Photocatalytic Reduction of Hexavalent Chromium Using Cu3.21Bi4.79S9/g-C3N4 Nanocomposite

The photocatalytic reduction of hexavalent chromium, Cr(VI), to the trivalent species, Cr(III), has continued to inspire the synthesis of novel photocatalysts that are capable of achieving the task of converting Cr(VI) to the less toxic and more useful species. In this study, a novel functionalized graphitic carbon nitride (Cu3.21Bi4.79S9/gC3N4) was synthesized and characterized by using X-ray diffraction (XRD), thermogravimetry analysis (TGA), energy-dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), transmission electron microscope (TEM), and scanning electron microscope (SEM). The composite was used for the photocatalytic reduction of hexavalent chromium, Cr(VI), under visible light irradiation. A 92.77% efficiency of the reduction was achieved at pH 2, using about 10 mg of the photocatalyst and 10 mg/L of the Cr(VI) solution. A pseudo-first-order kinetic study indicated 0.0076 min−1, 0.0286 min−1, and 0.0393 min−1 rate constants for the nanoparticles, pristine gC3N4, and the nanocomposite, respectively. This indicated an enhancement in the rate of reduction by the functionalized gC3N4 by 1.37- and 5.17-fold compared to the pristine gC3N4 and Cu3.21Bi4.79S9, respectively. A study of how the presence of other contaminants including dye (bisphenol A) and heavy-metal ions (Ag(I) and Pb(II)) in the system affects the photocatalytic process showed a reduction in the rate from 0.0393 min−1 to 0.0019 min−1 and 0.0039 min−1, respectively. Finally, the radical scavenging experiments showed that the main active species for the photocatalytic reduction of Cr(VI) are electrons (e−), hydroxyl radicals (·OH−), and superoxide (·O2−). This study shows the potential of functionalized gC3N4 as sustainable materials in the removal of hexavalent Cr from an aqueous solution.

Self-assembly of colloidal single-layer carbon nitride

We introduce a new concept of a "bottom-to-top" design of intercalate carbon nitride compounds based on the effects of self-assembly of colloidal single-layer carbon nitride (SLCN) sheets stabilized by tetraethylammonium hydroxide NEt₄OH upon ambient drying of the water solvent. These effects include (i) formation of stage-1 intercalates of NEt₄OH during the ambient drying of SLCN colloids on glass substrates and (ii) the spontaneous formation of layered hexagonally-shaped networks of SLCN sheets on freshly-cleaved mica surfaces. The dynamics of the intercalate formation was followed by in situ X-ray diffraction allowing different stages to be identified, including the deposition of a primary "wet" intercalate of hydrated NEt₄OH and the gradual elimination of excessive water during its ambient drying. The intercalated NEt₄⁺ cations show a specific "flattened" conformation allowing the dynamics of formation and structure of the intercalate to be probed by vibrational spectroscopies. The two-dimensional self-assembly on mica is assumed to be driven both by the internal hexagonal symmetry of heptazine units and by a templating effect of the mica surface.

Semiconducting Soft Submicron Particles from the Microwave-Driven Polymerization of Diaminomaleonitrile

The polymers based on diaminomaleonitrile (DAMN polymers) are a special group within an extensive set of complex substances, namely HCN polymers (DAMN is the formal tetramer of the HCN), which currently present a growing interest in materials science. Recently, the thermal polymerizability of DAMN has been reported, both in an aqueous medium and in bulk, offering the potential for the development of capacitors and biosensors, respectively. In the present work, the polymerization of this plausible prebiotic molecule has been hydrothermally explored using microwave radiation (MWR) via the heating of aqueous DAMN suspensions at 170–190 °C. In this way, polymeric submicron particles derived from DAMN were obtained for the first time. The structural, thermal decomposition, and electrochemical properties were also deeply evaluated. The redox behavior was characterized from DMSO solutions of these highly conjugated macromolecular systems and their potential as semiconductors was described. As a result, new semiconducting polymeric submicron particles were synthetized using a very fast, easy, highly robust, and green-solvent process. These results show a new example of the great potential of the polymerization assisted by MWR associated with the HCN-derived polymers, which has a dual interest both in chemical evolution and as functional materials.

