Protein-Based Flexible Conductive Aerogels for Piezoresistive Pressure Sensors.

Gelatin is an excellent gelling agent and is widely employed for hydrogel formation. Because of the poor mechanical properties of gelatin when dry, gelatin-aerogels are comparatively rare. Herein we demonstrate that protein nanofibrils can be employed to improve the mechanical properties of gelatin aerogels, and the materials can moreover be functionalized with a an electrically conductive polyelectrolyte resulting in formation of an elastic electrically conductive aerogel that can be employed as a piezoresistive pressure sensor. The aerogel sensor shows a good linear relationship in a wide pressure range (1.8-300 kPa) with a sensitivity of 1.8 kPa-1. This work presents a convenient way to produce electrically conductive elastic aerogels from low-cost protein precursors.

Rational design of two-dimensional flaky Fe/void/C composites for enhanced microwave absorption properties.

Owing to their unique electromagnetic properties and structure anisotropy, two-dimensional (2D) magnetic metal flakes are attracting special attention for applications as microwave absorption materials. However, the conductive network formed by the connected metal flakes may lead to impedance mismatching and reduced performance. In this study, a facile and rational strategy was developed to fabricate yolk-shell-structured 2D flaky Fe/void/C composites by using α-Fe2O3 hexagonal flakes as the template, followed by the coating of polydopamine (PDA) on the composite surface and calcination under H2/Ar. The volume shrinkage from Fe2O3 to Fe and PDA to carbon led to the formation of several irregular holes in Fe flakes and void space between the Fe cores and carbon cages. The thickness of carbon cages of the composites can be tailored by the simple modulation of the synthetic parameters. As a result of the synergistic effects of multiple chemical components, the shape anisotropy of iron flakes, and unique yolk-shell structures, the optimized sample exhibited excellent microwave absorption properties. With a matching thickness of only 1.6 mm, the strongest reflection loss (RL) was up to -27.80 dB at 14.72 GHz, and the effective absorption bandwidth (EAB, RL < -10 dB) reached 6.40 GHz (11.60-18.00 GHz), which can cover the whole Ku-band. This study provides a novel approach to adjust and balance the permeability and permittivity of 2D magnetic metal flakes, which may promote the practical applications of flaky magnetic metal materials in microwave absorption.

Mechanochemical Preparation of Protein : hydantoin Hybrids and Their Release Properties.

Mechanochemistry is a versatile methodology that can be employed both for covalent bond formation in organic synthesis as well as a mediator to allow preparation novel colloidal dispersions for drug delivery. Herein, ball-milling was employed for the solid-state preparation of fluorescent hydrophobic hydantoins, followed by the unprecedented mechanochemically-mediated complexation of hydrophobic hydantoins within hydrophilic protein ß-lactoglobulin (BLG) and BLG nanofibrils (BLGNFs). These hydantoin:protein materials were in turn incorporated into hydrogels. The effect of incorporation of hydantoins into proteins, as well as the effect of protein structure, on the release properties were then investigated. The conversion of BLG to BLGNFs led to a more sustained release demonstrating that heat treatment of BLG into BLGNFs could be employed to modify release properties. To the best of our knowledge, this is the first example where protein : hydantoin complexes were prepared by mechanochemical methodology and mechanochemistry was combined with self-assembly in order to prepare protein nanomaterials for drug-delivery applications. In addition, the use of the developed protein materials is not limited to delivery of drugs but can for example be employed as components of smart food (delivery of nutrients) or release systems of pesticides.

Mechanochemical Preparation and Self-Assembly of Protein:Dye Hybrids for White Luminescence.

