Efficient Proton Transfer and Charge Separation within Covalent Organic Frameworks via Hydrogen-Bonding Network to Boost H2O2 Photosynthesis.

Photocatalytic synthesis based on the oxygen reduction reaction (ORR) has shown great promise for H2O2 production. However, the low activity and selectivity of 2e- ORR result in a fairly low efficiency of H2O2 production. Herein, we propose a strategy to enhance the proton-coupled electron transfer (PCET) process in covalent organic frameworks (COFs), thereby significantly boosting H2O2 photosynthesis. We demonstrated that the construction of a hydrogen-bonding network, achieved by anchoring the H3PO4 molecular network on COF nanochannels, can greatly improve both proton conductivity and photogenerated charge separation efficiency of COFs. Thus, COF@H3PO4 exhibited superior photocatalytic performance in generating H2O2 without sacrificial agents, with a solar-to-chemical conversion efficiency as high as 0.69%. Results indicated that a much more localized spatial distribution of energy band charge density on COF@H3PO4 led to efficient charge separation, and the small energy barrier of the rate-limiting step from *OOH to H2O2 endowed COF@H3PO4 with higher 2e- ORR selectivity.

Amorphous Modulation of Atomic Nb-O/N Clusters with Asymmetric Coordination in Carbon Shells for Advanced Sodium-Ion Hybrid Capacitors.

Anode materials with excellent properties have become the key to develop sodium-ion hybrid capacitors (SIHCs) that combine the advantages of both batteries and capacitors. Amorphous modulation is an effective strategy to realize high energy/power density in SIHCs. Herein, atomically amorphous Nb-O/N clusters with asymmetric coordination are in situ created in N-doped hollow carbon shells (Nb-O/N@C). The amorphous clusters with asymmetric Nb-O3/N1 configurations have abundant charge density and low diffusion energy barriers, which effectively modulate the charge transport paths and improve the reaction kinetics. The clusters are also enriched with unsaturated vacancy defects and isotropic ion-transport channels, and their atomic disordering exhibits high structural stress buffering, which are strong impetuses for realizing bulk-phase-indifferent ion storage and enhancing the storage properties of the composite. Based on these features, Nb-O/N@C achieves notably improved sodium-ion storage properties (reversible capacity of 240.1 mAh g-1 at 10.0 A g-1 after 8000 cycles), and has great potential for SIHCs (230 Wh Kg-1 at 4001.5 W Kg-1). This study sheds new light on developing high-performance electrodes for sodium-ion batteries and SIHCs by designing amorphous clusters and asymmetric coordination.

Bidirectional Enhancement of Nitrogen Removal by Indigenous Synergetic Microalgal-Bacterial Consortia in Harsh Low-C/N Wastewater.

Conventional microalgal-bacterial consortia have limited capacity to treat low-C/N wastewater due to carbon limitation and single nitrogen (N) removal mode. In this work, indigenous synergetic microalgal-bacterial consortia with high N removal performance and bidirectional interaction were successful in treating rare earth tailing wastewaters with low-C/N. Ammonia removal reached 0.89 mg N L-1 h-1, 1.84-fold more efficient than a common microalgal-bacterial system. Metagenomics-based metabolic reconstruction revealed bidirectional microalgal-bacterial interactions. The presence of microalgae increased the abundance of bacterial N-related genes by 1.5- to 57-fold. Similarly, the presence of bacteria increased the abundance of microalgal N assimilation by 2.5- to 15.8-fold. Furthermore, nine bacterial species were isolated, and the bidirectional promotion of N removal by the microalgal-bacterial system was verified. The mechanism of microalgal N assimilation enhanced by indole-3-acetic acid was revealed. In addition, the bidirectional mode of the system ensured the scavenging of toxic byproducts from nitrate metabolism to maintain the stability of the system. Collectively, the bidirectional enhancement system of synergetic microalgae-bacteria was established as an effective N removal strategy to broaden the stable application of this system for the effective treatment of low C/N ratio wastewater.

Nitrogen-Rich WN Clusters with Atomic Disorders and Non-Grain Boundaries Confined in Carbon Nanosheets Boosting Sodium-Ion Storage.

