Non-Thermal Plasma Reduction of Ag+ Ions into Silver Nanoparticles in Open Atmosphere under Statistically Optimized Conditions for Biological and Photocatalytic Applications

Abstract

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%.

Comment on Altaf et al. Non-Thermal Plasma Reduction of Ag+ Ions into Silver Nanoparticles in Open Atmosphere under Statistically Optimized Conditions for Biological and Photocatalytic Applications. Materials 2022, 15, 3826

“…We are writing in response to the article by Altaf et al, Materials, 2022;15(11), 3826, "Non-Thermal Plasma Reduction of Ag + Ions into Silver Nanoparticles in Open Atmosphere under Statistically Optimized Conditions for Biological and Photocatalytic Applications" [1]. This article is in line with our experience of plasma treatment for material modifications [2][3][4][5].…”

“…These coded units were not accompanied by the actual or the uncoded units in the Materials and Methods section. They finally can be found, although indirectly, from the x-and y-axes labels of Figure 4a-c (page 9) [1], where, on one hand, A = 1-5 mM, B = 1-5 mM, and C = 30-60 min, or in other words, the middle levels for A must be 3 mM, for B = 3 mM, and for C = 45 min. This inconvenience must be corrected.…”

“…This is very unrealistic, especially when the regression model falsely claims that it matches almost all the predicted values within the range of a ±5% error. Besides this critical statistical problem, there are other issues based on the comments from a reviewer with high attention to detail to the original manuscript by Altaf and coworkers [1]. In Table 4 (page 14) [1], the difference in the size of the particles is very large, where those measured using XRD are 19-33 nm, while those measured via SEM are 82-102 nm.…”

“…Besides this critical statistical problem, there are other issues based on the comments from a reviewer with high attention to detail to the original manuscript by Altaf and coworkers [1]. In Table 4 (page 14) [1], the difference in the size of the particles is very large, where those measured using XRD are 19-33 nm, while those measured via SEM are 82-102 nm. Moreover, the UV-vis peak of the AgNPs (20-80 nm) purchased by the reviewer has a maximum peak of UV-vis spectroscopy from 395 (AgNPs 20 nm) to 466 nm (AgNPs 80 nm).…”

Experimental Study on the Degradation of Acaricides on the Surface of Kumquat Cuimi by Nonthermal Air Plasma

“…This synthesis technique is eco-friendly and easy to perform compared with other known techniques. As one of the potential advanced oxidation processes (AOPs), nonthermal plasma production during various discharges has long been exploited for the reduction of metal salts and stabilizers in various emission processes [22]. Its effectiveness is based on the production of in situ oxidative species (OH•, H•, O•, H 2 O 2 , H 2 , O 2 , O 3 ), as well as its ability to initiate a variety of chemical and physical processes (a high electric field, intense ultraviolet radiation, overpressure shock waves) in water for decomposing toxic compounds, while further advantages include its operational simplicity (realized under the conditions of ambient temperature and pressure), its variable reactor configuration, and its good performance degradation of low-concentration organic compounds [23][24][25][26].…”