The Influence of Bond Valence on Bond Covalency in RMn_2O_5 (R=La, Pr, Nd, Sin, Eu)

The relationship between bond valence and bond covalency in RMn2O5 (R = La, Pr, Nd.Sm, Eu) has been investigated by a semiempirical method. This method is the generalization of thedielectric description theory of Phillips. Van Vechten, Levine and Tanaka scheme. The resultsindicate that larger valences usually result in higher bond covalencies, in good agreement with thepoint that the excess charge in the bonding region is the origin of formation of bond covalency.Other factors, such as oxidation state of elements, only make a small contribution to bondcovalency.

Ultrathin Metal Silicate Hydroxide Nanosheets with Moderate Metal-Oxygen Covalency Enables Efficient Oxygen Evolution

Exploring efficient,cost-effective,and durable electrocatalysts for electrochemical oxygen evolution reaction(OER)is pivotal for the large-scale application of water electrolysis.Recent advance has demonstrated that the activity of electrocatalysts exhibits a strong dependence on the surface electronic structure.Herein,a series of ultrathin metal silicate hydroxide nanosheets(UMSHNs)M_(3)Si_(2)O_(5)(OH)_(4)(M=Fe,Co,and Ni)synthesized without surfactant are introduced as highly active OER electrocatalysts.Cobalt silicate hydroxide nanosheets show an optimal OER activity with overpotentials of 287 and 358 m V at 1 and 10 m A cm^(-2),respectively.Combining experimental and theoretical studies,it is found that the OER activity of UMSHNs is dominated by the metal-oxygen covalency(MOC).High OER activity can be achieved by having a moderate MOC as reflected by aσ^(*)-orbital(e_(g))filling near unity and moderate[3d]/[2p]ratio.Moreover,the UMSHNs exhibit favorable chemical stability under oxidation potential.This contribution provides a scientific guidance for further development of active metal silicate hydroxide catalysts.

Covalency triggers high catalytic activity of amorphous molybdenum oxides for oxidative desulfurization

Oxidative desulfurization(ODS)is a promising technology to produce clean fuel with requiring superior catalysts to lower kinetic barriers.Although most ODS catalysts are based on crystalline transition-metal oxides(TMOs),extraordinary activity also can be achieved with amorphous TMOs.However,the origin of the remarkable catalytic activity of the amorphous TMOs remains greatly ambiguous.Here,we found the crucial role of Mo–O covalency in ruling the intrinsic catalytic activity of amorphous molybdenum oxides(MoO_(x)).Experimental and theoretical analysis indicated that the nonequivalent connectivity in the amorphous structure strongly enhanced Mo–O covalency,thereby increasing the content of electrophilic oxygen and nucleophilic molybdenum to favor the MoO_(x)–H_(2)O_(2) interaction.With the boosted Mo–O covalency to improve the flexibility of the charge state,the amorphous MoO_(x)-based composite catalyst(PE-MoO_(x)/S-0.05)exhibited outstanding catalytic activity for ODS of fuel oil.The turnover frequency(TOF)value of the catalyst(18.63 h^(-1))was almost an order of magnitude higher than that of most reported crystalline MoO_(x)/molecular sieve composite catalysts.The in-depth understanding of the origin of the amorphous TMOs activity for ODS provides a valuable reference for developing ODS catalysts.

Strengthen metal-oxygen covalency of CoFe-layered double hydroxide for efficient mild oxygen evolution

Oxygen evolution reaction(OER)is crucial for hydrogen production as well as other energy storage technologies.CoFe-layered double hydroxide(CoFe-OH)has been widely considered as one of the most efficient electrocatalysts for OER in basic aqueous solution.However,it still suffers from low activity in neutral electrolyte.This paper describes partially oxidized CoFe-OH(PO-CoFe-OH)with enhanced covalency of M-O bonds and displays enhanced OER performance under mild condition.Mechanism studies reveal the suitably enhanced M-O covalency in PO-CoFe-OH shifts the OER mechanism to lattice oxygen oxidation mechanism and also promotes the rate-limiting deprotonation,providing superior OER performance.It just requires the overpotentials of 186 and 365 mV to drive the current density densities of 1 and 10 mA·cm^(-2) in 0.1 M KHCO_(3) aqueous solution(pH=8.3),respectively.It provides a new process for rational design of efficient catalysts for water oxidation in mild conditions.

