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Nanjing, China

Xia T.,Nankai University | Fortner J.D.,Washington University in St. Louis | Zhu D.,Nanjing UniversityJiangsu | Qi Z.,Nankai University | Chen W.,Nankai University
Environmental Science and Technology

We describe how the reduction of graphene oxide (GO) via environmentally relevant pathways affects its transport behavior in porous media. A pair of sulfide-reduced GOs (RGOs), prepared by reducing 10 mg/L GO with 0.1 mM Na2S for 3 and 5 days, respectively, exhibited lower mobility than did parent GO in saturated quartz sand. Interestingly, decreased mobility cannot simply be attributed to the increased hydrophobicity and aggregation upon GO reduction because the retention mechanisms of RGOs were highly cation-dependent. In the presence of Na+ (a representative monovalent cation), the main retention mechanism was deposition in the secondary energy minimum. However, in the presence of Ca2+ (a model divalent cation), cation bridging between RGO and sand grains became the most predominant retention mechanism; this was because sulfide reduction markedly increased the amount of hydroxyl groups (a strong metal-complexing moiety) on GO. When Na+ was the background cation, increasing pH (which increased the accumulation of large hydrated Na+ ions on grain surface) and the presence of Suwannee River humic acid (SRHA) significantly enhanced the transport of RGO, mainly due to steric hindrance. However, pH and SRHA had little effect when Ca2+ was the background cation because neither affected the extent of cation bridging that controlled particle retention. These findings highlight the significance of abiotic transformations on the fate and transport of GO in aqueous systems. © 2015 American Chemical Society. Source

Rui Q.-Q.,Nanjing University of Technology | Zhou Y.,Nanjing University of Technology | Fang Y.,Nanjing University of Technology | Yao C.,Nanjing University of Technology | Yao C.,Nanjing UniversityJiangsu
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy

Two new rhodamine B-based fluorescent probes PyRbS and PyRbO containing pyrene moiety were designed and synthesized. Both of the probes showed colorimetric and fluorometric sensing abilities for Hg2+ with high selectivity over other metal ions. The binding analysis using Job's plot suggested 1:1 stoichiometry for the complexes formed for Hg2+. Compared with PyRbO, the PyRbS showed higher selectivity and sensitivity due to the thiophilic property of Hg2+ ion. The PyRbS exhibited the linear fluorescence quenching to Hg2+ in the range of 0.3 to 4.8 μM (λex = 365 nm) and 0.3 to 5.4 μM (λex = 515 nm), and the detection limit was 0.72 μM. Moreover, ratiometric changes of PyRbS with Hg2+ in absorption spectrum were observed, which could not be obtained in the combination of PyRbO with Hg2+. In addition, the methyl thiazolyl tetrazolium (MTT) assay demonstrated that RbPyS had low cytotoxicity and was successfully used to monitor intracellular Hg2+ levels in living cells. © 2016 Elsevier B.V. All rights reserved. Source

Kumar K.V.,Queen Mary, University of London | Preuss K.,Queen Mary, University of London | Lu L.,Nanjing UniversityJiangsu | Guo Z.X.,University College London | Titirici M.M.,Queen Mary, University of London
Journal of Physical Chemistry C

Nitrogen (N) doping is considered an effective design strategy to improve CO2 adsorption in carbon materials. However, experimental quantification of such an effect is riddled with difficulties, due to the practical complexity involved in experiments to control more than one parameter, especially at the nanoscale level. Here, we use molecular simulations to clarify the role of N doping on the CO2 uptake and the CO2/N2 selectivity in representative carbon pore architectures (slit and disordered carbon structures) at 298 K. Our results indicate that N doping shows a marginal improvement on the CO2 uptake, although it can improve the CO2/N2 selectivity. CO2 uptake and CO2/N2 selectivity are predominantly controlled by the pore architecture as well as ultra-micropores; the tendency of linear CO2 molecules to lie flat on the carbon surface favors the CO2 uptake in slit pore architectures rather than disordered carbon pore structures. We also demonstrated through molecular simulations that the N doping effect may be difficult to exemplify experimentally if the material has a disordered pore architecture and complex surface chemistry (such as the presence of other functional groups). © 2015 American Chemical Society. Source

Chen H.,University of Florida | Gao B.,University of Florida | Yang L.-Y.,Nanjing UniversityJiangsu | Ma L.Q.,University of Florida | Ma L.Q.,Nanjing UniversityJiangsu
Journal of Contaminant Hydrology

Antibiotic ciprofloxacin (CIP) is immobile in the subsurface but it has been frequently detected in the aquatic system. Therefore it is important to investigate the factors impacting CIP's mobilization in aquifer. Laboratory columns packed with sand were used to test colloid-facilitated CIP transport by 1) using kaolinite or montmorillonite to mobilize presorbed-CIP in a column or 2) co-transporting with CIP by pre-mixing them before transport. The Langmuir model showed that CIP sorption by montmorillonite (23 g kg-1) was 100 times more effective than sand or kaolinite. Even with strong CIP complexation ability to Fe/Al coating on sand surface, montmorillonite promoted CIP transport, but not kaolinite. All presorbed-CIP by sand was mobilized by montmorillonite after 3 pore volumes through co-transporting of CIP with montmorillonite. The majority of CIP was fixed onto the montmorillonite interlayer but still showed inhibition of bacteria growth. Our results suggested that montmorillonite with high CIP sorption ability can act as a carrier to enhance CIP's mobility in aquifer. © 2015, Elsevier B.V. All rights reserved. Source

Qu X.,Nanjing UniversityJiangsu | Fu H.,Nanjing UniversityJiangsu | Mao J.,Old Dominion University | Ran Y.,CAS Guangzhou Institute of Geochemistry | And 2 more authors.

Black carbon (BC) has drawn wide interest due to its important role in the global carbon budget and pollutant sequestration. Its soluble carbonaceous component, dissolved BC, is the key for understanding many geological and environmental processes of BC. In this study, we show that dissolved BC can be readily released in water under stirring from bulk BC produced by the slow pyrolysis of biomass. The chemical and structural properties of bulk, colloidal, and dissolved BC were thoroughly examined using elemental analysis and a variety of spectroscopic techniques. Compared with bulk BC, dissolved BC contained 30-40% more oxygen and more polar functional groups, but lower aromaticity and less condensed aromatic clusters. It is concluded that dissolved BC consists primarily of small aromatic clusters substituted by carboxylic groups, and by phenolic groups to a less extent. Dissolved BC represents an important source for soil and aquatic natural organic matter. The structure of dissolved BC was compared with some well-characterized humic substances. Results obtained from this work would shed new light on the mobility, liability, and reactivity of BC, as well as its impact on the global carbon budget and contaminant transport. © 2015 Elsevier Ltd. Source

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