Synthesis of vacant graphitic carbon nitride in argon atmosphere and its utilization for photocatalytic hydrogen generation

Graphitic carbon nitride (C₃N₄) was synthesised from melamine at 550 °C for 4 h in the argon atmosphere and then was reheated for 1–3 h at 500 °C in argon. Two band gaps of 2.04 eV and 2.47 eV were observed in all the synthetized materials. Based on the results of elemental and photoluminescence analyses, the lower band gap was found to be caused by the formation of vacancies. Specific surface areas of the synthetized materials were 15–18 m²g⁻¹ indicating that no thermal exfoliation occurred. The photocatalytic activity of these materials was tested for hydrogen generation. The best photocatalyst showed 3 times higher performance (1547 μmol/g) than bulk C₃N₄ synthetized in the air (547 μmol/g). This higher activity was explained by the presence of carbon (V_C) and nitrogen (V_N) vacancies grouped in their big complexes 2V_C + 2V_N (observed by positron annihilation spectroscopy). The effect of an inert gas on the synthesis of C₃N₄ was demonstrated using Graham´s law of ammonia diffusion. This study showed that the synthesis of C₃N₄ from nitrogen-rich precursors in the argon atmosphere led to the formation of vacancy complexes beneficial for hydrogen generation, which was not referred so far.

Elucidation of Metal Local Environments in Single-Atom Catalysts Based on Carbon Nitrides

The ability to tailor the properties of metal centers in single-atom heterogeneous catalysts depends on the availability of advanced approaches for characterization of their structure. Except for specific host materials with well-defined metal adsorption sites, determining the local atomic environment remains a crucial challenge, often relying heavily on simulations. This article reports an advanced analysis of platinum atoms stabilized on poly(triazine imide), a nanocrystalline form of carbon nitride. The approach discriminates the distribution of surface coordination sites in the host, the evolution of metal coordination at different stages during the synthesis of the material, and the potential locations of metal atoms within the lattice. Consistent with density functional theory predictions, simultaneous high-resolution imaging in high-angle annular dark field and bright field modes experimentally confirms the preferred localization of platinum in-plane in the corners of the triangular cavities. X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and dynamic nuclear polarization enhanced ¹⁵ N nuclear magnetic resonance (DNP-NMR) spectroscopies coupled with density functional theory (DFT) simulations reveal that the predominant metal species comprise Pt(II) bound to three nitrogen atoms and one chlorine atom inside the coordination sites. The findings, which narrow the gap between experimental and theoretical elucidation, contribute to the improved structural understanding and provide a benchmark for exploring the speciation of single-atom catalysts based on carbon nitrides.

Developing Benign Ni/g-C3N4 Catalysts for CO2 Hydrogenation: Activity and Toxicity Study

This research discusses the CO2 valorization via hydrogenation over the non-noble metal clusters of Ni and Cu supported on graphitic carbon nitride (g-C3N4). The Ni and Cu catalysts were characterized by conventional techniques including XRD, AFM, ATR, Raman imaging, and TPR and were tested via the hydrogenation of CO2 at 1 bar. The transition-metal-based catalyst designed with atom-economy principles presents stable activity and good conversions for the studied processes. At 1 bar, the rise in operating temperature during CO2 hydrogenation increases the CO2 conversion and the selectivity for CO and decreases the selectivity for methanol on Cu/CN catalysts. For the Ni/CN catalyst, the selectivity to light hydrocarbons, such as CH4, also increased with rising temperature. At 623 K, the conversion attained ca. 20%, with CH4 being the primary product of the reaction (CH4 yield >80%). Above 700 K, the Ni/CN activity increases, reaching almost equilibrium values, although the Ni loading in Ni/CN is lower by more than 90% compared to the reference NiREF catalyst. The presented data offer a better understanding of the effect of the transition metals' small metal cluster and their coordination and stabilization within g-C3N4, contributing to the rational hybrid catalyst design with a less-toxic impact on the environment and health. Bare g-C3N4 is shown as a good support candidate for atom-economy-designed catalysts for hydrogenation application. In addition, cytotoxicity to the keratinocyte human HaCaT cell line revealed that low concentrations of catalysts particles (to 6.25 μg mL-1) did not cause degenerative changes.

Structure-Activity Relationship of Carbon Nitride Dots in Inhibiting Tau Aggregation

Due to the numerous failed clinical trials of anti-amyloid drugs, microtubule associated protein tau (MAPT) now stands out as one of the most promising targets for AD therapy. In this study, we report for the first time the structure-dependent MAPT aggregation inhibition of carbon nitride dots (CNDs). CNDs have exhibited great promise as a potential treatment of Alzheimer's disease (AD) by inhibiting the aggregation of MAPT. In order to elucidate its structure-activity relationship, CNDs were separated via column chromatography and five fractions with different structures were obtained that were characterized by multiple spectroscopy methods. The increase of surface hydrophilic functional groups is consistent with the increase of polarity from fraction 1 to 5. Particle sizes (1-2 nm) and zeta potentials (~-20 mV) are similar among five fractions. With the increase of polarity from fraction 1 to 5, their MAPT aggregation inhibition capacity was weakened. This suggests hydrophobic interactions between CNDs and MAPT, validated via molecular dynamics simulations. With a zebrafish blood-brain barrier (BBB) model, CNDs were observed to cross the BBB through passive diffusion. CNDs were also found to inhibit the generation of multiple reactive oxygen species, which is an important contributor to AD pathogenesis.

