Photoresponsive Membrane Research Articles

Spiropyran molecular aggregates implanted photo-responsive graphene oxide membrane with self-cleaning ability for enhanced water purification

Stimuli-responsive separation membranes with adjustable interfacial properties are highly desired for energy-efficient and sustainable water purification, owing to their exceptional antifouling capability and separation selectivity. However, the construction of highly efficient responsive membranes continues to present a substantial challenge. Herein, photo-responsive spiropyran (SP) molecular aggregates obtained via a "good-poor" solvent self-assembly strategy were implanted into lamellar graphene oxide (GO) membrane. The obtained GO/SP membrane with enriched water transport channels and enhanced hydrophilicity demonstrated superior water permeability (95.0 L h−1 m−2 bar−1). Benefiting from the reversible photoisomerization of SP molecules between the hydrophobic SP upon light irradiation and the hydrophilic zwitterionic merocyanine (MC) in dark conditions, the GO/SP membrane possessed captivating photo-response property verified by tunable water permeability and molecular rejection. Theoretical calculation revealed that the thermodynamic interface energy between bovine serum albumin (BSA) and membrane surface changed from attraction in dark conditions to repulsion under light conditions. Consequently, the water permeability of BSA-fouled membranes could recover to 96.2 % of its initial level after light irradiation, exhibiting fascinating photo-driven self-cleaning capability. The designed photo-responsive membrane with feasible membrane fouling control holds great promise for efficient water purification.

Fabrication of polypyrrole-graphitic carbon nitride nanocomposite containing hyper-cross-linked polyamide photoresponsive membrane with self-cleaning properties for water decontamination and desalination applications

A new photoresponsive hyper-cross-linked polyamide thin film nanocomposite nanofiltration membrane was fabricated by incorporating polypyrrole-graphitic carbon nitride (PPy@G-CN) nanocomposite photo-catalyst through interfacial polymerization for water decontamination and desalination applications. An ultrafiltration polysulfone/polyethylene terephthalate (PSf/PET) membrane support was prepared through phase inversion and a hyper-cross-linked PPy@G-CN/polyamide active layer was fabricated on the PSf/PET by using N,N-bis(2-aminoethyl)-1,3-propanediamine (as an aqueous amine) and terephthaloyl chloride (TPC as a non-aqueous solution) while different amounts of PPy@G-CN nanocomposite photo-catalyst were homogeneously dispersed in aqueous amine solution before interfacial polymerization reaction and three fabricated membranes were named as x%-PPy@G-CN/HCPAMs. Out of the three fabricated membranes, 0.10%-PPy@G-CN/HCPAM was found to be the best performing membrane in terms of flux and % rejection. The maximum water flux of the membrane was found to be 78.57 L m−2 h−1 at 25 bars with rejection of Eriochrom Black T (EBT) approaching 99.90% at 20 bar. Moreover, the 0.10%-PPy@G-CN/HCPAM also showed a remarkable rejection of 79.58% and 72.88% for MgSO4 and NaCl, respectively. The 0.10%-PPy@G-CN/HCPAM showed exceptionally high photocatalytic self-cleaning as all of the organic fouling (coloration) due to EBT was removed under simulated solar light irradiation for 1 h leading to photocatalytic degradation of EBT. The 0.10%-PPy@G-CN/HCPAM membrane remained physically intact even after elongated exposure to light source.

Bioinspired photo-responsive membrane enhanced with "light-cleaning" feature for controlled molecule release.

Inspired by the stomatal feature of plant leaves, a photo-responsive membrane was developed to enhance the removal of irreversible membrane fouling and to control molecule release. Photo-responsive polymers were prepared by reacting the amine group of 4-amineazobenzene with about 3, 5 and 9 out of 12 carboxylic groups of PMAA which was grafted from P(VDF-CTFE) with a certain length. Subsequently, high-flux photo-responsive membranes (PRMs) were prepared from the heterogeneous polymers with different contents of photo-switchable azobenzene following a non-solvent-induced phase-inversion protocol. The pore size and surface hydrophilicity of PRMs could be reversibly increased by switching visible light to UV irradiation, which dramatically enhanced the backflushing efficiency on PRMs under UV irradiation. The "light-cleaning" process could recover more than 90% of the irreversible flux decline caused by typical organic foulant (BSA) and biological foulant (E. coli) on PRMs. The higher the content of azobenzene, the more obvious the pore size and hydrophilicity variation after light switching but the smaller the absolute pore size observed for PRMs. On the other hand, the light-switching gates of PRMs enabled the controlled release of molecules with different sizes. The novel PRM provided an efficient solution to mitigate irreversible membrane fouling and a light-triggered molecule release protocol, which would improve the membrane performance and further expand the application field of the membrane.

