Development of Graphene Oxide Framework Membranes via the "from" and "to" Cross-Linking Approach for Ion-Selective Separations.

Graphene oxide (GO) membranes with well-defined nanochannels formed between the stacked GO nanosheets find great interest in molecular separations. However, GO membranes are unstable in aqueous solution environments because of weak interactions between the stacked nanosheets. Herein, we developed a preparation method by diminishing the self-contained oxidized functional groups in GO and subsequent cross-linking to form GO framework (GOF) membranes with excellent aqueous solution stability. GOF membranes were fabricated by alternate deposition of branched polyethylenimine (BPEI) and a mixed solution of GO and thiourea (TU). Structural elucidation illustrated that the TU partially reduced the GO molecules and acted as a "to" cross-linker by bridging adjacent GO nanosheets through in-plane and out-of-plane of interactions. During the GO deposition, BPEI performed the role as a "from" cross-linker by binding the TU-linked GO laminates to form stable GOF membranes with well-defined nanochannels. Morphological studies confirmed the formation of the tightly packed structure for BPEI/GO_TU membranes due to the high Π-Π interactions between the GO nanosheets and bridging effect of TU. The GOF membranes exhibited a rejection of 99.5% for anionic dye methyl orange and cationic dye rhodamine B. The BPEI/GO_TU membranes fabricated from 12 bilayers using 0.25 mg/mL of GO solution have a pure water flux of 24 L m-2 h-1 and a Na2SO4 rejection of 94%; this permeability is 2.5 times higher than that of commercial nanofiltration membranes. Moreover, (BPEI/GO_TU)12 GOF membranes exhibited excellent aqueous solution stability in acidic and basic conditions. The excellent separation performance and aqueous solution stability of the BPEI/GO_TU membranes are intricately linked to the partial reduction and cross-linking of GO nanosheets in GOF membranes. Thus, the "from" and "to" cross-linking approach developed in this work can be extended for the fabrication of structurally stable membranes from other 2D materials.

Mechanochemistry of supramolecules.

The urge to use alternative energy sources has gained significant attention in the eye of chemists in recent years. Solution-based traditional syntheses are extremely useful, although they are often associated with certain disadvantages like generation of waste as by-products, use of large quantities of solvents which causes environmental hazard, etc. Contrastingly, achieving syntheses through mechanochemical methods are generally time-saving, environmentally friendly and more economical. This review is written to shed some light on supramolecular chemistry and the synthesis of various supramolecules through mechanochemistry.

An intramolecular C(sp3)-H imination using PhI-mCPBA.

Herein, a highly exothermic primary amine-polyvalent iodine reaction has been used successfully for selective functionalization of acidic C(sp3)-H groups for a dehydrogenative C-H imination reaction by 4H elimination. Overall, C(sp3)-H imination at 1,5 distances was readily done via organocatalysis using PhI (10 mol%)-mCPBA under ambient conditions.

Oxidative N-Arylation for Carbazole Synthesis by C-C Bond Activation.

Activation of strong C-C σ-bonds is quite challenging. We report here an intramolecular oxidative N-arylation method of biarylsulfonamides via cleavage of C-C bonds toward synthesis of heterocycle carbazoles. The stability of generated carbocations could control the reactivity of a nitrenium ion for the C-N bond formations at the ipso-carbon via a retro-Friedel-Crafts-type reaction using hypervalent iodine(III) reagent PhI(OAc)2.

Mechanochemical synthesis of small organic molecules.

With the growing interest in renewable energy and global warming, it is important to minimize the usage of hazardous chemicals in both academic and industrial research, elimination of waste, and possibly recycle them to obtain better results in greener fashion. The studies under the area of mechanochemistry which cover the grinding chemistry to ball milling, sonication, etc. are certainly of interest to the researchers working on the development of green methodologies. In this review, a collection of examples on recent developments in organic bond formation reactions like carbon-carbon (C-C), carbon-nitrogen (C-N), carbon-oxygen (C-O), carbon-halogen (C-X), etc. is documented. Mechanochemical syntheses of heterocyclic rings, multicomponent reactions and organometallic molecules including their catalytic applications are also highlighted.

Using weak interactions to control C-H mono-nitration of indolines.

An unprecedented C-H mononitration of indolines either at the -C5 or -C7 positions under mild condition is reported here. The roles of multiple weak interactions and factors such as steric factors, electronic effects, cation-π interactions, and solvent polarity were established, and we achieved a 100% regioselective electrophilic aromatic (EArS) nitration using Cu(NO3)2 or AgNO3.

Cross Redox Coupling of Aryl-Aldehydes and p-Benzoquinone.

Herein, we report an unprecedented Cross Redox Coupling (CRC) reaction catalyzed by Cu(OAc)2·H2O. As a proof-of-concept, direct coupling of aromatic aldehydes (or alcohols) and p-benzoquinone led to an ester in the presence of the Cu(II)-TBHP combination. During the coupling process, the C-H bond of the aldehydes was converted directly to a C-O bond. Mechanistically, we propose that the reaction proceeded via a radical pathway. In addition, atom and electron economies were well-conserved during this CRC reaction.

Strong electron-acceptor methylviologen dications confined in a 2D inorganic host: synthesis, structural characterization, charge transport and electrochemical properties of (MV)(0.25)V(2)O(5).

The reaction of methylviologen iodide with crystalline V2O5 in the molar ratio of 1 to 3.8 at 100 degrees C in water led to the formation of (MV)0.25V2O5 in quantitative yield. The structure of this organic-inorganic multilayered hybrid compound was determined by single-crystal X-ray crystallography. Strong van der Waals interactions were found between the electron-deficient aromatic organic molecules and the inorganic layers. In the solid state, the compound is a semiconductor due to small polaron hopping and shows novel reversible alkali-ion intercalation/deintercalation via electrochemistry.

Adsorption and Thermogravimetric Studies of Mesoporous Silica Coated with Siloxane Polymer.

Nitrogen adsorption and high-resolution thermogravimetry were used to study a series of samples prepared by coating porous silica with different amounts of siloxane polymer. Thermogravimetry was employed to investigate the thermal behavior of the coated samples as well as the polymer-silica interactions. Nitrogen adsorption was used to monitor the changes in the specific surface area, porosity, and surface properties upon polymer coating. It is shown that the gradual changes in the aforementioned properties are observed up to some limiting coating level. Also, in this coating range a rather uniform film is formed by siloxane polymer on the silica surface. Copyright 2001 Academic Press.

Fourier-Transform Infrared Spectroscopy Studies of the Interaction of Functionalized Siloxane Polymers with Porous Silica.

Adsorption behavior of the siloxane polymer, cyanopropylmethyl-phenyl-methyl-siloxane, in contact with a mesoporous silica has been investigated by Fourier-transform infrared spectroscopy (FT-IR) using a series of physically modified materials with different coating levels up to 20 w/w%. The nitrile stretch bands, which are observed in the 2150-2350 cm(1) range, exhibited complex profiles due to a variety of interactions of the cyano groups within the polymer and with the surface silanols. These complex bands have been resolved into multiple components using a curve-fitting procedure. Three major spectral components have been found and assigned to the nitrile stretch in the bulk polymer, interfacial polymer, and polymer attached to surface silanols via hydrogen bonding. The latter spectral component is dominating for the samples with low coating levels. Its relative contribution decreased with the increasing amount of the polymer on the silica surface due to increasing contribution of the pure-polymer spectral component. Copyright 2000 Academic Press.