Abstract: Frequent oil spill accidents and the massive discharge of industrial oily sewage have destroyed the ecological balance and threatened marine life. Graphene (G) and graphene oxide (GO) have emerged as important materials in the field of oil/water separation because of their remarkable physicochemical properties including high specific surface area, low density, high porosity and tailorable surface functionality. To take full advantage of G and GO, their incorporation with polymers to build functional G/polymer and GO/polymer composites has recently gained increasing popularity because of their improved oil clean-up capability, outstanding mechanical performance, relatively low cost and adjustable surface chemical composition. Tremendous efforts have contributed to the development of G/polymer and GO/polymer composite oil clean-up sorbents and filtration membranes in 3D structural forms such as aerogels, foams, sponges and membranes. In this review, a comprehensive picture from the basic theory of the surface wettability to the recent advances in G/polymer and GO/polymer composite oil clean-up sorbents and filtration membranes are highlighted. The strategies for oil recovery and regeneration of the sorbents are also summarized. Current challenges and future research directions in this topic are provided, aimed at providing new perspectives for in-depth exploration in this field.
Abstract: Potassium-ion capacitors (PICs) are promising energy storage devices, which are competitive with lithium-ion and sodium ion capacitors. PICs combine the advantages of a battery-type anode and a capacitive cathode, resulting in a low cost, high energy density, high power density and long cycle life. However, there is still a mismatch between the anode and cathode materials for achieving the optimum specific capacity and kinetics in PICs. Early studies have shown that the careful selection of electrode materials and their optimization is an effective way to solve this problem. We focus on the development of PIC anode materials including insertion-type and conversion-type materials. The insertion-type materials include carbon materials (graphite, soft carbons, hard carbons, etc.), K-based titanates, MXenes, and dipotassium terephthalate. The conversion-type materials include metal sulfides/selenides, metal phosphides and sodium super ionic conductor-type phosphates (NASICON). Their preparation, structural characteristics, electrochemical performance as anode materials in half-cell and PIC devices are summarized and discussed. The future prospects and challenges of PICs are also considered.
Abstract: Porous carbons with well-developed pores, tunable microstructures and stable chemistry play a significant role in energy storage and environmental pollution control. Biomass is a carbon precursor that is abundant, low cost, sustainable and carbon neutral, and is promising for the large-scale production of porous carbons. Among the various types of biomass, algae usually contain abundant cellulose and heteroatoms, which are suitable precursors for heteroatom-doped carbons. Recent advances in synthesis methods for algae-based porous carbons are reviewed and their pore formation mechanisms discussed. Their potential applications in adsorption, catalysis and energy storage are highlighted, and strategies for improving their performance are proposed. Future research trends and challenges for algae-based carbons are discussed, especially as they relate to their low-cost production and performance improvement.
Abstract: Photoelectrocatalysis is a sustainable process that plays a central role in clean energy production and pollution removal. Due to the constraints of current photoelectrocatalysts such as instability and scarcity, scientists have resorted to carbon nanomaterials that are more stable and abundant. It has been found that γ-graphdiyne (GDY), the most stable carbon phase among graphynes that contains a diacetylene bond, has some striking properties such as well-ordered pores, non-uniform electronic structure, easily tunable bandgap and excellent photoelectric performance. It has become a new “star” as a highly active photoelectrocatalyst. Its properties, synthesis strategies and photoelectrocatalytic applications are reviewed. Five reaction systems are summarized based on the phase state of the precursors and catalysts, which include liquid-solid, liquid-liquid, gas-liquid, gas-solid, and solid-gas systems. The roles GDY play in photoelectrocatalysis itself, or as a support for single atom catalytic species are discussed. Problems for current research work are discussed and future research trends are proposed.
