Ultrasensitive electrochemical determination of metronidazole based on polydopamine/carboxylic multi-walled carbon nanotubes nanocomposites modified GCE

An ultrasensitive electrochemical sensor based on polydopamine/carboxylic multi-walled carbon nanotubes(MWCNTs à COOH) nanocomposites modified glassy carbon electrode(GCE) was presented in this work, which has been developed for highly selective and highly sensitive determination of an antimicrobial drug, metronidazole. The preparation of polydopamine/MWCNTs–COOH nanocomposites/GCE sensor is simple and possesses high reproducible, where polydopamine can be coated on the surface of MWCNTs–COOH via a simple electropolymerization process. Under optimized conditions, the proposed sensor showed ultrasensitive determination for metronidazole with a wide linear detection range from5 to 5000 mmol/dm^3 and a low detection limit of 0.25 mmol/dm^3(S/N=3). Moreover, the proposed sensor has been successfully applied for the quantitative determination of metronidazole in real drug samples. This work may provide a novel and effective analytical platform for determination of metronidazole in application of real pharmaceutical and biological samples analysis.

Highly sensitive simultaneous electrochemical determination of myricetin and rutin via solid phase extraction on a ternary Pt@r-GO@MWCNTs nanocomposite

The simultaneous electrochemical determination of myricetin and rutin remains a challenge due to their indistinguishable potentials.To solve this problem,we constructed a ternary platinum nanoparticle,reduced graphene oxide,multi-walled carbon nanotubes (Pt@r-GO@MWCNTs) nanocomposite via a facile one-pot synthetic method.Under the optimized conditions,the ternary Pt@r-GO@MWCNTs nanocomposite exhibited good electrocatalytic activity toward myricetin and rutin via solid phase extraction and excellent performance for the simultaneous determination of myricetin and rutin.The oxidation peak current of myricetin was proportional to its concentrations in the range of 0.05-50μM with a detection limit of 0.01μM (S/N=3).The linear range for rutin was 0.05-50μM with a detection limit of 0.005μM(S/N=3).The ternary nanocomposite sensor also exhibited good reproducibility and stability,and was successfully used for the simultaneous determination of myricetin and rutin in real orange juice samples with recoveries ranging between 100.57% and 108.46%.

Amplitude gradient-based metasurfaces for off-chip terahertz wavefront shaping

Metasurfaces provide an effective technology platform for manipulating electromagnetic waves,and the existing design methods all highlight the importance of creating a gradient in the output phase across light scattering units.However,in the emerging research subfield of meta-waveguides where a metasurface is driven by guided modes,this phase gradient-oriented approach can only provide a very limited emission aperture,significantly affecting the application potential of such meta-waveguides.In this work,we propose a new design approach that exploits the difference between meta-atoms in their light scattering amplitude.By balancing this amplitude gradient in the meta-atoms against the intensity decay in the energy-feeding waveguide,a large effective aperture can be obtained.Based on this new design approach,three different wavefront shaping functionalities are numerically demonstrated here on multiple devices in the terahertz regime.They include beam expanders that radiate a plane wave,where the beam width can increase by more than 900 times as compared to the guided wave.They also include a metalens that generates a Bessel-beam focus with a width 0.59 times the wavelength,and vortex beam generators that emit light with a tunable topological charge that can reach-30.This amplitude gradient design approach could benefit a variety of off-chip light shaping applications such as remote sensing and 6G wireless communications.

