arXiv subjects

A. Mekki

Publications and source records attributed to A. Mekki.

6 recordsLinked to original sources

arXiv2025

Interfacial Synergy in Ag-Doped CuO-AgCl-g-C3N4 Composites for Efficient Charge Separation and Low-power Methylene Blue Degradation

An Ag-doped CuO-AgCl-g-C3N4 heterostructure has been designed to achieve rapid Methylene Blue (MB) degradation through a synergistic photo-Fenton mechanism driven by low-power UV illumination. The composite integrates narrow-bandgap CuO, plasmonic Ag/AgCl, and visible-responsive g-C3N4 into a dual Z-scheme configuration that promotes efficient interfacial charge transfer while preserving strong redox potentials. Diffuse reflectance UV-Vis spectra ascertained the bandgap positions of the composite corresponding to those of its constituents: 2.9 eV (g-C3N4) and 1.42 eV (Ag-doped CuO-AgCl), indicating enhanced absorption and efficient charge carrier generation. BET analysis confirmed the presence of mesoporosity and revealed an effective surface area, ensuring the availability of abundant adsorption and reaction sites. A commercial 11 W UV irradiation was used for the photocatalytic test. Almost complete degradation of MB occurred within 10 min, following pseudo-first-order kinetics with a high apparent rate constant of 0.45/min. The remarkable activity arises from the synergistic interplay of Fenton-like redox cycling and efficient photoinduced charge carrier generation and separation. In addition, it has been demonstrated that intentionally incorporated AgCl plays an active role as a plasmonic-semiconducting interface, strengthening charge separation and catalyst stability under neutral conditions, rather than acting as a passive chloride byproduct. Overall, by linking defect engineering, heterojunction design, and photo-Fenton synergy, this study establishes a low-power, catalytic platform offering a viable pathway towards sustainable dye wastewater remediation.

cond-mat.mtrl-sci↗

arXiv2024

Enhancing Fenton-like Photo-degradation and Electrocatalytic Oxygen Evolution Reaction (OER) in Fe-doped Copper Oxide (CuO) Catalysts

Although hydrogen generation by water electrolysis is the cheapest of all other available sources, water splitting still occurs with sluggish kinetics. It is a challenging barrier for H2 production on a large scale. Moreover, research is still underway to understand the oxygen evolution reaction (OER) and design the catalysts with improved OER performance. Herein, we report the synthesis, characterization, and OER performance of iron-doped copper oxide (CuO) as low-cost catalysts for water oxidation. The OER occurs at about 1.49 V versus the RHE with a Tafel slope of 69 mV/dec in a 1 M KOH solution. The overpotential of 338 mV at 10 mA/cm2 is among the lowest compared with other copper-based materials. The catalyst can deliver a stable current density of >10 mA/cm2 for more than 10 hours. Additionally, wastewater treatment, particularly synthetic dye wastewater, is vital for preventing water scarcity and adverse effects on human health and ecotoxicology. The as-synthesized catalysts are also utilized for Fenton-like photo-degradation under low-power visible household LED lights toward the most commonly industrially used simulated Methylene blue dye wastewater. Almost complete degradation of the MB dye has been achieved within 50 minutes of visible light irradiation with a first-order rate constant of 0.0973/min. This dual functionality feature can open new pathways as a non-noble, highly efficient, and robust catalyst for OER and wastewater treatments.

physics.app-ph↗

arXiv2024

Characteristic times for gap relaxation and heat escape in nanothin NbTi superconducting filaments: thickness dependence and effect of substrate

We measured the temporal voltage response of NbTi superconducting filaments with varied nanoscale thicknesses to step current pulses that induce non-equilibrium superconducting states governed by a hot-spot mechanism. Such detected voltage emerges after a delay time td, which is intimately connected to the gap relaxation and heat escape times. By employing time-dependent Ginzburg-Landau theory to link the delay time to the applied current, we determined that the gap relaxation time depends linearly on film thickness, aligning with the acoustic mismatch theory for phonon transmission at the superconductor-substrate interface. We thereby find a gap relaxation time of 104 ps per nm of thickness for NbTi films on polished sapphire. We further show that interfacial interaction with the substrate significantly impacts the gap relaxation time, with observed values of 9 ns on SiOx, 6.8 ns on fused silica, and 5.2 ns on sapphire for a 50 nm thick NbTi strip at T = 5.75 K. These insights are valuable for optimizing superconducting sensing technologies, particularly the single-photon detectors that operate in the transient regime of nanothin superconducting bridges and filaments

cond-mat.supr-con↗

arXiv2022

Room Temperature Magneto-dielectric coupling in the CaMnO3 modified NBT lead-free ceramics