Sodium-ion batteries (SIBs) as economic candidates have received considerable attention for large-scale energy storage applications. However, crystalline metal compounds with specific transport routes and rigid structures restrict their practical applications. Herein, the atomically dispersed N-rich amorphous WN clusters confined in the carbon nanosheets (WN/CNSs) are reported. Through advanced tests and calculations, the structural advantages, reaction mechanisms, and kinetic behaviors of the clusters are systematically analyzed. Compared with the crystalline W2 N with low theoretical capacity (only 209.3 mAh g-1 ), the amorphous WN clusters have the advantages of atomic disorders and non-grain boundaries and can afford abundant active sites (unsaturated dangling bonds) and isotropic charge transfer channels, which can be further enhanced by the N-rich characteristics and high electronegativity of the clusters. The encapsulation of CNSs has high conductivity and structural stability, which promotes electron transfer and effectively buffers volume expansions. As a SIB anode, the reversible capacity of WN/CNSs reaches 421.2 mAh g-1 at 0.1 A g-1 . Even at 20 A g-1 , the reversible capacity of 170.7 mAh g-1 is maintained after 8000 cycles. This study focuses on the advantages of amorphous nitrides, which have important guiding significance for the design of atomic clusters for high-performance metal ion batteries.

Targeted Decomplexation of Metal Complexes for Efficient Metal Recovery by Ozone/Percarbonate.

Traditional methods cannot efficiently recover Cu from Cu(II)-EDTA wastewater and encounter the formation of secondary contaminants. In this study, an ozone/percarbonate (O3/SPC) process was proposed to efficiently decomplex Cu(II)-EDTA and simultaneously recover Cu. The results demonstrate that the O3/SPC process achieves 100% recovery of Cu with the corresponding kobs value of 0.103 min-1 compared with the typical •OH-based O3/H2O2 process (81.2%, 0.042 min-1). The carbonate radical anion (CO3•-) is generated from the O3/SPC process and carries out the targeted attack of amino groups of Cu(II)-EDTA for decarboxylation and deamination processes, resulting in successive cleavage of Cu-O and Cu-N bonds. In comparison, the •OH-based O3/H2O2 process is predominantly responsible for the breakage of Cu-O bonds via decarboxylation and formic acid removal. Moreover, the released Cu(II) can be transformed into stable copper precipitates by employing an endogenous precipitant (CO32-), accompanied by toxic-free byproducts in the O3/SPC process. More importantly, the O3/SPC process exhibits excellent metal recovery in the treatment of real copper electroplating wastewater and other metal-EDTA complexes. This study provides a promising technology and opens a new avenue for the efficient decomplexation of metal-organic complexes with simultaneous recovery of valuable metal resources.

Superselective Hg(II) Removal from Water Using a Thiol-Laced MOF-Based Sponge Monolith: Performance and Mechanism.

Point-of-use (POU) devices with satisfying mercury (Hg) removal performance are urgently needed for public health and yet are scarcely reported. In this study, a thiol-laced metal-organic framework (MOF)-based sponge monolith (TLMSM) has been investigated for Hg(II) removal as the POU device for its benchmark application. The resulting TLMSM was characterized by remarkable chemical resistance, mechanical stability, and hydroscopicity (>2100 wt %). Importantly, the TLMSM has exhibited high adsorption capacity (∼954.7 mg g-1), fast kinetics (kf ∼ 1.76 × 10-5 ms-1), broad working pH range (1-10), high selectivity (Kd > 5.0 × 107 mL g-1), and excellent regeneration capability (removal efficiency >90% after 25 cycles). The high applicability of TLMSM in real-world scenarios was verified by its excellent Hg(II) removal performance in various real water matrices (e.g., surface waters and industrial effluents). Moreover, a fixed-bed column test demonstrated that ∼1485 bed volumes of the feeding streams (∼500 µg L-1) can be effectively treated with an enrichment factor of 12.6, suggesting the great potential of TLMSM as POU devices. Furthermore, the principal adsorption complexes (e.g., single-layer -S-Hg-Cl and double-layer -S-Hg-O-Hg-Cl and -S-Hg-O-Hg-OH) formed during the adsorption process under a wide range of pH were synergistically and systematically unveiled using advanced tools. Overall, this work presents an applicable approach by tailoring MOF into a sponge substrate to achieve its real application in heavy metal removal from water, especially for Hg(II).

