Z. John Zhang

Adsorption of sulfur dioxide by CoFe2O4 spinel ferrite nanoparticles and corresponding changes in magnetism.

Adsorption of sulfur dioxide on 10 nm CoFe(2)O(4) spinel ferrite nanoparticles was examined. Adsorption loadings of sulfur dioxide at breakthrough conditions were determined to be approximately 0.62 mol/kg, which is significant given the 150 m(2)/g surface area of the nanoparticles. Adsorption proceeds through a chemisorption mechanism with sulfur dioxide forming a sulfate upon adsorption on the particle surface, which leads to a 23% decrease in the remnant magnetization, a 20% decrease in the saturation magnetization, and a 9% decrease in the coercivity of the magnetic nanoparticles. Adsorbent materials that provide a magnetic signal when adsorption occurs could have broad implications on adsorption-based separations.

Chemisorption of cyanogen chloride by spinel ferrite magnetic nanoparticles.

Spinel ferrite magnetic nanoparticles, MnFe2O4, NiFe2O4, and CoFe2O4, were synthesized and used as gas-phase adsorbents for the removal of cyanogen chloride from dry air. Fixed-bed adsorption breakthrough experiments show adsorption wave behavior at the leading edge of the breakthrough curve that is not typical of physically adsorbed species. Fourier transform infrared spectroscopy (FTIR) results indicate that CK is reacting with the spinel ferrite surface and forming a carbamate species. The reaction is shown to be a function of the hydroxyl groups and adsorbed water on the surface of the particles as well as the metallic composition of the particles. The surface reaction decreases the remnant and saturation magnetism of the MnFe2O4 and CoFe2O4 particles by approximately 25%.

Three-dimensional magnetite replicas of pollen particles with tailorable and predictable multimodal adhesion

The ability to synthesize large quantities of 3-D microparticles with tunable adhesion is critically important for a variety of mature and emerging technologies, such as for paints, inks, chemical/water purification, drug delivery, cell manipulation, and assembly of hierarchical structures. Nature provides impressive examples of sustainable, complex-shaped microparticles with chemistries and structures tailored for adhesion, among the most common of which are pollen grains. We have recently used a surface sol–gel (SSG) coating process to generate iron oxide replicas of sunflower pollen grains. While these replicas exhibited multimodal adhesion, the tailorability and predictability of such adhesion was not examined. In the present paper, the layer-by-layer SSG process has been used to carefully adjust the amount of iron oxide deposited onto the pollen grains. Controlled-atmosphere thermal treatments then yielded freestanding replicas with tailored hematite (α-Fe2O3) or magnetite (Fe3O4) contents. The 3-D morphology of the starting pollen was well-preserved in the all-oxide replicas, and the shrinkage upon firing could be controlled by increasing the number of Fe–O-bearing layers deposited on the pollen. While the short-range van der Waals (VDW) adhesion of the oxide replicas to a variety of surfaces was lower than for the larger starting pollen grains, this difference was not due to shrinkage of the replicas. Analyses with a simple Hamaker model indicated that VDW adhesion of the oxide replicas was governed by the contact of oxide nanocrystals located on the spine tips (as opposed to the curvature of the entire spine tip). The longer-range attraction to a magnetic substrate could be tailored independently of the short-range VDW attraction by controlling the magnetite content of the replicas, and a simple and effective model for describing such magnetic attraction was developed. This work demonstrates that sustainable pollen microparticles can be converted into high-fidelity 3-D oxide replicas with predictable and tailorable multimodal adhesion.

