Endowing g‐C 3 N 4 Membranes with Superior Permeability and Stability by Using Acid Spacers

Construction of an Electron Capture and Transfer Center for Highly Efficient and Selective Solar-Light-Driven CO2 Conversion

Exploring high-efficiency photocatalysts for selective CO2 reduction is still challenging because of the limited charge separation and surface reactions. In this study, a noble-metal-free metallic VSe2 nanosheet was incorporated on g-C3N4 to serve as an electron capture and transfer center, activating surface active sites for highly efficient and selective CO2 photoreduction. Quasi in situ X-ray photoelectron spectroscopy (XPS), soft X-ray absorption spectroscopy (sXAS), and femtosecond transient absorption spectroscopy (fs-TAS) unveiled that VSe2 could capture electrons, which are further transferred to the surface for activating active sites. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory (DFT) calculations revealed a kinetically feasible process for the formation of a key intermediate and confirmed the favorable production of CO on the VSe2/PCN (protonated C3N4) photocatalyst. As an outcome, the optimized VSe2/PCN composite achieved 97% selectivity for solar-light-driven CO2 conversion to CO with a high rate of 16.3 μmol·g-1·h-1, without any sacrificial reagent or photosensitizer. This work offers new insights into the photocatalyst design toward highly efficient and selective CO2 conversion.

New directions on membranes for removal and degradation of emerging pollutants in aqueous systems

Emerging pollutants (EPs) refer to a group of non-regulated chemical or biological substances that have been recently introduced or detected in the environment. These pollutants tend to exhibit resistance to conventional treatment methods and can persist in the environment for prolonged periods, posing potential adverse effects on ecosystems and human health. As we enter a new era of managing these pollutants, membrane-based technologies hold significant promise in mitigating impact of EPs on the environment and safeguarding human health due to their high selectivity, efficiency, cost-effectiveness and capability for simultaneous separation and degradation. Moreover, these technologies continue to evolve rapidly with the development of new membrane materials and functionalities, advanced treatment strategies, and analyses for effectively treating EPs of more recent concerns. The objective of this review is to present the latest directions and advancements in membrane-based technologies for addressing EPs. By highlighting the progress in this field, we aim to share valuable perspectives with researchers and contribute to the development of future directions in sustainable treatments for EPs.

Polymer carbon nitride nanosheet-based lamellar membranes inspired by "couple hardness with softness" for ultrafast molecular separation in organic solvents

Membranes with ultrafast molecular separation ability in organic solvents can offer unprecedented opportunities for efficient and low-cost solvent recovery in industry. Herein, a graphene-like polymer carbon nitride nanosheet (PCNN) with a low-friction surface was applied as the main membrane building block to boost the ultrafast transport of the solvent. Meanwhile, inspired by the concept of "couple hardness with softness", soft and flexible graphene oxide (GO) was chosen to fix the random stack of the rigid PCNN and tailor the lamellar structure of the PCNN membrane. The optimal PCNN/GO lamellar membrane shows a remarkable methanol permeance of 435.5 L m-2 h-1 bar-1 (four times higher than that of the GO membrane) while maintaining a high rejection for reactive black (RB, 98.9% in ethanol). Molecular dynamics simulations were conducted to elucidate the ultrafast transport mechanism of the PCNN/GO membrane. This study reveals that PCNN is a promising building block for lamellar membranes and may open up new avenues for high-performance molecular separation membranes.

