Flexible Thermopiles Based on Hydrogels with Carriers Moving in Opposite Directions

Thermoelectric generators based on body heat are green, sustainable, and flexible power sources, and their efficiency could be greatly improved by thermopiles. Herein, a unique concept of thermopiles is proposed in which two types of hydrogels with positively charged carriers moving in different directions are fabricated. One of them shows a positive Seebeck coefficient of 3.81 mV/K due to the movement of cations from the cold to hot region, while the other displays a negative Seebeck coefficient of −2.33 mV/K due to the movement of cations in the opposite direction. Notably, the Seebeck coefficient of the latter is increased by 50 times in comparison to that of the original component due to the conversion from an electronic to an ionic thermoelectric conductor. Also, the thermopile with a Seebeck coefficient of 6.18 mV/K shows excellent flexibility and stability when applied in wearable textiles. Compared to traditional wearable thermopiles, the thermopiles based on hydrogels containing carriers with opposite thermal motion directions exhibit a much more outstanding thermoelectric performance. This work contributes to addressing the lack of n-type thermoelectric materials and extending the field of thermoelectric devices

Smartly Aligning Nanowires by a Stretching Strategy and Their Application As Encoded Sensors

The nanotechnology world is being more and more attracted toward high aspect ratio one-dimensional nanostructures due to their potentials as building blocks for electronic/optical devices. Here, we propose a novel method to generate nanowire patterns with assistance of superhydrophobic flexible polydimethylsiloxane (PDMS) substrates. Micropillar gaps are tunable <i>via</i> a stretching process of the PDMS surface; thus, diverse nanowire patterns can be formed by stretching the same PDMS surface in various ways. Importantly, square nanowire loops with alternative compositions can be generated through a double-stretching process, showing an advanced methodology in controlling the alignment of nanowires. Since alternative fluorescent molecules will be quenched by diverse chemical substances, this alternative nanowire loop shows a selective detection for diverse target compounds, which greatly improves the application of this nanowire patterning approach. Furthermore, such alternative nanowire patterns can be transferred from pillar-structured surfaces to flat films, indicating further potentials in microcircuits, sensitive sensors, and other organic functional nanodevices

Biomimetic Oxygen Reduction Reaction Catalyzed by Microperoxidase-11 at Liquid/Liquid Interfaces

An investigation of oxygen reduction reaction (ORR) catalyzed by microperoxidase-11 (MP-11) at the polarized water/1,2-dichloroethane (DCE) interface is reported. MP-11 contains a heme group covalently bonded to an undecapeptide chain via two thioether bonds of cysteine residues, as in cytochrome <i>c</i> oxidases (C<i>c</i>Os), and has been widely studied as a biomimetic model of C<i>c</i>Os. Herein we demonstrated that MP-11 can adsorb at the water/DCE interface and catalyze the O₂ reduction by lipophilic electron donors, namely tetrathiafulvalene (TTF) and 1,1′-dimethylferrocene (DFc). The overall catalytic ORR corresponds to a proton coupled electron transfer (PCET) reaction and is kinetically controlled by the heterogeneous conversion of MP-11 from ferric (Fe^III-MP-11) to ferrous state (Fe^II-MP-11). Given that a significant amount of H₂O₂ was produced for both electron donors, it indicates that MP-11 has a remarkable impact on the ORR pathway and that MP-11, similar to other mononuclear macrocyclic compounds, cannot selectively catalyze the 4e^–/4H⁺ reduction of O₂ to H₂O. The results also suggest that one should carefully considers the role of Cu site in C<i>c</i>Os and the reaction environment to understand respiratory ORR and to develop more selective catalysts for practical applications (e.g., fuel cells)

Molecular Filtration by Ultrathin and Highly Porous Silica Nanochannel Membranes: Permeability and Selectivity

An ideal molecular filtration membranes should be highly permeable and selective, thus desiring the membranes to be ultrathin, be highly porous, and consists of small and uniform pores or channels. In this work, we report the molecular filtration by free-standing ultrathin silica nanochannel membranes (SNMs) using a U-shaped cell and spectrophotometric detection, focusing on the quantitative evaluation of permeability and selectivity of SNMs. Thanks to the ultrasmall channel size, namely, ∼2–3 nm, and the negatively charged channel surface arising from the deprotonation of silanol groups, the SNM displayed excellent size and charge selectivity for molecular filtration. The selectivity coefficient for separation of small methyl viologen from large cytochrome <i>c</i> is as high as 273, because of the uniform pore/channel size. The charge-based filtration can be modulated by the salt concentration and solution pH, which control the overlap of radial electrical double layer and surface charge sign/density, respectively. Owing to the high relative pore density, namely, 16.7%, and the straight and vertical channel orientation, the SNM is highly permeable, displaying a molecule flux much higher than commercially available dialysis membrane and others reported previously. In addition, we demonstrated that, by biasing a small voltage across the SNM, both the flux and separation selectivity could be significantly enhanced