Protein nanofibrils (PNFs) functionalized with multiple dyes are prepared by a combination of mechanochemistry and liquid-phase self-assembly. The three employed dyes are Fluorescent Brightener 378 (F378), 2-butyl-6-(butylamino)-1H-benzo[de]isoquinoline-1,3(2H)-dione (Fluorol 555), and Nile red (NR). F378 acts as the donor with Fluorol 555 as the acceptor. F555 in turn acts as the donor and NR as the acceptor. This enables a FRET cascade that enables conversion of UV light to white light. The efficiency of FRET can be influenced by the details of the self-assembly process. If proteins milled with different dyes are mixed prior to self-assembly, nanofibrils are formed containing all three dyes, thus favoring FRET processes. By tuning the ratio of the three luminescent dyes, PNF dispersions are obtained that display bright white light emission. Moreover, the PNF dispersions can be converted into white luminescent films and gels where the PNFs may help to organize dye molecules. Additionally, the PNF materials can be employed as coatings on commercial LEDs, enabling emission of white light.

Collaboratively boosting charge transfer and CO2 chemisorption of SnO2 to selectively reduce CO2 to HCOOH.

In this study, we have facilely developed a SnO2-based electrocatalyst (SnO2-VO@N-C), which can combine together the favorable structure features of oxygen vacancies, porosity, and full-coating with N-doped carbon layers (N-C). Our experimental and theoretical calculation results indicated that with the facile engineering of oxygen vacancies and the full-coating of the N-doped carbon layer, the adsorption/activation of CO2 and charge transfer can be promoted in the CO2 reduction process, making SnO2-VO@N-C the electrocatalyst with improved activity and selectivity (FEHCOOH = 84%) toward the reduction of CO2 to HCOOH.

Double Insurance of Continuous Band Structure and N-C Layer Induced Prolonging of Carrier Lifetime to Enhance the Long-Wavelength Visible-Light Catalytic Activity of N-Doped In2O3.

Nonmetallic doped metal oxides can be broad in their visible-light-response range. However, the half-filled or isolated impurity state can also be the new recombination center for photogenerated electrons/holes, which seriously influence the photocatalytic activity of the catalyst in the visible-light region. Therefore, how to prolong the photogenerated carrier life of nonmetallic doping metal oxides is the difficult and challenging topic in the field of photocatalysis. In this work, the hexagonal nanosheets assembled by N-doped C (N-C)-coated N-doped In2O3 (N-In2O3) nanoparticles (N-C/N-In2O3 HS) was obtained by simply pyrolyzing the In(2,5-PDC) hexagonal sheets. The N-C/N-In2O3 HS catalyst exhibit good photocatalytic activity and cycle stability in the long-wavelength region of visible light (λ = 520 and 595 nm). The effective utilization of long-wavelength visible light for N-C/N-In2O3 HS was mainly attributed to the acceptor-donor-acceptor compensation mechanism between the oxygen vacancy (VO) and substitutional N-doping (Ns) sites, which made the N-C/N-In2O3 HS possess a continuous band structure, without the half-filled or isolated impurity state in the band gap, and extended its light absorption edge to 733 nm. The compensation mechanism of nitrogen doping on In2O3 can promote the photocatalytic activity under longer-wavelength yellow light (595 nm) irradiation. The N-C layer coated on the N-In2O3 nanoparticles acted as a good acceptor of photogenerated electrons, facilitating the effective spatial separation of photogenerated carriers and extend photogenerated carrier lifetimes. The comparative photocatalytic experiments (N-In2O3 HS and N-C/N-In2O3 HS) show that the presence of N-doped C layer can enhance the photocatalytic efficiency by nearly 10-fold. This double-doping and carbon-coating strategy provided a novel research idea to solve the problem that nonmetal atoms doped metal oxides led to the secondary combination of photogenerated electrons/holes.

Engineering a Highly Improved Porous Photocatalyst Based on Cu2O by a Synergistic Effect of Cation Doping of Zn and Carbon Layer Coating.

