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1.
J Colloid Interface Sci ; 614: 603-616, 2022 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-35123214

RESUMO

This is the first report of the metal Fe-Ti oxide/biochar (Fe2TiO5/BC) composite for simultaneous removal of aqueous Pb2+, Cr6+, F- and methylene blue (MB). Primary Fe2TiO5 nano particles and aggregates were dispersed on a high surface area Douglas fir BC (∼700 m2/g) by a simple chemical co-precipitation method using FeCl3 and TiO(acac)2 salts treated by base and heated to 80 °C. This was followed by calcination at 500 °C. This method previously was used without BC to make the neat mixed oxide Fe2TiO5, exhibiting a lower energy band gap than TiO2. Adsorption of Cr(VI), Pb(II), fluoride, and MB on Fe2TiO5/BC was studied as a function of pH, equilibrium time, initial adsorbate concentration, and temperature. Adsorption isotherm studies were conducted at 5, 25, and 45 ℃ and kinetics for all four adsorbates followed the pseudo second order model. Maximum Langmuir adsorption capacities for Pb2+, Cr6+, F- and MB at their initial pH values were 141 (pH 2), 200 (pH 5), 36 (pH 6) and 229 (pH 6) mg/g at 45 ℃ and 114, 180, 26 and 210 mg/g at 25 ℃, respectively. MB was removed from the water on Fe2TiO5/BC by synergistic adsorption and photocatalytic degradation at pH 3 and 6 under UV (365 nm) light irradiation. Cr6+, Pb2+, F-, and MB each exhibited excellent removal capacities in the presence of eight different competitive ions in simulated water samples. The removal mechanisms on Fe2TiO5/BC and various competitive ion interactions were proposed. Some iron ion leaching at pH 3 catalyzed Photo-Fenton destruction of MB. Fe2TiO5, BC, and Fe2TiO5/BC bandgaps were studied to help understand photocatalysis of MB and to advance supported metal oxide photodegradation using smaller energy band gaps than the larger bandgap of TiO2 for water treatment. A long range goal is to photocatalytically destroy some sorbates with adsorbents to avoid the need for regeneration steps.


Assuntos
Azul de Metileno , Poluentes Químicos da Água , Adsorção , Carvão Vegetal , Cromo/análise , Fluoretos , Ferro , Cinética , Chumbo , Óxidos , Titânio , Poluentes Químicos da Água/análise
2.
J Environ Manage ; 296: 113186, 2021 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-34256294

RESUMO

Biochar adsorbents can remove environmental pollutants and the remediation of Cr(VI) and nitrate are considered. Cr(VI) is a proven carcinogen causing serious health issues in humans and nitrate induced eutrophication causes negative effect on aquatic systems around the world. Douglas fir biochar (DFBC), synthesized by fast pyrolysis during syn gas production, was treated with aniline. Then, a polyaniline biochar (PANIBC) composite containing 47 wt% PANI was prepared by precipitating PANI on DFBC surfaces by oxidative chemical polymerization of aniline in 2M HCl. PANIBC exhibited a point of zero charge (PZC) of 3.0 and 8.2 m2/g BET (N2) surface area. This modified biochar was characterized by thermogravimetric analysis (TGA), scanning electron microscopy (SEM) morphology and surface elements, and oxidation states by X-ray photoelectron spectroscopy (XPS). PANIBC exhibited positive surface charge below pH 3, making it an outstanding adsorbent, for Cr(VI) removal. Cr(VI) and nitrate removal mechanisms are presented based on XPS analysis. DFBC and PANIBC Cr(VI) and nitrate adsorption data were fitted to Langmuir and Freundlich isotherm models with maximum Langmuir adsorption capacities of 150 mg/g and 72 mg/g, respectively. Cr(VI) and nitrate removal at pH 2 and 6 were evaluated by reducing the amount of PANI (9 wt%) dispersed on to DFBC. Adsorption capacities verses temperature studies revealed that both Cr(VI) and nitrate adsorption are endothermic and thermodynamically favored. Regeneration studies were conducted on both DFBC and PANIBC using 0.1M NaOH and PANIBC exhibited excellent sorption capacities for Cr(VI) and nitrate in lake water samples and in the presence of competitive ions.


