Sol Processing of Conjugated Carbon Nitride Powders for Thin-Film Fabrication

Outstanding CO2 Photoreduction in Single-Atom Thulium Modified Carbon Nitride

CO2 reduction photocatalysts are favorable for obtaining renewable energy. Enriched active sites and effective photogenerated-carriers separation are keys for improving CO2 photo-reduction. A thulium (Tm) single atom tailoring strategy introducing carbon vacancies in porous tubular graphitic carbon nitride (g-C3N4) surpassing the ever-reported g-C3N4 based photocatalysts, with 199.47 µmol g-1 h-1 CO yield, 96.8% CO selectivity, 0.84% apparent quantum efficiency and excellent photocatalytic stability, is implemented in this work. Results revealed that in-plane Tm sites and interlayer-bridged Tm-N charge transfer channels significantly enhanced the aggregation/transfer of photogenerated electrons thus promoting CO2 adsorption/activation and contributing to *COOH intermediates formation. Meanwhile, Tm atoms and carbon vacancies both benefit for rich active sites and enhanced photogenerated-charge separation, thus optimizing reaction pathway and leading to excellent CO2 photo-reduction. This work not only provides guidelines for CO2 photo-reduction catalysts design but also offers mechanistic insights into single-atom based photocatalysts for solar fuel production.

Carbon Nanotubes as a Solid-State Electron Mediator for Visible-Light-Driven Z-Scheme Overall Water Splitting

So-called Z-scheme systems, which typically comprise an H2 evolution photocatalyst (HEP), an O2 evolution photocatalyst (OEP), and an electron mediator, represent a promising approach to solar hydrogen production via photocatalytic overall water splitting (OWS). The electron mediator transferring photogenerated charges between the HEP and OEP governs the performance of such systems. However, existing electron mediators suffer from low stability, corrosiveness to the photocatalysts, and parasitic light absorption. In the present work, carbon nanotubes (CNTs) were shown to function as an effective solid-state electron mediator in a Z-scheme OWS system. Based on the high stability and good charge transfer characteristics of CNTs, this system exhibited superior OWS performance compared with other systems using more common electron mediators. The as-constructed system evolved stoichiometric amounts of H2 and O2 at near-ambient pressure with a solar-to-hydrogen energy conversion efficiency of 0.15%. The OWS reaction was also promoted in the case that this CNT-based Z-scheme system was immobilized on a substrate. Hence, CNTs are a viable electron mediator material for large-scale Z-scheme OWS systems.

Large-Scale Syntheses of Multicolor Stimulus Responsive Room-Temperature Phosphorescent Polymer-Carbonyl-Modified Carbon Nitrogen Quantum Dots

Carbonyl-modified solid-state carbon nitrogen quantum dots (m-O═CNQDs) have emerged as promising room-temperature phosphorescent (RTP) materials close to commercialization. However, high-crystallinity m-O═CNQDs are insensitive to external stimuli such as water and heat due to strong stacking interactions between layers, restricting their applications in stimulus responsive fields. Here, a polymer template space-confined growth strategy is established for the large-scale synthesis of water stimulus responsive polyvinylpyrrolidone-functionalized m-O═CNQDs with ultralong room-temperature phosphorescence (181 ms) using urea and PVP as precursors. Theoretical and experimental results indicate that the PVP template linked at the rim of m-O═CNQDs formed by in situ self-polymerization of urea inhibits interactions between layers and increases their affinity for water, which is the key to increasing their sensitivity with water. This strategy offers a new path for developing commercial stimulus responsive RTP materials.

Direct Growth of Polymeric Carbon Nitride Nanosheet Photoanode for Greatly Efficient Photoelectrochemical Water-Splitting

A general method for the direct synthesis of highly homogeneous and dense polymerized carbon nitride (PCN) nanosheet films on F: SnO2 (FTO) is developed. Detailed photoelectrochemical (PEC) water-splitting studies reveal that the as-synthesized PCN films exhibit outstanding performance as photoanode for PEC water-splitting. The optimal PCN photoanode exhibits excellent photocurrent density of 650 µA cm-2 , and monochromatic incident photon-to-electron conversion efficiency (IPCE) value up to 30.55% (λ = 400 nm) and 25.97% (λ = 420 nm) at 1.23 VRHE in 0.1 m KOH electrolyte. More importantly, the PCN photoanode has an excellent hole extraction efficiency of up to 70 ± 3% due to the abundance of active sites provided by the PCN photoanode nanosheet, which promotes the transport rates of OER-relevant species. These PCN films provide a new benchmark for PCN photoanode materials.

Radial Nano-Heterojunctions Consisting of CdS Nanorods Wrapped by 2D CN:PDI Polymer with Deep HOMO for Photo-Oxidative Water Splitting, Dye Degradation and Alcohol Oxidation

Solar energy harvesting using semiconductor photocatalysis offers an enticing solution to two of the biggest societal challenges, energy scarcity and environmental pollution. After decades of effort, no photocatalyst exists which can simultaneously meet the demand for excellent absorption, high quantum efficiency and photochemical resilience/durability. While CdS is an excellent photocatalyst for hydrogen evolution, pollutant degradation and organic synthesis, photocorrosion of CdS leads to the deactivation of the catalyst. Surface passivation of CdS with 2D graphitic carbon nitrides (CN) such as g-C₃N₄ and C₃N₅ has been shown to mitigate the photocorrosion problem but the poor oxidizing power of photogenerated holes in CN limits the utility of this approach for photooxidation reactions. We report the synthesis of exfoliated 2D nanosheets of a modified carbon nitride constituted of tris-s-triazine (C₆N₇) linked pyromellitic dianhydride polydiimide (CN:PDI) with a deep oxidative highest occupied molecular orbital (HOMO) position, which ensures sufficient oxidizing power for photogenerated holes in CN. The heterojunction formed by the wrapping of mono-/few layered CN:PDI on CdS nanorods (CdS/CN:PDI) was determined to be an excellent photocatalyst for oxidation reactions including photoelectrochemical water splitting, dye decolorization and the photocatalytic conversion of benzyl alcohol to benzaldehyde. Extensive structural characterization using HR-TEM, Raman, XPS, etc., confirmed wrapping of few-layered CN:PDI on CdS nanorods. The increased photoactivity in CdS/CN:PDI catalyst was ascribed to facile electron transfer from CdS to CN:PDI in comparison to CdS/g-C₃N₄, leading to an increased electron density on the surface of the photocatalyst to drive chemical reactions.

