Atmospheric-Pressure Microplasma Synthesis of Palladium Nanoparticles for Environmental Catalysis

Atmospheric-pressure plasma–liquid interactions (PLIs) enable nanoparticle synthesis by generating reactive reducing species directly at the plasma–liquid interface, without the addition of a separate chemical reductant. In this work, d-fructose-stabilized palladium nanoparticles (Pd NPs) were synthesized in a one-step atmospheric-pressure DC microplasma process using chloropalladic acid as the precursor. Optical emission spectroscopy was used to examine plasma characteristics governing nanoparticle formation. The discharge produced OH radicals, UV radiation, and excited argon species, while electron and gas temperatures were evaluated with discharge current. Increasing current enhanced UV emission, relative OH emission intensity, and gas temperature, whereas electron temperature decreased because of greater collisional energy transfer. These plasma-driven processes promoted Pd2+ reduction and influenced nanoparticle nucleation and growth. UV–Vis spectroscopy showed progressive conversion of Pd2+ to metallic Pd, with most growth completed within 30 min. SEM and EDX confirmed predominantly spherical, d-fructose-stabilized metallic Pd nanostructures, while XRD further supported the formation of crystalline metallic Pd0 with an fcc structure. The Pd NPs showed strong catalytic activity for reducing 4-nitrophenol, methyl orange, and Congo red, with apparent rate constants of 0.2508, 0.6346, and 0.3416 min−1, respectively. These findings demonstrate atmospheric-pressure PLI as a controllable platform for producing catalytically active palladium nanoparticles in an aqueous medium.