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The coadsorption of ciprofloxacin (Cip) and Cu(II) on montmorillonite and kaolinite was studied between pH 4.0 and 9.5. At pH5.0, Cu(2+), Cip(+) and [Cu(II)(Cip(+/-))](2+) were the main species in solution. Between pH 5.0-7.0 [Cu(II)(Cip(+/-))](2+) was the dominant complex species. Above pH 8.0 [Cu(II)(Cip(-))(2)](0) precipitated. The presence of Cu(II) exerted no effect on the Cip sorption onto montmorillonite at low pH, whereas it increased Cip sorption on montmorillonite at pH6.0 due to the stronger affinity of Cip-Cu(II) complexes compared to sole Cip(-) or Cip(+/-), or Cip sorption via a Cu(II) bridge increased. In contrast, Cip increased Cu(II) adsorption on montmorillonite at pH7.0, whereas it decreased the adsorption of Cu(II) on kaolinite at pH 6.0-8.0. Cip was sorbed onto the kaolinite surface via interaction of carboxyl groups over the entire pH range. At pH 4.0-4.7, Cip(+) sorption onto kaolinite's positively charged surface was more favorable than sorption of Cip-Cu(II) complexes. Batch experiments and FTIR analyses indicated that the coordination between Cip(+/-), Cip(-) and Cu(II) were most likely present on kaolinite surface at pH 7.0. At pH8.0, Cu(OH)(2) (s) and [Cu(II)(Cip(-))(2)](0) precipitated out of solution or on the montmorillonite or kaolinite surface, which was not considered evidence for either the sorption of Cip or the adsorption of Cu(II).

Land application of wastes from concentrated animal feeding operations results in accumulation of copper (Cu) and antimicrobials in terrestrial systems. Interaction between Cu and antimicrobials may change Cu speciation in soil solution, and affect Cu bioavailability and toxicity. In this study, earthworms were exposed to quartz sand percolated with different concentrations of Cu and ciprofloxacin (CIP). Copper uptake by earthworms, its subcellular partition, and toxicity were studied. An increase in the applied CIP decreased the free Cu ion concentration in external solution and mortalities of earthworm, while Cu contents in earthworms increased. Copper and CIP in earthworms were fractionated into five fractions: a granular fraction (D), a fraction consisting of tissue fragments, cell membranes, and intact cells (E), a microsomal fraction (F), a denatured proteins fraction (G), and a heat-stable proteins fraction (H). Most of the CIP in earthworms was in fraction H. Copper was redistributed from the metal-sensitive fraction E to fractions D, F, G, and H with increasing CIP concentration. These results challenge the free ion activity model and suggested that Cu may be partly taken up as Cu-CIP complexes in earthworms, changing the bioavailability, subcellular distribution, and toxicity of Cu to earthworms.

The effects of copper (Cu2+), lead (Pb2+), and cadmium (Cd2+) on the sorption of 2,4,6-trichlorophenol (TCP) to and desorption from wheat ash and two commercial humic acids were studied. Copper and Pb2+ diminished the sorption of TCP onto all adsorbents, and made desorption of TCP less hysteretic from ash and German humic acids (GeHA), but more hysteretic from Tianjin humic acids (TJHA). Cadmium had little effect on TCP sorption and desorption. Fourier-transform infra red (FTIR) and X-ray absorption spectroscopy (XAS) in conjunction with fluorescence quenching studies provided insights into the mechanisms of TCP sorption and desorption as affected by Cu2+ and Pb2+, indicating that complexation of Cu2+ and Pb2+ was likely via carboxylic, hydroxylic and phenolic groups of ash, TJHA and GeHA, and that theses same functional groups also reacted with TCP during sorption. In contrast, Cd, a "soft acid", had no effect on the adsorption of TCP. Hydration shells of dense water around adsorbed Cu2+ and Pb2+ ions may also compete with TCP for available surface area. Fluorescence quenching of pyrene verified that for TJHA, Cu2+ and Pb2+ promoted the formation of supramolecular associations with interior hydrophobic regions separated from aqueous surroundings by exterior hydrophilic layers.