Assuntos
Cromo , Poluentes Químicos da Água , Adsorção , Compostos de Anilina , Carvão Vegetal , Cromo/análise , Humanos , Concentração de Íons de Hidrogênio , Cinética , Nitratos , Água , Poluentes Químicos da Água/análise
3.
J Colloid Interface Sci ; 597: 182-195, 2021 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-33866210

RESUMO

Phosphate is a primary plant nutrient, serving integral role in environmental stability. Excessive phosphate in water causes eutrophication; hence, phosphate ions need to be harvested from soil nutrient levels and water and used efficiently. Fe-Mg (1:2) layered double hydroxides (LDH) were chemically co-precipitated and widely dispersed on a cheap, commercial Douglas fir biochar (695 m2/g surface area and 0.26 cm3/g pore volume) byproduct from syn gas production. This hybrid multiphase LDH dispersed on biochar (LDHBC) robustly adsorbed (~5h equilibrium) phosphate from aqueous solutions in exceptional sorption capacities and no pH dependence between pH 1-11. High phosphate Langmuir sorption capacities were found for both LDH (154 to 241 mg/g) and LDH-modified biochar (117 to 1589 mg/g). LDHBC was able to provide excellent sorption performance in the presence of nine competitive anion contaminants (CO32-, AsO43-, SeO42-, NO3-, Cr2O72-, Cl-, F-, SO42-, and MoO42-) and also upon remediating natural eutrophic water samples. Regeneration was demonstrated by stripping with aqueous 1 M NaOH. No dramatic performance drop was observed over 3 sorption-stripping cycles for low concentrations (5 ppm). The adsorbents and phosphate-laden adsorbents were characterized using Elemental analysis, BET, PZC, TGA, DSC, XRD, SEM, TEM, and XPS. The primary sorption mechanism is ion-exchange from low to moderate concentrations (10-500 ppm). Chemisorption and stoichiometric phosphate compound formation were also considered at higher phosphate concentrations (>500 ppm) and at 40 °C. This work advances the state of the art for environmentally friendly phosphate reclamation. These phosphate-laden adsorbents also have potential to be used as a slow-release phosphate fertilizer.


Assuntos
Poluentes Químicos da Água , Adsorção , Carvão Vegetal , Hidróxidos , Cinética , Fosfatos , Água , Poluentes Químicos da Água/análise
4.
Environ Res ; 192: 110283, 2021 01.
Artigo em Inglês | MEDLINE | ID: mdl-33022217

