In situ growth of self-supported CuO nanorods from Cu-MOFs for glucose sensing and elucidation of the sensing mechanism.

Herein, we present a simple and mild method to in situ prepare CuO nanostructures for non-enzymatic glucose sensing. A Cu-metal organic framework (Cu-MOF) precursor was first directly grown on a pencil lead electrode with 3D graphene-like surfaces (EPLE) and then in situ transformed into CuO nanorods. The CuO nanorod-modified EPLE (CuO/EPLE) shows high sensitivity (1138.32 µA mM-1 cm-2), fast response time (1.5 s) and low detection limit (0.11 µM) for glucose oxidation. It has been found that NaOH promoted the generation of ˙OH groups and Cu(III) on the CuO surface, which then facilitated the electrochemical oxidation of glucose. Signals characteristic of hydroxyl and carbon-centered radical adducts were detected by EPR. Furthermore, the CuO/EPLE sensor also shows good accuracy in glucose determination in human serum samples.

Acidic CO2 Electrolysis Addressing the "Alkalinity Issue" and Achieving High CO2 Utilization.

Electrochemical CO2 reduction reaction (CO2 RR) provides a promising approach for sustainable chemical fuel production of carbon neutrality. Neutral and alkaline electrolytes are predominantly employed in the current electrolysis system, but with striking drawbacks of (bi)carbonate (CO3 2- /HCO3 - ) formation and crossover due to the rapid and thermodynamically favourable reaction between hydroxide (OH- ) with CO2 , resulting in low carbon utilization efficiency and short-lived catalysis. Very recently, CO2 RR in acidic media can effectively address the (bi)carbonate issue; however, the competing hydrogen evolution reaction (HER) is more kinetically favourable in acidic electrolytes, which dramatically reduces CO2 conversion efficiency. Thus, it is a big challenge to effectively suppress HER and accelerate acidic CO2 RR. In this review, we begin by summarizing the recent progress of acidic CO2 electrolysis, discussing the key factors limiting the application of acidic electrolytes. We then systematically discuss addressing strategies for acidic CO2 electrolysis, including electrolyte microenvironment modulation, alkali cations adjusting, surface/interface functionalization, nanoconfinement structural design, and novel electrolyzer exploitation. Finally, the new challenges and perspectives of acidic CO2 electrolysis are suggested. We believe this timely review can arouse researchers' attention to CO2 crossover, inspire new insights to solve the "alkalinity problem" and enable CO2 RR as a more sustainable technology.

Simple pyrolysis of graphene-wrapped PtNi nanoparticles supported on hierarchically N-doped porous carbon for sensitive detection of carbendazim.

A novel electrochemical sensor was established based on graphene-wrapped PtNi nanoparticles supported on three-dimensional (3D) N-doped porous carbon (G-PtNi/3D-NPC) for the highly sensitive and selective detection of carbendazim (CBZ). In this sensing system, the encapsulation of PtNi nanoparticles (NPs) by graphene can effectively prevent the aggregation tendency and enhance the structural stability. The hierarchically porous nanostructures have a large specific surface area to expose a large number of active sites and the resulting enhanced electrical conductivity ultimate improves the electrocatalytic activity towards CBZ. Under the optimal conditions, the prepared sensor showed excellent electrochemical responses for the determination of CBZ with a linear range of 0.5-30 µM and lower limit of detection (LOD) of 0.04 µM (S/N = 3). It also shows excellent anti-interference ability at a working potential of 0.74 V. The feasibility of the senor is demonstrated for its practical assays in diluted peach and vegetable samples with acceptable recovery (95.8-97.3 %, peach; 97.2-97.6 %, vegetable) and a relative standard deviation (RSD) below 2.3%.

Determination of 5-Hydroxymethylfurfural (5-HMF) in milk products by surface-enhanced Raman spectroscopy and its simulation analysis.

