Self-Assembled and One-Step Synthesis of Interconnected 3D Network of Fe3O4/Reduced Graphene Oxide Nanosheets Hybrid for High-Performance Supercapacitor Electrode

Linker Encouraged Solid State Synthesis of MOF Derived Z-Scheme NiCo2O4/NiO/C toward Efficient Removal of Organic and Inorganic Pollutants from Water

Here, we represent a solid-state route for the construction of MOF derived multifunctional Z-scheme NiCo2O4/NiO/C applied for the photocatalytic removal of methylene blue (dye) and tetracycline (drug) and the reduction of Cr(VI) (heavy metal). The developed solid-state method yielded a highly effective NiCo2O4/NiO/C catalyst by mechanically grinding independently produced Ni and Co-MOFs and subsequently pyrolyzing them. The use of different linkers in the Ni MOF (H3-BTC linker) and Co-MOF (2-methylimidazole linker) proved to be effective in constructing the NiCo2O4/NiO/C composite, ensuring a nonaggregated distribution on a carbon framework. Such a synthesized Z-scheme NiCo2O4/NiO/C composite has performed exceptionally well to achieve excellent degradation of MB (98.23% in 120 min) and TC (92.85% in 25 min) and Cr(VI) reduction (98.22% in 20 min), with excellent recyclability and stability. The NiCo2O4/NiO/C composite, synthesized using Ni and Co-MOFs prepared with different linkers, outperformed its counterpart prepared using Ni and Co-MOFs with identical linkers (either 2-methylimidazole or H3BTC). This study paves the way for the future synthesis of MOF derived bimetallic composites for photocatalytic applications.

Lamella-heterostructured nanoporous bimetallic iron-cobalt alloy/oxyhydroxide and cerium oxynitride electrodes as stable catalysts for oxygen evolution

Developing robust nonprecious-metal electrocatalysts with high activity towards sluggish oxygen-evolution reaction is paramount for large-scale hydrogen production via electrochemical water splitting. Here we report that self-supported laminate composite electrodes composed of alternating nanoporous bimetallic iron-cobalt alloy/oxyhydroxide and cerium oxynitride (FeCo/CeO_2-xN_x) heterolamellas hold great promise as highly efficient electrocatalysts for alkaline oxygen-evolution reaction. By virtue of three-dimensional nanoporous architecture to offer abundant and accessible electroactive CoFeOOH/CeO_2-xN_x heterostructure interfaces through facilitating electron transfer and mass transport, nanoporous FeCo/CeO_2-xN_x composite electrodes exhibit superior oxygen-evolution electrocatalysis in 1 M KOH, with ultralow Tafel slope of ~33 mV dec^-1. At overpotential of as low as 360 mV, they reach >3900 mA cm^-2 and retain exceptional stability at ~1900 mA cm^-2 for >1000 h, outperforming commercial RuO₂ and some representative oxygen-evolution-reaction catalysts recently reported. These electrochemical properties make them attractive candidates as oxygen-evolution-reaction electrocatalysts in electrolysis of water for large-scale hydrogen generation.

Three-Dimensional Hybrid Nanostructures of Fe3O4 Nanoparticles/Vertically-Aligned Carbon Nanotubes for High-Performance Supercapacitors

A three-dimensional (3D) hybrid nanostructure of Fe3O4 nanoparticles uniformly anchored on vertically-aligned carbon nanotubes (VACNTs) was fabricated by a facile two-step method. Assisted by supercritical carbon dioxide (SCCO2), the Fe precursor was firstly absorbed on CNT surface and then transformed into Fe3O4 nanoparticles by vacuum thermal annealing. Owing to the synergetic effects of well-distributed Fe3O4 nanoparticles (~7 nm) and highly conductive VACNTs, the hybrid electrode exhibits a high specific capacitance of 364.2 F g−1 at 0.5 A g−1 within the potential range from −0.9 to +0.1 V in Na2SO3 electrolyte and an excellent cycling stability of 84.8% capacitance retention after 2000 cycles at a current density of 4 A/g. This 3D hybrid architecture consisting of aligned CNTs and pseudocapacitive metal oxide may be a promising electrode for high-performance supercapacitors.

