Responsive Macroscopic Materials From Self‐Assembled Cross‐Linked SiO2‐PNIPAAm Core/Shell Structures

A way to obtain macroscopic responsive materials from silicon‐oxide polymer core/shell microstructures is presented. The microparticles are composed of a 60 nm SiO₂‐core with a random copolymer corona of the temperature responsive poly‐N‐isopropylacrylamide (PNIPAAm) and the UV‐cross‐linkable 2‐(dimethyl maleinimido)‐N‐ethyl‐acrylamide. The particles shrink upon heating and form a stable gel in both water and tetrahydrofuran (THF) at 3–5 wt% particle content. Cross‐linking the aqueous gel results in shrinkage when the temperature is increased above the lower critical solution temperature and it regains its original size upon cooling. By freeze drying with subsequent UV irradiation, thin stable layers are prepared. Stable fibers are produced by extruding a THF gel into water and subsequent UV irradiation, harnessing the cononsolvency effect of PNIPAAm in water/THF mixtures. The temperature responsiveness translates to the macroscopic materials as both films and fibers show the same collapsing behavior as the microcore/shell particle. The collapse and re‐swelling of the materials is related to the expelling and re‐uptake of water, which is used to incorporate gold nanoparticles into the materials by a simple heating/cooling cycle. This allows for future applications, as various functional particles (antibacterial, fluorescence, catalysis, etc.) can easily be incorporated in these systems.     

Understanding and Controlling the Self‐Folding Behavior of Poly (N‐Isopropylacrylamide) Microgel‐Based Devices

Poly(N‐isopropylacrylamide) (pNIPAm) microgel‐based materials can be fabricated that self‐fold into three‐dimensional structures in response to changes in the environmental humidity. The materials are composed of a semi‐rigid polymer substrate coated with a thin layer of Au; the Au layer is subsequently coated with a pNIPAm‐based microgel layer and finally covered with a solution of polydiallyldimethylammonium chloride (pDADMAC). The pDADMAC layer contracts upon drying causing the material to deform (typically bending); this deformation is completely reversible over many cycles as the environmental humidity is systematically varied. Here, by varying the size and aspect ratio of the polymer substrate, it is possible to develop a set of empirical rules that can be applied to predict the material's self‐folding behavior. From these rules, materials that self‐fold from two‐dimensional, flat objects into discrete three‐dimensional structures, which are fully capable of unfolding and folding multiple times in response to humidity, are designed.     

Highly Robust Indium‐Free Transparent Conductive Electrodes Based on Composites of Silver Nanowires and Conductive Metal Oxides

A hybrid approach for the realization of In‐free transparent conductive layers based on a composite of a mesh of silver nanowires (NWs) and a conductive metal‐oxide is demonstrated. As metal‐oxide room‐temperature‐processed sol–gel SnO_x or Al:ZnO prepared by low‐temperature (100 °C) atomic layer deposition is used, respectively. In this concept, the metal‐oxide is intended to fuse the wires together and also to “glue” them to the substrate. As a result, a low sheet resistance down to 5.2 Ω sq^‐1 is achieved with a concomitant average transmission of 87%. The adhesion of the NWs to the substrate is significantly improved and the resulting composites withstand adhesion tests without loss in conductivity. Owing to the low processing temperatures, this concept allows highly robust, highly conductive, and transparent coatings even on top of temperature sensitive objects, for example, polymer foils, organic devices. These Indium‐ and PEDOT:PSS‐free hybrid layers are successfully implemented as transparent top‐electrodes in efficient all‐solution‐processed semitransparent organic solar cells. It is obvious that this approach is not limited to organic solar cells but will generally be applicable in devices which require transparent electrodes.     

Preparation of Smart Polymer/Carbon Nanotube Conjugates via Stimuli‐Responsive Linkages

In this paper, we modified carbon nanotubes with the thiol‐reactive species, subsequently combined the thiol‐coupling reaction and reversible addition‐fragmentation chain transfer (RAFT) polymerization to prepare temperature‐responsive PNIPAAm (poly(N‐isopropylacrylamide))‐carbon nanotube conjugates. The prepared PNIPAAm‐carbon nanotube conjugates have temperature‐responsive PNIPAAm chain, and disulfide linkages between PNIPAAm and carbon nanotube which are sensitive to bio‐stimuli such as glutathione, therefore dual‐responsive polymer‐carbon nanotube conjugates have been prepared.     