Advances of Electrochemical and Electrochemiluminescent Sensors Based on Covalent Organic Frameworks

Covalent organic frameworks(COFs),a rapidly developing category of crystalline conjugated organic polymers,possess highly ordered structures,large specific surface areas,stable chemical properties,and tunable pore microenvironments.Since the first report of boroxine/boronate ester-linked COFs in 2005,COFs have rapidly gained popularity,showing important application prospects in various fields,such as sensing,catalysis,separation,and energy storage.Among them,COFs-based electrochemical(EC)sensors with upgraded analytical performance are arousing extensive interest.In this review,therefore,we summarize the basic properties and the general synthesis methods of COFs used in the field of electroanalytical chemistry,with special emphasis on their usages in the fabrication of chemical sensors,ions sensors,immunosensors,and aptasensors.Notably,the emerged COFs in the electrochemiluminescence(ECL)realm are thoroughly covered along with their preliminary applications.Additionally,final conclusions on state-of-the-art COFs are provided in terms of EC and ECL sensors,as well as challenges and prospects for extending and improving the research and applications of COFs in electroanalytical chemistry.

Challenges and Opportunities in Preserving Key Structural Features of 3D-Printed Metal/Covalent Organic Framework

Metal-organic framework(MOF)and covalent organic framework(COF)are a huge group of advanced porous materials exhibiting attractive and tunable microstructural features,such as large surface area,tunable pore size,and functional surfaces,which have significant values in various application areas.The emerging 3D printing technology further provides MOF and COFs(M/COFs)with higher designability of their macrostructure and demonstrates large achievements in their performance by shaping them into advanced 3D monoliths.However,the currently available 3D printing M/COFs strategy faces a major challenge of severe destruction of M/COFs’microstructural features,both during and after 3D printing.It is envisioned that preserving the microstructure of M/COFs in the 3D-printed monolith will bring a great improvement to the related applications.In this overview,the 3D-printed M/COFs are categorized into M/COF-mixed monoliths and M/COF-covered monoliths.Their differences in the properties,applications,and current research states are discussed.The up-to-date advancements in paste/scaffold composition and printing/covering methods to preserve the superior M/COF microstructure during 3D printing are further discussed for the two types of 3D-printed M/COF.Throughout the analysis of the current states of 3D-printed M/COFs,the expected future research direction to achieve a highly preserved microstructure in the 3D monolith is proposed.

Covalently Bonded Ni Sites in Black Phosphorene with Electron Redistribution for Efficient Metal‑Lightweighted Water Electrolysis

The metal-lightweighted electrocatalysts for water splitting are highly desired for sustainable and economic hydrogen energy deployments,but challengeable.In this work,a low-content Ni-functionalized approach triggers the high capability of black phosphorene(BP)with hydrogen and oxygen evolution reaction(HER/OER)bifunctionality.Through a facile in situ electro-exfoliation route,the ionized Ni sites are covalently functionalized in BP nanosheets with electron redistribution and controllable metal contents.It is found that the as-fabricated Ni-BP electrocatalysts can drive the water splitting with much enhanced HER and OER activities.In 1.0 M KOH electrolyte,the optimized 1.5 wt%Nifunctionalized BP nanosheets have readily achieved low overpotentials of 136 mV for HER and 230 mV for OER at 10 mA cm^(−2).Moreover,the covalently bonding between Ni and P has also strengthened the catalytic stability of the Ni-functionalized BP electrocatalyst,stably delivering the overall water splitting for 50 h at 20 mA cm^(−2).Theoretical calculations have revealed that Ni–P covalent binding can regulate the electronic structure and optimize the reaction energy barrier to improve the catalytic activity effectively.This work confirms that Ni-functionalized BP is a suitable candidate for electrocatalytic overall water splitting,and provides effective strategies for constructing metal-lightweighted economic electrocatalysts.

