1. A hydrogel composition for fluoride removal from a sample, where said composition is based on a three dimensional network porous hydrogel structure with two dimensional sheets of graphene oxide, wherein said composition comprises two dimensional sheets of graphene oxide, with the dispersion of Al2O3 nanoparticles, Ag2O nanoparticles, carbon quantum dots onto the gel; wherein, graphene oxide is present in an amount ranging from 0.7-1.7 mg mL-1 , Al2O3 nanoparticles (1N) is present in an amount ranging from 70-170 mL, Ag2O nanoparticles is present in an amount ranging from 70-170 mL, carbon quantum dots is present in an amount ranging from 40-85 µL amount.

2. The composition as claimed in claim 1, wherein Al2O3 nanoparticle/s is prepared through green route using waste peel of pencil, comprising the steps of: a) Preparing the pencil peel extract using waste peel after pencil being sharpened followed by grinding in grinder to obtain the peel powder wherein approximately 20 g of pencil peel powder is mixed in 100 ml Millipore water and heating at 80°C for approximately 30 minutes followed by cooling and filtering with Whatman’s No.1 filter paper to obtain pencil peel extract; b) Mixing Al2(SO4)3 with pencil peel extract obtained from step (a) in 1:3 ratio followed by continuous stirring to obtain the suspension; c) Microwaving/heating the suspension obtained from step (b) at 540 W for approximately 5 minutes, which results into a yellow brown precipitate followed by centrifuging and rinsing the precipitate with distilled water and methanol; d) Oven drying the precipitate resulting from step (c) at 100 °C.

3. The composition as claimed in claim 1, wherein Ag2O nanoparticle/s is prepared through green route using waste peel of pencil, comprising the steps of: a) Preparing the pencil peel extract using waste peel after pencil being sharpened followed by grinding in grinder to obtain the peel powder wherein approximately 20 g of pencil peel powder is mixed in 100 ml Millipore water and heating at 80°C for approximately 30 minutes followed by cooling and filtering with Whatman’s No.1 filter paper to obtain the pencil peel extract; -22- b) Mixing approximately 25 ml of pencil peel extract obtained from step (a) with approximately 225 ml of 1mM AgNO3 to obtain the suspension followed by shaking the suspension at 120 rpm at room temperature; c) Centrifuging the suspension resulting from step (b ) at 10000 rpm for approximately 30 min to obtain a precipitate; d) Rinsing the precipitate atleast twice with distilled water followed by oven drying at 100°C and storing at - 4°C.

4. The composition as claimed in claim 1, wherein the graphene oxide is prepared from pencil lead by modified Hummer’s method.

5. The composition as claimed in claim 1, wherein the carbon quantum dots is prepared from pencil peel waste by green method.

6. The composition as claimed in claim 1, is in the form of a pencil or a candle or cartridge

7. A method of preparing hydrogel composition by sol-gel method as claimed in claim 1, comprising the steps of: a) Sonicating the Graphene oxide uniformly at least for an hour in millipore water (1 mg mL-1 ) for complete dispersion followed by mixing the resulting graphene oxide suspension present in an amount ranging from 0.7-1.7 mg mL-1 with Al2O3 solution (1N) present in an amount ranging from 70-170 mL, Ag2O solution (1N) present in an amount ranging from 70-170 mL along with carbon quantum dots solution present in an amount ranging from 40-85 µL followed by sonicating the resulting suspension for an hour; b) Adding 1:1 NH3 solution dropwise into the suspension until the pH of the mixture is raised upto ~7.0; c) Adding approximately 2.0 g acrylamide in suspension followed by mixing approximately 7% w/w potassium persulfate as an initiator and approximately 7% w/w N,N’-methylenebisacrylamide as a crosslinker through continuous stirring to obtain a jelly like solid mass; d) Filtering and washing the jelly like solid mass resulting from step (c), after being kept for 24 hrs, with Millipore water for obtaining neutral pH and drying at 60º-65ºC in oven to obtain the hydrogel; e) Crushing the hydrogels and sieving out to desirable particle range.

8. A method of removing fluoride from a sample by the composition as claimed in claim 1, wherein said method comprises treating approximately 500 mL of water -23- sample with approximately 2gm of the composition as claimed in claim 1 by dipping in the water and leaving the solution for approximately 8 minutes.

9. The method as claimed in claim 8, wherein the composition is in the form of a pencil or a candle or cartridge.

10. The method as claimed in claim 8, wherein said method removes fluoride content by approximately 95.5% for the initial 2 mg L−1 F concentration.

[0001] The present invention relates generally to a hydrogel composition useful for
removal of fluoride from a sample. The Invention in particular provides three dimensional
network porous structure comprising 2D sheets of graphene oxide, with the uniform
dispersion of Al2O3/ Ag2O/CQDs onto the gels.
BACKGROUND
[0002]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) is the major toxic pollutant for humans and ecosystem, affecting 200 million
people worldwide. Recently, 3D adsorbents have gained enormous interest in water
purification sector. Fluoride is one of the main contributor of contamination of drinking
water worldwide. It acts as a double edge sword as its concentration upto 1.5 mg L-1 in
water is beneficial to humans, but excessive intake (above 1.5 mg L-1
) causes fluorosis
(Biswas et al., 2010). It was reported that approximately 663 million people lack access to
safe drinking water and among all 200 million people are affected by F contamination
worldwide (Kumari and Khan, 2017).