Portable Sensor for the Detection of Choline and Its Derivatives Based on Silica Isoporous Membrane and Gellified Nanointerfaces

A portable amperometric ion sensor was fabricated by integrating silica isoporous membrane (SIM) and organogel composed of polyvinyl chloride and 1,2-dichloroethane (PVC-DCE) on a 3D-printed polymer chip. The detection of ionic species in aqueous samples could be accomplished by adding a microliter of sample droplet to the sensor and by identifying the ion-transfer potential and current magnitude at the water/organogel interface array templated by SIM. Thanks to the ultrasmall channel size (2–3 nm in diameter), high channel density (4 × 10⁸ μm^–2), and ultrathin thickness (80 nm) of SIM, the ensemble of nanoscopic water/organogel (nano-W/Gel) interface array behaved like a microinterface with two back-to-back hemispherical mass diffusion zones. So, the heterogeneous ion-transfer across the nano-W/Gel interface array generated a steady-state sigmoidal current wave. The detection of choline (Ch) and its derivatives, including acetylcholine (ACh), benzoylcholine (BCh), and atropine (AP), in aqueous samples was examined with this portable sensor. Using differential pulse stripping voltammetry (DPSV), the quantification of these analytes was achieved with a limit of detection (LOD) down to 1 μM. Moreover, the portable ion sensor was insensitive to various potential interferents that might coexist in vivo, owing to size-/charge-based selectivity and antifouling capacity of SIM. With this priority, the portable ion sensor was able to quantitatively determine Ch and its derivatives in diluted urine and blood samples. The LODs for Ch, ACh, AP, and BCh in urine were 1.12, 1.30, 1.08, and 0.99 μM, and those for blood samples were 3.61, 3.38, 2.32, and 1.81 μM, respectively

Ultrathin Silica Membranes with Highly Ordered and Perpendicular Nanochannels for Precise and Fast Molecular Separation

Membranes with the ability of molecular/ionic separation offer potential in many processes ranging from molecular purification/sensing, to nanofluidics and to mimicking biological membranes. In this work, we report the preparation of a perforative free-standing ultrathin silica membrane consisting of straight and parallel nanochannels with a uniform size (∼2.3 nm) for precise and fast molecular separation. Due to its small and uniform channel size, the membrane exhibits a precise selectivity toward molecules based on size and charge, which can be tuned by ionic strength, pH or surface modification. Furthermore, the ultrasmall thickness (10–120 nm), vertically aligned channels, and high porosity (4.0 × 10¹² pores cm^–2) give rise to a significantly high molecular transport rate. In addition, the membrane also displays excellent stability and can be consecutively reused for a month after washing or calcination. More importantly, the membrane fabrication is convenient, inexpensive, and does not rely on sophisticated facilities or conditions, providing potential applications in both separation science and micro/nanofluidic chip technologies

Permselective Ion Transport Across the Nanoscopic Liquid/Liquid Interface Array

Free-standing silica nanochannel membrane (SNM) with perforated channels was utilized to create arrays of nanoscale interfaces between two immiscible electrolyte solutions (nano-ITIES), at which permselective ion transfer and detection were achieved. The SNM consisted of a high density of straight nanochannels with a diameter of 2–3 nm and a length of 70 nm. The silicon wafer coated by 150 nm-thick porous silicon nitride film (p-SiNF) with pores of 5 μm-in-diameter was used to support the SNM in a form of nanochannel-on-micropore. Considering the material surface lipophilicity, the nano-ITIES array was formed at the boundary between SNM and p-SiNF, with a diffusion geometry equivalent to two back-to-back inlaid microdisc interfaces. Thus, the transfer of tetraethylammonium (TEA⁺) across the nano-ITIES array yielded symmetric sigmoidal current responses. In addition, because of the ultrasmall size and negatively charged surface of silica nanochannels, the nano-ITIES displayed obvious size and charge permselectivities. Transfer of ions with a size comparable with or larger than the nanochannel was sterically blocked. Also that of anions with a size smaller than the nanochannels encountered the strong electrostatic repulsion from channel walls, showing obvious dependence on the ionic strength of aqueous solution. The present approach is facile and inexpensive for building a nano-ITIES array with potential applications in ion detection and separation

Highly Ordered Binary Assembly of Silica Mesochannels and Surfactant Micelles for Extraction and Electrochemical Analysis of Trace Nitroaromatic Explosives and Pesticides

