An electrochemical process for selective conversion of co2 to value-added 1,2-diol

Abstract

The current disclosure pertains to an electrochemical process of the reduction of carbon dioxide (CO2) to 1,2-diols using new metal-free electrocatalysts in the form of size-dependent carbon nitride quantum dots (CNQDs). The current disclosure offers a green and effective pathway for CO2 utilization at room temperature, hence reducing environmental mitigation and generating useful chemicals. The CNQDs are prepared with size control accuracy and display amplified catalytic activity, selectivity, and stability due to their considerable surface area and adjustable electronic properties. Efficient conversion of CO2 to 1,2-diols with up to about 21% yield is achieved at room temperature. The development not only increases the viability of chemical production in a sustainable manner but also constitutes a cost-effective and eco-friendly technology for CO2 valorization

Description

AN ELECTROCHEMICAL PROCESS FOR SELECTIVE CONVERSION OF CO2 TO VALUE-ADDED 1,2-DIOLRELATED PATENT APPLICATIONThis application claims the priority to and benefit of Indian Patent Application No. 202441049165 filed on June 26, 2024; the disclosures of which are incorporated herein by reference.TECHNICAL FIELD

[0001] The instant disclosure falls mostly in the field of Electro -organic Synthesis, namely the electrochemical reduction of carbon dioxide (CO2) for the simultaneous alleviation of climate change and the synthesis of renewable chemicals. More specifically, this disclosure is concerned with the syntheses of 1,2- diols from CO2 by the targeted use of electrocatalysts.BACKGROUND

[0002] The widespread enhancement of atmospheric carbon dioxide (CO2) level, which is largely caused by anthropogenic emissions due to the burning of fossil fuels for energy generation, greatly enhances the greenhouse effect and leads to global temperature rise. This rising environmental issue has driven considerable research efforts into diverting this greenhouse gas into industrially useful chemicals.

[0003] In the past, research on converting CO2 into valuable chemicals, most importantly 1,2-diols (i.e., dihydroxylation of CO2), has been ongoing for decades. There were early attempts that mostly involved the catalytic hydrogenation of CO2 to produce compounds such as methanol or formic acid, yet the processes mostly required high temperatures and pressures and thus were energetically inefficient. Traditional syntheses of 1,2-diols tend to be dominated by multi-step processes and severe conditions highlighting an exciting need for more cost-effective and environmentally friendly approaches.

[0004] The idea of electrochemical CO2 reduction was a groundbreaking phenomenon in the late 20th century that motivated scientists to explore metal-catalyzed reactions for direct conversion of CO2 into 1,2-diols. These strategies normally used transition metal catalysts, e.g., zinc, copper, or palladium, along with hydrogen gas, to selectively reduce CO2. Nevertheless, conventional catalysts used for electrochemical CO2 reduction to valuable chemicals, such as 1,2-diols, are often reliant on high energy inputs, run at high temperatures, and lack selectivity. Such shortcomings drastically limit their practical feasibility in sustainable chemical synthesis. In addition, initial catalysts were usually associated with excessive overpotentials, lack of selectivity, and problems involving stability.

[0005] The recent discovery of nanomaterials and quantum dots has witnessed a new dawn in catalysis, characterized by their tunable electronic characteristics and extremely high surface areas. These features make them uniquely suitable to catalyze the electrochemical reduction of CO2 to diols. Quantum dots, or semiconductor nanoparticles with peculiar electronic characteristics imparted by quantum confinement effects, provide CO2 conversion with added advantage. Among these new -generation materials, carbon nitride has been the focus of significant interest because of its inherent metal-free nature, high durability, and significant catalytic activity. Follow-up studies aimed at utilizing the size-tailored nature of carbon nitride quantum dots towards enhancing their performance in CO2 reduction reactions. The current disclosure is specifically aimed at creating a metal-free electrocatalyst to address the above challenges in totality.OBJECTIVES

