Search

There is currently a lack of scientific understanding regarding how bio-surfactants influence the mobility of graphene oxide (GO) through saturated porous media. In this study, the transport characteristics of GO through porous media with different heterogeneities ( i.e. , quartz sand and goethite-coated sand) after the addition of saponin (a representative bio-surfactant) were investigated. The results demonstrated that saponin (3-10 mg L -1 ) promoted GO mobility in both types of porous media at pH 7.0. This trend was attributed to the competitive deposition between nanoparticles and bio-surfactant molecules for attachment sites, the enhanced electrostatic repulsion, the decreased strain, the presence of steric effects induced by the adsorbed saponin, and the increase in the hydrophilicity of nanoparticles. Intriguingly, saponin promoted GO mobility in goethite-coated sand ( i.e. , chemically heterogeneous porous media) to a greater extent than that in sand ( i.e. , relatively homogeneous porous media) when saponin concentrations increased, which stemmed from the differences in the extent of the deposition site competition for saponin on the two porous media and the electrostatic repulsion between GO and the porous media. Furthermore, a cation-bridging mechanism was also involved in the ability of saponin to increase GO mobility when the electrolyte solution was 0.1 mM Cu 2+ . Moreover, the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and the colloid transport model were applicable to elucidate the mobility properties of GO with or without saponin in porous media. The findings from this work highlight the important status of bio-surfactants in the fate of colloidal carbon-based nanomaterials in subsurface systems.

Column experiments were carried out to investigate the transport of TiO 2 nanoparticles (nTiO 2 ) in water-saturated porous media in the presence of various imidazolium-based ionic liquids (ILs) with different alkyl chain lengths and counteranions. The results indicated that the effects of ILs on nTiO 2 transport were considerably dependent upon IL species. In general, the transport-inhibition effects increased with the increasing length of branched alkyl chain on the ILs (i.e., [C 6 mim]Cl > [C 4 mim]Cl > [C 2 mim]Cl). The trend was dominated by the hydrophobicity effects of ILs. Meanwhile, the inhibitory effects of ILs were strongly related to the counteranions and followed the order of [C 4 mim]Cl > [C 4 mim][TOS] > [C 4 mim][PF 6 ], mainly due to different electrostatic repulsion force between nanoparticles and porous media in the presence of various ILs. Furthermore, the inhibitory role of [C 4 mim][TOS] in nTiO 2 transport under acidic conditions (i.e., pH 6.5) was greater than that under alkaline conditions (i.e., pH 8.0). The dominant mechanism was that the differences in the extent of electrostatic repulsion between sand grains and nTiO 2 with or without ILs at pH 6.5 were larger than that at pH 8.0. Moreover, two-site kinetic retention model and DLVO theory provided good descriptions for the transport behaviors of nTiO 2 with different ILs., (Copyright © 2021 Elsevier B.V. All rights reserved.)

In this study, transport behaviors of graphene oxide (GO) in saturated uncoated (i.e., clean sand) and goethite-coated sand porous media were examined as a function of the phosphate. We found that phosphate enhanced the transport of GO over a wide range of solution chemistry (i.e., pH 5.0-9.0 and the presence of 10 mmol/L Na + or 0.5 mmol/L Ca 2+ ). The results were mainly ascribed to the increase of electrostatic repulsion between nanoparticles and porous media. Meanwhile, deposition site competition induced by the retained phosphate was another important mechanism leading to promote GO transport. Interestingly, when the phosphate concentration increased from 0.1 to 1.0 mmol/L, the transport-enhancement effect of phosphate in goethite-coated sand was to a much larger extent than that in clean sand. The observations were primarily related to the difference in the total mass of retained phosphate between the iron oxide-coated sand and clean sand columns, which resulted in different degrees of the electrostatic repulsion and competitive effect of phosphate. When the background solution contained 0.5 mmol/L Ca 2+ , phosphate could be bind to sand/ goethite-coated sand surface by cation bridging; and consequently, promoted competition between phosphate and nanoparticles for deposition sites, which was an important mechanism for the enhanced effect of phosphate. Moreover, the DLVO theory was applicable to describe GO transport behaviors in porous media in the absence or presence of phosphate. Taken together, these findings highlight the important status and role of phosphate on the transport and fate of colloidal graphene oxide in the subsurface environment., (Copyright © 2020. Published by Elsevier B.V.)

