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Membrane-based separation is an appealing solution to mitigate CO2 emission sustainably due to its energy efficiency and environmental friendliness. Attributed to its excellent separation endowed by nanomaterial incorporation, nanocomposite membrane is rigorously developed. This study explored the feasibility of boron nitride (BN) embedment and changes to formation mechanism of ultrathin selective layer of thin film nanocomposite (TFN) are investigated. The effects of amine-functionalization on nanosheet-polymer interaction and CO2 separation performance are also identified. Participation of nanosheets during interfacial polymerization reduced the crosslinking of selective layer, hence, improved TFN permeance while the formation of contorted diffusion paths by the nanosheets favors transport of small gases. Amine-functionalization enhanced the nanosheet-polymer interaction and elevated the membrane affinity towards CO2 which led to enhanced CO2 selectivity. The best TFN prepared in this study exhibited 37% and 20% increment in permeability and selectivity, respectively with respect to neat thin film composite (TFC). It is found that the CO2 separation performance of BN incorporated TFN is on par with many non-porous nanosheet-incorporated TFNs reported in literatures. The transport and barrier effects of BN and functionalized BN are discussed in detail to provide further insights into the development of commercially attractive CO2 selective TFN membranes.

Electrochemical (EC) reduction of graphene oxide (GO) serves as a green chemistry pathway to produce reduced GO (rGO). However, the mechanistic understanding of this process is still limited due to the structural complexity of GO-based materials. In the present study, we employ an inductive approach that consists of investigating the structures afforded by alternating EC reduction and oxidation steps to elucidate the electrochemical reduction reactions in aqueous solution. The initial EC reduction of chemically derived GO mainly converts epoxides (C–O–C) to COH/CH pairs. Simultaneously, carbon-centered radicals (C•) are eliminated. Subsequent EC oxidation does not result in restoration of epoxides but reverse dehydrogenation and radical formation. The second EC reduction and oxidation cycle involves reversible C–H formation coupled with radical elimination, suggesting that C• serves as an active site for the hydrogenation. As a result of this study, COH–CH is revealed as a plausible characteristic structure in electrochemically derived rGO. The reversible radical hydrogenation reaction can offer an effective route to manipulate the chemical reactivities of GO-based materials. We demonstrate that the electrons transferred by EC reduction can delocalize in the rGO to some extent, activating the pseudocapacitance that probably originates from COH.

Carbon nanotube (CNT) incorporated thin film nanocomposite (TFN) is a promising membrane for gas separation. However, agglomeration of CNT tends to occur due to its high aspect ratio and strong Van de Waals force. This study aims to improve the dispersion of CNT in TFN membrane through the addition of amphiphilic graphene oxide (GO) nanosheet. Interfacial polymerization (IP) technique was employed for the synthesis of thin selective layer atop a porous polysulfone (PSF) support. Amino acid functionalization was performed on CNT and GO and its impact on IP was evaluated. It was observed that the nanomaterials properties such as dispersibility, absorptivity and hydrophilicity could affect the reactivity of IP which in turn altered the characteristics of selective layer. Separation results showed that co-incorporation of amino acid modified CNT and GO improved the permeability and selectivity of TFNs by 30% and 60%, respectively. The resulted TFN was also more reproducible and stable under different applied pressures and exposure to air. The outcome of this study suggested that synergetic incorporation of the two geometrically different carbon-based nanomaterial could provide an additional degree of freedom to control the selective film formation as compared to single-filler incorporation.

Ceria nanoparticles with controlled crystal orientations were fabricated via an oleate-modified hydrothermal method, which involved varying the molar ratio of oleate ions to cerium ions in the reaction solution ([Ole/Ce]) from 0 to 1. Quasicubic nanoparticles having primary {1 0 0} facets in addition to {1 1 0} edges were obtained for [Ole/Ce] values greater than 1/2. On the other hand, polyhedral nanoparticles surrounded by primary {1 1 1} facets appeared on nanoparticle surface at [Ole/Ce] smaller than 1/4. It was found that the bonding of the carboxyl terminals of the oleate ions with the cerium(IV) ions on the {1 0 0} surfaces balanced the electric charge of the stacked layers and that this is what resulted in the formation of cubic nanoparticles surrounded by {1 0 0} facets for [Ole/Ce] values larger than 1/2.