[0006] The major aim of the current disclosure is to depict a process for CO2 electrochemical reduction into valuable chemicals.Another aim of the current disclosure is to depict a sustainable and effective approach for CO2 utilization, thus contributing synergistically towards environmental mitigation as well as the generation of valuable chemicals.Still another object of the current disclosure is to enable electrochemical conversion of CO2 into 1,2-diols at room temperature.Another goal of the current disclosure is to establish an electrocatalyst for efficient electrochemical reduction of CO2 into value-added 1,2-diols.Another aim is to take advantage of the size-dependent carbon nitride quantum dots' special properties to enable efficient room-temperature electrochemical CO2 reduction to 1,2-diols.Furthermore, an object of the current disclosure is to present a complete process for the synthesis of carbon nitride quantum dots.Once again, another object of the current disclosure is to detail a costefficient and promising approach to alleviate atmospheric CO2 concentrations by the synthesis of useful chemical compounds.SUMMARY

[0007] The current disclosure presents a new process for the electrochemical conversion of carbon dioxide (CO2) to 1,2-diols using an advanced electrocatalyst. This disclosure offers a sustainable and highly effective method of CO2 utilization, thus addressing simultaneously critical environmental issues and promoting the synthesis of useful chemicals. One of the key features of this disclosure is the use of size-dependent carbon nitride quantum dots, with unusual electronic properties and excellent catalytic activity, that facilitate the electrochemical reduction of CO2 to 1,2-diols in high efficiency at ambient temperatures. These size-controlled quantum dots show significant catalytic performance due to their large surface area and beneficial electronic properties. The size-dependent barrier-free features allow maximum interaction with CO2 molecules to be converted into 1,2-diols with high selectivity and minimal energy requirements. The electrocatalysts revealed in the present disclosure profoundly impact the selectivity and efficiency of the reaction, where quantum dots of optimalsize yield about 21% 1,2-diols' yield at room temperature. The present disclosure also emphasizes the significant role of metal-free electrocatalysts in highly controlling the selectivity towards CO2 reduction reactions (CO2RR) and offers valuable insights into the very complex relationship between quantum dot size and catalytic performance. This advancement in technology not only increases the viability of sustainable chemical manufacture but also plays a significant role in developing environmentally friendly technologies for CO2 utilization. The disclosure further provides a process for the effective synthesis of these carbon nitride quantum dots. The electrochemical reduction of CO2 to value-added 1,2- diols is clearly aided by these carbon nitride quantum dots.BRIEF DESCRIPTION OF DRAWINGS

[0008] FIG. 1: a) Carbon Nitride QDs under the absence of UV radiation, b) Carbon Nitride QDs under the presence of UV radiation, c) UV-vis absorption spectra obtained for violet, cyan, and yellow carbon nitride QDs formed at -1.5, -3, and -4.5 V respectively, d) Photoluminescence spectra for violet carbon nitride QDs, e) Photoluminescence spectra for cyan carbon nitride QDs, f) Photoluminescence spectra for yellow carbon nitride QDs.FIG. 2 illustrates a comparison of FT-IR spectra of carbon nitride QDs of different sizes with that of pristine melamine.FIG. 3 depicts the Cyclic voltammograms of carbon nitride QDs coated with glassy carbon and CO2 purged of carbon nitride QDs-1 (red), carbon nitride QDs-2 (blue), and carbon nitride QDs-3 (green) compared with blank (black). Working Electrode: Carbon Nitride QDs coated on glassy carbon , Counter Electrode: Pt-foil, Reference electrode: Standard Calomel Electrode (SCE), Scan rate: 100 mV s-1.FIG. 4 illustrates HPLC of the electrolyte after CO2 reduction a) carbon nitride QDs-1, b) 1,2-diols (reference), c) carbon nitride QDs-2, and d) carbon nitride QDs-3.FIG. 5 denotes the Scanning Electron Micrographs of carbon nitride QDs a) before and b) after the reaction. Elemental mapping images of carbon nitride QDs c) before and d) after the reaction.FIG. 6 depicts the Comparison of Galvanostatic Tafel Plots for three sizes of carbon nitride QDs.FIG. 7 gives a Comparison of Electrochemical Impedance spectra of CO2 purged, and Argon purged electrolyte of 4.1 nm carbon nitride quantum dot electrocatalyst.FIG. 8 illustrates the Stability test done up to 2000 cycles using 4.1 nm carbon nitride quantum dot electrocatalysts.FIG. 9 delineates the Mass Spectrometry of the electrolyte after CO2 reduction and HPLC.FIG. 10 showcases the Labelled Mass Spectrometry of the electrolyte after 13CO2 reduction.DETAILED DESCRIPTION

