Insights into the Understanding of the Nickel-Based Pre-Catalyst Effect on Urea Oxidation Reaction Activity.

Nickel-based catalysts are regarded as the most excellent urea oxidation reaction (UOR) catalysts in alkaline media. Whatever kind of nickel-based catalysts is utilized to catalyze UOR, it is widely believed that the in situ-formed Ni3+ moieties are the true active sites and the as-utilized nickel-based catalysts just serve as pre-catalysts. Digging the pre-catalyst effect on the activity of Ni3+ moieties helps to better design nickel-based catalysts. Herein, five different anions of OH-, CO32-, SiO32-, MoO42-, and WO42- were used to bond with Ni2+ to fabricate the pre-catalysts ß-Ni(OH)2, Ni-CO3, Ni-SiO3, Ni-MoO4, and Ni-WO4. It is found that the true active sites of the five as-fabricated catalysts are the same in situ-formed Ni3+ moieties and the five as-fabricated catalysts demonstrate different UOR activity. Although the as-synthesized five catalysts just serve as the pre-catalysts, they determine the quantity of active sites and activity per active site, thus determining the catalytic activity of the catalysts. Among the five catalysts, the amorphous nickel tungstate exhibits the most superior activity per active site and can catalyze UOR to reach 158.10 mA·cm-2 at 1.6 V, exceeding the majority of catalysts. This work makes for a deeper understanding of the pre-catalyst effect on UOR activity and helps to better design nickel-based UOR catalysts.

Bioinspired electrically stable, optically tunable thermal management electronic skin via interfacial self-assembly.

The skin is the largest organ in the human body and serves vital functions such as sensation, thermal management, and protection. While electronic skin (E-skin) has made significant progress in sensory functions, achieving adaptive thermal management akin to human skin has remained a challenge. Drawing inspiration from squid skin, we have developed a hybrid electronic-photonic skin (hEP-skin) using an elastomer semi-embedded with aligned silver nanowires through interfacial self-assembly. With mechanically adjustable optical properties, the hEP-skin demonstrates adaptive thermal management abilities, warming in the range of +3.5°C for heat preservation and cooling in the range of -4.2°C for passive cooling. Furthermore, it exhibits an ultra-stable high electrical conductivity of âˆ¼4.5×104 S/cm, even under stretching, bending or torsional deformations over 10,000 cycles. As a proof of demonstration, the hEP-skin successfully integrates stretchable light-emitting electronic skin with adaptive thermal management photonic skin.

Highly sensitive, wide-pressure and low-frequency characterized pressure sensor based on piezoresistive-piezoelectric coupling effects in porous wood.

Lightweight and highly compressible materials have received considerable attention in flexible pressure sensing devices. In this study, a series of porous woods (PWs) are produced by chemical removal of lignin and hemicellulose from natural wood by tuning treatment time from 0 to 15 h and extra oxidation through H2O2. The prepared PWs with apparent densities varying from 95.9 to 46.16 mg/cm3 tend to form a wave-shaped interwoven structure with improved compressibility (up to 91.89 % strain under 100 kPa). The sensor assembled from PW with treatment time of 12 h (PW-12) exhibits the optimal piezoresistive-piezoelectric coupling sensing properties. For the piezoresistive properties, it has high stress sensitivity of 15.14 kPa-1, covering a wide linear working pressure range of 0.06-100 kPa. For its piezoelectric potential, PW-12 shows a sensitivity of 0.443 V·kPa-1 with ultralow frequency detection as low as 0.0028 Hz, and good cyclability over 60,000 cycles under 0.41 Hz. The nature-derived all-wood pressure sensor shows obvious superiority in the flexibility for power supply requirement. More importantly, it presents fully decoupled signals without cross-talks in the dual-sensing functionality. Sensor like this is capable of monitoring various dynamic human motions, making it an extremely promising candidate for the next generation artificial intelligence products.

The degradation of printing and dyeing wastewater by manganese-based catalysts.