Zn-doped cuprous oxide (Cu2O) nanoparticles coated by carbon layers (Zn/Cu2O@C) have been obtained via a bimetallic MOF (Zn/Cu-MOF-199) as the sacrificial precursor. Originated from the octahedral morphology of Zn/Cu-MOF-199, the as-synthesized Zn/Cu2O@C shows a porous octahedron structure. The obtained Zn/Cu2O@C can afford the following merits. (1) The cation doping of Zn inside Cu2O can enhance the light absorption by introducing impurity energy levels and facilitate the separation of photoinduced electrons and holes. (2) The coating of a carbon layer in Zn/Cu2O@C can also efficiently enhance the separation efficiency of photoinduced charge carriers. (3) The porous structure of Zn/Cu2O@C can provide increased active sites. Therefore, these merits lead to the highly improved photocatalytic activities toward various chemical reactions. In addition, the fully coated carbon layer can facilitate the cycle stability of Zn/Cu2O@C in the photocatalytic processes.

Engineering Cu/TiO2@N-Doped C Interfaces Derived from an Atom-Precise Heterometallic CuII4TiIV5 Cluster for Efficient Photocatalytic Hydrogen Evolution.

Engineering interfaces is an effective method to create efficient photocatalysts by reducing the recombination of photogenerated carriers. Still, there is a lack of proficient strategies to construct suitable interfaces. In this work, we design and synthesize an atom-precise heterometallic CuII4TiIV5 cluster, [Ti5Cu4O6(ba)16]·2CH3CN (1, Hba = benzoic acid), which is used as a precursor for fabricating efficient photocatalytic interfaces. The cluster has a precise composition and structure with hierarchical bimetal atom distribution and favorable binding properties. The resulting Cu/TiO2@N-doped C interfaces are obtained via the thermal treatment. Combined Cu/TiO2 with N-doped C interfaces provide multiple channels for the transmission of photogenerated carriers and effectively reduce the recombination probability of photogenerated charge carriers. Consequently, the novel interface structure exhibits an excellent hydrogen evolution rate via the photocatalytic water splliting. Density functional theory calculations also support high activity of the interfaces toward hydrogen evolution. As a proof-of-concept application, we show that choosing well-defined metal clusters as precursors can offer a valuable method for engineering photocatalytically efficient interfaces.

Synergistic Modulation of Active Sites and Charge Transport: N/S Co-doped C Encapsulated NiCo2O4/NiO Hollow Microrods for Boosting Oxygen Evolution Catalysis.

Developing high-efficiency and cost-effective electrocatalysts for the oxygen evolution reaction (OER) is crucial for various energy conversion systems. Herein, N/S co-doped C encapsulated hollow NiCo2O4/NiO hexagonal rods (HNHR@N/S-C) as the electrocatalysts for OER have been successfully prepared with rational control of structure and composition. Experimental and theoretical results have highlighted that the NiCo2O4/NiO heterojunction in the obtained electrocatalyst can provide abundant active Ni and Co sites for the OER, leading to the highly enhanced OER performance. Moreover, attributed to the hierarchical hollow structure, which can provide a large surface area, and the improved electric conductivity with a coating of the N/S co-doped carbon layer, which can facilitate charge transport during the catalytic processes, a remarkable OER activity over HNHR@N/S-C with a low overpotential (η) of 285 mV (at j = 10 mA cm-2) and a Tafel slope of 53.0 mV decade-1 has been achieved, which is comparable to that of the noble metal catalyst IrO2. Because of the protection of the N/S doped C layer coating, HNHR@N/S-C can also maintain the current density of 10 mA cm-2 for at least 12 h in alkaline media without obvious losses of activity.

Engineering Nickel/Palladium Heterojunctions for Dehydrogenation of Ammonia Borane: Improving the Catalytic Performance with 3D Mesoporous Structures and External Nitrogen-Doped Carbon Layers.

