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In this work, column experiments were conducted to investigate the transport characteristics of graphene oxide (GO) nanoparticles in limestone media under various electrolytes, solution pH, and humic acid (HA) concentration conditions. In the limestone media, GO exhibited relatively low mobility with the mass recovery rate lower than 65.2%, even when solution ionic strength was low. The presence of HA enhanced its mobility. In addition, the presence of S 2- , a divalent anion, also promoted GO transport in limestone media compared to Cl − under similar ionic strength conditions through neutralizing more positive charge and thus diminishing the cation bridging. Solution pH showed slight effect on the transport of GO in limestone with the mass recovery range from 40.3% to 51.7%. Over all, decreases in solution pH, HA concentration and increases in solution ionic strength reduced the mobility of GO in the limestone media under the tested conditions. These results indicated both environmental conditions and media characteristics played important roles in controlling GO fate and transport in porous media. The one-site kinetic deposition model was applied to describe the interactions between the GO and limestone media and model simulations fitted the observed experimental data very well. As limestone is an important component of aquiferous media in subsurface, findings from this study elucidated the key factors and processes controlling the fate of GO particles in limestone media, which can inform the prediction and assessment of the risks of GO in groundwater environment. [ABSTRACT FROM AUTHOR]

A hybrids film for reduced graphene oxide with reduced graphene oxide quantum dots (rGO+rGOQDs) was simply prepared by irradiation in Ar atmosphere. The rGO+rGOQDs film has better photoconductivity properties compared to the reduced graphene oxide (rGO) film. The photocurrent responsivity and external quantum efficiency values for the rGO+rGOQDs film reach ~120 mA W −1 and ~34% at 1 V, respectively. The photoconductivity enhancement is attributed to the strong absorption of rGOQDs and the photogenerated charge transfering from rGOQDs to rGO film. [ABSTRACT FROM AUTHOR]

There is an increasing need to develop novel and high-efficiency water purification technologies. This work systematically evaluated the potential of using graphene oxide (GO) directly as filter media for the removal of levofloxacin (LEV), an emerging contaminate, and lead (Pb), a heavy metal, from aqueous solution. Batch and fixed-bed experiments were conducted to determine the sorption behaviors of LEV and Pb onto the GO. In the batch system, GO showed strong sorption of the two contaminants with Langmuir maximum adsorption capacities of 256.6 and 227.2 mg g −1 , respectively. The removal of LEV and Pb by GO in fixed-bed columns was high under all tested conditions in both single and mixed solution systems. The removal efficiency of the two contaminants in the GO-sand columns increased with increasing GO content, but decreased with increasing injection flow rate. In the mixed solution system, although LEV and Pb competed for sorption, the GO media still had high removal efficiencies for them. The column experimental data were well described by the Bed Depth Service Time (BDST) model, suggesting the model can be used for the design of GO-sand filters in large-scale applications. Findings from this work demonstrated that GO is a promising nano-adsorbent that can be used as a high-efficiency filter media in water treatment to remove hazardous metal elements and emerging contaminants. [ABSTRACT FROM AUTHOR]

Accurately predicting the fate and transport of graphene oxide (GO) in porous media is critical to assess its environmental impact. In this work, sand column experiments were conducted to determine the effect of input concentration and grain size on transport, retention, and size perturbation of GO in saturated porous media. The mobility of GO in the sand columns reduced with decreasing grain size and almost all GO were retained in fine sand columns for all of the tested conditions. This result can be explained with colloid filtration and XDLVO theories. Input concentration also influenced the retention and transport of GO in the sand columns because of the ‘blocking’ mechanism that reduces the particle retention rate. After passing through the column, average GO sizes increased dramatically. In addition, the sizes of GO retained in the sand also increased with travel distance. These results suggested that transport through the porous media induced GO aggregation. A mathematical model based on the advection–dispersion equation coupled with the second-order kinetics to reflect the blocking effect simulated the experimental data well. [ABSTRACT FROM AUTHOR]

