Iron Nanoparticles-Confined Graphene Oxide Membranes Coupled with Sulfite-Based Advanced Reduction Processes for Highly Efficient and Stable Removal of Bromate.

Advanced reduction processes (ARPs) are promising for pollutant removal in drinking water treatment. In this study, we demonstrated highly efficient reduction of bromate, a harmful disinfection byproduct, by coupling ARPs with an iron nanoparticles-intercalated graphene oxide (GO@FeNPs) catalytic membrane. In the presence of 1.0 mM sulfite (S(IV)), the GO@FeNPs membrane/S(IV) system achieved nearly complete removal of 80 µg/L bromate in 3 min. The first-order reaction rate constant for bromate removal in this system was 420 ± 42 min-1, up to 5 orders of magnitude faster than previously reported ARPs. The GO@FeNPs catalytic membrane may offer potential advantages of nanoconfinement and facilitated electron shuttling in addition to the high surface area of the fine FeNPs, leading to the remarkable ARP performance. The GO@FeNPs membrane showed excellent stability, maintaining >97.0% bromate removal over 20 cycles of repeated runs. The membrane can also be applied for fast catalytic reduction of other oxyanions, showing >98.0% removal of nitrate and chlorate. This work may present a viable option for utilizing high-performance reductive catalytic membranes for water decontamination.

A Novel Thermoresponsive Catalytic Membrane with Multiscale Pores Prepared via Vapor-Induced Phase Separation.

A novel thermoresponsive catalytic polyethersulfone membrane with multiscale pores is developed by constructing silver nanoparticles (Ag NPs) loaded poly(N-isopropylacrylamide) (PNIPAM) nanogels on pore walls of cellular pores as thermoresponsive gates and catalysts via vapor-induced phase separation. The Ag NPs are stably immobilized on the PNIPAM nanogels by an in situ reduction method based on the versatile adhesion and reduction properties of polydopamine. The micrometer cellular pores decorated with Ag NPs loaded PNIPAM nanogels are formed throughout the membrane and act as numerous microreactors with a large pore surface. The proposed membrane exhibits both satisfactory thermoresponsive characteristics and stable catalytic properties. The effects of operation temperature and reactant concentration of feed solution on the catalytic properties are investigated systematically. The results show that the apparent kinetic rate constant of catalytic reduction of 4-nitrophenol (4-NP) in water by reductant sodium borohydride (NaBH4 ), is ranging from 3.7 to 37.9 min-1 at temperatures from 20 to 45 ºC and the molar ratio of NaBH4 to 4-NP from 100:1 to 500:1. When the reactant concentration in feed solution fluctuates, the permeability or throughput of the membrane is simply adjusted by virtue of the thermoresponsive characteristics of membranes to achieve high catalytic conversion of reactant.

Special Issue "Membrane Catalysis".

Membrane technology is recognized as a scientific sector of multidisciplinary interest.[...].

Advancements in Nanoenabled Membrane Distillation for a Sustainable Water-Energy-Environment Nexus.

The emergence of nano innovations in membrane distillation (MD) has garnered increasing scientific interest. This enables the exploration of state-of-the-art nano-enabled MD membranes with desirable properties, which significantly improve the efficiency and reliability of the MD process and open up opportunities for achieving a sustainable water-energy-environment (WEE) nexus. This comprehensive review provides broad coverage and in-depth analysis of recent innovations in nano-enabled MD membranes, focusing on their role in achieving desirable properties, such as strong liquid-repellence, high resistance to scaling, fouling, and wetting, as well as efficient self-heating and self-cleaning functionalities. The recent developments in nano-enhanced photothermal-catalytic applications for water-energy co-generation within a single MD system are also discussed. Furthermore, the bottlenecks are identified that impede the scale-up of nanoenhanced MD membranes and a future roadmap is proposed for their sustainable commercialiation. This holistic overview is expected to inspire future research and development efforts to fully harness the potential of nano-enabled MD membranes to achieve sustainable integration of water, energy, and the environment.

Advanced Oxidation Processes Coupled to Nanofiltration Membranes with Catalytic Fe0 Nanoparticles in Symmetric and Asymmetric Polyelectrolyte Multilayers.

