FLEXIBLE FILM PHOTOCATALYSTS FOR FORMIC ACID PRODUCTION FROM CO2 AND CYCLIZATION OF THIOAMIDES IN THE AIR'S EMBRACE

Abstract

Achieving efficient carbon dioxide (CO2) reduction and aerobic oxidative cyclization reactions using Eosin-Y-based light-harvesting photocatalysts remains a significant challenge. Here, we present the first-ever synthesis of an in-situ selenium (Se)-infused Eosin-Y (Sein-EY) flexible photocatalyst, created via a straightforward one-pot process. The resulting Sein-EY flexible film photocatalyst demonstrates exceptional performance, producing formic acid at a concentration of 204 µM within 2 hours and enabling the aerobic oxidative cyclization of thioamides with remarkable C–N and C–S bond formation yields of 98.6% under solar light. Selenium infusion notably extends the solar light absorption range of the Sein-EY photocatalyst up to 580 nm. This study establishes a new approach for the rational design and scalable synthesis of Se-infused Eosin-Y photocatalysts, facilitating both solar-driven chemical production and efficient one-pot, three-component reactions.

Specification

DESC:FIELD OF THE INVENTION
The present invention relates to a flexible film photocatalysts for formic acid production from CO2 and cyclization of thioamides in the air's embrace.
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.
Using solar radiation to create solar chemicals or fuels is one of the most promising approaches to reducing our carbon footprint. Additionally, it has increased demand for solar-powered wearable technology.1,2 Several covalent and non-covalent donor-acceptor conjugate dyes have been investigated as carbon dioxide reduction systems, using natural photosynthesis as a model. Despite their ability to effectively transfer electrons between and within molecules through photoinduced intra- and intermolecular ET, they are not photostable and have low conversion efficiency.3-5 Visible light-driven carbon dioxide reduction and the transformation of organic compounds into cyclic forms offer long-term solutions to several urgent environmental problems. To use photons for artificial goals, visible-light photoredox catalysis has emerged as a powerful tool for carrying out a number of organic reactions. 6-8 Photocatalysts are frequently necessary for visible-light-driven carbon dioxide reduction and aerobic oxidative cyclization reactions because photons in the visible spectrum are not easily absorbed by the majority of organic substituents used in these processes.
To date, expensive metal-based systems, such as ruthenium,9 iridium and others complexes, have been utilized to photoredox reactions such as solar chemical productions, radical addition,10 asymmetric alkylation of aldehydes,11 cycloaddition reactions,12 and various other reactions. 13-15 Photoredox catalysis, which harnesses light to drive redox reactions, has recently emerged as a powerful tool in organic synthesis. Expensive metal-based catalysts, particularly those using utilizing transition metals, have been widely employed in photoredox catalysis.16-19 However, the use of expensive metal-free alternatives, such as organic dyes, offers several advantages, including cost-effectiveness, sustainability, and reduced environmental impact. According, the development of robust and reusable heterogeneous photocatalytic systems offers a multifaceted solution, addressing concerns regarding contamination, cost, sustainability, scalability, robustness, and flexibility. These advancements contribute significantly to the advancement of green and sustainable chemistry practices in industrial applications. Porous organic polymers (POP), constructed from convenient organic monomers, have garnered significant scientific consideration in the fields of gas storage and separation, organic photovoltaics, and heterogeneous catalysis. Examples of POPs include covalent organic frameworks (COF), conjugated microporous polymers (CMP), and hyper-cross-linked polymers (HCP). Conjugated covalent organic frameworks (COF) in particular, with their extended p-conjugation structure and tuneable compositions, and properties, provide an excellent framework for integrating photosensitive monomers into highly stable, renewable, and feasible heterogeneous photocatalyst systems. Moreover, several studies have reported the synthesis of highly stable and porous HCP using phosphorescent, yet expensive, metal-based building blocks for efficient photocatalysis.20 The resulting polymer exhibited particularly in the oxidative conversion of amines into imines and high photocatalytic activity. Additionally, few researchers worked on the synthesis of conjugated polymeric frameworks, 21 which were used as organic heterogeneous photocatalysts for water splitting under visible light. These studies demonstrate the diverse range of approaches employed in designing and utilizing cross-linked polymers for photocatalytic applications. The choice of building blocks and the structural modifications implemented in the polymers significantly influence their stability, porosity, and catalytic efficiency across various reactions. Despite remarkable progress in developing photosensitive monomer-based two-dimensional covalent organic frameworks for efficient heterogeneous photocatalysis, the majority of these photosensitive monomers remain expensive or require time-consuming synthesis procedures. This limits their scalability and affordability for large-scale polymer production. Consequently, creating heterogeneous photocatalysts bottom-up from readily available and cost-effective monomers, without requiring additional synthetic elaboration, presents a promising strategy to overcome these limitations. Organic dyes have attracted a lot of interest in the domains of and homogeneous catalysis22 and dye-sensitized solar cells. 23,24 The chromophore eosin Y (Scheme 2), the most frequently employed organic dye, has been substantiated to be an effective noble-metal-free photo-organic-catalysts and has been extensively prepared in the vicinity of homogeneous photocatalysis due to its reasonable cost and low perniciousness. 22,25
Its unique properties make Eosin Y an ideal candidate for constructing photoactive two-dimensional organic polymeric frameworks. The soft structure of the monomers, readily provided by the central metal, could contribute significantly to the construction of robust two-dimensional organic polymeric frameworks. However, addressing the challenges associated with Eosin Y as a photocatalyst for practical applications typically involves material engineering and modification strategies. Researchers are actively working on enhancing its surface area, improving its light absorption properties, reducing charge recombination rates, and enhancing its electrical conductivity.6 In this context, some approaches include functionalizing the light-harvesting donor materials with other acceptor materials, creating covalently and non-covalently bonded compounds and composites, and modifying the surface structure to optimize these properties.
