METAL-FREE FUNCTIONALIZED CARBON NITRIDE AS A PHOTOCATALYST DRIVEN BY SUNLIGHT FOR ACETAL SYNTHESIS AND SELECTIVE REGENERATION OF NAD(P)H CO-FACTOR

Abstract

The present invention relates to a functionalized graphitic carbon-based photocatalyst that utilizes solar light to regenerate the coenzymes NADH and NADPH, which play essential roles in various biological redox reactions. This system, achieved by doping boron and fluorine into native graphitic carbon nitride, is capable of efficient NAD(P)+ photoreduction under physiological conditions, facilitating integrated photochemical and catalytic processes. The resulting metal-free photocatalyst, denoted as BFGCN-x, demonstrates high yields for NADH (61.89%) and NADPH (59.84%) regeneration. Additionally, it catalyzes acetalization reactions without requiring Lewis or Brønsted acids, marking an advancement in sustainable photocatalysis for both coenzyme regeneration and chemical synthesis.

Specification

DESC:FIELD OF THE INVENTION
The present invention relates to metal-free functionalized carbon nitride as a photocatalyst driven by sunlight for acetal synthesis and selective regeneration of NAD(P)H Co-factor. The field of the invention pertains to photocatalysis and photochemical reactions, specifically focusing on the development of metal-free, solar-light-active photocatalysts for biological and chemical applications. This invention involves the synthesis and use of doped graphitic carbon-based materials to facilitate the regeneration of coenzymes such as NADH and NADPH, as well as to catalyze acetalization reactions.
BACKGROUND OF THE INVENTION
References which are cited in the present disclosure are not necessarily prior art and therefore their citation does not constitute an admission that such references are prior art in any jurisdiction. All publications, patents and patent applications herein are incorporated by reference to the same extent as if each individual or patent application was specifically and individually indicated to be incorporated by reference.
To functionalized chemical properties in any carbonyl compound acetalization is the key point that helps in the introduction and protection of the native chemical properties of carbonyl moiety in a multistep synthesis of organic compounds (1). However, many researchers reported acetalization via involving acidic catalysis which may require harmful and toxic reagents (2-4). Furthermore, the environment having acidic surroundings is sensitive to many groups like alkenes, alkynes, silyl, and hydroxyl (1). In addition, hemiacetal reversible reaction from acetal is highly unstable in an acidic medium because of its thermodynamic stability (low equilibrium constant (K~0.01-0.05mol-1) but feasible at basic and neutral pH (5). During the reversible reaction, water is eliminated as a byproduct which requires some chemical and mechanical treatment to avoid the backward reaction (1). Conventionally, acetal reactions are catalyzed in an aqueous medium by bronsted and lewis acids. Nevertheless, there were some exceptions in acetalization reactions in organic solvents from homogeneous catalysis for example, N, N'-bis (3,5-bis(trifluoromethyl)phenyl) (6), LiBF4(3), NBS (7), thiourea (8) and ionic liquids (5), etc. Besides the issues of separation, these systems were costly, toxic, and had no generality. Here, solid catalysts are desirable and have less effect on the environment (9-11). So, for environment friendly acetalization, this solid catalyst should be developed having non-transition metal to perform acetalization for acid free environment with high stability in a friendly manner. Additionally, acetal compounds have various applications in pharmaceutical industries (in stabilizing and improving pharmaceutical ingredients), polymer industries (they serve as cross-linkers), dyes and pigments (acetal has a specific role in the synthesis of dyes), additives in fuels (to improve its efficiency), etc. Overall, acetals have importance in various fields including organic and industrial synthesis (12-15). Thus, this route does not been exist yet, therefore, we develop a route for performing acetalization via solid catalyst having semiconductor properties i.e. generation of holes and electrons with a suitable band gap which helps in the conversion of product via activating organic moiety because not all organic moieties absorb light. Nowadays, the catalyst of carbon nitride fascinated huge attention because of it's capability to absorb light without incorruption of transition metal (12-14). Many literatures reported graphitic carbon nitride (GCN) with a tuning band gap of 2.7eV via poly-condensation with different monomers (dyes, etc.) (15,16). However, in this present work, the native GCN has been functionalized with boron and fluorine to form a BFGCN photocatalyst. Due to functionalization, the de-excitation of electrons increases more rapidly as compared to native GCN due to a decrease in the forbidden energy band gap between the HOMO (highest occupied molecular orbital) and LUMO (least unoccupied molecular orbital) such instance increases the feasibility of organic transformation by activating the O2 molecule present in atmosphere (air) in O2 radical for performing organic transformation when irradiated without formation of OH radical as an intermediate(17,18). Therefore, here we reported photo-acetalization of aldehydes via molecular O2 radical under visible light in ambient environmental conditions.
