Improved chiral electrochemical recognition of tryptophan enantiomers based on three-dimensional molecularly imprinted overoxidized polypyrrole/MnO2 /carbon felt composites.

A three-dimensional molecularly imprinted overoxidized polypyrrole/MnO2 /carbon felt (MIOPPy/MnO2 /CF) composites were fabricated, which results in increased active area of the surface of the molecularly imprinted polymers film and greatly improved electrochemical chiral recognition effect for tryptophan isomers. The composites were characterized by field emission scanning electron microscope, transmission electron microscope, X-ray diffractometer, UV-visible spectra, N2 adsorption-desorption isotherms, and electrochemical methods. The manuscript provides a proof of concept and shows promising potential of the prepared composites for chiral recognition.

Gold nanorods decorated with graphene oxide and multi-walled carbon nanotubes for trace level voltammetric determination of ascorbic acid.

An ultra-sensitive sensor is described for the voltammetric determination of ascorbic acid (AA). A glassy carbon electrode (GCE) was modified with graphene oxide (GO), multi-walled carbon nanotubes (MWCNTs) and gold nanorods (AuNRs). GO was used to prevent the aggregation of MWCNTs. The integration of positively charged AuNRs reduces the overpotential and increases the peak current of AA oxidation. Figures of merit of this sensor, typically operated at a low working potential of 0.036 V (vs. Ag/AgCl), include a low detection limit (0.85 nM), high sensitivity (7.61 µA·µM-1·cm-2) and two wide linear ranges (from 1 nM to 0.5 µM and from 1 µM to 8 mM). The use of GO simplifies the manufacture and results in a highly reproducible and stable sensor. It was applied to the quantification of AA in spiked serum. Graphical abstract Graphical abstract contains poor quality and small text inside the artwork. Please do not re-use the file that we have rejected or attempt to increase its resolution and re-save. It is originally poor, therefore, increasing the resolution will not solve the quality problem. We suggest that you provide us the original format. We prefer replacement figures containing vector/editable objects rather than embedded images. Preferred file formats are eps, ai, tiff and pdf.We have provided the original format with the attachments named g.tif. Graphene oxide (GO) in combination with multiwalled carbon nanotubes (MWCNTs) and gold nanorods (AuNRs) were used to construct a sensing interface with outstanding electrocatalytic performance for ascorbic acid detection.

A graphene-based platform for fluorescent detection of SNPs.

A novel fluorescent single nucleotide polymorphism (SNP) assay was developed by using Graphene Oxide (GO), which provides a fast, sensitive and simple method for SNP detection. The strategy was based on the single base extension reaction and different absorption capacity of fluorescein labeled dGTP (dGTP-Fl) and double-stranded DNA (dsDNA) to GO. dGTP-Fl is incorporated into the probe by extension reaction for the mutant target but not for the wild target, which leads to recovered fluorescence for the mutant target because of weak interaction between dsDNA and GO and weak fluorescence for the wild target because of the quenched fluorescence of dGTP-Fl by GO. The method shows a linear range for the mutant-type target from 3 nM to 50 nM and 3 nM is the detection limit. It was noted that as low as 10% mutant-type target could be detected in the presence of the wild-type target, in which the concentration is 9 times higher than that of the mutant-type target.

Facile oxidative conversion of TiH2 to high-concentration Ti(3+)-self-doped rutile TiO2 with visible-light photoactivity.