Molecular assembly of carbon nitride-based composite membranes for photocatalytic sterilization and wound healing

A multifactorial mechanism for successful dissolution of polymeric carbon nitrides (pCN) was disclosed, enabling pCN to compound more advanced nanocomposites at the molecular level, beyond the traditional solar fuel applications in powders.

Design of few-layer carbon nitride/BiFeO3 composites for efficient organic pollutant photodegradation

Heterojunction-driven photocatalysis can degrade various organic pollutants, and developing carbon nitride-based composite photocatalysts is of great significance and gains growing interest. In this study, a two-dimensional graphitic carbon nitride nanosheets/BiFeO₃ (GCNNs/BiFeO₃) Z-scheme heterojunction has been synthesized through the electrostatic spinning and post-calcination The obtained GCNNs/BiFeO₃ nanofibers show large surface contact between GCNNs the and BiFeO₃ nanostructures. The Z-scheme heterojunction shows a remarkably enhanced photocatalytic performance, which could degrade 94% of tetracycline (TC) and 88% of Rhodamine B (RhB) under LED visible light irradiation in 150 min. Radical trapping experiments demonstrate the effective construction of Z-scheme heterojunctions, and •O₂^- and h⁺ are the main active species in the photocatalytic degradation process. This study realizes a novel nanostructured GCNNs/BiFeO₃ heterojunction for photodegradation applications, which would guide the design of next-generation efficient photocatalysts.

Smart apparel using nano graphitic carbon nitride/PVA in a cotton cloth for military application

An eco-friendly, low-cost smart attire was made of metal-free graphitic carbon nitride (GCN) as a semiconductor material in a biodegradable synthetic polymer (polyvinyl alcohol) and cotton material. Various concentrations such as 0.04, 0.08, 0.12, 0.16, and 0.2 weight percentage of GCN is entrenched in PVA. UV absorption spectra displayed two peaks, one matching PVA (317 nm) and the other excitonic peak of GCN (390 nm).0.2% GCN in PVA showed a low bandgap (2.84 eV) harnessing maximum solar light. Due to the charge transfer mechanism, enhanced blue emission at 450 nm was observed for the higher concentration of graphitic carbon nitride. Due to more defect centers of higher weight percentage of GCN, higher electrical conductivity (7.6462 × 10⁻³ S/cm) and optical conductivity (0.113 S) were noticed. Due to the higher conductivity of 5GCN, it was embedded with cotton fabric. The fabricated smart apparel can be used to manufacture flexible, lightweight, eco-friendly optoelectronic devices. Further, according to literature, GCN possesses high antibacterial activity, hence it can serve as clothing for the military and medical community.

Protonated g-C3N4 coated Co9S8 heterojunction for photocatalytic H2O2 production

Photocatalytic H₂O₂ production is an eco-friendly technique because only H₂O, molecular O₂ and light are involved. However, it still confronts the challenges of the unsatisfactory productivity of H₂O₂ and the dependence on organic electron donors or high purity O₂, which restrict the practical application. Herein, we construct a type-II heterojunction of the protonated g-C₃N₄ coated Co₉S₈ semiconductor for photocatalytic H₂O₂ production. The ultrathin g-C₃N₄ uniformly spreads on the surface of the dispersed Co₉S₈ nanosheets by a two-step method of protonation and dip-coating, and exhibits improved photogenerated electrons transportability and e^--h⁺ pairs separation ability. The photocatalytic system can achieve a considerable productivity of H₂O₂ to 2.17 mM for 5 h in alkaline medium in the absence of the organic electron donors and pure O₂. The optimal photocatalyst also obtains the highest apparent quantum yield (AQY) of 18.10% under 450 nm of light irradiation, as well as a good reusability. The contribution of the type-II heterojunction is that the migrations of electrons and holes within the interface between g-C₃N₄ and Co₉S₈ matrix promote the separation of photocarriers, and another channel is also opened for H₂O₂ generation. The accumulated electrons in conduction band (CB) of Co₉S₈ contribute to the major channel of two-electron reduction of O₂ for H₂O₂ production. Meanwhile, the electrons in CB of g-C₃N₄ participate in the single electron reduction of O₂ as an auxiliary channel to enhance the H₂O₂ production.

Recent Progress on Photoelectrochemical Water Splitting of Graphitic Carbon Nitride (g−CN) Electrodes

Graphitic carbon nitride (g−CN), a promising visible-light-responsive semiconductor material, is regarded as a fascinating photocatalyst and heterogeneous catalyst for various reactions due to its non-toxicity, high thermal durability and chemical durability, and “earth-abundant” nature. However, practical applications of g−CN in photoelectrochemical (PEC) and photoelectronic devices are still in the early stages of development due to the difficulties in fabricating high-quality g−CN layers on substrates, wide band gaps, high charge-recombination rates, and low electronic conductivity. Various fabrication and modification strategies of g−CN-based films have been reported. This review summarizes the latest progress related to the growth and modification of high-quality g−CN-based films. Furthermore, (1) the classification of synthetic pathways for the preparation of g−CN films, (2) functionalization of g−CN films at an atomic level (elemental doping) and molecular level (copolymerization), (3) modification of g−CN films with a co-catalyst, and (4) composite films fabricating, will be discussed in detail. Last but not least, this review will conclude with a summary and some invigorating viewpoints on the key challenges and future developments.

Photocatalytic degradation of pharmaceuticals by pore-structured graphitic carbon nitride with carbon vacancy in water: Identification of intermediate degradants and effects of active species

Pharmaceuticals are increasingly used in daily life and have been massively discharged to the aquatic environment. The removal of pharmaceuticals from water by various nanomaterials including graphitic carbon nitride (g-C₃N₄) has received extensive attention. Herein, we synthesized a carbon-defective carbon nitride with pore structure through a simple thermal polymerization method for photodegradation of lidocaine, mepivacaine and ropivacaine (typical amide local anesthetics). The results showed that the degradation process conformed to the pseudo-first-order reaction kinetics, and the degradation rate constant of organic pollutants using CCN-600 (i.e., g-C₃N₄ synthesized at 600 °C) reached 5.05 × 10^-2 min^-1, about 2.5 times higher than that of the prototype g-C₃N₄ (2.09 × 10^-2 min^-1). The capture experiment of active species and the electron paramagnetic resonance (EPR) test demonstrated that superoxide radical (O₂^-) played a major role in the degradation process. Based on the possible photodegraded intermediate products identified, the degradation pathways were deduced. This study provides not only a new strategy for fabrication of pore-structured g-C₃N₄ with carbon vacancy, but also a reference method for the treatment of pharmaceuticals in water bodies.

