Carbon quantum dots (CQDS) and method for synthesizing the same thereof for lubrication and photoluminescence

Abstract

The present invention discloses a novel, cost-effective, and scalable method for synthesizing Carbon Quantum Dots (CQDs) with applications in lubrication and solar energy conversion. The CQDs are produced via a hydrothermal process using organic precursors with hydroxyl (- OH) groups, followed by acidification and thermal treatment. The synthesized CQDs, with a 5 size range of 2-5 nm, exhibit strong photoluminescence, high dispersion stability, and superior tribological properties. CQDs are incorporated into base lubricants to form nanolubricants, which reduce the coefficient of friction (CoF) by 48-50%, improving machinery efficiency. Additionally, CQDs are dispersed in organic solvents and encapsulated in solar PV modules, enhancing photon down-conversion and increasing solar efficiency. The invention provides an 0 eco-friendly alternative to conventional CQD synthesis, ensuring high performance, chemical stability, and industrial scalability across automotive, renewable energy, and nanotechnology sectors.

Description

CARBON QUANTUM DOTS (CQDS) AND METHOD FOR SYNTHESIZING THE SAME THEREOF FOR EUBRICATION AND PHOTOEUMINESCENCEFIEED OF THE INVENTION

[0001] The present discosure relates to the synthesis of Carbon Quantum Dots (CQDs) and their applications in lubrication and photoluminescence-based solar energy conversion. More specifically, the invention provides a hydrothermal process for producing CQDs with controlled size and morphology, their incorporation into nanolubricants for friction reduction in industrial and automotive applications, and their utilization in organic dispersions for enhancing the efficiency of photovoltaic (PV) modules via photoluminescence downconversion. The disclosure also covers the method of formulating CQD-based nanofluids, optimizing their dispersion in lubricants and organic solvents, and evaluating their performance in tribological and optoelectronic applicationsBACKGROUND OF THE INVENTION

[0002] Background description 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.

[0003] Carbon Quantum Dots (CQDs) are a class of zero-dimensional carbon nanomaterials that have gained significant attention due to their unique optical, electronic, and tribological properties. Their strong photoluminescence in the visible spectrum makes them ideal candidates for applications in solar energy conversion, bioimaging, optoelectronics, and sensing. Additionally, their spherical morphology and inherent chemical stability make them highly effective as lubricant additives, reducing friction and wear while improving energy efficiency in mechanical systems. The synthesis of CQDs is broadly categorized into two approaches: the top-down approach, which involves breaking down bulk carbon materials like graphite or carbon nanotubes using techniques such as laser ablation, arc discharge, or chemical oxidation, and the bottom-up approach, where molecular precursors undergo controlled reactions such as hydrothermal or microwave-assisted synthesis. Despite various developments in CQD synthesis, existing methods suffer from limitations such as complex processing, inconsistent size control, stability issues, and high production costs.

[0004] Several prior-art documents have explored different methods of CQD synthesis and their applications in lubrication and photoluminescence. CN119177134A discloses a biomassbased ionic liquid-modified CQD synthesized from tea leaves, which enhances lubricant performance but suffers from batch-to-batch inconsistency and complex modification steps. CN 114686216B describes a double -function nano lubricating additive using citric acid-derived CQDs modified with polyethylene glycol (PEG) and polyethyleneimine (PEI); however, the reliance on polyethylene-based modifiers limits its thermal stability, and the multiple functionalization steps increase overall cost and complexity. CN114410217A presents a biomass-derived carbon quantum dot / polyimide composite lubricant for wear resistance applications, but the high viscosity of the polyimide matrix reduces fluidity, making it less suitable for commercial lubricants. Similarly, CN113258007A discusses a hydrothermal method for preparing CQDs from dimethylformamide (DMF) and sucrose for perovskite solar cells (PSCs), yet the use of toxic solvents raises environmental concerns, and the method does not address lubrication applications.

[0005] Other patents, such as CN116924391 A and CN117447840A, focus on self-assembled CQDs for lithium-ion batteries and tobacco-waste-derived CQD composites for supercapacitors, respectively, but neither of these technologies is optimized for lubrication or photoluminescence enhancement. CN109904270A discloses a fluorescence solar light collector based on CQDs synthesized from glucose, which improves light absorption in solar systems but lacks scalability. Additionally, CN110550617A describes a CQD preparation method using activated carbon through a hydrothermal process for biomedical applications but requires high-temperature treatments that lead to higher energy consumption and do not explore tribological performance.

[0006] Despite the advancements in CQD synthesis, existing technologies face several limitations. Many methods involve multiple chemical modification steps, require harsh reaction conditions, or rely on toxic solvents, making them unsuitable for large-scale production. Another challenge is the lack of precise control over CQD size and morphology, which affects their performance in lubrication and photoluminescence applications. The environmental and safety concerns associated with the use of strong oxidants, ionic liquids, or polyethylene-based modifiers further complicate their industrial adoption. Furthermore, while some patents discuss CQD-based lubricants, they fail to provide comprehensive data on friction reduction, wear resistance, and long-term stability. In the case of solar energy applications, existing CQD-based encapsulation methods for photovoltaic modules lack durability, optical transparency, and efficiency under real-world conditions.

