Search Results (10)

Significant research has focused on cost–effective, highly active, and exceptionally stable non–noble metal electrocatalysts (NNMEs) to boost the performance of the oxygen reduction reaction (ORR). Of note, the development of design and synthesis of Fe–N–C electrocatalysts is essential but remains challenging. Herein, the Fe and N co–doped porous carbon material with a yolk–shell (YS) structure, termed SA–H₂TPyP@PDA–Fe (900), was fabricated by self–assembly of metal–free porphyrin as a yolk and polymerization of dopamine as a shell with an addition of iron salts, followed by the high–temperature pyrolysis and acid–leaching. As a result, active sites, like FeN₄ and N–doped C, within rich porous YS carbon structures, play an important role for ORR in an alkaline media. The SA–H₂TPyP@PDA–Fe (900) electrocatalyst shows positive ORR performances than those of SA–H₂TPyP (900) and SA–H₂TPyP@PDA (900), indicating the dominating function of the YS carbon structure decorated with Fe–based species. This efficient route of template–free–induced preparation of the YS structure discovers the design and synthesis of NNMEs for ORR. Full article

The tailored crystalline configuration coupled with submicron particles would be conducive to superior ionic conductivity, which could further improve the cycle life of lithium-ion batteries (LIBs). Here, manganese phosphide (Mn_5.64P₃) particles with hexagonal crystal structure embedded into nitrogen/phosphorus (N/P) co-doped carbon shells (Mn_5.64P₃-C) are successfully prepared by the self-template and recrystallization–self-assembly method. The electrochemical properties of as-synthesized Mn_5.64P₃-C as anode materials for LIBs are systematically investigated. The XRD and HRTEM combined with SAED indicate that the prepared Mn_5.64P₃-C hybrid with the ratio of 1:10 of Mn:C present a hexagonal crystal structure covered with a carbon layer. During charging/discharging at the current density of 0.5 A g⁻¹, the Mn_5.64P₃-C electrode exhibits the reversible capacity of 160 mAh g⁻¹ after 3000 cycles with high-capacity retention. The ex-situ XRD of initial discharge/charge process at different voltages implies that the Mn_5.64P₃ could be transformed to the amorphous Li_xMn_yP_z. The N/P co-doped carbon shells can provide high specific area for electrolyte infiltration, and act as the buffer matrix to suppress the loss of the Mn_5.64P₃ active material during cycling. The Mn_5.64P₃ with the hexagonal crystal structure and N/P co-doped carbon shells could promote the further optimization and development of manganese phosphide for high-performance LIBs. Full article

Modifying the electronic structure of a catalyst through interface engineering is an effective strategy to enhance its activity in the hydrogen evolution reaction (HER). Interface engineering is a viable strategy to enhance the catalytic activity of transition metal phosphides (TMPs) in the HER process. The interface-engineered FeP/NiP₂/Ni₅P₄/NiP multi-metallic phosphide nanoparticles confined in a N, P-doped carbon matrix was developed by a simple one-step low-temperature phosphorization treatment, which only requires 72 and 155 mV to receive the current density of 10 mA/cm² in acid and alkaline electrolyte, respectively. This enhanced performance can be primarily attributed to the heterointerface of FeP/NiP₂/Ni₅P₄/NiP multi-metallic phosphides, which promotes electron redistribution and optimizes the adsorption/desorption strength of H* on the active sites. Furthermore, the N, P-doped carbon framework that encapsulates the nanoparticles inhibits their aggregation, leading to an increased availability of active sites throughout the reaction. The results of this study open up a straightforward and innovative approach to developing high-performance catalysts for hydrogen production. Full article

