Metal-phenolic network green flame retardants

Eco-friendly flame-retardant bamboo fiber/polypropylene composite based on the immobilization of halloysite nanotubes by tannic acid-Fe3+ complex

Bamboo fibers (BF), as an important sustainable natural material, are becoming a hot alternative to synthetic fibers for the reinforcement of polypropylene (PP)-based composites. However, the weak interfacial compatibility between BF and PP as matrix and their inherent flammability limit the practical application of BF/PP composites (BPC). Here, a fire-safe BPC was fabricated by constructing flame-retardant interfacial layers containing tannic acid (TA)-Fe3+ complex and halloysite nanotubes (HNTs) on the fiber matrix followed by a hot-pressing process. The results showed that the interfacial chelating of TA with Fe3+ improved the dispersion of HNTs on the fibers and the interfacial interactions within the fiber matrix, resulting in the as-fabricated composite with significantly improved mechanical properties and water resistance. In addition, the flame-retardant composite exhibited higher thermal stability and enhanced residual char content. Moreover, the composite possessed significant flame-retardant performances with a reduction of 23.75 % in the total heat release and 32.44 % in the total smoke production, respectively, owing to the flame retarding in gaseous phase and condensed phase of TA-Fe3+@HNTs layers. This work offers a green and eco-friendly strategy to address the inherent problems of BPC material in terms of fire safety and interfacial compatibility, thus broadening their applications in the automotive interior and construction industries.

Modification of cellulosic adsorbent via iron-based metal phenolic networks coating for efficient removal of chromium ion

Surface modification of durian rind cellulose (DCell) was done by utilizing the strong coordination effect of polyphenol-based metal phenolic networks (MPNs). MPNs from Fe(III)-tannic acid (FTN) and Fe(III)-gallic acid (FGN) were coated on DCell via a self-assembly reaction at pH 8, resulting in adsorbent composites of FTN@DCell and FGN@DCell for removal of Cr(VI). Batch adsorption experiments revealed that FTN coating resulted in an adsorbent composite with higher adsorption capacity than FGN coating, owing to the greater number of additional adsorption sites from phenolic hydroxyl groups of tannic acid. FTN@DCell exhibits an equilibrium adsorption capacity at 30°C of 110.9 mg/g for Cr(VI), significantly higher than FGN@DCell (73.63 mg/g); the adsorption capacity was increased at higher temperature (i.e., 155.8 and 116.8 mg/g at 50°C for FTN@DCell and FGN@DCell, respectively). Effects of pH, adsorbent dose, initial concentration, and coexisting ions on Cr(VI) removal were investigated. The kinetics fractal-based model Brouers-Sotolongo indicates the 1st and 2nd order reaction for Cr(VI) adsorption on FTN@DCell and FGN@DCell, respectively. The isotherm data can be described with a fractal-based model, which implies the heterogeneous nature of the adsorbent surface sites. The Cr(VI) adsorption via surface complexation with phenolic hydroxyl groups was confirmed by evaluating the functional groups shifting. FGN@DCell and FTN@DCell were found to have good reusability, maintaining over 50 % of their adsorption efficiency after four adsorption-desorption cycles. Environmental assessment with Arabidopsis thaliana demonstrated their potential in eliminating the Cr(VI) phytotoxic effect. Thus, this study has shown the efficient and economical conversion of durian waste into environmentally benign adsorbent for heavy metal treatment.

Nanocellulose-based composite aerogels toward the environmental protection: Preparation, modification and applications

Nanocellulose aerogel has the advantages of porosity, low density and high specific surface area, which can effectively realize the adsorption and treatment of wastewater waste gas. The methods of preparing nanocellulose mainly include mechanical, chemical and biological methods. Nanocellulose is formed into nanocellulose aerogel after gelation, solvent replacement and drying processes. Based on the advantages of easy modification of nanocellulose aerogels, nanocellulose aerogels can be functionalized with conductive fillers, reinforcing fillers and other materials to give nanocellulose aerogels in electrical, mechanical and other properties. Through functionalization, the properties of nanocellulose composite aerogel such as hydrophobicity and adsorption are improved, and the aerogel is endowed with the ability of electrical conductivity and electromagnetic shielding. Through functionalization, the applicability and general applicability of nanocellulose composite aerogel in the field of environmental protection are improved. In this paper, the preparation and functional modification methods of nanocellulose aerogels are reviewed, and the application prospects of nanocellulose composite aerogels in common environmental protection fields such as dye adsorption, heavy metal ion adsorption, gas adsorption, electromagnetic shielding, and oil-water separation are specifically reviewed, and new solutions are proposed.