It has become a major geo-environmental concern in many parts of the world particularly
in developing countries like Kenya, Egypt, Ethiopia, Argentina, Australia, India,
Bangladesh and Sri Lanka. Several treatment techniques i.e. adsorption, ion exchange,
precipitation, electrodialysis, reverse osmosis and membrane filtration has been utilized,
aiming to reduce F level from water. However, adsorption method is best accepted for F
remediation owing to its simple operation, cost effectiveness, small space requirement and
chemical dosing. Consequently, numerous traditional adsorbent materials were reported
which include low cost materials (Xu et al., 2011; Mariappan et al., 2015), metal mixed
oxides, surface modified metal oxides, activated carbon, polymeric materials (Karkar et
al., 2016) and nanomaterials which proved to be highly efficient for F removal owing high
surface-to-volume ratio (Gupta et al., 2015). Several methods have been known for
nanostructural materials synthesis, such as reverse micelles, microwave, electrochemical,
-3-
nonelectrochemical and green synthesis technique (Sonkar et al., 2010). The green route
proved beneficial as compare to chemical method for the synthesis of nanomaterials in
respect to environmental friendly nature, labour and cost-effectiveness (Das and Saha,
2013).
Hence, there is a need of an efficient and cost effective technical solution for
removing/treating the sample to remove fluoride from a sample.
The present invention overcomes the problems/disadvantages noted above and problems
encountered in conventional methods. The objects, advantages and novel features of the
invention may be realized and obtained by means of the instrumentalities and
combinations particularly pointed out in the detailed description.
OBJECTS OF THE PRESENT DISCLOSURE
[0003] Some of the objects of the present disclosure, which at least one
embodiment herein satisfies are as listed herein below.
[0004] It is an object of the present disclosure to overcome problems associated
with the conventional prior art.
[0005] It is an object of the present disclosure to provide an efficient and cost
effective technical solution for removing/treating the sample to remove fluoride from a
sample.
[0006] It is an object of the present disclosure to provide an efficient composition
which exhibits 3D network porous structure based on 2D sheets of graphene oxide, with
the uniform dispersion of Al2O3/ Ag2O/CQDs onto the gels.
[0007] It is an object of the present disclosure to provide an efficient method of
preparing composition which exhibits 3D network porous structure based on 2D sheets of
graphene oxide, with the uniform dispersion of Al2O3/ Ag2O/CQDs onto the gels.
SUMMARY OF THE INVENTION
[0008] The present invention relates generally to light fidelity (Li-Fi)
communication. More particularly, the present disclosure relates to transmission and
reception of data over Li-Fi communication.
-4-
[0009] According to an aspect of the present disclosure, the present Invention
provides hydrogels exhibiting a 3D network porous structure consisting of 2D sheets of
graphene oxide, with the uniform dispersion of Al2O3/ Ag2O/CQDs onto the gels. All the
nanomaterials (Al2O3, Ag2O, CQDs and GO) utilized were synthesized via green route
utilizing pencil peel waste.
[00010] In an embodiment, the invention provides a hydrogel composition for
fluoride removal from a sample, where said composition is based on a three dimensional
network porous hydrogel structure with two dimensional sheets of graphene oxide,
wherein said composition comprises two dimensional sheets of graphene oxide, with the
dispersion of Al2O3 nanoparticles, Ag2O nanoparticles, carbon quantum dots onto the gel;
wherein, graphene oxide is present in an amount ranging from 0.7-1.7 mg mL-1
, Al2O3
nanoparticles (1N) is present in an amount ranging from 70-170 mL, Ag2O nanoparticles
is present in an amount ranging from 70-170 mL, carbon quantum dots is present in an
amount ranging from 40-85 µL amount.
[00011] In an embodiment, the Al2O3 nanoparticle/s is prepared through green route
using waste peel of pencil, comprising the steps of:
a) Preparing the pencil peel extract using waste peel after pencil being sharpened
followed by grinding in grinder to obtain the peel powder wherein
approximately 20 g of pencil peel powder is mixed in 100 ml Millipore
water and heating at 80°C for approximately 30 minutes followed by cooling
and filtering with Whatman’s No.1 filter paper to obtain pencil peel extract;
b) Mixing Al2(SO4)3 with pencil peel extract obtained from step (a) in 1:3 ratio
followed by continuous stirring to obtain the suspension;
c) Microwaving/heating the suspension obtained from step (b) at 540 W for
approximately 5 minutes, which results into a yellow brown precipitate
followed by centrifuging and rinsing the precipitate with distilled water and
methanol;
d) Oven drying the precipitate resulting from step (c) at 100 °C.
[00012] In an embodiment, Ag2O nanoparticle/s is prepared through green route
using waste peel of pencil, comprising the steps of:
-5-
a) Preparing the pencil peel extract using waste peel after pencil being sharpened
followed by grinding in grinder to obtain the peel powder wherein
approximately 20 g of pencil peel powder is mixed in 100 ml Millipore
water and heating at 80°C for approximately 30 minutes followed by cooling
and filtering with Whatman’s No.1 filter paper to obtain the pencil peel extract;
b) Mixing approximately 25 ml of pencil peel extract obtained from step (a) with
approximately 225 ml of 1mM AgNO3 to obtain the suspension followed by
shaking the suspension at 120 rpm at room temperature;
c) Centrifuging the suspension resulting from step (b ) at 10000 rpm for
approximately 30 min to obtain a precipitate;
d) Rinsing the precipitate atleast twice with distilled water followed by oven
drying at 100°C and storing at - 4°C.
[00013] In an embodiment, the method of preparing hydrogel composition by solgel method as described above, comprises following steps:
a) Sonicating the Graphene oxide uniformly at least for an hour in millipore
water (1 mg mL-1
) for complete dispersion followed by mixing the resulting
graphene oxide suspension present in an amount ranging from 0.7-1.7 mg
mL-1 with Al2O3 solution (1N) present in an amount ranging from 70-170
mL, Ag2O solution (1N) present in an amount ranging from 70-170 mL
along with carbon quantum dots solution present in an amount ranging from
40-85 µL followed by sonicating the resulting suspension for an hour;
b) Adding 1:1 NH3 solution dropwise into the suspension until the pH of the
mixture is raised upto ~7.0;
c) Adding approximately 2.0 g acrylamide in suspension followed by mixing
approximately 7% w/w potassium persulfate as an initiator and
approximately 7% w/w N,N’-methylenebisacrylamide as a crosslinker
through continuous stirring to obtain a jelly like solid mass;
d) Filtering and washing the jelly like solid mass resulting from step (c), after
being kept for 24 hrs, with Millipore water for obtaining neutral pH and
drying at 60º-65ºC in oven to obtain the hydrogel;
e) Crushing the hydrogels and sieving out to desirable particle range.
