Rapid in situ degradation of chlorinated solvents present as nonaqueous phase liquids (NAPL) can be accomplished using reactive zerovalent nanoiron particles. Prior studies have shown that nanoiron transport in the subsurface is limited, and successful delivery of the nanoiron is essential for effective remediation. Here, the physical properties of bare and modified nanoiron are measured, and laboratory column reactors are used to compare the transport of three types of surface-modified nanoiron; triblock polymer-modified, surfactant-modified, and a commercially available polymer-modified nanoiron. The effect of particle concentration and solution ionic strength on the transport of each modified nanoiron is evaluated, and the filtration mechanisms for bare and modified particles are determined in microfluidic flow cells and quartz crystal microbalance (QCM) experiments that probe the particle-collector grain interaction. The effect of surface modification on nanoiron reactivity is evaluated in batch experiments. Transport of modified nanoiron does not directly correlate with-potential or colloidal stability, but rather correlates to particle-grain interactions. Filtration of bare nanoiron is caused by straining and subsequent clogging rather than by deposition to clean sand grains, suggesting that filter ripening models rather than clean bed filtration models should be used to describe nanoiron transport at high particle concentrations. Surface modification decreased nanoiron reactivity by two to four times, but as high as a factor of nine depending on the modifier used. Amphiphilic triblock copolymer modified nanoiron with a high hydrophobe/hydrophile ratio shows promise for in situ targeting of NAPL, but requires further optimization.

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.

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.

Surface-initiated atom transfer radical polymerization (ATRP) was used to graft uniform layers of polyacrylonitrile (PAN), poly(2-(dimethylamino)ethyl methacrylate), and polystyrene on concave surfaces of cylindrical mesopores of diameter ∼10 nm and spherical mesopores of diameter ∼15 nm. The grafting process was optimized through the introduction of appropriate amounts of Cu(II) species that act as a deactivator, allowing us to grow polymer layers of controlled thickness (as seen from gas adsorption), which consisted of monodisperse polymer chains of controlled molecular weight (as seen from gel permeation chromatography). For PAN, the degrees of polymerization ranged from DP ) 25 to 70, and the polydispersity indexes of the polymer grafted under optimal conditions were as low as M w /M n ) 1.06-1.07. Grafted chain densities up to 0.28 chains/nm 2 and initiation efficiencies up to 37% were achieved. In cases of spherical mesopores of diameter ∼15 nm, it was possible to introduce significant loadings of polymer (up to 28 wt % in resulting composite) without making the uniform mesopores inaccessible. The specific surface areas of the silica/polymer hybrids were 70-350 m 2 g -1 , and the thicknesses of the polymer films were controlled in the range up to 1-2 nm without causing any major pore blockage. This work demonstrates new opportunities in the synthesis of well-defined nanostructured/ nanoporous silica/polymer hybrids.