Recent advances in metal-family flame retardants: a review

The use of polymer materials is inextricably linked to our manufacturing life. However, most of them are easily combusted in the air and the combustion process generates a large amount of toxic fumes and dangerous smoke. This can result in injuries and property damage, as well as limiting their use. It is essential to enhance the flame-retardant properties and smoke suppression performance by using multiple flame retardants. Metal-based flame retardants have a unique chemical composition. They are environmentally friendly flame retardants, which can impart good smoke suppression, flame retardancy to polymers and further reduce the production of toxic gases. The differences in the compounds formed between the transition metals and the main group metals make them act differently as flame retardants for polymers. As a result, this study presents the research progress and flame-retardant mechanism of flame-retardant polymers for flame retardants from different groups of metals in the periodic table of elements in a systematic manner. In view of the differences between the main group metals and transition metals, the mechanism of their application in flame retardant polymer materials is carefully detailed, as are their distinct advantages and disadvantages. And ultimately, prospects for the development of transition metals and main group metals are outlined. It is hoped that this paper will provide valuable references and insights for scholars in the field.

Synthesis and Applications of Supramolecular Flame Retardants: A Review

The development of different efficient flame retardants (FRs) to improve the fire safety of polymers has been a hot research topic. As the concept of green sustainability has gradually been raised to the attention of the whole world, it has even dominated the research direction of all walks of life. Therefore, there is an urgent calling to explore the green and simple preparation methods of FRs. The development of supramolecular chemistry in the field of flame retardancy is expanding gradually. It is worth noting that the synthesis of supramolecular flame retardants (SFRs) based on non-covalent bonds is in line with the current concepts of environmental protection and multi-functionality. This paper introduces the types of SFRs with different dimensions. SFRs were applied to typical polymers to improve their flame retardancy. The influence on mechanical properties and other material properties under the premise of flame retardancy was also summarized.

An Organometallic Flame Retardant Containing P/N/S-Cu2+ for Epoxy Resins with Reduced Fire Hazard and Smoke Toxicity

Epoxy resins (EPs) have superior physical and chemical features and are used in a wide range of applications in everyday life and engineering. However, its poor flame-retardant performance has hindered its wide application. Over the past decades of extensive research, metal ions have received increasing attention for their highly effective smoke suppression properties. In this work, we used an "aldol-ammonia condensation" reaction to structure the Schiff base structure, together with grafting using the reactive group on 9,10-dihydro-9-oxa-10-phospha-10-oxide (DOPO). Then, Cu²⁺ was used to replace Na⁺ to obtain DCSA-Cu flame retardant with smoke suppression properties. Attractively, DOPO and Cu²⁺ can collaborate, thus effectively improving EP fire safety. At the same time, the addition of a double-bond initiator at low temperatures allows small molecules to form in situ macromolecular chains through the EP network, enhancing the tightness of the EP matrix. With the addition of 5 wt % flame retardant, the EP shows well-defined fire resistance, and the limiting oxygen index (LOI) reaches 36% with a significant reduction in the values of peak heat release (29.72%). In addition, the glass-transition temperature (T_g) of the samples with in situ formations of macromolecular chains was improved, and the physical properties of EP materials are also retained.