Printing and dyeing wastewater generally has high pH, high turbidity, poor biodegradability, complex composition, and high chroma, which make it one of the most difficult industrial wastewaters to treat. Herein, heterogeneous ozone oxidation technology is applied to oxidize and degrade printing and dyeing wastewater. A metal oxide catalyst supported on activated carbon (γ-MnO2/AC) was prepared by hydrothermal synthetic method and shown to enable synergistic catalysis involving MnO2 metal sites and N/C sites. A simulated methyl orange solution was used to determine the effects of various preparation and operation parameters. The results confirmed that the γ-MnO2/AC catalyst exhibited good chemical oxygen demand (COD) removal and reusability. Additionally, γ-MnO2/AC demonstrated excellent degradation of the secondary biochemical effluent of printing and dyeing wastewater (COD removal = 72.45% within 120 min). The γ-MnO2/AC catalyst was fully characterized, and the mechanism governing its catalytic ozone oxidation process was investigated experimentally.

Preparation of highly efficient ion-imprinted polymers with Fe3O4 nanoparticles as carrier for removal of Cr(VI) from aqueous solution.

Fe3O4 magnetic nanoparticles were prepared by hydrothermal synthesis and their surface was modified by the sol-gel method. Polymers imprinted with magnetic Cr (VI) were prepared by using Cr2O72- as template ion, 4-vinyl pyridine (4-VP) as monomer, isopropanol as solvent and Fe3O4 as matrix. The effects of solvent type, amount of Cr (VI) addition and volume of crosslinking agent on the adsorption properties of the imprinted polymers were investigated. The polymers were characterized by Fourier transform infrared (FT-IR) spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). The adsorption equilibrium was reached within 50 min, and the maximum adsorption capacity was 201.55 mg·g-1. The adsorption process conformed to the Langmuir model, and the results of kinetic fitting showed that the pseudo-first-order kinetic model applied. In the Cr2O72-/AlF4- and Cr2O72-/CrO42- competitive systems, the imprinted polymer showed good selectivity to the template ions, with relative selectivity factors of 6.91 and 5.99, respectively. When the imprinted polymer was reused 6 times, the adsorption capacity decreased by only 8.2%, demonstrating good reusability.

Preparation and Application of CO2-Triggered Switchable Solvents in Separation of Toluene/n-Heptane.

Extraction is a common approach to separating aromatics and alkanes, but solvent recovery remains an issue. The polarity, hydrophobic/hydrophilic balance, and other properties of switchable solvents can be reversibly changed in the presence of various triggers, and taking advantage of this property can greatly simplify the process of solvent recovery. In this work, quaternation and anion exchange were used to prepare several switchable solvents by introducing OH- ions to derivatives of the amidine compound 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). The resulting compounds exhibited reversible switching in response to exposure to CO2. Using toluene/n-heptane as a model hydrocarbon mixture, a reversible phase change extraction process was established. Among the four switchable solvents prepared, [C2DBU]OH showed the highest selectivity value and so was used to investigate the effect of various parameters on hydrocarbon separation. The extraction process was found to rapidly reach equilibrium when a two-phase system was generated by bubbling CO2 through the extraction mixture. Increasing the proportion of the solvent increased the selectivity for toluene, while a 1:1 ratio between the solvent and the toluene/n-heptane mixture enhanced the extraction. Increasing the initial toluene concentration reduced the selectivity for toluene, with a value of 5.97 at a toluene concentration of 20%. The switchable solvent recovered its initial state when heated at 60 °C for 1 h. Upon being reused after removal of CO2, the solvent exhibited poor separation characteristics, although the selectivity coefficient remained constant at approximately 3.1 during 10 regenerations. Finally, the mechanism of the switchable solvent effect and modeling of experimental data were investigated.

Ultra-wide temperature electronic synapses based on self-rectifying ferroelectric memristors.