Enhanced biological nitrate removal by gC3N4/TiO2 composite and role of extracellular polymeric substances

The biological denitrification in the presence of gC₃N₄ doped TiO₂ composite was investigated through series of batch experiment. gC₃N₄ doped TiO₂ was synthesized and characterized by FT-IR, XRD, SEM-EDAX and the prepared composite used as electron donor for the enhancement biological denitrification. The role of extracellular polymeric substances in the biological nitrate reduction and electron transfer process has been elucidated. The XRD result confirms that TiO₂ nanoparticle has 80% anatase and 20% rutile phase. The gC₃N₄ shows the diffraction peaks at 27.57°, corresponds to the diffraction planes of (002) the hexagonal graphitic carbon nitride. The SEM image of modified gC₃N₄/TiO₂ nanocomposites showed agglomerated small spherical TiO₂ nanoparticles attached on the surface of gC3N4. The highest level of nitrate removal was 90% (from 100 mg/L to 10 mg/L nitrate) in gC3N4/TiO2 nanocomposite in the 15% wt TiO₂ doped gC3N4. The nitrate reduction in the biofilm with gC₃N₄ doped TiO₂ composite have significantly enhanced the nitrate reduction than the control. Photoexcited electrons were generated from gC₃N₄ doped TiO₂ photocatalyst act as excellent electron donor to the microbial communities. Extracellular polymeric substances acted as a passing media for microbial extracellular electron transfer and protective barrier for microbes. The electroactive microbes were harvested electrons from the gC₃N₄ doped TiO₂ composite under irradiation and enhancing the biological nitrate reduction. Overall, the present study suggests that insight into the mechanism of photoexcited electron facilitated biological nitrate reduction and role of extracellular polymeric substances. The successful integration of gC₃N₄ doped TiO₂ photocatalyst and biofilm is a promising technology for nitrate removal.

Semiconducting Polymers for Oxygen Evolution Reaction under Light Illumination

Sunlight-driven water splitting to produce hydrogen fuel has stimulated intensive scientific interest, as this technology has the potential to revolutionize fossil fuel-based energy systems in modern society. The oxygen evolution reaction (OER) determines the performance of overall water splitting owing to its sluggish kinetics with multielectron transfer processing. Polymeric photocatalysts have recently been developed for the OER, and substantial progress has been realized in this emerging research field. In this Review, the focus is on the photocatalytic technologies and materials of polymeric photocatalysts for the OER. Two practical systems, namely, particle suspension systems and film-based photoelectrochemical systems, form two main sections. The concept is reviewed in terms of thermodynamics and kinetics, and polymeric photocatalysts are discussed based on three key characteristics, namely, light absorption, charge separation and transfer, and surface oxidation reactions. A satisfactory OER performance by polymeric photocatalysts will eventually offer a platform to achieve overall water splitting and other advanced applications in a cost-effective, sustainable, and renewable manner using solar energy.

2D-C3N4 encapsulated perovskite nanocrystals for efficient photo-assisted thermocatalytic CO2 reduction

Very recently, halide perovskites, especially all-inorganic CsPbBr₃, have received ever-increasing attention in photocatalysis owing to their superior optoelectronic properties and thermal stability. However, there is a lack of study on their application in thermocatalysis and photo-thermocatalysis. Herein, we rationally designed a core–shell heterojunction formed by encapsulating CsPbBr₃ nanoparticles with the 2D C₃N₄ (m-CN) layer via a solid-state reaction (denoted as m-CN@CsPbBr₃). A series of experiments suggest that abundant adsorption and active sites of CO₂ molecules as well as polar surfaces were obtained by utilizing m-CN-coated CsPbBr₃, resulting in significant improvement in CO₂ capture and charge separation. It is found that the m-CN@CsPbBr₃ effectively drives the thermocatalytic reduction of CO₂ in H₂O vapor. By coupling light into the system, the activity for CO₂-to-CO reduction is further improved with a yield up to 42.8 μmol g⁻¹ h⁻¹ at 150 °C, which is 8.4 and 2.3 times those of pure photocatalysis (5.1 μmol g⁻¹ h⁻¹) and thermocatalysis (18.7 μmol g⁻¹ h⁻¹), respectively. This work expands the application of general halide perovskites and provides guidance for using perovskite-based catalysts for photo-assisted thermocatalytic CO₂ reduction.

A water-stable CsPbBr₃ catalyst is designed using core–shell encapsulation of the perovskite nanoparticle by 2D-C₃N₄ for photo-assisted thermocatalytic CO₂ reduction by H₂O. The m-CN@CsPbBr₃ heterojunction shows surprisingly high CO₂-to-CO yield.

Exfoliation-induced O-doped g-C3N4 Nanosheets with improved photoreactivity towards RhB degradation and H2 evolution

Graphitic carbon nitride (g-C3N4) nanosheets exfoliated from bulk-sized counterparts are limited by quantum size effect-induced widened bandgap. In this work, a (NH4)2S2O8 (APS) induced thermal exfoliation approach is introduced to...

Recent advances in photocatalytic remediation of emerging organic pollutants using semiconducting metal oxides: an overview

Many untreated and partly treated wastewater from the home and commercial resources is being discharged into the aquatic environment these days, which contains numerous unknown and complex natural and inorganic compounds. These compounds tend to persist, initiating severe environmental problems, which affect human health. Conventionally, physicochemical treatment methods were adopted to remove such complex organic chemicals, but they suffer from critical limitations. Over time, photocatalysis, an advanced oxidation process, has gained its position for its efficient and fair performance against emerging organic pollutant decontamination. Typically, photocatalysis is a green technology to decompose organics under UV/visible light at ambient conditions. Semiconducting nanometal oxides have emerged as pioneering photocatalysts because of large active surface sites, flexible oxidation states, various morphologies, and easy preparation. The current review presents an overview of emerging organic pollutants and their effects, advanced oxidation processes, photocatalytic mechanism, types of photocatalysts, photocatalyst support materials, and methods for improving photodegradation efficiency on the degradation of complex emerging organic pollutants. In addition, the recent reports of metal-oxide-driven photocatalytic remediation of emerging organic pollutants are presented in brief. This review is anticipated to reach a broader scientific community to understand the first principles of photocatalysis and review the recent advancements in this field.