[0007] Given these challenges, there is a pressing need for a cost-effective, scalable, and environmentally friendly method for CQD synthesis that ensures controlled particle size (2-5 nm), high dispersion stability in lubricants and organic solvents, and simple processing without requiring additional surface modifications.

[0008] A commercially viable solution must provide measurable performance improvements in lubrication, with sufficient reduction in the coefficient of friction, and in solar energy applications, where CQD coatings can enhance photovoltaic efficiency. The ability to integrate CQDs seamlessly into industrial applications, including automotive lubricants and solar encapsulation materials, is essential for realizing the full potential of this nanotechnology. The need of the hour is to develop an optimized synthesis and application framework that overcomes the shortcomings of existing technologies while ensuring compatibility with large-scale manufacturing, cost-efficiency, and sustainability.OBJECTIVE OF THE INVENTION

[0009] The primary objective of the present invention is to develop a cost-effective, scalable, and environmentally friendly method for synthesizing Carbon Quantum Dots (CQDs) and their applications in lubrication and photoluminescence-based solar energy conversion. The invention aims to address the challenges associated with existing CQD synthesis methods, which include complex processing, inconsistent size control, stability issues, and high production costs.

[0010] Another objective of the present disclosure is to develop an optimized hydrothermal synthesis process that enables the production of CQDs with controlled size (2-5 nm), uniform morphology, and high dispersibility.

[0011] Another objective of the present disclosure is to ensure high efficiency in lubrication applications by incorporating CQDs into base fluids to reduce friction and wear while improving thermal stability and tribological performance.

[0012] Another objective of the present disclosure is to enhance the photoluminescence properties of solar photovoltaic (PV) modules through CQD-based encapsulation, which enables UV-to-visible down-conversion, thereby increasing solar cell efficiency.

[0013] Another objective of the present disclosure is to achieve high dispersion stability of CQDs in nonpolar and polar solvents for extended usability in industrial applications.

[0014] Another objective of the present disclosure is to reduce reliance on toxic precursors and complex functionalization steps, making the method environmentally sustainable and industrially scalable.

[0015] Another objective of the present disclosure is to improve the performance of lubricants by reducing the coefficient of friction (CoF) by at least 48-50%, enhancing their longevity and energy efficiency.

[0016] Another objective of the present disclosure is to enhance the efficiency of solar cells through efficient photon conversion mechanisms facilitated by CQDs.

[0017] Another objective of the present disclosure is to provide a simple yet effective encapsulation method that integrates CQD dispersions into solar cell protective layers, improving their durability and light absorption efficiency.

[0018] Another objective of the present disclosure is to ensure the synthesized CQDs possess strong optical stability with minimal degradation over time, making them suitable for longterm applications in energy conversion and lubrication.

[0019] Another objective of the present disclosure is to create an industrially viable process that supports large-scale production of CQDs and their integration into commercial lubricants and solar energy technologies.SUMMARY OF THE INVENTION

[0020] The present invention generally relates to the a novel method for synthesizing Carbon Quantum Dots (CQDs) and their applications in nanolubricants and photolumine scent coatings for solar PV modules. The CQDs are synthesized using a hydrothermal carbonization process, where an organic precursor containing hydroxyl (-OH) groups is subjected to controlled acidification and thermal treatment. The resulting CQDs exhibit strong photoluminescence, high dispersibility, and excellent tribological properties, making them suitable for industrial lubrication and solar energy applications.

[0021] The invention further describes a method for preparing nanolubricant fluids by incorporating CQDs into base fluids such as commercial automobile and machinery lubricants. The addition of CQDs significantly enhances the anti-friction and anti-wear characteristics of the lubricants, leading to a reduction in energy losses and improved performance of mechanical systems.

[0022] Additionally, the invention discloses a method for formulating organic solventbased CQD dispersions for photoluminescence applications. These dispersions, when spray-coated onto ethylene vinyl acetate (EVA) sheets and encapsulated into solar PV modules, contribute to enhanced photon conversion efficiency, resulting in an increase in solar energy absorption and power output.

[0023] In an aspect, the present invention discloses a a method for producing carbon quantum dots (CQDs) for lubrication and photoluminescence applications, comprising:dispersing an organic precursor with two hydroxide groups in deionized water; mechanically stirring the mixture to form a uniform aqueous precursor mixture; acidifying the precursor using a concentrated inorganic acid and further stirring; transferring the reaction solution into an autoclave and heating at a specified temperature and duration to synthesize CQDs;separating the synthesized CQDs using a separating funnel; andwashing the CQDs with distilled water repeatedly to remove residual acid and obtain CQDs.

[0024] In another embodiment, the present disclosure provides a method for preparing nanolubricant fluids for friction reduction in automotive and industrial applications, comprising:incorporating CQDs into commercial lubricant base oils;mixing the CQD-based nanolubricants using a mechanical stirrer producing CQD-enhanced lubricants with a reduced coefficient of friction (CoF) by 48-50%, improving energy efficiency and wear resistance.

[0025] In another embodiment, the present disclosure provides a method for producing organic solvent-based CQD suspensions for photoluminescence applications, comprising:dispersing CQDs in an organic nonpolar solvent;subjecting the dispersion to ultrasonication;spraying the CQD dispersion onto an ethylene vinyl acetate (EVA) sheet and embedding it in a solar PV module through an encapsulation process;enhancing solar cell efficiency by up to 10% through a down-conversion process, where CQDs convert UV light into visible light, thereby increasing electron generation.

