Mesoporous Electrocatalysts with p-n Heterojunctions for Efficient Electroreduction of CO2 and N2 to Urea.

The electrocatalytic synthesis of high-value-added urea by activating N2 and CO2 is a green synthesis technology that has achieved carbon neutrality. However, the chemical adsorption and C-N coupling ability of N2 and CO2 on the surface of the catalyst are generally poor, greatly limiting the improvement of electrocatalytic activity and selectivity in electrocatalytic urea synthesis. Herein, novel hierarchical mesoporous CeO2/Co3O4 heterostructures are fabricated, and at an ultralow applied voltage of -0.2 V, the urea yield rate reaches 5.81 mmol g-1 h-1, with a corresponding Faraday efficiency of 30.05%. The hierarchical mesoporous material effectively reduces the mass transfer resistance of reactants and intermediates, making it easier for them to access active centers. The emerging space-charge regions at the heterointerface generate local electrophilic and nucleophilic regions, facilitating CO2 targeted adsorption in the electrophilic region and activation to produce *CO intermediates and N2 targeted adsorption in the nucleophilic region and activation to generate *N ═ N* intermediates. Then, the electrons in the σ orbitals of *N ═ N* intermediates can be easily accepted by the empty eg orbitals of Co3+ in CeO2/Co3O4, which presents a low-spin state (LS: t2g6eg0). Subsequently, *CO couples with *N ═ N* to produce the key intermediate *NCON*. Interestingly, it was discovered through in situ Raman spectroscopy that the CeO2/Co3O4 catalyst has a reversible spinel structure before and after the electrocatalytic reaction, which is due to the surface reconstruction of the catalyst during the electrocatalytic reaction process, producing amorphous active cobalt oxides, which is beneficial for improving electrocatalytic activity.

Identification of ammonium source for groundwater in the piedmont zone with strong runoff of the Hohhot Basin based on nitrogen isotope.

Groundwater with high ammonium concentration (HANC groundwater), mostly caused by anthropogenic pollution, is widely distributed in China, which could also result from natural geological genesis. Groundwater in the piedmont zone with strong runoff in the central Hohhot Basin has featured its excessive ammonium concentration since the 1970s. Currently, chemical factories also serve as potential pollution sources. In this study, based on the nitrogen isotopic technique and combined with hydrochemical methods, the sources of high concentration ammonium in the groundwater was identified. The HANC groundwater is mainly distributed in the alluvial-proluvial fan and the interfan depression in the western and central parts of the study area, and a maximum ammonium concentration of 529.32 mg/L was observed in the groundwater in the mid-fan of the Baishitou Gully (BSTG) alluvial-proluvial fan. Although the BSTG mid-fan is part of the piedmont zone with strong runoff, some of the HANC groundwater in this area still presents the typical hydrochemical characteristics in the discharge area. Moreover, an extremely high concentration of volatile organic compounds was observed in groundwater in the BSTG alluvial-proluvial fan, which indicated significant anthropogenic pollution. Besides, 15N-NH4+ is enriched in groundwater in the BSTG root-fan and the interfan depression, which is consistent with the situation of organic nitrogen and exchangeable ammonium in natural sediments, as well as the natural HANC groundwater in other regions of China. These δ15N-NH4+ values indicate that the ammonium of the groundwater in the BSTG root-fan and the interfan depression is derived from natural sediments. The 15N-NH4+ in groundwater is depleted in the BSTG mid-fan, and the δ15N-NH4+ values are similar with those of the pollution sources from the chemical factories in the mid-fan. Both hydrochemical and nitrogen isotopic characteristics indicate significant pollution in the mid-fan, but the ammonium pollution is limited to the area near the chemical factories.

Total recycle strategy of phosphorus recovery from wastewater using granule chitosan inlaid with γ-AlOOH.

Eutrophication which caused by excessive phosphorus in aquatic environment is a worldwide problem. Phosphorus is a nonrenewable resource widely used in agriculture and industry. Therefore, the development of economical methods for phosphorus capture and reuse from wastewater is urgently needed. In this study, a novel granule chitosan inlaid with γ-AlOOH on its structure (γ-AlOOH@CS) was prepared for phosphate removal with a recycle manner. Results showed that γ-AlOOH@CS exhibited a fast phosphate removal of 0.5 h for half adsorption capacity. The material presented a high adsorption capacity of 45.82 mg/g, the adsorption capacity maintained stability at pH 4-6, and favorable selectivity was observed when compared with other common anions. Column experiment was also performed well in treatment of the simulated wastewater. Isotherms and thermodynamics studies indicated that phosphate adsorption onto γ-AlOOH@CS was heterogeneous, spontaneous and exothermic. In material recycle experiment, by using NaOH solution as solvent and phosphoric acid as precipitant under hydrothermal reaction conditions, the products of chitosan, aluminum phosphate and sodium dihydrogen phosphate were obtained, with their purity reaching the industrial standard. Meanwhile, chitosan can be reused for new γ-AlOOH@CS preparation. This study provides a total recycle strategy of phosphorus removal from wastewater.

Ionic liquids-water interfacial preparation of triangular Ag nanoplates and their shape-dependent antibacterial activity.

As a class of green and designable solvents, ionic liquids (ILs) have been used extensively in inorganic synthesis. In those schemes, ILs were usually used as reaction media to replace water and organic solvents, and/or used as stabilizer and capping agents to act like an amphiphilic molecule or polymer. However, the unique properties of ILs were not fully utilized in the area of material preparation. In this study, a new protocol of "ILs-water interfacial synthesis" was developed and used for the preparation of Ag nanomaterials. Taking the advantage of tunable property of ILs-water interface, Ag nanomaterials with different morphology such as triangular nanoplates, polygonal nanoplates, and nanoparticles could be facilely obtained. Growth mechanism of the triangular Ag nanoplates has been investigated from structural characterization and molecular dynamics (MD) simulation. It was shown that growth of the nanoplates was under kinetic control mainly due to high viscosity and ionicity of the ILs. Furthermore, the antimicrobial performance of these Ag samples was tested to study the influence of shape of the Ag nanomaterials on the antimicrobial activity and the related antimicrobial mechanism. The results suggested that the efficient antimicrobial activity of the triangular Ag nanoplates was ascribed to their sharp corners and edges and large areas of active (111) crystal plane, which leads to the higher amount of leaching Ag(+) ion.

Tunable synthesis of Ag films at ionic liquid-aqueous interfaces.

A new concept of "tunable ionic liquid (IL)-H(2)O interfacial synthesis" is proposed and used practically in the synthesis of Ag films with various morphologies at the IL-H(2)O interface by employing ILs with different anions and/or different alkyl chain lengths.

Uniform and continuous silica nanocoatings on ZnS phosphors.

The penetration depth of the primary electrons into amorphous silica, anatase titania, Y(2)O(3), ZnO, In(2)O(3), indium and tin oxides is compared at lower voltages. It shows that amorphous silica has the largest penetration depth, thus the silica coatings will lead to minimal energy loss and maximal cathodoluminescence intensity. Almost uniform and continuous silica coatings on ZnS phosphors have successfully been obtained by a sol-gel method with the catalysis of ammonia. Zeta potential analysis shows that the ZnS phosphors are covered almost completely. An adsorption-catalysis-growth mechanism is suggested, and used to explain other ammonia-catalyzed coating processes.