Selective adsorption of tetracycline by β-CD-immobilized sodium alginate aerogel coupled with ultrafiltration for reclaimed water

In this work,a novel composite material based on β-cyclodextrin-immobilized sodium alginate aerogel(β-CD/NaAlg) was developed utilizing cross-linker of epichlorohydrin and applied as an adsorbent to remove tetracycline antibiotics from reclaimed wastewater.A series of characterizations were utilized to confirm the successful synthesis of the adsorbent and this β-CD/NaAlg presented a three-dimensional network at the nanoscale or microscale.Under optimal conditions(pH=4,t=8 h,β-CD:NaAlg=9,adsorbent dosage = 1.5 g·L-1),the maximum removal rate of β-CD/NaAlg to tetracycline was 70%.The adsorption behavior of tetracycline on β-CD/NaAlg conformed to the Freundlich isotherm model(R2=0.9977) and the pseudo-second-order kinetic model(R^(2)=0.9993).Moreover,the adsorbent still removed 55.3% of tetracycline after five cycles.Specially,the adsorbent was integrated with ultrafiltration to adsorb tetracycline antibiotics from simulated reclaimed wastewater,and the removal rate of tetracycline reached 78.9% within 2 h.The existence of Cr(Ⅵ) had a negligible impact on tetracycline removal,while the presence of humic acid exhibited a promoting effect.The possible adsorption mechanisms were also elucidated through X-ray photoelectron spectroscopy and density functional theory analysis.In summary,β-CD/NaAlg represents an environmentally friendly,efficient,and sustainable adsorbent for removing tetracycline antibiotics from reclaimed water.

Metal-free two-dimensional phosphorene-based electrocatalyst with covalent P-N heterointerfacial reconstruction for electrolyte-lean lithium-sulfur batteries

The use of lithium-sulfur batteries under high sulfur loading and low electrolyte concentrations is severely restricted by the detrimental shuttling behavior of polysulfides and the sluggish kinetics in redox processes.Two-dimensional(2D)few layered black phosphorus with fully exposed atoms and high sulfur affinity can be potential lithium-sulfur battery electrocatalysts,which,however,have limitations of restricted catalytic activity and poor electrochemical/chemical stability.To resolve these issues,we developed a multifunctional metal-free catalyst by covalently bonding few layered black phosphorus nanosheets with nitrogen-doped carbon-coated multiwalled carbon nanotubes(denoted c-FBP-NC).The experimental characterizations and theoretical calculations show that the formed polarized P-N covalent bonds in c-FBP-NC can efficiently regulate electron transfer from NC to FBP and significantly promote the capture and catalysis of lithium polysulfides,thus alleviating the shuttle effect.Meanwhile,the robust 1D-2D interwoven structure with large surface area and high porosity allows strong physical confinement and fast mass transfer.Impressively,with c-FBP-NC as the sulfur host,the battery shows a high areal capacity of 7.69 mAh cm^(−2) under high sulfur loading of 8.74 mg cm^(−2) and a low electrolyte/sulfur ratio of 5.7μL mg^(−1).Moreover,the assembled pouch cell with sulfur loading of 4 mg cm^(−2) and an electrolyte/sulfur ratio of 3.5μL mg^(−1) shows good rate capability and outstanding cyclability.This work proposes an interfacial and electronic structure engineering strategy for fast and durable sulfur electrochemistry,demonstrating great potential in lithium-sulfur batteries.

Multifunctional MOF@COF Nanoparticles Mediated Perovskite Films Management Toward Sustainable Perovskite Solar Cells

Although covalent organic frameworks(COFs)with highπ-conjugation have recently exhibited great prospects in perovskite solar cells(PSCs),their further application in PSCs is still hindered by face-to-face stacking and aggregation issues.Herein,metal-organic framework(MOF-808)is selected as an ideal platform for the in situ homogeneous growth of a COF to construct a core-shell MOF@COF nanoparticle,which could effectively inhibit COF stacking and aggregation.The synergistic intrinsic mechanisms induced by the MOF@COF nanoparticles for reinforcing intrinsic stability and mitigating lead leakage in PSCs have been explored.The complementary utilization ofπ-conjugated skeletons and nanopores could optimize the crystallization of large-grained perovskite films and eliminate defects.The resulting PSCs achieve an impressive power conversion efficiency of 23.61%with superior open circuit voltage(1.20 V)and maintained approximately 90%of the original power conversion efficiency after 2000 h(30-50%RH and 25-30℃).Benefiting from the synergistic effects of the in situ chemical fixation and adsorption abilities of the MOF@COF nanoparticles,the amount of lead leakage from unpackaged PSCs soaked in water(<5 ppm)satisfies the laboratory assessment required for the Resource Conservation and Recovery Act Regulation.

