@article{tang_saquing_morton_glatz_kelly_khan_2014, title={Cross-linked Polymer Nanofibers for Hyperthermophilic Enzyme Immobilization: Approaches to Improve Enzyme Performance}, volume={6}, ISSN={["1944-8244"]}, DOI={10.1021/am5033633}, abstractNote={We report an enzyme immobilization method effective at elevated temperatures (up to 105 °C) and sufficiently robust for hyperthermophilic enzymes. Using a model hyperthermophilic enzyme, α-galactosidase from Thermotoga maritima, immobilization within chemically cross-linked poly(vinyl alcohol) (PVA) nanofibers to provide high specific surface area is achieved by (1) electrospinning a blend of a PVA and enzyme and (2) chemically cross-linking the polymer to entrap the enzyme within a water insoluble PVA fiber. The resulting enzyme-loaded nanofibers are water-insoluble at elevated temperatures, and enzyme leaching is not observed, indicating that the cross-linking effectively immobilizes the enzyme within the fibers. Upon immobilization, the enzyme retains its hyperthermophilic nature and shows improved thermal stability indicated by a 5.5-fold increase in apparent half-life at 90 °C, but with a significant decrease in apparent activity. The loss in apparent activity is attributed to enzyme deactivation and mass transfer limitations. Improvements in the apparent activity can be achieved by incorporating a cryoprotectant during immobilization to prevent enzyme deactivation. For example, immobilization in the presence of trehalose improved the apparent activity by 10-fold. Minimizing the mat thickness to reduce interfiber diffusion was a simple and effective method to further improve the performance of the immobilized enzyme.}, number={15}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Tang, Christina and Saquing, Carl D. and Morton, Stephen W. and Glatz, Brittany N. and Kelly, Robert M. and Khan, Saad A.}, year={2014}, month={Aug}, pages={11899–11906} }
 @article{tang_saquing_sarin_kelly_khan_2014, title={Nanofibrous membranes for single-step immobilization of hyperthermophilic enzymes}, volume={472}, ISSN={["1873-3123"]}, DOI={10.1016/j.memsci.2014.08.037}, abstractNote={We report a single-step method to immobilize hyperthermophilic enzymes within chemically crosslinked polyvinyl alcohol (PVA) nanofibrous membranes. The polymer crosslinking that entraps the enzyme within the fiber is not affected by the particular enzyme and can thus be applied to any enzyme. Using a reactive electrospinning process, the chemical crosslinking that occurs during processing effectively entraps the enzyme within the fiber preventing enzyme leaching at elevated temperature establishing that the system is sufficiently robust for immobilization of hyperthermophilic enzymes. Upon immobilization, the enzyme retains 20% of its catalytic activity as well as its hyperthermophilicity, as the maximum activity occurs at ~90 °C, and that activity at 90 °C is an order of magnitude higher than at 37 °C. Furthermore, thermostability of the enzyme is enhanced upon immobilization as indicated by the 2-fold increase in half-life at 90 °C and pH 5.5 which extends the use of these biocatalysts at high temperatures. Compared to alternative methods, the apparent activity using the single-step method is significantly higher than alternative two-step methods (4 orders of magnitude higher than non-solvent based crosslinking and 3-fold higher than vapor-phase crosslinking). Analysis of this immobilization method indicates that the apparent decrease in specific activity could be attributed to enzyme deactivation arising from the crosslinking reaction, whereas mass transfer limits the apparent activity using alternative two-step immobilization methods. Based on this understanding, enzyme activity upon immobilization may be improved by using enzymes with higher intrinsic stability. Since significant enzyme activity is observed upon immobilization and the stability under high temperatures is enhanced, this versatile approach leverages the unique properties of hyperthermophilc enzymes and electrospun nanofibers providing a platform to produce catalytically active nanofibrous membranes appropriate for high temperature processes.}, journal={JOURNAL OF MEMBRANE SCIENCE}, author={Tang, Christina and Saquing, Carl D. and Sarin, Pooja K. and Kelly, Robert M. and Khan, Saad A.}, year={2014}, month={Dec}, pages={251–260} }
