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The structural alteration of carbon nitride (CN) for photocatalytic CO2 reduction is a promising research topic in the environmental and energy sectors. This work discusses the fabrication of photocatalyst through a heterojunction architecture obtained from the molecular engineering of electron-rich organic monomer 2,6-pyridinedicarboxylic acid (PDA) with CN precursor (CN/PDAx). The successful integration of PDA in the structure of CN served as a charge inducting entity to enhance charge separation and photocatalytic CO2 reduction under visible light (λ = 420 nm). The DFT results indicated that the upshift in the HOMO level of CN after integration of PDA in its framework was the most lawful for the charge separation and for obtaining a high reduction potential. As-synthesized photocatalysts were demonstrated for various integral analysises and after evaluating the process of photocatalytic CO2 reduction under visible light region (λ = 420 nm). The optimized sample CN/PDA10 has the most excellent photocatalytic activity producing 85.4 μmol/h of CO and 21.3 μmol/h of H2, achieving a 7.5-fold enhanced catalytic efficiency as compared to pure CN. We hope that this work will attract more attention to synthesizing efficient photocatalysts for energy production and environmental remediation.

One of the most frequent ways to widen the adsorption range of carbon nitride (CN) is to add a well-known photosensitizer into its basic structure. So far, such attachments have been accomplished by using weak van der Waals forces. However, using strong covalent bonding to attach such photosensitizer with CN is yet to be determined. Here, for the first time, we covalently bonded porphyrin (5,10,15,20-tetrakis(4-(2,4-diamino-1,3,5-triazinyl) phenyl)-Porphyrin (TDP)), a renowned photosensitizer, effectively with CN by thermally balanced molecular strategy. A photoreaction system was set up for the deoxygenated conversion of CO2 to CO under visible light, where cobalt acted as a redox controller to speed up the charge transportation, while CN-TDP worked as a CO2 activating photocatalyst. The subsequent photocatalyst has a broader absorbance range, a greater specific surface area, and intramolecular organic connections that help to decrease the electron-hole pairs’ recombination rate. Furthermore, the average weight ratio between urea and TDP was well-tuned, resulting in a fantastic CO2 photoconversion for CN-TDP7.0 compared to the blank sample. This substantial increase in photocatalytic activity predicts a significant shift in CN’s specific surface area, band gap, chemical composition, and structure, as well as the efficient separation of photogenerated charge carriers from the ground state (HOMO) to the excited state (LUMO), making it a top candidate for CO2 photoreduction. At the same time, this approach paves the path for the bottom-up fabrication of carbon nitride nanosheets.

One of the most frequent ways to widen the adsorption range of carbon nitride (CN) is to add a well-known photosensitizer into its basic structure. So far, such attachments have been accomplished by using weak van der Waals forces. However, using strong covalent bonding to attach such photosensitizer with CN is yet to be determined. Here, for the first time, we covalently bonded porphyrin (5,10,15,20-tetrakis(4-(2,4-diamino-1,3,5-triazinyl) phenyl)-Porphyrin (TDP)), a renowned photosensitizer, effectively with CN by thermally balanced molecular strategy. A photoreaction system was set up for the deoxygenated conversion of CO2 to CO under visible light, where cobalt acted as a redox controller to speed up the charge transportation, while CN-TDP worked as a CO2 activating photocatalyst. The subsequent photocatalyst has a broader absorbance range, a greater specific surface area, and intramolecular organic connections that help to decrease the electron-hole pairs' recombination rate. Furthermore, the average weight ratio between urea and TDP was well-tuned, resulting in a fantastic CO2 photoconversion for CN-TDP7.0 compared to the blank sample. This substantial increase in photocatalytic activity predicts a significant shift in CN's specific surface area, band gap, chemical composition, and structure, as well as the efficient separation of photogenerated charge carriers from the ground state (HOMO) to the excited state (LUMO), making it a top candidate for CO2 photoreduction. At the same time, this approach paves the path for the bottom-up fabrication of carbon nitride nanosheets. [ABSTRACT FROM AUTHOR]