Photocatalytic Air Purification Using Functional Polymeric Carbon Nitrides

The techniques for the production of the environment have received attention because of the increasing air pollution, which results in a negative impact on the living environment of mankind. Over the decades, burgeoning interest in polymeric carbon nitride (PCN) based photocatalysts for heterogeneous catalysis of air pollutants has been witnessed, which is improved by harvesting visible light, layered/defective structures, functional groups, suitable/adjustable band positions, and existing Lewis basic sites. PCN-based photocatalytic air purification can reduce the negative impacts of the emission of air pollutants and convert the undesirable and harmful materials into value-added or nontoxic, or low-toxic chemicals. However, based on previous reports, the systematic summary and analysis of PCN-based photocatalysts in the catalytic elimination of air pollutants have not been reported. The research progress of functional PCN-based composite materials as photocatalysts for the removal of air pollutants is reviewed here. The working mechanisms of each enhancement modification are elucidated and discussed on structures (nanostructure, molecular structue, and composite) regarding their effects on light-absorption/utilization, reactant adsorption, intermediate/product desorption, charge kinetics, and reactive oxygen species production. Perspectives related to further challenges and directions as well as design strategies of PCN-based photocatalysts in the heterogeneous catalysis of air pollutants are also provided.

Thermal Analysis of Metal-Organic Precursors for Functional Cu:ΝiOx Hole Transporting Layer in Inverted Perovskite Solar Cells: Role of Solution Combustion Chemistry in Cu:ΝiOx Thin Films Processing

Low temperature solution combustion synthesis emerges as a facile method for the synthesis of functional metal oxides thin films for electronic applications. We study the solution combustion synthesis process of Cu:NiO_x using different molar ratios (w/o, 0.1 and 1.5) of fuel acetylacetone (Acac) to oxidizer (Cu, Ni Nitrates) as a function of thermal annealing temperatures 150, 200, and 300 °C. The solution combustion synthesis process, in both thin films and bulk Cu:NiO_x, is investigated. Thermal analysis studies using TGA and DTA reveal that the Cu:NiO_x thin films show a more gradual mass loss while the bulk Cu:NiO_x exhibits a distinct combustion process. The thin films can crystallize to Cu:NiO_x at an annealing temperature of 300 °C, irrespective of the Acac/Oxidizer ratio, whereas lower annealing temperatures (150 and 200 °C) produce amorphous materials. A detail characterization study of solution combustion synthesized Cu:NiO_x, including XPS, UV-Vis, AFM, and Contact angle measurements, is presented. Finally, 50 nm Cu:NiO_x thin films are introduced as HTLs within the inverted perovskite solar cell device architecture. The Cu:NiO_x HTL annealed at 150 and 200 °C provided PVSCs with limited functionality, whereas efficient triple-cation Cs_0.04(MA_0.17FA_0.83)_0.96 Pb(I_0.83Br_0.17)₃-based PVSCs achieved for Cu:NiO_x HTLs for annealing temperature of 300 °C.

Photocatalytic Mechanism Control and Study of Carrier Dynamics in CdS@C3N5 Core-Shell Nanowires

We present a potential solution to the problem of extraction of photogenerated holes from CdS nanocrystals and nanowires. The nanosheet form of C₃N₅ is a low-band-gap (E_g = 2.03 eV), azo-linked graphenic carbon nitride framework formed by the polymerization of melem hydrazine (MHP). C₃N₅ nanosheets were either wrapped around CdS nanorods (NRs) following the synthesis of pristine chalcogenide or intercalated among them by an in situ synthesis protocol to form two kinds of heterostructures, CdS-MHP and CdS-MHPINS, respectively. CdS-MHP improved the photocatalytic degradation rate of 4-nitrophenol by nearly an order of magnitude in comparison to bare CdS NRs. CdS-MHP also enhanced the sunlight-driven photocatalytic activity of bare CdS NWs for the decolorization of rhodamine B (RhB) by a remarkable 300% through the improved extraction and utilization of photogenerated holes due to surface passivation. More interestingly, CdS-MHP provided reaction pathway control over RhB degradation. In the absence of scavengers, CdS-MHP degraded RhB through the N-deethylation pathway. When either hole scavenger or electron scavenger was added to the RhB solution, the photocatalytic activity of CdS-MHP remained mostly unchanged, while the degradation mechanism shifted to the chromophore cleavage (cycloreversion) pathway. We investigated the optoelectronic properties of CdS-C₃N₅ heterojunctions using density functional theory (DFT) simulations, finite difference time domain (FDTD) simulations, time-resolved terahertz spectroscopy (TRTS), and photoconductivity measurements. TRTS indicated high carrier mobilities >450 cm² V^-1 s^-1 and carrier relaxation times >60 ps for CdS-MHP, while CdS-MHPINS exhibited much lower mobilities <150 cm² V^-1 s^-1 and short carrier relaxation times <20 ps. Hysteresis in the photoconductive J-V characteristics of CdS NWs disappeared in CdS-MHP, confirming surface passivation. Dispersion-corrected DFT simulations indicated a delocalized HOMO and a LUMO localized on C₃N₅ in CdS-MHP. C₃N₅, with its extended π-conjugation and low band gap, can function as a shuttle to extract carriers and excitons in nanostructured heterojunctions, and enhance performance in optoelectronic devices. Our results demonstrate how carrier dynamics in core-shell heterostructures can be manipulated to achieve control over the reaction mechanism in photocatalysis.