-6-
[00014] In an embodiment, the method of removing fluoride from a sample
comprises treating approximately 500 mL of water sample with approximately 2gm of the
composition as described above by dipping in the water and leaving the solution for
approximately 8 minutes.
[00015] Various objects, features, aspects and advantages of the present disclosure
will become more apparent from the following detailed description of preferred
embodiments, along with the accompanying drawing figures in which like numerals
represent like features.
[00016] Within the scope of this application it is expressly envisaged that the
various aspects, embodiments, examples and alternatives set out in the preceding
paragraphs, in the claims and/or in the following description and drawings, and in
particular the individual features thereof, may be taken independently or in any
combination. Features described in connection with one embodiment are applicable to all
embodiments, unless such features are incompatible.
BRIEF DESCRIPTION OF DRAWINGS
[00017] The accompanying drawings are included to provide a further
understanding of the present disclosure, and are incorporated in and constitute a part of
this specification. The drawings illustrate exemplary embodiments of the present
disclosure and, together with the description, serve to explain the principles of the present
disclosure. The diagrams are for illustration only, which thus is not a limitation of the
present disclosure.
[00018] FIG. 1 (a) and (b) illustrates FESEM and EDX of Al NPs, (c) and (d) show
FESEM and EDX of Ag NPs, (e) and (f) illustrates FESEM and EDX of GO.
[00019] FIG. 2 (a) and (b) illustrates TEM and EDX of CQDs.
[00020] FIG. 3 (a) and (b) illustrates FESEM and EDX of GAAC hydrogel before
adsorption, (c) and (d) shows FESEM and EDX of GAAC hydrogel after adsorption.
[00021] FIG. 4 illustrates XRD pattern of (a)Ag2O NPs, (b) Al2O3 NPs and (c)
CQDs
[00022] FIG. 5 illustrates FTIR of GO, Al2O3 NPs, Ag2O NPs, CQDs and GAAC
before and after F adsorption.
-7-
[00023] FIG. 6 illustrates effect of (a) pH, (b) Initial F concentration and (c) contact
time
[00024] FIG. 7 illustrates Adsorption isotherms (a) Langmuir, (b) Freundlich and
(c) Temkin
[00025] FIG. 8 illustrates novel designed of Fluoride removal Pencil having GAAC
nanocomposite.
[00026] FIG. 9 illustrates schematic diagram illustrate mechanism of F adsorption
[00027] FIG. 10 illustrates an embodiment of the Invention removing fluoride from
the water
DETAILED DESCRIPTION
[00028] The following is a detailed description of embodiments of the disclosure
depicted in the accompanying drawings. The embodiments are in such detail as to clearly
communicate the disclosure. However, the amount of detail offered is not intended to limit
the anticipated variations of embodiments; on the contrary, the intention is to cover all
modifications, equivalents, and alternatives falling within the spirit and scope of the
present disclosure as defined by the appended claims.
[00029] In the following description, numerous specific details are set forth in order
to provide a thorough understanding of embodiments of the present invention. It will be
apparent to one skilled in the art that embodiments of the present invention may be
practiced without some of these specific details.
[00030] If the specification states a component or feature “may”, “can”, “could”, or
“might” be included or have a characteristic, that particular component or feature is not
required to be included or have the characteristic.
[00031] As used in the description herein and throughout the claims that follow, the
meaning of “a,” “an,” and “the” includes plural reference unless the context clearly
dictates otherwise. Also, as used in the description herein, the meaning of “in” includes
“in” and “on” unless the context clearly dictates otherwise.
[00032] Exemplary embodiments will now be described more fully hereinafter with
reference to the accompanying drawings, in which exemplary embodiments are shown.
These exemplary embodiments are provided only for illustrative purposes and so that this
disclosure will be thorough and complete and will fully convey the scope of the invention
to those of ordinary skill in the art. The invention disclosed may, however, be embodied in
many different forms and should not be construed as limited to the embodiments set forth
-8-
herein. Various modifications will be readily apparent to persons skilled in the art. The
general principles defined herein may be applied to other embodiments and applications
without departing from the spirit and scope of the invention. Moreover, all statements
herein reciting embodiments of the invention, as well as specific examples thereof, are
intended to encompass both structural and functional equivalents thereof. Additionally, it
is intended that such equivalents include both currently known equivalents as well as
equivalents developed in the future (i.e., any elements developed that perform the same
function, regardless of structure). Also, the terminology and phraseology used is for the
purpose of describing exemplary embodiments and should not be considered limiting.
Thus, the present invention is to be accorded the widest scope encompassing numerous
alternatives, modifications and equivalents consistent with the principles and features
disclosed. For purpose of clarity, details relating to technical material that is known in the
technical fields related to the invention have not been described in detail so as not to
unnecessarily obscure the present invention.
[00033] Thus, for example, it will be appreciated by those of ordinary skill in the art
that the diagrams, schematics, illustrations, and the like represent conceptual views or
processes illustrating systems and methods embodying this invention. The functions of the
various elements shown in the figures may be provided through the use of dedicated
hardware as well as hardware capable of executing associated software. Similarly, any
switches shown in the figures are conceptual only. Their function may be carried out
through the operation of program logic, through dedicated logic, through the interaction of
program control and dedicated logic, or even manually, the particular technique being
selectable by the entity implementing this invention. Those of ordinary skill in the art
further understand that the exemplary hardware, software, processes, methods, and/or
operating systems described herein are for illustrative purposes and, thus, are not intended
to be limited to any particular named element.
