Melanie David | De La Salle University (original) (raw)
Papers by Melanie David
Pb-doped BSCCO superconducting films were prepared on Ag electrode in a three-electrode cell cont... more Pb-doped BSCCO superconducting films were prepared on Ag electrode in a three-electrode cell containing nitrates of Bi, Pb, Sr, Ca and Cu dissolved in DMSO (dimethyl sulfoxide). The nitrates were varied to obtain Bi2-xPbxSr2Ca2Cu3O10 (x = 0.2, 0.4, 0.6, 0.8). Pt was used as counter electrode and Ag/Ag+ as reference electrode. DC deposition was used with electrode potential of -3.5V for 30, 45, and 60 minutes. Heat treatment was done at 250 degrees Centigrade for 3 hours, 700 degrees Centigrade for 3 hours and 750 degrees Centigrade for 6 hours in oxygen-rich environment to allow solid state reaction to occur on the film. SEM analysis showed the formation of randomly oriented plate-like and bar-like structures which can be attributed to the low-Tc phase and high-Tc phase, respectively. These were observed in films prepared in 0.2 Pb concentration. Melted and step-like growths were found in films with 0.2 and 0.8 Pb concentrations. Pinholes, cracks and impurities were also present. Sp...
Journal of Applied Phycology, 2017
The continuous threat of increasing CO 2 concentration in the atmosphere has altered the carbon b... more The continuous threat of increasing CO 2 concentration in the atmosphere has altered the carbon balance of our planet causing global climate change. Biological fixation of atmospheric CO 2 by unicellular microorganisms such as microalgae is a promising technology pursued extensively by researchers as a means for carbon capture. The study aimed to provide an atomic level of study that will demonstrate the effect of the salinity on the mechanism of CO 2 absorption across microalgae lipid bilayer. Molecular dynamics simulations were utilized to calculate the free energies of CO 2 molecule as it permeates inside the microalgae cell. In thermodynamics, the transport process of a molecule can be demonstrated through its free energy gradient. Thus, calculating the free energies of CO 2 molecule across microalgae lipid bilayer can elucidate the mechanisms of permeation processes. Four microalgae lipid bilayer structures were constructed that contains 128-DPPC (dipalmitoylphosphatidylcholine) lipid bilayer with 3640 water molecules with different NaCl concentrations: 0, 3, 13, and 19 NaCl molecules which correspond to a salinity level of 0, 50, 200, and 300 mM, respectively. The cavity insertion Widom method was used to calculate the free energy of CO 2 molecule along the lipid bilayer. The results demonstrated that the salinity does not affect the free energies significantly, thus, it does not hamper CO 2 transport across microalgae lipid membrane.
Clean Technologies and Environmental Policy, 2016
Algal biofuels serve as a promising alternative energy source for liquid fuels. However, one of t... more Algal biofuels serve as a promising alternative energy source for liquid fuels. However, one of the bottlenecks in the conversion of microalgae to biofuels is the drying process. A moisture content of at most 10 % is desired for algal biomass prior to oil extraction to maximise biofuel yield. Conventional means of drying results to longer drying time and uneven drying of algal biomass. This study investigated the drying characteristics of microwave for microalgae (Chlorella vulgaris). Three microwave intensity levels (300, 600, and 900 W) were considered to dry 10, 20, and 30 of algal mass. Page model gave a better fit on the moisture ratio with time of microwave drying than the exponential model. Furthermore, the specific energy requirement was computed, and a relationship was found between moisture ratio with power and mass. Fourier transform infrared spectroscopy results showed significant reduction of infrared signal intensities of the functional groups present in the algae after drying at higher microwave power level. It was concluded that the 20 W/g microwave drying setting gave a lower specific energy requirement with good quality of remaining high lipid content qualitatively. Furthermore, it was recommended to use gas chromatography mass spectroscopy to further quantify the algal lipids and other functional groups.
