We investigated the pH-dependent energetics and mechanisms of doxorubicin (DOX) drug adsorption on graphene oxide nanocarriers using molecular dynamics simulation.

Molecular dynamics simulations were performed to gain fundamental molecular insights on the concentration-dependent adsorption and gas transport properties of the components in a CH4/CO2 gaseous mixture in single- and double-layered nanoporous graphene (NPG) and graphene oxide (NPGO) separation platforms. While these platforms are promising for a variety of separation applications, much about the relevant gas separation mechanisms in these systems is still unexplored. Based on the gas adsorption results in this work, at least two layers of CO2 are formed on the gas side of both NPG and NPGO, while no adsorption is observed for pure CH4 on the single-layered NPG. In contrast, increasing the CH4 concentration in the CH4/CO2 mixture leads to an enhancement of the CH4 adsorption on both separation platforms. The through-the-pore diffusion coefficients of both CO2 and CH4 increase with an increase in the CH4 concentration for all NPG and NPGO systems. The permeance of CO2 is smaller than that of CH4, suggesting the NPG and NPGO platforms are more suitable as CO2 adsorbents or membranes for the CH4/CO2 (rather than the CO2/CH4) separation. The highest observed selectivities for the CH4/CO2 separation in the NPG and NPGO platforms are about 5 and 6, respectively.

Reactive molecular dynamics simulation was employed to compare the damage mitigation efficacy of pristine and polyimide (PI)-grafted polyoctahedral silsesquioxane (POSS), graphene (Gr), and carbon nanotubes (CNTs) in a PI matrix exposed to atomic oxygen (AO) bombardment. The concentration of POSS and the orientation of Gr and CNT nanoparticles were further investigated. Overall, the mass loss, erosion yield, surface damage, AO penetration depth, and temperature evolution are lower for the PI systems with randomly oriented CNTs and Gr or PI-grafted POSS compared to those of the pristine POSS or aligned CNT and Gr systems at the same nanoparticle concentration. On the basis of experimental early degradation data (before the onset of nanoparticle damage), the amount of exposed PI, which has the highest erosion yield of all material components, on the material surface is the most important parameter affecting the erosion yield of the hybrid material. Our data indicate that the PI systems with randomly oriented Gr and CNT nanoparticles have the lowest amount of exposed PI on the material surface; therefore, a lower erosion yield is obtained for these systems compared to that of the PI systems with aligned Gr and CNT nanoparticles. However, the PI/grafted-POSS system has a significantly lower erosion yield than that of the PI systems with aligned Gr and CNT nanoparticles, again due to a lower amount of exposed PI on the surface. When comparing the PI systems loaded with PI-grafted POSS versus pristine POSS at low and high nanoparticle concentrations, our data indicate that grafting the POSS and increasing the POSS concentration lower the erosion yield by a factor of about 4 and 1.5, respectively. The former is attributed to a better dispersion of PI-grafted POSS versus that of the pristine POSS in the PI matrix, as determined by the radial distribution function.

No abstract

No abstract