[0026] Various objects, features, aspects, and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments. BRIEF DESCRIPTION OF FIGURES

[0027] The accompanying drawings are included to provide a clear understanding of the present invention and a detailed description, and they constitute a part of this complete specification.

[0028] Figure 1: Flowchart showing the systematic steps for the synthesis of carbon nanostructure materials, specifically carbon quantum dots (CQDs), according to some embodiments.

[0029] Figure 2: Flowchart showing the systematic steps for the preparation of CQD-based nanolubricant fluids according to some embodiments.

[0030] Figure 3: Flowchart showing the systematic steps for the preparation of organic solvent-based CQD dispersions according to some embodiments.

[0031] Figure 4: TEM micrographs of carbon quantum dots (CQDs) synthesized under optimum process conditions.

[0032] Figure 5: Particle size distribution of the carbon quantum dots (CQDs) synthesized under optimum process conditions.

[0033] Figure 6: Raman spectra of carbon nanostructure materials, specifically carbon quantum dots (CQDs).

[0034] Figure 7: Coefficient of friction measurements of base high-machinery lubricant and nanolubricant fluids containing an optimum amount (0.5 wt%) of carbon quantum dots (CQDs), measured using a four-ball tribometer.

[0035] Figure 8: Coefficient of friction measurements of base automobile lubricant and nanolubricant fluids with varying concentrations of carbon quantum dots (CQDs), measured using a pin-on-disc tribometer.

[0036] Figure 9: Transmission spectra of glass-encapsulated EVA sheets with spray-coated CQDs dispersed in solvent at varying CQD concentrations, including magnified graphs.

[0037] Figure 10: Photoemission spectra of glass-encapsulated EVA sheets with spray-coated CQDs dispersed in solvent at varying CQD concentrations, including magnified graphs.

[0038] Figure 11 : 1-V characteristic curves of encapsulated solar PV modules with EVA sheets containing different CQD concentrations.DETAILED DESCRIPTION OF THE INVENTION

[0039] The following is a full description of the disclosure's embodiments. The embodiments are described in such a way that the disclosure is clearly communicated. The level of detail provided, on the other hand, is not meant to limit the expected variations of embodiments; rather, it is designed to include all modifications, equivalents, and alternatives that come within the spirit and scope of the current disclosure as defined by the attached claims. Unless the context indicates otherwise, the term "comprise" and variants such as "comprises"and "comprising" throughout the specification are to be read in an open, inclusive meaning, that is, as "including, but not limited to."

[0040] When "one embodiment" or "an embodiment" is used in this specification, it signifies that a particular feature, structure, or characteristic described in conjunction with the embodiment is present in at least one embodiment. As a result, the expressions "in one embodiment" and "in an embodiment" that appear throughout this specification do not necessarily refer to the same embodiment. Furthermore, in one or more embodiments, the specific features, structures, or qualities may be combined in any appropriate way.

[0041] Unless the context clearly demands otherwise, the singular terms "a," "an," and "the" include plural referents in this specification and the appended claims. Unless the content explicitly mandates differently, the term "or" is normally used in its broad definition, which includes "and / or."

[0042] All processes described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of 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.

[0043] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.

[0044] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

[0045] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and / or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description that follows, and the embodiments described herein, are provided by way of illustration of an example, or examples, of particular embodiments of the principles and aspectsof the present disclosure. These examples are provided for the purposes of explanation, and not of limitation, of those principles and of the disclosure.

[0046] It should also be appreciated that the present invention can be implemented in numerous ways, including as a system, a method, or a device. In this specification, these implementations, or any other form that the invention may take, may be referred to as processes. In general, the order of the steps of the disclosed processes may be altered within the scope of the invention.

[0047] 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.Definitions

[0048] For the purpose of the present disclosure, Carbon Quantum Dots (CQDs) may refer to the Nanoscale carbon-based materials exhibiting quantum confinement and photoluminescence properties, with atypical size range of 2-5 nm.

[0049] For the purpose of the present disclosure, Hydrothermal Carbonization may refer to the thermal processing technique involving the reaction of organic precursors under high-temperature and high-pressure conditions in the presence of water.

[0050] For the purpose of the present disclosure, Photoluminescence (PL) may refer to the emission of light by CQDs upon excitation, commonly utilized in solar energy conversion and bioimaging applications.

[0051] For the purpose of the present disclosure, Tribology may refer to the science of friction, lubrication, and wear in mechanical systems, where CQDs serve as effective lubricant additives.

[0052] For the purpose of the present disclosure, Coefficient of Friction (CoF) may refer to a measure of the resistance to sliding between two surfaces, which is significantly reduced in CQD-based nanolubricants.

[0053] For the purpose of the present disclosure, Nanofluids may refer to the Suspensions of nanoparticles in base fluids, used in lubrication to enhance thermal conductivity, viscosity, and wear resistance.

[0054] For the purpose of the present disclosure, EVA (Ethylene Vinyl Acetate) Sheet may refer to a transparent encapsulation material used in solar PV modules, where CQDs are incorporated to enhance light absorption efficiency.

