States of graphene oxide and surface functional groups amid adsorption of dyes and heavy metal ions

Water pollution regarding dyes and heavy metal ions is crucial facing the world.How to effectively separate these contaminants from water has been a key issue.Graphene oxide(GO)promises the greenwater world as a long-lasting spotlight adsorbent material and therefore,harnessing GO has been the research hotspot for over a decade.The state of GO as well as its surface functional groups plays an important role in adsorption.And the way of preparation and structural modification matters to the performance of GO.In this review,the significance of the state of existence of stock GO and surface functional groups is explored in terms of preparation,structural modification,and adsorption.Besides,various adsorbates for GO adsorption are also involved,the discussion of which is rarely established elsewhere.

Vacancy defect MoSeTe embedded in N and F co-doped carbon skeleton for high performance sodium ion batteries and hybrid capacitors

Sodium-ion batteries(SIBs) and hybrid capacitors(SIHCs) have garnered significant attention in energy storage due to their inherent advantages,including high energy density,cost-effectiveness,and enhanced safety.However,developing high-performance anode materials to improve sodium storage performa nce still remains a major challenge.Here,a facile one-pot method has been developed to fabricate a hybrid of MoSeTe nanosheets implanted within the N,F co-doped honeycomb carbon skeleton(MoSeTe/N,F@C).Experimental results demonstrate that the incorporation of large-sized Te atoms into MoSeTe nanosheets enlarges the layer spacing and creates abundant anion vacancies,which effectively facilitate the insertion/extraction of Na^(+) and provide numerous ion adsorption sites for rapid surface capacitive behavior.Additionally,the heteroatoms N,F co-doped honeycomb carbon skeleton with a highly conductive network can restrain the volume expansion and boost reaction kinetics within the electrode.As anticipated,the MoSeTe/N,F@C anode exhibits high reversible capacities along with exceptional cycle stability.When coupled with Na_(3)V_(2)(PO_(4))_(3)@C(NVPF@C) to form SIB full cells,the anode delivers a reversible specific capacity of 126 mA h g^(-1) after 100 cycles at 0.1 A g^(-1).Furthermore,when combined with AC to form SIHC full cells,the anode demonstrates excellent cycling stability with a reversible specific capacity of50 mA h g^(-1) keeping over 3700 cycles at 1.0 A g^(-1).In situ XRD,ex situ TEM characterization,and theoretical calculations(DFT) further confirm the reversibility of sodium storage in MoSeTe/N,F@C anode materials during electrochemical reactions,highlighting their potential for widespread practical application.This work provides new insights into the promising utilization of advanced transition metal dichalcogenides as anode materials for Na^(+)-based energy storage devices.

Enhancement of the formic acid electrooxidation activity of palladium using graphene/carbon black binary carbon supports

Combinations of graphene(Gr)and carbon black(C)were employed as binary carbon supports to fabricate Pd‐based electrocatalysts via one‐pot co‐reduction with Pd2+.The electrocatalytic performance of the resulting Pd/Gr‐C catalysts during the electrooxidation of formic acid was assessed.A Pd/Gr0.3C0.7(Gr oxide:C=3:7,based on the precursor mass ratio)electrocatalyst exhibited better catalytic performance than both Pd/C and Pd/Gr catalysts.The current density generated by the Pd/Gr0.3C0.7catalyst was as high as102.14mA mgPd?1,a value that is approximately3times that obtained from the Pd/C(34.40mA mgPd?1)and2.6times that of the Pd/Gr material(38.50mA mgPd?1).The anodic peak potential of the Pd/Gr0.3C0.7was120mV more negative than that of the Pd/C and70mV more negative than that of the Pd/Gr.Scanning electron microscopy images indicated that the spherical C particles accumulated on the wrinkled graphene surfaces to form C cluster/Gr hybrids having three‐dimensional nanostructures.X‐ray photoelectron spectroscopy data confirmed the interaction between the Pd metal and the binary Gr‐C support.The Pd/Gr0.3C0.7also exhibited high stability,and so is a promising candidate for the fabrication of anodes for direct formic acid fuel cells.This work demonstrates a simple and cost‐effective method for improving the performance of Pd‐based electrocatalysts,which should have potential industrial applications.

