Facile Method To Prepare Microcapsules Inspired by Polyphenol Chemistry for Efficient Enzyme Immobilization

In this study, a method inspired by polyphenol chemistry is developed for the facile preparation of microcapsules under mild conditions. Specifically, the preparation process includes four steps: formation of the sacrificial template, generation of the polyphenol coating on the template surface, cross-linking of the polyphenol coating by cationic polymers, and removal of the template. Tannic acid (TA) is chosen as a representative polyphenol coating precursor for the preparation of microcapsules. The strong interfacial affinity of TA contributes to the formation of polyphenol coating through oxidative oligomerization, while the high reactivity of TA is in charge of reacting/cross-linking with cationic polymer polyethylenimine (PEI) through Schiff base/Michael addition reaction. The chemical/topological structures of the resultant microcapsules are simultaneously characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier Transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), <i>etc.</i> The wall thickness of the microcapsules could be tailored from 257 ± 20 nm to 486 ± 46 nm through changing the TA concentration. The microcapsules are then utilized for encapsulating glucose oxidase (GOD), and the immobilized enzyme exhibits desired catalytic activity and enhanced pH and thermal stabilities. Owing to the structural diversity and functional versatility of polyphenols, this study may offer a facile and generic method to prepare microcapsules and other kinds of functional porous materials

Free-Standing Graphene Oxide-Palygorskite Nanohybrid Membrane for Oil/Water Separation

Graphene oxide (GO) is an emerging kind of building block for advanced membranes with tunable passageway for water molecules. To synergistically manipulate the channel and surface structures/properties of GO-based membranes, the different building blocks are combined and the specific interfacial interactions are designed in this study. With vacuum-assisted filtration self-assembly, palygorskite nanorods are intercalated into adjacent GO nanosheets, and GO nanosheets are assembled into laminate structures through π–π stacking and cation cross-linking. The palygorskite nanorods in the free-standing GOP nanohybrid membranes take a 3-fold role, rendering enlarged mass transfer channels, elevating hydration capacity, and creating hierarchical nanostructures of membrane surfaces. Accordingly, the permeate fluxes from 267 L/(m² h) for GO membrane to 1867 L/(m² h) for GOP membrane. The hydration capacity and hierarchical nanostructures synergistically endow GOP membranes with underwater superoleophobic and low oil-adhesive water/membrane interfaces. Moreover, by rationally imparting chemical and physical joint defense mechanisms, the GOP membranes exhibit outstanding separation performance and antifouling properties for various oil-in-water emulsion systems (with different concentration, pH, or oil species). The high water permeability, high separation efficiency, as well as superior anti-oil-fouling properties of GOP membranes enlighten the great prospects of graphene-based nanostructured materials in water purification and wastewater treatment

Preparation of Dopamine/Titania Hybrid Nanoparticles through Biomimetic Mineralization and Titanium(IV)–Catecholate Coordination for Enzyme Immobilization

In this study, a facile approach is proposed to prepare dopamine/titania hybrid nanoparticles (DTHNPs), which are synthesized via directly blending titanium­(IV) bis­(ammonium lactato) dihydroxide (Ti-BALDH) and dopamine aqueous solution. The amino group in dopamine is mainly in charge of inducing the hydrolysis and condensation of titanium precursor to form titania, and the catechol group in dopamine acts as an organic ligand to form titanium­(IV)–catecholate coordination. These DTHNPs were characterized by tranmission electron miscroscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The morphology of DTHNPs is changed from slightly cotton-shaped aggregates to monodisperse nanoparticles with the increase of dopamine concentration. As a model enzyme, catalase (CAT) is entrapped in the DTHNPs during the nanoparticle preparation process. Surprisingly, the entrapment efficiency of CAT can be high up to nearly 100%, and no enzyme leakage could be detected. Moreover, immobilized CAT possesses 90% the catalytic activity of free enzyme

An Efficient, Recyclable, and Stable Immobilized Biocatalyst Based on Bioinspired Microcapsules-in-Hydrogel Scaffolds

