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排序方式: 共有258条查询结果,搜索用时 15 毫秒
1.
Transport of surface-modified iron nanoparticle in porous media and application to arsenic(III) remediation 总被引:1,自引:0,他引:1
Sushil Raj Kanel Dhriti Nepal Bruce Manning Heechul Choi 《Journal of nanoparticle research》2007,9(5):725-735
The surface-modified iron nanoparticles (S-INP) were synthesized, characterized and tested for the remediation of arsenite
(As(III)), a well known toxic groundwater contaminant of concern. The S-INP material was fully dispersed in the aqueous phase
with a particle size distribution of 2–10 nm estimated from high-resolution transmission electron microscopy (HR-TEM). X-ray
photoelectron spectroscopy (XPS) revealed that an Fe(III) oxide surface film was present on S-INP in addition to the bulk
zero-valent Fe0 oxidation state. Transport of S-INP through porous media packed in 10 cm length column showed particle breakthroughs of 22.1,
47.4 and 60 pore volumes in glass beads, unbaked sand, and baked sand, respectively. Un-modified INP was immobile and aggregated
on porous media surfaces in the column inlet area. Results using S-INP pretreated 10 cm sand-packed columns containing ∼2 g
of S-INP showed that 100 % of As(III) was removed from influent solutions (flow rate 1.8 mL min−1) containing 0.2, 0.5 and 1.0 mg L−1 As(III) for 9, 7 and 4 days providing 23.3, 20.7 and 10.4 L of arsenic free water, respectively. In addition, it was found
that 100% of As(III) in 0.5 mg/L solution (flow rate 1.8 mL min−1) was removed by S-INP pretreated 50 cm sand packed column containing 12 g of S-INP for more than 2.5 months providing 194.4
L of arsenic free water. Field emission scanning electron microscopy (FE-SEM) showed S-INP had transformed to elongated, rod-like
shaped corrosion product particles after reaction with As(III) in the presence of sand. These results suggest that S-INP has
great potential to be used as a mobile, injectable reactive material for in-situ sandy groundwater aquifer treatment of As(III). 相似文献
2.
Howard C. Haas Monis J. Manning Martin H. Mach 《Journal of polymer science. Part A, Polymer chemistry》1970,8(7):1725-1730
Differential thermal analysis has been used to study the fusion of aqueous thermally reversible gels of gelatin and polyacrylylglycinamide (PAG). In the case of gelatin gels, endotherms close to the melting point are readily observed and these are sometimes preceeded by a small exothermic heat of gel reorganization. Calculations are presented to show that breaking of the gelatin gel network requires only a small fraction of the observed endothermic heat of fusion and that most of the heat is required for melting larger crystallites within gelatin aggregates and for perhaps a helix → coil transition. Failure to observe endotherms by DTA over the known temperature range of fusion of PAG gels is consistent with prior measurements and conclusions. The noncrystallinity of PAG gels and soluble aggregates together with a heat of crosslinking of only ?5 to ?10 kcal/mole of crosslinks places the heat of fusion of PAG gels outside the lower limits of DTA sensitivity. 相似文献
3.
-A spectrophotometric method has been developed which is applicable to the determination of extremely small quantities of osmium. Osmium is oxidised to the octovalent state, then added to an acidic aqueous solution containing 1:5-diphenylcarbohydrazide (DPC). After heating the aqueous solution to 65°, the osmium-DPC complex is extracted with chloroform. A molar absorbancy index of about 150,000 is obtained. From 7 to 25 μg of osmium can be determined with a coefficient of variation of 6%. It was established that FeIII, CuII, RuIII and AuIII seriously interfere in the determination of osmium by this method, while CrVI, NiII, MoVI, IrIII and chloride interfere only when present in relatively high concentrations. 相似文献
4.
M.J. Boylan J. Bellerby Josephine Newman A.R. Manning 《Journal of organometallic chemistry》1973,47(2):C33-C35
Whereas Co2(CO)8 and RNC (R= Me, Et, and Cy) react to give mixtures of [(RNC)5Co] [Co(CO)4] and the covalent, carbonyl-bridged [(RNC)mCo2(CO)8?m] derivatives (m = 1–3), [(π-dienyl)Fe(CO)2]2 give only [(π-dienyl)2Fe2(CO)4?n(CNR)n] complexes (dienyl = C5H5, MeC5H4 and C9H7; n = 1–2) that exist in solution as mixtures of cis- and trans-CO- and RNC-bridged tautomers with the μ-RNC species decreasing in importance as the bulk of R increases. 相似文献
5.
Knight-Scott J Farace E Simnad VI Siragy HM Manning CA 《Magnetic resonance imaging》2002,20(9):681-689
The (1)H NMR water signal from spectroscopic voxels localized in gray matter contains contributions from tissue and cerebral spinal fluid (CSF). A typically weak CSF signal at short echo times makes separating the tissue and CSF spin-lattice relaxation times (T(1)) difficult, often yielding poor precision in a bi-exponential relaxation model. Simulations show that reducing the variables in the T(1) model by using known signal intensity values significantly improves the precision of the T(1) measurement. The method was validated on studies on eight healthy subjects (four males and four females, mean age 21 +/- 2 years) through a total of twenty-four spectroscopic relaxation studies. Each study included both T(1) and spin-spin relaxation (T(2)) experiments. All volumes were localized along the Sylvian fissure using a stimulated echo localization technique with a mixing time of 10 ms. The T(2) experiment consisted of 16 stimulated echo acquisitions ranging from a minimum echo time (TE) of 20 ms to a maximum of 1000 ms, with a repetition time of 12 s. All T(1) experiments consisted of 16 stimulated echo acquisition, using a homospoil saturation recovery technique with a minimum recovery time of 50 ms and a maximum 12 s. The results of the T(2) measurements provided the signal intensity values used in the bi-exponential T(1) model. The mean T(1) values when the signal intensities were constrained by the T(2) results were 1055.4 ms +/- 7.4% for tissue and 5393.5 ms +/- 59% for CSF. When the signal intensities remained free variables in the model, the mean T(1) values were 1085 ms +/- 19.4% and 5038.8 ms +/- 113.0% for tissue and CSF, respectively. The resulting improvement in precision allows the water tissue T(1) value to be included in the spectroscopic characterization of brain tissue. 相似文献
6.