RESUMO

Biochar-based hybrid composites containing added nano-sized phases are emerging adsorbents. Biochar, when functionalized with nanomaterials, can enhance pollutant removal when both the nanophase and the biochar surface act as adsorbents. Three different pine wood wastes (particle size < 0.5 mm, 10 g) were preblended with 1 wt% of three different graphenes in aqueous suspensions, designated as G1, G2, and G3. G1 (SBET, 8.1 m2/g) was prepared by sonicating graphite made from commercial synthetic graphite powder (particle size 7-11 µm). G2 (312.0 m2/g) and G3 (712.0 m2/g) were purchased commercial graphene nanoplatelets (100 mg in 100 mL deionized water). These three pine wood-graphene mixtures were pyrolyzed at 600 °C for 1 h to generate three graphene-biochar adsorbents, GPBC-1, GPBC-2, and GPBC-3 containing 4.4, 4.9, and 5.0 wt% of G1, G2, and G3 respectively. Aqueous Cu2+ adsorption capacities were 10.6 mg/g (GPBC-1), 4.7 mg/g (GPBC-2), and 5.5 mg/g (GPBC-3) versus 7.2 mg/g for raw pine wood biochar (PBC) (0.05 g adsorbent dose, Cu2+ 75 mg/L, 25 mL, pH 6, 24 h, 25 ± 0.5 °C). Increased graphene surface areas did not result in adsorption increases. GPBC-1, containing the lowest nanophase surface area with the highest Cu2+ capacity, was chosen to evaluate its Cu2+ adsorption characteristics further. Results from XPS showed that the surface concentration of oxygenated functional groups on the GPBC-1 is greater than that on the PBC, possibly contributing to its greater Cu2+ removal versus PBC. GPBC-1 and PBC uptake of Cu2+ followed the pseudo-second-order kinetic model. Langmuir maximum adsorption capacities and BET surface areas were 18.4 mg/g, 484.0 m2/g (GPBC-1) and 9.2 mg/g, 378.0 m2/g (PBC). This corresponds to 3.8 × 10-2 versus 2.4 × 10-2 mg/m2 of Cu2+ removed on GPBC-1 (58% more Cu2+ per m2) versus PBC. Cu2+ adsorption on both these adsorbents was spontaneous and endothermic.


Assuntos
Grafite , Pinus , Poluentes Químicos da Água , Adsorção , Carvão Vegetal , Cobre , Cinética , Água , Poluentes Químicos da Água/análise , Madeira/química
5.
Chemosphere ; 269: 128409, 2021 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-33069440

RESUMO

Biochar has become a popular research topic in sustainable chemistry for use both in agriculture and pollution abatement. To enhance aqueous Cr(VI), Pb(II) and Cd(II) removal efficiency, high surface area (535 m2/g) byproduct Douglas fir biochar (DFBC) from commercial syn-gas production obtained by fast pyrolysis (900-1000 °C, 1-10 s), was subjected to a KOH activation. KOH-activated biochar (KOHBC) underwent a remarkable surface area increase to 1049 m2/g and a three-fold increase in pore volume (BET analysis). Batch sorption studies on KOHBC verses pH revealed that the highest chromium, lead and cadmium removal capacities occurred at pH 2.0, 5.0 and 6.0, respectively. KOHBC exhibited much higher adsorption capacities than unactivated DFBC. Heavy metal loadings onto KOHBC were characterized by scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. Sorption of Cr(VI), Pb(II) and Cd(II) all followed pseudo-second order kinetics and the Langmuir adsorption model. The highest Langmuir adsorption capacities at the respective pH's of maximum adsorption were 140.0 mg g-1 Pb(II), 127.2 mg g-1 Cr(VI) and 29.0 mg g-1 Cd(II). Metal ions spiked into natural and laboratory waste water systems exhibited high sorption capacities. Desorption studies carried out using 0.1 M HCl revealed that Pb(II) adsorption onto the KOHBC surface is reversible. Portions of Cd(II) and Cr(VI) adsorbed strongly onto KOHBC were unable to be desorbed by 0.1 M HCl and 0.1 M NaOH.


Assuntos
Pseudotsuga , Poluentes Químicos da Água , Adsorção , Cádmio , Carvão Vegetal , Cromo/análise , Concentração de Íons de Hidrogênio , Cinética , Chumbo , Poluentes Químicos da Água/análise
6.
J Colloid Interface Sci ; 587: 767-779, 2021 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-33309243