5-Hydroxymethylfurfural (5-HMF) is a useful indicator of thermal damage degree and freshness of milk. It is of great importance to develop simple, rapid and accurate analytical methods for the sensitive detection of 5-HMF in milk and milk-based products. In this work, surface-enhance Raman spectroscopy (SERS) was used for rapid determination of 5-HMF in processed cheese by colloidal Au nanoparticles (AuNPs) substrate synthesized by the classical solvothermal reduction method. Density functional theory (DFT) calculations were carried out to determine the vibration assignments of 5-HMF and the surface enhancement effect of AuNPs substrate. The results found that a good linear response on the AuNPs substrate for 5-HMF in the concentration range of 0.1-75 mM was established with the detection limit of 75 µM (S/N = 3). Furthermore, the present method could be applied to the determination of 5-HMF in a cheese real sample which revealed its promising application in food safety and analysis.

Voltammetric Determination of 5-Hydroxymethyl-2-furfural in Processed Cheese Using an Easy-Made and Economic Integrated 3D Graphene-like Electrode.

The concentration of 5-hydroxymethyl-2-furfural (HMF) is an important quality-related index in milk and milk products. Fast, cost-effective and environmentally friendly determination of HMF is of great significance in milk products control. In this study, a three-dimensional (3D) graphene-like surface (3DGrls) was successfully prepared within 5 min by an electrochemical amperometric pretreatment on a pencil graphite electrode (PGE). The fast-obtained 3D graphene-like surface increased the electrode surface area and enhanced the electron transfer capability without the addition of any harmful chemicals. The morphology and chemical composition of the obtained electrode were characterized by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and electrochemical impedance spectroscopy (EIS). The results found that the electrochemical response to HMF at the prepared 3DGrls/PGE was 34 times higher than that at PGE. The modified electrode showed a good linear response to HMF in a concentration range of 0.35~116 µM with a low limit of detection (LOD) of 0.099 µM. The integrated electrode also exhibited excellent stability and wonderful antifouling property. Furthermore, the 3DGrls/PGE was successfully applied for the determination of HMF in three processed cheese samples with satisfactory results.

A one-step electrochemically reduced graphene oxide based sensor for sensitive voltammetric determination of furfural in milk products.

Designing of fast, inexpensive and sensitive furfural determination methods for dairy milk is crucial in analytical and food chemistry. In this study, an electrochemical sensor was developed for the cathodic determination of furfural using a one-step electrochemically reduced graphene oxide (ErGO) modified glassy carbon electrode (GCE). The morphology and chemical constituents of the obtained ErGO/GCE were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman and X-ray photoelectron spectroscopy (XPS). The results showed that the fast and green electrochemical reduction process effectively eliminated the oxygen-containing groups in GO and produced reduced graphene with a high surface area and improved electron transfer kinetics. In addition, the ErGO based sensor displayed excellent responses for furfural in a Na2HPO4-NaH2PO4 solution (pH = 9.18) with a wide linear range from 2 to 2015 µM and a low detection limit of 0.4 µM (S/N = 3). The reduction mechanism of furfural was also discussed. Furthermore, the feasibility of the sensor was confirmed by the determination of furfural in three milk samples which generated acceptable outputs.

Well-dispersed Co3Fe7 alloy nanoparticles wrapped in N-doped defect-rich carbon nanosheets as a highly efficient and methanol-resistant catalyst for oxygen-reduction reaction.

To explore alkaline fuel cells in practice, searching low-cost and efficient alternatives to Pt-based catalysts is urgent yet challenging for oxygen reduction reaction (ORR). Herein, Co3Fe7 alloy nanoparticles wrapped in N-doped defect-rich carbon nanosheets (Co3Fe7/CNs) were synthesized at 800 °C by a one-step pyrolysis of the mixture (dicyandiamide, iron (II) phthalocyanine (FePc), cobalt (II) phthalocyanine (CoPc) and Fe2O3), defined as Co3Fe7/CNs-800 for simplicity. The pyrolysis temperature and the dosages of dicyandiamide closely correlated to the ORR performance of the resultant catalysts in 0.1 M KOH solution. Significantly, the optimized Co3Fe7/CNs-800 exhibited encouraging onset potential (Eonset = 0.97 V) and half-wave potential (E1/2 = 0.85 V) in the alkaline media, surpassing commercial Pt/C (50 wt%, Eonset = 0.96 V, E1/2 = 0.84 V). This work provides a feasible strategy for developing efficient non-noble metal ORR electrocatalysts in the alkaline condition.