All‑Covalent Organic Framework Nanofilms Assembled Lithium‑Ion Capacitor to Solve the Imbalanced Charge Storage Kinetics

Free-standing covalent organic framework(COFs)nanofilms exhibit a remarkable ability to rapidly intercalate/de-intercalate Li^(+) in lithium-ion batteries,while simultaneously exposing affluent active sites in supercapacitors.The development of these nanofilms offers a promising solution to address the persistent challenge of imbalanced charge storage kinetics between battery-type anode and capacitor-type cathode in lithium-ion capacitors(LICs).Herein,for the first time,custom-made COFBTMB-TP and COFTAPB-BPY nanofilms are synthesized as the anode and cathode,respectively,for an all-COF nanofilm-structured LIC.The COFBTMB-TP nanofilm with strong electronegative–CF3 groups enables tuning the partial electron cloud density for Li^(+) migration to ensure the rapid anode kinetic process.The thickness-regulated cathodic COFTAPB-BPY nanofilm can fit the anodic COF nanofilm in the capacity.Due to the aligned 1D channel,2D aromatic skeleton and accessible active sites of COF nanofilms,the whole COFTAPB-BPY//COFBTMB-TP LIC demonstrates a high energy density of 318 mWh cm^(−3) at a high-power density of 6 W cm^(−3),excellent rate capability,good cycle stability with the capacity retention rate of 77%after 5000-cycle.The COFTAPB-BPY//COFBTMB-TP LIC represents a new benchmark for currently reported film-type LICs and even film-type supercapacitors.After being comprehensively explored via ex situ XPS,7Li solid-state NMR analyses,and DFT calculation,it is found that the COFBTMB-TP nanofilm facilitates the reversible conversion of semi-ionic to ionic C–F bonds during lithium storage.COFBTMB-TP exhibits a strong interaction with Li^(+) due to the C–F,C=O,and C–N bonds,facilitating Li^(+) desolation and absorption from the electrolyte.This work addresses the challenge of imbalanced charge storage kinetics and capacity between the anode and cathode and also pave the way for future miniaturized and wearable LIC devices.

d-Orbital steered FeN_(4)moiety through N,S dual-site adjustation for zinc-air flow battery

The implementation of pristine covalent organic polymer(CO_(2)P)with well-defined structure as air electrode may spark fresh vitality to rechargeable zinc-air flow batteries(ZAFBs),but it still remains challenges in synergistically regulating their electronic states and structural porosity for the great device performance.Here,we conquer these issues by exploiting N and S co-doped graphene with COP rich in metal-ligand nitrogen to synergistically construct an effective catalyst for oxygen reduction reaction(ORR).Among them,the N and S co-doped sites with high electronegativity properties alter the number of electron occupations in the d orbital of the iron centre and form electron-transfer bridges,thereby boosting the selectivity of the ORR-catalysed four-electron pathway.Meanwhile,the introduction of COP materials aids the formation of pore interstices in the graphene lamellae,which both adequately expose the active sites and facilitate the transport of reactive substances.Benefiting from the synergistic effect,as-prepared catalyst exhibits excellent half-wave potentials(E_(1/2)=912 mV)and stability(merely 8.8%drop after a long-term durability test of 50000 s).Further,ZAFBs assembled with the N/SG@CO_(2)P catalyst demonstrate exceptional power density(163.8 mW cm^(-2))and continuous charge and discharge for approximately 140 h at 10 mA cm^(-2),outperforming the noble-metal benchmarks.