Shinku, 2006
We investigate the adhesion strength of poly(butylene terephthalate) or PBT on aluminum using den... more We investigate the adhesion strength of poly(butylene terephthalate) or PBT on aluminum using density functional theorybased energy calculations on periodic models. Instead of dealing with a bigger polymer system, we considered, as aˆrst step, a small scale conˆguration to examine the key point of adhesion between PBT and Al surface. We placed the PBT monomer horizontally and vertically on aluminum surface. We also considered placing aluminum on top of the bulk PBT. By calculating the total energy of the system when PBT monomer approaches aluminum surface and comparing them with their energies when they are isolated, we obtain the binding energy of PBT on aluminum surface. The adhesion is stronger when the PBT monomer is oriented vertically than horizontally. Strong binding is also observed when the aluminum atom is placed on bulk PBT.
Japanese Journal of Applied Physics, 2006
We investigate the stable structures of Fe-filled single-walled carbon nanotubes (SWNTs) on Ni(11... more We investigate the stable structures of Fe-filled single-walled carbon nanotubes (SWNTs) on Ni(111), using density functional theory calculations. We find stable geometries and electronic states for the nanotube on Ni(111). We propose the possibility that the CC bonds of carbon nanotube are broken by Fe wire and Ni surface. That is, when Fe-filled SWNT(3, 3) adsorb on Ni(111) surface, SWNT transforms into arch-like structure.
e-Journal of Surface Science and Nanotechnology, 2009
The formations, binding energies and monomer dipole moments of small water cluster systems (H2O)n... more The formations, binding energies and monomer dipole moments of small water cluster systems (H2O)n with n = 1-12, have been investigated by the density functional calculations using B3LYP/6-311++(2d,2p) level theory. A new method based on reactivity indices from Fukui functions has been introduced to generate the initial structures. Constant adding one by one water molecule from monomer to the cluster systems (hydration reactions) have transformed the cluster shapes by following formation order: linear (n = 2), cyclic planar (n = 3-6) and 3-dimensional (n = 7-12) ones. The average binding energies of small water cluster systems have converged asymptotically to the intermolecular binding of bulk water, concerning the local binding energy fluctuation effects on the average binding energy trend. Based on total electronic energies, zero point energies and optimized transition structures energies (activation energies) analysis, we have predicted that the cyclic planar is the most stable hexamer formation to compete with the cage and the book ones. Considering the monomer dipole moment calculations with regard to the experimental data references, we have discovered new findings which have not clarified yet before, that the smallest piece of ice water is the cyclic tetramer (n =4) and the cage hexamer is the smallest stable liquid formation.
Meeting Abstracts of the Physical Society of Japan, 2018
Abstract. Adsorption based on the immobilization of amino acids, i.e. leucine and glycine, on the... more Abstract. Adsorption based on the immobilization of amino acids, i.e. leucine and glycine, on the surface of undoped polypyrrole (Ppy) is investigated. Calculations are done based on density functional theory using Gaussian03 software and applying GGA with 6-31G(d) basis set and exchange-correlation model of PBE (Perdew, Burke, Ernzerhof) level of theory. The energy of the Ppy doped with amino acids are minimized with respect to the orientation and distance of the amino acids to the Ppy. Neutral leucine carboxyl shows greater binding energy as compared to that other leucine configurations. It has adsorption energy of 0.25 eV at optimum distance of 2.2 Å from the surface of Ppy. As for the glycine, the zwitterionic carboxyl exhibits the strongest binding energy among other glycine configurations. It has adsorption energy of 0.76 eV at optimum distance of 1.7 Å from the surface of Ppy. The adsorption processes for both amino acids should proceed easily because the activation barriers ...