 @article{aykut_saquing_pourdeyhimi_parsons_khan_2012, title={Templating Quantum Dot to Phase-Transformed Electrospun TiO2 Nanofibers for Enhanced Photo-Excited Electron Injection}, volume={4}, ISSN={["1944-8252"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000307698600011&KeyUID=WOS:000307698600011}, DOI={10.1021/am300524a}, abstractNote={We report on the microstructural crystal phase transformation of electrospun TiO(2) nanofibers generated via sol-gel electrospinning technique, and the incorporation of as-synthesized CdSe quantum dots (QDs) to different phases of TiO(2) nanofibers (NFs) via bifunctional surface modification. The effect of different phases of TiO(2) on photo-excited electron injection from CdSe QDs to TiO(2) NFs, as measured by photoluminescence spectroscopy (PL) is also discussed. Nanofiber diameter and crystal structures are dramatically affected by different calcination temperatures due to removal of polymer carrier, conversion of ceramic precursor into ceramic nanofibers, and formation of different TiO(2) phases in the fibers. At a low calcination temperature of 400 (o)C only anatase TiO(2) nanofiber are obtained; with increasing calcination temperature (up to 500 (o)C) these anatase crystals became larger. Crystal transformation from the anatase to the rutile phase is observed above 500(o)C, with most of the crystals transforming into the rutile phase at 800(o)C. Bi-functional surface modification of calcined TiO(2) nanofibers with 3-mercaptopropionic acid (3-MPA) is used to incorporate as-synthesized CdSe QD nanoparticles on to TiO(2) nanofibers. Evidence of formation of CdSe/TiO(2) composite nanofibers is obtained from elemental analysis using Energy Dispersive X-ray spectroscopy (EDS) and TEM microscopy that reveal templated quantum dots on TiO(2) nanofibers. Photoluminescence emission intensities increase considerably with the addition of QDs to all TiO(2) nanofiber samples, with fibers containing small amount of rutile crystals with anatase crystals showing the most enhanced effect.}, number={8}, journal={ACS APPLIED MATERIALS & INTERFACES}, author={Aykut, Yakup and Saquing, Carl D. and Pourdeyhimi, Behnam and Parsons, Gregory N. and Khan, Saad A.}, year={2012}, month={Aug}, pages={3837–3845} }
 @article{saquing_saquing_knappe_barlaz_2010, title={Impact of Plastics on Fate and Transport of Organic Contaminants in Landfills}, volume={44}, ISSN={["0013-936X"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-77956547698&partnerID=MN8TOARS}, DOI={10.1021/es101251p}, abstractNote={Factors controlling organic contaminant sorption to common plastics in municipal solid waste were identified. Consumer plastics [drinking water container, prescription drug bottle, soda bottle, disposable cold cup, computer casing, furniture foam, carpet, vinyl flooring, formica sheet] and model polymers [high-density polyethylene (HDPE), medium-density polyethylene, low-density polyethylene, poly(vinyl chloride) (PVC)] were characterized by X-ray diffractometry, differential scanning calorimetry, and elemental analysis. The material characterization was used to interpret batch isotherm and kinetic data. K(p) values describing toluene sorption to rubbery or "soft" polymers could be normalized by the amorphous polymer fraction (f(amorphous)) but not by the organic carbon fraction (f(oc)). Diffusion coefficients (D) describing the uptake rate of toluene by rubbery plastics (HDPE, drinking water container, prescription drug bottle) were similar (D approximately 10(-10) cm(2)/s), indicating that pure HDPE can be used as a model for rubbery plastics. Toluene diffusivity was similar among glassy or "hard" plastics (PVC, soda bottle, computer casing, disposable cold cup; D approximately 10(-12) cm(2)/s) but lower than for rubbery plastics. Plastics in landfills are potential sinks of hydrophobic organic contaminants (HOCs) because of their higher affinity for HOCs compared to lignocellulosic materials and the slow desorption of HOCs from glassy plastics.}, number={16}, journal={ENVIRONMENTAL SCIENCE & TECHNOLOGY}, author={Saquing, Jovita M. and Saquing, Carl D. and Knappe, Detlef R. U. and Barlaz, Morton A.}, year={2010}, month={Aug}, pages={6396–6402} }
