NAD(P)H is a critical cofactor (biological source of hydrogen) that participates in many enzymatic hydrogenations for energy conversion and storage with resultant oxidation to NAD(P)+. Due to its high cost, the regeneration of NAD(P)H is a critical and feasible way to ensure the sustainability of these enzymatic hydrogenations. Intrigued by the photoreaction process in thylakoid membrane, we explored a two-dimensional (2D) isotype heterojunction photocatalyst, termed as quantum dots@flake graphitic carbon nitride (QDs@Flake g-C3N4), for visible-light-driven NAD(P)H regeneration. The catalyst was synthesized by one-step calcination using cyanamide-treated cyanuric acid–melamine (CM) complex as starting material, where cyanamide plays dual roles: (a) assisting the transformation of CM from bulky to stacked structure and further to flakes after calcination, and (b) acting as raw material for the generation of QDs on the flakes. To replicate both the functional and structural properties of the natural photoreaction system, QDs@Flake g-C3N4 exploited the two types of g-C3N4 (i.e., QDs and flake) and a heterojunction interface to, respectively, mimic the functional components of light-harvesting systems (LHSs, i.e., photosystem I and photosystem II) and electron transport chains (ETCs), and utilize the flake structure as the analogue of 2D thylakoid membrane. Therefore, QDs@Flake g-C3N4 showed remarkably improved capability in visible light harvesting and charge separation, and exhibited elevated performance in photocatalytic NADH regeneration with a regeneration yield of up to 40%. The NADH regeneration approach was then coupled with alcohol dehydrogenase catalyzed hydrogenation of formaldehyde, achieving continuous methanol production.

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.Keywords: biomimetic mineralization; catalysis; cationic polymers; graphene-based composite cellular foams; redox assembly;

Herein, a facile and generic method is developed to prepare ultrathin, robust nanohybrid capsules by manipulating the dynamic structure of supramolecular nanocoatings on CaCO3 sacrificial templates by incorporating a multivalent–anion substitution process into biomineralization. Above the biomineralization level, multivalent anions, for example, phosphate, sulfate, or citrate, are used to initiate the assembly of polyamine into continuous (nonsegregated) polyamine-anion supramolecular nanocoatings on CaCO3 sacrificial templates. When contacting with the sodium silicate solution, the multivalent anions in the supramolecular nanocoatings are substituted by silicate because of the difference in dissociation behavior, facilitating the structure-reconstruction of supramolecular nanocoatings. At the biomineralization level, the substituted silicate can not only bind to the polyamine through electrostatic and hydrogen bonding interactions but also undergo silicification to generate an interpenetrating silica framework. After dissolution of CaCO3, polyamine–silica nanohybrid capsules bearing an ultrathin wall of ∼10–17 nm in thickness are formed, which exhibit a super-high mechanical strength of ∼2337 MPa in elasticity modulus. The capsules are then utilized for bioreactor construction by encapsulating glucose oxidase. The ultrathin capsule wall facilitates the diffusion of substrates/products and elevates the conversion efficiency, whereas the high mechanical strength ensures the structural integrity of the capsules during multiple-cycle reactions. This method can also be applied for the preparation of ultrathin films on planar substrates, which would open a feasible way to prepare nanohybrid materials with different compositions and shapes.Keywords: biomineralization; bioreactor; multivalent−anion substitution; supramolecular nanocoating; ultrathin nanohybrid capsules;

In this study, a well-designed polysulfone with dense phenyl groups surrounding its backbone (designated as P(ES1-co-ES2)) was synthesized and then modified with abundant quaternary ammoniums (QA). The QA functionalized P(ES1-co-ES2) was added to QA functionalized poly (ether ether ketone) with N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) as crosslinking reagent to fabricate anion exchange imembranes (AEM). The incorporation of abundant QA groups substantially increased the ion exchange capacity of the blend membranes. Meanwhile, the densely QA functionalized P(ES1-co-ES2) acted as “hydroxide ion wires” in blend membranes, constructing efficient ion channels for high-speed ion transfer. High hydroxide conductivity up to 215.4 mS cm−1 at 90 °C and the maximum power density of single fuel cell up to 137.2 mW cm−2 at 60 °C were thus achieved. In addition, the strong covalent interaction caused by TMHDA led to significantly enhanced physical stability (anti-swelling, tensile strength and elongation etc.), while the steric hindrance by the long aliphatic chain of TMHDA enhanced the chemical stability of the blend membranes. This study presents a novel AEM with simultaneously enhanced hydroxide conductivity, physical and chemical stabilities.

