Boron and Nitrogen Co-Doped Porous Graphene Nanostructures for the Electrochemical Detection of Poisonous Heavy Metal Ions.

Heavy metal poisoning has a life-threatening impact on the human body to aquatic ecosystems. This necessitates designing a convenient green methodology for the fabrication of an electrochemical sensor that can detect heavy metal ions efficiently. In this study, boron (B) and nitrogen (N) co-doped laser-induced porous graphene (LIGBN) nanostructured electrodes were fabricated using a direct laser writing technique. The fabricated electrodes were utilised for the individual and simultaneous electrochemical detection of lead (Pb2+) and cadmium (Cd2+) ions using a square wave voltammetry technique (SWV). The synergistic effect of B and N co-doping results in an improved sensing performance of the electrode with better sensitivity of 0.725 µA/µM for Pb2+ and 0.661 µA/µM for Cd2+ ions, respectively. Moreover, the sensing electrode shows a low limit of detection of 0.21 µM and 0.25 µM for Pb2+ and Cd2+ ions, with wide linear ranges from 8.0 to 80 µM for Pb2+ and Cd2+ ions and high linearity of R2 = 0.99 in case of simultaneous detection. This rapid and facile method of fabricating heteroatom-doped porous graphene opens a new avenue in electrochemical sensing studies to detect various hazardous metal ions.

Novel Materials in Perovskite Solar Cells: Efficiency, Stability, and Future Perspectives.

Solar energy is regarded as the finest clean and green energy generation method to replace fossil fuel-based energy and repair environmental harm. The more expensive manufacturing processes and procedures required to extract the silicon utilized in silicon solar cells may limit their production and general use. To overcome the barriers of silicon, a new energy-harvesting solar cell called perovskite has been gaining widespread attention around the world. The perovskites are scalable, flexible, cost-efficient, environmentally benign, and easy to fabricate. Through this review, readers may obtain an idea about the different generations of solar cells and their comparative advantages and disadvantages, working mechanisms, energy alignment of the various materials, and stability achieved by applying variable temperature, passivation, and deposition methods. Furthermore, it also provides information on novel materials such as carbonaceous, polymeric, and nanomaterials that have been employed in perovskite solar in terms of the different ratios of doping and composite and their optical, electrical, plasmonic, morphological, and crystallinity properties in terms of comparative solar parameters. In addition, information on current trends and future commercialization possibilities of perovskite solar have been briefly discussed based on reported data by other researchers.

Nanoarchitectonics of Three-Dimensional Carbon Nanofiber-Supported Hollow Copper Sulfide Spheres for Asymmetric Supercapacitor Applications.

Three-dimensional carbon nanofiber (3D-CNF)-supported hollow copper sulfide (HCuS) spheres were synthesized by the facile hydrothermal method. The morphology of the as-synthesized HCuS@3D-CNF composite clearly revealed that the 3D-CNFs act as a basement for HCuS spheres. The electrochemical performance of as-synthesized HCuS@3D-CNFs was evaluated by cyclic voltammetry (CV) tests, gravimetric charge-discharge (GCD) tests, and Nyquist plots. The obtained results revealed that the HCuS@3D-CNFs exhibited greater areal capacitance (4.6 F/cm2) compared to bare HCuS (0.64 F/cm2) at a current density of 2 mA/cm2. Furthermore, HCuS@3D-CNFs retained excellent cyclic stability of 83.2% after 5000 cycles. The assembled asymmetric device (HCuS@3D-CNFs//BAC) exhibits an energy density of 0.15 mWh/cm2 with a working potential window of 1.5 V in KOH electrolyte. The obtained results demonstrate that HZnS@3D-CNF nanoarchitectonics is a potential electrode material for supercapacitor applications.

Fly Ash-Incorporated Polystyrene Nanofiber Membrane as a Fire-Retardant Material: Valorization of Discarded Materials.

Reusing or recycling waste into new useful materials is essential for environmental protection. Herein, we used discarded polystyrene (PS) and fly-ash (FA) particles and a fabricated fly-ash incorporated polystyrene fiber (FA/PS fiber) composite. The electrospinning process produced continuous PS fibers with a good distribution of FA particles. The prepared nanofibers were characterized by state-of-the-art techniques. The performances of the composite nanofibers were tested for fire-retardant applications. We observed that the incorporation of FA particles into the PS fibers led to an improvement in the performance of the composite as compared to the pristine PS fibers. This study showed an important strategy in using waste materials to produce functional nanofibers through an economical procedure. We believe that the strategy presented in this paper can be extended to other waste materials for obtaining nanofiber membranes for various environmental applications.