[00034] Each of the appended claims defines a separate invention, which for
infringement purposes is recognized as including equivalents to the various elements or
limitations specified in the claims. Depending on the context, all references below to the
"invention" may in some cases refer to certain specific embodiments only. In other cases it
will be recognized that references to the "invention" will refer to subject matter recited in
one or more, but not necessarily all, of the claims.
[00035] All methods described herein may be performed in any suitable order
unless otherwise indicated herein or otherwise clearly contradicted by context. The use of
-9-
any and all examples, or exemplary language (e.g., “such as”) provided with respect to
certain embodiments herein is intended merely to better illuminate the invention and does
not pose a limitation on the scope of the invention otherwise claimed. No language in the
specification should be construed as indicating any non-claimed element essential to the
practice of the invention.
[00036] Various terms as used herein are shown below. To the extent a term used in
a claim is not defined below, it should be given the broadest definition persons in the
pertinent art have given that term as reflected in printed publications and issued patents at
the time of filing.
[00037] The present Invention provides hydrogels exhibited a 3D network porous
structure consisted of 2D sheets graphene oxide, with the uniform dispersion of Al2O3/
Ag2O/CQDs onto the gels.
The nanomaterials i.e. Al2O3, Ag2O, Carbon Quantum Dots (CQDs) and Graphene Oxide
(GO) utilized were synthesized via green route utilizing pencil peel waste.
In an embodiment, the Invention provides hydrogel composition which exhibits 3D
network porous structure based on 2D sheets of graphene oxide, with the uniform
dispersion of Al2O3/ Ag2O/CQDs onto the gels. The Invention in other aspect also
provides process of preparation of the hydrogel composition.
In an embodiment, waste of pencil peel was utilized for the synthesis of all nanoparticles
(NPs) and CQDs via green route. Fluoride removal using composition based on 3D Al2O3
NPs, Ag2O NPs, CQDs, GO based (GAAC) hydrogel is the novel and inventive feature of
the present invention.
In an embodiment, the 3D hydrogel is synthesized to achieve following:
(a) To avoid the leaching of nanomaterials in aqueous solution;
(b) To regulate pore size of the nanomaterials via crosslinker, so that the flow of water in
and out can be maintained;
(c) For easy swallowing.
-10-
Different physico-chemical methods, such as high resolution transmission electron
microscopy (HRTEM), field emission scanning electron microscopy (FESEM), energy
dispersive X-ray (EDX), X-Ray diffraction spectroscopy (XRD) and Fourier transformed
infrared (FTIR) were used to characterize the adsorbent.
In an embodiment, the Invention demonstrates the successful Fluoride adsorption and its
mechanism through following three steps:
(a) Green synthesis of Al2O3 NPs, Ag2O NPs and CQDs using pencil peel waste after
being sharpen;
(b) Synthesis of GAAC hydrogel by Sol-gel method;
(c) Kinetics and isotherm studies were done with proposed mechanism.
All chemical and reagents were of analytical grade and were used without any further
purification. Sodium fluoride (NaF), aluminium sulfate (Al2(SO4)3), silver nitrate
(AgNO3), acrylamide, bis-acrylamide and ammonium persulphate (APS) purchased from
Himedia. All chemical and reagents stock solution was prepared from millipore ultrapure
water.
In an embodiment, the hydrogel composition for fluoride removal from a sample, where
said composition is based on a three dimensional network porous hydrogel structure with
two dimensional sheets of graphene oxide, wherein said composition comprises two
dimensional sheets of graphene oxide, with the dispersion of Al2O3 nanoparticles, Ag2O
nanoparticles, carbon quantum dots onto the gel.
In an embodiment, the hydrogel composition for fluoride removal from a sample
comprises two dimensional sheets of graphene oxide, with the dispersion of Al2O3
nanoparticles, Ag2O nanoparticles, carbon quantum dots onto the gel.
In an embodiment, the hydrogel composition comprises graphene oxide present in an
amount ranging from 0.7-1.7 mg mL-1
, Al2O3 nanoparticles (1N) present in an amount
ranging from 70-170 mL, Ag2O nanoparticles present in an amount ranging from 70-170
mL, carbon quantum dots present in an amount ranging from 40-85 µL amount.
Aluminum and Silver NPs Synthesis:
Waste peel of pencil was utilized for the production of Al2O3 and Ag NPs through green
route.
-11-
In an embodiment, the pencil peel extract was synthesized using waste peel after pencil
being sharpen and then ground in grinder. After this, 20 g of pencil peel powder was
mixed in 100 ml Millipore water and heated at 80 °C for 30 min. The synthesized mixture
was cooled and filtered with Whatman’s No.1 filter paper and stored at 4°C for further
use.
For Al2O3 NPs production, Al2(SO4)3 was mixed with pencil peel extract with 1:3 ratios
and stirred constantly. The suspension was microwaved at 540 W for 5 min, which
produced a yellow brown precipitate that was further centrifuged. The precipitate was
rinsed with distilled water and methanol. Finally, the obtained precipitate was oven dried
at 100 °C and stored in a sealed container.
In an embodiment, the Al2O3 nanoparticle/s is prepared through green route using waste
peel of pencil, comprising the steps of:
e) Preparing the pencil peel extract using waste peel after pencil being sharpened
followed by grinding in grinder to obtain the peel powder wherein
approximately 20 g of pencil peel powder is mixed in 100 ml Millipore
water and heating at 80°C for approximately 30 minutes followed by cooling
and filtering with Whatman’s No.1 filter paper to obtain pencil peel extract;
f) Mixing Al2(SO4)3 with pencil peel extract obtained from step (a) in 1:3 ratio
followed by continuous stirring to obtain the suspension;
g) Microwaving/heating the suspension obtained from step (b) at 540 W for
approximately 5 minutes, which results into a yellow brown precipitate
followed by centrifuging and rinsing the precipitate with distilled water and
methanol;
h) Oven drying the precipitate resulting from step (c) at 100 °C.
