Effects of Acetate on Cation Exchange Capacity of a Zn-Containing Montmorillonite:Physicochemical Significance and Metal Uptake

Fundamental properties such as cation exchange capacity (CEC), permanent charge, pH(PZC), and metal uptake of a Zn-containing montmorillonite are modified, in a predictable manner, by a mild chemical treatment using acetate. Acetate treatment allows a controllable increase of the CEC of montmorillonite up to 180 mequiv/100 g. The CEC of the clay is increasing for decreasing Zn content, with a slope of Delta[Zn/Delta[CEC] approximate to -2. X-ray powder diffraction analysis shows that the lamellar structure of the clay remains unaltered by the acetate treatment, while XPS substantiates the removal of Zn. H(+) uptake data show that the intrinsic protonation pK values and concentration of the variable charge sites ( SOH) are not modified by the acetate treatment. In contrast, the concentration of the permanent charge sites ( X(-)) increased linearly with Zn removal by acetate, leading to a significant H(+) and Cd(2+) uptake enhancement. A physical model is suggested where acetate removes Zn ions strongly bound in the clay, and this in turn modulates the permanent charge and the CEC of the clay

Enhancing photocatalytic degradation of the cyanotoxin microcystin-LR with the addition of sulfate-radical generating oxidants.

This study investigated the coupling of sulfate radical generating oxidants, (persulfate, PS and peroxymonosulfate, PMS) with TiO2 photocatalysis for the degradation of microcystin-LR (MC-LR). Treatment efficiency was evaluated by estimating the electrical energy per order (EEO). Oxidant addition at 10 mg/L reduced the energy requirements of the treatment by 60% and 12% for PMS and PS, respectively compared with conventional photocatalysis. Quenching studies indicated that both sulfate and hydroxyl radicals contributed towards the degradation of MC-LR for both oxidants, while Electron Paramagnetic Resonance (EPR) studies confirmed that the oxidants prolonged that lifetime of both radicals (concentration maxima shifted from 10 to 20min), allowing for bulk diffusion and enhancing cyanotoxin removal. Structural identification of transformation products (TPs) formed during all treatments, indicated that early stage degradation of MC-LR occurred mainly on the aromatic ring and conjugated carbon double bonds of the ADDA amino acid. In addition, simultaneous hydroxyl substitution of the aromatic ring and the conjugated double carbon bonds of ADDA (m/z= 1027.5) are reported for the first time. Oxidant addition also increased the rates of formation/degradation of TPs and affected the overall toxicity of the treated samples. The detoxification and degradation order of the treatments was UVA/TiO2/PMS > UVA/TiO2/PS>> UVA/TiO2

The polymer phase of the TDAE-C60_{60} organic ferromagnet

The high-pressure Electron Spin Resonance (ESR) measurements were preformed on TDAE-C$_{60}$ single crystals and stability of the polymeric phase was established in the $P - T$ parameter space. At 7 kbar the system undergoes a ferromagnetic to paramagnetic phase transition due to the pressure-induced polymerization. The polymeric phase remains stable after the pressure release. The depolymerization of the pressure-induced phase was observed at the temperature of 520 K. Below room temperature, the polymeric phase behaves as a simple Curie-type insulator with one unpaired electron spin per chemical formula. The TDAE$^+$ donor-related unpaired electron spins, formerly ESR-silent, become active above the temperature of 320 K and the Curie-Weiss behavior is re-established.Comment: Submitted to Phys. Rev.

Alzheimer's Aβ Peptides with Disease-Associated N-Terminal Modifications: Influence of Isomerisation, Truncation and Mutation on Cu2+ Coordination

coordination of various Aβ peptides has been widely studied. A number of disease-associated modifications involving the first 3 residues are known, including isomerisation, mutation, truncation and cyclisation, but are yet to be characterised in detail. In particular, Aβ in plaques contain a significant amount of truncated pyroglutamate species, which appear to correlate with disease progression. coordination modes between pH 6–9 with nominally the same first coordination sphere, but with a dramatically different pH dependence arising from differences in H-bonding interactions at the N-terminus. coordination of Aβ, which may be critical for alterations in aggregation propensity, redox-activity, resistance to degradation and the generation of the Aβ3–× (× = 40/42) precursor of disease-associated Aβ3[pE]–x species