Silicon Carbide Nanostructures as Potential Carbide Material for Electrochemical Supercapacitors: A Review.

Silicon carbide (SiC) is a very promising carbide material with various applications such as electrochemical supercapacitors, photocatalysis, microwave absorption, field-effect transistors, and sensors. Due to its enticing advantages of high thermal stability, outstanding chemical stability, high thermal conductivity, and excellent mechanical behavior, it is used as a potential candidate in various fields such as supercapacitors, water-splitting, photocatalysis, biomedical, sensors, and so on. This review mainly describes the various synthesis techniques of nanostructured SiC (0D, 1D, 2D, and 3D) and its properties. Thereafter, the ongoing research trends in electrochemical supercapacitor electrodes are fully excavated. Finally, the outlook of future research directions, key obstacles, and possible solutions are emphasized.

An electrochemically reduced ultra-high mass loading three-dimensional carbon nanofiber network: a high energy density symmetric supercapacitor with a reproducible and stable cell voltage of 2.0 V.

Commercial supercapacitors need a high mass loading of more than 10 mg cm-2 and a high working potential window to resolve the low energy density concern. Herein, we have demonstrated a thick, ultrahigh mass loading (35 mg cm-2) and wide cell voltage electrochemically reduced layer-by-layer three-dimensional carbon nanofiber network (LBL 3D-CNF) electrode via electrospinning, sodium borohydride treatment, carbonization, and electro-reduction techniques. During the electro-reduction technique, Na+ is adsorbed onto the various defect sites of LBL 3D-CNFs, which properly inhibits the formation of the intermediate HER (hydrogen evolution reaction) product, leading to a wide cell voltage, whereas the LBL 3D-CNF network evokes an opportunity for storing a greater number of charges, resulting in excellent electrochemical performances. A symmetric supercapacitor with a reproducible and stable cell voltage of 2.0 V is constructed and demonstrated. The as-constructed device can deliver an areal energy output of 1922 µW h cm-2 at a power density of 3979 W kg-1 equal to a gravimetric energy density of 27 W h kg-1, and an outstanding cyclic durability of 97.4% after 20 000 GCD cycles. These record-breaking performances would make our device one of the most promising candidates from an industrial point of view.

Recent Progress in Metal-Organic Framework-Derived Nanostructures in the Removal of Volatile Organic Compounds.

Air is the most crucial and life-supporting input from nature to the living beings of the planet. The composition and quality of air significantly affects human health, either directly or indirectly. The presence of some industrially released gases, small particles of anthropogenic origin, and the deviation from the normal composition of air from the natural condition causes air pollution. Volatile organic compounds (VOCs) are common contaminants found as indoor as well as outdoor pollutants. Such pollutants represent acute or chronic health hazards to the human physiological system. In the environment, such polluted gases may cause chemical or photochemical smog, leading to detrimental effects such as acid rain, global warming, and environmental pollution through different routes. Ultimately, this will propagate into the food web and affect the ecosystem. In this context, the efficient removal of volatile organic compounds (VOCs) from the environment remains a major threat globally, yet satisfactory strategies and auxiliary materials are far from being in place. Metal-organic frameworks (MOFs) are known as an advanced class of porous coordination polymers, a smart material constructed from the covalently bonded and highly ordered arrangements of metal nodes and polyfunctional organic linkers with an organic-inorganic hybrid nature, high porosities and surface areas, abundant metal/organic species, large pore volumes, and elegant tunability of structures and compositions, making them ideal candidates for the removal of unwanted VOCs from air. This review summarizes the fundamentals of MOFs and VOCs with recent research progress on MOF-derived nanostructures/porous materials and their composites for the efficient removal of VOCs in the air, the remaining challenges, and some prospective for future efforts.

Engineering triangular bimetallic metal-organic-frameworks derived hierarchical zinc-nickel-cobalt oxide nanosheet arrays@reduced graphene oxide-Ni foam as a binder-free electrode for ultra-high rate performance supercapacitors and methanol electro-oxidation.