To acquire valuable insights into the impact of selenium (Se) infusion for tuning and enhancing the charge transfer mobility, slow recombination, and photocatalytic performance of EY, a creative synthetic strategy utilizing readily available chemicals to obtain in situ two-dimensional Sein-EY organic polymeric framework photocatalyst of paramount importance. This work reports on the synthesis and development of a simple one-pot two-step synthesis approach for obtaining a unique in situ Sein-EY flexible film photocatalyst. The as-prepared Sein-EY flexible film photocatalyst (Fig. S2) demonstrates excellent solar light activity for both the production of formic acid (HCOOH) from CO2 and the aerobic oxidative cyclization of thioamides into thiodiazoles through the formation of C-N/C-S bonds, while also exhibiting high stability.
Several patents issued for photocatalysts but none of these are related to the present invention. Patent US11724253B2 concerns a method for the photocatalytic reduction of carbon dioxide carried out in the liquid phase and/or in the gas phase under irradiation using a photocatalyst comprising a support made from alumina or silica or silica-alumina and nanoparticles of molybdenum sulfide or tungsten sulfide having a band gap greater than 2.3 eV, said method comprising the following steps: a) bringing a feedstock containing carbon dioxide and at least one sacrificial compound into contact with said photocatalyst, b) irradiating the photocatalyst with at least one source of irradiation producing at least one wavelength smaller than the width of the band gap of said photocatalyst so as to reduce the carbon dioxide and oxidise the sacrificial compound in the presence of said photocatalyst activated by said source of irradiation, in such a way as to produce an effluent containing, at least in part, C1 or above carbon-containing molecules, different from CO2.
Another patent CN110152711B belongs to the field of nano material preparation and discloses CeO2@MoS2/g C3N4The composite photocatalytic material is prepared through (1) adding cerium oxide hexahydrate into the mixed solution of butylamine and toluene, hydrothermal treatment of the mixed solution, and calcining the reaction product to obtain CeO2A nanocrystal; (2) mixing sodium molybdate dihydrate with g-C3N4The nano-sheets are ultrasonically dispersed in a mixed solution of L-cysteine and dimethyl sulfoxide, and the obtained mixed solution is subjected to hydrothermal treatment to obtain MoS2/g C3N4Nanosheets; (3) adding CeO2Nanocrystalline and MoS2/g C3N4Ultrasonically dispersing in methanol solution, volatilizing methanol, and collecting the obtained product as CeO2 MoS2/g C3N4A composite material; (4) adding CeO2 MoS2/g C3N4The composite material is placed in a tube furnace and calcined in the nitrogen atmosphere to obtain CeO2@MoS2/g C3N4A ternary composite photocatalyst. The preparation method is simple and has strong controllability, and the obtained composite photocatalyst has excellent photocatalytic degradation performance.
Another patent US20200179916A1 discloses monolithic metal-organic framework (MOF) composite body is disclosed, comprising: MOF crystallites adhered to each other via a binder comprising MOF; and at least 0.15 vol % nanoparticles encapsulated in the MOF body. The nanoparticles have an average particle size corresponding to an average particle diameter in the range 3-200 nm. The nanoparticles may have photocatalytic activity. The MOF composite body is of use for treating water containing an organic dye, the photocatalytic reaction supported by the photocatalytic nanoparticles being a degradation reaction of the organic dye.
Another patent US20220395821A1 describes a covalent organic framework. The covalent organic frameworks have unique structural and physical properties, which lends them to be versatile in a number of different applications and uses. In one aspect, the covalent organic frameworks are composed of a plurality of fused aromatic groups and electron-deficient chromophores. The covalent organic frameworks are useful as photocatalysts in a number of different applications.
Another patent US11628432B2 discloses a nitrogen-doped mesoporous carbon-coated Titanium dioxide composite photocatalyst, a preparation method and use thereof. The preparation method comprises the steps of: dissolving an organic ligand and Ti(OC3H7)4 in a mixture of methanol and DMF at a certain ratio, performing a hydrothermal reaction, centrifuging and drying to obtain a Titanium-based metal organic framework (Ti-MOF); pyrolyzing the obtained Ti-MOF under an inert atmosphere, and oxidizing the same for etching to obtain a nitrogen-doped mesoporous carbon-coated Titanium dioxide composite photocatalyst. The obtained composite photocatalyst not only facilitates the adsorption, enrichment and mass transfer of low concentration VOCs, but also efficiently degrades VOCs under sunlight. It has high degradation activity and stability when performing photocatalytic removal of VOCs in the presence of visible light, is simple in synthesis, low in preparation cost, and has strong potential for the use in environmental protection.
OBJECTS OF THE INVENTION
Main object of the present invention is flexible film photocatalysts for formic acid production from CO2 and cyclization of thioamides in the air's embrace.