Bandwidth-constrained queries in sensor networks

Sensor networks consist of battery-powered wireless devices that are required to operate unattended for long periods of time. Thus, reducing energy drain is of utmost importance when designing algorithms and applications for such networks. Aggregate queries are often used by monitoring applications to assess the status of the network and detect abnormal behavior. Since radio transmission often constitutes the biggest factor of energy drain in a node, in this paper we propose novel algorithms for the evaluation of bandwidth- constrained queries over sensor networks. The goal of our techniques is, given a target bandwidth utilization factor, to program the sensor nodes in a way that seeks to maximize the accuracy of the produced query results at the monitoring node, while always providing strong error guarantees to the monitoring application. This is a distinct difference of our framework from previous techniques that only provide probabilistic guarantees on the accuracy of the query result. Our algorithms are equally applicable when the nodes have ample power resources, but bandwidth consumption needs to be minimized, for instance in densely distributed networks, to ensure proper operation of the nodes. Our experiments with real sensor data show that bandwidth-constrained queries can substantially reduce the number of messages in the network while providing very tight error bounds on the query result. © 2006 Springer-Verlag

A humic-acid-like polycondensate produced with no use of catalyst

The synthesis and physicochemical characterization of a water soluble humic-acid-like polycondensate (HALP), which mimics fundamental physicochemical and spectroscopic properties of natural humic acids is presented. The polymer can be synthesized under ambient O2 by oxidative co-polymerization of gallic (GA) and protocatechuic (PA) acid at pH >9, with no need for a catalyst. Solid state 13C NMR spectra for GA-PA-HALP show that ring-opening reactions of GA, PA monomers are involved in GA-PA-HALP formation. EPR spectroscopy shows that GA-PA-HALP contains stable phenol-based radicals, with pH-dependent concentration. The H-binding profile of GA-PA-HALP follows the NICA-Donnan model, with two sets of distributed pKa values in the range 4-6 corresponding to carboxyl groups, and 7-9 corresponding to phenolic groups, as in natural HA. GA-PA-HALP bears a permanent negative charge Q0 = -2.3 equiv kg-1 which is higher than the literature Q0 values of -1 to -2 equiv kg-1 observed for natural HAs. A critical comparison of the present data with literature data is provided. © 2009 Elsevier Inc. All rights reserved

A novel bentonite-humic acid composite material Bephos™ for removal of phosphate and ammonium from eutrophic waters

A novel low-cost composite material was prepared (Bephos™) by embedding Fe, Cu ions and humic acid using in the interlayer space of a natural bentonite. Bench-scale batch experiments were performed to examine its efficiency as adsorbent for phosphate and ammonium removal from natural waters. Phosphate and ammonium uptake was evaluated vs. pH in adsorption kinetics and adsorption isotherms. The effect of salinity (fresh, brackish and marine waters) and adsorption thermodynamics were also investigated. Bephos™ exhibits higher adsorption than other pertinent materials. Moreover Bephos™ is cable for simultaneous adsorption of both phosphorus and ammonia and this is an important advantage against other materials used to restore eutrophic water bodies. The maximum phosphate and ammonium adsorption capacities were 26.5. mg/g and 202.1. mg/g respectively. Bephos™ can function efficiently within a wide range of pH, e.g. 5-9. Adsorption kinetics showed that more than 90% and 70% removal of phosphate and ammonium respectively from water within 30. min. Bephos™ is potent for remediation of phosphate and ammonium at low concentrations that occur in natural water ecosystems. © 2013 Elsevier B.V

Eutrophication control using a novel bentonite humic-acid composite material Bephos™

The main objective of the present study was to estimate the efficiency of Bephos™ as an active capping agent preventing the phosphate release from eutrophic lake sediments. Bephos™ was compared with unmodified bentonite (N-bentonite) and natural zeolite (N-zeolite), in a ratio 1/10/10 respectively. Bephos™ as a P-inactivation agent resulted in about ∼96.6% reduction of the phosphate flux and ∼75.2% reduction of the ammonium flux from the sediments respectively. N-Zeolite and N-bentonite as capping materials resulted in about 64% and 91.8% reduction of the phosphorus flux and in about 70% and 35.6% reduction of the ammonium flux from the sediments respectively. Moreover, an additional purpose of this study was to investigate the different P-forms present in sediments, their contributions to the P-loadings of the ecosystem and also the effect of Bephos™ amendment on P-binding properties of sediments. The results show that Bephos™ restrained P release from the sediments, reducing the proportion of P-mobile in sediments, which was transformed into non-reactive species. The application of Bephos™ caused an increase in the mass of P present in the more refractory 'apatite bound P' fraction compared to P-mobile, and also more P was stored in the residual P fraction of sediment post-application