Simultaneously achieving high energy density and responsivity in submicron BaTiO_(3) film capacitors integrated on Si

In the research field of energy storage dielectrics,the“responsivity”parameter,defined as the recyclable/recoverable energy density per unit electric field,has become critically important for a comprehensive evaluation of the energy storage capability of a dielectric.In this work,high recyclable energy density and responsivity,i.e.,W_(rec)=161.1 J·cm^(-3) and ξ=373.8 J·(kV·m^(2))^(-1),have been simultaneously achieved in a prototype perovskite dielectric,BaTiO_(3),which is integrated on Si at 500℃ in the form of a submicron thick film.This ferroelectric film features a multi-scale polar structure consisting of ferroelectric grains with different orientations and inner-grain ferroelastic domains.A LaNiO_(3) buffer layer is used to induce a{001}textured,columnar nanograin microstructure,while an elevated deposition temperature promotes lateral growth of the nanograins(in-plane diameter increases from~10-20 nm at lower temperatures to~30 nm).These preferably oriented and periodically regulated nanograins have resulted in a small remnant polarization and a delayed polarization saturation in the film’s P-E behavior,leading to a high recyclable energy density.Meanwhile,an improved polarizability/dielectric constant of the BaTiO_(3) film has produced a much larger maximum polarization than those deposited at lower temperatures at the same electric field,leading to a record-breaking responsivity for this simple perovskite.

Experimental design of paraffin/methylated melamine-formaldehyde microencapsulated composite phase change material and the application in battery thermal management system

In order to maintain the optimal operating temperature of the battery surface and meet the demand for thermal storage technology,battery thermal management system based on phase change materials has attracted increasing interest.In this work,a kind of core-shell structured microcapsule was synthesized by an in-situ polymerization,where paraffin was used as the core,while methanol was applied to mod-ify the melamine-formaldehyde shell to reduce toxicity and improve thermal stability.Moreover,three different types of heat conductive fillers with the same content of 10 wt.%,i.e.,nano-Al_(2)O_(3),nano-ZnO and carbon nanotubes were added,generating composites.The microcapsules were uniform,and were not affected by the thermal fillers,which were evenly dispersed around.The composite sample with carbon nanotubes(10 wt.%)showed the highest thermal conductivity of 0.50 W/(m K)and latent heat of 139.64 J/g.Furthermore,according to the leakage testing and battery charge/discharge experiments,compared with Al_(2)O_(3)and ZnO,the addition of carbon nanotubes remarkably enhances the heat storage ability as latent heat from 126.98 J/g for the prepared sample with Al_(2)O_(3)and 125.86 J/g for the one with ZnO,then to 139.64 J/g,as well as dissipation performance as a cooling effect by decreasing the sur-face temperature of battery from 2%to 12%of microcapsule,composite sample with carbon nanotubes presents a broad application prospect in battery thermal management system and energy storage field.

Surface decoration of mesocarbon microbeads with multifunctional TiNbO_(4-x)@C coating layer as high rate and stable anode of Li-ion batteries

Surface modification of graphite anode with electroactive matters has been proven of a more practical strategy in enhancing the performance of Li-ion batteries than exploring alternative novel anode materials.Herein,rutile TiNbO_(4-x) nanoparticles with a tunnel structure are employed as multifunctional decoration substances in combination with a carbon coating layer to improve the rate and cycle properties of mesocarbon microbeads(MCMBs).As compared to pristine MCMB,the Li^(+)diffusion coefficients of the composite anodes are enhanced due to the synergistic effect of TiNbO_(4-x)@C.Meanwhile,the overcharge and voltage polarization of the composite anodes at high rate are obviously minimized due to the current sharing effect of the high-potential TiNbO_(4-x).Moreover,the amorphous Li_(y)TiNbO_(4-x) converted from TiNbO_(4-x) in the initial lithiation process can deliver pseudocapacitive capacity to the composite anodes from the second cycle.All of these functions of TiNbO_(4-x)@Ccoating layer have directly contributed to the improved rate and cycle performance of the MCMB/TiNbO_(4-x)@C composite anodes.The one containing 12.0 wt%TiNbO_(4-x) exhibits a high reversible specific capacity of 118 m Ah·g^(-1)at 10C(1C=372 m A·g^(-1)),together with a high capacity retention of 90.9%after 300 cycles at 3C,which are all much superior to those of pristine MCMB.