Design and preparation of high-performance immobilized biocatalysts with exquisite structures and elucidation of their profound structure-performance relationship are highly desired for green and sustainable biotransformation processes. Learning from nature has been recognized as a shortcut to achieve such an impressive goal. Loose connective tissue, which is composed of hierarchically organized cells by extracellular matrix (ECM) and is recognized as an efficient catalytic system to ensure the ordered proceeding of metabolism, may offer an ideal prototype for preparing immobilized biocatalysts with high catalytic activity, recyclability, and stability. Inspired by the hierarchical structure of loose connective tissue, we prepared an immobilized biocatalyst enabled by microcapsules-in-hydrogel (MCH) scaffolds via biomimetic mineralization in agarose hydrogel. In brief, the in situ synthesized hybrid microcapsules encapsulated with glucose oxidase (GOD) are hierarchically organized by the fibrous framework of agarose hydrogel, where the fibers are intercalated into the capsule wall. The as-prepared immobilized biocatalyst shows structure-dependent catalytic performance. The porous hydrogel permits free diffusion of glucose molecules (diffusion coefficient: ∼6 × 10^–6 cm² s^–1, close to that in water) and retains the enzyme activity as much as possible after immobilization (initial reaction rate: 1.5 × 10^–2 mM min^–1). The monolithic macroscale of agarose hydrogel facilitates the easy recycling of the immobilized biocatalyst (only by using tweezers), which contributes to the nonactivity decline during the recycling test. The fiber-intercalating structure elevates the mechanical stability of the in situ synthesized hybrid microcapsules, which inhibits the leaching and enhances the stability of the encapsulated GOD, achieving immobilization efficiency of ∼95%. This study will, therefore, provide a generic method for the hierarchical organization of (bio)­active materials and the rational design of novel (bio)­catalysts

Synthesis of Ag/TiO₂ Nanotube Heterojunction with Improved Visible-Light Photocatalytic Performance Inspired by Bioadhesion

Inspired by the bioadhesion mechanism found in mussel, a catechol derivative, 3-(3,4-dihydroxyphenyl)­propionic acid (diHPP), is employed as both linker and reducer of Ag⁺ to synthesize the Ag/TiO₂ nanotube (Ag/TNT) heterojunction under ambient conditions in this study. In the prepared Ag/TNT composite, Ag nanocrystals about 3.8 nm in diameter distribute over the TNT surface uniformly and form the heterojunction structure with TNT. The diHPP first links to the TNT surface through the bidentate chelation of catechol group with Ti⁴⁺ and then acts as both an anchor and a reducer to <i>in situ</i> nucleate and grow Ag nanocrystals on the TNT surface. By adjusting the AgNO₃ concentration, the loading amount of Ag nanocrystals on the TNT surface can be controlled easily, and the visible-light absorption ability of Ag/TNT heterojunctions enhances with increasing the Ag loading amount. Moreover, their photocatalytic activity was evaluated by the degradation capability of Rhodamine B (RhB) under visible light. The Ag/TNT heterojunctions exhibit the high visible-light photocatalytic activity, which can almost degrade 100% RhB within 2 h. This excellent performance can be attributed to the local electric field caused by the surface plasmon resonance (SPR) of Ag nanocrystals and the high adsorption capability of TNTs with large specific surface area

Biomimetic Synthesis of TiO₂–SiO₂–Ag Nanocomposites with Enhanced Visible-Light Photocatalytic Activity

Ternary TiO₂–SiO₂–Ag nanocomposites with enhanced visible-light photocatalytic activity have been synthesized through a facile biomimetic approach by utilizing lysozyme as both inducing agent of TiO₂ and reducing agent of Ag⁺. TiO₂ nanoparticles (∼280 nm) are at first fabricated by the inducing of lysozyme. Afterward, SiO₂ layers are formed as “pancakes” stuck out of TiO₂ nanoparticles through a sol–gel process. Finally, Ag nanocrystals (∼24.5 nm) are deposited onto the surface of TiO₂–SiO₂ composites via the reduction of lysozyme, forming TiO₂–SiO₂–Ag nanocomposites. The resultant nanocomposites display a high photocatalytic activity for the degradation of Rhodamine B under the visible-light irradiation, which can be attributed to the synergistic effect of enhanced photon absorption from the surface plasma resonance of Ag nanocrystals and the elevated adsorption capacity for Rhodamine B from the high specific surface area of SiO₂. This study may provide some inspiration for the rational design and the facile synthesis of composite catalysts with a high and tunable catalytic property through a green, efficient pathway

Three-Dimensional Porous Aerogel Constructed by g‑C₃N₄ and Graphene Oxide Nanosheets with Excellent Visible-Light Photocatalytic Performance

It is curial to develop a high-efficient, low-cost visible-light responsive photocatalyst for the application in solar energy conversion and environment remediation. Here, a three-dimensional (3D) porous g-C₃N₄/graphene oxide aerogel (CNGA) has been prepared by the hydrothermal coassembly of two-dimensional g-C₃N₄ and graphene oxide (GO) nanosheets, in which g-C₃N₄ acts as an efficient photocatalyst, and GO supports the 3D framework and promotes the electron transfer simultaneously. In CNGA, the highly interconnected porous network renders numerous pathways for rapid mass transport, strong adsorption and multireflection of incident light; meanwhile, the large planar interface between g-C₃N₄ and GO nanosheets increases the active site and electron transfer rate. Consequently, the methyl orange removal ratio over the CNGA photocatalyst reaches up to 92% within 4 h, which is much higher than that of pure g-C₃N₄ (12%), 2D hybrid counterpart (30%) and most of representative g-C₃N₄-based photocatalysts. In addition, the dye is mostly decomposed into CO₂ under natural sunlight irradiation, and the catalyst can also be easily recycled from solution. Significantly, when utilized for CO₂ photoreduction, the optimized CNGA sample could reduce CO₂ into CO with a high yield of 23 mmol g^–1 (within 6 h), exhibiting about 2.3-fold increment compared to pure g-C₃N₄. The photocatalyst exploited in this study may become an attractive material in many environmental and energy related applications