The rigorous fabrication of electrode materials using upper-ranked porous precursor especially metal organic frameworks (MOFs) are challenging but appealing task to procure electrochemical energy storage and conversion system with altitudinous performance. Herein, we replenish the rational construction of atypical electrode of hollow Zn-Ni-Co-oxide (ZNCO) nanosheet arrays onto rGO garnished Ni foam (rGO/NF) via two step solution based method. Firstly, 2D Zn-Co-MOFs derived nanoleave arrays are prepared by co-precipitation method. Next, hollow and porous ZNCO nanostructure from 2D solid nanoleave arrays are achieved by ion-exchange and etching process conjoined with post annealing treatment. The as-fabricated hierarchical ZNCO nanosheet arrays offer large numbers of electroactive sites with short ion-diffusion pathways, reflecting the outstanding electrochemical performance in-terms of excellent specific capacity (267 mAh g-1) ultra-high rate capability (83.82% at 50 A/g) and long-term cycling life (~90.16%) in three electrode configuration for supercapacitor (SCs). Moreover, the hollow and porous ZNCO nanostructure responds as immensely active and substantial electrocatalyst for methanol oxidation with lowest onset potential of 0.27 V. To demonstrate the practicability, hybrid supercapacitor (HSC) device is constructed using ZNCO@rGO-NF nanostructure as positive and rGO decorated MOF derived porous carbon (rGO-MDPC) as negative electrode. The as-assembled ZNCO//rGO-MDPC ASC device delivers higher energy density of 61.25 Wh kg-1 at the power density of 750 W kg-1 with long-term cyclic stability (<6% to its initial specific capacity value) after 6000 cycles.

Modish Designation of Hollow-Tubular rGO-NiMoO4@Ni-Co-S Hybrid Core-shell Electrodes with Multichannel Superconductive Pathways for High-Performance Asymmetric Supercapacitors.

The scrupulous designation of hollow and porous electroactive materials incorporating prolific redox-active polyphase transition-metal oxide decorated with polyphase transition-metal sulfide onto rGO (reduced graphene oxide)-supported conductive substrate has never been an easy task due to the very good coordination affair of sulfur toward transition metals. Herein, cost-effective hydrothermal growth followed by a metal-organic framework (MOF)-mediated sulfidation approach is employed to achieve burl-like Ni-Co-S nanomaterial-integrated hollow and porous NiMoO4 nanotubes onto rGO-coated Ni foam (rGO-NiMoO4@Ni-Co-S) as the electrode material for supercapacitors. The open framework of the rGO-Co-MOF template after the etching and sulfidation process not only enables the creation of a tubular structure of NiMoO4 nanorods but also provides convenient ion-electron pathways to promote rapid faradic reactions for the hybrid composite electrode. Owing to the unique hollow and tubular structure, the as-fabricated rGO-NiMoO4@Ni-Co-S electrode exhibits a high specific capacity of 318 mA h g-1 at 1 A g-1 and remarkable cyclic performance of 88.87% after 10,000 consecutive charge-discharge cycles in an aqueous 2 M KOH electrolyte on a three-electrode configuration. Moreover, the assembled rGO-NiMoO4@Ni-Co-S//rGO-MDC (MOF-derived carbon) asymmetric supercapacitor device exhibits a satisfactory energy density of 57.24 W h kg-1 at a power density of 801.8 W kg-1 with an admirable life span of 90.89% after 10,000 repeated cycles.

Synthesis and Characterization of ZnO-TiO2/Carbon Fiber Composite with Enhanced Photocatalytic Properties.

Herein, we prepared a novel photocatalytic ZnO-TiO2 loaded carbon nanofibers composites (ZnO-TiO2-CNFs) via electrospinning technique followed by a hydrothermal process. At first, the electrospun TiO2 NP-embedded carbon nanofibers (TiO2-CNFs) were achieved using electrospinning and a carbonization process. Next, the ZnO particles were grown into the TiO2-CNFs via hydrothermal treatment. The morphology, structure, and chemical compositions were studied using state-of-the-art techniques. The photocatalytic performance of the ZnO-TiO2-CNFs composite was studied using degrading methylene blue (MB) under UV-light irradiation for three successive cycles. It was noticed that the ZnO-TiO2-CNFs nanocomposite showed better MB removal properties than that of other formulations, which might be due to the synergistic effects of carbon nanofibers and utilized metal oxides (ZnO and TiO2). The adsorption characteristic of carbon fibers and matched band potentials of ZnO and TiO2 combinedly help to boost the overall photocatalytic performance of the ZnO-TiO2-CNFs composite. The obtained results from this study indicated that it can be an economical and environmentally friendly photocatalyst.

