Hollow nanosphere alloys were synthesized for electrochemical methanol oxidation reactions. The hollow nanoalloys were prepared by the galvanic replacement reaction at room temperature, utilizing hollow gold nanoparticles as templates and amalgam as an intermediate, by the electrochemical potential difference between mercury and palladium. Morphological, structural, and elemental distribution analyses confirm the successful synthesis of the ternary nanosphere alloys. The methanol oxidation reaction catalytic activity of the hollow nanoalloys in alkaline solutions was evaluated using cyclic voltammetry and chronoamperometry. The results demonstrate that the peak current density of the hollow nanoalloys reached 4.26 mA/cm2, which is 1.8 times that of commercial Pd/C, and the current density retained 85.4% of the initial activity after 300 cycles of testing.
This study presented the electrochemical optimization and synthesis of molybdenum disulfide/tin oxide (MoS2/SnO2) nanocomposites for high-performance supercapacitor electrodes. Two nanocomposite formulations were effectively fabricated using simple two-step approach that combined hydrothermal and wet-chemical methods. Trisodium citrate (C6H5Na3O7·2H2O) was indispensable as a ligand that directed the structure. Its citrate ions bind to Sn4+ and Mo4+ precursors, thereby regulating nucleation and inhibiting spontaneous precipitation. The weight ratios of MoS2:SnO2 were (1:1) and (2:8). MS (2:8) composite exhibited improved crystallinity, as validated by X-ray diffraction (XRD) analysis, which also confirmed the coexistence of both crystalline phases in all samples. The MS (2:8) electrode displayed specific capacitance of 260 F g−1 at current density (1 A g−1). This better performance had been attributed to synergistic redox contributions from both Mo4+ and Sn4+ ions, which facilitate multi-electron Faradaic reactions. Additionally, optimal SnO2 content results in increased ion accessibility and diminished charge-transfer resistance. An asymmetric supercapacitor device (MS (2:8)//AC) was constructed to verify its practical applicability. Cathode was made up of MS (2:8) composite, and anode from activated carbon (AC). The device's potential for energy storage applications was underscored by its ability to attained maximum energy density of 32 Wh kg−1 and sustained regulated operating voltage window of 1.6 V. Additionally, the device exhibited notable long-term cycling stability, retaining 88% of its initial capacitance after 7000 galvanostatic charge-discharge (GCD) cycles at 3 A g−1 under potential range of (−0.8 to 0.8) V. MS (2:8) has been verified as a viable, low-cost supercapacitor electrode substrate with a balanced energy density, power capability, and cycle life, as proven by durability tests.
Spinel NiMn2O4 was synthesized using a simple one-pot solution combustion approach, which promotes rapid formation of the material without complex steps. XRD and FTIR confirmed that the spinel phase had formed, and FESEM revealed that the formation of truncated polyhedral microcrystals. The UV–Vis diffuse reflectance analysis confirmed an indirect band gap of 1.79 eV. A comprehensive optical analysis, including refractive index, dielectric response, optical conductivity, energy-loss functions, and skin depth, provided insights into the light-matter interaction and electronic response of the material. The photocatalytic performance of NiMn2O4 was studied by the degradation of cationic dyes malachite green (MG) and methylene blue (MB) dyes under visible light exposure, resulting in a 95.87% removal of MG dye within 90 min. The degradation followed pseudo-first-order kinetics with apparent rate constants of k = 0.00652 min−1 for methylene blue and k = 0.03623 min−1 for malachite green. The reactive species trapping experiments identified photogenerated holes (h+) and electrons (e−) as the dominant reactive species, confirming the direct participation of charge carriers in the photocatalytic dye degradation mechanism. Furthermore, the catalyst exhibited good structural stability and reusability with negligible loss in photocatalytic efficiency after repeated cycles. These findings demonstrate that one-pot solution combustion synthesized spinel NiMn2O4 is a promising visible-light photocatalyst and provide a comprehensive understanding of its optical characteristics in relation to photocatalytic performance, offering useful insights for the development of multifunctional spinel oxide photocatalysts.