The electrons carriers like dihydro nicotinamide adenine dinucleotide phosphate (NADH) and nicotinamide adenine dinucleotide phosphate (NADPH) are the two important electrons carriers used in various oxidoreductase enzymatic conversions (redox reactions)(19-21). The co-factor NAD(P)+ is uses as an oxidant to produce valuable gluconic acid, carbonyl compounds, and aliphatic aldehyde from glucose, aldehyde dehydrogenase and alcohols(22). Therefore, all these conversions require the consumption of co-enzymes NAD(P)+/NAD(P)H, which makes the catalytic process expensive and confer waste generation. Additionally, decreasing the consumption of NAD(P)+ co-enzymes and regenerating NAD(P)H has been an interesting topic for research nowadays. Despite its importance, the regeneration of NAD(P)H comprises NAD(P)H dehydrogenase, formate dehydrogenase or any carbonyl reductance enzymes has been reported and still exploring(23). However, these reductive enzymes are sensitive and need proper care to maintain their stability. The non-enzymatic reduction of NAD(P)+ will be the better alternative to overcome these enzymatic limitations. Currently, many approaches of electro/photochemical oxidation of NAD(P)H are employed which require a variety of electrodes(24). Nevertheless, the potential >1V is required for the oxidation of NAD(P)H which may oxidize and decompose other analytes i.e. interfering with their practical limitations. These limitations can be overcome via involving redox mediators which makes the process complex and expensive. In this framework, the solar driven ecofriendly protocol for the photocatalytic process has been employed for the reduction of co-factors which possess low complexity, low cost, and sustainable. Some conjugated hydrogel and microporous polymers have been reported for photo-oxidation of NAD(P)H(25). However, these polymers based photocatalyst has unsatisfactory ability in photo-oxidation. Consequently, the visible light driven photocatalyst which has the capability of photo-oxidation of NAD(P)H is highly desirable(26-27).
Metal free visible light driven photocatalysts are widely known for performing photocatalytic reactions i.e. carbon dioxide fixation, treatment of pollutants(31-33), nitrogen detoxification, degradation of dyes(34), and splitting of water(35-37). However, graphitic carbon nitride (GCN) is predominantly, known for its eco-friendly nature, low cost, thermal stability, and easy to synthesize(29). However, the bulk GCN shows poor conductivity due to high charge recombination, low absorption of visible light, and less active sites which restrict its practical use(17, 39). Although, this restriction can be overcome via functioning of native GCN with heteroatoms like boron and fluorine(28,30,31). Thus, by functioning with these non-metallic atoms ameliorate the electronic structure of native GCN (non-functionalized) by decreasing and increasing charge recombination and active sites respectively also, provide suitable band structure for photo-excitation of charge to perform photocatalytic applications. Prior many efforts have been made to improve the recombination rate, active sites, band structure and photocatalytic performance. Therefore, by modulating the band structure of GCN define via defect engineering which accelerate the excited photo-charge dissociation to enhance charge transfer (32,33). For illustration, optoelectronic properties of GCN are modulated with introduction of various organic moieties and dopants (surface engineering) resulting in the configuration of band and electronic structure known as band defect(33,34). Thus, these inherent chops reduce carriers recombination and stretch the visible region range. The existence of defect state authorities the uplifting of the conduction band which enables the reduction capability of functionalized GCN.
Subsequently, this work sets the novelty towards a new approach for an exhaustive analysis in the dynamic field for regeneration of NAD(P)H and acetalization phenomenon, emphasizing the importance to promote the development of a photocatalyst which meets the demands of selectivity, stability and reusability. The novelty of this method have the ability to proposed a cost-effective, sustainable and efficient pathway of the development of BFGCN-x photocatalyst, which have photo-generated charge carriers i.e. electrons and holes, stability, reusability and easy to use type behavior. This makes our BFGCN-x photocatalyst highly active under visible light source with efficient optical and electronic properties, in order to regenerate NAD(P)H in a most efficient manner. Also, the synthesized BFGCN-x photocatalyst also have ability to perform acetalization reactions to promote acetal products which have various applications in pharmaceutical, polymeric, and cosmetics industries.
Several patents issued for photocatalysts but none of these are related to the present invention. Patent CN106563481B discloses ultra-thin graphite phase carbon nitride photocatalyst materials of a kind of ammonification and preparation method thereof. It is similar to the tulle with fold, and in the gauze-like with fold, thickness is uniform, is 3-5nm;Material surface is smooth, amino group rich in. Preparation: melamine is acidified; the melamine supramolecular structure crystal protonated; then calcined under the conditions of inert protective atmosphere and graphite phase carbon nitride material be made, after through Homogenization Treatments obtain graphite phase carbon nitride photocatalyst material superfine powder;The ammonia source substance that graphite phase carbon nitride photocatalyst material superfine powder and thermal decomposition generate ammonia is placed in tube furnace; carry out logical inert gas deoxygenation processing; then ladder calcining is carried out under the conditions of inert protective atmosphere: being first warming up to 500-540 DEG C; keep the temperature 2-4h; then it is warming up to 560-600 DEG C again; and 2-3h is kept the temperature, it can be obtained after cooling.It improves photocatalysis efficiency with can dramatically, and is used for CO2Catalysis reduction has excellent photocatalysis performance.
