DESC:FIELD OF THE INVENTION:
The present invention relates to carbon dot and its nanohybrid with copper oxide and more specifically to controlled size fluorescent carbon dot and its nanohybrid with copper oxide and its single step one pot industrially scalable and microprocessor controlled process to achieve advancement in fluorescent carbon dot and its nanohybrid with copper oxide and its related characteristics as well as obtain excellent yield of carbon quantum dot and its nanohybrid with copper oxide and subsequent use of the nanohybrid in paint formulation.

BACKGROUND OF THE INVENTION:
Carbon quantum dot or carbon dot is a special class of fluorescent nanomaterial and an attractive alternate to the traditional semiconductor nanocrystals due to the superior properties of the former. These advantages include resistance to photobleaching, chemical inertness, no optical blinking, easy functionalizability, non-toxicity, biocompatibility and water solubility (Li, Q., et al. J. Phys. Chem. C 2010; 114, 12062-12068; Goh, E. J., et al., Biomacromolecules 2012; 13, 2554-2561; Yang, S. T., et al. J. Am. Chem. Soc. 2009; 131, 11308-11309; Baker, S. N., et al. Angew. Chem. Int. Ed. 2010; 49, 6726 – 6744; Qiao, Z. A., et al. Chem. Commun. 2010; 46, 8812 - 8814). Thus carbon dot is a young star of carbon nanomaterials’ family, first obtained during purification of single-walled carbon nanotubes (Xu, X., et al. J. Am. Chem. Soc. 2004; 126, 12736-12737). It has oxygenous functional groups on its surface like hydroxyl, epoxy, carboxyl, etc. and the particles size below 10 nm with mainly spherical shape (Jia, X., et al., Nanoscale 2012; 4, 5572-5575). Carbon dot gradually becomes exciting nanomaterials because of its benign and inexpensive nature with easy availability, which resulted numerous possible applications in optoelectronics and energy sector, biomedical science, sensor and catalysis as well as in field of polymer (Li, H., et al. J. Mater. Chem. 2012; 22, 24230-24253). Several strategies are demonstrated for the synthesis of carbon dot with desired properties. High energy ion beam radiation and laser ablation are two common approaches for the preparation of carbon dot from cement and graphite powders (Li, H., et al. J. Mater. Chem. 2012; 22, 24230-24253; Sun, Y. P., et al. J. Am. Chem. Soc. 2006; 128, 7756-7757). However, to prevent the use of expensive precursors and energetic systems, different chemical methods are being adopted. Oxidation of gas soot, carbon soot or activated carbon using strong acids like nitric acid are also relatively inexpensive way to prepare carbon dot (Liu, H., et al. Angew. Chem. Int. Ed. 2007; 46, 6473-6475; Qiao, Z. A., et al., Chem. Commun. 2010; 46, 8812-8814), but the use of large amount of such strong acids is undesirable and hazardous. Again, the carbonization of glucose, sucrose, glycol, glycerol, citric acid, ascorbic acid, etc. has achieved significant attention for the production of fluorescent carbon dot as precursors, though most of these methods need multi-step operations and strong acids as well as post-treatment with surface passivating agents to improve the water solubility and luminescent properties (Zhang, J., et al. New J. Chem. 2010; 34, 591-593; Puvvada, N., et al., Sci. Technol. Adv. Mater. 2012; 13, 045008; Zhai, X., et al. Chem. Commun. 2012; 48, 7955-7957). Recently, serious efforts are being made to obtain self-passivated carbon dot by one step hydrothermal carbonization with high temperature or microwave assisted hydrothermal carbonization of different carbon precursors (Yang, Z. C., et al. Chem. Commun. 2011; 47, 11615-11617; Hsu, P. C. et al. Chem. Commun. 2012; 48, 3984-3986; Yang, Y., et al. Chem. Commun. 2012; 48, 380-382; Zhang, Z., et al. RSC Adv. 2012; 2, 8599-8601; Sahu, S., et al. Chem. Commun. 2012; 48, 8835-8837).

Thus, the production of carbon dot from renewable bio-precursor with inexpensive and greener method is a challenging but worthy concept. Many researchers reported such types of endeavor from readily available natural bio-resources, like orange peel, pericarp, peppermint oil, cow milk, food-waste, natural proteins, banana juice, starch, citric acid, etc such as Sahu, S., et al. reported simple one-step synthesis of highly luminescent carbon dots from orange juice and application as excellent bio-imaging agents, (Chem. Commun. 2012; 48, 8835-8837; Du, W., et al. proposed green synthesis of fluorescent carbon quantum dots and carbon spheres from pericarp (Sci. Chin. Chem. 2015, DOI: 10.1007/s11426-014-5256); Kung, M. L., et al. disclosed bifunctional peppermint oil nanoparticles for antibacterial activity and fluorescence imaging (ACS Sustainable Chem. Eng. 2014; 2 1769-1775; Han, S., et al. described fabrication, gradient extraction and surface polarity-dependent photoluminescence of cow milk-derived carbon dots (RSC Adv. 2014; 4, 58084-58089); Park, S. Y., et al. stated photo luminescent green carbon nanodots from food-waste-derived sources (ACS Appl. Mater. Interfaces 2014; 6, 3365-3370) and Wu, Z. L., et al. reported one-pot hydrothermal synthesis of highly luminescent nitrogen-doped amphoteric carbon dots for bioimaging from Bombyxmori silk-natural proteins (J. Mater. Chem. B 2013; 1, 2868-2873).