Herein, we synthesize inverse spinel Zn2TiO4 via controlling pH of the hydrothermal synthesis reaction to understand the phase formation, defect chemistry and other optical-defect properties. Five different samples with strong acidic (pH 1) to strong basic environment (pH 13) were prepared. The X-ray diffraction results suggest that the highly crystalline phase of Zn2TiO4 is obtained at pH 10. The band gap increases with an increase in the pH when determined using UV–visible studies. Photoluminescence studies reveal strong blue and green emission for samples prepared in acidic and basic media, respectively. Similarly, luminescence lifetime, thermoluminescence and persistent luminescence studies suggest that the trap density of shallower defects and deeper defects is highest for samples prepared under acidic and basic environments, respectively. The trap depth is found to be suitable for the application of Zn2TiO4-inverse spinel for dosimetry and energy storage applications.
Silicon (Si) has become a promising anode material due to its ultra-high theoretical specific capacity, but it is accompanied by severe volume changes during the deintercalation of lithium, which seriously restricts its practical application. At present, silicon nanoparticles are deposited into the pores of porous carbon by chemical vapor deposition (CVD) method, which can prepare vapor-deposited silicon‑carbon materials with high specific capacity and low volume expansion, showing broad application prospects. However, the structural differences of porous carbons with different precursors will significantly affect the deposition behavior of silicon. Based on this, biomass-based silicon carbon (B-PCSC), petroleum coke-based silicon carbon (PC-PCSC) and resin-based silicon carbon (R-PCSC) were prepared by CVD method using biomass-based porous carbon (B-PC), petroleum coke-based porous carbon (PC-PC) and resin-based porous carbon (R-PC) as substrates. The pore size of R-PC is the highest in 1.5–3 nm, which is more conducive to the deposition of silane. The proportion of ultramicropores (<0.7 nm) in B-PC is the highest, which is not conducive to the deposition of silane. The single particle crushing force of R-PCSC is 39.5% and 8.1% higher than that of B-PCSC and PC-PCSC, respectively. Expansion tests on pouch battery revealed that, after 100 cycles at 0.5C rate, the charge specific capacity of R-PCSC is 1135.59 mAh g−1, which is better than that of B-PCSC and PC-PCSC. After 100 cycles at 1C, the irreversible expansion thickness of R-PCSC is 5.9 μm and 2.3 μm lower than that of B-PCSC and PC-PCSC, respectively.
Efficient thermal management under low assembly pressure requires thermal interface materials (TIMs) that combine continuous through-plane heat-flow pathways, low contact resistance, and resistance to compression-induced cracking. Here, we report an oriented pre-bending strategy for constructing crack-resistant vertically aligned graphene film (VGF) TIMs. In this architecture, graphene foam lamellae are directionally pre-bent and fixed within an epoxy matrix, forming a compliant vertical network with a built-in deformation allowance before device assembly. The VGF TIMs contain 77.42 wt% graphene and exhibit a through-plane thermal conductivity of 143.54 W m−1 K−1. The pre-bent lamellar framework also maintains a low contact thermal resistance of 16.6–25.8 mm2 K W−1 over 10–100 psi by improving surface conformity and suppressing local stress concentration. Finite-element simulations show that, compared with a randomly deformed wavy vertical lamellar structure, the oriented pre-bent architecture suppresses uncontrolled deformation and redistributes compressive stress along preset bent pathways, thereby mitigating bending-induced fracture. Under the same liquid-cooling conditions, VGF TIMs exhibited superior device-level thermal management performance, reducing the steady-state heater temperature to approximately 47 °C at 40 W cm−2, which is 71 °C lower than the case without TIM and 35 °C lower than the commercial thermal pad. This work establishes oriented pre-bending as a structural design strategy for combining high thermal conductivity, crack-resistant compliance, and low thermal resistance in graphene-based TIMs.