An injectable all-small-molecule dynamic metallogel for suppressing sepsis

All-small-molecule dynamic hydrogels have shown great promise in cell culture, tissue engineering, and controlled drug release. The further development of more kinds of all-small-molecule dynamic hydrogels is severely hindered by the lack of enough commensurate building blocks from nature and on the market. Inspired by the widely developed metal-organic framework structures, herein we report a facile fabrication of metallogels by direct gelation of small molecular compounds including aminoglycosides (AGs), 2,2'-bipyridine-4,4'-dicarboxaldehyde (BIPY), and metal ions via coordination interactions and Schiff base reactions. These prepared metallogels exhibited good biodegradability and biosafety, excellent conductivity, tunable mechanical properties and potent antibacterial activities both in vitro and in vivo. This study provides a new strategy for expanding the scope of all-small-molecule dynamic metallogels for various biomedical applications.

Polyphenolic-modified cellulose acetate membrane for bone regeneration through immunomodulation

To enhance the bioactivity of cellulosic derivatives has become an important strategy to promote their value for clinical applications. Herein, protocatechualdehyde (PCA), a polyphenolic molecule, was used to modify a cellulose acetate (CA) membrane by combining with metal ions to confer an immunomodulatory activity. The PCA-modified CA membrane has shown a significant radical scavenging activity, thereby suppressed the inflammatory response and created a favorable immune microenvironment for osteogenesis and mineralization. Moreover, addition of metal ions could further stimulate the osteogenic differentiation of stem cells and accelerate bone regeneration both in vitro and in vivo. This study may provide a strategy to promote the immunomodulatory activity of cellulose-based biomaterials for bone regeneration.

High Value Utilization of Waste Wood toward Porous and Lightweight Carbon Monolith with EMI Shielding, Heat Insulation and Mechanical Properties

With the increasing pollution of electromagnetic (EM) radiation, it is necessary to develop low-cost, renewable electromagnetic interference (EMI) shielding materials. Herein, wood-derived carbon (WC) materials for EMI shielding are prepared by one-step carbonization of renewable wood. With the increase in carbonization temperature, the conductivity and EMI performance of WC increase gradually. At the same carbonization temperature, the denser WC has better conductivity and higher EMI performance. In addition, due to the layered superimposed conductive channel structure, the WC in the vertical-section shows better EMI shielding performance than that in the cross-section. After excluding the influence of thickness and density, the specific EMI shielding effectiveness (SSE/t) value can be calculated to further optimize tree species. We further discuss the mechanism of the influence of the microstructure of WC on its EMI shielding properties. In addition, the lightweight WC EMI material also has good hydrophobicity and heat insulation properties, as well as good mechanical properties.

Versatile Assembly of Metal-Phenolic Network Foams Enabled by Tannin-Cellulose Nanofibers

Metal-phenolic network (MPN) foams are prepared using colloidal suspensions of tannin-containing cellulose nanofibers (CNFs) that are ice-templated and thawed in ethanolic media in the presence of metal nitrates. The MPN facilitates the formation of solid foams by air drying, given the strength and self-supporting nature of the obtained tannin-cellulose nanohybrid structures. The porous characteristics and (dry and wet) compression strength of the foams are rationalized by the development of secondary, cohesive metal-phenolic layers combined with a hydrogen bonding network involving the CNF. The shrinkage of the MPN foams is as low as 6% for samples prepared with 2.5-10% tannic acid (or condensed tannin at 2.5%) with respect to CNF content. The strength of the MPN foams reaches a maximum at 10% tannic acid (using Fe^(III) ions), equivalent to a compressive strength 70% higher than that produced with tannin-free CNF foams. Overall, a straightforward framework is introduced to synthesize MPN foams whose physical and mechanical properties are tailored by the presence of tannins as well as the metal ion species that enable the metal-phenolic networking. Depending on the metal ion, the foams are amenable to modification according to the desired application.

Plasma Meets MOFs: Synthesis, Modifications, and Functionalities

As a porous and network materials consisting of metals and organic ligands, metal-organic frameworks (MOFs) have become one of excellent crystalline porous materials and play an important role in the era about materials science. Plasma, as a useful tool for stimulating efficient reactions under many conditions, and the plasma-assisted technology gets more attractions and endows MOFs more properties. Based on its feature, the research about the modifications and functionalities of MOFs have been developing a certain extent. This review contains a description of the methods for plasma-assisted modification and synthesis of MOFs, with specifically focusing on the plasma-assisted potential for modifications and functionalities of MOFs. The different applications of plasma-assisted MOFs were also presented.