Copper//terbium dual metal organic frameworks incorporated side-by-side electrospun nanofibrous membrane: A novel tactics for an efficient adsorption of particulate matter and luminescence property.

Particulate matters with different sizes (PM2.5 and PM10) in the air have become a supreme environmental concern to human health globally. Herein, the magnetic-luminescent Cu//Tb dual metal-organic frameworks (MOFs) incorporated side-by-side nanofibrous (SBS-NFs) membrane has been successfully fabricated via the electrospinning technique with the self-designed nozzle for the first time. The fabricated SBS-NFs membrane was composed of Cu-MOF/PAN at one side and Tb-MOF/PAN at another side with their individual characteristics. The Cu-MOF was used to improve the filtration efficiency and reduced the pressure drop by enhancing the electrostatic interaction, whereas, Tb-MOF was incorporated to investigate the PM adsorption process through the changes in luminescence intensity. Compared to polyacrylonitrile nanofibers (PAN NFs), Cu//Tb dual MOFs incorporated SBS-NFs membrane showed an enhanced filtration efficiency (90.2%) and a reduced pressure drop (60.7 Pa) when sodium chloride (NaCl) aerosols with particle size less than 300 nm were used for testing. As a result of the filter test using car exhaust, Cu//Tb SBS-NFs membrane still maintained >91% PM removal efficiency for >30 h. In addition, it was confirmed that the luminescence intensity over the PM adsorption time was linearly weakened. Therefore, Cu//Tb dual MOFs incorporated SBS-NFs membrane can be used for a variety of applications.

Phytic acid controlled in situ synthesis of amorphous cobalt phosphate/carbon composite as anode materials with a high mass loading for symmetrical supercapacitor: amorphization of the electrode to boost the energy density.

Transition metal phosphate (TMPi)-based composites as anode electrode materials in supercapacitor applications are less reported. Herein, we report a phytic acid (PA)-assisted in situ-formed amorphous cobalt phosphate/carbon (CoPi/C) composite grown on a flexible woven carbon cloth (CC) via a simple one-step carbonization approach. The tunable synthesis of amorphous and crystalline composites is shown by simply controlling the concentration of the cobalt salts. The strategy for high mass loading to 12 mg cm-2 is also shown in this report. Importantly, the resulting amorphous electrode materials exhibit electric double-layer capacitance (EDLC) behavior that works over a wide potential range from -1.4 to +0.5 V in an aqueous solution of potassium hydroxide (2 M KOH) and from -1.5 to +1.5 V in sodium sulfate (1 M Na2SO4). The amorphous electrode as an anode is capable of delivering an areal capacitance up to 2.15 F cm-2 at a current density of 4 mA cm-2 (gravimetric capacitance up to 606.1 F g-1 at 1 Ag-1) and has a retention of 94.2% at 10 000 cycles. The flexible solid-state symmetric device fabricated shows an energy density of approximately 620.0 µW h cm-2 at a power density of 4.7 mW cm-2 (31.1 W h kg-1 at 476.0 W kg-1). This study offers a novel route for the generation of metal phosphate-based anode materials with high capacitance for symmetrical supercapacitor device with high energy density.

Three-dimensional porous carbonaceous network with in-situ entrapped metallic cobalt for supercapacitor application.

