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Summary: Conjugated monomer 2,6‐dimethylindole (DMI) was integrated into the triazine framework of polymeric carbon nitride (PCN) via molecular engineering. As‐prepared samples were utilized for photocatalytic evolution of hydrogen (H2) through water splitting and photodegradation of RhB dye under visible light. The integration of this monomer DMI has been dominated within the internal framework of PCN and operated as a substitution reaction membrane, retarding an appropriate control and promote the charge density in π‐electron conjugated system. It also promotes the charge transferring and separation to elevate the photocatalytic activity of PCN under visible light. The HER for pure PCN was found as 77.9 μmol/h, while for PCN‐DMI18.0 was predicted at 701.2 μmol/h, which is exclusively output approximately nine times higher than that of pure PCN respectively. Besides, the pseudo‐order kinetic constant of PCN‐DMI18.0 degradation of RhB was multiple times higher when contrasted to pristine PCN. [ABSTRACT FROM AUTHOR]

Reference 1 Hayat A., Sohail M., Taha T.A., Alenad A.M., Uddin I., Hayat A., Ali T., Shah R., Irfan A., Khan W.U. A superficial intramolecular alignment of carbon nitride through conjugated monomer for optimized photocatalytic CO2 reduction. However, the morphology did not sustain after adding the TDP monomer (change from nanosheets to irregular, rough surface nanoparticles). A Superficial Intramolecular Alignment of Carbon Nitride through Conjugated Monomer for Optimized Photocatalytic CO 2 Reduction. [Extracted from the article]

Light-driven heterogeneous photocatalysis has gained great significance for generating solar fuel; the challenging charge separation process and sluggish surface catalytic reactions significantly restrict the progress of solar energy conversion using a semiconductor photocatalyst. Herein, we propose a novel and feasible strategy to incorporate dihydroxy benzene (DHB) as a conjugated monomer within the framework of urea containing CN (CNU-DHBx) to tune the electronic conductivity and charge separation due to the aromaticity of the benzene ring, which acts as an electron-donating species. Systematic characterizations such as SPV, PL, XPS, DRS, and TRPL demonstrated that the incorporation of the DHB monomer greatly enhanced the photocatalytic CO2 reduction of CN due to the enhanced charge separation and modulation of the ionic mobility. The significantly enhanced photocatalytic activity of CNU–DHB15.0 in comparison with parental CN was 85 µmol/h for CO and 19.92 µmol/h of the H2 source. It can be attributed to the electron–hole pair separation and enhance the optical adsorption due to the presence of DHB. Furthermore, this remarkable modification affected the chemical composition, bandgap, and surface area, encouraging the controlled detachment of light-produced photons and making it the ideal choice for CO2 photoreduction. Our research findings potentially offer a solution for tuning complex charge separation and catalytic reactions in photocatalysis that could practically lead to the generation of artificial photocatalysts for efficient solar energy into chemical energy conversion. [ABSTRACT FROM AUTHOR]

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]

Photocatalytic mechanism proposed for PCN-BTD 008 copolymer sample for overall water splitting under the illumination. [Display omitted] • BTD integrated copolymer (PCN-BTD) via thermal process. • An incorporation of BTD is reinforced by DFT data. • Eight-time enhanced HER of PCN-BTD 008 (744.2 μmol/h) than pure PCN (88.2 μmol/h). • The OER, generates 0.2 μmol/h−1 and 1.6 μmol/h−1 for PCN, while PCN-BTD 008 yield 2.2 μmol/h−1 (visible) and 14.8 μmol/h−1 (non-visible) respectively. Well-organized water splitting semiconducting photocatalyst is an important concept, but stimulating aimed at decisive energy and environmental emergencies. In this context, visible light-based photocatalytic water splitting with low-dimensional semiconducting materials is proposed to produce sustainable energy. Here we optimized the sequential of organic electron-rich heterocyclic monomer namely benzothiadiazole (BTD) quenched within polymeric carbon nitride (PCN) semiconductor via copolymerization, thereby assembling a sanctum of donor-π-acceptor (D-π-A) photocatalysts. The selection of BTD is based on the benzene ring, which consequently anticipating a π cross-linker unit for hydrogen and oxygen evolution. A hydrogen evolution rates (HER) of 88.2 μmol/h for pristine PCN and 744.2 μmol/h for PCN-BTD 008 (eight times higher than pure PCN) are observed. Additionally, a remarkable apparent quantum yield (AQY) of about 58.6% at 420 nm has been observed for PCN-BTD 008. Likewise, the oxygen evolution rate (OER) data reflect the generation of 0.2 μmol/h1 (visible) and 1.6 μmol/h1 (non-visible) for pure PCN. Though, OER of PCN-BTD 008 is found to be 2.2 μmol/h1 (visible) and 14.8 μmol/h1 (non-visible), which are economically better than pure PCN. As such, the results show an important step toward modifying the design and explain a vital part of the D-π-A scheme at a balanced theme for fruitful photocatalysts intended for future demand. [ABSTRACT FROM AUTHOR]

