Latest ArticlesRational design and building of high efficiency, secure and inexpensive electrocatalyst is a pressing demand and performance to promote sustainable improvement of hydrogen energy. The bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution response (HER) with high catalytic performance and steadiness in the equal electrolyte are extra treasured and meaningful. Herein, a unique three-dimensional (3D) structure electrocatalyst for NiCo2S4 growing on the flower-like NiFeP was designed and synthesized in this study. The results show that the flower-like NiCo2S4/NiFeP/NF composite electrocatalyst has large specific surface area, appropriate electrical conductivity, and greater lively websites uncovered in the three-dimensional structure, and affords extraordinary electrocatalytic overall performance for the ordinary water splitting. In alkaline solution, the OER and HER overpotentials of NiCo2S4/NiFeP/NF only need 293 mV and 205 mV overpotential to provide the current densities of 100 mA/cm2 and 50 mA/cm2, respectively. This high electrocatalytic activity exceeds the catalytic activity of most nickel-iron based electrocatalysts for OER and HER process. Accordingly, the optimized NiCo2S4/NiFeP/NF sample has higher stability (24 h) at 1.560 and 10 mA/cm2, which extensively speeds up the overall water splitting process. In view of the above performance, this work offers a fine approach for the further improvement of low fee and excessive effectivity electrocatalyst.
Relying on the electron energy loss spectrum (EELS) of metallic elements to obtain microstructure analysis is an investigation method of the reaction mechanisms of transition metal oxides (TMOs) in catalysis, energy storage and conversion. However, the low signal from K shell owing to insufficient electron beam energy, and the complicated electronic structure in L shell of the metal element restrict the analysis of the coordination environment of the TMOs. Herein, density functional theory (DFT) calculation, Fourier transform (FT) and wavelet transform (WT) were employed to probe the relationship between the four individual peaks in O K-edge spectra of iron oxides and the microstructure information (chemical bonds and atomic coordination). The findings show that the peak amplitude ration is in a linear correlation with the valence state of Fe element, and that the coordination number obtained by radial distribution function (RDF) is favorably linearly correlative with that from the standard coordination structure model. As a result, the quantitative analysis on the change of valence state and atomic coordination in microstructure can be realized by EELS O K-edge spectra. This study establishes EELS O K-edge spectrum as a promising pathway to quantitatively analyze the valence state and atomic coordination information of TMOs, and offers an effective method to conduct microstructure analysis via the EELS spectra of the non-metal element.
Carbon dioxide electrochemical reduction (CO2RR) has been recognized as an efficient way to mitigate CO2 emissions and alleviate the pressure on global warming and associated environmental consequences. Gold (Au) is reported as stable and active electrocatalysts to convert CO2 to CO at low overpotential due to its moderate adsorption strength of *COOH and *CO. The request for improved catalytic performance, however, is motivated by current unsatisfied catalytic selectivity because of the side hydrogen evolution reaction. In this context, the design of Au based binary catalysts that can boost CO selectivity is of great interest. In the present work, we report that Au nanoparticles can be feasibly dispersed and anchored on silicon nanowires to form Au-Si binary nanomaterials. The Au-Si may stably drive CO2RR with a CO Faraday efficiency of 95.6% at −0.6 V vs. RHE in 0.5 mol/L KHCO3 solution. Such selectivity outperforms Au particles by up to 61%. Controlled experiments illustrate that such catalytic enhancement can chiefly be ascribed to electronic effects of binary catalysts. Theoretical calculations reveal that spontaneously produced silicon oxide may not only inhibit hydrogen evolution reaction, but also stabilize the key intermediate *COOH in CO formation.
The BiOCl (BOC) synthesized by the water bath heating method was treated with sodium borohydride (NaBH4) to introduce oxygen vacancies (OVs). At the same time, Au nanoparticles were loaded to prepare a series of Au/BiOCl samples with different ratios. OVs and Au nanoparticles can promote the light absorption of host photocatalyst in the visible region. The calculated work function of BiOCl and Au can verify the existence of Ohmic contact between the interface of them, which is conducive to the separation of charge carriers. Through a series of photoelectric tests, it was verified experimentally that the separation of charge carriers is indeed enhanced. The high-energy hot electrons produced by Au under the surface plasmon resonance (SPR) effect can increase the counts of electrons to participate in the CO2 reduction reaction. Especially for 1.0%-Au/BOC, the yields of CO can reach 43.16 µmol g−1 h−1, which is 6.6 times more than that of BOC. Therefore, loading precious metal on semiconductors is an effective strategy to promote the photocatalytic performance of CO2 reduction reactions.