TiO2, in the rutile phase with a high concentration of self-doped Ti(3+), has been synthesized via a facile, all inorganic-based, and scalable method of oxidizing TiH2 in H2O2 followed by calcinations in Ar gas. The material was shown to be photoactive in the visible-region of the electromagnetic spectrum. Powdered X-ray diffraction (PXRD), transmission electron microscopy (TEM), ultraviolet-visible-near-infrared (UV-vis-NIR), diffuse reflectance spectroscopy (DRS), and Brunauer-Emmett-Teller (BET) methods were used to characterize the crystalline, structural, and optical properties and specific surface area of the as-synthesized Ti(3+)-doped rutile, respectively. The concentration of Ti(3+) was quantitatively studied by electron paramagnetic resonance (EPR) to be as high as one Ti(3+) per ~4300 Ti(4+). Furthermore, methylene blue (MB) solution and an industry wastewater sample were used to examine the photocatalytic activity of the Ti(3+)-doped TiO2 which was analyzed by UV-vis absorption, Fourier transform infrared spectroscopy (FT-IR), and electrospray ionization mass spectrometry (ESI-MS). In comparison to pristine anatase TiO2, our Ti(3+) self-doped rutile sample exhibited remarkably enhanced visible-light photocatalytic degradation on organic pollutants in water.

Construction of Spindle-Shaped Ti3+ Self-Doped TiO2 Photocatalysts Using Triethanolamine-Aqueous as the Medium and Its Photoelectrochemical Properties.

To enhance the utilization efficiency of visible light and reduce the recombination of photogenerated electrons and holes, spindle-shaped TiO2 photocatalysts with different Ti3+ concentrations were fabricated by a simple solvothermal strategy using low-cost, environmentally friendly TiH2 and H2O2 as raw materials and triethanolamine-aqueous as the medium. The photocatalytic activities of the obtained photocatalysts were investigated in the presence of visible light. X-ray diffraction (XRD), Raman spectra, transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FT-IR) spectra were applied to characterize the structure, morphologies, and chemical compositions of as-fabricated Ti3+ self-doped TiO2. The concentration of triethanolamine in the mixed solvent plays a significant role on the crystallinity, morphologies, and photocatalytic activities. The electron-hole separation efficiency was found to increase with the increase in the aspect ratio of as-fabricated Ti3+ self-doped TiO2, which was proved by transient photocurrent response and electrochemical impedance spectroscopy.

Stacked Cu2-xSe nanoplates with 2D nanochannels as high performance anode for lithium batteries.

Transition metal chalcogenides are considered as promising alternative materials for lithium-ion batteries owing to their relatively high theoretical capacity. However, poor cycle stability combined with low rate capacity still hinders their practical applications. In this work, the Cu-N chemical bonding directed the stacking Cu2-xSe nanoplates (DETA-Cu2-xSe) is developed to solve this issue. Such unique structure with small nanochannels can enhance the reactive site, facilitate the Li-ion transport as well as inhibit the structural collapse. Benefitting of these advantages, the DETA-Cu2-xSe exhibits high specific capacity, better rate capacity and long cyclability with the specific capacities of 565mAhg-1 after 100 cycles at 200 mA g-1 and 368mAhg-1 after 500 cycles at 5000 mA g-1. This novel DETA-Cu2-xSe structure with nanochannels is promising for next generation energy storage and the synthetic process can be extended to fabricate other transition metal chalcogenides with similar structure.

A yellow-emitting carbon quantum dot-based fluorescent logic gate for the continuous detection of Au3+ and biothiols.

Yellow-emitting carbon quantum dots, named Y-CQDs, were synthesized from O-phenylenediamine and ethylene glycol via a one-pot hydrothermal method. A fluorescent IMPLICATION logic gate for the continuous and "on-off-on" detection of Au3+ and biothiols in tap water at the nanoscale level was constructed based on these QDs. It showed promise in real sample detection and also as a fluorescent ink.

Continuous response fluorescence sensor for three small molecules based on nitrogen-doped carbon quantum dots from prunus lannesiana and their logic gate operation.