Another object of the present invention is to efficiently convert CO2 into formic acid under solar light, utilizing a flexible, selenium-infused Eosin-Y (Sein-EY) photocatalyst film.
Another object of the present invention is to facilitate the formation of C-N and C-S bonds through the aerobic oxidative cyclization of thioamides under ambient air, achieving high yields through a single-step, photocatalytic process.
Another object of the present invention is to extend the solar light absorption capability of the Sein-EY photocatalyst up to 580 nm, enhancing its effectiveness in solar-driven chemical production.
Another object of the present invention is to provide a scalable, one-pot synthesis method for Se-infused Eosin-Y-based photocatalysts, promoting practical application in green chemistry for solar-powered reactions and complex one-pot synthesis.
SUMMARY OF THE INVENTION
This summary is provided to introduce a selection of concepts, in a simplified format, that are further described in the detailed description of the invention.
This summary is neither intended to identify key or essential inventive concepts of the invention and nor is it intended for determining the scope of the invention.
To further clarify advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings.
This invention presents a hydrothermal approach for synthesizing a selenium-infused Eosin-Y (Sein-EY) photocatalyst with high precision. The synthesis begins with the thorough mixing of 1.5 g of black selenium (Se) powder and 0.5 g of Eosin-Y (E-Y) using an agate mortar and pestle. The mixture is then subjected to in-situ thermal polymerization in a muffle furnace under a nitrogen atmosphere at 160 ºC for 2 hours, with a controlled temperature ramp of 1.9 ºC per minute. Following this process, a greyish-pink Sein-EY photocatalyst product, weighing 1.2 g, is obtained. This preparation method enables efficient selenium infusion, creating a flexible photocatalyst with extended solar light absorption capabilities, ideal for applications in CO2 reduction and aerobic oxidative cyclization reactions.
Herein enclosed a flexible film photocatalysts for formic acid production from CO2 comprising of:
Selenium powder (Se), eosin Y (EY), nicotinamide dinucleotide (NAD+).
The photocatalyst as claimed in claim 1, wherein the system is comprising the steps of:
Mixing 1.5 g of black selenium powder (Se) and 0.5 g of eosin-Y (E-Y) thoroughly using agate mortar and pestle;
placing the resulting mixture in a muffle furnace in flow of N2 at 160 ºC for 2 hrs with a 1.9 ºC per minute ramping rate; and
obtaining a greyish-pink product of Sein-EY photocatalyst 1.2 g after the workup.
The formic acid produced from CO2 using the Sein-EY photocatalyst in combination with a rhodium complex (Rh) as an electron mediator and formate dehydrogenase enzyme to catalyze the reduction of CO2 into formic acid, wherein the photocatalyst absorbs photons to initiate the electron transition necessary for CO2 fixation.
The Sein-EY photocatalyst system's capability to produce formic acid with high yield and selectivity verified through GC-MS and ¹H NMR analysis.
The framework facilitates the efficient regeneration of 1,4-NADH/NADPH under solar irradiation, enabling sustainable chemical transformations with high selectivity.
The integrated artificial photosynthetic system comprising the Sein-EY photocatalyst, rhodium complex, and formate dehydrogenase enzyme, for the selective and sustainable production of formic acid from CO2 under solar light with NADH regeneration.
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. Design and synthesis of in situ Se-infused eosinY (Sein-EY) via thermal method under an inert atmosphere..
Figure 2. (a) Photocatalytic activity of Sein--EY photocatalyst for 1,4-NADH regeneration (b- NAD+, Rh, AsA, Sein-EY photocatalyst in NPB solution), (b) Selective production of formic acid (HCOOH) from CO2 under solar light on integration with b-NAD+, Rh, AsA, Sein--EY photocatalyst and enzyme FDH.
Figure 3. General representation reaction for 1,2,4- thiadiazoles synthesis from primary thioamides derivatives.
(R = Ph, PhCl, PhOMe, PhOH, Pyridine.
Figure 4. Photocatalytic cycle for oxidative cyclization of primary thioamides through C-N/C-S bond.
Figure 5. (a) The UV-visible absorbance spectra on inset Tauc plot with optical bad gap of Sein-EY photocatalyst, and (b) Fourier transform infrared spectroscopic analysis of EY (red), Se (blue), and Sein-EY (grey).
Figure 6. (a) Comparison of PXRD patterns of EY (red) and Sein-EY (blue) photocatalyst, along with (b) TGA thermogram of Sein-EY photocatalyst.
Figure 7. (a) 3D illustration of the Sein-EY, (b) HR-TEM image of SeinE-Y, and (c) SEM image of Sein-EY photocatalyst.
Figure 8. Elemental mapping images of (a) Carbon of Sein-EY, (b) Selenium of Sein-EY, (c) Oxygen of Sein-EY, and (d) SEM image of Sein-EY monomer.
Figure 9. XPS characterization of SeinE-Y photocatalyst (a) XPS spectra of C1s, (b) XPS spectra of O1s (c) XPS spectra of Se 3d, and (d) XPS survey data of SeinE-Y photocatalyst.
Figure 10. CV of (a) Sein-EY photocatalyst, (b) Rh, SeinE-Y, and NAD+ solutions with three-armed cell consisting of Pt-electrode (counter) reference (Hg/Hg2Cl2), working (carbon electrode) and using an electrochemical analyzer.
