Reinforcing the tetracene-based two-dimensional C48H16 sheet by decorating the Li, Na, and K atoms for hydrogen storage and environmental application -A DFT study.

To meet the increasing need of energy resources, hydrogen (H2) is being considered as a promising candidate for energy carrier that has motivated research into appropriate storage materials among scientists. Thus, in this study for the first time, zig-zag and armchair edged tetracene based porous carbon sheet (C48H16) is investigated for H2 storage using the density functional theory. To explore the hydrogen storage capacity, the hydrogen molecule is initially positioned parallel to the C48H16 sheet at three different sites, resulting in lower adsorption energies of -0.020, -0.024, and -0.015 eV respectively. The Li, Na, and K atoms are decorated to improve H2 adsorption on the C48H16 sheet. The Li atom decorated C48H16 sheet has a higher binding energy value of -2.070 eV than the Na and K atom decorated C48H16 sheet. The presence of Li, Na, and K atoms on the C48H16 sheet enhance the H2 adsorption energy than the H2 on the pristine C48H16 sheet. The decrease of Mulliken charge in alkali metal atoms (Li, Na, and K atom) on the C48H16 sheet reveal that the electron is transferred from H-σ orbital to s orbital of alkali metal atoms on the C48H16 sheet, leads to the enhancement of H2 binding. Compared to H2 adsorption on Na and K atom decorated C48H16 sheet, the H2 adsorption on Li atom decorated C48H16 sheet has the maximum adsorption energy value of -0.389 eV. The obtained hydrogen storage capacity of Li, Na, and K atoms decorated C48H16 sheets are about 7.49 wt%, 7.31 wt%, and 7.14 wt% respectively for four H2 molecules, which is greater than the targeted hydrogen storage capacity of the United States Department of Energy (DOE). Thus the obtained results in this work reveal that the decorated C48H16 sheets with Li, Na, and K atom plays the potential role in the H2 storage.

Ultra-Thin Wrinkled Carbon Sheet as an Anode Material of High-Power-Density Potassium-Ion Batteries.

Although K+ is readily inserted into graphite, the volume expansion of graphite of up to 60% upon the formation of KC8, together with its slow diffusion kinetics, prevent graphite from being used as an anode for potassium-ion batteries (PIBs). Soft carbon with low crystallinity and an incompact carbon structure can overcome these shortcomings of graphite. Here, ultra-thin two-dimensional (2D) wrinkled soft carbon sheets (USCs) are demonstrated to have high specific capacity, excellent rate capability, and outstanding reversibility. The wrinkles themselves prevent the dense stacking of micron-sized sheets and provide sufficient space to accommodate the volume change of USCs during the insertion/extraction of K+. The ultra-thin property reduces strain during the formation of K-C compounds, and further maintains structural stability. The wrinkles and heteroatoms also introduce abundant edge defects that can provide more active sites and shorten the K+ migration distance, improving reaction kinetics. The optimized USC20-1 electrode exhibits a reversible capacity of 151 mAh g-1 even at 6400 mA g-1, and excellent cyclic stability up to 2500 cycles at 1000 mA g-1. Such comprehensive electrochemical performance will accelerate the adoption of PIBs in electrical energy applications.

Nitrogen-enriched carbon sheet for Methyl blue dye adsorption.

In this work, nitrogen-enriched carbon sheet (NECS) was successfully fabricated by using sodium gluconate as a carbon source via melamine assisted chemical blowing approach. The obtained material exhibits sheet-like morphology with ultra-thin thickness and has a high specific surface area of 604 m2g-1 and high nitrogen contents of 11.2 wt%. The NECS showed an excellent adsorption performance towards the removal of anionic dye Methyl blue (a-Mb). The adsorption of a-Mb onto NECS better fitted the Langmuir isotherm model with the highest adsorption capacity of 847 mg g-1. Interestingly, the NECS showed a pH-sensitive behavior towards the adsorption efficiency of a-Mb dye in which the adsorption capacity abruptly increased from 34 to 701 mg g-1 when the pH of the solution was decreased from 10 to 2. Furthermore, the adsorbed materials can be easily regenerated without obvious efficiency loss over a five adsorption-desorption cycles.

