[Show abstract][Hide abstract] ABSTRACT: In this study, two CO2 solid sorbents based on polyethyleneimine, PEI (423 and 10k) impregnated into mesoporous silica (MPS) foam prepared by in kg quantities via a scale-up process were synthesized and characterized by a range of analytical and surface techniques. The lower molecular weight PEI-423/MPS showed higher capacity towards CO2 sorption than the higher molecular weight PEI-10k/MPS. On the other hand, the higher molecular weight PEI-10k/MPS exhibited higher thermal stability than PEI-423/MPS. The kinetics of CO2 adsorption on both PEI/MPS fitted well with a double exponential model. According to this model CO2 adsorption can be divided into two steps: the first is fast and is attributed to CO2 adsorption on the sorbent surface; the second is slower and assigned to the diffusion of CO2 within and between the mesoporous particles. In contrast, the desorption process obeyed first order kinetics with activation energies of 64.3 and 140.7 kJmol-1 for PEI-423/MPS and PEI-10k/MPS, respectively.
[Show abstract][Hide abstract] ABSTRACT: The potential to incorporate silver nanoparticles (Ag-NPs) as biocides in membranes for water purification has gained much interest in recent years. However, a viable strategy for loading the Ag-NPs on the membrane remains challenging. This paper presents a novel, facile procedure for loading Ag-NPs on thin-film composite (TFC) reverse osmosis membranes. Reaction of silver salt with a reducing agent on the membrane surface resulted in uniform coverage of Ag-NPs, irreversibly bound to the membrane, as confirmed by XPS, TEM, and SEM analyses. Salt selectivity of the membrane as well its surface roughness, hydrophilicity, and zeta potential were not impacted by Ag-NP functionalization, while a slight reduction (up to 17%) in water permeability was observed. The formed Ag-NPs imparted strong antibacterial activity to the membrane, leading to reduction of more than 75% in the number of live bacteria attached to the membrane for three model bacteria strains. In addition, confocal microscopy analyses revealed that Ag-NPs significantly suppressed biofilm formation, with 41% reduction in total biovolume and significant reduction in EPS, dead, and live bacteria on the functionalized membrane. The simplicity of the method, the short reaction time, the ability to load the Ag-NPs on site, and the strong imparted antibacterial activity highlight the potential of this method in real-world RO membrane applications.
Water Research 10/2014; 62:260–270. DOI:10.1016/j.watres.2014.05.049 · 5.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study systematically investigates the organic fouling behavior of a superhydrophilic polyvinylidene fluoride (PVDF) ultrafiltration membrane functionalized via post fabrication tethering of surface-tailored silica nanoparticles to poly(methacrylic acid) grafted PVDF membrane surface. Sodium alginate (SA), Suwannee River natural organic matter (SRNOM), and bovine serum albumin (BSA) were used as model organic foulants to investigate the antifouling behavior of the superhydrophilic membrane with combined fouling (mixture of foulants) and individual fouling (single foulard.) tests. A membrane bioreactor (MBR) plant supernatant was also used to verify the organic antifouling property of the superhydrophilic membrane under realistic conditions. Foulant size distributions and foulant-membrane interfacial forces were measured to interpret the observed membrane fouling behavior. Molecular weight cutoff measurements confirmed that membrane functionalization did not adversely affect the intrinsic membrane selectivity. Both filtration tests with the synthetic foulant-mixture solution (containing SA, SRNOM, and BSA) and MBR plant supernatant demonstrated the reliability and durability of the antifouling property of the superhydrophilic membrane. The conspicuous reduction in foulant-membrane interfacial forces for the functionalized membrane further verified the antifouling properties of the superhydrophilic membrane, suggesting great potential for applications in wastewater treatment.
[Show abstract][Hide abstract] ABSTRACT: Series of nanocomposites with gamma-Fe2O3 supported on SiO2-capsules were prepared by adsorption of hydrophobic iron acetylacetonate on the hydrophilic surface of SiO2-capsules in the evaporation process of the solvent and then calcination the complex at 450 degrees C. The adsorption and calcination conditions were studied and the resultant nanaoparticles were characterized by XRD, XRF and TEM in detail. The results indicated that gamma-Fe2O3 loaded discontinuously but uniformly on the surface of SiO2-capsules at appropriate content. The specific surface area characterization and doxorubicin hydrochloride release shown although the surface area of the target composites decreased slightly, the nanoparticles still had large potential using as drug delivery and magnetic targeting system.