RESUMO

Commercialization of novel adsorbents technology for providing safe drinking water must consider scale-up methodological approaches to bridge the gap between laboratory and industrial applications. These imply complex matrix analysis and large-scale experiment designs. Arsenic concentrations up to 200-fold higher (2000 µg/L) than the WHO safe drinking limit (10 µg/L) have been reported in Latin American drinking waters. In this work, biochar was developed from a single, readily available, and taxonomically identified woody bamboo species, Guadua chacoensis. Raw biochar (BC) from slow pyrolysis (700 °C for 1 h) and its analog containing chemically precipitated Fe3O4 nanoparticles (BC-Fe) were produced. BC-Fe performed well in fixed-bed column sorption. Predicted model capacities ranged from 8.2 to 7.5 mg/g and were not affected by pH 5-9 shift. The effect of competing matrix chemicals including sulfate, phosphate, nitrate, chloride, acetate, dichromate, carbonate, fluoride, selenate, and molybdate ions (each at 0.01 mM, 0.1 mM and 1 mM) was evaluated. Fe3O4 enhanced the adsorption of arsenate as well as phosphate, molybdate, dichromate and selenate. With the exception of nitrate, individually competing ions at low concentration (0.01 mM) did not significantly inhibit As(V) sorption onto BC-Fe. The presence of ten different ions in low concentrations (0.01 mM) did not exert much influence and BC-Fe's preference for arsenate, and removal remained above 90%. The batch and column BC and BC-Fe adsorption capacities and their ability to provide safe drinking water were evaluated using a naturally contaminated tap water (165 ± 5 µg/L As). A 960 mL volume (203.8 Bed Volumes) of As-free drinking water was collected from a 1 g BC-Fe fixed bed. Adsorbent regeneration was attempted with (NH4)2SO4, KOH, or K3PO4 (1 M) strippers. Potassium phosphate performed the best for BC-Fe regeneration. Safe disposal options for the exhausted adsorbents are proposed. Adsorbents and their As-laden analogues (from single and multi-component mixtures) were characterized using high resolution XPS and possible competitive interactions and adsorption pathways and attractive interactions were proposed including electrostatic attractions, hydrogen bonding and weak chemisorption to BC phenolics. Stoichiometric precipitation of metal (Mg, Ca and Fe) oxyanion (phosphate, molybdate, selenate and chromate) insoluble compounds is considered. The use of a packed BC-Fe cartridge to provide As-free drinking water is presented for potential commercial use. BC-Fe is an environmentally friendly and potentially cost-effective adsorbent to provide arsenic-free household water.


Assuntos
Arsênio , Sasa , Poluentes Químicos da Água , Purificação da Água , Adsorção , Arsênio/análise , Carvão Vegetal , Compostos Férricos , Ferro , Cinética , Transferência de Tecnologia , Poluentes Químicos da Água/análise
7.
Langmuir ; 37(1): 499-508, 2021 01 12.
Artigo em Inglês | MEDLINE | ID: mdl-33372781

RESUMO

To assess the feasibility of utilizing reagent-loaded, porous polymeric nanocapsules (NCs) for chemical and biochemical sensor design, the surfaces of the NCs were decorated with 3,4-ethylenedioxythiophene (EDOT) moieties. The pores in the capsule wall allow unhindered bidirectional diffusion of molecules smaller than the programmed pore sizes, while larger molecules are either entrapped inside or blocked from entering the interior of the nanocapsules. Here, we investigate two electrochemical deposition methods to covalently attach acrylate-based porous nanocapsules with 3,4-ethylenedioxythiophene moieties on the nanocapsule surface, i.e., EDOT-decorated NCs to the surface of an existing PEDOT film: (1) galvanostatic or bilayer deposition with supporting EDOT in the deposition solution and (2) potentiostatic deposition without supporting EDOT in the deposition solution. The distribution of the covalently attached NCs in the PEDOT films was studied by variable angle FTIR-ATR and XPS depth profiling. The galvanostatic deposition of EDOT-decorated NCs over an existing PEDOT (tetrakis(pentafluorophenyl)borate) [PEDOT(TPFPhB)] film resulted in a bilayer structure, with an interface between the NC-free and NC-loaded layers, that could be traced with variable angle FTIR-ATR measurements. In contrast, the FTIR-ATR and XPS analyses of the films deposited potentiostatically from a solution without EDOT and containing only the EDOT-decorated NCs showed small amounts of NCs in the entire cross section of the films.