An overview on the progress and development of modified sulfonated polyether ether ketone membranes for vanadium redox flow battery applications

Vanadium redox flow batteries (VRFB) are among the most promising approaches to efficiently store renewable energies. In such battery type, Nafion is commonly used as membrane material but suffers from high vanadium crossover and cost. These drawbacks negatively influence the widespread commercial application of VRFBs. Alternative membrane materials with high performance and low cost are thus being developed to address these shortfalls. Among those, possible materials for the VRFB membrane is sulfonated polyether ether ketone (SPEEK), which recently attracted considerable attention due to its low cost, combined with mechanical and chemical stability, and ease of preparation. This review summarizes the research activities related to the development of SPEEK-based membranes for VRFB applications and gives an overview of the properties of PEEK and its sulfonated form. A critical analysis on the challenges of SPEEK-based membranes is also discussed.

Polyethylenimine-modified graphitic carbon nitride nanosheets: a label-free Raman traceable siRNA delivery system

Since the nanotoxicity of gene delivery carriers has raised world-wide concerns, it is important to trace their intracellular performance, for example via uptake visualization. Here, we develop a novel ultrathin graphitic carbon nitride (g-C₃N₄) composite nanosystem for label-free Raman-traceable small interfering RNA (siRNA) delivery. Through low molecular weight polyethylenimine (PEI) modifications, these nanosystems can obtain siRNA loading capabilities. The lateral size of the PEI-g-C₃N₄ composite is around 100-150 nm with a thickness of nearly 0.6 nm. The designed label-free delivery system could avoid possible obstacles associated with artificial labels and it shows cytotoxicity toward cancer cells and good biocompatibility in normal human cells. The label-free PEI-g-C₃N₄ gene nanocarrier can be directly traced via Raman microscopy, which makes it suitable for intracellular visualization. Intracellular uptake of the self-fluorescent g-C₃N₄ nanosheets can also be traced via fluorescence imaging. The PEI modified g-C₃N₄ ultrathin nanosheets possess gene delivery capacity together with unique dual-traceable Raman and fluorescence features. Raman traces not only have higher specificity than fluorescence ones but they can also avoid background noises. Thus, they may replace widely implemented fluorescence tracing. This work could provide a label-free traceable platform for investigating the intracellular performances of gene delivery nanosystems.

Water-splitting photoelectrodes consisting of heterojunctions of carbon nitride with ap-type low bandgap double perovskite oxide

Quinary and senary non-stoichiometric double perovskites such as Ba₂Ca_0.66Nb_1.34-xFe_xO_6-δ(BCNF) have been utilized for gas sensing, solid oxide fuel cells and thermochemical CO₂reduction. Herein, we examined their potential as narrow bandgap semiconductors for use in solar energy harvesting. A cobalt co-doped BCNF, Ba₂Ca_0.66Nb_0.68Fe_0.33Co_0.33O_6-δ(BCNFCo), exhibited an optical absorption edge at ∼800 nm,p-type conduction and a distinct photoresponse up to 640 nm while demonstrating high thermochemical stability. A nanocomposite of BCNFCo and g-C₃N₄(CN) was prepared via a facile solvent-assisted exfoliation/blending approach using dichlorobenzene and glycerol at a moderate temperature. The exfoliation of g-C₃N₄followed by wrapping on perovskite established an effective heterojunction between the materials for charge separation. The conjugated 2D sheets of CN enabled better charge migration resulting in increased photoelectrochemical performance. A blend composed of 40 wt% perovskites and CN performed optimally, whilst achieving a photocurrent density as high as 1.5 mA cm^-2for sunlight-driven water-splitting with a Faradaic efficiency as high as ∼88%.

Sub-level engineering strategy of nitrogen-induced Bi2O3/g-C3N4: a versatile photocatalyst for oxidation and reduction

Herein, the α-Bi₂O₃ nanocrystal decorated by nitrogen dopant and its heterojunction nanocomposite with g-C₃N₄ (N_0.1/Bi₂O₃/g-C₃N₄) is successfully fabricated for the first time, for photo-oxidation of RhB and photo-reduction of Cr(VI) to Cr(III). The resulting N_0.1/Bi₂O₃/g-C₃N₄ (3%) nanocomposite showed an optimal Cr(VI) photo-reduction and RhB photo-oxidation rates under visible-light irradiation, being 3-4 times higher than that of pure α-Bi₂O₃. The results from XPS confirmed the substitution of nitrogen with various oxidation states from N³⁺ to N^x+ (x < 5), due to the existence of different nitrogen oxides including N-O, O-N=O, and NO₃^- in the crystal structure. We investigated the reaction mechanism using catalytic tests, impedance spectroscopy, EPR technique, and density functional calculations. The DFT calculations presented the appearance of a new mid-gap hybrid of p states, comprised of N 2p, O 2p, and Bi 6P states, which enhance light absorption capacity and narrow band gap. The theoretical results were in excellent agreement with experimental UV-Vis data. The N_0.1/Bi₂O₃/g-C₃N₄ nanocomposite exhibited acceptable practical application value and recycling ability for removal of the contaminants. Such improved photocatalytic activity is originated from the modified band positions, new electron evolution pathway, introducing defects in α-Bi₂O₃ by insertion of N atoms into the Bi sites, and the enhanced charge carrier mobility between N_0.1/Bi₂O₃ and g-C₃N₄. The strategy to form nitrogen-doped bismuth-based nanocomposites may open a new opportunity to design atomic-level electronic defects by feasible methods to obtain a versatile photocatalyst material with simultaneous photo-reduction and photo-oxidation ability for removal of Cr(VI) and organic dyes from water.

Unconventional, Gram-Scale Synthesis of a Molecular Dimer Organic Luminogen with Aggregation-Induced Emission

Organic luminogens have been widely used in optoelectronic devices, bioimaging, and sensing. Conventionally, the synthesis of organic luminogens requires sophisticated, multistep design, reaction, and isolation procedures. Herein, the products of the melt-phase condensation of benzoguanamine (BG; 2,4-diamino-6-phenyl-1,3,5-triazine) at 370-410 °C display interesting reaction-condition-dependent luminescence properties, including photoluminescence (PL) at a variety of wavelengths in the visible spectrum and quantum efficiencies (PLQE) of up to 58% in the powder form. With a simple and straightforward solvent washing procedure, the prominent blue luminescent component BG dimer was obtained in gram scale with >93% purity (96.5% purity after fractional sublimation). The BG dimer exhibited distinct aggregation-induced emission (AIE) properties. PL measurements indicate that the electronically excited state of the BG dimer undergoes efficient intramolecular nonradiative deactivation in room-temperature solution, leading to a significantly reduced PLQE (<0.1%) in solution. These nonradiative processes are substantially inhibited when the dimer existed in the form of crystals, solid aggregates in solution or being fixed in a rigid polymer film, resulting in a significant increase in the PLQE and lifetime. This work not only provided a new understanding for PL properties of self-condensation luminescent products but also represented an unconventional strategy for large-scale preparation of organic luminogens with high purity.