Nitrobenzene inarched carbon nitride nanotube drives efficient directional carriers separation for superior photocatalytic hydrogen production

Carbon nitride (g-C₃N₄) is aussichtsreich for photocatalytic hydrogen evolution, but its photocatalytic activity is not ideal due to the existence of photogenerated electrons and holes in the form of excitons. Herein, a novel nitrobenzene inarched g-C₃N₄ nanotube photocatalyst (CN-DNP) was firstly fabricated via a facial copolymerization method. The aromatic ring in nitrobenzene could enhance the conjugation of carbon nitride to promote electron delocalization. The nitro group enabled electrons to transfer from center to the both ends of g-C₃N₄ nanotube, which drove the separation of photogenerated electrons and holes more effectively. Compared with bulk g-C₃N₄ (CN), CN-DNP had narrower bandgap that can acquire adequate visible light harvesting and improve its photocatalytic performance. Consequently, CN-DNP0.1 displayed an excellent photocatalytic H₂ evolution of 2262.4 μmol g^-1h^-1, which was 11.2 folds higher than that of CN. This strategy provides a new guidance for constructing carbon nitride nanotube materials with carrier directional transfer to enhance the photocatalytic performance.

Ab Initio Electronic Structure Study of the Photoinduced Reduction of Carbon Dioxide with the Heptazinyl Radical

The photocatalytic conversion of carbon dioxide to liquid fuels with electrons taken from water with solar photons is one of the grand goals of renewable energy research. Polymeric carbon nitrides recently emerged as metal-free materials with promising functionalities for hydrogen evolution from water as well as the activation of carbon dioxide. Molecular heptazine (Hz), the building block of polymeric carbon nitrides, is one the strongest known organic photo-oxidants and has been shown to be able to photo-oxidize water with near-visible light, resulting in reduced (hydrogenated) heptazine (HzH) and OH radicals. In the present work, we explored with ab initio computational methods whether the HzH chromophore is able to reduce carbon dioxide to the hydroxy-formyl (HOCO) radical in hydrogen-bonded HzH-CO₂ complexes by the absorption of a photon. In remarkable contrast to the high barrier for carbon dioxide activation in the electronic ground state, the excited-state proton-coupled electron transfer (PCET) reaction is nearly barrierless, but requires the diabatic passage of three conical intersections. The possibility of barrierless carbon dioxide activation by excited-state PCET has so far not been taken into consideration in the interpretation of photocatalytic carbon dioxide reduction on carbon nitride materials.

Effect of Band Bending in Photoactive MOF-Based Heterojunctions

Semiconductor/metal-organic framework (MOF) heterojunctions have demonstrated promising performance for the photoconversion of CO₂ into value-added chemicals. To further improve performance, we must understand better the factors which govern charge transfer across the heterojunction interface. However, the effects of interfacial electric fields, which can drive or hinder electron flow, are not commonly investigated in MOF-based heterojunctions. In this study, we highlight the importance of interfacial band bending using two carbon nitride/MOF heterojunctions with either Co-ZIF-L or Ti-MIL-125-NH₂. Direct measurement of the electronic structures using X-ray photoelectron spectroscopy (XPS), work function, valence band, and band gap measurements led to the construction of a simple band model at the heterojunction interface. This model, based on the heterojunction components and band bending, enabled us to rationalize the photocatalytic enhancements and losses observed in MOF-based heterojunctions. Using the insight gained from a promising band bending diagram, we developed a Type II carbon nitride/MOF heterojunction with a 2-fold enhanced CO₂ photoreduction activity compared to the physical mixture.

2D Personality of Multifunctional Carbon Nitrides towards Enhanced Catalytic Performance in Energy Storage and Remediation

Numerous scholars in the scientific and management areas have been overly focused on contemporary breakthroughs in two-dimensional objects for multiple prospective applications. Photochemical and electrocatalytic functions of integrated circuits associated with multi-component tools have been enhanced by designing the macro- and microstructures of the building blocks. Therefore, the current research attempts to explore a larger spectrum of layered graphitic carbon nitrides (g-C3N4) and their derivatives as an efficient catalyst. By executing systematic manufacturing, optimization, and evaluation of its relevance towards astonishing energy storage devices, adsorption chemistry, and remediation, many researchers have focused on the coupling of such 2D carbon nitrides combined with suitable elementals. Hybrid carbon nitrides have been promoted as reliable 2D combinations for the enhanced electrophotocatalytic functionalities, proved by experimental observations and research outputs. By appreciating the modified structural, surface, and physicochemical characteristics of the carbon nitrides, we aim to report a systematic overview of the g-C3N4 materials for the application of energy storages and environments. It has altered energy band gap, thermal stability, remarkable dimensional texturing, and electrochemistry, and therefore detailed studies are highlighted by discussing the chemical architectures and atomic alternation of g-C3N4 (2D) structures.