Catalysts based on metallic NPs have shown high activities in heterogeneous catalysis, due to their high fractions of surface-active atoms, which, however, will lead to the sacrifices in stability and recycle of catalysts. In order to balance well the relationship between activity, stability, and recovery, in this paper, we have constructed a 3D mesoporous sphere structure assembled by N-doped carbon coated Ni/Pd NP heterojunctions (Ni/Pd@N-C). This obtained Ni/Pd@N-C has shown high catalytic activity, durability and recyclability for the hydrolytic dehydrogenation of ammonia borane (AB). Further investigations, including experimental and theoretical results, have shown that the unique structural features, the synergistic effect between Ni and Pd, and the coating of N-doped carbon layer are responsible for the good catalytic performance of Ni/Pd@N-C mesoporous spheres.

Modulating the Charge-Transfer Step of a p-n Heterojunction with Nitrogen-Doped Carbon: A Promising Strategy To Improve Photocatalytic Performance.

Engineering p-n heterojunctions among metal oxide semiconductors to provide a built-in electric field is an efficient strategy to facilitate the separation of photogenerated electrons and holes and improve their photocatalytic activities. However, the inherent poor conductivity of p-n heterojunctions still limits the charge-transfer step and thus hampers their practical application in photocatalysis. In this work, a nitrogen-doped carbon-coated NiO/TiO2 p-n (NCNT) heterojunction with hierarchical mesoporous sphere morphology was synthesized by in situ pyrolytic decomposition of nickel-titanium complexes. The NiO/TiO2 p-n heterojunction in NCNT was fully characterized by several techniques, supported by theoretical calculations and Mott-Schottky plots. On coating with a thin nitrogen-doped carbon layer, the electron transfer of the obtained p-n heterojunction could be significantly enhanced. On account of the favorable structural features of the p-n heterojunction with nitrogen-doped carbon coating and hierarchical mesoporous structure, NCNT exhibited excellent photocatalytic activity toward various reaction systems, including the hydrogen evolution reaction and the visible-light-induced hydroxylation of phenylboronic acids.

Double-shelled hollow rods assembled from nitrogen/sulfur-codoped carbon coated indium oxide nanoparticles as excellent photocatalysts.

Excellent catalytic activity, high stability and easy recovery are three key elements for fabricating efficient photocatalysts, while developing a simple method to fabricate such photocatalysts with these three features at the same time is highly challenging. In this study, we successfully synthesized double-shelled hollow rods (DHR) assembled by nitrogen (N) and sulfur (S)-codoped carbon coated indium(III) oxide (In2O3) ultra-small nanoparticles (N,S-C/In2O3 DHR). N,S-C/In2O3 DHR exhibits remarkable photocatalytic activity, high stability and easy recovery for oxidative hydroxylation reaction of arylboronic acid substrates. The catalyst recovery and surface area were well balanced through improved light harvesting, contributed by concurrently enhancing the reflection on the outer porous shell and the diffraction in the inside double-shelled hollow structure, and increased separation rate of photogenerated carriers. Photocatalytic mechanism was investigated to identify the main reactive species in the catalytic reactions. The electron separation and transfer pathway via N,S-codoped graphite/In2O3 interface was revealed by theoretical calculations.

Hierarchical NiO@N-Doped Carbon Microspheres with Ultrathin Nanosheet Subunits as Excellent Photocatalysts for Hydrogen Evolution.

Achieving highly efficient hierarchical photocatalysts for hydrogen evolution is always challenging. Herein, hierarchical mesoporous NiO@N-doped carbon microspheres (HNINC) are successfully fabricated with ultrathin nanosheet subunits as high-performance photocatalysts for hydrogen evolution. The unique architecture of N-doped carbon layers and hierarchical mesoporous structures from HNINC could effectively facilitate the separation and transfer of photo-induced electron-hole pairs and afford rich active sites for photocatalytic reactions, leading to a significantly higher H2 production rate than NiO deposited with platinum. Density functional theory calculations reveal that the migration path of the photo-generated electron transfer is from Ni 3d and O 2p hybrid states of NiO to the C 2p state of graphite, while the photo-generated holes locate at Ni 4s and Ni 4p hybrid states of NiO, which is beneficial to improve the separation of photo-generated electron-hole pairs. Gibbs free energy of the intermediate state for hydrogen evolution reaction is calculated to provide a fundamental understanding of the high H2 production rate of HNINC. This research sheds light on developing novel photocatalysts for efficient hydrogen evolution.

