N/P co-doped MXene hollow microcapsules by surfactants assisted hydrothermal-freeze drying for adjustable permeability.

The assembly of MXene materials into microcapsules has drawn great attentions due to their unique properties. However, rational design and synthesis of MXene-based microcapsules with specific nanostructures at the molecular scale remains challenging. Herein, we report a strategy to synthesize N/P co-doped MXene hollow flower-like microcapsules with adjustable permeability via dual surfactants assisted hydrothermal-freeze drying method. In contrast to anionic surfactants, cationic surfactants exhibited effective electrostatic interactions with MXene nanosheets during the hydrothermal process. Manipulation of dual surfactants in hydrothermal process realized N and P co-doping of MXene to improve flexibility and promoted the generation of abundant internal cavities in flower-like microcapsules. Based on the unique microstructure, the prepared hollow flower-like microcapsules showed excellent performance, stability and reusability in size-selective release of small organic molecules. Moreover, the release rate can be controlled by turning the oxidation state and type of MXene. The strategy delineates promising prospects for the design of MXene-based microcapsules with specific structures.

Preparation of a CAB-GO/PES Mixed Matrix Ultrafiltration Membrane and Its Antifouling Performance.

Serious membrane fouling has limited the development of ultrafiltration membrane technology for water purification. Synthesis of an ultrafiltration membrane with prominent anti-fouling ability is of vital importance. In this study, CAB-GO composite nanosheets were prepared by grafting graphene oxide (GO) with a zwitterionic material cocamidopropyl betaine (CAB) with strong antifouling properties. Anti-fouling CAB-GO/PES mixed matrix ultrafiltration membrane (CGM) was prepared by the phase inversion method with polyethersulfone (PES). Due to its electrostatic interaction, the interlayer distance between CAB-GO nanosheets was increased, and the dispersibility of GO was improved to large extent, thereby effectively avoiding the phenomenon of GO agglomeration in organic solvents. Based on the improvement of the surface porosity and surface hydrophilicity of the CAB-GO/PES mixed matrix membrane, the pure water flux of CGM-1.0 can reach 461 L/(m2·h), which was 2.5 times higher than that of the original PES membrane, and the rejection rates toward BSA and HA were above 96%. Moreover, when the content of CAB-GO was 0.1 wt%, the prepared CAB-GO/PES membrane exhibited very high BSA (99.1%) and HA (98.1%) rejection during long-term operation, indicating excellent anti-fouling ability.

Two-dimensional titanium carbide MXene produced by ternary cations intercalation via structural control with angstrom-level precision.

Highly effective decontamination of lead is a primary challenge for ecosystem protection and public health. Herein, we report a methodology of ternary cations intercalation to synthesize Ti3C2Tx MXene by structural control with angstrom-level precision through mixed fluorinated salts wet etching-alkalization approach for high-efficient lead adsorption. The successive introduction of lithium, potassium, and sodium ions continuously weakens interaction forces between Ti3C2Tx layers, resulting in achieving fine tailored interlayer distance from 9.8 to 15.9 Å. A high density of complexing groups are formed after ternary cations intercalation, which greatly improve the hydrophilicity of Ti3C2Tx to enhance the accessibility and shorten the mass transfer and provide abundant adsorption sites to exhibit strong complexing effects with lead ions. The prepared ternary cations-intercalated Ti3C2Tx nanosheets exhibited a high adsorption capacity (267.2 mg/g) toward lead ions and sharply cut down lead concentration from 10 to 0.009 mg/L, far below the drinking water standards (0.015 mg/L).

MOF-on-MOF heterojunction-derived Co3O4-CuCo2O4 microflowers for low-temperature catalytic oxidation.

Through the exchange-extended growth method (EEGM), MOF-on-MOF heteroarchitectures with distinct crystallography were produced and pyrolyzed into hybrid metal oxides. The strong exchange ability of organometallic compounds realized the component reconstruction of the MOF matrix and enhanced the interfacial forces between MOFs, showing an excellent performance in low-temperature catalytic oxidation.

ZnO/Cu2O/g-C3N4 heterojunctions with enhanced photocatalytic activity for removal of hazardous antibiotics.

