Hybrid versus global thermostatting in molecular-dynamics simulation of methane-hydrate crystallisation

Molecular-dynamics(MD)simulations have been performed for the growth of a spherical methane-hydrate nano-crystallite,surrounded by a supersaturated water–methane liquid phase,using both a hybrid and globalsystem thermostatting approach.It was found that hybrid thermostatting led to more sluggish growth and the establishment of a radial temperature profile about the spherical hydrate crystallite,in which the growing crystal phase is at a higher temperature than the surrounding liquid phase in the interfacial region,owing to latent-heat dissipation.In addition,Onsager’s-hypothesis fluctuation–dissipation analysis of fluctuations in the number of crystal-state water molecules at the interface shows slower growth.

Diverse morphologies of zinc oxide nanoparticles and their electrocatalytic performance in hydrogen production

Hydrogen is considered an attractive alternative to fossil fuels,but only a small amount of it is produced from renewable energy,making it not such a clean energy carrier after all.Producing hydrogen through water electrolysis is promising,but using a cost-effective and high-performing catalyst that has longterm stability is still a challenge.This study exploits,for the first time,the potential of zinc oxide nanoparticles with diverse morphologies as catalysts for the electrocatalytic production of hydrogen from water.The morphology of the nanoparticles(wires,cuboids,spheres)was easily regulated by changing the concentration of sodium hydroxide,used as the shape controlling agent,during the synthesis.The spherical morphology exhibited the highest electrocatalytic activity at the lowest potential voltage.These spherical nanoparticles had the highest number of oxygen vacancies and lowest particle size compared to the other two morphologies,features directly linked to high catalytic activity.However,the nanowires were much more stable with repeated scans.Density-functional theory showed that the presence of oxygen vacancies in all three morphologies led to diminished band gaps,which is of catalytic interest.

Magnetic ferrite/carbonized cotton fiber composites for improving electromagnetic absorption properties at gigahertz frequencies

Ferrite/carbon composited materials,especially the bio-derived composited materials possessing both environmental friendliness and outstanding microwave absorption performance,attract numerous attentions for solving the"electromagnetic problem"in the Gigahertz frequency range.In this work,we demonstrate a bio-derived ferrite/carbon material by compositing functional carbonized cotton fibers(CCFs)and Fe_(3)O_(4)nanoparticles with optimized microwave-absorption properties.By adjusting the carbonization conditions systematically,the Fe_(3)O_(4)loading contents and the microwave absorption properties can be varied simultaneously-and,indeed,optimized and tuned.The CCFs-Fe_(3)O_(4)composites exhibited a minimum reflection-loss capacity RL(d B)of-56.8 d B at 10.9 GHz with a thickness of 1.67 mm,and its effective absorption bandwidth(RL(d B)<-20 d B)was found to broaden to 7.1 GHz.Electromagnetic characterizations,coupled with microstructure analyses,revealed that the enhancement in microwave absorption was triggered by the different microstructures of CCFs-Fe_(3)O_(4)composites-attributable to the different carbonization processes.These different conditions result in different amounts of Fe_(3)O_(4)attachment sites and lead to the enhancement of dielectric polarization at localized microstructures.The present work of bio-derived ferrite/carbon materials has important implications in understanding structure-performance relationships in dielectric-magnetic materials,and,meanwhile,could well be extended to a microwave-absorber design approach.

Microbial stabilisation and kinetic enhancement of marine methane hydrates in both deionised-and sea-water

The large quantity of marine methane hydrates has driven substantial interest in methane-gas-fuel potential,especially with the qualified success of Shensu(2017)and Nankai-Trough(2014&17)production trials via depressurisation(blighted ultimately by sanding out),building on an earlier Malik-2008 trial for permafrost-bound hydrate.In particular,obviating deep-water-drilling approaches,such as the MeBO production rig(without such a drill bit),together with blowout preventers,constitutes a tantalising cost-saving measure.Tailored means of addressing sand production by customised gravel packs,wellbore screens and slotted liners with from-seafloor drilling will be expected to lead to future production-trial success.However,despite these exciting engineering advances and a few marinemimicking laboratory studies of methane-hydrate kinetics and stabilisation from microbial perspectives,relatively little is known about the thermogenic or microbial origin of marine hydrates,nor their possible formation kinetics or potential stabilisation by microbial sources as an exponent of Gaia's hypothesis,or within the context of“Gaia's breath”as regards global methane‘exhalations’.Here,for the first time,we elucidate the methylotrophic-microbial basis for kinetic enhancement and stabilisation of marine-hydrate formation in both deionised-and sea-water,identifying the key protein at play,which has some similarity to porins in other methylotrophic communities.In so doing,we suggest such phenomena in marine hydrates as evidence of Gaia's hypothesis.