Figure 11. (a) Simulated Nyquist plot of EY (orange) and SeinE-Y photocatalyst (blue) derive by electrochemical impedance spectroscopy, and (b) The current response of EY and SeinE-Y photocatalyst was measured (three electrodes; Pt- electrode, Hg/Hg2Cl2 electrode, glassy carbon electrode.
BRIEF DESCRIPTION OF THE TABLES
Table 1. Solar light driven oxidative cyclization reaction of primary thioamides into 1,2,4-thiadiazoles.
DETAILED DESCRIPTION OF THE INVENTION
In some embodiments of the present invention, the Sein-EY photocatalyst was prepared via in-situ thermal polymerization techniques. Primarily, 1.5 g of black selenium powder (Se) and 0.5 g of eosin-Y (E-Y) were thoroughly mixed using agate mortar and pestle.
In some embodiments of the present invention, subsequently, the resulting mixture was placed in a muffle furnace in flow of N2 at 160 ºC for 2 hrs with a 1.9 ºC per minute ramping rate. After the workup, we received a greyish-pink product of Sein-EY photocatalyst 1.2 g.
In some embodiments of the present invention, in order to reduce the Rh, the light-harvesting eosin Y (acting as e- donor) gathers photons that are incident due to electronic transition between a localized orbital around it (HOMO to LUMO) and conducts via selenium bridge (acting as multi e- acceptor).
In some embodiments of the present invention, when the Rh is reduced, it abstracts a proton from the aqueous media followed by transfer of hydride ion to NAD+ then changes into cofactor NADH, thus accomplishing the photocatalytic cycle. Rhodium complex (Rh) functions as an electron (e-) mediator between NAD+ and Sein-EY photocatalyst, in this manner causing the NADH cofactor to regenerate.
In some embodiments of the present invention, as a result of this, two layers were formed in the solution, one was chloroform and other was water. We then separated the compound dissolved in chloroform by a separating funnel. The solution was later filtered to remove impurities. Further, the filtered solution was passed through sodium sulphate to trap the water. Finally, we dried the filtrate and stored the powder compound.
In some embodiments of the present invention, ultimately, formate dehydrogenase an enzyme uses up NADH to convert CO2 substrate into formic acid. This results in the release of NAD+, which once more serves as a substrate for the photocatalytic cycle and photo regenerates NADH. As a result, the photocatalytic and enzymatic cycles couple completely, producing formic acid as the only by product of CO2. The yield of formic acid was calculated by GC-MS data
Herein enclosed a flexible film photocatalysts for formic acid production from CO2 comprising of:
Selenium powder (Se), eosin Y (EY), nicotinamide dinucleotide (NAD+).
The photocatalyst as claimed in claim 1, wherein the system is comprising the steps of:
Mixing 1.5 g of black selenium powder (Se) and 0.5 g of eosin-Y (E-Y) thoroughly using agate mortar and pestle;
placing the resulting mixture in a muffle furnace in flow of N2 at 160 ºC for 2 hrs with a 1.9 ºC per minute ramping rate; and
obtaining a greyish-pink product of Sein-EY photocatalyst 1.2 g after the workup.
The formic acid produced from CO2 using the Sein-EY photocatalyst in combination with a rhodium complex (Rh) as an electron mediator and formate dehydrogenase enzyme to catalyze the reduction of CO2 into formic acid, wherein the photocatalyst absorbs photons to initiate the electron transition necessary for CO2 fixation.
The Sein-EY photocatalyst system's capability to produce formic acid with high yield and selectivity verified through GC-MS and ¹H NMR analysis.
The framework facilitates the efficient regeneration of 1,4-NADH/NADPH under solar irradiation, enabling sustainable chemical transformations with high selectivity.
The integrated artificial photosynthetic system comprising the Sein-EY photocatalyst, rhodium complex, and formate dehydrogenase enzyme, for the selective and sustainable production of formic acid from CO2 under solar light with NADH regeneration.
EXAMPLE 1
EXPERIMENTAL SECTION
Method and materials:
Selenium powder (Se), eosin Y (EY), nicotinamide dinucleotide (NAD+), ascorbic acid (AsA), sodium phosphate buffer (NPB), formate dehydrogenase (FDH), dimethylformamide (DMF), dichloromethane (DCM), thiobenzamide, 4-hydroxythiobenzamide,4-methoxythiobenzamide, 4-chlorothibenzamide, pyridine-4-carbothioamide were purchased from TCI chemicals and used as without further purification. DI water used. Rhodium complex (Rh) synthesized in lab.