In this paper, three new polyoxometalates (POM)-based metal–organic complexes constructed from a new semi-rigid organic ligand N,N'-bis(4-pyrimidinecarboxamido)-1,2-cyclohexane (4-bpmah) H2[Cu(4-bpmah)2(SiMo12O40)(H2O)2]·2H2O (1), H[Cu(4-bpmah)2(PMo12O40)(H2O)2]·2H2O (2) and [Cu(4-bpmah)(H2O)2]·[Cu2(TeMo6O24)(H2O)10]·4H2O (3) were synthesized by hydrothermal method. Single crystal X-ray analyses showed that complexes 1 and 2 were isostructural, in which the isolated Keggin-type [SiMo12O40]4–/[PMo12O40]3– anions and [Cu(4-bpmah)2(H2O)2]2n+ units were expanded into 3D supramolecular structures through hydrogen bond interactions. In complex 3, the 1D [Cu(4-bpmah)(H2O)2]2n+ metal–organic chains and isolated [Cu2(TeMo6O24)(H2O)10]2n– units were expanded into a 3D supramolecular framework by the hydrogen bond interactions. In this paper, carbon cloth working electrodes composited by the title complexes (1/CC, 2/CC and 3/CC) were prepared and used as electrodes for supercapacitors. The performance of supercapacitors as well as the influence of electrolyte solution and title complexes quality load on the performance of supercapacitors were studied. Furthermore, the electrochemistry and electrocatalytic behaviors of complexes 1–3 bulk-modified carbon paste electrodes (1-CPE, 2-CPE and 3-CPE) toward the reduction of KBrO3, KNO2, Cr(Ⅵ), as well as their sensing behaviors on Cr(Ⅵ) were investigated.
The visible-light-induced selective oxidation of ubiquitous C–H bonds into valuable C=O bonds under aerobic conditions is one of the most attractive approaches for the construction of carbonyl-containing molecules. In this work, two transition metal-containing Nb/W mixed-addendum POMs dimers with the formula of K2Na2H5[(Fe(H2O)4)3(P2W15Nb3O62)2]·24H2O (POM[Fe]) and K2Na3H4[(Cr(H2O)4)3(P2W15Nb3O62)2]·32H2O (POM[Cr]) have been synthesized and characterized by various analytical and spectral techniques. POM[Fe] was proved to be an efficient photocatalyst for benzylic C–H oxidation under visible light and using oxygen as an oxidant to produce the corresponding carbonyl complex in good yields. A plausible mechanism involving superoxide radical was proposed for the catalytic reaction. POM[Fe] showed good reusability in the recycling experiments. IR spectroscopy and XRD analysis indicate that POM[Fe] can retain its integrity after catalysis.
Photo-assisted electrochemical technique provides a promising approach towards carcinogen chromium(Ⅵ) detection, which requires reasonable catalyst design. Herein, an unusual hexa-nuclear cadmium cluster functionalized reductive phosphomolybdate hybrid as photo-electrochemical sensor was designed and synthesized with formula of {[Cd(H2O)2]2[Cd(btmbp)]2}{Cd(P4Mo6O31H7)2}·20H2O (1) (btmbp= 4,4′-bis((1H-1,2,4-triazol-1-yl)methyl)biphenyl), in which the photoactive hexa-nuclear {Cd6} clusters cooperated with reductive phosphomolybdate [P4Mo6O31]12− endow the material with wide light absorption and remarkable redox activity, thus achieving efficient photo-assisted electrochemical Cr(Ⅵ) detection performance. Under visible-light assistance, the detection limit (LOD) and sensitivity of Cr(Ⅵ) is 4.17 nmol/L (0.225 ppb) and 226.32 µA L/µmol, which is apparently superior to the performance without photo-assistance (6.25 nmol/L and 106.95 µA L/µmol) and far satisfies the demands of world health organization (WHO) for potable water (50 ppb). Moreover, compound 1 showed prominent Cr(Ⅵ) detection performance in practical water samples together with remarkable anti-interference capacity and good electrochemical durability. This work provides an important guidance for designing efficient polyoxometalate-based crystalline sensors for Cr(Ⅵ) detection.