A portable synthesis of water-soluble carbon dots for highly sensitive and selective detection of chlorogenic acid based on inner filter effect.

In this work, a simple and facile hydrothermal method for synthesis of water-soluble carbon dots (CDs) with malic acid and urea, and were then employed as a high-performance fluorescent probe for selective and sensitive determination of chlorogenic acid (CGA) based on inner filter effect. The as-synthesized CDs was systematically characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Energy disperse spectroscopy (EDS), UV-vis absorption spectroscopy, spectrofluorophotometry, and the results indicated that the sizes of CDs were mainly distributed in the range of 1.0nm-3.0nm with an average diameter of 2.1nm. More significantly, the as-prepared CDs possessed remarkable selectivity and sensitivity towards CGA with the linear range of 0.15µmolL-1-60µmolL-1 and the detection limit for CGA was 45nmolL-1 (3σ/k). The practical applications of CDs for detection of CGA have already been successfully demonstrated in Honeysuckle. This sensitive, selective method has a great application prospect in the pharmaceutical and biological analysis field owing to its simplicity and rapidity for the detection of CGA.

Determination of Sunset Yellow Based on Its Quenching Effect on the Fluorescence of Acridine Orange.

Acridine orange (AO) is widely applied as an organic fluorescent probe. In this work, AO was reacted with sunset yellow (SY) to form an ion-association complex in pH 3.4 Britton-Robinson (BR) buffer solution medium. This resulted in the fluorescence quenching of the former and helped to detect the latter with the maximum excitation wavelengths (λex) and emission wavelengths (λem) near 490 and 530 nm, respectively. The assay exhibits high sensitivity and selectivity with a detection limit of 0.002 µmol L-1 and the remarkable quenching of fluorescence was proportional to the concentration of SY in the range of 0.008 - 9.0 µmol L-1. Herein, this finding was utilized to develop a new strategy for simple, rapid, sensitive and selective detection of SY by combining AO based on fluorescence quenching. In addition, the optimum reaction conditions and the effect of foreign substances were studied. The reasons for fluorescence quenching were also investigated, which showed the quenching of fluorescence of AO with SY was a static quenching process. Furthermore, the proposed method was applied in a real sample analysis with satisfactory results.

Enzyme-catalyzed Michael addition for the synthesis of warfarin and its determination via fluorescence quenching of l-tryptophan.

A sensitive fluorescence sensor for warfarin was proposed via quenching the fluorescence of l-tryptophan due to the interaction between warfarin and l-tryptophan. Warfarin, as one of the most effective anticoagulants, was designed and synthesized via lipase from porcine pancreas (PPL) as a biocatalyst to catalyze the Michael addition of 4-hydroxycoumarin to α, ß-unsaturated enones in organic medium in the presence of water. Furthermore, the spectrofluorometry was used to detect the concentration of warfarin with a linear range and detection limit (3σ/k) of 0.04-12.0µmolL-1 (R2=0.994) and 0.01µmolL-1, respectively. Herein, this was the first application of bio-catalytic synthesis and fluorescence for the determination of warfarin. The proposed method was applied to determine warfarin of the drug in tablets with satisfactory results.

A Simple and Sensitive Method for Auramine O Detection Based on the Binding Interaction with Bovin Serum Albumin.