A Hydrothermal alchemy: Crafting Sein-EY photocatalyst with signature precision:
The Sein-EY photocatalyst was prepared via in-situ thermal polymerization techniques (Fig. 1). Primarily, 1.5 g of black selenium powder (Se) and 0.5 g of eosin-Y (E-Y) were thoroughly mixed using agate mortar and pestle. Subsequently, the resulting mixture was placed in a muffle furnace in flow of N2 at 160 ºC for 2 hrs with a 1.9 ºC per minute ramping rate. After the workup, we received a greyish-pink product of Sein-EY photocatalyst 1.2 g (Scheme 2). 1H NMR (300 MHz, CDCl3): d = 6.16 ppm (s,1H), 6.83 (s, 2H), 7.64-7.68 (m, 2H), 8.0-8.02 (d,1H) , 7.10-7.09 (d, 1H). 26
Catalysing Change: Sein-EY photocatalytic symphony in CO2 fixation
The photocatalyst-biocatalyst/enzyme coupled system that produces formic acid (HCOOH) from CO2. In order to reduce the Rh, the light-harvesting eosin Y (acting as e- donor) gathers photons that are incident due to electronic transition between a localised orbital around it (HOMO to LUMO) and conducts via selenium bridge (acting as multi e- acceptor).27 When the Rh is reduced, it abstract a proton from the aqueous media followed by transfer of hydride ion to NAD+ then changes into cofactor NADH, thus accomplishing the photocatalytic cycle. Rhodium complex (Rh) functions as an electron (e-) mediator between NAD+ and Sein-EY photocatalyst, in this manner causing the NADH cofactor to regenerate. Ultimately, formate dehydrogenase an enzyme uses up NADH to convert CO2 substrate into formic acid. This results in the release of NAD+, which once more serves as a substrate for the photocatalytic cycle and photoregenerates NADH. As a result, the photocatalytic and enzymatic cycles couple completely, producing formic acid as the only by product of CO2. The yield of formic acid was calculated by GC-MS data. The 1HNMR spectra of produced formic acid confirms the achievement of experiment as peak of functional group shows at d8.02. Furthermore, C-13 isotope labelling experiments demonstrated that CO2 is the sole source of formic acid produced in the Sein-EY photocatalyst-biocatalyst integrated artificial photosynthetic system.
The Sein-EY photocatalyst sparks photochemical regeneration of NADH and Formic acid (HCOOH) production as solar fuel from CO2:
For the photochemical regeneration of NADH, inside the quartz reactor a cut-off filter of 420 nm as a light source was utilized at room temperature under an inert atmosphere. A technique for photocatalysis was employed in order to regenerate NADH. Within the quartz reactor, the following substituents were involved in the reaction: b-NAD+ (1.24 mM), AsA (1.24 mM), Rh (0.62 mM), and the Sein--EY (1x1cm2) film photocatalyst in 3.1 mL NPB (100 mM, pH7.0). The NADH regeneration was monitored using a UV-vis spectrophotometer. Formic acid (HCOOH) was also synthesised from CO2 inside a quartz reactor in an inert environment at room temperature, using a light source (cut-off filter of 420 nm), Sein-EY photocatalyst, b-NAD+(1.24 mM), Rh (0.62 mM), AsA (1.24 mM), and FDH (3 units) were combined in 3.1 mL of NPB (100 mM, pH 7.0) in the presence of CO2 (flow rate: 0.5 mL min-1). After bubbling CO2 for 1 hour in dark (light off), the reactor was exposed to light (light on). Production of formic acid was measured using HPLC. 28-30 A characteristic absorption peak of 340 nm according to the Lambert-Beer law was used for the calculation of quantitative analysis of (molar extinction coefficient, e = 6.22 mM-1 cm-1, of NADH cofactor.31,32 The yield of formic acid is calculated by GC-MS data. The cyclic stability and reusability of Sein-EY film photocatalyst were tested by subjecting it to 5 cycles of NADH photoregeneration and formic acid synthesis from CO2. In comparison to the first cycle wherein the photocatalyst carried out 83.60% NADH and 204µM formic acid production, remarkably high 74.32% NADH and 189.56 µM formic acid was obtained in the fifth cycle (Fig. 2). These results indicate that Sein-EY film photocatalyst is a stable and reusable film photocatalyst for practical application. Additionally, a literature comparative studies performed with Sein-EY photocatalyst to understand the supremacy of newly designed Sein-EY photocatalyst for NADH photoregeneration and formic acid synthesis.
EXAMPLE 2
RESULTS
General procedure for the photocatalytic organic transformation via Sein-EY photocatalyst
Primary thioamide (Fig. 3) 1a-e (1.0 mmol), 3mL DMF was added in a 25 mL glass vial. A film of Sein-EY (1x1 cm2) photocatalyst dipped in solution. The mixture was irradiated under a blue bulb (light source), stirring it for 2- 3 hours in aerobic conditions at room temperature (r.t.). A thin layer chromatography (TLC) was used for monitoring progress of the reaction. After completion of the reaction, film of photocatalyst removed from solution and added 5mL H2O, and extracted with EtOAc (15 mL). The organic layer solution separated and passed through magnesium sulphate (MgSO4) to trap moisture. The filtrate dried under reduced pressure and a solid crude product was obtained. The product 2a-e was further purified by Colum chromatography. Finally, the 1,2,4-thiadiazoles were isolated in (95-98.6%) yield. 33 All the products 2a-e were characterized 1H-NMR and 13C-NMR spectral data as per literature. 34-36
Table 1. Solar light driven oxidative cyclization reaction of primary thioamides into 1,2,4-thiadiazoles.
Reaction conditions: Substrate (1 mmol) and DMF (3 mL), 20 W blue LED bulb,1x1 cm2 film of SeinE-Y photocatalyst, r.t., aerobic condition.
