Self-assembled dendrimer polyamide nanofilms with enhanced effective pore area for ion separation.

Membrane technology using well-defined pore structure can achieve high ion purity and recovery. However, fine-tuning the inner pore structure of the separation nanofilm to be uniform and enhance the effective pore area is still challenging. Here, we report dendrimers with different peripheral groups that preferentially self-assemble in aqueous-phase amine solution to facilitate the formation of polyamide nanofilms with a well-defined effective pore range and uniform pore structure. The high permeabilities are maintained by forming asymmetric hollow nanostripe nanofilms, and their well-designed ion effective separation pore ranges show an enhancement, rationalized by molecular simulation. The self-assembled dendrimer polyamide membrane provides Cl-/SO42- selectivity more than 17 times that of its pristine polyamide counterparts, increasing from 167.9 to 2883.0. Furthermore, the designed membranes achieve higher Li purity and Li recovery compared to current state-of-the-art membranes. Such an approach provides a scalable strategy to fine-tune subnanometre structures in ion separation nanofilms.

Asymmetric polyamide nanofilms with highly ordered nanovoids for water purification.

Tailor-made structure and morphology are critical to the highly permeable and selective polyamide membranes used for water purification. Here we report an asymmetric polyamide nanofilm having a two-layer structure, in which the lower is a spherical polyamide dendrimer porous layer, and the upper is a polyamide dense layer with highly ordered nanovoids structure. The dendrimer porous layer was covalently assembled in situ on the surface of the polysulfone (PSF) support by a diazotization-coupling reaction, and then the asymmetric polyamide nanofilm with highly ordered hollow nanostrips structure was formed by interfacial polymerization (IP) thereon. Tuning the number of the spherical dendrimer porous layers and IP time enabled control of the nanostrips morphology in the polyamide nanofilm. The asymmetric polyamide membrane exhibits a water flux of 3.7-4.3 times that of the traditional monolayer polyamide membrane, showing an improved divalent salt rejection rate (more than 99%), which thus surpasses the upper bound line of the permeability-selectivity performance of the existing various structural polyamide membranes. We estimate that this work might inspire the preparation of highly permeable and selective reverse osmosis (RO), organic solvent nanofiltration (OSNF) and pervaporation (PV) membranes.

ß-FeOOH self-supporting electrode for efficient electrochemical anodic oxidation process.

In this work, ß-FeOOH was synthesized and grown on carbon paper with the assistance of dopamine (PDA) via a facile hydrothermal method, producing ß-FeOOH self-supporting electrode eventually. Electrochemical anodic oxidation performance to methyl orange (MO) solution using ß-FeOOH anode was investigated and the major influencing factors such as current density, initial pH value and initial MO concentration on MO degradation efficiency were further explored. Experimental results suggested that 99.4% degradation rate of MO could be achieved only after 25 min electrolysis, its pseudo first-order reaction kinetic constant was 11.3 ⅹ 10-2 min-1 and the COD removal ratio was 37.3% after 120 min electrolysis under optimized conditions: current density was 10 mA cm-2, initial pH value was 3 and initial MO concentration was 10 mg L-1. At the same time, ß-FeOOH electrode also exhibited a high cycling stability and the MO removal ratio was still keeping at 84.9% after eight cycles. Moreover, this electrode showed efficient decomposition performance to multiple simulated pollutants, indicating the well potential practical application values of ß-FeOOH electrode. At last, the proposed degradation mechanism of MO was evaluated according to the analyzing results of UV-vis and HPLC-MS to MO solution under different degradation durations.

Ultrathin Film Composite Membranes Fabricated by Novel In Situ Free Interfacial Polymerization for Desalination.

Ultrathin polyamide nanofilms are desirable as the separation layers for the highly permeable thin-film composite (TFC) membranes, and recently, their lowest thickness limits have attracted a lot of attention from researchers. Due to the interference of the underlying substrate, preparing a defect-free, ultrathin polyamide nanofilm directly on top of a membrane substrate remains a great challenge. Herein, we report a novel fabrication technique of TFC membranes, named in situ free interfacial polymerization (IFIP), where the IP reaction occurs at the uniform, free oil-water interface dozens of microns above the substrate, and then the resulting nanofilm spontaneously assembles into the TFC structure without extra manual transfer. This IFIP method not only overcomes the limitations of conventional IP, succeeding in preparing ultrathin-nanofilm composite membranes for nanofiltration and reverse osmosis application, but also enables scale membrane manufacturing that is not feasible via previously reported free-standing IP. Based on the IFIP method, the thickness of the polyamide nanofilm was successfully reduced to ca. 3-4 nm, which we believe is close to the ultrathin limit of the polyamide nanofilm for separation application. Meanwhile, the structure-performance relationship revealed that the strategy of increasing TFC membrane permeance by reducing polyamide layer thickness also had a limit. Besides, the IP mechanisms in regard to the formation of surface morphology and film growth were explored by combining experimental and molecular simulation methods. Overall, this work is expected to push forward the fundamental study and practical application of the ultrathin-film composite membrane.

In Situ Assembly of a Zeolite Imidazolate Framework Hybrid Thin-Film Nanocomposite Membrane with Enhanced Desalination Performance Induced by Noria-Polyethyleneimine Codeposition.