Self-assembly, crystal structures and properties of metal–3,4,5-tris(carboxymethoxy)benzoic acid frameworks based on polynuclear metal-hydroxyl clusters (M = Zn, Co)

3,4,5-Tris(carboxymethoxy)benzoic acid (H4TCBA) has been used as a structure-directing agent to prepare three new inorganic–organic hybrid frameworks based on polynuclear metal-hydroxyl clusters, [Zn2.5(OH)(TCBA)(H2O)4]·H2O (1), [Zn2.5(OH)(TCBA)(H2O)] (2), [Co3(OH)2(TCBA)(H2O)4]·2H2O (3) through hydro/solvothermal reactions. The results show that complexes 1 and 2 both own I0O3 hybrid frameworks with a highly-connected binodal 4,8-c network, while 3 reveals a I0O2 hybrid framework with a 3,6-c 2-nodal topology. The multiple coordination system originated from the branching out carboxylate groups in TCBA ligands results in the formation of the multi-stranded helical chains in the high-dimensional metal–organic frameworks of complexes 1–3. The thermal stabilities of complexes 1–3, the photophysical properties of complexes 1 and 2 and the magnetic properties of complex 3 were also investigated. Complexes 1 and 2 emit strong blue light under ultraviolet light, and complex 3 shows typical paramagnetic behavior and an interesting partial spin-crossover has been observed.

A rare I2O3 hybrid organic–inorganic material with high connectivity and quadruple-stranded helices

A novel organic–inorganic hybrid material with 2-D inorganic and 3-D organic connectivity has been assembled with one Cd–Ohydroxyl helix and two kinds of quadruple-stranded Cd–ligand helices, which also shows a highly-connected binodal (5,14-c) topological net.

Tunable multimodal adhesion of 3D, nanocrystalline CoFe2O4 pollen replicas

Three-dimensional (3-D) replicas of sunflower pollen microparticles, comprised of a multicomponent magnetic spinel ferrite (CoFe2O4) with tailorable adhesive properties, have been synthesized for the first time via a conformal layer-by-layer (LbL) surface sol-gel (SSG) deposition process followed by organic pyrolysis and oxide compound formation at a peak temperature of 600oC to 900oC. These high-fidelity ferrite pollen replicas exhibited multimodal (van der Waals, vdW, and magnetic) adhesion that could be tuned via control of the CoFe2O4 nanoparticle and crystal sizes. The CoFe2O4 pollen replicas exhibited a non-monotonic change in short-range (∽10 nm) vdW adhesion with an increase in the peak firing temperature, which was consistent with the counteracting effects of particle coarsening on the size and number of nanoparticles present on the sharp tips of the echini (spines) on the pollen replica surfaces. The longer-range (up to ∽1 mm) magnetic force of adhesion increased monotonically with an increase in firing temperature, which was consistent with the observed increases in the values of the saturation and remanent magnetization of CoFe2O4 with an increase in average nanocrystal size. By adjusting the nanocrystal/nanoparticle sizes of the CoFe2O4 pollen replicas, the total force of adhesion (vdW + magnetic) to a magnetic substrate could be increased by a factor of ~3 relative to native pollen grains. .3D replicas of sunflower pollen microparticles, comprised of a multicomponent magnetic spinel ferrite (CoFe2O4) with tailorable adhesive properties, have been synthesized for the first time via a conformal layer-by-layer (LbL) surface sol-gel (SSG) deposition process followed by organic pyrolysis and oxide compound formation at a peak temperature of 600 °C-900 °C. These high-fidelity ferrite pollen replicas exhibited multimodal (van der Waals, vdW, and magnetic) adhesion that could be tuned via control of the CoFe2O4 nanoparticle and crystal sizes. The CoFe2O4 pollen replicas exhibited a non-monotonic change in short-range (~10u2009nm) vdW adhesion with an increase in the peak firing temperature, which was consistent with the counteracting effects of particle coarsening on the size and number of nanoparticles present on the sharp tips of the echini (spines) on the pollen replica surfaces. The longer-range (up to ~1u2009mm) magnetic force of adhesion increased monotonically with an increase in firing temperature, which was consistent with the observed increases in the values of the saturation and remanent magnetization of CoFe2O4 with an increase in average nanocrystal size. By adjusting the nanocrystal/nanoparticle sizes of the CoFe2O4 pollen replicas, the total force of adhesion (vdWu2009u2009+u2009u2009magnetic) to a magnetic substrate could be increased by a factor of ~3 relative to native pollen grains.

