Coordination-Enabled One-Step Assembly of Ultrathin, Hybrid Microcapsules with Weak pH-Response

Enhancing corrosion resistance and self-healing of water-borne epoxy coatings using Ti3C2Tx-supported tannic acid on UIO-66-NH2

In this study, we developed a composite material comprising UIO-66-NH2 encapsulated tannic acid (TA) loaded on Ti3C2Tx to improve the corrosion resistance of water borne epoxy (WEP) coatings. The successful synthesis of the material was determined by FT-IR, XRD, XPS, EDS, TGA, SEM and TEM characterization. Furthermore, ultraviolet (UV)tests were conducted to evaluate the release rate of TA at varying pH levels, revealing a release rate of approximately 95 % at pH 2. Electrochemical impedance spectroscopy (EIS) results over 60 d indicated that the Rc value of TU-T/WEP remained unchanged at 3.934 × 108, demonstrating a two-order magnitude increase compared to those of pure epoxy coatings, attributed to the synergistic active and passive protection of TU-T materials. The self-healing ability of the TU-T/WEP coating was validated through manual scratch experiments. Additionally, the EIS test showed that the Rc value of TU-T/WEP coating increased to 3.5 × 105 after 72 h, representing a two-order magnitude increase over that of the WEP coating alone. This study introduces a novel approach using green tannic acid as a corrosion inhibitor and amino-functionalized Ti3C2Tx with UIO-66-NH2 to enhance corrosion resistance and self-healing aproperties of coatings.

Efficient adsorption of chloroquine phosphate by a novel sodium alginate/tannic acid double-network hydrogel in a wide pH range

In this work, a novel double-network composite hydrogel (SA/TA), composed of sodium alginate (SA) and tannic acid (TA), was designed and fabricated by a successive cross-linking method using Ti(IV) and Ca(II) as crosslinkers. SA/TA exhibited reinforced mechanical strength and anti-swelling properties because of the double-network structure. SA/TA was used as an adsorbent for removal of a popular antiviral drug, chloroquine phosphate (CQ), in water. The adsorption performance of SA/TA was systematically investigated, to study various effects including those of TA mass content, solution pH, adsorption time, and initial CQ concentration. Adsorption was also examined in presence of inorganic and organic coexisting substances commonly found in wastewater, and under different actual water samples. Batch experimental results indicated that SA/TA could maintain higher and more stable CQ uptakes within a wide solution pH range from 3.0 to 10.0, compared to its precursor, SA hydrogel, owing to the addition of TA-Ti(IV) coordination network. The maximum experimental CQ uptake exhibited by the 1:1 (by wt) SA/TA (SA/TA2) was as high as 0.699 mmol/g at the initial pH of 9.0. A high concentration of coexisting NaCl evidently reduced the CQ uptakes of SA/TA2 due to the electrostatic shielding effect, moreover, divalent cations including Ca(II) and Mg(II) also inhibited the adsorption of CQ due to competitive adsorption. However, humic acid had little effect on this adsorption. Considering the apparent adsorption performance, the aforementioned effects of various factors and the spectroscopic characterizations, multi-interactions are suggested for adsorption including chelation, electrostatic interactions, π-π electron donor-acceptor interaction and hydrogen bonding. SA/TA showed a slight loss in adsorption capacity toward CQ and sustained physicochemical structural stability, even after six adsorption-desorption cycles. In addition to CQ, SA/TA could be efficiently used for adsorption of two other antivirus drugs, namely, hydroxychloroquine sulfate and oseltamivir phosphate. This work provides an effective strategy for the design and fabrication of novel adsorbents that can effectively adsorb antiviral drugs over a wide pH range.

