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In this work, we detail a hydrothermal synthesis of MnO₂ nanorods at a temperature of 120 °C, employing different ratios of precursors. The precursors used include manganese chloride tetrahydrate and potassium permanganate with molar ratios of 1:3, 1:1, and 3:1. Thermal analysis indicated that the 1:3 precursor ratio exhibited the lowest activation energy of 40 kJ/mol, making it suitable for MnO₂ synthesis. Analysis through X-ray diffraction confirmed the presence of β-MnO₂ in all ratios studied, with the smallest crystals, measuring 7 nm, identified specifically in the 1:3 ratio. X-ray photoelectron spectroscopy analysis demonstrated that manganese in MnO₂ exists in an oxidation state of + 4. Moreover, we synthesized MnO₂ employing a 1:3 precursor ratio at hydrothermal temperatures of 150, 180, and 210 °C, and assessed the influence of the synthesis temperature on the electrochemical features. The cyclic voltammetry (CV) analysis demonstrated that the MnO₂ synthesized at 120 °C reached a specific capacitance of 452 F/g at a scan rate of 2 mV/s. In addition, the galvanostatic charge–discharge (GCD) analysis provided evidence of an energy density of 35 Wh/kg and a power density of 495 W/kg at a current density of 5 A/g, suggesting its substantial potential as a superior electrode material for the fabrication of supercapacitors.

This study focuses on gahnite (Zinc aluminate, ZnAl₂O₄)-based microwave dielectric ceramics for prototype patch antennas in the 4–12 GHz range. ZnAl₂O₄ was modified with TiO₂ and V₂O₅ to improve key properties like dielectric permittivity (ε_r) and dielectric loss (tan δ). X-ray Diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) confirmed the formation of a two-phase system. The dielectric permittivity values for ZA (ZnAl₂O₄), ZAT (ZnAl₂O₄TiO₂), ZAV (ZnAl₂O₄V₂O₅), and ZAVT (ZnAl₂O₄0.6wt%V₂O₅0.4wt%TiO₂) were 21.8, 24.9, 18.9, and 22.83, respectively, while dielectric losses were 0.050, 0.060, 0.049, and 0.058. Antenna return losses (RL), bandwidth, and voltage standing wave ratio (VSWR) were − 19.42 dB/616 MHz/1.24 (ZA), − 20.25 dB/2.57 GHz/1.23 (ZAT), − 20.73 dB/3.34 GHz/1.05 (ZAV), and − 44.69 dB/1.9 GHz/1.23 (ZAVT), demonstrating significant improvements in performance. This research highlights the role of TiO₂ and V₂O₅ in increasing crystallite and grain size, contributing to enhanced dielectric properties. The optimized composites show potential for miniaturizing wireless patch antennas, making them suitable for advanced telecommunications applications.

The barium ferrites (BaFeO₁₂) thin films with barium ions of over stoichiometry ratio of Ba/Fe = x/12 (x = 1.0–3.0) in sol precursor were successfully prepared on silicon substrates by sol–gel and spin-coating method. Results show that the rod-like ferrite grains of 100 ~ 200 nm in size were formed densely in the thin film. The (00 l) orientation of the ferrite phase was controlled to form in the thin film. Excess Ba²⁺ existed in cell lattice and doped in the interstitial sites of triangular biconical or octahedral interstices. Fe²⁺/Fe³⁺ electron pair dipoles were generated by doping Ba²⁺, increasing initially and decreasing finally. The highest content of Fe²⁺/Fe³⁺ dipoles appeared in the 4-layered thin film prepared with over stoichiometry ratio of Ba:Fe = 2:12 in sol precursor, contributing a highest dielectric tunability of 69%, low dielectric loss of 0.03 and FOM of 21.6 at 10 kHz under super low DC bias of ~ 200 V/cm. Such high tunability and low loss under super low electric field in the barium ferrite thin films show great potential for novel applications in dielectric tunable devices.

Background

Aquatic communities are constantly exposed to multiple pulses of pesticides caused by spray drift or runoff that can have significant short- and long-term effects. In particular, short pulses can lead to chronic effects that may only occur considerable time after the end of exposure. Furthermore, in the environment, pesticide pulses vary in frequency, duration and intensity. For this reason, we conducted a higher tier study with a long observation period (98 days) using artificial indoor streams to compare the effects on an aquatic community, consisting of the oligochaete Lumbriculus variegatus, the snail Potamopyrgus antipodarum, the amphipod Gammarus pulex and the mayfly Ephemera danica. Four pesticide pulses with different recovery times (from one to seven days) between pulses were applied using the model insecticide deltamethrin. Two different deltamethrin concentrations (1st, 3rd and 4th pulses with 0.64 ng/L, 2nd pulse with 2 ng/L) were tested.

Results

For E. danica, we observed a significant increase in mortality and a significantly reduced emergence success with increasing days of recovery between the pulses. The snails appeared to benefit from the toxicity-induced mortality of the mayfly larvae; they showed an opposite pattern compared to the mayfly larvae that was reflected in significantly higher energy levels. In addition, the juvenile gammarids were very sensitive to pyrethroid exposure, reflected by the significantly lower number of offspring. No adverse effects were observed for L. variegatus.

Conclusion

Our results indicate that the temporal spacing of the insecticide pulses is important. Exposure over longer periods at longer intervals is more harmful than the same number of pulses in quick succession, particularly for insects. In addition, it is important to ensure that toxicity tests are conducted over a sufficiently long period of time to reliably detect chronic effects after short-term exposures. Furthermore, our results show that the current regulatory thresholds for deltamethrin do not adequately protect aquatic insects and should therefore be lowered.