Graphitic carbon nitride membranes intercalated with nano-sized Fe-MOF for enhanced water purification via synergistic separation and Fenton-like processes

Versatile two-dimensional nanomaterials have offered a promising prospect to enhance the water purification efficiency and overcome the fouling obstacle in membrane technology. In this work, a graphitic carbon nitride (g-C3N4) nanosheet membrane intercalated with the nano-sized Fe-based metal-organic framework (MIL-100(Fe)) is developed for the enhanced removal of aqueous organic contaminants by synergically promoting separation and Fenton-like processes. The g-C3N4/MIL-100(Fe) membrane is constructed through a self-assembly route in which the nano-MIL-100(Fe) is anchored into g-C3N4 layers by the coordination bonds between Fe nodes and pyridinic N. The MIL-100(Fe) intercalation not only enlarges the interlayer spacing to raise the membrane permeability, but also expedites the electron transfer between Fe2+ and Fe3+ to improve the Fenton-like activity. With a stable water flux of 98.2 L m2·h-1·bar-1 under wide-range pH and pressures, the g-C3N4/MIL-100(Fe) membrane shows high dye removal efficiency (≥99%) and prominent self-cleaning ability. Mechanism insight proposes a combination of size exclusion, electrostatic interaction and steady radical generation. The intercalation of nano-MIL-100(Fe) into g-C3N4 membranes can realize the mutual promotion between separation and Fenton-like processes, the synergistic effect of which provides an effective and feasible strategy for aqueous pollution abatement.

Photozyme-Catalyzed ATP Generation Based on ATP Synthase-Reconstituted Nanoarchitectonics

We demonstrate that ATP synthase-reconstituted proteoliposome coatings on the surface of microcapsules can realize photozyme-catalyzed oxidative phosphorylation. The microcapsules were assembled through layer-by-layer deposition of semiconducting graphitic carbon nitride (g-C3N4) nanosheets and polyelectrolytes. It is found that electrons from polyelectrolytes are transferred to g-C3N4 nanosheets, which enhances the separation of photogenerated electron-hole pairs. Thus, the encapsulated g-C3N4 nanosheets as the photozyme accelerate oxidation of glucose into gluconic acid to yield protons under light illumination. The outward transmembrane proton gradient is established to drive ATP synthase to synthesize adenosine triphosphate. With such an assembled system, light-driven oxidative phosphorylation is achieved. This indicates that an assembled photozyme can be used for oxidative phosphorylation, which creates an unusual way for chemical-to-biological energy conversion. Compared to conventional oxidative phosphorylation systems, such an artificial design enables higher energy conversion efficiency.

Robust self-cleaning membrane with superhydrophilicity and underwater superoleophobicity for oil-in-water separation

The discharge of oily wastewater has increased dramatically and will bring serious environmental problems. In this work, a self-cleaning and anti-fouling g-C₃N₄/TiO₂/PVDF composite membrane was fabricated via the layer-by-layer approach. The surface of as-prepared composite membrane displayed a superhydrophilic and underwater superoleophobic behavior under irradiation with visible light. Also, upon irradiation with visible light, the fabricated g-C₃N₄/TiO₂/PVDF composite membrane displayed enhanced permeation flux and improved oil removal efficiency as a result of the generation of hydroxyl free radicals during the photocatalytic filtration process. Significantly, irradiation with visible light remarkably improved reusability of the composite membrane by initiating photocatalytic decomposition of deposited oil foulants, which enabled removal of over 99.75% of oils, thus reaching a nearly 100% flux recovery ratio. Furthermore, the g-C₃N₄/TiO₂/PVDF composite membrane exhibited great anti-fouling behavior in photocatalysis-assisted filtration. The mechanistic study revealed that underwater superhydrophobicity and the generation of free hydroxyl radicals jointly contributed to membrane anti-fouling. The greatest advantages of this g-C₃N₄/TiO₂/PVDF composite membrane are that not only does it degrades the oil pollutants, but it also makes the membrane less vulnerable to fouling.

