Anhui Normal University

The construction of highly active and stable non-noble-metal electrocatalysts for hydrogen and oxygen evolution reactions is a major challenge for overall water splitting. Herein, we report a novel hybrid nanostructure with CoP nanoparticles (NPs) embedded in a N-doped carbon nanotube hollow polyhedron (NCNHP) through a pyrolysis–oxidation–phosphidation strategy derived from core–shell ZIF-8@ZIF-67. Benefiting from the synergistic effects between highly active CoP NPs and NCNHP, the CoP/NCNHP hybrid exhibited outstanding bifunctional electrocatalytic performances. When the CoP/NCNHP was employed as both the anode and cathode for overall water splitting, a potential as low as 1.64 V was needed to achieve the current density of 10 mA·cm–2, and it still exhibited superior activity after continuously working for 36 h with nearly negligible decay in potential. Density functional theory calculations indicated that the electron transfer from NCNHP to CoP could increase the electronic states of the Co d-orbital around the Fermi level, which could increase the binding strength with H and therefore improve the electrocatalytic performance. The strong stability is attributed to high oxidation resistance of the CoP surface protected by the NCNHP.

We develop an N-coordination strategy to design a robust CO2 reduction reaction (CO2RR) electrocatalyst with atomically dispersed Co–N5 site anchored on polymer-derived hollow N-doped porous carbon spheres. Our catalyst exhibits high selectivity for CO2RR with CO Faradaic efficiency (FECO) above 90% over a wide potential range from −0.57 to −0.88 V (the FECO exceeded 99% at −0.73 and −0.79 V). The CO current density and FECO remained nearly unchanged after electrolyzing 10 h, revealing remarkable stability. Experiments and density functional theory calculations demonstrate single-atom Co–N5 site is the dominating active center simultaneously for CO2 activation, the rapid formation of key intermediate COOH* as well as the desorption of CO.

A facile ultrasonic route for the fabrication of graphene quantum dots (GQDs) with upconverted emission is presented. The as-prepared GQDs exhibit an excitation-independent downconversion and upconversion photoluminescent (PL) behavior, and the complex photocatalysts (rutile TiO(2)/GQD and anatase TiO(2)/GQD systems) were designed to harness the visible spectrum of sunlight. It is interesting that the photocatalytic rate of the rutile TiO(2)/GQD complex system is ca. 9 times larger than that of the anatase TiO(2)/GQD complex under visible light (λ > 420 nm) irradiation in the degradation of methylene blue.

A pair to fret about: Biotinylated phosphor nanoparticles that emit upconversion luminescence have been taken with biotinylated Au nanoparticles, which act as energy acceptors, and the pair has been applied to the determination of trace amounts of avidin based on fluorescence resonant energy transfer (FRET; see picture).

Developing bifunctional efficient and durable non-noble electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desirable and challenging for overall water splitting. Herein, Co–Mn carbonate hydroxide (CoMnCH) nanosheet arrays with controllable morphology and composition were developed on nickel foam (NF) as such a bifunctional electrocatalyst. It is discovered that Mn doping in CoCH can simultaneously modulate the nanosheet morphology to significantly increase the electrochemical active surface area for exposing more accessible active sites and tune the electronic structure of Co center to effectively boost its intrinsic activity. As a result, the optimized Co1Mn1CH/NF electrode exhibits unprecedented OER activity with an ultralow overpotential of 294 mV at 30 mA cm–2, compared with all reported metal carbonate hydroxides. Benefited from 3D open nanosheet array topographic structure with tight contact between nanosheets and NF, it is able to deliver a high and stable current density of 1000 mA cm–2 at only an overpotential of 462 mV with no interference from high-flux oxygen evolution. Despite no reports about effective HER on metal carbonate hydroxides yet, the small overpotential of 180 mV at 10 mA cm–2 for HER can be also achieved on Co1Mn1CH/NF by the dual modulation of Mn doping. This offers a two-electrode electrolyzer using bifunctional Co1Mn1CH/NF as both anode and cathode to perform stable overall water splitting with a cell voltage of only 1.68 V at 10 mA cm–2. These findings may open up opportunities to explore other multimetal carbonate hydroxides as practical bifunctional electrocatalysts for scale-up water electrolysis.