Overcoming Electrostatic Interaction via Strong Complexation for Highly Selective Reduction of CN- into N2.

Limited by the electrostatic interaction, the oxidation reaction of cations at the anode and the reduction reaction of anions at the cathode in the electrocatalytic system nearly cannot be achieved. This study proposes a novel strategy to overcome electrostatic interaction via strong complexation, realizing the electrocatalytic reduction of cyanide (CN- ) at the cathode and then converting the generated reduction products into nitrogen (N2 ) at the anode. Theoretical calculations and experimental results confirm that the polarization of the transition metal oxide cathodes under the electric field causes the strong chemisorption between CN- and cathode, inducing the preferential enrichment of CN- to the cathode. CN- is hydrogenated by atomic hydrogen at the cathode to methylamine/ammonia, which are further oxidized into N2 by free chlorine derived from the anode. This paper provides a new idea for realizing the unconventional and unrealizable reactions in the electrocatalytic system.

Atomic-Level and Modulated Interfaces of Photocatalyst Heterostructure Constructed by External Defect-Induced Strategy: A Critical Review.

Despite the existence of numerous photocatalyst heterostructures, their separation efficiency and charge flow precision remain low due to the poor study on interfacial properties. The photocatalysts with confined defects can effectively control the photogenerated carrier migration, but the metastability of such defects considerably decreases the photocatalyst stability. Meanwhile, the introduction of defective region can increase the coordinative unsaturation and delocalize local electrons to promote their interactions with the molecules/ions in that region. The selective growth of modulated heterogeneous interface by defect-induced strategy may not only increase the stability of defective structures, but also enhance the migration of interfacial charges. Using this method, photocatalytic heterostructures with low contact resistances and intimate interfaces are constructed to achieve the optimal charge migration in terms of efficiency and accuracy. In this work, the point, linear, and planar heterogeneous interfaces and related defect engineering techniques are discussed. Particularly, it is focused on the external, defect-induced interfacial heterogeneities with various spatial and dimensional configurations, which exhibit modulated and controllable interfacial properties. Furthermore, the main aspects of fabricating photocatalyst heterostructures by the defect-induced strategy, including the i) controllable generation of defects, ii) advanced characterization methods, and iii) elaborate construction of the minimal interface, are described.

Synthesis and Structural Elucidation of Bisdibenzocorannulene in Multiple Redox States.

We report an anti-folded bowl-shaped bisdibenzocorannulene (BDBC) featuring a new chair-cyclohexane-like hexagon as a bridge of two dibenzocorannulene moieties. The neutral compound showed multiple redox-active properties and could be converted to the corresponding redox states through chemical reduction or oxidation. Chemical reduction of BDBC by stoichiometric addition of metallic potassium in the presence of [18]crown-6 ether, provided a radical anion BDBC.- and a dianion BDBC2- , respectively; while chemical oxidation by silver hexafluoroantimonate(V), converted the neutral compound to an open-shell singlet diradical dication (BDBC.. )2+ . The structural consequences of both electron-reduction and oxidation were closely related to the release of ring-strain of the bowl-shaped π-scaffold and imposed steric hindrance of the hexagonal bridge. In addition, the unusual open-shell nature of the dication could mainly be attributed to the changing of localized antiaromaticity in the closed-shell structure to delocalized character in the biradical, and thus the emergence of weakly bonded π-electrons.

Carbon Nitride Supported High-Loading Fe Single-Atom Catalyst for Activation of Peroxymonosulfate to Generate 1 O2 with 100 % Selectivity.

Singlet oxygen (1 O2 ) is an excellent active species for the selective degradation of organic pollutions. However, it is difficult to achieve high efficiency and selectivity for the generation of 1 O2 . In this work, we develop a graphitic carbon nitride supported Fe single-atoms catalyst (Fe1 /CN) containing highly uniform Fe-N4 active sites with a high Fe loading of 11.2 wt %. The Fe1 /CN achieves generation of 100 % 1 O2 by activating peroxymonosulfate (PMS), which shows an ultrahigh p-chlorophenol degradation efficiency. Density functional theory calculations results demonstrate that in contrast to Co and Ni single-atom sites, the Fe-N4 sites in Fe1 /CN adsorb the terminal O of PMS, which can facilitate the oxidization of PMS to form SO5 .- , and thereafter efficiently generate 1 O2 with 100 % selectivity. In addition, the Fe1 /CN exhibits strong resistance to inorganic ions, natural organic matter, and pH value during the degradation of organic pollutants in the presence of PMS. This work develops a novel catalyst for the 100 % selective production of 1 O2 for highly selective and efficient degradation of pollutants.