In this study, an environmentally friendly and water-soluble nitrogen-doped carbon quantum dots (N-CQDs) with quantum yield (QY) of 8.59% were prepared by one-step hydrothermal synthesis without any chemical reagent using the leaves of prunus lannesiana as precursors. The properties and quality of N-CQDs were investigated by Ultraviolet-visible absorption spectroscopy, infrared spectroscopy, X-ray photoelectron spectroscopy, zeta potential, high-resolution transmission electron microscopy and fluorescence spectroscopy. The fluorescence of the prepared N-CQDs can be quenched by Fe3+ through the synergistic effect of the formation of non-fluorescent complex and internal filtration effect (IFE) between Fe3+ and N-CQDs. And the quenched fluorescence can be "turned on" after adding ascorbic acid (AA) because Fe3+ can be released from the surface of N-CQDs through the redox reaction between AA and Fe3+. While the restored fluorescence can be "turned off" again by hydrogen peroxide (H2O2) due to the re-oxidation of Fe2+ to Fe3+. So, the three inputs "logic gate" is achieved and the "on-off-on-off" continuous response fluorescence sensor is formed, which can be applied for the continuous detection of Fe3+, AA and H2O2 with the linear range of 40-260 µM, 10-200 µM and 40-140 µM, respectively. Finally, the sensor was successfully applied to determine Fe3+, AA and H2O2 in real samples with the satisfactory recoveries (95.35%-104.10%) and repeatability (relative standard deviation (RSD) ≤ 1.68%). The continuous response fluorescence sensor prepared by simple green synthesis route has the characteristics of fast response, acceptable sensitivity and good selectivity.

NiMoS4 nanocrystals anchored on N-doped carbon nanosheets as anode for high performance lithium ion batteries.

Owing to the excellent electrical conductivity and high theoretical capacity, binary transition metal sulfides have attracted extensive attention as promising anodes for lithium ion batteries (LIBs). However, the relatively poor electrical conductivity and serious capacity fading originated from large volume change still hinder their practical applications. Herein, binary NiMoS4 nanoparticles are deposited on N doped carbon nanosheets (NC@NiMoS4) through a facile hydrothermal method. The N doped carbon nanosheets and the strong chemical bonding between NC and NiMoS4 can accommodate the volume change, keep the structural integrity and promote the ion/electron transfer during electrochemical reaction. The extra voids between NiMoS4 nanoparticles enlarge the contact area and reduce the lithium migration barriers. As anode for LIBs, the NC@NiMoS4 exhibits the excellent cycle stability with 834 mAh g-1 after 100 cycles at the current density of 100 mA g-1. Even at high rate of 2000 mA g-1, the specific capacity of 544 mAh g-1 can be achieved after 500 cycles.

Sustainable supercapacitors of nitrogen-doping porous carbon based on cellulose nanocrystals and urea.

The development of porous carbon materials from sustainable natural sources is an attractive topic in the field of energy storage materials. This study proposed the production of nitrogen-doped porous carbon (NPC) materials from the renewable cellulose nanocrystal (CNC) as carbon source and water-soluble urea as nitrogen source without any external activation. The liquid compounding treatment and subsequent carbonization provided the NPC materials a uniform and stable N-doping (7.4% nitrogen content), high specific surface area (366.5 m2/g) and various superior electrochemical properties. The fabricated NPC sample (CU-3, with the weight ratio of 1:10 for CNC and urea) exhibited a high specific capacitance of 570.6 F/g at a current density load of 1 A/g and good cycling stability (91.2% capacitance retention after 1000 cycles at a current density of 10 A/g) in the 6 M KOH electrolyte. Applying this NPC material as the electrode component in the assembled symmetric supercapacitor demonstrated the promising electrochemical stability with the specific capacitances of 88.2 F/g at the current density of 1 A/g and capacitance retention of 99.8% after 5000 cycles. The developed N-doped porous carbon material from CNCs and urea is expected to be a sustainable electrode component for the supercapacitor materials.

Enhanced the photoelectrocatalytic performance of TiO2 nanotube arrays by the synergistic sensitization of Ag-AgBr nanospheres.