 @article{tang_saquing_harding_khan_2010, title={In Situ Cross-Linking of Electrospun Poly(vinyl alcohol) Nanofibers}, volume={43}, ISSN={["1520-5835"]}, DOI={10.1021/ma902269p}, abstractNote={We examine single step reactive electrospinning of poly(vinyl alcohol) (PVA) and a chemical cross-linking agent, glutaraldehyde (GA), with hydrochloric acid (HCl) as a catalyst to generate water insoluble PVA nanofibers. Such an approach using a conventional setup with no modification enables the fibers to cross-link during the electrospinning process, thereby eliminating the need for post-treatment. Significant changes in the rheological properties occur during in situ cross-linking, which we correlate with electrospinnability. In particular, we associate changes in dynamic rheological properties to changes in fiber morphology for two regions: (1) below the critical concentration to electrospin PVA only and (2) above the critical concentration to electrospin PVA only. In region 1 fiber morphology changes from beaded fibers to uniform fibers to flat fibers, and in region 2 fiber morphology changes from uniform fibers to flat fibers. Electrospinning windows to generate uniform fibers for both regions are d...}, number={2}, journal={MACROMOLECULES}, author={Tang, Christina and Saquing, Carl D. and Harding, Jonathon R. and Khan, Saad A.}, year={2010}, month={Jan}, pages={630–637} }
 @article{peng_sun_spagnola_saquing_khan_spontak_parsons_2009, title={Bi-directional Kirkendall Effect in Coaxial Microtuble Nanolaminate Assemblies Fabricated by Atomic Layer Deposition}, volume={3}, ISSN={["1936-086X"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000264535200010&KeyUID=WOS:000264535200010}, DOI={10.1021/nn8006543}, abstractNote={The solid-state reaction within a coaxial Al2O3/ZnO/Al2O3 multilayered microtubular structure can be used to prepare discrete microtube-in-microtube ZnAl2O4 spinel assemblies through a Kirkendall void production mechanism at 700 degrees C. In contrast with previous studies of the nanoscale Kirkendall effect, the reaction observed here proceeds through a bi-directional vacancy diffusion mechanism wherein ZnO species diffuse into inner- and outer-Al2O3 concentric layers, thereby resulting in vacancy supersaturation and void production between two isolated spinel microtubes. Low-temperature atomic layer deposition (ALD) of Al2O3 and ZnO enables the fabrication of complex coaxial multilayered microtubes with precise control of the starting film thicknesses and relative composition. When a molar excess of ZnO is present between two Al2O3 layers, electron microscopy images reveal incomplete ZnO consumption after annealing at 700 degrees C. At higher initial Al2O3 concentrations, however, complete reaction with ZnO is observed, and the size of the Kirkendall gap between isolated spinel microtubes appears to be directly influenced by the thickness of the intermediate ZnO layer.}, number={3}, journal={ACS NANO}, author={Peng, Qing and Sun, Xiao-Yu and Spagnola, Joseph C. and Saquing, Carl and Khan, Saad A. and Spontak, Richard J. and Parsons, Gregory N.}, year={2009}, month={Mar}, pages={546–554} }
 @article{gupta_saquing_afshari_tonelli_khan_kotek_2009, title={Porous Nylon-6 Fibers via a Novel Salt-Induced Electrospinning Method}, volume={42}, ISSN={["1520-5835"]}, DOI={10.1021/ma801918c}, abstractNote={Porous nylon-6 fibers are obtained from Lewis acid-base complexation of gallium trichloride (GaCl3) and nylon-6 using electrospinning followed by GaCl3 removal. DSC and FTIR results reveal that the electrospun fibers, prior to GaCl3 removal, are amorphous with no hydrogen bonds present between nylon-6 chains. GaCl3 being a Lewis acid interacts with the Lewis base sites (CdO groups) on the nylon-6 chains, thereby preventing the chains to crystallize via intermolecular hydrogen bonding. Subsequent removal of GaCl3 from the as-spun fibers by soaking the electrospun web in water for 24 h leads to the formation of pores throughout the fibers. While the average fiber diameter remains effectively the same after salt removal, the average surface area increases by more than a factor of 6 for the regenerated fibers. The dual use of a metal salt (Lewis acid) to (a) facilitate fiber formation by temporary removal of polymer interchain interactions and (b) act as a porogen provides a facile approach to obtain porous fibers via electrospinning.