Another patent CN108772093B belongs to the technical field of preparation of new materials, and particularly discloses a graphite-phase carbon nitride nanosheet with high visible light activity, a preparation method of the graphite-phase carbon nitride nanosheet and application of the graphite-phase carbon nitride nanosheet in hydrogen production through visible light catalytic decomposition of water. The preparation method of the graphite-phase carbon nitride nanosheet takes common nitrogen-rich dicyanodiamine as a raw material, and directly prepares the graphite-phase carbon nitride nanosheet by calcining an intermediate obtained by hydrothermal reaction of the raw material. Compared with graphite-phase carbon nitride obtained by directly calcining dicyanodiamine, the product obtained by the method is the carbon nitride nanosheet. Meanwhile, compared with the preparation method of the carbon nitride nanosheet in the prior art, the preparation method of the carbon nitride nanosheet adopted by the invention has the characteristics of environmental friendliness, economy and high efficiency, and the method also greatly inhibits the blue shift of the light absorption band edge of the carbon nitride nanosheet, so that the photocatalytic hydrogen production performance of the obtained catalyst is obviously enhanced. The method has simple process, single and easily obtained raw materials, easy mass industrial production and wide application prospect.
Another patent CN109569691B relates to a preparation method of boron-doped carbon nitride and a product and application thereof. A mode of carrying out hydrothermal reaction on melamine and boric acid promotes boron atoms and melamine to carry out chemical reaction so that boron and carbon nitrogen elements form atomic-level mixing on one hand, and carries out hydrothermal reaction on the melamine in an acid environment so that the melamine can form a supermolecular structure, which is beneficial to the separation of a carbon nitride lamellar structure in the subsequent roasting process; and then roasting the precursor synthesized by the reaction to prepare the boron-doped carbon nitride which is uniformly doped and has a thinner lamellar structure. The boron-doped carbon nitride prepared by the method has the advantages of uniform element doping, thinner lamella, better photocatalytic performance, simple preparation operation and lower difficulty, and is suitable for large-scale production.
Another patent WO2019229255A1 provides methods for producing hydrogen using a carbon nitride (CN x) photocatalyst or a carbon dot (CD) photocatalyst. The method may include exposing a photocatalyst to visible and/or ultraviolet light in the presence of an organic substrate, such as a biomass or an organic component having a molecular weight of 200 or more, and a co-catalyst that is a hydrogen evolution catalyst. The method may include exposing a photocatalyst within untreated water to visible and/or ultraviolet light in the presence of a co-catalyst that is a hydrogen evolution catalyst.
Another patent CN106540732B provides a kind of redox graphene/mesoporous graphitization carbon nitride material and preparation methods, the preparation method is the following steps are included: (1) disperses cationic surfactant (S), nitrogen-rich carbon source (P) and graphene oxide (GO) in alkaline alcohol-water mixed solution, then low temperature (40-80 DEG C) evaporation induced self-assembly is carried out, obtains being situated between and sees S-P-GO ternary supramolecular aggregation;(2) it will give an account of and see two sections of heatings roastings of S-P-GO ternary supramolecular aggregation progress, redox graphene/mesoporous graphitization carbon nitride material is made.Above-mentioned redox graphene/mesoporous graphitization carbon nitride material preparation method simple and efficient, and overcome current g-C3N4Class catalysis material there are specific surface areas it is low, photogenerated charge is compound fast the problems such as, thus the catalytic performance in degradation of organic dyes can be significantly improved.
Another patent CN108940344B discloses a modified graphite-phase carbon nitride photocatalyst, and a preparation method and application thereof, wherein the modified graphite-phase carbon nitride photocatalyst is prepared by calcining urea and salicylic acid serving as raw materials, wherein the mass ratio of the urea to the salicylic acid is 1: 0.002-0.02. The modified graphite-phase carbon nitride photocatalyst has the advantages of high specific surface area, many reaction active sites, wide light absorption range, low electron-hole pair recombination rate, good photocatalytic performance and the like, has good application value and application prospect, and the preparation method has the advantages of simple process, wide raw material source, low cost, high preparation efficiency, high yield and the like, is suitable for large-scale preparation, and is beneficial to industrial production. The modified graphite-phase carbon nitride photocatalyst can be used for degrading organic pollutants, has the advantages of simple process, convenience in operation, low cost, high treatment efficiency, good degradation effect and the like, and has a good degradation effect on various organic pollutants.
Another patent CN107297217B provides a porous thin-layer graphite-phase carbon nitride-supported platinum photocatalyst as well as a preparation method and application thereof, wherein the method comprises the steps of firstly selecting melamine as a raw material, and preparing graphite-phase carbon nitride by adopting a pyrolysis method; and finally, carrying noble metal platinum on the porous thin-layer graphite-phase carbon nitride obtained by the rapid high-temperature post-treatment by a photoreduction method to obtain a target product. Compared with the graphite phase carbon nitride which is not subjected to rapid high-temperature post-treatment, the porous thin-layer graphite phase carbon nitride platinum-loaded photocatalyst prepared by the invention has high-efficiency visible light catalytic hydrogen production performance and good stability. The method is simple to operate and good in repeatability, effectively improves the photocatalytic performance of the graphite-phase carbon nitride, and further expands the efficient means of modifying the graphite-phase carbon nitride.