Magnetite Nanoparticles In-Situ Grown and Clustered on Reduced Graphene Oxide for Supercapacitor Electrodes

Fe3O4 nanoparticles with average sizes of 3-8 nm were in-situ grown and self-assembled as homogeneous clusters on reduced graphene oxide (RGO) via coprecipitation with some additives, where RGO sheets were expanded from restacking and an increased surface area was obtained. The crystallization, purity and growth evolution of as-prepared Fe3O4/RGO nanocomposites were examined and discussed. Supercapacitor performance was investigated in a series of electrochemical tests and compared with pure Fe3O4. In 1 M KOH electrolyte, a high specific capacitance of 317.4 F g-1 at current density of 0.5 A g-1 was achieved, with the cycling stability remaining at 86.9% after 5500 cycles. The improved electrochemical properties of Fe3O4/RGO nanocomposites can be attributed to high electron transport, increased interfaces and positive synergistic effects between Fe3O4 and RGO.

Microwave as a Tool for Synthesis of Carbon-Based Electrodes for Energy Storage

This Spotlight on Applications highlights the significant impact of microwave-assisted methods for synthesis and modification of carbon materials with enhanced properties for electrodes in energy storage applications (supercapacitors and batteries). For the past few years, microwave irradiation has been increasingly used for the synthesis of carbon materials with different morphologies using various precursors. Microwave processing exhibits numerous advantages, such as short processing times, high yield, expanded reaction conditions, high reproducibility, and high purity of products. On this frontier research area, we have discussed microwave-assisted synthesis, defect creation, simultaneous reduction and exfoliation, and heteroatom doping in carbon materials. By careful manipulation of microwave irradiation parameters, the method becomes a powerful and efficient tool to generate different morphologies in carbon-based materials. Other important outcomes are the flexible control over the degree of reduction and exfoliation of graphene derivatives, the generation of defects in graphene-based materials by metals, the intercalation of metal oxides into graphene derivatives, and heteroatom doping of graphene materials. The Spotlight on Applications aims to provide a condensed overview of the current progress in carbon-based electrodes synthesized by microwave, pointing out outstanding challenges and offering a few suggestions to trigger more research endeavors in this important field.

Carbon-Supported Noble-Metal Nanoparticles for Catalytic Applications—A Review

Noble-metal nanoparticles (NMNPs), with their outstanding properties, have been arousing the interest of scientists for centuries. Although our knowledge of them is much more significant today, and we can obtain NMNPs in various sizes, shapes, and compositions, our interest in them has not waned. When talking about noble metals, gold, silver, and platinum come to mind first. Still, we cannot forget about elements belonging to the so-called platinum group, such as ruthenium, rhodium, palladium, osmium, and iridium, whose physical and chemical properties are very similar to those of platinum. It makes them highly demanded and widely used in various applications. This review presents current knowledge on the preparation of all noble metals in the form of nanoparticles and their assembling with carbon supports. We focused on the catalytic applications of these materials in the fuel-cell field. Furthermore, the influence of supporting materials on the electrocatalytic activity, stability, and selectivity of noble-metal-based catalysts is discussed.

Fe3O4 Nanoparticles: Structures, Synthesis, Magnetic Properties, Surface Functionalization, and Emerging Applications

Magnetite (Fe3O4) nanoparticles (NPs) are attractive nanomaterials in the field of material science, chemistry, and physics because of their valuable properties, such as soft ferromagnetism, half-metallicity, and biocompatibility. Various structures of Fe3O4 NPs with different sizes, geometries, and nanoarchitectures have been synthesized, and the related properties have been studied with targets in multiple fields of applications, including biomedical devices, electronic devices, environmental solutions, and energy applications. Tailoring the sizes, geometries, magnetic properties, and functionalities is an important task that determines the performance of Fe3O4 NPs in many applications. Therefore, this review focuses on the crucial aspects of Fe3O4 NPs, including structures, synthesis, magnetic properties, and strategies for functionalization, which jointly determine the application performance of various Fe3O4 NP-based systems. We first summarize the recent advances in the synthesis of magnetite NPs with different sizes, morphologies, and magnetic properties. We also highlight the importance of synthetic factors in controlling the structures and properties of NPs, such as the uniformity of sizes, morphology, surfaces, and magnetic properties. Moreover, emerging applications using Fe3O4 NPs and their functionalized nanostructures are also highlighted with a focus on applications in biomedical technologies, biosensing, environmental remedies for water treatment, and energy storage and conversion devices.

