In this study, Plasma-Activated Water (PAW) was synthesized using a coaxial Dielectric Barrier Discharge (DBD) reactor, benefiting from the elevated capacity of air-flow-assisted DBD discharges to enhance nitrogen-based species concentration. By manipulating operational parameters, including gas flow rate, activation time, and DI water volume, we achieved significant concentrations of reactive oxygen and nitrogen species (RONS). As a result, the PAW obtained displayed pronounced physicochemical attributes: a pH of 2.06, an ORP of 275 mV, conductivity of 3 mS/cm, and TDS of 1200 mg/L. A pivotal aspect of this research was the evaluation of the reactor’s efficiency, as indicated by metrics like the specific input energy and ozone efficiency yield. The antimicrobial potential of the PAW was also assessed against pathogenic microbes, with remarkable reductions in viability for both Staphylococcus aureus and Escherichia coli (99.99%) and a more moderate decrease for Candida albicans (37%). These findings underscore the capability of coaxial DBD reactors in crafting high-quality PAW with significant antimicrobial properties, necessitating further studies to validate its broad-spectrum and safe applications.

Methylene blue (MB), a widely used industrial dye, is a persistent pollutant with documented toxicity to aquatic organisms and potential health risks to humans, even at ultra-trace levels. Conventional monitoring techniques such as UV–Vis spectroscopy and fluorescence emission suffer from limited sensitivity, typically failing to detect MB below ~10⁻⁷ M. In this study, we introduce a surface-enhanced Raman spectroscopy (SERS) platform based on silver nanowire (AgNW) substrates that enables MB detection over an unprecedented dynamic range—from 1.5 × 10⁻⁴ M down to 1.5 × 10⁻¹⁶ M. Raman mapping confirmed the presence of individual signal hot spots at the lowest concentration, consistent with the theoretical number of analyte molecules in the probed area, thereby demonstrating near-single-molecule detection capability. The calculated enhancement factors reached up to 1.90 × 10¹², among the highest reported for SERS-based detection platforms. A semi-quantitative calibration curve was established spanning twelve orders of magnitude, and this platform was successfully applied to monitor MB degradation during two advanced oxidation processes (AOPs): TiO₂ nanotube-mediated photocatalysis under UV irradiation and atmospheric-pressure dielectric barrier discharge (DBD) plasma treatment. While UV–Vis and fluorescence techniques rapidly lost sensitivity during the degradation process, the SERS platform continued to detect the characteristic MB Raman peak at ~1626 cm⁻¹ throughout the entire treatment duration. These persistent SERS signals revealed the presence of residual MB or partially degraded aromatic intermediates that remained undetectable by conventional optical methods. The results underscore the ability of AgNW-based SERS to provide ultra-sensitive, molecular-level insights into pollutant transformation pathways, enabling time-resolved tracking of degradation kinetics and validating treatment efficiency. This work highlights the importance of integrating SERS with AOPs as a powerful complementary strategy for advanced environmental monitoring and water purification technologies. By delivering an ultra-sensitive, low-cost sensor (<USD 0.16 per test) and promoting reagent-free treatment methods, this study directly advances SDG 6 (Clean Water and Sanitation) and SDG 12 (Responsible Consumption and Production).

This research explores the synergistic application of Dielectric Barrier Discharge (DBD) and Gliding Arc Plasma Jet (GAPJ) in a Hybrid Plasma Discharge (HPD) setup for enhanced water activation. The HPD system demonstrated balanced and sustained generation of reactive oxygen and nitrogen species (RONS), maintaining efficiency at higher specific input energy (SIE) values. Comparative analyses with DBD and GAPJ systems highlighted the superior performance of the HPD system in generating RONS and modifying water’s molecular structure. Key observations included a decrease in water’s pH and an increase in oxidation-reduction potential, total dissolved solids, and conductivity, stabilizing beyond 5 l min⁻¹ airflow and 10 min of treatment. UV−Vis spectroscopy identified nitrites, nitrates, hydrogen peroxide, and nitrous acid, while Raman spectroscopy captured shifts in vibrational modes, particularly in librational and O–H stretching bands. These changes correlated with alterations in reactive species concentrations and pH levels. Overall, the HPD system emerged as a versatile and efficient approach for generating plasma-activated water, suitable for applications in microbial deactivation, surface sterilization, and electrocatalytic process optimization, offering stable and continuous production of reactive species across a range of SIE values.