Thermal, Mechanical and Dielectric Properties of Polyimide Composite Films by In-Situ Reduction of Fluorinated Graphene

Materials with outstanding mechanical properties and excellent dielectric properties are increasingly favored in the microelectronics industry. The application of polyimide (PI) in the field of microelectronics is limited because of the fact that PI with excellent mechanical properties does not have special features in the dielectric properties. In this work, PI composite films with high dielectric properties and excellent mechanical properties are fabricated by in-situ reduction of fluorinated graphene (FG) in polyamide acid (PAA) composites. The dielectric permittivity of pure PI is 3.47 and the maximum energy storage density is 0.664 J/cm³ at 100 Hz, while the dielectric permittivity of the PI composite films reaches 235.74 under the same conditions, a 68-times increase compared to the pure PI, and the maximum energy storage density is 5.651, a 9-times increase compared to the pure PI films. This method not only solves the problem of the aggregation of the filler particles in the PI matrix and maintains the intrinsic excellent mechanical properties of the PI, but also significantly improves the dielectric properties of the PI.

Robust and multifunctional natural polyphenolic composites for water remediation

The scarcity of clean water has become a global environmental problem which constrains the development of public health, economy, and sustainability. In recent years, natural polyphenols have drawn increasing interests as promising platforms towards diverse water remediation composites and devices, owing to their abundant and renewable resource in nature, highly active surface chemistry, and multifunctionality. This review aims to summarize the most recent advances and highlights of natural polyphenol-based composite materials (e.g., nanofibers, membranes, particles, and hydrogels) for water remediation, by focusing on their structural and functional features, as well as their diversified applications including membrane filtration, solar distillation, adsorption, advanced oxidation processes, and disinfection. Finally, the future challenges in this field are also prospected. It is anticipated that this review will provide new opportunities towards the future development of natural polyphenols and other kinds of naturally occurring molecules in water purification applications.

Phytic Acid-Iron/Laponite Coatings for Enhanced Flame Retardancy, Antidripping and Mechanical Properties of Flexible Polyurethane Foam

The use of flexible polyurethane foam (FPUF) is severely limited due to its flammability and dripping, which can easily cause major fire hazards. Therefore, choosing an appropriate flame retardant to solve this problem is an urgent need. A coating was prepared on the FPUF surface by dipping with phytic acid (PA), Fe2(SO4)3·xH2O, and laponite (LAP). The influence of PA-Fe/LAP coating on FPUF flame-retardant performance was explored by thermal stability, flame retardancy, combustion behavior, and smoke density analysis. FPUF/PA-Fe/LAP has a good performance in the small fire test, which can pass the UL-94 V-0 rating and the limiting oxygen index reaches 24.5%. Meanwhile, the peak heat release rate values and maximum smoke density of FPUF/PA-Fe/LAP are reduced by 38.7% and 38.5% compared with those of neat FPUF. After applying PA-Fe/LAP coating, the value of fire growth rate index decreases from 10.5 kW/(m2·s) to 5.1 kW/(m2·s), dramatically reducing the fire risk. Encouragingly, the effect of PA-Fe/LAP coating on cyclic compression and permanent deformation is small, which is close to that of neat FPUF. This work provides an effective strategy for making a flame-retardant FPUF with antidripping and keeping mechanical properties.