Memristors have been intensively studied in recent years as promising building blocks for next-generation nonvolatile memory, artificial neural networks and brain-inspired computing systems. However, most memristors cannot simultaneously function in extremely low and high temperatures, limiting their use for many harsh environment applications. Here, we demonstrate that the memristors based on high-Curie temperature ferroelectrics can resolve these issues. Excellent synaptic learning and memory functions can be achieved in BiFeO3 (BFO)-based ferroelectric memristors in an ultra-wide temperature range. Correlation between electronic transport and ferroelectric properties is established by the coincidence of resistance and ferroelectricity switch and the direct visualization of local current and domain distributions. The interfacial barrier modification by the reversal of ferroelectric polarization leads to a robust resistance switching behavior. Various synaptic functions including long-term potentiation/depression, consecutive potentiation/depression and spike-timing dependent plasticity have been realized in the BFO ferroelectric memristors over an extremely wide temperature range of -170 °C âˆ¼ 300 °C, which even can be extended to 500 °C due to the robust ferroelectricity of BFO at high temperatures. Our findings illustrate that the BFO ferroelectric memristors are promising candidates for ultra-wide temperature electronic synapse in extreme or harsh environments.

Highly linear polarized photoluminescence from a rippled WSe2 monolayer.

Shaping the topography of an atomically thin film is a novel way to engineer the optoelectronic performances of an ideal surface. In this letter, we study the photoluminescence characters of a WSe2 monolayer of spiky nanostructures and rippled morphology, which are induced during the transfer process of monolayer to a Bi2Se3 flake. Photo-excited excitons are trapped by these nanostructures, resulting in energy redshifts up to 150 meV at low temperature. We study the polarization degrees of the corresponding radiation signals and the polarization directions. Interestingly, the appearance features of monolayer correlates with the optical polarization property of the photoluminescence. Our work attracts insight to the relevance between surface topography and the dipole polarization on an ideal surface.

Mediation in the second-order synaptic emulator with conductive atomic force microscopy.

Memristors have been extensively studied for synaptic simulation and neuromorphic computation. Instead of focusing on implementing specific synaptic learning rules by carefully engineering external programming parameters, researchers recently have paid more attention to taking advantage of the second-order memristor that is more analogous to biologic synapses and modulated not only by external inputs but also by internal mechanisms. However, experimental evidence is still scarce. Here, we explore a BiMnO3 memristor by applying simple spike forms. The filament evolution dynamics, including processes of forming and spontaneous decay, were directly observed by the conductive atomic force microscopy (c-AFM) technique. We propose that the unique conductance state of the BMO memristor is regulated by the oxygen vacancy (VO) dynamic process. We believe this primary result is helpful to improve understanding of the internal mechanisms of the second-order oxide memristor, which exhibits promising application in building selectors, memories and neuromorphic-computing systems.

Facile preparation of a nano-imprinted polymer on magnetite nanoparticles for the rapid separation of lead ions from aqueous solution.

A novel nanostructured magnetic ion-imprinted polymer (IIP) was synthesized for the selective adsorption of Pb(ii) from aqueous solution. The IIP was prepared on functional Fe3O4@SiO2 core/shell nanoparticles as a support. Monomer units in the polymer featured the typical bidentate ligand itaconic acid. We used ethylene glycol dimethacrylate and 2,2-azoisobisbutyronitrile as a cross-linker and an initiator, respectively. Monomers with different acid-base properties and different proportions of cross-linker were investigated to obtain high-performance adsorbents. Our results showed that the IIP prepared from itaconic acid had a high adsorption capacity owing to the strong binding between the monomer and Pb(ii) template ion. The IIPs were characterized using Fourier transform infrared spectroscopy, Brunauer-Emmett-Teller surface area analysis, thermogravimetric analysis, and transmission electron microscopy. We confirmed the formation of a nano-imprinted shell layer on the surface of Fe3O4@SiO2. The adsorption rate was fast, conforming to a pseudo-second-order kinetic and Langmuir adsorption model; the adsorption mechanism was deemed to be chemisorption as a single molecular layer. The maximum adsorption capacity of the IIP (51.2 mg g-1) was approximately three times as large as that of the non-imprinted polymer (17.9 mg g-1). The selectivity factors for Pb(ii) in mixed solutions of Pb(ii)/Co(ii), Pb(ii)/Cu(ii), and Pb(ii)/Zn(ii) were 45.6, 6.45, and 8.3, respectively. Pb-IIP exhibited a high selectivity towards Pb(ii), which enabled the enrichment of Pb(ii) in aqueous solution.