For Ag2O NPs production, 25 ml of pencil peel extract was mixed with 225 ml of 1mM
AgNO3. Further, the suspension mixture was kept in a shaker at 120 rpm at room
temperature. The obtained reaction mixture was further centrifuged at 10000 rpm for 30
min and obtained precipitate was rinsed twice with distilled water. Finally, the precipitate
was oven dried at 100 °C and stored at - 4°C in a sealed container for further analysis.
-12-
In an embodiment, the Ag2O nanoparticle/s is prepared through green route using waste
peel of pencil, comprising the steps of:
e) Preparing the pencil peel extract using waste peel after pencil being sharpened
followed by grinding in grinder to obtain the peel powder wherein
approximately 20 g of pencil peel powder is mixed in 100 ml Millipore
water and heating at 80°C for approximately 30 minutes followed by cooling
and filtering with Whatman’s No.1 filter paper to obtain the pencil peel extract;
f) Mixing approximately 25 ml of pencil peel extract obtained from step (a) with
approximately 225 ml of 1mM AgNO3 to obtain the suspension followed by
shaking the suspension at 120 rpm at room temperature;
g) Centrifuging the suspension resulting from step (b ) at 10000 rpm for
approximately 30 min to obtain a precipitate;
h) Rinsing the precipitate atleast twice with distilled water followed by oven
drying at 100°C and storing at - 4°C.
Synthesis of Graphene Oxide:
Modified Hummer’s method was employed for the GO preparation from graphite pencil
lead. In brief, 2 g of finely powdered graphite powder was added to 35 ml of 98% H2SO4
and stirred magnetically over an ice-bath. After that, 6 g of solid KMnO4 was gradually
added into the mixture and stirred vigorously by keeping the temperature under 20˚C to
generate graphite solution. The stirring of the reaction mixture was continued for another 2
hours at room temperature to oxidize the un-oxidized graphite left. The final mixture was
diluted via addition of 90 ml of millipore water and mixture generated a yellowish paste
with effervescence with temperature of about 98˚C. The diluted suspension was
magnetically stirred for another 4 h and 30% H2O2 solution was added to the mixture (He
et al., 2018). Finally, the mixture filtered through Whatman’s No.1 filter paper and washed
with 5% HCl and 30% H2O2 to eliminate the remaining acid until the pH obtained
becomes neutral. Finally, a sheet like solid mass was obtained after drying at 55° - 60oC
under vacuum.
Synthesis of Carbon Quantum Dots [CQDs ]:
CQDs were also synthesized by using a green route as reported earlier with fewer
alterations (Himaja et al., 2014). Briefly, 10 g of pencil peel waste was taken and washed
thoroughly with distilled water. Then, pencil peel waste was properly crushed in grinder to
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get fine powder and the volume was make upto 50 ml with distilled water. The mixture
was heated at 80 ºC for 2 hr and filtered with Whatman’s No. 1 filter 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. Further, centrifuge for 10 min at 4,500 rpm and obtained solution was suspended
with 1 N 5 ml NaOH (Himaja et al. 2014). The obtained CQDs solution was then observed
under UV light for fluorescence and stored at 4˚C for further use.
The NPs, CQDs and GO synthesized were further characterized using different techniques
for the confirmation of its composition, size and shape. The techniques utilized were
HRTEM, FESEM (MIRA3 TESCAN), EDX and XRD (Bruker D8 Discover).
Synthesis of GO-Al2O3-Ag2O-CQDs (GAAC) hydrogel
3D hydrogel utilized in the formation of F removal pencil was synthesized by Sol-gel
method. In brief, GO was taken separately in erlenmeyer flasks and sonicated uniformly at
least for an hour in millipore water (1 mg mL-1
) for complete dispersion. Then, well
dispersed GO suspension was mixed with 100 ml of Al2O3 solution (1N), 100 ml of Ag2O
solution (1N) along with 50 µL of CQDs solution and sonicated again for an hour. Once
the sonicated time was over, 1:1 NH3 solution was added drop wise into the suspension
until the pH of the mixture raised upto ~7.0. Further, acrylamide (AM) (2.0 g) was mixed
in suspension followed by the mixing of potassium persulfate as an initiator (7% w/w of
AM) and N,N’-methylenebisacrylamide (7% w/w of AM) as a crosslinker through
continuous stirring to avoid aggregation in produced hydrogels. Then, jelly like solid mass
was kept for 24 hrs, filtered and washed with Millipore water for obtaining neutral pH and
dried at 60º-65ºC in oven. Finally, produced hydrogels was crushed and sieved out to
desirable particle range to carry out the experiments.
The alumina is a lewis acid so it forms a nanocomposite with graphene oxide. The formed
nanocomposite with Al2O3 also has hydroxyl groups bonded with Al atom and can
undergo nucleophilic substitution with F ion. The carboxylic group of graphene oxide get
bonded with aluminium ions. When this nanocomposite is treated with CQDs in presence
of Ag2O, a tetrahedral complex was formed. The CQDs and aluminium nanocomposite get
reduced by Ag2O. This complex has hydroxyl groups which can be displaced by F- ion
present in the water under treatment.
-14-
In an embodiment, the composition as described above is in the form of a pencil or a
candle or cartridge.
In an embodiment, the method of preparing hydrogel composition by sol-gel method as
described above comprises following steps:
f) Sonicating the Graphene oxide uniformly at least for an hour in millipore
water (1 mg mL-1
) for complete dispersion followed by mixing the resulting
graphene oxide suspension present in an amount ranging from 0.7-1.7 mg
mL-1 with Al2O3 solution (1N) present in an amount ranging from 70-170
mL, Ag2O solution (1N) present in an amount ranging from 70-170 mL
along with carbon quantum dots solution present in an amount ranging from
40-85 µL followed by sonicating the resulting suspension for an hour;
g) Adding 1:1 NH3 solution dropwise into the suspension until the pH of the
mixture is raised upto ~7.0;
h) Adding approximately 2.0 g acrylamide in suspension followed by mixing
approximately 7% w/w potassium persulfate as an initiator and
approximately 7% w/w N,N’-methylenebisacrylamide as a crosslinker
through continuous stirring to obtain a jelly like solid mass;
i) Filtering and washing the jelly like solid mass resulting from step (c), after
being kept for 24 hrs, with Millipore water for obtaining neutral pH and
drying at 60º-65ºC in oven to obtain the hydrogel;
j) Crushing the hydrogels and sieving out to desirable particle range.