Double-charged self-assembled rGO/g-C3N4 membrane prepared by "functional group substitution" for heavy metal ions rejection at low pressure

Heavy metals are still the critical pollutants in industrial wastewater and there is an urgent need for efficient and environmentally friendly treatment technologies. Reduced graphene oxide (rGO) is widely used for preparations of nanofiltration (NF) membranes but suffers from poor hydrophilicity and electronegativity. In this work, a double-charged rGO/g-C₃N₄-P membrane was prepared for removal of heavy metals at low pressure. Graphitic carbon nitride (g-C₃N₄) assisted reduction of GO membranes under ultraviolet (UV) irradiation, and the modification of functional groups with high polarity improved the hydrophilicity of membrane surface. The filtration performance for heavy metals of rGO/g-C₃N₄-P membrane was evaluated under low pressure (1-2 bar). The rejection rates of Cu²⁺, Cr³⁺, Mn²⁺, Cd²⁺, and Pb²⁺ by membranes reduced by UV for 18 h (rGO/g-C₃N₄-18-P membrane) reached 94.72 %, 98.05 %, 82.32 %, 88.2 % and 77.15 %, respectively. In the experiment of mixed simulated wastewater, the rejection rates of NO₃^- and SO₄^2- both reached >95 %. Outstanding rejection rates were attributed to the interaction and the synergy effect of double-charged layers as well as steric effects. Meanwhile, the water flux of rGO/g-C₃N₄-18-P membrane was as high as 37.14-50.16 L m^-2h^-1bar^-1 (1-2 bar). The high flux was due to the reduced degree of oxidation so that water molecules transported between GO nanochannels more smoothly and the transport path was shortened through the nanopores of g-C₃N₄. Obviously, flux and heavy metal rejection of rGO/g-C₃N₄-18-P membrane were simultaneously improved, breaking "trade-off" effect. Furthermore, rGO/g-C₃N₄-18-P membrane showed excellent antifouling ability and the potential for heavy metal wastewater filtration in comparison with other NF membranes reported in literature.

Selective Ion Transport in Two-Dimensional Lamellar Nanochannel Membranes

Precise and ultrafast ion sieving is highly desirable for many applications in environment-, energy-, and resource-related fields. The development of a permselective lamellar membrane constructed from parallel stacked two-dimensional (2D) nanosheets opened a new avenue for the development of next-generation separation technology because of the unprecedented diversity of the designable interior nanochannels. In this Review, we first discuss the construction of homo- and heterolaminar nanoarchitectures from the starting materials to the emerging preparation strategies. We then explore the property-performance relationships, with a particular emphasis on the effects of physical structural features, chemical properties, and external environment stimuli on ion transport behavior under nanoconfinement. We also present existing and potential applications of 2D membranes in desalination, ion recovery, and energy conversion. Finally, we discuss the challenges and outline research directions in this promising field.

Regulating electron configuration of single Cu sites via unsaturated N,O-coordination for selective oxidation of benzene

Developing highly efficient catalyst for selective oxidation of benzene to phenol (SOBP) with low H2O2 consumption is highly desirable for practical application, but challenge remains. Herein, we report unique single-atom Cu1-N1O2 coordination-structure on N/C material (Cu-N1O2 SA/CN), prepared by water molecule-mediated pre-assembly-pyrolysis method, can efficiently boost SOBP reaction at a 2:1 of low H2O2/benzene molar ratio, showing 83.7% of high benzene conversion with 98.1% of phenol selectivity. The Cu1-N1O2 sites can provide a preponderant reaction pathway for SOBP reaction with less steps and lower energy barrier. As a result, it shows an unexpectedly higher turnover frequency (435 h−1) than that of Cu1-N2 (190 h−1), Cu1-N3 (90 h−1) and Cu nanoparticle (58 h−1) catalysts, respectively. This work provides a facile and efficient method for regulating the electron configuration of single-atom catalyst and generates a highly active and selective non-precious metal catalyst for industrial production of phenol through selective oxidation of benzene.