Ag-AgBr nanospheres were synthesized on the tubular surface of TiO2 nanotube arrays (TiO2 NTA/Ag-AgBr) by the one-pot hydrothermal deposition strategy using cetyltrimethyl ammonium bromide (CTAB) as bromine source and morphology controlling agent. The results showed that the TiO2 NTA/Ag-AgBr (0.025) prepared with 0.025 g CTAB had the uniform particle distribution, high visible light absorption, photoelectric conversion activity and photoelectrocatalytic (PEC) removal of organic dyes and heavy metal ions. The high photocatalytic decomposition of organic pollutants in waste water was attributed to the synergistic effect of Ag-AgBr nanospheres with the strong visible light response and effective separation of electron-hole pairs. The active group and photocatalytic mechanism for the rapid pollutant removal were systematically explored. This work will open the window of TiO2 NTA based photoelectrodes for the applications in solar energy conversion and dyeing waste water purification.

Diethylenetriamine directed the assembly of Co0.85Se nanosheets layer by layer on N-doped carbon nanosheets for high performance lithium ion batteries.

Co0.85Se nanosheets assembled layer by layer on N-doped carbon nanosheets (NC@Co0.85Se) are designed and fabricated through a facile solvothermal process. The hexamethylenetetramine as the solvent and complexing agent promotes the accumulation of Co0.85Se layer by layer. The long chain diethylenetriamine between the Co0.85Se nanosheets provides buffer space and nanochannels for accelerating the Li+ transportation. The N-doped carbon nansheets in NC@Co0.85Se provide effective conductive network during charge-discharge process. As an anode material for lithium-ion batteries, the NC@Co0.85Se nanocomposites deliver a high specific capacity of 636 mAh g-1 after 100 cycles at current density of 200 mA g-1, and 399 mAh g-1 for 500 cycles at high current density of 5000 mA g-1.

Nitrogen-Doped Carbon Quantum Dots from Poly(ethyleneimine) for Optical Dual-Mode Determination of Cu2+ and l-Cysteine and Their Logic Gate Operation.

In this work, nitrogen-doped carbon quantum dots from poly(ethyleneimine) (PQDs) were synthesized by a low-cost and facile one-step hydrothermal method without other reagents. A quantum yield (QY) of up to 23.2% with maximum emission at 460 nm under an excitation wavelength of 340 nm was ascribed to the high nitrogen doping (20.59%). The PQDs selectively form a blue complex with Cu2+ accompanied by strong quenching of the fluorescence emission. Meanwhile, the PQD-Cu2+ complex exhibited selective fluorescence recovery and color disappearance on exposure to l-cysteine (Cys). The electron transfer from amino or oxygen groups on the PQDs to Cu2+ leads to fluorescence quenching, and a chromogenic reaction of the cuprammonium complex results in a color change. The strong affinity between Cys and Cu2+ causes the detachment of Cu2+ from the surface of PQDs, so the color of the solution disappears and the fluorescence of PQDs recovers. Under the optimized condition, the proposed sensor was applied to detect Cu2+ in the linear range of 0-280 µM. A detection limit of 4.75 µM is achieved using fluorescence spectroscopy and 4.74 µM by monitoring the absorbance variation at 272 nm. For Cys detection, the linear range of 0-800 µM with detection limits of 28.11 µM (fluorescence determination) and 19.74 µM (peak shift determination at 272 nm) was obtained. Meanwhile, the PQD-Cu2+ system exhibits distinguishable responses to other biothiols such as l-glutathione (GSH) and dl-homocysteine (Hcy). Based on the multimode signals, an "AND" logic gate was constructed successfully. Interestingly, besides Cu2+, Fe3+ can also quench the fluorescence of PQDs and the PQD-Fe3+ system exhibits superior selectivity for Cys detection. Most importantly, the proposed assay is not only simple, cheap, and stable but also suitable for detecting Cu2+ and Cys in some real samples.

Electrochemical Chiral Recognition of Tryptophan Isomers Based on Nonionic Surfactant-Assisted Molecular Imprinting Sol-Gel Silica.

