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Modulator-mediated functionalization (MoFu) is introduced as a new and versatile platform tool to improve the separation performance of metal-organic framework (MOF)-based membranes, exemplified here by the creation of mixed-matrix membranes (MMMs) with enhanced CO2 separation efficiency. The unique structure of MOF-808 allows incorporation of CO2-philic modulators in the MOF framework during a one-pot synthesis procedure in water, thus creating a straightforward way to functionalize both MOF and corresponding MMM. As a proof of concept, a series of fluorinated carboxylic acids [trifluoroacetic acid (TFA), pentafluoropropionic acid (PFPA), and heptafluorobutyric acid (HFBA)] and nonfluorinated alkyl carboxylic acids (acetic acid (AA), propionic acid (PA), and butyric acid (BA)) were used as a modulator during MOF-808 synthesis. Two of the best MMMs prepared with 30 wt % MOF-TFA (100% increase in CO2/CH4 separation factor, 350% increase in CO2 permeability) and 10 wt % MOF-PFPA (140% increase in CO2/CH4 separation factor, 100% increase in CO2 permeability) scored very close to or even crossed the 2008 and 2018 upper bound limits for CO2/CH4. Because of its facile functionalization (and its subsequent excellent performance), MOF-808 is proposed as an alternative for widely used UiO-66, which is, from a functionalization point-of-view and despite its widespread use, a rather limited MOF. ispartof: ACS APPLIED MATERIALS & INTERFACES vol:11 issue:47 pages:44792-44801 ispartof: location:United States status: published

A range of commercially available and lab-made membranes was screened for use in feeds containing acetonitrile (ACN). ACN was selected as it is one of the most widely used solvents in pharmaceutical industry and surprisingly absent in earlier studies on solvent resistant nanofiltration (SRNF). The selected membranes ranged from the tight nanofiltration range to the lower end ultrafiltration range, prepared from different membrane chemistries and with different membrane preparation methods. Multiple dyes were tested as probe molecules to study the retention behavior of the membranes in ACN. Gel content measurements were conducted on the membranes and interaction parameters with ACN, the dyes and the membranes were calculated to link physico-chemical properties to separation performances. ACN was found to be a very appropriate solvent for SRNF applications, as most membranes reached high fluxes and retentions, comparable to those obtained in most other solvents. As most membrane polymers did not dissolve in ACN, membrane crosslinking is not even strictly necessary to ensure stability of the membranes when applied in these feeds. This study thus showed that for ACN-based solutions, many different types of SRNF membranes can potentially be selected to achieve the aimed separations.

A novel synthesis method of partially crosslinking a polymer solution prior to casting, has been successfully developed for the preparation of solvent-tolerant nanofiltration (STNF) membranes. STNF merges solvent resistant nanofiltration (SRNF) with aqueous nanofiltration. The feed solution consists of a mixture of solvent(s) and water, requiring a membrane with both high water permeability and solvent stability. In this work, epoxy resins are proposed to meet these requirements. The well-known epoxy curing bulk chemistry via ring-opening reactions has been applied followed by a phase inversion process, to form membranes with intermediate polarity, excellent stability and permeability, making them particularly suitable for the treatment of solvent/water mixtures. Several epoxy monomers were screened, based on size and number of epoxide functional groups. Different amines with varying length and reactivity were chosen as curing agent. Both reagents were dissolved in dimethyl sulfoxide (DMSO) and left to react. The increasing solution viscosity was monitored as a function of time and related to the reaction rate of the epoxy-amine curing system. Integrally skinned asymmetric membranes were prepared via non-solvent induced phase inversion. Filtration experiments were carried out in 20/80 dimethyl formamide (DMF)/water mixtures with Rose Bengal (RB, 1018 g mol−1), Rhodamine 6G (R6G, 479 g mol−1) and Methyl Orange (MO, 327 g mol−1) as solutes. A blend of 2 epoxides, i.e. EPON 1009F (20 wt%) and EPON SU-8 (10 wt%), in DMSO resulted in RB retention of 99+ % and a R6G retention of 77% in DMF/water with a permeance of 0.75 Lm−2h−1bar−1. Addition of tetrahydrofuran (THF) as co-solvent (5/1, DMSO/THF) increased the selectivity further towards a 99% RB and R6G retention and an 85% MO retention with a permeance of 0.29 Lm−2h−1bar−1. ATR-FTIR spectra indicated that the membranes are stable after immersion of 5 days in very harsh conditions, i.e. pH = 0–14, and in a variety of solvents.

The applicability of state-of-the-art water purification membranes in harsh feed streams is limited due to their insufficient chemical robustness. Epoxide chemistry has been recently introduced to achieve pH- and chlorine-stable nanofiltration (NF). This study further investigated the influence of interfacial polymerization (IP) synthesis parameters on the resulting epoxide-based thin-film composite (TFC) membrane structure and performance. Epoxide polymerization could be initiated by N,N,N′,N′-tetramethyl-1,6-hexanediamine and NaOH. Surprisingly, neither the type of initiator, nor the initiator concentration used during IP, influenced membrane rejection of rose bengal (RB) dye (1017 g mol-1), which was constant at ~ 90%. This consistent RB rejection was primarily determined by annealing of the cross-linked polyimide support by toluene, which is the solvent used during IP. In contrast, the poly(epoxyether) top-layer determined membrane selectivity for methyl orange, a smaller dye of 327 g mol-1. The effect of solvent annealing of the membrane support by diethyl carbonate, dimethyl sulfoxide and m-xylene was also investigated and revealed that the changes induced by solvent contact are physical rather than chemical in nature. This study shows, for the first time, the substantial direct impact of the solvents used during IP to influence support properties and the resulting membrane performance. Solvent annealing can therefore be considered as a tool in membrane fabrication—during IP or as a post-treatment step—to further tune the separation performance for specific applications.