Efficient oil-water emulsion treatment via novel composite membranes fabricated by CaCO3-based biomineralization and TA-Ti(IV) coating strategy

Continuous increasing discharge of industrial oily wastewater and frequent occurrence of oil spill accidents have taken heavy tolls on global environment and human health. Organic-inorganic modifications can fabricate superhydrophilic/submerged superoleophobic membranes for efficient oil-water separation/treatment though they still suffer from complex operation, non-environmental friendliness, expensive cost or uneven distribution. Herein, a new strategy regarding tannic acid (TA)-Ti(IV) coating and CaCO₃-based biomineralization through simple inkjet printing processes was proposed to modify polyvinylidene fluoride (PVDF) membrane, endowing the membrane with high hydrophilicity (water contact angle (WCA) decreased from 86.01° to 14.94°) and underwater superoleophobicity (underwater contact angle (UOCA) > 155°). The optimized TA-Ti(IV)-CaCO₃ modified membrane possessed perfect water permeation to various oil/water emulsions (e.g., 355.7 L·m^-2·h^-1 for gasoline emulsion) under gravity with superior separation efficiency (>98.8 %), leading the way in oil/water emulsion separation performance of PVDF membranes modified with polyphenolic surfaces to our knowledge. Moreover, the modified membrane displayed rather high flux recovery after eight cycles of filtration while maintaining the original excellent separation efficiency. The modification process proposed in this study is almost independent of the nature of the substrate, and meets the demand for simple, inexpensive, rapid preparation of highly hydrophilic antifouling membranes, showing abroad application prospect for oil-water emulsion separation/treatment.

Biopolymer coating for particle surface engineering and their biomedical applications

Surface engineering of particles based on a polymeric coating is of great interest in materials design and applications. Due to the disadvantages of non-biodegradability and undesirable biocompatibility, the application of petroleum-based synthetic polymers coating in the biomedical field has been greatly limited. In addition, there is lack of a universal surface modification method to functionalize particles of different compositions, sizes, shapes, and structures. Thus, it is imperative to develop a versatile biopolymeric coating with good biocompatibility and tunable biodegradability for the preparation of functional particle materials regardless of their surface chemical and physical structures. Recently, the natural polysaccharide polymers (e.g. chitosan and cellulose), polyphenol-based biopolymers (e.g. polydopamine and tannic acid), and proteins (e.g. amyloid-like aggregates) have been utilized in surface modification of particles, and applications of these modified particles in the field of biomedicine have been also intensively exploited. In this review, the preparation of the above three coatings on particles surface are summarized, and the applications of these materials in drug loading/release, biomineralization, cell immobilization/protection, enzyme immobilization/protection, and antibacterial/antiviral are exemplified. Finally, the challenges and the future research directions on biopolymer coating for particles surface engineering are prospected.

Preparation and characterization of long-term antibacterial and pH-responsive Polylactic acid/Octenyl succinic anhydride-chitosan @ tea tree oil microcapsules

Encapsulation technology can increase the stability and maintain the volatile active substances of plant essential oils. In the present study, tree essential oil (TTO) was encapsulated with polylactic acid (PLA) modified by octenyl succinic anhydride chitosan (OSA-CS) as shell materials to form long-term antibacterial and pH-responsive microcapsules. The PLA/OSA-CS@TTO microcapsules were characterized by high performance liquid chromatography (HPLC), scanning electron microscopy (SEM) and antibacterial performance testing. The results showed that the average particle size of microcapsules was 10 μm, and the encapsulation efficiency and drug loading efficiency of TTO reached 81.5 % and 60.3 %. After 4800 min of release in media at different pH (5 and 7) still sequestered 55.32 % and 56.74 % of TTO which approved the shell of microcapsules responded to different pH values. The microcapsules remained stable for 80 days after drying, and preserving 39.7 % of the core material. The morphology of PLA/OSA-CS@TTO microcapsules revealed that the PLA/OSA-CS@TTO microcapsules presented smooth and firm structure. Antibacterial test for staphylococcus aureus of those microcapsules implied that the bacteriostatic rate reached 100 % after 72 h. Bio-based macromolecular modification strategies can provide inspiration for the development of green microcapsules.