Hybrid Capsules via Self‐Assembly of Thermoresponsive and Interfacially Active Bionanoparticle–Polymer Conjugates

New bionanoparticles have been prepared from horse spleen ferritin by grafting thermoresponsive poly(N‐isopropyl acrylamide) (PNIPAAm) and photo‐crosslinkable 2‐(dimethyl maleinimido)‐N‐ethyl‐acrylamide (DMIAAm) from the protein surface. The 72 addressable amino groups on the exterior of HSF were modified with N‐hydroxysuccinimide‐activated 2‐bromo‐isobutyrate to form a macro‐initiator for atom transfer radical polymerization, which was performed in water/DMF solutions at low temperature. The modification of the HSF and the presence of the polymer shell were confirmed by size exclusion chromatography (SEC), sodium dodecyl sulfate‐polyacrylamide gel‐electrophoresis, transmission electron microscopy, and scanning force microscopy. The thermoresponsive behavior of the ferritin‐PNIPAAm conjugates was investigated in solution by UV–vis spectroscopy showing a phase transition in the form of a cloud point around 32 °C. Further, dynamic light scattering revealed an increasing hydrodynamic radius around this transition, indicating aggregation of the particles at elevated temperatures which was confirmed by transmission electron microscopy. Initial experiments show that the particles are highly surface active, much more than the individual components alone, which was demonstrated by pendant‐drop interfacial tension measurements. This leads to the fact that they form stable Pickering emulsions, i.e., emulsion droplets decorated with polymer‐modified bionanoparticles which can be cross‐linked successively. This allows the formation of capsules with thermoresponsiveness for controlled release purposes, e.g., in drug delivery.     

Unprecedentedly Tough,Folding‐Endurance,and Multifunctional Graphene‐Based Artificial Nacre with Predesigned 3D Nanofiber Network as Matrix

Mimicking the hierarchical brick‐and‐mortar architecture of natural nacre provides great opportunities for the design and synthesis of multifunctional artificial materials. The crucial challenge to push nacre‐mimetic functional materials toward practical applications is to achieve ample ductility, toughness, and folding endurance with simultaneously maintaining high‐level functional properties. In this study, the microstructure of nacre‐mimetics is reformed through predesigning a 3D nanofiber network to replace conventional polymer matrices. A unique sol–gel–film transformation approach is developed to fabricate a graphene‐based artificial nacre containing a preforming 3D, interconnective, inhomogeneous poly(p‐phenylene benzobisoxazole) nanofiber network. The fabulous coupling of the extensive sliding of graphene nanoplatelets and intensive stretching of the 3D nanofiber network over a large scale enables the artificial nacre to display natural nacre‐like deformation behavior, achieving ultralarge strain‐to‐failure (close to 35%), unprecedented toughness (close to 50 MJ m^?3), and fold endurance (no decrease in tensile properties after folding for 10 000 times or folding at increasing stress). The new levels of ductility, toughness, and folding endurance are integrated with outstanding thermal properties, including thermal conductivity (≈130 W m^?1 K^?1), thermal stability (520 °C) and nonflammability, rendering the lightweight nacre‐mimetics promising in flexible electronic devices, particularly for aerospace electronics.     

Nanopatterned Polymer Brushes for Triggered Detachment of Anchorage‐Dependent Cells

Surfaces modified with thermoresponsive poly(N‐isopropylacrylamide) (PNIPAAm) support mild and efficient harvesting of anchorage‐dependent cells. To enable cellular detachment, however, the surfaces must exhibit a narrow range of PNIPAAm thicknesses. In this work, this limitation is circumvented by introducing nanopatterns to grafted PNIPAAm brushes, eliminating the critical thickness requirement for cell‐culturing applications. Nanopatterned PNIPAAm surfaces are prepared using a combination of interferometric lithography (IL) and surface‐initiated polymerization. Above the lower critical solution temperature (LCST) of PNIPAAm (～32 °C), these surfaces support the attachment and proliferation of mammalian cells (e.g., fibroblasts and endothelial cells). Below the LCST of PNIPAAm, cells readily detach from the nanopatterned PNIPAAm surfaces without influence from the period of nanopatterns, which vary between 157 ± 9 nm to 1021 ± 17 nm. Cells selectively attach and proliferate on PNIPAAm nanopatterns as compared to thick unpatterned PNIPAAm, which is further exploited to spatially direct cellular growth to generate cellular micropatterns. Nanopatterned PNIPAAm surfaces provide a unique solution to the critical thickness issue for cell harvesting and facilitate spatial control of cellular growth on surfaces.     