[0055] For the purpose of the present disclosure, Down-Conversion may refer to a photonic process where high-energy ultraviolet (UV) photons are converted into lower-energy visible photons to improve solar cell performance.

[0056] For the purpose of the present disclosure, Passivation may refer to chemical modification technique used to stabilize the surface of CQDs to enhance their optical and dispersion properties.

[0057] For the purpose of the present disclosure, Autoclave Reactor may refer to the sealed high-pressure vessel used for hydrothermal synthesis of CQDs at elevated temperatures.

[0058] For the purpose of the present disclosure, Surface Functionalization may refer to the modification of CQDs with specific chemical groups to improve solubility, stability, and tribological properties.

[0059] For the purpose of the present disclosure, Nanostructure Morphology may refer to theshape, size, and structure of CQDs, which directly influences their performance in lubrication and photoluminescence.

[0060] For the purpose of the present disclosure, Quantum Yield may refer to the measure of the efficiency of photoluminescence, determining the fraction of absorbed photons that result in emitted light.

[0061] For the purpose of the present disclosure, Solar PV Efficiency may refer to the ability of a solar cell to convert sunlight into electrical energy, which is improved using CQD-based encapsulation layers.

[0062] For the purpose of the present disclosure, High-Temperature Stability may refer to the ability of CQDs to maintain their structure and performance at elevated temperatures.

[0063] For the purpose of the present disclosure, Dispersion Stability may refer to the capability of CQDs to remain uniformly suspended in a fluid without aggregation or sedimentation.

[0064] For the purpose of the present disclosure, Nonpolar Solvent may refer to the class of solvents, such as acetone, hexane, and cyclohexane, in which CQDs are effectively dispersed for photoluminescence applications.

[0065] For the purpose of the present disclosure, Tribometer Testing may refer to the standardized method for evaluating the friction and wear characteristics of lubricants under controlled conditions.

[0066] For the purpose of the present disclosure, Optical Transparency may refer to the ability of a material, such as CQD-coated EVA sheets, to allow maximum light transmission with minimal loss.

[0067] For the purpose of the present disclosure, Encapsulation Process may refer to the method of embedding CQDs in protective coatings, such as EVA sheets in solar PV modules, to improve material durability and optical performance.

[0068] In an embodiment, The present invention describes a novel and scalable method for synthesizing Carbon Quantum Dots (CQDs) with controlled size, morphology, and enhanced photoluminescence and tribological properties. The method involves the hydrothermal carbonization of organic precursors containing hydroxyl groups, followed by controlled acidification and thermal treatment in an autoclave reactor. The resulting CQDs exhibit a uniform size distribution (2-5 nm), high dispersibility, and strong optical emission.

[0069] The invention further provides a method for producing nanolubricant fluids by dispersing CQDs in commercial lubricant base oils at optimized concentrations (0.2-1 wt%). These CQD-based lubricants demonstrate a significant reduction in friction and wear, leading to enhanced performance in automotive and industrial applications.

[0070] Additionally, the invention discloses a method for preparing CQD-based organic solvent dispersions at optimized concentration (0.01-lwt%), which are spray-coated onto EVA sheets and encapsulated in solar PV modules. This encapsulation technique enhances the efficiency of solar cells by 10% or more, enabling better light absorption and energy conversion.

[0071] In an embodiment, the present disclosure provides a method for producing carbon quantum dots (CQDs) for lubrication and photoluminescence applications, comprising:dispersing an organic precursor with two hydroxide groups in deionized water; mechanically stirring the mixture to form a uniform aqueous precursor mixture; acidifying the precursor using a concentrated inorganic acid and further stirring; transferring the reaction solution into an autoclave and heating at a specified temperature and duration to synthesize CQDs;separating the synthesized CQDs using a separating funnel; andwashing the CQDs with distilled water repeatedly to remove residual acid and obtain CQDs.

[0072] In another embodiment, the organic precursor is dispersed in an amount ranging from 25-100 g in 25-100 mb of deionized water.

[0073] In another embodiment, said organic precursors are selected from 1,2-propanediol, 2,3-propanediol, 1,2-butanediol, or 3,4-butanediol or a combination thereof.

[0074] In another embodiment, the mechanical stirrig is performed 10-60 minutes, preferably at room temperature to produce a uniform aqueous precursor mixture.

[0075] In another embodiment, the acidification of the precursor mixture is performed by adding concentrated inorganic acid in a ratio range of 5-20 g and by further mechanical stirring for 30 minutes to 3 hours.

[0076] In another embodiment, said inorganic acid is selected from hydrochloric acid, sulfuric acid, acetic acid, phosphoric acid, hydrofluoric acid, or nitric acid or a combination thereof.

[0077] In another embodiment, the transferring of reaction solution is performed into a Teflon-coated autoclave and heating at 100-300°C for 5-100 hours to synthesize CQDs.

[0078] In another embodiment, the synthesized CQDs are separated from the reaction residue using a separating funnel, followed by multiple washing cycles with distilled water to remove any residual acid.

[0079] In another embodiment, particle size of the synthesized and washed CQDs ranges between of 2-5 nm.

[0080] In another embodiment, the precursor-to-acid weight ratio is maintained between the ranges of 2: 1 to 10: 1 to ensure optimized CQD formation.