8.
Inorg Chem ; 59(8): 5433-5446, 2020 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-32237741

RESUMO

A group of copper complexes supported by polydentate pyridylamide ligands H2bpda and H2ppda were synthesized and characterized. The two Cu(II) dimers [CuII2(Hbpda)2(ClO4)2] (1) and [CuII2(ppda)2(DMF)2] (2) were constructed by using neutral ligands to react with Cu(II) salts. Although the dimers showed similar structural features, the second-sphere interactions affect the structures differently. With the application of Et3N, the tetranuclear cluster (HNEt3)[CuII4(bpda)2(µ3-OH)2(ClO4)(DMF)3](ClO4)2 (3) and hexanuclear cluster (HNEt3)2[CuII6(ppda)6(H2O)2(CH3OH)2](ClO4)2 (4) were prepared under similar reaction conditions. The symmetrical and unsymmetrical arrangement of the ligand donors in ligands H2bpda and H2ppda led to the dramatic conformation difference of the two Cu(II) complexes. As part of our effort to explore mixed-valence copper chemistry, the triple-decker pentanuclear cluster [CuII3CuI2(bpda)3(µ3-O)] (5) was prepared. XPS examination demonstrated the localized mixed-valence properties of complex 5. Magnetic studies of the clusters with EPR evidence showed either weak ferromagnetic or antiferromagnetic interactions among copper centers. Due to the trigonal-planar conformation of the trinuclear Cu(II) motif with the µ3-O center, complex 5 exhibits geometric spin frustration and engages in antisymmetric exchange interactions. DFT calculations were also performed to better interpret spectroscopic evidence and understand the electronic structures, especially the mixed-valence nature of complex 5.

9.
ACS Appl Mater Interfaces ; 12(8): 9248-9260, 2020 Feb 26.
Artigo em Inglês | MEDLINE | ID: mdl-31990524

RESUMO

Oil spills cause massive loss of aquatic life. Oil spill cleanup can be very expensive, have secondary environmental impacts, or be difficult to implement. This study employed five different adsorbents: (1) commercially available byproduct Douglas fir biochar (BC) (SA ∼ 695 m2/g, pore volume ∼ 0.26 cm3/g, and pore diameter ∼ 13-19.5 Å); (2) BC modified with lauric acid (LBC); (3) iron oxide-modified biochar (MBC); (4) LBC modified with iron oxide (LMBC); and (5) MBC modified with lauric acid (MLBC) for oil recovery. Transmission, engine, machine, and crude oils were used to simulate oil spills and perform adsorption experiments. All five adsorbents adsorbed large quantities of each oil in fresh and simulated seawater with only a slight pH dependence, fast kinetics (sorptive equilibrium reached before 15 min), and high regression fits to the pseudo-second-order kinetic model. The Sips isotherm model oil sorption capacities for these sorbents were in the range ∼3-11 g oil/1 g adsorbent. Lauric acid-decorated (60-2 wt %) biochars gave higher oil adsorption capacities than the undecorated biochar. Lauric acid enhances biochar hydrophobicity and its water contact angle and reduces water influx into biochar's porosity preventing it from sinking in water for 3 weeks. These features were observed even at 2% wt of lauric acid (sinks only after 2 weeks). Magnetization by magnetite nanoparticle deposition onto BC and LBC allows the recovery of the exhausted adsorbent by a magnetic field as an alternative to filtration. Oil sorption was endothermic. Recycling was demonstrated after toluene stripping. The oil-laden adsorbents' heating values were obtained, suggesting an alternative use of these spent adsorbents as a low-cost fuel after recovery, avoiding waste disposal costs. The initial and oil-laden adsorbents were characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer-Emmet-Teller surface area, contact angle, thermogravimetric analyses, differential scanning calorimetry, vibrating sample magnetometry, elemental analysis, and X-ray photoelectron spectroscopy.