Since iron oxide minerals are ubiquitous in natural environments, the release of graphene oxide (GO) into environmental ecosystems can potentially interact with iron oxide particles and thus alter their surface properties, resulting in the change of their transport behaviors in subsurface systems. Column experiments were performed in this study to investigate the co-transport of GO nanoparticles and hematite colloids (a model representative of iron oxides) in saturated sand. The results demonstrated that the presence of hematite inhibited GO transport in quartz sand columns due to the formation of less negatively charged GO-hematite heteroaggregates and additional deposition sites provided by the adsorbed hematite on sand surfaces. Contrarily, GO co-present in suspensions significantly enhanced the transport of hematite colloids through different mechanisms such as the increase of electrostatic repulsion, decreased physical straining, GO-facilitated transport of hematite (i.e., highly mobile GO nanoparticles served as a mobile carrier for hematite). We also found that the co-transport behaviors of GO and hematite depended on solution chemistry (e.g., pH, ionic strength, and divalent cation (i.e., Ca 2+ )), which affected the electrostatic interaction as well as heteroaggregation behaviors between GO nanoparticles and hematite colloids. The findings provide an insight into the potential fate of carbon nanomaterials affected by mineral colloids existing in natural waters and soils., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In this study, batch and column tests were performed to investigate the co-transport of graphene oxide (GO) nanoparticles and tetracycline in saturated porous media under various solution chemistry conditions. Research indicated that GO and tetracycline had mutual promotion effect on their transport in the porous media under all the tested conditions, which was ascribed to the high adsorption capacity of tetracycline onto GO and the increased electrostatic repulsion as well as their competition for deposition sites on sand surfaces. Interestingly, the mutually promoting function of GO and tetracycline under acidic conditions was greater than that under alkaline conditions, the dominant mechanism was that the increased solution pH decreased the sorption of tetracycline onto GO and weakened the deposition site competition. Furthermore, the mutually promoting effect of GO and tetracycline was Na + or Ca 2+ concentration-dependent. Specially, increased Ca 2+ concentration weakened the promoting effect of GO on tetracycline transport but magnified the promoting effect of tetracycline on GO transport. This is because higher Ca 2+ concentration could cause a decrease in the adsorption of tetracycline on GO and facilitate more tetracycline molecules to occupy the deposition sites on sand surfaces. Additionally, sodium dodecyl sulfate had enhancement effect on co-transport of GO and tetracycline. Findings from this study clearly indicated that antibiotics and carbon based nanomaterials may transport together under various solution chemistry conditions, and consequently affect their fates in aquatic environments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Utilizing the low‐cost catalysts with excellent catalytic activities to replace the expensive ones for H2 evolution still faces great challenges. It is significant to design the new catalysts with the synergistic effect to improve the activities and decrease the cost of the applications. Herein, the novel nanocatalyst of graphene quantum dots loaded bimetallic nanoparticles (Pt‐Co/GQDs) has been synthesized for the H2 evolution from hydrolysis of amine borane (AB) for the first time. The result indicates that the Pt‐Co/GQDs nanocatalyst holds the better catalytic activities than Pt/GQDs, exhibiting the bimetallic synergies in the hydrolysis process. The synthesized catalyst has been characterized by various measurements, such as TEM, XPS, EDS, UV–Vis, and PL spectra. The effect of the catalyst on the hydrolysis of AB is investigated. It is demonstrated that the value of total turnover frequencies (TOFs) can arrive to 520 molH2·molPt−1·min−1 via the catalyst designing, which is very high in comparison with other reported catalysts. This work has developed an effective nanocatalyst with a lower cost which is never reported in the hydrolysis of AB, possessing both great significance and huge potential in the H2 evolution by hydrolysis of the hydrogen storage materials. [ABSTRACT FROM AUTHOR]