Defect engineering of oxide perovskites for catalysis and energy storage: synthesis of chemistry and materials science

Oxide perovskites have emerged as an important class of materials with important applications in many technological areas, particularly thermocatalysis, electrocatalysis, photocatalysis, and energy storage. However, their implementation faces numerous challenges that are familiar to the chemist and materials scientist. The present work surveys the state-of-the-art by integrating these two viewpoints, focusing on the critical role that defect engineering plays in the design, fabrication, modification, and application of these materials. An extensive review of experimental and simulation studies of the synthesis and performance of oxide perovskites and devices containing these materials is coupled with exposition of the fundamental and applied aspects of defect equilibria. The aim of this approach is to elucidate how these issues can be integrated in order to shed light on the interpretation of the data and what trajectories are suggested by them. This critical examination has revealed a number of areas in which the review can provide a greater understanding. These include considerations of (1) the nature and formation of solid solutions, (2) site filling and stoichiometry, (3) the rationale for the design of defective oxide perovskites, and (4) the complex mechanisms of charge compensation and charge transfer. The review concludes with some proposed strategies to address the challenges in the future development of oxide perovskites and their applications.

Toward enhanced catalytic activity of magnetic nanoparticles integrated into 3D reduced graphene oxide for heterogeneous Fenton organic dye degradation

Composite Fenton nanocatalyst was prepared by water-based in situ creation of Fe3O4 nanoparticles integrated within the self-assembly 3D reduced graphene oxide (rGO) aerogel. The hybrid applied for the degradation of Acid Green 25 (AG-25) organic dye in an aqueous solution, in the presence of H2O2. By investigating the conditions that maximize the dye adsorption by the 3D composite, it was found that the pH of the solution should be adjusted between the pKa of the functional groups present on the rGO surface (carboxylic acid) and that of the dye (sulfonic acid) to promote electrostatic interactions dye-3D structure. Performed under these conditions, Fenton degradation of AG-25 in presence of H2O2 was completed in less than 30 min, including all the intermediate products, as demonstrated by MALDI-TOF-MS analysis of the aqueous solution after discoloration. Moreover, this was achieved in a solution with as high a dye concentration of 0.5 mg/mL, with only 10 mg of 3D composite catalyst, at room temperature and without additional energy input. The high performance was attributed to the creation of charge-transfer complex between rGO and Fe3O4 nanoparticles throughout covalent bond C-O-Fe, the formation of which was promoted by the in situ synthesis procedure. For the first time, up to the authors' knowledge, AG-25 degradation mechanism was proposed.

A review of the microwave-assisted synthesis of carbon nanomaterials, metal oxides/hydroxides and their composites for energy storage applications

Currently, nanomaterials are considered to be the backbone of modern civilization. Especially in the energy sector, nanomaterials (mainly, carbon- and metal oxide/hydroxide-based nanomaterials) have contributed significantly. Among the various green approaches for the synthesis of these nanomaterials, the microwave-assisted approach has attracted significant research interest worldwide. In this context, it is noteworthy to mention that because of their enhanced surface area, high conducting nature, and excellent electrical and electrochemical properties, carbon nanomaterials are being extensively utilized as efficient electrode materials for both supercapacitors and secondary batteries. In this review article, we briefly demonstrate the characteristics of microwave-synthesized nanomaterials for next-generation energy storage devices. Starting with the basics of microwave heating, herein, we illustrate the past and present status of microwave chemistry for energy-related applications, and finally present a brief outlook and concluding remarks. We hope that this review article will positively convey new insights for the microwave synthesis of nanomaterials for energy storage applications.

Novel Three-Dimensional Graphene-Like Networks Loaded with Fe3O4 Nanoparticles for Efficient Microwave Absorption

A novel three-dimensional graphene-like networks material (3D-GLN) exhibiting the hierarchical porous structure was fabricated with a large-scale preparation method by employing an ion exchange resin as a carbon precursor. 3D-GLN was first studied as the effective microwave absorbing material. As indicated from the results of the electromagnetic parameter tests, and the minimum reflection loss (R_L) of the 3D-GLN reached −34.75 dB at the frequency of 11.7 GHz. To enhance the absorption performance of the nonmagnetic 3D-GLN, the magnetic Fe₃O₄ nanoparticles were loaded on the surface of the 3D-GLN by using the hydrothermal method to develop the 3D-GLN/Fe₃O₄ hybrid. The hybrid exhibited the prominent absorbing properties. Under the matching thickness of 3.0 mm, the minimum R_L value of hybrid reached −46.8 dB at 11.8 GHz. In addition, under the thickness range of 2.0–5.5 mm, the effective absorption bandwidth (R_L < 10 dB) was 13.0 GHz, which covered part of the C-band and the entire X-band, as well as the entire Ku-band. The significant microwave absorption could be attributed to the special 3D network structure exhibited by the hybrid and the synergistic effect exerted by the graphene and the Fe₃O₄ nanoparticles. As revealed from the results, the 3D-GLN/Fe₃O₄ hybrid could be a novel microwave absorber with promising applications.