The development of a single analytical platform with different functions is highly desirable but remains a challenge at present. Here, a paper-based device based on fluorescent carbon dots (CDs) functionalized paper/MnO2 nanosheets (MnO2 NS) hybrid devices (PCD/NS) was proposed for single-device multi-function applications. MnO2 NS functioned as a fluorescence quencher of CDs and recognizer of H2O2 released from the oxidase catalyzed system. Fluorescence recovery would occur after the decomposition of MnO2 NS induced by H2O2, by which a simple and effective strategy could be developed for fluorescence monitoring multiplex biological events. Xanthine (XA) sensing, xanthine oxidase (XOD) inhibitors screening analysis and chiral recognition of glucose enantiomers were performed on PCD/NS to investigate the multifunctional application of the paper-based device. By means of PCD/NS, XA could be determined in the range of 0.1–40 µmol/L with a low detection of limit of 0.06 µmol/L. The IC50 value of allopurinol, the model inhibitor of XOD, was sensitively detected to be 7.4 µmol/L. Glucose enantiomers were also recognized in terms of the specific fluorescence response to d-glucose. This work firstly presented a paper-based device capable of biomarkers detection, inhibitors screening and chiral recognition, which enlightened a promising strategy for the construction of multifunctional devices and hold the great potential application in clinical diagnosis and drug discovery.
In this study, an ambient mass spectrometry (AMS) based method was developed for rapid detection of organophosphorus pesticides in strawberry. This method combines an electric arc and a microsyringe tip to realize tip-assisted ambient electric arc ionization (TAAEAI). A high-voltage electric arc can be applied to the microsyringe tip to generate an electric field, which results in corona discharge at the microsyringe tip. The juiced strawberry sample loaded on the tip could be directly ionized with TAAEAI and then analyzed by a mass spectrometer. TAAEAI-MS was successfully applied to analyze 6 organophosphorus pesticides in three strawberry samples. Malathion and profenofos were detected from the investigated strawberry samples. This method could quantitatively determine the contents of organophosphorus pesticides in strawberry with high reproducibility, high precision, and high sensitivity. Sample matrices did not interfere with the pesticide analysis. The recoveries of organophosphorus pesticides spiked in strawberry samples varied between 82.6% and 116% with relative standard deviations (RSDs) less than 9.2%. The limits of detection (LODs) varied between 0.0124 µg/g and 0.0245 µg/g, while the limits of quantification (LOQs) varied between 0.0413 µg/g and 0.0817 µg/g. The coefficients of determination (R2) of the method were determined to be > 0.995. The method established here may have potential application in the detection of organophosphorus pesticides in vegetables and fruits.
Luminescent metal organic cages (MOCs) have attracted great interest as a unique class of sensing substrates. In this work, intrinsically fluorescent Zr-MOCs were successfully used as fluorescent probes for the sensitive and selective detection of phosphate anions in water and real samples. When the ligand and Zr ion clusters form a cage, the intrinsic fluorescence of the ligand was tuned from high to weak emission due to the ligand-to-metal charge transfer (LMCT) effect, and this weakened fluorescence can be restored by the addition of phosphate. The degree of fluorescence enhancement is positively correlated with the added phosphate concentration, and the efficacy of this strategy is demonstrated by a linear phosphate detection range of 5–500 µmol/L and a detection limit of 1.06 µmol/L. We discuss the interaction between phosphate and Zr in scattering spectrum and MS, respectively. In comparison to phosphate adsorption on Zr-metal organic frameworks (MOFs), where phosphate connects different numbers of cages, both blocking the LMCT effect and causing the cages to aggregate. We also found that the phosphate displaces the ligand from the cage when the phosphate concentration is further expanded, resulting in the formation of new derivatives. This derivative was shown to be useful as a Lewis acid catalyst and as a rare earth ion adsorbent.
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