Removal of Ibuprofen from Water by Different Types Membranes.

Ibuprofen separation from water by adsorption and pertraction processes has been studied, comparing 16 different membranes. Tailor-made membranes based on Matrimid, Ultem, and diaminobenzene/diaminobenzoic acid with various contents of zeolite and graphene oxide, have been compared to the commercial polystyrene, polypropylene, and polydimethylsiloxane polymeric membranes. Experimental results revealed lower ibuprofen adsorption onto commercial membranes than onto tailor-made membranes (10-15% compared to 50-70%). However, the mechanical stability of commercial membranes allowed the pertraction process application, which displayed a superior quantity of ibuprofen eliminated. Additionally, the saturation of the best-performing commercial membrane, polydimethylsiloxane, was notably prevented by atomic layer deposition of (3-aminopropyl)triethoxysilane.

6FDA-DAM:DABA Co-Polyimide Mixed Matrix Membranes with GO and ZIF-8 Mixtures for Effective CO2/CH4 Separation.

This work presents the gas separation evaluation of 6FDA-DAM:DABA (3:1) co-polyimide and its enhanced mixed matrix membranes (MMMs) with graphene oxide (GO) and ZIF-8 (particle size of <40 nm). The 6FDA-copolyimide was obtained through two-stage poly-condensation polymerization, while the ZIF-8 nanoparticles were synthesized using the dry and wet method. The MMMs were preliminarily prepared with 1-4 wt.% GO and 5-15 wt.% ZIF-8 filler loading independently. Based on the best performing GO MMM, the study proceeded with making MMMs based on the mixtures of GO and ZIF-8 with a fixed 1 wt.% GO content (related to the polymer matrix) and varied ZIF-8 loadings. All the materials were characterized thoroughly using TGA, FTIR, XRD, and FESEM. The gas separation was measured with 50:50 vol.% CO2:CH4 binary mixture at 2 bar feed pressure and 25 °C. The pristine 6FDA-copolyimide showed CO2 permeability (PCO2) of 147 Barrer and CO2/CH4 selectivity (αCO2/CH4) of 47.5. At the optimum GO loading (1 wt.%), the PCO2 and αCO2/CH4 were improved by 22% and 7%, respectively. A combination of GO (1 wt.%)/ZIF-8 fillers tremendously improves its PCO2; by 990% for GO/ZIF-8 (5 wt.%) and 1.124% for GO/ZIF-8 (10 wt.%). Regrettably, the MMMs lost their selectivity by 16-55% due to the non-selective filler-polymer interfacial voids. However, the hybrid MMM performances still resided close to the 2019 upper bound and showed good performance stability when tested at different feed pressure conditions.

Tuning of Nano-Based Materials for Embedding Into Low-Permeability Polyimides for a Featured Gas Separation.

Several concepts of membranes have emerged, aiming at the enhancement of separation performance, as well as some other physicochemical properties, of the existing membrane materials. One of these concepts is the well-known mixed matrix membranes (MMMs), which combine the features of inorganic (e.g., zeolites, metal-organic frameworks, graphene, and carbon-based materials) and polymeric (e.g., polyimides, polymers of intrinsic microporosity, polysulfone, and cellulose acetate) materials. To date, it is likely that such a concept has been widely explored and developed toward low-permeability polyimides for gas separation, such as oxydianiline (ODA), tetracarboxylic dianhydride-diaminophenylindane (BTDA-DAPI), m-phenylenediamine (m-PDA), and hydroxybenzoic acid (HBA). When dealing with the gas separation performance of polyimide-based MMMs, these membranes tend to display some deficiency according to the poor polyimide-filler compatibility, which has promoted the tuning of chemical properties of those filling materials. This approach has indeed enhanced the polymer-filler interfaces, providing synergic MMMs with superior gas separation performance. Herein, the goal of this review paper is to give a critical overview of the current insights in fabricating MMMs based on chemically modified filling nanomaterials and low-permeability polyimides for selective gas separation. Special interest has been paid to the chemical modification protocols of the fillers (including good filler dispersion) and thus the relevant experimental results provoked by such approaches. Moreover, some principles, as well as the main drawbacks, occurring during the MMM preparation are also given.

Chemical Crosslinking of 6FDA-ODA and 6FDA-ODA:DABA for Improved CO2/CH4 Separation.