Again, different zero-dimensional metal and metal oxide nanoparticles like copper, copper oxides, silver, gold, titanium oxide, zinc oxide, etc. are widely used as nanomaterial to achieve various interesting properties like optical, electrical, antimicrobial, catalysis, degradation of organic pollutant and or methyl orange under visible light, near IR photocatalytic activity and so on (Roy, B., et al., Bioresour. Technol. 2013; 127, 175-180; Mahapatra, S. S. et al. J. Macromol. Sci., Pure Appl. Chem. 2009; 46, 296-303; Karak, N., et al. Macromol. Mater. Eng. 2009; 294 (2), 159 – 169; Shi, H., et al. ACS Appl. Mater. Interfaces 2013; 5, 6959-6967; Sun, L. et al. Polym. Compos. 2013; 34, 1076-1080; Kaur, J., et al. Physica B 416, 33-38, 2013; Tu, K., et al. J. Phys. Chem. C 2014; 118, 7202-7210; Li, H., et al. J. Mater. Chem. 2012; 22, 17470 - 17475).
Metal oxide nanoparticles like TiO2, ZnO, Cu2O, etc. are extensively used as photocalysts for degradation of organic pollutants (Sun, L. et al. Polym. Compos. 2013; 34, 1076-1080; Kaur, J., et al. Physica B 2013; 416, 33-38; Tu, K., et al. J. Phys. Chem. C 2014; 118, 7202-7210; Li, H., et al. J. Mater. Chem. 2012; 22, 17470-17475, Tang, J., et al., Angew. Chem. Int. Ed. 2004; 43, 4463-4466). Photocatalysis is one of the greenest approaches for the destruction of different hazardous anthropogenic organic contaminants because the photodegradation of the contaminants is economically favourable and the process is fast even at their very low concentration under ambient conditions. Apparently, formation of O2._, , .-O-O-H and .OH radicals from oxygen and water by nanocomposite of carbon dot / copper oxide in presence of visible sunlight which possess strong oxidizing capability to convert organic molecules into water and carbondioxide is responsible for self cleaning attribute to the aforementioned composite. (Gawande, H., et al. Chemical Review, 2016; 116, 3722 - 3811).
However, in most of the cases used catalysts, semiconductor quantum dots and metal oxide nanoparticles are toxic in nature and catalytic efficiency at visible light are also very low (Kaur, J., et al. Physica B 2013; 416, 33-38; Kisch, H., Angew. Chem. Int. Ed. 2013 52, 812-847; Kang, Z., et al. J. Am. Chem. Soc. 2007; 129, 12090-12091).

Further, among the different hazardous anthropogenic organic chemicals, pesticides are the most common non-degradable anthropogenic chemical contaminants both in water and soil (Aragay, G., et al. Chem. Rev. 2012; 112, 5317-5338) Copley, S. D., Nat. Chem. Biol. 2009 5, 559-566). They are extensively used in industry as well as in agriculture. Organophosphates like paraoxon are mainly used as nerve agents, chemical warfare agents as well as pesticides and insecticides in agriculture. They enter into the water and cause convulsions and respiratory paralysis by prolongation of cholinergic effects to the living system. However, degradation of pesticide by nanophotocatalyst is limited and the efficiency of such reported catalysts is very poor even under UV irradiation (Mattozzi, M. D. L. P., et al. Appl. Environ. Microbiol. 2006; 72, 6699-6706). In this respect, attributes like low-toxicity, easy availability, low cost, p-type semiconductor with a direct band gap of 2.2 eV, photocatalytic activity under visible light and others endow Cu2O nanoparticles a unique position in the domain of metal oxide based photocatalyst. But, preparation and stabilization of Cu2O nanoparticles are the major issues as in maximum cases Cu2O nanoparticles are formed with mixture of Cu and CuO nanoparticles (Abboud, Y., et al. Appl. Nanosci. 2014; 4, 571-576; Yin, M., et al. Copper oxide nanocrystals, J. Am. Chem. Soc. 2005; 127, 9506-9511). Recently, it is also intensively used as a photocatalyst because of its tuneable emissions from near-infrared to blue wavelength (Li, H., et al. J. Mater. Chem. 2012; 22, 24230 - 24253). Again, researchers designed carbon dot with other metal or metal oxide nanoparticles for enhancing catalytic efficiency by exploiting the up-conversion luminescence properties of it (Tu, K., et al, J. Phys. Chem. C 2014; 118, 7202-7210; Li, H., et al. J. Mater. Chem. 2012; 22, 24230 -24253; Li, H., et al. Angew. Chem. Int. Ed. 2010; 49, 4430-4434, 2010) Furthermore, control reduction of Cu2+ and stabilization of Cu2O could be performed in presence of suitable stabilizing agents.

