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

Chitosan-based carbon nitride-polydopamine‑silver composite dressing with antibacterial properties for wound healing

Infection represents a major clinical barrier that delays wound healing, while the overuse of antibiotics can lead to bacterial resistance. Hence, it is of particular important to develop a new type of dressing to combat bacterial resistance. Herein, a carbon nitride-polydopamine‑silver complex (C₃N₄-PDA-Ag) was prepared using the photocatalyst C₃N₄ and silver nanoparticles (Ag NPs) to achieve a synergistic antimicrobial effect. The solution casting method was then employed to further modify the C₃N₄-PDA-Ag complex by compounding it with chitosan (CS), thereby forming a C₃N₄-PDA-Ag@CS film. The results revealed that the C₃N₄-PDA-Ag@CS film exhibits superior antibacterial activity against Staphylococcus aureus and Pseudomonas aeruginosa compared to the CS group. The hemolysis, cytotoxicity, and in vivo implantation experiments indicated that the composite film possesses excellent in vitro and in vivo biocompatibility. In addition, the composite dressing promoted wound healing in infected mice by facilitating collagen deposition and accelerating epidermal regeneration. Collectively, the findings of this study clearly demonstrate that the C₃N₄-PDA-Ag@CS composite dressing has excellent antibacterial properties, biocompatibility, and enhances wound healing, thus providing a strategy for the application of photocatalytic materials for the treatment of infected wounds.

Achieving Functionality and Multifunctionality through Bulk and Interfacial Structuring of Colloidal-Crystal-Templated Materials

Over the past 25 years, the field of colloidal crystal templating of inverse opal or three-dimensionally ordered macroporous (3DOM) structures has made tremendous progress. The degree of structural control over multiple length scales, understanding of mechanical properties, and complexity of systems in which 3DOM materials are a component have increased substantially. In addition, we are now seeing applications of 3DOM materials that make use of multiple features of their architecture at the same time. This Feature Article focuses on the different properties of 3DOM materials that provide functionality, including a relatively large surface area, the interconnectedness of the pores and the resulting good accessibility of the internal surface, the nanostructured features of the walls, the structural hierarchy and periodicity, well-defined surface roughness, and relative mechanical robustness at low density. It provides representative examples that illustrate the properties of interest related to applications including energy storage and conversion systems, sensors, catalysts, sorbents, photonics, actuators, and biomedical materials or devices.

Controlled synthesis of solid-shelled non-spherical and faceted microbubbles

The ability to control the shape of hollow particles (e.g., capsules or bubbles) holds great promise for enhancing the encapsulation efficiency and mechanical/optical properties. However, conventional preparation methods suffer from a low yield, difficulty in controlling the shape, and a tedious production process, limiting their widespread application. Here, we present a method for fabricating polyhedral graphene oxide (GO)-shelled microbubbles with sharp edges and vertices, which is based on the microfluidic generation of spherical compound bubbles followed by shell deformation. Sphere-to-polytope deformation is a result of the shell instability due to gradual outward gas transport, which is dictated by Laplace pressure across the shell. The shape-variant behaviours of the bubbles can also be attributed to the compositional heterogeneity of the shells. In particular, the high degree of control of microfluidic systems enables the formation of non-spherical bubbles with various shapes; the structural motifs of the bubbles are easily controlled by varying the size and thickness of the mid-shell in compound bubbles, ranging from tetrahedra to octahedra. The strategy presented in this study provides a new route for fabricating 3D structured solid bubbles, which is particularly advantageous for the development of high-performance mechanical or thermal material applications.

Biomimetic reconstruction of butterfly wing scale nanostructures for radiative cooling and structural coloration

A great number of butterfly species in the warmer climate have evolved to exhibit fascinating optical properties on their wing scales which can both regulate the wing temperature and exhibit structural coloring in order to increase their chances of survival. In particular, the Archaeoprepona demophon dorsal wing demonstrates notable radiative cooling performance and iridescent colors based on the nanostructure of the wing scale that can be characterized by the nanoporous matrix with the periodic nanograting structure on the top matrix surface. Inspired by the natural species, we demonstrate a multifunctional biomimetic film that reconstructs the nanostructure of the Archaeoprepona demophon wing scales to replicate the radiative cooling and structural coloring functionalities. We resorted to the SiO₂ sacrificial template-based solution process to mimic the random porous structure and laser-interference lithography to reproduce the nanograting architecture of the butterfly wing scale. As a result, the biomimetic structure of the nanograted surface on top of the porous film demonstrated desirable heat transfer and optical properties for outstanding radiative cooling performance and iridescent structural coloring. In this regard, the film is capable of inducing the maximum temperature drop of 8.45 °C, and the color gamut of the biomimetic film can cover 91.8% of the standardized color profile (sRGB).

