William D. Samuels

Selective removal of copper (II) from natural waters by nanoporous sorbents functionalized with chelating diamines

Copper has been identified as a pollutant of concern by the U.S. Environmental Protection Agency (EPA) because of its widespread occurrence and toxic impact in the environment. Three nanoporous sorbents containing chelating diamine functionalities were evaluated for Cu(2+) adsorption from natural waters: ethylenediamine functionalized self-assembled monolayers on mesoporous supports (EDA-SAMMS), ethylenediamine functionalized activated carbon (AC-CH(2)-EDA), and 1,10-phenanthroline functionalized mesoporous carbon (Phen-FMC). The pH dependence of Cu(2+) sorption, Cu(2+) sorption capacities, rates, and selectivity of the sorbents were determined and compared with those of commercial sorbents (Chelex-100 ion-exchange resin and Darco KB-B activated carbon). All three chelating diamine sorbents showed excellent Cu(2+) removal (approximately 95-99%) from river water and seawater over the pH range 6.0-8.0. EDA-SAMMS and AC-CH(2)-EDA demonstrated rapid Cu(2+) sorption kinetics (minutes) and good sorption capacities (26 and 17 mg Cu/g sorbent, respectively) in seawater, whereas Phen-FMC had excellent selectivity for Cu(2+) over other metal ions (e.g., Ca(2+), Fe(2+), Ni(2+), and Zn(2+)) and was able to achieve Cu below the EPA recommended levels for river and sea waters.

SOL-GEL SYNTHESIS OF PHOSPHATE CERAMIC COMPOSITES I

Monolithic gels of phosphate ceramics were synthesized using PO(OH){sub 3{minus}{ital x}}(OR){sub {ital x}} and alkoxides of silicon and titanium. The PO(OH){sub 3{minus}{ital x}}(OR){sub {ital x}} species were synthesized from the reaction of P{sub 2}O{sub 5} and ethanol or {ital n}-butanol, and the products consisted of approximately equal molar amounts of mono- and dialkyl phosphate. The phosphate gels containing titanium lost less phosphorus than from the gels of silicon/phosphorus upon firing of gels in air. At phosphorus contents above 60 mole {percent}, the gels were completely crystallized upon firing at temperatures above 700{degree}C, while the gels containing zinc and alkali metals remained amorphous after firing at 850{degree}C. Solid state nuclear magnetic resonance spectroscopy showed that all of the silicon is hexacoordinated in the phosphate gels containing silicon and titanium upon firing at temperature above 520{degree}C. {copyright} {ital 1996 Materials Research Society.}

The influence of α-aryl ethers on the asymmetric reduction of carbonyls

Abstract The asymmetric reduction of α-aryl ethers 1 was found to be strongly influenced by the presence of ortho substituents on the aryl ring. Groups (methoxy or hydroxy) that chelate metal cations tend to stabilize a “locked” bicyclic 4 which, intermediate when reduced, yielded preferentially the erytho isomer.

31 P and 29Si NMR study of sol–gel-synthesized phosphate ceramics

31 P and 29Si solid-state magic angle spinning (MAS) and liquid-state nuclear magnetic resonance (NMR) techniques have been applied to the study of sol–gel-synthesized phosphate ceramic composites. This study emphasizes the chemistry and structural properties for both sols and gels prepared by directly reacting P2O5 with tetraethoxysilane (TEOS). This new method of formation of both the sols and gels is a drastic improvement in the retention of phosphorus during the formation of the phosphosilicate gels, and it provides a lower temperature route to six-coordinate silicon. Both31P and 29Si liquid-state NMR spectra for sols prepared without water showed the presence of P–O–Si bonds. The 31P NMR spectra for sols prepared with water resembled those for the PO(OH)x(OR)3–xprecursors, while29Si NMR spectra indicated that TEOS had undergone partial hydrolysis and condensation. Hexacoordinated silicon was observed for the first time in gels prepared at low temperature (70 °C). P–Si gels prepared directly by using P2O5 were compared with those using other molecular precursors.

