Layered g-C3N4@Reduced Graphene Oxide Composites as Anodes with Improved Rate Performance for Lithium-Ion Batteries

Synthesis and up-to-date applications of 2D microporous g-C3N4 nanomaterials for sustainable development

In recent years, with the development of industrial technology and the increase of people's environmental awareness, the research on sustainable materials and their applications has become a hot topic. Among two-dimensional (2D) materials that have been selected for sustainable research, graphitic phase carbon nitride (g-C3N4) has become a hot research topic because of its many outstanding advantages such as simple preparation, good electrochemical properties, excellent photochemical properties, and better thermal stability. Nevertheless, the inherent limitations of g-C3N4 due to its relatively poor specific surface area, rapid charge recombination, limited light absorption range, and inferior dispersion in aqueous and organic media have limited its practical application. In the review, we summarize and analyze the unique structure of the 2D microporous nanomaterial g-C3N4, its synthesis method, chemical modification method, and the latest application examples in various fields in recent years, highlighting its advantages and shortcomings, with a view to providing ideas for overcoming the difficulties in its application. Furthermore, the pressing challenges faced by g-C3N4 are briefly discussed, as well as an outlook on the application prospects of g-C3N4 materials. It is expected that the review in this paper will provide more theoretical strategies for the future practical application of g-C3N4-based materials, as well as contributing to nanomaterials in sustainable applications.

An electrochemical biosensor for detecting DNA methylation based on AuNPs/rGO/g-C3N4 nanocomposite

DNA methylation as a ubiquitously regulation is closely associated with cell proliferation and differentiation. Growing data shows that aberrant methylation contributes to disease incidence, especially in tumorigenesis. The approach for identifying DNA methylation usually depends on treatment of sodium bisulfite, which is time-consuming and conversion-insufficient. Here, with a special biosensor, we establish an alternative approach for detecting DNA methylation. The biosensor is consisted of two parts, which are gold electrode and nanocomposite (AuNPs/rGO/g-C₃N₄). Nanocomposite was fabricated by three components, which are gold nanoparticles (AuNPs), reduced graphene oxide (rGO) and graphite carbon nitride (g-C₃N₄). For methylated DNA detection, the target DNA was captured by probe DNA immobilized on the gold electrode surface through thiolating process and subjected to hybrid with anti-methylated cytosine conjugated to nanocomposite. When the methylated cytosines in target DNA were recognized by anti-methylated cytosine, a change of electrochemical signals will be observed. With different size of target DNAs, the concentration and methylation level were tested. It is shown that in short size methylated DNA fragment, the linear range and LOD of concentration is 10^-7M-10^-15M and 0.74 fM respectively; in longer size methylated DNA, the linear range of methylation proportion and LOD of copy number is 3%-84% and 10³ respectively. Also, this approach has a high sensitivity and specificity as well as anti-disturbing ability.

On the Road to the Frontiers of Lithium-Ion Batteries: A Review and Outlook of Graphene Anodes

Graphene has long been recognized as a potential anode for next-generation lithium-ion batteries (LIBs). The past decade has witnessed the rapid advancement of graphene anodes, and considerable breakthroughs are achieved so far. In this review, the aim is to provide a research roadmap of graphene anodes toward practical LIBs. The Li storage mechanism of graphene is started with and then the approaches to improve its electrochemical performance are comprehensively summarized. First, morphologically engineered graphene anodes with porous, spheric, ribboned, defective and holey structures display improved capacity and rate performance owing to their highly accessible surface area, interconnected diffusion channels, and sufficient active sites. Surface-modified graphene anodes with less aggregation, fast electrons/ions transportation, and optimal solid electrolyte interphase are discussed, demonstrating the close connection between the surface structure and electrochemical activity of graphene. Second, graphene derivatives anodes prepared by heteroatom doping and covalent functionalization are outlined, which show great advantages in boosting the Li storage performances because of the additionally introduced defect/active sites for further Li accommodation. Furthermore, binder-free and free-standing graphene electrodes are presented, exhibiting great prospects for high-energy-density and flexible LIBs. Finally, the remaining challenges and future opportunities of practically available graphene anodes for advanced LIBs are highlighted.