Single-atom metal–nitrogen–carbon (M–N–C) catalysts have sparked intense interests, but the catalytic contribution of N-bonding environment neighboring M–N4 sites lacks attention. Herein, a series of Fe–N–C nanoarchitectures have been prepared, which confer adjustable numbers of atomically dispersed Fe–N4 sites, tunable hierarchical micro-mesoporous structures and intensified exposure of interior active sites. The optimization between Fe–N4 single sites and carbon matrix delivers superior oxygen reduction reaction activity (half-wave potential of 0.915 V vs RHE in alkaline medium) with remarkable stability and high atom-utilization efficiency (almost 10-fold enhancement). Both experiments and theoretical calculations verified the selective C–N bond cleavage adjacent to Fe center induced by porosity engineering could form edge-hosted Fe–N4 moieties, and therefore lower the overall oxygen reduction reaction barriers comparing to intact atomic configuration. These findings provide a new pathway for the integrated engineering of geometric and electronic structures of single-atom materials to improve their catalytic performance.

A central topic in single-atom catalysis is building strong interactions between single atoms and the support for stabilization. Herein we report the preparation of stabilized single-atom catalysts via a simultaneous self-reduction stabilization process at room temperature using ultrathin two-dimensional Ti3–xC2TyMXene nanosheets characterized by abundant Ti-deficit vacancy defects and a high reducing capability. The single atoms therein form strong metal–carbon bonds with the Ti3–xC2Ty support and are therefore stabilized onto the sites previously occupied by Ti. Pt-based single-atom catalyst (SAC) Pt1/Ti3–xC2Ty offers a green route to utilizing greenhouse gas CO2, via the formylation of amines, as a C1 source in organic synthesis. DFT calculations reveal that, compared to Pt nanoparticles, the single Pt atoms on Ti3–xC2Ty support feature partial positive charges and atomic dispersion, which helps to significantly decrease the adsorption energy and activation energy of silane, CO2, and aniline, thereby boosting catalytic performance. We believe that these results would open up new opportunities for the fabrication of SACs and the applications of MXenes in organic synthesis.

at the atomic scale.

Single-atom-site catalysts (SASCs) featuring maximized atom utilization and isolated active sites have progressed tremendously in recent years as a highly prosperous branch of catalysis research. Varieties of SASCs have been developed that show excellent performance in many catalytic applications. The major goal of SASC research is to establish feasible synthetic strategies for the preparation of high-performance catalysts, to achieve an in-depth understanding of the active-site structures and catalytic mechanisms, and to develop practical catalysts with industrial value. This Perspective describes the up-to-date development of SASCs and related catalysts, such as dual-atom-site catalysts (DASCs) and nano-single-atom-site catalysts (NSASCs), analyzes the current challenges encountered by these catalysts for industrial applications, and proposes their possible future development path.

We perform a comprehensive first-principles study of the electronic properties of phosphorene nanoribbons, phosphorus nanotubes, multilayer phosphorene sheets, and heterobilayers of phosphorene and two-dimensional (2D) transition-metal dichalcogenide (TMDC) monolayer. The tensile strain and electric-field effects on electronic properties of low-dimensional phosphorene nanostructures are also investigated. Our calculations show that the bare zigzag phosphorene nanoribbons (z-PNRs) are metals regardless of the ribbon width, whereas the bare armchair phosphorene nanoribbons (a-PNRs) are semiconductors with indirect bandgaps and the bandgaps decrease with increasing ribbon width. We find that compressive (or tensile) strains can reduce (or enlarge) the bandgap of the bare a-PNRs while an in-plane electric field can significantly reduce the bandgap of the bare a-PNRs, leading to the semiconductor-to-metal transition beyond certain electric field. For edge-passivated PNR by hydrogen, z-PNRs become semiconductor with nearly direct bandgaps and a-PNRs are still semiconductor but with direct bandgaps. The response to tensile strain and electric field for the edge-passivated PNRs is similar to that for the edge-unpassivated (bare) a-PNRs. For single-walled phosphorus nanotubes, both armchair and zigzag nanotubes are semiconductors with direct bandgaps. With either tensile strains or transverse electric field, behavior of bandgap modulation similar to that for a-PNRs can arise. It is known that multilayer phosphorene sheets are semiconductors whose bandgaps decrease with an increase in the number of multilayers. In the presence of a vertical electric field, the bandgaps of multilayer phosphorene sheets decrease with increasing electric field and the bandgap modulation is more significant with more layers. Lastly, heterobilayers of phosphorene (p-type) with an n-type TMDC (MoS2 or WS2) monolayer are still semiconductors while their bandgaps can be reduced by applying a vertical electric field as well. We also show that the combined phosphorene/MoS2 heterolayers can be an effective solar cell material. Our estimated power conversion efficiency for the phosphorene/MoS2 heterobilayer has a theoretical maximum value of 17.5%.