Flower-like platinum-cobalt-ruthenium alloy nanoassemblies as robust and highly efficient electrocatalyst for hydrogen evolution reaction.

Exploring hydrogen evolution reaction (HER) catalyst with highly catalytic features in alkaline conditions is considered as significance for water splitting. In this study, a general and simple method was developed to prepare flower-like platinum-cobalt-ruthenium alloy nanoassemblies (PtCoRu NAs) by using murexide and cetyltrimethylammonium chloride (CTAC) as the co-structure-directing agents. Benefiting from the structural advantages and multimetallic compositions, the as-prepared PtCoRu NAs displayed remarkably enhanced electrocatalytic performance for the HER in 1.0 M KOH, with a low overpotential (η, 22 mV) to drive 10 mA cm-2, small Tafel slope (46 mV dec-1), and high exchange current density (j0, 3.30 mA cm-2) during the long-term electrolysis. The as-developed strategy sheds some valuable guidelines for preparing advanced multimetallic catalysts for production of hydrogen in fuel cells.

Nitrogen and sulfur co-doped carbon nanodots toward bovine hemoglobin: A fluorescence quenching mechanism investigation.

A deep understanding of the molecular interactions of carbon nanodots with biomacromolecules is essential for wider applications of carbon nanodots both in vitro and in vivo. Herein, nitrogen and sulfur co-doped carbon dots (N,S-CDs) with a quantum yield of 16% were synthesized by a 1-step hydrothermal method. The N,S-CDs exhibited a good dispersion, with a graphite-like structure, along with the fluorescence lifetime of approximately 7.50 ns. Findings showed that the fluorescence of the N,S-CDs was effectively quenched by bovine hemoglobin as a result of the static fluorescence quenching. The mentioned quenching mechanism was investigated by the Stern-Volmer equation, temperature-dependent quenching, and fluorescence lifetime measurements. The binding constants, number of binding sites, and the binding average distance between the energy donor N,S-CDs and acceptor bovine hemoglobin were calculated as well. These findings will provide for valuable insights on the future bioapplications of N,S-CDs.

Co-reductive fabrication of carbon nanodots with high quantum yield for bioimaging of bacteria.

A simple and straightforward synthetic approach for carbon nanodots (C-dots) is proposed. The strategy is based on a one-step hydrothermal chemical reduction with thiourea and urea, leading to high quantum yield C-dots. The obtained C-dots are well-dispersed with a uniform size and a graphite-like structure. A synergistic reduction mechanism was investigated using Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The findings show that using both thiourea and urea during the one-pot synthesis enhances the luminescence of the generated C-dots. Moreover, the prepared C-dots have a high distribution of functional groups on their surface. In this work, C-dots proved to be a suitable nanomaterial for imaging of bacteria and exhibit potential for application in bioimaging thanks to their low cytotoxicity.

One-pot aqueous fabrication of reduced graphene oxide supported porous PtAg alloy nanoflowers to greatly boost catalytic performances for oxygen reduction and hydrogen evolution.

Herein, reduced graphene oxide supported porous PtAg alloy nanoflowers (PtAg NFs/rGO) were synthesized by a simple one-pot aqueous method using pyridinium-based dicationic ionic liquid (1,4-bis(pyridinium)butane dibromide, Bpb-2Br) as the new structure-director and stabilizing agent. The products were characterized by a series of techniques. The obtained nanocomposite had more positive onset potential (1.03 V) for oxygen reduction reaction (ORR) in alkaline electrolyte than those of commercial Pt/C (50 wt%, 0.96 V) and home-made Pt nanoparticles (NPs)/rGO (Pt NPs/rGO, 0.97 V), showing the enhanced catalytic performance for hydrogen evolution reaction (HER) with the positive onset potential (-26 mV) and a small Tafel slope (31 mV dec-1) relative to Pt/C (-18 mV, 31 mV dec-1) and Pt NPs/rGO (-42 mV, 36 mV dec-1) in 0.5 M H2SO4.