An insight into the sodium-ion and lithium-ion storage properties of CuS/graphitic carbon nitride nanocomposite

Metal sulfides are gaining prominence as conversion anode materials for lithium/sodium ion batteries due to their higher specific capacities but suffers from low stability and reversibility issues. In this work, the electrochemical properties of CuS anode material has been successfully enhanced by its composite formation using graphitic carbon nitride (g-C3N4). The CuS nanoparticles are distributed evenly in the exfoliated g-C3N4 matrix rendering higher electronic conductivity and space for volume alterations during the repeated discharge/charge cycles. The 0.8CuS:0.2g-C3N4 composite when used as an anode for lithium ion coin cell exhibits a reversible capacity of 478.4 mA h g-1 at a current rate of 2.0 A g-1 after a run of 1000 cycles which is better than that reported for CuS composites with any other carbon-based matrix. The performance is equally impressive when 0.8CuS:0.2g-C3N4 composite is used as an anode in a sodium ion coin cell and a reversible capacity of 408 mA h g-1 is obtained at a current rate of 2.0 A g-1 after a run of 800 cycles. A sodium ion full cell with NVP cathode and 0.8CuS:0.2g-C3N4 composite anode has been fabricated and cycled for 100 runs at a current rate of 0.1 A g-1. It can be inferred that the g-C3N4 matrix improves the ion transfer properties, alleviates the volume alteration happening in the anode during the discharge/charge process and also helps in preventing the leaching of polysulfides generated during the electrochemical process.

Molten salt synthesis of KCl-preintercalated C3N4 nanosheets with abundant pyridinic-N as a superior anode with 10 K cycles in lithium ion battery

The graphitic carbon nitride is considered as the promising anode of lithium ion battery due to its high theoretical capacity (>1000 mAh g^-1) and easy synthesis method. But the electrochemical inactivity and the structural collapse during cycles lead to its poor electrochemical performance in practice. Here, an interesting molten salt method is used to obtain the KCl-preintercalated carbon nitride nanosheets with abundant N vacancies and pyridinic-N. The KCl as a prop enhances the interlayer distance and the structural stability. And the N vacancy and the pyridinic-N increase the conductivity, the active sites and the reversibility of Li⁺ storage. Thus, the optimized electrode shows a higher specific discharge capacity (389 mAh g^-1 at 0.1 A g^-1) and a longer cyclic life (66% capacity retention after 10 K cycles at 3.0 A g^-1) compared to those of bulk g-C₃N₄.

Unveiling the Working Mechanism of g-C3N4 as a Protection Layer for Lithium- and Sodium-Metal Anode

The practical application of lithium-/sodium-metal batteries is currently hindered by severe safety issues caused by uncontrolled continuous dendrite growth. Semiconductive nanoporous g-C₃N₄ film has been demonstrated to be an effective protection layer for lithium-/sodium-metal anode, which can suppress the growth of dendrite. However, the underlying mechanism of how this semiconductive flexible thin film works to suppress dendrite growth remains unclear. In this work, we investigate the detailed working mechanism of g-C₃N₄ protection layer employing both density functional theory calculations and ab initio molecular dynamics simulations. The calculation results indicate that g-C₃N₄ layers show strong adhesion toward the lithium-/sodium-metal surface. When contacting with lithium/sodium metal, the intrinsic triangular nanopores of g-C₃N₄ will be quickly filled with lithium/sodium atoms, turning the semiconductive g-C₃N₄ into a metallic material. Lithium/sodium atoms can migrate through the triangular nanopores of stacked g-C₃N₄ layers via a vacancy-mediated approach with moderate energy barriers of 0.42 and 0.61 eV, respectively. With a low current density, the newly deposited lithium/sodium atoms can permeate through the g-C₃N₄ protection layers, therefore resulting in a flat electrode surface with no dendrite; with a high current density, however, the newly deposited lithium/sodium atoms cannot transport across the protection layer timely, which will result in the aggregation of lithium/sodium atoms on the surface of the g-C₃N₄ protection layer.