Chemical grafting or crosslinking of polyimide chains are known to be feasible approaches to increase polymer gas-pair selectivity and specific gas permeance. Different co-polyimides; 6FDA-ODA and 6FDA-ODA:DABA were synthesized using a two-step condensation method. Six different cross-linkers were used: (i) m-xylylene diamine; (ii) n-ethylamine; and (iii) n-butylamine, by reacting with 6FDA-ODA's imide groups in a solid state crosslinking; while (iv) ethylene glycol monosalicylate (EGmSal); (v) ethylene glycol anhydrous (EGAn); and (vi) thermally labile iron (III) acetylacetonate (FeAc), by reacting with DABA carboxyl groups in 6FDA-ODA:DABA. The gas separation performances were evaluated by feeding an equimolar CO2 and CH4 binary mixture, at a constant feed pressure of 5 bar, at 25 °C. Fractional free volume (FFV) was calculated using Bondi's contribution method by considering the membrane solid density property, measured by pycnometer. Other characterization techniques: thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) were performed accordingly. Depending on the type of amine, the CO2/CH4 selectivity of 6FDA-ODA increased between 25 to 100% at the expense of CO2 permeance. We observed the similar trend for 6FDA-ODA:DABA EGmSal-crosslinked with 143% selectivity enhancement. FeAc-crosslinked membranes showed an increment in both selectivity and CO2 permeability by 126% and 29% respectively. Interestingly, FeAc acted as both cross-linker which reduces chain mobility; consequently improving the selectivity and as micro-pore former; thus increases the gas permeability. The separation stability was further evaluated using 25⁻75% CO2 in the feed with CH4 as the remaining, between 2 and 8 bar at 25 °C. We also observed no CO2-induced plasticization to the measured pressure with high CO2 content (max. 75%).

Progress on Incorporating Zeolites in Matrimid®5218 Mixed Matrix Membranes towards Gas Separation.

Membranes, as perm-selective barriers, have been widely applied for gas separation applications. Since some time ago, pure polymers have been used mainly for the preparation of membranes, considering different kinds of polymers for such preparation. At this point, polyimides (e.g., Matrimid®5218) are probably one of the most considered polymers for this purpose. However, the limitation on the performance relationship of polymeric membranes has promoted their enhancement through the incorporation of different inorganic materials (e.g., zeolites) into their matrix. Therefore, the aim of this work is to provide an overview about the progress of zeolite embedding in Matrimid®5218, aiming at the preparation of mixed matrix membranes for gas separation. Particular attention is paid to the relevant experimental results and current findings. Finally, we describe the prospects and future trends in the field.

A New Member of the Graphene Family: Graphene Acid.

A new member of the family of graphene derivatives, namely, graphene acid with a composition close to C1 (COOH)1 , was prepared by oxidation of graphene oxide. The synthetic procedure is based on repeated oxidation of graphite with potassium permanganate in an acidic environment. The oxidation process was studied in detail after each step. The multiple oxidations led to oxidative removal of other oxygen functional groups formed in the first oxidation step. Detailed chemical analysis showed only a minor amount of other oxygen-containing functional groups such as hydroxyl and the dominant presence of carboxyl groups in a concentration of about 30 wt %. Further oxidation led to complete decomposition of graphene acid. The obtained material exhibits unique sorption capacity towards metal ions and carbon dioxide. The highly hydrophilic nature of graphene acid allowed the assembly of ultrathin free-standing membranes with high transparency.

Phenolic compounds recovered from agro-food by-products using membrane technologies: An overview.

Typically, the various agro-food by-products of the food industry are treated by standard membrane processes, such as microfiltration, ultrafiltration and nanofiltration, in order to prepare them for final disposal. Recently, however, new membrane technologies have been developed. The recovery, separation and fractionation of high-added-value compounds, such as phenolic compounds from food processing waste, are major current research challenges. The goal of this paper is to provide a critical review of the main agro-food by-products treated by membrane technologies for the recovery of nutraceuticals. State-of-the-art of developments in the field are described. Particular attention is paid to experimental results reported for the recovery of polyphenols and their derivatives of different molecular weight. The literature data are analyzed and discussed in relation to separation processes, molecule properties, membrane characteristics and other interesting phenomena that occur during their recovery.

Dynamic response of ultrathin highly dense ZIF-8 nanofilms.

Ultrathin ZIF-8 nanofilms are prepared by facile step-by-step dip coating. A critical withdrawal speed allows for films with a very uniform minimum thickness. The high refractive index of the films denotes the absence of mesopores. The dynamic response of the films to CO2 exposure resembles behaviour observed for non-equilibrium organic polymers.