Dendrite-like PtAg alloyed nanocrystals: Highly active and durable advanced electrocatalysts for oxygen reduction and ethylene glycol oxidation reactions.

In this work, well-defined dendrite-like PtAg alloyed nanocrystals were prepared by a facile one-pot l-hydroxyproline-assisted successive coreduction approach on a large scale, where no any template or seed involved. l-Hydroxyproline was employed as a green structuring director. The formation mechanism of the alloyed dendritic nanocrystals was investigated in details. The as-prepared frameworks exhibited boosted electrocatalytic activity, improved stability and enhanced tolerance toward oxygen reduction reaction (ORR) and ethylene glycol oxidation reaction (EGOR) in alkaline media in contrast with commercial Pt black catalyst. The developed method provides novel strategy for preparing other shape-controlled nanocatalysts with superior catalytic activity and durability.

Simple one-pot synthesis of solid-core@porous-shell alloyed PtAg nanocrystals for the superior catalytic activity toward hydrogen evolution and glycerol oxidation.

In this work, solid-core@porous-shell alloyed PtAg nanocrystals (PtAg NCs) were fabricated via a simple one-pot co-reduction wet-chemical method on a large scale. Diprophylline (DPP) was employed as the stabilizing agent and shape-directing agent, without any surfactant, polymer, seed or template. The products were mainly analyzed by a series of characterization technique. The hierarchical architectures had enhanced stability and improved electrocatalytic activity for hydrogen evolution reaction (HER) and glycerol oxidation reaction (GOR) in contrast with commercial available Pt/C and Pt black catalysts. For the prepared PtAg NCs catalyst, the Tafel slope is 40mVdec-1 toward HER in 0.5M H2SO4, coupled with the specific activity and mass activity of 77.91mAcm-2 and 1303mAmg-1Pt toward GOR, respectively.

Novel indicators for thermodynamic prediction of interfacial interactions related with adhesive fouling in a membrane bioreactor.

This study focused on developing indicators to predict adhesive membrane fouling in a membrane bioreactor (MBR). Thermodynamic interactions between membrane surface and foulants in various interaction scenes were comprehensively evaluated. It was revealed that, the total interaction energy in contact could be considered as a critical value affecting adhesion of foulants. Surface hydrophilicity cannot be simply represented by water contact angle. Statistical analysis showed that membrane acid-based (AB) surface tension, Lifshitz-Van der waals (LW) surface tension, total tension, zeta potential and water contact angle had no apparent correlation with adhesive fouling, suggesting the infeasibility of these parameters as fouling predictors. It was found that, interaction between two identical membrane surface in water (ΔGsws) and membrane surface electron donor tension (γ-) strongly correlated with adhesive fouling, and could be reliable indicators to predict adhesive fouling. This study identified the relationships of series membrane surface properties with adhesive fouling in MBRs.

Facile synthesis of three-dimensional Pt-Pd alloyed multipods with enhanced electrocatalytic activity and stability for ethylene glycol oxidation.

A facile one-pot solvothermal method was developed for the fabrication of well-defined three-dimensional highly branched Pt-Pd alloyed multipods, using ethylene glycol as a solvent and a reducing agent, along with N-methylimidazole as a structure-directing agent, without any seed, template, or surfactant. The as-prepared nanocrystals exhibited a relatively large electrochemically active surface area, improved electrocatalytic activity and superior stability for ethylene glycol oxidation in alkaline media, compared with commercial Pt black and Pd black, making them promising electrocatalysts in fuel cells.

Formation of fluorescent carbon nanodots from kitchen wastes and their application for detection of Fe(3.).

This work reports a scalable synthesis of water-dispersible fluorescent carbon nanodots based on the simple hydrothermal method (180 °C for 6 h) of kitchen wastes (grape peel for example). We discuss the feasibility of synthesis from kitchen wastes both experimentally and theoretically, and the as-prepared nanodots have high selectivity for Fe(3+) ions based on fluorescence quenching which is due to the complexes between nanodots and metal ions.

Synthesis, characterization, optical properties and theoretical calculations of 6-fluoro coumarin.