Photocurrent and Gelation Properties of Polyphenol-Modified Titanium-Oxo Compounds

Organic-inorganic hybrid metal-polyphenols as stable structural modules have gained extensive interest due to their diverse applications. However, titanium-oxo compounds (TOCs) with large molecular polyphenols have been less explored, and they were expected to be different from small polyphenols with isolated metal ions. Herein, 4-methyl-esculetin (Mesc), a catechol derivative, was selected to construct three TOCs, namely, [Ti₁₇O₂₄(Mesc)₄(OⁱPr)₁₆] (1), [Ti₁₂O₁₄(OⁱPr)₁₈][Ti₁₆O₁₄(Mesc)₁₂(OⁱPr)₁₄] (2), and [Ti₃O(Mesc)₂(OAc)₂(OⁱPr)₄] (3). These compounds were structurally characterized. Photocurrent responses were evaluated using the compound-sensitized TiO₂ electrodes. It was found that the current densities of 1-3 electrodes are in the order of 1 ≫ 3 > 2, which relates to the ligand-to-TiO core and ligand-to-ligand charge transfers (LMCT and LLCT, respectively). Density functional theory calculations showed that the lowest band gap of 1 originates from its LLCT. Compound 1 reacted with polyphenol tannin (TA) to form a fully transparent and robust gel (1-TA), and the gelation properties were investigated. Using the gel as a nano-TiO₂ fixing agent, solar cell electrodes were prepared by a low-temperature wet method. The photocurrent responsive behavior of the 1-TA/TiO₂ electrode was compared with that of the 1-sensitized traditional high-temperature-treated TiO₂ electrode. Although the current density of the former is somewhat lower than that of the traditional electrode, the low-temperature wet preparation of the 1-TA/TiO₂ electrode is more energy-efficient and sustainable.

Metal Ion-Directed Functional Metal-Phenolic Materials

Metal ions are ubiquitous in nature and play significant roles in assembling functional materials in fields spanning chemistry, biology, and materials science. Metal-phenolic materials are assembled from phenolic components in the presence of metal ions through the formation of metal-organic complexes. Alkali, alkali-earth, transition, and noble metal ions as well as metalloids interacting with phenolic building blocks have been widely exploited to generate diverse hybrid materials. Despite extensive studies on the synthesis of metal-phenolic materials, a comprehensive summary of how metal ions guide the assembly of phenolic compounds is lacking. A fundamental understanding of the roles of metal ions in metal-phenolic materials engineering will facilitate the assembly of materials with specific and functional properties. In this review, we focus on the diversity and function of metal ions in metal-phenolic material engineering and emerging applications. Specifically, we discuss the range of underlying interactions, including (i) cation-π, (ii) coordination, (iii) redox, and (iv) dynamic covalent interactions, and highlight the wide range of material properties resulting from these interactions. Applications (e.g., biological, catalytic, and environmental) and perspectives of metal-phenolic materials are also highlighted.

Controlled release of metal phenolic network protected phage for treating bacterial infection

Phage is a promising therapeutic agent for treating antibiotic resistant bacteria. However, in the process of treatment, phage may be cleared by the immune system and cleaved by protease, which could affect the efficacy of phage. In order to solve the above problems, phage encapsulation is usually adopted. In this study, we employed metal phenolic network (MPN) for efficient phage encapsulation which could protect phage from the cleavage of protease, and keep cytotoxicity weak. In the model of skin wound infection, the encapsulated phage could be released in response to pH change to achieve good antibacterial effect. Furthermore, the MPN encapsulation could prolong the T4 phage residence time at the wound. Our findings suggest that MPN can be a promising material for phage encapsulation.

