable sensitive towards F
ions at concentration as low as 2 ppm, as it not offer any color change with other anions
such as Cl-
, Br-
, Iand HPO4
-2 (Fig. 4b).
For further evaluation of sensitivity of CQDs-TiO2 complex solution for other ions, the
adsorption titration of CQDs-TiO2 complex solution was done (Fig. 5a). Maximum
wavelength of CQDs-TiO2 complex solution was observed at about 300 nm (Baruah et al.
2014). But with the addition of F solution, new peak was observed at 550 nm. On titration
with F ions solution of high ppm, the absorbance intensity increases. Titration showed the
variation in values of adsorption ratio (A550/300) for CQDs-TiO2 complex solution on
addition of F ions solution and other anions. Absorption ratio A550/300 variation of CQDsTiO2 complex solution on addition of F and other anions is shown in Fig. 5b. As observed
in the Fig. 5b, only F ions were reported with significant increase in A550/300 value. This
suggests that the developed detector is highly selective for the F ions in comparison to
other ions.
Fig. 6a shows the UV titration of CQDs-TiO2 complex solution upon addition of F ions
with different concentrations. Firstly, CQDs-TiO2 complex solution showed absorption
band at around 300 nm which is displayed due to the presence of OH functional group.
But upon addition of different concentration of F ions, a new band at 550 nm was
observed with bathochromic shift of 183 nm attributed to the intramolecular charge
transfer (ICT) transition between the CQDs-TiO2 complex solution and F ion complex. A
linear relationship between the R2
-value and the concentrations of F ions could be
-14-
observed in the range of 2 ppm to 8 ppm (R2
= 0.980). Thus, F ions concentration in
different water could be identified through developed colorimetric detector.
TiO2NPs and CQDs showed excellent performance for sensing F-
. The comparison of
performance of different colorimetric nanosensors for F
-
is in Table 1. In view of the
simplicity TiO2NPs/ CQDs colorimetric nanosensors with LOD 0.057 µM, more desirable
for Fdetection with high sensitivity and selectivity.
S. No. Material Detection
Techniques
Linear Range Limit of
Detection
References
1. AuNPs Colorimetric 120-1500 µM 120 µM Gu et al.,
2013
2. AuNPs Colorimetric 26-368.6 µM
(0.5-7.0 µg/µl)
23.7 µM (0.45
µg/µl)
Sun et al.,
2014
3. GO-SPS Colorimetric 5.0-100 µM 0.86 µM Li et al.,
2013
4. Ceo2NPs Colorimetric 0-100 µM 0.64 µM Liu et al.,
2016
5. Fe3O4@SiO
2/carbon
quantum
dot
Colorimetric 1-20 µM 0.06 µM Mohapatra
et al., 2015
6. BNSCQDdopamine
Colorimetric 0.01×10-3
-5×10-
3
µM
0.76×10-6
µM Mohapatra
and Das .,
2019
7. Tio2NPsCQDs
Colorimetric 0.105 µM-0.421
µM
0.057 µM Present
work
Example 7:
Repeated experiments were conducted with different concentration of the components of
the composition.
The experiment involved two groups as mentioned below:
Group A: Composition comprising 20 μL Carbon Quantum dots (1 mgml-1
), 400 μL TiO2
nanoparticles, 400 μL H2PO4, 400 μL CuSO4 and 1ml C6H8O6.
Group B: Composition comprising 40 μL Carbon Quantum dots (1 mgml-1
), 600 μL TiO2
nanoparticles, 600 μL H2PO4, 600 μL CuSO4 and 2ml C6H8O6
The above mentioned Group A and Group B composition was used for testing fluoride
content in a water sample. The results, as illustrated in figure 8, shows no change in the
color and the Group A and Group B composition was thus found ineffective for the
detection of fluoride content in the water sample.

We Claim:

1. A naked eye colorimetric sensor of Fluoride comprising composition based on
Titanium Nanoparticles/ Carbon Quantum dots; said composition comprises
Carbon Quantum dots -TiO2NPs-H2PO4-CuSO4-C6H8O6, wherein said
composition comprises 30 μL Carbon Quantum dots (1 mgml-1
), 500 μL TiO2
nanoparticles, 500 μL H2PO4, 500 μL CuSO4 and 1.5 ml C6H8O6, wherein said
Titanium Nanoparticles and Carbon Quantum dots are synthesized by green
process.
2. The sensor as claimed in claim 1,wherein said Titanium nanoparticle is synthesized
by a green process, comprising following steps:
a) washing waste flowers with deionized water followed by chopping into fine
pieces to obtain a solution;
b) heating the solution resulting from step (a) at 80ºC for approximately 30
minutes followed by filtering the supernatant to obtain the flower extract acting
as a reducing cum stabilizer agent for synthesis of titanium nanoparticle;
c) mixing approximately 10 ml of flowers waste extract obtained from the above
step (b) in 20 ml of freshly prepared 0.01 M Ti4Cl solution with continuous
stirring at 60 ºC;
d) centrifuging the suspension obtained from step ( c) at approximately 10,000
rpm for about 20 min to obtain the pellet of Titanium nanoparticle.
3. The sensor as claimed in claim 2, wherein said pellet was repeatedly washed with
millipore water and dried in oven at 100°C.
4. The sensor as claimed in claim 1,wherein said fluorescent Carbon Quantum Dots
(CQDs) is synthesized by a green process, comprising following steps:
a) washing approximately 10 g of flower waste with distilled water followed by
crushing to obtain the fine paste and finally making the volume upto 50 ml
with distilled water to obtain a solution;
b) heating the solution obtained in step (a) at 80ºC for 2 hr followed by filtering it
and centrifuging at 4,500 rpm for 10 min;
c) suspending the solution obtained from step (b) with 1 N 5 ml NaOH to obtain
CQDs solution followed by storing at 4 ˚C for further use.
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5. The sensor as claimed in claim 1, wherein said sensor is highly sensitive to detect
the presence of fluoride concentration of as low as 0.057 µM.
6. A method for the detection of unhealthy concentration of fluoride present in a
water sample by the calorimetric sensor composition as claimed in claim 1,
comprising the steps of:
a) Mixing the water sample to be tested with the sensor composition as claimed in
claim 1, wherein said composition and water to be tested for the presence of the
fluoride ion is in the ratio of 1:1 followed by incubation for the time period of 1
to 2 minutes;
b) observing the color change in the solution by the naked eye wherein the color
change from yellow to green shows the presence of anion in the water sample.