Coordination-Assistant Chiral Agent Anchoring on Amphiphilic Graphitic Phase Carbon Nitride Membrane for Multiple Molecular Separation

Membranes composed of two-dimensional (2D) materials suffer from low stability and structural swelling and are usually restricted to applications in aqueous systems. Among various 2D materials, graphitic phase carbon nitride (GCN, g-C3N4) has shown great application potential owing to its structural tunability. Herein, we develop a coordination-assisted strategy to regulate the GCN layer spacing and chemical environment via copper ion (Cu2+) coordination-assisted intercalation of enantiopure (1S,2S)-(-)-1,2-diphenyl-1,2-ethanediamine (DPE) between GCN nanosheets. The obtained GCN-Cu-DPE membrane is continuous and intact, free of cracks and pinholes, stable under acidic and alkaline conditions, and exhibits water permeability above 215 L m-2 h-1 bar-1 and a high rejection rate to dye molecules. The membrane is amphiphilicity and thus allows both polar solvent (water) and nonpolar solvent (hexane) to freely pass through. Remarkably, the permeation rate is proportional to the viscosity of the solvent. Benefiting from the chiral space between nanosheets, the GCN-Cu-DPE membrane shows selective permeation of aspartic acid racemate in aqueous systems and limonene racemate in the organic phase. Our work demonstrates a general and promising strategy for chiral membrane fabrication toward high-value-added chiral separation, especially in the pharmaceutical industry.

Poly(ionic liquid)‐Armored MXene Membrane: Interlayer Engineering for Facilitated Water Transport

Two‐dimensional (2D) MXene‐based lamellar membranes bearing interlayers of tunable hydrophilicity are promising for high‐performance water purification. The current challenge lies in how to engineer the pore wall's surface properties in the subnano‐confinement environment while ensuring its high selectivity. Herein, poly(ionic liquid)s, equipped with readily exchangeable counter anions, succeeded as a hydrophilicity modifier in addressing this issue. Lamellar membranes bearing nanochannels of tailorable hydrophilicity are constructed via assembly of poly(ionic liquid)‐armored MXene nanosheets. By shifting the interlayer galleries from being hydrophilic to more hydrophobic via simple anion exchange, the MXene membrane performs drastically better for both the permeance (by two‐fold improvement) and rejection (≈99 %). This facile method opens up a new avenue for building 2D material‐based membranes of enhancing molecular transport and sieving effect.

MXene Composite Membranes with Enhanced Ion Transport and Regulated Ion Selectivity

Two-dimensional (2D) material-based membranes are promising candidates for various separation applications. However, the further enhancement of membrane ion conductance is difficult, and the regulation of membrane ion selectivity remains a challenge. Here, we demonstrate the facile fabrication of MXene composite membranes by incorporating spacing agents that contain SO₃H groups into the MXene interlayers. The synthesized membrane shows enhanced ion conductance and ion selectivity. Subsequently, the membranes are utilized for salinity gradient power (SGP) generation and lithium-ion (Li⁺) recovery. The membrane containing poly(sodium 4-styrenesulfonate) (PSS) as the spacing agent shows a much higher power density for SGP generation as compared to the pristine MXene membrane. Using artificial seawater and river water, the power density reaches 1.57 W/m² with a testing area of 0.24 mm². Also, the same membrane shows Li⁺/Na⁺ and Li⁺/K⁺ selectivities of 2.5 and 3.2, respectively. The incorporation of PSS increases both the size and charge density of the nanochannels inside the membrane, which is beneficial for ion conduction. In addition, the density functional theory (DFT) calculation shows that the binding energy between Li⁺ and the SO₃H group is lower than other alkali ion metals, and this might be one major reason why the membrane possesses high Li⁺ selectivity. This study demonstrates that incorporating spacing agents into the 2D material matrix is a viable strategy to enhance the performance of the 2D material-based membranes. The results from this study can inspire new membrane designs for emerging applications including energy harvesting and monovalent ion recovery.