We confirmed a specific copolymerization (molecular doping) method for the covalent integration of 2,4-dihydroxyoxazole (DHO) monomer within the framework of carbon nitride (CN). The obtained composites xCN/DHO reveal a sophisticated dual-phase photocatalytic activity, which can effectively reduce and oxidize the CO 2 and NO 2 sources in an aqueous solution and simultaneously performed the oxidation of olefin (C C) in an organic state. This momentous dual state activity is concerned with the lipophilicity elevation from the convolution of oxazole (DHO) monomer within the shell of CN semiconductor. This modulation demonstrates the probability of hydrophobic olefin molecules, escorted in the bulk of CN and associated with the oxidation of hydroxyl radicals (∗OH) caused by photogenerated electrons/holes. In this approach, the olefinic compound allusively consumes the photoinduced electrons/holes through elevated CN/DHO, thus stimulating the entire photocatalytic route. Recent research provides a novel strategy for the production of solar fuels upon organic synthesis via the oxidizing capacity of photoinduced holes within free semiconductors of amphiphilic metals. Likewise, the results of the NO 2 photocatalytic reaction demonstrated that molecular doping drastically reduces the oxidative capacity and improves its reducing propensity. More importantly, the CO 2 reduction process supervenes into an extreme aggregation of methane (CH 4) as well as carbon monoxide (CO) in the presence of co-catalyst Pt respectively. The photocatalytic results demonstrate that the copolymerized CN provide the greatest reduction/oxidation potential, which is due to its chemical oxidation phase that causes superior fluctuations in whole performance under solar irradiation. • Synthesis of oxazole (DHO) based carbon nitride (CN) through molecular engineering. • Samples were utilized for photocatalytic CO 2 reduction and NO 2 oxidation. • The momentous activity is concerned towards the convolution of DHO within CN. • Samples alter the probability for hydrophobic olefin molecules due to *OH radicals. • The reduction/oxidation process happen due to excess of electrons/holes in materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Recently, the graphite based heterogeneous photocatalysts has attained tremendous research attention in various environmental applications. Among them, the graphitic carbon nitride (g-C 3 N 4) is categorized as a unique solar active particle with its outstanding intrinsic properties i.e., adequate band configuration, excellent light absorptivity and thermo-physical durability, which make it highly useful and reliable for revenue transformation and ecological concerns. Considering the intrinsic potential of g-C 3 N 4 in photocatalysis, so far, no report has been done in literature for its extraordinary configuration, morphological characteristics and perspective tuning for said applications. To overcome this research gap, our primary emphasis of this review regarding photocatalysis is to provide layout as well as the advancement of visible-light-fueled materials as highly stabilized and extremely effective ones for pragmatic implementation. Thus, this existing comprehensive assessment conducts a systematic survey over visible light driven non-metal novel g-C 3 N 4. The major advancement of this evaluation is the fabrication of well-designed nanosized g-C 3 N 4 photocatalysts with unique configurable frameworks and compositions. Furthermore, alternative techniques in order to customize the analogue band configuration and noticeable cultivation such as metal (cation), nonmetal (anion) doping, worthy metal activating, and alloy initiation with certain semiconductors are discussed in detail. In addition to this, g-C 3 N 4 photocatalytic functionalities towards photocatalytic hydrogen evolution, CO 2 photoreduction, biological metal ions deterioration as well as bacterial sanitization are also presented and discussed in detail. Therefore, we believe that such a pivotal compact assessment can provide a roadmap in several perspectives on the currently underway obstacles in the innovation of effective g-C 3 N 4 catalytic design processes. Moreover, this critical assessment will ultimately serve as a useful supplement in the research area of g-C 3 N 4 nanosized photocatalysts and for the researchers working on its key aspects in diverse range of natural, chemistry, engineering and environmental applications. • Graphitic carbon nitride (g-C 3 N 4) is a metal-free sustainable photocatalyst with a band gap of 2.7 eV. • G-C 3 N 4 has improved light absorption performance as well as electronic features. • Multiple synthetic approaches are being used with g-C 3 N 4 to improve its photocatalytic capabilities. • Metals/nonmetals doping, activation, and alloy formation are employed for g-C 3 N 4 nanocomposites. • Our review includes the latest current g-C 3 N 4 nanocomposites and their photocatalytic implications. [ABSTRACT FROM AUTHOR]