A photo-responsive membrane for tailored drug delivery with spatially and temporally controlled release.

Accurate delivery of therapeutics to tumor regions and effective sparing of normal tissue structures are important principles for the treatment of widespread metastases or malignant lesions in close proximity to vital organs. However, the currently available drug delivery techniques do not support precise drug release within the identified disease margins. We propose a tailored drug delivery strategy that utilizes a photo-responsive material in combination with tumor margin imaging for automated and tailored release of therapeutics. As a proof of concept, a poly(ethylene oxide)-b-PSPA (PEO-b-PSPA) diblock copolymer is synthesized by spiropyran (SP) polymerization. A photo-responsive membrane (PRM) is formed and irradiated with light sources of different wavelengths. Switching irradiation between ultraviolet light (UV) and green light (Vis) controls the permeability of the PRM in coincidence with the programmed irradiation patterns. The dynamic process of photo-switchable drug permeation through the PRM is modeled and compared with the experimental results. The strategy of tailored drug release is verified using both regular geometric shapes and metastatic cancer images. The therapeutic effect of this tailored drug release strategy is demonstrated in vitro in human breast cancer cells. Our pilot study implies the technical potential of using photo-responsive carriers for image-guided chemotherapy with precisely controlled drug release patterns.

Molecularly engineered switchable photo-responsive membrane in gas separation for environmental protection

In recent years, stimuli-responsive materials have garnered interest due to their ability to change properties when exposed to external stimuli, making it useful for various applications including gas separation. Light is a very attractive trigger for responsive materials due to its speedy and non-invasive nature as well as the potential to reduce energy costs significantly. Even though light is deemed as an appealing stimulus for the development of stimuli-responsive materials, this avenue has yet to be extensively researched, as evidenced by the fewer works done on the photo-responsive membranes. Of these, there are even less research done on photo-responsive materials for the purpose of gas separation, thus, we have collected the examples that answer both these criteria in this review. This review covers the utilisation of photo-responsive materials specifically for gas separation purposes. Photo-chromic units, their integration into gas separation systems, mechanism and research that have been done on the topic so far are discussed.

Photo-responsive membrane surface: Switching from bactericidal to bacteria-resistant property

In this paper, a photo-responsive bactericidal and bacteria-resistant membrane was successfully prepared via the integration of atom transfer radical polymerization (ATRP) and click chemistry. Azide-functionalized polycationic poly (N, N-dimethyl-N-(2-(methacryloyloxy)ethyl)-N-((2-nitrobenzyl)oxy)-2-oxoethanaminium bromide) (PDMAEMA-NBE) was synthesized by ATRP. Then, the PDMAEMA-NBE was clicked on alkynyl-functionalized polyethersulfone (PES) membrane surface, and proved by X-ray photoelectron spectrometer (XPS). Upon UV irradiation, the polycationic surface would switch to polyzwitterionic one. Before and after the irradiation, the zeta potentials of the surface altered from +14.7 to −3.8mV, and the water contact angle decreased from 64.0° to 52.7°. The polycationic surface exhibited excellent bactericidal property and the dead bacteria could detach from the polyzwitterionic surface induced by the subsequent UV irradiation. It demonstrated that the designing of photo-responsive membrane surface could be a new strategy for antibacterial adhesion.

Fabrication of Photocontrolled Surfaces for Oil/Water Separation through Sulfur(VI) Fluoride Exchange.

Smart surfaces with controllable wettability have attracted substantial interest owing to the potential use of these materials for the separation of oil from oily water caused by frequent oil-spill accidents. Because there are few separation materials on the market that are capable of switching between hydrophobicity and hydrophilicity, this work reports an efficient and low-cost method to fabricate a photoresponsive membrane through the sulfur(VI) fluoride exchange reaction (SuFEx) between poly(4-vinylphenol sulfofluoridate) and (E)-1-(4-(tert-butoxy)phenyl)-2-(4-(trifluoromethoxy)phenyl)diazene. The resulting material displays switchable wettability between hydrophobic and hydrophilic states when subjected to ultraviolet or visible irradiation. This membrane can be recycled (greater than five times) and features superior efficiency (up to 97.9 %) for the separation of oils that have both higher and lower densities than water. This work is the first proof-of-concept application of SuFEx to fabricate functional materials for environmental remediation.

Self-Cleaning Membranes from Comb-Shaped Copolymers with Photoresponsive Side Groups.