Possible mechanistic route for organic transformation
Solar light-induced organic transformations are a compelling alternative approach that presents an environmentally friendly, cost-effective, and energy-efficient route for the direct formation of C-N/C-S bonds. A possible mechanistic route (Fig 4) for the synthesis of 1,2,4-thiadiazoles (g) from primary thioamides (a) via oxidative cyclization was shown in Scheme 4. On absorption of solar light (blue bulb used as light source), a photoexcitation of Sein--EY (1) photocatalyst reaches into its singlet state, by which inter system crossing (ISC) evolves into its more stable triplet state SeinEY* (2) undergoes SET (single electron transfer) gives Sein--EY •- (3). A thiolic (b) form of thioamide (a) generates sulphur radical cation (c) via SET method (from Sein-EY* photocatalyst) which generate anionic radical of Sein--EY•- (3). By loss of proton a sulfur radical (d) was generated. The sulfur radical d reacts with other sulfur radical molecule via decyclosulfurization forms sulfur radical (e). The sulfur radical (e) was oxidized with O2 (aerobic condition) forms peroxysulfenate (f). The peroxysulfenate (f) on an intramolecular nucleophilic cyclization followed by loss of sulfurdioxide anion (SO2-) gives final product 1,2,4-thiadiazoles (g). 33,37-39
Unveiling Brilliance: Probing the Soul of Seen-EY Photocatalyst through Multifaceted Characterization Techniques:
Significant molecular structural information regarding the impact of Se infusion on EY was obtained by the analysis of fourier transform infrared spectroscopy (FTIR). The FTIR spectrum of the EY monomer (Fig. 5b) shows peaks at 1420 and 1464 cm-1 vibrations for the carboxylic and phenyl groups, respectively.40 In the FTIR spectrum of E-Y, the various peaks that emerged in the range of 1210 cm-1 , 1746 cm-1, 1595 cm-1, and 3491 cm-1 are attributed to the C-C, -CO, C=C, and OH bands, respectively.40-42 One peak, located at 467 cm-1 on the Se spectrum, is indicative of the -Se-Se- bond. The FTIR spectra of Sein-EY photocatalyst consist similar C-C, -CO, C=C, and -OH vibrational frequencies found as in EY. The presence of the -OH stretching vibrational mode of E-Y is revealed by peaks in the Sein-EY spectrum corresponding to approximately 3468 cm-1, and the -Se-Se- peak corresponds to 467 cm-1. The appearance of a 467 cm-1 peaks of the -Se-Se- band in the newly synthesized Sein-EY framework photocatalyst clearly suggested that the incorporation of EY and Se.
UV-Vis diffuse reflectance spectra was used to illustrate the optical property of Sein-EY photocatalyst (Fig. 5a). The spectra of Sein-EY photocatalyst showed a strong absorption band between 420 to 560 nm (Soret and Q- band) and which indicated a strong solar light absorption in this region than EY.25 These results imply that the number of optically active centers and the capacity to absorb visible light will likely accelerate the formation of electron-hole pairs. Along with visible light activity the optical band gap energy (Eg = 2.21 eV) of Sein-EY was calculated by the Tauc plot (Inset of Fig. 2a) using Tauc expression given as,
ahv=?A(hv-Eg)?^n
where a = 2.303A/d, where v is the incident radiation frequency, h is the Plank constant, A is the absorbance, d is the path length, Eg is the optical band gap, and the nature of the electronic transition is determined by the value of exponent n. The plot of (ah?)2 versus h? (photon energy) was used to create the Tauc plot, and the optical band gap (Eg) was calculated by extrapolating the linear region to the x-axis. Finally, we achieved the 2.21 eV band gap energy intersection point on x-axis of newly designed Sein-EY photocatalyst by Tauc plot, which was almost similar to the experimentally calculated optical band gap by cyclic voltammetry techniquech.43
Further the impact of selenium infusion on E-Y investigated by powder X-ray diffraction (PXRD) technique. The PXRD of EY and Sein-EY photocatalyst shown in Fig. 6a. An intense diffraction peaks 2? at 23.51and 29.65 with d-spacing 0.37 nm and 0.30 nm respectively due to strong p-p stacking in Sein-EY polymeric framework photocatalyst. The XRD spectra of E-Y intense diffraction peak 2? at 22.74° and 25.08° with d-spacing at 0.38 nm and 0.35 nm. In comparison to E-Y (25.08º), a right shift of the peak to 29.65º was observed for Sein-EY polymeric framework photocatalyst. Which attributed to infusion of EY and Se powder to form C-Se bond between carbon of EY and -Se-Se- bridge in Selenium powder. The existence of C-Se bond was also confirmed by XPS and elemental mapping technique.
The thermal behaviour of polymeric Sein-EY framework photocatalyst was studied by thermogravimetric analysis (TGA) (Fig. 6b) by observing the change in mass with the variation of temperature and time. TGA analysis (heating rate 5 °C min-1) was carried out within the range of temperature 5-800°C in N2 atmosphere. The TGA graph of Sein--EY showed high thermal stability for with no decomposition up to 300 °C. The slow weight loss observes at approximately 320 °C and sharp weight loss at approximately 395°C up to 512°C and again exhibited third slow weight up to 800°C. These results were confirmed the high thermal stability of Sein-EY photocatalyst. 44
In addition to this, 3D-structure of Sein-EY, high HR-TEM and SEM images are also provided in Fig. 7(a-c) to investigate the surface morphology of polymeric Sein-EY photocatalyst. The HR-TEM Fig. 4b clearly illustrate the polymeric conglomerate structure consists of porous crystalline particles with scale bar 200 nm. The SEM image show that the Sein-EY photocatalyst consists of a conglomerated structure, whereas the SEM image of EY sensitizer have aggregated morphology. The infusion of E-Y with Se discovered marginal change in the surface morphology of SeinE-Y which may originated by covalent infusion (C-Se bond) of E-Y with selenium (Se).