Elasticity,Flexibility, and Ideal Strength of Borophenes

The mechanical properties of 2D boron—borophene—are studied by first‐principles calculations. The recently synthesized borophene with a 1/6 concentration of hollow hexagons (HH) is shown to have in‐plane modulus C up to 210 N m^?1 and bending stiffness as low as D = 0.39 eV. Thus, its Foppl–von Karman number per unit area, defined as C /D , reaches 568 nm^?2, over twofold higher than graphene's value, establishing the borophene as one of the most flexible materials. Yet, the borophene has a specific modulus of 346 m² s^?2 and ideal strength of 16 N m^?1, rivaling those (453 m² s^?2 and 34 N m^?1) of graphene. In particular, its structural fluxionality enabled by delocalized multicenter chemical bonding favors structural phase transitions under tension, which result in exceptionally small breaking strains yet highly ductile breaking behavior. These mechanical properties can be further tailored by varying the HH concentration, and the boron sheet without HHs can even be stiffer than graphene against tension. The record high flexibility combined with excellent elasticity in boron sheets can be utilized for designing advanced composites and flexible devices.     

Programmed Deformations of 3D‐Printed Tough Physical Hydrogels with High Response Speed and Large Output Force

Shape‐morphing hydrogels have emerging applications in biomedical devices, soft robotics, and so on. However, successful applications require a combination of excellent mechanical properties and fast responding speed, which are usually a trade‐off in hydrogel‐based devices. Here, a facile approach to fabricate 3D gel constructs by extrusion‐based printing of tough physical hydrogels, which show programmable deformations with high response speed and large output force, is described. Highly viscoelastic poly(acrylic acid‐co‐acrylamide) (P(AAc‐co‐AAm)) and poly(acrylic acid‐co‐N‐isopropyl acrylamide) (P(AAc‐co‐NIPAm)) solutions or their mixtures are printed into 3D constructs by using multiple nozzles, which are then transferred into FeCl₃ solution to gel the structures by forming robust carboxyl–Fe³⁺ coordination complexes. The printed gel fibers containing poly(N‐isopropyl acrylamide) segment exhibit considerable volume contraction in concentrated saline solution, whereas the P(AAc‐co‐AAm) ones do not contract. The mismatch in responsiveness of the gel fibers affords the integrated 3D gel constructs the shape‐morphing ability. Because of the small diameter of gel fibers, the printed gel structures deform and recover with a fast speed. A four‐armed gripper is designed to clamp plastic balls with considerable holding force, as large as 115 times the weight of the gripper. This strategy should be applicable to other tough hydrogels and broaden their applications.     

Thermally Responsive Biomineralization on Biodegradable Substrates

Biomineralization offers an elegant example of how nature can design complex, hierarchical, and structurally/morphologically controllable materials. In this work, the surface of bioactive substrates prepared from poly(L ‐lactic acid) and reinforced with Bioglass are modified by the graft polymerization of poly(N‐isopropylacrylamide), (PNIPAAm) after plasma activation. It is found that such treatment, together with temperature, could trigger the formation of apatite on the biodegradable substrate upon immersion in simulated body fluid above the PNIPAAm lower critical solution temperature (LCST); in contrast, no apatite is formed at room temperature. A control experiment on a material that is not subjected to surface treatment does not show any evidence of mineral deposition at the two analyzed temperatures. This “smart” biomineralization concept is combined with patterning methodologies to control the microstructure of the surface onto which PNIPAAm is grafted. In this case, the apatite is formed at 37 °C in the modified regions. We suggest that this concept could be extended in the biomimetic production of other minerals, where it would be triggered by another kind of stimulus (e.g., pH or ionic strength) in substrates with more complex geometries.     