[0081] In another embodiment, quantum yield of said synthesized CQDs ranges from 30-90% in photoluminescence applications.

[0082] In another embodiment, the present disclosure provides a method for preparing nanolubricant fluids for friction reduction in automotive and industrial applications, comprising:incorporating CQDs into commercial lubricant base oils;mixing the CQD-based nanolubricants using a mechanical stirrer producing CQD-enhanced lubricants with a reduced coefficient of friction (CoF) by 48-50%, improving energy efficiency and wear resistance.

[0083] In another embodiment, said CQDs are used at concentrations ranging from 0.2 wt% to 1 wt%.

[0084] In another embodiment, said lubricant base oils are selected from, but not limited to, automobile lubricants, industrial machinery oils, hydraulic oils, synthetic lubricants or a combination thereof.

[0085] In another embodiment, the mechanical stirring is performed at speeds between 500-5000 rpm for 10-100 minutes to obtain a uniform dispersion.

[0086] In another embodiment, reduction in wear rate of nanolubricant fluids is 40-60% in tribological testing compared to conventional lubricants.

[0087] In another embodiment, wherein the CQD concentration of the nanolubricant ranges from 0.2-1 wt%.

[0088] In another embodiment, the present disclosure provides a method for producing organic solvent-based CQD suspensions for photoluminescence applications, comprising:dispersing CQDs in an organic nonpolar solvent;subjecting the dispersion to ultrasonication;spraying the CQD dispersion onto an ethylene vinyl acetate (EVA) sheet and embedding it in a solar PV module through an encapsulation process;enhancing solar cell efficiency by up to 10% through a down-conversion process, where CQDs convert UV light into visible light, thereby increasing electron generation.

[0089] In another embodiment, said organic nonpolar solvent is selected from acetone, cyclohexane, or hexane or a combination thereof at a concentration range of 0.01-1 wt% relative to the total volume of the solvent;

[0090] In another embodiment, the ultra-sonication is performed for 5-30 minutes to ensure uniform dispersion.

[0091] In an additional embodiment, the CQD concentration in the nanolubricant is optimized to 0.2-1 wt%, beyond which stability and dispersion issues arise.

[0092] In another embodiment, the CQD-based photoluminescence suspension enhances transmission efficiency by 0.3-0.6% in EVA sheets at lower concentrations but leads to a 1-2% decrease at higher concentrations (>0.5 wt%).

[0093] In another embodiment, the spray-coated CQD dispersion exhibits stable luminescence properties for at least 12 months under ambient conditions.

[0094] In another embodiment, the encapsulated solar PV module coated with CQDs exhibits an improvement in power conversion efficiency (PCE) by 5-12%.

[0095] In another embodiment, the CQDs possess a spherical morphology with high dispersibility in nonpolar solvents, enabling efficient integration into lubrication and photovoltaic applications.

[0096] In another embodiment, the Raman spectra of the synthesized CQDs exhibit a D-band at 1342-1355 cm1andaG-bandat 1585-1595 cm '. confirming their amorphous structure with partial graphitization.

[0097] In another embodiment, the CQDs retain their stability and functionality at temperatures up to 300°C and remain dispersible in both polar and nonpolar solvents.

[0098] In another embodiment, the synthesized CQDs show an average fluorescence lifetime of 5-15 ns, making them suitable for optoelectronic applications.

[0099] In another embodiment, the nanolubricant exhibits long-term stability, maintaining homogeneity for over 6 months without sedimentation or agglomeration.

[0100] In another embodiment, the CQD-based photoluminescence solution is optimized for high-performance LEDs, bioimaging, and energy harvesting applications.

[0101] In another embodiment, the CQD dispersions enhance the stability of perovskite solar cells by reducing UV -induced degradation.

[0102] In an additional embodiment, the present disclosure provides a method of producing photoluminescence CQD based organic dispersion fluids wherein the transmission of the EVA sheets encapsulated with glasses on both sides significantly decreases with higher concentrations of CQDs wt%), while lower concentrations show no significant loss of transmission.

[0103] In another embodiment, the CQDs exhibit spherical morphology with high dispersibility in nonpolar solvents.

[0104] In another embodiment, the nanofluids exhibit high uniformity and homogeneity in lubrication applications.

[0105] In another embodiment, the encapsulated CQDs improve photon downconversion in solar cells, enhancing electron generation.

[0106] By addressing the shortcomings of prior-art methods, this invention provides a simple, cost-effective, and environmentally sustainable approach for integrating CQDs into lubrication and solar energy technologies, making it highly suitable for industrial-scale implementation.

[0107] While the foregoing describes various embodiments of the disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. The scope of the invention is determined by the claims that follow. The invention is not limited to the described embodiments, versions, or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.EXAMPLES

[0108] The present invention is further explained in the form of the following examples. However, it is to be understood that the following examples are merely illustrative and are not to be taken as limitations upon the scope of the invention.

