Triazine-based porous organic polymers for reversible capture of iodine and utilization in antibacterial application

Emerging trends in the development and applications of triazine-based covalent organic polymers: a comprehensive review

Owing to unique structural features, triazine-based covalent organic polymers (COPs) have attracted significant attention and emerged as novel catalysts or support materials for an array of applications. Typically formed by reacting triazine-based monomers or the in situ creation of triazine rings from nitrile monomers, these COPs possess 2D/3D meso/microporous structures held together via strong covalent linkages. The quest for efficient, stable and recyclable catalytic systems globally necessitates the need for a well-structured and comprehensive review summarizing the synthetic methodologies and applications of triazine-based COPs. This review explores the various synthetic routes and applications of these COPs in photocatalysis, heterogeneous catalysis, electrocatalysis, adsorption and sensing. By exploring the latest advancements and future directions, this review offers valuable insights into the synthesis and applications of triazine-based COPs.

Thiophene-Based Covalent Triazine Frameworks as Visible-Light-Driven Heterogeneous Photocatalysts for the Oxidative Coupling of Amines

This study reports on a metal-free Covalent Triazine Framework (CTF) incorporating bithiophene structural units (TP-CTF) with a semicrystalline structure as an efficient heterogeneous photocatalyst under visible light irradiation. The physico-chemical properties and composition of this material was confirmed via different characterization solid-state techniques, such as XRD, TGA, CO2 adsorption and FT-IR, NMR and UV-Vis spectroscopies. The compound was synthesized through a solvothermal process and was explored as a heterogeneous photocatalyst for the oxidative coupling of amines to imines under visible light irradiation. TP-CTF demonstrated outstanding photocatalytic activity, with high conversion rates and selectivity. Importantly, the material exhibited exceptional stability and recyclability, making it a strong candidate for sustainable and efficient imine synthesis. The low bandgap of TP-CTF enabled the efficient absorption of visible light, which is a notable advantage for visible-light-driven photocatalysis.

Reusable cellulose-based biosorbents for efficient iodine adsorption by economic microcrystalline cellulose production from walnut shell

Sustainable management of walnut shell (WS) for the extraction of cellulose and preparation of cellulose-based biosorbents of iodine was carried out as a new approach to simultaneously solve the environmental challenge of agricultural solid waste and iodine-contaminated water. A rapid recyclable nitric acid treatment and NaOH-H2O2 alkaline-peroxide treatment of WS (33 % cellulose) extracted pure microcrystalline (Cac) and impure cellulose (Cal) with a 21.70 % and 47.37 % isolation yield, respectively. The techno-economic assessment of cellulose production showed a net profit of 9.02 $/kg for Cac, whereas it was estimated as negative for Cal. The simultaneous carbonization and magnetization of Cac at 550 °C resulted in an amorphous, magnetic cellulose-derived biochar (MB550Cac) with a BET specific surface area of 12.64 m2/g, decorated with scattered irregular Fe3O4 microparticles. The adsorption capacity of MB550Cac for iodine was 555.63 mg/g, which was lost only 17.45 % after six successful cycles of regeneration. Freundlich isotherm model sufficiently described the reversible iodine adsorption on the heterogenous surface. The adsorption kinetics followed the pseudo-second-order model. Further, the adsorption thermodynamics demonstrated spontaneous and favorable adsorption. These findings suggest the valorization of WS to commercially produce cellulose and MB550Cac as a sustainable, efficient biosorbent with a good application prospect in wastewater treatment.

Construction of Ketoenamine-Based Covalent Organic Frameworks with Electron-Rich Sites for Efficient and Rapid Removal of Iodine from Solution