In this paper, we have presented a novel strategy to fabricate fluorescent boronic acid modified carbon dots (C-dots) for nonenzymatic blood glucose sensing applications. The functionalized C-dots are obtained by one-step hydrothermal carbonization, using phenylboronic acid as the sole precursor. Compared with conventional two-step fabrication of nanoparticle-based sensors, the present "synthesis-modification integration" strategy is simpler and more efficient. The added glucose selectively leads to the assembly and fluorescence quenching of the C-dots. Such fluorescence responses can be used for well quantifying glucose in the range of 9-900 μM, which is 10-250 times more sensitive than that of previous boronic acid based fluorescent nanosensing systems. Due to "inert" surface, the C-dots can well resist the interferences from various biomolecules and exhibit excellent selectivity. The proposed sensing system has been successfully used for the assay of glucose in human serum. Due to simplicity and effectivity, it exhibits great promise as a practical platform for blood glucose sensing.

Abstract Developing an efficient single‐atom material (SAM) synthesis and exploring the energy‐related catalytic reaction are important but still challenging. A polymerization–pyrolysis–evaporation (PPE) strategy was developed to synthesize N‐doped porous carbon (NPC) with anchored atomically dispersed Fe‐N 4 catalytic sites. This material was derived from predesigned bimetallic Zn/Fe polyphthalocyanine. Experiments and calculations demonstrate the formed Fe‐N 4 site exhibits superior trifunctional electrocatalytic performance for oxygen reduction, oxygen evolution, and hydrogen evolution reactions. In overall water splitting and rechargeable Zn–air battery devices containing the Fe‐N 4 SAs/NPC catalyst, it exhibits high efficiency and extraordinary stability. This current PPE method is a general strategy for preparing M SAs/NPC (M=Co, Ni, Mn), bringing new perspectives for designing various SAMs for catalytic application.

Site preferences of dopant Eu2+ on the locations of K+, Ba2+, and Ca2+ in the mixed cation phosphate K2BaCa(PO4)2 (KBCP) are quantitatively analyzed via a combined experimental and theoretical method to develop a blue-emitting phosphor with thermally stable luminescence. Eu2+ ions are located at K2 (M2) and K3 (M3) sites of KBCP, with the latter occupation relatively more stable than the former, corresponding to emissions at 438 and 465 nm, respectively. KBCP:Eu2+ phosphor exhibits highly thermal stable luminescence even up to 200 °C, which is interpreted as due to a balance between thermal ionization and recombination of Eu2+ 5d excited-state centers with the involvement of electrons trapped at crystal defect levels. Our results can initiate more exploration of activator site engineering in phosphors and therefore allow predictive control of photoluminescence tuning and thermally stable luminescence for emerging applications in white LEDs.

We report a facile way to grow various porous NiO nanostructures including nanoslices, nanoplates, and nanocolumns, which show a structure-dependence in their specific charge capacitances. The formation of controllable porosity is due to the dehydration and re-crystallization of β-Ni(OH)2 nanoplates synthesized by a hydrothermal process. Thermogravimetric analysis shows that the decomposition temperature of the β-Ni(OH)2 nanostructures is related to their morphology. In electrochemical tests, the porous NiO nanostructures show stable cycling performance with retention of specific capacitance over 1000 cycles. Interestingly, the formation of nanocolumns by the stacking of β-Ni(OH)2 nanoslices/plates favors the creation of small pores in the NiO nanocrystals obtained after annealing, and the surface area is over five times larger than that of NiO nanoslices and nanoplates. Consequently, the specific capacitance of the porous NiO nanocolumns (390 F/g) is significantly higher than that of the nanoslices (176 F/g) or nanoplates (285 F/g) at a discharge current of 5 A/g. This approach provides a clear illustration of the process-structure-property relationship in nanocrystal synthesis and potentially offers strategies to enhance the performance of supercapacitor electrodes.

This paper presents a new method of improving the disturbance-rejection performance of a servo system based on the estimation of an equivalent input disturbance (EID). First, the concept of EID is defined. Next, the configuration of an improved servo system employing the new disturbance-estimation method is described. Then, a method of designing a control law employing a disturbance estimate is explained. Finally, the speed control of a rotational control system is used to demonstrate the validity of the method, and some design guidelines are presented.