Highly active CoNi nanoparticles confined in N-doped carbon microtubes for efficient catalytic performance

CoNi@NCMT magnetic composites with a tubular structure and high coverage of tiny CoNi bimetallic nanoparticles are fabricated as efficient catalysts for the reduction of 4-nitrophenol (4-NP).

Correlation between the bending angle and protein sensing properties of molecularly imprinted hydrogel strips with a one-sided porous pattern

A visual observation of the bending angle changes of molecularly imprinted hydrogel strips with a one-sided porous pattern for the novel and easy detection of proteins.

Infusion of Silver-Polydopamine Particles into Polyethersulfone Matrix to Improve the Membrane's Dye Desalination Performance and Antibacterial Property

The advancement in membrane science and technology, particularly in nanofiltration applications, involves the blending of functional nanocomposites into the membranes to improve the membrane property. In this study, Ag-polydopamine (Ag-PDA) particles were synthesized through in situ PDA-mediated reduction of AgNO₃ to silver. Infusing Ag-PDA particles into polyethersulfone (PES) matrix affects the membrane property and performance. X-ray photoelectron spectroscopy (XPS) analyses confirmed the presence of Ag-PDA particles on the membrane surface. Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) describe the morphology of the membranes. At an optimum concentration of Ag-PDA particles (0.3 wt % based on the concentration of PES), the modified membrane exhibited high water flux 13.33 L∙m⁻²∙h⁻¹ at 4 bar with high rejection for various dyes of >99%. The PES_Ag-PDA0.3 membrane had a pure water flux more than 5.4 times higher than that of a pristine membrane. Furthermore, in bacterial attachment using Escherichia coli, the modified membrane displayed less bacterial attachment compared with the pristine membrane. Therefore, immobilizing Ag-PDA particles into the PES matrix enhanced the membrane performance and antibacterial property.

Highly Efficient Silver Catalyst Supported by a Spherical Covalent Organic Framework for the Continuous Reduction of 4-Nitrophenol

Developing new materials and novel technologies for the highly efficient treatment of toxic organic pollutants is highly desirable. Chemical reduction based on heterogeneous substrate/noble metal catalysts and the reducing agent NaBH₄ has become an effective method in recent years. Here, a spherical covalent organic framework (SCOF) was designed to provide basic sites for Ag ions, by which small Ag NPs were immobilized on the SCOF to form Ag NPs@SCOF microspheres. The prepared microspheres exhibited a high catalytic reduction ability toward 4-nitrophenol (4-NP). An optimized permeation flux of 2000 L m^-2 h^-1 (LMH) and a more than 99% 4-NP reduction efficiency were obtained with flow-through experiments, which are far better than the reported results (below 200 LMH). Moreover, the microspheres could maintain stable catalytic performance under a continuous flow-through process. Our work provides an efficient material and technology that can be applied to easily treat toxic organic pollutants.

High efficient reduction of 4-nitrophenol and dye by filtration through Ag NPs coated PAN-Si catalytic membrane

Catalytic membrane plays an important role in environmental remedy. In this study, we reported an Ag coated membrane (PAN-Si-Cu-Ag) with a high catalytic activity to reduce 4-nitrophenol (4-NP) and methyl orange (MO) from water. The best performance is 99% reduction degree and 280 L m^-2.h^-1.bar^-1 flux for (4-NP) reduction at 4-NP: NaBH₄ = 1:50 (mM) during a 12-h filtration. The reduction degree for MO is above 90% and the flux is about 230 L m^-2·h^-1·bar^-1, which is almost the best report till now. The Ag coated membrane was prepared by metal displacement-epitaxial growth on silica covalent grafted PAN membrane (PAN-Si). Silica atoms were used as linker to ensure the good adhesion between polymer and metal NPs, the loss amount of Ag NPs from the coated catalytic membrane is loss about 2 μg/cm² after one month storage. Cheap metal NPs were firstly reduced on the surface of PAN-Si membrane and then used to displace Ag ions. Thus the obtained catalytic membrane showed a very high loading (28%). Finally, the catalytic filtration mechanism of 4-NP was distinguished by Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and adsorption measurement.