Broad-Band Excited and Tunable Luminescence of CaTbAl3O7:RE3+ (RE3+ = Ce3+ and/or Eu3+) Nanocrystalline Phosphors for Near-UV WLEDs.

Here, we demonstrate a novel donor-intermediate-receptor energy transfer model through a Ce3+ → Tb3+ → Eu3+ scheme in a CaTbAl3O7:Ce3+,Eu3+ nanocrystalline phosphor. A new type of CaTbAl3O7 and CaTbAl3O7:RE3+ (RE3+ = Ce3+ and/or Eu3+) nanocrystalline phosphors were prepared by a simple sol-gel method. There exist efficient energy transfers of Ce3+ → Tb3+, Tb3+ → Eu3+, and Ce3+ → Tb3+ → Eu3+ in CaTbAl3O7:RE 3+ (RE 3+ = Ce3+ and/or Eu3+) nanocrystalline phosphors. With near-UV or UV light excitation, the as-prepared CaTbAl3O7:RE 3+ (RE 3+ = Ce3+ and/or Eu3+) nanocrystalline phosphors' luminous color can be regulated from green to green-yellow, yellow, orange, and orange-red by adjusting the doping concentration, categories, and different proportions of codoping Ce3+ to Eu3+ ions in the CaTbAl3O7 matrix. The luminescence mechanism with respect to the CaTbAl3O7:RE3+ (RE3+ = Ce3+ and/or Eu3+) nanocrystalline phosphors has been tentatively proposed. Due to their excellent luminescence properties, the as-prepared CaTbAl3O7, CaTbAl3O7:Ce3+, CaTbAl3O7:Eu3+, and CaTbAl3O7:Ce3+,Eu3+ nanocrystalline phosphors exhibit bright prospects in NUV-LEDs and other photoelectric field.

Silver Single Atom in Carbon Nitride Catalyst for Highly Efficient Photocatalytic Hydrogen Evolution.

Single atom catalysts (SACs) with the maximized metal atom efficiency have sparked great attention. However, it is challenging to obtain SACs with high metal loading, high catalytic activity, and good stability. Herein, we demonstrate a new strategy to develop a highly active and stable Ag single atom in carbon nitride (Ag-N2 C2 /CN) catalyst with a unique coordination. The Ag atomic dispersion and Ag-N2 C2 configuration have been identified by aberration-correction high-angle-annular-dark-field scanning transmission electron microscopy (AC-HAADF-STEM) and extended X-ray absorption. Experiments and DFT calculations further verify that Ag-N2 C2 can reduce the H2 evolution barrier, expand the light absorption range, and improve the charge transfer of CN. As a result, the Ag-N2 C2 /CN catalyst exhibits much better H2 evolution activity than the N-coordinated Ag single atom in CN (Ag-N4 /CN), and is even superior to the Pt nanoparticle-loaded CN (PtNP /CN). This work provides a new idea for the design and synthesis of SACs with novel configurations and excellent catalytic activity and durability.

Dechlorination-Hydroxylation of Atrazine to Hydroxyatrazine with Thiosulfate: A Detoxification Strategy in Seconds.

Hydroxylation of atrazine to nontoxic hydroxyatrazine is generally considered an efficient detoxification method to remediate atrazine-contaminated soil and water. However, previous studies suggested that hydroxylation was not the dominant pathway for atrazine degradation in the hydroxyl radical-generating systems such as Fenton reaction, ozonation and UV/H2O2. Herein we report that the addition of sodium thiosulfate can realize rapid hydroxylation of atrazine to hydroxyatrazine at pH ≤ 4 under room temperature. High resolution mass spectra and isotope experiments results revealed that the hydroxylation of atrazine was involved with nucleophilic substitution and subsequent hydrolysis reaction as follows. HS2O3-, as a species of thiosulfate only at pH ≤ 4, first attacked C atom connecting to chlorine of atrazine to dechlorinate atrazine and produce C8H14N5S2O3-. Subsequently, the S-S bond of C8H14N5S2O3- was cleaved easily to form SO3 and C8H14N5S-. Next, C8H14N5S- was hydrolyzed to generate hydroxyatrazine and H2S. Finally, the comproportionation of SO3 and H2S in situ produced S0 during hydroxylation of atrazine with thiosulfate. This study clarifies the importance of degradation pathway on the removal of pollutants, and also provides a nonoxidative strategy for atrazine detoxification in seconds.