In an aspect, there is provided a method of removing fluoride from a sample by the
composition as described above. The method comprises treating approximately 500 mL of
water sample with approximately 2gm of the composition as described above by dipping
in the water and leaving the solution for approximately 8 minutes.
In an embodiment, the composition is in the form of a pencil or a candle or cartridge.
Adsorption spectrum for F
F removal study was conducted with finalized F concentrations as 2, 4, 6, 8 and 10 mg L−1
with 100 ml suspension. The contact time was 2, 4, 6 and 8 min and beakers were placed
in shaker at 120 rpm during adsorption. Influence of pH on adsorption process was studied
-15-
in range of 2–9 and remaining F content was reported through fluoride ion meter. Removal
% was obtained through given equation.
Removal efficiency (%) = Co − Ce /Co × 100
The Invention is further described with the help of non-limiting examples:
Example 1:
Al2O3 NPs, Ag2O NPs, CQDs and GO were synthesized via waste of pencil peel and
pencil lead by green and chemical method as explained in experimental section.
Morphology and composition of prepared materials was characterized through FESEM,
HRTEM and EDX spectrum. Figure 1 (a–f) represents the formation of Al2O3 NPs, Ag2O
NPs and GO. Figure 2 (a-b) shows the formation CQDs.
The FESEM image demonstrates the surface morphology of Al2O3 NPs which was
observed as flakes with irregular shape, (Fig. 1a) whereas the surface morphology of Ag2O
NPs was spherical (Fig. 1c). Figure 1e, FESEM image of GO illustrates morphology that it
is multilayered in nature with rough surface and wrinkles. The elemental composition
from EDX examination established that the Al2O3 NPs sample has O (23.34%), Al
(62.85%) and Si (13.81%) (Fig. 1b). EDX of Ag2O NPs illustrate the existence of Ag
(48.4%) and O (4.7%) (Fig. 1d). EDX of GO illustrate the existence of C (86.23%), O
(9.73%) and Au (4.04%) (Fig. 1f).
Example 2:
High resolution transmission electronic microscopy (HRTEM) showed the morphology of
CQDs indicating the obtained C-dots are spherical in shape regardless of the starting
material (Vasimalai et al., 2018) (Fig. 2a), EDX analysis of CQDs showed the presence of
C (94.7%), O (3.5%), Na (0.2%) and Cl (0.3%) (Fig. 2b).
The surface morphology of GAAC composite hydrogel before and after F adsorption was
studied and presented in Fig. 3(a and c). FESEM analysis showed the uniform distribution
and coating of nanocomposite. The elemental spectrum confirmed the presence of Al, Ag
and C in GAAC hydrogel before and after adsorption (Fig. 3b and d). EDX confirmed the
presence of one extra peak along with respective peaks in GAAC hydrogel i.e. F peak
confirmed the F adsorption from aqueous solution (Fig. 3d).
Example 3:
Phase composition
Phase purity and crystallinity of the synthesized Al2O3, Ag2O NPs and CQDs was
calculated using XRD analysis. Three major diffraction peaks in synthesized Ag2O NPs
-16-
were obtained at 2θ = 32.67°, 37.98° and 54.70° (Pawar et al., 2016) (Fig. 4a) and Al2O3
NPs were 2θ = 32.47°, 36.92°, 45.35° and 66.17° (Kumari and Khan, 2017) (Fig. 4b). The
XRD pattern of CQDs shows an intense diffraction peak at 2θ = 30.10° (Baruah et al.
2014) (Fig. 4c). However, the crystalline size of NPs was calculated through DebyeScherrer equation (Kumari and Khan, 2017).

The calculated average crystallite size through Debye-Scherrer equation of Al2O3 NPs was
15.73 nm and Ag2O NPs was 23.38 nm.
Example 4:
FTIR Analysis
The surface functionalization of GO, Al2O3 NPs, Ag2O NPs, CQDs and GAAC before and
after F adsorption was analyzed via FTIR spectra (Fig. 5). In GO, bands at 1200 cm−1
,
1070 cm−1
and 1720 cm−1 are attributed to the C–O epoxy stretching, C–O alkoxy
stretching and C=O carbonyl stretching vibrations, respectively; the absorption band at
3779 cm−1
corresponds to the O–H stretching (Zhang et al., 2014). In Al2O3 sample, the
characteristic peaks were observed at 574 and 3779 cm−1 which are assigned to the
stretching of metal-oxygen because of the Al-O and O-H group, respectively (Kumari and
Khan, 2017). The adsorption peak at 3781 cm-1
, 1596 cm-1
of Ag2O sample corresponds to
O-H stretching and carboxylic group respectively. Meanwhile, the peak at 1042 cm-1
can
be described as vibration band of C-O whereas band at 2959 and 1484 cm-1
indicate
stretching and bending of aliphatic C-H respectively. In addition, 860–740 cm-1
bands are
the out of plane vibration bands of N–H group and 599 cm-1
corresponds to stretching of
metal-oxygen Ag-O (Kurdekar et al., 2017). For, CQDs characteristic adsorption peak of
−OH stretching could be observed at 3773 and 1095 cm−1
and band at 2923 cm−1
corresponds to the C−H stretching mode. Moreover, the peaks shown at 1598 and 1401
cm−1 may be caused by the asymmetric and symmetric stretching vibration of COO−
,
respectively (Xu et al., 2015). All the characteristic peaks of GO, Al2O3 NPs, Ag2O NPs
and CQDs were also observed in GAAC samples. The increased intensity of O-H and N-H
band in GAAC spectrum before F adsorption indicated Ag chelation of N-H groups in
GAAC. After F adsorption, the intensity of Al-O and Ag-O band decreased as associated
with F ions interaction and no significant change was observed in GGAC spectra before
and after F adsorption indicating that no structural change happen during adsorption
-17-
process (Kumari and Khan, 2017). In addition, decreased intensity of O-H bond after F
absorption indicates the replacement of OH ions by F ions.