OBJECTS OF THE INVENTION
Main object of the present invention is metal-free functionalized carbon nitride as a photocatalyst driven by sunlight for acetal synthesis and selective regeneration of NAD(P)H Co-factor.
Another object of the present invention is to create a functionalized, metal-free graphitic carbon nitride-based photocatalyst.
Another object of the present invention is to achieve selective and high-yield regeneration of biologically relevant coenzymes NADH and NADPH under physiological conditions.
Another object of the present invention is to enable acetalization reactions without the need for Lewis or Brønsted acid catalysts.
Another object of the present invention is to enhance photocatalytic efficiency through boron and fluorine doping of graphitic carbon nitride.
Another object of the present invention is to advance green chemistry by utilizing sunlight as the primary energy source
SUMMARY OF THE INVENTION
The invention involves the synthesis of a functionalized graphitic carbon nitride (GCN) photocatalyst, optimized for solar-driven catalytic applications. In this method, 500 mg of melamine is combined with varying volumes (2 mL to 5 mL) of ethyl borate in separate beakers. A few drops of triethylamine (TEA) are added to each mixture, which is then stirred overnight to ensure thorough mixing. The samples are subsequently calcinated at 550°C for 4 hours, a process that integrates boron and fluorine into the graphitic carbon nitride structure. This doping step enhances the photocatalytic efficiency of GCN, enabling it to function as a metal-free photocatalyst with applications in NAD(P)H coenzyme regeneration and acid-free acetal synthesis under sunlight.
Herein enclosed a method for synthesizing a metal-free, functionalized graphitic carbon nitride (GCN) photocatalyst, comprising the steps of:
mixing 500 mg of melamine with ethyl borate in volumes ranging from 2 mL to 5 mL;
adding a few drops of triethylamine (TEA) to the mixture and stirring overnight; and
calcining the mixture at 550°C for 4 hours to incorporate boron and fluorine, producing a functionalized GCN photocatalyst.
The method as claimed in claim 1, wherein the functionalized GCN photocatalyst is doped with boron and fluorine to enhance photocatalytic efficiency under sunlight for applications in acetal synthesis and NAD(P)H regeneration.
A method for the regeneration of NAD(P)H co-factors using the synthesized photocatalyst comprising the steps of:
preparing a reaction mixture containing a sacrificial agent, ascorbic acid, rhodium complex, NAD(P)+ co-factor, and the BFGCN-x photocatalyst in a phosphate buffer with a pH of approximately 7;
equilibrating the reaction medium in the dark to allow for adsorption-desorption equilibrium;
irradiating the reaction medium with light from a 450-watt Xenon lamp filtered to wavelengths >420 nm;
keeping it under light for 2 hours afterwards; and
monitoring the regeneration of NAD(P)H via UV-visible spectrometry at intervals to determine the percentage yield of NADH and NADPH.
The percentage yields of regenerated NADH and NADPH are 61.89% and 59.84%, when utilizing the BFGCN-4 photocatalyst, as compared to yields of 12% NADH and 14% NADPH using unmodified GCN.
The GCN is doped with boron and fluorine, enabling the photocatalytic regeneration of NAD(P)H and catalyzing acetal synthesis reactions under sunlight without the need for additional metal or acid catalysts.
These and other aspects of the embodiments herein will be better appreciated and understood when considered in concurrence with the following explanation and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications.
BRIEF DESCRIPTION OF THE DRAWINGS
The illustrated embodiments of the subject matter will be understood by reference to the drawings, wherein like parts are designated by like numerals throughout. The following description is intended only by way of example, and simply illustrates certain selected embodiments of devices, systems, and methods that are consistent with the subject matter as claimed herein, wherein:
Figure 1. Schematic representation of synthesis of functionalized graphitic carbon (BFGN-x) as a photocatalyst by calcination of melamine at 500oC.
Figure 2. Percentage yield of (a) NADH from NAD+ co-factor (b) NADPH from NAD(P)+ co-factor by BFGCN-4 photocatalyst.
Figure 3. Graphical representation of concentration ratio versus time (a) NADH (b) NADPH, where Co= initial concentration of NAD(P)+ and C= concentration of NAD(P)H at "t" time.
Figure 4. Photo-acetalization of Benzaldehye in presence of BFGCN-x photocatalyst under 20W LED light source at optimum conditions.
Figure 5. (a) UV-visible diffuse reflectance spectroscopy (DRS) of BFGCN-4 and BFGCN-1 (inset), (b) Tauc plot calculated via DRS of BFGCN-4 and BFGCN-1 (inset), (c) FT-IR spectra of non-functionalized GCN (green) with functionalized GCN i.e. BFGCN-4 (blue) and BFGCN-1 (red), (d) X-ray diffraction spectroscopy of GCN (green), BFGCN-4 (blue) and BFGCN-1 (red).
Figure 6. Scanning electron microscopy (SEM) along with energy dispersive spectroscopy (EDX) (a), (b) of BFGCN-1 and (c), (d) of BFGCN-4.