10.
Sci Total Environ ; 706: 135943, 2020 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-31862592

RESUMO

Discarded bamboo culms of Guadua chacoensis were used for biochar remediation of aqueous As(V). Raw biochar (BC), activated biochar (BCA), raw Fe3O4 nanoparticle-covered biochar (BC-Fe), and activated biochar covered with Fe3O4 nanoparticles (BCA-Fe) were prepared, characterized and tested for As(V) aqueous adsorption. The goal is to develop an economic, viable, and sustainable adsorbent to provide safe arsenic-free water. Adsorbents were characterized using scanning electron microscopy (SEM) and energy dispersive analysis by X-ray (SEM-EDX), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (TEM-EDS), X-ray photoelectron spectroscopy (XPS), X-ray powder diffraction (XRD), Brunauer-Emmett-Teller surface area measurements (SBET), point of zero charge determinations (PZC), and elemental analysis. Activation with KOH increased the O/C ratio and the surface area of BC from 6.7 m2/g to 1239.7 m2/g (BCA). As(V) sorption equilibrium was achieved within <2 h for all four adsorbents and kinetics followed the pseudo-second-order model. At a 10 mg/L initial As(V) concentration, BC-Fe achieved a 100% removal (5 mg/g) over a pH 5 to 9 window. Sorption was endothermic on all four adsorbents and the capacities rose with the increasing temperature. Langmuir capacities at 40 °C for BC, BCA, BC-Fe, and BCA-Fe were 256, 217, 457, and 868 mg/g, respectively, and capacities were compared with other sorbents. Breakthrough fixed-bed column sorption was carried out for BC and BC-Fe producing 6.6 mg/g and 13.9 mg/g bed capacities, respectively. Potassium phosphate was a better As stripping agent than sodium bicarbonate. Performance of the adsorbents in an As(V)-spiked natural water and a naturally As(V)-contaminated domestic water were assessed. Robust arsenate sequestration occurred generating As-safe water (As <0.01 mg/L), despite the presence of competing ions. Stoichiometric precipitation of iron-arsenate complexes triggered by iron dissolution was also established.


Assuntos
Sasa , Purificação da Água , Adsorção , Arsênio , Carvão Vegetal , Compostos Férricos , Cinética , Nanopartículas Metálicas , Poluentes Químicos da Água
11.
J Environ Manage ; 250: 109429, 2019 Nov 15.
Artigo em Inglês | MEDLINE | ID: mdl-31491719

RESUMO

Magnetic Fe3O4/Douglas fir biochar composites (MBC) were prepared with a 29.2% wt. Fe3O4 loading and used to treat As(III)-contaminated water. Toxicity of As(III) (inorganic) is significantly greater than As(V) and more difficult to remove from water. Removal efficiency was optimized verses pH, contact time and initial concentration. Column sorption and regeneration were also studied. Adsorption kinetics data best fitted the pseudo second order model (R2 > 0.99). Adsorption was analyzed with three isotherm models at 20, 25 and 40 °C. The Sips isotherm showed the best fit at 25 °C with a 5.49 mg/g adsorption capacity, which is comparable with other adsorbents. MBC gave faster kinetics (~1-1.5 h) at pH 7 and ambient temperature than previous adsorbents. The Gibbs free energy (ΔG) of this spontaneous As(III) adsorption was -35 kJ/mol and ΔH = 70 kJ/mol was endothermic. Experiments were performed on industrial and laboratory wastewater samples in the presence of other co-existing contaminants (pharmaceutical residues, heavy metals ions and oxi-anions). The composite reduced the arsenic concentrations below the WHO's safe limit of 0.2 mg/L for waste water discharge. X-ray photoelectron spectroscopy (XPS) studies found As(III) and less toxic As(V) on Fe3O4 surfaces indicating adsorbed (or adsorbing) As(III) oxidation occurred upon contact with O2 and possibly dissolved Fe(III) or upon drying under oxic conditions. Under anoxic conditions magnetite to maghemite transformation drives the oxidation. A pH-dependent surface chemisorption mechanism was proposed governing adsorption aided by XPS studies vs pH.