A range of nearly monodispersed NaYF4 single-crystal nanorods, hexagonal nanoplates, and nanoparticles have been successfully prepared via a facile wet chemical technology. Varying the dopants leads to different luminescence. These as-prepared nanocrystals not only present novel room-temperature downconversion (DC) and upconversion (UC) fluorescence but can also be transparently dispersed in cyclohexane. The effects of reaction temperature and time, doped ion concentration, ratio of NaF to Ln(NO3)3, and the reactant content on the shape, size, and crystal phase purity of the as-prepared nanocrystals have been investigated in detail. The fluorescence photos, spectra, luminescence mechanism, and the formation mechanism of the nanorods have also been demonstrated. For the next biolabel applications, the colloidal nanoparticles dispersed in cyclohexane have also been transferred into water by surface silane modification. For their unique DC and UC luminescence and high processability, these nanocrystals will open new avenues in biolabels, light-emitting diodes (LEDs), color displays, anti-counterfeiting, and solid-state lasers.

Magnetic chitosan nanocomposites have been synthesized on the basis of amine-functionalized magnetite nanoparticles. These nanocomposites can be removed conveniently from water with the help of an external magnet because of their exceptional properties. The nanocomposites were applied to remove heavy metal ions from water because chitosan that is inactive on the surface of the magnetic nanoparticles is coordinated with them. The interaction between chitosan and heavy metal ions is reversible, which means that those ions can be removed from chitosan in weak acidic deionized water with the assistance of ultrasound radiation. On the basis of the reasons referred to above, synthesized magnetic chitosan nanocomposites were used as a useful recyclable tool for heavy metal ion removal. This work provides a potential platform for developing a unique route for heavy metal ion removal from wastewater.

Abstract The discovery of high efficiency narrow‐band green‐emitting phosphors is a major challenge in backlighting light‐emitting diodes (LEDs). Benefitting from highly condensed and rigid framework structure of UCr 4 C 4 ‐type compounds, a next‐generation narrow green emitter, RbLi(Li 3 SiO 4 ) 2 :Eu 2+ (RLSO:Eu 2+ ), has emerged in the oxide‐based family with superior luminescence properties. RLSO:Eu 2+ phosphor can be efficiently excited by GaN‐based blue LEDs, and shows green emission at 530 nm with a narrow full width at half maximum of 42 nm, and very low thermal quenching (103%@150 °C of the integrated emission intensity at 20 °C), however its chemical stability needs to be improved later. The white LED backlight using optimized RLSO:8%Eu 2+ phosphor demonstrates a high luminous efficacy of 97.28 lm W −1 and a wide color gamut (107% National Television System Committee standard (NTSC) in Commission Internationale de L'Eclairage (CIE) 1931 color space), suggesting its great potential for industrial applications as liquid crystal display (LCD) backlighting.

To demonstrate their applications in biological and medical fields such as in immunoassays, magnetic separation of cells or proteins, drug or gene delivery, and magnetic resonance imaging, the template-free syntheses of water-soluble and surface functionalized magnetic nanomaterials have become essential and are challenging. Herein, we developed a facile one-pot template-free method for the preparation of amine-functionalized magnetite nanoparticles and hollow nanospheres by using FeCl(3)6 H(2)O as single iron source. These magnetic nanomaterials were characterized by TEM, SEM, XRD, and FTIR technologies. Their magnetic properties were also studied by using a superconducting quantum interference device (SQUID) magnetometer at room temperature. Then the amine-functionalized magnetite nanoparticles were applied to immunoassays and magnetic resonance imaging in live mice.

A well-known gas sensing material SnO2 in combination with reduced graphene oxide was used in heavy metal ions detection for the first time. This work reports the detailed study on the SnO2/reduced graphene oxide nanocomposite modified glass carbon electrode, which could be used for the simultaneous and selective electrochemical detection of ultratrace Cd(II), Pb(II), Cu(II), and Hg(II) in drinking water. The SnO2/reduced graphene oxide nanocomposite electrode was characterized voltammetrically using redox couples (Fe(CN)63–/4–), complemented with electrochemical impedance spectroscopy (EIS). Square wave anodic stripping voltammetry (SWASV) has been used for the detection of Cd(II), Pb(II), Cu(II), and Hg(II). The detection limit (3σ method) of the SnO2/reduced graphene oxide nanocomposite modified GCE toward Cd(II), Pb(II), Cu(II) and Hg(II) is 1.015 × 10–10 M, 1.839 × 10–10 M, 2.269 × 10–10 M, and 2.789 × 10–10 M, respectively, which is very well below the guideline value given by the World Health Organization. The chemical and electrochemical parameters that exert influence on deposition and stripping of metal ions, such as supporting electrolytes, pH value, deposition potential, and deposition time, were carefully studied. An interesting phenomenon of mutual interference was observed. Most importantly, we pose a potential for the use of gas sensing material in heavy metal ions detection.