Browsing by Author "Zhang, Nan"

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    Influence of citrate ligands on ferric hydroxide nucleation at low molar ratios: Application for arsenic removal
    (2010) Zhang, Nan; Tomson, Mason B.
    The U.S. EPA recommends adding of 5-25mg/L ferric salt to remove arsenate (V) at pH 5 to 8 in water treatment plants. Citrate has been proven to inhibit ferric hydroxide floc formation and corresponding arsenic adsorption. Although most research has been conducted at high molar ratios of citrate to iron, low molar ratios were used in this work and the inhibition of floc formation remained constant above a molar ratio of 0.05. Nucleation kinetics of ferric hydroxides and arsenic removal was investigated in the presence of citrate at low molar ratios (citrate/Fe ranging from 0 to 0.28). At concentrations found in natural waters (4.5-25muM), citrate effectively inhibited ferric hydroxide nucleation and precipitation by forming a non-crystalline macromolecular complex (FeO(Fe3O12H3)Cit) detected in aqueous phase by electrospray ionization mass spectrometry (ESI-MS). Arsenate removal by nano magnetite was also retarded by a low concentration of citrate. The effectiveness of citrate was more significant at higher pH values. Possible mechanisms of citrate inhibition at low molar ratios were compared and discussed. This research demonstrated that the citrate impact upon arsenate removal should be considered when using the iron coagulation and precipitation method in water treatment plants.
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    Interaction of phosphonates onto the immobilized surface: application to scale control in oil and gas flow assurance
    (2013-07-19) Zhang, Nan; Tomson, Mason B.; Hirasaki, George J.; Bedient, Philip B.
    The flow assurance in oil and gas production faces several challenges related to scale formation and control. In order to assess scaling risk in pipes, set a realistic inhibitor limits for scale treatment and improve the efficiency of treatment techniques, a better understanding of the mechanisms that govern scale precipitation kinetics and the interaction between scale inhibitor and the immobilized surface is needed. In this study, a newly developed automatic titration method was firstly presented to simultaneously measure total alkalinity and weak organic acids concentrations of brine, which served as a robust tool to calculate the pH, bicarbonate concentration, and carbonate thermodynamic scaling tendencies at different conditions from downhole to wellhead. Scaling kinetics of CaCO3 and the phosphonate inhibitor (diethylenetriamine penta (DTPMP)) interaction with the CaCO3 surface was studied CaCO3 pre-coated steel tubing. Three stages including (1) induction, (2) initial deposition and (3) stable surface growth were observed during the scaling process, which can be described by the heterogeneous nucleation theory. With the presence of DTPMP, scaling process of CaCO3 was prevented by precipitation/dissolution of calcium phosphoante precipitates on/from the CaCO3 surface. DTPMP retention on the CaCO3 surface was facilitated by the coprecipitation of calcium carbonate and calcium phosphonate precipitates. Not only does this study contribute to the limited data base of scaling kinetics in absence and present with scale inhibitor, but also provides a new approach to better understand the inhibitor reaction with the subsurface.
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    Super-stretchable, Transparent Carbon Nanotube-Based Capacitive Strain Sensors for Human Motion Detection
    (Nature Publishing Group, 2013) Cai, Le; Song, Li; Luan, Pingshan; Zhang, Qiang; Zhang, Nan; Gao, Qingqing; Zhao, Duan; Zhang, Xiao; Tu, Min; Yang, Feng; Zhou, Wenbin; Fan, Qingxia; Luo, Jun; Zhou, Weiya; Ajayan, Pulickel M.; Xie, Sishen
    Realization of advanced bio-interactive electronic devices requires mechanically compliant sensors with the ability to detect extremely large strain. Here, we design a new multifunctional carbon nanotube (CNT) based capacitive strain sensors which can detect strains up to 300% with excellent durability even after thousands of cycles. The CNT-based strain gauge devices exhibit deterministic and linear capacitive response throughout the whole strain range with a gauge factor very close to the predicted value (strictly 1), representing the highest sensitivity value. The strain tests reveal the presented strain gauge with excellent dynamic sensing ability without overshoot or relaxation, and ultrafast response at sub-second scale. Coupling these superior sensing capabilities to the high transparency, physical robustness and flexibility, we believe the designed stretchable multifunctional CNT-based strain gauge may have various potential applications in human friendly and wearable smart electronics, subsequently demonstrated by our prototypical data glove and respiration monitor.