No abstract

The influence of hydrogen coverage on the thermal conductivity of typical armchair hydrogen functionalized graphene is investigated using a nonequilibrium molecular dynamics simulation. We also study the effects of easy-rotation of unsupported sp3 bonds. We find that the system exhibits a rapid drop in thermal conductivity with hydrogen coverage, where hydrogen coverage down to as little as 2.5% of the graphene carbon atoms reduces the thermal conductivity by about 40%. The simulation results indicate that the effect is due to a reduction in the phonon mean free path.

Managed aquifer recharge (MAR) is a water reuse technique with the potential to meet growing water demands. However, MAR sites have encountered arsenic mobilization resulting from recharge operations. To combat this challenge, it is imperative to identify the mechanisms of arsenic mobilization during MAR. In this bench-scale study, arsenic mobilization from arsenopyrite (FeAsS) was characterized for conditions relevant to MAR operations. Experimentally determined activation energies for arsenic mobilization from FeAsS under aerobic conditions were 36.9 ± 2.3 kJ/mol for 10 mM sodium chloride, 40.8 ± 3.5 kJ/mol for 10 mM sodium nitrate, and 43.6 ± 5.0 kJ/mol for secondary effluent from a wastewater treatment plant. Interestingly, the sodium chloride system showed higher arsenic mobilization under aerobic conditions. In addition, secondary mineral precipitation varied among systems and further affected arsenic mobilization. For example, the wastewater system inhibited precipitation, while in the sodium chloride system, faster phase transformation of iron­(III) (hydr)­oxide precipitates was observed, resulting in hematite formation after 7 days. The phase transformation to hematite will result in less available surface area for arsenic attenuation. These new observations and activation energies can be useful to develop improved reactive transport models for the fate of arsenic during MAR, and develop strategies to minimize arsenic release.

No abstract

No abstract

No abstract

No abstract

No abstract