Palladium-Catalyzed Reductive [5+1] Cycloaddition of 3-Acetoxy-1,4-enynes with CO: Access to Phenols Enabled by Hydrosilanes.

A new palladium-catalyzed reductive [5+1] cycloaddition of 3-acetoxy-1,4-enynes with CO, enabled by hydrosilanes, has been developed for delivering valuable functionalized phenols. This methodology employs hydrosilanes as the external reagent to facilitate the [5+1] carbonylative benzannulation. The reaction is a conceptually and mechanistically novel carbonylative cycloaddition route for the construction of substituted phenols, through the formation of four new chemical bonds, with excellent functional-group tolerance.

B-N-B Bond Embedded Phenalenyl and Its Anions.

Despite the great potential of heteroatom-containing polycyclic aromatic hydrocarbons in organic optoelectronics, there are very limited reports on heteroaromatics containing a B-N-B bond in the π-scaffold. Herein, stable 1,9-dibora-9a-azaphenalenyl (DBAP) derivatives, named BNB-embedded phenalenyls, are presented. The DBAP skeleton contains a three-center two-π-electron B-N-B moiety with 12 π-electrons and can be regarded as the isoelectronic structure of the phenalenyl cation. Chemical reduction of the phenyl derivative of DBAP by potassium generated the dianion containing 14 delocalized π-electrons, which can be regarded as the isoelectronic structure of the phenalenyl anion. The dianion is sandwiched and stabilized by two bulky [K([18]crown-6)]+ counterions according to its X-ray structure. However, its monoanion (an isoelectronic structure of the henalenyl radical) generated by mixing equal moles of neutral compound and dianion gave an unusual B-N-B-embedded benzo[cd]fluoranthene dianion, which again was confirmed by X-ray crystallographic analysis. The new dianion containing 20 π-electrons is highly aromatic and is further stabilized by [K([18]crown-6)]+ counterions. An aromaticity driven rearrangement mechanism was proposed for this unusual transformation. Based on X-ray structures and theoretical calculations, the B-N-B moiety in the neutral and anionic DBAP participates in the π-electron delocalization along the whole DBAP skeleton like their phenalenyl cation/radical/anion counterparts, but with more localized character. Therefore, our studies report the first synthesis and characterization of a B-N-B-embedded phenalenyl and its anionic species, which show unique electronic structure and unusual reactivity different from that of their all-carbon phenalenyl analogues.

A Stable N-Annulated Perylene-Bridged Bisphenoxyl Diradicaloid and the Corresponding Boron Trifluoride Complex.

Organic π-extended radicals display unique electronic structures, and could be used as promising functional materials. However, design and synthesis of stable radicals are challenging for chemists due to their high reactivity. In this work, we synthesized a stable N-annulated perylene-bridged bisphenoxyl diradicaloid, and its complex with Lewis acid boron trifluoride. Their ground-state geometric and electronic structures were systematically studied by various experimental methods, including X-ray crystallographic analysis, variable-temperature NMR spectroscopy, electron-spin resonance spectroscopy (ESR), and superconducting quantum interference device (SQUID) measurements, supported by density functional theory. Both were observed as open-shell singlet diradicaloids in the ground state. The bisphenoxyl diradicaloid demonstrated string features of strong near-infrared (NIR) absorption, closely packed π-dimer structure in crystals, amphoteric redox behavior with a small HOMO-LUMO energy band gap, and a rather small singlet-triplet gap, whereas the complex showed very different photophysical, electrochemical, and magnetic properties. Our studies provide an efficient method of making stable diradicaloids by Lewis acid/base complexation.