2017IEEE 9th International Conference on Humanoid, Nanotechnology, Information Technology, Communication and Control, Environment and Management (HNICEM)
The persistent increase in carbon dioxide concentration in the atmosphere remains the main contri... more The persistent increase in carbon dioxide concentration in the atmosphere remains the main contributor to global climate change. This has prompted various researchers to design, develop and investigate materials to stabilize its growing threat. One of the best known methods is the biological approach of using microorganisms such as microalgae that have higher conversion efficiency as compared to terrestrial plants. Apparently, its full potential has not been achieved due to variations in several cultivation parameters such as temperature and salinity, which have not been well understood in the current experimental studies. The study is conducted in the atomic level to demonstrate the effects of temperature and salinity on the transport processes of carbon dioxide molecules coming from the flue gas to the microalgae lipid membranes using molecular dynamics. The transport process was described through the calculation of free energies of the carbon dioxide molecules across the membrane using the Cavity Insertion Widom method. The resulting free energy profile of the carbon dioxide molecule at different levels of temperature and salinity has shown no significant changes to its mobility in permeating inside the membrane despite changes in the lipid hydrocarbon chain structure. This suggests that microalgae are capable of absorbing carbon dioxide molecules at high temperature and salinity levels.
Optik, 2020
Here, we show that the electronic and optical properties of silicon (Si) can be controlled by var... more Here, we show that the electronic and optical properties of silicon (Si) can be controlled by varying the amount of dangling bonds and the number of Si Si bonds in the system. By introducing pores in the bulk (in the form of Si vacancies), we can induce the appearance of gap states (states in the energy gap/forbidden region) in porous Si (pSi), as compared to pure Si. Terminating the Si atoms in the pores with hydrogen atoms (H) induces the disappearance of these induced gap states (IGS). As a result, we can continuously decrease (increase) the corresponding refractive indices of both pSi and H-terminated pSi by increasing (decreasing) the porosity.
Biofuels are biomass derived fuels which is considered to have a low carbon emitting characterist... more Biofuels are biomass derived fuels which is considered to have a low carbon emitting characteristics. Biodiesel is one type of biofuels that was introduced in the public and plays a crucial role in the global energy demand particularly in the transport sector. Challenges in making biodiesel commercialization include minimization of the energy inputs on the every process particularly the drying process. Drying microalgae is one of the post harvesting process in converting algal biomass to biodiesel which accounts for 20-30% of the total production cost and energy consumption. A Search for a drying method that requires less energy intensive is needed to address a more efficient production of oil from microalgae for biofuels. This paper is the first step in modelling the drying process wherein a nanoscale understanding on the structure and components of microalgae will be discussed. The main objective of this paper is to model the topology (molecular geometry) of microalgae particularl...
As a first step in studying the molecular-level water transport and reverse solute diffusion mech... more As a first step in studying the molecular-level water transport and reverse solute diffusion mechanisms in forward osmosis (FO) process, this paper presents the molecular modeling and simulation of a polyamide (PA) membrane used in FO. In this study, a repeat unit of the starting monomers (m-phenylenediamine (MPD) and trimesoyl chloride (TMC)) was first modeled and then packed into chain, forming a linear PA chain. Geometry optimization and partial charge calculations of the linear PA chain were undergone using Density Functional Theory (DFT) calculations. A fully atomistic molecular dynamics (MD) simulation of the PA chains was performed to create a final representative model of PA membrane. The generated dehydrated and linear (un-crosslinked) PA membrane structure obtained a density value which is in close agreement with recent experimental and other simulation results. In addition, the calculated small-angle x-ray scattering intensities show that the obtained PA membrane structur...