Modelling of Electron and Thermal Transport in Quasi-Fractal Carbon Nitride Nanoribbons

In this work, using calculations based on the density functional theory, molecular dynamics, non-equilibrium Green functions method, and Monte Carlo simulation, we study electronic and phonon transport in a device based on quasi-fractal carbon nitride nanoribbons with Sierpinski triangle blocks. Modifications of electronic and thermal conductance with increase in generation g of quasi-fractal segments are estimated. Introducing energetic disorder, we study hopping electron transport in the quasi-fractal nanoribbons by Monte Carlo simulation of a biased random walk with generalized Miller–Abrahams transfer rates. Calculated time dependencies of the mean square displacement bear evidence of transient anomalous diffusion. Variations of anomalous drift-diffusion parameters with localization radius, temperature, electric field intensity, and energy disorder level are estimated. The hopping in quasi-fractal nanoribbons can serve as an explicit physical implementation of the generalized comb model.

New functionalisation reactions of graphitic carbon nitrides: Computational and experimental studies

The functionalisation of two-dimensional materials is key to modify their properties and facilitate assembly into functional devices. Here, new reactions have been proposed to modify crystalline two-dimensional carbon nitrides of polytriazine imide structure. Both amine alkylation and aryl-nitrene-based reactions have been explored computationally and with exploratory synthetic trials. The approach illustrates that alkylation is unfavourable, particularly at basal-plane sites. In contrast, while initial trial reactions were inconclusive, the radical-addition of nitrenes is shown to be energetically favourable, with a preference for functionalising sheet edges to minimise steric effects.

Synthesis of Vitamin B3 through a Heterogeneous Photocatalytic Approach Using Metal-Free Carbon Nitride-Based Catalysts

Vitamin B3 (nicotinic acid, VB3) was synthesized through the photocatalytic oxidation of 3-pyridinemethanol (3PM) under visible-light-emitting diode (LED) irradiation using metal-free graphitic carbon nitride (GCN) - based materials. A bulk (GCN) material was prepared by a simple thermal treatment using dicyandiamide as the precursor. A post-thermal treatment under static air and nitrogen flow was employed to obtain the GCN-T and GCN-T-N materials, respectively. The conditions adopted during the post-treatment revealed differences in the resulting materials' morphological, electronic, and optical properties. The post-treated photocatalysts revealed an enhanced efficiency in the oxidation of 3PM into VB3, with the GCN-T-N photocatalyst being the best-performing material. The defective surface, reduced crystallinity, and superior photoabsorption of GCN-T-N account for this material's improved performance in the production of VB3. Nevertheless, the presence of nitrogen vacancies in the carbon nitride structure and, consequently, the creation of mid-gap states also accounts to its highly oxidative ability. The immobilization of GCN-T-N in sodium alginate hydrogel was revealed as a promising strategy to produce VB3, avoiding the need for the photocatalyst separation step. Concerning the mechanism of synthesis of VB3 through the photocatalytic oxidation of 3PM, it was possible to identify the presence of 3-pyridinecarboxaldehyde (3PC) as the intermediary product.

Synthesis of CxNy-rich polycyclic oligomers from primeval monomers in aqueous media

A multichannel, non-thermolytic and efficient pathway is described toward the formation of functionalized carbon nitride-like oligomers, starting from readily available cyanamide and glyoxal (in ratios >2), in aqueous media under mild conditions. Such oligomers can be isolated as stable solids that result from structures involving cyanamide self-additions along with structures formally derived from the condensation of cyanamide, dicyandiamide or melamine with glyoxal, leading occasionally to oxygen-containing units. The oligomeric aggregates have masses up to 500 u, as inferred from mass spectra analyses, and their formation can be rationalized in terms of polyadditions of cyanamide (up to 10-mer) and glyoxal. The latter is not only a willing reaction partner, but also promotes facile condensation by enhancing the reactivity of nitrile fragments and inducing a significant lowering of the energy barriers. This mechanistic surmise is also supported by DFT calculations of the early condensation steps. As a result, melamine/triazine-type structures are obtained in aquatic environments under much milder conditions than those usually required by other synthetic procedures. Moreover, our results also help unveil the abiotic processes affording complex organic matter on celestial bodies and early earth.