De. B., et al. (RSC Advances 2014 4 (102) 58453-58459) teaches the preparative technique of carbon dot reduced Cu2O nanohybrid by the reduction of aqueous cupric acetate solution by carbon dots at 70 °C for 6 h. The above prior art also teaches the preparative technique of a highly tough thermostable hyperbranched epoxy nanocomposite with the above nanohybrid, as an efficient reusable photocatalyst activity towards the degradation of pesticide under solar light (light intensity: 800-1000 lx).
Photocatalytic degradation of organic contaminants under solar light using carbon dot/titanium dioxide nanohybrid, obtained through a facile approach by Hazarika, D., et al. (Applied Surface Science 2016 376, 276-285) teaches a novel, simple and green method to synthesize highly luminescent nitrogen containing carbon dot (CD) using carbon resources like bio-based citric acid and glycerol in the presence of cost free cow urine. A nanohybrid of CD and TiO2 (CD@TiO2) was also synthesized from the above carbon resources and titanium butoxide through a facile one pot single step hydrothermal protocol.

A renewable resource based carbon dot decorated hydroxyapatite nanohybrid and its fabrication with waterborne hyperbranched polyurethane for bone tissue engineering By Gogoi, S., et al. (RSC Advances 2016, 6(31), 26066-26076, publishes the preparative method of a carbon dot (CD) decorated hydroxyapatite (HAp) nanohybrid (CD@HAp) from renewable resources like aqueous extracts of corms of Colocasiaesculenta as the CD precursor and egg shell for CaO, which served as the precursor for HAp.
On a publication De, B., et al. (Materials Science & Engineering, C: Materials for Biological Applications 2015, 56, 74-83) teaches the preparative method of a transparent thermosetting nanocomposite with antimicrobial and photoluminescence attributes. The nanocomposite was fabricated by incorporation of different wt.% (1, 2 and 3) of a biocide, 2-methyl-4-isothiazolin-3-one hydrochloride (MITH) immobilized OMMT carbon dot reduced Cu2O nanohybrid (MITH-NH) in the hyperbranched epoxy matrix. Here also procedure is not obvious or comparable, as the biocide immobilized nanohybrid is incorporated only in epoxy matrix to improve the mechanical performance of the composite coating.

The report by Li, H., et al. (Journal of Materials Chemistry 2012, 22(34), 17470-17475) is directed to the state of the art which teaches the preparative method of a carbon quantum dots (CQDs)/Cu2O nanohybrid with protruding nanostructures on the surface by facile single step ultrasonic method. This photocatalytic system could harness the (near) IR light to enhance the photocatalytic activity based on the collective effect of superior light reflecting ability of the Cu2O protruding nanostructures and the upconverted photoluminescence property of CQDs.

CN 104477967 is related to a preparative method of cuprous oxide microcrystal by using carbon quantum dot as reducing agent. The prior art comprises preparing carbon quantum dot from grass as raw material by hydrothermal method using carbon quantum dot as reducing agent to prepare cuprous oxide with copper salt as copper source in the presence of surfactant and NaOH solution.

The report by Uthirakumar, P., et al. (RSC Advances 2015, 5(88), 71968-71972) is related to a simple method for synthesizing carbon quantum dot (CQD) decorated leaf-like CuO nanosheets is disclosed. The CQDs not only relay to improve the dispersion of CuO but also offer higher UV-shielding properties. Excellent UV-shielding properties were exhibited by a polymer film containing 0.5 wt% of CQD/CuO nanocomposites.

H; Li., et al. (Advanced energy material 5 14010772015) described a method for the synthesis of nanocomposite (Cu2O/CD) following a simple ultrasonic method and the nanocomposite thus obtained when applied as a catalyst resulted efficient conversion of atmospheric carbondioxide to methanol.

It would be clearly apparent from the above state of the art that all the aforementioned methods suffer from drawbacks like requirement of complex and time consuming process with poor process control resulting in batch to batch performance variations, harsh synthetic conditions, charring \ and low to moderate yield. None of the existing arts are directed to any simple and cost effective manner of synthesis of carbon quantum dot and its nanohybrid with copper oxide and more importantly to any industrially viable procedure resulting carbon quantum dot and its nanohybrid with copper oxide of controlled sizes and with superior characteristics for wide range of end uses and applications.

Moreover, in spite of such numerous reports for synthesis and catalytic application of carbon quantum dots and CD/Cu2O composite in public domain (journals, patents etc.), it appears that there is no prior art documenting industrially scalable process with desired control of the reaction condition for producing carbon dots and/or its nanohybrids of desired specifications and higher yields .

OBJECTS OF THE INVENTION
It is thus the basic object of the present invention to provide for an industry viable method for preparation of carbon dot and carbon dot/copper oxide nanohybrid with controlled size and with excellent yield from readily available low cost commercial raw materials.