Synergistic effects of the hybridization between boron-doped carbon quantum dots and n/n-type g-C3N4 homojunction for boosted visible-light photocatalytic activity

Dye wastewater has raised a prevalent environmental concern due to its ability to prevent the penetration of sunlight through water, thereby causing a disruption to the aquatic ecosystem. Carbon quantum dots (CQDs) are particularly sought after for their highly tailorable photoelectrochemical and optical properties. Simultaneously, graphitic carbon nitride (g-C₃N₄) has gained widespread attention due to its suitable band gap energy as well as excellent chemical and thermal stabilities. Herein, a novel boron-doped CQD (BCQD)-hybridized g-C₃N₄ homojunction (CN) nanocomposite was fabricated via a facile hydrothermal route. The optimal photocatalyst sample, 1-BCQD/CN (with a 1:3 mass ratio of boron to CQD) accomplished a Rhodamine B (RhB, 10 mg/L) degradation efficiency of 96.8% within 4 h under an 18 W LED light irradiation. The kinetic rate constant of 1.39 × 10^-2 min^-1 achieved by the optimum sample was found to be 3.6- and 2.8-folds higher than that of pristine CN and un-doped CQD/CN, respectively. The surface morphology, crystalline structure, chemical composition and optical properties of photocatalyst samples were characterized via TEM, FESEM-EDX, XRD, FTIR, UV-Vis DRS and FL spectrometer. Based on the scavenging tests, it was revealed that the photogenerated holes (h⁺), superoxide anions (∙O₂^-) and hydroxyl radicals (∙OH) were the primary reactive species responsible for the photodegradation process. Overall, the highly efficient 1-BCQD/CN composite with excellent photocatalytic activity could provide a cost-effective and robust means to address the increasing concerns over global environmental pollution.

2D Polymer Nanosheets for Membrane Separation

Since the discovery of single-layer graphene in 2004, the family of 2D inorganic nanosheets is considered as ideal membrane materials due to their ultrathin atomic thickness and fascinating physicochemical properties. However, the intrinsically nonporous feature of 2D inorganic nanosheets hinders their potential to achieve a higher flux to some extent. Recently, 2D polymer nanosheets, originated from the regular and periodic covalent connection of the building units in 2D plane, have emerged as promising candidates for preparing ultrafast and highly selective membranes owing to their inherently tunable and ordered pore structure, light weight, and high specific surface. In this review, the synthetic methodologies (including top-down and bottom-up methods) of 2D polymer nanosheets are first introduced, followed by the summary of 2D polymer nanosheets-based membrane fabrication as well as membrane applications in the fields of gas separation, water purification, organic solvent separation, and ion exchange/transport in fuel cells and lithium-sulfur batteries. Finally, based on their current achievements, the authors' personal insights are put forward into the existing challenges and future research directions of 2D polymer nanosheets for membrane separation. The authors believe this comprehensive review on 2D polymer nanosheets-based membrane separation will definitely inspire more studies in this field.

Recent developments in architecturing the g-C3N4 based nanostructured photocatalysts: Synthesis, modifications and applications in water treatment

Water pollution is becoming an inevitable problem in today's world. Tons and tons of wastewater with hazardous pollutants are getting discharged into the clean water bodies every day. In this regard, photocatalytic environmental remediation using nanotechnology such as the use of organic, metal and non-metal based semiconductor photocatalysts for photodegradation of pollutants has gained enormous attention in the past few decades. This review is focused particularly on graphitic carbon nitride (g-C₃N₄) which is a cheap, metal-free, polymeric photoactive compound and it is used as a potential photocatalyst in wastewater treatment. Though, pristine g-C₃N₄ is a good photocatalyst, it has certain drawbacks such as poor visible light absorption capacity, quicker recombination of photoelectrons and holes, delayed mass and charge transfer, etc. As a result, the pristine g-C₃N₄ catalyst is modified into novel 0D, 1D, 2D and 3D morphologies such as nano-quantum dots, nanorods, nanotubes, nanowires, nanosheets, nanoflakes, nanospheres, nanoshells, etc. It was also tailored into novel composites along with various compounds through doping, metal deposition, heterojunction formation, etc., to enhance the photocatalytic property of pure g-C₃N₄. The modified catalysts showed promising photocatalytic performance such as degradation of majority of pollutants in the environment. It also showed excellent results in the removal or reduction of heavy metals. This review provides a detailed record of g-C₃N₄ and its diverse photocatalytic applications in the past years and it provides knowledge for the development of such similar novel compounds in the future.