Abstract: Nanoporous carbons (NPCs) are widely used in gas adsorption, catalysis and electrochemistry because of their high specific surface area, good thermal and chemical stability, etc. Although a lot of work has been done, there are still great challenges in the fabrication of NPCs. Metal organic frameworks (MOFs) with tailorable structures have the advantages of a regular and adjustable pore size, high porosity and high specific surface area, and have proved to be ideal precursors for the preparation of NPCs. To better grasp the state of the art in the preparation of NPCs, we review recent research progress on the fabrication of NPCs by the carbonization of MOFs, with a focus on the carbonization of different combinations of MOFs and guest precursors, both to tune the resulting pore sizes/textures and surface chemical structures/species and to improve the electrical conductivity and structural stability of the product in different applications.
Abstract: The lithium sulfur battery has a high theoretical capacity of 1675 mAh g-1, and is cheap and environmentally friendly, which make it a very promising secondary battery. However, its cycling stability cannot meet the requirements of industrialization due to the shuttle effect caused by the dissolution of polysulfides in the discharge process, the insulating nature of sulfur and the volume expansion of the sulfur cathode. Graphene has an excellent electrical conductivity, an extremely large specific surface area, good mechanical flexibility, and thermal and chemical stability, making it and its derivatives promising candidates to modify both the electrodes of an all-solid-state lithium-sulfur battery and the separator. The mechanisms, by which graphene and its derivatives inhibit the shuttle effect are summarized. The graphene network is very favorable for improving electron transfer rate, limiting volume expansion and facilitating lithium ion migration in the sulfur cathode of all-solid-state lithium-sulfur batteries. As modifiers of the separator, the hexagonal layer structure of graphene and its derivatives forms channels for lithium-ion transport and sulfur capture. Development strategies for using graphene and its derivatives in lithium-sulfur batteries are proposed.
Abstract: Graphene and graphene-like carbons (G-carbons) have many excellent properties, such as a high specific surface area, and good electrical and thermal conductivities. Recent advances in the synthesis of large amounts of G-carbons from biomass are discussed, including the types of biomass materials used as the precursors and the various synthesis routes. The latter include high-temperature graphitization, growth on substrates, template-assisted synthesis, template-free catalysis, a g-C3N4-derived approach, plasma-assisted synthesis, and laser-induced synthesis. The uses of G-carbons in electrochemical energy storage and conversion, and sensing are also discussed.
Abstract: As a type of carbon dot (CD) with a positive charge on their surface, cationic carbon dots (CCDs) can be obtained from CDs and amino-containing cationic compounds by one-step or two-step preparation. They not only retain the good fluorescence performance, low toxicity and biocompatibility of CDs, but also improve their gene delivery efficiency and cell uptake capacity. These excellent properties give CCDs potential advantages in the fields of the targeted fluorescence imaging of cancers and gene therapy. This paper reviews the preparation methods and properties of CCDs, suggesting that they can be used as good targeting carriers for imaging cancer and gene therapy. In addition, the basic principles of CCDs for cancer detection and treatment, and their uses in integrated cancer diagnosis and gene therapy are introduced. Current problems and future development trends of CCDs for this purpose are discussed.
Abstract: Multi-component porous Si-SiOx (pSi) consisting of Si, SiO and SiO2 was formed by the pretreatment of SiO at 950 °C for 3 h in an inert atmosphere (He) using a disproportionation reaction. Hybrids of pSi and carbon nanofibers (pSi-CNFs) with a core-shell structure were prepared by catalytic chemical vapor deposition (CVD) using Fe-Ni species as the catalyst and a mixture of CO/H2/C2H4 (volumetric ratio 3∶1∶1) as the reactant for 0.5, 1 and 2 h, and were characterized by SEM, TEM, EDS, XRD, Raman spectroscopy and XPS. Results indicate that the pSi-CNF particle sizes are 5−20 μ m with the diameters of the CNFs being 5−40 nm. The CNFs are uniformly coated on the surface of the pSi to form a core-shell structure. Electrochemical performance testing shows that the reversible capacity of the pSi-CNF (0.5 h) remains at 1 411 mAh.g−1 and the capacity retention is 74% after 100 cycles at a current density of 0.2 A.g−1. The reversible capacity remains at 735 mAh.g−1 at a current density of 1 A g−1 after 300 cycles with a capacity retention of 86%. In the pSi, Si and SiO provide the electrochemical reversible capacity. The core-shell structure with the CNF coating effectively improves the conductivity of the composites, and also inhibits the volume expansion of silicon to maintain the integrity of the core shell structure.