Boosting energy storage performance of low-temperature sputtered CaBi_(2)Nb_(2)O_(9) thin film capacitors via rapid thermal annealing

CaBi_(2)Nb_(2)O_(9) thin film capacitors were fabricated on SrRuO_(3)-buffered Pt(111)/Ti/Si(100)substrates by adopting a two-step fabrication process.This process combines a low-temperature sputtering deposition with a rapid thermal annealing(RTA)to inhibit the grain growth,for the purposes of delaying the polarization saturation and reducing the ferroelectric hysteresis.By using this method,CaBi_(2)Nb_(2)O_(9) thin films with uniformly distributed nanograins were obtained,which display a large recyclable energy density Wrec≈69 J/cm^(3) and a high energy efficiencyη≈82.4%.A superior fatigue-resistance(negligible energy performance degradation after 10^(9) charge-discharge cycles)and a good thermal stability(from-170 to 150℃)have also been achieved.This two-step method can be used to prepare other bismuth layer-structured ferroelectric film capacitors with enhanced energy storage performances.

Achieving a high energy storage density in Ag(Nb,Ta)O_(3) antiferroelectric films via nanograin engineering

Due to its lead-free composition and a unique double polarization hysteresis loop with a large maximum polarization(Pmax)and a small remnant polarization(Pr),AgNbO_(3)-based antiferroelectrics(AFEs)have attracted extensive research interest for electric energy storage applications.However,a low dielectric breakdown field(Eb)limits an energy density and its further development.In this work,a highly efficient method was proposed to fabricate high-energy-density Ag(Nb,Ta)O_(3) capacitor films on Si substrates,using a two-step process combining radio frequency(RF)-magnetron sputtering at 450℃and post-deposition rapid thermal annealing(RTA).The RTA process at 700℃led to sufficient crystallization of nanograins in the film,hindering their lateral growth by employing short annealing time of 5 min.The obtained Ag(Nb,Ta)O_(3) films showed an average grain size(D)of~14 nm(obtained by Debye-Scherrer formula)and a slender room temperature(RT)polarization-electric field(P-E)loop(Pr≈3.8 mC·cm^(−2) and P_(max)≈38 mC·cm^(−2) under an electric field of~3.3 MV·cm^(−1)),the P-E loop corresponding to a high recoverable energy density(W_(rec))of~46.4 J·cm^(−3) and an energy efficiency(η)of~80.3%.Additionally,by analyzing temperature-dependent dielectric property of the film,a significant downshift of the diffused phase transition temperature(T_(M2-M3))was revealed,which indicated the existence of a stable relaxor-like AFE phase near the RT.The downshift of the T_(M2-M3) could be attributed to a nanograin size and residual tensile strain of the film,and it led to excellent temperature stability(20-240℃)of the energy storage performance of the film.Our results indicate that the Ag(Nb,Ta)O_(3) film is a promising candidate for electrical energy storage applications.

The role of central heteroatom in electrochemical nitrogen reduction catalyzed by polyoxometalate-supported single-atom catalyst

Single-atom catalysts(SACs)have recently emerged as stars in boosting the synthesis of NH3 from N_(2),as the catalytic performance of the supported single atoms can be modulated by their coordination environment.In this work,we propose a new strategy,based on comprehensive density functional theory calculations,whereby the coordination environment of a single Mo atom can be tuned by a central heteroatom(X=Fe,Co,Ni,Cu,Zn,Ga,Ge,and As)in the Kegging-type polyoxometalate(POM,(XW12O40)n−)substrate to catalyze the electrochemical nitrogen reduction reactions(NRR).Firstly,we demonstrate that the single Mo atom binds strongly to the POM surface oxygen hollow sites without aggregation.Secondly,the adsorption of*N_(2)on the POM-supported Mo atom is investigated and the reactivity is assessed by calculating the thermodynamics of the NRR.The results show that the POM(X=Co and As)supported Mo atom has high NRR activity with low limiting potentials.Finally,we reveal the origin of the NRR activity by analyzing the electronic structure.The results show that the charge on the O atoms of oxygen hollow sites is affected by the central heteroatom.Due to such effect,it can be found that more d electrons are transferred from Mo supported by POM(X=Co and As)to*N_(2),thus the N≡N triple bond is activated.This strategy of coordination environment tuning proposed in this work provides a useful guide for the design of efficient catalysts for electrocatalysis.