Wetting-Controlled Localized Placement of Surface Functionalities within Nanopores

In the context of sensing and transport control, nanopores play an essential role. Designing multifunctional nanopores and placing multiple surface functionalities with nanoscale precision remains challenging. Interface effects together with a combination of different materials are used to obtain local multifunctionalization of nanoscale pores within a model pore system prepared by colloidal templating. Silica inverse colloidal monolayers are first functionalized with a gold layer to create a hybrid porous architecture with two distinct gold nanostructures on the top surface as well as at the pore bottom. Using orthogonal silane- and thiol-based chemistry together with a control of the wetting state allows individual addressing of the different locations within each pore resulting in nanoscale localized functional placement of three different functional units. Ring-opening metathesis polymerization is used for inner silica-pore wall functionalization. The hydrophobized pores create a Cassie-Baxter wetting state with aqueous solutions of thiols, which enables an exclusive functionalization of the outer gold structures. In a third step, an ethanolic solution able to wet the pores is used to self-assemble a thiol-containing initiator at the pore bottom. Subsequent controlled radical polymerization provides functionalization of the pore bottom. It is demonstrated that the combination of orthogonal surface chemistry and controlled wetting states can be used for the localized functionalization of porous materials.

Polydopamine Induced in-Situ Formation of Metallic Nanoparticles in Confined Microchannels of Porous Membrane as Flexible Catalytic Reactor

Oxidant-regulated polymerization of dopamine was exploited, for the first time, for effective surface engineering of the well-defined cylindrical pores of nuclear track-etched membranes (NTEMs) to develop novel catalytic membrane reactor. First, in the presence of a strong oxidant, controlled synthesis of polydopamine (PDA) with tunable particle size was achieved, allowing a homogeneous deposition to the confined pore channels of NTEMs. The PDA interfaces rich in catechol and amine groups provided enhanced hydrophilicity to promote mass transport across the membrane and abundant nucleation sites for formation and stabilization of metallic nanoparticles (NPs). In-situ reductive growth of multiple metallic NPs, including Pd, Ag, and Au, was then achieved inside the cylindrical pores of NTEMs. Using the functionalized membrane as a catalytic reactor, efficient reduction of 4-nitrophenol (4-NP) was demonstrated in a flow-through mode. Moreover, after dissolution removal of the NTEMs, self-sustained one-dimensional (1D) PDA/M (M = Pd, Ag, or Au) hybrid nanotubes (NTs), with determined aspect ratio and a length reaching up to 10 μm, were obtained for catalysis of 4-NP in a batch reaction mode. This study established a facile and versatile method, by rational tuning of the polymerization behavior of dopamine, for effective modification of confined microscale/nanoscale cavities with different surface characteristics. The integration of PDA chemistry with NTEMs would provide more opportunities for development of novel catalytic membrane reactors as well as for the tailored synthesis of functional 1D nanotubes for broadened applications.

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.

Self-assembled selenium nanoparticles and their application in the rapid diagnostic detection of small cell lung cancer biomarkers

By coupling molecular imprinting, chitosan biosorption and TiO₂ photocatalysis, selenium nanoparticles (Se NPs) were self-assembled in a controlled manner on the molecular imprinting sites of zeolite-chitosan-TiO₂ microspheres. Se NPs with different sizes and areal densities were individually synthesized by controlling the rapid adsorption of molecular-imprinted nanocomposites and photocatalytic reaction of TiO₂ nanoparticles. In order to improve the sensitivity and specificity of rapid diagnostic detection, Se NPs were self-assembled again into high-order and spherically stable structures with an average size of 80 nm by well-defined monomer units, after separation from zeolite-chitosan-TiO₂ microspheres with a stabilizer of 0.3% (v/v) bovine serum albumin. Due to their biological activity, spherical-shaped Se NPs were used for dot-blot immunoassays with multiple native antigens for rapid serodiagnosis of human lung cancer. The sensitivity of the dot immunoassays for detecting progastrin-releasing peptide (ProGRP) was 75 pg mL^-1. The detection time of colloidal Se dot immunoassays for ProGRP was only 5 min. No positive results were observed with other commonly potential interfering substances, including carcinoembryonic antigen, α-fetoprotein antigen and BSA. The research presents a simple and green method for the reuse of SeO₃^2- and the controlled synthesis of Se NPs for biological and medical applications by bioaffinity adsorption and photoreduction.

Assembly of large area crack free clay porous films

A method for making inverse opal-like porous clay films that are crack-free over a large area (on the scale of square centimeters).

