Unveiling the Impact of Diverse Morphology of Ionic Porous Organic Polymers with Mechanistic Insight on the Ultrafast and Selective Removal of Toxic Pollutants from Water

Heavy Metal-Based Toxic Oxo-Pollutants Sequestration by Advanced Functional Porous Materials for Safe Drinking Water

ConspectusWater scarcity as a consequence of either environmental or economic actions is the most compelling global concern of the 21st century, as ∼2 billion people (26% of the total population) struggle to access safe drinking water and ∼3.6 billion (46% of the total population) lack access to clean water sanitation. In this context, groundwater pollution by toxic heavy metals and/or their oxo-pollutants, such as CrO42-, Cr2O72-, AsO43-, SeO32-, SeO42-, TcO4-, UO22+, etc., have been becoming rapidly growing global concerns. The severe toxicity upon bioaccumulation of these oxo-anions has prompted the US Environment Protection Agency (EPA) to mark these persistent and hazardous substances as priority pollutants. Additionally, the heavy-metal-based pollutants are difficult to transform into eco-friendly substances, thus presenting serious challenges toward human health and environmental preservation. To this end, the emergence of advanced functional porous materials (AFPMs), including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), metal-organic polyhedrons (MOPs), porous organic polymers (POPs), etc., have presented extraordinary opportunities in material research and water treatment applications. The liberty in designing and structural tunability of AFPMs, facilitated by utilization of structure-encoded molecular building blocks, enables precise control over target-specificity and structure-property correlations. Bridging the gap between strategic material design and on-demand real-world application can facilitate the development of next-generation sorbents/ion-exchangers for efficient water treatment.In this Account, we summarize the recent advancements from our group toward the development of cutting-edge multifunctional ionic-porous sorbents, offering viable solutions toward providing clean and safe drinking water. Our vision allows us to comprehend this challenge through two strategic factors: efficient oxo-anion capture via ion-exchange and specific host-guest interactions via installation of modular functional groups. To provide an overview, we first highlight the different structural variants and coexistance of various toxic oxo-anions depending on the pH of the medium and their adverse effects. Next, we highlight the promising potential of water stable cationic MOFs toward selective remediation of toxic Cr(VI), Mn(VII), Tc(VI), Se(IV), Se(VI), U (VI), As(III), and As(V)-based toxic oxo-pollutants from water. In the subsequent sections, we summarize the target-specific design strategies and oxo-anion remediation performances of ionic porous organic polymers and hybrid functional porous materials. The key role of target-specific designability and/or structural fine-tuning of AFPMs toward preferential sorption of oxo-pollutants is systematically demonstrate. Particularly, the role of ion-exchange (anion-exchange) processes toward targeted oxo-pollutant capture by ionic AFPMs has been discussed in details. In several examples, the AFPMs were successful in reducing the toxic oxo-anion concentration levels lower than the permitted values for drinking water by the World Health Organizing Committee (WHO), showcasing their real-world applicability potency.Our contemporaneous endeavors in exploring ionic AFPMs for selective toxic oxo-anion sequestration may serve as a blueprint to researchers for future development of the next generation sorbent materials for energy-economically feasible water treatment methods.

Scavenging Radionuclide by Shapeable Porous Materials

Nuclear energy is a competitive and environmentally friendly low-carbon energy source. It is seen as an important avenue for satisfying energy demands, responding to the energy crisis, and mitigating global climate change. However, much attention has been paid to achieving the effective treatment of radionuclide ions produced in nuclear waste. Initially, advanced adsorbents were mainly available in powder form, which meant that additional purification processes were usually required for separation and recovery in industrial applications. Therefore, to meet the practical requirements of industrial applications, materials need to be molded and processed into forms such as beads, membranes, gels, and resins. Here, we summarize the fabrication of porous materials used for capturing typical radionuclide ions, including UO2 2+, TcO4 -, IO3 -, SeO3 2-, and SeO4 2-.

