174 research outputs found
Localized hydrogels based on cellulose nanofibers and wood pulp for rapid removal of methylene blue
Access to clean water has become increasingly difficult, motivating the need for materials that can efficiently remove pollutants. Hydrogels have been explored for remediation, but they often require long times to reach high levels of adsorption. To overcome this limitation, we developed a rapid, locally formed hydrogel that adsorbs dye during gelation. These hydrogels are derived from celluloseâa renewable, nontoxic, and biodegradable resource. More specifically, we found that sulfated cellulose nanofibers or sulfated wood pulps, when mixed with a waterâsoluble, cationic cellulose derivative, efficiently remove methylene blue (a cationic dye) within seconds. The maximum adsorption capacity was found to be 340â±â40âmg methylene blue/g cellulose. As such, these localized hydrogels (and structural analogues) may be useful for remediating other pollutants.Access to clean water has become increasingly difficult, motivating the need for materials that can efficiently remove pollutants. In this work, locally formed hydrogels made from mixing anionic and cationic cellulose derivatives are developed, which rapidly adsorb cationic dye during the gel formation process. A maximum adsorption efficiency of 340 ± 40mg methylene blue/g cellulose was observed, rivaling comparable celluloseâbased gels reported. These localized hydrogels (and structural analogues) may be useful for remediating other pollutants.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163385/2/pola29833.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163385/1/pola29833_am.pd
ChainâGrowth Polymerization of Aryl Grignards Initiated by a Stabilized NHCâPd Precatalyst
An Nâheterocyclic carbeneâligated palladium catalyst was discovered to mediate living, chainâgrowth polymerizations of both phenyleneâ and thiopheneâbased monomers. Polymerization of a fluoreneâbased monomer, on the other hand, did not proceed through a living, chainâgrowth pathway. Excitingly, block copolymerizations of phenylene and thiophene proceeded via a chainâgrowth pathway, regardless of the order of monomer addition. Although some chain termination was observed during these copolymerizations, this pathway could be minimized when the second monomer was added shortly after consumption of the first monomer. These results suggest that the catalyst restingâstate at the end of polymerization is unstable. As a result, modifications to the NHCâscaffold or the 3âchloropyridine ligand will be necessary to generate an improved catalyst. A Pd catalyst that can mediate a living, chainâgrowth polymerization of Ïâconjugated monomers is reported. Using (IPr)Pd(3âchloropyridine)Cl 2 as a precatalyst, both homopolymers and block copolymers of phenyleneâ and thiopheneâbased monomers were prepared. Although a living, chainâgrowth mechanism is observed during polymerization, the catalyst resting state is somewhat unstable after the monomer is consumed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92031/1/marc_201200096_sm_suppl.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/92031/2/842_ftp.pd
Improving Information Literacy through Wikipedia Editing in the Chemistry Classroom: Lessons Learned
Assignments in which students edit Wikipedia may help students learn about the complexities of information creation and production, while engaging them in researching and writing about topics related to class content. This chapter presents two case studies that illustrate how Wikipedia-based activities can be designed to achieve both chemistry and information literacy learning outcomes. In both examples, faculty partnered with a librarian to implement the Wikipedia editing assignments. Through these experiences, those involved learned about Wikipedia and its community, and identified promising practices for project requirements based on formal and informal assessment and observations. Reflections are offered on the value of using Wikipedia editing assignments and concrete suggestions for creating effective projects are offered
Random Copolymers Outperform Gradient and Block Copolymers in Stabilizing Organic Photovoltaics
Recent advances have led to conjugated polymerâbased photovoltaic devices with efficiencies rivaling amorphous silicon. Nevertheless, these devices become less efficient over time due to changes in active layer morphology, thereby hindering their commercialization. Copolymer additives are a promising approach toward stabilizing blend morphologies; however, little is known about the impact of copolymer sequence, composition, and concentration. Herein, the impact of these parameters is determined by synthesizing random, block, and gradient copolymers with a poly(3âhexylthiophene) (P3HT) backbone and sideâchain fullerenes (phenylâC61âbutyric acid methyl ester (PC61BM)). These copolymers are evaluated as compatibilizers in photovoltaic devices with P3HT:PC61BM as the active layer. The random copolymer with 20 mol% fullerene side chains and at 8 wt% concentration in the blend gives the most stable morphologies. Devices containing the random copolymer also exhibit higher and more stable power conversion efficiencies than the control device. Combined, these studies point to the random copolymer as a promising new scaffold for stabilizing bulk heterojunction photovoltaics.Photovoltaic devices made from conjugated polymers now exhibit efficiencies rivaling amorphous silicon; however, the poor longevity of these devices continues to stymie their commercial impact. Copolymer additives represent a promising solution, yet little is known about how the copolymer sequence, composition, and concentration influence their compatibilizing abilities. Herein, random copolymer additives lead to higher efficiency and longerâlasting photovoltaic devices.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150505/1/adfm201900467.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150505/2/adfm201900467_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150505/3/adfm201900467-sup-0001-S1.pd
Toward oneâpot olefin/thiophene block copolymers using an in situ ligand exchange