Assuntos
Arsênio , Pseudotsuga , Poluentes Químicos da Água , Purificação da Água , Adsorção , Carvão Vegetal , Compostos Férricos , Óxido Ferroso-Férrico , Concentração de Íons de Hidrogênio , Cinética , Água
12.
J Colloid Interface Sci ; 511: 335-343, 2018 Feb 01.
Artigo em Inglês | MEDLINE | ID: mdl-29031153

RESUMO

The stability of citrate-residues on gold nanoparticles (AuNPs) against ligand displacement has been controversial. Using AuNPs synthesized with deuterated citrate in combination with in-situ surface-enhanced Raman spectroscopic (SERS) analysis, we report that both citrate-residues and solution impurities can be simultaneously adsorbed onto citrate-reduced AuNPs in solution. The citrate-residues can be readily displaced from AuNPs by organosulfur such as organothiols (RS-H), organodisuflide (R-S-S-R), and non-specific ligands including halides and adenine. Control experiments conducted on high-purity gold films sputter-coated onto silicone substrates indicate that air-borne and solvent-borne impurities rapidly contaminate the gold surfaces. Head-to-head comparison of ligand-functionalized AuNPs by in-situ SERS measurements verses those from the ex-situ X-ray photoelectron spectroscopic (XPS) measurements reveal that the impurity deposition can compromise the reliability of ex-situ XPS identification of surface adsorbates on AuNPs in solution. These insights are of general significance to nanoscience research given the broad interest in nanoparticle surface chemistry and popularity of XPS for nanomaterial characterizations.

13.
Anal Chem ; 89(6): 3508-3516, 2017 03 21.
Artigo em Inglês | MEDLINE | ID: mdl-28194968

RESUMO

To understand the rate determining processes during the equilibration of poly(3,4-ethylenedioxythiophene):polystyrenesulfonate-based (PEDOT(PSS)-based) solid contact (SC) ion-selective electrodes (ISEs), the surfaces of Pt, Au, and GC electrodes were coated with 0.1, 1.0, 2.0, and 4.0 µm thick galvanostatically deposited PEDOT(PSS) films. Next, potential vs time transients were recorded with these electrodes, with and without an additional potassium ion-selective membrane (ISM) coating, following their first contact with 0.1 M KCl solutions. The transients were significantly different when the multilayered sensor structures were assembled on Au or GC compared to Pt. The differences in the rate of equilibration were interpreted as a consequence of differences in the hydrophilicity of PEDOT(PSS) in contact with the substrate electrode surfaces based on X-ray photoelectron spectroscopy (XPS) and synchrotron radiation-XPS (SR-XPS) analysis of 10-100 nm thick PEDOT(PSS) films. The influence of the layer thickness of the electrochemically deposited PEDOT(PSS)-films on the hydrophilicity of these films has been documented by contact angle measurements over PEDOT(PSS)-coated Au, GC, and Pt electrode surfaces. This study demonstrates that it is possible to minimize the equilibration (conditioning) time of SC ISEs with aqueous solutions before usage by optimizing the thickness of the SC layer with a controlled ISM thickness. PEDOT(PSS)-coated Au and GC electrodes exhibit a significant negative potential drift during their equilibration in an aqueous solution. By coating the PEDOT(PSS) surface with an ISM, the negative potential drift is compensated by a positive potential drift related to the hydration of the ISM and activity changes at the PEDOT(PSS)|ISM interface. The potential drifts related to activity changes in the ISM have been determined by a novel adaptation of the "sandwich membrane" method.