Dielectric ultracapacitors based on columnar nano-grained ferroelectric oxide films with gradient phases along the growth direction

In this work,dielectric ultracapacitors were designed and fabricated using a combination of phase boundary and nanograin strategies.These ultracapacitors are based on submicron-thick Ba(Zr_(0.2)Ti_(0.8))O_(3) ferroelectric films sputterdeposited on Si at 500℃.With a composition near a polymorphic phase boundary(PPB),a compressive strain,and a high nucleation rate due to the lowered deposition temperature,these films exhibit a columnar nanograined microstructure with gradient phases along the growth direction.Such a microstructure presents three-dimensional polarization inhomogeneities on the nanoscale,thereby significantly delaying the saturation of the overall electric polarization.Consequently,a pseudolinear,ultraslim polarization(P)-electric field(E)hysteresis loop was obtained,featuring a high maximum applicable electric field(~5.7 MV/cm),low remnant polarization(~5.2μC/cm^(2))and high maximum polarization(~92.1μC/cm^(2)).This P-E loop corresponds to a high recyclable energy density(W_(rec)~208 J/cm^(3))and charge‒discharge efficiency(~88%).An indepth electron microscopy study revealed that the gradient ferroelectric phases consisted of tetragonal(T)and rhombohedral(R)polymorphs along the growth direction of the film.The T-rich phase is abundant near the bottom of the film and gradually transforms into the R-rich phase near the surface.These films also exhibited a high Curie temperature of~460℃and stable capacitive energy storage up to 200℃.These results suggest a feasible pathway for the design and fabrication of high-performance dielectric film capacitors.

Pushing the high-k scalability limit with a superparaelectric gate layer

To meet the expectation set by Moore’s law on transistors,the search for thickness-scalable high dielectric constant(k)gate layers has become an emergent research frontier.Previous investigations have failed to solve the“polarizability–scalability–insulation robustness”trilemma.In this work,we show that this trilemma can be solved by using a gate layer of a high k ferroelectric oxide in its superparaelectric(SPE)state.In the SPE,its polar order becomes local and is dispersed in an amorphous matrix with a crystalline size down to a few nanometers,leading to an excellent dimensional scalability and a good field-stability of the k value.As an example,a stable high k value(37±3)is shown in ultrathin SPE films of(Ba_(0.95),Sr_(0.05))(Zr_(0.2),Ti_(0.8))O_(3)deposited on LaNiO_(3)-buffered Pt/Ti/SiO_(2)/(100)Si down to a 4 nm thickness,leading to a small equivalent oxide thickness of~0.46 nm.The aforementioned characteristic microstructure endows the SPE film a high breakdown strength(~10.5 MV·cm^(−1)for the 4 nm film),and hence ensures a low leakage current for the operation of the complementary metal oxide semiconductor(CMOS)gate.Lastly,a high electrical fatigue resistance is displayed by the SPE films.These results reveal a great potential of superparaelectric materials as gate dielectrics in the next-generation microelectronics.

Nitrogen-doped amorphous carbon coated mesocarbon microbeads as excellent high rate Li storage anode materials

A composite anode material consisting of a stable inner core of mesocarbon microbeads and a porous nitrogen-doped amorphous carbon shell active for lithium storage is prepared. The thin birnessite MnO_2 nanosheets hydrothermally deposited on mesocarbon microbeads are in situ replaced by polypyrrole,which is then transformed to nitrogen-doped amorphous carbon layer by calcination in nitrogen atmosphere. The surface modified mesocarbon microbeads exhibit average discharge capacities of 444 and103 m A h g^(-1) at the current densities of 0.1 and 3 A g^(-1) , respectively, obvious higher than the corresponding values of the bare sample, 371 and 60 mA h g^(-1) . Moreover, the composite anode maintains a discharge capacity of 306 mA h g^(-1) after 500 cycles at 1 A g^(-1) , suggesting an excellent cycle stability. It is believed that the nitrogen-doped amorphous carbon layer has provided additional lithium storage capacity and stabilized the structure integrity of mesocarbon microbeads. This work demonstrates that the capacity and rate performance of commercial graphitic carbons can be much improved by simply introducing a nitrogen-doped carbon coating layer active for Li storage, making them attractive for high power Li-ion batteries.