Zeolite imidazolate framework-8 (ZIF-8) has emerged as an excellent candidate for the preparation of thin-film nanocomposite (TFN) membranes. Nevertheless, it still remains a great challenge to make the effective incorporation of ZIF-8 into the resulting TFN membrane feasible for facile application. Herein, we propose an in situ strategy to fabricate a ZIF-8 nanocrystal hybrid reverse osmosis membrane induced by the ultrafast surface modification of Noria-polyethyleneimine codeposition. By this method, ZIF-8 nanocubes with monodispersity were first formed on a modified support through the step-by-step deposition of precursor solutions. Afterward, a TFN membrane was fabricated by interfacial polymerization (IP) on a ZIF-8 loaded support. Due to the significantly altered IP process induced by the coexistence of Noria and ZIF-8 on the support surface, the TFN membrane depicts a distinct nanostrand-nanoparticle hybrid morphology, which endows the TFN membrane with excellent antifouling ability. Moreover, the permeance of the as-fabricated TFN membrane is up to 3.64 L·m-2·h-1·bar-1, nearly 2.7-fold higher than that of the nascent membrane, while it still maintains a high rejection toward NaCl. The in situ assembly strategy reported here could also pave a promising way for the fabrication of TFN membranes with other nanomaterials in future.

Ultrathin Polyamide Membrane with Decreased Porosity Designed for Outstanding Water-Softening Performance and Superior Antifouling Properties.

Poly(piperazine-amide)-based nanofiltration membranes exhibit a smooth surface and superior antifouling properties but often have lower Ca2+ and Mg2+ rejection due to their larger inner micropore and thus cannot be extensively used in water-softening applications. To decrease the pore size of poly(piperazine-amide) membranes, we designed and synthesized a novel monomer, 1,2,3,4-cyclobutane tetracarboxylic acid chloride (BTC), which possesses a smaller molecular conformation than trimesoyl chloride (TMC). The thickness of the prepared BTC-piperazine (PIP) polyamide nanofilm via interfacial polymerization is as thin as 15 nm, significantly lower than the 50 nm thickness of the TMC-PIP nanofilm. The surface characterization reveals that the BTC-PIP polyamide membrane exhibits an enhanced hydrophilicity, a smooth surface, and a decreased surface-negative charge. The desalination performance (both rejection and water flux) of these membranes in terms of Ca2+ and Mg2+ exceeds that of the current commercial water-softening membranes. In addition, the BTC-PIP polyamide membrane also exhibits superior antifouling properties compared to the TMC-based polyamide membrane. More importantly, molecular simulations show that the BTC-PIP membrane has a lower average pore size than that of the TMC-PIP membrane, which demonstrates an enhanced steric hindrance effect, as confirmed by desalination performance. Our results demonstrate that in the household and industrial water-softening market, BTC-PIP membrane with decreased porosity, enhanced hydrophilicity, and smooth surface is preferred alternative to the conventional TMC-based polyamide membranes.

Propylene/propane permeation properties of ethyl cellulose (EC) mixed matrix membranes fabricated by incorporation of nanoporous graphene nanosheets.

Nanopore containing graphene nanosheets were synthesized by graphene oxide and a reducing agent using a facile hydrothermal treatment in sodium hydroxide media. The as-prepared nanoporous graphene was incorporated into ethyl cellulose (EC) to prepare the mixed matrix membranes (MMMs) for C3H6/C3H8 separation. Transmission electron microscopy (TEM) photograph and X-ray photoelectron spectroscopy (XPS) analysis of nanoporous graphene nanosheets indicated that the structure of nano-pore was irregular and the oxygen-containing groups in the surface were limited. More importantly, the as-prepared MMMs presented better separation performance than that of pristine EC membrane due to simultaneous enhancement of C3H6 permeability and ideal selectivity. The ideal selectivity of the MMMs with 1.125 wt‰ nanoporous graphene content for C3H6/C3H8 increased from 3.45 to 10.42 and the permeability of C3H6 increased from 57.9 Barrer to 89.95 Barrer as compared with the pristine membrane. The presumed facilitated mechanism was that the high specific surface area of nanoporous graphene in polymer matrix increased the length of the tortuous pathway formed by nanopores for the gas diffusion as compared with the pristine graphene nanosheets, and generated a rigidified interface between the EC chains and fillers, thus enhanced the diffusivity selectivity. Therefore, it is expected that nanoporous graphene would be effective material for the C3H6/C3H8 separation.

Polymers for 193-nm Microlithography: Regioregular 2-Alkoxycarbonylnortricyclene Polymers by Controlled Cyclopolymerization of Bulky Ester Derivatives of Norbornadiene.

Double duty for the tert-butyl residue: The bulky substituent in monomer 1 favors free-radical cyclopolymerization with maleic anhydride to give the regioregular nortricyclene copolymer 2. When the polymer is irradiated with a photoacid generator, the tert-butyl ester is cleaved and the polymer becomes soluble in aqueous base. This type of copolymer can be used in 193-nm microlithography; images with resolutions of less than 200 nm have been obtained.

Direct Formation of Secondary and Tertiary Alkylzinc Bromides and Subsequent Cu(I)-Mediated Couplings.

Secondary and tertiary alkylzinc bromides can be generated from the direct oxidative addition of Rieke zinc to secondary and tertiary alkyl bromides in high yield. These organozinc reagents have been found to undergo copper-catalyzed conjugate addition, cross-coupling with acid chlorides, and carbocupration to activated alkynes.