Effects of Fe Impurities on Self-Discharge Performance of Carbon-Based Supercapacitors

Activated carbon is widely used as an electrode material in supercapacitors due to its superior electrochemical stability, excellent electrical conductivity, and environmental friendliness. In this study, the self-discharge mechanisms of activated carbon electrodes loaded with different contents of Fe impurities (Fe and Fe₃O₄) were analyzed by multi-stage fitting to explore the tunability of self-discharge. It is was found that a small quantity of Fe impurities on carbon materials improves the self-discharge performance dominated by redox reaction, by adjusting the surface state and pore structure of carbon materials. As the content of Fe impurities increases, the voltage loss of activated carbon with the Fe impurity concentrations of 1.12 wt.% (AF-1.12) decreases by 37.9% of the original, which is attributable to the reduce of ohmic leakage and diffusion, and the increase in Faradic redox at the electrode/electrolyte interface. In summary, self-discharge performance of carbon-based supercapacitors can be adjusted via the surface state and pour structure, which provides insights for the future design of energy storage.

Multifunctional Photothermal Conversion Nanocoatings Toward Highly Efficient and Safe High-Viscosity Oil Cleanup Absorption

Efficient and safe cleanup for the high-viscosity heavy oil spill has been a worldwide challenge due to its sluggish flowability, while classic absorption methods by electric/solar heating are seriously limited by low efficiency and high fire hazards during heating of highly flammable oil. Facing this dilemma, we reported a novel flame-retardant photothermal conversion nanocoating to endow commercial foams with highly efficient and safe heavy oil cleanup absorption. This multifunctional nanocoating consisting of nano-Fe₃O₄ and reduced graphene oxide (rGO) that both showed photothermal conversion ability and non-flammable nature can be firmly deposited on the polymer foam skeletons via facile coprecipitation and dip-coating processes. The composite foam showed a tough morphology with high hydrophobicity and low density, thus leading to selective high absorption for various oils and organic solvents. Due to the double photothermal conversion effects of nano-Fe₃O₄ and rGO, the temperature of the foam can be rapidly heated at a rate of ∼103.5 °C/min (the fastest rate ever) under 1 sun irradiation. Consequently, the foam with a high absorption capacity of 75.1 times its weight demonstrated a rapid absorption rate of 9000 g m^-2 min^-1 for large-viscosity oil under 1 sun irradiation, which was 3 times faster than previously reported. Furthermore, benefitting from high flame retardancy, elasticity, and magnetism, the foam can be safely and repeatedly used for magnetically controllable oil cleanup absorption, which effectively avoids oil spill hazards.

Advanced Boiling-A Scalable Strategy for Self-Assembled Three-Dimensional Graphene

Currently, researchers are paying much attention to the development of effective 3D graphene for applications in energy storage and environmental purification. Before commercialization, however, it is necessary to develop a method that allows for the large-scale production of such materials and enables good control over their structural and chemical properties. With this objective, we herein developed a simple method for the formation of large-scale (4 in. wafer) 3D graphene networks via the self-assembly of graphene sheets at a superheated liquid-vapor interface. The structural morphology of this porous network could be modified by controlling the vaporization rate, surface temperature of the target substrate, and amount of discharged colloids. The key mechanism behind this intriguing result was investigated by high-speed visualization of microdroplet behavior and extensive thermal analysis. This self-assembled 3D graphene had excellent electrical and mechanical properties. Our approach can be directly used for the mass production of graphene-based materials.