Solid State Sciences 08/2014; 34. DOI:10.1016/j.solidstatesciences.2014.05.006 · 1.68 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Layered double hydroxides (LDHs) with a hierarchical mesostructure are successfully synthesized on mesoporous silica foams by simple impregnation and hydrothermal treatment. The as-synthesized LDH/silica foam nanocomposites show well-defined mesostructures with high surface areas, large pore volumes, and mesopores of 6–7 nm. The nanocomposites act as carbon dioxide (CO2) sorbents under simulated flue gas conditions. They also exhibit significantly enhanced CO2 capacities under high-pressure conditions and high CO2/N2 and CO2/CH4 selectivities.
[Show abstract][Hide abstract] ABSTRACT: Adsorption using solid amine sorbents is an attractive emerging technology for energy-efficient carbon capture. Current syntheses for solid amine sorbents mainly based on physical impregnation or grafting-to methods (for example, aminosilane-grafting) lead to limited sorbent performance in terms of stability and working capacity, respectively. Here we report a family of solid amine sorbents using a grafting-from synthesis approach and synthesized by cationic polymerization of oxazolines on mesoporous silica. The sorbent with high amount of covalently tethered amines shows fast adsorption rate, high amine efficiency and sorbent capacity well exceeding the highest value reported to date for low-temperature carbon dioxide sorbents under simulated flue gas conditions. The demonstrated efficiency of the new amine-immobilization chemistry may open up new avenues in the development of advanced carbon dioxide sorbents, as well as other nitrogen-functionalized systems.
[Show abstract][Hide abstract] ABSTRACT: Biofouling is a major operational challenge in reverse osmosis (RO) desalination, motivating a search for improved biofouling control strategies. Copper, long known for its antibacterial activity and relatively low cost, is an attractive potential biocidal agent. In this paper, we present a method for loading copper nanoparticles (Cu-NPs) on the surface of thin-film composite (TFC) RO membranes. Cu-NPs were synthesized using polyethyleneimine (PEI) as a capping agent, resulting in particles with an average radius of 34 nm and a copper content between 39 and 49 wt.%. The positive charge of the Cu-NPs, imparted by the PEI, allowed a simple electrostatic functionalization of the negatively charged RO membrane. We confirmed functionalization and irreversible binding of the Cu-NPs to the membrane surface with SEM and XPS after exposing the membrane to bath sonication. We also demonstrated that Cu-NP functionalization can be repeated after the Cu-NPs dissolve from the membrane surface. The Cu-NP functionalization had minimal impact on the membrane intrinsic transport properties. Surface hydrophilicity and surface roughness were also maintained, and the membrane surface charge became positive after functionalization. The functionalized membrane exhibited significant antibacterial activity, leading to 80-95% reduction in the number of attached live bacteria for three different model bacterial strains. Challenges associated with this functionalization method and its implementation in RO desalination are discussed.
[Show abstract][Hide abstract] ABSTRACT: By combining elements of hard- and soft-templating, a facile synthesis method for carbon foams with large mesopores has been demonstrated. A commercial Pluronic surfactant was used as the structure-directing agent as well as the carbon precursor. No micelle swelling agent or post treatment is necessary to enlarge mesopores. As such this method requires fewer synthesis steps and is highly scalable. The as-synthesized meso-carbons showed potential applications in the fields of carbon oxide capture and lithium-sulfur batteries.
[Show abstract][Hide abstract] ABSTRACT: Surfactant-intercalated Zn and Al layered double hydroxides (ZnAl-LDHs) were synthesized via spontaneous self-assembly of the surfactants (sodium dodecyl sulfate and sodium dodecyl benzene sulfonate) and the LDH salt precursors. To understand the function of the surfactants in the synthesis, the surfactant-modified ZnAl-LDHs and their intermediates before aging were characterized via X-ray diffraction, Fourier transform infrared spectroscopy, Field emission scanning electron microscopy, and thermogravimetric analysis. In addition, fluorescence spectroscopy was used to in situ trace the microenvironmental variations of the reactants in the synthesis. It was found that the anionic surfactants can interact with the LDH precursors to form cooperative micellar assemblies, which increase the concentration of cationic counter ions around the micelles leading to enhanced growth of the LDH sheets along their lamellar surface direction and the stacking of LDH sheets into nanoparticles as the surfactant possesses longer molecular length. Because of the hydrophobicity of the intermediate sheets coated with surfactants, the reaction between the dissolved CO3 (2-) and the LDH intermediate sheets can be greatly reduced, and thus no strict N-2 protection was necessary in this method. This mechanistic understanding of the effects of the surfactants on the formation of LDHs is critical in successful synthesis of organic-intercalated LDHs in complicated system by void the interruption of competitive ions.