In this study, we present a novel self-cleaning, photoresponsive membrane that is capable of removing predeposited foulant layers upon changes in surface morphology in response to UV or visible light irradiation while maintaining stable pore size and water permeance. These membranes were prepared by creating thin film composite (TFC) membranes by coating a porous support membrane with a thin layer of novel comb-shaped graft copolymers at two side-chain lengths featuring polyacrylonitrile (PAN) backbones and photoreactive side chains, synthesized by atom transfer radical polymerization (ATRP). Photoregulated control over membrane properties is attained through a light-induced transition, where the side chains switch between a hydrophobic spiropyran (SP) state and a zwitterionic, hydrophilic merocyanine (MC) state. The light-induced switch between the SP and MC forms changes surface hydrophilicity and causes morphological changes on the membrane surface as evidenced by atomic force microscopy (AFM). Before any phototreatment, the as-coated membrane surface comprises mostly hydrophobic SP groups that allow the adsorption of organic solutes such as proteins the membrane surface, reducing flow rate. Once exposed to UV light, conversion of the SP groups to hydrophilic MC groups leads to the release of adsorbed molecules and the full recovery of the initial water flux. A fouled membrane in the more hydrophilic MC form is also capable of self-cleaning upon conversion to the less hydrophilic SP form by visible light irradiation. The self-cleaning behavior observed for this system, where the surface became less hydrophilic but also experienced a morphological change, demonstrates a novel mechanism that has a mechanical component in addition to the changes in hydrophilicity. It is also the first report, to our knowledge, of self-cleaning performance accompanied by a decrease in hydrophilicity.

Photocontrol of ion permeation in lipid vesicles with (bola)amphiphilic spirooxazines.

Three (bola)amphiphilic spirooxazines have been synthesized and their photochromism has been characterized. The large biphotochromic structure of 2 significantly affects its conformational flexibility and the rate constants for thermal ring closure are particularly dependent on the lipid phase state. Two comprehensive ion permeation studies were performed to examine the effect of spirooxazine inclusion and isomerization on membrane permeability. In all cases, the open-ring isomers of these spirooxazines are more disruptive in bilayer membranes than their closed-ring isomers. Further, the rate of ion permeation and net release are highly dependent on the lipid bilayer phase state and the relative position of the photochromic moiety in the bilayer membrane. Moreover, the difference in potassium ion permeability under UV and visible irradiation is more pronounced than previously reported photoresponsive membrane disruptors with reversible photocontrols.

Photo Induced Membrane Separation for Water Purification and Desalination Using Azobenzene Modified Anodized Alumina Membranes.

Water purification and desalination to produce end-use water are important agendas in 21st century, because the global water shortage is becoming increasingly serious. Those processes using light energy, especially solar energy, without the consumption of fossil fuels are desired for creating sustainable society. For these earth-friendly water treatments, nanoporous materials and membranes are expected to provide new technologies. We have reported before that the repetitive photo isomerization of azobenzene groups between the trans and cis isomers induced by the simultaneous irradiation of UV and visible lights accelerates the molecular movement of nearby molecules in nanoporous materials. After further studies, we recently found that the permeation of water through azobenzene modified anodized alumina membranes as a photo responsive nanoporous membrane was achieved by the simultaneous irradiation of UV and visible lights, while no water penetration occurred under no light, only single UV or visible light. The photo induced permeation of water was promoted by the vaporization of water with the repetitive photo isomerization of azobenzene. This membrane permeation achieved the purification of water solutions, because dye molecules and a protein dissolved in aqueous solutions were not involved in the photo induced penetrated water. When 3.5% of sodium chloride solution as model seawater was employed for this membrane separation, the salt content of the permeated water was less than 0.01% to accomplish the complete desalination of seawater.

A Generalized System for Photo-Responsive Membrane Rupture in Polymersomes.

Polymersomes are vesicles whose membranes are comprised of self-assembled block co-polymers. We recently showed that co-encapsulating conjugated multi-porphyrin dyes in a polymersome membrane with ferritin protein in the aqueous lumen confers photo-lability to the polymersome. In the present study, we illustrate that the photo-lability can be extended to vesicles containing dextran, an inert and inexpensive polysaccharide, as the luminal solute. Here we explore how structural features of the polymersome/porphyrin/dextran composite affect its photo-response. Increasing dextran molecular weight, decreasing block copolymer molecular weight, and altering fluorophore-membrane interactions results in increasing the photo-responsiveness of the polymersomes. Amphiphilic interactions of the luminal encapsulant with the membrane coupled with localized heat production in the hydrophobic bilayer likely cause differential thermal expansion in the membrane and the subsequent membrane rupture. This study suggests a general approach to impart photo-responsiveness to any biomimetic vesicle system without chemical modification, as well as a simple, bio-inert method for constructing photo-sensitive carriers for controlled release of encapsulants.