Hydrogen peroxide (H₂O₂) is an important chemical with a diverse range of industrial applications in chemical synthesis and medical disinfection. The traditional anthraquinone oxidation process, with high energy consumption and complexity, is being replaced by cost-effective and environmentally friendly alternatives. In order to explore suitable catalysts for the electrocatalytic synthesis of H₂O₂, the stability of B,N-doped graphene loaded with various p-block metal (PM) single atoms (i.e., PM-N_xB_y: x and y represent the number of atoms of N and B, respectively) and the effects of different numbers and positions of B dopants in the second coordination shell on the catalytic performance were studied by density functional theory (DFT) calculations. The results show that Ga-N₄B₆ and Sb-N₄B₆ exhibit enhanced stability and 2e⁻ oxygen reduction reaction (ORR) activity and selectivity. Their thermodynamic overpotential η values are 0.01 V, 0.03 V for Ga-N₄B₆’s two configurations and 0.02 V, 0 V for Sb-N₄B₆’s two configurations. Electronic structure calculations indicate that the PM single atom adsorbs OOH* intermediates and transfers electrons into them, resulting in the activation of the O-O bond, which facilitates the subsequent hydrogenation reaction. In summary, Sb-N₄B₆ and Ga-N₄B₆ exhibit extraordinary 2e⁻ ORR performance, and their predicted activities are comparable to those of known outstanding catalysts (such as PtHg₄ alloy). We propose effective strategies on how to enhance the 2e⁻ ORR activities of carbon materials, elucidate the origin of the activity of potential catalysts, and provide insights for the design and development of electrocatalysts that can be used for H₂O₂ production. Full article

This Special Issue includes 12 research papers on the development of various materials for adsorbing different contaminants in water, such as Sb, Cr(VI), Cu(II), Zn(II), fluorine, phenol, dyes (indigo carmine, Congo red, methylene blue, and crystal violet), and drugs (dlevofloxacin, captopril, and diclofenac, and paracetamol). The commercial, natural, and synthetic materials used as adsorbents comprise commercial activated carbon, natural clay and montmorillonite, biosorbent based on sugarcane bagasse or algal, graphene oxide, graphene oxide-based magnetic nanomaterial, mesoporous Zr-G-C₃N₄ nanomaterial, nitrogen-doped core–shell mesoporous carbonaceous nano-sphere, magnetic Fe-C-N composite, polyaniline-immobilized ZnO nanorod, and hydroxy-iron/acid–base-modified sepiolite composite. Various operational conditions are evaluated under batch adsorption experiments, such as pH, NaCl, solid/liquid ratio, stirring speed, contact time, solution temperature, initial adsorbate concentration. The re-usability of laden materials is evaluated through adsorption–desorption cycles. Adsorption kinetics, isotherm, thermodynamics, and mechanisms are studied and discussed. Machine learning processes and statistical physics models are also applied in the field of adsorption science and technology. Full article

It continues to be a challenge to design innovative NiCoP composite anode materials to further improve rate capacity. In this work, bimetallic flower-like NiCoP encapsulated in an N-doped carbon shell (designated as NiCoP@NC) as a high-rate capable anode material for lithium-ion batteries (LIBs) was successfully designed and synthesized. The novel structure design combines the advantages of flower-like NiCoP (core) and N-doped carbon (shell). Flower-like NiCoP offers numerous interface and redox reaction sites for improving lithium storage, while the N-doped carbon shell effectively buffers volume expansion and enhances electrical conductivity. The synergistic effect between NiCoP and the N-doped carbon shell proposes a marvelous high-rate capacity (320 mA h/g even at 5 A/g) and a good cycle life with high reversible capacity (369.8 mA h/g for 700 cycles at 3 A/g with 81% retention). An investigation of kinetics performance shows that the introduction of the N-doped carbon shell enhances the charge transfer, and the pseudocapacitive behavior dominates the rapid Li⁺ storage of the NiCoP@NC electrode. Full article

Nickel phosphide (Ni₂P), as an anode material for both lithium- and sodium-ion batteries, offers high theoretical specific and volumetric capacities. However, considerable challenges include its limited rate capability and low cycle stability arising from its volume change and degradation during cycling. To solve these issues, appropriate composite micro/nanoparticle designs can improve conductivity and provide confinement. Herein, we report a simple pyrolysis method to synthesize nitrogen-doped carbon-coated Ni₂P nanorod arrays (Ni₂P@NC) from nickel foam and an ionic resin as a source of carbon, nitrogen and phosphorus. The N-doped open-ended carbon shells provide Ni₂P containment, good electrical conductivity, efficient electrolyte access and the buffering of bulk strain during cycling. Consequently, as a LIB anode material, Ni₂P@NC has impressive specific capacity in long-term cycling (630 mAh g⁻¹ for 150 cycles at 0.1 A g⁻¹) and a high rate capability of 170 mAh g⁻¹ for 6000 cycles at 5 A g⁻¹. Similarly, as a SIB anode, Ni₂P@NC retains a sizable 288 mAh g⁻¹ over 300 cycles at 0.1 A g⁻¹, and 150 mAh g⁻¹ over 2000 cycles at 2 A g⁻¹. Furthermore, due to a sizable portion of its capacity coinciding with adequately low voltage, the material shows promise for high volumetric energy storage in full-cell format. Lastly, the simple synthesis method has the potential to produce other carbon-coated metal phosphides for electrochemical applications. Full article