Enhanced peroxydisulfate oxidation via Cu(III) species with a Cu-MOF-derived Cu nanoparticle and 3D graphene network

The contribution of Cu(III) produced during heterogeneous peroxydisulfate (PDS) activation to pollutant removal is largely unknown. Herein, a composite catalyst is prepared with Cu-based metal organic framework (Cu-MOF) derived Cu nanoparticles decorated in a three-dimensional reduced graphene oxide (3D RGO) network. The 3D RGO network overcomes the aggregation of nanosized zero-valent copper and reduces the copper consumption during the PDS activation reaction. The Cu/RGO catalyst exhibits high catalytic activity for 2,4-dichlorophenol (2,4-DCP) degradation in a wide pH range of 3-9, with a low Cu dosage that is only 0.075 times that of previous reports with zero-valent copper. Moreover, a high mineralization ratio (69.2 %) of 2,4-DCP is achieved within 30 min, and the Cu/RGO catalyst shows high reactivity toward aromatic compounds with hydroxyl and chlorinated groups. Unlike normal sulfate radical-based advanced oxidation, alcohols show negligible impacts on the reaction, suggesting that Cu(III), rather than SO₄^- and OH, dominates the degradation process. We believe that PDS activation by 3D Cu/RGO, with Cu(III) as the main active species, provides new insights in selective organic pollutant removal in wastewater treatment.

Advanced asymmetric supercapacitors with a squirrel cage structure Fe3O4@carbon nanocomposite as a negative electrode

Carbon materials have been used as negative electrodes for supercapacitor applications; nevertheless, owing to the low capacitance, they have limited ability to enhance the supercapacitor electrochemical properties.

Inherent Impurities in Graphene/Polylactic Acid Filament Strongly Influence on the Capacitive Performance of 3D-Printed Electrode

Additive manufacturing or 3D-printing have become promising fabrication techniques in the field of electrochemical energy storage applications such as supercapacitors, and batteries. Of late, a commercially available graphene/polylactic acid (PLA) filament has been commonly used for Fused Deposition Modeling (FDM) 3D-printing in the fabrication of electrodes for supercapacitors and Li-ion batteries. This graphene/PLA filament contains metal-based impurities such as titanium oxide and iron oxide. In this study, we show a strong influence of inherent impurities in the graphene/PLA filament for supercapacitor applications. A 3D-printed electrode is prepared and subsequently thermally activated for electrochemical measurement. A deep insight has been taken to look into the pseudocapacitive contribution from the metal-based impurities which significantly enhanced the overall capacitance of the 3D-printed graphene/PLA electrode. A systematic approach has been shown to remove the impurities from the printed electrodes. This has a broad implication on the interpretation of the capacitance of 3D-printed composites.

From 2D Graphene Nanosheets to 3D Graphene-based Macrostructures

The combination of exceptional functionalities offered by 3D graphene-based macrostructures (GBMs) has attracted tremendous interest. 2D graphene nanosheets have a high chemical stability, high surface area and customizable porosity, which was extensively researched for a variety of applications including CO₂ adsorption, water treatment, batteries, sensors, catalysis, etc. Recently, 3D GBMs have been successfully achieved through few approaches, including direct and non-direct self-assembly methods. In this review, the possible routes used to prepare both 2D graphene and interconnected 3D GBMs are described and analyzed regarding the involved chemistry of each 2D/3D graphene system. Improvement of the accessible surface of 3D GBMs where the interface exchanges are occurring is of great importance. A better control of the chemical mechanisms involved in the self-assembly mechanism itself at the nanometer scale is certainly the key for a future research breakthrough regarding 3D GBMs.

Synthesis and Microwave Absorption Properties of Sulfur-Free Expanded Graphite/Fe3O4 Composites

In this study, sulfur-free expanded graphite (EG) was obtained by using flake graphite as the raw material, and EG/Fe₃O₄ composites with excellent microwave absorption properties were prepared by a facile one-pot co-precipitation method. The structure and properties of as-prepared EG/Fe₃O₄ were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Raman, X-ray photoelectron spectrometry (XPS), thermogravimetric (TG), and vibrating sample magnetometry (VSM) characterizations. The Fe₃O₄ intercalated between the layers of expanded graphite forms a sandwich-like structure which is superparamagnetic and porous. When applied as a microwave absorber, the reflection loss (R_L) of EG/Fe₃O₄ reaches −40.39 dB with a thickness of 3.0 mm (10 wt% loading), and the effective absorption bandwidth (EAB < −10 dB) with R_L exceeding −10 dB is 4.76–17.66 GHz with the absorber thickness of 1.5–4.0 mm. Considering its non-toxicity, easy operation, low cost, suitability for large-scale industrial production, and excellent microwave absorbing performance, EG/Fe₃O₄ is expected to be a promising candidate for industrialized electromagnetic absorbing materials.