In view of the environmental pollution caused by antibiotics, the creation of an efficient photocatalytic material is an effectual way to carry out water remediation. Herein, we developed a smart strategy to synthesize ZnO/Cu2O/g-C3N4 heterojunction photocatalysts for the photodegradation of hazardous antibiotics by one-pot synthesis method. In this system, the Cu2O nanoparticles with electrons reducing capacity were coupled with g-C3N4 composites. The photocarriers were generated from the electric field of type Ⅰ heterojunction between ZnO and g-C3N4 and type Ⅱ heterojunction between Cu2O and g-C3N4. ZnO as a co-catalyst was doped to Cu2O/g-C3N4 catalyst system for removal of broad-spectrum antibiotics with the condition of visible light to protect Cu2O from photocorrosion, which thereby accelerated photocatalytic reactivity. Benefiting by new p-n-n heterojunction, the resulting ZnO/Cu2O/g-C3N4 composites had an excellent degradation performance of broad-spectrum antibiotics such as tetracycline (TC), chlortetracycline (CTC), oxytetracycline (OTC) and ciprofloxacin (CIP), the degradation of which were 98.79%, 99.5%, 95.35% and 73.53%. In particular, ZnO/Cu2O/g-C3N4 photocatalysts showed a very high degradation rate of 98.79% for TC in first 30 min under visible light, which was 1.35 and 10.62 times higher than that of Cu2O/g-C3N4 and g-C3N4, respectively. This work gives a fresh visual aspect for simultaneously solving the instability deficiencies of traditional photocatalysts and improving photocatalytic performance.

Confined assembly of ultrathin nanoporous nitrogen-doped graphene nanofilms with dual metal coordination chemistry.

Graphene oxide (GO) nanosheets with unique structure have received much attention in providing opportunity for high-performance membranes in separation. However, the rational design of ultrathin graphene membranes with controlled structures remains a big challenge. Here, we report a methodology to synthesize dual metal-coordinated ultrathin nanoporous graphene nanofilms by tailoring well-aligned nanocrystals as building blocks on heteroatom-doped GO nanosheets with tunable architectures. Manipulation of metal nitrate as bifunctional dopants realizes N-doping of graphene oxide and preferential growth of α-Mn2O3 nanocrystals. Generation of Mn-O-C bond during cross-linking greatly strengthens the stability of membranes for long-term steady operation. Meanwhile, because of spatial confinement effects and high binding energy, N-doped reduced GO nanosheets are desirable supports to construct numerous Mn-N-C bonds, thus generating artificial nanopores to significantly increase nanochannels for ultrafast mass transport. Moreover, the size-selective permeability of ultrathin nanoporous GO-based nanofilms can be optimized by managing the types of metal source for target coordination.

Crystal Facet Induced Single-Atom Pd/Cox Oy on a Tunable Metal-Support Interface for Low Temperature Catalytic Oxidation.

Atomic dispersed metal sites in single-atom catalysts are highly mobile and easily sintered to form large particles, which deteriorates the catalytic performance severely. Moreover, lack of criterion concerning the role of the metal-support interface prevents more efficient and wide application. Here, a general strategy is reported to synthesize stable single atom catalysts by crafting on a variety of cobalt-based nanoarrays with precisely controlled architectures and compositions. The highly uniform, well-aligned, and densely packed nanoarrays provide abundant oxygen vacancies (17.48%) for trapping Pd single atoms and lead to the creation of 3D configured catalysts, which exhibit very competitive activity toward low temperature CO oxidation (100% conversion at 90 °C) and prominent long-term stability (continuous conversion at 60 °C for 118 h). Theoretical calculations show that O vacancies at high-index {112} facet of Cox Oy nanocrystallite are preferential sites for trapping single atoms, which guarantee strong interface adhesion of Pd species to cobalt-based support and play a pivotal role in preventing the decrement of activity, even under moisture-rich conditions (≈2% water vapor). The progress presents a promising opportunity for tailoring catalytic properties consistent with the specific demand on target process, beyond a facile design with a tunable metal-support interface.

Synthesis of amino-functionalized Ti3C2Tx MXene by alkalization-grafting modification for efficient lead adsorption.