[Show abstract][Hide abstract] ABSTRACT: Suited for heavy stuff: An efficient mesoporous sorbent based on a pure ethylendiamine-bridged polysilsesquioxane is presented. This material, with both a high amine loading and a high surface area, is applied for heavy metal ion removal.
[Show abstract][Hide abstract] ABSTRACT: A series of high-capacity, amine impregnated sorbents based on a cost-effective silica foam with ultra-large mesopores is reported. The sorbents exhibit fast CO2 capture kinetics, high adsorption capacity (of up to 5.8 mmol g−1 under 1 atm of dry CO2), as well as good stability over multiple adsorption–desorption cycles. A simple theoretical analysis is provided relating the support structure to sorbent performance.
[Show abstract][Hide abstract] ABSTRACT: A novel high efficiency nanocomposite sorbent for CO2 capture has been developed based on oligomeric amine (polyethylenimine, PEI, and tetraethylenepentamine, TEPA) functionalized mesoporous silicacapsules. The newly synthesized sorbents exhibit extraordinary capture capacity up to 7.9 mmol g−1 under simulated flue gas conditions (pre-humidified 10% CO2). The CO2 capture kinetics were found to be fast and reached 90% of the total capacities within the first few minutes. The effects of the mesoporous capsule features such as particle size and shell thickness on CO2 capture capacity were investigated. Larger particle size, higher interior void volume and thinner mesoporous shell thickness all improved the CO2 capacity of the sorbents. PEI impregnated sorbents showed good reversibility and stability during cyclic adsorption–regeneration tests (50 cycles).
[Show abstract][Hide abstract] ABSTRACT: We report an interesting approach for efficient synthesis of SnO(2) hollow spheres inside mesoporous silica "nanoreactors". The as-prepared products are shown to have a uniform size distribution and good structural stability. When evaluated for their lithium storage properties, these SnO(2) hollow spheres manifest improved capacity retention.
Journal of the American Chemical Society 01/2011; 133(1):21-3. DOI:10.1021/ja108720w · 11.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: An amine functionalized silica nanocomposite was synthesized by a one-pot reaction in the presence of surfactant templates. Carbon dioxide adsorption from a simulated flue gas stream and pure dried CO2 under atmospheric pressure was successfully performed with the hybrid nanocomposite. The captured CO2 can be easily and completely recovered by a purge gas or heating to 50-100 C. The multi-cycle experiments have shown that the adsorbent has very good stability and regenerability. A high organic loading, up to ~45 wt %, was achieved by the covalently bonding the organic groups to the silica support instead of physical impregnation, and as a result, a large CO2 absorption capacity ( 100mg CO2/g adsorbent) was observed for the absorbent. Results of analytical characterization of the hybrid nanocomposite will also be discussed.
[Show abstract][Hide abstract] ABSTRACT: The kinetics of RAFT inverse miniemulsion polymerization of acrylamide are presented. The polymerizations exhibit typical behavior of controlled polymerizations under conditions where the hydrolytic degradation of the RAFT agent is less favorable. The effects of different reaction parameters such as temperature, initiator concentration, pH of the aqueous phase, RAFT agent, and surfactant concentration on RAFT inverse miniemulsion polymerization are presented. The particle nucleation process in the inverse miniemulsion polymerizations is evaluated by the use of radical scavengers. The presence of RAFT agent was found to have a significant impact on the particle nucleation process. The fate of desorbed monomeric radicals in inverse miniemulsion polymerizations is evaluated by the comparison of the rates of propagation, re-entry, and termination. One of the potential reasons for the induction time observed in the RAFT inverse miniemulsion polymerizations is suggested to be associated with desorption of monomeric and oligomeric radicals from the particles to the continuous oil phase.
[Show abstract][Hide abstract] ABSTRACT: Well defined hydrophilic or amphiphilic polymer latexes and polymer composites in submicron size have important applications in various fields such as drug delivery, industrial catalysis, and coatings. However, these well defined polymer latexes and composites are usually difficult to produce in large scale due to the issue of mixing and heat transfer. To overcome the above problems, RAFT inverse miniemulsion polymerization is applied here as a unique approach to synthesize these nanosized hydrophilic polymer latexes and composites. Moreover, the polymers derived from RAFT inverse miniemulsion polymerizations maintain their “livingness” and can be easily functionalized. The kinetic behavior of inverse RAFT miniemulsion polymerization is studied and effects of reaction parameters on inverse miniemulsion polymerizations are investigated. Responsive nanoparticles are synthesized and the applications of RAFT inverse miniemulsion polymerization are also discussed.