Spring 2022 Superhydrophobic Materials

Many natural surfaces, such as lotus leaves and a water strider’s leg, have shown striking water repellency so that they remain clean and dry even in “dirty” habitats. Such water repellency is called superhydrophobicity, which has stimulated lots of science and engineering imagination for self-cleaning windows, never dirty clothes, drag-reduction swimming suits, etc. In this workshop, we will use superhydrophobicity as a model to guide an integrative teaching and learning experience through hands-on experiments, critical thinking, basic science, as well as a lecture on state-of-the-art research discoveries. The objectives of this workshop are to (1) stimulate student curiosity and imagination through simple hands-on experiments to reproduce a superhydrophobic surface with simple resources like candles or sandpapers with dishes or glass slides, (2) link diverse daily life phenomena to superhydrophobic science and demonstrate how high-school physics plus critical thinking can be used together to advance fundamental science even today, (3) establish lesson plans for STEM education with a wide range of activities that can be adopted by different education levels (K-12), in different classes, and on different subjects. This superhydrophobic surface model can be easily extended to various bioinspired designs to further the interdisciplinary education on biology, chemistry, mechanics, etc. In general, this workshop will foster a life-learning habit that encourages students to keep their eyes open on daily observations and correlate them to the fundamental concepts they learn in the classroom

Status and Prospects of Organic Redox Flow Batteries toward Sustainable Energy Storage

Redox flow batteries (RFBs) are regarded a promising technology for large-scale electricity energy storage to realize efficient utilization of intermittent renewable energy. Redox -active materials are the most important components in the RFB system because their physicochemical and electrochemical properties directly determine their battery performance and energy storage cost. Designable, tunable, and potentially low-cost redox-active organic compounds are promising alternatives to traditional redox-active inorganic compounds for RFB applications. Herein, the representative designs of redox-active molecules, recent development of organic RFBs (ORFBs), and advantages/disadvantages of different ORFB are reviewed. Especially the relationship between redox-active molecules’ physicochemical properties and their battery performance is discussed with an emphasis on the side reactions that cause fading of battery capacity. Finally, we provide an outlook on the development of high-performance ORFBs for practical energy storage applications

An Efficient Viologen-Based Electron Donor to Nitrogenase

Nitrogenase catalyzes the reduction of N2 to NH3, supporting all biological nitrogen fixation. Electron donors to this enzyme are ferredoxin or flavodoxin (in vivo) and sodium dithionite (in vitro). Features of these electron donors put a limit on spectrophotometric studies and electrocatalytic applications of nitrogenase. Although it is common to use methyl viologen as an electron donor for many low-potential oxidoreductases, decreased nitrogenase activity is observed with an increasing concentration of methyl viologen, limiting its utility under many circumstances. In this work, we suggest that this concentration-dependent decrease in activity can be explained by the formation of a dimer of the radical cation of methyl viologen (Me2V•+)2 at higher methyl viologen concentrations. In addition, viologens functionalized with positively and negatively charged groups were synthesized and studied using spectroscopy and cyclic voltammetry. A sulfonated viologen derivative, 1,1′-bis(3-sulfonatopropyl)-4,4′-bipyridinium radical {[(SPr)2V•]−}, was found to support full nitrogenase activity up to a mediator concentration of 3 mM, while the positively charged viologen derivative was not an efficient reductant of nitrogenase due to the high standard redox potential. The utility of [(SPr)2V•]− as an electron donor for nitrogenase was demonstrated by a simple, sensitive spectrophotometric assay for nitrogenase activity that can provide accurate values for the specific activity and turnover rate constant under argon. Under N2, the formation of ammonia was confirmed. Because of the observed full activity of nitrogenase and low overpotential, [(SPr)2V•]− should also prove to be valuable for nitrogenase electrocatalysis, including bioelectrosynthetic N2 reduction

Highly Active Nanostructured CoS2/CoS Heterojunction Electrocatalysts for Aqueous Polysulfide/Iodide Redox Flow Batteries

