Dong-Hee Lim

Transition metal alloying effect on the phosphoric acid adsorption strength of Pt nanoparticles: an experimental and density functional theory study

The effect of alloying with transition metals (Ni, Co, Fe) on the adsorption strength of phosphoric acid on Pt alloy surfaces was investigated using electrochemical analysis and first-principles calculations. Cyclic voltammograms of carbon-supported Pt3M/C (M = Ni, Co, and Fe) electrocatalysts in 0.1 M HClO4 with and without 0.01 M H3PO4 revealed that the phosphoric acid adsorption charge density near the onset potential on the nanoparticle surfaces was decreased by alloying with transition metals in the order Co, Fe, Ni. First-principles calculations based on density functional theory confirmed that the adsorption strength of phosphoric acid was weakened by alloying with transition metals, in the same order as that observed in the electrochemical analysis. The simulation suggested that the weaker phosphoric acid adsorption can be attributed to a lowered density of states near the Fermi level due to alloying with transition metals.

A Density Functional Theory Study on the Ozone Oxidation of Sulfonamide Antibiotics

Abstract The electronic structures of sulfonamide antibiotics (the ground state and the lowest singlet excited-state geometries) have been investigated by using density functional theory (DFT) simulations. Experimental studies on the removal of sulfamethazine, sulfathiazole and sulfamethoxazole by ozone have also been conducted by using liquid chromatography with tandem mass spectrometric detection (LC/MS/MS). The calculated ground and excited state geometries exhibited low energy of the inter-ring bonds, which suggests the weakest bonds that can be broken during the ozone oxidation process. The orbital energy calculations (HOMO-LUMO and its energy gap) demonstrate that the smaller HOMO-LUMO energy gap, the higher reactivity toward ozone oxidation. Additionally, the current study suggests potential products of the three pharmaceutical compounds based on their electronic properties, which may help better understand the unknown reaction pathways of the pharmaceutical compounds.

A Study on the Adsorption of Sulfonamide Antibiotics on Activated Carbon Using Density Functional Theory

The removal of sulfonamide antibiotics (SAs) by activated carbon was investigated by using granular activated carbon (GAC) tests and density functional theory (DFT) simulations. The GAC absorption tests show the removal efficiency of 68.4~90.7% and 99.0~99.9% in 1 and 24 hours, respectively. In both GAC tests, the removal efficiency of sulfamethazine (SMZ) was the highest followed by those of sulfathiazole (STZ) and sulfamethoxazole (SMTZ): SMZ > STZ > SMTZ. In DFT adsorption simulations, we found that the 4-aminobenzenesulfonamide parts of SMZ and STZ and the 3-methyl-1,2-oxazol-5-amine part of SMTZ are preferentially adsorbed on the edges of graphene model, provided that the adsorbates keep their structures without dissociation upon adsorption process. The adsorption energies of SMZ, STZ, and SMTZ are -4.91, -4.64, and -4.62 eV, respectively. This adsorption strength (SMZ > STZ > STMZ) agrees with the trend of the removal efficiency of SAs by GAC. In addition, dissociative adsorption configurations of SAs are discussed.