Hermawan Kresno Dipojono

Adsorption of O2 on Cobalt-(n)Pyrrole Molecules from First-Principles Calculations

In order to clarify the adsorption mechanism of the O 2 molecule on Co–polypyrrole composite metallo-organic catalyst, we have investigated the interaction between the molecule and Co–( n )pyrrole model clusters ( n =4,6) using the density functional theory. The stable adsorption site of the O 2 molecule on Co–(4)pyrrole is found to be at the O–O center of mass located on top of the Co atom in side-on configuration, while for the case of Co–(6)pyrrole cluster, the O 2 molecule is slightly deviated from the side-on configuration. The O–O bonds of the O 2 /Co–(4)pyrrole and the O 2 /Co–(6)pyrrole systems have elongated by 10.84 and 9.86%, respectively. The elongation mechanism of O 2 on Co–( n )pyrrole is induced by the interaction between the cobalt d -orbitals and the O 2 anti-bonding π * orbital, which results in a charge transfer from the cobalt atom toward the O 2 molecule. This effect seems important in the adsorption of the O 2 molecule on Co–( n )pyrrole. It is likely that the extra charge in the O ...

Density Functional Theory Study on the Interaction of O2 Molecule with Cobalt–(6)Pyrrole Clusters

We have investigated the interaction between cobalt?(6)pyrrole [Co?(6)Ppy] clusters and O2 molecule, including the adsorption and dissociation of O2 molecule using the density functional theory (DFT) calculations. We found that O2 molecule is adsorbed on Co?(6)Ppy clusters with side-on configuration and the O?O bond length elongated around 10%. The elongation of the O?O bond when O2 is adsorbed on the clusters will weaken the O?O bond and increase the reactivity of the molecule. The calculated dissociation energies of O2 molecule on Co?(6)Ppy clusters span from 0.89 to 1.23 eV. The order of the dissociation energy is affected by the amount of the charge transferred from Co?(6)Ppy clusters to the O2 molecule in the transition state.

A First Principles Study on Dissociation and Adsorption Processes of H2 on Pd3Ag(111) Surface

We investigated dissociative adsorption of H2 molecule on Pd3Ag(111) surface based on the constructed potential energy surfaces (PESs) from the results of first principles calculations. This study is performed to understand H2 dissociative adsorption mechanism on Pd3Ag(111) surface which acts as permeable film for H2 which is a product of biomass gasification. The PES results indicate that when the H2 molecule approaches the Ag atom of the 1st atomic layer, the activation barriers for dissociation start to increase. The dissociation of H2 on the surface has negligible activation barrier when the H2 center of mass (CM) is directly above the bridge site of Pd atoms while the hydrogen atoms are directed towards the hcp and fcc hollow sites. The average local density of states (LDOS) of the d-orbital of surface Pd atoms show peak in the region around the Fermi level which is not observed from the LDOS of the Ag atom in Pd3Ag(111) surface. This strongly supports the results of the constructed PES for H2 dissociative adsorption mechanism towards Pd3Ag(111) surface. This study will be significant for the design of hydrogen-permeable films which has applications on biomass-operated fuel cells.

A combined spectroscopic and TDDFT study of natural dyes extracted from fruit peels of Citrus reticulata and Musa acuminata for dye-sensitized solar cells

This study reports the novel spectroscopic investigations and enhanced the electron transfers of Citrus reticulata and Musa acuminata fruit peels as the photosensitizers for the dye-sensitized solar cells. The calculated TD-DFT-UB3LYP/6-31+G(d,p)-IEFPCM(UAKS), experiment spectra of ultra-violet-visible spectroscopy, and Fourier transform infrared spectroscopy studies indicate the main flavonoid (hesperidin and gallocatechin) structures of the dye extracts. The optimized flavonoid structures are calculated using Density functional theory (DFT) at 6-31+G(d,p) level. The rutinosyl group of the hesperidin pigment (Citrus reticulata) will be further investigated compared to the gallocatechin (Musa acuminata) pigment. The acidity of the dye extract is treated by adding 2% acetic acid. The energy levels of the HOMO-LUMO dyes are measured by a combined Tauc plot and cyclic voltammetry contrasted with the DFT data. The electrochemical impedance spectroscopy will be performed to model the dye electron transfer. As for the rutinosyl group presence and the acidic treatment, the acidified Citrus reticulata cell under continuous light exposure of 100mW·cm-2 yields a short-circuit current density (Jsc) of 3.23mA/cm2, a photovoltage (Voc) of 0.48V, and a fill factor of 0.45 corresponding to an energy conversion efficiency (η) of 0.71% because the shifting down HOMO-LUMO edges and the broadening dyes absorbance evaluated by a combined spectroscopic and TD-DFT method. The result also leads to the longest diffusion length of 32.2μm, the fastest electron transit of 0.22ms, and the longest electron lifetime of 4.29ms.

