Search Results (23)

The accelerating generation of waste streams is observed globally. Spanning lignocellulosic biomass, plastic waste, sewage sludge, and industrial residues, this review presents both an urgent management challenge and a compelling materials opportunity. Carbon materials derived from these waste streams offer a sustainable route to functional carbons applicable in electrochemical energy storage, adsorption, heterogeneous catalysis, and high-temperature applications. Yet their rational design remains constrained by incomplete understanding of the relationships between feedstock composition, processing pathway, structural characteristics, and functional performance. This review provides an integrated analysis of waste-derived carbon materials from processing pathways to structure–property–function relationships. The principal feedstock categories are examined for their compositional characteristics and implications for carbon yield and structure. Five primary processing routes are assessed. The five routes examined are pyrolysis, hydrothermal carbonisation, physical and chemical activation, and microwave-assisted processing. They are assessed comparatively with emphasis on structural outcomes and governing parameters. The resulting structural characteristics are discussed. These are morphology, hierarchical pore architecture, surface chemistry, heteroatom doping, and crystallinity. They are discussed alongside their characterisation methods and known limitations as performance predictors. Structure–property relationships are examined quantitatively. Heteroatom-doped hierarchical porous carbons achieve 612 F/g specific capacitance. Turbostratic hard carbons deliver 450 mAh/g sodium storage with over 90% retention. Hierarchical porous carbons demonstrate CO₂ uptake of 5.0 mmol/g and dye adsorption exceeding 9000 mg/g under optimised laboratory conditions; these values reflect individual studies and are not directly comparable across systems. Biomass-derived sulfonated carbon catalysts sustain biodiesel yields above 90% over multiple cycles. Challenges of feedstock variability, process scalability, environmental compliance, and economic feasibility are addressed, and machine learning-guided design, standardised characterisation methodology, and circular economy policy frameworks are identified as key enablers for translating laboratory performance into industrial reality. Full article

Developing sustainable, low-cost carbon materials for advanced energy storage remains a major challenge. This study reports the synthesis of three-dimensional (3D) hierarchical porous carbon foams using a polybenzoxazine-coated melamine sponge template, followed by carbonization at 600, 700, and 800 °C. The melamine sponge provided an interconnected porous framework, while nitrogen-rich polybenzoxazine enabled the formation of heteroatom-doped carbon structures. Structural analyses (SEM, XRD, Raman, and XPS) showed that carbonization temperature strongly influenced graphitization, pore development, and nitrogen functionalities. Among all samples, the foam carbonized at 800 °C showed the best electrochemical performance, delivering a specific capacitance of 287 F g⁻¹ at 1 A g⁻¹, 84% retention at 10 A g⁻¹, and 94% capacitance retention after 10,000 cycles. Its superior behavior is attributed to the synergistic effect of improved conductivity, hierarchical porosity, and favorable nitrogen doping. These findings demonstrate that controlled carbonization is an effective strategy for designing high-performance carbon electrodes for supercapacitors, with additional potential in catalysis, adsorption, and EMI shielding. Full article

This research presents the development of spinel-type high-entropy oxide (HEO) catalysts with the general composition (MnFeNiCoX)₃O₄, where X represents Cr, Cu, Zn, and Cd, synthesized through a solution combustion method. The impact of the fifth metal element on the oxygen evolution reaction (OER) was systematically explored using structural, morphological, and electrochemical characterization techniques. Among the various compositions, the Cr-containing catalyst, (MnFeNiCoCr)₃O₄, displayed outstanding electrocatalytic behavior, delivering a notably low overpotential of 323 mV at a current density of 10 mA/cm² in 1.0 M KOH—surpassing the performance of benchmark RuO₂. Additionally, this material exhibited the smallest Tafel slope (56 mV/dec), the greatest double-layer capacitance (3.35 mF/cm²), and the most extensive electrochemically active surface area, all indicating enhanced charge transfer capability and high catalytic proficiency. The findings highlight the potential of element tailoring in HEOs as a promising strategy for optimizing water oxidation catalysis. Full article