Another object of the present advancement is directed to a reproducible synthesis of nanomaterials like water soluble carbon dot and organic dispersible carbon dot/copper oxide nanohybrid.

A further object of the present advancement is directed to development of process for manufacture of carbon dot and carbon dot/copper oxide nanohybrid with controlled size and with excellent yield involving selective control of the process and operating parameters for desired yield with even particle size and with minimum/no charring.

Another object of the present advancement is directed to a process manufacture of carbon dot and carbon dot/copper oxide nanohybrid wherein process parameters like temperature, pressure, stirring speed and reaction time can be monitored, recorded and controlled at each moment during the reaction process.

Yet further object of the present advancement is directed to carbon dot and carbon dot/copper oxide nanohybrid obtained with desired specifications under selected operating conditions which would be capable of exhibiting high fluorescent property, different colours on exposure to different wavelengths of light, anti-counterfeiting and organic contaminants degradation ability, up-conversion luminesces, etc., which are reproducible, comparable or better than presently available nanomaterials.

Another object of the present advancement is directed to carbon dot and carbon dot/copper oxide nanohybrid with special features of the nanohybrid to degrade organic contaminants under normal day light, antimicrobial activity.

Another object of the present advancement is directed to carbon dot and carbon dot/copper oxide nanohybrid and its compatibility with most of the binder systems of paints to be utilized to produce advanced self-cleaning outdoor paints.

Yet further object of the present advancement is directed to formulations including paint formulation of desired specifications involving carbon dot and carbon dot/copper oxide nanohybrid with special features obtained in accordance with the present advancement.

SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a process for the manufacture of fluorescent carbon dot and/or carbon dot and its nano hybrid with copper oxide comprising:
producing said carbon dot by subjecting source of carbohydrate as carbon precursor to hydrothermal carbonization under one pot single step autoclaving process under microprocessor control involving high reactor pressure and temperature under constant stirring to effect said hydrothermal carbonization of carbon precursors under uniform heat distribution free of char formation and controlled reproducibility.

According to another aspect there is provided a process for the manufacture of fluorescent carbon dot based nano hybrid with copper oxide comprising:
producing said carbon dot by subjecting source of carbohydrate as carbon precursor to hydrothermal carbonization in the presence of a copper source under one pot single step autoclaving process under microprocessor control involving high reactor pressure and temperature under constant stirring to effect said hydrothermal carbonization of carbon precursors in the presence of said coper source under uniform heat distribution to obtain said carbon dot based nano hybrid with copper oxide free of char formation and controlled reproducibility.

According to yet another aspect there is disclosed a process as above wherein the step of hydrothermal carbonisation involves source of carbohydrate selected from starch, fruit juice, sorbitol as well as other carbon sources like glycerol, citric acid, in the presence of solvent selected from alcohol, water and catalysts selected from citric acid, ascorbic acid.

According to yet another aspect there is disclosed a process as above comprising carrying out said hydrothermal carbonisation by charging together said carbon source, catalysts and solvents and water involving microprocessor based controlled high pressure in the range of 200-430 Psi preferably 360 Psi and temperature in the range of 180 to 240 0C preferably 230 0C and maintaining a stirrer speed of 80 to 120 RPM preferably about 100 RPM of a period of 3 to 5 hours preferably 4 hours.

According to yet another aspect there is disclosed a process as above wherein the ratio of water and alcohol is maintained in the range of 2 to 3 preferably about 2.58.

According to yet another aspect there is disclosed a process as above wherein said producing said carbon dot following said one pot single step autoclaving process in microprocessor control comprises
i) charging water and ethanol separately the in a microprocessor controlled stainless steel reactor associated with a continuous mechanical stirrer and water circulation;
ii) adding carbon source preferably sorbitol to the reactor followed by catalyst preferably citric acid ;
iii) setting the temperature in the range of 180 to 240 0C preferably 230 0C and keeping the water line on with RPM 80 to 120 preferably 100;
iv) carrying on the reaction for 3 to 5 preferably about 4 hours with strict monitoring of the reaction parameter including max pressure of 430 psi; and
v) allowing the reaction mass to cool at room temperature and obtaining there from the carbon dots having yield in the range of 70 to 90%.

According to yet another aspect there is disclosed a process as above comprising producing carbon dot / Cu2O nanohybrid comprising:
i) charging water and ethanol separately into a microprocessor controlled stainless steel reactor equipped with a continuous mechanical stirrer and water circulation;
ii) adding said carbon source preferably sorbitol and copper source preferably copper acetate to the reactor followed by catalyst preferably citric acid ;
iii) setting and maintain the temperature in the range of 180 to 240 0C preferably to 230 0C and keeping the water line on with RPM 80 to 120 preferably 100;
iv) carrying out the reaction continued for 3 to 5 hours preferably 4 hours with continuous monitoring of the reaction pressure of 430 psi. max; and
v) cooling the reaction mass at room temperature and obtaining therefrom the said carbon dot / Cu2O nanocomposite having yield in the range of 50 to 70%.