International Journal of Hydrogen Energy
2018 IEEE 10th International Conference on Humanoid, Nanotechnology, Information Technology,Communication and Control, Environment and Management (HNICEM)
Both the preparation of a reliable all-atom model of a polyamide (PA) membrane and the determinat... more Both the preparation of a reliable all-atom model of a polyamide (PA) membrane and the determination of its electrostatic parameters are considered significant challenges in a proposal to study forward-osmosis-dewatering of microalgae using molecular dynamics (MD). Density functional theory (DFT)-based calculations can effectively calculate for optimized structure and electrostatic properties, thus, employed to model and characterize the PA membrane starting from its molecular unit. The performed structural optimization resulted to the most stable configuration of the PA unit with bond length values that showed strong stability in the molecule such as the amide bond length of 1.413 Å which was found to differ from that of a related study by ~3%. The calculated charge density distributions, electrostatic potential isosurface, and Mulliken charges on the PA unit provided potential binding sites and insights on the formation of amide bonds on the PA molecule. The non-amidebonded nitrogen atom of m-phenylene diamine (MPD) was found to be the most active site in the molecule due to its highest magnitude of negative charge (positive Coulomb potential), suggesting that amide bond-formation with a carbon atom of a trimesoyl chloride (TMC) monomer is most likely to occur during polymerization. The calculated charges in the amide group and the zero-net sum of these charges also agreed reasonably well with another study. The results are of vital importance in parameterizing the interaction potentials of PA for use in the MD simulations.
SSRN Electronic Journal
Microalgal biomass is an essential source of renewable energy and the production of high-valued b... more Microalgal biomass is an essential source of renewable energy and the production of high-valued bio-products. Nannochloropsis sp. is a marine microalgae which contains high valued bio-compounds. However, it contains elevated moisture which hinders extraction of important significant bio-compounds. A dewatering process of Nannochloropsis sp via forward osmosis is proposed. The objective of the study is to evaluate the effect of salinity on the lipid membrane of microalgae Nannochloropsis sp by inducing osmotic pressure difference. A microalgae lipid membrane model was developed using molecular dynamics and evaluated through relative structural changes and water dynamics by varying the salinity. The results revealed at elevated salinity, compression occurs to the lipid membrane based on the tail order and area per head groups. The dynamics of water molecules showed that water migration happens as early as 20 ns. Despite membrane compression, a total of 5 water molecules migrated within the 150 ns. This suggests that forward osmosis is a promising alternative for microalgal dewatering.
Applied Surface Science
Abstract We conducted X-ray photoelectron spectroscopy (XPS) and first-principles calculations ba... more Abstract We conducted X-ray photoelectron spectroscopy (XPS) and first-principles calculations based on density functional theory (DFT) to confirm the presence of Ga2O sub-oxide in high-pressure water vapor annealed AlGaN surface. We note that the Ga 3d XPS peak broadens and shifts towards higher binding energies, which suggests surface oxide formation. Deconvoluted Ga 3d XPS profiles between HPWVA-treated and reference samples reveal reasonable inclusion of Ga2O peak, suggesting formation of Ga2O sub-oxide. To theoretically confirm the presence of Ga2O, we calculated the Ga 3d core-level shift using initial state approximation. We obtained a 0.74 eV shift, in reasonable agreement with that of Ga2O. Moreover, based on the calculation of net charge on Ga using DFT, we also obtained a +1 oxidation state for Ga, indicating its existence in Ga2O form. By combining theory and experiment, therefore, we have explored the possibility of the formation of Ga2O sub-oxide, which may provide new avenues for obtaining highly stable operation in GaN-based devices.
Bioresource Technology
This study aimed to investigate the transport mechanisms of ions during forward-osmosis-driven (F... more This study aimed to investigate the transport mechanisms of ions during forward-osmosis-driven (FO-driven) dewatering of microalgae using molecular dynamics (MD) simulations. The dynamical and structural properties of ions in FO systems of varying NaCl or MgCl2 draw solution (DS) concentrations were calculated and correlated. Results indicate that FO systems with higher DS concentration caused ions to have lower hydration numbers and higher coordination numbers leading to lower diffusion coefficients. The higher hydration number of Mg2+ ions resulted in significantly lower ionic permeability as compared to Na+ ions at all concentrations (p = 0.002). The simulations also revealed that higher DS concentrations led to higher accumulation of ions in the membrane. This study provides insights on the proper selection of DS for FO systems.