The in situ synthesis of Fe0 particles using poly-(acrylic acid) (PAA) is an effective tool for fabricating catalytic membranes relevant to advanced oxidation processes (AOPs). Through their synthesis in polyelectrolyte multilayer-based nanofiltration membranes, it becomes possible to reject and degrade organic micropollutants simultaneously. In this work, we compare two approaches, where Fe0 nanoparticles are synthesized in or on symmetric multilayers and asymmetric multilayers. For the membrane with symmetric multilayers (4.0 bilayers of poly (diallyldimethylammonium chloride) (PDADMAC)/PAA), the in situ synthesized Fe0 increased its permeability from 1.77 L/m2/h/bar to 17.67 L/m2/h/bar when three Fe2+ binding/reducing cycles were conducted. Likely, the low chemical stability of this polyelectrolyte multilayer allows it to become damaged through the relatively harsh synthesis. However, when the in situ synthesis of Fe0 was performed on top of asymmetric multilayers, which consist of 7.0 bilayers of the very chemically stable combination of PDADMAC and poly(styrene sulfonate) (PSS), coated with PDADMAC/PAA multilayers, the negative effect of the Fe0 in situ synthesized can be mitigated, and the permeability only increased from 1.96 L/m2/h/bar to 2.38 L/m2/h/bar with three Fe2+ binding/reducing cycles. The obtained membranes with asymmetric polyelectrolyte multilayers exhibited an excellent naproxen treatment efficiency, with over 80% naproxen rejection on the permeate side and 25% naproxen removal on the feed solution side after 1 h. This work demonstrates the potential of especially asymmetric polyelectrolyte multilayers to be effectively combined with AOPs for the treatment of micropollutants (MPs).

Membrane-based nanoconfined heterogeneous catalysis for water purification: A critical review✰.

Progress in heterogeneous advanced oxidation processes (AOPs) is hampered by several issues including mass transfer limitation, limited diffusion of short-lived reactive oxygen species (ROS), aggregation of nanocatalysts, and loss of nanocatalysts to treated water. These issues have been addressed in recent studies by executing the heterogeneous AOPs in confinement, especially in the nanopores of catalytic membranes. Under nanoconfinement (preferably at the length of less than 25 nm), the oxidant-nanocatalyst interaction, ROS-micropollutant interaction and diffusion of ROS have been observed to significantly improve, which results in enhanced ROS yield and mass transfer, improved reaction kinetics and reduced matrix effect as compared to conventional heterogenous AOP configuration. Given the significance of nanoconfinement effect, this study presents a critical review of the current status of membrane-based nanoconfined heterogeneous catalysis system for the first time. A succinct overview of the nanoconfinement concept in the context of membrane-based nanofluidic platforms is provided to elucidate the theoretical and experimental findings related to reaction kinetics, reaction mechanisms and molecule transport in membrane-based nanoconfined AOPs vs. conventional AOPs. In addition, strategies to construct membrane-based nanoconfined catalytic systems are explained along with conflicting arguments/opinions, which provides critical information on the viability of these strategies and future research directions. To show the desirability and applicability of membrane-based nanoconfined catalysis systems, performance governing factors including operating conditions and water matrix effect are particularly focused. Finally, this review presents a systematic account of the opportunities and technological constraints in the development of membrane-based nanoconfined catalytic platform to realize effective micropollutant elimination in water treatment.

Preparation and Characterization of Strongly Sulfonated Acid Block and Random Copolymer Membranes for Acetic Acid Esterification with 2-Propanol.

In this paper, we report the synthesis of block and random copolymers of 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) and methyl methacrylate (MMA), with different AMPS feed ratios. These solution-processable copolymers with strongly sulfonated acid groups resulted in membranes with tunable ion exchange (IEC) and water absorption capacities. AFM images confirmed the microphase separation of PAMPS-b-PMMA-1:1 block copolymer membrane, annealed under the appropriate conditions. The resulting copolymers from the random combination of a 1:1 molar ratio of AMPS and MMA monomers are effective at enhancing the esterification conversion of acetic acid, when compared with a reaction catalyzed by PAMPS-b-PMMA block copolymers and the previously studied catalytic membranes. With the PAMPS-co-PMMA-1:1 membrane, the esterification reaction using acetic acid achieved 85% isopropyl acetate. These results are closely correlated with the increase in IEC (2.63 mmol H+g-1) and the relationship between weight loss (20.3%) and swelling degree (68%) in 2-propanol.