Block copolymers containing both conducting and insulating segments are of interest due to their enhanced electrical properties arising from their increased crystallization. Yet few methods exist for generating these copolymers, because the reaction conditions for synthesizing each block are often incompatible. Herein, efforts toward identifying a oneâpot, living polymerization method for synthesizing block copolymers of 1âpentene and 3âhexylthiophene is described. An in situ ligand exchange enables the optimal catalyst to be utilized for synthesizing each block. Even under these conditions, however, only homopolymers are observed. Computational studies modeling the ligand exchange reveal that the added stabilizing ligands likely inhibit propagation of the second block. These results suggest an ancillary ligandâbased âgoldilocksâ effect wherein catalysts that are stable yet still reactive are required. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 1601â1605Combined experimental and computational studies revealed unexpected challenges in applying sequential catalysis for the streamlined synthesis of insulating/conducting block copolymers.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/150553/1/pola29426_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150553/2/pola29426.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/150553/3/pola29426-sup-0001-AppendixS1.pd
Trials and tribulations of designing multitasking catalysts for olefin/thiophene block copolymerizations
Block copolymers containing both insulating and conducting segments have been shown to exhibit improved charge transport properties and air stability. Nevertheless, their syntheses are challenging, relying on multiple postâpolymerization functionalization reactions and purifications. A simpler approach would be to synthesize the block copolymer in one pot using the same catalyst to enchain both monomers via distinct mechanisms. Such multitasking polymerization catalysts are rare, however, due to the challenges of finding a single catalyst that can mediate living, chainâgrowth polymerizations for each monomer under similar conditions. Herein, a diimineâligated Ni catalyst is evaluated and optimized to produce block copolymer containing both 1âpentene and 3âhexylthiophene. The reaction mixture also contains both homopolymers, suggesting catalyst dissociation during and/or after the switch in mechanisms. Experimental and theoretical studies reveal a high energy switching step coupled with infrequent catalyst dissociation as the culprits for the low yield of copolymer. Combined, these studies highlight the challenges of identifying multitasking catalysts, and suggest that further tuning the reaction conditions (e.g., ancillary ligand structure and/or metal) is warranted for this specific copolymerization. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 132â137Block copolymers containing insulating segments (derived from 1âpentene) and conducting segments (derived from 3âhexylthiophene) are synthesized in one pot using a single multitasking catalyst. Notably, this process requires different enchainment mechanisms (coordination/insertion vs. crossâcoupling) mediated by the same precatalyst. Nevertheless, the block copolymer is the minor product due to a slow switching step between the mechanisms coupled with catalyst dissociation from the polymer chain.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/139919/1/pola28885_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139919/2/pola28885.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139919/3/pola28885-sup-0001-suppinfo.pd
Molecular weight dependent structure and charge transport in MAPLEâdeposited poly(3âhexylthiophene) thin films
In this work, poly(3âhexylthiophene) (P3HT) films prepared using the matrixâassisted pulsed laser evaporation (MAPLE) technique are shown to possess morphological structures that are dependent on molecular weight (MW). Specifically, the structures of low MW samples of MAPLEâdeposited film are composed of crystallites/aggregates embedded within highly disordered environments, whereas those of high MW samples are composed of aggregated domains connected by long polymer chains. Additionally, the crystallite size along the sideâchain (100) direction decreases, whereas the conjugation length increases with increasing molecular weight. This is qualitatively similar to the structure of spinâcast films, though the MAPLEâdeposited films are more disordered. Inâplane carrier mobilities in the MAPLEâdeposited samples increase with MW, consistent with the notion that longer chains bridge adjacent aggregated domains thereby facilitating more effective charge transport. The carrier mobilities in the MAPLEâdeposited simples are consistently lower than those in the solventâcast samples for all molecular weights, consistent with the shorter conjugation length in samples prepared by this deposition technique. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 652â662The structure of MAPLEâdeposited P3HT thin films is shown to possess molecular weight (MW) dependence behavior. The MAPLE films deposited from low MW materials consist of crystallite domains embedded within a highly amorphous environment, whereas those deposited from high MW materials are composed of long polymer chains bridging the aggregate domains. The inâplane mobility is shown to increase with MW, highlighting the importance of domain connectivity in facilitating charge transport in conjugated polymers.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/142537/1/polb24588-sup-0001-suppinfo1.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142537/2/polb24588_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/142537/3/polb24588.pd
Association of polygenic scores with chronic kidney disease phenotypes in a longitudinal study of older adults
Risk of chronic kidney disease (CKD) is influenced by environmental and genetic factors and increases sharply in individuals 70 years and older. Polygenic scores (PGS) for kidney disease-related traits have shown promise but require validation in well-characterized cohorts. Here, we assessed the performance of recently developed PGSs for CKD-related traits in a longitudinal cohort of healthy older individuals enrolled in the Australian ASPREE randomized controlled trial of daily low-dose aspirin with CKD risk at baseline and longitudinally. Among 11,813 genotyped participants aged 70 years or more with baseline eGFR measures, we tested associations between PGSs and measured eGFR at baseline, clinical phenotype of CKD, and longitudinal rate of eGFR decline spanning up to six years of follow-up per participant. A PGS for eGFR was associated with baseline eGFR, with a significant decrease of 3.9 mL/min/1.73m2 (95% confidence interval -4.17 to -3.68) per standard deviation (SD) increase of the PGS. This PGS, as well as a PGS for CKD stage 3 were both associated with higher risk of baseline CKD stage 3 in cross-sectional analysis (Odds Ratio 1.75 per SD, 95% confidence interval 1.66-1.85, and Odds Ratio 1.51 per SD, 95% confidence interval 1.43-1.59, respectively). Longitudinally, two separate PGSs for eGFR slope were associated with significant kidney function decline during follow-up. Thus, our study demonstrates that kidney function has a considerable genetic component in older adults, and that new PGSs for kidney disease-related phenotypes may have potential utility for CKD risk prediction in advanced age
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