[0009] The current disclosure offers a general method for electrochemical reduction of carbon dioxide (CO2) to 1,2-diols based on the novel catalytic characteristics of size-tunable carbon nitride quantum dots (CNQDs). This method marks a milestone for sustainable chemistry, providing an eco-friendly and economically feasible route for utilization of CO2.

[0010] Synthesis of Carbon Nitride Quantum Dots (CNQDs): The CNQDs, which are essential to the effectiveness of the current disclosure, are synthesized successfully through a highly controlled electrochemical process. The general method includes the addition of 100-200 mg of melamine monomer (CsHeNe) into a solution containing 1-10 mL of an appropriate solvent and 50-100 pL of a 5% binder solution. Appropriate solvents used in this synthesis are chosen from thegroup including ethanol, methanol, acetone, or ethyl acetate. The binder solution, which is important for quantum dot formation and stability, is chosen from the group including Nafion 117, Polyvinyl Alcohol (PVA), Polydopamine (PDA), Polyvinylpyrrolidone (PVP), or Chitosan.

[0011] Example Embodiment 1: Specific Synthesis of CNQDs: In one exemplary embodiment, 150 mg of melamine powder (CsHeNe, monomer) was accurately sonicated in a mixture that included 5 mL of 99% ethanol (C2H5OH) and 100 pL of a 5% Nafion 117 solution (CVHBOSS-CIF , the binder, for 15 minutes. The resulting homogeneous suspension was carefully drop-cast onto an inert platinum electrode, which was used as the working electrode with a nominal area of 200 mm2, until a uniform and complete coating was attained, confirmed by the lack of appreciable weight change. Following electrosynthesis, three CNQDs of different sizes were obtained, which can be visually differentiated based on their emitted colours as violet (for 431 nm emission), cyan (502 nm emission), and yellow (510 nm emission). The size-specific quantum dots were synthesized by subjecting constant potentials of -1.5 V, -3 V, and -4.5 V, respectively. Platinum wire was used as the counter electrode, and a silver wire was used as the quasireference electrode, and 5.35 M BMIMBF4 was used as the electrolyte. The optical properties, which are more specifically regarding these size changes, were exhaustively examined by UV- Visible spectroscopy and PL spectroscopy at room temperature in ethanol.