This study investigates the impact of vapour-phase precursor flow rates—specifically those of trimethylaluminum (TMA) and deionized water (H₂O)—on the deposition of aluminum oxide (Al₂O₃) thin films through atomic layer deposition (ALD). It explores how these flow rates influence film growth kinetics and surface reactions, which are critical components of the ALD process. The research combines experimental techniques with a zero-dimensional theoretical model, designed specifically to simulate the deposition dynamics. This model integrates factors such as surface reactions and gas partial pressures within the ALD chamber. Experimentally, Al₂O₃ films were deposited at varied TMA and H₂O flow rates, with system conductance guiding these rates across different temperature settings. Film properties were rigorously assessed using optical reflectance methods and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. The experimental findings revealed a pronounced correlation between precursor flow rates and film growth. Specifically, at 150 °C, film thickness reached saturation at a TMA flow rate of 60 sccm, while at 200 °C, thickness peaked and then declined with increasing TMA flow above this rate. Notably, higher temperatures generally resulted in thinner films due to increased desorption rates, whereas higher water flow rates consistently produced thicker films, emphasizing the critical role of water vapour in facilitating surface reactions. This integrative approach not only deepens the understanding of deposition mechanics, particularly highlighting how variations in precursor flow rates distinctly affect the process, but also significantly advances operational parameters for ALD. These insights are invaluable for enhancing the application of ALD technologies across diverse sectors, including microelectronics, photovoltaics, and biomedical coatings, effectively bridging the gap between theoretical predictions and empirical results.

The influence of the oxygen gas supply on the stoichiometry, structure, and orientation texture of polycrystalline cobalt oxide films was investigated in this study. The films were grown by direct current reactive magnetron sputtering using a metallic Co target and different O2 inlet flow rates (0.5–5.0 SCCM). The deposition power (80 W), the argon gas flow (40 SCCM), and the total working pressure (0.67 Pa) were kept constant during depositions. The results evidence a strong influence of the oxygen flow over the film’s stoichiometry and structure, where low oxygen flows (2.5 SCCM) favor the spinel Co3O4 phase formation. The coexistence of monoxide and tetraoxide phases is only observed for the 2.5 SCCM oxygen flow condition. Strain effects related to the oxygen partial pressure are also observed and discussed. Computer simulations of the reactive sputtering growth supported the analysis of the film properties and its correlation to the oxygen partial pressure.

Plasma-Activated Saline Solutions (PAS), derived from Plasma-Activated Water (PAW), are increasingly recognized for their versatile applications in infection control, wound healing, and sterilization. These solutions are produced by exposing liquids to cold plasma, generating a rich mixture of reactive oxygen and nitrogen species (RONS) and reactive chlorine species (RCS). This study investigates the production of PAS using a coaxial dielectric barrier discharge (DBD) operating with compressed air and evaluates the impact of varying sodium chloride (NaCl) concentrations (0.9%, 1.8%, 3.6%, and 7.2%) on the generation of RONS and RCS. Deionized water (DI water) was also activated as a baseline comparison. Physicochemical properties, including pH, oxidation–reduction potential (ORP), conductivity, and total dissolved solids (TDS), were measured before and after plasma activation. Real-time UV–Vis and Raman spectroscopy were employed to monitor the formation and stability of reactive species. To complement the UV–Vis data, additional analytical methods, such as colorimetric test strips and estimations based on pH and equilibrium constants, were employed. The analyses revealed that NaCl concentration significantly influences the composition and behavior of PAS, with lower concentrations favoring the generation of RONS such as nitrites ( NO 2 − ) and nitrates ( NO 3 − ), while higher concentrations modulate the production of RCS like hypochlorous acid (HClO). The results demonstrated a pronounced decrease in pH and an increase in ORP, indicating enhanced oxidative and antimicrobial potential. Spectroscopic analyses revealed distinct patterns of RONS formation, including NO 3 − , NO 2 − , H₂O₂, and HClO, with notable interactions between RCS and RONS at higher NaCl concentrations. These findings underscore the dynamic interplay between ionic strength, reactive species production, and solution stability, providing critical insights into optimizing PAS for biomedical applications. The study highlights PAS’s potential as eco-friendly, residue-free alternatives for disinfection and wound care, offering tailored properties based on NaCl concentration to meet specific therapeutic needs.