Robert J. Wiacek

Selective Capture of Cesium and Thallium from Natural Waters and Simulated Wastes with Copper Ferrocyanide Functionalized Mesoporous Silica

Copper(II) ferrocyanide on mesoporous silica (FC-Cu-EDA-SAMMS) has been evaluated against iron(III) hexacyanoferrate(II) (insoluble Prussian Blue) for removing cesium (Cs(+)) and thallium (Tl(+)) from natural waters and simulated acidic and alkaline wastes. From pH 0.1-7.3, FC-Cu-EDA-SAMMS had greater affinities for Cs and Tl and was less affected by the solution pH, competing cations, and matrices. SAMMS also outperformed Prussian Blue in terms of adsorption capacities (e.g., 21.7 versus 2.6 mg Cs/g in acidic waste stimulant (pH 1.1), 28.3 versus 5.8 mg Tl/g in seawater), and rate (e.g., over 95 wt% of Cs was removed from seawater after 2 min with SAMMS, while only 75 wt% was removed with Prussian Blue). SAMMS also had higher stability (e.g., 2.5-13-fold less Fe dissolved from 2 to 24 h of contact time). In addition to environmental applications, SAMMS has great potential to be used as orally administered drug for limiting the absorption of radioactive Cs and toxic Tl in gastrointestinal tract.

Phosphate Removal by Anion Binding on Functionalized Nanoporous Sorbents

Phosphate was captured from aqueous solutions by cationic metal-EDA complexes anchored inside mesoporous silica MCM-41 supports (Cu(II)-EDA-SAMMS and Fe(III)-EDA-SAMMS). Fe-EDA-SAMMS was more effective at capturing phosphate than the Cu-EDA-SAMMS and was further studied for matrix effects (e.g., pH, ionic strength, and competing anions) and sorption performance (e.g., capacity and rate). The adsorption of phosphate was highly pH dependent; it increased with increasing pH from 1.0 to 6.5, and decreased above pH 6.5. The adsorption was affected by high ionic strength (0.1 M of NaCl). In the presence of 1000-fold molar excess of chloride and nitrate anions, phosphate removal by Fe-EDA-SAMMS was not affected. Slight, moderate and large impacts were seen with bicarbonate, sulfate, and citrate anions, respectively. The phosphate adsorption data on Fe-EDA-SAMMS agreed well with the Langmuir model with the estimated maximum capacity of 43.3 mg/g. The material displayed rapid sorption rate (99% of phosphate removal within 1 min) and lowering the phosphate content to approximately 10 microg/L of phosphorus, which is lower than the EPAs established freshwater contaminant level for phosphorus (20 microg/L).

Selective removal of lanthanides from natural waters, acidic streams and dialysate

The increased demand for the lanthanides in commercial products result in increased production of lanthanide containing ores, which increases public exposure to the lanthanides, both from various commercial products and from production wastes/effluents. This work investigates lanthanide (La, Ce, Pr, Nd, Eu, Gd and Lu) binding properties of self-assembled monolayers on mesoporous silica supports (SAMMS), that were functionalized with diphosphonic acid (DiPhos), acetamide phosphonic acid (AcPhos), propionamide phosphonic acid (Prop-Phos), and 1-hydroxy-2-pyridinone (1,2-HOPO), from natural waters (river, ground and sea waters), acid solutions (to mimic certain industrial process streams), and dialysate. The affinity, capacity, and kinetics of the lanthanide sorption, as well as regenerability of SAMMS materials were investigated. Going from the acid side over to the alkaline side, the AcPhos- and DiPhos-SAMMS maintain their outstanding affinity for lanthanides, which enable the use of the materials in the systems where the pH may fluctuate. In acid solutions, Prop-Phos- and 1,2-HOPO-SAMMS have differing affinity along the lanthanide series, suggesting their use in chromatographic lanthanide separation. Over 95% of 100 microg/L of Gd in dialysate was removed by the Prop-Phos-SAMMS after 1 min and 99% over 10 min. SAMMS can be regenerated with an acid wash (0.5M HCl) without losing the binding properties. Thus, they have a great potential to be used as in large-scale treatment of lanthanides, lanthanide separation prior to analytical instruments, and in sorbent dialyzers for treatment of acute lanthanide poisoning.