Combination of Redox Assembly and Biomimetic Mineralization To Prepare Graphene-Based Composite Cellular Foams for Versatile Catalysis

Graphene-based materials with hierarchical structures and multifunctionality have gained much interest in a variety of applications. Herein, we report a facile, yet universal approach to prepare graphene-based composite cellular foams (GCCFs) through combination of redox assembly and biomimetic mineralization enabled by cationic polymers. Specifically, cationic polymers (e.g., polyethyleneimine, lysozyme, etc.) could not only reduce and simultaneously assemble graphene oxide (GO) into cellular foams but also confer the cellular foams with mineralization-inducing capability, enabling the formation of inorganic nanoparticles (e.g., silica, titania, silver, etc.). The GCCFs show highly porous structure and appropriate structural stability, where nanoparticles are well distributed on the surface of the reduced GO. Through altering polymer/inorganic pairs, a series of GCCFs are synthesized, which exhibit much enhanced catalytic performance in enzyme catalysis, heterogeneous chemical catalysis, and photocatalysis compared to nanoparticulate catalysts

Thylakoid-Inspired Multishell g‑C₃N₄ Nanocapsules with Enhanced Visible-Light Harvesting and Electron Transfer Properties for High-Efficiency Photocatalysis

Inspired by the orderly stacked nanostructure and highly integrated function of thylakoids in a natural photosynthesis system, multishell g-C₃N₄ (MSCN) nanocapsule photocatalysts have been prepared by SiO₂ hard template with different shell layers. The resultant triple-shell g-C₃N₄ (TSCN) nanocapsules display superior photocatalysis performance to single-shell and double-shell counterparts owing to excellent visible-light harvesting and electron transfer properties. Specially, with the increase of the shell layer number, light harvesting is greatly enhanced. There is an increase of the entire visible range absorption arising from the multiple scattering and reflection of the incident light within multishell nanoarchitectures as well as the light transmission within the porous thin shells, and an increase of absorption edge arising from the decreased quantum size effect. The electron transfer is greatly accelerated by the mesopores in the thin shells as nanoconduits and the high specific surface area of TSCN (310.7 m² g^–1). With the tailored hierarchical nanostructure features, TSCN exhibits a superior visible-light H₂-generation activity of 630 μmol h^–1 g^–1 (λ > 420 nm), which is among one of the most efficient metal-free g-C₃N₄ photocatalysts. This study demonstrates a bioinspired approach to the rational design of high-performance nanostructured visible-light photocatalysts

g‑C₃N₄@α-Fe₂O₃/C Photocatalysts: Synergistically Intensified Charge Generation and Charge Transfer for NADH Regeneration

Graphitic carbon nitride (g-C₃N₄) is an emergent metal-free photocatalyst because of its band position, natural abundance, and facile preparation. Synergetic intensification of charge generation and charge transfer of g-C₃N₄ to increase solar-to-chemical efficiency remains a hot yet challenging issue. Herein, a nanoshell with two moieties of α-Fe₂O₃ and carbon (C) is in situ formed on the surface of a g-C₃N₄ core through calcination of Fe³⁺/polyphenol-coated melamine, thus acquiring g-C₃N₄@α-Fe₂O₃/C core@shell photocatalysts. The α-Fe₂O₃ moiety acts as an additional photosensitizer, offering more photogenerated electrons, whereas the C moiety bridges a “highway” to facilitate the electron transfer either from α-Fe₂O₃ moiety to g-C₃N₄ or from g-C₃N₄ to C moiety. By tuning the proportion of these two moieties in the nanoshell, a photocurrent density of 3.26 times higher than pristine g-C₃N₄ is obtained. When utilized for photocatalytic regeneration of reduced nicotinamide adenine dinucleotide (NADH, a dominant cofactor in biohydrogenation reaction), g-C₃N₄@α-Fe₂O₃/C exhibits an equilibrium NADH yield of 76.3% with an initial reaction rate (<i>r</i>) of 7.7 mmol h^–1 g^–1, among the highest <i>r</i> for photocatalytic NADH regeneration ever reported. Manipulating the coupling between charge generation and charge transfer may offer a facile, generic strategy to improve the catalytic efficiency of a broad range of photocatalysts other than g-C₃N₄