The rapid and sensitive detection of nitroaromatic compounds is of great significance for human health, the environment, and public security. The present work reports on the extraction and electrochemical analysis of trace nitroaromatic compounds, such as explosives and organophosphate pesticides (OPs), using the indium tin oxide (ITO) electrodes modified with a highly ordered and aligned binary assembly of silica mesochannels and micelles (BASMM). With a pore diameter of ca. 2–3 nm, silica mesochannels (SMs) perpendicularly oriented to the ITO electrode surface can provide hard and robust supports to confine the soft cylindrical micelles formed by the aggregation of cationic surfactants, namely, cetyltrimethylammonium bromide (CTAB). Due to the organized self-assembly of hydrocarbon tails of CTAB surfactants, each micelle has a hydrophobic core, which acts as an excellent adsorbent for rapid extraction and preconcentration of trace nitroaromatic compounds from aqueous solutions via the hydrophobic effect. Furthermore, the cylindrical micelles are directly in contact with the underlying electrode surface, to which extracted compounds can freely diffuse and then be reduced therein, thus allowing their determination by means of voltammetry. Using the BASMM/ITO sensor, electrochemical analysis of trace nitroaromatic explosives, including 2,4,6-trinitrotoluene (TNT), 2,4,6-trinitrophenol, 2,6-dinitrotoluene, 3-nitrophenol, and nitrobenzene, and OPs, such as paraoxon, methyl parathion, and fenitrothion, was achieved with a fast response, wide linear range, high sensitivity, and low detection limit at the ppb level. TNT and paraoxon in real apple, tea, and water samples were also determined. By combining the heterogeneous extraction and determination in one ordered binary nanostructure, the BASMM sensor provides a very simple, rapid, and cost-effective way for analysis of nitroaromatic compounds and can be extended to a wide range of lipophilic yet redox-active analytes

Additional file 2 of High precision measurement of trace F and Cl in olivine by electron probe microanalysis

Additional file 2. Table S1. Analytical results for trace F and Cl in San Carlos olivine, synthetic olivine and MgO by new EPMA method. Table S2. Analytical results for trace F and Cl in hornblende standards by new EPMA method. Table S3. Analytical results of secondary fluorescence effects of San Carlos olivines mounted in epoxy rensin and tin metal. Table S4. Compositions of (wt%) epoxy-128 used in this study obtained using element analyzer and ion chromatograph. Table S5. Analytical results for trace F and Cl in natural olivine (Ol-1) by new EPMA method. Table S6. Representative compositions (wt%) of antigorite adjacent to olivine sample (Ol-2). Table S7. Representative compositions (wt%) of olivine sample (Ol-2)

Additional file 1 of High precision measurement of trace F and Cl in olivine by electron probe microanalysis

Additional file 1. Fig. S1. Backscattered electron images of synthetic olivine samples. Fig. S2. Backscattered electron images of natural olivine samples. (a) and (b): Ol-1; (c) and (d): Ol-2. Fig. S3. Count rates for F (a) and absorbed beam current (b) for natural Ol-1 olivine sample over 600 s measurements with various beam currents of 400, 600, and 800 nA. The 2 standard deviations of count rates for F for Ol-1 at 400, 600, and 800 nA were 42, 60 and 62 cps, respectively. Count rates for Cl (c) and absorbed beam current (d) for natural Ol-2 olivine sample over 600 s measurements with various beam currents of 400, 600, and 800 nA. The 2 standard deviations of count rates for Cl for Ol-2 at 400, 600, and 800 nA were 26, 30 and 32 cps, respectively. (Accelerating voltage: 20 kV, beam diameter: 5 μm). Fig. S4. Count rates for F (a), Cl (b), and absorbed beam current (c) for Kakanui hornblende standard over 600 s measurements with various beam currents of 400, 600, and 800 nA (Accelerating voltage: 20 kV, beam diameter: 5 μm). The 2 standard deviations of count rates for F for Kakanui hornblende at 400, 600, and 800 nA were 52, 60 and 82 cps, respectively. The 2 standard deviations of count rates for Cl for Kakanui hornblende at 400, 600, and 800 nA were 37, 45 and 51 cps, respectively. Fig. S5. (a) Smoothed averaged accumulated spectral scans of Kakanui hornblende at the F Kα peak using integral and differential mode on CAMECA SXFive microprobe. The second-order Mg Kβ line was minimized using the optimized differential mode compared to the integral mode. Accelerating voltage = 20 kV; beam current = 150 nA; beam diameter = 10 μm; dwell time = 500 ms; step = 10 (Sinθ*105); accumulation number = 5; differential mode: base line = 2300 mV, window = 2170 mV, PC1 analyzing crystal. Fig. S6. Backscattered electron images of San Carlos olivine samples mounted in epoxy resin (a) and tin metal (b). Fig. S7. Secondary fluorescence effects evaluation of Cl in natural olivine (Ol-2) from the boundary antigorite using FANAL computer code in CalcZAF/Standard softwar