Semiconducting graphitic carbon nitride integrated membranes for sustainable production of clean water: A review

Semiconducting membranes integrated with nanomaterials have placed themselves in new emerging researches tremendously for seawater desalination, oil-water separation, disinfection, removal of inorganic as well as organic pollutants. Howbeit, only nanoparticles unified membranes show quite a lot lags in their performance, although some of these particles associated with the demerits of high cost. In contrast, graphitic carbon nitride incorporated membranes offered improved aforementioned properties corresponding to absolute essential qualities such as cost-effective, environmentally friendly, easy-to-operate, green manufacturing, anti-fouling, and low energy consumption. Moreover, their high mechanical strength, high stability against harsh environment and long-term utilization without flux reduction are strong plus. Even though there are some undeniable downsides of these membranes in real world applications as bulk synthesis, consistent dispersion of graphitic carbon nitride, low photocatalytic efficiency etc. Accordingly, in the present article, these frailties of the membranes having graphitic carbon nitride as a filler and their respective synthesis procedures and properties are discussed. A comprehensive analysis over the application of semiconducting graphitic carbon nitride incorporated membranes with and without special surface modification; and exploration of the future challenges and difficulties associated to these membranes are also reviewed. Consequently, the current article provides brief overview about graphitic carbon nitride integrated composite membranes as well as their applications, and it finished up with new thoughts of further improvements/modifications to overcome their shortcomings in actual environmental conditions.

Hydrophilic and underwater superoleophobic porous graphitic carbon nitride (g-C3N4) membranes with photo-Fenton self-cleaning ability for efficient oil/water separation

Due to the great fouling resistance property, (super)hydrophilic/underwater superoleophobic membranes are prevalent candidates for oil-polluted wastewater treatment. Even so, membrane fouling inevitably occurs during long-term operation. Therefore, it is of great significance to construct anti-fouling membranes with robust flux recovery. Herein, a polyvinyl pyrrolidone (PVP) coated porous potassium-doped g-C₃N₄ (PKCN) membrane was fabricated for the first time by vacuum filtration. The as-prepared membrane displays enhanced hydrophilicity and underwater superoleophobicity. The permeability of the membrane increased significantly after sonication treatment, which is attributed to the increased pore volume and small nanosheets size that shorten the transport pathway of water molecules. Importantly, owing to the high photo-Fenton activity, the PKCN membrane exhibits fast (within 15 min) and excellent flux recovery (96.5%) after the photo-Fenton cleaning process. Furthermore, after 10 repeated usages, the PKCN membrane still keeps stable permeability and excellent purification efficiency. This work opens a door for developing self-cleaning membranes with the superior anti-fouling ability for effective oil/water separation.

Photo-assisted simultaneous electrochemical detection of multiple heavy metal ions with a metal-free carbon black anchored graphitic carbon nitride sensor