Utilization of nonprecious metals to replace precious metals in the catalytic hydrolysis of hydrogen storage materials causes wide attention. Herein, nonprecious bimetallic nanoparticles loaded on N-doped graphene quantum dots (Co-Ni/N-GQDs) have been synthesized and applied in the hydrolysis of NH3BH3 for the first time. It is demonstrated that Co-Ni/N-GQDs exhibit the obvious bimetallic synergies in the hydrolysis of NH3BH3, and the total turnover frequency (TOF) value reaches 19.94 mol H2 ⋅ mol Cat − 1 ⋅ min − 1 via the optimized design. This work first explored the catalytic performance for the nonprecious bimetallic nanoparticles loaded on N-GQDs in the hydrolysis of NH3BH3, greatly facilitating the development of both nonprecious metals and N-GQDs in the hydrogen evolution. Nonprecious bimetallic nanoparticles loaded on N-doped graphene quantum dots (Co-Ni/N-GQDs) were developed in the hydrolysis of NH3BH3 for the first time. It is demonstrated that Co-Ni/N-GQDs exhibit excellent catalytic performances in the hydrolysis of NH3BH3, and the total turnover frequency (TOF) value can reach 19.94 molH2⋅molCat–1⋅min–1. [ABSTRACT FROM AUTHOR]

Composite electrocatalysts of carbon and metals or metal compounds with homogeneous active sites can be obtained through the carbonization of metal organic framework (MOF) materials under inert atmosphere. In this work, a three-phase composite electrocatalysts NiFe2O4/Ni@C were prepared via pyrolysis from self-assembled MOF nanosheets aggregates. The excellent electrocatalytic activity of the obtained electrocatalysts with various Ni:Fe ratios is demonstrated. Especially, the NiFe2O4/Ni@C sample with the mole ratio of Ni:Fe = 1:1 can use the overpotential (η) of 330 and 423 mV to drive 10 and 50 mA cm−2 respectively. After 80 000 s/22 h, the current density could retained 90% of the initial current density. The excellent activity and stability of the electrocatalysts are attributed to nickel and iron ions with uniform dispersion at atomic level in the NiFe2O4 phase and the synergistic effect of nickel and NiFe2O4 nanoparticles with amorphous carbon atoms or nanoparticles around. [ABSTRACT FROM AUTHOR]

The design and synthesis of highly efficient and ultrafine bimetallic nanoparticles catalysts is challenging. Here we report synthesis of graphene quantum dots-stabilized bimetallic AgRh nanoparticles and their exceptional catalytic activity in the reduction of 4-nitrophenol, 2,4-dinitrophenol and 4-nitrobenzene diazonium tetrafluoroborate and generation of hydroxyl radicals. • The design of highly efficient and ultrafine bimetallic nanoparticles catalysts. • Here we report the synthesis of GQDs stablized AgRh BNPs. • Their catalytic activities in the 4-nitrophenol reduction and OH generation. The design and synthesis of highly efficient and ultrafine bimetallic nanoparticles catalysts is challenging. Here we report the synthesis of AgRh bimetallic nanoparticles (AgRh BNPs) stabilized by graphene quantum dots (GQDs) and their exceptional catalytic activities in the reduction of 4-nitrophenol, 2,4-dinitrophenol and 4-nitrobenzene diazonium tetrafluoroborate and generation of hydroxyl radicals. Construction of AgRh BNPs nanocomposites is accomplished by mixing of GQDs and sodium borohydride, followed by the addition of simple commercial Ag and Rh salt at 0 °C in water. Among them, AgRh BNPs 4 exhibits excellent catalytic performance owing to a positive synergistic effects between the Ag and Rh atoms on GQDs, and its catalytic activity is better than those of both monometallic counterparts. [ABSTRACT FROM AUTHOR]

For preparation of surface-enhanced Raman scattering (SERS) substrate with high stability, reproducibility, and sensitivity performances, graphene/Ag nanoparticles were chosen to make further improvement by introducing molecularly imprinted polymer (MIP) film to protect Ag nanoparticles. The thickness of the resulting ultra-thin MIP layer is 2 nm on the surface of Ag nanoparticles. The preparation of two-dimensional/core-shell structure SERS substrate (G/Ag@MIP) possesses high SERS activity toward the probe of bovine serum albumin (BSA) target molecule, which exhibits a 10−12 M detection limit. The G/Ag@MIP shows good selectivity and recycle rate in the detecting process. These results show that the hybrid material as a SERS sensor is potential for medical diagnosis in life sciences. Unlabelled Image • G/Ag@MIP was successfully obtained through a green route. • G/Ag@MIP possesses core-shell nanoparticles decorated two-dimension structure. • SERS sensitivities of G/Ag@MIP and Ag nanoparticles were studied. • G/Ag@MIP improves the detection limit by 7 orders of magnitude than Ag nanoparticles. [ABSTRACT FROM AUTHOR]