Magnetite ultrafine particles/porous reduced graphene oxide in situ grown onto Ni foam as a binder-free electrode for supercapacitors

Here, we report a simple and green electrochemical route to fabricate a porous network of a Fe3O4 nanoparticle-porous reduced graphene oxide (p-rGO) nanocomposite supported on a nickel-foam substrate, which is directly used as a binder-free charge storage electrode. Through this method, pristine Fe3O4 NPs/Ni, p-rGO/Ni and Fe3O4 NPs@p-rGO/Ni electrodes are fabricated and compared. In the fabricated Fe3O4 NPs@p-rGO/Ni electrode, the porous rGO sheets served as a conductive network to facilitate the collection and transportation of electrons during the charge/discharge cycles, improving the conductivity of magnetite NPs and providing a larger specific surface area. As a result, the Fe3O4 NPs@p-rGO/Ni exhibited a specific capacitance of 1323 F g-1 at 0.5 A g-1 and 79% capacitance retention when the current density is increased 20 times, where the Fe3O4 NPs/Ni electrode showed low specific capacitance of 357 F g-1 and 43% capacity retention. Furthermore, the composite electrode kept 95.1% and 86.7% of its initial capacitances at the current densities of 1 and 4 A g-1, respectively, which were higher than those of a Fe3O4/NF electrode at similar loads (i.e. 80.4% and 65.9% capacitance retentions at 1 and 4 A g-1, respectively). These beneficial effects proved the synergistic contribution between p-rGO and Fe3O4. Hence, such ultrafine magnetite particles grown onto a porous reduced GO network directly imprinted onto a Ni substrate could be a promising candidate for high performance energy storage aims.

Bimetallic Metal-Organic Framework-Derived Pomegranate-like Nanoclusters Coupled with CoNi-Doped Graphene for Strong Wideband Microwave Absorption

Metal-organic frameworks (MOFs) featuring high porosity and tunable structure make them become promising candidates to fabricate carbon-based microwave absorption (MA) materials to meet the requirements of electronic reliability and defense security. However, it is challenging to rationally design a well-organized micro-nanostructure to simultaneously achieve strong and wideband MA performance. Herein, a three-dimensional (3D) hierarchical nanoarchitecture (CoNi@NC/rGO-600) comprising pomegranate-like CoNi@NC nanoclusters and ultrasmall CoNi-decorated graphene has been successfully fabricated to broaden the absorption bandwidth and enhance the absorption intensity. The results confirm that the bimetallic MOF CoNi-BTC-derived pomegranate-like CoNi@NC nanoclusters with porous carbon shell as "peel" and sub-5 nm CoNi nanoparticles as "seeds" favor multiple polarization, magnetic loss, and impedance matching. Moreover, the interconnected 3D CoNi-doped graphene acts not only as a bridge to connect pomegranate-like CoNi@NC nanoclusters but also as a conductive network to supply multiple electron transportation paths. Consequently, the optimized CoNi@NC/rGO-600 exhibits extraordinary MA performance in terms of wide bandwidth (6.7 GHz) and strong absorption (-68.0 dB). As an effective strategy, this work provides a new insight into fabricating hierarchical composite structures for advancing MA performances and other applications.

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

Solar radiation is becoming increasingly appreciated because of its influence on living matter and the feasibility of its application for a variety of purposes. It is an available and everlasting natural source of energy, rapidly gaining ground as a supplement and alternative to the nonrenewable energy feedstock. Actually, an increasing interest is involved in the development of efficient materials as the core of photocatalytic and photothermal processes, allowing solar energy harvesting and conversion for many technological applications, including hydrogen production, CO2 reduction, pollutants degradation, as well as organic syntheses. Particularly, photosensitive nanostructured hybrid materials synthesized coupling inorganic semiconductors with organic compounds, and polymers or carbon-based materials are attracting ever-growing research attention since their peculiar properties overcome several limitations of photocatalytic semiconductors through different approaches, including dye or charge transfer complex sensitization and heterostructures formation. The aim of this review was to describe the most promising recent advances in the field of hybrid nanostructured materials for sunlight capture and solar energy exploitation by photocatalytic processes. Beside diverse materials based on metal oxide semiconductors, emerging photoactive systems, such as metal-organic frameworks (MOFs) and hybrid perovskites, were discussed. Finally, future research opportunities and challenges associated with the design and development of highly efficient and cost-effective photosensitive nanomaterials for technological claims were outlined.