Electrochemical Formation of Ionic Porous Organic Polymers Based on Viologen for Electrochromic Applications

The systematic study of two ionic porous organic polymers (iPOPs) based on viologens and their first applications in the electrochromic field are reported. The viologen-based iPOPs are synthesized by electrochemical polymerization with cyano groups, providing a simple and controllable method for iPOPs that solves the film preparation problems common to viologens. After the characterization of these iPOPs, a detailed study of their electrochromic properties is conducted. The iPOP films based on viologens structure exhibit excellent electrochromic properties. In addition, the resulting iPOP films show high sensitivity to electrolyte ions of different sizes in the redox process. Electrochemical and electrochromic data of the iPOPs explain this phenomenon in detail. These results demonstrate that iPOPs of this type are ideal candidates as electrochromic materials due to their inherent porous structures and ion-rich properties.

Synthesis and performance of guanidinium-based cationic organic polymer for the efficient removal of TcO4-/ReO4. JOURNAL OF HAZARDOUS MATERIALS 2024;466:133602. [PMID: 38286051 DOI: 10.1016/j.jhazmat.2024.133602] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Cationic organic polymers have found relatively extensive utility for TcO4-/ReO4- removal, but the harsh preparation conditions constrain their practical application. The bifunctional guanidinium-based cationic organic polymer (GBCOP) was successfully and facilely synthesized in benign conditions within 1 h. Batch experiments showed that GBCOP exhibited rapid removal kinetics (1 min, >98.0%) and a substantial removal capacity of 536.8 mg/g for ReO4-. Even in 1000-fold co-existing NO3- anions, the removal efficiency of GBCOP for ReO4- was 74.0%, indicating its good selectivity. Moreover, GBCOP had high removal efficiencies for ReO4- across a wide pH (3.0-10.0) range and presented remarkable stability under the conditions of strong acid and base. GBCOP could be reused four times while removing 80.8% ReO4- from simulated Hanford wastewater. SEM and XPS results revealed that the mechanism of ReO4- removal involved Cl- ion exchange within the channels of GBCOP. Theoretical calculation results supported that existing the strong electrostatic interaction between guanidinium and ReO4-. This dual-function GBCOP material is cost-effective and holds significant potential for large-scale preparation, making it a promising solution for TcO4- removal from nuclear wastewater.

Synthesis of cyano and ionic dual-functional hypercrosslinked porous polymer for effective adsorption and detection of endocrine disrupting chemicals in milk matrix

Endocrine disrupting chemicals (EDCs) can interfere with the normal function of endocrine system, posing serious risk to human health. The monitoring of EDCs in foods is of great importance to ensure food security. Herein, a cyano and ionic dual-functionalized hypercrosslinked porous polymer (CN-iHCP) was designed and prepared for the first time through hyper-crosslink of 1-(4-cyanophenyl)imidazole and 1,4-bis(chloromethyl)benzene. The adsorption mechanism mainly involves electrostatic interaction, hydrogen bonding and π-π stacking interaction. A sensitive analytical method for simultaneous detection of the four phenolic EDCs was established by coupled CN-iHCP based solid-phase extraction with high performance liquid chromatography. Under optimal conditions, the target EDCs exhibited good linearity with coefficient r > 0.993 and high enrichment factors of 164-243. The detection limits (S/N = 3) of EDCs were 0.20-0.50 ng mL-1 for milk sample. The extraction recoveries for the spiked milk samples were in the range of 85.5%- 116.0%. This work not only highlights the CN-iHCP as a promising adsorbent to efficiently enrich EDCs and other pollutants, but also provides a new strategy for the functionalization of HCP for wide applications.