As we face global challenges in energy, resources, and the environment, sustainable chemical processing must consider minimizing the use of natural resources, toxic materials, and energy and the generation of waste and pollutants. Biocatalysis can contribute to these goals and has been widely used because of its high activity, selectivity, and specificity and low energy requirement. The practical application of oxidoreductases, responsible for producing critical chemicals and pharmaceuticals, is limited by the dependence on an expensive cofactor that must be regenerated for reuse.This review introduces cofactor regeneration methods and highlights the use of heterogeneous systems toward enhancing sustainability. Future research should consider the use of hydrogen gas and strategies for improving catalytic efficiency, simplicity, and cleanliness and energy and/or cost savings, which will contribute to the UN Sustainable Development Goal of Responsible Consumption and Production for societal benefits.Biocatalysis can empower chemical, pharmaceutical, and energy industries, where the use of enzymes facilitates low-energy, sustainable methods of producing high-value chemicals and pharmaceuticals that are otherwise impossibly troublesome or costly to obtain. One of the largest classes of enzymes (oxidoreductases, ∼25% of the total) capable of promoting bioreduction reactions is vital for the global pharmaceutical and chemical market because of their intrinsic enantioselectivity and specificity. Enzymatic reduction depends on a coenzyme or cofactor as a hydride source, namely nicotinamide adenine dinucleotide (NADH) or its phosphorylated form (NADPH). Given the high cost, stoichiometric usage, and physical instability of NAD(P)H, a suitable method for NAD(P)H regeneration is essential for practical application. This review summarizes the existing methods for NAD(P)H regeneration, including enzymatic, chemical, homogeneous catalytic, electrochemical, photocatalytic, and heterogeneous catalytic routes. Particular focus is given to recent progress in developing heterogeneous systems with potential significance in terms of process simplicity, cleanliness, and energy and/or cost savings.Download high-res image (216KB)Download full-size image

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.Keywords: hierarchical structure; immobilized biocatalyst; in situ synthesis; loose connective tissue; microcapsules-in-hydrogel scaffolds

Nature has given us great inspirations to fabricate high-performance materials with extremely exquisite structures. Presently, particles with a superhydrophobic surface are prepared through nature-inspired polyphenol chemistry. Briefly, adhering of a typical polyphenol (tannic acid, widely existed in tea, red wine, chocolate, etc.) is first conducted on titania particles to form a multifunctional coating, which is further in charge of reducing Ag+ into Ag nanoparticles/nanoclusters (NPs/NCs) and responsible for grafting 1H,1H,2H,2H-perfluorodecanethiol, thus forming a lotus-leaf-mimic surface structure. The chemical/topological structure and superhydrophobic property of the as-engineered surface are characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), water contact angle measurements, and so on. On the basis of the hierarchical, superhydrophobic surface, the particles exhibit a fascinating capability to form liquid marble and show some possibility in the application of oil removal from water. After particles are in situ adhered onto melamine sponges, the acquired particle-functionalized sponge exhibits an absorption capacity of 73–175 times of its own weight for a series of oils/organic solvents and shows superior ease of recyclability, suggesting an impressive capability for treating oil spills.Keywords: Liquid marble formation; Lotus-leaf-mimic surface structure; Nature-inspired polyphenol chemistry; Oil spills treatment; Particles; Sponges; Superhydrophobic surface

•Enhanced biodiesel yield was obtained as CaO catalysts were treated by ethanol.•Abalone shell-derived CaO was synthesized and used for biodiesel.•The CaO catalyst modified by ethanol showed an enhanced activity compared to U-CaO.•The CaO catalyst modified by ethanol presented a higher reusability than U-CaO.•Strong basicity and porous structure of the catalyst led to good performance.In the present study, a highly efficient CaO-based catalyst was synthesized by using abalone shell as a precursor and ethanol as a modification agent for biodiesel production. The physico/chemical properties of the catalysts, which could be tailored by altering the ethanol-treatment temperature (room temperature, 100 °C and 160 °C), were monitored by X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis and Hammett indicator. Once treated with ethanol, the modified CaO (M-CaO) catalyst exhibited an increased catalytic activity mainly due to the high surface area, increased specific basicity and decreased crystalline size compared to the unmodified CaO (U-CaO) catalyst. Particularly, when the ethanol treatment temperature was 100 °C, the maximal yield of fatty acid methyl ester (FAME) for the M-CaO catalyst could reach 96.2% (87.5% for the U-CaO catalyst). Furthermore, the M-CaO catalyst exhibited good reusability, having a superior catalytic activity compared to the U-CaO catalyst after recycling for more than five cycles.