According to yet further aspect of the present invention there is provided a paint formulation comprising carbon dot copper nano hybrid obtained of subjecting source of carbohydrate as carbon precursor to hydrothermal carbonization in the presence of a copper source under one pot single step autoclaving process under microprocessor control involving high reactor pressure and temperature under constant stirring to effect said hydrothermal carbonization of carbon precursors in the presence of said coper source under uniform heat distribution to obtain said carbon dot based nano hybrid with copper oxide free of char formation and controlled reproducibility.

According to a further aspect there is provided a paint formulation comprising silicone resin hybrids including acrylics, epoxy, polyesters and inorganic silicate binders wherein the proportion of actives with hybrid: binder is in the range of 0.05 to 0.1 .

According to yet another aspect of the present invention there is provided a process for manufacture of paint formulation as claimed in anyone of claims 8 or 9 comprising:
I) charge all the raw materials into the high speed disperser one by one and start mixing at 400-600 RPM for 10 to 20 minutes preferably about 15 minutes;
ii) adding thickeners and mixing;
iii) adding surfactants and wetting agents and continued mixing; and
iv) adding the carbon dot copper nano hybrid and continuing mixing including defoamers, demineralized water and nano zinc oxide dispersion.

The above process for producing carbon dot and/or carbon dot and its nano hybrid with copper oxide which would avoid the limitations of low yield, un-scalable operation, non-reproducible result, uneven particle size distribution and poor fluorescence, charring and low photocatalytic activity of the existing carbon dot and its nanohybrid with copper oxide.
The present advancement there would provide for uniformly size carbon dot and carbon dot/copper oxide nanohybrid having selectively very high fluorescent property, different colours on exposure of different wavelengths of light, anti-counterfeiting and organic contaminants degradation ability, up-conversion luminesces, etc.
According to yet another aspect of the present advancement there is provided for uniformly sized carbon dot and carbon dot/copper oxide nanohybrid having selective degradation of organic contaminants under normal day light, antimicrobial especially antifungal activity and compatibility with most of the binder systems of paints to produce advanced self-cleaning outdoor paints.
According to yet further aspect of the present advancement there is provided self cleaning formulations including paint formulations including carbon dot and carbon dot/copper oxide nanohybrid of the advancement having special and selective attributes for degrading organic contaminants under normal day light, antimicrobial activity and compatibility with most of the binder systems of paints.
The present invention is thus distinguished from the known art in terms of a single step one pot industrially scalable unique process with precisely controllable conditions including mechanical stirring using readily available raw materials and a microprocessor controlled reactor to obtain excellent yield of carbon quantum dot and its nanohybrid with copper oxide.

The present invention is also directed to advancements involving combinations of carbon quantum dot and its nanohybrid with copper for variety of applications including exterior architectural application where it is used along with Silicone resin hybrids with acrylics, epoxy, polyesters and also the inorganic silicate binders in a proportion where the active compound is major part and binder is just to glue the active particles.

Also the advancement in carbon quantum dot and its nanohybrid with copper according to the invention would enable development of paint compositions when applied on exterior walls display the self -cleaning performance.

The nano hybrids for preparing self-cleaning exterior coating are adapted to decompose the exterior dirt by photochemical degradation in presence of visible light and thus the coated surface will be cleaned by itself under the action of rain or water showering.

The advanced process is thus completely microprocessor controlled and all the process parameters (temperature, pressure, etc.) at every point of the process can be recorded as well as monitored. Further, the complete process is very simple and safe. The unique feature of this process is to produce controlled size carbon dot and its nanohybrid under precisely controlled conditions with continuous mechanical stirring and hence no char product formation, which is commonly found in any prior art process.

Thus the present advancement is directed to solve the common problems of low yield, un-scalable operation, non-reproducible result, uneven particle size distribution and poor fluorescence, low photocatalytic activity of the existing methods for carbon dot and its nanohybrid with copper oxide synthesis. The conventional process is not scalable due to uncontrolled reaction which leads to undesired products formation via charring, polymerization etc. and hence results in lower yield and inferior product performance. Strict control of process parameter thus controlled reaction generates the nanohybrid by present invention is constitutionally distinct to provide for the unique characteristics of high fluorescence, enhanced photocatalytic activity etc.

DETAILED DESCRIPTION OF THE INVENTION:

The present method comprises one pot single step microprocessor controlled autoclaving process and requires 4 hours at 230°C under pressure of 360 Psi. The carbon dot and its nanohybrid copper oxide obtained by the present invention are reproducible displaying uniformity of particle size and particle size distribution and exhibit different colours under exposure of different wavelengths of light (UV). The process of the present invention favours attainment of said nanohybrids in highest yield that possesses photocatalytic activity under visible light for degradation of different organic contaminants including dye and exhibit antimicrobial activity and thus will be useful in advanced self-cleaning outdoor coatings. The advanced preparation method is suitable for industrial production of carbon dot and its nanohybrid with copper oxide as no extra care is necessary to be taken during the operation, and enjoys the advantages of industrially available equipment and readily available carbon source along with convenience in operation. Further this method can be extended to prepare other nanohybrids of carbon dot with different metals and metal oxides.