[0012] Example 1 further provided more details on the successful synthesis and characterization of the CNQDs. Figure 1(a) pictorially presents the three various sizes of carbon nitride quantum dots under the conditions of UV light irradiation, displaying the blank, violet, cyan, and yellow-emitting 0-D materials from left to right. Figure 1(b) depicts the obvious luminescence of these CNQDs under UV light irradiation, verifying their own emission features. Figure 1(c) shows that three excitation wavelengths (299 nm, 293 nm, and 298 nm) match the sizes produced at -1.5 V, -3 V, and -4.5 V, respectively, assigning these wavelengths to transitions of the C=C and C=N bonds in sp2carbon domains of carbonnitrides with the tri-s-triazine ring. Photoluminescence spectra (Figures 1(d), 1(e), and 1(f)) gave additional information: Figure 1(d) revealed two emission peaks at 412 nm and 431 nm for violet CNQDs, the result of trace fluorescent molecules on the surface of the QDs, a by-product of electrochemical exfoliation of melamine. The excitation-independent peaks indicated transition between valence band and lone pair state intra-tri-s-triazine nitrogen. Figures 1(e) and 1(f) displayed emissions at 502 nm and 510 nm, respectively, on excitation at 420 nm, wherein excitationdependent wavelength spectra featured minimal by-products inducing red shift with rising excitation wavelength. The size-dependent characteristics of the carbon nitride QDs were clearly reflected in their separate photoluminescence spectra. Additionally, Fourier-Transform Infrared (FT-IR) spectroscopy (Figure 2) proved the occurrence of N-H stretching vibrations at 3347 cm-1and 3412 cm-1, which reflect nitrogen content. Bands at 3209 cm-1and 3080 cm-1were related to O-H stretching, while weak C-H stretching peaks at 2961 cm-1and 2875 cm-1reflected terminal alkanes. Most importantly, the appearance of new peaks following electrochemical exfoliation, e.g., C-H bending vibrations at 1446 cm-1and 743 cm-1, C=C stretching frequency at 1648 cm-1and 1650 cm-1, C=C bending at 818 cm-1(graphitic structure), N-0 at 1550 cm-1(oxygen functionalities), and a broad CO-O-CO band at 1077 cm-1, established the effective development of the target product not-existing in pristine melamine.

[0013] Electrochemical Investigation and CO2 Reductive Process: The electrochemical CO2 reduction is performed in a three-electrode configuration at room temperature. The working electrode is made up of freshly prepared carbon nitride deposited on glassy carbon. A saturated calomel electrode (SCE) is used as the reference electrode, while the counter electrode is a platinum foil. The electrolyte system plays an integral role for efficient conversion and is composed of 0.1 M KHCO3 in a 3:2 ratio of water and acetonitrile.

[0014] Example Embodiment 2: Electrochemical Characterization and CO2 Reduction: Cyclic voltammograms were obtained in inert conditions. The potentiodynamic method was used to extensively study the reduction of CO2 withthe three different carbon nitride types. Open circuit potentials were found to be - 170 mV, -439 mV, and -383 mV for carbon nitride QDs-1, carbon nitride QDs-2, and carbon nitride QDs-3, respectively. The onset potentials for the reduction of CO2 were computed as -1.6 V for carbon nitride QDs-1, -1.47 V for carbon nitride QDs-2, and -1.55 V for carbon nitride QDs-3. Voltammograms showed a sharp rise in current density when CO2 was present but was not observed in blank experiments, indicating strongly the formation of electroactive species and potential utility of the catalysts. Potentiostatic polarization tests were carried out at a potential of -2 V for 16 hours to yield the reaction product.

[0015] Product Analysis through High-Performance Liquid Chromatography (HPLC): The liquid products from the electrochemical reduction of CO2 were analyzed and quantified based on offline High-Performance Liquid Chromatography (HPLC). The HPLC setup had an autosampler, a UV-visible detector, and a refractive index detector (RID). Separation was obtained on a C- 18 column with injection volumes of 10 pL, a runtime of 25 minutes, flow rate of 0.6 mLmin-1, and temperature of 45°C. Product assignment was determined by matching retention times with standard knowns.

[0016] Example Embodiment 3: HPLC Confirmation of 1,2-Diols: Figure 4 is the product analysis following the CO2 reduction, which clearly indicates the presence of 1,2-diols. There was a remarkable similarity in all different sizes of CNQDs, with reference from ethylene glycol proving consistent occurrence in the product. Significantly, the yield for 1,2-diols of carbon nitride- 1, relative to an internal standard, was around 21%. The best results were repeatedly achieved using the combination of water and acetonitrile as the electrolyte.

[0017] Morphological and Elemental Analysis by Scanning Electron Microscopy (SEM) and Energy-Dispersive X-ray Spectroscopy (EDX): SEM in conjunction with EDX gave high-resolution imaging and elemental analysis of the surface of the sample prior to and following the reaction. SEM works by scanning a focused electron beam over the sample to generate high-resolution images ofsurface morphology. EDX builds on this by analyzing characteristic X-rays released by the sample, allowing it to identify and quantify its elemental content.