Triboelectric nanogenerators (TENGs) can convert low-frequency mechanical excitations into electrical energy and have been widely applied in various fields, including smart wearables, sports monitoring, and human–machine interaction. Enhancing the output of TENGs and increasing the equivalent capacitance of the triboelectric layer are key to their practical application. To this end, this paper proposes a method in which a magnetic field induces an ordered arrangement of particles inside the triboelectric layer. By establishing an equivalent-capacitance model for the chain-like structure within the triboelectric layer, the influence of filler concentration, magnetic flux density, and magnetic-field angle on the equivalent capacitance is investigated, and a PMN-TENG with a PDMS/MWCNTs/NdFeB composite triboelectric layer is fabricated. The micro-morphology of the triboelectric layer is observed, and the performance and applications of the PMN-TENG are tested. The results show that the magnetic field can drive magnetic particles to form ordered chain-like structures along the field direction, thereby increasing the equivalent capacitance of the triboelectric layer. When the NdFeB mass fraction is 6 wt%, the magnetic flux density is 40 mT. The included angle between the magnetic field and the horizontal plane is 90°; the triboelectric nanogenerator delivers an open-circuit voltage of 274 V, a short-circuit current of 18 μA, and a transferred charge of 43 nC; the current density reaches 30 mA/m2, and the equivalent capacitance of the triboelectric layer increases from 18 pF to 88 pF. Furthermore, the device exhibits stable output performance under various operating conditions, including rectification-based energy storage, powering external loads, and on-body wearable operation, demonstrating its potential for wearable self-powered applications.
Industrial chromium emissions pose severe environmental contamination and health risks due to the high toxicity and persistence of chromium ions (Cr6+), driving the need for rapid and sensitive detection methods. In this study, we utilized “defect engineering” to cleave 2D MXene precursors with pyrrole as the nitrogen source, followed by a reduction strategy to passivate the surfaces of MXene quantum dots (r-N-MQDs). The quantum yield (QY) of r-N-MQDs reaches 12.09%, which is attributed to quantum confinement effects and defect-related luminescence. The r-N-MQDs are further employed as fluorescent probes for the sensitive and reliable detection of Cr6+, exhibiting a detection limit of 7.2 μM and a linear response range of 0.08–2.7 mM. The fluorescence of r-N-MQDs can be efficiently quenched by Cr6+ through a synergistic effect of redox-driven electron transfer and an inner filter effect (IFE). The constructed fluorescent probe shows considerable potential for environmental heavy-metal monitoring, benefiting from its favorable analytical performance, reliable response, and practical applicability.
To achieve photodegradation of organic dye rhodamine B (RhB), the ellipsoidal α-Fe2O3@β-Bi2O3 microspheres as photocatalysts were prepared by a PVP-assisted solvothermal method. The morphology and structures of α-Fe2O3@β-Bi2O3 core-shell microspheres could be synergistically regulated by the polyvinylpyrrolidone (PVP) addition and the Bi/Fe molar ratio. To further improve the photocatalytic efficiency, hierarchical α-Fe2O3/BiOCl microspheres were designed and fabricated by the Cl-doping methods using five chlorine sources including KCl, NH4Cl, SnCl2, CoCl2, and CuCl2. Compared with the photocatalytic activity, the flower-like α-Fe2O3/BiOCl microspheres utilized CoCl2 as the chlorine source exhibit the optimal photodegradation efficiency, which achieves a degradation rate of 92.1% for RhB in 30 min under visible light irradiation. As a possible mechanism, the stable p-n heterojunction was formed between α-Fe2O3 and BiOCl, which plays a main role in photocatalytic process. In trapping experiment, superoxide radicals (·O2−) and holes (h+) are the primary active species responsible for the photocatalytic process.