Porous covalent organic frameworks (COFs) have been widely used for the efficient removal of iodine from solution due to their abundance of electron-rich sites. In this study, two kinds of ketoenamine-based COFs, TpBD-(OMe)2 and TpBD-Me2, are successfully synthesized via Schiff base reaction under solvothermal conditions using 1, 3, 5-triformylphoroglucinol as aldehyde monomer, o-tolidine and o-dianisidine as amino monomers. The ability of TpBD-(OMe)2 and TpBD-Me2 to adsorb iodine in cyclohexane or aqueous solutions has been quantitatively analyzed and interpreted in terms of adsorption sites. TpBD-Me2 possesses two adsorption sites, -NH- and -C=O, and exhibits an adsorption capacity of 681.67 mg/g in cyclohexane, with an initial adsorption rate of 0.6 g/mol/min with respect to COF unit cell. The adsorption capacity of TpBD-(OMe)2 can be as high as 728.77 mg/g, and the initial adsorption rate of TpBD-(OMe)2 can reach 1.2 g/mol/min in the presence of oxygen atoms between the methyl group and the benzene ring. Compared with TpBD-Me2, the higher adsorption capacity and adsorption rate of TpBD-(OMe)2 towards iodine are not only reflected in organic solvents, but also in aqueous solutions. It is proven through X-ray photoelectron spectroscopy and Raman spectroscopy that iodine exists in the form of I2, I3-, and I5- within TpBD-(OMe)2 and TpBD-Me2 after adsorption. This work not only expands the application of COFs in the field of iodine adsorption, but also provides research ideas and important an experimental basis for the optimization of iodine adsorption sites.

Microbial involvement in iodine cycle: mechanisms and potential applications

Stable iodine isotopes are essential for humans as they are necessary for producing thyroid gland hormones. However, there are hazardous radioactive iodine isotopes that are emitted into the environment through radioactive waste generated by nuclear power plants, nuclear weapon tests, and medical practice. Due to the biophilic character of iodine radionuclides and their enormous biomagnification potential, their elimination from contaminated environments is essential to prevent the spread of radioactive pollution in ecosystems. Since microorganisms play a vital role in controlling iodine cycling and fate in the environment, they also can be efficiently utilized in solving the issue of contamination spread. Thus, this paper summarizes all known on microbial processes that are involved in iodine transformation to highlight their prospects in remediation of the sites contaminated with radioactive iodine isotopes.

Porous organic materials for iodine adsorption

The nuclear industry will continue to develop rapidly and produce energy in the foreseeable future; however, it presents unique challenges regarding the disposal of released waste radionuclides because of their volatility and long half-life. The release of radioactive isotopes of iodine from uranium fission reactions is a challenge. Although various adsorbents have been explored for the uptake of iodine, there is still interest in novel adsorbents. The novel adsorbents should be synthesized using reliable and economically feasible synthetic procedures. Herein, we discussed the state-of-the-art performance of various categories of porous organic materials including covalent organic frameworks, covalent triazine frameworks, porous aromatic frameworks, porous organic cages, among other porous organic polymers for the uptake of iodine. This review discussed the synthesis of porous organic materials and their iodine adsorption capacity and reusability. Finally, the challenges and prospects for iodine capture using porous organic materials are highlighted.

SiO2 nanospheres as surfactant and template in aqueous dispersion polymerizations yielding highly nanoporous resin particles

HYPOTHESIS

High nitrogen containing resins such as poly(melamine-co-formaldehyde) (PMF) are known for their very good adsorption properties. Until now, using an ecofriendly hard-templating approach with SiO₂ nanospheres in water for synthesis, only yielded either highly porous particles with diameters up to 1 µm or non-porous particles with diameters above 1 µm. Small particles cannot be used as fixed bed adsorbents in columns because of the very high pressure occurring.

EXPERIMENTS

To yield particles with high porosity and larger diameters for the use as fixed bed adsorbent, we investigated the influence of several synthesis parameters on porosity and particle morphology.

FINDINGS

From all variations, we proposed a mechanism for the complex interplay between the PMF prepolymer and resin species with SiO₂ nanoparticles acting both as Pickering-like surfactant and template particle. With this knowledge we were able to produce a suitable column material with high specific surface area up to 260 m²/g. We then proved the application of this material for aqueous dichromate adsorption in batch, yielding a maximum capacity of 138 mg/g with recyclability. In column experiments, the contamination of 5 mg/L dichromate in water was reduced to drinking water safe levels for an influent volume equal to over 160 bed volumes.