The simultaneous detection of multiple heavy metal ions in solution is an important yet highly challenging problem. In this work, a metal-free g-C₃N₄/carbon black (CB) composite electrode was synthesized by a one-step thermal polycondensation method and characterized by transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and ultraviolet visible light spectroscopy. In addition, the photoelectrochemical response of the g-C₃N₄/CB nanocomposite to Cd²⁺, Pb²⁺ and Hg²⁺ both separately and as a mixture of the three analytes was investigated by differential pulse anodic stripping voltammetry. The g-C₃N₄/CB electrode demonstrated an excellent sensing performance to Cd²⁺, Pb²⁺ and Hg²⁺ in the range of 0-700 nM, 0-300 nM and 0-500 nM, respectively, with limits of detection (LOD) of Cd²⁺, Pb²⁺, and Hg²⁺ of 2.1, 0.26 and 0.22 nM, respectively. The LOD of the combined solution of the three analytes was slightly higher at 3.3 nM. Additionally, the metal-free g-C₃N₄/CB photoelectrochemical sensor exhibited excellent electrochemical stability and electrode reproducibility. Finally, g-C₃N₄/CB sensor also showed satisfactory results in the detection of trace analyte ions in real environmental systems. This work provides a novel and promising approach in the simultaneous detection of multiple heavy metal ions in solution for practical applications.

A review on graphitic carbon nitride (g-C3N4) based hybrid membranes for water and wastewater treatment

Graphitic carbon nitride (g-C₃N₄) has gained enormous attention for water and wastewater treatment. Compared with g-C₃N₄ nanopowders, g-C₃N₄ based hybrid membranes have demonstrated great potential for its superior practicability. This review outlines the preparation and characterization of g-C₃N₄ based hybrid membranes and presents their representative applications in water and wastewater treatment (e.g., removal of organic dyes, phenolic compounds, pharmaceuticals, salt ions, heavy metals, and oils). Meanwhile, g-C₃N₄ based films for the removal of contaminants through photocatalytic degradation is also summarized. In addition, the corresponding mechanisms and relevant findings are discussed. Finally, the challenges and research needs in the future and application of g-C₃N₄ based hybrid membranes are highlighted.

Zwitterionic Copolymer-Regulated Interfacial Polymerization for Highly Permselective Nanofiltration Membrane

A highly permselective nanofiltration membrane was engineered via zwitterionic copolymer assembly regulated interfacial polymerization (IP). The copolymer was molecularly synthesized using single-step free-radical polymerization between 2-methacryloyloxyethyl phosphorylcholine (MPC) and 2-aminoethyl methacrylate hydrochloride (AEMA) (P[MPC-co-AEMA]). The dynamic network of P[MPC-co-AEMA] served as a regulator to precisely control the kinetics of the reaction by decelerating the transport of piperazine toward the water/hexane interface, forming a polyamide (PA) membrane with ultralow thickness of 70 nm, compared to that of the pristine PA (230 nm). Concomitantly, manipulating the phosphate moieties of P[MPC-co-AEMA] integrated into the PA matrix enabled the formation of ridge-shaped nanofilms with loose internal architecture exhibiting enhanced inner-pore interconnectivity. The resultant P[MPC-co-AEMA]-incorporated PA membrane exhibited a high water permeance of 15.7 L·m^-2·h^-1·bar^-1 (more than 3-fold higher than that of the pristine PA [4.4 L·m^-2·h^-1·bar^-1]), high divalent salt rejection of 98.3%, and competitive mono-/divalent ion selectivity of 52.9 among the state-of-the-art desalination membranes.

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.

Recent advances in graphite carbon nitride-based nanocomposites: structure, antibacterial properties and synergies

Bacterial infections and transmission threaten human health and well-being. Graphite carbon nitride (g-C₃N₄), a promising photocatalytic antibacterial nanomaterial, has attracted increasing attention to combat bacterial transmission, due to the outstanding stability, high efficiency and environmental sustainability of this material. However, the antibacterial efficiency of g-C₃N₄ is affected by several factors, including its specific surface area, rapid electron/hole recombination processes and optical absorption properties. To improve the efficiency of the antibacterial properties of g-C₃N₄ and extend its range of applications, various nanocomposites have been prepared and evaluated. In this review, the advances in amplifying the photocatalytic antibacterial efficiency of g-C₃N₄-based nanocomposites is discussed, including different topologies, noble metal decoration, non-noble metal doping and heterojunction construction. The enhancement mechanisms and synergistic effects in g-C₃N₄-based nanocomposites are highlighted. The remaining challenges and future perspectives of antibacterial g-C₃N₄-based nanocomposites are also discussed.