Recent Advances in Metal-Phenolic Networks for Cancer Theranostics

Nanomedicine integrates different functional materials to realize the customization of carriers, aiming at increasing the cancer therapeutic efficacy and reducing the off-target toxicity. However, efforts on developing new drug carriers that combine precise diagnosis and accurate treatment have met challenges of uneasy synthesis, poor stability, difficult metabolism, and high cytotoxicity. Metal-phenolic networks (MPNs), making use of the coordination between phenolic ligands and metal ions, have emerged as promising candidates for nanomedicine, most notably through the service as multifunctional theranostic nanoplatforms. MPNs present unique properties, such as rapid preparation, negligible cytotoxicity, and pH responsiveness. Additionally, MPNs can be further modified and functionalized to meet specific application requirements. Here, the classification of polyphenols is first summarized, followed by the introduction of the properties and preparation strategies of MPNs. Then, their recent advances in biomedical sciences including bioimaging and anti-tumor therapies are highlighted. Finally, the main limitations, challenges, and outlooks regarding MPNs are raised and discussed.

Sonochemical preparation of folate-decorated reductive-responsive carboxymethylcellulose-based nanocapsules for targeted drug delivery

In this study, a biocompatible folate-decorated reductive-responsive carboxymethylcellulose-based nanocapsules (FA-RCNCs) were designed and prepared via sonochemical method for targeted delivery and controlled release of hydrophobic drugs. The shell of FA-RCNCs was cross-linked by disulfide bonds formed from hydrosulfuryl groups on the thiolated carboxymethylcellulose (TCMC) and encapsulated hydrophobic drug dispersed in the oil phase into nanocapsules. Moreover, the size and morphology of drug loaded FA-RCNCs were characterized by DLS, SEM and CLSM which indicated that the synthesized nanocapsules have suitable size range and excellent stability for circulating in the bloodstream. The drug release rate of FA-RCNCs could be controlled by adjusting their sizes and shell thickness, which could be dominated by the concentration of TCMC and sonochemical conditions. Furthermore, the obtained FA-RCNCs could be ingested into Hela cells via folate-receptor (FR)-mediated endocytosis and quickly release drugs under reductive environment, which demonstrated that FA-RCNCs could become potential hydrophobic drugs carries for cancer therapy.

Three-dimensional nanoporous starch-based material for fast and highly efficient removal of heavy metal ions from wastewater

The development of advanced adsorbents with fast adsorption rate, simple preparation, low cost, and high adsorption capacity is one of the most important topics for water purification. Herein, a novel and pollution-free adsorbent, three-dimensional nanoporous starch-based nanomaterial (3D-PSN), was prepared via sacrifice template method and functionalized for the first time in this work. Relevant characterization was performed through XRD, SEM, TGA, zeta potential analysis, FTIR, and XPS to confirm the formation of nanomaterials. Owing to its unique three-dimensional network nanostructure and abundant active sites, this adsorbent displayed outstanding adsorption properties for heavy metal ions removal, as high as 532.28 mg/g for Cd (II), 381.47 mg/g for Hg(II), 354.15 mg/g for Cu(II), 238.39 mg/g for Pb(II), completed within 30 min. In this process, the pseudo-second-order kinetic model appeared more consistent with the adsorption kinetic data, and the adsorption behavior complied with the Langmuir adsorption model. The adsorption mechanism mainly replied on the ion-exchange reaction, as well as chemical complexation formation. This adsorbent has remarkable recyclability, exhibiting strong application prospects for water purification and environmental remediation.

pH-Triggered Release of NaNO2 Corrosion Inhibitors from Novel Colophony Microcapsules in Simulated Concrete Pore Solution

Herein, pH-sensitive microcapsules containing NaNO₂ corrosion inhibitors for protection of steel reinforced concrete were synthesized via water-in-oil-in-water (W/O/W) double emulsion using colophony as the wall material. The average microcapsule size was 79.07 μm in diameter and exhibited a high encapsulation efficiency of 83.2%. Study of the release of corrosion inhibitors from microcapsules in deionized water (DI water, pH 6.8), carbonate/bicarbonate buffer solution (CBS, pH 9.1), and simulated concrete pore solution (SCPS, pH 12.6) demonstrates that the microcapsules are sensitive to pH and display higher release in alkaline media. This is the first study of colophony as an encapsulating agent for corrosion inhibitors. Furthermore, the alkaline pH-triggered release shows the suitability of its use in reinforced concrete systems. A wide thermal stability range was also found for the colophony microcapsules up to 100 °C. These high pH environments (CBS and SCPS) present pH values above the pK_a of colophony (7.2), thus triggering enhanced inhibitor release by the ionization and deprotonation of colophony shell. The higher release in CBS and SCPS is demonstrated by the increases of the corrosion inhibitor diffusion coefficient by an order of magnitude from 3.30 × 10^-17 m²/s in DI water up to 1.66 × 10^-16 m²/s for SCPS. The release performance indicates that the proposed approach can be used to encapsulate a variety of inhibitors for the protection of steel reinforcements. After immersion in different pH solutions, the corrosion potentials of a carbon steel substrate with microcapsules containing nitrite were more noble than when immersed without microcapsules and the corrosion current densities showed comparable values to free corrosion inhibitors. The formation of a passive ferric oxide layer was confirmed by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy.