To further understand the composition of each element in the EY and Sein-EY photocatalyst, the elemental mapping were used shown in Fig. 8(a-c). All element constituents of EY appeared in elemental mapping spectra including carbon, oxygen, and bromine while Sein-EY photocatalyst appeared in the elemental mapping including carbon, oxygen, and selenium. Here, a difference in the particle is observed, selenium (Fig.8b) is detected with good carbon (Fig. 8a) distribution in whole area of newly synthesized polymeric Sein-EY photocatalyst.
X-ray photoelectron spectroscopic (XPS) analysis confirmed the chemical composition of the Sein-EY. The XPS spectra of Sein-EY consist of C, O and Se (Fig. 9a-c). It was taken as the preliminary evidence for the successful infusion of Se in EY. The high-resolution XPS spectra of C1s indicated deconvoluted C=C, C-O and O-C-O peaks at binding energy 284.7, 286.9 and 288.6eV. 45,46 The deconvoluted peaks of O1s consist of C-O, C=O and C-OH at binding energy 530.5, 531.1 and 532.5 eV. 46,47 Furthermore, the deconvoluted spectra of Se 3d shows a peak of C-Se and -Se-Se- at binding energy 56.2 eV and 55.07 eV .45 The XPS survey of Sein-EY (Fig. 9d) further confirmed the presence of C (80.4%), O (16.6%), and Se (2.2%). As a result of XPS spectra, bromine (C-Br) was replaced by selenium (C-Se) confirming the infusion of selenium in the newly designed Sein-EY framework photocatalyst.
Cyclic voltammetry (CV) offers helpful information on the workings of the process. Thus, we used glassy carbon electrode (working), calomel electrode (reference), and Pt- electrode (counter) in NPB (100 mM, at pH 7.0) to study the electrochemical characteristics of Sein-EY + Rh + NAD+ with CV. It was discovered that Rh and Sein-EY had reduction potentials of around -0.71 V 8 and -1.22 V (Fig. 10a), respectively. According to published research,48 the change in reduction potential of Rh observed when Sein-EY + Rh present together. With cathodic shift, the reduction potential of Rh changed into -0.85 V and additionally, it can also be suggested as anodic shift of Sein-EY reduction. The system made up of Sein-EY and Rh, was capable to catalyse the reduction of NAD+, as evidenced by the Sein-EY-Rh complex, which also showed a remarkable increment in the reduction peak current with NAD+ (Fig. 10b). According to earlier reports 49,50, a strong inflated reduction of Rh was observed, due to high catalytic activity of Rh in presence of NAD+. The lack of an oxidation potential peak additionally demonstrated that the electrochemical behaviour of Rh (2e- reduction followed by chemical protonation) was followed by the Sein-EY-Rh complex. The photoelectrical behaviour of Sein-EY could be responsible for the efficient catalytic activity of the Sein-EY-Rh complex. However, Rh can easily accept the photoexcited electron (e-) from Sein-EY. The photoexcitation of electrons occurs from the valence band or HOMO (5.96 eV) to the conjugate band or LUMO (3.58eV) of the Sein-EY photocatalyst and subsequent transfer of the photoexcited electrons into the Rh. According to researchers.48 In the current instance, the photoexcitation of the Sein-EY electron causes it to cascade into Rh (E = -3.46 eV) without emitting any radiation from VB/HOMO (E = -5.76 eV) to CB/LUMO (E = -3.46 eV). The efficient electron transfer from light harvester Sein-EY photocatalyst, to the electrocatalytic electron mediator Rh centre was made possible by their contiguity and potential gradient between two. Following chemical protonation in aqueous conditions, the electrically reduced Rh resulting from this process, [Cp*Rh(bpy)], catalyses a reaction with NAD+ to produce NADH regeneration (83.60%) which coupled with FDH enzyme to produce formic acid (204 mM).