14.
Inorg Chem ; 55(21): 11462-11472, 2016 Nov 07.
Artigo em Inglês | MEDLINE | ID: mdl-27783503

RESUMO

A series of copper complexes supported by a simple dipyridylamide ligand (H2pcp) were isolated and characterized. Treatment of H2pcp with NaH and copper(I) salts led to the formation of [Cu2(2pcp)2] (1a) and {Na[(Cu2(2pcp)2)2]PF6}n (1b). The X-ray crystal structures of both complexes feature CuICuI cores with close Cu···Cu interactions. Electrochemical studies of 1a showed a reversible one-electron oxidation wave in CH2Cl2. On the basis of the work on 1a, we began studying the mixed-valence copper species supported by this ligand. The reaction of H2pcp with Cu(OAc)2 and CuCl in different stoichiometries yielded [Cu2(2pcp)2Cl] (2) and [Cu3(2pcp)2Cl2] (3). X-ray crystallography and spectroscopic characterization suggested delocalized Cu1.5Cu1.5 core structures of both compounds. These results further inspired us to explore the coordination properties of H2pcp toward CuII ions. The complexes [HNEt3][Cu2(2pcp)3(ClO4)](ClO4) (4a), [Cu2(2pcp)3(NO3)] (4b), and [Cu2(2pcp)3(H2O)]BF4 (4c) featuring dinuclear CuIICuII cores were prepared and characterized by X-ray crystallography and spectroscopic methods. Structural analysis of these complexes implied that the accommodation of CuICuI, Cu1.5Cu1.5, and CuIICuII is attributed to the structural flexibility of the ligand H2pcp. Complexes 1a, 2, 3, and 4a were examined by X-ray photoelectron spectroscopy, which confirmed the oxidation state assignments. Computational studies were also performed to provide insight into the electronic structures of these complexes.

15.
Phys Rev Lett ; 114(9): 097201, 2015 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-25793845

RESUMO

Three-dimensional antiferromagnets with random magnetic anisotropy (RMA) that have been experimentally studied to date have competing two-dimensional and three-dimensional exchange interactions which can obscure the authentic effects of RMA. The magnetic phase diagram of Fe_{x}Ni_{1-x}F_{2} epitaxial thin films with true random single-ion anisotropy was deduced from magnetometry and neutron scattering measurements and analyzed using mean-field theory. Regions with uniaxial, oblique, and easy-plane anisotropies were identified. A RMA-induced glass region was discovered where a Griffiths-like breakdown of long-range spin order occurs.

16.
J Am Chem Soc ; 128(26): 8374-5, 2006 Jul 05.
Artigo em Inglês | MEDLINE | ID: mdl-16802783

RESUMO

The cytochrome P450 enzymes represent an important class of heme-containing enzymes. There is considerable interest in immobilizing these enzymes on a surface so that interactions between a single enzyme and other species can be studied with respect to electron transfer, homodimer or heterodimer interactions, or for construction of biological-based chips for standardizing cytochrome P450 metabolism or for high-throughput screening of pharmaceutical agents. Previous studies have generally immobilized P450 enzymes in a matrix or on a surface. Here, we have attached CYP2C9 to gold substrates such that the resulting construct maintains the ability to bind and metabolize substrates in the presence of NADPH and cytochrome P450 reductase. The activity of these chips is directly dependent upon the linkers used to attach CYP2C9 and to the presence of key molecules in the active site during enzyme attachment. A novel method to detect substrate-enzyme binding, namely, superconducting quantum interference device (SQUID) magnetometry, was used to monitor the binding of substrates. Most significantly, conditions that allow measurable CYP2C9 metabolism to occur have been developed.


Assuntos
Hidrocarboneto de Aril Hidroxilases/química , Hidrocarboneto de Aril Hidroxilases/metabolismo , Ouro/química , Ouro/metabolismo , Sítios de Ligação , Citocromo P-450 CYP2C9 , Humanos , NADP/química , NADP/metabolismo , NADPH-Ferri-Hemoproteína Redutase/química , NADPH-Ferri-Hemoproteína Redutase/metabolismo , Conformação Proteica , Estrutura Terciária de Proteína
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