Emerging graphitic carbon nitride-based membranes for water purification

Membrane separation is a promising technology that can effectively remove various existing contaminants from water with low energy consumption and small carbon footprint. The critical issue of membrane technology development is to obtain a low-cost, stable, tunable and multifunctional material for membrane fabrication. Graphitic carbon nitride (g-C₃N₄) has emerged as a promising membrane material, owing to the unique structure characteristics and outstanding catalytic activity. This review paper outlined the advanced material strategies used to regulate the molecule structure of g-C₃N₄ for membrane separation. The presentative progresses on the applications of g-C₃N₄-based membranes for water purification have been elaborated. Essentially, we highlighted the innovation integration of physical separation, catalysis and energy conversion during water purification, which was of great importance for the sustainability of water treatment techniques. Finally, the continuing challenges of g-C₃N₄-based membranes and the possible breakthrough directions in the future research was prospected.

Oxygen functionalized g-C3N4 strengthen Fe(III)/H2O2 system by accelerating Fe(III)/Fe(II) cycles under natural solar light: A mutual-promoting configuration

In response to the inherent restriction of low Fe(II) regeneration in the Fenton process, this study demonstrated a mutual-promoting configuration, where oxygen functionalized g-C₃N₄ (OCN) was applied in Fe(III)/H₂O₂ system to utilize mild natural solar light (SL) for persistent Fe(II) generation. The constructed OCN/Fe(III)/H₂O₂/SL system exhibited strong adaptability to various pollutants, and it well outperformed the g-C₃N₄ (GCN) modified system and the traditional Fenton system in pollutants degradation efficiency. Compared with GCN, OCN could significantly promote the Fe(II) generation under solar light (SL), leading to more efficient H₂O₂ activation. The characterization analyses revealed the larger surface area and enhanced charge separation of OCN, which were considered to take main responsibility for its enhanced photoactivity. The complexation of Fe(III) with the carboxyl groups of OCN also benefited the Fe(II) generation. ·OH was detected as the dominant radical responsible for metronidazole (MNZ) degradation, and its production in the OCN modified system was about twice that in the GCN modified system and the Fenton system. Moreover, the precipitation of FeO_x on the OCN surface benefited the charge separation of the OCN, so that the improved OCN enabled a slight enhancement of MNZ degradation in the reuse experiments. The intermediates of MNZ degradation were analyzed based on the results of LC-MS, which provided insight into MNZ degradation pathways. This work highlighted the concept of self-improving photocatalyst, the ingenious combination of photocatalysis and Fenton-like system formed a mutual-promoting situation where the OCN and the Fenton-like system could both be improved, which endowed the configuration great potential for green and economical oxidation in environmental remediation.

Sol-Gel Processing of Water-Soluble Carbon Nitride Enables High-Performance Photoanodes*

In spite of the enormous promise that polymeric carbon nitride (PCN) materials hold for various applications, the fabrication of high-quality, binder-free PCN films and electrodes has been a largely elusive goal to date. Here, we tackle this challenge by devising, for the first time, a water-based sol-gel approach that enables facile preparation of thin films based on poly(heptazine imide) (PHI), a polymer belonging to the PCN family. The sol-gel process capitalizes on the use of a water-soluble PHI precursor that allows formation of a non-covalent hydrogel. The hydrogel can be deposited on conductive substrates, resulting in formation of mechanically stable polymeric thin layers. The resulting photoanodes exhibit unprecedented photoelectrochemical (PEC) performance in alcohol reforming and highly selective (∼100 %) conversions with very high photocurrents (>0.25 mA cm-2 under 2 sun) down to <0 V vs. RHE. This enables even effective PEC operation under zero-bias conditions and represents the very first example of a 'soft matter'-based PEC system capable of bias-free photoreforming. The robust binder-free films derived from sol-gel processing of water-soluble PCN thus constitute a new paradigm for high-performance 'soft matter' photoelectrocatalytic systems and pave the way for further applications in which high-quality PCN films are required.

Facile synthesis of highly crystalline g-C3N4 nanosheets with remarkable visible light photocatalytic activity for antibiotics removal

g-C₃N₄ has attracted much attention in photocatalysis field because of its good visible light response. However, its photocatalytic activity is still greatly limited by fast carriers recombination and small specific surface. In order to promote carriers separation and pollutants adsorption, a facile synthesis scheme combining hydrothermal method with secondary calcination process under N₂ gas protection was developed, and highly crystalline g-C₃N₄ nanosheets (HCCNNS) were successfully prepared. During ciprofloxacin (CIP) and sulfamethazine (SMZ) degradation, it showed excellent visible light photocatalytic activity, wherein CIP and SMZ with 10 mg/L could achieve degradation efficiency of 98.4% and 96.9% in 60 min under visible light irradiation. Compared with conventional g-C₃N₄, the degradation rate constants were enhanced by 6.9 and 5.8 times, respectively. From the perspectives of morphology, optical property and surface chemistry, the ultra-high activity of HCCNNS is mainly attributed to its highly crystalline structure and nanosheet morphology, which not only reduce the carriers transfer resistance, promote the pollutants adsorption capability, but also expand the light absorption range, and promote the carriers separation. Furthermore, the synthesis procedure of HCCNNS possesses the nature of high yield and excellent cost performance, thus, HCCNNS possesses great potential for mass production and practical application for antibiotics removal.

