Molecular dynamics study on growth of carbon dioxide and methane hydrate from a seed crystal

In the current work,molecular dynamics simulation is employed to understand the intrinsic growth of carbon dioxide and methane hydrate starting from a seed crystal of methane and carbon dioxide respectively.This comparison was carried out because it has relevance to the recovery of methane gas from natural gas hydrate reservoirs by simultaneously sequestering a greenhouse gas like CO2.The seed crystal of carbon dioxide and methane hydrate was allowed to grow from a super-saturated mixture of carbon dioxide or methane molecules in water respectively.Two different concentrations(1:6 and 1:8.5)of CO2/CH4 molecules per water molecule were chosen based on gas–water composition in hydrate phase.The molecular level growth as a function of time was investigated by all atomistic molecular dynamics simulation under suitable temperature and pressure range which was well above the hydrate stability zone to ensure significantly faster growth kinetics.The concentration of CO2 molecules in water played a significant role in growth kinetics,and it was observed that maximizing the CO2 concentration in the aqueous phase may not result in faster growth of CO2 hydrate.On the contrary,methane hydrate growth was independent of methane molecule concentration in the aqueous phase.We have validated our results by performing experimental work on carbon dioxide hydrate where it was seen that under conditions appropriate for liquid CO2,the growth for carbon dioxide hydrate was very slow in the beginning.

Multifunctional applications of gadolinium-doped cerium oxide(Ce_(1-x)Gd_(x)O_(2-■))ceramics:A review

Cerium oxide(CeO_(2)),or ceria,and its doped derivatives have been extensively studied for several decades and are well-known oxides valued for their unique structural properties and wide range of applications.These materials play a crucial role in sustainable development within society.Structural modification through de fect e ngineering of the highly stable cubic fluorite phase enhances the versatility of this doped ceria to a new level.Among the numerous dopants of the CeO_(2)matrix,ceria doped with gadolinium(Gd),known as Ce_(1-x)Gd_(x)O_(2-■)(CGO),is gaining popularity due to its multifunctionality.The introduction of defect-induced vacancies in the oxygen sublattice(V_(o))and a change in the average valence of cerium(Ce^(3+)/Ce^(4+))are primarily responsible for the improved performance compared to pristine CeO_(2).These materials are currently undergoing intensive research for potential use as electrolytes in intermediate-temperature solid oxide fuel cells(IT-SOFCs)and dense oxygen-permeable membranes(OPMs).Additionally,they are being commercially utilized for power generation and oxygen separation.CGO materials are also attracting significant attention in various fields such as optics,photocatalysis,electrostriction,spintronics,gas sensing,electrocatalysis,and biomedical applications.This review paper aims to compile the latest contributions to CGO materials and comprehensively cover their various application areas.The crystal structure,defect equilibrium in Gd^(3+)-doped CeO_(2),the origin of multifunctionality,and the prospects of these materials are also exclusively discussed.