[0018] Example Embodiment 4: SEM and EDX Analysis of CNQDs: Scanning Electron Microscopy (SEM) was used to study the morphology and microstructure of the CNQDs under both as-synthesized and CO2 electroreduction conditions. Figure 5(a) showed the as-synthesized CNQDs showing a three- dimensional, multi-porous morphology formed by the drying-induced aggregation of quantum dots. Elemental mapping (Figures 5(c) and 5(d)) confirmed the effective integration of nitrogen and oxygen into the structure. By contrast, Figure 5(b) showed a damage to the porous framework post-reaction, reflecting CO2 reduction-triggered structural alteration.

[0019] Kinetic Analysis through Galvanostatic Tafel Plots: Tafel analysis, a technique in electrochemistry, was used to probe the electrochemical reaction kinetics, gaining knowledge about the rate-determining step as well as the global reaction mechanism. Through analysis of current density vs. overpotential, the catalytic activity of the material was very well understood.

[0020] Example Embodiment 5: Tafel Plot Comparison: Tafel plots were investigated to assess the effect of size on CO2RR kinetics, as shown in Figure 6. The findings strongly suggested that smaller quantum dots of carbon nitride had lower Tafel slopes, which implies better reaction kinetics. This is due to greater exposure of active surface sites provided by the smaller size of the quantum dots. The exchange current densities were found to vary between 10-11and 10-8A cm-2. Table 1 presents the Tafel slopes and exchange current densities for the three carbon nitride quantum dots sizes:Table 1: Three sizes of carbon nitride quantum dots and their Tafel slopes and exchange current densities.Size of Carbon Nitride Emission colour emitted Tafel ExchangeQuantum dot (in nm) by the Carbon Nitride Slope (in Current DensityQuantum Dot mV dec1) (in A cm'2)2.5 Violet 22 1.74 x 10’118.7 Green 52 2.88 x 10’8

[0021] Electrochemical Impedance Spectroscopy (EIS) Studies: EIS was a robust tool to investigate the electrochemical characteristics of the catalysts, surfaces, and interfaces. By analyzing the impedance of the system, EIS yielded valuable information on the kinetics of electrocatalytic phenomena, such as charge5 transfer, mass transport, and reaction mechanisms.

[0022] Example Embodiment 6: CNQDs EIS Analysis: Electrochemical impedance spectra of the 4.1 nm carbon nitride quantum dots on a glassy carbon electrode were measured in a frequency range from 100 kHz to 0.1 pHz, as indicated in Figure 7. The measurements were taken in CO2- saturated and Argon-10 saturated 0.1 M KHCO3 solutions using a 3:2 water-acetonitrile mixture as the electrolyte. A noticeable change at the high-frequency area revealed a rise in charge transfer resistance (5.09 -cm-2) under CO2 saturation. The observation reveals augmented intermediate adsorption, which actually enhances selectivity toward such intermediate products as ethylene glycol. The diffusion coefficient for this15 mixed solvent system was also found to be about 9.8x 10-6 cm2s-1.

[0023] Stability Testing using Cyclic Voltammetry: The electrochemical stability of the electrocatalyst was stringently evaluated using cyclic voltammetry (CV) cycling.

[0024] Example Embodiment 7: Cyclic Voltammetry Cycle Stability 0 Testing: Figure 8 shows the electrochemical stability of the 4.1 nm carbon nitridequantum dot (CNQD)-based electrocatalyst for a long duration of 2000 cyclic voltammetry (CV) cycles. The catalyst, at first, showed large current density, reflecting strong catalytic activity. Nonetheless, upon sustained cycling, there was a progressive reduction of current density, indicative of partial deactivation or potential restructuring of the active surface sites. Such reduction is generally indicative of catalyst degradation mechanisms such as oxidation on the surface, detachment from the electrode substrate, or aggregation of the quantum dots. For the verification of the synthesis of the desired reaction product and further justification of the detected catalytic activity, High-Performance Liquid Chromatography (HPLC) was conducted after electrolysis. The chromatogram clearly confirmed the presence of the target compound, hence validating the effectiveness of the catalyst and selectivity of the product. This correlation between electrochemical performance and analytical confirmation gives a comprehensive insight into the catalyst's longevity and functional performance under long-term operation.