Covalent Fixing of MoS2 Nanosheets with SnS Nanoparticles Anchored on g-C3N4/Graphene Boosting Fast Charge/Ion Transport for Sodium-Ion Hybrid Capacitors

The sluggish layered structural sodium reaction kinetics and the easy restacking property are major obstacles hindering the practical application of MoS₂-based electrodes for sodium storage. Herein, covalently assembled two-phase MoS₂-SnS supported by a hierarchical graphitic carbon nitride/graphene (MoS₂-SnS@g-C₃N₄/G) composite is constructed to improve cycling cyclability and rate performances for Na storage. The multiphase MoS₂-SnS@g-C₃N₄/G is featured with a covalent assembly strategy and an interconnected network architecture. This unique structural design can not only enhance the conductivity and facilitate fast interfacial electron transport, which is confirmed by experiments and density functional theory, but also buffer the volumetric changes of MoS₂-SnS. As a result, the as-obtained MoS₂-SnS@g-C₃N₄/G anode delivers a high reversible capacity of 834 mA h g^-1 at 0.1 A g^-1, a high rate capability of 452 mA h g^-1 at 5 A g^-1, and a long-term cycling stability (320 mA h g^-1 at 2 A g^-1 with 54.7% retention after 500 cycles) for the Na half-cell. Coupling with activated carbon (AC), our MoS₂-SnS@g-C₃N₄/G||AC sodium-ion hybrid capacitor delivers high energy/power densities (193.1 W h kg^-1/90 W kg^-1 and 41.5 W h kg^-1/18,000 W kg^-1) and a stable cycle life in the potential range of 0-4.0 V.

Synthesis of lignin-derived nitrogen-doped carbon as a novel catalyst for 4-NP reduction evaluation

In this study, nitrogen-doped carbon (NC) was fabricated using lignin as carbon source and g-C₃N₄ as sacrificial template and nitrogen source. The structural properties of as-prepared NC were characterized by TEM, XRD, FT-IR, Raman, XPS and BET techniques. Attractively, NC has proved efficient for reducing 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) using NaBH₄ as hydrogen donor with high apparent rate constant (k_app = 4.77 min^-1) and specific mass activity (s = 361 mol kgcat^-1 h^-1), which values are superior to the previously reported catalysts in the literature. Density functional theory (DFT) calculations demonstrate that four kinds of N dopants can change the electronic structure of the adjacent carbon atoms and contribute to their catalytic properties dependant on N species, however, graphitic N species has much greater contribution to 4-NP adsorption and catalytic reduction. Furthermore, The preliminary mechanism of this transfer hydrogenation reaction over as-prepared NC is proposed on the basis of XPS and DFT data. Astoundingly, NC has excellent stability and reusability of six consecutive runs without loss of catalytic activity. These findings open up a vista to engineer lignin-derived NC as metal-free catalyst for hydrogenation reaction.

A Nitrogen-Doped Manganese Oxide Nanoparticles/Porous Carbon Nanosheets Hybrid Material: A High-Performance Anode for Lithium Ion Batteries

A nitrogen-doped MnO nanoparticles/ porous carbon nanosheets (N-MnO/PCS) composite was synthesized by the room-temperature redox reaction between KMnO₄ and PCS followed by a facile carbothermal reduction, and a subsequent coating process of urea onto MnO/PCS and heat treatment. N-MnO nanoparticles with a grain size of about 30 nm are homogenously embedded on the surface of the N-PCS, corresponding to a high loading of 50.09 wt.% in the resulting composite. Benefiting from the enhanced reaction kinetics as well as electrical conductivity and continuous transport pathways of Li⁺ /electron resulting from the N-doping and hybridization of the cross-linked porous carbon substrate, the as-synthesized N-MnO/PCS-1 electrode delivers a large reversible specific capacity (1497.2 mA h g^-1 at 100 mA g^-1 after 160 cycles), outstanding rate capacities (710.6 mA h g^-1 at 1 A g^-1 and 640.1 mA h g^-1 at 2 A g^-1 ) and long-term cycling stability with specific capacity (976 mA h g^-1 at 0.5 A g^-1 after cycling 300 cycles). The simple and green synthesis and electronic properties of this composite mean that it has great potential as a high-capacity anode material for practical application in large-scale energy storage devices.