[0109] The The invention is described in detail in the following description and further illustrated by way of examples. Disclosed herein is a method for producing carbon nanostructure materials, such as carbon quantum dots (CQDs), and related products, such asnanolubricant fluids and CQD-based organic dispersions, for various functional applications, including lubrication and photoluminescence. Also disclosed is a method for preparing carbon nanostructure materials, such as CQDs, by an effective hydrothermal process followed by deacidification through successive mixing and separation with distilled water. Further disclosed is a method for preparing nanolubricant fluids and photolumine scent organic solutions by incorporating CQDs into base lubricants or organic solvents, resulting in high uniformity and stability and exhibiting excellent low-friction coefficients for lubrication applications and photoluminescence for down-conversion and bioimaging applications. Furthermore, the disclosed methods for preparing carbon nanostructure materials and their respective products for various applications are simple, economical, and industrially scalable.

[0110] Figure 1 is a flowchart showing the systematic steps for the synthesis of carbon nanostructure materials, specifically CQDs, according to some embodiments. The procedure used for Carbon Quantum Dots (CQDs) synthesis involves the following steps: (a) dispersing a carbonizing precursor in deionized water (FLO); (b) producing a uniform aqueous precursor mixture by mechanical stirring; (c) acidifying the precursor mixture by adding a concentrated inorganic acid; (d) using a high-pressure and high-temperature autoclave reactor for CQD generation; (e) separating the synthesized CQDs, which float due to lower density, from the residue using a separating funnel after the reaction; and (f) repeatedly mixing and separating the CQD clusters with distilled water to remove any residual acid.

[0111] According to an embodiment of the invention, the chemicals used include an organic precursor with two hydroxide groups, such as 1,2-propanediol, 2,3 -propanediol, 1,2-butanediol, or 3,4-butanediol (preferably 1,2-propanediol), and a concentrated inorganic acid, such as hydrochloric, sulfuric, acetic, phosphoric, hydrofluoric, or nitric acid (preferably hydrochloric acid as a catalyst).

[0112] The process used for preparing CQDs is a hydrothermal process in an autoclave reactor at a temperature range of 100-300 °C for 5-100 hours (preferably 200 °C for 25 hours) for the synthesis of CQDs.

[0113] After the autoclave process, the CQDs-containing liquid is separated from the precursor using a separating funnel, followed by repeated mixing and separation of the CQD clusters with distilled water to remove residual acid.

[0114] Figure 2 is a schematic diagram illustrating a method for producing nanolubricant fluids for lubrication applications. According to an embodiment of the invention, the procedure for nanofluid preparation involves the following steps: (a) incorporating CQDs at different weight percentages (wt%) into respective base fluids (such as machinery lubricant oil andautomobile lubricant oil); and (b) mixing the nanofluids by mechanical stirring for 10-100 minutes (preferably 30 minutes) at varying concentrations (0.2-1 wt%, preferably 0.5 wt%) using various automobile and commercial machinery lubricant oils to form a uniform nanolubricant oil. The prepared nanofluid is uniform, stable, and suitable for the aforementioned applications.

[0115] Figure 3 is a schematic diagram illustrating a method for producing an organic solvent-based CQD dispersion solution. The procedure for preparing the CQD-based dispersion solution involves (a) incorporating CQDs into an organic nonpolar solvent (acetone, cyclohexane, or hexane, preferably acetone) at a concentration of 0.01-1 wt% (preferably 0.3 wt%) with respect to the organic solvent; and (b) dispersing the CQDs in the organic solvent through ultrasonication for 5-30 minutes (preferably 20 minutes).

[0116] The CQDs produced by the present invention exhibit a significant morphological structure, as shown in Figure 1. TEM morphological studies indicate that the CQDs form clusters of spherical particles of quantum size ranging from 2 to 5 nm in size. Raman spectroscopy shows that the CQDs exhibit characteristic bands: a G-band located in the range of X = 1585-1595 cm1and a D-band located in the range of X = 1342-1355 cmThe G-band corresponds to graphite in-plane vibrations, and the D-band is associated with a doubleresonance Raman process in disordered carbons.

[0117] According to a preferred embodiment, the CQDs produced by the present invention have high dispersibility in solvents, preferably nonpolar solvents, and can be easily incorporated into nonpolar-based lubricants and organic solvents for lubrication and photoluminescence for Solar PV applications, respectively. The prepared nanofluids, such as nanolubricants and CQD dispersions, produced by incorporating the synthesized CQDs with commercial base lubricants and organic solvents, exhibit high uniformity and homogeneity. In addition, the nanolubricant fluids exhibit a low friction coefficient in lubrication applications and photon emission properties in the visible region for photoluminescence applications.

[0118] The CQDs and their respective products, such as nanofluids, produced by the process mentioned in the present invention are simple, economical, easily scalable, and highly suitable for various applications, including lubrication and photoluminescence.Example 1 : Production of Carbon quantum dots (CQDs)

[0119] Carbon quantum dots (CQDs) with high dispersibility in nonpolar solvents and lubricant oils, suitable for photoluminescence and lubrication applications, respectively, are produced as depicted in Figure 1. For the production of Carbon quantum dots (CQDs), 25-100g, preferably 52g of an organic precursor with two hydroxide groups (diols), such as 1,2-propanediol, 2,3 -propanediol, 1,2-butanediol, or 3,4-butanediol, was dispersed in distilled water (1: 1 volume ratio). This mixture was stirred for 10 to 60 minutes, preferably 30 minutes to obtain a homogeneous suspension at room temperature. After obtaining a uniform transparent solution, the precursor mixture was acidified by adding 5-20 g of a concentrated inorganic acid such as hydrochloric, sulfuric, acetic, phosphoric, hydrofluoric, or nitric acid (preferably hydrochloric acid as the catalyst) and further mixed by mechanical stirring for 30 min to 3 hours (preferably 1 hour). The final reactant mixture had a weight ratio of diobdeionized water (DW):acid = 25-60:25-60:5-20 (preferably 46.34:44.56: 9.1 wt%). After thorough mixing, the reaction mixture was transferred to a Teflon-coated autoclave reactor and heated from 100-300 °C for 5-100 hours (preferably 200 °C for 25 hours). After the autoclave reaction, the low-density CQDs were separated from the residue using a separating funnel. The CQD clusters were repeatedly mixed and separated with distilled water to remove residual acid.