Due to the future uses of solar energy in different areas, such as the oxidation of fossil fuel-based contaminants, the reduction of carbon dioxide, heterogeneous photocatalysis, and the generation of inexhaustible and renewable hydrogen gas exploits semiconductors. As a metal free photocatalyst, graphitic carbon nitride (g-C 3 N 4) is classified to solve these energy hazards and ecological difficulties owing to its excellent electronic structure with band energy of about 2.7 eV, robust photochemical stability, and better light-harvesting efficiency. However, its photocatalytic performance is still insufficient due to a minor surface area and poor conductivity. Therefore, heterojunction formation by combining it with a giant band gap material is a potential approach to reestablish polarization in its distinctive band structure, increase its light absorption capacity and enhance its surface area. In this regard, various synthesis techniques have been applied so far to integrate g-C 3 N 4 and other materials for boosting its photocatalytic activity. So far, metal oxide, sulfides, and ferrites are three crucial groups of materials that have been identified and defined to be used to synthesize g-C 3 N 4 dependent nanocomposites. As a result, in this review, we have compiled a list of the most recent g-C 3 N 4 nanocomposites with their applications in solar energy adaptation and pollution control. This study concludes an overview about the next steps to study the nanomaterials based g-C 3 N 4 composites and a range of additional insights to solve the present problems. • This review addresses the properties and structures of g-C 3 N 4 photocatalyst structure. • Pros and cons of their synthesis techniques. • The types of the g-C 3 N 4 -based nanocomposite are emphasized. • Approaches to improve the photocatalytic activity of g-C 3 N 4. • The most up-to-date photocatalytic applications were thoroughly discussed. [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]

• A carbon abundant 2‐D structure material 5,8-dibromoisoquinoline (BQ) has been integrated as an aromatic organic monomer within carbon nitride (CN) via molecular aggregation process. • The BQ copolymerized CN with distinguish characteristics leads to a significant increment in the applied application. • The copolymerized samples demonstrating narrowed band gap, high surface area, splendid morphology, and wide optical absorbance which enhanced electron transport ability. • The spinal material, i.e., 10BQ/CN exhibited a superior H 2 evolution of ten‐fold higher activity and also photodegradation of RhB under visible light driven. Graphitic carbon nitride, g-C 3 N 4 (CN) is regarded as an excellent metal-free semiconductor known for its potential solar fuel generation and pollutant degradation. In this study, a carbon richer substance, (5,8-dibromoisoquinoline (BQ)) was used to feed its catalytic function through conventional copolymerization (molecular doping) process at 550°C under a nitrogen atmosphere. The incorporation of BQ monomer in the triazine oligomers of CN in turn enhanced the specific surface area, thereby, improving the lifespan of photoexcited charge carriers, decreasing the charge recombination rate, energy bandgap, and altering the optoelectronic characteristics of CN. On average, the rate of hydrogen (H 2) production over-optimized 10BQ/CN was 710.1 µmol/h much superior and 10 times higher than that of pure CN (71.9 µmol/h). Particularly, the kinetics of the photocatalytic degradation of RhB over 10BQ/CN followed pseudo-order kinetics and the rate constant was three times larger than pure CN. Our results illustrate the crucial importance of conjugated monomers in improving photocatalysis process for future energy demand by providing key steps towards sustainable energy production. [Display omitted]. [ABSTRACT FROM AUTHOR]

