arXiv subjects

Mohammed Shihab

Publications and source records attributed to Mohammed Shihab.

4 recordsLinked to original sources

arXiv2026

Atmospheric-Pressure Ar/Air Plasma Jet-Induced Degradation of Azo Dyes in Aqueous Solutions: Kinetic and Mechanistic Insights

Atmospheric-pressure non-thermal plasmas are promising platforms for advanced oxidation in water treatment, yet quantitative coupling between reactive species delivery, solution chemistry, and molecular fragmentation remains unclear. We investigate degradation of two structurally related azo dyes using an Ar plasma jet in a plasma-liquid discharge configuration with an immersed counter-electrode to enhance interfacial coupling. Plasma exposure generated a reactive oxygen and nitrogen species environment and strong acidification, increasing proton concentration up to 49-fold. UV-Vis analysis showed rapid chromophore decay, achieving 0.88 and 0.94 removal within 40 min. Biphasic kinetics indicated a transition from radical-flux-controlled to transport-influenced regimes. Fluorescence and Raman spectroscopy confirmed transient oxidized intermediates and progressive pi-conjugation breakdown, elucidating plasma-driven oxidative fragmentation mechanisms.

physics.plasm-ph↗

arXiv2026

Tuning Optical Properties of FTO via Carbonaceous Al2O3 Microdot Deposition by DC plasma sputtering

Fluorine-doped tin oxide (FTO) is a key transparent conductive oxide for photovoltaic and optoelectronic devices, yet its high reflectance limits light-trapping efficiency. This work demonstrates a simple DC plasma sputtering approach to deposit carbonaceous Al2O3 microdots on FTO under controlled Ar, O2, and Ar-O2 atmospheres. For plasma discharge in the normal mode, with plasma density 10^9 cm^-3 and temperature of 2 eV, Volmer-Weber growth produced discrete microdots whose size and distribution were tuned by gas composition: dense, uniform dots in Ar (approximately 0.89 um radius), agglomerated structures in O2, and intermediate morphologies in mixed atmospheres. Structural analysis confirmed Al2O3 formation with carbon incorporation, while SEM revealed morphology-driven optical behavior. UV-Vis measurements showed that Ar-O2 coatings achieved the lowest reflectance across the visible range, outperforming bare FTO and other conditions. These findings establish a clear link between sputtering parameters, surface morphology, and optical performance, offering a scalable route to anti-reflective, light-trapping coatings for next-generation solar cells and optoelectronic devices.

physics.plasm-ph↗

arXiv2024

Degradation of Cyanobacterium Nostoc muscorum via Air, Oxygen, and Nitrogen low temperature plasmas

Cyanobacteria are prokaryotic microorganisms that possess the capability to convert light energy into chemical energy through the process of photosynthesis. These organisms exhibit numerous potential applications, including the production of bioethanol, the synthesis of food colorants, the development of dietary supplements, and the provision of raw materials. Cyanobacteria demonstrate a wide ecological distribution, inhabiting diverse environments such as freshwater and terrestrial ecosystems, as well as extreme habitats including hot springs, hypersaline aquatic systems, polar regions, and low-oxygen environments. Plasma proves to be a highly effective method for cellular degradation. When Nostoc muscorum, a type of cyanobacterium, was exposed to air-source plasma plasma, it was completely destroyed within fifteen minutes. In contrast, the use of oxygen and nitrogen plasma required at least an hour to achieve the same result. The atmospheric plasma generated chemical species such as N2^+ , N^+ and OH^- at higher concentrations than the oxygen and nitrogen plasma. The plasma spectrum was measured during the treatment of the cyanobacteria, and the electron temperature and density of the air plasma were also estimated. The light absorption of the cyanobacteria's pigments and the characteristic Raman peaks disappeared after the plasma treatment, which served as clear evidence of the complete degradation of the cyanobacterium.

physics.plasm-ph↗

arXiv2014

Ion energy distribution functions behind the sheaths of magnetized and non magnetized radio frequency discharges

The effect of a magnetic field on the characteristics of capacitively coupled radio frequency discharges is investigated and found to be substantial. A one-dimensional particle-in-cell simulation shows that geometrically symmetric discharges can be asymmetrized by applying a spatially inhomogeneous magnetic field. This effect is similar to the recently discovered electrical asymmetry effect. Both effects act independently, they can work in the same direction or compensate each other. Also the ion energy distribution functions at the electrodes are strongly affected by the magnetic field, although only indirectly. The field influences not the dynamics of the sheath itself but rather its operating conditions, i.e., the ion flux through it and voltage drop across it. To support this interpretation, the particle-in-cell results are compared with the outcome of the recently proposed ensemble-in-spacetime algorithm. Although that scheme resolves only the sheath and neglects magnetization, it is able to reproduce the ion energy distribution functions with very good accuracy, regardless of whether the discharge is magnetized or not.

physics.plasm-ph↗