Simultaneous removal of Cr and organic matters via coupling Cr-Fenton-like reaction with Cr flocculation: The key role of Cr flocs on coupling effect

Cr contamination is frequently combined with organic pollution. Cr flocculation using flocculants results in difficulty in Cr recovery and increase of salinity. Moreover, the fates of coexisted organic pollutants are rarely attended. In this study, the Fenton-like reaction based on Cr redox reaction (Cr-Fenton-like reaction) coupled with Cr flocculation was established using H₂O₂ as additives, which gave the opportunity to realize simultaneous removal of Cr and organic matters sustainably. In the coupling system, Cr-Fenton-like reaction generated more OH^- for Cr flocculation via the H₂O₂ decomposition, meanwhile, Cr flocculation provided heterogeneous catalytic regions for Cr-Fenton-like reaction. The formation of Cr flocs was the key to the coupling effect. They created partially alkaline regions, therefore Cr-Fenton-like reaction (reaction condition: pH > 5) and Cr flocculation (reaction condition: pH > 8) occurred in these heterogeneous regions, although the pH of the solutions was below 5. Besides, the Cr flocs in the coupling system tended to adsorb Cr(III) which also contributed to the coupling effect. Although Cr-Fenton-like reaction generated Cr(VI) inevitably, the dissolved Cr(VI) didn't accumulate due to the persistent acidic condition and the heterogeneous catalysis of Cr flocs in the coupling system. When the coupling effect was applied to a stimulated tannery wastewater with Cr and organic co-pollution, the simultaneous removal rates for Cr and total organic carbon were 81.2% and 41.34% respectively after an 8-h running. This study gives deep insights into the coupling effect and provides a sustainable and eco-friendly strategy for the remediation of wastewater with Cr and organic co-pollution.

Metal Organic Frameworks as Heterogeneous Catalysts in Olefin Epoxidation and Carbon Dioxide Cycloaddition

Metal–organic frameworks (MOFs) are a family of porous crystalline materials that serve in some cases as versatile platforms for catalysis. In this review, we overview the recent developments about the use of these species as heterogeneous catalysts in olefin epoxidation and carbon dioxide cycloaddition. We report the most important results obtained in this field relating them to the presence of specific organic linkers, metal nodes or clusters and mixed-metal species. Recent advances obtained with MOF nanocomposites were also described. Finally we compare the results and summarize the major insights in specific Tables, outlining the major challenges for this emerging field. This work could promote new research aimed at producing coordination polymers and MOFs able to catalyse a broader range of CO2 consuming reactions.

l-Cysteine-Modified Graphene Oxide-Based Membrane for Chiral Selective Separation

A novel chiral separation membrane was fabricated by assembling l-cysteine (l-Cys)-modified graphene oxide sheets. l-Cys modification leads to an enantiomer separation membrane with an accessible interlayer spacing of 8 Å, which allows high solvent permeability. In the racemate separation experiments under isobaric conditions, the enantiomeric excess (ee) values of alanine (Ala), threonine (Thr), tyrosine (Tyr), and penicillamine (Pen) racemates in the permeation solution were 43.60, 44.11, 27.43, and 46.44%, respectively. In the racemate separation experiments under negative pressure, the separation performances of Ala, Thr, and Tyr were still maintained, and the enantiomeric excess (ee) values of the filtrate after separation were 56.80, 54.57, and 32.34%, respectively. These results indicate that the as-prepared GO-Cys membrane has a great practical value in the field of enantiomer separation.

Oxido- and Dioxido-Vanadium(V) Complexes Supported on Carbon Materials: Reusable Catalysts for the Oxidation of Cyclohexane

Oxidovanadium(V) and dioxidovanadium(V) compounds, [VO(OEt)L] (1) and [Et3NH][VO2L] (2), were synthesized using an aroylhydrazone Schiff base (5-bromo-2-hydroxybenzylidene)-2-hydroxybenzohydrazide (H2L). They were characterized by elemental analysis, Fourier-transform infrared spectroscopy (FT-IR), (1H and 51V) nuclear magnetic resonance (NMR), electrospray ionization mass spectrometry (ESI-MS) and single crystal X-ray diffraction analyses. Both complexes were immobilized on functionalized carbon nanotubes and activated carbon. The catalytic performances of 1 and 2, homogenous and anchored on the supports, were evaluated for the first time towards the MW-assisted peroxidative oxidation (with tert-butylhydroperoxide, TBHP) of cyclohexane under heterogeneous conditions. The immobilization of 1 and 2 on functionalized carbon materials improved the efficiency of catalytic oxidation and allowed the catalyst recyclability with a well-preserved catalytic activity.