High-quality amino-functionalized Ti3C2Tx MXene (alk-MXene-NH2) nanosheets were successfully synthesized by a facile alkalization-grafting modification for lead adsorption. The alk-MXene-NH2 achieved the highest BET specific area among all MXene-based adsorbents, and the generated abundant -NH2, -OH and -ONa complexing groups exhibited strong interactions with lead ions, resulting in attractively high adsorption capacity.

Template-free Synthesis of Stable Cobalt Manganese Spinel Hollow Nanostructured Catalysts for Highly Water-Resistant CO Oxidation.

Development of spinel oxides as low-cost and high-efficiency catalysts is highly desirable; however, rational synthesis of efficient and stable spinel systems with precisely controlled structure and components remains challenging. We demonstrate the design of complex nanostructured cobalt-based bimetallic spinel catalysts for low-temperature CO oxidation by a simple template-free method. The self-assembled multi-shelled mesoporous spinel nanostructures provide high surface area (203.5 m2/g) and favorable unique surface chemistry for producing abundant active sites and lead to the creation of robust microsphere configured by 16-nm spinel nanosheets, which achieve satisfactory water-resisting property and catalytic activity. Theoretical models show that O vacancies at exposed {110} facets in cubic spinel phase guarantee the strong adsorption of reactive oxygen species on the surface of catalysts and play a key role in the prevention of deactivation under moisture-rich conditions. The design concept with architecture and composition control can be extended to other mixed transition metal oxide compositions.

In-situ green assembly of spherical Mn-based metal-organic composites by ion exchange for efficient electrochemical oxidation of organic pollutant.

In this study, we develop a facile ion exchange strategy for in-situ assembly of novel spherical metal-organic composites on a large scale. The functional groups (-NH2, -COOH and -SO3H) on chelating and exchange resins had significant effects on improving uniform distribution of metallic sites and metal-support interaction. Without any addition of H2O2, Mn-based metal-organic composites realized the recovery of waste metallic ions and exhibited high activity for methylene blue (MB) electro-Fenton degradation (97.8% decoloration and 54.7% TOC removal) within 150 min under low current density (7.53 mA·cm-2) and 3.0 g·L-1 catalyst dosage. Analyses of performance on different active sites (FeII, MnII, CoII, CeIII and CuII) and supports clearly indicated that synergetic effect of MnII and organic supports played crucial roles in electrochemical oxidation. Kinetic rate constant of 0.037 min-1 and turn over frequency of 0.23 h-1 were much better than those of inorganic supported catalysts, which were attributed to intramolecular electron transfer greatly accelerating MnII/MnIII autocatalytic cycle. Meanwhile, possible degradation pathway of MB was proposed by analysis of oxidative intermediate products. Benefiting from excellent properties and millimeter-level size structure, metal-organic composites can be applied in wide pH range of 2.0-9.0 and easily separated in the industrial application.

Guanidyl-functionalized graphene/polysulfone mixed matrix ultrafiltration membrane with superior permselective, antifouling and antibacterial properties for water treatment.

Mixed matrix membranes blended with graphene-based nanomaterials have great potential in water and wastewater treatment on account of their multiple functionalities. To solve the complicated biofouling problem and diversify the applications of membranes, novel synergistic antibacterial guanidyl-functionalized graphene/polysulfone (GFG/PSF) mixed matrix ultrafiltration membranes were prepared by a non-solvent induced phase separation method. The guanidyl-functionalized graphene nanosheets were achieved by a two-step grafting process consisting of amination and guanidination and exhibited high dispersibility in the casting solution, which showed good compatibility with the polymer matrix. Besides the advantages of partially reduced graphene oxide (GO) nanosheets in creating a stronger interaction with the bacterial cell membrane to destroy the bacteria, the induced bidendate binding between guanidyl groups and phosphate groups on the cell wall can make high sterilization rate even at low concentrations. Different techniques including XRD, FTIR, XPS, SEM, TEM, EDX, contact angle meter, filtration and antibacterial experiments were employed to characterize and investigate the performance of nanosheets and membranes. Compared with pure PSF membrane, the GFG/PSF mixed matrix membranes not only exhibited superior permeability and prominent antifouling property performance toward bovine serum albumin (BSA), but also displayed excellent antimicrobial activity and long-term duration toward Escherichia coli and Staphylococcus aureus.