7.
Molality as a unit of measure for expressing 1H MRS brain metabolite concentrations in vivo 总被引:1,自引:0,他引:1
Knight-Scott J Haley AP Rossmiller SR Farace E Mai VM Christopher JM Manning CA Simnad VI Siragy HM 《Magnetic resonance imaging》2003,21(7):787-797
Absolute concentrations of cerebral metabolite in in vivo 1H magnetic resonance spectroscopy studies (1H-MRS) are widely reported in molar units as moles per liter of tissue, or in molal units as moles per kilogram of tissue. Such measurements require external referencing or assumptions as to local water content. To reduce the scan time, avoid assumptions that may be invalid under specific pathologies, and provide a universally accessible referencing procedure, we suggest that metabolite concentrations from 1H-MRS measurements in vivo be reported in molal units as moles per kilogram of tissue water. Using internal water referencing, a two-compartment water model, a simulated brain spectrum for peak identification, and a spectroscopic bi-exponential spin-spin relaxation segmentation technique, we measured the absolute concentrations for the four common 1H brain metabolites: choline (Cho), myo-inositol (mIno), phosphocreatine + creatine (Cr), and N-acetyl-aspartate (NAA), in the hippocampal region (n = 26) and along the Sylvian fissure (n = 61) of 35 healthy adults. A stimulated echo localization method (20 ms echo time, 10 ms mixing time, 4 s repetition time) yielded metabolite concentrations, uncorrected for metabolite relaxation or contributions from macromolecule resonances, that were expectantly higher than with molar literature values. Along the Sylvian fissure the average concentrations (coefficient of variation (CV)) in mmoles/kg of tissue water were 17.6 (12%) for NAA, 14.2 (9%) for Cr, 3.6 (13%) for Cho, and 13.2 (15%) for mIno. Respective values for the hippocampal region were 15.7 (20%), 14.7 (16%), 4.6 (19%), and 17.7 (26%). The concentrations of the two regions were significantly different (p = 0.001) for NAA, mIno, and Cho, a trend in agreement with previous studies. All gray matter Sylvian fissure CV values, except for NAA, were also in agreement with previous 1H-MRS gray matter studies. The reduced precision of the NAA concentration was attributed to overlapping signal contributions from glutamate and glutamine (Glx), suggesting that a detailed Glx model is critical for accurate quantitation of the NAA 2.02 ppm resonance. The reduced precision of the measurements in the hippocampal region was attributed to poor spectral resolution. 相似文献
8.
Although very bulky ligands e.g.(o-MeC6H4)3E or (μ-C10H7)3E (E = P or As) are inert, the normal photochemical or thermal reaction of tertiary phosphines or arsines, L, with [Mn2(CO)10] is CO substitution with the formation of [Mn2(CO)8(L)2] derivatives (I). At elevated temperatures some triarylarsines, R3As, undergo Lambert's reaction with ligand fragmentation to give [Mn2(CO)8(μ-AsR2)2] complexes (II) (R = Ph, p-MeOC6H4, p-FC6H4, or p-CIC6H4) even though, in the absence of [Mn2(CO)10] R3As are stable under the same conditions. Exceptional behaviour is exhibited by (p-Me2NC6H4)3- As which forms a product of type I; by some HN(C6H4)2AsR which give a product of type II as a result of loss of the non-aryl groups R = PhCH2, cyclo-C6H11, or MeO; and by Ph(α-C10H72P which is the only phosphine to form a product of type II, albeit in trace amounts only. The thermal decomposition of a n-butanol solution of [Mn2(CO)8(AsPh3)2] in a sealed tube gives C6H6 and [Mn2(CO)8(α-AsPh2)2], whilst in an open system in the presence of various tertiary phosphines, L, [Mn(H)(CO)3(L)2] are obtained. It is suggested that Lambert's reaction is a thermal fragmentation of [Mn(CO)4(AsR3]* radicals, the first to be recognised. They lose the radical R* which abstracts hydrogen from the solvent. The resulting [Mn(CO)4(AsR2)] moiety dimerises to [Mn2(CO)8-(α-AsR2)2]. the reaction is facilitated by the stability of the departing radical (e.g. PhCH2 or MeO) and, as the crowding about As is relieved, by its size (e.g. Ph, cyclo-C6H11, o-MeC6H4, or α-C10H7). In general, phosphine-substituted radicals [Mn(CO)4(PR)3]* do not undergo this decomposition, probably because the PC bonds are much stronger than AsC. 相似文献
9.
A.R. Manning Gerald McNally Reg Davis Christopher C. Rowland 《Journal of organometallic chemistry》1983,259(2):C15-C16
Depending on the substrate and the reaction conditions, SO2Cl2 is a useful reagent which brings about either chlorination or the formation of cationic species on reaction with transition metal carbonyl complexes. 相似文献
10.