Concentration efficiency of doping in phosphors: Investigation of the copper- and aluminum-doped zinc sulfide

We studied the effect of dopant concentration in ZnS:Cu, Al phosphor. Photoluminescent (PL) intensity of the chemically etched phosphor particles increased up to 140%, which proved the existence of a dopant concentration gradient. Calculation revealed the quantitative relationship between the dopant concentration and the luminescent intensity by relating the concentration gradient to the PL intensity. The result showed that the most efficient concentration is 100 ppm copper and the concentration quenching starts at 152 ppm.

Morphology control of hierarchically ordered ceramic materials prepared by surfactant-directed sol-gel mineralization of wood cellular structures

Abstract We here report the synthesis of ordered ceramic materials with hierarchy produced by an in-situ mineralization of ordered wood cellular structures with surfactant-templated sol-gel at different pHs. At low pH, a silicic acid is coated onto inner surface of wood cellular structure and it penetrates into pores left, where degraded lignin and hemicellulose are leached out, to form a positive replica, while at high pH the precipitating silica particles due to fast condensation clog the cells and pit structures to form a negative replica of wood. The calcined monoliths produced in different pHs contain ordered wood cellular structures, multi-layered cell walls, pits, vessels well-preserved with positive or negative contrasts, respectively. The surfactant-templated mineralization produces ordered hexagonal mesopores with 2nm in the cell walls after calcination.

Photoluminescence of Eu3+ ion doped phosphate ceramics

Phosphate ceramics doped with Eu3+ ions were synthesized through sol-gel process. The fluorescence spectra of Eu3+ as a function of firing temperature, dopant concentration, composition, and structure of the matrices were investigated. The gels synthesized by the reaction of P2O5 with tetraethoxy silane or titanium tetraethoxide (Ti(OEt)4) and EuCl3⋅6H2O as the dopant were fired in air from the temperature range 200–900 °C to form P–Si or P–Ti crystalline phases. The crystal structure was examined by powder x-ray diffractometry. Si5O(PO4)6 was the only crystalline phase for the P–Si system. The amount of doping Eu3+ varied from 1 up to 10 at %, and no obvious concentration quenching was observed in the concentration range. It was found that the phosphosilicates gave stronger fluorescence emission than the phosphotitanates. For both systems, the intensity of Eu3+ emission increased with higher firing temperatures. For the P–Si system, the emission intensity increased with greater amounts of phosphorus, whi...

Photoresponse of Tb3+ doped phosphosilicate thin films

Abstract Phosphosilicate ceramic was doped with Tb 3+ using sol-gel technique to prepare thin films. The films were prepared by spin coating the phosphosilicate sols on SiO x /indium-tin-oxide/glass substrates. The photocurrent of the films at 355 nm laser excitation was observed. The photoresponse as a function of applied field and laser energy was linear and showed no sign of saturation. The films exhibited very stable photoresponse under a very high number of laser shots.

Chloromethylated activated carbon: A useful new synthon for making a novel class of sorbents for heavy metal separations

The chloromethylation of activated carbon is described. Chloromethylation was found to produce a carbon derivative with a surface area of 1310 m2/g and no significant change in the pore structure. The product was found to contain ∼1.5 mmole of ‒CH2Cl groups per g of material, similar to the functional density reported in the original Merrifield resin synthesis. Displacement of the benzylic chloride was achieved by treating this material with an excess of sodium thiosulfate in refluxing aqueous methanol. The resulting Bunte salt was then hydrolyzed by treatment with warm 3 M HCl to afford the corresponding thiol (“AC-CH2-SH”) cleanly and in high yield. AC-CH2-SH was found to be an effective heavy metal sorbent, efficiently capturing Hg, Pb, Ag, and Cu. Sorption kinetics were rapid, with equilibrium achieved in less than 30 minutes.

Thermal Behavior of Sol-Gel Derived Phosphate Ceramics

Abstract A series of phosphosilicate and phosphotitanate ceramics with different compositions was prepared through sol–gel process. The phase evolution was studied using X-ray diffractometry. P:Si gels remain amorphous up to the compositions of P:Si=0.4:1 mole ratio, and begin to crystallize to Si 5 O(PO 4 ) 6 at higher phosphorus contents. The sintering property examined by push-rod dilatometer technique showed that P:Si gels can be densified at 400°C. Weight loss and phase transition of samples upon firing was investigated using thermogravimetric analysis and differential thermal analysis. Linear percentage thermal expansion of P:Si and P:Ti crystal phase was observed and briefly discussed.