Single-atom Pd catalysts as oxidase mimics with maximum atom utilization for colorimetric analysis

Pd-based nanomaterials have shown great promise as potential mimic enzymes,but conventional catalysts use only a small fraction of the Pd content that located on the catalyst's surface.Herein,we demonstrated that maximum atom utilization could be achieved by using single-atom Pd catalysts as oxidase mimic.The single-atom Pd nanozymes exhibit significantly enhanced catalytic efficiency,with a catalytic rate constant(Kcat)and the catalytic efficiency(Kcat/Km)values more than 625 and 4,837 times higher than those of horseradish peroxidase,respectively.A combined experimental and theoretical calculation reveals reactive oxygen species involved catalytic mechanism which endows single-atom Pd catalysts with excellent colorimetric analysis performance.Benefiting from the maximum atom utilization efficiency and well-defined structural features,the single-atom Pd nanozymes could be successfully applied for the total antioxidant capacity of fruit,determining the serum acid phosphatase activity as well as constructing NAND logic gate.This finding not only provides an effective strategy to maximize the noble-metal atom utilization efficiency as enzyme mimics,but also provides a new idea for extending their possible applications.

An effective pumping method for increasing atomic utilization in a compact cold atom clock

We propose a simple pumping method to increase the effective population of cold atoms in the clock state and investigate the factors which affect the pumping efficiency in cold atom systems.We report the theory and demonstrate the corresponding experiment in an ^(87)Rb integrating sphere cold atom clock.The experimental results show that the population of cold atoms in the Zeeman sublevel|F=2,mF=0>is approximately 1.62 times that of the result using optical pumping alone.This method can also be applied to increase the effective population in any one of the target Zeeman sublevels in other cold atom systems.

Effects of ceria/zirconia ratio on properties of mixed CeO_2-ZrO_2-Al_2O_3 compound

A series of CexZr0.50-xAl0.50O1.75(0.05≤x≤0.45) mixed oxides with different Ce/Zr ratio were prepared by co-precipitation method and characterized by means of X-ray diffraction(XRD),Brunauer-Emmet Teller method(BET),temperature-programmed reduction(H2-TPR) and oxygen pulsing technique.The XRD results showed that all samples kept the single CeO2 cubic fluorite structure after calcination at 600 and 1000 oC for 5 h.The results of BET revealed that CexZr0.50-xAl0.50O1.75 with Ce/Zr molar ratio 1/1 exhibited hi...

Single-atomic Fe anchored on hierarchically porous carbon frame for efficient oxygen reduction performance

Exploring platinum group metal-free electrocatalysts with superior catalytic performance and favorable durability for oxygen reduction reaction is a remaining bottleneck in process of developing sustainable techniques in energy storage and conversion. Herein, a hierarchical porous single atomic Fe electrocatalyst(Fe/Z8-E-C) is rationally designed and synthesized via acid etching, calcination, adsorption of Fe precursor and recalcination processes. This unique electrocatalyst Fe/Z8-E-C shows excellent oxygen reduction performance with a half-wave potential of 0.89 V in 0.1 mol/L KOH, 30 m V superior to that of commercial Pt/C(0.86 V), which is also significantly higher than that of typical Fe-doped ZIF-8 derived carbon nanoparticles(Fe/Z8-C) with a half-wave potential of 0.84 V. Furthermore, Fe/Z8-E-C-based Zn-air battery exhibits greatly enhanced peak power density and specific capacity than those of original Fe/Z8-C,verifying the remarkable performance and practicability of this specially designed hierarchical structure due to its efficient utilization of the active sites and rapid mass transfer. This present work proposes a new method to rationally synthesize single atom electrocatalysts loaded on hierarchical porous frame materials for catalysis and energy conversion.

Intermetallic PdBi aerogels with improved catalytic performance for the degradation of organic pollutants in water

It is always highly pursued to develop efficient and durable catalysts for catalytic applications.Herein,intermetallic PdBi aerogels with tunable activity were prepared successfully via a surfactant-free spontaneous gelation process.The prepared PdBi aerogels have a three-dimensional high porous structure and plentiful active sites pervaded on the ultrathin interlinked nanowires network.These unique structures,as well as the synergistic effect between Pd and Bi,can accelerate mass and electron transfer,and improve the atom utilization ratio of Pd atoms to promote the catalytic efficiency.As a proofof-concept application,the optimized Pd_(2) Bi_(1) aerogels exhibit 4.2 and 6.2 times higher catalytic activity for the reduction of 4-nitrophenol(4-NP)and methylene blue(MB)than those of commercial Pd/C,respectively.With the introduction of non-noble metal of Bi,the cost of the resulted Pd Bi aerogels can be dropped signi ficantly while the catalytic capability of Pd Bi aerogel will be improved sharply.This strategy will bring good hints to rationally design fine catalysts for various applications.

Effective electrocatalytic hydrodechlorination of 2,4,6-trichlorophenol by a novel Pd/MnO_(2)/Ni foam cathode

Pd modified electrodes possess problems such as easy agglomeration and low electrolytic ability,and the use of manganese dioxide(MnO_(2)) to facilitate Pd reduction of organic pollutants is just started.However,there is still a limited understanding of how to match the Pd load and MnO_(2) to realize optimal dechlorination efficiency at minimum cost.Here,a Pd/MnO_(2)/Ni foam cathode was successfully fabricated and applied for the efficient electrochemical dechlorination of 2,4,6-trichlorophenol(2,4,6-TCP).The optimal electrocatalytic hydrodechlorination(ECH)performance with 2,4,6-TCP dechlorination efficiency(92.58%in 180 min)was obtained when the concentration of PdCl_(2) precipitation was 1 mmol/L,the deposition time of MnO_(2) was 300 s and cathode potential was-0.8 V.Performance influenced by the exogenous factors(e.g.,initial pH and coexisted ions)were further investigated.It was found that the neutral pH was the most favorable for ECH and a reduction in dechlorination efficiency(6%~47.6%)was observed in presence of 5 mmol/L of NO_(2)^(-),NO_(3)^(-),S^(2-)or SO_(3)^(2-).Cyclic voltammetry(CV)and quenching experiments verified the existence of three hydrogen species on Pd surface,including adsorbed atomic hydrogen(H^(*)_(ads)),absorbed atomic hydrogen(H^(*)_(abs)),and molecular hydrogen(H_(2)).And the introduction of MnO_(2)promoted the generation of atomic H^(*).Only adsorbed atomic hydrogen(H^(*)_(ads)) was confirmed that it truly facilitated the ECH process.Besides H^(*)_(ads) induced reduction,the direct reduction by cathode electrons also participated in the 2,4,6-TCP dechlorination process.Pd/MnO_(2)/Ni foam cathode shows excellent dechlorination performance,fine stability and recyclable potential,which provides strategies for the effective degradation of persistent halogenated organic pollutants in groundwater.