The photoelectrochemical properties of the EY and Sein-EY photocatalyst were investigated by electrochemical impedance spectroscopy.51 Fig. 8a shows EIS Nyquist curves for EY and Sein-EY photocatalyst with two semicircle which was related to charge transport. The Nyquist curve of EY consist large semicircle with low frequency zone was related to diffusive resistance, whereas the Sein-EY photocatalyst consist small semicircle with the high frequency zone. The smaller the arc radius of semicircles were associated with low charge transfer resistant which was responsible for fast separation efficiency between holes and photogenerated electrons and fast interfacial charge transfer. The arc radius of the semicircles for Sein-EY photocatalyst is smaller than arc radius of semicircle for EY, suggesting -Se-Se- bridges in the newly designed SeinE-Y photocatalyst apparently enhanced the photocatalytic activity by improving the interfacial charge transfer . 52
When compared to the EY light harvesting monomer, the Tafel plot (Fig. 11b) clearly showed that the corrosion potential of the Sein-EY photocatalyst was moving towards the positive zone. When comparing the Sein-EY photocatalyst to the bare E-Y light harvesting monomer, the Tafel plot shows a drop in current density. The observed EY photocatalyst's polarisation resistance increased as a result of a drop in corrosion current and corrosion rate. Through Se-Se-bridges, this results in an increase in the corrosion resistance of the EY light harvesting monomer. Remarkably, compared to EY light harvesting monomer, the Sein-EY photocatalyst exhibits greater enhanced corrosion resistance.53
Plausible mechanism for production of formic acid from CO2
A coherent mechanistic explanation that is fully consistent with the literature for the formic acid synthesis from CO2.54-56 Sein-EY photocatalyst absorbs visible light, which causes photo-excited electrons from VB or HOMO to CB or LUMO. The in situ formed organometallic species Rhox is reduced to a Rh (I) complex (Rhred), upon absorption of two such photo-excited electrons from Sein-EY photocatalyst. The catalytic cycle is completed when the electron mediator Rh-complex is brought back to its starting state, Rhox, by H2O molecule in tandem with the hydride transfer that generates 1,4-NADH. Finally, the formate dehydrogenase (FDH) binds to the regenerated cofactor 1,4-NADH for the production of formic acid from CO2. The NAD+ is liberated, which serves as a substrate for the photocatalytic cycle mentioned above, resulting in NADH photoregeneration. As a result, the photocatalytic and enzymatic cycles work together to produce only formic acid from CO2. Ascorbic acid used as a sacrificial agent in this photocatalytic cycle which provided electron to the photocatalyst in presence of solar light.
Selective regeneration of 1,4-NADH regeneration in presence of Sein-EY photocatalyst under solar light
Direct electrochemical reduction of NAD+ at high overpotentials results in unselective protonation and radical coupling, yielding several NADH isomers and dimers. Only the 1,4-dihydro derivative is helpful for enzymatic processes, while the others are considered 'enzymatically inactive'. To use NADH in artificial photosynthesis, it must be regenerated in its 'enzymatically active' 1,4-dihydro form. Using an electron mediator Rh complex can limit the production of inactive isomers in enzymes. The electron mediator rhodium complex can only regenerate the enzymatically active 1,4-NADH isomer when exposed to solar light. 57,58
Conclusions
In summary, polymeric Selenium infused eosin Y photocatalyst have been synthesized that enable for solar fuel formation and oxidative cyclization via C-N/C-S bond activation to be undertaken. Due to the high thermal, chemical stability, high charge transfer activity, broad visible light absorption edge and suitable band gap Sein-EY photocatalyst showed the anaerobic enzyme coupled reactions, where the photoactive material regenerates the cofactor 1,4-NADH (83.60%). This reduced cofactor consumed in the remarkably efficient conversion of CO2 into formic acid (204mM). Furthermore, an oxidative cyclization of thioamides which has various medicinal use. These routes offer a fresh, environmentally benign method for creating solar compounds, which have enormous advantages for both business and society. This method sets a new standard for Sein-EY photocatalysts that are capable of efficiently harvesting solar energy and reviving interest in the field of producing solar chemicals.
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(58) Hollmann, F.; Schmid, A. Electrochemical Regeneration of Oxidoreductases for Cell-Free Biocatalytic Redox Reactions. Biocatal. Biotransformation 2004, 22 (2), 63-88. ,CLAIMS:1. A flexible film photocatalysts for formic acid production from CO2 comprising of:
Selenium powder (Se), eosin Y (EY), nicotinamide dinucleotide (NAD+), ascorbic acid (AsA), sodium phosphate buffer (NPB), formate dehydrogenase (FDH), dimethylformamide (DMF), dichloromethane (DCM), thiobenzamide, 4-hydroxythiobenzamide,4-methoxythiobenzamide, 4-chlorothibenzamide, pyridine-4-carbothioamide.
2. The photocatalyst as claimed in claim 1, wherein the system is comprising the steps of:
i. Mixing 1.5 g of black selenium powder (Se) and 0.5 g of eosin-Y (E-Y) thoroughly using agate mortar and pestle;
ii. placing the resulting mixture in a muffle furnace in flow of N2 at 160 ºC for 2 hrs with a 1.9 ºC per minute ramping rate; and
iii. obtaining a greyish-pink product of Sein-EY photocatalyst 1.2 g after the workup.
3. The method as claimed in claim 2, wherein formic acid produced from CO2 using the Sein-EY photocatalyst in combination with a rhodium complex (Rh) as an electron mediator and formate dehydrogenase enzyme to catalyze the reduction of CO2 into formic acid, wherein the photocatalyst absorbs photons to initiate the electron transition necessary for CO2 fixation.
4. The method as claimed in claim 2, wherein Sein-EY photocatalyst system's capability to produce formic acid with high yield and selectivity verified through GC-MS and ¹H NMR analysis.
5. The method as claimed in claim 2, wherein the framework facilitates the efficient regeneration of 1,4-NADH/NADPH under solar irradiation, enabling sustainable chemical transformations with high selectivity.

6. The method as claimed in claim 2, wherein integrated artificial photosynthetic system comprising the Sein-EY photocatalyst, rhodium complex, and formate dehydrogenase enzyme, for the selective and sustainable production of formic acid from CO2 under solar light with NADH regeneration.

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