Copolymerization-Assisted Preparation of Porous LiMn_2O_4 Hollow Microspheres as High Power Cathode of Lithium-ion Batteries

Porous LiMn2O4 hollow microspheres were facilely prepared by incorporation of Li and Mn elements into a spherical polymeric precursor through copolymerization of lithium and manganese acetates with resorcinol and hexamethylenetetramine and then burning off the organic matrix at appropriate temperatures in air. The LiMn2O4 inherited the spherical morphology of the polymeric precursor but showed hollow porous structure assembled by nanocrystals of about 50–100 nm in size. When tested as cathode of Li-ion batteries, the LiMn2O4 hollow spheres exhibited excellent rate capability and cycle stability.A discharge capacity of above 90 mAh g-1was maintained at 10 C（1C = 120 mAg-1）, and the cells can still deliver a discharge capacity over 100 mAhg-1after another 115 cycles at 0.5 C. With such excellent electrochemical properties, the prepared LiMn2O4 hollow microspheres could be promising cathode of Li-ion batteries for long term and high power applications.

Preparation of Mg,N-co-doped lignin adsorbents for enhanced selectivity and high adsorption capacity of As(Ⅴ) from wastewater

Among various environmental problems,water pollution has drawn more and more attention.To develop an adsorbent with enhanced selectivity and high capacity for As(V)oxyanion,a novel lignin-based adsorbent was prepared by doping with N and modifying with Mg^(2+),using thiethylenetetramine(TETA)and MgCl_(2) as the source of N and Mg^(2+),respectively.N-doped lignin(NL)shows a high selectivity for As(Ⅴ),which is further enhanced by modifying with Mg^(2+)(MNL).MNL shows an excellent reusability.The adsorption isotherms and kinetics of MNL for As(Ⅴ)follow Langmuir isotherms model and pseudo-second-order kinetics model,respectively.The adsorption of MNL for As(Ⅴ)achieved a maximum adsorption capacity of 687.46 mg g^(−1) and the equilibrium was established within 30 min.This study offers a novel idea on the recycle of the waste of paper industry and provides a new technology for As(Ⅴ)adsorption from wastewater.

Highly efficient removal of trace lead(Ⅱ)from wastewater by 1,4-dicarboxybenzene modified Fe/Co metal organic nanosheets

A novel Fe/Co metal organic complex nanosheet modified by 1,4-dicarboxybenzene(BDC),i.e.,FeCo@BDC,was prepared,and highly efficient removal performance for trace lead(Ⅱ)(Pb^(2+))was demonstrated in the neutral aqueous solutions.The removal rates were higher than 95%and the adsorption was equilibrated in 15 min.The isotherms and kinetics for the adsorption Pb^(2+)by the FeCo@BDC adsorbents followed Langmuir model and pseudo-second-order model,respectively.The maximum adsorption capacity was 220.48 mg g^(-1).The FeCo@BDC adsorbents also own a prominent regeneration performance.The prominent performance of in the removal of trace Pb^(2+)makes FeCo@BDC an ideal candidate as commercial adsorbent materials.

Achieving excellent energy storage reliability and endurance via mechanical performance optimization strategy in engineered ceramics with core-shell grain structure

Although dielectric ceramic capacitors possess attractive properties for high-power energy storage,their pronounced electrostriction effect and high brittleness are conducive to easy initiation and propagation of cracks that significantly deteriorate electrical reliability and lifetime of capacitors in practical applications.Herein,a new strategy for designing relaxor ferroelectric ceramics with K_(0.5)Na_(0.5)NbO_(3)-core/SiO_(2)-shell structured grains was proposed to simultaneously reduce the electric-field-induced strain and enhance the mechanical strength of the ceramics.The simulation and experiment declared that the bending strength and compression strength of the core-shell structured ceramic were shown to increase by more than 50% over those of the uncoated sample.Meanwhile,the electric-field-induced strain was reduced by almost half after adding the SiO_(2) coating.The suppressed electrical deformation and enhanced mechanical strength could alleviate the probability of generation of cracks and prevent their propagation,thus remarkably improving breakdown strength and fatigue endurance of the ceramics.As a result,an ultra-high breakdown strength of 425 kV cm^(-1) and excellent recoverable energy storage density(Wrec~4.64 J cm^(-3))were achieved in the core-shell structured sample.More importantly,the unique structure could enhance the cycling stability of the ceramic(Wrec variation<±2% after 105 cycles).Thus,mechanical performance optimization via grain structure engineering offers a new paradigm for improving electrical breakdown strength and fatigue endurance of dielectric ceramic capacitors.