6-Fluoro coumarin is synthesized and characterized by (1)H NMR and (13)C NMR. The optical properties of the title compound are investigated by UV-vis absorption and fluorescence emission spectra, the results show the title compound can absorb UV-vis light at 319, 269 and 215nm, moreover it exhibits blue-purple fluorescence emission at 416nm. Theoretical studies on molecular structure, infrared spectra (IR), nuclear magnetic resonance ((1)H NMR, (13)C NMR) chemical shifts, UV-vis absorption and fluorescence emission of the synthesized compound have been worked out. Most chemical calculations were performed by density functional theory (DFT) method at the B3LYP/6-311G(d,p) level (NMR at B3LYP/Aug-CC-Pvdz level) using Gaussian 09 program. The compared results reveal that the scaled theoretical vibrational frequencies are in good accordance with the observed spectra; computational chemical shifts are consistent with the experimental values in most parts, except for some minor deviations; the UV-vis absorption calculated matches the experimental one very well, and the fluorescence emission spectrum is in good agreement with the experimental one when the solute-solvent hydrogen-bonding interaction is considered. These good coincidences prove that the computational methods selected can be used to predict these properties of other similar materials where it is difficult to arrive at experimental results.

Membrane fouling in a submerged membrane bioreactor: effect of pH and its implications.

The effect of pH on membrane fouling in a submerged membrane bioreactor (MBR) was investigated in this study. It was found that, pH increase slightly increased the resistance of virgin membrane and fouled membrane. Pore clogging resistance was quite low, which was not apparently affected by the pH variation. Lower pH resulted in higher adherence of sludge flocs on membrane surface. Thermodynamic analysis showed that a repulsive energy barrier existed in the process of the foulants approaching to membrane surface. This energy barrier would decrease with pH decreased, suggesting the existence of a critical pH below which the repulsive energy barrier would disappear, which would facilitate attachment of the foulants. The resistance of the formed cake layer would significantly increase with the feed pH. This result could be explained by the osmotic pressure mechanism. The obtained findings also provided important implications for membrane fouling mitigation in MBRs.

Simultaneous determination of dopamine and uric acid using layer-by-layer graphene and chitosan assembled multilayer films.

Multilayer films containing graphene (Gr) and chitosan (CS) were prepared on glassy carbon electrodes with layer-by-layer (LBL) assembly technique. After being characterized with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM), the electrochemical sensor based on the resulted films was developed to simultaneously determine dopamine (DA) and uric acid (UA). The LBL assembled electrode showed excellent electrocatalytic activity towards the oxidation of DA and UA. In addition, the self-assembly electrode possessed an excellent sensing performance for detection of DA and UA with a linear range from 0.1 µM to 140 µM and from 1.0 µM to 125 µM with the detection limit as low as 0.05 µM and 0.1 µM based on S/N=3, respectively.

Recognition of FT-IR Data Cuscutae Semen, Japanese Dodder, and Sinapis Semen Using Discrete Wavelet Transformation and RBF Networks.

Horizontal attenuation total reflection Fourier transformation infrared spectroscopy (HATR-FT-IR) studies on cuscutae semen and its confusable varieties Japanese dodder and sinapis semen combined with discrete wavelet transformation (DWT) and radial basis function (RBF) neural networks have been conducted in order to classify them. DWT is used to decompose the FT-IRs of cuscutae semen, Japanese dodder, and sinapis semen. Two main scales are selected as the feature extracting space in the DWT domain. According to the distribution of cuscutae semen, Japanese dodder, and sinapis semen's FT-IRs, three feature regions are determined at detail 3, and two feature regions are determined at detail 4 by selecting two scales in the DWT domain. Thus five feature parameters form the feature vector. The feature vector is input to the RBF neural networks to train so as to accurately classify the cuscutae semen, Japanese dodder, and sinapis semen. 120 sets of FT-IR data are used to train and test the proposed method, where 60 sets of data are used to train samples, and another 60 sets of FT-IR data are used to test samples. Experimental results show that the accurate recognition rate of cuscutae semen, Japanese dodder, and sinapis semen is average of 100.00%, 98.33%, and 100.00%, respectively, following the proposed method.