A Water-Stable Cationic SIFSIX MOF for Luminescent Probing of Cr2 O7 2- via Single-Crystal to Single-Crystal Transformation

The sensing and monitoring of toxic oxo-anion contaminants in water are of significant importance to biological and environmental systems. A rare hydro-stable SIFSIX metal-organic framework, SiF6 @MOF-1, {[Cu(L)2 (H2 O)2 ]·(SiF6 )(H2 O)}n , with exchangeable SiF6 2- anion in its pore is strategically designed and synthesized, exhibiting selective detection of toxic Cr2 O7 2- oxo-anion in an aqueous medium having high sensitivity, selectivity, and recyclability through fluorescence quenching phenomena. More importantly, the recognition and ion exchange mechanism is unveiled through the rarely explored single-crystal-to-single crystal (SC-SC) fashion with well-resolved structures. A thorough SC-SC study with interfering anions (Cl- , F- , I- , NO3 - , HCO3 - , SO4 2- , SCN- , IO3 - ) revealed no such transformations to take place, as per line with quenching studies. Density functional theory calculations revealed that despite a lesser binding affinity, Cr2 O7 2- shows strong orbital mixing and large driving forces for electron transfer than SiF6 2- , and thus enlightens the fluorescence quenching mechanism. This work inaugurates the usage of a SIFSIX MOF toward sensing application domain under aqueous medium where hydrolytic stability is a prime concern for their plausible implementation as sensor materials.

Porous organic polymers (POPs) for environmental remediation

Modern global industrialization along with the ever-increasing growth of the population has resulted in continuous enhancement in the discharge and accumulation of various toxic and hazardous chemicals in the environment. These harmful pollutants, including toxic gases, inorganic heavy metal ions, anthropogenic waste, persistent organic pollutants, toxic dyes, pharmaceuticals, volatile organic compounds, etc., are destroying the ecological balance of the environment. Therefore, systematic monitoring and effective remediation of these toxic pollutants either by adsorptive removal or by catalytic degradation are of great significance. From this viewpoint, porous organic polymers (POPs), being two- or three-dimensional polymeric materials, constructed from small organic molecules connected with rigid covalent bonds have come forth as a promising platform toward various leading applications, especially for efficient environmental remediation. Their unique chemical and structural features including high stability, tunable pore functionalization, and large surface area have boosted the transformation of POPs into various macro-physical forms such as thick and thin-film membranes, which led to a new direction in advanced level pollutant removal, separation and catalytic degradation. In this review, our focus is to highlight the recent progress and achievements in the strategic design, synthesis, architectural-engineering and applications of POPs and their composite materials toward environmental remediation. Several strategies to improve the adsorption efficiency and catalytic degradation performance along with the in-depth interaction mechanism of POP-based materials have been systematically summarized. In addition, evolution of POPs from regular powder form application to rapid and more efficient size and chemo-selective, "real-time" applicable membrane-based application has been further highlighted. Finally, we put forward our perspective on the challenges and opportunities of these materials toward real-world implementation and future prospects in next generation remediation technology.

Ultra-stable 3D pyridinium salt-based polymeric network nanotrap for selective 99TcO4-/ReO4- capture via hydrophobic and steric engineering

Selective capture of radioactive ⁹⁹TcO₄^- from highly alkaline nuclear waste is highly desirable for environmental remediation and waste disposal. However, the combined features of adsorbents with excellent chemical stability and high capture selectivity for ⁹⁹TcO₄^- have not yet been achieved. Herein, we report an ultra-stable 3D pyridinium salt-based polymeric network (TMP-TBPM) nanotrap with remarkable radiation, acid and base stability for selective capture of ReO₄^- via hydrophobic engineering and steric hindrance, a non-radioactive surrogate of ⁹⁹TcO₄^-. The batch capture experiments show that TMP-TBPM has high capture capacity (918.7 mg g^-1) and fast sorption kinetics (94.3 % removal in 2 min), which can be attributed to the high density of pyridinium salt-based units on the highly accessible pore channels of 3D interconnected low-density skeleton. In addition, the introduction of abundant alkyl and tetraphenylmethane units into the 3D framework not only greatly enhanced the hydrophobicity and stability of TMP-TBPM, but also significantly improved the affinity toward ⁹⁹TcO₄^-/ReO₄^-, enabling reversible and selective capture of ⁹⁹TcO₄^-/ReO₄^- even under highly alkaline conditions. This study exhibits the great potential of 3D pyridinium salt-based polymeric network nanotrap for ⁹⁹TcO₄^-/ReO₄^- capture from highly alkaline nuclear waste, providing a new strategy to construct high-performance cationic polymeric sorbents for radioactive wastewater treatment.