International Journal of Hydrogen Energy
JOURNAL OF THE JAPAN WELDING SOCIETY
Pb-doped BSCCO superconducting films were prepared on Ag electrode in a three-electrode cell cont... more Pb-doped BSCCO superconducting films were prepared on Ag electrode in a three-electrode cell containing nitrates of Bi, Pb, Sr, Ca and Cu dissolved in DMSO (dimethyl sulfoxide). The nitrates were varied to obtain Bi2-xPbxSr2Ca2Cu3O10 (x = 0.2, 0.4, 0.6, 0.8). Pt was used as counter electrode and Ag/Ag+ as reference electrode. DC deposition was used with electrode potential of -3.5V for 30, 45, and 60 minutes. Heat treatment was done at 250 degrees Centigrade for 3 hours, 700 degrees Centigrade for 3 hours and 750 degrees Centigrade for 6 hours in oxygen-rich environment to allow solid state reaction to occur on the film. SEM analysis showed the formation of randomly oriented plate-like and bar-like structures which can be attributed to the low-Tc phase and high-Tc phase, respectively. These were observed in films prepared in 0.2 Pb concentration. Melted and step-like growths were found in films with 0.2 and 0.8 Pb concentrations. Pinholes, cracks and impurities were also present. Sp...
Journal of Applied Phycology, 2017
The continuous threat of increasing CO 2 concentration in the atmosphere has altered the carbon b... more The continuous threat of increasing CO 2 concentration in the atmosphere has altered the carbon balance of our planet causing global climate change. Biological fixation of atmospheric CO 2 by unicellular microorganisms such as microalgae is a promising technology pursued extensively by researchers as a means for carbon capture. The study aimed to provide an atomic level of study that will demonstrate the effect of the salinity on the mechanism of CO 2 absorption across microalgae lipid bilayer. Molecular dynamics simulations were utilized to calculate the free energies of CO 2 molecule as it permeates inside the microalgae cell. In thermodynamics, the transport process of a molecule can be demonstrated through its free energy gradient. Thus, calculating the free energies of CO 2 molecule across microalgae lipid bilayer can elucidate the mechanisms of permeation processes. Four microalgae lipid bilayer structures were constructed that contains 128-DPPC (dipalmitoylphosphatidylcholine) lipid bilayer with 3640 water molecules with different NaCl concentrations: 0, 3, 13, and 19 NaCl molecules which correspond to a salinity level of 0, 50, 200, and 300 mM, respectively. The cavity insertion Widom method was used to calculate the free energy of CO 2 molecule along the lipid bilayer. The results demonstrated that the salinity does not affect the free energies significantly, thus, it does not hamper CO 2 transport across microalgae lipid membrane.
Clean Technologies and Environmental Policy, 2016
Algal biofuels serve as a promising alternative energy source for liquid fuels. However, one of t... more Algal biofuels serve as a promising alternative energy source for liquid fuels. However, one of the bottlenecks in the conversion of microalgae to biofuels is the drying process. A moisture content of at most 10 % is desired for algal biomass prior to oil extraction to maximise biofuel yield. Conventional means of drying results to longer drying time and uneven drying of algal biomass. This study investigated the drying characteristics of microwave for microalgae (Chlorella vulgaris). Three microwave intensity levels (300, 600, and 900 W) were considered to dry 10, 20, and 30 of algal mass. Page model gave a better fit on the moisture ratio with time of microwave drying than the exponential model. Furthermore, the specific energy requirement was computed, and a relationship was found between moisture ratio with power and mass. Fourier transform infrared spectroscopy results showed significant reduction of infrared signal intensities of the functional groups present in the algae after drying at higher microwave power level. It was concluded that the 20 W/g microwave drying setting gave a lower specific energy requirement with good quality of remaining high lipid content qualitatively. Furthermore, it was recommended to use gas chromatography mass spectroscopy to further quantify the algal lipids and other functional groups.