The advancement according to the present invention is discussed in further detail in relation to the following non-limiting exemplary illustrations wherein:

BRIEF DESCRIPTION OF FIGURES:
The process of the present advancement, its advantages and utilities are discussed further in greater detail in relation to the accompanying figures wherein:
Figure 1 FESEM image of Cu2O/carbon dot nanohybrid
Figure 2: XRD pattern of Cu2O/carbon dot nanohybrid
Figure 3: FESEM image of Cu2O/carbon dot nanohybrid
Figure 4: XRD pattern of Cu2O/carbon dot nanohybrid
Figure 5a UV spectrum of carbon dots
Figure 5b UV spectrum of carbon dots
Figure 5c UV spectrum of carbon dots
Figure 6 UV spectra of carbon dots (QCD-001: 3% Sorbitol and 25% Ethanol, QCD-002: 5 % Sorbitol and 25% Ethanol, QCD-008: 7% Sorbitol and 25% Ethanol, QCD-009:7% Sorbitol and 0% Ethanol)
Figure 7 Carbon dots showing fluorescence (1st: Short UV, 2nd: Visible Light, 3rd: Long UV)
Figure 8 UV spectra of carbon dot processed in a microprocessor (Repeatability check)
Figure 9 UV spectra of carbon dot processed in heating furnace (oven, Repeatability Check)
Figure 10 TEM images of carbon dots, left: conventional oven heating process, right: Microprocessor
Figure 11 Blue dye concentration reduction by Cu2O/carbon dot nanohybrid (QCD-003) in solution phase.
Figure 12 Photocatalytic activity of Cu2O/carbon dot nanohybrid processed in microprocessor by Methylene Dye degradation compared to photocatalytic TiO2 obtained from commercial market, conventional Cu2O/carbon dot nanohybrid made in oven.
Both the carbon dot and its copper oxide nanohybrid were prepared following the microprocessor controlled process one-pot, single step approach in a stainless steel under continuous mechanical stirring as detailed hereunder:

Example I: Method for manufacture of carbon dot was carried out following the steps as discussed hereunder:
Materials
Carbohydrate: sorbitol (70%), Medium: Ethanol, DM Water, Catalyst: Citric acid
Process Steps:
1. water (67.65 gm) and ethanol (25 gm) were charged separately the in microprocessor controlled stainless steel reactor associated with a continuous mechanical stirrer and water circulation;
2. the specific amount of carbon source (sorbitol, 7.15 gm), was added to the reactor followed by catalyst (citric acid 0.2 gm);
3. the temperature was set to 230°C and kept the water line on with RPM ~ 100;
4. cooking of the reaction continued for 4 hours with strict monitoring of the reaction parameter like max pressure of 430 Psi; and
5. the reaction mass was allowed to cool at room temperature and the content was centrifuged at 7000 RPM for 20 minutes, supernatant decanted, washed with ethanol and preserved in ethanol for further study.

The carbon quantum dots thus obtained were duly characterised and reference to accompanying Figure 1 (FESEM image) reveals uniform particle size distribution and Figure 2 displays XRD pattern.

Example II: Method of manufacture of carbon dots / Cu2O nanocomposite.
Materials
Carbohydrate: sorbitol (70%), Medium: Ethanol, DM Water, Catalyst: Citric acid, Copper Source: Copper acetate
Process Steps:
1. Water (62.77 gm) and ethanol (25 gm) were charged separately into the micro -processor controlled stainless steel reactor equipped with a continuous mechanical stirrer and water circulation;
2. The specific amount of carbon source (sorbitol 4.8 gm and copper acetate 7.23 gm) were added to the reactor followed by catalyst (citric acid 0.2 gm);
3. The temperature was set to 230°C and kept the water line on with RPM ~ 100;
4. Cooking of the reaction continued for 4 hours with strict monitoring of the reaction parameter like max pressure of 430 psi; and
5. The reaction mass was allowed to cool at room temperature and the content was centrifuged at 7000 RPM for 20 minutes, supernatant decanted, washed with ethanol and preserved in ethanol for further study.
The copper nano hybrids thus obtained were duly characterised and reference to accompanying Figure 3 (FESEM image) reveals uniform particle distribution. The hybrids were characterized by XRD for their analysis (Figure 4).

Example III: Under this example the preferred manner of manufacture of carbon nano dots was studied as discussed hereunder:
For the purpose studies were carried out with varying quantity of the sorbitol and ethanol with respect to the yield and particle size of the prepared carbon dot. From the UV spectra obtained as per accompanying Figures 5(a) to 5(c) it was quite obvious that the best quality quantum dots were obtained from 5% Sorbitol. For the higher concentration of sorbitol, a broader peak was observed which refers to poor quality of the carbon quantum dots formed. Hence even for the synthesis of the Copper nano hybrid this concentration of 5% Sorbitol was found to be the best option. A comparative UV spectra of carbon dots with concentration is described in Figure 6. The carbon dot obtained displays different colour when aq. Solution was exposed to different wave length from UV, visible and near IR (Figure 7).