Covalent Organic Framework with 3D Ordered Channel and Multi-Functional Groups Endows Zn Anode with Superior Stability

Achieving a highly robust zinc(Zn)metal anode is extremely important for improving the performance of aqueous Zn-ion batteries(AZIBs)for advancing“carbon neutrality”society,which is hampered by the uncontrollable growth of Zn dendrite and severe side reactions including hydrogen evolution reaction,corrosion,and passivation,etc.Herein,an interlayer containing fluorinated zincophilic covalent organic framework with sulfonic acid groups(COF-S-F)is developed on Zn metal(Zn@COF-S-F)as the artificial solid electrolyte interface(SEI).Sulfonic acid group(-SO_(3)H)in COF-S-F can effectively ameliorate the desolvation process of hydrated Zn ions,and the three-dimensional channel with fluoride group(-F)can provide interconnected channels for the favorable transport of Zn ions with ion-confinement effects,endowing Zn@COF-S-F with dendrite-free morphology and suppressed side reactions.Consequently,Zn@COF-S-F symmetric cell can stably cycle for 1,000 h with low average hysteresis voltage(50.5 m V)at the current density of 1.5 m A cm^(-2).Zn@COF-S-F|Mn O_(2)cell delivers the discharge specific capacity of 206.8 m Ah g^(-1)at the current density of 1.2 A g^(-1)after 800 cycles with high-capacity retention(87.9%).Enlightening,building artificial SEI on metallic Zn surface with targeted design has been proved as the effective strategy to foster the practical application of high-performance AZIBs.

Peripheral carbazole units-decorated MR emitter containing B−N covalent bond for highly efficient green OLEDs with low roll-off

Boron−nitrogen doped multiple resonance(BN-MR)emitters,characterized by B−N covalent bonds,offer distinctive advantages as pivotal building blocks for facile access to novel MR emitters featuring narrowband spectra and high efficiency.However,there remains a scarcity of exploration concerning synthetic methods and structural derivations to expand the library of novel BN-MR emitters.Herein,we present the synthesis of a BN-MR emitter,tCz[B−N]N,through a one-pot borylation reaction directed by the amine group,achieving an impressive yield of 94%.The emitter is decorated by incorporating two 3,6-di-tbutylcarbazole(tCz)units into a B−N covalent bond doped BN-MR parent molecule via para-C−π−D and para-N−π−D conjugations.This peripheral decoration strategy enhances the reverse intersystem crossing process and shifts the emission band towards the pure green region,peaking at 526 nm with a narrowband full-width at half maximum(FWHM)of 41 nm.Consequently,organic light emitting diodes(OLEDs)employing this emitter achieved a maximum external quantum efficiency(EQEmax)value of 27.7%,with minimal efficiency roll-off.Even at a practical luminance of 1000 cd·m^(−2),the device maintains a high EQE value of 24.6%.

One stone two birds:electrochemical and colorimetric dual-mode biosensor based on copper peroxide/covalent organic framework nanocomposite for ultrasensentive norovirus detection

Norovirus(NoV)is regarded as one of the most common causes of foodborne diarrhea in the world.It is urgent to identify the pathogenic microorganism of the diarrhea in short time.In this work,we developed an electrochemical and colorimetric dual-mode detection for NoV based on the excellent dual catalytic properties of copper peroxide/COF-NH_(2)nanocomposite(CuO_(2)@COF-NH_(2)).For the colorimetric detection,NoV can be directly detected by the naked eye based on CuO_(2)@COF-NH_(2)as a laccase-like nonazyme using“peptide-NoV-antibody”recognition mode.The colorimetric assay displayed a wide and quality linear detection range from 1 copy/mL to 5000 copies/mL of NoV with a low limit of detection(LOD)of 0.125 copy/mL.For the electrochemical detection of NoV,CuO_(2)@COF-NH_(2)showed an oxidation peak of copper ion from Cu^(+)to Cu^(2+)using“peptide-NoV-antibody”recognition mode.The electrochemical assay showed a linear detection range was 1-5000 copies/mL with a LOD of 0.152 copy/mL.It's worthy to note that this assay does not need other electrical signal molecule,which provide the stable and sensitive electrochemial detection for NoV.The electrochemical and colorimetric dual-mode detection was used to detect NoV in foods and faceal samples,which has the potential for improving food safety and diagnosing of NoV-infected diarrhea.