Reaction of antibiotic sulfadiazine with manganese dioxide in aqueous phase: Kinetics, pathways and toxicity assessment.

Sulfonamide antibiotics are often detected in terrestrial and aquatic environment, but little is known about abiotic degradation of these antibiotics. In the present study, the degradation of the sulfonamide antibiotic sulfadiazine by a synthesized δ-MnO2 was investigated. The initial reaction rate of sulfadiazine oxidized by manganese dioxide increased as the solution pH decreased by weakening electrostatic attraction between sulfadiazine and MnO2 and enhancing the reduction potential of MnO2. The presence of metal ions (Mn2+, Na+ and Ca2+), especially Mn2+, decreased the initial reaction rate by competitively adsorbing and reacting with MnO2. Two different products were identified during the reaction of sulfadiazine with MnO2 and the transformation of parent compound started with the formation of sulfadiazine radicals. Furthermore, toxicity assay results showed that the toxicity of products produced by bacteria decreased with elapse of reaction time. Results from the present study indicate that manganese dioxides in environmental matrix could be helpful in dissipation of sulfadiazine released into the environment.

Iron-Catalyzed Intermolecular 1,2-Difunctionalization of Styrenes and Conjugated Alkenes with Silanes and Nucleophiles.

The first iron-catalyzed 1,2-difunctionalization of styrenes and conjugated alkenes with silanes and either N or C, using an oxidative radical strategy, is described. Employing FeCl2 and di-tert-butyl peroxide allows divergent alkene 1,2-difunctionalizations, including 1,2-aminosilylation, 1,2-arylsilylation, and 1,2-alkylsilylation, which rely on a wide range of nucleophiles, namely, amines, amides, indoles, pyrroles, and 1,3-dicarbonyls, thus providing a powerful platform for producing diverse silicon-containing alkanes.

Fabrication of 2D sheet-like BiOCl/carbon quantum dot hybrids via a template-free coprecipitation method and their tunable visible-light photocatalytic activities derived from different size distributions of carbon quantum dots.

A series of two-dimensional (2D) interlaced BiOCl/carbon quantum dot composites (denoted as BiOCl/CQD composites) were synthesized by a template-free coprecipitation method at room temperature, and the influence of different particle size distributions of the CQDs on the physiochemical properties and photocatalytic activities of the BiOCl/CQD composites was studied. CQDs can change the morphology and increase the specific surface area of the BiOCl/CQD composites. Moreover, the particle size distribution of the CQDs (CQD loading amount) has some effect on the light absorption, separation of photogenerated charge carriers, and photocatalytic performance of  the BiOCl/CQD composites. The optimized size distribution of the CQDs is 50-150 nm. BiOCl/CQD (50-150 nm) composites showed the best improvement of light absorption and the highest photocurrent density of 0.44 µA cm(-2), and exhibited the highest photocatalytic activity with almost 100% 2-nitrophenol removal under visible-light irradiation. The high efficacy of BiOCl/CQD (50-150 nm) composites could be attributed to their excellent light absorption and highly effective separation of photogenerated charge carriers.

Capturing Lithium from Wastewater Using a Fixed Bed Packed with 3-D MnO2 Ion Cages.

3-D MnO2 ion cages (CMO) were fabricated and shown to have a high capacity for lithium removal from wastewater. CMO had a maximum Li(I) adsorption capacity of 56.87 mg/g, which is 1.38 times greater than the highest reported value (41.36 mg/g). X-ray photoelectron spectroscopy indicated that the stability of the -Mn-O-Mn-O- skeleton played an essential role in Li adsorption. The lattice clearance had a high charge density, forming a strong electrostatic field. The Dubinin-Ashtakhov (DA) site energy distribution model based on Polanyi theory described the linear increase of Li adsorption capacity (Q0) with increasing temperature (Q0 = k3 × Em + d3 = k3 × (a × T) + d3). Furthermore, the pore diffusion model (PDM) accurately predicted the lithium breakthrough (R2 ≈ 0.99). The maximum number of bed volumes (BVs) treated was 1374, 1972, and 2493 for 200 µg/L at 20, 30, and 40 °C, respectively. Higher temperatures increased the number of BVs that may be treated, which implies that CMO will be useful in treating industrial Li(I) wastewater in regions with different climates (e.g., Northern or Southern China).