Supramolecular design and applications of polyphenol-based architecture: A review

Polyphenol-based materials are of wide-spread interest because of the unique properties of the polyphenol itself. Tannic acid, contains high level of galloyl groups, could be coordinated to a range of metal ions to generate robust mental ion-TA films on substrate or even forming hollow capsules. These films or capsules can be used in the field of sensing, separation and catalysis, most importantly in drug/nutraceutical delivery, allowing for the high loading efficiency, high mechanical and thermal stability, pH-responsive disassembly and fluorescence behavior. Additionally, such coating could also provide protection of the sensitive molecules and cells. With the numerous carbonyl and phenolic functional groups, TA has also been demonstrated to form strong hydrogen bonded multilayers with various non-ionic polymers. The properties of the hydrogen-bonded system were highly influenced by the chemical structure of the polymers, which will change the behavior of pH-, temperature- or ionic strength-responsive release of the loading molecules. Additionally, the ionization of galloyl phenol group was attributed to the interaction between TA and other ionic polymers by electrostatic interaction. The electrostatic interaction/hydrogen bonding derived TA/polyme$$%r complexes could deposit on glass slides, microcores or even forming hollow capsules, promising in their applicability to nutraceutical encapsulation, delivery and depot. Notably, polyphenols self-polymerizing could also deposit coatings on different substrates without any exogenous additives, while the comprehensive undertanding about the self-polymerizing mechenism remains unclear. This review provides a promising prospect for utilizing polyphenol-based materials to design versatile architecture in different system, used in the field of chemistry and materials science.

Bio-Inspired Underwater Super Oil-Repellent Coatings for Anti-Oil Pollution

Underwater superoleophobic surfaces have attracted great attention due to their broad applications such as anti-oil adhesion, oil capture and transportation, and oil/water separation. However, it is often fairly complex and time-consuming, involved in the construction of micro/nanostructures and the regulation of chemical compositions; there is an urgent need to develop new strategies to conquer these problems. Inspired by the strong anchoring capability and easy accessibility of plant polyphenols, we can readily and rapidly fabricate tannic acid (TA) coated copper surfaces with the excellent underwater super oil-repellent property. To achieve the optimal condition for TA modification, the influence of immersion time, TA concentration, and pH value on underwater-oil wettability and adhesion has been systematically explored. Furthermore, the underwater super oil-repellent feature can be widely achieved for different oils and on various metal sheets, suggesting the potential applications for plenty of fields such as anti-oil pollution.

Antifouling membranes for sustainable water purification: strategies and mechanisms

One of the greatest challenges to the sustainability of modern society is an inadequate supply of clean water. Due to its energy-saving and cost-effective features, membrane technology has become an indispensable platform technology for water purification, including seawater and brackish water desalination as well as municipal or industrial wastewater treatment. However, membrane fouling, which arises from the nonspecific interaction between membrane surface and foulants, significantly impedes the efficient application of membrane technology. Preparing antifouling membranes is a fundamental strategy to deal with pervasive fouling problems from a variety of foulants. In recent years, major advancements have been made in membrane preparation techniques and in elucidating the antifouling mechanisms of membrane processes, including ultrafiltration, nanofiltration, reverse osmosis and forward osmosis. This review will first introduce the major foulants and the principal mechanisms of membrane fouling, and then highlight the development, current status and future prospects of antifouling membranes, including antifouling strategies, preparation techniques and practical applications. In particular, the strategies and mechanisms for antifouling membranes, including passive fouling resistance and fouling release, active off-surface and on-surface strategies, will be proposed and discussed extensively.