Improving the efficiency of dye-sensitized solar cells by photoanode surface modifications

Dye-sensitized solar cells(DSSCs) provide a promising alternative solar cell technology because of their high efficiency, environmental friendliness, easy fabrication,and low cost. Power conversion efficiency is an important parameter to measure the performance of DSSCs, but the severe charge recombination that occurs at the photoanode hinders the future improvement of power conversion efficiency. Therefore, one of the key goals for achieving high efficiency is to reduce the energy loss caused by the unwanted charge recombination at various interfaces. From this perspective, surface modification of the photoanode is the simplest method among the various approaches available in the literature for enhancing the performance of DSSCs by inhibiting the interfacial charge recombination. After some brief notes on DSSCs, in this review, we present a comprehensive discussion on surface modifications of different photoanodes that have been adopted in the literature not only for reducing recombination but also for enhancing light harvesting. Depending on the electrode materials, we discuss surface modifications of binary oxides such as TiO_2 and ZnO and ternary oxides, including Zn_2SnO_4, SrSnO_3, and BaSnO_3.We also talk about methods of surface modification and the materials suitable for surface treatment. Finally, we end with a brief future outlook of DSSCs.

Nitrogen and oxygen co-doped mesoporous carbon spheres as capacitive anode for high performance sodium-ion capacitors

The poor rate capability of battery-type anode is usually the bottleneck of the power-energy outputs of a hybrid alkaline metal ion capacitor.In this work,nitrogen and oxygen co-doped mesoporous carbon spheres with excellent rate performance and cycle stability are used as anode materials of sodium ion capacitors(SICs).The high N and O element doping levels as well as the amorphous and mesoporous structure have enabled prominent capacitive Na ion storage behavior,which in turn match well with the capacitive cathode in the hybrid device.Under optimum conditions,the SIC delivers a high energy density of 103.1 Wh kg^(-1)at a power density of 205.6 W kg^(-1).Even at a high power density of 7520 W kg^(-1),an energy density of 23.5 Wh kg^(-1)is still maintained.Moreover,a robust cycle stability with capacity retention of 84.6%after 2500 cycles at 1 A g^(-1)is maintained.Such excellent electrochemical performances convincingly demonstrate that the all-carbon based SICs with the highly capacitive N and O co-doped mesoporous carbon anode can be promising Na ion-based energy storage devices alternative to their Li ion-based counterparts.

Achieving a high dielectric tunability in strain-engineered tetragonal K_(0.5)Na_(0.5)NbO_(3) films

Using a modified Landau-Devonshire type thermodynamic potential,we show that dielectric tunabilityηof a tetragonal ferroelectric film can be analytically solved.At a given electric field E,ηis a function of the remnant polarization(P_(0)^(f))and the smallfield relative dielectric permittivity(χ_(0)^(f)),which are commonly measured material properties.After a survey of materials,a largeη~80%is predicted to be achievable in a(001)-oriented tetragonal(K_(0.5),Na_(0.5))NbO_(3)film.This strain-stabilized tetragonal phase is verified by density functional theory(DFT)calculations.(K_(0.5),Na_(0.5))NbO_(3)films based on this design were successfully prepared via a sputtering deposition process on SrRuO_(3)-buffered(100)SrTiO_(3) substrates.The resulted epitaxial films showed a sizable Pf0(~0.21C m^(−2))and a largeχ_(0)^(f)(~830–860),as well as a largeηclose to the theoretical value.The measured dielectric tunabilities as functions of E are well described by the theoreticalη(E)curves,validating our integrated approach rooted in a theoretical understanding.