Oxygen functional groups (OFGs) in graphene oxide (GO) are responsible for the unique optical, electrical, magnetic as well as ionic, liquid and gaseous transport properties. In the present study, we have discovered reversible epoxide opening/closing reactions in GO upon alkaline and acid treatments, respectively, under ambient conditions. We suggest that unique properties of GO including stability of the carbocation and fast proton migration on the surfaces enable the unusual pH-driven epoxide ring opening/closing reactions. Our experimental results indicate that an irreversible epoxy formation observed in base-treated GO under flux conditions is due to the decomposition of the vic-diol groups formed by epoxy ring opening in alkaline solutions. A high concentration of basal plane epoxides is a remarkable feature of GO. Thus, the reversible epoxy formation should be an important part of our understanding of reactivity and properties of GO. For example, the epoxy ring opening can be a mechanism for anomalous photoluminescent (PL) quenching of GO dispersions in alkaline conditions.

Reduction largely affects the properties of graphene oxide (GO), because the content of each functional group changes by the oxidation degree. So far no study about re-oxidation and re-reduction of GO has been carried out. Herein, we report the effects of oxidation/reduction cycle of graphite oxide (GtO, multilayered GO) on its composition and electrochemical capacitance property. Electrochemical oxidation and reduction of glassy carbon (GC) were conducted at potentials of +2.0 and −1.1 V (vs. Ag/AgCl), respectively, and then the electrochemical capacitances were measured. According to X-ray photoelectron spectroscopy (XPS) analysis, C C bonds were produced from CH defects of the reduced graphite oxide (rGtO) by the electrochemical re-oxidation. The conductivities of the reduced samples, with CH defects, and re-oxidized samples, with newly produced C C bonds, were high and low, respectively. The high electrochemical capacitance observed for the rGtO electrodes is caused by the activity of the CH defects and good conduction.

Exfoliation of layered materials into ultrathin nanosheets introduces a new cost-effective and environmentally safe fabrication method for novel nanostructured devices. In the present study, we have developed for the first time inorganic oxide nanosheets with near-infrared (NIR) luminescence properties. KLa1−xNdxNb2O7 (x=0.025, 0.05, 0.1, 0.2, or 0.3) powders obtained by a solid state reaction were exfoliated into single-layer metal oxide nanosheets with approximately 1.7 nm thickness by osmotic swelling with tetrabutylammonium cations, followed by the protonation of KLa1−xNdxNb2O7. We observed strong coupling of high-energy OH vibration with the Nd3+ energy levels upon protonation and exfoliation steps because of the extremely thin nature of oxide nanosheet-layers. Colloidal oxide nanosheets with an optimized Nd-doping concentration yielded detectable NIR luminescence due to 4F3/2–4I11/2 (Nd3+) radiative transitions, which opens possible application of these oxide nanosheets as bioimaging probes and bioanalytical sensors.

Low-cost graphene oxide (GO) and related materials are considered supermaterials because of their unique and excellent properties for many applications that are greatly affected by oxidation degree and dopants (impurities). Conventional GO prepared by the multistep Hummers’ method is unable to control degree of the oxidation and impurities. Here, we demonstrate a facile one-step method for preparing pure GO on graphite substrates [i.e. glassy carbon (GC), highly oriented pyrolytic graphite-basal plane surface (HOPG-b), and highly oriented pyrolytic graphite-edge surface (HOPG-e)] by electrolysis in pure water under high voltage; the resultant GO is called electrolytic GO (eGO). The degree of oxidation in eGO can be easily controlled by adjusting the applied voltage and the electrolysis time, and small-sized eGO can be obtained by using a counter tip electrode on the substrate during the electrolysis. Photoelectrochemically reduced eGO (r-eGO) had a large double-layer charging capacitance and high electrocatalytic activity for the oxygen reduction reaction (ORR), and acted as an n-type semiconductor electrode. The r-eGO formed on HOPG-b had larger capacitance and higher activity for ORR than that on HOPG-e. The excellent properties of r-eGO were due to carbon defects and/or OH groups produced by the reduction of epoxide groups formed at the basal plane, as evidenced by X-ray photoelectron spectroscopy and Raman spectroscopy. The photoelectrochemical deposition of metal oxides or hydroxides on r-eGO increased the capacitance and catalytic activity of the material.

Graphene oxide (GO) has many functions, because it has many kinds of functional groups and defects. However, a detailed analysis of the functions and the relationships between the functions and functional groups, has never been made. Here, a detailed analysis of these functions and relationships is given based on our results. The epoxide of GO is unique, and shows a reversible reaction with changing pH. The high proton conductivity of GO is attributed to the presence of epoxide in the interlayers of GO. New types of electrochemical devices such as fuel cells and lead acid batteries where GO is used as a solid proton electrolyte, are proposed. CH defects are also important for the electrode with a high capacitance in supercapacitor and magnetism. GO is also very useful as electrocatalyst substrates because there are both hydrophilic and hydrophobic nano-level areas on the surface. [TANSO 2015 (No. 266) 31–34.]