There are currently few studies on the dual effects of metal ions on the sorption of atrazine and conversely of atrazine on metal adsorption on multiwalled carbon nanotubes (MWCNTs). While a number of sorption models were considered to describe the sorption of atrazine on MWCNTs, the Polanyi-Manes model (PMM) fit the sorption isotherms well with the lowest mean weighted square errors. Atrazine was mainly adsorbed onto the surface and micropores of MWCNTs bundles or aggregates. Hydrogen bonding between azo and amino nitrogen of atrazine and functional groups on MWCNTs also occurred. Oxygenated functionalities, mainly carboxylic groups on MWCNTs surface, decreased the sorption of atrazine. Metal cations Cu2+, Pb2+, and Cd2+ diminished the sorption of atrazine depending on the oxygenated functionalities densities. The mechanisms ascribed were due to the formation of surface or inner-sphere complexes of Cu2+, Pb2+, and Cd2+ through carboxylic groups and hydration, which may occupy part of the surface of MWCNTs-O. The large hydration shell of metal cations may intrude or shield the hydrophobic and hydrophilic sites and indirectly compete with atrazine for surface sites, leading to the inhibition of atrazine adsorption around the metal-complexed moieties.

Adsorption equilibrium of 2,4,6-trichlorophenol (TCP) on multi-walled carbon nanotubes (MWCNTs) was investigated to explore the possibility of using MWCNTs for concentration, detection and removal of TCP from contaminated water. The adsorption of TCP on MWCNTs at pH 4 was nonlinear, reversible and best fit by a Polanyi-Manes model. Oxidation treatment increased surface area and introduced hydrophilic carboxylic groups to the defect sites of MWCNTs, hence increased the sorption of TCP and Cu(II) individually. Cu(II) suppressed the sorption of TCP on oxidized MWCNTs15A, but had little effect on as-grown MWCNTs15. TCP had no influence on Cu(II) sorption to either. The mechanisms of Cu(II) suppression effect on TCP adsorption are ascribed to the formation of surface complexes of Cu(II), which was verified by X-ray absorption spectroscopy. Cu(II) exerts a cross-linking effect of functional groups on adjacent tubes, creating a more tightly knit bundle and suppressing the condensation of TCP in the pore spaces between the tubes. The large hydration sphere around surface complexes of Cu(II) may also intrude or shield hydrophilic sites, leading to the "crowding out" of TCP around the Cu(II)-complexed sites. (C) 2009 Elsevier Ltd. All rights reserved.

Adsorption of cationic methylene blue and anionic orange II onto unmodified and surfactant-modified zeolites was studied using a batch equilibration method. The effects of equilibrium time, solution pH, and sorption temperature were examined. The results suggested that 2% sodium dodecyl benzenesulfonate (SDBS)- and 3% sodium dodecyl sulfate (SDS)-modified zeolites had higher adsorption capacities for methylene blue than the unmodified zeolite, while 2% cetylpyridinium bromide hexadecyl (CPB)- and 2% hexadecylammonium bromide (HDTMA)-modified zeolites were the best adsorbents for orange II. The adsorption conditions were optimized, and the mechanisms of adsorption are briefly discussed.

The effect of cationic copper (Cu2+) on the sorption of anionic metsulfuron-methyl (Me) and cationic difenzoquat (DZ) to peat and soil was studied using a batch equilibration method. The results showed that Cu2+ increased the sorption of Me but diminished the sorption of DZ. The adsorption of Cu2+ on the surface of peat and soil neutralizes the negative charge, making the zeta potential (zeta) of peat and soil less negative, consequently decreasing the repulsion between the surface of peat or soil and Me and increasing the sorption of Me. Cu2+ may additionally form Cu-Me complexes in aqueous solution, which was preferentially sorbed to peat and soil over the anionic Me. In contrast, the decreased negative surface charge of soil and peat does not favor the sorption of cationic DZ. Fourier transform infrared showed that DZ may be sorbed through interaction with -OH or -COOH groups of peat and soil and that surface complexes of Cu2+ may form through these groups. A competitive sorption between Cu2t and DZ for the same sorption sites is indicated, leading to mutual sorption inhibition of both cations.