[Display omitted] Constructing photocatalysts with high activity and anti-photocorrosion is a key to harvesting hydrogen energy from seawater efficiently. Herein, graphene oxide closely coupled high-index facets CdZnS with rich sulfur vacancies (Vs-CZS@GO) has been successfully synthesized via one-pot sulfidation accompanied pyrolysis. DFT calculation confirmed the delicate surface/interface/defect engineering endowed high-index facets Vs-CZS@GO with a lower ΔG H* value and significant charge transfer behavior for efficient H 2 -generation. The synergistic effect of sulfur vacancy, high-index facets, and tightly coupling interface not only enhanced intrinsic active sites and carrier separation efficiencies, but also greatly promoted H 2 evolution rate and stability. Consequently, Vs-CZS@GO displayed a significantly high H 2 -generation rate of 23.2 mmol∙g−1∙h−1 in natural seawater under visible-light irradiation, which is up to 82% of that in pure water. This work provides deeply insight into the synergistic regulation of electronic structure for exposed high-index facets photocatalysts via defect engineering and interface engineering for synergistic boosting visible-light-to-H 2 evolution. [ABSTRACT FROM AUTHOR]

• The effect of thermal annealing on the magnetic properties of GOQDs was clarified. • All the annealed GOQDs samples show paramagnetism. • The magnetic moment and the magnetic density vary with the annealing temperature. • The main magnetic source of the annealed GOQDs change with the annealing temperature. The magnetism of graphene oxide quantum dots (GOQDs) has attracted much attention for the prospective applications in spintronics, which is relevant to the oxidation degree. Although the oxidation degree of GOQDs can be tuned by altering the annealing temperature, the specific effect of thermal annealing on the magnetic properties of GOQDs have not been identified. In this study, we report the effect of thermal annealing on the magnetic properties of GOQDs. All the annealed GOQDs samples show paramagnetism. Hydroxyl groups and vacancies on the basal-plane, and the phenolic hydroxyl passivated zigzag edges give various contribution to the magnetism determined by the annealing temperature. Our studies clarified the effect of thermal annealing on the magnetic properties of GOQDs, that would give benefits to their prospective applications in spintronics. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • LTV technology was effective in visualizing GO transport in the 2-D porous media. • Preferential flow affected GO transport in 2-D heterogeneous porous media. • GO spread vertically through dispersion in 2-D porous media. • Double Monod model described GO transport and retention very well. Abstract Graphene oxide (GO) has been indicated to be biotoxic and risky in environment, its environmental behavior thus has received increasing attention in recent. In this study, homogeneous and heterogeneous sand tanks were used to examine the transport behaviors of GO nanoparticles in two-dimensional (2-D) porous media under various conditions. Light transmission visualization (LTV) technology was applied to visualize the real-time transport, retention, and release of GO. GO transport in 2-D porous media was simulated with a simplified Double Monod model. GO mobility decreased with the increasing solution ionic strength (IS) and decreasing media grain size. Preferential flow played an important role in GO transport in 2-D heterogeneous porous media. Even without vertical flow in the sand tanks, GO still spread vertically through dispersion, suggesting the importance of the dispersion process to nanoparticle fate and transport in 2-D porous media. LTV images and breakthrough curves showed that some of the previous retained GO particles were instantaneously remobilized with IS decreasing. With the consideration of the vertical dispersion, simulations of the Double Monod model matched the experimental data well. Findings from this work contribute to expand current knowledge of environmental fate and transport of GO, leading to better assessment and prediction of its environmental risks. [ABSTRACT FROM AUTHOR]