Versatile polyphenolic platforms in regulating cell biology

Polyphenolic materials are a class of fascinating and versatile bioinspired materials for biointerfacial engineering. In particular, due to the presence of active chemical groups, a series of unique physicochemical properties become accessible and tunable of the as-prepared polyphenolic platforms, which could delicately regulate the cell activities via cell-material contact-dependent interactions. More interestingly, polyphenols could also affect the cell behaviors via cell-material contact-independent manner, which arise due to their intrinsically functional characteristics (e.g., antioxidant and photothermal behaviors). As such, a comprehensive understanding on the relationship between material properties and desired biomedical applications, as well as the underlying mechanism at the cellular and molecular level would provide material design principles and accelerate the lab-to-clinic translation of polyphenolic platforms. In this review, we firstly give a brief overview of cell hallmarks governed by surrounding cues, followed by the introduction of polyphenolic material engineering strategies. Subsequently, a detailed discussion on cell-polyphenols contact-dependent interfacial interaction and contact-independent interaction was also carefully provided. Lastly, their biomedical applications were elaborated. We believe that this review could provide guidances for the rational material design of multifunctional polyphenols and extend their application window.

Fabrication of Functional Polycatechol Nanoparticles

While low-dimensional (1D and 2D) polycatechol materials have been widely described for a range of biomedical and surface engineering applications, very few examples have been explored that focus on the construction of functional polycatechol nanoparticles. Herein, we report the facile fabrication of a series of polycatechol nanoparticles via a general and robust strategy based on the one-step oxidation reaction. IO₃^--induced catechol redox chemistry could facilitate the precise size control of the resulting nanoparticles and also allow the successful transfer and amplification of microscopic monomer function into macroscopic polycatechol material properties. The ease, facileness, and controllability of such a one-step fabrication process could highly promote the development of polycatechol nanomaterials for various applications.

Therapeutic Nanoparticles from Grape Seed for Modulating Oxidative Stress

The therapeutic potential of nanomaterials toward oxidative damage relevant diseases has attracted great attentions by offering promising advantages compared with conventional antioxidants. Although different kinds of nanoantioxidants have been well developed, the facile fabrication of robust and efficient nanoscavengers is still met with challenges like the use of toxic and high-cost subunits, the involvement of multistep synthetic process, and redundant purification work. Herein, a direct fabrication strategy toward polyphenol nanoparticles with tunable size, excellent biocompatibility, and reactive oxygen species (ROS) scavenging capacities from grape seed via an enzymatic polymerization method is reported. The resulting nanoparticles can efficiently prevent cell damage from ROS and exert promising in vivo antioxidant therapeutic effects on several oxidative stress-related diseases, including accelerating wound healing, inhibiting ulcerative colitis, and regulating the oxidative stress in dry eye disease. This study can stimulate the development of more kinds of low-cost, safe, and efficient biomass-based antioxidative nanomaterials via similar fabrication methodologies.

Synthesis of a Reactive Template-Induced Core-Shell PZS@ZIF-67 Composite Microspheres and Its Application in Epoxy Composites

Developing superior properties of epoxy resin composites with high fire resistance, light smoke, and low toxicity has been the focus of the research in the flame-retardant field. In particular, it is essential to decrease the emissions of toxic gases and smoke particles generated during the thermal decomposition of epoxy resin (EP) to satisfy the industrial requirements for environmental protection and safety. Consequently, the PZS@ZIF-67 composite was designed and synthesized by employing the hydroxyl group-containing polyphosphazene (poly(cyclotriphosphazene-co-4,4'-dihydroxydiphenylsulfone), PZS) as both the interfacial compatibility and an in situ template and the ZIF-67 nanocrystal as a nanoscale coating and flame-retardant cooperative. ZIF-67 nanocrystal with multidimensional nanostructures was uniformly wrapped on the surface of PZS microspheres. Subsequently, the acquired PZS@ZIF-67 composite was incorporated into the epoxy resin to prepare composite samples for the study of their fire safety, toxicity suppression, and mechanical performance. Herein, the EP/5% PZS@ZIF-67 passed the V-0 rating in a UL-94 test with a 31.9% limit oxygen index value. More precisely, it is endowed with a decline of 51.08%, 28.26%, and 37.87% of the peak heat release rate, the total heat release, and the total smoke production, respectively. In addition, the unique structure of PZS@ZIF-67 microsphere presented a slight impact on the mechanical properties of EP composites at low loading. The PZS@ZIF-67 possible flame-retardant mechanism was speculated based on the analysis of the condensed phase and the gas phase of EP composites.