The oxygen evolution reaction (OER) plays a central role as an anode in electrocatalytic processes such as energy conversion and storage and the generation of molecular oxygen from the electrolysis of water. Currently, precious metal oxides such as IrO₂ and RuO₂ are recognized as reference OER electrocatalysts with reasonably high activity; however, their widespread use in practical devices has been severely hindered by their high cost and scarcity. It is essential to design alternative OER electrocatalysts made of low-cost and abundant earth elements with significant activity and robustness. We report four new nanocellulose-derived Fe–zeolite nanocomposites, namely Fe/Zeolite@CCNC (1), Fe/Zeolite@CCNF (2), Fe/Zeolite/CNT@CCNC (3), and Fe/Zeolite/CNT@CCNF (4). Two different types of nanocellulose were investigated: nanocellulose nanofibrils and nanocellulose nanocrystals. Characterization with TEM, SEM-EDS, PXRD, and XPS is reported. The nanocomposites exhibited electrocatalytic activity for OER that varies based on the origin of biocarbon and the composition content. The effect of adding carbon nanotubes to the nanocomposites was studied, and an improvement in OER catalysis was observed. The electrochemical double-layer capacitance and electrochemical impedance spectroscopy of the nanocomposites are reported. The nanocomposite 3 exhibited the highest performance, with an onset potential value of 1.654 V and an overpotential of 551 mV, which exceeds the activity of RuO₂ for OER catalysis at 10 mA/cm² in the glassy carbon electrode. A 24 h chronoamperometry study revealed that the catalyst is active for ~2 h under continuous operating conditions. BET surface analysis showed that the crystalline nanocellulose-derived composite exhibited 301.47 m²/g, and the fibril nanocellulose-derived composite exhibited 120.39 m²/g, indicating that the increased nanoporosity of the former contributes to the increase in OER catalysis. Full article

Nitrogen-doped graphene quantum dots (N-GQDs) are widely used in biosensing, catalysis, and energy storage due to their excellent conductivity, high specific surface area, unique quantum size effects, and optical properties. In this paper, we successfully synthesized N-GQDs using a facile hydrothermal approach and investigated the effects of different hydrothermal temperatures and times on the morphology and structure of N-GQDs. The results indicated that the size of N-GQDs gradually increased and they eventually aggregated into graphene fragments with increasing temperature or reaction time. Notably, N-GQDs synthesized at 180 °C for 6 h exhibited the most uniform size, with an average diameter of approximately 3.48 nm, a height of 5–6 graphene layers, as well as favorable fluorescence properties. Moreover, the surface of N-GQDs contained abundant oxygen- and nitrogen-containing functional groups, which could provide numerous active sites for electrode reactions. The assembled electrode exhibited typical pseudocapacitive behavior with exceptional electrochemical performance, achieving a specific capacitance of 102 F g⁻¹ at a current density of 1 A g⁻¹. In a 10,000-cycle test, the electrode demonstrated excellent cycling stability with a capacitance retention rate of 78.5%, which laid the foundation for practical application of the electrode. This work successfully applied N-GQDs in supercapacitors, offering new insights into their development for the energy storage field. Full article