Studies of Iron-Sulfur Covalency in the Model System and Proteins

It was found that the highly covalent nature of the metal-ligand interactions in the Fe-S cluster clearly played an important role in determining the reactivity of the sites. A semi-empirical model, based on the Phillips theory of bonding was developed for quantitative explanation of covalency in Fe-S cluster, showing that Mossbauer spectroscopy and electronic absorption spectroscopy provided the direct experimental probe of covalency of Fe-S4 clusters.

Influence of bond valence on bond covalency in calcium doped lanthanum chromite

The influence of bond valence on bond covalence in Lal-xCaxCrO3(x = 0.0, 0.1, 0.2, 0.3) has been studied by using semi empirical method. This method is the extortion of the dialectic description theory proposed by Phillips, Van Vetches, Levine and Tanaka (PVLT). In the calculation of bond valence, two schemes were adopted. The first is the equal-valence scheme, and the second is Bond Valence Sums (BVS) scheme. Bath schemes suggest that for the title compound bond covalence be mainly influenced by bond valence, and insensitive to the Ca doping level. Generally speaking, larger bond valences usually result in higher bond covalence's.

Outstanding Humidity Chemiresistors Based on Imine-Linked Covalent Organic Framework Films for Human Respiration Monitoring

Human metabolite moisture detection is important in health monitoring and non-invasive diagnosis.However,ultra-sensitive quantitative extraction of respiration information in real-time remains a great challenge.Herein,chemiresistors based on imine-linked covalent organic framework(COF)films with dual-active sites are fabricated to address this issue,which demonstrates an amplified humidity-sensing signal performance.By regulation of monomers and functional groups,these COF films can be pre-engineered to achieve high response,wide detection range,fast response,and recovery time.Under the condition of relative humidity ranging from 13 to 98%,the COFTAPB-DHTA film-based humidity sensor exhibits outstanding humidity sensing perfor-mance with an expanded response value of 390 times.Furthermore,the response values of the COF film-based sensor are highly linear to the relative humidity in the range below 60%,reflecting a quantitative sensing mechanism at the molecular level.Based on the dual-site adsorption of the(-C=N-)and(C-N)stretching vibrations,the revers-ible tautomerism induced by hydrogen bonding with water molecules is demonstrated to be the main intrinsic mechanism for this effective humidity detection.In addition,the synthesized COF films can be further exploited to effectively detect human nasal and oral breathing as well as fabric permeability,which will inspire novel designs for effective humidity-detection devices.

Metal-Free 2D/2D van der Waals Heterojunction Based on Covalent Organic Frameworks for Highly Efficient Solar Energy Catalysis

Covalent organic frameworks(COFs)have emerged as a kind of rising star materials in photocatalysis.However,their photocatalytic activities are restricted by the high photogenerated electron-hole pairs recombination rate.Herein,a novel metal-free 2D/2D van der Waals heterojunction,composed of a two-dimensional(2D)COF with ketoenamine linkage(TpPa-1-COF)and 2D defective hexagonal boron nitride(h-BN),is successfully constructed through in situ solvothermal method.Benefitting from the presence of VDW heterojunction,larger contact area and intimate electronic coupling can be formed between the interface of TpPa-1-COF and defective h-BN,which make contributions to promoting charge car-riers separation.The introduced defects can also endow the h-BN with porous structure,thus providing more reactive sites.Moreover,the TpPa-1-COF will undergo a structural transformation after being integrated with defective h-BN,which can enlarge the gap between the conduction band position of the h-BN and TpPa-1-COF,and suppress electron backflow,corroborated by experimental and density functional theory calculations results.Accordingly,the resulting porous h-BN/TpPa-1-COF metal-free VDW heterojunction displays out-standing solar energy catalytic activity for water splitting without co-catalysts,and the H_(2) evolution rate can reach up to 3.15 mmol g^(−1) h^(−1),which is about 67 times greater than that of pristine TpPa-1-COF,also surpassing that of state-of-the-art metal-free-based photocatalysts reported to date.In particular,it is the first work for constructing COFs-based heterojunctions with the help of h-BN,which may provide new avenue for designing highly efficient metal-free-based photocatalysts for H_(2) evolution.