A simple, rapid and effective method for auramine O (AO) detection was proposed by fluorescence and UV-Vis absorption spectroscopy. In the BR buffer system (pH 7.0), AO had a strong quenching ability to the fluorescence of bovin serum albumin (BSA) by dynamic quenching. In terms of the thermodynamic parameters calculated as ΔH > 0 and ΔS > 0, the resulting binding of BSA and AO was mainly attributed to the hydrophobic interaction forces. The linearity of this method was in the concentration range from 0.16 to 50 µmol L(-1) with a detection limit of 0.05 µmol L(-1). Based on fluorescence resonance energy transfer (FRET), the distance r (1.36 nm) between donor (BSA) and acceptor (AO) was obtained. Furthermore, the effects of foreign substances and ionic strength were evaluated under the optimum reaction conditions. BSA as a selective probe could be applied to the analysis of AO in medicines with satisfactory results.

Determination of sunset yellow in soft drinks based on fluorescence quenching of carbon dots.

Fluorescent carbon dots was prepared by heating N-(2-hydroxyethyl)ethylene diaminetriacetic acid in air. The carbon dots were not only highly soluble in water but also uniform in size, and possessed strong blue fluorescence and excitation wavelength-dependent emission properties with the maximum excitation and emission wavelength at 366nm and 423nm, respectively. Food colorant sunset yellow whose excitation and emission wavelength at 303nm and 430nm could selectively quench the fluorescence of carbon dots, efficient fluorescent resonance energy transfer between the carbon dots and sunset yellow is achieved. This was exploited to design a method for the determination of sunset yellow in the concentration range from 0.3 to 8.0µmolL(-1), with a limit of detection (3σ/k) of 79.6nmolL(-1). Furthermore the fluorimetric detection method was established and validated for sunset yellow in soft drinks samples with satisfactory results.

The fluorescence and resonance Rayleigh scattering spectral study and analytical application of cerium (IV) and cefoperazone system.

In weak acidic medium of pH3.5-5.6, Ce(IV) can be reduced by cefoperazone (CPZ) to be Ce(III), which further combined with CPZ to form complex Ce(OH)3CPZ. This complex not only has higher fluorescence than Ce(III), but also results in significant increase of resonance Rayleigh scattering (RRS), second order scattering (SOS) and frequency doubling scattering (FDS). The wavelengths of maximum fluorescence exciting and emission are located at 356 nm/349 nm, while the maximum wavelengths of RRS, SOS and FDS are at 312 nm, 550 nm and 390 nm, respectively. The intensity of fluorescence and scattering are all linear with the concentration of CPZ in certain conditions. The detection limit of most sensitive RRS method for CPZ is 2.1 ng mL(-1). The optimum conditions for detecting CPZ using RRS method are investigated. The effect of co-existing substances shows that the method has excellent selectivity, especially since other cephalosporins don't have similar reactions. Therefore, it can be achieved to determine CPZ in cephalosporins selectively. The paper also focuses on the reaction mechanism, the consistent and contracture of the resultant. The reasons for enhanced intensity are presumed in the meantime.

Determination of adenine based on the fluorescence recovery of the L-Tryptophan-Cu(2+) complex.

A simple and sensitive method for determination of adenine was developed based on fluorescence quenching and recovery of L-Tryptophan (L-Trp). The fluorescence of L-Trp could efficiently quenched by copper ion compared with other common metal ions. Upon addition of adenine (Ade) in L-Trp-Cu(II) system, the fluorescence was reoccurred. Under the optimum conditions, the recovery fluorescence intensity was linearly correlated with the concentration of adenine in the range from 0.34 to 25.0µmolL(-1), with a correlation coefficient (R(2)) of 0.9994. The detection limit (3σ/k) was 0.046µmolL(-1), indicating that this method could applied to detect trace adenine. In this study, amino acids including L-Trp, D-Trp, L-Tyr, D-Tyr, L-Phe, D-Phe were investigated and only L-Trp could well chelated copper ion. Additionally, the mechanism of quench and recovery also were discussed and the method was successfully applied to detect the adenine in DNA with satisfactory results.