Monodisperse Carbon Nitride Nanosheets as Multifunctional Additives for Efficient and Durable Perovskite Solar Cells

Two-dimensional (2D) materials are promising components for defect passivation of metal halide perovskites. Unfortunately, commonly used polydisperse liquid-exfoliated 2D materials generally suffer from heterogeneous structures and properties while incorporated into perovskite films. We introduce monodisperse multifunctional 2D crystalline carbon nitride, poly(triazine imide) (PTI), as an effective defect passivation agent in perovskite films via typical solution processing. Incorporation of PTI into perovskite film can be readily attained by simple solution mixing of PTI dispersions with perovskite precursor solutions, resulting in the highly selective distribution of PTI localized at the defective crystal grain boundaries and layer interfaces in the functional perovskite layer. Several chemical, optical, and electronic characterizations, in conjunction with density functional theory calculations, reveal multiple beneficial roles from PTI: passivation of undercoordinated organic cations at the surface of perovskite crystal, suppression of ion migration by blocking diffusion channels, and prevention of hole quenching at perovskite/SnO₂ interfaces. Consequently, a noticeably improved power conversion efficiency is achieved in perovskite solar cells, accompanied with promoted stability under humid air and thermal stress. Our strategy highlights the potential of judiciously designed 2D materials as a simple-to-implement material for various optoelectronic devices, including solar cells, based on hybrid perovskites.

A top-down design for easy gram scale synthesis of melem nano rectangular prisms with improved surface area

An unprecedented top-down design for the preparation of melem by 1 h stirring of melamine-based g-C₃N₄ in 80 °C concentrated sulfuric acid (95-98%) was discovered. The melem product was formed selectively as a monomer on the gram scale without the need for controlled conditions, inert atmosphere, and a special purification technique. The as-prepared air-stable melem showed a distinctive nano rectangular prism morphology that possesses a larger surface area than the melems achieved by traditional bottom-up designs making it a promising candidate for catalysis and adsorption processes.

Two-dimensional Dirac half-metal in porous carbon nitride C6N7monolayer via atomic doping

Motivated by the recent experimental discovery of C₆N₇monolayer (Zhaoet al2021Science Bulletin66, 1764), we show that C₆N₇monolayer co-doped with C atom is a Dirac half-metal by employing first-principle density functional theory calculations. The structural, mechanical, electronic and magnetic properties of the co-doped C₆N₇are investigated by both the PBE and HSE06 functionals. Pristine C₆N₇monolayer is a semiconductor with almost isotropic electronic dispersion around the Γ point. As the doping of the C₆N₇takes place, the substitution of an N atom with a C atom transforms the monolayer into a dilute magnetic semiconductor, with the spin-up channel showing a band gap of 2.3 eV, while the spin-down channel exhibits a semimetallic phase with multiple Dirac points. The thermodynamic stability of the system is also checked out via AIMD simulations, showing the monolayer to be free of distortion at 500 K. The emergence of Dirac half-metal in carbon nitride monolayer via atomic doping reveals an exciting material platform for designing novel nanoelectronics and spintronics devices.

Pristine Graphic Carbon Nitride Quantum Dots for the Visualized Detection of Latent Fingerprints

User-friendly fingerprint powders, namely efficient, low-cost and nontoxic ones, are always desirable for the development of latent fingerprints (LFPs). Here, we described the use of pristine graphic carbon nitride quantum dots (g-C₃N₄ QDs) as a new kind of user-friendly fingerprint powder. The g-C₃N₄ QDs can be easily prepared from urea and sodium citrate precursors through low temperature solid-phase reaction. Due to their good optical properties and selective interactions with secretion residuals, the g-C₃N₄ QDs powders were exploited to develop LFPs on different substrates by the powder dusting technique. The LFP images on a plastic bag exhibited a high ridge and furrow contrast ratio, allowing for easy identification of level 1 - 3 details of LFPs. This work indicates that the g-C₃N₄ QD powders provide good performance for LFP visualization and is likely to be adopted for some applications in forensic investigations.

Phenyl-Modified Carbon Nitride Quantum Nanoflakes for Ultra-Highly Selective Sensing of Formic Acid: A Combined Experimental by QCM and Density Functional Theory Study