[0120] Based on the TEM morphological analysis (Figure 4), the CQDs appear as clusters of spherical particles with size ranging from 2 to 5 nm, as shown in the particle size distribution (Figure 5). Raman spectroscopy (Figure 6) reveals that the CQDs exhibit a G-band at 1583 cm1and a D-band at 1355 cm The G-band indicates in-plane vibrations, while the D-band corresponds to a double-resonance process in disordered carbon structures. The Raman analysis suggests that the CQDs possess amorphous characteristics.Example 2: Measurment of coefficient of friction

[0121] To achieve low-friction properties for lubrication applications, nanofluids with CQD concentrations ranging from 0.2 wt% to 1 wt%, preferably 0.5 wt%, were prepared. The coefficient of friction was measured using a pin-on-disc tribometer according to ASTM G99-17 standards. Pure aluminum pins (10x10 mm) were used against a rotating steel (EN36) disc at a velocity of 1 m / s and a load of 5 kg (Table 1).Table 1: Tabulated Coefficient of friction (p) in four ball tribometer with bare machinery lubricant oil and 0.5wt% of CQDs incorporated lubricant oil.

[0122] The coefficient of friction for CQD-incorporated machinery lubricant oil and automobile lubricants (at the 0.5% optimum loading) is shown in Figure 8 and Table 2, respectively. In the case of automobile lubricant oils, incorporating 0.5 wt% CQDs reduced the coefficient of friction by 48%. For machinery lubricant oil, the coefficient of friction was studied using a four-ball tribometer, which simulates real machinery applications. The coefficient of friction was observed to be 0.06 for the base machinery lubricant and 0.03 for the CQD-incorporated nanolubricant, representing a 50% reduction in the coefficient of friction with the 0.5 wt% CQD nanolubricant (Figure 7).Table 2: Tabulated Coefficient of friction (p) in pin-on-disc tribometer with bare automobile lubricant oil and CQDs incorporated lubricant oil with varied concentration.Example 3 : The photoemission spectra of the CQD

[0123] Carbon quantum dots (CQDs) exhibit high dispersibility in organic solvents, making them suitable for photoluminescence applications. In one embodiment, CQDs are dispersed in an organic solvent at concentrations ranging from 0.01 wt% to 1 wt% with respect to the dispersing solvent. The photoemission spectra of the CQD-based organic solvent dispersions were collected with excitation at 390 nm, and the corresponding spectra are shown in Figure 10. The areas under the photoemission spectra are tabulated in Table 3. The area under the curve increased exponentially with the incorporation of CQDs compared to the bare organic solvent.Table 3: Tabulated calculated area of curve for the photoemission spectra, obtained from CQDs dispersion coated EVA sheet exited at 390 nm

[0124] To examine the potential of the synthesized CQDs in down-conversion by embedding them into solar cells through an encapsulation process, ethylene vinyl acetate (EVA) sheets were spray-coated with CQD dispersion solutions at different CQD concentrations (0.01 wt% to 1 wt% with respect to the dispersing solvent). The transmission of the spray-coated EVA sheets was examined using a UV-Vis-NIR spectrophotometer, and the corresponding transmission spectra are shown in Figure 9, with average transmission values tabulated in Table 4. The transmission of the glass-encapsulated EVA sheets showed a significant decrease with higher CQD concentrations (0.5 wt% and 0.75 wt%). At lower concentrations (up to 0.3 wt% CQDs), show no significant loss of transmission. These coated EVA sheets were used to encapsulate 15.6 cm x 15.6 cm solar cells with a cover glass. The efficiencies of the encapsulated solar PV modules were measured through I-V characteristic studies under a one-sun xenon lamp source. The corresponding I-V curves are shown in Figure 11. Solar cells with the 0.3 wt% CQD dispersion coating showed a 10% enhancement in solar cell efficiency due to the down-conversion phenomenon, converting lower-wavelength photons to photons in the visible region, which further participate in electron generation in the solar cell.Table 4: Tabulated average transmission values of EVA sheets coated with different concentrations of the CQDs.