Aqueous polysulfide/iodide redox flow batteries are attractive for scalable energy storage due to their high energy density and low cost. However, their energy efficiency and power density are usually limited by poor electrochemical kinetics of the redox reactions of polysulfide/iodide ions on graphite electrodes, which has become the main obstacle for their practical applications. Here, CoS2/CoS heterojunction nanoparticles with uneven charge distribution, which are synthesized in situ on graphite felt by a one-step solvothermal process, can significantly boost electrocatalytic activities of I−/I3− and S2−/Sx2−redox reactions by improving absorptivity of charged ions and promoting charge transfer. The polysulfide/iodide flow battery with the graphene felt-CoS2/CoS heterojunction can deliver a high energy efficiency of 84.5% at a current density of 10 mA cm−2, a power density of 86.2 mW cm−2 and a stable energy efficiency retention of 96% after approximately 1000 h of continuous operation

Electrolyzer Design for Flexible Decoupled Water Splitting and Organic Upgrading with Electron Reservoirs

The Bigger Picture Electrocatalytic water splitting is a green approach to producing clean H2 fuel, especially when it is driven by renewable energy sources. Conventional water electrolysis always produces H2 and O2 simultaneously under corrosive acidic or alkaline conditions with large voltage inputs, posing safety concerns of H2/O2 mixing. Therefore, it is desirable to develop a new electrolyzer design for decoupled water splitting in an eco-friendly neutral solution with small voltage inputs to enable separated H2 and O2 evolution. Herein, we report (ferrocenylmethyl)trimethylammonium chloride and Na4[Fe(CN)6] as proton-independent electron reservoirs for achieving separated H2 and O2 evolution in near-neutral solution driven by electricity or solar cells under sunlight irradiation. Na4[Fe(CN)6] can also integrate H2 evolution with organic oxidation to yield H2 and high-value organic products. This work offers promising economic and safety advantages for sustainable H2 production and organic transformation

Targeting the Pseudomonas aeruginosa Virulence Factor Phospholipase C With Engineered Liposomes.

Engineered liposomes composed of the naturally occurring lipids sphingomyelin (Sm) and cholesterol (Ch) have been demonstrated to efficiently neutralize toxins secreted by Gram-positive bacteria such as Streptococcus pneumoniae and Staphylococcus aureus. Here, we hypothesized that liposomes are capable of neutralizing cytolytic virulence factors secreted by the Gram-negative pathogen Pseudomonas aeruginosa. We used the highly virulent cystic fibrosis P. aeruginosa Liverpool Epidemic Strain LESB58 and showed that sphingomyelin (Sm) and a combination of sphingomyelin with cholesterol (Ch:Sm; 66 mol/% Ch and 34 mol/% Sm) liposomes reduced lysis of human bronchial and red blood cells upon challenge with the Pseudomonas secretome. Mass spectrometry of liposome-sequestered Pseudomonas proteins identified the virulence-promoting hemolytic phospholipase C (PlcH) as having been neutralized. Pseudomonas aeruginosa supernatants incubated with liposomes demonstrated reduced PlcH activity as assessed by the p-nitrophenylphosphorylcholine (NPPC) assay. Testing the in vivo efficacy of the liposomes in a murine cutaneous abscess model revealed that Sm and Ch:Sm, as single dose treatments, attenuated abscesses by >30%, demonstrating a similar effect to that of a mutant lacking plcH in this infection model. Thus, sphingomyelin-containing liposome therapy offers an interesting approach to treat and reduce virulence of complex infections caused by P. aeruginosa and potentially other Gram-negative pathogens expressing PlcH

Nonlinear optical interactions in silicon waveguides

The strong nonlinear response of silicon photonic nanowire waveguides allows for the integration of nonlinear optical functions on a chip. However, the detrimental nonlinear optical absorption in silicon at telecom wavelengths limits the efficiency of many such experiments. In this review, several approaches are proposed and demonstrated to overcome this fundamental issue. By using the proposed methods, we demonstrate amongst others supercontinuum generation, frequency comb generation, a parametric optical amplifier, and a parametric optical oscillator