Figure 7. (a) Cyclic voltammetry of GCN (green), BFGCN-1 (red) and BFGCN-4 (blue), (b) Cyclic voltammetry of Rh-complex and NAD(P)+, (c) Cyclic voltammetry of GCN (green), BFGCN-1 (red) and BFGCN-4 (blue) influenced with Rh-complex, (d) Cyclic voltammetry of GCN (green), BFGCN-1 (red) and BFGCN-4 (blue) influenced with Rh-complex and NAD(P)+ co-factor.
Figure 8. (a) Electrochemical impedance spectroscopy (EIS) of GCN (green), BFGCN-1 (red) and BFGCN-4 (blue), (b) Tafel plot of GCN (green), BFGCN-1 (red) and BFGCN-4 (blue), (c) Chronopotentiometry of GCN (green), BFGCN-1 (red) and BFGCN-4 (blue) and (d) Latimer diagram of BFGCN-4 showing oxidation and reduction potentials.
DETAILED DESCRIPTION OF THE INVENTION
In some embodiments of the present invention, 500mg of melamine was taken in four beakers. Ethyl borate was added by using a dropper with varying the volume of ethyl borate range from 2mL to 5mL.
In some embodiments of the present invention, the photocatalytic regeneration of 1,4 NAD(P)H (enzymatically active form of NAD(P)H) was performed in a pyrex glass photo-reactor under 450 watt Xenon lamp along with the cut-off filter of >420nm.
In some embodiments of the present invention, the reaction medium consists of a sacrificial agent as ascorbic acid, rhodium complex (synthesized via reported paper), NAD(P)+ co-factor and BFGCN-x photocatalyst configurated in phosphate buffer for maintaining pH~7.
In some embodiments of the present invention, the regeneration of NAD(P)H was carried out in an inert medium. The reaction medium was kept in dark for performing adsorption-desorption equilibrium. Afterwards, it was kept under light for 2 hours.
In some embodiments of the present invention, the regeneration of NAD(P)H was monitored via using UV-visible spectrometer at an interval of 30minutes. The standard curve of NAD(P)H provided via UV-visible spectrometer was used for calculating the percentage yield of NADH (61.89%) and NADPH (59.84%) as per BFGCN-4 photocatalyst which shows better photocatalytic activity compared to GCN (NADH=12% and NADPH=14%).
Herein enclosed a method for synthesizing a metal-free, functionalized graphitic carbon nitride (GCN) photocatalyst, comprising the steps of:
mixing 500 mg of melamine with ethyl borate in volumes ranging from 2 mL to 5 mL;
adding a few drops of triethylamine (TEA) to the mixture and stirring overnight; and
calcining the mixture at 550°C for 4 hours to incorporate boron and fluorine, producing a functionalized GCN photocatalyst.
The method as claimed in claim 1, wherein the functionalized GCN photocatalyst is doped with boron and fluorine to enhance photocatalytic efficiency under sunlight for applications in acetal synthesis and NAD(P)H regeneration.
A method for the regeneration of NAD(P)H co-factors using the synthesized photocatalyst comprising the steps of:
preparing a reaction mixture containing a sacrificial agent, ascorbic acid, rhodium complex, NAD(P)+ co-factor, and the BFGCN-x photocatalyst in a phosphate buffer with a pH of approximately 7;
equilibrating the reaction medium in the dark to allow for adsorption-desorption equilibrium;
irradiating the reaction medium with light from a 450-watt Xenon lamp filtered to wavelengths >420 nm;
keeping it under light for 2 hours afterwards; and
monitoring the regeneration of NAD(P)H via UV-visible spectrometry at intervals to determine the percentage yield of NADH and NADPH.
The percentage yields of regenerated NADH and NADPH are 61.89% and 59.84%, when utilizing the BFGCN-4 photocatalyst, as compared to yields of 12% NADH and 14% NADPH using unmodified GCN.
The GCN is doped with boron and fluorine, enabling the photocatalytic regeneration of NAD(P)H and catalyzing acetal synthesis reactions under sunlight without the need for additional metal or acid catalysts.
EXAMPLE 1
BEST METHOD
Experimental
Material Required
Melamine (C3H6N6), Ethyl Borate (BF3.OEt2), triethylamine (TEA) were purchased from Merck. Ascorbic acid, NAD+ co-factor, NADP+ co-factor, Monobasic-diabasic phosphate, methanol were purchased from Sigma Aldrich and Avra. All chemical were used as they are without purification. Powder X-ray diffraction spectroscopy (PXRD) was done via using a Rigaku Mini Flex benchtop having 40kV over range of 350° (2) and 2°C min-1 speed with radiation tube of CuKa (=1.542). To capture FT-IR spectrum over a span of 4000 to 500 cm-1 (512 scan average), ATR-IR spectroscopy was used by cary600 series FT-IR spectrometer. UV-visible diffuse reflectance spectroscopy was performed in the range of 200nm-800 nm via and spectrum was recorded by using Shimadzu UV-1900i spectrophotometer. Electrochemical properties like cyclic voltammetry, Tafel plot, chronopotentiometry, and electrochemical impedance spectroscopy were recorded on CHl608E, 220V instrument. Scanning electron microscope (SEM) images and electron dispersive X-ray spectroscopy (EDS), along with elemental mapping, were recorded using an instrument JSM 6490 LV (constructed by JEOL, Japan) running by 30kV voltage at high vacuum.