Preparation and adsorption characteristics of an ion-imprinted polymer for fast removal of Ni(II) ions from aqueous solution.

A novel Ni(II) ion-imprinted polymer (IIP) was synthesized by bulk polymerization for fast removal of Ni(II) ions from aqueous solution. Effects of preparation conditions on adsorption performance were investigated. Diphenylcarbazide (DPC) and N,N-azobisisobutyronitrile (AIBN) were used as ligand and initiator, respectively. Various monomers, solvents, cross-linking agents and molar ratios of template, monomer and cross-linking agent for polymerization were studied to obtain the largest adsorption capacity. The prepared Ni(II)-IIPs were characterized using Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), energy dispersive X-ray spectroscopy (EDX) and thermogravimetric analysis (TGA). The elution process has no influence on the three-dimension network structure observed on the surfaces of Ni(II)-IIPs. Ni(II) ions could be eluted from IIPs successfully with HCl solution. Effects of operating time, pH and initial concentration of Ni(II) in aqueous solution on adsorption performance were investigated too. The adsorption equilibrium was reached within 30min. The maximum adsorption capacity of Ni(II)-IIPs was 86.3mgg-1 at pH 7.0 with initial Ni(II) concentration of 500mgL-1. The adsorption by Ni(II)-IIPs followed a pseudo-second-order kinetic and Freundlich isotherm models. The selectivity coefficients for all Ni(II)/interfering ions are larger than one because of the imprinting effect. The Ni(II)-IIPs also showed high reusability and stability.

Immobilization of lipase on porous monodisperse chitosan microspheres.

Porous monodisperse chitosan microspheres were synthesized for enzyme immobilization. The microspheres were prepared using microchannels and modified with glutaraldehyde. The microspheres had a mean diameter of 495 µm; the polydispersity indices were less than 0.08, and the specific surface area was between 121 and 173 m(2) /g. Candida sp. 1619 lipase was selected as a model lipase. Immobilization conditions such as enzyme loading, glutaraldehyde concentration, and immobilization time were optimized. The temperature, pH, and storage stability of the free and immobilized enzymes were also investigated. The immobilized enzyme had broad-ranging pH and temperature optima as compared with free enzyme. The storage stability of the immobilized enzyme was higher than that of the free enzyme.

Lipase immobilized catalytically active membrane for synthesis of lauryl stearate in a pervaporation membrane reactor.

A composite catalytically active membrane immobilized with Candida rugosa lipase has been prepared by immersion phase inversion technique for enzymatic synthesis of lauryl stearate in a pervaporation membrane reactor. SEM images showed that a "sandwich-like" membrane structure with a porous lipase-PVA catalytic layer uniformly coated on a polyvinyl alcohol (PVA)/polyethersulfone (PES) bilayer was obtained. Optimum conditions for lipase immobilization in the catalytic layer were determined. The membrane was proved to exhibit superior thermal stability, pH stability and reusability than free lipase under similar conditions. In the case of pervaporation coupled synthesis of lauryl stearate, benefited from in-situ water removal by the membrane, a conversion enhancement of approximately 40% was achieved in comparison to the equilibrium conversion obtained in batch reactors. In addition to conversion enhancement, it was also found that excess water removal by the catalytically active membrane appears to improve activity of the lipase immobilized.

Lipase immobilized on the hydrophobic polytetrafluoroethene membrane with nonwoven fabric and its application in intensifying synthesis of butyl oleate.