In this study, immobilized penicillin G acylase (PGA) was prepared via a facile and rapid approach of generating the TA-TiIV layer on PGA-adsorbed commercial resins (PGA@Resins). In brief, the TA-TiIV layer was constructed through coordination-enabled self-assembly of tannic acid (TA) and titanium(IV) bis(ammonium lactate) dihydroxide (Ti-BALDH). In comparison to PGA@Resins, TA-TiIV-capped PGA@Resins exhibited higher 6-aminopenicillanic acid (6-APA) productivity and enhanced operational stability along with comparable activity recovery during the catalytic hydrolysis of penicillin G potassium (PGK). Particularly, TA-TiIV-capped PGA@Resins exhibited relative activities of 103.7% and 81.51%, respectively, after 68-day storage and 20 cycles, indicating significantly enhanced storage and recycling stabilities compared to PGA@Resins (68.98% and 62.88%). Both immobilized PGA were further packed into a glass column for hydrolyzing PGK in a continuous flow reactor, where TA-TiIV-capped PGA@Resins displayed a much higher 6-APA yield (initial yield: 49.22% vs 28.99%; yield after 10 days: 17.39% vs 6.11%) than PGA@Resins.

An inverse replication method based on porous CaCO3 templates was developed to fabricate porous magnetic polymer microspheres (PMMSs) composed of biocompatible polydopamine and magnetic Fe3O4 nanoparticles. The preparation procedure involved the synthesis of Fe3O4@CaCO3 templates, infiltration and spontaneous polymerization of dopamine in template pores and finally the mild removal of templates. The particle size, the surface morphology and the pore structure (e.g., average pore size, pore volume, surface area, etc.) of porous PMMSs were facilely tailored by altering the templates. The as-prepared polydopamine microspheres PMMSs were applied to covalently immobilize YADH for catalyzing the conversion of formaldehyde to methanol. In comparison to the enzyme-conjugated PDA-coated Fe3O4 nanoparticles (PMNPs), the immobilized enzyme on porous PMMSs exhibited remarkably enhanced activity (specific activity: 162.3 U mg−1 enzyme vs. 97.6 U mg−1 enzyme; methanol yield: 95.5% vs. 57.1%; initial reaction rate: 0.15% s−1vs. 0.08% s−1), and desirable thermal/pH/recycling/storage stabilities, and particularly, easy separation from the bulk solution by an external magnetic field.

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), etc. 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.Keywords: enzyme immobilization; glucose oxidase; microcapsules; polyphenol chemistry; tannic acid;

In this study, an ultrathin, hybrid microcapsule is prepared though coordination-enabled one-step assembly of tannic acid (TA) and titanium(IV) bis(ammonium lactate) dihydroxide (Ti-BALDH) upon a hard-templating method. Briefly, the PSS-doped CaCO3 microspheres with a diameter of 5–8 μm were synthesized and utilized as the sacrificial templates. Then, TA-TiIV coatings were formed on the surface of the PSS-doped CaCO3 templates through soaking in TA and Ti-BALDH aqueous solutions under mild conditions. After removing the template by EDTA treatment, the TA-TiIV microcapsules with a capsule wall thickness of 15 ± 3 nm were obtained. The strong coordination bond between polyphenol and TiIV conferred the TA-TiIV microcapsules high structural stability in the range of pH values 3.0–11.0. Accordingly, the enzyme-immobilized TA-TiIV microcapsules exhibited superior pH and thermal stabilities. This study discloses the formation of TA-TiIV microcapsules that are suitable for use as supports in catalysis due to their extensive pH and thermal stabilities.Keywords: enzyme catalysis; hybrid materials; metal−organic coordination; microcapsules; weak pH-response;

In this study, a superhydrophobic, fire-resistant, and mechanical robust sponge was fabricated through a two-step polyphenol chemistry strategy for efficiently absorbing oils/organic solvents (rapidness in absorption rate and large quantity in absorption capacity). Specifically, the Fe(III)–polyphenol complex is formed upon the metal–organic coordination between tannic acid (TA, a typical polyphenol) and Fe(III) ions, which is spontaneously coated on the surface of the pristine melamine sponge. Then, free catechol groups in the polyphenol are applied for grafting 1-dodecanethiol, thus generating the superhydrophobic sponge. Several characterizations have confirmed the chemical/topological structures, superhydrophobicity, fire-resistant merits, and mechanical robust property of the sponge. As a result, this sponge exhibits excellent absorption capacities of oils/organic solvents up to 69–176 times its own weight, indicating promising sorbents for removing oily pollutants from water. Meanwhile, owing to the facile fabrication process and inexpensive/easy available raw materials, the large-scale production of this sponge will be convenient and cost-effective.