Ultrathin Carbon Sheet Obtained by Self-Template Method toward Highly Effective Charge Transfer for Si-Based Anodes.

A dynamic and stable charge transfer process is the key to exerting lithium storage characteristics of the silicon anode with a large volume change. In this work, the composite with an ultrathin carbon sheet skeleton is prepared by freeze-drying and a copyrolysis process after uniformly mixing citric acid and hydroxylated Si NPs, which is different from traditional conformal carbon coating derived from citric acid. A flexible carbon sheet reduces internal particle (Si-OH@NC) slip and cooperates with interfacial Si-O-C bonding to buffer machinal stress in the electrode during cycling. More importantly, the carbon sheet network increases the point-to-surface contact area between the active material and the conductive agent, ensures continuous electrical connection from the current collector to the active material, and promotes a rapid and stable electron transfer process. Besides, the N-doped C structure with remarkable nucleophilicity guarantees fast ion transport, which is confirmed by theoretical calculation. In this way, the reaction reversibility of the Si-based electrode is further realized during cycles. As a result, the electrode delivers excellent cycle performance (reversible capacity of 1001.9 mAh g-1 at 1 A g-1 after 500 cycles) and rate performance (capacity retention of 86.8 and 65.8% at 1 and 3 A g-1, respectively, compared to 0.2 A g-1). The idea of constructing a highly efficient electrode conductive network through a doped-carbon sheet network is also applicable to other active materials with huge volume changes during lithium storage.

Some new results on the face index of certain polycyclic chemical networks.

Silicate minerals make up the majority of the earth's crust and account for almost 92 percent of the total. Silicate sheets, often known as silicate networks, are characterised as definite connectivity parallel designs. A key idea in studying different generalised classes of graphs in terms of planarity is the face of the graph. It plays a significant role in the embedding of graphs as well. Face index is a recently created parameter that is based on the data from a graph's faces. The current draft is utilizing a newly established face index, to study different silicate networks. It consists of a generalized chain of silicate, silicate sheet, silicate network, carbon sheet, polyhedron generalized sheet, and also triangular honeycomb network. This study will help to understand the structural properties of chemical networks because the face index is more generalized than vertex degree based topological descriptors.

Mesoporous Weaved Turbostratic Nanodomains Enable Stable Na+ Ion Storage and Micropore Filling is Revealed to be More Unsafe than Adsorption and Deintercalation.

Advanced wave-shape non-graphitizable carbon sheets are derived, comprising mesoporous weaved turbostratic micropore enabled stable Na+ ion storage. The non-graphitizable amorphous characteristics are determined from the obtained two broad diffraction peaks at 22.7° and 43.8°. The observed D-band at 1325 cm-1 and G-band at 1586 cm-1 confirm the disordered graphitic structure, attributed to the measured specific surface area of 54 m2 g-1. Mesoporous weaved wave-shape carbon sheet architecture is confirmed by surface morphological studies, showing lattice fringes of disordered graphitic structures and dispersed ring patterns for the non-crystalline characteristics. The predominant stable redox peak at 0.014 V/0.185 V and the broader rectangular shape between 0.9 and 0.15 V depict the adsorption-micropore filling mechanism. The mesoporous hard carbon sheet delivers discharge-charge capacities of 450/311 mAh g-1 (1st cycle) and 263/267 mAh g-1 (250th cycle) at 25 mA g-1, exhibiting a superior anode for sodium-ion batteries. Besides, in situ multimode calorimetry results disclose that the micropore filling Na+ ion storage shows a higher released total heat energy of 721 J g-1 than the adsorption (471 J g-1). Ultimately, differential scanning calorimetry analysis of micropore filling Na+ ion storage (discharged state at 0.01 V) has revealed a predominant exothermic peak at 156 °C with the highest released total heat energy of 2183 J g-1 compared to adsorption (553 J g-1) and deintercalation (85 J g-1), indicating that micropore filling status is more unsafe than the adsorption and deintercalation for SIBs.

Azo-dye derived oxidized-nitrogen rich carbon sheets with high adsorption capability for dye effluent under both batch and continuous conditions.