Heavy metals and organic contaminants often coexist in soils. However, very little information is available regarding the effect of metals on the sorption of organic contaminants onto soils and/or of organic contaminants on metal sorption. In the present study, the effect of Cu on the sorption of p-nitrophenol on two Chinese soils was investigated using a batch-equilibration method for three conditions: Copper and p-nitrophenol were sorbed simultaneously, either Cu or p-nitrophenol was sorbed previously, or the soil colloidal phase was removed in part previously. The results suggested that Cu suppressed the sorption of p-nitrophenol on soils, whereas p-nitrophenol had little effect on Cu sorption because of the higher affinity of Cu for soils. Mechanisms of the Cu suppression effect were suggested by the results. First, large hydrated Cu occupy the siloxane surface of soils and prevent nonspecific interaction between p-nitrophenol and soils. Second, the soil colloidal phase is an effective adsorbent of p-nitrophenol; thus, more p-nitrophenol is retained in the aqueous phase. In addition, the aggregation of the colloidal particles may occur, which blocks soil pores, thereby decreasing the sorption of p-nitrophenol on the solid soil phase. Third, x-ray absorption spectroscopy revealed that Cu forms inner-sphere complexes with the carboxyl and hydroxyl functional moieties of the soil particles (clay minerals and organic matter). Fourier-transform infrared spectroscopy study indicated that these groups also react with p-nitrophenol through H-bond formation. These results suggested that Cu and p-nitrophenol have common sorption sites, at least in the soil organic matter domain, which is partially responsible for the observed overall Cu suppression effect.

The effect of lead on the sorption of 2,4,6-trichlorophenol (2,4,6-TCP) on soil and peat was investigated using a batch equilibration method. Lead markedly diminished the sorption of 2,4,6-TCP, and 2,4,6-TCP had little effect on lead sorption. Peat was a more effective adsorbent for 2,4,6-TCP than soil. The desorption hysteresis of 2,4,6-TCP verified the presence of high-energy sorption sites. Mechanisms of lead suppression effect on the 2,4,6-TCP sorption included the following: Firstly, lead accelerated the aggregation of colloids, the aggregates covered the surface in part and shrunk the pore sizes of the adsorbents, hence decreased the sorption of 2,4,6-TCP. Secondly, X-ray absorption and Fourier transform infrared spectroscopy study suggested that lead competed with 2,4,6-TCP for carboxylic, phenolic and Si-OH groups of organic matter and clay minerals. Such competition was partly responsible for the overall suppression effect of lead on the sorption of 2,4,6-TCP.

The effect of copper on adsorption of p-nitrophenol on two typical Chinese soils was investigated using a batch-equilibration method. Adsorption experiments were carried out when both copper and p-nitrophenol were adsorbed Simultaneously, and when copper was previously adsorbed oil soils. It was observed that adsorption of p-nitrophenol decreased with increasing copper concentrations thereby indicating a competition between copper and p-nitrophenol for occupying the adsorption sites oil soils. Moisture increased the hydrated sphere and the acidity of Water Surrounding the cation, which further reduced the adsorption of p-nitrophenol. Fourier transform infrared Spectroscopy study provided the direct evidence for the coordination of p-nitrophenol sorbed by soils with metal cation in n-hexane system. It was observed that the perturbations included a red shift of the v(sym) (NO) hand, a concomitant blue-shift of the v(sym) (NO) hand and a blue-shift of C-N hand when compared with the infrared spectra obtained from water solution. (c) 2005 Elsevier Ltd. All rights reserved.

Characterizing the photoactivation performance of highlighter fluorescence proteins (FPs) is crucial for screening better highlighter FPs and optimizing the photoactivation efficiency of a certain highlighter FP. Currently, photoactivation contrast and half-time values of photoactivation and photobleaching processes are used for such purpose. However, the relations among these parameters are not clear, and little guidance for practical experiments could be obtained from the half-time values. Here, we show that light dose dependent fluorescence curve, which is calculated from activation-intensity-dependent photoactivation and photobleaching rates, is capable of quantifying the photoactivation performance straightforwardly. Moreover, the photoactivation contrast is easily obtained from the curve.

Evidence exists for significant metal enrichment in particulate organic matter (POM) compared to other soil constituents, but the relevant mechanisms are poorly understood. In the present study, adsorption of the heavy metals Pb, Cu, and Cd on a loamy soil and on POM separated from this soil was investigated. The adsorption kinetic data can be well described with a pseudo-second order model, whereas the equilibrium data are well fitted by a Langmuir model. Adsorption isotherms and kinetics data, in addition to the influence of pH on metal adsorption, showed that POM had a much higher adsorption capacity for Pb, Cu, and Cd compared to the whole soil. Ionic strength effects on metal adsorption, Fourier transform infrared spectroscopy, x-ray absorption spectroscopy x-ray absorption spectroscopy including x-ray absorption near-edge structure and extended x-ray absorption fine-structure spectroscopy were employed to elucidate the adsorption mechanisms. The results suggested that Pb and Cu adsorption on POM was mainly through inner-sphere complexes with carboxyl and hydroxyl groups. Cadmium was possibly adsorbed via outer-sphere complexation, indicated by the influence of ionic strength on Cd adsorption.