}, number={3}, journal={MACROMOLECULES}, author={Gupta, Amit and Saquing, Carl D. and Afshari, Mehdi and Tonelli, Alan E. and Khan, Saad A. and Kotek, Richard}, year={2009}, month={Feb}, pages={709–715} }
 @article{ji_saquing_khan_zhang_2008, title={Preparation and characterization of silica nanoparticulate-polyacrylonitrile composite and porous nanofibers}, volume={19}, ISSN={["1361-6528"]}, url={https://publons.com/publon/7178323/}, DOI={10.1088/0957-4484/19/8/085605}, abstractNote={In this study, polyacrylonitrile (PAN) composite nanofibers containing different amounts of silica nanoparticulates have been obtained via electrospinning. The surface morphology, thermal properties and crystal structure of PAN/silica nanofibers are characterized using attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy, wide-angle x-ray diffraction (WAXD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and differential scanning calorimetry (DSC). The results indicate that the addition of silica nanoparticulates affects the structure and properties of the nanofibers. In addition to PAN/silica composite nanofibers, porous PAN nanofibers have been prepared by selective removal of the silica component from PAN/silica composite nanofibers using hydrofluoric (HF) acid. ATR-FTIR and thermal gravimetric analysis (TGA) experiments validate the removal of silica nanoparticulates by HF acid, whereas SEM and TEM results reveal that the porous nanofibers obtained from composite fibers with higher silica contents exhibited more nonuniform surface morphology. The Brunauer–Emmett–Teller (BET) surface area of porous PAN nanofibers made from PAN/silica (5 wt%) composite precursors is higher than that of pure nonporous PAN nanofibers.}, number={8}, journal={NANOTECHNOLOGY}, publisher={IOP Publishing}, author={Ji, Liwen and Saquing, Carl and Khan, Saad A. and Zhang, Xiangwu}, year={2008}, month={Feb} }
 @article{soriano_venditti_saquing_bushey_argyropoulos_2008, title={Solubilizing amino acids and polypeptides in supercritical CO2 via reverse micelle formation}, volume={315}, ISSN={0927-7757}, url={http://dx.doi.org/10.1016/j.colsurfa.2007.07.019}, DOI={10.1016/j.colsurfa.2007.07.019}, abstractNote={Water-in-CO2 reverse micelles stabilized by ionic perfluoroalkyl and non-ionic perfluoropolyether surfactants were used to host amino acids and polypeptides in supercritical (SC) CO2. The minimum pressure at which micellization occurs (Ptrans) was found to be affected by the surfactant concentration and H2O/CO2 ratio. Due to the differences in hydrophilic/CO2 balance, the two surfactants exhibited different phase behaviors at 19.3 MPa and 40 °C. At certain H2O/CO2/surfactant compositions, while coagulation was more evident when using perfluoroalkyl surfactant, flocculation was found to dominate the system containing perfluoropolyether surfactant. The presence of amino acid and polypeptide in reverse micelles was found to increase the Ptrans of the system due to enthalpic and entropic changes. In perfluoroalkyl reverse micelles, the Ptrans was found to increase with increasing hydrophilicity of the amino acid added. The presence of hydrophobic moieties in amino acids promotes interfacial solubilization that eventually resulted in lower Ptrans. On the other hand, the nature of the amino acid was not found to affect Ptrans in perfluoropolyether reverse micelle. Overall, this work demonstrates that polypeptides with varying molecular weight could be solubilized in water-in-CO2 reverse micelles using perfluoropolyether while perfluoroakyl surfactants were ineffective.}, number={1-3}, journal={Colloids and Surfaces A: Physicochemical and Engineering Aspects}, publisher={Elsevier BV}, author={Soriano, Nestor U., Jr. and Venditti, Richard and Saquing, Carl D. and Bushey, Dean and Argyropoulos, Dimitris S.}, year={2008}, month={Feb}, pages={110–116} }