Supercapacitors hold promise for energy storage due to their exceptional power density and fast charge/discharge cycles. However, their performance hinges on the electrode material. Zeolitic imidazolate frameworks (ZIFs) are attractive options due to their tailorable structure and high surface area. But traditional ZIF synthesis relies on toxic solvents derived from fossil fuels, hindering their envisioned environmental benefit. This study explores using bio-derived solvents for a greener and potentially superior approach. The researchers employed anodic electrodeposition to synthesise cobalt-based ZIFs (Co-ZIFs) as supercapacitor electrode materials. Two linkers (2-methylimidazole and benzimidazole) and two bio-derived solvents (Cyrene^TM and γ-valerolactone (GVL)) were investigated. X-ray diffraction analysis revealed that bio-derived solvents enhanced the crystallinity of Co-ZIFs compared to traditional solvents. Notably, Cyrene^TM promoted better crystallinity for Co-bIM/Co-mIM structures. The Full Width at Half Maximum (FWHM) analysis suggests Cyrene^TM promotes Co-bIM/Co-mIM crystallinity (lower FWHM). Co-mIM in Cyrene^TM exhibits the best crystallinity (FWHM = 0.233) compared to other ZIF samples. Scanning electron microscopy confirmed these findings, showing larger and well-defined crystals for bio-derived solvent-synthesised ZIFs. The choice of solvent significantly impacted the final ZIF structure. While 2-methylimidazole consistently formed ZIF-67 regardless of the solvent, benzimidazole exhibited solvent-dependent behaviour. GVL yielded the highly porous Co-ZIF-12 structure, whereas DMF (N,N-dimethylformamide) and Cyrene^TM produced the less porous ZIF-9. This work reports the first-ever instance of ZIF-12 synthesis via an electrochemical method, highlighting the crucial interplay between solvent and precursor molecule in determining the final ZIF product. The synthesised binder-free Co-ZIF electrodes were evaluated for supercapacitor performance. The capacitance data revealed GVL as the most effective solvent, followed by DMF and then Cyrene^TM. This suggests GVL is the preferred choice for this reaction due to its superior performance. The ZIF-12-based electrode exhibits an impressive specific capacitance (C_sp) of 44 F g⁻¹, significantly higher than those achieved by ZIF-9-Cyrene (1.2 F g⁻¹), ZIF-9-DMF (2.5 F g⁻¹), ZIF-67-GVL (35 F g⁻¹), ZIF-67-Cyrene (6 F g⁻¹), and ZIF-67-DMF (16 F g⁻¹) at 1 A g⁻¹. This surpasses the C_sp of all other ZIFs studied, including high-performing ZIF-67(GVL). ZIF-12(GVL) maintained superior C_sp even at higher current densities, demonstrating exceptional rate capability. Among the bio-derived solvents, GVL outperformed Cyrene^TM. Notably, the Co-bIM in the GVL sample exhibited a ZIF-12-like structure, offering potential advantages due to its larger pores and potentially higher surface area compared to traditional ZIF-67 and ZIF-9 structures. This work presents a significant advancement in Co-ZIF synthesis. By utilising bio-derived solvents, it offers a more sustainable and potentially superior alternative. This paves the way for the eco-friendly production of Co-ZIFs with improved properties for supercapacitors, gas separation, catalysis, and other applications. Full article

Molybdenum disulfide (MoS₂), a typical layered material, has important applications in various fields, such as optoelectronics, catalysis, electronic devices, sensors, and supercapacitors. Extensive research has been carried out on few-layered MoS₂ in the field of electrochemistry due to its large specific surface area, abundant active sites and short electron transport path. However, the preparation of few-layered MoS₂ is a significant challenge. This work presents a simple one-pot hydrothermal method for synthesizing few-layered MoS₂. Furthermore, it investigates the exfoliation effect of different amounts of sodium borohydride (NaBH₄) as a stripping agent on the layer number of MoS₂. Na⁺ ions, as alkali metal ions, can intercalate between layers to achieve the purpose of exfoliating MoS₂. Additionally, NaBH₄ exhibits reducibility, which can effectively promote the formation of the metallic phase of MoS₂. Few-layered MoS₂, as an electrode for supercapacitor, possesses a wide potential window of 0.9 V, and a high specific capacitance of 150 F g⁻¹ at 1 A g⁻¹. This work provides a facile method to prepare few-layered two-dimensional materials for high electrochemical performance. Full article

This work investigates the electrocatalytic properties of carbon paste electrodes (CPEs) modified with ionic liquids (IL) and metallic ionic liquid (ILFe) for the hydrazine oxidation reaction (HzOR). The results indicate that ILFe significantly enhances the catalytic activity of the electrode, exhibiting catalysis towards hydrazine oxidation, reducing overpotential, and increasing reaction current. It is determined that the HzOR on the MWCNT/MO/ILFe electrode involves the transfer of four electrons, with high selectivity for nitrogen formation. Additionally, ILFe is observed to improve the wettability of the electrode surface, increasing its capacitance and reaction efficiency. This study highlights the advantages of ILFe-modified CPEs in terms of simplicity, cost-effectiveness, and improved performance for electrochemical applications, demonstrating how the ionic liquid catalyzes hydrazine oxidation despite its lower conductivity. Full article

