Liyan Liu

Insight into hydrogen bonds and characterization of interlayer spacing of hydrated graphene oxide

AbstractThe number of hydrogen bonds and detailed information on the interlayer spacing of graphene oxide (GO) confined water molecules were calculated through experiments and molecular dynamics simulations. Experiments play a crucial role in the modeling strategy and verification of the simulation results. The binding of GO and water molecules is essentially controlled by hydrogen bond networks involving functional groups and water molecules confined in the GO layers. With the increase in the water content, the clusters of water molecules are more evident. The water molecules bounding to GO layers are transformed to a free state, making the removal of water molecules from the system difficult at low water contents. The diffuse behaviors of the water molecules are more evident at high water contents. With an increase in the water content, the functional groups are surrounded by fewer water molecules, and the distance between the functional groups and water molecules increases. As a result, the water molecules adsorbed into the GO interlamination will enlarge the interlayer spacing. The interlayer spacing is also affected by the number of GO layers. These results were confirmed by the calculations of number of hydrogen bonds, water state, mean square displacement, radial distribution function, and interlayer spacing of hydrated GO. Graphical AbstractThis work research the interaction between GO functional groups and confined water molecules. The state of water molecules and interlayer spacing of graphene oxide were proved to be related to the number of hydrogen bonds.

Nitrate contamination in a coastal soil and water system: A case study after the Tianjin Port 8·12 explosion, China

ABSTRACT In the Tianjin Port 8·12 explosion, the leakage of enormous amounts of nitrate into the coastal soil-water system threatened the environment and human health. This work aimed to assess the nitrate transport process in unsaturated dredger fills and to conduct an environmental risk assessment to establish guidelines that safeguard groundwater against contamination. The impacts of the bulk density, initial water content, recharge rate, and initial concentration of the nitrate transport process were investigated through an L9 (34) matrix. A field simulation was conducted with Hydrus-1D to explore nitrate transport at the accident site. The results showed the recharge rate and initial water content were the dominant factors affecting the nitrate transport rate and concentration distribution, followed by the initial concentration and bulk density. The contaminant reached the water table in approximately 1.2 years and that approximately 9% of the leaked nitrate entered the aquifer after two years, while the rest of the nitrate remained in the unsaturated zone. The nitrate concentration at a depth of 5.0 m was nearly 1000 mg L–1, which was much higher than the groundwater concentration standard of 30 mg L–1. The soil and groundwater quality warrant special attention due to the excessive nitrate contaminants.

A visible coalescence of droplets on hydrophobic and hydrophilic fibers in water-in-oil emulsion

ABSTRACT The droplets’ coalescence is instantaneous and rather complex in emulsion. The theoretical analysis of this process was presented by a former research, while visible experiments to verify these are still scarce. This work aims to show and analyze the visible water droplets’ coalescence on hydrophobic bamboo charcoal fibers and hydrophilic glass fibers in water-in-oil emulsion. An experimental setup with microscope and high-speed camera was designed and established to record the water droplets’ coalescence. The water droplets’ collision coalescence on bamboo charcoal fibers was observed, and the diameters of water droplets detaching from the fibers with different angles were measured. The angle between the fiber and the flow velocity can affect the diameters of water droplets detaching from the bamboo charcoal fibers, and cross-fibers can the enormously increase water diameters compared with single fiber. Meanwhile, the water droplets’ collision coalescence on glass fibers was observed and the result shows that the collision coalescence also occurred on the hydrophilic glass fibers when the droplet diameter was small. In addition, other factors, including flow velocity and droplets’ diameter for the coalescence on the hydrophilic glass fibers were investigated. GRAPHICAL ABSTRACT