Metal-Phenolic Carbon Nanocomposites for Robust and Flexible Energy-Storage Devices

Future electronics applications such as wearable electronics depend on the successful construction of energy-storage devices with superior flexibility and high electrochemical performance. However, these prerequisites are challenging to combine: External forces often cause performance degradation, whereas the trade-off between the required nanostructures for strength and electrochemical performance only results in diminished energy storage. Herein, a flexible supercapacitor based on tannic acid (TA) and carbon nanotubes (CNTs) with a unique nanostructure is presented. TA was self-assembled on the surface of the CNTs by metal-phenolic coordination bonds, which provides the hybrid film with both high strength and high pseudocapacitance. Besides 17-fold increased mechanical strength of the final composite, the hybrid film simultaneously exhibits excellent flexibility and volumetric capacitance.

Efficient incorporation of diverse components into metal organic frameworks via metal phenolic networks

A general and rapid strategy was explored for metal organic frameworks coating on various core components mediated by metal phenolic networks.

A Novel Platelet-Repellent Polyphenolic Surface and Its Micropattern for Platelet Adhesion Detection

Surface patterning provides a powerful tool to the diagnosis of platelet adhesion. However, the current methodologies of constructing platelet-patterned surfaces require laborious and complicated steps. Herein, a novel and simple platelet-repellent surface was reported by metal (Fe³⁺ ions)-polyphenol (tannic acid, TA) coordination interaction. The platelet-repellent effect was significantly better than that of poly(ethylene glycol) (PEG) in a long-term. Moreover, the platelet-repellent behavior could extend to other polyphenols-functionalized surfaces. On the basis of these observations, a TA-based micropattern was fabricated in situ by one-step microcontact printing for well-defined platelet adhesion, which can effectively avoid the traditional introduction of inert hydrophilic polymers and bioactive ligands. Afterward, the TA-based micropattern was applied to monitor the adhesion of defective platelets treated with an antiplatelet drug (tirofiban). This work provided a facile, versatile, and environmentally friendly strategy to construct platelet-repellent polyphenolic surfaces and their micropattern. We expect that this simple micropattern could act as a low-cost and label-free platform for biomaterials and biosensors, and could be widely used in the clinical diagnoses of platelet adhesive functions and the evaluation of antiplatelet therapies.

Conferring Natural-Derived Porous Microspheres with Surface Multifunctionality through Facile Coordination-Enabled Self-Assembly Process

In this study, multifunctional chitin microspheres are synthesized and utilized as a platform for multiple potential applications in enzyme immobilization, catalytic reduction and adsorption. Porous chitin microspheres with an average diameter of 111.5 μm and a porous architecture are fabricated through a thermally induced phase separation method. Then, the porous chitin microspheres are conferred with surface multifunctionality through facile coordination-enabled self-assembly of tannic acid (TA) and titanium (Ti(IV)) bis(ammonium lactate)dihydroxide (Ti-BALDH). The multipoint hydrogen bonds between TA and chitin microspheres confer the TA-Ti(IV) coating with high adhesion capability to adhere firmly to the surface of the chitin microspheres. In view of the biocompatibility, porosity and surface activity, the multifunctional chitin microspheres are used as carriers for enzyme immobilization. The enzyme-conjugated multifunctional porous microspheres exhibit high catalytic performance (102.8 U·mg(-1) yeast alcohol dehydrogenase). Besides, the multifunctional chitin microspheres also find potential applications in the catalytic reduction (e.g., reduction of silver ions to silver nanoparticles) and efficient adsorption of heavy metal ions (e.g., Pb(2+)) taking advantages of their porosity, reducing capability and chelation property.