Shinku, 2006
We investigate the adhesion strength of poly(butylene terephthalate) or PBT on aluminum using den... more We investigate the adhesion strength of poly(butylene terephthalate) or PBT on aluminum using density functional theorybased energy calculations on periodic models. Instead of dealing with a bigger polymer system, we considered, as aˆrst step, a small scale conˆguration to examine the key point of adhesion between PBT and Al surface. We placed the PBT monomer horizontally and vertically on aluminum surface. We also considered placing aluminum on top of the bulk PBT. By calculating the total energy of the system when PBT monomer approaches aluminum surface and comparing them with their energies when they are isolated, we obtain the binding energy of PBT on aluminum surface. The adhesion is stronger when the PBT monomer is oriented vertically than horizontally. Strong binding is also observed when the aluminum atom is placed on bulk PBT.
Japanese Journal of Applied Physics, 2006
We investigate the stable structures of Fe-filled single-walled carbon nanotubes (SWNTs) on Ni(11... more We investigate the stable structures of Fe-filled single-walled carbon nanotubes (SWNTs) on Ni(111), using density functional theory calculations. We find stable geometries and electronic states for the nanotube on Ni(111). We propose the possibility that the CC bonds of carbon nanotube are broken by Fe wire and Ni surface. That is, when Fe-filled SWNT(3, 3) adsorb on Ni(111) surface, SWNT transforms into arch-like structure.
e-Journal of Surface Science and Nanotechnology, 2009
The formations, binding energies and monomer dipole moments of small water cluster systems (H2O)n... more The formations, binding energies and monomer dipole moments of small water cluster systems (H2O)n with n = 1-12, have been investigated by the density functional calculations using B3LYP/6-311++(2d,2p) level theory. A new method based on reactivity indices from Fukui functions has been introduced to generate the initial structures. Constant adding one by one water molecule from monomer to the cluster systems (hydration reactions) have transformed the cluster shapes by following formation order: linear (n = 2), cyclic planar (n = 3-6) and 3-dimensional (n = 7-12) ones. The average binding energies of small water cluster systems have converged asymptotically to the intermolecular binding of bulk water, concerning the local binding energy fluctuation effects on the average binding energy trend. Based on total electronic energies, zero point energies and optimized transition structures energies (activation energies) analysis, we have predicted that the cyclic planar is the most stable hexamer formation to compete with the cage and the book ones. Considering the monomer dipole moment calculations with regard to the experimental data references, we have discovered new findings which have not clarified yet before, that the smallest piece of ice water is the cyclic tetramer (n =4) and the cage hexamer is the smallest stable liquid formation.
Meeting Abstracts of the Physical Society of Japan, 2018
Abstract. Adsorption based on the immobilization of amino acids, i.e. leucine and glycine, on the... more Abstract. Adsorption based on the immobilization of amino acids, i.e. leucine and glycine, on the surface of undoped polypyrrole (Ppy) is investigated. Calculations are done based on density functional theory using Gaussian03 software and applying GGA with 6-31G(d) basis set and exchange-correlation model of PBE (Perdew, Burke, Ernzerhof) level of theory. The energy of the Ppy doped with amino acids are minimized with respect to the orientation and distance of the amino acids to the Ppy. Neutral leucine carboxyl shows greater binding energy as compared to that other leucine configurations. It has adsorption energy of 0.25 eV at optimum distance of 2.2 Å from the surface of Ppy. As for the glycine, the zwitterionic carboxyl exhibits the strongest binding energy among other glycine configurations. It has adsorption energy of 0.76 eV at optimum distance of 1.7 Å from the surface of Ppy. The adsorption processes for both amino acids should proceed easily because the activation barriers ...