Complex three-dimensional lanthanide metal–organic frameworks with variable coordination spheres based on pyrazine-2,3,5,6-tetracarboxylate

Metal–organic frameworks {[Ln4(pztc)3(H2O)11]·10(H2O)}n (Ln = Gd(1), Tb(2); pztc = pyrazine-2,3,5,6-tetracarboxylate) containing variable coordination spheres and with a complex and unusual three dimensional structure, were synthesized by the reaction of H4pztc with the respective Ln(III) salt in water under hydrothermal conditions. The compounds were characterized by single crystal X-ray crystallography, elemental and thermal analysis, and FTIR spectroscopy. The asymmetric units in these compounds have four symmetry-independent Ln(III) ions and these are octa- and nona-coordinate centers, with irregular coordination polyhedra from [Ln(pztc)2(H2O)6], [Ln(pztc)2(H2O)4], [Ln(pztc)3(H2O)3], [Ln(pztc)3(H2O)], and [Ln(pztc)4] cluster units. The fully deprotonated ligand, pztc, coordinates to the Ln3+ ions through seven or through ten of its atoms (i.e., the maximum coordination number for this ligand). The three-dimensional open framework contains irregular channels along the [001] crystallographic direction. The channels are approximately 12 A wide at their largest dimension and contain strongly hydrogen bonded water molecules of crystallization which further stabilize the structure. The solvent accessible volume is 20% of the total volume. The structures exhibit magnetic behavior that is characteristic of the respective isolated paramagnetic lanthanide ions.

A hydrogen bonded Co(II) coordination complex and a triply interpenetrating 3-D manganese(II) coordination polymer from diaza crown ether with dibenzoate sidearms

The diaza crown ether dicarboxylate ligand, 4,4′-((1,7-dioxa-4,10-diazacyclododecane-4,10-diyl)bis(methylene)dibenzoate), L, forms a monomeric coordination complex of Co(II) ions, CoL(H2O)2·2H2O, 1, and a coordination polymer (MnL·H2O)n, 2, with Mn(II) ions under hydrothermal conditions. The monomeric coordination complex (structure 1) is polar with mirror symmetry and crystallizes in the non-centrosymmetric space group Cm. The mirror plane bisects the complex at the six-coordinate Co(II) ion, the two oxygen atoms of the crown moiety and the two oxygen atoms from coordinated water molecules. The coordinated water molecules take part in strong, linear hydrogen bonds with carboxylate oxygens provided by neighboring Co(II)–crown complexes resulting in a three-dimensional (1u2006:u20061)n polar network in which the topology of the underlying 8-coordinated net is sqc3. The structure of 2 crystallizes in the orthorhombic Fdd2 space group as an infinite, polar triply interpenetrating three-dimensional network. The eight-coordinate Mn(II) ion coordinates two oxygen and two nitrogen atoms of the crown moiety, as well as single carboxylate O atom from each of two neighboring ligands. In both structures, the ligand assumes a flexed-wing bird shape, with the two benzoate sidearms of the crown moiety locked in a syn orientation. The metal ion elevated above the plane of the diaza-crown oxygen and nitrogen atoms. The diaza-crown moiety with its two benzoate sidearms has the peculiar property of forming an oriented crystal structure where the metal-crown vectors are oriented parallel to each other in the crystal. However, the structures are achiral, but the rigid crystal lattice prevents re-orientation of the structure through inversion. The coordination polymer (MnL·H2O)n, 2, is a 3-center uninodal net with ths (ThSi2) topology. Computational results using the density functional theory (DFT) calculations explain why the flexed-wing bird shape is the preferred and most stable ligand conformation for metal ion binding. Both structures demonstrate magnetic properties that are characteristics of the respective non-interacting isolated paramagnetic transition metal ions that are present.