Unambiguously Enhanced Ultraviolet Luminescence of AlGaN Wavy Quantum Well Structures Grown on Large Misoriented Sapphire Substrate

High‐quality epitaxy consisting of Al_1?xGa_xN/Al_1?yGayN multiple quantum wells (MQWs) with sharp interfaces and emitting at ≈280 nm is successfully grown on sapphire with a misorientation angle as large as 4°. Wavy MQWs are observed due to step bunching formed at the step edges. A thicker QW width accompanied by a greater accumulation of gallium near the macrostep edge than that on the flat‐terrace is observed on 4° misoriented sapphire, leading to the generation of potential minima with respect to their neighboring QWs. Consequently, a significantly enhanced photoluminescence intensity (at least ten times higher), improved internal quantum efficiency (six times higher at low excitation laser power), and a much longer carrier lifetime are achieved. Importantly, the wafer‐level output‐power of the ultraviolet light emitting diodes on 4° misoriented substrate is nearly increased by 2–3 times. This gain is attributed to the introduction of compositional inhomogeneities in AlGaN alloys induced by gallium accumulation at the step‐bunched region thus forming a lateral potential well for carrier localization. The experimental results are further confirmed by a numerical modeling in which a 3D carrier confinement mechanism is proposed. Herein, the compositional modulation in active region arising from the substrate misorientation provides a promising approach in the pursuit of high‐efficient ultraviolet emitters.     

Rationally Designed Dynamic Protein Hydrogels with Reversibly Tunable Mechanical Properties

Protein hydrogels have attracted considerable interest due to their potential applications in biomedical engineering. Creating protein hydrogels with dynamic mechanical properties is challenging. Here, the engineering of a novel, rationally designed protein‐hydrogel is reported that translates molecular level protein folding‐unfolding conformational changes into macroscopic reversibly tunable mechanical properties based on a redox controlled protein folding‐unfolding switch. This novel protein folding switch is constructed from a designed mutually exclusive protein. Via oxidation and reduction of an engineered disulfide bond, the protein folding switch can switch its conformation between folded and unfolded states, leading to a drastic change of protein's effective chain length and mechanical compliance. This redox‐responsive protein can be readily photochemically crosslinked into solid hydrogels, in which molecular level conformational changes (folding‐unfolding) can result in significant macroscopic changes in hydrogel's physical and mechanical properties due to the change of the effective chain length between two crosslinking points in the protein hydrogel network. It is found that when reduced, the hydrogel swells and is mechanically compliant; when oxidized, it swells to a less extent and becomes resilient and stiffer, exhibiting an up to fivefold increase in its Young's modulus. The changes of the mechanical and physical properties of this hydrogel are fully reversible and can be cycled using redox potential. This novel protein hydrogel with dynamic mechanical and physical properties could find numerous applications in material sciences and tissue engineering.     

Macroscopic Nanotemplating of Semiconductor Films with Hydrogen‐Bonded Lyotropic Liquid Crystals

Aqueous gel‐like lyotropic liquid crystals with extensive hydrogen bonding and nanoscale hydrophilic compartments have been used to define the growth of macroscopic nanotemplated CdS and CdTe thin films. These mesoporous semiconductor films contain a hexagonal array of 2.5 nm pores, 7 nm center‐to‐center, that extend in an aligned fashion perpendicular to the substrate. The CdS is deposited on a polypropylene substrate by a reaction between Cd(NO₃)₂ dissolved in the liquid crystal and H₂S transported via diffusion through the substrate. The CdTe is electrodeposited on indium‐tin‐oxide‐coated glass from TeO₂ and Cd(NO₃)₂, both of which are dissolved in the liquid‐crystal template. The porous nature of the CdTe films enables chemical transformations of the entire bulk of the film. As electrodeposited, the CdTe films are Te rich and, in contrast to a non‐templated film, the excess Te could be removed via a chemical treatment, proving the continuity of the pores in the nanotemplated films. These results suggest that liquid‐crystal lithography with hydrogen‐bonding amphiphiles may be a useful approach to create materials with nanoscale features over macroscopic dimensions.     

Formation of a Quasi‐Free‐Standing Single Layer of Graphene and Hexagonal Boron Nitride on Pt(111) by a Single Molecular Precursor

It is shown that on Pt(111) it is possible to prepare hexagonal boron nitride (h‐BN) and graphene (G) in‐plane heterojunctions from a single molecular precursor, by thermal decomposition of dimethylamine borane (DMAB). Photoemission, near‐edge X‐ray absorption spectroscopy, low energy electron microscopy, and temperature programmed desorption measurements indicate that the layer fully covers the Pt(111) surface. Evidence of in‐plane layer continuity and weak interaction with Pt substrate has been established. The findings demonstrate that dehydrogenation and pyrolitic decomposition of DMAB is an efficient and easy method for obtaining a continuous almost freestanding layer mostly made of G, h‐BN with only a low percentage (<3%) of impurities (B and N‐doped G domains or C‐doped h‐BN or boron carbonitride, BCN at the boundaries) in the same 2D sheet on a metal substrate, such as Pt(111), paving the way for the advancement of next‐generation G‐like‐based electronics and novel spintronic devices.     