The removal of methyl blue (MB) from wastewater using graphene and its derivative is very successful due to their high aromaticity which drives adsorption via π-π and electron-donor-acceptor (EDA) interactions; however, graphene is expensive and difficult to synthesize, which limit its practical application. Meanwhile, low aromatic carbon materials (LACM) derived from farm-water and other materials are cheaper and easier to synthesize but have limited π-π and EDA interactions and low adsorption capacity. Herein, we demonstrate that LACM with oxidized-nitrogen (N-O-) functionality overcomes this limitation via chemisorption of MB through a combination of hydrophobic-hydrophobic interactions and EDA interactions. This is confirmed using XPS analysis of LACM/N-O- post MB adsorption. Consequently, a remarkable adsorption capacity of 3904 mg g-1 is achieved under batch condition which is the highest ever reported for any MB adsorbent. Furthermore, LACM/N-O- works equally well under continuous-flow adsorption conditions which shows its practicability. Amongst several LACM precursors tested, only Azo-dyes are able to generate LACM/N-O- implying that the NN moiety is key to N-O- formation. A carbonization temperature of 700 °C generates the highest N-O- sites hence the highest adsorption capacity. Characterization of LACM/N-O- is done mainly using BET, XPS, Raman, TGA, and FTIR analysis.

Co/CoOx heterojunctions encapsulated N-doped carbon sheets via a dual-template-guided strategy as efficient electrocatalysts for rechargeable Zn-air battery.

Developing highly efficient oxygen electrocatalysts is of vital importance for rechargeable Zn-air batteries (ZABs). Herein, Co/CoOx nano-heterojunctions encapsulated into nitrogen-doped carbon sheets (NCS@Co/CoOx) are fabricated via a dual-template-guided approach by using zeolitic imidazolate frameworks (ZIFs) as templates. The synergistic integration of structural and compositional advantages endows such catalyst with superior catalytic properties to benchmark noble-metal catalysts. To be specific, the hierarchical micro/mesopores affords massive mass transport channels and maximizes the exposure of accessible active sites, whereas the NCS matrix accelerates electron transfer and prevents the self-aggregation of active species during the electrocatalytic reaction. Moreover, abundant and synergistic Co-based active sites (CoO, Co3O4, Co-Nx) greatly promote the catalytic activity. As the cathode of both liquid and flexible solid-state ZABs, excellent device properties are achieved, outperforming those assembled with commercial Pt/C+RuO2 catalyst. This work presents a feasible and cost-effective strategy for developing oxygen electrocatalysts derived from ZIFs templates.

Folic Acid Self-Assembly Enabling Manganese Single-Atom Electrocatalyst for Selective Nitrogen Reduction to Ammonia.

Efficient and robust single-atom catalysts (SACs) based on cheap and earth-abundant elements are highly desirable for electrochemical reduction of nitrogen to ammonia (NRR) under ambient conditions. Herein, for the first time, a Mn-N-C SAC consisting of isolated manganese atomic sites on ultrathin carbon nanosheets is developed via a template-free folic acid self-assembly strategy. The spontaneous molecular partial dissociation enables a facile fabrication process without being plagued by metal atom aggregation. Thanks to well-exposed atomic Mn active sites anchored on two-dimensional conductive carbon matrix, the catalyst exhibits excellent activity for NRR with high activity and selectivity, achieving a high Faradaic efficiency of 32.02% for ammonia synthesis at - 0.45 V versus reversible hydrogen electrode. Density functional theory calculations unveil the crucial role of atomic Mn sites in promoting N2 adsorption, activation and selective reduction to NH3 by the distal mechanism. This work provides a simple synthesis process for Mn-N-C SAC and a good platform for understanding the structure-activity relationship of atomic Mn sites.

Porogen-in-Resin-Induced Fe, N-Doped Interconnected Porous Carbon Sheets as Cathode Catalysts for Proton Exchange Membrane Fuel Cells.

