Highly selective synthesis of surface FeIV=O with nanoscale zero-valent iron and chlorite for efficient oxygen transfer reactions.

High-valent iron-oxo species (FeIV=O) has been a long-sought-after oxygen transfer reagent in biological and catalytic chemistry but suffers from a giant challenge in its gentle and selective synthesis. Herein, we propose a new strategy to synthesize surface FeIV=O (≡FeIV=O) on nanoscale zero-valent iron (nZVI) using chlorite (ClO2-) as the oxidant, which possesses an impressive ≡FeIV=O selectivity of 99%. ≡FeIV=O can be energetically formed from the ferrous (FeII) sites on nZVI through heterolytic Cl-O bond dissociation of ClO2- via a synergistic effect between electron-donating surface ≡FeII and proximal electron-withdrawing H2O, where H2O serves as a hydrogen-bond donor to the terminal O atom of the adsorbed ClO2- thereby prompting the polarization and cleavage of Cl-O bond for the oxidation of ≡FeII toward the final formation of ≡FeIV=O. With methyl phenyl sulfoxide (PMS16O) as the probe molecule, the isotopic labeling experiment manifests an exclusive 18O transfer from Cl18O2- to PMS16O18O mediated by ≡FeIV=18O. We then showcase the versatility of ≡FeIV=O as the oxygen transfer reagent in activating the C-H bond of methane for methanol production and facilitating selective triphenylphosphine oxide synthesis with triphenylphosphine. We believe that this new ≡FeIV=O synthesis strategy possesses great potential to drive oxygen transfer for efficient high-value-added chemical synthesis.

Fluorine Modification Promoted Water Dissociation into Atomic Hydrogen on a Copper Electrode for Efficient Neutral Nitrate Reduction and Ammonia Recovery.

Electrocatalytic nitrate reduction to ammonia (NITRR) offers an attractive solution for alleviating environmental concerns, yet in neutral media, it is challenging as a result of the reliance on the atomic hydrogen (H*) supply by breaking the stubborn HO-H bond (∼492 kJ/mol) of H2O. Herein, we demonstrate that fluorine modification on a Cu electrode (F-NFs/CF) favors the formation of an O-H···F hydrogen bond at the Cu-H2O interface, remarkably stretching the O-H bond of H2O from 0.98 to 1.01 Å and lowering the energy barrier of water dissociation into H* from 0.64 to 0.35 eV at neutral pH. As a benefit from these advantages, F-NFs/CF could rapidly reduce NO3- to NH3 with a rate constant of 0.055 min-1 and a NH3 selectivity of ∼100%, far higher than those (0.004 min-1 and 9.2%) of the Cu counterpart. More importantly, we constructed a flow-through coupled device consisting of a NITRR electrolyzer and a NH3 recovery unit, realizing 98.1% of total nitrogen removal with 99.3% of NH3 recovery and reducing the denitrification cost to $5.1/kg of N. This study offers an effective strategy to manipulate the generation of H* from water dissociation for efficient NO3--to-NH3 conversion and sheds light on the importance of surface modification on a Cu electrode toward electrochemical reactions.

Surface Modification of Transition Metal Dichalcogenide Nanosheets for Intrinsically Self-Healing Hydrogels with Enhanced Mechanical Properties.

Nanocomposites with enhanced mechanical properties and efficient self-healing characteristics can change how the artificially engineered materials' life cycle is perceived. Improved adhesion of nanomaterials with the host matrix can drastically improve the structural properties and confer the material with repeatable bonding/debonding capabilities. In this work, exfoliated 2H-WS2 nanosheets are modified using an organic thiol to impart hydrogen bonding sites on the otherwise inert nanosheets by surface functionalization. These modified nanosheets are incorporated within the PVA hydrogel matrix and analyzed for their contribution to the composite's intrinsic self-healing and mechanical strength. The resulting hydrogel forms a highly flexible macrostructure with an impressive enhancement in mechanical properties and a very high autonomous healing efficiency of 89.92%. Interesting changes in the surface properties after functionalization show that such modification is highly suitable for water-based polymeric systems. Probing into the healing mechanism using advanced spectroscopic techniques reveals the formation of a stable cyclic structure on the surface of nanosheets, mainly responsible for the improved healing response. This work opens an avenue toward the development of self-healing nanocomposites where chemically inert nanoparticles participate in the healing network rather than just mechanically reinforcing the matrix by slender adhesion.

Visible Light-Driven Conversion of Carbon-Sequestrated Seawater into Stoichiometric CO and HClO with Nitrogen-Doped BiOCl Atomic Layers.