Catalytic Reduction of Graphene Oxide Membranes and Water Selective Channel Formation in Water-Alcohol Separations.

Graphene oxide (GO) is a promising membrane system for chemical separation applications due to its 2-D nanofluidics properties and an ability to control interplanar spacing for selectivity. The permeance of water, methanol (MeOH) and isopropyl alcohol (IPA) through 5 µm thick membranes was found to be 0.38 ± 0.15, 0.33 ± 0.16 and 0.42 ± 0.31 LMH/bar (liter/m2·h·bar), respectively. Interestingly, the permeance of a water-alcohol mixture was found to be dramatically lower (~0.01 LMH/bar) than any of its components. Upon removing the solvent mixture, the transmembrane flux of the pure solvent was recovered to near the original permeance. The interlayer space of a dried GO membrane was found to be 8.52 Å, which increased to 12.19 Å. 13.26 Å and 16.20 Å upon addition of water, MeOH and IPA. A decrease in d-space, about 2 Å, was consistently observed when adding alcohol to water wetted GO membrane and an optical color change and reduction in permeance. A newly proposed mechanism of a partial reduction of GO through a catalytic reaction with the water-alcohol mixture is consistent with experimental observations.

Semiconducting graphitic carbon nitride integrated membranes for sustainable production of clean water: A review.

Semiconducting membranes integrated with nanomaterials have placed themselves in new emerging researches tremendously for seawater desalination, oil-water separation, disinfection, removal of inorganic as well as organic pollutants. Howbeit, only nanoparticles unified membranes show quite a lot lags in their performance, although some of these particles associated with the demerits of high cost. In contrast, graphitic carbon nitride incorporated membranes offered improved aforementioned properties corresponding to absolute essential qualities such as cost-effective, environmentally friendly, easy-to-operate, green manufacturing, anti-fouling, and low energy consumption. Moreover, their high mechanical strength, high stability against harsh environment and long-term utilization without flux reduction are strong plus. Even though there are some undeniable downsides of these membranes in real world applications as bulk synthesis, consistent dispersion of graphitic carbon nitride, low photocatalytic efficiency etc. Accordingly, in the present article, these frailties of the membranes having graphitic carbon nitride as a filler and their respective synthesis procedures and properties are discussed. A comprehensive analysis over the application of semiconducting graphitic carbon nitride incorporated membranes with and without special surface modification; and exploration of the future challenges and difficulties associated to these membranes are also reviewed. Consequently, the current article provides brief overview about graphitic carbon nitride integrated composite membranes as well as their applications, and it finished up with new thoughts of further improvements/modifications to overcome their shortcomings in actual environmental conditions.

A Facile and Scalable Route to the Preparation of Catalytic Membranes with in Situ Synthesized Supramolecular Dendrimer Particle Hosts for Pt(0) Nanoparticles Using a Low-Generation PAMAM Dendrimer (G1-NH2) as Precursor.