The sol-gel prepared (1-x) Na0.5Bi0.5TiO3- (x) CaMnO3 (x=0, 0.03, 0.06, 0.12) compositions show a Rhombohedral (R3c) phase for x=0.06 while a mixed Rhombohedral (R3c) and orthorhombic (Pnma) phases for the x=0.12. The lattice volume consistently decreased with an increase in the CaMnO3 content. The phase transition temperature (Tc) decreased with an increase in the CaMnO3 compositions. The room temperature dielectric constant increased, and loss decreased for the x=0.03 composition due to a decrease in the oxygen vacancy and Bi loss confirmed by the valence state study (XPS). All the compositions show a variation of the room temperature dielectric property with an application of magnetic field confirming a magnetodielectric coupling. The x=0.06 composition shows the highest negative magnetodielectric constant (MD%) of 3.69 at 100kHz at an applied field of 5 kG.

cond-mat.mtrl-sci↗

arXiv2021

Defect Dipole Induced Improved Electrocaloric Effect in Modified NBT-6BT Lead-Free Ceramics

The Rietveld refinement of the polycrystalline powders of 1% Fe and Mn-doped (Na0.5Bi0.5)0.94Ba0.06Ti0.98V0.02O3 at the Ti-site confirmed a single rhombohedral (R3c) phase. The bandgap, (Eg) was affected by the anti-phase octahedral tilt angle and the spin-orbit splitting energy of Ti4+2p3/2 and Ti4+2p1/2 states. The decrease in Bi loss and increase in the binding energy of Ba due to Fe/Mn doping has been correlated to the strengthening of Bi-O and Ba-O bonds which was revealed from the XPS studies thereby further related to the average A-O bond length from structural studies. Hence, a reduction of oxygen vacancy (VO) for the doped samples has been justified. A significant improvement of the dielectric constant, relaxation time (τ0), and the decrease in conductivity due to doping was revealed from the frequency-dependent (10Hz-1MHz) dielectric measurement study. The conduction and relaxation process is dominated by the short-range movement of defects. The activation energy (Ea ~1eV) revealed that there is a presence of double-ionized VOs. The ECE study showed a significant enhancement of the changes in entropy, and the adiabatic temperature difference due to doping, with the change in tempearture being highest in the Fe-doped sample. Such improvement of dielectric and ECE properties was confirmed due to the reduction of the mobility of oxygen vacancy because of the formation defect dipoles.

cond-mat.mtrl-sci↗

arXiv2020

Pbnm to R3-c phase transformation in (1-x)LaFeO3.xLaMnO3 solid solution due to modifications in structure, octahedral tilt and valence states of Fe-Mn

A theoretically supported experimental study of the (1-x)LaFeO3.xLaMnO3 (LFO-LMO) solid solution is being reported for the first time which reveals a phase transformation from the Pbnm and R3-c phase at a chemical composition of x=0.625. Correlation of octahedral distortion and phase transition was extensively investigated using x-ray photoelectron spectroscopy (XPS), Raman and x-ray diffraction (XRD) measurements and density functional theory (DFT) calculation. A detailed study of the structural lattice parameters, bond lengths, bond angles have been done, supported by valence state and electronic properties studies. All the above parameters show a correlated modification to the phase transition. The distortion and tilting of the BO6 octahedra has been studied as a function of different Fe:Mn content and expressed by Glazer representation from the refined Crystallographic Information Files (CIF). The angle of tilting from the central non-tilted position also shows a correlated modification with the phase transformation. The valence state and size of cations influences the octahedral tilting. Octahedral volume is reduced as the entire perovskite structure is relatively flattened with increasing Mn-content implying a flattening of both the BO6 octahedra and the La8O6 cage. The vibrational properties were studied experimentally and supported by DFT phonon calculations, detailing the displacement pattern (eigen vectors) revealing considerable insight into the lattice dynamics of the compounds. The optoelectronic modifications in the band properties were studied experimentally and supported with theory. Hence, this manuscript is a in-depth analysis of the structure correlated phase transition of the LFO-LMO solid solution.

cond-mat.mtrl-sci↗