Environmentally Safe Mercury(II) Ions Aided Zero-Background and Ultrasensitive SERS Detection of Dipicolinic Acid

Field, reliable, and ultrasensitive detection of dipicolinic acid (DPA), a general biomarker of bacterial spores and especially Bacillus anthracis, is highly desirable but still challenging in current biometric security emergency response system. Herein we report an environmentally safe mercury­(II) ions-mediated and competitive coordination interaction based approach for rationally designed surface-enhanced Raman scattering (SERS)-active gold nanoparticles (AuNPs), enabling rapid, ultrasensitive and zero-background detection of DPA without the pretreatment of samples. By means of competitiveness, these papain-capped gold nanoparticles (P-AuNPs) are induced to undergo controllable aggregation upon the addition of Hg²⁺ ions and DPA with a concentration range (1 nM∼8 μM), which correspondingly cause quantitative changes of SERS intensity of cresyl violet acetate (CVa) conjugated AuNPs. The decreased Raman intensity obtained by subtracting two cases of additives that contain only Hg²⁺ and the mixture of Hg²⁺ and DPA is proportional to the concentration of DPA over a range of 1 nM∼8 μM (<i>R</i>² = 0.9824), with by far the lowest limit of detection (LOD) of 67.25 pM (0.01 ppb, <i>S</i>/<i>N</i> = 3:1). Of particular significance, mercury­(II) ions actually play two roles in the process of measurements: a mediator for two designed competitive ligands (DPA and papain), and also a scavenger for the possibly blended ligands due to the different interaction time between DPA and the interferent with Hg²⁺ ions, which guarantees the interference-free detection of DPA even under real conditions

Dynamic Hosts for High-Performance Li–S Batteries Studied by Cryogenic Transmission Electron Microscopy and in Situ X‑ray Diffraction

Developing a high-performance sulfur host is central to the commercialization and general development of lithium–sulfur batteries. Here, for the first time, we propose the concept of dynamic hosts for lithium–sulfur batteries and elucidate the mechanism through which TiS₂ acts in such a fashion, using in situ X-ray diffraction and cryogenic scanning transmission electron microscopy (cryo-STEM). A TiS₂–S composite electrode delivered a reversible capacity of 1120 mAh g^–1 at 0.3 C after 200 cycles with a capacity retention of 97.0% and capacities of 886 and 613 mAh g^–1 at 1.0 C up to 200 and 1000 cycles, respectively. Our results indicate that it is Li_<i>x</i>TiS₂ (0 < <i>x</i> ≤ 1), rather than TiS₂, that effectively traps polysulfides and catalytically decomposes Li₂S

Achieving Highly Efficient, Selective, and Stable CO₂ Reduction on Nitrogen-Doped Carbon Nanotubes

The challenge in the electrosynthesis of fuels from CO₂ is to achieve durable and active performance with cost-effective catalysts. Here, we report that carbon nanotubes (CNTs), doped with nitrogen to form resident electron-rich defects, can act as highly efficient and, more importantly, stable catalysts for the conversion of CO₂ to CO. The unprecedented overpotential (−0.18 V) and selectivity (80%) observed on nitrogen-doped CNTs (NCNTs) are attributed to their unique features to facilitate the reaction, including (i) high electrical conductivity, (ii) preferable catalytic sites (pyridinic N defects), and (iii) low free energy for CO₂ activation and high barrier for hydrogen evolution. Indeed, DFT calculations show a low free energy barrier for the potential-limiting step to form key intermediate COOH as well as strong binding energy of adsorbed COOH and weak binding energy for the adsorbed CO. The highest selective site toward CO production is pyridinic N, and the NCNT-based electrodes exhibit no degradation over 10 h of continuous operation, suggesting the structural stability of the electrode

A Synergistic Effect in a Composite Cathode Consisting of Spinel and Layered Structures To Increase the Electrochemical Performance for Li-Ion Batteries

In this work, a composite consisting of layered Li­[Li₀.₂Ni₀.₁₂ Mn₀.₅₆Co₀.₁₂]­O₂ (LNMC) and spinel Li­[Ni₀.₅Mn₁.₅]­O₄ (LNMO) was synthesized by a modified Pechini method. Extensive analysis was carried out to investigate the synergistic effect between the layered oxide and spinels in the composite by comparing its properties with baseline individual compounds, as well as a physical mixture of LMNC and LNMO. Comparing to the LNMC, the compsoite cathode exhibited a similar initial capacity of ∼250 mA·h/g at 0.1 C, but a much higher first-cycle effeciency, better cyclability and rate capability, attributed to the presence of spinel. The synertistic effect of integrated spinel on the microstructure, crystal strucutre, Mn oxidation states, and Li⁺/Ni²⁺ disordering of the composite was studied by X-ray absorption near edge structure (XANES), electron microscopy, and X-ray diffraction (XRD). The presence of a spinel component in the composite cathode is the origin for the improvement of cyclability and rate capability, largely due to a lower Li⁺/Ni²⁺ disordering, milder redox reaction of manganese ions, and suppressed converting reaction to form Li_<i>x</i>Mn₂O₄-like spinel