[0025] Product Identification and Pathway Elucidation by Mass Spectrometry: Mass spectrometry is a strong analysis method used to establish the mass-to-charge ratio (m / z) of ions in a sample, allowing identification of unknown materials, quantitation of individual compounds, and determination of molecular structures. The process entails ionization of the sample, separation of ions as per their m / z, and detection of their relative intensities.

[0026] Example Embodiment 8: Mass Spectrometry Analysis: Fig. 9(a) shows mass-to-charge (m / z) data acquired from CNQDs engaged in CO2RR, in addition to data from a positive control (ethylene glycol) and a negative control (electrolyte alone). There was a persistent peak at m / z 60.04 that appeared in all the samples, including controls, and was assigned to species of the electrolyte, e.g., water and acetonitrile. This was confirmed by high-resolution mass spectrometry (HRMS) data, which gave a calculated m / z of 60.0444 for C2HeNO+([M+H]+), in very close agreement with the experimental value of 60.0445. Figure 9(b) clearly established the occurrence of oxalate as an intermediate generated under CO2RRon CNQDs, as evidenced by a peak representing a mixture of the electrolyte and oxalic acid. HRMS data corroborated this task, with the computed m / z of 150.0402 for C4H8NO5+([M+H]+) identical to the 150.0407 found. In Figure 9(c), glyoxal was also recognized as an intermediate, found solely in the CNQD sample and not in the blank, strongly pointing towards its specificity in formation towards CO2 electroreduction with quantum dots. The observed m / z of 59.0129 was consistent with the calculated m / z of 59.0128 for C2H6O2+([M+H]+), verifying the existence of glyoxal, which is then reduced to ethylene glycol. The end product, ethylene glycol (after HPLC), was again established by HRMS (Figure 9(d)), exhibiting a calculated m / z of 63.0446 and an almost identical observed value of 63.0436.

[0027] Example Embodiment 9: Mass Spectrometry of Labelled CO2 Gases: For the unequivocal verification of the carbon source in the product, the reduction was also carried out using13CO2 gas, and it resulted in the production of ethylene glycol in the crude electrolyte. This was strongly confirmed by high- resolution mass spectrometry (HRMS), indicated in Figure 10, which observed a mass that corresponds to the co-presence of the electrolyte and ethylene glycol. The calculated m / z for C4Hi2NO3+([M+H]+) was 124.0878, incredibly close to the found value of 124.0877. This conclusively confirms that the carbon in the resultant 1,2-diols comes directly from the CO2 feedstock.

[0028] These detailed experimental results unambiguously show the successful electrochemical reduction of CO2 to 1,2-diols at room temperature using metal-free electrocatalysts. The study also unveiled the indispensable role played by these electrocatalysts in controlling the efficiency and selectivity of the CO2RR process. These revelations highlight the utmost significance of accurate control over electrocatalyst properties to achieve maximum production of 1,2-diols, a precious chemical intermediate with widespread industrial usage. The application of these new electrocatalysts to CO2RR presents a feasible route for CO2 utilization and is in tight compliance with sustainable and environmentally compatible chemical reactions. The ability to perform these reactions at room temperature only serves to highlight the convenience and energy savings of this innovative method.In general, the current disclosure considerably enhances the basic understanding of the complex relationship between nanomaterial properties and catalytic activity, offering a very promising route for the creation of next-generation catalysts designed for CO2 reduction. The understanding obtained from this thorough research is crucial to creating more efficient CO2 conversion systems and thus making significant contributions to both carbon management strategies as well as high-value chemical synthesis.Advantages