Guanidine-Functionalized Fluorescent sp2 Carbon-Conjugated Covalent Organic Framework for Sensing and Capture of Pd(II) and Cr(VI) Ions

Palladium is a key element in fuel cells, electronic industries, and organic catalysis. At the same time, chromium is essential in leather, electroplating, and metallurgical industries. However, their unpremeditated leakage into aquatic systems has caused human health and environmental apprehensions. Herein, we reported the development of an sp² carbon-conjugated fluorescent covalent organic framework with a guanidine moiety (sp² c-gCOF) that showed excellent thermal and chemical stability. The sp² c-gCOF showed effective sensing, capture, and recovery/removal of Pd(II) and Cr(VI) ions, which could be due to the highly accessible pore walls decorated with guanidine moieties. The fluorescent sp² c-gCOF showed higher selectivity for Pd(II) and Cr(VI) ions, with an ultra-low detection limit of 2.7 and 3.2 nM, respectively. The analysis of the adsorption properties with a pseudo-second-order kinetic model showed that sp² c-gCOF could successfully and selectively remove both Pd(II) and Cr(VI) ions from aqueous solutions. The polymer also showed excellent capture efficacy even after seven consecutive adsorption-desorption cycles. Hence, this study reveals the potential of fluorescent sp² c-gCOF for detecting, removing, and recovering valuable metals and hazardous ions from wastewater, which would be useful for economic benefit, environmental safety, human health, and sustainability. The post-synthetic modification of sp² c-COF with suitable functionalities could also be useful for sensing and extracting other water pollutants and valuable materials from an aqueous system.

Twofold Interpenetrated Cationic Metal-Organic Framework with Hydrophobic Channels for Effectively Trapping Toxic Oxo-Anions

Sequestration of toxic oxo-anions (such as ⁹⁹TcO₄^- and ClO₄^-) from wastewater has received constant attention due to the existing serious threat to public health and the sustainability of the environment. In view of the low energy of hydration of TcO₄^- and ClO₄^-, cationic metal-organic framework (MOF) materials with the hydrophobic microenvironment are preferred in the selection of sorbents. Herein, a twofold interpenetrated cationic MOF (ZJU-X15) with double-helical chains was constructed by tetrakis[4-(pyridin-4-yl)phenyl]ethene (TPPE) and Cd²⁺ for the elimination of ⁹⁹TcO₄^- and ClO₄^-. Profiting from hydrophobic channels, ZJU-X15 could remove most of ReO₄^- (a surrogate for ⁹⁹TcO₄^-) and ClO₄^- in less than 10 and 20 min, respectively. As the result of batch experiments, ZJU-X15 could capture 356 mg of ReO₄^- and 221 mg of ClO₄^- per 1 g of sorbent, showcase decent selectivity, and still maintain high removal efficiency for anions after four recycles. Furthermore, the process of anion-exchange was confirmed by ion chromatography, Fourier-transform infrared spectroscopy, scanning electron microscopy combined with an energy-dispersive X-ray spectrometer, and X-ray photoelectron spectroscopy, indicating that target anions successfully entered into the body of ZJU-X15 through anion exchange.

Synthesis of a Triazaisotruxene-Based Porous Organic Polymer and Its Application in Iodine Capture

A new triazaisotruxene-based porous organic polymer (POP) was designed and successfully synthesized by a FeCl3-promoted crosslinking reaction. As a result of its porosity and good thermal stability, the designed POP can be utilized as a promising adsorbent for iodine, not only in the gaseous phase, but also in organic and aqueous solutions. Compared to its triazatruxene (TN) analogue, the ITN-based POP shows equal iodine uptake in the gaseous phase and in hexane solution, and better uptake in aqueous solution.