We report a new way of storing CO2 in a highly porous hydrate structure, stabilized by silica nanoparticles (NPs). Such a porous CO2 hydrate structure was generated either by cooling down NP-stabilized CO2-in-seawater foams, or by gently mixing CO2 and seawater that contains silica NPs under CO2 hydrate-generating conditions. With the highly porous structure, enhanced desalination was also achievable when the partial meltdown of CO2 hydrate was allowed
Three techniques to measure and understand the contact angle, θ, of a CO2/brine/rock system relevant to geologic carbon storage were performed with Mount Simon sandstone. Traditional sessile drop measurements of CO2/brine on the sample were conducted and a water-wet system was observed, as is expected. A novel series of measurements inside of a Mount Simon core, using a micro X-ray computed tomography imaging system with the ability to scan samples at elevated pressures, was used to examine the θ of residual bubbles of CO2. Within the sandstone core the matrix appeared to be neutrally wetting, with an average θ around 90°. A large standard deviation of θ (20.8°) within the core was also observed. To resolve this discrepancy between experimental measurements, a series of Lattice Boltzmann model simulations were performed with differing intrinsic θ values. The model results with a θ=80° were shown to match the core measurements closely, in both magnitude and variation. The small volume and complex geometry of the pore spaces that CO2 was trapped in is the most likely explanation of this discrepancy between measured values, though further work is warranted.
Recently, N,N-trans Re(O)(LN–O)2X (LN–O = monoanionic N–O chelates; X = Cl or Br prior to being replaced by solvents or alkoxides) complexes have been found to be superior to the corresponding N,N-cis isomers in the catalytic reduction of perchlorate via oxygen atom transfer. However, reported methods for Re(O)(LN–O)2X synthesis often yield only the N,N-cis complex or a mixture of trans and cis isomers. This study reports a geometry-inspired ligand design rationale that selectively yields N,N-trans Re(O)(LN–O)2Cl complexes. Analysis of the crystal structures revealed that the dihedral angles (DAs) between the two LN–O ligands of N,N-cis Re(O)(LN–O)2Cl complexes are less than 90°, whereas the DAs in most N,N-trans complexes are greater than 90°. Variably sized alkyl groups (−Me, −CH2Ph, and −CH2Cy) were then introduced to the 2-(2′-hydroxyphenyl)-2-oxazoline (Hhoz) ligand to increase steric hindrance in the N,N-cis structure, and it was found that substituents as small as −Me completely eliminate the formation of N,N-cisisomers. The generality of the relationship between N,N-trans/cis isomerism and DAs is further established from a literature survey of 56 crystal structures of Re(O)(LN–O)2X, Re(O)(LO–N–N–O)X, and Tc(O)(LN–O)2X congeners. Density functional theory calculations support the general strategy of introducing ligand steric hindrance to favor synthesis of N,N-trans Re(O)(LN–O)2X and Tc(O)(LN–O)2X complexes. This study demonstrates the promise of applying rational ligand design for isomeric control of metal complex structures, providing a path forward for innovations in a number of catalytic, environmental, and biomedical applications.
A novel ultrafast reflective grating-imaging technique has been developed to measure ambipolar carrier diffusion in GaAs/AlAs quantum wells and bulk GaAs. By integrating a transmission grating and an imaging system into the traditional pump–probe setup, this technique can acquire carrier diffusion properties conveniently and accurately. The fitted results of the diffusion coefficient and diffusion length in bulk GaAs agree well with the literature values obtained by other techniques. The diffusion coefficient and diffusion length of GaAs/AlAs quantum wells are found to increase with the well layer thickness, which suggests that interface roughness scattering dominates carrier diffusion in GaAs/AlAs quantum wells. With the advantages of simple operation, sensitive detection, rapid and nondestructive measurement, and extensive applicability, the ultrafast reflective grating-imaging technique has great potential in experimental study of carrier diffusion in various materials.
Brain function can be best studied by simultaneous measurements and modulation of the multifaceted signaling at the cellular scale. Extensive efforts have been made to develop multifunctional neural probes, typically involving highly specialized fabrication processes. Here, we report a novel multifunctional neural probe platform realized by applying ultra-thin nanoelectronic coating (NEC) on the surfaces of conventional microscale devices such as optical fibers and micropipettes. We fabricated the NECs by planar photolithography techniques using a substrate-less and multi-layer design, which host arrays of individually addressed electrodes with an overall thickness below 1 µm. Guided by an analytic model and taking advantage of the surface tension, we precisely aligned and coated the NEC devices on the surfaces of these conventional micro-probes, and enabled electrical recording capabilities on par with the state-of-the-art neural electrodes. We further demonstrated optogenetic stimulation and controlled drug infusion with simultaneous, spatially resolved neural recording in a rodent model. This study provides a low-cost, versatile approach to construct multifunctional neural probes that can be applied to both fundamental and translational neuroscience.
Members of the Geobacteraceae family are ubiquitous metal reducers that utilize conductive ‘nanowires’ to reduce Mn(IV) and Fe(III) oxides in anaerobic sediments. However, it is not currently known if and to what extent the Mn(IV) and Fe(III) oxides in soil grains and low permeability sediments that are sequestered in pore spaces too small for cell passage can be reduced by long-range extracellular electron transport via Geobacter nanowires, and what mechanisms control this reduction. We developed a microfluidic reactor that physically separates Geobacter sulfurreducens from the Mn(IV) mineral birnessite by a 1.4 μm thick wall containing <200 nm pores. Using optical microscopy and Raman spectroscopy, we show that birnessite can be reduced up to 15 μm away from cell bodies, similar to the reported length of Geobacter nanowires. Reduction across the nanoporous wall required reducing conditions, provided by Escherichia coli, and an exogenous supply of riboflavin. Our results discount electron shuttling by dissolved flavins, and instead support their role as bound redox cofactors in electron transport from nanowires to metal oxides. We also show that upon addition of a soluble electron shuttle (i.e., AQDS), reduction extends beyond the reported nanowire length up to 40 μm into a layer of birnessite.
Fibrosis and hence capsule formation around the glaucoma implants are the main reasons for glaucoma implant failure. To address these issues, we designed a microfluidic meshwork and tested its biocompatibility in a rabbit eye model. The amount of fibrosis elicited by the microfluidic meshwork was compared to the amount elicited by the plate of conventional glaucoma drainage device
All-optical switches have been considered as a promising solution to overcome the fundamental speed limit of the current electronic switches. However, the lack of a suitable third-order nonlinear material greatly hinders the development of this technology. Here we report the observation of ultrahigh third-order nonlinearity about 0.45 cm2/GW in graphene oxide thin films at the telecommunication wavelength region, which is four orders of magnitude higher than that of single crystalline silicon. Besides, graphene oxide is water soluble and thus easy to process due to the existence of oxygen containing groups. These unique properties can potentially significantly advance the performance of all-optical switches.