In Vitro And In Vivo Evaluation Of A Novel Ferrocyanide Functionalized Nanopourous Silica Decorporation Agent For Cesium In Rats

Novel decorporation agents are being developed to protect against radiological terrorist attacks. These sorbents, known as the self-assembled monolayer on mesoporous supports (SAMMS™), are hybrid materials where differing organic moieties are grafted onto mesoporous silica (SiO2). In vitro experiments focused on the evaluation and optimization of SAMMS for capturing radiocesium (137Cs); therefore, based on these studies, a ferrocyanide copper (FC-Cu-EDA)-SAMMS was advanced for in vivo evaluation. In vivo experiments were conducted comparing the performance of the SAMMS vs. insoluble Prussian blue. Groups of jugular cannulated rats (4/treatment) were evaluated. Animals in Group I were administered 137Cs chloride (∼40 &mgr;g kg−1) by intravenous (i.v.) injection or oral gavage; Group II animals were administered pre-bound 137Cs-SAMMS or sequential 137Cs chloride + SAMMS (∼61 ng kg−1) by oral gavage; and Group III was orally administered 137Cs chloride (∼61 ng kg−1) followed by either 0.1 g of SAMMS or Prussian blue. Following dosing, the rats were maintained in metabolism cages for 72 h and blood, urine, and fecal samples were collected for 137Cs analysis (gamma counting). Rats were then humanely euthanized, and selected tissues analyzed. Orally administered 137Cs chloride was rapidly and well absorbed (∼100% relative to i.v. dose), and the pharmacokinetics (blood, urine, feces, and tissues) were very comparable to the i.v. dose group. For both exposures the urine and feces accounted for 20 and 3% of the dose, respectively. The prebound 137Cs-SAMMS was retained primarily within the feces (72% of the dose), with ∼1.4% detected in the urine, suggesting that the 137Cs remained tightly bound to SAMMS. SAMMS and Prussian blue both effectively captured available 137Cs in the gut with feces accounting for 80–88% of the administered dose, while less than 2% was detected in the urine. This study suggests that the functionalized SAMMS outperforms Prussian blue in vitro at low pH, but demonstrates comparable in vivo sequestration efficacy at low exposure concentrations. The comparable response may be the result of the low 137Cs chloride dose and high sorbent dosage that was utilized. Future studies are planned to optimize the performance of SAMMS in vivo over a broader range of doses and conditions.

FUNCTIONAL SORBENTS FOR SELECTIVE CAPTURE OF PLUTONIUM, AMERICIUM, URANIUM, AND THORIUM IN BLOOD

Self-assembled monolayer on mesoporous supports (SAMMS™) are hybrid materials created from attachment of organic moieties onto very high surface area mesoporous silica. SAMMS with surface chemistries including three isomers of hydroxypyridinone, diphosphonic acid, acetamide phosphonic acid, glycinyl urea, and diethylenetriamine pentaacetate (DTPA) analog were evaluated for chelation of actinides (239Pu, 241Am, uranium, thorium) from blood. Direct blood decorporation using sorbents does not have the toxicity or renal challenges associated with traditional chelation therapy and may have potential applications for critical exposure cases, reduction of nonspecific dose during actinide radiotherapy, and for sorbent hemoperfusion in renal insufficient patients, whose kidneys clear radionuclides at a very slow rate. Sorption affinity (Kd), sorption rate, selectivity, and stability of SAMMS were measured in batch contact experiments. An isomer of hydroxypyridinone (3,4-HOPO) on SAMMS demonstrated the highest affinity for all four actinides from blood and plasma and greatly outperformed the DTPA analog on SAMMS and commercial resins. In batch contact, a fifty percent reduction of actinides in blood was achieved within minutes, and there was no evidence of protein fouling or material leaching in blood after 24 h. The engineered form of SAMMS (bead format) was further evaluated in a 100-fold scaled-down hemoperfusion device and showed no blood clotting after 2 h. A 0.2 g quantity of SAMMS could reduce 50 wt.% of 100 ppb uranium in 50 mL of plasma in 18 min and that of 500 dpm mL−1 in 24 min. 3,4-HOPO-SAMMS has a long shelf-life in air and at room temperature for at least 8 y, indicating its feasibility for stockpiling in preparedness for an emergency. The excellent efficacy and stability of SAMMS materials in complex biological matrices suggest that SAMMS can also be used as orally administered drugs and for wound decontamination. By changing the organic groups of SAMMS, they can be used not only for actinides but also for other radionuclides. By using the mixture of these SAMMS materials, broad spectrum decorporation of radionuclides is very feasible.