2017IEEE 9th International Conference on Humanoid, Nanotechnology, Information Technology, Communication and Control, Environment and Management (HNICEM)
The persistent increase in carbon dioxide concentration in the atmosphere remains the main contri... more The persistent increase in carbon dioxide concentration in the atmosphere remains the main contributor to global climate change. This has prompted various researchers to design, develop and investigate materials to stabilize its growing threat. One of the best known methods is the biological approach of using microorganisms such as microalgae that have higher conversion efficiency as compared to terrestrial plants. Apparently, its full potential has not been achieved due to variations in several cultivation parameters such as temperature and salinity, which have not been well understood in the current experimental studies. The study is conducted in the atomic level to demonstrate the effects of temperature and salinity on the transport processes of carbon dioxide molecules coming from the flue gas to the microalgae lipid membranes using molecular dynamics. The transport process was described through the calculation of free energies of the carbon dioxide molecules across the membrane using the Cavity Insertion Widom method. The resulting free energy profile of the carbon dioxide molecule at different levels of temperature and salinity has shown no significant changes to its mobility in permeating inside the membrane despite changes in the lipid hydrocarbon chain structure. This suggests that microalgae are capable of absorbing carbon dioxide molecules at high temperature and salinity levels.
Optik, 2020
Here, we show that the electronic and optical properties of silicon (Si) can be controlled by var... more Here, we show that the electronic and optical properties of silicon (Si) can be controlled by varying the amount of dangling bonds and the number of Si Si bonds in the system. By introducing pores in the bulk (in the form of Si vacancies), we can induce the appearance of gap states (states in the energy gap/forbidden region) in porous Si (pSi), as compared to pure Si. Terminating the Si atoms in the pores with hydrogen atoms (H) induces the disappearance of these induced gap states (IGS). As a result, we can continuously decrease (increase) the corresponding refractive indices of both pSi and H-terminated pSi by increasing (decreasing) the porosity.
Biofuels are biomass derived fuels which is considered to have a low carbon emitting characterist... more Biofuels are biomass derived fuels which is considered to have a low carbon emitting characteristics. Biodiesel is one type of biofuels that was introduced in the public and plays a crucial role in the global energy demand particularly in the transport sector. Challenges in making biodiesel commercialization include minimization of the energy inputs on the every process particularly the drying process. Drying microalgae is one of the post harvesting process in converting algal biomass to biodiesel which accounts for 20-30% of the total production cost and energy consumption. A Search for a drying method that requires less energy intensive is needed to address a more efficient production of oil from microalgae for biofuels. This paper is the first step in modelling the drying process wherein a nanoscale understanding on the structure and components of microalgae will be discussed. The main objective of this paper is to model the topology (molecular geometry) of microalgae particularl...
As a first step in studying the molecular-level water transport and reverse solute diffusion mech... more As a first step in studying the molecular-level water transport and reverse solute diffusion mechanisms in forward osmosis (FO) process, this paper presents the molecular modeling and simulation of a polyamide (PA) membrane used in FO. In this study, a repeat unit of the starting monomers (m-phenylenediamine (MPD) and trimesoyl chloride (TMC)) was first modeled and then packed into chain, forming a linear PA chain. Geometry optimization and partial charge calculations of the linear PA chain were undergone using Density Functional Theory (DFT) calculations. A fully atomistic molecular dynamics (MD) simulation of the PA chains was performed to create a final representative model of PA membrane. The generated dehydrated and linear (un-crosslinked) PA membrane structure obtained a density value which is in close agreement with recent experimental and other simulation results. In addition, the calculated small-angle x-ray scattering intensities show that the obtained PA membrane structur...
