Preparation of FePd-RGO Bimetallic Composites with High Catalytic Activity for Formic Acid Electro-Oxidation

Pronounced effect of yttrium oxide on the activity of Pd/rGO electrocatalyst for formic acid oxidation reaction

A highly efficient and stable electrocatalyst comprised of yttrium oxide (Y₂O₃) and palladium nanoparticles has been synthesized via a sodium borohydride reduction approach. The molar ratio of Pd and Y was varied to fabricate various electrocatalysts and the oxidation reaction of formic acid was checked. X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X-ray powder diffraction (XRD) are used to characterize the synthesized catalysts. Among the synthesized catalysts (Pd_yY_x/rGO), the optimized catalyst i.e., Pd₆Y₄/rGO exhibits the highest current density (106 mA cm^-2) and lowest onset potential compared to Pd/rGO (28.1 mA cm^-2) and benchmark Pd/C (21.7 mA cm^-2). The addition of Y₂O₃ to the rGO surface results in electrochemically active sites due to the improved geometric structure and bifunctional components. The electrochemically active surface area 119.4 m² g^-1 is calculated for Pd₆Y₄/rGO, which is ∼1.108, ∼1.24, ∼1.47 and 1.55 times larger than Pd₄Y₆/rGO, Pd₂Y₈/rGO, Pd/C and Pd/rGO, respectively. The redesigned Pd structures on Y₂O₃-promoted rGO give exceptional stability and enhanced resistance to CO poisoning. The outstanding electrocatalytic performance of the Pd₆Y₄/rGO electrocatalyst is ascribed to uniform dispersion of small size palladium nanoparticles which is possibly due to the presence of yttrium oxide.

Fenton-oxidation of rifampicin via a green synthesized rGO@nFe/Pd nanocomposite

Antibiotics are an emerging class of persistent contaminants that are now of major environmental concern because they pose potential risks to both environmental and human health. Here reduced graphene oxide composited with bimetallic iron/palladium nanoparticles (rGO@nFe/Pd) was synthesized via a green tea extract and used to remove a common antibiotic, rifampicin from aqueous solution. The innate physical rifampicin removal efficiency of the composite (79.9 %) was increased to 85.7 % when combined with Fenton-oxidation. The mechanism and the main factors controlling Fenton-oxidation of rifampicin by rGO@nFe/Pd were investigated. Oxidation followed a pseudo-second-order degradation kinetic model with an activation energy of 47.3 kJ mol^-1. rGO@nFe/Pd were characterized by Brunauer-Emmett-Teller (BET), fourier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray energy spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), X-Ray powder diffraction (XRD), and zeta potential. Rifampicin degradation products observed by LC-UV, where subsequently confirmed to be mainly 5,6,9-trihydroxynaphtho [2,1-b] furan-1(2 H)-one, 5,6-dihydroxy-1-oxo-1,2-dihydronaphtho [2,1-b] furan-2-yl formate and (S)-5,6,9-trihydroxy-2-(3-methoxypropoxy)-2-methylnaphtho [2,1-b] furan-1(2 H)-one by LC-MS. Finally, the practical effectiveness of the composite material for antibiotic removal was demonstrated by the treatment of representative wastewaters, where rifampicin removal efficiencies of 80.4, 77.9 and 70.2 % were observed for river, aquaculture wastewater and domestic wastewater, respectively.