Synthesis of functionalized graphitic carbon nitride (GCN)
500mg of melamine was taken in four beakers. Ethyl borate was added by using a dropper with varying the volume of ethyl borate range from 2mL to 5mL. The mixture was then allowed to stir overnight along with a few drops of triethylamine (TEA). Now, the samples were calcinated at 550°C for 4 hours, resulting in the functionalizing of graphitic carbon nitride with boron and fluorine (Fig.1).
EXAMPLE 2
RESULTS AND DISCUSSION
Photocatalytic Regeneration of 1,4 NAD(P)H
The photocatalytic regeneration of 1,4 NAD(P)H (enzymatically active form of NAD(P)H) was performed in a pyrex glass photo-reactor under 450 watt Xenon lamp along with the cut-off filter of >420nm. The reaction medium consists of a sacrificial agent as ascorbic acid, rhodium complex (synthesized via reported paper) (35), NAD(P)+ co-factor and BFGCN-x photocatalyst confrigated in phosphate buffer for maintaining pH~7. The regeneration of NAD(P)H was carried out in an inert medium. The reaction medium was kept in dark for performing adsorption-desorption equilibrium. Afterwards, it was kept under light for 2 hours. The regeneration of NAD(P)H was monitored via using UV-visible spectrometer at an interval of 30minutes (Fig. 2). The standard curve of NAD(P)H provided via UV-visible spectrometer was used for calculating the percentage yield of NADH (61.89%) and NADPH (59.84%) as per BFGCN-4 photocatalyst which shows better photocatalytic activity compared to GCN (NADH=12% and NADPH=14%) (35).
The UV-visible spectrometer can fruitfully acknowledge the regeneration of NAD(P)H from NAD(P)+ co-factor. The heterocyclic ring of NAD+ reduces and creates a new absorption band around 340nm, which helps in determination of NAD(P)H regeneration percentage. The isomers produce during regeneration of NAD(P)H are 1,2 NAD(P)H, 1,4 NAD(P)H and 1,6 NAD(P)H having absorption peaks at 395 nm, 340 nm and 345 nm respectively. The concentration of 1,4 NAD(P)H was calculated via using Lambert-Beer law at 340 nm as per reported literature. On addition of this, we have also calculated concentration of NAD(P)H with respect to concentration of NAD(P)+ shown in Fig 3. However, this graph indicates the concentration of NAD(P)H increases successively with time. Initially in absence of light the concentration of NAD+ and NADP+ was 0.246mM and 0.115mM respectively. At 120minutes, the concentration of NADH and NADPH was 1.052mM and 1.243mM respectively in presence of light with molar extinction coefficient (?) 6220 M-1 cm-1(37,38) as per BFGCN-4 photocatalyst.
The BFGCN-x photocatalyst absorbs the solar radiation, creating photoactive pairs in its valence band. The electrons excited are transferred from highest occupied molecular orbital (HOMO) through ascorbic acid to the conduction band of BFGCN-x. Subsequently, photo-excited electrons are transferred to NAD+ through Rhodium complex, establishing the least occupied molecular orbital (LUMO) of the BFGCN-x photocatalyst and boasting regeneration of NADH. Additionally, the energy flow diagram of NADPH also follows the same path as regeneration of NADH (39,40).
Photocatalytic acetalization of Benzaldehyde in oxidative environment
The photo-acetalization reaction was carried out in the pyrex glass photo-reactor using 20W blue LED light (Fig.4). The distance between the photo-reactor and the light source was kept where the intensity of the light was maximum. The reaction medium containing 0.025 g of BFGCN-x, 5mL methanol and 1mM substrate stirs using magnetic stirrer for maintaining homogeneity. Afterwards, O2 was purged in the reaction medium and further kept under irradiation source. The crude product (97%) then obtained via filtration and identified via GC as per reported paper (1).
EXAMPLE 3
Characterization
UV-visible spectroscopy: Fig 5(a) shows the UV-visible diffuse reflectance spectroscopy (DRS) of functionalized and non-functionalized GCN. Native GCN shows the absorption capability at 450nm but interestingly the functionalized GCN shows the absorption bands at a range of 400-500nm while a red-shift is perceived when the dopants (B and F) concentration increases. This shifting in wavelengths attributed to introduction of the dopants (B and F) in the lattice structure of native GCN, due to which the electronic spectra of GCN altered and the optical properties of GCN improved i.e. extension of absorption edges. However, the longer absorption region will leads to higher photo-generation of electron-hole pairs therefore, which helps in the establishing the photocatalytic reactions and activities of functionalized GCN (41). Furthermore, the band gap was calculated via Tauc plot as shown in Fig. 5(b) which explains the optical spectra of the GCN (functionalized and non-functionalized). The band gap corresponds to functionalized GCN is BFGCN-1 (2.53eV), BFGCN-4 (2.50eV) and non-functionalized GCN is 2.70eV. This functionalized GCN band gap has the capability to perform photocatalytic reactions. Also as the dopants concentration increases i.e. from BFGCN-1 to BFGCN-4 can slightly lower the band gap of BFGCN. Therefore, suggesting the better photo-excitation capability of BFGCNs (30).