A new molecularly imprinted SiO2 (MISiO2) film on the surface of indium tin oxide (ITO) electrode was prepared by the sol-gel method and was then applied successfully in the electrochemical chiral recognition of tryptophan (Trp) isomers. Owing to the high chemical stability, excellent rigidity, and low cost, the resultant sol-gel SiO2 is a good matrix material for molecular imprinting. Nonionic surfactant cicosaethylene glycol hexadecyl ether (Brij58) arranged directionally on the surface of the hydrophobic ITO electrode possesses a large amount of oxygen-containing functional groups and may induce the accumulation of template molecules (L-Trp) on the surface of ITO, resulting in L-MISiO2/ITO after the removal of L-Trp templates by calcination. The characterizations of the L-MISiO2/ITO reveal that the L-Trp templates could be successfully removed from the matrix, producing complementary cavities within the L-MISiO2/ITO. The resultant L-MISiO2/ITO exhibits greatly higher affinity toward L-Trp than D-Trp due to the three-point interaction mechanism, and therefore it exhibits good chiral recognition ability for the Trp isomers. In addition, the as-prepared L-MISiO2/ITO or D-MISiO2/ITO (D-Trp as the templates) can predict the ratio of L- and D-isomers in racemic mixture. Last, the MISiO2 films exhibited quick binding kinetics and good recognition reproducibility.

Solvothermal fabrication and construction of highly photoelectrocatalytic TiO2 NTs/Bi2MoO6 heterojunction based on titanium mesh.

The fabrication of TiO2 NTs/Bi2MoO6 type-II heterojunction photocatalyst was carried out by a simple solvothermal method. Bi2MoO6 nanoparticles with nanosheet microstructures were successfully loaded on TiO2 NTs surface through the adjustment of reaction intervals. The heterojunction photocatalyst showed excellent organic dye and heavy metal ion removal performances, and nearly 100%, 75%, 100% and 100% of MO, RhB, MB and Cr (VI) were removed by simulative sunlight irradiation for 3 or 2 h, respectively. The outstanding photocatalyic performance was mainly due to the formation of type-II heterojunction between TiO2 and Bi2MoO6. The type-II heterojunction not only enhanced visible light response but also accelerated photogenerated charge carrier transfer and restrained the recombination of photogenerated electron-hole pairs with the assistance of internal electric field.

2-Aminopurine modified DNA probe for rapid and sensitive detection of l-cysteine.

A rapid, cost-effective and quencher-free fluorescence-based analytical method for sensitive detection of l-cysteine (Cys) based on 2-aminopurine (2-AP) labeled DNA probe and exonuclease I (Exo I) activity was developed. 2-AP labeled DNA probe includes two thymine (T)-T mismatches, which can bind with Hg2+ to form T-Hg2+-T pairing bases, resulting in stable hairpin with five base pairs in its stem. The target Cys can remove Hg2+ from the stem of the hairpin probe based on the high affinity of Cys with Hg2+, leading to the unfolding of the hairpin probe. At last, by adding Exo I, the resulted single-stranded DNA (ssDNA) will be digested to release free 2-AP with strong fluorescence. Under the optimal conditions, the sensing system exhibited a good and wider linear range from 0.4 to 400 nM (R2 = 0.997) and a detection limit as low as 0.16 nM for Cys. Furthermore, other amino acids without reductive sulfur group did not generate obvious change in fluorescence signals. Finally, the sensor can be used in diluted real samples with a good recovery rate, showing promising application in food, environmental and medical analysis.

Synergetic Effect of Ti3+ and Oxygen Doping on Enhancing Photoelectrochemical and Photocatalytic Properties of TiO2/g-C3N4 Heterojunctions.