Advancements Toward the Greener Processing of Engineered Nanomaterials—Effect of Core Size on the Dispersibility and Transport of Gold Nanocrystals in Near-Critical Solvents†

The ability to process and purify engineered nanomaterials using near critical or supercritical fluids (NcFs or ScFs) has enormous potential for the application at various stages of the development of green nanomaterials. The dispersibility of octanethiol-stabilized gold nanocrystals of different core sizes is explored, which were chosen to serve as model nanomaterials of general interest in compressed ethane and propane over a wide range of fluid conditions. Both solvents have enormous potential for the environmentally benign processing and transport of engineered nanomaterials due to their nominal toxicity and high degree of tunability and processability that can essentially eliminate solvent waste. The dispersibility is determined by measuring the absorption spectra of dispersions of various sizes of nanocrystals in NcFs. To better understand the obtained results three models, the total interaction theory, the sedimentation coefficient equation, and the Chrastil method, are discussed. Nanoparticle dispersibility versus density plots are strongly dependent on nanoparticle size and solvent conditions, with the dispersion of larger nanocrystals more dependent on changes of pressure or density at a given temperature. For the range of nanoparticle sizes studied, compressed ethane at 25 degrees C leads to a greater tunability of nanoparticle dispersion when compared with compressed propane at 65 degrees C. For equivalent pressures, compressed propane is found to provide better solubility than ethane due to its higher density. The results quantitatively demonstrate that NcFs can offer pressure-tunable, size-selective control of nanoparticle solvation and transport at easily obtainable temperature and pressure conditions. These capabilities provide clear advantages over conventional solvents and direct application to various nanomaterials processes, such as synthesis, separation, transport, and purification of nanocrystals.

Effect of the Ligand Shell Composition on the Dispersibility and Transport of Gold Nanocrystals in Near-Critical Solvents

The development of more efficient and environmentally benign methods for the synthesis and manipulation of nanomaterials has been a major focus of research among the scientific community. Supercritical (ScFs) and near-critical fluids (NcFs) offer numerous advantages over conventional solvents for these purposes. Among them, ScFs and NcFs offer dramatic reductions in the volume of organic waste typically generated during advanced material processes with the feasibility of changing a number of physicochemical properties by discrete variations in solvent pressure or temperature. In this work, we study the dispersibility of gold nanocrystals with a 3.7 nm core size stabilized by different ligand shells in NcF ethane and propane over a wide range of densities by fine-tuning the pressure of these fluids. Dispersibility vs density plots are obtained by following the variation in the surface plasmon resonance (SPR) absorption spectra of the nanoparticles. To understand the results obtained in this study, three models are briefly discussed: the total interaction theory, the sedimentation coefficient equation, and the Chrastil method. The dispersibility and behavior of the nanocrystals with variations in fluid density are strongly dependent on the surface chemistry of the nanocrystal and the solvent employed. A correlation between measured dispersibility values and calculated sedimentation coefficients was observed in both compressed solvents. In addition, we successfully applied the Chrastil equation to predict and describe the dispersibility of gold nanocrystals with different shells as a function of density, determining that the reason for the high stabilities of some of the nanocrystal dispersions is the strong solvent-nanocrystal interactions. While NcF propane showed higher nanocrystal dispersibilities, using NcF ethane led to improved tunability of nanoparticle dispersions formed in the pressure range studied. Therefore, with a judicious selection of the fluid, NcFs seem to offer a remarkable advantage over conventional solvents for manipulation of nanomaterials, which could be applied to transport, purification, and separation of nanocrystals.