Biasing Buckling Direction in Shape‐Programmable Hydrogel Sheets with Through‐Thickness Gradients

A photocrosslinkable poly( N , N ′‐diethylacrylamide) copolymer allows for the photolithographic fabrication of hydrogel sheets with nonuniform crosslinking density and swelling ratio. Using this material system, different 3D shapes with nonzero Gaussian curvature K are successfully programmed by prescribing a “metric” defined by in‐plane variations in swelling. However, this methodology does not control the direction of buckling adopted by each positive K feature, and therefore cannot controllably select between different isometric shapes defined by a single metric. Here, by introducing gradients in swelling through the thickness of the gel sheet by tuning the absorption of the UV‐light used for crosslinking, a preferential buckling direction is locally specified for each feature by the direction of UV exposure. By also controlling the strength of coupling between neighboring features, this is shown to be an effective method to program buckling direction of each unit within a canonical corrugated surface shape.     

Antibacterial Surface Coatings from Zinc Oxide Nanoparticles Embedded in Poly(N‐isopropylacrylamide) Hydrogel Surface Layers

Despite multiple research approaches to prevent bacterial colonization on surfaces, device‐associated infections are currently responsible for about 50% of nosocomial infections in Europe and significantly increase health care costs, which demands development of advanced antibacterial surface coatings. Here, novel antimicrobial composite materials incorporating zinc oxide nanoparticles (ZnO NP) into biocompatible poly(N‐isopropylacrylamide) (PNIPAAm) hydrogel layers are prepared by mixing the PNIPAAm prepolymer with ZnO NP, followed by spin‐coating and photocrosslinking. Scanning electron microscopy (SEM) characterization of the composite film morphology reveals a homogeneous distribution of the ZnO NP throughout the film for every applied NP/polymer ratio. The optical properties of the embedded NP are not affected by the matrix as confirmed by UV‐vis spectroscopy. The nanocomposite films exhibit bactericidal behavior towards Escherichia coli (E. coli) for a ZnO concentration as low as ≈0.74 μg cm^?2 (1.33 mmol cm^?3), which is determined by inductively coupled plasma optical emission spectrometry. In contrast, the coatings are found to be non‐cytotoxic towards a mammalian cell line (NIH/3T3) at bactericidal loadings of ZnO over an extended period of seven days. The differential toxicity of the ZnO/hydrogel nanocomposite thin films between bacterial and cellular species qualifies them as promising candidates for novel biomedical device coatings.     

A Copper Silicide Nanofoam Current Collector for Directly Grown Si Nanowire Networks and their Application as Lithium‐Ion Anodes

Silicon nanowires (Si NWs) have been identified as an excellent candidate material for the replacement of graphite in anodes, allowing for a significant boost in the capacity of lithium‐ion batteries (LIBs). Herein, high‐density Si NWs are grown on a novel 3D interconnected network of binary‐phase Cu‐silicide nanofoam (3D Cu_xSi_y NF) substrate. The nanofoam facilitates the uniform distribution of well‐segregated and small‐sized catalyst seeds, leading to high‐density/single‐phase Si NW growth with an areal‐loading in excess of 1.0 mg cm^?2 and a stable areal capacity of ≈2.0 mAh cm^?2 after 550 cycles. The use of the 3D Cu_xSi_y NF as a substrate is further extended for Al, Bi, Cu, In, Mn, Ni, Sb, Sn, and Zn mediated Si NW growth, demonstrating the general applicability of the anode architecture.     

High‐Performance,Air‐Stable,Top‐Gate,p‐Channel WSe2 Field‐Effect Transistor with Fluoropolymer Buffer Layer

High‐performance, air‐stable, p‐channel WSe₂ top‐gate field‐effect transistors (FETs) using a bilayer gate dielectric composed of high‐ and low‐k dielectrics are reported. Using only a high‐k Al₂O₃ as the top‐gate dielectric generally degrades the electrical properties of p‐channel WSe₂, therefore, a thin fluoropolymer (Cytop) as a buffer layer to protect the 2D channel from high‐k oxide forming is deposited. As a result, a top‐gate‐patterned 2D WSe₂ FET is realized. The top‐gate p‐channel WSe₂ FET demonstrates a high hole mobility of 100 cm²_­ V^?1 s^?1 and a I_ON/I_OFF ratio > 10⁷ at low gate voltages (V_GS ca. ?4 V) and a drain voltage (V_DS) of ?1 V on a glass substrate. Furthermore, the top‐gate FET shows a very good stability in ambient air with a relative humidity of 45% for 7 days after device fabrication. Our approach of creating a high‐k oxide/low‐k organic bilayer dielectric is advantageous over single‐layer high‐k dielectrics for top‐gate p‐channel WSe₂ FETs, which will lead the way toward future electronic nanodevices and their integration.     