Example 5:
Effect of pH
F adsorption is primarily governed by the pH of solution over an oxide surface. Since, a
release of OHions is coupled with anion adsorption, so the F adsorption over GAAC
hydrogel is favoured in low pH values (Fig. 6a). Figure 6 (a) depict the plot of F removal
% over GAAC hydrogel against the pH solution, which shows that F removal % elevated
with increasing pH up to 5. Therefore, the result demonstrated that with the enhancement
in pH above 5, F removal % reduced (Fig. 6a). In acidic pH environment, the development
of hydrofluoric acid (HF) is accountable for decreasing of F adsorption. Under alkaline
environment, F remediation decreased due to the competition between F ions and hydroxyl
ions for the active surface sites.
Example 6:
Initial F concentration and contact time
F removal % was reported as 95.5% for the initial 2 mg L−1 F concentration, which
reduced to 80% for initial 10 mg L−1 F concentration at contact period of 8 min (Fig. 6b).
The difference in the F removal % may be because of the reduction in the amount of
accessible adsorption sites as they gets saturated at an excess F concentration. Adsorption
performance was calculated as a function of contact period from 2 to 8 min with GAAC
hydrogel at pH 5 at 30 °C. It is established from the above results that the adsorption
elevates with time and an equilibrium state is obtained after a contact period of 8 min (Fig.
6c).
Example 7:
Kinetics
Adsorption kinetics was calculated with pseudo-first-order and pseudo-second-order
models. The data attained was utilized for both models to describe the adsorption kinetics
of F ions on the GAAC. Pseudo-first and second-order model equations (Kumari and
Khan, 2017) are:
log (qe - qt) = log qe - ( k1/2.303 ) t
t/qt = 1/k2qe
2
+ t/qe
-18-
The parameters estimated in Table 1 shows that pseudo-second-order model is
more fit for the adsorption with maximum correlation coefficient (R2
=0.999) than
pseudo-first-order model. Thus, pseudo-second-order shows that the F adsorption
is through chemisorption mechanism.
Table 1. Kinetics for F adsorption onto GAAC.
Fluoride initial concentration (mg L-1
)
Model Parameters 2 4 6 8 10
Pseudo-firstorder
R
2
0.867 0.853 0.726 0.930 0.927
k1 0.2828 0.1612 0.1856 0.1734 0.3705
Pseudo-secondorder
R
2
0.893 0.970 0.999 0.991 0.916
k2 0.0367 0.0437 0.029 0.017 0.068
Example 8:
Isotherm
To calculate the defluoridation capacity, three chief isotherms were considered. The
Langmuir isotherm explains the monolayer adsorption and is shown as (Kumari and Khan,
2017)
Ce/qe = Ce(1/Qo
) + 1/Qo
b
Fig. 7a shows that experimental data fitted well with the Langmuir isotherm, maximum
adsorption capacity was found to be 12.04 mg g−1 with R2
values of 0.978.
The Freundlich represents adsorption on the heterogeneous surfaces and is expressed as
(Kumari and Khan, 2017) (Fig. 7b)
log qe = log kF + (1/n) log Ce
The values of n > 1 stand for the favourable adsorption condition and the obtained n value
indicates the favourable isotherm. The attained value of 1/n was 1.07.
The Temkin isotherm demonstrates adsorbent-adsorbate interaction, which is defined by
the following eq. (Fig. 7c)
qe = RT/bTIn(AT) + RT/bTIn(Ce)
The heat of adsorption values calculated using the Temkin model was 1.51 kJ mol−1
.
Example 9:
Developed Product
-19-
F removal pencil was developed for F removal from drinking water. The developed
product (Fluoride removal Pencil) was developed by utilizing nanocomposite GAAC (GOAl2O3-Ag2O-CQDs), plastic sheet and Whatman’s No. 2 filter paper. In brief, plastic sheet
was made porous so that water can flow in and out by punching and Whatman’s No. 2
filter paper has been kept inside the plastic sheet mould in order to avoid leaching of
nanocomposite in water sample and lastly wire has been attached to the top of pencil for
easy dip mechanism.
Example 10:
Comparison of F adsorption efficiency for various adsorbents
A comparison of GAAC hydrogel adsorption efficiency with other reported adsorbents
(Table 2). GAAC hydrogel in the study has higher adsorbent capacity than other
adsorbents in the literature.
Table 2. Adsorption capacity of present adsorbent with other adsorbents
S.No. Adsorbent Adsorption
capacity (mg g1
)
References
1. Nano AlOOH 3.26 Wang et al., 2009
2. Graphene oxide supported
polyaniline
1.39 Sun et al., 2013
3. Magnetic Prussian
blue/graphene oxide
nanocomposites
0.41 Yang et al., 2014b
4. Magnetic Prussian
blue/graphene oxide caged in
calcium alginate
0.32 Yang et al., 2014a
5. Porous three-dimensional
graphene foam/Prussian blue
composite
0.14 Jang et al., 2015
6. Graphene oxide 0.30 Tan et al., 2016
7. 3D rGO-hydrogel 7.85 Halouane et al.,
2017
-20-
8. ED-RGO 5.00 Luo et al., 2012
9. Ag-GNs 10.90 Sreeprasad et al.,
2011
10. MnO2-GNs 10.80 Sreeprasad et al.,
2011
11. GO-Al2O3-Ag2O-CQDs
(GAAC) composite
12.04 Present Work
Example 11:
Experiment design for composition of GO/Al2O3/Ag2O/CQDs based hydrogel
Repeated experiments were conducted with different concentration of the components of
the composition.