Self-Assembly of Mn(II)-Amidoximated PAN Polymeric Beads Complex as Reusable Catalysts for Efficient and Stable Heterogeneous Electro-Fenton Oxidation.

A facile postsynthetic amidoxime modification method was reported on the preparation of transition-metal ions (Mn, Fe, and Co)-polyacrylonitrile (PAN) polymeric beads complex as reusable catalysts for efficient and stable heterogeneous electro-Fenton oxidation. Through one-step phase inversion, low-cost and chemically resistant polymeric PAN beads were fabricated on a large scale with controllable sizes and abundant porous structure. The postfunctionalization strategy led more active sites to be uniformly distributed into modified PAN beads owing to the favorable channel confined effect and chelate coordination. Compared with pure PAN beads, the modified composite catalysts exhibited remarkably higher activity and stability in electro-Fenton oxidation over wide pH range of 3-10 without any addition of H2O2. By analysis, the grafted amidoxime group was extremely beneficial for improving metal loading and binding force between active sites and organic supports, which accelerated the active sites autocatalytic cycle to promote H2O2 activation by means of excited electron transfer from composites' functional groups. The catalytic activity of Mn-amidoximated PAN evaluated by the turnover frequency was 15 times more than that of traditional iron oxide and very competitive to the reported metal-organic framework-based composites. Moreover, a strong metal and polymeric support interaction significantly enhanced the stabilization of active sites dispersed in porous matrix and solved the ever-present problem of metallic ions leaching to the greatest extent. The scalable introduction of functionalities into sophisticated structures after host framework synthesis will bring valuable insights to develop highly efficient and stable heterogeneous catalysts for green electrochemical oxidation in practical application.

Advanced membrane bioreactors systems: New materials and hybrid process design.

Membrane bioreactor (MBR) is deemed as one of the most powerful technologies for efficient municipal and industrial wastewater treatment around the world. However, low microbial activity of activated sludge and serious membrane fouling still remain big challenges in worldwide application of MBR technology. Nowadays, more and more progresses on the research and development of advanced MBR with new materials and hybrid process are just on the way. In this paper, an overview on the perspective of high efficient strains applied into MBR for biological activity enhancement and fouling reduction is provided first. Secondly, as emerging fouling control strategy, design and fabrication of novel anti-fouling composited membranes are comprehensively highlighted. Meanwhile, hybrid MBR systems integrated with some novel dynamic membrane modules and/or with other technologies like advanced oxidation processes (AOPs) are introduced and compared. Finally, the challenges and opportunities of advanced MBRs combined with bioenergy production in wastewater treatment are discussed.

Ultrathin metal-organic framework membrane production by gel-vapour deposition.

Ultrathin, molecular sieving membranes composed of microporous materials offer great potential to realize high permeances and selectivities in separation applications, but strategies for their production have remained a challenge. Here we show a route for the scalable production of nanometre-thick metal-organic framework (MOF) molecular sieving membranes, specifically via gel-vapour deposition, which combines sol-gel coating with vapour deposition for solvent-/modification-free and precursor-/time-saving synthesis. The uniform MOF membranes thus prepared have controllable thicknesses, down to ~17 nm, and show one to three orders of magnitude higher gas permeances than those of conventional membranes, up to 215.4 × 10-7 mol m-2 s-1 Pa-1 for H2, and H2/C3H8, CO2/C3H8 and C3H6/C3H8 selectivities of as high as 3,400, 1,030 and 70, respectively. We further demonstrate the in situ scale-up processing of a MOF membrane module (30 polymeric hollow fibres with membrane area of 340 cm2) without deterioration in selectivity.MOF-based membranes have shown great promise in separation applications, but producing thin membranes that allow for high fluxes remains challenging. Here, the authors use a gel-vapour deposition strategy to fabricate composite membranes with less than 20 nm thicknesses and high gas permeances and selectivities.