Formic acid (HCOOH) is an important intermediate in chemical synthesis, pharmaceuticals, the food industry, and leather tanning and is considered to be an effective hydrogen storage molecule. Direct contact with its vapor and its inhalation lead to burns, nerve injury, and dermatosis. Thus, it is critical to establish efficient sensing materials and devices for the rapid detection of HCOOH. In the present study, we introduce a chemical sensor based on a quartz crystal microbalance (QCM) sensor capable of detecting trace amounts of HCOOH. This sensor is composed of colloidal phenyl-terminated carbon nitride (Ph-g-C₃N₄) quantum nanoflakes prepared using a facile solid-state method involving the supramolecular preorganization technology. In contrast to other synthetic methods of modified carbon nitride materials, this approach requires no hard templates, hazardous chemicals, or hydrothermal treatments. Comprehensive characterization and density functional theory (DFT) calculations revealed that the QCM sensor designed and prepared here exhibits enhanced detection sensitivity and selectivity for volatile HCOOH, which originates from chemical and hydrogen-bonding interactions between HCOOH and the surface of Ph-g-C₃N₄. According to DFT results, HCOOH is located close to the cavity of the Ph-g-C₃N₄ unit, with bonding to graphitic carbon and pyridinic nitrogen atoms of the nanoflake. The sensitivity of the Ph-g-C₃N₄-nanoflake-based QCM sensor was found to be the highest (128.99 Hz ppm^-1) of the substances studied, with a limit of detection (LOD) of HCOOH down to a sub-ppm level of 80 ppb. This sensing technology based on phenyl-terminated attached-g-C₃N₄ nanoflakes establishes a simple, low-cost solution to improve the performance of QCM sensors for the effective discrimination of HCOOH, HCHO, and CH₃COOH vapors using smart electronic noses.

Development of metal-free layered semiconductors for 2D organic field-effect transistors

To this day, the active components of integrated circuits consist mostly of (semi-)metals. Concerns for raw material supply and pricing aside, the overreliance on (semi-)metals in electronics limits our abilities (i) to tune the properties and composition of the active components, (ii) to freely process their physical dimensions, and (iii) to expand their deployment to applications that require optical transparency, mechanical flexibility, and permeability. 2D organic semiconductors match these criteria more closely. In this review, we discuss a number of 2D organic materials that can facilitate charge transport across and in-between their π-conjugated layers as well as the challenges that arise from modulation and processing of organic polymer semiconductors in electronic devices such as organic field-effect transistors.

Energy landscapes of perfect and defective solids: from structure prediction to ion conduction

The energy landscape concept is increasingly valuable in understanding and unifying the structural, thermodynamic and dynamic properties of inorganic solids. We present a range of examples which include (i) structure prediction of new bulk phases including carbon nitrides, phosphorus carbides, LiMgF3 and low-density, ultra-flexible polymorphs of B2O3, (ii) prediction of graphene and related forms of ZnO, ZnS and other compounds which crystallise in the bulk with the wurtzite structure, (iii) solid solutions, (iv) understanding grossly non-stoichiometric oxides including the superionic phases of δ-Bi2O3 and BIMEVOX and the consequences for the mechanisms of ion transport in these fast ion conductors. In general, examination of the energy landscapes of disordered materials highlights the importance of local structural environments, rather than sole consideration of the average structure.

Optimized Synthesis of Solution-Processable Crystalline Poly(Triazine Imide) with Minimized Defects for OLED Application

Poly(triazine imide) (PTI) is a highly crystalline semiconductor, and though no techniques exist that enable synthesis of macroscopic monolayers of PTI, it is possible to study it in thin layer device applications that are compatible with its polycrystalline, nanoscale morphology. We find that the by‐product of conventional PTI synthesis is a C−C carbon‐rich phase that is detrimental for charge transport and photoluminescence. An optimized synthetic protocol yields a PTI material with an increased quantum yield, enabled photocurrent and electroluminescence. We report that protonation of the PTI structure happens preferentially at the pyridinic N atoms of the triazine rings, is accompanied by exfoliation of PTI layers, and contributes to increases in quantum yield and exciton lifetimes. This study describes structure–property relationships in PTI that link the nature of defects, their formation, and how to avoid them with the optical and electronic performance of PTI. On the basis of our findings, we create an OLED prototype with PTI as the active, metal‐free material.

Single-layer carbon nitride: synthesis, structure, photophysical/photochemical properties, and applications

This Perspective provides a critical summary of the current state of the art in the synthesis and properties of polyheptazine single-layer carbon nitride (SLCN). The summary combines the authors' research and literature reports on SLCN concerning the synthesis of single-layer polyheptazine sheets, light absorption and emission by SLCN, photochemical and photocatalytic properties of SLCN as well as examples of applications of SLCN sheets as "building blocks" in heterostructures with nanocrystalline semiconductors and metals. The Perspective is concluded with an outlook discussing the most promising directions for further studies and applications of SLCN and related composites.

