Gary L. McPherson

Electron spin resonance spectra of V2+, Mn2+, and Ni2+ in single crystals of CsMgBr3 and CsMgI3

The electron spin resonance spectra of V2+, Mn2+, and Ni2+ doped into single crystals of CsMgBr3 and CsMgI3 have been studied at room and liquid nitrogen temperatures. The host lattices adopt the CsNiCl3 structure in which the basic structural feature is a linear array of [MX6]4− octahedra sharing faces. The site symmetry of the Mg2+ ion in this type of lattice is D3d, and the spectra can be described by an axial spin Hamiltonian. Well developed superhyperfine structure resulting from coupling with the bromine and iodine nuclei is observed in a number of the spectra at certain crystal orientations. The g values obtained for V2+ in CsMgI3 (g∥≃ g⊥≃ 2.04) are unusually large for a d3 ion and may be indicative of considerable metal to ligand delocalization. The spin Hamiltonian parameters for V2+, Mn2+, and Ni2+ in CsMgBr3 and CsMgI3, and the variation of the parameters from lattice to lattice is discussed.

Recent developments in materials synthesis in surfactant systems

The paper reviews the use of surfactant self-assembly to template the synthesis of polymers, ceramics with extended structures, and nanoparticles. The objective of the review is to highlight newer concepts linking self-assembly to materials nanostructure and to the realization of functional materials.

Magnetic and luminescence characteristics of dinuclear complexes of lanthanides and a phenolic schiff base macrocyclic ligand

Abstract The magnetic and luminescence characteristics of trimorphic homodinuclear macrocyclic complexes of lanthanides and a 2:2 phenolate Schiffs base L, derived from 2,6-diformyl- p -cresol and triethylenetetramine were determined. The complexes of Pr 3+ exhibit non-Curie-Weiss temperature dependent magnetic susceptibilities for which satisfactory fits to an axial relationship depends on crystal field splitting and a weak binuclear Pr 3+ Pr 3+ antiferromagnetic interaction. The exchange interaction parameters are z J ′ = −2.2, −4.4 and −7.0 cm −1 for ‘off-white’ Pr 2 L(NO 3 ) 4 ·2H 2 O, ‘yellow’ Pr 2 L(NO 3 ) 4 , and ‘orange’ Pr 2 L(NO 3 ) 2 (OH) 2 , respectively. In contrast, magnetic susceptibilities of the Ln 2 L(NO 3 ) 3 (OH) complexes (Ln = Dy, Ho) follow Curie-Weiss behavior over the entire temperature range (6 K to 300 K). The complexes of closed shell ions La 3+ , Lu 3+ , Y 3+ and those of the half filled shell ion Gd 3+ exhibit a strong ligand fluorescence in the 450 nm to 650 nm range with decay times at 77 K of 5–8 ns for Ln≠Gd or 2–4 ns for Ln = Gd. The complexes of Gd 3+ also exhibit a phosphorescence at 600 nm (decay time ∼ 200 μs). The complexes containing Ce 3+ , Eu 3+ , Tb 3+ and Er 3+ show very weak ligand luminescence indicative of effective quenching processes. Sensitized emission from the lanthanide ion is observed only with the Eu 3+ complexes ( 5 D o → 7 F j transitions). The emission lifetimes are on the order of 250 μs in the pure Eu 3+ complexes. The emission decay curves from dilute samples of Eu 3+ in ‘off-white’ La 2 L(NO 3 ) 4 n H 2 O show a noticeable rise time as well as a biphasic decay (fast component ∼ 400 μs; slow component ∼ 2500 μs). The luminescing states of L and Eu 3+ have a common excitation spectrum which is similar to the electronic absorption spectrum of L indicating that ligand-to-metal ion energy transfer processes are dominant. Overall the result if this study suggest that the spectral properties of the complexes are determined by the coordination mode of the lanthanide ions to the Schiff base portion of macrocyclic ligand.

Structures of CsMgBr3, CsCdBr3 and CsMgI3— diamagnetic linear chain lattices

Abstract The diamagnetic salts, CsMgBr 3 , CsCdBr 3 and CsMgI 3 , are shown by X-ray diffraction studies to adopt the CsNiCl 3 structure. This hexagonal lattice possesses a distinct one-dimensional character. The divalent metal ions in these salts are surrounded by octahedral arrays of halide ions ; however, there is a noticeable trigonal distortion. The structures are compared with those of other one-dimensional AMX 3 salts.

Multifunctional Iron−Carbon Nanocomposites through an Aerosol-Based Process for the In Situ Remediation of Chlorinated Hydrocarbons

Spherical iron-carbon nanocomposites were developed through a facile aerosol-based process with sucrose and iron chloride as starting materials. These composites exhibit multiple functionalities relevant to the in situ remediation of chlorinated hydrocarbons such as trichloroethylene (TCE). The distribution and immobilization of iron nanoparticles on the surface of carbon spheres prevents zerovalent nanoiron aggregation with maintenance of reactivity. The aerosol-based carbon microspheres allow adsorption of TCE, thus removing dissolved TCE rapidly and facilitating reaction by increasing the local concentration of TCE in the vicinity of iron nanoparticles. The strongly adsorptive property of the composites may also prevent release of any toxic chlorinated intermediate products. The composite particles are in the optimal range for transport through groundwater saturated sediments. Furthermore, those iron-carbon composites can be designed at low cost, the process is amenable to scale-up for in situ application, and the materials are intrinsically benign to the environment.

