Freshwater is only 2.5% of the total water on the Earth and rest is contaminated or brackish. Various physical and chemical techniques are being used to purify the contaminated water. This study deals with catalytic plasma treatment of contaminated water collected from different sites of Faisalabad-Pakistan. A non-thermal DC plasma jet technique was used to treat the water samples in the presence of TiO₂ catalyst. The plasma-assisted catalytic treatment introduced some oxidative species (O₃, H₂O₂, HO₂⁻, OH⁻) in the water. These species reacted with pollutants and cause the degradation of harmful contaminants, especially dyes. The degradation of dye sample during plasma treatment was more pronounced as compared to other samples. pH, conductivity and TDS of dye containing sample decreased after catalytic plasma treatment. The degradation of organic pollutants increased due to presence of several oxidants, such as TiO₂, ferrous ions and hydrogen peroxide. FT-IR analysis revealed the degradation of some functional groups during treatment process and confirmed the effectiveness of the process. The residue of the treated samples was consisted of amines, amides and N-H functional groups. XRD analysis showed the presence of Alite, Ferrite, aluminate, Si, S and some heavy metals in the residue. The effect of plasma treatment on activity of gram-negative Escherichia coli (E. coli) bacteria in water was also checked. The bacterial activity was reduced by almost 50% after 2 min of plasma treatment.

Pure TiO₂ nanoparticles (TiO₂NPs) were produced via the sol–gel method and then coated with silver nanoparticles (AgNPs) to reduce their optical band gap. The concurrent synthesis and immobilization of AgNPs over TiO₂NPs was achieved through the interaction of an open-air argon plasma jet with a solution of silver nitrate/stabilizer/TiO₂NPs. The one-pot plasma synthesis and coating of AgNPs over TiO₂NPs is a more straightforward and environmentally friendly method than others. The plasma-produced Ag/TiO₂ nanocomposites were characterized and tested for their photocatalytic potential by degrading different concentrations of methyl blue (MB) in water. The dye concentration, oxidant dose, catalyst dose, and reaction time were also optimized for MB degradation. XRD results revealed the formation of pure AgNPs, pure TiO₂NPs, and Ag/TiO₂ nanocomposites with an average grain size of 12.36 nm, 18.09 nm, and 15.66 nm, respectively. The immobilization of AgNPs over TiO₂NPs was also checked by producing SEM and TEM images. The band gap of AgNPs, TiO₂NPs, and Ag/TiO₂ nanoparticles was measured about 2.58 eV, 3.36 eV, and 2.86 eV, respectively. The ultraviolet (UV) results of the nanocomposites were supportive of the degradation of synthetic dyes in the visible light spectrum. The AgNPs in the composite not only lowered the band gap but also obstructed the electron–hole recombinations. The Ag/TiO₂ composite catalyst showed 90.9% degradation efficiency with a 5 ppm dye concentration after 120 min of light exposure.

In this study, silver nanoparticles (AgNPs) were produced through an atmospheric pressure plasma reduction reaction and tested for photodegradation of methyl blue (MB) under sunlight exposure. The argon plasma born reactive species were used to reduce silver ions to AgNPs in the solution. Glucose, fructose and sucrose were also added in the solution to stabilize the growth process. The glucose stabilized reaction produced the smallest nanoparticles of 12 nm, while sucrose stabilized reaction produced relatively larger nanoparticles (14 nm). The nanoparticles exhibited rough morphology and narrow diameter distribution regardless of stabilizer type. The narrow diameter distribution and small band gap helped activating majority of nanoparticles at a single wavelength of light spectrum. The band gap energy of AgNPs varied from 2.22 eV to 2.41 eV, depending on the saccharide type. The photoluminescence spectroscopy of AgNPs produced emission peaks at 413 nm, 415 nm, and 418 nm. The photocatalytic potential of AgNP samples was checked by degrading MB dye under sunlight. The degradation reaction reached a saturation level of 98% after 60 min of light exposure.

Various conventional approaches have been reported for the synthesis of nanomaterials without optimizing the role of synthesis parameters. The unoptimized studies not only raise the process cost but also complicate the physicochemical characteristics of the nanostructures. The liquid–plasma reduction with optimized synthesis parameters is an environmentally friendly and low-cost technique for the synthesis of a range of nanomaterials. This work is focused on the statistically optimized production of silver nanoparticles (AgNPs) by using a liquid–plasma reduction process sustained with an argon plasma jet. A simplex centroid design (SCD) was made in Minitab statistical package to optimize the combined effect of stabilizers on the structural growth and UV absorbance of AgNPs. Different combinations of glucose, fructose, sucrose and lactose stabilizers were tested at five different levels (−2, −1, 0, 1, 2) in SCD. The effect of individual and mixed stabilizers on AgNPs growth parameters was assumed significant when p-value in SCD is less than 0.05. A surface plasmon resonance band was fixed at 302 nm after SCD optimization of UV results. A bond stretching at 1633 cm⁻¹ in FTIR spectra was assigned to C=O, which slightly shifts towards a larger wavelength in the presence of saccharides in the solution. The presence of FCC structured AgNPs with an average size of 15 nm was confirmed from XRD and EDX spectra under optimized conditions. The antibacterial activity of these nanoparticles was checked against Staphylococcus aureus and Escherichia coli strains by adopting the shake flask method. The antibacterial study revealed the slightly better performance of AgNPs against Staph. aureus strain than Escherichia coli.

An environmentally friendly non-thermal DC plasma reduction route was adopted to reduce Ag⁺ ions at the plasma–liquid interface into silver nanoparticles (AgNPs) under statistically optimized conditions for biological and photocatalytic applications. The efficiency and reactivity of AgNPs were improved by statistically optimizing the reaction parameters with a Box–Behnken Design (BBD). The size of the AgNPs was chosen as a statistical response parameter, while the concentration of the stabilizer, the concentration of the silver salt, and the plasma reaction time were chosen as independent factors. The optimized parameters for the plasma production of AgNPs were estimated using a response surface methodology and a significant model p < 0.05. The AgNPs, prepared under optimized conditions, were characterized and then tested for their antibacterial, antioxidant, and photocatalytic potentials. The optimal conditions for these three activities were 3 mM of stabilizing agent, 5 mM of AgNO₃, and 30 min of reaction time. Having particles size of 19 to 37 nm under optimized conditions, the AgNPs revealed a 82.3% degradation of methyl orange dye under UV light irradiation. The antibacterial response of the optimized AgNPs against S. aureus and E. coli strains revealed inhabitation zones of 15 mm and 12 mm, respectively, which demonstrate an antioxidant activity of 81.2%.