Non-activation MOF arrays as a coating layer to fabricate a stable superhydrophobic micro/nano flower-like architecture.

Non-activation metal-organic framework (MOF) arrays are directly applied as a coating layer to fabricate a stable superhydrophobic micro/nano flower-like architecture. The MOF functionalized surfaces can be synthesized easily on different substrates without any activation procedure or modification by low free energy materials, which exhibit attractive performance in oil/water separation.

One-pot assembly of metal/organic-acid sites on amine-functionalized ligands of MOFs for photocatalytic hydrogen peroxide splitting.

A one-pot organic-acid-directed post-synthetic modification allows molecular iron/citric acid complexes to be anchored into amine-functionalized MOFs by a simple and rapid liquid spraying method. Amidation between organic acid and -NH2 groups of ligands can lead to more small nanoparticles (NPs) that are well-dispersed into MOFs and exhibit high activity for photocatalytic H2O2 splitting.

Transformation of metal-organic frameworks for molecular sieving membranes.

The development of simple, versatile strategies for the synthesis of metal-organic framework (MOF)-derived membranes are of increasing scientific interest, but challenges exist in understanding suitable fabrication mechanisms. Here we report a route for the complete transformation of a series of MOF membranes and particles, based on multivalent cation substitution. Through our approach, the effective pore size can be reduced through the immobilization of metal salt residues in the cavities, and appropriate MOF crystal facets can be exposed, to achieve competitive molecular sieving capabilities. The method can also be used more generally for the synthesis of a variety of MOF membranes and particles. Importantly, we design and synthesize promising MOF membranes candidates that are hard to achieve through conventional methods. For example, our CuBTC/MIL-100 membrane exhibits 89, 171, 241 and 336 times higher H2 permeance than that of CO2, O2, N2 and CH4, respectively.

Assembly of MOF Microcapsules with Size-Selective Permeability on Cell Walls.

The assembly of metal-organic frameworks (MOFs) into microcapsules has attracted great interest because of their unique properties. However, it remains a challenge to obtain MOF microcapsules with size selectivity at the molecular scale. In this report, we used cell walls from natural biomaterials as non-toxic, stable, and inexpensive support materials to assemble MOF/cell wall (CW) microcapsules with size-selective permeability. By making use of the hollow structure, small pores, and high density of heterogeneous nucleation sites of the cell walls, uniform and continuous MOF layers could be easily obtained by inside/outside interfacial crystallization. The prepared MOF/CW microcapsules have excellent stability and enable the steady, slow, and size-selective release of small molecules. Moreover, the size selectivity of the microcapsules can be adjusted by changing the type of deposited MOF.

Iron oxide nanoparticles immobilized to mesoporous NH2-SiO2 spheres by sulfonic acid functionalization as highly efficient catalysts.

A novel SiO2 nanosphere was synthesized by the post-synthetic grafting of sulfonic acid groups on to anionic-surfactant-templated mesoporous NH2-silica (AMAS). This one-pot post-functionalization strategy allowed more metal ions to be homogeneously anchored into the channel of the meso-SiO2 nanosphere. After hydrothermal and calcination treatment, the in situ growth of α-Fe2O3 on sulfonic acid-functionalized mesoporous NH2-SiO2 (SA-AMAS) exhibited much higher activity in the visible-light assisted Fenton reaction at neutral pH than that for AMAS or meso-SiO2 nanospheres. By analysis, the grafted sulfonic acid group can not only enhance the acid strength of the catalyst, but can also bring more orbital-overlapping between the active sites (Fe(II) and Fe(III)) and the surface peroxide species, to facilitate the decomposition of H2O2 to hydroxyl radical. The present results provide opportunities for developing heterogeneous catalysts with high-performance in the field of green chemistry and environmental remediation.

Self-assembled graphene oxide microcapsules with adjustable permeability and yolk-shell superstructures derived from atomized droplets.

GO microcapsules were assembled on the surface of atomized droplets prepared by a spray-drying strategy. The nanochannels in the microcapsule wall can be adjusted by water-soluble polymers and make the microcapsule exhibit sustained release. The strategy can further be employed to encapsulate metal organic frameworks to obtain MOF-GO yolk-shell superstructures.