Fourier Transform Infrared Spectroscopy: Fig 5(c) shows the fourier transform infra-red spectroscopy (FT-IR) of non-functionalized and functionalized GCN. The characteristic functional group peaks of native GCN and functionalized GCN shows similar behaviour. This elaborate that the surface functional groups of the native GCN are maintained after complexation with heteroatoms like B and F. The bending mode of triazine in native GCN attributed at 889cm-1 whereas, at a range of 1200-1650cm-1 comprising many small vibrations including 1235, 1323, 1410, 1561 and 1640 cm-1, indicating heterocyclic aromatic C-N bonds like C=N, C-N and C-N-C (42). Additionally, a broad peak at 3000-3200cm-1 is the characteristic peak of -NH2. However, 885cm-1 and 812cm-1 define the bending vibration of s-triazine ring and N-H deformation mode (43). Thus, the characteristic peak of B-N located at 15, 1181, 1413 cm-1 confirms the presence of complexation of B with N (44).
X-ray Diffraction Spectroscopy (XRD): X-ray diffraction pattern of functionalized and non-functionalized graphitic carbon nitride was shown by Fig. 5(d) The characteristic peaks are located at 13.1o (weak) indexed at 100 and 27.5o (strong) indexed at 002 of non-functionalized GCN which is the result of tri-s-triazine in-plane structure and stacking of inter-plane of aromatic rings (melon networks) respectively (see supporting information). After functionalizing the GCN with boron and fluorine, the 002 indexed peak of 27.5o is shifted to 27.92o as the volume of BF3.OEt2 increases from 2mL to 5mL indicating vigorous complexation of B and F in the triazine crystal structure of native GCN (non-functionalized). Therefore, results in increasing inter-planar stacking distance and distortion in the lattice. However, it was observed that there is no additional peak of F was present (45). This indicates that the fluorine (F) have same graphitic like structure as native GCN comprised i.e. no change in crystalline structure (46). Nevertheless, the (002) peak intensity is lower as compared to native GCN implies that more defects were appeared in structure during complexation. The decrease in the peak intensity may also attributed to the loss of partial N lattice (due to complexation) and alteration of local crystalline structure (decrease in ordering of crystalline nature) due to calcination of the precursor.
Morphological and Elemental Features (SEM&EDX): The morphology of non-functionalized GCN shows an irregular, porous structure having thick layered or lamellar structure as shown in Fig.6. The sheets of native GCN also have wrinkles with irregular shapes (47). The huge cross-sectional area between the layers could be functions for complexation of dopants (B and F). The increase of dopants concentration leads to rigidity and agglomeration. It is clear from the SEM that the morphology of the functionalized GCN changes from soft to harder and rigid with increase in dopant concentration. The content of B and F in functionalized GCN was estimated by energy-dispersive spectroscopy (EDS). The result indicated the presence of B, F, C and N in functionalized GCN photocatalyst. Therefore, it is remarkably that the weight % of B and F are in functionalized GCN, which increases successively as the dopant concentration increases. (see supporting information).
Electrochemical Properties: Cyclic voltammetry (CV) explains the electrochemical properties of the light harvesting moiety. The electrochemical studies were done by using three electrodes (i) mercury-mercury electrode as reference electrode, (ii) glassy carbon electrode as working electrode and (iii) platinum electrode as a counter electrode in 0.01M H2SO4 solution used as an electrolyte. The electrochemical properties include cyclic voltammetry, Tafel plot, electrochemical impedance spectroscopy (EIS) and chronopotentiometry.
The reduction potential of native GCN, BFGCN-1 and BFGCN-4 were found to be -1.056, -1.086 and -1.21V respectively as shown in Fig.7(a). There was a change observed in the voltammogram of the solution, when the two components were found to be together i.e. Rh and BFGCN-x/GCN as shown in Fig.7(c). However, when GCN and Rh were present solution the reduction potential was observed to be -1.104V while with BFGCN-1 it is -1.226V and with BFGCN-4 it is 1.233V. Therefore, from here we can conclude that the BFGCN-x shows more interaction with Rh than GCN. The complex Rh-BFGCN-x also shows the increment of reduction potential when implies with NAD+ co-factor as shown in Fig.7(d) (48,49). This may attribute that the complex Rh-BFGCN-x is capable of catalyzing reduction of NAD(P)+ to NAD(P)H. Nevertheless, the complex made by GCN with Rh was also capable for catalyzing NAD+ reduction but is less efficient. Here by, after functionalizing the GCN with dopants (B and F), the reduction potential of successively increases as the dopant concentration increases. Therefore, the NAD(P)+ catalyzing capability of the moiety also increases, which in turns increases the reduction of NAD(P)+ to NAD(P)H. It was also observed in literatures, that the reduction of Rh in presence of NAD(P)+ is results of catalytic activity of Rh. However, absence of oxidation (anodic peak) in the voltammogram proves the electrochemical activity of Rh-BFGCN-x complex i.e. (two-electron reduction followed by chemical protonation). According to some literature, the excitation of electrons to Rh-complex from the highest occupied molecular orbital (HOMO) followed by lowest occupied molecular orbital (LUMO) of the light harvesting moiety fulfilled the electrochemical properties. This potential gradient enables the electron transfer mechanism to fascinate the regeneration of NAD(P)H which is also supported by latimer diagram of BFGCN-4 as shown in Fig.7(d) (50).