A transport channel-regulated MXene membrane via organic phosphonic acids for efficient water permeation

A series of organic phosphonic acids (OPAs) were applied as multifunctional spacers to enlarge the inner space of carbide MXene (Ti3C2Tx) laminates. A synergistic improvement in permeance, rejection and stability is achieved via introducing OPA to create pillared laminates. This strategy provides a universal way to regulate transport channels of MXene-based membranes.

2D Heterostructured Nanofluidic Channels for Enhanced Desalination Performance of Graphene Oxide Membranes

The two-dimensional (2D) lamellar membrane assembly technique shows substantial potential for sustainable desalination applications. However, the relatively wide and size-variable channels of 2D membranes in aqueous solution result in inferior salt rejections. Here we show the establishment of nanofluidic heterostructured channels in graphene oxide (GO) membranes by adding g-C₃N₄ sheets into GO interlamination. Benefiting from the presence of stable and sub-nanometer wide (0.42 nm) GO/g-C₃N₄ channels, the GO/g-C₃N₄ membrane exhibits salt rejections of ∼90% with water permeances of above 30 L h^-1 m^-2 bar^-1, while the pure GO membrane only has salt rejections of below 30% accompanied by water permeances of below 4 L h^-1 m^-2 bar^-1. Combining experimental and theoretical investigations, size exclusion has proved to be the dominating mechanism for high rejections, and the ultralow friction water flow along g-C₃N₄ sheets is responsible for permeation enhancements. Importantly, the GO/g-C₃N₄ membrane shows promising long-term, antioxidation, and antipressure stability.

Direct Synthesis of Atomically Dispersed Palladium Atoms Supported on Graphitic Carbon Nitride for Efficient Selective Hydrogenation Reactions

Heterogeneous catalysts with atomically precise metal sites have enabled unique insight into structure-property relationships in materials science. Herein, we report the construction and selective hydrogenation performance of a single-atom palladium catalyst by confining the palladium atoms into the six-fold N-coordinating cavities of graphitic carbon nitride (g-C₃N₄) through a facile spatial confinement-reduction approach under mild reducing conditions. Spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements confirm the presence of atomically dispersed palladium atoms stabilized by the g-C₃N₄ support. Its exceptional catalytic activity was demonstrated by the hydrogenation of styrene (98% conversion, 1.5 h) and furfural (conversion of 64% and selectivity of 99%, 4 h) and hydrodechlorination of 4-chlorophenol (99% conversion and 99% selectivity, 10 min). This palladium catalyst can be reused at least five times with negligible deterioration of its activity. Importantly, the palladium atoms retained their atomic dispersion following the thermal treatment. Moreover, this synthetic method can be scaled up while retaining similar catalytic activity. Fundamental insights are provided to elucidate how the material's structure significantly impacts the catalytic performance at the atomic scale.

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.

A new Ni-diaminoglyoxime-g-C3N4 complex towards efficient photocatalytic ethanol splitting via a ligand-to-metal charge transfer (LMCT) mechanism

We report a novel Ni-diaminoglyoxime-g-C₃N₄ (Ni-DAG-CN) complex for H₂ evolution through photocatalytic ethanol splitting. Compared to that of pristine g-C₃N₄, Ni-DAG-CN exhibits a 21-fold enhancement of photocatalytic activity (296.1 μmol h^-1 g^-1) under irradiation with excellent stability. The enhanced photocatalytic activity can be attributed to a proposed ligand-to-metal charge transfer (LMCT) mechanism, which is illustrated both experimentally and theoretically. This work provides great potential in the future design of low-cost, high-performance photocatalysts for H₂ evolution from alcohol splitting.