Recent advances in therapeutic targets identification and development of treatment strategies towards Pseudomonas aeruginosa infections

The opportunistic human pathogen Pseudomonas aeruginosa is the causal agent of a wide variety of infections. This non-fermentative Gram-negative bacillus can colonize zones where the skin barrier is weakened, such as wounds or burns. It also causes infections of the urinary tract, respiratory system or bloodstream. P. aeruginosa infections are common in hospitalized patients for which multidrug-resistant, respectively extensively drug-resistant isolates can be a strong contributor to a high rate of in-hospital mortality. Moreover, chronic respiratory system infections of cystic fibrosis patients are especially concerning, since very tedious to treat. P. aeruginosa exploits diverse cell-associated and secreted virulence factors, which play essential roles in its pathogenesis. Those factors encompass carbohydrate-binding proteins, quorum sensing that monitor the production of extracellular products, genes conferring extensive drug resistance, and a secretion system to deliver effectors to kill competitors or subvert host essential functions. In this article, we highlight recent advances in the understanding of P. aeruginosa pathogenicity and virulence as well as efforts for the identification of new drug targets and the development of new therapeutic strategies against P. aeruginosa infections. These recent advances provide innovative and promising strategies to circumvent infection caused by this important human pathogen.

Quinoid-Thiophene-Based Covalent Organic Polymers for High Iodine Uptake: When Rational Chemical Design Counterbalances the Low Surface Area and Pore Volume

A novel 2D covalent organic polymer (COP), based on conjugated quinoid-oligothiophene (QOT) and tris(aminophenyl) benzene (TAPB) moieties, is designed and synthesized (TAPB-QOT COP). Some DFT calculations are made to clarify the equilibrium between different QOT isomers and how they could affect the COP formation. Once synthetized, the polymer has been thoroughly characterized by spectroscopic (i.e., Raman, UV-vis), SSNMR and surface (e.g., SEM, BET) techniques, showing a modest surface area (113 m² g^-1) and micropore volume (0.014 cm³ g^-1 with an averaged pore size of 5.6-8 Å). Notwithstanding this, TAPB-QOT COP shows a remarkably high iodine (I₂) uptake capacity (464 %wt) comparable to or even higher than state-of-the-art porous organic polymers (POPs). These auspicious values are due to the thoughtful design of the polymer with embedded sulfur sites and a conjugated scaffold with the ability to counterbalance the relatively low pore volumes. Indeed, both morphological and Raman data, supported by computational analyses, prove the very high affinity between the S atom in our COP and the I₂. As a result, TAPB-QOT COP shows the highest volumetric I₂ uptake (i.e., the amount of I₂ uptaken per volume unit) up to 331 g cm^-3 coupled with a remarkably high reversibility (>80% after five cycles).

Covalent Organic Framework as a Metal-Free Photocatalyst for Dye Degradation and Radioactive Iodine Adsorption

Exploring a covalent organic framework (COF) material as an efficient metal-free photocatalyst and as an adsorbent for the removal of pollutants from contaminated water is very challenging in the context of sustainable chemistry. Herein, we report a new porous crystalline COF, C₆-TRZ-TPA COF, via segregation of donor-acceptor moieties through the extended Schiff base condensation between tris(4-formylphenyl)amine and 4,4',4″-(1,3,5-triazine-2,4,6-triyl)trianiline. This COF displayed a Brunauer-Emmett-Teller (BET) surface area of 1058 m² g^-1 with a pore volume of 0.73 cc g^-1. Again, extended π-conjugation, the presence of heteroatoms throughout the framework, and a narrow band gap of 2.2 eV, all these features collectively work for the environmental remediation in two different perspectives: it could harness solar energy for environmental clean-up, where the COF has been explored as a robust metal-free photocatalyst for wastewater treatment and as an adsorbent for iodine capture. In our endeavor of wastewater treatment, we have conducted the photodegradation of rose bengal (RB) and methylene blue (MB) as model pollutants since these are extremely toxic, are health hazard, and bioaccumulative in nature. The catalyst C₆-TRZ-TPA COF showed a very high catalytic efficiency of 99% towards the degradation of 250 parts per million (ppm) of RB solution in 80 min under visible light irradiation with the rate constant of 0.05 min^-1. Further, C₆-TRZ-TPA COF is found to be an excellent adsorbent as it efficiently adsorbed radioactive iodine from its solution as well as from the vapor phase. The material exhibits a very rapid iodine capturing tendency with an outstanding iodine vapor uptake capacity of 4832 mg g^-1.