Fluorescence quenching of CdS nanocrystallites in AOT water-in-oil microemulsions

Abstract The luminescence of CdS nanoparticles suspended in “dry” AOT reversed micelles is quite intense but is quenched by water and even more effectively by thiol-containing compounds. Stern-Volmer plots provide information about the quenching efficiencies of various compounds. Of particular interest is 4-hydroxythiophenol which interacts strongly with the surfactant headgroups and thereby partitions to the nanoparticle surface. The quenching efficiency of 4-hydroxythiophenol is more than an order of magnitude greater than that of thiophenol. At the very low concentrations of 4-hydroxythiophenol required to bring about quenching, a remarkable recovery of fluorescence is observed upon continued irradiation. The fluorescence recovery is attributed to photochemical oxidation which consumes the hydroxythiophenol presumably giving a disulfide product.

Attachment of a hydrophobically modified biopolymer at the oil-water interface in the treatment of oil spills.

The stability of crude oil droplets formed by adding chemical dispersants can be considerably enhanced by the use of the biopolymer, hydrophobically modified chitosan. Turbidimetric analyses show that emulsions of crude oil in saline water prepared using a combination of the biopolymer and the well-studied chemical dispersant (Corexit 9500A) remain stable for extended periods in comparison to emulsions stabilized by the dispersant alone. We hypothesize that the hydrophobic residues from the polymer preferentially anchor in the oil droplets, thereby forming a layer of the polymer around the droplets. The enhanced stability of the droplets is due to the polymer layer providing an increase in electrostatic and steric repulsions and thereby a large barrier to droplet coalescence. Our results show that the addition of hydrophobically modified chitosan following the application of chemical dispersant to an oil spill can potentially reduce the use of chemical dispersants. Increasing the molecular weight of the biopolymer changes the rheological properties of the oil-in-water emulsion to that of a weak gel. The ability of the biopolymer to tether the oil droplets in a gel-like matrix has potential applications in the immobilization of surface oil spills for enhanced removal.

Multifunctional Colloidal Particles for in Situ Remediation of Chlorinated Hydrocarbons

Effective in situ injection technology for the remediation of dense nonaqueous phase liquids (DNAPLs) such as trichloroethylene (TCE) requires the use of decontamination agents that effectively migrate through the soil media and react efficiently with dissolved TCE and bulk TCE. We describe the use of a novel decontamination system containing highly uniform carbon microspheres in the optimal size range for transport through the soil. The microspheres are enveloped in a polyelectrolyte (carboxymethyl cellulose, CMC) to which a bimetallic nanoparticle system of zero-valent iron and Pd is attached. The carbon serves as a strong adsorbent to TCE, while the bimetallic nanoparticle system provides the reactive component. The polyelectrolyte serves to stabilize the carbon microspheres in aqueous solution. The overall system resembles a colloidal micelle with a hydrophilic shell (polyelectrolyte coating) and hard hydrophobic core (carbon). In contact with bulk TCE, there is a sharp partitioning of the system to the TCE side of the interface due to the hydrophobicity of the core. These multifunctional systems appear to satisfy criteria related to remediation and are made with potentially environmentally benign materials.

Release of surfactant cargo from interfacially-active halloysite clay nanotubes for oil spill remediation.

Naturally occurring halloysite clay nanotubes are effective in stabilizing oil-in-water emulsions and can serve as interfacially-active vehicles for delivering oil spill treating agents. Halloysite nanotubes adsorb at the oil-water interface and stabilize oil-in-water emulsions that are stable for months. Cryo-scanning electron microscopy (Cryo-SEM) imaging of the oil-in-water emulsions shows that these nanotubes assemble in a side-on orientation at the oil-water interface and form networks on the interface through end-to-end linkages. For application in the treatment of marine oil spills, halloysite nanotubes were successfully loaded with surfactants and utilized as an interfacially-active vehicle for the delivery of surfactant cargo. The adsorption of surfactant molecules at the interface serves to lower the interfacial tension while the adsorption of particles provides a steric barrier to drop coalescence. Pendant drop tensiometry was used to characterize the dynamic reduction in interfacial tension resulting from the release of dioctyl sulfosuccinate sodium salt (DOSS) from halloysite nanotubes. At appropriate surfactant compositions and loadings in halloysite nanotubes, the crude oil-saline water interfacial tension is effectively lowered to levels appropriate for the dispersion of oil. This work indicates a novel concept of integrating particle stabilization of emulsions together with the release of chemical surfactants from the particles for the development of an alternative, cheaper, and environmentally-benign technology for oil spill remediation.

Synthesis and magnetic properties of a novel ferrite organogel

A novel magnetic organogel that can be considered a precursor example of a magnetoresponsive gel is reported. The gel is formed by the bridging of ferrite containing anionic bis(2-ethlhexyl) sodium sulfosuccinate reverse micelles with 2,6-dihydroxynaphthalene (2,6-DHN). The addition of 2,6-DHN leads to a room temperature quotes “freezing in” of the liquid solution to a clear organogel. Ferrite particles in the size range 10–15 nm are doped into the gel network and are thus suspended in the optically clear gel media. The magnetic properties of the gel were measured using a superconducting quantum interference device magnetometer. The results reveal that the gel exhibits superparamagnetic behavior with a blocking temperature of 6 K (at an applied field of 1000 G), and a coercivity of 850 G at 2 K. The ferrites introduced into the gel serve the function of magnetic “seeds” via which magnetic properties are acquired by the gel.