Amphiphilic block copolymers significantly influence functions of bacteriorhodopsin in water

This paper investigates the effects of a macromolecular amphiphile poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (PEO–PPO–PEO) on a photoresponsive membrane protein, bacteriorhodopsin (BR). After incubation of BR in EO23–PO65–EO23 (P123) solution, BR maintained its function as a light-driven proton pump; however, the rate of proton uptake and lifetime of the M intermediate in the photocycle of BR upon illumination were, under appropriate conditions, prolonged by about three orders of magnitude compared with that of native BR, even at neutral pH. Measurements using circular dichroism spectroscopy and dynamic light scattering indicated that BR molecules were still in a trimer state after treatment with the copolymers. This is quite different to BR, which showed a much slower photoresponse during drying. The BR–P123 assemblies did not exhibit significantly different photoresponsive behavior with changes to the water content, which implied that in the case of dried BR films or dried BR–polymer films, the elongation of the M decay may be caused not by lack of water molecules necessary for proton transfer, but by protein immobilization. Determination of the critical micelle concentration of P123 with and without BR revealed that this prolongation effect is closely related to the formation of micelles. The above phenomenon was also observed with 6 other Pluronic copolymers. In solutions of small molecular detergents, such as Triton X-100, the photoresponse of BR was prolonged as well; the extent of prolongation was, however, much less than in solutions of macromolecular amphiphiles. The formation of a local polymer coating due to self assembly of the copolymer and protein molecules might be responsible for this very significant prolongation effect, which is beneficial for the potential application of BR as an information material.

Development of Photoresponsive Membrane SystemsComposed of Photochromic Polymers

Development of Photoresponsive Membrane SystemsComposed of Photochromic Polymers

Application of Photoresponsive Polymers Carrying Crown Ether and Spirobenzopyran Side Chains to Photochemical Valve

A vinyl copolymer carrying crown ether and spirobenzopyran side chains, which undergoes significant photoinduced rheology changes, i.e., contraction and extension of its polymer chain, was applied to a material for photocontrol system of solvent permeation rate, so-called, photochemical valve. Macroporous polyethylene membranes coated by the crown ether-spirobenzopyran copolymer can work as a functional membrane controlling solvent permeation rate photochemically. UV-light irradiation on the photoresponsive membrane decreased the permeation rate of hexane, due to the increased polarity of the membrane pore, which was in turn derived from the photoisomerization of its spirobenzopyran moiety to the corresponding ionic merocyanine form. The following visible-light irradiation on the membrane restored the permeation rate by isomerization back to the electrically neutral spiropyran form. To the contrary, the permeation of ethanol through the membrane was enhanced by UV-light irradiation due to the increase in the apparent membrane pore size induced by the polymer chain contraction and vice versa by visible light. Similar photoresponses in the permeation rate of nonpolar and polar solvents were also observed with a sintered glass filter modified chemically by both silane-coupling reagents containing crown ether and spirobenzopyran moieties.

Photo-responsive membranes : III. Photo-induced potential across a retinal-entrapped membrane

A photo-responsive membrane was prepared by casting a solution of 11- cis-retinal, phosphatidyl choline, and triacetyl cellulose. The membrane-bound 11- cis-retinal exhibited three steps of photospectroscopic change on light irradiation. The photoisomerization of the membrane-bound 11- cis-retinal appeared to be complete on light irradiation for 1-2 rain. The potential difference across the membrane drastically changed under these conditions. On the other hand, a membrane incorporating only 11- cis-retinal exhibited little light-induced transmembrane potential. The light-induced change in membrane potential occurred in association with the photo-isomerization of the membrane-bound 11- cis-retinal. Phosphatidyl choline is thought to play an important role in transducing the conformational change of 11- cis-retinal to the dynamic photo-response in membrane potential.

Photo-responsive membranes : I. Light-induced potential changes across membranes incorporating a photochromic compound

A photo-responsive membrane has been prepared by casting an acetone solution of a spiropyran compound, phosphatidyl choline, and acetyl cellulose. Since the membrane showed excellent transparency in either the dry or wet state, absorption spectra of bound spiropyran were easily obtained. The membrane-bound spiropyran exhibited normal photochromism: a colored form under UV irradiation and a colorless form under visible irradiation p]The potential difference across the membrane was drastically changed by switching from visible light to UV light irradiation. This light-induced membrane potential change was reversible and was synchronized with a change in absorbance of the membrane-bound spiropyran at 533 nm. A change of membrane charge density associated with the photoisomerization of spiropyran is thought to cause this dynamic photo-response in membrane potential