•A biomimetic silicification approach was developed to prepare CaO–SiO2 catalysts.•The catalysts were synthesized by using eggshell and Na2SiO3 as raw materials.•With increase of Si compound, the reusability of catalysts enhanced significantly.In the present study, CaO–SiO2 catalysts were successfully synthesized through a biomimetic silicification approach by using eggshell and Na2SiO3 as raw materials. More specifically, the powdered egg shells, where lysozyme (the inducer) was located, were dispersed into Na2SiO3 aqueous solution to implement the biomimetic silicification under ambient conditions. The as-obtained egg shell-SiO2 composites were then calcined at 800 °C under oxygen atmosphere, thus acquiring the CaO–SiO2 catalysts. These catalysts were detailedly characterized by SEM, EDS, 29Si NMR, FTIR, XRD, BET analysis, and Hammett indicator. When utilized for catalytic transesterification of palm oil, the CaO–SiO2 catalysts exhibited decreased catalytic activity and increased reusability as the amount of Si compounds increased. Particularly, when the Na2SiO3 concentration was below 0.4 M, a slight decrease in the catalytic activity could be observed (0Si5Ca, 1Si5Ca and 2Si5Ca showed good performance with biodiesel yields of 90.2%, 87.7% and 80.1%, respectively), whereas the reusability of the catalyst was significantly improved (little deactivation was found after 12 cycles on the 2Si5Ca catalyst during the transesterification reaction). Hopefully, this biomimetic silicification approach can be applied for the synthesis of a wide range of efficient and stable solid base catalysts for transesterification/esterification reactions.

Carbon materials have shown great potential in solving environmental problems resulting from the pollution from oils or organic solvents. However, developing low-cost and high-performance carbon-based three-dimensional (3D) frameworks is still a great challenge and highly desired. Herein, monolithic macroporous carbon (MMC) materials have been synthesized through the pyrolysis of kapok wadding materials (ultralow-cost fibrous materials, those comprised of fibers with the highest hollow degree in nature). Owing to their unique and superior properties, such as tubular structure, light weight, high porosity, desirable flexibility, and strong thermal/mechanical stability, the MMC materials exhibit a high loading capacity for organic solvents and oils (87–273 times their own weight) and excellent recyclability. Coupled with the easy, economical, and environment-friendly synthesis process, MMC materials will be promising candidates for industrial application for removing organic pollutants. Hopefully, the MMC materials and the corresponding synthesis approach will be further applied to wider applications (e.g., energy storage, synthesis of composite materials, and so on).

•The rGO–Fe3O4 nanocomposites are in situ synthesized via a metal ion-induced method.•Catalase is immobilized on the rGO–Fe3O4 nanocomposites through physical adsorption.•The immobilized CAT shows zero leaching, high activity recovery and excellent reusability.Herein, the reduced graphene oxide–Fe3O4 (rGO–Fe3O4) nanocomposites are synthesized by the simultaneous reduction of graphene oxide (GO) and in situ deposition of Fe3O4 nanoparticles (ca. 20 nm) enabled by Fe2+ ions. The rGO–Fe3O4 nanocomposites integrate the magnetic property of Fe3O4 nanoparticles and the large specific surface area of rGO nanosheets. Catalase (CAT), as a commonly used enzyme, can be efficiently immobilized on the rGO–Fe3O4 nanocomposites through physical adsorption. The CAT loading capacity is as high as 312.5 ± 12.6 mg g−1, while the activity recovery of CAT can be high up to nearly 98%. The strong magnetic response of immobilized CAT ensures its easy separation from the reaction system when an external magnetic field is applied. Owing to the hydrophobic and hydrogen bonding interactions between enzyme and the support, the immobilized CAT exhibits zero leaching, desirable stability and excellent reusability.Download high-res image (214KB)Download full-size image

An inverse replication method based on porous CaCO3 templates was developed to fabricate porous magnetic polymer microspheres (PMMSs) composed of biocompatible polydopamine and magnetic Fe3O4 nanoparticles. The preparation procedure involved the synthesis of Fe3O4@CaCO3 templates, infiltration and spontaneous polymerization of dopamine in template pores and finally the mild removal of templates. The particle size, the surface morphology and the pore structure (e.g., average pore size, pore volume, surface area, etc.) of porous PMMSs were facilely tailored by altering the templates. The as-prepared polydopamine microspheres PMMSs were applied to covalently immobilize YADH for catalyzing the conversion of formaldehyde to methanol. In comparison to the enzyme-conjugated PDA-coated Fe3O4 nanoparticles (PMNPs), the immobilized enzyme on porous PMMSs exhibited remarkably enhanced activity (specific activity: 162.3 U mg−1 enzyme vs. 97.6 U mg−1 enzyme; methanol yield: 95.5% vs. 57.1%; initial reaction rate: 0.15% s−1vs. 0.08% s−1), and desirable thermal/pH/recycling/storage stabilities, and particularly, easy separation from the bulk solution by an external magnetic field.