Synthesis of mesoporous carbons using ordered and disordered mesoporous silica templates and polyacrylonitrile as carbon precursor.

Mesoporous carbons were synthesized from polyacrylonitrile (PAN) using ordered and disordered mesoporous silica templates and were characterized using transmission electron microscopy (TEM), powder X-ray diffraction, nitrogen adsorption, and thermogravimetry. The pores of the silica templates were infiltrated with carbon precursor (PAN) via polymerization of acrylonitrile from initiation sites chemically bonded to the silica surface. This polymerization method is expected to allow for a uniform filling of the template with PAN and to minimize the introduction of nontemplated PAN, thus mitigating the formation of nontemplated carbon. PAN was stabilized by heating to 573 K under air and carbonized under N2 at 1073 K. The resulting carbons exhibited high total pore volumes (1.5-1.8 cm3 g(-1)), with a primary contribution of the mesopore volume and with relatively low microporosity. The carbons synthesized using mesoporous templates with a 2-dimensional hexagonal structure (SBA-15 silica) and a face-centered cubic structure (FDU-1 silica) exhibited narrow pore size distributions (PSDs), whereas the carbon synthesized using disordered silica gel template had broader PSD. TEM showed that the SBA-15-templated carbon was composed of arrays of long, straight, or curved nanorods aligned in 2-D hexagonal arrays. The carbon replica of FDU-1 silica appeared to be composed of ordered arrays of spheres. XRD provided evidence of some degree of ordering of graphene sheets in the carbon frameworks. Elemental analysis showed that the carbons contain an appreciable amount of nitrogen. The use of our novel infiltration method and PAN as a carbon precursor allowed us to obtain ordered mesoporous carbons (OMCs) with (i) very high mesopore volume, (ii) low microporosity, (iii) low secondary mesoporosity, (iv) large pore diameter (8-12 nm), and (v) semi-graphitic framework, which represent a desirable combination of features that has not been realized before for OMCs.

Effect of adsorbed polyelectrolytes on nanoscale zero valent iron particle attachment to soil surface models.

Polyelectrolyte coatings significantly increase the mobility of nanoscale zerovalent iron (NZVI) in saturated porous media. The effect can be attributed to improved colloidal stability of NZVI suspensions, decreased adhesion to soil surfaces, or a combination of the two effects. This research explicitly examines how coatings control NZVI adhesion to model soil surfaces. NZVI was coated with three different polyeleotrolyte block copolymers based on poly(methacrylic acid), poly(methyl methacrylate or butyl methacrylate), and poly(styrenesulfonate) or with a poly(styrenesulfonate) homopolymer. SiO2 and a humic acid film served as model soil surfaces. The polyelectrolytes increased the magnitude of the electrophoretic mobility of NZVI over a broad pH range relative to unmodified NZVI and shifted the isoelectric point outside the typical groundwater pH range. Quartz crystal microgravimetry measurements indicated extensive adhesion of unmodified NZVI to SiO2. Polyelectrolyte coatings decreased adhesion by approximately 3 orders of magnitude. Adding 50 mM NaCL to screen electrostatic repulsions did not significantly increase adhesion of modified NZVI. Coated NZVI did not adhere to humic acid films for either 1 mM NaHCO3 or 1 mM NaHCO3 + 50 mM NaCl. The lack of adhesion even in a high ionic strength medium was attributed to electrosteric repulsion, as opposed to electrostatic double layer repulsion, between the polyelectrolyte-coated NZVI and the negatively charged surfaces. The lack of significant adhesion on either model surface was observed for all polymer architectures investigated.

Adsorbed triblock copolymers deliver reactive iron nanoparticles to the oil/water interface.

Reactive zero valent iron nanoparticles can degrade toxic nonaqueous phase liquids (NAPL) rapidly in contaminated groundwater to nontoxic products in situ, provided they can be delivered preferentially to the NAPL/water (oil/water) interface. This study demonstrates the ability of novel triblock copolymers to modify the nanoiron surface chemistry in a way that both promotes their colloidal stability in aqueous suspension and drives their adsorption to the oil/water interface. The ability of the copolymers to drive adsorption is demonstrated by the ability of copolymer-modified iron nanoparticles, but not the unmodified iron nanoparticles, to stabilize oil-in-water emulsions.