Supercapacitors (SCs) are a novel type of energy storage device that exhibit features such as a short charging time, a long service life, excellent temperature characteristics, energy saving, and environmental protection. The capacitance of SCs depends on the electrode materials. Currently, carbon-based materials, transition metal oxides/hydroxides, and conductive polymers are widely used as electrode materials. However, the low specific capacitance of carbon-based materials, high cost of transition metal oxides/hydroxides, and poor cycling performance of conductive polymers as electrodes limit their applications. Copper–sulfur compounds used as electrode materials exhibit excellent electrical conductivity, a wide voltage range, high specific capacitance, diverse structures, and abundant copper reserves, and have been widely studied in catalysis, sensors, supercapacitors, solar cells, and other fields. This review summarizes the application of copper–sulfur compounds in SCs, details the research directions and development strategies of copper–sulfur compounds in SCs, and analyses and summarizes the research hotspots and outlook, so as to provide a reference and guidance for the use of copper–sulfur compounds. Full article

An accurate humidity measurement is essential in various industries, including product stability, pharmaceutical and food preservation, environmental control, and precise humidity management in experiments and industrial processes. Crafting effective humidity sensors through precise material selection is crucial for detecting minute humidity levels across various fields, ultimately enhancing productivity and maintaining product quality. Metal–organic frameworks (MOFs), particularly zeolitic imidazolate frameworks (ZIFs), exhibit remarkable properties and offer a wide range of applications in catalysis, sensing, and gas storage due to their structural stability, which resembles zeolites. The previous research on MOF-based humidity sensors have primarily used electrical resistance-based methods. Recently, however, interest has shifted to capacitive-based sensors using MOFs due to the need for humidity sensors at low humidity and the resulting high sensitivity. Nevertheless, further studies are required to optimize particle structure and size. This study analyzes ZIF-8, a stable MOF synthesized in varying particle sizes, to evaluate its performance as a humidity sensor. The structural, chemical, and sensing properties of synthesized ZIF-8 particles ranging from 50 to 200 nanometers were examined through electron microscopy, spectroscopic, and electrochemical analyses. The fabricated copper electrodes combined with these particles demonstrated stable and linear humidity sensing capabilities within the range of 3% to 30% relative humidity (RH). Full article

As heterogeneous catalysis is a practical method for activating Oxone, the immobilization of transition metals (e.g., Co, Fe) on carbonaceous supports is a promising platform. Thus, this study attempts to develop a carbon-supported metallic catalyst by growing Co/Fe on carbon foam (CF) via adopting melamine foam as a readily available template which could be transferred to nitrogen-doped CF with marcoporous structures. Specifically, a unique adornment of Co/Fe species on this CF is facilely fabricated through a complexation of Co/Fe with a plant extract, tannic acid, on melamine foam, followed by carbonization to produce nano-needle-like Co/Fe on N-doped CF, forming a magnetic CF (MCF). This resultant MCF exhibits a much higher surface area of 54.6 m²/g than CF (9.5 m²/g), and possesses a much larger specific capacitance of 9.7 F/g, than that of CF as 4.0 F/g. These superior features of MCF enable it to accelerate Oxone activation in order to degrade an emerging contaminant, bis(4-hydroxyphenyl)methanone (BHPM). Furthermore, MCF + Oxone exhibits a lower activation energy as 18.6 kJ/mol for BHPM elimination and retains its effectiveness in eliminating BHPM over multiple rounds. More importantly, the CF is also prepared and directly compared with the MCF to study the composition-structure-property relationship to provide valuable insights for further understanding of catalytic behaviors, surficial characteristics, and application of such a functional carbon material. Full article