The experiments involved following groups as mentioned below:
Group A: Composition comprising 0.5 mg mL-1 GO, 50 mL Al2O3 (1N) nanoparticles, 50
mL Ag2O nanoparticles, and 25 µL Carbon Quantum dots.
Group B: Composition comprising 2 mg mL-1 GO, 200 mL Al2O3 (1N) nanoparticles,
200 mL Ag2O nanoparticles, and 100 µL Carbon Quantum dots.
Group C: The final composition comprises 1 mg mL-1 GO, 100 mL Al2O3 (1N)
nanoparticles, 100 mL Ag2O nanoparticles, and 50 µL Carbon Quantum dots
The above mentioned Group A and B composition was used for testing fluoride content in
a water sample. The results, as illustrated in figure 9, shows ineffective result for the
removal of fluoride content in the water sample when treated with Group A and Group B
composition whereas Group C shows effective result for the removal of fluoride content
in the water sample.

We Claim:

1. A hydrogel composition for fluoride removal from a sample, where said
composition is based on a three dimensional network porous hydrogel structure
with two dimensional sheets of graphene oxide, wherein said composition
comprises two dimensional sheets of graphene oxide, with the dispersion of Al2O3
nanoparticles, Ag2O nanoparticles, carbon quantum dots onto the gel;
wherein, graphene oxide is present in an amount ranging from 0.7-1.7 mg mL-1
,
Al2O3 nanoparticles (1N) is present in an amount ranging from 70-170 mL, Ag2O
nanoparticles is present in an amount ranging from 70-170 mL, carbon quantum
dots is present in an amount ranging from 40-85 µL amount.
2. The composition as claimed in claim 1, wherein Al2O3 nanoparticle/s is prepared
through green route using waste peel of pencil, comprising the steps of:
a) Preparing the pencil peel extract using waste peel after pencil being sharpened
followed by grinding in grinder to obtain the peel powder wherein
approximately 20 g of pencil peel powder is mixed in 100 ml Millipore
water and heating at 80°C for approximately 30 minutes followed by cooling
and filtering with Whatman’s No.1 filter paper to obtain pencil peel extract;
b) Mixing Al2(SO4)3 with pencil peel extract obtained from step (a) in 1:3 ratio
followed by continuous stirring to obtain the suspension;
c) Microwaving/heating the suspension obtained from step (b) at 540 W for
approximately 5 minutes, which results into a yellow brown precipitate
followed by centrifuging and rinsing the precipitate with distilled water and
methanol;
d) Oven drying the precipitate resulting from step (c) at 100 °C.
3. The composition as claimed in claim 1, wherein Ag2O nanoparticle/s is prepared
through green route using waste peel of pencil, comprising the steps of:
a) Preparing the pencil peel extract using waste peel after pencil being sharpened
followed by grinding in grinder to obtain the peel powder wherein
approximately 20 g of pencil peel powder is mixed in 100 ml Millipore
water and heating at 80°C for approximately 30 minutes followed by cooling
and filtering with Whatman’s No.1 filter paper to obtain the pencil peel extract;
-22-
b) Mixing approximately 25 ml of pencil peel extract obtained from step (a) with
approximately 225 ml of 1mM AgNO3 to obtain the suspension followed by
shaking the suspension at 120 rpm at room temperature;
c) Centrifuging the suspension resulting from step (b ) at 10000 rpm for
approximately 30 min to obtain a precipitate;
d) Rinsing the precipitate atleast twice with distilled water followed by oven
drying at 100°C and storing at - 4°C.
4. The composition as claimed in claim 1, wherein the graphene oxide is prepared
from pencil lead by modified Hummer’s method.
5. The composition as claimed in claim 1, wherein the carbon quantum dots is
prepared from pencil peel waste by green method.
6. The composition as claimed in claim 1, is in the form of a pencil or a candle or
cartridge
7. A method of preparing hydrogel composition by sol-gel method as claimed in
claim 1, comprising the steps of:
a) Sonicating the Graphene oxide uniformly at least for an hour in millipore
water (1 mg mL-1
) for complete dispersion followed by mixing the resulting
graphene oxide suspension present in an amount ranging from 0.7-1.7 mg
mL-1 with Al2O3 solution (1N) present in an amount ranging from 70-170
mL, Ag2O solution (1N) present in an amount ranging from 70-170 mL
along with carbon quantum dots solution present in an amount ranging from
40-85 µL followed by sonicating the resulting suspension for an hour;
b) Adding 1:1 NH3 solution dropwise into the suspension until the pH of the
mixture is raised upto ~7.0;
c) Adding approximately 2.0 g acrylamide in suspension followed by mixing
approximately 7% w/w potassium persulfate as an initiator and
approximately 7% w/w N,N’-methylenebisacrylamide as a crosslinker
through continuous stirring to obtain a jelly like solid mass;
d) Filtering and washing the jelly like solid mass resulting from step (c), after
being kept for 24 hrs, with Millipore water for obtaining neutral pH and
drying at 60º-65ºC in oven to obtain the hydrogel;
e) Crushing the hydrogels and sieving out to desirable particle range.
8. A method of removing fluoride from a sample by the composition as claimed in
claim 1, wherein said method comprises treating approximately 500 mL of water
-23-
sample with approximately 2gm of the composition as claimed in claim 1 by
dipping in the water and leaving the solution for approximately 8 minutes.
9. The method as claimed in claim 8, wherein the composition is in the form of a
pencil or a candle or cartridge.
10. The method as claimed in claim 8, wherein said method removes fluoride content
by approximately 95.5% for the initial 2 mg L−1
F concentration.