The synthesis of butyl oleate was studied in this paper with immobilized lipase. Five types of membrane were used as support to immobilize Rhizopus arrhizus lipase by following a procedure combining filtration and protein cross-linking. Results showed that hydrophobic polytetrafluoroethene membrane with nonwoven fabric (HO-PTFE-NF) was the favorite choice in terms of higher protein loading, activity, and specific activity of immobilized lipase. The factors including solvent polarity, lipase dosage, concentration, and molar ratio of substrate and temperature were found to have significant influence on conversion. Results showed that hexane (logP = 3.53) was a favorable solvent for the biosynthesis of butyl oleate in our studies. The optimal conditions were experimentally determined of 50 U immobilized lipase, molar ratio of oleic acid to butanol of 1.0, substrate concentration of 0.12 mol/L, temperature of 37 °C, and reaction time of 2 h. The conversion was beyond 91% and decreased slightly after 18 cycles. Lipase immobilization can improve the conversion and the repeated use of immobilized lipase relative to free lipase.

The study on pervaporation behaviors of dilute organic solution through PDMS/PTFE composite membrane.

As an energy-efficient alternative to distillation, pervaporation has been widely combined with fermentation to remove organic compounds from their dilute solutions in a fermentation broth. In this work, the organic permselective composite membrane is prepared by coating polydimethylsiloxane (PDMS) cross-linked with n-heptane on the substrate of polytetrafluoroethylene(PTFE) membrane. The separation behavior is studied in different dilute organic solutions, which include acetone dilute solution, butanone dilute solution, cyclohexanone dilute solution, ethanol dilute solution, isopropanol dilute solution, n-butyl alcohol dilute solution, acetic acid dilute solution, and ethyl acetate dilute solution. Most of these solutions are main reaction products or by-products from fermentation process. The effects of solubility of organics in the membrane, molecular weight, and polarity of the organics on the pervaporation performance are investigated. The effects of operating temperature and organic concentration in the feed solutions on the performance of composite membrane are studied as well. The experimental results show that molecular volume has less influence than solubility and molecular polarity for these organic solvent. The selectivity of PDMS membrane to ethyl acetate is relative high due to good solubility and diffusion of ethyl acetate molecules in polymer.

Simultaneous extraction and concentration of penicillin G by hollow fiber renewal liquid membrane.

In this article, hollow fiber renewal liquid membrane (HFRLM) technique was used for recovery of penicillin G from aqueous solution. The organic solution of 7 vol % di-n-octylamine (DOA) + 30 vol % iso-octanol + kerosene was used as liquid membrane phase, and Na(2)CO(3) aqueous solution was used as stripping phase. Experiments were performed as a function of carrier concentration in the organic phase, organic/aqueous volume ratio, pH, and initial penicillin G concentration in the feed phase, pH in the stripping phase, flow rates, etc. The results showed that the HFRLM process was stable and could carry out simultaneous extraction and concentration of penicillin G from aqueous solutions. As a carrier facilitated transport process, the addition of DOA in organic phase could greatly enhance the mass transfer rate; and there was a favorable organic/aqueous volume ratio of 1:20 to 1:30 for this system. The mass transfer flux and overall mass transfer coefficient increased with decreasing pH in the feed phase and increasing pH in the stripping phase, because of variation of the mass transfer driving force caused by pH gradient and distribution equilibrium. The flow rate of the shell side had significant influence on the mass transfer performance, whereas the effect of flow rate of lumen side on the mass transfer performance was slight because of the mass transfer intensification of renewal effect in the lumen side. The results indicated that the HFRLM process was a promising method for the recovery of penicillin G from aqueous solutions.

Facilitated transport of penicillin G by bulk liquid membrane with TBP as carrier.

The facilitated transport of penicillin G from aqueous solutions to the stripping phase through bulk liquid membrane (BLM) containing TBP in 3% iso-octanol and n-butyl acetate was studied. Na(2)CO(3) solution was used as the stripping phase. Experiments were performed as a function of stirring rate, TBP concentration and type of diluent in the liquid membrane phase, pH, and initial penicillin G concentration in the feed phase, Na(2)CO(3) concentration in the stripping phase, etc. The results showed that the BLM process could carry out the simultaneous separation and concentration of penicillin G from dilute aqueous solutions, and arise "up-hill" effect due to the characteristic of non-equilibrium mass transfer. The diffusion of penicillin G complex in the liquid membrane phase played an important role in BLM process. The mass transfer mechanism of BLM for this system was also discussed.