First principles calculation on the adsorption of water on lithium?montmorillonite (Li?MMT)

The interaction of water molecules and lithium-montmorillonite (Li-MMT) is theoretically investigated using density functional theory (DFT) based first principles calculation. The mechanism of water adsorption at two different water concentrations on Li-MMT as well as their structural and electronic properties are investigated. It is found that the adsorption stability in Li-MMT is higher in higher water concentration. It is also found that an adsorbed water molecule on Li-MMT causes the Li to protrude from the MMT surface, so it is expected that Li may be mobile on H(2)O/Li-MMT.

Oxygen Reduction Reaction on Cobalt-(6)Pyrrole Cluster: Density Functional Theory Study

We investigate the potential energy surface profile for various water formation reaction schemes on an unsupported cobalt–(6)pyrrole [Co–(6)Ppy] cluster in the vacuum state by density functional theory (DFT) calculations. We find that in the Co–(6)Ppy cluster, the formation of H 2 O 2 is energetically not favorable. Instead of forming H 2 O 2ad , the HO 2ad + H reaction forms 2OH ad or O ad + H 2 O immediately. The adsorption of H 2 O 2 on the Co–(6)Ppy cluster is possible only if the H 2 O 2 molecule comes from or forms outside of the cluster. The formation of two OH molecules instead of H 2 O 2 on the Co–(6)Ppy cluster suggests that the oxygen reduction reaction (ORR) mechanism on the unsupported Co–(6)Ppy cluster in the vacuum state prefers the direct four-electron reduction to water.

First-Principles Calculations for Chemical Reaction between Sodium Diethyldithiocarbamate and Transition-Metal (Cr) atom to Produce Cr(DDC)3 and Cr(DDC)2ODDC

We investigate the chemical reaction between a Cr transition-metal atom and sodium diethyldithiocarbamate (NaDDC), a complexing agent used to detect and extract Cr in human blood samples. Using density-functional-theory-based calculations, we determine their stable structures of Cr(DDC)2ODDC and Cr(DDC)3 complexes and obtain their dissociation energies. We found dissociation energies of -10.66 and -3.24 eV for Cr(DDC)2ODDC and Cr(DDC)3 complexes, respectively. Hence, on the basis of dissociation energies, we have verified that the reaction of NaDDC with Cr produces Cr(DDC)2ODDC as a major product.

Density functional study of adsorptions of CO2, NO2 and SO2 molecules on Zn(0002) surfaces

We report on a theoretical study of adsorptions of CO2, NO2 and SO2 molecules on ZnO(0002) surfaces using density functional theory-based (DFT-based) calculations. These adsorptions are done on perfect and defective ZnO(0002) surfaces. We find that all of these molecules are chemically adsorbed on the perfect ZnO(0002) surface. In the presence of Zn vacancy, we find that the surface is only active toward SO2 molecule. On the hydroxylated ZnO(0002) surfaces, CO2 and SO2 molecules can react with the preadsorbed OH molecule to form various adsorbates such as: carboxyl (COOH), bicarbonate (CO3H), sulfonyl hydroxide (SO3H), SO3 and water. However, NO2 molecule cannot react with the pre-adsorbed OH molecule and only physically adsorbed on the surface.

DFT study of adsorption of CO2 on palladium cluster doped by transition metal

We report on a theoretical study of CO2 adsorption on Pd6-M (M: Ni, Cu, Pt, Rh) cluster using first-principles density functional theory (DFT) calculations. We find that CO2 molecule is adsorbed with a bidendate configuration on Pd7 and on most of Pd6M clusters. The bidendate adsorption configuration is formed due to the filling of the unoccupied n* orbital of CO2 molecule upon its interaction with d-orbitals of the cluster. We find that transition metal doping could modify the adsorption energy, adsorption site and adsorption configuration of CO2 molecule on Pd7 cluster. We also predict that the usage of Pd6M clusters as CO2 hydrogenation catalysts might facilitate the formations of HCOO/COOH.

Ground and excited state properties of high performance anthocyanidin dyes-sensitized solar cells in the basic solutions

The aglycones of anthocyanidin dyes were previously reported to form carbinol pseudobase, cis-chalcone, and trans-chalcone due to the basic levels. The further investigations of ground and excited state properties of the dyes were characterized using density functional theory with PCM(UFF)/B3LYP/6-31+G(d,p) level in the basic solutions. However, to the best of our knowledge, the theoretical investigation of their potential photosensitizers has never been reported before. In this paper, the theoretical photovoltaic properties sensitized by dyes have been successfully investigated including the electron injections, the ground and excited state oxidation potentials, the estimated open circuit voltages, and the light harvesting efficiencies. The results prove that the electronic properties represented by dyes’ LUMO-HOMO levels will affect to the photovoltaic performances. Cis-chalcone dye is the best anthocyanidin aglycone dye with the electron injection spontaneity of −1.208 eV, the theoretical open circuit ...