Mechanism of high sensitivity proton acids doped polypyrrole molecularly imprinted electrochemical sensor and its application in urea detection.

Molecularly imprinted electrochemical sensor is a kind of convenient, fast, and stable analyzer, but the conductivity of electrode materials and their affinity with the analyte affect its performance. A proton acid (PSS, SA, SSA) doping method was proposed to improve the electrochemical performance of the polypyrrole molecularly imprinted polymer (PPy-MIP), which promoted the electropolymerization of pyrrole, reduced the charge transfer resistance, and increased the electrochemical surface area. In terms of both improving conductivity and affinity, the response of the proton acids doped the polypyrrole molecularly imprinted electrochemical sensors (PPy-MIECS) to urea was improved by 25-fold (PSS), 5-fold (SA), and 3-fold (SSA) over that of PPy-MIECS. In addition, the PSS-PPy-MIECS was validated for the practical application with a linear detection range from 0.1 mM to 100 mM, high selectivity (α = 39.73), reusability (RSD% = 4.54 %), reproducibility (RSD% = 0.93 %), and stability (11 days). The advantage of proton acid doping method in PSS-PEDOT-MIECS to urea and PSS-PPy-MIECS to glucose extended its application in the performance enhancement of MIECS design.

An electrochemically cleanable pH electrode based on an electrodeposited iridium oxide-ruthenium oxide-titanium composite.

Biological contamination is an important issue in environmental pH detection, and our prepared electrochemically cleanable electrode may be an effective solution. By electrodepositing an iridium oxide-ruthenium oxide composite on a titanium sheet substrate, the electrode shows a sensitivity of 59.4 mV per pH in the pH range of 2-12 with high reproducibility, low hysteresis, high selectivity and high stability. It is worth mentioning that the electrode was proved to be electrochemically cleanable from biological contamination. When the cleaning time was 30 minutes, the electrode sensitivity rose from 50 to 58 mV per pH. Furthermore, the pH sensor, assembled from the prepared iridium-ruthenium oxide electrode and a home-made Ag/AgCl electrode, has similar electrode properties to those of commercial glass electrodes, but is also mechanically strong and electrochemically cleanable, which is promising for long-term deployment in natural environments.

NiFe nanosheets as urea oxidation reaction electrocatalysts for urea removal and energy-saving hydrogen production.

The preparation of high-performance electrocatalysts is a breakthrough to solve the increasingly prominent problems of environmental degradation and energy depletion. Urea oxidation reaction (UOR) plays a vital role in treating urea-rich wastewater and assisting hydrogen production with low energy consumption. To alleviate the sluggish intrinsic reaction kinetic barrier of six-electron transfer involved in UOR, we develop a NiFe ultra-thin two-dimensional nanosheet array supported on nickel foam as UOR electrocatalyst by one-step hydrothermal method. Benefiting from the in-situ synthesis strategy, abundant mesoporous structure, and the electronic structure change of Ni after the introduction of Fe, NiFe nanosheets (NiFe NSs) exhibit remarkable UOR catalytic activity and excellent long-term stability. Moreover, we assemble a two-electrode electrolytic cell with NiFe NSs/NF as the anode. The results show that the cell voltage of urea assisted water electrolysis for hydrogen production decreased by 15.2% rather than the regular water splitting, as well as that the urea concentration in electrolyte is degraded 55.6% after electrolysis for 36 h at 1.70 V. This work indicates a feasibility verification for the electrocatalytic removal of urea in wastewater treatment, and an efficient and energy-saving method for urea-assisted electrolytic hydrogen production based on NiFe nanosheets.

Fluorometry detection for trypsin via inner filter effect between cytochrome C and in-situ formed fluorescent thiochrome.