Herein, we outline the fabrication of highly porous three-dimensional carbon-fiber network anchored with uniform metallic cobalt (Co) via electrospinning and subsequent post-modification approaches. First, cobalt acetate solution saturated electrospun polyacrylonitrile (PAN) nanofibrous mat was subjected to sodium borohydride (NaBH4) solution which results in the fabrication of three dimensional (3D) hierarchical multilayer network. Restructuring of the 2D mat into multilayered sponges with metal particles entrapment is attributed to the in-situ generated hydrogen gas into the interconnected pores of the fibrous network simultaneous with reduction of cobalt salt into metallic cobalt by NaBH4. The resulting mesh was stabilized and carbonization at inert atmosphere to obtain metallic cobalt (Co) embedded 3D carbon nanofibrous networks (Co@3D-CNFs). Physicochemical characterization and electrochemical analysis were performed. Results show carbon network was found to be expanded with bubbling like structures often embedded metallic Co nanoparticles. X-ray diffraction (XRD) pattern confirms the existence of the metallic cobalt particles on the carbon fiber networks. Furthermore, we establish a resulting composite (Co@3D-CNFs) identify the enhanced electrochemical performance having specific capacitance 762 F g-1 compared to 173 and 180 F g-1 for corresponding @3D-CNFs and 2D carbon nanofiber network with cobalt doped (Co@2D-CNFs) counterparts, respectively. The assembled Co2@3D-CNFs//NGH ASC device exhibits a high energy density 24.6 W h Kg-1 at 797 W kg-1 power density with an operating voltage of 1.6 V (vs Ag/AgCl). The device further shows good capacitance retention (90.1%) after 5000 cycles. This research shows the simple and cost-effective strategy to make metallic particles embedded 3D porous carbonaceous electrode materials which can have great potential for energy storage application.

Fly-ash-incorporated electrospun zinc oxide nanofibers: Potential material for environmental remediation.

Fly ash (FA), a solid waste generated in thermal power plants, is considered an environmental pollutant. Therefore, measures must be taken to dispose of FA in an environmentally friendly manner. In this paper, an electrospinning technique was employed to incorporate FA particles onto zinc oxide nanofibers (ZnO NFs), and the product (FA/ZnO composite) was used for the removal of methylene blue (MB) from the water. Herein, ZnO NFs may serve as effective semiconductor photocatalysts and provide sufficient surface area for FA, while the FA particles serve as an effective adsorbent. The adsorption capacity and photocatalytic efficiency of the as-synthesized nanocomposite fibers were enhanced compared to those of the pristine ZnO NFs, and this result is attributed to the uniform distribution of FA on the surface of the ZnO NFs. The as-synthesized nanocomposite could have great significance in wastewater treatment.

Carbon nanofibers wrapped with zinc oxide nano-flakes as promising electrode material for supercapacitors.

A combination of electrospinning technique and hydrothermal process was carried out to fabricate zinc oxide nano-flakes wrapped carbon nanofibers (ZnO/CNFs) composite as an effective electrode material for supercapacitor. The morphology of the as-synthesized composite clearly revealed that the carbon nanofibers were successfully wrapped with ZnO nano-flakes. The electrochemical performance of the as-synthesized nanocomposite electrode was evaluated by the cyclic voltammetry (CV), galvanostatic charge-discharge (GDC), and electrochemical impedance spectroscopy (EIS), and compared with the pristine ZnO nanofibers. It was found that the composite exhibited a higher specific capacitance (260 F/g) as compared to pristine ZnO NFs (118 F/g) at the scan rate of 5 mV/s. Furthermore, the ZnO/CNFs composite also exhibited good capacity retention (73.33%). The obtained results indicated great potential applications of ZnO/CNFs composite in developing energy storage devices with high energy and power densities. The present work might provide a new route for utilizing ZnO based composites for energy storage applications.

Synthesis and characterization of reduced graphene oxide decorated with CeO2-doped MnO2 nanorods for supercapacitor applications.

A novel and efficient CeO2-doped MnO2 nanorods decorated reduced graphene oxide (CeO2-MnO2/RGO) nanocomposite was successfully synthesized via hydrothermal method. The growth of the CeO2 doped MnO2 nanorods over GO sheets and reduction of GO were simultaneously carried out under hydrothermal treatment. The morphology and structure of as-synthesized nanocomposite were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman spectroscopy, which revealed the formation of CeO2-MnO2 decorated RGO nanocomposites. The electrochemical performance of as-prepared CeO2-MnO2/RGO nanocomposites as an active electrode material for supercapacitor was evaluated by cyclic voltammetry, charge-discharge, and electrochemical impedance spectroscopy (EIS) methods in 2M alkaline medium. The obtained results revealed that as-synthesized CeO2-MnO2/RGO nanocomposite exhibited higher specific capacitance (648F/g) as compared to other formulations (MnO2/RGO nanocomposites: 315.13 F/g and MnO2 nanorods: 228.5 F/g) at the scan rate of 5mV/s. After 1000 cycles, it retained ∼90.4%, exhibiting a good stability. The high surface area, enhanced electrical conductivity, and good stability possess by the nanocomposite make this material a promising candidate to be applied as a supercapacitor electrode.