Mussel-inspired chitosan-polyurethane coatings for improving the antifouling and antibacterial properties of polyethersulfone membranes

A straightforward mussel-inspired approach was proposed to construct chitosan-polyurethane coatings and load Ag nanoparticles (AgNPs) to endow polyethersulfone (PES) membranes with dual-antibacterial and antifouling properties. The macromolecule O-carboxymethyl chitosan (CMC) was directly reacted with catechol in the absence of carbodiimide chemistry to form the coating and load AgNPs via in situ reduction; while lysine (Lys) was used as a representative small molecule for comparison. Then, PEG-based polyurethane (PU) was used for constructing Lys-Ag-PU and CMC-Ag-PU composite coatings, which substantially improved the protein antifouling property of the membranes. Furthermore, the CMC-Ag-PU coating exhibited superior broad-spectrum antibacterial property towards E. coli and S. aureus than Lys-Ag-PU coating. Meanwhile, the CMC-Ag-PU coating showed sustained antifouling property against bacteria and could reload AgNPs to be regenerated as antibacterial and antifouling coating. This approach is believed to have potential to fabricate reusable antifouling and antibacterial coatings on materials surfaces for aquatic industries.

Ellipsoidal Colloids with a Controlled Surface Roughness via Bioinspired Surface Engineering: Building Blocks for Liquid Marbles and Superhydrophobic Surfaces

Understanding the important role of the surface roughness of nano/colloidal particles and harnessing them for practical applications need novel strategies to control the particles' surface topology. Although there are many examples of spherical particles with a specific surface roughness, nonspherical ones with similar surface features are rare. The current work reports a one-step, straightforward, and bioinspired surface engineering strategy to prepare ellipsoidal particles with a controlled surface roughness. By manipulating the unique chemistry inherent to the oxidation-induced self-polymerization of dopamine into polydopamine (PDA), PDA coating of polymeric ellipsoids leads to a library of hybrid ellipsoidal particles (PS@PDA) with a surface that decorates with nanoscale PDA protrusions of various densities and sizes. Together with the advantages originated from the anisotropy of ellipsoids and rich chemistry of PDA, such a surface feature endows these particles with some unique properties. Evaporative drying of fluorinated PS@PDA particles produces a homogeneous coating with superhydrophobicity that arises from the two-scale hierarchal structure of microscale interparticle packing and nanoscale roughness of the constituent ellipsoids. Instead of water repelling that occurs for most of the lotus leaf-like superhydrophobic surfaces, such coating exhibits strong water adhesion that is observed with certain species of rose pedals. In addition, the as-prepared hybrid ellipsoids are very efficient in preparing liquid marble-isolated droplets covered with solid particles. Such liquid marbles can be placed onto many surfaces and might be useful for the controllable transport and manipulation of small volumes of liquids.

Antibacterial activity and osseointegration of silver-coated poly(ether ether ketone) prepared using the polydopamine-assisted deposition technique

PEEK-PDA-Ag substrates may be a promising orthopaedic implant material due to the outstanding biocompatibility and antibacterial properties.

Co-deposition towards mussel-inspired antifouling and antibacterial membranes by using zwitterionic polymers and silver nanoparticles

Bacterial attachment and the subsequent colonization on the surfaces of bio-materials usually result in biofilm formation, and thus lead to implant failure, inflammation and so on.

Quasi-ballistic Electronic Thermal Conduction in Metal Inverse Opals

Porous metals are used in interfacial transport applications that leverage the combination of electrical and/or thermal conductivity and the large available surface area. As nanomaterials push toward smaller pore sizes to increase the total surface area and reduce diffusion length scales, electron conduction within the metal scaffold becomes suppressed due to increased surface scattering. Here we observe the transition from diffusive to quasi-ballistic thermal conduction using metal inverse opals (IOs), which are metal films that contain a periodic arrangement of interconnected spherical pores. As the material dimensions are reduced from ∼230 nm to ∼23 nm, the thermal conductivity of copper IOs is reduced by more than 57% due to the increase in surface scattering. In contrast, nickel IOs exhibit diffusive-like conduction and have a constant thermal conductivity over this size regime. The quasi-ballistic nature of electron transport at these length scales is modeled considering the inverse opal geometry, surface scattering, and grain boundaries. Understanding the characteristics of electron conduction at the nanoscale is essential to minimizing the total resistance of porous metals for interfacial transport applications, such as the total electrical resistance of battery electrodes and the total thermal resistance of microscale heat exchangers.

Simple and facile preparation of silver–polydopamine (Ag–PDA) core–shell nanoparticles for selective electrochemical detection of cysteine

A simple one-step method for the preparation of silver–polydopamine (Ag–PDA) core–shell nanoparticles is proposed and its application for non-enzymatic electrochemical detection of cysteine is demonstrated.