Evaluation of an Imine-Linked Polymer Organic Framework for Storage and Release of H2S and NO

Hydrogen sulfide (H₂S) and nitric oxide (NO) are especially known as toxic and polluting gases, yet they are also endogenously produced and play key roles in numerous biological processes. These two opposing aspects of the gases highlight the need for new types of materials to be developed in addition to the most common materials such as activated carbons and zeolites. Herein, a new imine-linked polymer organic framework was obtained using the inexpensive and easy-to-access reagents isophthalaldehyde and 2,4,6-triaminopyrimidine in good yield (64%) through the simple and catalyst-free Schiff-base reaction. The polymeric material has microporosity, an A_BET surface area of 51 m²/g, and temperature stability up to 300 °C. The obtained 2,4,6-triaminopyrimidine imine-linked polymer organic material has a higher capacity to adsorb NO (1.6 mmol/g) than H₂S (0.97 mmol/g). Release studies in aqueous solution showed that H₂S has a faster release (3 h) from the material than NO, for which a steady release was observed for at least 5 h. This result is the first evaluation of the possibility of an imine-linked polymer organic framework being used in the therapeutic release of NO or H₂S.

Superfast Capture of Iodine from Air, Water, and Organic Solvent by Potential Dithiocarbamate-Based Organic Polymer

Organic polymers are widely explored due to their high stability, scalability, and more facile modification properties. We developed cost-effective dithiocarbamate-based organic polymers synthesized using diamides, carbon disulfide, and diamines to apply for environmental remediation. The sequestration of radioiodine is a serious concern to tackle when dealing with nuclear power for energy requirements. However, many of the current sorbents have the problem of slower adsorption for removing iodine. In this report, we discuss the utilization of an electron-rich dithiocarbamate-based organic polymer for the removal of iodine in a very short time and with high uptake. Our material showed 2.8 g/g uptake of vapor iodine in 1 h, 915.19 mg/g uptake of iodine from cyclohexane within 5 s, 93% removal of saturated iodine from water in 1 min, and 1250 mg/g uptake of triiodide ions from water within 30 s. To the best of our knowledge, the iodine capture was faster than previously observed for any existing material. The material was fully recyclable when applied for up to four cycles. Hence, this dithiocarbamate-based polymer can be a promising system for the fast removal of various forms of iodine and, thus, enhance environmental security.

Multifunctional nanoreactors with nutrient consumption and ROS generation capabilities for antibacterial and skin repair

Bacterial wound infection has brought a serious threat to human health and caused huge economic losses. Attempts to develop biomaterials with excellent antibacterial effects are meaningful to promote wound healing. Herein, we report a multifunctional nanoreactor with nutrient consumption and reactive oxygen species (ROS) generation capabilities for antibacterial and skin wound repair. The nanoreactor was constructed by the encapsulation of glucose oxidase (GOx) into a Cu²⁺-doped zeolite-based imidazole framework (ZIF-8) through a one-pot synthesis method. The nanoreactor not only consumes the nutrients of bacteria by the GOx-driven oxidation reaction, but also generates highly toxic hydroxyl radicals (˙OH) to kill bacteria via a Cu⁺-mediated Fenton-like reaction. Moreover, Zn²⁺ released from the nanoreactor is also capable of exhibiting synergistic antibacterial activity. In addition to mediating Fenton-like reactions, Cu²⁺ promotes angiogenesis to accelerate wound healing. Thus, the multifunctional nanoreactor has the ability to cut off the nutrient supply and starve the bacteria, produce ROS to kill bacteria, and promote angiogenesis to accelerate wound healing, enabling it to be promising for the treatment of wound infection.

Antiseptic Polymer-Surfactant Complexes with Long-Lasting Activity against SARS-CoV-2

Antiseptic polymer gel–surfactant complexes were prepared by incorporating the low-molecular-weight cationic disinfectant cetylpyridinium chloride into the oppositely charged, slightly cross-linked polymer matrices. Three types of polymers were used: copolymers of acrylamide and sodium 2-acrylamido-2-methylpropane sulfonate; copolymers of acrylamide and sodium methacrylate; copolymers of vinylpyrrolidone and sodium methacrylate. It was shown that the rate of the release of the cationic disinfectant from the oppositely charged polymer gels could be tuned in a fairly broad range by varying the concentration of the disinfectant, the degree of swelling, and degree of cross-linking of the gel and the content/type of anionic repeat units in the polymer matrix. Polymer–surfactant complexes were demonstrated to reduce SARS-CoV-2 titer by seven orders of magnitude in as little as 5 s. The complexes retained strong virucidal activity against SARS-CoV-2 for at least one week.