Direct 3D Printing of High Strength Biohybrid Gradient Hydrogel Scaffolds for Efficient Repair of Osteochondral Defect

The emerging 3D printing technique allows for tailoring hydrogel‐based soft structure tissue scaffolds for individualized therapy of osteochondral defects. However, the weak mechanical strength and uncontrollable swelling intrinsic to conventional hydrogels restrain their use as bioinks. Here, a high‐strength thermoresponsive supramolecular copolymer hydrogel is synthesized by one‐step copolymerization of dual hydrogen bonding monomers, N‐acryloyl glycinamide, and N‐[tris(hydroxymethyl)methyl] acrylamide. The obtained copolymer hydrogels demonstrate excellent mechanical properties—robust tensile strength (up to 0.41 MPa), large stretchability (up to 860%), and high compressive strength (up to 8.4 MPa). The rapid thermoreversible gel ? sol transition behavior makes this copolymer hydrogel suitable for direct 3D printing. Successful preparation of 3D‐printed biohybrid gradient hydrogel scaffolds is demonstrated with controllable 3D architecture, owing to shear thinning property which allows continuous extrusion through a needle and also immediate gelation of fluid upon deposition on the cooled substrate. Furthermore, this biohybrid gradient hydrogel scaffold printed with transforming growth factor beta 1 and β‐tricalciumphosphate on distinct layers facilitates the attachment, spreading, and chondrogenic and osteogenic differentiation of human bone marrow stem cells (hBMSCs) in vitro. The in vivo experiments reveal that the 3D‐printed biohybrid gradient hydrogel scaffolds significantly accelerate simultaneous regeneration of cartilage and subchondral bone in a rat model.     

Inside Front Cover: Nanocrystalline TiO2 Photocatalytic Membranes with a Hierarchical Mesoporous Multilayer Structure: Synthesis,Characterization, and Multifunction (Adv. Funct. Mater. 8/2006)

The inside cover shows a hierarchical, mesoporous, multilayer TiO2 photocatalytic membrane synthesized via a novel sol–gel dip‐coating process employing surfactant templates reported by Dionysiou and co‐workers on p. 1067. The resulting asymmetric mesoporous TiO2 membrane supported onto a porous Al2O3 substrate exhibited hierarchical changes in pore diameter and materials porosity from the top to the bottom layer. The TiO2 membrane has multiple simultaneous functions, including photocatalysis, disinfection, separation, and anti‐biofouling. A novel sol–gel dip‐coating process to fabricate nanocrystalline TiO₂ photocatalytic membranes with a robust hierarchical mesoporous multilayer and improved performance has been studied. Various titania sols containing poly(oxyethylenesorbitan monooleate) (Tween 80) surfactant as a pore‐directing agent to tailor‐design the porous structure of TiO₂ materials at different molar ratios of Tween 80/isopropyl alcohol/acetic acid/titanium tetraisopropoxide = R:45:6:1 have been synthesized. The sols are dip‐coated on top of a homemade porous alumina substrate to fabricate TiO₂/Al₂O₃ composite membranes, dried, and calcined, and this procedure is repeated with varying sols in succession. The resulting asymmetric mesoporous TiO₂ membrane with a thickness of 0.9 μm exhibits a hierarchical change in pore diameter from 2–6, through 3–8, to 5–11 nm from the top to the bottom layer. Moreover, the corresponding porosity is incremented from 46.2, through 56.7, to 69.3 %. Compared to a repeated‐coating process using a single sol, the hierarchical multilayer process improves water permeability significantly without sacrificing the organic retention and photocatalytic activity of the TiO₂ membranes. The prepared TiO₂ photocatalytic membrane has great potential in developing highly efficient water treatment and reuse systems, for example, decomposition of organic pollutants, inactivation of pathogenic microorganisms, physical separation of contaminants, and self‐antifouling action because of its multifunctional capability.