MoO2 Formed on Mesoporous Graphene Oxide: Efficient and Stable Catalyst for Epoxidation of Olefins

A novel mesoporous MoO2 composite supported on graphene oxide (m-MoO2/GO) has been designed and applied as an efficient epoxidation catalyst. The m-MoO2/GO composite was characterised by X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, Brunauer–Emmet–Teller surface area analysis, field emission scanning electron microscopy, and transmission electron microscopy. Compared with pure mesoporous MoO2 (m-MoO2) and amorphous MoO2-graphene oxide (a-MoO2/GO), m-MoO2/GO exhibits the best catalytic activity. The conversion and selectivity for cyclooctene are both over 99 % in 6 h. Remarkably, the mesoporous structure in m-MoO2/GO which derives from SiO2 nanospheres endows the catalyst better catalytic performance for long chain olefins: the conversion of methyl oleate can be as high as 82 %. Such a robust catalyst can be easily recycled and reused five times without significant loss of catalytic activity. This novel catalyst is promising in the synthesis of epoxides with a long carbon chain or large ring size.

Syntheses, crystal structures and catalytic activities of two solvent-induced homotrinuclear Co(ii) complexes with a naphthalenediol-based bis(Salamo)-type tetraoxime ligand

Two homotrinuclear cobalt(ii) complexes with different solvent molecules that coordinate to the central Co(ii) ion, show different supramolecular interactions and exhibit catalytic activities in relation to catechol oxidase.

The mechanism of electropolymerization of nickel(ii) salen type complexes

Ni(ii) complexes with (±)-trans-N,N′-bis(salicylidene)-1,2-cyclohexanediamine ([Ni(salen)]), and its methyl ([Ni(salen(Me))]) and tert-butyl ([Ni(salen(Bu))]) derivatives have been synthesized.

Synthesis and characterization of a Cu(ii) Schiff base complex immobilized on graphene oxide and its catalytic application in the green synthesis of propargylamines

A Cu(ii) Schiff base complex immobilized on graphene oxide has been synthesized and characterized by FTIR, FT-RAMAN, XRD, UV, TEM, FE-SEM, EDAX, TGA, N₂ adsorption–desorption and AAS analysis.

Iridium and rhodium “PNP” aminodiphosphine complexes used as catalysts in the oxidation of styrene

New Ir and Rh “PNP” aminodiphosphine complexes are effective catalysts in styrene oxidation withtert-butyl hydroperoxide as the oxidant. The Ir catalysts were more active than the Rh catalysts with high yields to benzaldehyde in comparison to styrene oxide.

Encapsulation of chiral Fe(salen) in mesoporous silica structures for use as catalysts to produce optically active sulfoxides

Solid catalysts which are heterogeneous at the macroscopic scale but homogeneous at the microscopic level were prepared by the encapsulation of Fe(salen) by a “ship in a bottle” approach.

The advantages of covalently attaching organometallic catalysts to a carbon black support: recyclable Rh(i) complexes that deliver enhanced conversion and product selectivity

A bidentate Rh(i) coordination complex was covalently anchored to a carbon black support. The resultant hybrid catalyst was found to be active for both hydroamination and dihydroalkoxylation reactions and was readily recycled.

Oxidovanadium(iv), oxidomolybdenum(vi) and cobalt(iii) complexes of o-phenylenediamine derivatives: oxidative dehydrogenation and photoluminescence

Oxidovanadium(iv), cis-dioxidomolybdenum(vi) amide complexes and cobalt(iii) imine complex of an o-phenylenediamine derivatives are reported.

Epoxidation of styrene over Fe(Cr)-MIL-101 metal–organic frameworks

Fe(Cr)-MIL-101 metal–organic frameworks as efficient heterogeneous catalysts for the selective oxidation of styrene.