Abstract: Polyacrylonitrile (PAN) nanofibers obtained by electrospinning were used to prepare PAN-based carbon nanofibers (PCNFs) by pre-oxidation, carbonization and high-temperature treatment in NH3. The PCNFs were used for the removal of low concentrations of NO (5×10−5) near room temperature (20 °C) by catalytic oxidation. Results indicated that the PCNFs had high porosity and a large specific surface area, and their diameters could be regulated by changing the PAN concentration. The smaller the diameter of the PCNFs the more micropores were developed, and the larger the specific surface area the better the adsorption and catalytic oxidation performance.
Abstract: The gas diffusion layer (GDL) is an important component of the membrane electrode assembly of fuel cells (FCs). Its roles include supporting the catalyst layer, collecting current, and transferring and redistributing materials. A conventional GDL consists of a backing layer, typically of commercial carbon paper or carbon cloth, but it suffers from its high cost, narrow pore-size distribution, lack of flexibility and poor conductivity, and a micro-porous layer (MPL) is necessary for better gas/liquid management. A novel flexible gas diffusion layer (GDL) was prepared by vacuum filtration of a suspension of carbon fibers (CFs) and highly-dispersed multi-wall carbon nanotubes (MWCNTs) in a polytetrafluoroethylene (PTFE) binder and water repellent. SEM observations, gas permeability and porosity tests indicate that there is a gradient in the concentration of highly-conductive MWCNTs in the CNT-CF GDL network that facilitates electron transport. A multi-level pore structure is formed, which is beneficial to mass transport. The PTFE is distributed uniformly, which is favorable for the discharge of condensed water from the FCs. When the GDL/CNT-CF is used in the cathode, or in both the cathode and anode in direct methanol FCs, the maximum power densities of single cells are increased by 20% and 35%, respectively, compared with those using a commercial GDL consisting of carbon paper with a MPL due to its excellent mass transfer performance.
Abstract: Graphene has been considered as an ideal reinforcement filler for metal matrix composites because of its ultra-high strength and stiffness, and exceptional thermal and electrical properties. Graphene-reinforced copper (Gr/Cu) nanocomposites were fabricated by ball milling followed by pressureless vacuum sintering, and were characterized by SEM, TEM, XRD, Raman spectroscopy and mechanical tests. Results indicate that the graphene platelets are well dispersed in the nanocomposites without apparent damage. The graphene filler dramatically improves the hardness and reduces the coefficient of friction of the Gr/Cu nanocomposites compared to pure Cu.
Abstract: The control of the molecular weight of polyacrylonitrile and its distribution is important for carbon fiber preparation. Polyacrylonitrile was synthesized by photo-induced solution polymerization using acrylonitrile as the monomer and dimethyl sulfoxide as a solvent. The molecular weight and molecular weight distribution of the polyacrylonitrile were respectively determined by a viscosity method with an Ubbelohde viscometer and gel permeation chromatography. The functional groups on and the chain structure of polyacrylonitrile were analyzed by infrared spectroscopy and nuclear magnetic resonance spectroscopy. Results showed that with an increase of polymerization temperature or monomer concentration, the conversion of the monomer and the molecular weight increased. Compared with the traditional initiator-induced radical polymerization of acrylonitrile, photo-induced polymerization significantly narrows the molecular weight distribution. Polyacrylonitrile with both a high molecular weight and a relatively narrow molecular weight distribution was manufactured by photo-induced solution polymerization.