International Journal of Hydrogen Energy
2018 IEEE 10th International Conference on Humanoid, Nanotechnology, Information Technology,Communication and Control, Environment and Management (HNICEM)
Both the preparation of a reliable all-atom model of a polyamide (PA) membrane and the determinat... more Both the preparation of a reliable all-atom model of a polyamide (PA) membrane and the determination of its electrostatic parameters are considered significant challenges in a proposal to study forward-osmosis-dewatering of microalgae using molecular dynamics (MD). Density functional theory (DFT)-based calculations can effectively calculate for optimized structure and electrostatic properties, thus, employed to model and characterize the PA membrane starting from its molecular unit. The performed structural optimization resulted to the most stable configuration of the PA unit with bond length values that showed strong stability in the molecule such as the amide bond length of 1.413 Å which was found to differ from that of a related study by ~3%. The calculated charge density distributions, electrostatic potential isosurface, and Mulliken charges on the PA unit provided potential binding sites and insights on the formation of amide bonds on the PA molecule. The non-amidebonded nitrogen atom of m-phenylene diamine (MPD) was found to be the most active site in the molecule due to its highest magnitude of negative charge (positive Coulomb potential), suggesting that amide bond-formation with a carbon atom of a trimesoyl chloride (TMC) monomer is most likely to occur during polymerization. The calculated charges in the amide group and the zero-net sum of these charges also agreed reasonably well with another study. The results are of vital importance in parameterizing the interaction potentials of PA for use in the MD simulations.
SSRN Electronic Journal
Microalgal biomass is an essential source of renewable energy and the production of high-valued b... more Microalgal biomass is an essential source of renewable energy and the production of high-valued bio-products. Nannochloropsis sp. is a marine microalgae which contains high valued bio-compounds. However, it contains elevated moisture which hinders extraction of important significant bio-compounds. A dewatering process of Nannochloropsis sp via forward osmosis is proposed. The objective of the study is to evaluate the effect of salinity on the lipid membrane of microalgae Nannochloropsis sp by inducing osmotic pressure difference. A microalgae lipid membrane model was developed using molecular dynamics and evaluated through relative structural changes and water dynamics by varying the salinity. The results revealed at elevated salinity, compression occurs to the lipid membrane based on the tail order and area per head groups. The dynamics of water molecules showed that water migration happens as early as 20 ns. Despite membrane compression, a total of 5 water molecules migrated within the 150 ns. This suggests that forward osmosis is a promising alternative for microalgal dewatering.
Applied Surface Science
Abstract We conducted X-ray photoelectron spectroscopy (XPS) and first-principles calculations ba... more Abstract We conducted X-ray photoelectron spectroscopy (XPS) and first-principles calculations based on density functional theory (DFT) to confirm the presence of Ga2O sub-oxide in high-pressure water vapor annealed AlGaN surface. We note that the Ga 3d XPS peak broadens and shifts towards higher binding energies, which suggests surface oxide formation. Deconvoluted Ga 3d XPS profiles between HPWVA-treated and reference samples reveal reasonable inclusion of Ga2O peak, suggesting formation of Ga2O sub-oxide. To theoretically confirm the presence of Ga2O, we calculated the Ga 3d core-level shift using initial state approximation. We obtained a 0.74 eV shift, in reasonable agreement with that of Ga2O. Moreover, based on the calculation of net charge on Ga using DFT, we also obtained a +1 oxidation state for Ga, indicating its existence in Ga2O form. By combining theory and experiment, therefore, we have explored the possibility of the formation of Ga2O sub-oxide, which may provide new avenues for obtaining highly stable operation in GaN-based devices.
Bioresource Technology
This study aimed to investigate the transport mechanisms of ions during forward-osmosis-driven (F... more This study aimed to investigate the transport mechanisms of ions during forward-osmosis-driven (FO-driven) dewatering of microalgae using molecular dynamics (MD) simulations. The dynamical and structural properties of ions in FO systems of varying NaCl or MgCl2 draw solution (DS) concentrations were calculated and correlated. Results indicate that FO systems with higher DS concentration caused ions to have lower hydration numbers and higher coordination numbers leading to lower diffusion coefficients. The higher hydration number of Mg2+ ions resulted in significantly lower ionic permeability as compared to Na+ ions at all concentrations (p = 0.002). The simulations also revealed that higher DS concentrations led to higher accumulation of ions in the membrane. This study provides insights on the proper selection of DS for FO systems.
International Journal of Hydrogen Energy
JOURNAL OF THE JAPAN WELDING SOCIETY