Example IV: The process of the present advancement for generation of carbon dots and copper nano hybrids involving high pressure microprocessor controlled method was further studied under comparative trial vis-à-vis oven method and the details are discussed hereunder:
For the purpose repeat Carbon dots and Cu2O /carbon dot nanohybrid batches both in heating furnace (oven) and in high pressure reactor were carried out and evaluate properties.

Batch used for the study were as hereunder:
Carbon dots
Raw Materials Qty (gm)
Sorbitol 10
Citric Acid 0.3
Ethanol 25
Water 64.7
Total 100

Cu2O /carbon dot nanohybrid
Raw Materials Qty (gm)
Copper Acetate 7.23
Ethanol 25
Sorbitol 4.8
Citric Acid 0.2
Water 62.77
Total 100

The process parameters involved for the high pressure method of the present advancement was as per Example I above while for the oven method the protocol followed was as discussed hereunder:
The results obtained following the above comparative runs are provided hereunder in Table I
Table I
Techniques Sample No. % Yield Colour State
Carbon dots by oven QCD-002-ov batch1 69.91 Brown Liquid
QCD-002-ov batch2 68.65 Brown Liquid
QCD-002-ov batch3 69.99 Brown Liquid
Carbon dots by high pressure QCD-002 batch1 86.5 Brown Liquid
QCD-002 batch2 87 Brown Liquid
QCD-002 batch3 86.8 Brown Liquid
Cu2O carbon dot nanohybrid by high pressure QCD-003 batch1 66.29 Brown Solid
QCD-003 batch2 67.3 Brown Solid
QCD-003 batch3 66.25 Brown Solid
Cu2O carbon dot nanohybrid by oven QCD-003-ov batch1 23.64 Brown Solid
QCD-003-ov batch2 24.01 Brown Solid
QCD-003-ov batch3 22.9 Brown Solid

The above results clearly go to reveal the superior attributes of the high pressure method of the present advancement vis-à-vis the oven method in terms of higher yields.
Also, reference is invited to accompanying Figures 8, 9 and 10 which would go to reveal that the microprocessor based controlled high pressure reaction in accordance with the present advancement lead to not only higher yield as apparent from Table I above but also the same resulted in much more uniform particle size which is much desired for desired industrial utility of carbon nano dots and hybrids there from. Photocatalytic activity of the nanocomposite thus obtained is demonstrated by Figure 11 and Figure 12.

Example V: Paint Formulation with Copper oxide Carbon Dot nano hybrid and its processing parameters
Clear coats were prepared with the copper nano hybrid to assess the properties. A detailed formulation and process are as follows. The coating was processed in a high speed disperser.
Raw Material Type Chemistry Qty Process
Water De mineralized 14.6 Charge all the raw materials into the high speed disperser one by one and start mixing at 400-600 RPM for 15 minutes
Rocima 623 Biocide Chlormethyl - / Methylisothiazolone And Formaldehyde 0.2
AM 1512 Defoamer Mineral oil based 0.2
Bindzil CC 301 Silica Nano silica dispersion 30

Aquaflow NHS 300 Thickener Polyurethane 1 Add NHS 300 and AMP-95 and mix for 10 minutes
AMP 95 Neutralizer 2-amino-2-methyl-1-propanol 0.1

Capstone FS 63 Surfactant Anionic fluorosurfactant 0.1 Increased RPM to 1000 and charge the materials and mix for 20 minutes
Dynol 810 Wetting agent Non ionic surfactant 0.2
Propylene Glycol Glycol 1
Water 2

BS 45 Binder silicone acrylic binder 45 Maintain RPM and add the materials. Mix for 30 minutes and discharge batch
Rheolate 278 Thickener Polyurethane Thickener 1
Cu2O carbon dot nanohybrid Nanohybrid 2
AM1512 Defoamer Mineral oil based 0.1
Water De mineralized 0.8
Nanobyk 3820 UV resister Nano zinc oxide dispersion 1

The physical properties of the paint was studied and noted as follows:
Viscosity on Stormer: 80 gm
WPL: 1.08 kg/L
Film Appearance: Brown to greyish
% NVM: 25
It is thus possible by way of the present advancement to provide for an industrial scalable advanced method for preparation of controlled size carbon dot and carbon dot/copper oxide nanohybrid with excellent yield from readily available low cost commercial raw materials and pressure reactor. Advantageously, the process enables reproducible synthesis of nanomaterials like water soluble carbon dot and organic dispersible carbon dot/copper oxide nanohybrid under microprocessor based controlled conditions with continuous mechanical stirring (uniform heat distribution).Importantly, the carbon dot and its nanohybrid produced by the process of the present advancement exhibited very high fluorescent property, different colours on exposure of different wavelengths of light, anti-counterfeiting and organic contaminants degradation ability, up-conversion luminesces, etc., which are reproducible, comparable or better than prior art produced same nanomaterials. Moreover, the special features of the nanohybrid to degrade organic contaminants under normal day light, antimicrobial activity and compatibility with most of the binder systems of paints is specially suited to produce advanced self-cleaning outdoor paints.