In this work, effects of graphene oxide (GO) on the co-transport of the two typical Fluoroquinolones (FQs) - levofloxacin (LEV) and ciprofloxacin (CIP) in saturated and unsaturated quartz sand media were studied. The adsorption isotherms showed that GO had much larger sorption capacities to LEV and CIP than sand with the largest Langmuir adsorption capacity of 409 mg g −1 (CIP-GO); while the sorption affinity of the two FQs onto the two adsorbents might follow the order of CIP-sand > LEV-sand > LEV-GO > CIP-GO. GO promoted the mobility of the two FQs in both saturated and unsaturated porous media due to its strong mobility and sorption capacity. The GO-bound LEV/CIP was responsible for the LEV/CIP transport in the porous media, and transport of GO-bound FQs increased with the increasing of initial GO concentration. Under unsaturated conditions, moisture showed little effect on the transport of GO-bound CIP; however, the mobility of GO-bound LEV reduced with the decreasing of moisture content, suggesting the transport of adsorbed LEV from GO to air-water interface. GO sorption reduced the antibacterial ability of the two FQs, but they were still effective in inhibiting E. coli growth. [ABSTRACT FROM AUTHOR]

[Display omitted] • Synthesis of flexible TNO/rGO@NC anode by high pressure solvothermal method. • TNO/rGO@NC anode with adjustable areal mass-loading achieves ultrahigh areal capacity. • HGS cathode with high surface area and abundant mesopores shows superior capacitance. • Assembled LIC without metal collector and binder achieves high energy/power density. Flexible power sources are a vital component for smart and wearable electronics. The portability and functionality of these devices are limited by the size, weight, and flexibility of the available batteries. Herein, using the high-pressure solvothermal method, we explored the controllable mass-loading of active materials for flexible lithium-ion capacitor (LIC) and a representative of "PDA-carbon encapsulated reduced graphene oxide supported Ti 2 Nb 10 O 29 " (TNO/rGO@NC) anode and "three-dimensional holey graphene sheets" (HGS) cathode. When using a commercial application mass-loading level of 10.5 mg cm−2 for study, the TNO/rGO@NC anode achieves a high specific areal capacity of 2.4 mAh cm−2 at 0.5C, and 1.2 mAh cm−2 at an ultra-high rate of 50C, while maintaining 92.4% of initial capacity over 500 cycles at 10C. For the cathode part, the HGS shows 125 mAh g−1 at 1C and no degeneration after 1500 cycles. The assembled LICs achieves a high power density of 6230 kW kg−1 with 123 Wh kg−1 energy density, and good cycling retention of 82.2 % over 1000 cycles at 10C in 0.5–4.0 V. The advantages of flexibility, facile shape design, high mass-loading, high energy/power densities make it a promising energy-storage candidate for wearable and smart electronic devices. [ABSTRACT FROM AUTHOR]

Root exudates are a major source of dissolved organic matters that strongly affect the stability and transport behaviors of nanomaterials in porous media. This study investigated the effect of citric acid (CA) and oxalic acid (OA), two common low molecular weight root exudates, on the stability and transport of graphene oxide (GO) in saturated sand columns under different combinations of pH (4.5, 7.0), ionic strength (IS: 10, 50 mM), and organic acid concentrations (10, 25 mM). Both OA and CA accelerated GO aggregation, especially under high IS and acid concentration conditions. With the presence of OA/CA (≥ 10 mM), the transport of GO was higher at pH of 7.0 than 4.5, and the GO mobility decreased with increasing IS and OA/CA concentrations, whereas, enhanced GO transport was observed at a low concentration of OA/CA (0.1 mM), indicating that the influence of organic acid was concentration-dependent. All the results suggest that perturbations of surface potential of GO and sand, as well as the chemical structure of organic acids under different solution chemistry conditions are crucial in controlling GO stability and transport behaviors. Mathematical models based on the advection-dispersion equation with one-site kinetics simulated the experimental breakthrough curves of GO very well. [Display omitted] • Organic acid type and concentration strongly affected GO stability and mobility. • Enhancement or inhibition of OA/CA on GO mobility was concentration-dependent. • GO aggregation and retention increased with increasing OA/CA concentration (≥ 10 mM). • Inhibition on GO mobility by OA/CA was more profound at lower pH, higher IS. • Mathematical models simulated the experimental breakthrough curves of GO very well. [ABSTRACT FROM AUTHOR]