[0125] Novel aspects of the invention is highlighted by describing several preferred embodiments, enabling those skilled in the art to understand and visualize our innovation. It should be understood that the invention is not limited to the specific details provided in the description or depicted in the drawings. While the invention has been described in detail with reference to certain preferred embodiments, various modifications and adjustments may be made without departing from the spirit and scope of the invention as outlined above and defined in the following claims.ADVANTAGES OF THE INVENTIONThe present disclosure provides the invention with multiple benefits as below:Cost-Effective and Scalable Synthesis - The hydrothermal process enables large-scale production of CQDs without requiring expensive precursors or complex modifications. Eco-Friendly and Non-Toxic - The method eliminates the need for hazardous solvents like DMF, ensuring environmental sustainability.Optimized Lubrication Performance - CQD-based nanolubricants reduce the coefficient of friction (CoF) by 48-50%, enhancing machinery lifespan and efficiency. Improved Solar PV Efficiency - CQDs facilitate UV-to-visible down-conversion, increasing solar energy absorption by 10%.High Thermal and Chemical Stability - CQDs remain stable up to 300°C, ensuring durability in extreme conditions.Superior Dispersion Stability - CQDs disperse uniformly in both polar and nonpolar solvents, preventing aggregation.Versatile Industrial Applications - The invention benefits automotive, industrial lubrication, and renewable energy sectors.Simple Encapsulation Process - CQD coatings on EVA sheets enhance solar module performance without affecting transparency.

Claims

We Claim:

1. A method for producing carbon quantum dots (CQDs) for lubrication and photoluminescence applications, comprising:dispersing an organic precursor with two hydroxide groups in deionized water; mechanically stirring the mixture to form a uniform aqueous precursor mixture; acidifying the precursor using a concentrated inorganic acid and further stirring; transferring the reaction solution into an autoclave and heating at a specified temperature and duration to synthesize CQDs;separating the synthesized CQDs using a separating funnel; andwashing the CQDs with distilled water repeatedly to remove residual acid and obtain CQDs.

2. The method of producing CQDs as claimed in claim 1, wherein the organic precursor is dispersed in an amount ranging from 25-100 g in 25-100 mL of deionized water.

3. The method of producing CQDs as claimed in claim 1, wherein said organic precursors are selected from 1,2-propanediol, 2,3-propanediol, 1,2-butanediol, or 3,4-butanediol or a combination thereof.

4. The method of producing CQDs as claimed in claim 1, wherein the mechanical stirrig is performed 10-60 minutes, preferably at room temperature to produce a uniform aqueous precursor mixture.

5. The method of producing CQDs as claimed in claim 1, acidification of the precursor mixture is performed by adding concentrated inorganic acid in a ratio range of 5-20 g and by further mechanical stirring for 30 minutes to 4 hours.

6. The method of producing CQDs as claimed in claim 5, said inorganic acid is selected from hydrochloric acid, sulfuric acid, acetic acid, phosphoric acid, hydrofluoric acid, or nitric acid or a combination thereof.

7. The method of producing CQDs as claimed in claim 1 , transferring the reaction solution is performed into a Teflon-coated autoclave and heating at 100-300°C for 5-100 hours to synthesize CQDs.

8. The method of producing CQDs as claimed in claim 1, wherein synthesized CQDs are separated from the reaction residue using a separating funnel, followed by multiple washing cycles with distilled water to remove any residual acid.

9. The method of producing CQDs as claimed in claim 1, wherein particle size of the synthesized and washed CQDs ranges between of 2-5 nm.

10. The method of producing CQDs as claimed in claim 1, wherein the precursor-to-acid weight ratio is maintained between the ranges of 2: 1 to 10: 1 to ensure optimized CQD formation.

11. The method of producing CQDs as claimed in claim 1, wherein the quantum yield of said synthesized CQDs ranges from 30-90% in photoluminescence applications.

12. A method for preparing nanolubricant fluids for friction reduction in automotive and industrial applications, comprising:incorporating CQDs into commercial lubricant base oils;mixing the CQD-based nanolubricants using a mechanical stirrer producing CQD-enhanced lubricants with a reduced coefficient of friction (CoF) by 48-50%, improving energy efficiency and wear resistance.

13. The method as claimed in claim 12, wherein said CQDs are used at concentrations ranging from 0.2 wt% to 1 wt%.

14. The method as claimed in claim 12, wherein said lubricant base oils are selected from, but not limited to, automobile lubricants, industrial machinery oils, hydraulic oils, synthetic lubricants or a combination thereof.

15. The method as claimed in claim 12, wherein the mechanical stirring is performed at speeds between 500-5000 rpm for 10-100 minutes to obtain a uniform dispersion.

16. The method as claimed in claim 12, wherein reduction in wear rate of nanolubricant fluids is 40-60% in tribological testing compared to conventional lubricants.

17. The method of claim 2, wherein the CQD concentration of the nanolubricant ranges from 0.2-1 wt%.

18. A method for producing organic solvent-based CQD suspensions for photoluminescence applications, comprising:dispersing CQDs in an organic nonpolar solvent;subjecting the dispersion to ultrasonication;spraying the CQD dispersion onto an ethylene vinyl acetate (EVA) sheet and embedding it in a solar PV module through an encapsulation process;enhancing solar cell efficiency by up to 10% through a down-conversion process, where CQDs convert UV light into visible light, thereby increasing electron generation.

19. The method as claimed in claim 16, organic nonpolar solvent is selected from acetone, cyclohexane, or hexane or a combination thereof at a concentration range of0.01-l wt% relative to the total volume of the solvent;20. The method as claimed in claim 16, the ultra-sonication is performed for 5-30 minutes to ensure uniform dispersion.

Images