Tunable porous composite materials to control metal and metal oxide functionalization, conductivity, pore structure, electrolyte mass transport, mechanical strength, specific surface area, and magneto-responsiveness are critical for a broad range of energy storage, catalysis, and sensing applications. Biotemplated transition metal composite aerogels present a materials approach to address this need. To demonstrate a solution-based synthesis method to develop cobalt and cobalt oxide aerogels for high surface area multifunctional energy storage electrodes, carboxymethyl cellulose nanofibers (CNF) and alginate biopolymers were mixed to form hydrogels to serve as biotemplates for cobalt nanoparticle formation via the chemical reduction of cobalt salt solutions. The CNF–alginate mixture forms a physically entangled, interpenetrating hydrogel, combining the properties of both biopolymers for monolith shape and pore size control and abundant carboxyl groups that bind metal ions to facilitate biotemplating. The CNF–alginate hydrogels were equilibrated in CaCl₂ and CoCl₂ salt solutions for hydrogel ionic crosslinking and the prepositioning of transition metal ions, respectively. The salt equilibrated hydrogels were chemically reduced with NaBH₄, rinsed, solvent exchanged in ethanol, and supercritically dried with CO₂ to form aerogels with a specific surface area of 228 m²/g. The resulting aerogels were pyrolyzed in N₂ gas and thermally annealed in air to form Co and Co₃O₄ porous composite electrodes, respectively. The multifunctional composite aerogel’s mechanical, magnetic, and electrochemical functionality was characterized. The coercivity and specific magnetic saturation of the pyrolyzed aerogels were 312 Oe and 114 emu/g_Co, respectively. The elastic moduli of the supercritically dried, pyrolyzed, and thermally oxidized aerogels were 0.58, 1.1, and 14.3 MPa, respectively. The electrochemical testing of the pyrolyzed and thermally oxidized aerogels in 1 M KOH resulted in specific capacitances of 650 F/g and 349 F/g, respectively. The rapidly synthesized, low-cost, hydrogel-based synthesis for tunable transition metal multifunctional composite aerogels is envisioned for a wide range of porous metal electrodes to address energy storage, catalysis, and sensing applications. Full article

Gold nanoparticles have been extensively studied due to their unique optical and electronic properties which make them attractive for a wide range of applications in biomedicine, electronics, and catalysis. Over the past decade, atmospheric pressure plasma jets in contact with a liquid have emerged as a sustainable and environmentally friendly approach for synthesizing stable and precisely controlled dispersions. Within the context of plasma jet/liquid configurations, researchers have explored various power sources, ranging from kHz frequencies to nanopulse regimes. In this study, we investigated the effects of coupling two distinct power supplies: a high-voltage micropulse and a radio frequency (RF) generator. The variations within the plasma induced by this coupling were explored by optical and electrical measurements. Our findings indicated a transition from a bullet plasma propagation mechanism to a capacitive coupling mechanism upon the introduction of RF energy. The impact on the production of metal nanoparticles was also examined as a function of the radio frequency power and of two distinct process gases, namely helium and argon. The characterization of gold nanoparticles included UV-visible spectroscopy, dynamic light scattering, and scanning electron microscopy. The results showed that the size distribution depended on the type of process gas used and on the power supplies coupling. In particular, the incorporation of RF power alongside the micropulse led to a decrease in both average particle size and distribution width. The comparison of the different set up suggested that the current density can influence the particle size distribution, highlighting the potential advantages of the use of a dual-frequency atmospheric pressure plasma jet configuration. Full article

The selective detection of different gas components will remain of huge importance in the future, either in the ambient air or in flue gases, e.g., for controlling purposes of combustion processes. The focus here is on the development of a highly selective ammonia sensor that will be exemplarily used in the flue gas of biomass combustion plants with catalysts for nitrogen oxide reduction. Such applications require a robust sensor design, in this case, based on a ceramic substrate. The gaseous ammonia is detected with the help of a zeolite film, whose selective adsorption properties towards ammonia are already intensively being used in the field of flue gas catalysis. The adsorption and desorption of ammonia on the gas-sensitive zeolite film lead to changes in the dielectric properties of the functional material. Using an interdigital electrode (IDE) structure below the zeolite film, the capacitance was determined as a measure of the ammonia concentration in the gas. In this context, the fabrication of all layers of the sensor in the thick film with subsequent laser patterning of the IDE structure enables a cost-efficient and effective method. The functionality of this sensor principle was extensively tested during measurements in the laboratory. A high and fast response to ammonia was detected at different sensor temperatures. In addition, very low cross-sensitivities to other gas components such as water (very low) and oxygen (zero) were found. Full article

As non-noble metal co-catalysts, Nitrides have received extensive attention for their high efficiency and low cost in photocatalytic hydrogen production. In this study, we develop a novel composite co-catalyst of Au/Ta₃N₅ that significantly enhanced the photocatalytic hydrogen production activity of CdS. The activity of photocatalyst (Au/Ta₃N₅)/CdS is 7.3 times of bare CdS and 2.2 times of Ta₃N₅/CdS. The proper capacitance and enhanced activity of Ta₃N₅ demonstrates the capacitance catalysis effect of Ta₃N₅, which improves the charges separation and storing of the photoexcited electrons from CdS. Au acts as an active site for proton reduction to further improve the activity. Full article