Proposed mechanism of BiVO 4 /CN-QA. [Display omitted] • Quinolinic acid (QA) doped g-CN (CN-QA) was developed via facile thermal approach. • Different samples of BiVO 4 /CN-QA with high stability were prepared via hydrothermal method. • Remarkable enhanced photocatalytic H 2 and O 2 evolution was achieved using these catalysts via overall water splitting. • A dual synergetic mechanism on BiVO 4 /CN-QA has been proposed. The development of copolymerized carbon nitride (CN)-based photocatalysts may support advances in photocatalytic overall water splitting. However, the recombination of charge carriers is the main bottleneck that reduces its overall photocatalytic activity. To overcome this problem, the construction of heterojunction technology has emerged as an effective approach to reduce the charge carrier recombination, thereby improving charge separation and transport efficiency. In this work, an innovative heterojunction was prepared between Quinolinic acid (QA) modified CN (CN-QA x) and novel nanorod-shaped bismuth vanadate (BiVO 4) (BiVO 4 /CN-QA x) for overall water splitting through a simple in-situ solvent evaporation technique. The obtained results show that the synthesized samples have efficient and improved activities for releasing H 2 (862.1 μmol/h) and O 2 (31.58 μmol/h) under visible light irradiation. Furthermore, an exceptional apparent quantum yield (AQY) of 64.52 % has been recorded for BiVO 4 /CN-QA 7.0 at 420 nm, which might be due to the substantial isolation of photoinduced charge carriers. Therefore, this work opens up a new channel toward efficient CN-based photocatalysts in the sustainable energy production processes. [ABSTRACT FROM AUTHOR]

Fig. Proposed mechanism of CN/BI 10.0. [Display omitted] • BI was incorporated within CN via molecular engineering (CN/BIx). • Endorsing charge transition dissociation and boosting the photocatalytic performance. • Superior sample CN/BI 10.0 demonstrate remarkable photocatalytic H 2 evolution and photoreduction of CO 2 respectively. • A dual synergetic mechanism of CN/BI 10.0 has been proposed. Due to a growing number of significant vitality and environmental issues, the standardized variation of carbon nitride (CN) for visible-light photocatalytic water splitting is an encouraging scientific topic. By revealing this, the functionalized monomer 2,6-dibromobenzimidazole (BI) was successfully embedded within the heptazine units of CN via a molecular engineering (Co-polymerization process) approach, and the as-synthesized product was named CN/BIx. Thereafter, as-synthesized materials were employed in the photocatalytic production of hydrogen (H 2) via water splitting and CO 2 reduction into CO under visible light irradiance (λ = 420 nm). Surprisingly, the substituent framework of CN, which was intimidated by the description of BI monomer, acted as a substitution reaction material and lubricated the electronic structure of CN by endorsing charge transition dissociation, which in turn boosted its photocatalytic performance under visible irradiation. The CN/BI 10.0 yields 62.8 mol of CO and 18.1 mol of H 2 for 4 h of the catalyzed reaction upon photooxidation under light irradiation, emphasizing the maximum photocatalytic performance with response to CO 2 +. Correspondingly, the H 2 evolution rate (HER) for bulk CN was estimated as 17.6 mol/h1, whereas it was approximated as 203.7 mol/h1 for CN/BI 10.0 , which is 10 times higher than that of CN. Such a phenomenon also predicts a substantial encroachment in the surface area, energy gap, and chemical properties, along with promotes the effective segregation of photoinduced charge separation from the valence band (VB) to the conduction band (CB) of CN, thereby, making it a good alternative for the photocatalytic water and CO 2 reduction reaction process. [ABSTRACT FROM AUTHOR]

The carbon nitride (CN) has good stability, a comprehensive band structure, and a more straightforward fabrication process that makes them a top candidate for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). So far, scientists have been involved broadly in utilizing smaller carbon-based molecules to modify the CN framework for better-quality solar to fuel energy conversion. Still, the modification of material with a natural macromolecule has been explored insufficiently. In this regard, we firstly a copolymerized carbon nitride (CNP x) by conjugating a novel monomer 2,6-dibenzolumazine with CN through molecular integration (CNP x). The copolymerized catalysts demonstrated noteworthy improvement in photocatalytic activities as compared to pristine CN. Following this, we further combine our superior sample (CNP 5.0) with the underlying biomass-based lignin molecules forming CNP-L x. The biomass-modified CNP-L x obtained through this process has an increased HER and OER under visible light (λ=420 nm). Findings demonstrate the catalytic performance seven times higher for CNP-L x and three times enhanced for CNP x sample than CN catalyst. These improvements can be attributed to the ultrathin nanostructure and efficient visible light absorption of the CN, well-balanced exciton states of the organic monomer, and the synergetic effect of lignin synergetic effect on its surface. Lignin-activated CNP 5.0 photocatalysts produced through this method can prove cost-effective and efficient alternatives for solar overall water splitting. A proposed graphical scheme on conduction band (CB) and valence band (VB) utilizing lignin modified copolymerized CNP for overall water splitting under visible light illumination. [Display omitted] [ABSTRACT FROM AUTHOR]