 @inbook{argyropoulos_saquing_gaspar_soriano_lucia_rojas_2007, title={Oxidative chemistry of lignin In supercritical carbon dioxide & expanded liquids}, volume={954}, ISBN={9780841239814}, DOI={10.1021/bk-2007-0954.ch020}, abstractNote={This paper explores the use of supercritical carbon dioxide (scCO{2}) as a medium for the oxidative degradation of three lignin model compounds, namely; 3-methoxy-4-hydroxy-benzaldehyde (1), 3,4-dimethoxy-benzylalcohol (2) and 3,3'-dimethoxy-5,5'-dimethyl-[1,1'-biphenyl]-2,2'-diol (3), as well as Residual Kraft Lignin (RKL), with hydrogen peroxide as the oxidant at variable temperatures and pressures. To do this we quantitatively followed the starting material and the main reaction products during the oxidative degradation. The actual yields of the various reaction products ranged from very good to almost quantitative. The most significant aspect of our findings was that peroxide-induced oxidations in scCO{2} did not require the creation of the precursor phenoxy anion since no alkali was used during our experiments. In addition, no radical coupling products were detected, signifying a novel, relatively clean and predictable product distribution in scCO{2}. Our work so far demonstrates that: - ScCO{2} oxidation conditions proceed in a manner that is rather different than for conventional aqueous systems. - Aromatic compounds, such as recalcitrant 5'5 biphenols, which are relatively stable under aqueous oxidative conditions, can be readily oxidized under scCO{2} peroxide in total absence of alkali. - The product distributions under scCO{2} oxidation conditions seem to be simpler than those that are formed under aqueous conditions in the presence of alkali. - Otherwise difficult to oxidize, residual kraft lignin is seen to be readily oxidized with peroxide in scCO{2}, selectively inducing the formation of large amounts of carboxylic acids on it via the elimination of phenolic moieties.}, booktitle={Materials, chemicals and energy from forest biomass}, publisher={Washington, DC: ACS Books}, author={Argyropoulos, Dimitris and Saquing, C. D. and Gaspar, A. R. and Soriano, N. U. and Lucia, L. A. and Rojas, O. J.}, year={2007}, pages={311–331} }
 @article{saquing_tang_monian_bonino_manasco_alsberg_khan, title={Alginate-polyethylene oxide blend nanofibers and the role of the carrier polymer in electrospinning}, volume={52}, number={26}, journal={Industrial & Engineering Chemistry Research}, author={Saquing, C. D. and Tang, C. and Monian, B. and Bonino, C. A. and Manasco, J. L. and Alsberg, E. and Khan, S. A.}, pages={8692–8704} }
 @article{manasco_saquing_tang_khan, title={Cyclodextrin fibers via polymer-free electrospinning}, volume={2}, number={9}, journal={RSC Advances}, author={Manasco, J. L. and Saquing, C. D. and Tang, C. and Khan, S. A.}, pages={3778–3784} }
 @article{saquing_manasco_khan, title={Electrospun nanoparticle-nanofiber composites via a one-step synthesis}, volume={5}, number={8}, journal={Small (Weinheim An Der Bergstrasse, Germany)}, author={Saquing, C. D. and Manasco, J. L. and Khan, S. A.}, pages={944–951} }
 @article{pirzada_arvidson_saquing_shah_khan, title={Hybrid carbon silica nanofibers through sol-gel electrospinning}, volume={30}, number={51}, journal={Langmuir}, author={Pirzada, T. and Arvidson, S. A. and Saquing, C. D. and Shah, S. S. and Khan, S. A.}, pages={15504–15513} }
 @article{pirzada_arvidson_saquing_shah_khan, title={Hybrid silica-PVA nanofibers via sol-gel electrospinning}, volume={28}, number={13}, journal={Langmuir}, author={Pirzada, T. and Arvidson, S. A. and Saquing, C. D. and Shah, S. S. and Khan, S. A.}, pages={5834–5844} }
 @article{manasco_tang_burns_saquing_khan, title={Rapidly dissolving poly(vinyl alcohol)/cyclodextrin electrospun nanofibrous membranes}, volume={4}, number={26}, journal={RSC Advances}, author={Manasco, J. L. and Tang, C. and Burns, N. A. and Saquing, C. D. and Khan, S. A.}, pages={13274–13279} }