Nickel–cobalt hydroxide: a positive electrode for supercapacitor applications

So far, numerous metal oxides and metal hydroxides have been reported as an electrode material, a critical component in supercapacitors that determines the operation window of the capacitor. Among them, nickel and cobalt-based materials are studied extensively due to their high capacitance nature. However, the pure phase of hydroxides does not show a significant effect on cycle life. The observed XRD results revealed the phase structures of the obtained Ni(OH)₂ and Co–Ni(OH)₂ hydroxides. The congruency of the peak positions of Ni(OH)₂ and Co–Ni(OH)₂ is attributed to the homogeneity of the physical and chemical properties of the as-prepared products. The obtained results from XPS analysis indicated the presence of Co and the chemical states of the as-prepared composite active electrode materials. The SEM analysis revealed that the sample had the configuration of agglomerated particle nature. Moreover, the morphology and structure of the hydroxide materials impacted their charge storage properties. Thus, in this study, Ni(OH)₂ and Co–Ni(OH)₂ composite materials were produced via a hydrothermal method to obtain controllable morphology. The electrochemical properties were studied. It was observed that both the samples experienced a pseudocapacitive behavior, which was confirmed from the CV curves. For the electrode materials Ni(OH)₂ and Co–Ni(OH)₂, the specific capacitance (C_s) of about 1038 F g⁻¹ and 1366 F g⁻¹, respectively, were observed at the current density of 1.5 A g⁻¹. The Ni–Co(OH)₂ composite showed high capacitance when compared with Ni(OH)₂. The cycle index was determined for the electrode materials and it indicated excellent stability. The stability of the cell was investigated up to 2000 cycles, and the cell showed excellent retention of 96.26%.

So far, numerous metal oxides and metal hydroxides have been reported as an electrode material, a critical component in supercapacitors that determines the operation window of the capacitor.

Recycling supercapacitor activated carbons for adsorption of silver (I) and chromium (VI) ions from aqueous solutions

In this study, we reported on the recycling of carbon materials from spent commercial supercapacitors and its application as low-cost adsorbent for high-efficiency removal of Ag(I) and Cr(VI) ions from aqueous solutions. Adsorption kinetics and isotherms, and effects of initial pH were carried out to investigate the adsorption performance of the recycled supercapacitor activated carbon (RSAC), whereas a series of characterizations such as SEM, EDX, BET, XPS, XRD and FTIR were employed to detailedly analyse the adsorption mechanism. The RSAC showed maximal adsorption capacity for Ag(I) and Cr(VI) of 104.0 and 96.3 mg g^-1, respectively, with adsorbent dosage of 2 g L^-1 and initial ions concentration of ∼2000 mg L^-1 at room temperature (23 ± 1 °C), and the adsorption was rapid and influenced by the initial pH value. The outstanding adsorption performance of RSAC was attributed to the high specific surface area (1403 m² g^-1) and abundant multifarious oxygenic groups which could participate in the electrostatic attraction and reduction reaction of Ag(I) and Cr(VI) during the adsorption process. Furthermore, the predominate species of the adsorbed toxic Ag(I) and Cr(VI) on the surface of RSAC was metallic silver particle (about 2 μm) and harmless Cr(III), respectively, thus it was possible for further recycling and disposal.

Iron oxide-based nanomaterials for supercapacitors

As highly efficient and clean electrochemical energy storage devices, supercapacitors (SCs) have drawn widespread attention as promising alternatives to batteries in recent years. Among various electrode materials, iron oxide materials have been widely studied as negative SC electrode materials due to their broad working window in negative potential, ideal theoretical specific capacitance, good redox activity, abundant availability, and eco-friendliness. However, iron oxides still suffer from the problems of low stability and poor conductivity. In this review, recent progress in iron oxide-based nanomaterials, including Fe₂O₃, Fe₃O₄, Fe_xO_y, and FeOOH, as electrode materials of SCs, is discussed. The nanostructure design and various synergistic effects of nanocomposites for improving the electrochemical performance of iron oxides are emphasized. Research on iron oxide-based symmetric/asymmetric SCs is also discussed. Future outlooks regarding iron oxides for SCs are likewise proposed.