Distribution of heavy metals in the water column,suspended particulate matters and the sediment under hydrodynamic conditions using an annular flume

Sediment resuspension plays an important role in the transport and fate of heavy metals in the aquatic environment. In the present study, the release and binding forms of Cr, Cu, Zn, Pb under hydrodynamic conditions were investigated using an annular flume. Two sediments located at YLZ and GBD from Liangshui River, Beijing were resuspended for 10 hr at 0.159 and 0.267 m/see, respectively. The concentrations of suspended particulate matters of YLZ were higher than those of GBD during resuspension, indicating that the former sediment is more sensitive to the velocity. Cr in the dissolved phase stayed nearly constant at about 2.25 and 1.84 I^g/L for YLZ and GBD, respectively, due to the high percentage of its stable binding fractions in both sediments, while Cu, Zn, and Pb showed a fast release in the initial period of time. However, their concentrations in SPM generally decreased with time and were higher at the lower velocity of 0.159 m/see, which resulted from the entrainment and depressing effect of larger size particles with lower heavy metal content, commonly referred to as the ＂particle concentration effect＂. In addition, the binding form and heavy metal fractions were also found to vary during the resuspension event. A decrease in the sulphide/organic matters bounded form in GBD sediment was observed, whereas no visible changes were perceived in YLZ site samples. This phenomenon is due to the oxidation of heavy metal-sulphide binding forms, which originated from its high acid volatile sulphide content in GBD sediment.

Oxidant or catalyst for oxidation? The role of manganese oxides in the activation of peroxymonosulfate (PMS)

Manganese oxides(MnOv)have been demonstrated to be effective materials to activate Oxone(i.e.,PMS)to degrade various contaminants.However,the contribution of direct oxidation by MnOx to the total contaminant degradation under acidic conditions was often neglected in the published work,which has resulted in different and even conflicting interpretations of the reaction mechanisms.Here,the role of MnOx(as both oxidants and catalysts)in the activation of Oxone was briefly discussed.The findings offered new insights into the reaction mechanisms in PMS-MnOr and provided a more accurate approach to examine contaminant degrada?tion for water/wastewater treatment.

Redox reactions of iron and manganese oxides in complex systems

Conspectus:Redox reactions of Fe-and Mn-oxides play important roles in the fate and transformation of many contaminants in natural environments.Due to experimental and analytical challenges associated with complex environments,there has been a limited understanding of the reaction kinetics and mechanisms in actual environmental systems,and most of the studies so far have only focused on simple model systems.To bridge the gap between simple model systems and complex environmental systems,it is necessary to increase the complexity of model systems and examine both the involved interaction mechanisms and how the interactions affected contaminant transformation.In this Account,we primarily focused on(1)the oxidative reactivity of Mn-and Fe-oxides and(2)the reductive reactivity of Fe(Ⅱ)/iron oxides in comolex model systems toward contaminant degradation.The effects of common metal ions such as Mn2+,Ca2+,Ni2+,Cr3+and Cu2+,ligands such as small anionic ligands and natural organic matter(NOM),and second metal oxides such as A1,Si and Ti oxides on the redox reactivity of the systems are briefly summarized.

Evolution of humic substances in polymerization of polyphenol and amino acid based on non-destructive characterization

Abiotic humification is important in the formation and evolution of organic matter in soil and compost maturing processes.However,the roles of metal oxides in abiotic humification reactions under micro-aerobic remain ambiguous.The aim of this study was to use non-destructive measurement methods to investigate the role of MnO_(2) in the evolution of humic substances(HSs)during oxidative polymerization of polyphenol-amino acid.Our results suggested a synergistic effect between MnO_(2) and O_(2) in promoting the polymerization reaction and identified that MnO_(2) alone had a limited ability in accelerating the transformation of fulvic acid(FA)to humic acid(HA),whereas O_(2) was the key factor in the process.Two-dimensional correlation spectroscopy(2D-COS)showed that the evolution in the UV-vis spectra followed the order of 475–525 nm>300–400 nm>240–280 nm in the humification process,indicating the formation of simple organic matter followed by FA and then HA.13C nuclear magnetic resonance(13C NMR)analysis revealed that the products under both air and N2 conditions in the presence of MnO_(2) had greater amounts of aromatic-C than in the absence of MnO_(2),demonstrating that MnO_(2) affected the structure of the humification products.The results of this study provided new insights into the theory of abiotic humification.