Since the first reports of Cu dendrimer-encapsulated nanoparticles (DENs) published in 1998, the dendrimer-templating method has become the best and most versatile method for preparing ultrafine metallic and bimetallic nanoparticles (1-3 nm) with well-defined compositions, high catalytic activity, and tunable selectivity. However, DENs have remained for the most part model systems with limited prospects for scale up and integration into high-performance and reusable catalytic modules and systems for industrial-scale applications. Here, we describe a facile and scalable route to the preparation of catalytic polyvinylidene fluoride (PVDF) membranes with in situ synthesized supramolecular dendrimer particles (SDPs) that can serve as hosts and containers for Pt(0) nanoparticles (2-3 nm). These new catalytic membranes were prepared using a reactive encapsulation process similar to that utilized to prepare Pt DENs by addition of a reducing agent (sodium borohydride) to aqueous complexes of Pt(II) + G4-OH/G6-OH polyamidoamine (PAMAM) dendrimers. However, the SDPs (2.4 µm average diameter) of our new mixed matrix PVDF-PAMAM membranes were synthesized in the dope dispersion without purification prior to film casting using (i) a low-generation PAMAM dendrimer (G1-NH2) as particle precursor and (ii) epichlorohydrin, an inexpensive functional reagent, as cross-linker. In addition, the membrane PAMAM particles contain secondary amine groups (∼1.9 mequiv per gram of dry membrane), which are more basic and thus have higher Pt binding affinity than the tertiary amine groups of the G4-OH and G6-OH PAMAM dendrimers. Proof-of-concept experiments show that our new PVDF-PAMAM-G1-Pt/membranes can serve as highly active and reusable catalysts for the hydrogenation of alkenes and alkynes to the corresponding alkanes using (i) H2 at room temperature and a pressure of 1 bar and (ii) low catalyst loadings of ∼1.4-1.6 mg of Pt. Using cyclohexene as model substrate, we observed near quantitative conversion to cyclohexane (∼98%). The regeneration studies showed that our new Pt/membrane catalysts are stable and can be reused for five consecutive reaction cycles for a total duration of 120 h including 60 h of heating at 100 °C under vacuum for substrate, product, and solvent removal with no detectable loss of cyclohexene hydrogenation activity. The overall results of our study point to a promising, versatile, and scalable path for the integration of catalytic membranes with in situ synthesized SDP hosts for Pt(0) nanoparticles into high-throughput modules and systems for heterogeneous catalytic hydrogenations, an important class of reactions that are widely utilized in industry to produce pharmaceuticals, agrochemicals, and specialty chemicals.

Simultaneous AuIII Extraction and In†Situ Formation of Polymeric Membrane-Supported Au Nanoparticles: A Sustainable Process with Application in Catalysis.

A polymeric membrane-supported catalyst with immobilized gold nanoparticles (AuNPs) was prepared through the extraction and in situ reduction of AuIII salts in a one-step strategy. Polymeric inclusion membranes (PIMs) and polymeric nanoporous membranes (PNMs) were tested as different membrane-support systems. Transport experiments indicated that PIMs composed of cellulose triacetate, 2-nitrophenyloctyl ether, and an aliphatic tertiary amine (Adogen 364 or Alamine 336) were the most efficient supports for AuIII extraction. The simultaneous extraction and reduction processes were proven to be the result of a synergic phenomenon in which all the membrane components were involved. Scanning electron microscopy characterization of cross-sectional samples suggested a distribution of AuNPs throughout the membrane. Transmission electron microscopy characterization of the AuNPs indicated average particle sizes of 36.7 and 2.9 nm for the PIMs and PNMs, respectively. AuNPs supported on PIMs allowed for >95.4 % reduction of a 0.05 mmol L-1 4-nitrophenol aqueous solution with 10 mmol L-1 NaBH4 solution within 25 min.

Ag Nanoparticle/Polydopamine-Coated Inverse Opals as Highly Efficient Catalytic Membranes.

Polymeric three-dimensional inverse-opal (IO) structures provide unique structural properties useful for various applications ranging from optics to separation technologies. Despite vast needs for IO functionalization to impart additional chemical properties, this task has been seriously challenged by the intrinsic limitation of polymeric porous materials that do not allow for the easy penetration of waterborne moieties or precursors. To overcome this restriction, we present a robust and straightforward method of employing a dipping-based surface modification with polydopamine (PDA) inside the IO structures, and demonstrate their application to catalytic membranes via synthetic incorporation of Ag nanoparticles. The PDA coating offers simultaneous advantages of achieving the improved hydrophilicity required for the facilitated infiltration of aqueous precursors and successful creation of nucleation sites for a reduction of growth of the Ag nanoparticles. The resulting Ag nanoparticle-incorporated IO structures are utilized as catalytic membranes for the reduction of 4-nitrophenol to its amino derivatives in the presence of NaBH4. Synergistically combined characteristics of high reactivity of Ag nanoparticles along with a greatly enhanced internal surface area of IO structures enable the implementation of remarkably improved catalytic performance, exhibiting a good conversion efficiency greater than 99% while minimizing loss in the membrane permeability.