Seawater is one of the most important CO2 sequestration media for delivering value-added chemicals/fuels and active chlorine; however, this scenario is plagued by sluggish reaction rates and poor product selectivity. Herein, we first report the synthesis of nitrogen-doped BiOCl atomic layers to directly split carbon-sequestrated natural seawater (Yellow Sea, China) into stoichiometric CO (92.8 µmol h-1 ) and HClO (83.2 µmol h-1 ) under visible light with selectivities greater than 90 %. Photoelectrons enriched on the exposed BiOCl{001} facet kinetically facilitate CO2 -to-CO reduction via surface-doped nitrogen bearing Lewis basicity. Photoholes, mainly located on the lateral facets of van der Waals gaps, promote the selective oxidation of Cl- into HClO. Sequestrated CO2 also maintains the pH of seawater at around 4.2 to prevent the alkaline earth cations from precipitating. The produced HClO can effectively kill typical bacteria in the ballast water of ocean-going cargo ships, offering a green and safe way for onsite sterilization.

An Electrochemical Strategy for Simultaneous Heavy Metal Complexes Wastewater Treatment and Resource Recovery.

Heavy metals chelated with coexisting organic ligands in wastewater impose severe risks to public health and the ambient ecosystem but are also valuable metal resources. For sustainable development goals, the treatment of heavy metal complexes wastewater requires simultaneous metal-organic bond destruction and metal resource recovery. In this study, we demonstrated that a neutral pH electro-Fenton (EF) system, which was composed of an iron anode, carbon cloth cathode, and sodium tetrapolyphosphate electrolyte (Na6TPP), could induce a successive single-electron activation pathway of molecular oxygen due to the formation of Fe(II)-TPP complexes. The boosted •OH generation in the Na6TPP-EF process could decomplex 99.9% of copper ethylene diamine tetraacetate within 8 h; meanwhile, the released Cu ions were in situ deposited on the carbon cloth cathode in the form of Cu nanoparticles with a high energy efficiency of 2.45 g kWh-1. Impressively, the recovered Cu nanoparticles were of purity over 95.0%. More importantly, this neutral EF strategy could realize the simultaneous removal of Cu, Ni, and Cr complexes from real electroplating effluents. This study provides a promising neutral EF system for simultaneous heavy metal complexes wastewater treatment and resource recovery and sheds light on the importance of molecular oxygen activation in the field of pollutant control.

Renewable energy driven electroreduction nitrate to ammonia and in-situ ammonia recovery via a flow-through coupled device.

Green ammonia production from wastewater via electrochemical nitrate reduction contributes substantially to the realization of carbon neutrality. Nonetheless, the current electrochemical technology is largely limited by the lack of suitable device for efficient and continuous electroreduction nitrate into ammonia and in-situ ammonia recovery. Here, we report a flow-through coupled device composed of a compact electrocatalytic cell for efficient nitrate reduction and a unit to separate the produced ammonia without any pH adjustment and additional energy-input from the circulating nitrate-containing wastewater. Using an efficient and selective Cl-modified Cu foam electrode, nearly 100% NO3- electroreduction efficiency and over 82.5% NH3 Faradaic efficiency was realized for a wide range of nitrate-containing wastewater from 50 to 200 mg NO3--N L-1. Moreover, this flow-through coupled device can continuingly operate at a large current of 800 mA over 100 h with a sustained NH3 yield rate of 420 µg h-1 cm-2 for nitrate-containing wastewater treatment (50 mg NO3--N L-1). When driven by solar energy, the flow-through coupled device can also exhibit exceptional real wastewater treatment performance, delivering great potential for practical application. This work paves a new avenue for clean energy production and environmental sustainability as well as carbon neutrality.

Van Der Waals gap-rich BiOCl atomic layers realizing efficient, pure-water CO2-to-CO photocatalysis.

Photocatalytic CO2 reduction (PCR) is able to convert solar energy into chemicals, fuels, and feedstocks, but limited by the deficiencies of photocatalysts in steering photon-to-electron conversion and activating CO2, especially in pure water. Here we report an efficient, pure water CO2-to-CO conversion photocatalyzed by sub-3-nm-thick BiOCl nanosheets with van der Waals gaps (VDWGs) on the two-dimensional facets, a graphene-analog motif distinct from the majority of previously reported nanosheets usually bearing VDWGs on the lateral facets. Compared with bulk BiOCl, the VDWGs-rich atomic layers possess a weaker excitonic confinement power to decrease exciton binding energy from 137 to 36 meV, consequently yielding a 50-fold enhancement in the bulk charge separation efficiency. Moreover, the VDWGs facilitate the formation of VDWG-Bi-VO••-Bi defect, a highly active site to accelerate the CO2-to-CO transformation via the synchronous optimization of CO2 activation, *COOH splitting, and *CO desorption. The improvements in both exciton-to-electron and CO2-to-CO conversions result in a visible light PCR rate of 188.2 µmol g-1 h-1 in pure water without any co-catalysts, hole scavengers, or organic solvents. These results suggest that increasing VDWG exposure is a way for designing high-performance solar-fuel generation systems.