• Molecular engineering (copolymerization) strategies has been utilized by modulating aromatic heterocyclic monomer Uric Acid (UA) within carbon nitride (CN) copolymer (CN/UA). • Incorporation of Uric acid (UA) alter a significant fluctuation in the surface area, electronic structure, band gap, chemical composition of CN and boosting the process of photogenerated electrons/holes. • The modified samples demonstrating a momentous enhancement in the photocatalytic performance of water reduction (H 2 evolution) and pollutants degradation (RhB). • This novel integrity of UA co-monomer with in CN matrix remarkably improve the photocatalytic activity toward prosperity and as such the best photocatalyst CN/UA 10.0 accelerate an outstanding photocatalytic activity of water reduction as 8 times higher compared of pure CN respectively. An ideal solution to water or pollutant contamination and energy problem is to advance photocatalysts that are highly effective for both reducing contaminants and cleaning water. In this regard, carbon nitride (CN) has strong stability with prominent band structure and can be used to produce hydrogen through water splitting due to an easier fabrication process. Uric acid (UA) was integrated as a conjugated monomer in the urea based CN system using the molecular doping (copolymerization) process. The photocatalysis of water reduction (HER) by using a new growth technique of minimally priced effective monomer UA inside CN, which also optimized the photodegradation of Rhodamine B dye (RhB) under light illumination (λ = 420 nm). By increasing light transmittance, speeding up photogenerated electrons and holes, and changing the physicochemical properties of CN, modified samples dramatically improve photocatalytic efficiency. The ideal samples CNU-UA 10.0 showed a substantial increase in photocatalytic activity, with an HER 690.01 μmol/h higher than CNU (82.89 μmol/h), based on the implications of different configurations on the reaction mechanism. Moreover, an extraordinary apparent quantum yield (AQY) of about 57.43% at 420 nm has been observed for CNU-UA 10.0. Under the same conditions and illuminations, H 2 performance versus RhB dye degradation was compared. CNU-UA, on the other hand, had a three-fold higher pseudo-order kinetic constant for photodegradation of RhB than CN. The results demonstrate a major step toward in the direction of custom-designed photocatalysts with efficient water reduction and pollutants degradation capability for future demand. [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]

An electrochemical quercetin (Q.R.) sensor based on carbon nitride (CN) copolymerized with 2,6-diaminoantandantquinone (DAQ) was assembled. The product has a humongous texture and excellent processability. The as-synthesized samples with uniform surface distribution were characterized by UV-Vis-spectroscopy, PL, XPS NMR, EPR, XRD, FT-IR, BET, and SEM. Furthermore, samples were electrochemically pickled in 0.1 MPBS solution via cyclic voltammetry (CV) for Q.R. electrochemical response, interference research, electrochemical active surface determination, stability, photocurrent and EIS. It was found that current response surges in a linear way with increasing Q.R. concentration from 0.015 µM to 260 µM with less than 2 s of response time and a recognition limit of 0.0025 µM. To assess this sample's feasibility to be used as a sensor, Q.R. content was determined in different real samples comprising green drink, fresh apple, lamella, and reasonable results were achieved. The current study proposed a new approach for identifying Q.R. as well as a novel breed of electrochemical detecting material. • We synthesized highly active and structurally uniform electrometric polymeric carbon nitride (PCN). • 2,6-diaminoantandantquinone (DAQ) was integrated into PCN to enhance its photocatalytic properties. • As-synthesized samples were characterized by UV-Vis-spectroscopy, PL, XPS, NMR, EPR, XRD, FT-IR, BET, and SEM. • Copolymerized samples demonstrate superior performances towards electrocatalytic oxidation of quercetin (QR). [ABSTRACT FROM AUTHOR]