A fluorometry assay for trypsin sensitive determination has been presented. The fluorescence of the system at 370/445 nm is derived from thiochrome obtained by in-situ oxidation of thiamine. Based on the inner filter effect, cytochrome C (Cyt C) can quench the fluorescence at 445 nm effectively. Cyt C is specifically hydrolyzed by trypsin through an enzymatic reaction, giving rise to the enhancement of the fluorescence intensity. The change value of fluorescence intensity is proportional to trypsin concentration, which is successfully used for trypsin quantitative detection. This method exhibits good repeatability and selectivity with a detection limit of 0.15 µg mL-1 and a quantification limit of 0.50 µg mL-1 for trypsin sensing. Moreover, it is applied to detect trypsin in practical serum and urine samples with accurate results. The proposed assay is not only a promising candidate for trypsin determination in practical application but also a potentially valuable tool in urine comprehensive analysis and disease diagnosis.

FRET-based fluorometry assay for curcumin detecting using PVP-templated Cu NCs.

A novel fluorometric strategy is proposed for detecting curcumin by polyvinyl pyrrolidone-templated Cu NCs (PVP-Cu NCs) as a fluorescent probe which exhibits excitation/emission peaks at 380/510 nm. The fluorescent excitation and emission spectra of PVP-Cu NCs have a striking overlap with the UV-vis spectrum of curcumin, and the fluorescence lifetime of PVP-Cu NCs decreases after the addition of curcumin. Curcumin leads to fluorescence quenching based on fluorescence resonance energy transfer. This method allows for the determination of curcumin in the range of 0.1-10 µg mL-1 and the detection limit is 21 ng mL-1. Furthermore, this method displays good selectivity and is successfully applied for real sample analysis.

In situ synthesis of nitrogen site activated cobalt sulfide@N, S dual-doped carbon composite for a high-performance asymmetric supercapacitor.

Cobalt sulfides with high theoretical capacity are considered as potential electrodes for supercapacitors (SCs). However, the insufficient reactive sites and low electrical conductivity of bulky cobalt sulfides restrict their applications. Here, we proposed an efficient approach for in situ formation of nitrogen site activated cobalt sulfide@N, S dual-doped carbon composite (CS@NSC) by vulcanizing the cobalt-glutamine complex (CG) precursor in a tube furnace. The effects of the molecular structure and calcination temperature of CG precursors on the morphology, structure and electrochemical performance of CS@NSC were studied. The designed CS@NSC-2 exhibited a specific capacity of 593 C g-1 at the current density of 1 A g-1 and good cyclic stability with 88.7% retention after 2000 cycles. Moreover, an asymmetric supercapacitor (ASC) was fabricated by CS@NSC-2 (positive electrode) and activated carbon (AC) (negative electrode), which delivered ultra-high energy density of 67.8 Wh kg-1 at a power density of 400 W kg-1 and possessed 83.1% capacitance retention after 5000 cycles. The eco-friendly method was also suitable for synthesizing nickel sulfide. This work may provide an innovative horizon for the in situ formation of active sites in electrode materials.

Tri-(Fe/F/N)-doped porous carbons as electrocatalysts for the oxygen reduction reaction in both alkaline and acidic media.

Developing a low cost, sustainable and high-performance precious-metal free catalyst to replace platinum (Pt)-based catalysts for the oxygen reduction reaction (ORR) in fuel cells has recently attracted significant attention. It is crucial to produce more abundant and more uniformly dispersed ORR active sites for improving the ORR performance of the catalyst. Herein, we synthesized tri-(Fe/F/N)-doped porous carbons as high-efficiency electrocatalysts for the ORR by using Fe-zeolitic imidazolate framework-8 (Fe-ZIF-8) and ammonium fluoride as precursors. The results indicate that the as-prepared FeFNC-5 catalysts exhibit superior ORR activity, methanol tolerance, and long-term stability compared to commercial 20 wt% Pt/C in both alkaline and acidic media because of the abundant and dispersed Fe-Nx and pyridinic-N active sites, high specific surface area, and hierarchical porous structure. This work provides a new method and insights into the synthesis of Fe, F, and N triple-doped porous carbons as high-efficiency ORR electrocatalysts.