3-Amino-1,2,4-triazole-derived graphitic carbon nitride for photodynamic therapy

Graphitic carbon nitride (g-C₃N₄) has been shown as a promising visible-light photosensitizer for photodynamic therapy (PDT) application. Nevertheless, its therapeutic efficiency is limited by the low efficiency of visible-light utilization. To overcome this issue, 3-amino-1,2,4-triazole-derived graphitic carbon nitride nanosheets (g-C₃N₅ NSs) are prepared for PDT application. The addition of nitrogen-rich triazole group into the g-C₃N₄ motif significantly makes the light absorption of g-C₃N₅ NSs red-shift with the band gap down to 1.95 eV, corresponding to a absorption edge at a wavelength of 636 nm. g-C₃N₅ NSs generate superoxide anion radicals (O₂^•-) and singlet oxygen (¹O₂) under the irradiation of a low-intensity white light emitting diode. Owing to the high efficiency of visible-light utilization, g-C₃N₅ NSs show about 9.5 fold photocatalytic activity of g-C₃N₄ NSs. In vitro anticancer studies based on the results of CCK-8 assay, Calcein-AM/PI cell-survival assay and photo-induced intracellular ROS level analysis in living HeLa cells demonstrate the potential of g-C₃N₅ NSs as a low-toxic and biocompatible high-efficient photosensitizer for PDT.

Polymeric Carbon Nitride-Derived Photocatalysts for Water Splitting and Nitrogen Fixation

Photocatalysis is a promising energy conversion and environmental restoration technology. The main focus of photocatalysis is the development and manufacture of highly efficient photocatalysts. Semiconductor-based photocatalysis technology based on harnessing solar energy is considered as an attractive approach to solve the problems of global energy shortage and environmental pollution. Since 2009 pioneering work has been carried out on polymeric carbon nitride (PCN) for visible photocatalytic water splitting, thus PCN-based photocatalysis has become a hot research topic, demanding significant research attention. This article reviews the physical and chemical properties, synthesis methods, and the methods to control the morphology, heteroatom doping, and construction of heterojunctions to improve the performance of PCN-based photocatalysts in water splitting and nitrogen fixation. Through different design strategies, the photo-generated electron-hole pair separation efficiency of PCN materials can be effectively improved, thereby improving their photocatalytic performance. Finally, the challenges of PCN-based photocatalysts in water splitting and nitrogen fixation applications are discussed herein. It is strongly believed that through different design strategies, efficient PCN-based photocatalysts can be constructed for both water splitting and nitrogen reduction. These excellent modification strategies can be used as a guiding theory for photocatalytic reactions of other promising catalysts and further promote the development of photocatalysis.

Metal Halide Perovskite/2D Material Heterostructures: Syntheses and Applications

The past decade has witnessed the great success achieved by metal halide perovskites (MHPs) in photovoltaic and related fields. However, challenges still remain in further improving their performance, as well as, settling the stability issue for future commercialization. Recently, MHP/2D material heterostructures that combining MHPs with the low-cost and solution-processable 2D materials have demonstrated unprecedented improvement in both performance and stability due to the distinctive features at hetero-interface. The diverse fabrication techniques of MHPs and 2D materials allow them to be assembled as heterostructures with different configurations in a variety of ways. Moreover, the large families of MHPs and 2D materials provide the opportunity for the rational design and modification on compositions and functionalities of MHP/2D materials heterostructures. Herein, a comprehensive review of MHP/2D material heterostructures from syntheses to applications is presented. First, various fabrication techniques for MHP/2D material heterostructures are introduced by classifying them into solid-state methods and solution-processed methods. Then the applications of MHP/2D heterostructures in various fields including photodetectors, solar cells, and photocatalysis are summarized in detail. Finally, current challenges for the development of MHP/2D material heterostructures are highlighted, and future opportunities for the advancements in this research field are also provided.

An electrochemiluminescence energy resonance transfer system for highly sensitive detection of brombuterol

In this work, an electrochemiluminescence resonance energy transfer (ECL-RET) system was established based on the modified graphite phase carbon nitride to detect brombuterol residues in food. The ultrasonic-assisted acidification exfoliation modification improved the conductivity and specific surface area of the graphite phase carbon nitride (g-C₃N₄). In addition, the carboxylated g-C₃N₄ nanosheets as ECL donors and the Au-Ag alloy nanoparticles as ECL acceptors could respectively directly carry antigen and antibody. Therefore, the trouble of introducing additional bridge molecules was avoided. A competitive immunoassay strategy was used for the detection of brombuterol, where brombuterol in the sample would compete with the coating antigen for the limited binding sites on antibody. The proposed ECL immunosensor for brombuterol detection exhibited high sensitivity with a wide linear range from 0.001 ng mL^-1 to 1000 ng mL^-1 and a low detection limit at 0.31 pg mL^-1. This work adopts a very simple way to design the sensor without losing its sensitivity, bringing convenience to its possible future applications.

High crystallinity and conjugation promote the polarization degree in O-doped g-C3N4 for removing organic pollutants

High crystallinity and extended conjugated system improve the polarization of O-doped g-C₃N₄, which efficiently promotes carrier separation.

Regulating morphological and electronic structures of polymeric carbon nitrides by successive copolymerization and stream reforming for photocatalytic CO2 reduction

Greatly reinforced photocatalytic CO₂ reduction is realized with carbon nitride polymers tailored via a coupled copolymerization and stream reforming strategy.

Graphene/graphitic carbon nitride decorated with AgBr to boost photoelectrochemical performance with enhanced catalytic ability

A novel graphene nanoplatelets (GNP) bridge between two semiconductors (AgBr and graphitic carbon nitride) was created to boost photoelectrochemical performance. The heterojunction created makes the whole system a Z-scheme catalyst. For the construction of this catalyst, the syringe pump methodology was adopted and different analytical techniques were used for the confirmation of structure and morphology. High angle annular dark field (HAADF), dark field (DF), DF-4 and DF-2 techniques, using Z-contrast phenomena, confirmed the heterostructure (ABGCN) and its composition. The constructed structure showed an enhanced photoelectrochemical and catalytic property against 'acute toxicity category-III (MM)' and 'category-IV (tetracycline hydrochloride (TH))' organic pollutants. The constructed catalyst degraded the MM in 57 min and the TH in 35 min with degradation rates of 0.01489 min^-1 and 0.02387 min^-1, respectively, due to the accumulation of photogenerated electrons on the conduction band (CB) of g-C₃N₄ and photogenerated holes on the valence band (VB) of AgBr by the transformation of charges through the graphene bridge. An ion trapping study also revealed that ·O₂ and h⁺ were the active species which actively participated in the photocatalytic reaction.