[0029] The utilization of size-dependent carbon nitride quantum dots for the electrochemical reduction of CO2 to 1,2-diols at room temperature, as disclosed in the present disclosure, offers several significant advantages:1. Enhanced Catalytic Activity: Unlike traditional metal catalysts that frequently necessitate high overpotentials and elevated temperatures for substantial CO2 reduction, the carbon nitride quantum dots exhibit high catalytic activity at room temperature, leading to considerable reductions in energy consumption and operational costs.2. Size-Dependent Tunability: The inherent capability to precisely fine-tune the size of the carbon nitride quantum dots enables meticulous control over their electronic properties. This tunability optimizes the interaction with CO2 molecules, significantly enhancing selectivity and efficiency in the production of 1,2-diols, a feat challenging to achieve with conventional catalysts.3. Improved Selectivity: Many traditional catalysts are plagued by poor selectivity, which often results in a complex mixture of undesired byproducts. In contrast, carbon nitride quantum dots, with their unique sizedependent properties, offer superior selectivity towards 1,2-diols, thereby minimizing the formation of by-products and substantially increasing the yield of the desired chemical.Metal-Free Composition: Distinct from a multitude of traditional catalysts that rely on costly precious or transition metals, carbon nitride quantum dots are entirely metal-free. This characteristic not only contributes to reduced material costs but also definitively eliminates the risk of metal contamination in the final product, rendering the process more environmentally friendly and safer for diverse applications. Stability and Durability: Carbon nitride quantum dots demonstrate exceptional chemical and thermal stability, which directly translates into extended catalyst lifetimes and consistent performance over prolonged operational periods. This inherent durability constitutes a significant improvement over numerous metal catalysts that typically degrade or experience a loss of activity over time. Reduced Environmental Impact: By operating efficiently at room temperature and utilizing abundant and non-toxic materials, this disclosure substantially reduces the environmental (carbon) footprint of the CO2 reduction process. It is in perfect alignment with the principles of green chemistry and sustainable development, as it efficiently converts a greenhouse gas into valuable chemicals without necessitating energy- intensive conditions or hazardous substances. Economic Feasibility: The low-cost synthesis of carbon nitride quantum dots, coupled with their high efficiency and remarkable stability, renders the overall process economically viable. This disclosure possesses significant potential for scalability to industrial applications, thereby providing a cost- effective solution for CO2 utilization.

Claims

We claim:

1. A process for the electrochemical reduction of carbon dioxide (CO2) to 1,2- diols, comprising:I. providing a metal-free electrocatalyst comprising size-dependent carbon nitride quantum dots (CNQDs);II. contacting the CO2 with the electrocatalyst in an electrolyte at ambient temperature; andIII. applying an electrical potential to facilitate the conversion of CO2 to 1,2-diols.

2. The process according to claim 1, wherein the size-dependent carbon nitride quantum dots exhibit enhanced catalytic activity and selectivity towards 1,2-diols.

3. The process according to claim 1, wherein the 1,2-diols are produced with a yield of at least 21% at room temperature.

4. The process according to claim 1, wherein the carbon nitride quantum dots are synthesized by sonicating melamine monomer in a mixture of a solvent and a binder solution.

5. The process according to claim 4, wherein the solvent is selected from the group consisting of ethanol, methanol, acetone, and ethyl acetate.

6. The process according to claim 4, wherein the binder solution is selected from the group consisting of Nafion 117, Polyvinyl Alcohol (PVA), Polydopamine (PDA), Polyvinylpyrrolidone (PVP), and Chitosan.

7. The process according to claim 1, wherein the size of the carbon nitride quantum dots is precisely controlled by varying the applied electrical potential during electrosynthesis.

8. The process according to claim 7, wherein the carbon nitride quantum dots have sizes corresponding to emission colors selected from violet, cyan, and yellow.

9. The process according to claim 1, wherein the electrolyte comprises 0.1 M KHCO3 in a 3:2 mixture of water and acetonitrile.

10. An electrocatalyst for the electrochemical reduction of CO2 to 1,2-diols, comprising size-dependent, metal-free carbon nitride quantum dots.

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