The Ag⁺ Reduction Process in a Plasma Electrochemical System Tuned by the pH Value

Abstract

The interactions between discharge plasmas and an aqueous solutions can enable the production of reactive species and charge transfer at the plasma-liquid interface, forming the plasma electrochemical system (PES). The PES are promising for diverse applications, such as nanomaterials synthesis, due to the activation of the solution chemistry by the plasma. In this paper, we investigate the influence of the solution’s pH value on the formation of silver nanoparticles (AgNPs) in a direct current (DC) PES. Dual argon DC plasmas are generated in an H-type electrochemical cell containing an aqueous solution of silver nitrate with pH values in the range of 1.99-10.71. By this design, the solution acts as a cathode at one end of the H-type cell, and as an anode at the other end. The results show that the AgNPs are formed at the anode except for the solution with the pH value of 1.99. However, at the cathode, the AgNPs only appear in the solution with the pH value of 10.71. We find that the solvated electrons and hydrogen peroxide produced by the plasma-liquid interactions are responsible for the Ag+ reduction at the solution anode and the solution cathode, respectively.

Influences of Plasma Plume Length on Structural, Optical and Dye Degradation Properties of Citrate-Stabilized Silver Nanoparticles Synthesized by Plasma-Assisted Reduction

“…The plasma reduction routes of silver ion ( ) to zero-valent silver ( ) nanoparticles are well established, and are based on the two following reactions [ 5 , 23 , 43 ]: …”

Rapid Synthesis of Noble Metal Colloids by Plasma–Liquid Interactions

“…Studies have shown that both Ag + reduction and oxidation processes occur during AgNP synthesis [46,47]. The e − aq , H, and alcohol fragment radicals are the main reducing agents for Ag + to AgNPs, whereas H 2 O 2 generated by the plasma-liquid interaction oxidises AgNPs to Ag + , as shown in Equation (7).…”

Silver Nanoparticle Synthesis in Glycerol by Low-Pressure Plasma-Driven Electrolysis: The Roles of Free Electrons and Photons

“…Through computational studies, we reveal that glycerol can undergo photodissociation of the O−H bonds for incident photon energies of >5 eV, forming various radicals, e.g., hydrogen radicals (H•, with a standard redox potential of −2.3 V), that then exhibit the ability to reduce silver ions (Ag + + H• → Ag 0 + H + ). 28,29 In this study, to differentiate among different plasma species such as electrons, ions, metastables, and UV photons, optical filters were introduced between the plasma and the droplet of the Ag/glycerol electrolyte solution, as depicted in panels a and b of Figure 1. The relevant experimental setup is described in section S1 of the Supporting Information.…”

“…We find that photons with energies as low as 5 eV deliver an important contribution to NP production, resulting from the fragmentation of glycerol upon UV irradiation composed of these comparatively low-energy photons. Through computational studies, we reveal that glycerol can undergo photodissociation of the O–H bonds for incident photon energies of >5 eV, forming various radicals, e.g., hydrogen radicals (H•, with a standard redox potential of −2.3 V), that then exhibit the ability to reduce silver ions (Ag + + H• → Ag 0 + H + ). , …”