,CLAIMS:WE CLAIM:

1. A process for the manufacture of fluorescent carbon dot and/or carbon dot and its nano hybrid with copper oxide comprising:
producing said carbon dot by subjecting source of carbohydrate as carbon precursor to hydrothermal carbonization under one pot single step autoclaving process under microprocessor control involving high reactor pressure and temperature under constant stirring to effect said hydrothermal carbonization of carbon precursors under uniform heat distribution free of char formation and controlled reproducibility.

2. A process for the manufacture of fluorescent carbon dot based nanohybrid with copper oxide comprising:
producing said carbon dot by subjecting source of carbohydrate as carbon precursor to hydrothermal carbonization in the presence of a copper source under one pot single step autoclaving process under microprocessor control involving high reactor pressure and temperature under constant stirring to effect said hydrothermal carbonization of carbon precursors in the presence of said coper source under uniform heat distribution to obtain said carbon dot based nano hybrid with copper oxide free of char formation and controlled reproducibility.

3. A process as claimed in anyone of claims 1 or 2 wherein the step of hydrothermal carbonisation involves source of carbohydrate selected from starch, fruit juice, sorbitol as well as other carbon sources like glycerol, citric acid, in the presence of solvent selected from alcohol, water and catalysts selected from citric acid, ascorbic acid.

4. A process as claimed in anyone of claims 1 to 3 comprising carrying out said hydrothermal carbonisation by charging together said carbon source, catalysts and solvents and water involving microprocessor based controlled high pressure in the range of 200-430 Psi preferably 360 Psi and temperature in the range of 180 to 2400C preferably 2300C and maintaining a stirrer speed of 80 to 120 RPM preferably about 100 rpm of a period of 3 to 5 hours preferably 4 hours.

5. A process as claimed in anyone of claims 1 to 4 wherein the ratio of water and alcohol is maintained in the range of 2 to 3 preferably about 2.58.

6. A process as claimed in anyone of claims 1 to 5 wherein said producing said carbon dot following said one pot single step autoclaving process under microprocessor control comprises
i. Charging water and ethanol separately the in a microprocessor controlled stainless steel reactor associated with a continuous mechanical stirrer and water circulation;
ii. adding carbon source preferably sorbitol to the reactor followed by catalyst preferably citric acid ;
iii. setting the temperature in the range of 180 to 2400C preferably 2300 C and keeping the water line on with RPM 80 to 120 preferably ~ 100;
iv. carrying on the reaction for 3 to 5 preferably about 4 hour with strict monitoring of the reaction parameter including max pressure of 430 Psi; and
v. allowing the reaction mass to cool at room temperature and obtaining therefrom the carbon dots having yield in the range of 70 to 90%.

7. A process as claimed in anyone of claims 2 to 6 comprising producing carbon dot / Cu2O nanocomposite comprising :
i) charging water and ethanol separately into a microprocessor controlled stainless steel reactor equipped with a continuous mechanical stirrer and water circulation;
ii) adding said carbon source preferably sorbitol and copper source preferably copper acetate to the reactor followed by catalyst preferably citric acid;
iii) setting and maintain the temperature in the range of 180 to 2400C preferably to 2300C and keeping the water line on with RPM 80 to 120 preferably 100;
iv) carrying out the reaction continued for 3 to 5 preferably 4 hours with continuous monitoring of the reaction pressure of 430 Psi max; and
v) Cooling the reaction mass at room temperature and obtaining therefrom the said carbon dot / Cu2O nanocomposite having yield in the range of 50 to 70%.

8. A paint formulation comprising carbon dot copper nano hybrid obtained of subjecting source of carbohydrate as carbon precursor to hydrothermal carbonization in the presence of a copper source under one pot single step autoclaving process under microprocessor control involving high reactor pressure and temperature under constant stirring to effect said hydrothermal carbonization of carbon precursors in the presence of said coper source under uniform heat distribution to obtain said carbon dot based nano hybrid with copper oxide free of char formation and controlled reproducibility.

9. A paint formulation as claimed in claim 8 comprising silicone resin hybrids including acrylics, epoxy, polyesters and inorganic silicate binders wherein the proportion of actives with hybrid : binder is in the range of 0.05 to 0.1.

10. A process for manufacture of paint formulation as claimed in anyone of claims 8 or 9 comprising:
i) charge all the raw materials into the high speed disperser one by one and start mixing at 400-600 RPM for 10 to 20 preferably about 15 minutes;
ii) adding thickeners and mixing;
iii) adding surfactants and wetting agents and continued mixing;
iv) adding the carbon dot copper nano hybrid and continuing mixing including defoamers, demineralized water and nano zinc oxide dispersion.

Dated this the 27th Day of September, 2017 Anjan Sen
Of Anjan Sen and Associates
(Applicants Agent)