Carbon quantum dots (CQDs) with their strong photoluminescence (PL) activity, high biocompatibility, robust stability, low cytotoxicity, and flexible surface structures have been employed in many fields including chemical sensing, biosensing, photocatalyst, energy storage, and biomedical applications. Of note, CQDs present an intrinsic pH-sensitive PL nature indicating their intense potential for pH-mediated sensing and imaging. Despite the numerous studies performed in the last two decades, the pH-sensitive PL mechanism of CQDs is still under debate and must be clarified to overcome the limitations in practical applications. Therefore, in this report, we performed a systematical study to determine the pH-sensitive PL nature of boron/nitrogen co-doped CQDs (B/N CQDs). In the first part, B/N CQDs with a strong blue emission were fabricated via a hydrothermal synthesis procedure. B/N-CQDs showed a strong blue PL emission with high quantum yield and excitation-dependent nature. Under the low pH conditions (pH 3), B/N-CQDs exhibited a robust green fluorescence emission with a significant red-shift (48 nm) and the loss of the excitation-dependent nature. The change in PL nature originated from the protonation of surface groups, a decrease in negative surface charge (from −20.6 to −1.23 eV), and finally, aggregation of the nanostructure (the size of CQDs from 4.8 to 7.5 nm). However, in the case of alkaline conditions, the deprotonation surface groups significantly enhanced the surface charge and led to the emergence of a negative ‘protective shell’ with a zeta potential of −71.3 eV. In a high pH medium (pH 13), PL spectra showed the loss of excitation-dependent features and a red-shift (35 nm) in emission peak maxima with lower intensity. This report provides significant progress in the clarification of the pH-sensitive PL mechanism of CQDs. We envision that the proposed CQDs would provide unique opportunities in the fabrication of novel pH sensor systems and fluorescence imaging where a wide range of pH sensitivity is required. Full article

The wide use of alizarin red S (ARS), a typical anthraquinone dye, has led to its continued accumulation in the aquatic environment, which causes mutagenic and carcinogenic effects on organisms. Therefore, this study focused on the removal of ARS dye by adsorption onto a magnetic chitosan core–shell network (MCN). The successful synthesis of the MCN was confirmed by ATR-FTIR, SEM, and EDX analysis. The influence of several parameters on the removal of ARS dye by the MCN revealed that the adsorption process reached equilibrium after 60 min, pH played a major role, and electrostatic interactions dominated for the ARS dye removal under acidic conditions. The adsorption data were described well by the Langmuir isotherm and a pseudo-second order kinetic model. In addition to the preferable adsorption of hydrophobic dissolved organic matter (DOM) fractions onto the MCN, the electrostatic repulsive forces between the previously adsorbed DOM onto MCN and ARS dye resulted in lower ARS dye removal. Furthermore, the MCN could easily be regenerated and reused for up to at least five cycles with more than 70% of its original efficiency. Most importantly, the spent MCN was pyrolytically converted into N-doped magnetic carbon and used as an adsorbent for various dyes, thus establishing a waste-free adsorption process. Full article

Developing superior efficient and durable oxygen reduction reaction (ORR) catalysts is critical for high-performance fuel cells and metal–air batteries. Herein, we successfully prepared a 3D, high-level nitrogen-doped, metal-free (N–pC) electrocatalyst employing urea as a single nitrogen source, NaCl as a fully sealed nanoreactor and gingko shells, a biomass waste, as carbon precursor. Due to the high content of active nitrogen groups, large surface area (1133.8 m² g⁻¹), and 3D hierarchical porous network structure, the as-prepared N–pC has better ORR electrocatalytic performance than the commercial Pt/C and most metal-free carbon materials in alkaline media. Additionally, when N–pC was used as a catalyst for an air electrode, the Zn–air battery (ZAB) had higher peak power density (223 mW cm⁻²), larger specific-capacity (755 mAh g⁻¹) and better rate-capability than the commercial Pt/C-based one, displaying a good application prospect in metal-air batteries. Full article