Graphitic Carbon Nitride Films: Emerging Paradigm for Versatile Applications

Graphitic carbon nitride (g-C₃N₄) is a well-known two-dimensional conjugated polymer semiconductor that has been broadly applied in photocatalysis-related fields. However, further developments of g-C₃N₄, especially in device applications, have been constrained by the inherent limitations of its insoluble nature and particulate properties. Recent breakthroughs in fabrication methods of g-C₃N₄ films have led to innovative and inspiring applications in many fields. In this review, we first summarize the fabrication of continuous and thin films, either supported on substrates or as free-standing membranes. Then, the novel properties and application of g-C₃N₄ films are the focus of the current review. Finally, some underlying challenges and the future developments of g-C₃N₄ films are tentatively discussed. This review is expected to provide a comprehensive and timely summary of g-C₃N₄ film research to the wide audience in the field of conjugated polymer semiconductor-based materials.

Superior antibacterial activity of sulfur-doped g-C3N4 nanosheets dispersed by Tetrastigma hemsleyanum Diels & Gilg's polysaccharides-3 solution

Bacterial resistance has become a serious global health issue over the past decades due to the misuse and abuse of antibiotics. The development of effective antibacterial drugs with a new antibacterial mechanism is thus very critical. At present, there are many reports on the antibacterial properties and mechanisms of two-dimensional materials. Currently, the modification of g-C₃N₄ materials, as widely used two-dimensional materials, has become a key step in extending their potential applications in the field of antimicrobial therapy. In the present work, we prepared sulfur-doped g-C₃N₄ nanosheets (SCNNSs), which have good water dispersibility and sharp tips. The electrostatic interaction of SCNNSs with Tetrastigma hemsleyanum Diels & Gilg's polysaccharide-3 (THDG-3) provides a new strategy that can improve the killing efficiency of SCNNSs. In addition, THDG-3 can rapidly inhibit bacterial proliferation in the early stage of administration. Combined with the antibacterial activity of the SCNNSs, TPS/SCNNSs can inhibit bacteria for a long time. Scanning electron microscopy (SEM) observation of Escherichia coli (E. coli) after administration of the materials revealed that the bacterial cells were ruptured and their intracellular contents were completely separated from the cell membrane. Therefore, we speculate that the bactericidal mechanism of the TPS/SCNNSs probably involves cell membrane damage. In summary, TPS/SCNNSs achieve fast, long-term, dual-function bacteriostatic properties.

A hybrid transition metal nanocrystal-embedded graphitic carbon nitride nanosheet system as a superior oxygen electrocatalyst for rechargeable Zn-air batteries

In this study, we, for the first time, demonstrate a general solid-phase pyrolysis method to synthesize hybrid transition metal nanocrystal-embedded graphitic carbon nitride nanosheets, namely M-CNNs, as a highly efficient oxygen electrocatalyst for rechargeable Zn-air batteries (ZABs). The ratios between metallic acetylacetonates and the g-C₃N₄ precursor can be controlled where Fe-CNNs_-0.7, Ni-CNNs_-0.7 and Co-NNs_-0.7 composites have been optimized to exhibit superior ORR/OER bifunctional electrocatalytic activities. Specifically, Co-CNNs_-0.7 exhibited not only a comparable half-wave potential (0.803 V vs. RHE) to that of the commercial Pt/C catalyst (0.832 V) with a larger current density for the ORR but also a lower overpotential (440 mV) toward the OER compared with the commercial IrO₂ catalyst (460 mV), revealing impressive application in rechargeable ZABs. As a result, ZABs using Co-CNNs_-0.7 as the cathode exhibited an excellent peak power density of 85.3 mW cm^-2 with a specific capacity of 675.7 mA h g^-1 and remarkable cycling stability of 1000 cycles, outperforming the commercially available Pt/C + IrO₂ catalysts. This study highlights the synergy from heterointerfaces in oxygen electrocatalysis, thus providing a promising approach for advanced metal-air cathode materials.

Oxygen Doping in Graphitic Carbon Nitride for Enhanced Photocatalytic Hydrogen Evolution

The incorporation of oxygenic groups could remarkably enhance the light absorption and charge separation of graphitic carbon nitride (g-C₃ N₄ ). The intrinsic role of oxygenic species on photocatalytic activity in g-C₃ N₄ has been intensively studied, but it is still not fully explored. Herein, the essential relationships between oxygenic functionalities and the catalytic performance are revealed. Results demonstrate that C-O-C functionality as an electron trap could help to increase the resistance of conduction transfer (R_ct ) by limiting electrons transfer in CNx. In contrast, N-C-O functionality between different tri-s-triazine unites could promote the electrons transfer, leading to a reduced R_ct in CNx. The best H₂ production rate (3.70 mmol h^-1  g^-1 , 12.76-fold higher than that of CN) is obtained over CN3, because of the highest N-C-O ratio (r_N-C-O ). The apparent quantum efficiency (AQE) of CN3 at 405 nm, 420 nm, 450 nm, 500 nm and 550 nm is 33.90 %, 20.88 %, 8.25 %, 3.66 % and 1.01 %, respectively.

Direct growth of uniform carbon nitride layers with extended optical absorption towards efficient water-splitting photoanodes

A general synthesis of carbon nitride (CN) films with extended optical absorption, excellent charge separation under illumination, and outstanding performance as a photoanode in water-splitting photoelectrochemical cells is reported. To this end, we introduced a universal method to rapidly grow CN monomers directly from a hot saturated solution on various substrates. Upon calcination, a highly uniform carbon nitride layer with tuned structural and photophysical properties and in intimate contact with the substrate is obtained. Detailed photoelectrochemical and structural studies reveal good photoresponse up to 600 nm, excellent hole extraction efficiency (up to 62%) and strong adhesion of the CN layer to the substrate. The best CN photoanode demonstrates a benchmark-setting photocurrent density of 353 µA cm⁻² (51% faradaic efficiency for oxygen), and external quantum yield value above 12% at 450 nm at 1.23 V versus RHE in an alkaline solution, as well as low onset potential and good stability.

Photoelectrochemical cells (PEC) can convert sunlight and water directly to a hydrogen fuel. Here a robust metal-free carbon nitride-based layer is used as an efficient photoanode for water-splitting PEC.