The high dependence of cathodic oxygen reduction reaction on precious Pt catalysts hinders the large-scale commercialization of proton exchange membrane (PEM) fuel cells, while the most promising alternative FeNC catalyst cannot achieve satisfying fuel cell performance yet. By considering the different requirements of atomically dispersed FeNC catalyst on the mass-transfer structure from that of nanoparticle Pt-based catalysts, this work develops a "porogen-in-resin" strategy to approach the Fe, N-doped interconnected porous carbon sheet (ip-FeNCS) catalyst. Three-dimensional (3D) interconnected porous structure and two-dimensional (2D) nanosheet morphology are therefore facilely combined in ip-FeNCS to simultaneously achieve the requirements on the transfer of reactants and accessibility of FeN active sites. Not only great ORR activity can be achieved under both alkaline and acid conditions but also the ip-FeNCS catalyst shows superb activity in practical PEM fuel cells from the high power output to 413 mW/cm2. Such fuel cell performance places this ip-FeNCS catalyst among the best FeNC ORR catalysts reported thus far. This work presents a general and facile approach toward the mass-transfer structure engineering of atomically dispersed carbon catalysts for practical PEM fuel cell applications.

Enhanced electro-generated ferrate using Fe(0)-plated carbon sheet as an anode and its online utilization for removal of cyanide.

Efficient electrochemical generation of ferrate (Fe(VI)) is still challenged by the passivation of iron materials. Herein, we employed Fe(0)-plated carbon sheet as an anode to enable an efficient production of Fe(VI) with its concentration reached up to 55 mM, which was 8 times higher than that with iron sheet of the same size as an anode. The SEM results showed that the close and uniform dispersion of tapered Fe(0) particles on the surface of carbon sheet helped prevent the formation of passivated layer. The preparative process of electro-deposited Fe(0) affected the generation of Fe(VI). The increase of electroplating time to 40 min and electroplating temperature to 30 °C promoted the production of Fe(VI), and the change in the concentration of Fe2+ in electroplated solution showed little impact on Fe(VI) generation. However, the addition of additives inhibited Fe(VI) generation. As well, an effective removal of cyanide was achieved using on-line production of Fe(VI), comparable to that by NaClO and higher than that by other traditional oxidants containing H2O2, O3, and KMnO4. This study would provide an simple and promising iron anode for efficient production of Fe(VI) by electrochemical method.

New Insights into Co-pyrolysis among Graphitic Carbon Nitride and Organic Compounds: Carbonaceous Gas Fragments Induced Synthesis of Ultrathin Mesoporous Nitrogen-Doped Carbon Nanosheets for Heterogeneous Catalysis.

N-doped carbon materials are well known as promising metal-free catalysts and applied in innumerable industrial synthetics. However, most of the N-doped carbon materials obtained by conventional synthetic means exhibit generally low mesoporosity, and their reported pore volumes reached only 1-3 cm3 g-1, which greatly limits their further industrial application in heterogeneous catalysis. Especially for oxidation reaction of alkylbenzenes, this type of reaction is almost always accompanied by many different byproducts, while the reaction activity and selectivity are mainly affected by mesoporosity of catalysts. Traditionally, graphitic carbon nitride (GCN) is commonly considered as a self-sacrificed nitrogen source together with multifarious organic compounds to obtain N-doped carbon materials by a co-pyrolysis process. However, the mechanisms of formation process are still complex and uncontrollable to date. In this work, we present a novel co-pyrolysis synthetic strategy by a facile chemical vapor deposition method for preparing a series of ultrathin N-doped carbon nanosheets with high mesoporosity. More importantly, it is found that GCN containing abundant hydrogen bonds can be irreversibly anchored by carbonaceous gas fragments (CxHy+) released from various organic substances via thermogravimetry-differential thermal analysis coupled with mass spectrometry and X-ray photoelectron spectroscopy analysis, and the CxHy+ fragments exhibit a non-negligible role during the transformation. Our results further demonstrated that the residue of incompletely decomposed GCN is a key point to enlarge porosity in final products which are obtained via mixing pyrolysis between an organic precursor and GCN (or GCN precursors). Benefitting from the outstanding mesoporosity and ultrathin morphology, the representative ABCNS-900 exhibits excellent catalytic performance for oxidizing ethylbenzene to acetophenone with extremely low dosage and high selectivity. Our findings show a universal synthetic strategy for ultrathin N-rich carbon nanosheets with a high mesopore volume, further promoting the application of N-doped carbon materials in heterogeneous catalytic industry.