The detection of hazardous Ni2+ and Cu2+ ions remained a critical priority for environmental monitoring. In this study, we report the development of a sustainable, dual-mode sensing platform utilizing silver nanoparticles (AgNPs) synthesized via a green, one-pot approach with γ-CDs as both reducing and stabilizing agents. Two distinct sensing probes were engineered: an aqueous-based assay for the rapid detection of Ni2+ and a paper-based device for the colorimetric determination of Cu2+. Both sensing platforms leveraged the optical surface plasmon resonance (SPR) properties of AgNPs. The colloidal solution of AgNPs showed an SPR band at 401 nm, as confirmed by spectrophotometer UV–Vis. The presence of Ni2+ ions in colloidal AgNPs and Cu2+ in AgNPs-paper induced particle aggregation, resulting in distinct, concentration-dependent chromatic shifts. The findings demonstrated both sensors exhibited excellent analytical performance, proven by acceptable precision and accuracy with no significant difference (p > 0.05) compared to AAS measurements. The colloidal AgNPs sensor reached a stable read-out within 5 min (LoD: 0.041 mg/L), while the AgNPs-paper achieved a 10 min constant reading (LoD: 0.027 mg/L). The linear calibration curve obtained R2 of 0.9997 for the aqueous-based sensor and 0.9992 for the paper-based sensor, signifying the linear equations could be used for Ni2+ and Cu2+ quantification in samples. In conclusion, this research provided a promising analytical framework for the development of Ni2+ and Cu2+ sensors. Their simplified operational workflow and high sensitivity underscored its potential for on-site environmental monitoring, ensuring the rapid detection of nickel and copper contamination in diverse water matrices.
Nanocrystalline La0.67Sr0.33-xCaxMn1-xMxO3 (denoted LSMN and LSMC, with M = Ni or Co and x = 0.05) perovskite manganites were synthesized by the sol–gel method and systematically investigated for their structural, optical, magnetic, and magnetocaloric properties. This dual-site co-substitution strategy is explored as an effective approach for simultaneously tuning the multifunctional properties of La0.67Sr0.33MnO3 based nanomanganites, with potential relevance to energy-efficient solid-state cooling and optoelectronic technologies. X-ray diffraction coupled with Rietveld refinement confirms the formation of single-phase orthorhombically distorted perovskite structures (space group Pbnm) with nanometric crystallite sizes. Halder–Wagner analysis gives average crystallite sizes of about 48 and 64 nm for LSMN and LSMC, respectively. UV–Vis–NIR spectroscopy reveals that B-site substitution significantly modifies the optical response, with Co doping enhancing near-infrared absorption, while Ni doping produces comparatively sharper absorption features. The optical analysis further reveals tunable band-gap characteristics, with indirect band-gap energies of 2.45 eV for LSMN and 0.61 eV for LSMC, demonstrating the strong influence of the B-site dopant on the optical response. Magnetic measurements show a ferromagnetic–paramagnetic transition close to room temperature with a second-order nature. The Curie temperature is approximately 300 K for both compounds, while deviations from Curie–Weiss behavior above the transition temperature reveal Griffiths-like magnetic correlations. Deviations from Curie–Weiss behavior above the transition temperature suggest the presence of Griffiths-like magnetic correlations. The magnetocaloric effect exhibits a moderate but broadened magnetic entropy change, favorable for magnetic refrigeration over an extended temperature range. At 5 T, the maximum magnetic entropy changes reach 2.36 and 2.31 J kg−1 K−1 for LSMN and LSMC, respectively, with corresponding relative cooling powers of 323.5 and 312.9J·kg−1, reaching approximately 78.9% and 76.3% of the corresponding benchmark Gd value. These results demonstrate that CaNi and CaCo co-substitution provides an effective route to tailoring multifunctional manganites for room-temperature magnetic cooling and infrared optoelectronic applications, offering a promising materials-design strategy for multifunctional and energy-efficient solid-state technologies.
