Guorui Zhu

Rheological Behavior of High Concentrated Dispersions of Graphite Oxide

The rheological properties of graphite oxide (GO) of high concentrations were studied, which is important for pumping and translating design. Steady test indicated GO displayed shear thinning behaviors at low shear rates. The viscosity and particle increased quickly above certain shear rates. The Herschel–Bulkley model represented flow behavior accurately. Correlations between solid content, temperature, and viscosity were expressed by an exponential equation and a modified Arrhenius type equation, respectively. The dynamic test indicated viscoelasticity of GO decreased remarkably at lower concentrations. Under shearing, network structure of GO broke down gradually, and viscosity decreased with time, causing flow acceleration.

Dewatering of drilling sludge by ultrasound assisted Fe(II)-activated persulfate oxidation

An ultrasound assisted Fe(II)-activated persulfate oxidation method was put forward to improve the dewaterability of drilling sludge in this research. The water content in the filter cake and specific resistance to filtration (SRF) were measured to evaluate the sludge dewaterability. Volatile suspended solids (VSS), transmittance of supernatant, microstructure, particle size distribution and zeta potential were tested to justify the proposed mechanism. The results showed that appropriate ultrasound assisted Fe(II)-activated persulfate oxidation could not only further enhance the sludge dewaterability but also reduce the reaction time as well. The optimal conditions for this method were 1.6% sodium persulfate, 0.8% ferrous sulfate, 40 W ultrasonic power and 45 min reaction time. Reduction of VSS and an increase of transmittance were further achieved compared to oxidation alone. SEM results and the decrease of particle size after the treatment confirmed the disintegration of sludge flocs, which promoted the release of bound water. A synergistic effect mechanism of ultrasound and chemical oxidation was proposed, with ultrasonic cavitation disintegrating the flocs, exposing the interior organics and persulfate further oxidizing the released organics.

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

The rheological behavior of graphite oxide/cationic polyacrylamide suspensions

Cationic polyacrylamide (CPAM) is added into graphite oxide (GO) suspensions to purify the GO. A proper understanding of the best addition amount of CPAM and the rheological properties of GO/CPAM is important for filtration and the design of pumping systems for transportation. Both experimental and theoretical analyses are carried out with analysis of the high shear viscosity, shear thinning behavior and temperature dependence of GO/CPAM suspensions containing 1–40 wt% CPAM. With increase of the CPAM concentration, GO particles and the CPAM aggregate together to form floccules. The filtration and purification efficiency are improved when the GO/CPAM suspension contains 20 wt% CPAM and this is beneficial for pipeline transportation. The addition of CPAM can improve the thermal stability of GO to a certain extent, because the comparatively strong interface interactions block the decomposition of GO. The GO/CPAM suspension exhibits non-Newtonian characteristics. The Herschel–Bulkley model represents the GO/CPAM flow behavior accurately and the non-Newtonian flow characteristics of GO/CPAM are strengthened with a higher CPAM content. Correlations between the CPAM content, temperature, and viscosity are expressed using an exponential equation and a modified Arrhenius type equation, respectively. The activation energy for the flow process increases with the CPAM concentration. Furthermore, the dynamic tests indicate that the viscoelasticity of GO/CPAM decreases remarkably with decrease of the CPAM concentration. Under shearing, the GO/CPAM suspension exhibits thixotropic properties, while the network structure of GO/CPAM breaks down gradually. Then the viscosity decreases with time, causing flow acceleration due to an avalanche effect.

Optimization of operating conditions in the purification of graphite oxide dispersions

In the graphite oxide (GO) suspension purification process, some metallic impurities in GO cannot be separated. The residual metallic impurities dominate graphite oxide properties and have a negative influence on applications. Therefore, the removal of metallic impurities from graphite oxide has been brought into focus now. Single factor experiments and orthogonal experiments are used to get the optimal purification condition. The results show that purification agent, temperature, stirring intensity and contact time affect the purification degree, and the purification agent is the most important element for the purification efficiency. The optimal purification condition is 10% hydrochloric acid (H10), 20 °C, 0 rpm and 60 min. Besides, the theoretical stage is calculated by the mass conservation equation and distribution balance equation and the minimum stage is 3 under the optimal purification condition.