To improve the utilization of visible light and reduce photogenerated electron/hole recombination, Ti3+ self-doped TiO2/oxygen-doped graphitic carbon nitride (Ti3+-TiO2/O-g-C3N4) heterojunctions were prepared via hydrothermal treatment of a mixture of g-C3N4 and titanium oxohydride sol obtained from the reaction of TiH2 with H2O2. In this way, exfoliated O-g-C3N4 and Ti3+-TiO2 nanoparticles were obtained. Simultaneously, strong bonding was formed between Ti3+-TiO2 nanoparticles and exfoliated O-g-C3N4 during the hydrothermal process. Charge transfer and recombination processes were characterized by transient photocurrent responses, electrochemical impedance test, and photoluminescence spectroscopy. The photocatalytic performances were investigated through rhodamine B degradation test under an irradiation source based on 30 W cold visible-light-emitting diode. The highest visible-light photoelectrochemical and photocatalytic activities were observed from the heterojunction with 1:2 mass ratio of Ti3+-TiO2 to O-g-C3N4. The photodegradation reaction rate constant based on this heterojuction is 0.0356 min-1, which is 3.87 and 4.56 times higher than those of pristine Ti3+-TiO2 and pure g-C3N4, respectively. The remarkably high photoelectrochemical and photocatalytic performances of the heterojunctions are mainly attributed to the synergetic effect of efficient photogenerated electron-hole separation, decreased electron transfer resistance from interfacial chemical hydroxy residue bonds, and oxidizing groups originating from Ti3+-TiO2 and O-g-C3N4.

Z-Scheme NiTiO3/g-C3N4 Heterojunctions with Enhanced Photoelectrochemical and Photocatalytic Performances under Visible LED Light Irradiation.

Direct Z-scheme NiTiO3/g-C3N4 heterojunctions were successfully assembled by using simple calcination method and the photoelectrochemical and photocatalytic performance were investigated by light emitting diode (LED). The photoanode composed by the heterojunction with about 50 wt % NiTiO3 content exhibits the best photoelectrochemical activity with photoconversion efficiency up to 0.066%, which is 4.4 and 3.13 times larger than NiTiO3 or g-C3N4. The remarkably enhanced photoelectrochemical and photocatalytic activity of the heterojunction can be due to the efficiently photogenerated electron-hole separation by a Z-scheme mechanism.

Sb Nanoparticles Anchored on Nitrogen-Doped Amorphous Carbon-Coated Ultrathin CoSx Nanosheets for Excellent Performance in Lithium-Ion Batteries.

Compared to single-component materials, hybrid materials with various components display superior electrochemical performance. In this work, two-dimensional CoSx@NC@Sb nanosheets assembled by ultrathin CoSx nanosheets (∼4 nm) and a thin layer of N-doped amorphous carbon (NC) combined with colloidlike Sb nanoparticles are designed and synthesized via a solvothermal route accompanied by a carbonization and Sb deposition procedure. If applied in lithium-ion batteries (LIBs), the hybrids exhibit a specific capacity of 960 mA h g-1 at the 100th cycle at 0.1 A g-1. Moreover, the reversible capacity still maintains at 494 mA h g-1 after 500 cycles at a high rate of 10 A g-1. All enhanced electrochemical properties of the hybrids are attributed to the synergistic effect of the two components and their unique structural features, which can effectively increase the electrical conductivity, shorten the pathway of Li+ diffusion, accommodate the volume variation, and inhibit the aggregation and pulverization of the electrode. We believe that the current work can provide a new strategy for designing and fabricating high-performance anode materials for LIBs.

Mercury detection based on label-free and isothermal enzyme-free amplified fluorescence platform.

A novel and convenient biosensor for Mercury (II) detection was developed based on toehold-mediated strand displacement isothermal enzyme-free amplification (EFA) technology and label-free fluorescence platform using Sybr Green Ι (SG) and graphene oxide (GO). The method is highly sensitive and selective, and the logarithmically related Hg2+ linearity range is from 0.1 to 50nM with a detection limit 0.091nM. Moreover, our strategy is simple, enzyme-free, and inexpensive and can be applied to detect spiked Hg2+ in environmental water samples with good recovery and accuracy, which demonstrates that the biosensor has a good potential in the environment surveys in the future.