The Nyquist plot is calculated via electrochemical impedance spectroscopy (EIS). Fig.8(a) shows the nyquist plot of non-functionalized GCN and functionalized GCN (BFGCN-1 and BFGCN-4). The impedance spectrum shows semicircle at low frequency region and straight line at higher frequency region. The charge transfer resistance (RCT) is defined by the arc area of the spectra of the GCN and BFGCN-x moieties, also the internal series resistance (RS) arising from the electrolyte intercept on Z' axis of the spectra. However, from the spectra it is clear that the BFGCN-4 exhibits smaller arc than other moieties therefore have lower charge transfer resistance. Also, the arc radius decreases from GCN to BFGCN-4 as the functionality of the GCN increases. In addition the RS for BFGCN-x is also lower than the GCN. Furthermore, this result also proved the enhancement of electrochemical properties due to functionalizing GCN (51,52).
Tafel analysis is one of the important analyses which define the charge transfer kinetics of the moiety. The slope of the plot shows its charge transfer capability i.e. the moiety is capable to acquire required current at low potential measurement. Also, the slope explains the flow of photo-excited electrons i.e. lower the slope of the curve greater will be its charge transfer capability to perform photo-catalytic reactions like regeneration of NAD(P)H. However, the slope of BFGCN-4 is lower than that of BFGCN-1and GCN as shown in Fig. 8(b). Therefore, the capability of photo-excitation of electrons is faster in case of BFGCN-4 among all, which concludes the charge transfer capacity enhanced by functionalizing the native graphitic carbon nitride (53).
The current carrying capacity was examined by chronopotentiometry which explains the separation and migration of electron-hole pairs. The high current density of the moieties is responsible for solar response photocatalytic activity. The electrons are excited as a response of solar radiation which was transferred from ascorbic acid (sacrificial agent) to FTO glass through the BFGCN-x photocatalyst. Fig.8(c) shows the better current carrying capability by BFGCN-4 than GCN which reflects its enhanced conductivity due to functionalizing (50).
Conclusions
Herein, we functionalized boron, fluorine doped graphitic carbon nitride (BFGCN-x) by varying different concentration of dopant (BF3.OEt2). The photocatalytic performance was estimated via photo-regeneration of NADH and NADPH. Also, the photo-acetalization reactions shows the photocatalytic behaviour of the functionalized graphitic carbon nitride. However, the acetal product have various applications in pharamacuetical, polymers, cosmetics and dyes. The functionalized graphitic carbon was characterized via UV-visible diffuse reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FT-IR), Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDX) and electrochemical analysis.
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,CLAIMS:1. A method for synthesizing a metal-free, functionalized graphitic carbon nitride (GCN) photocatalyst, comprising the steps of:
(a) mixing 500 mg of melamine with ethyl borate in volumes ranging from 2 mL to 5 mL;
(b) adding a few drops of triethylamine (TEA) to the mixture and stirring overnight; and
(c) calcining the mixture at 550°C for 4 hours to incorporate boron and fluorine, producing a functionalized GCN photocatalyst.
2. The method as claimed in claim 1, wherein the functionalized GCN photocatalyst is doped with boron and fluorine to enhance photocatalytic efficiency under sunlight for applications in acetal synthesis and NAD(P)H regeneration.
3. A method for the regeneration of NAD(P)H co-factors using the synthesized photocatalyst as claimed in claim 1, wherein the method comprising the steps of:
(a) preparing a reaction mixture containing a sacrificial agent, ascorbic acid, rhodium complex, NAD(P)+ co-factor, and the BFGCN-x photocatalyst in a phosphate buffer with a pH of approximately 7;
(b) equilibrating the reaction medium in the dark to allow for adsorption-desorption equilibrium;
(c) irradiating the reaction medium with light from a 450-watt Xenon lamp filtered to wavelengths >420 nm;
(d) keeping it under light for 2 hours afterwards; and
(e) monitoring the regeneration of NAD(P)H via UV-visible spectrometry at intervals to determine the percentage yield of NADH and NADPH.
4. The method as claimed in claim 3, wherein the percentage yields of regenerated NADH and NADPH are 61.89% and 59.84%, when utilizing the BFGCN-4 photocatalyst, as compared to yields of 12% NADH and 14% NADPH using unmodified GCN.

5. The method as claimed in claim 3, wherein the GCN is doped with boron and fluorine, enabling the photocatalytic regeneration of NAD(P)H and catalyzing acetal synthesis reactions under sunlight without the need for additional metal or acid catalysts.

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