A current overview of the oxidative desulfurization of fuels utilizing heat and solar light: from materials design to catalysis for clean energy

The ceaseless increase of pollution cases due to the tremendous consumption of fossil fuels has steered the world towards an environmental crisis and necessitated urgency to curtail noxious sulfur oxide emissions. Since the world is moving toward green chemistry, a fuel desulfurization process driven by clean technology is of paramount significance in the field of environmental remediation. Among the novel desulfurization techniques, the oxidative desulfurization (ODS) process has been intensively studied and is highlighted as the rising star to effectuate sulfur-free fuels due to its mild reaction conditions and remarkable desulfurization performances in the past decade. This critical review emphasizes the latest advances in thermal catalytic ODS and photocatalytic ODS related to the design and synthesis routes of myriad materials. This encompasses the engineering of metal oxides, ionic liquids, deep eutectic solvents, polyoxometalates, metal-organic frameworks, metal-free materials and their hybrids in the customization of advantageous properties in terms of morphology, topography, composition and electronic states. The essential connection between catalyst characteristics and performances in ODS will be critically discussed along with corresponding reaction mechanisms to provide thorough insight for shaping future research directions. The impacts of oxidant type, solvent type, temperature and other pivotal factors on the effectiveness of ODS are outlined. Finally, a summary of confronted challenges and future outlooks in the journey to ODS application is presented.

Tetramethylguanidine-functionalized melamine as a multifunctional organocatalyst for the expeditious synthesis of 1,2,4-triazoloquinazolinones

Novel nano-ordered 1,1,3,3-tetramethylguanidine-functionalized melamine (Melamine@TMG) organocatalyst was prepared and adequately identified by various techniques including FTIR, EDX, XRD and SEM spectroscopic or microscopic methods as well as TGA and DTG analytical methods. The Melamine@TMG, as an effective multifunctional organocatalyst, was found to promote smoothly the three-component synthesis of 1,2,4-triazoloquinazolinone derivatives using cyclic dimedone, 3-amino-1,2,4-triazole and different benzaldehyde derivatives in EtOH at 40 °C. This practical method afforded the desired products in high to excellent yields (86-99%) and short reaction times (10-25 min). The main advantages of this new method are the use of heterogeneous multifunctional nanocatalyst, simple work-up procedure with no need for chromatographic purification, highly selective conversion of substrates and recyclability of the catalyst, which could be used in five consecutive runs with only a small decrease in its activity.

A comparison study of sodium ion- and potassium ion-modified graphitic carbon nitride for photocatalytic hydrogen evolution

It is well known that modifying graphitic carbon nitride (GCN) is an imperative strategy to improve its photocatalytic activity. In this study, Na-doped and K-doped graphitic carbon nitride (GCN-Na and GCN-K) were prepared via the simple thermal polymerization of a mixture of melamine and NaCl or KCl, respectively. The structure characterization showed that both Na⁺ and K⁺ intercalation could reduce the interlayer distance of GCN and introduce cyano defects in GCN, while K⁺ apparently had a stronger influence on the structure variation of GCN. The chemical composition data showed that both Na⁺ and K⁺ could easily interact with GCN, while K-doping caused a greater change in the C/N ratio than Na-doping. Moreover, compared to GCN-Na-5 (5 represents weight ratio of alkali halide to melamine), the conduction and valence bands of GCN-K-5 both shifted upward based on the electronic and optical measurements. Consequently, GCN-K-5 yielded an H₂ evolution rate around 4 times higher than that of GCN-Na-5 under visible light irradiation (>420 nm). The cation size effect on GCN was proposed to be mainly responsible for the variation in the structure, optical and electronic properties of ion-doped GCNs, and hence the enhanced photocatalytic H₂ evolution. The current work can provide new insight into optimizing photocatalysts for enhanced photocatalytic performances.

The ion size effect on graphitic carbon nitride is responsible for variations in its structure, optical and electronic properties, and hence the enhancement in photocatalytic hydrogen evolution.

Pt nanoparticles embedded spine-like g-C3N4 nanostructures with superior photocatalytic activity for H2 generation and CO2 reduction

Conventional two-dimensional (2D) graphitic carbon nitride, 2D g-C₃N₄ with its layered structures and flat and smooth 2D surface possesses certain disadvantages that is affecting their photocatalytic performances. In this paper, new nanostructured spine-like three-dimensional (3D) g-C₃N₄ nanostructures are created for the first time via a new three-step synthesis method. In this method, self-assembly of layered precursors and H⁺ intercalation introduced by acid treatment play an important role for the unique nanostructure formation of 3D g-C₃N₄ nanostructures. The spine-like 3D g-C₃N₄ nanostructures show a superior photocatalytic performance for H₂ generation, achieving 4500 μmol·g^-1·h^-1, 8.2 times higher than that on conventional 2D g-C₃N₄. Remarkably spine-like 3D g-C₃N₄ nanostructures demonstrate a clear photocatalytic activity toward CO₂ reduction to CH₄ (0.71 μmol·g^-1·h^-1) in contrast to the negligible photocatalytic performance of conventional 2D g-C₃N₄ for the reaction. Adding Pt clusters as co-catalysts substantially enhance the CH₄ generation rate of the 3D g-C₃N₄ nanostructures by 4 times (2.7 μmol·g^-1·h^-1). Spine-like 3D g-C₃N₄ caged nanostructure leads to the significantly increased active sites and negatively shifted conduction band position in comparison with conventional 2D g-C₃N₄, favorable for the photocatalytic reduction reaction. This study demonstrates a new platform for the development of efficient photocatalysts based on nanostructured 3D g-C₃N₄ for H₂ generation and conversion of CO₂ to useful fuels such as CH₄.

Tailoring surface-supported water-melamine complexes by cooperative H-bonding interactions

The water-splitting photo-catalysis by carbon nitride heterocycles has been the subject of recent theoretical investigations, revealing a proton-coupled electron transfer (PCET) reaction from the H-bonded water molecule to the CN-heterocycle. In this context, a detailed characterization of the water-catalyst binding configuration becomes mandatory in order to validate and possibly improve the theoretical modeling. To this aim, we built a well-defined surface-supported water/catalyst interface by adsorbing water under ultra-high vacuum (UHV) conditions on a monolayer of melamine grown on the Cu(111) surface. By combining X-ray photoemission (XPS) and absorption (NEXAFS) spectroscopy we observed that melamine adsorbed onto copper is strongly tilted off the surface, with one amino group dangling to the vacuum side. The binding energy (BE) of the corresponding N 1s component is significantly higher compared to other N 1s contributions and displays a clear shift to lower BE as water is adsorbed. This finding along with density functional theory (DFT) results reveals that two adjacent melamine molecules concurrently work for stabilizing the H-bonded water-catalyst complex: one melamine acting as a H-donor via the amino-N (NH⋯OHH) and another one as a H-acceptor via the triazine-N (C[double bond, length as m-dash]N⋯HOH).

Understanding the role of soft linkers in designing hepatzine-based polymeric frameworks as heterogeneous (photo)catalyst

The emerging class of heptazine-based polymeric materials has shown potential candidature as photocatalyst materials for hydrogen evolution. At the same time, they have shown promising application as solid base materials to catalyse various organic transformations. Thus, the material design rationale needs to be developed around the heptazine-based polymeric frameworks in order to specifically design task specific materials. Herein, we utilised controlled reaction conditions to synthesize the desired polymeric networks with trichloroheptazine as precursor. Material design strategy employed nitrogen rich [tris(2-aminoethylamine) and hydrazine] as soft linkers to understand the effect on band structure of developed heptazine-based polymeric networks. The developed polymeric networks were explored as platform to study systematically the effect on their respective photophysical properties and understand their surface basicity. The framework having aminoalkyl linker showed superior activity in photocatalysis as well as heterogeneous base catalysis. Further, model catalysts revealed the importance of N-atoms as active basic sites in these systems.

Visible-Light Promoted C-O Bond Formation with an Integrated Carbon Nitride-Nickel Heterogeneous Photocatalyst

Ni-deposited mesoporous graphitic carbon nitride (Ni-mpg-CNx) is introduced as an inexpensive, robust, easily synthesizable and recyclable material that functions as an integrated dual photocatalytic system. This material overcomes the need of expensive photosensitizers, organic ligands and additives as well as limitations of catalyst deactivation in the existing photo/Ni dual catalytic cross-coupling reactions. The dual catalytic Ni-mpg-CNx is demonstrated for C-O coupling between aryl halides and aliphatic alcohols under mild condition. The reaction affords the ether product in good-to-excellent yields (60-92 %) with broad substrate scope, including heteroaryl and aryl halides bearing electron-withdrawing, -donating and neutral groups. The heterogeneous Ni-mpg-CNx can be easily recovered from the reaction mixture and reused over multiple cycles without loss of activity. The findings highlight exciting opportunities for dual catalysis promoted by a fully heterogeneous system.

Visible-Light Promoted C-O Bond Formation with an Integrated Carbon Nitride-Nickel Heterogeneous Photocatalyst

Ni-deposited mesoporous graphitic carbon nitride (Ni-mpg-CNx ) is introduced as an inexpensive, robust, easily synthesizable and recyclable material that functions as an integrated dual photocatalytic system. This material overcomes the need of expensive photosensitizers, organic ligands and additives as well as limitations of catalyst deactivation in the existing photo/Ni dual catalytic cross-coupling reactions. The dual catalytic Ni-mpg-CNx is demonstrated for C-O coupling between aryl halides and aliphatic alcohols under mild condition. The reaction affords the ether product in good-to-excellent yields (60-92 %) with broad substrate scope, including heteroaryl and aryl halides bearing electron-withdrawing, -donating and neutral groups. The heterogeneous Ni-mpg-CNx can be easily recovered from the reaction mixture and reused over multiple cycles without loss of activity. The findings highlight exciting opportunities for dual catalysis promoted by a fully heterogeneous system.