Triptycene-Based Cationic Porous Organic Polymer for the Swift and Effective Removal of Organic and Inorganic Anionic Water Pollutants

Inadequate access to clean water is an acute problem that is known to affect a sizable human population residing in several parts of our planet. Continuous growth in industrialization, energy production, and mining activities has significantly increased the presence of various environmental contaminants in water sources, including heavy metal ions, emerging organic pollutants, and radioactive nuclear wastes. Innovative methods are urgently needed in this sector as current technologies for purifying polluted water are often either expensive, operationally slow, have limited sustainability, or are restricted to specific pollutants. To address these concerns, it is necessary to develop improved and cost-effective water treatment technologies. Herein, a positively charged porous organic polymer (TP_iPOP-2) was synthesized via a facile one-step Menskhutin reaction. Subsequent to characterization, TP_iPOP-2 was tested as an adsorbent for the removal of several commonly detected anionic water pollutants. Experimental results show that TP_iPOP-2 has a remarkable potential to absorb diverse inorganic and organic water contaminants, such as CrO42–, TcO4–, I3–, picrate, and organic dyes (alizarin red S and methyl orange) with high uptake capacities in each case. Simultaneously, TP_iPOP-2 also exhibited fast sieving kinetics toward these pollutants. Our results demonstrate the ability of TP_iPOP-2 to successfully purify water containing a wider spectrum of contaminants. In addition, the effectiveness of TP_iPOP-2 in capturing toxic pollutants did not change to any significant extent, even in the presence of other competitive anions. The TP_iPOP-2 also shows high distribution coefficients (Kd > 105 mg/L), which is a characteristic feature of a good adsorbent. Overall, TP_iPOP-2 has most of the features that are expected for an ideal adsorbent for water purification. Hence, TP_iPOP-2 has the potential to be an affordable alternative to the adsorbent materials currently employed in water treatment applications

Chemically Stable and Heteroatom Containing Porous Organic Polymers for Efficient Iodine Vapor Capture and its Storage

The uses of nuclear reactions are gaining importance in energy and medical therapy applications. Production and safe management of radioactive waste is a major operational challenge. Proper treatment and storage of nuclear waste are important while considering nuclear energy for various applications. While reprocessing used nuclear fuel (UNF), handling of volatile radioactive wastes (e.g., radioisotopes of iodine: 129I/131I) requires special attention. Iodine is present in off-gas streams as either molecular iodine (I2) or organic iodides. 129I is less radioactive than 131I, but has an extremely long half-life. Both are highly toxic, and their nearly quantitative retention from off-gas streams requires packing of iodine filters with efficient adsorbents. Thus, there is a need to develop materials with efficient iodine vapor capture/storage capabilities. Herein, a set of four porous organic polymers are presented that are rich in heteroatoms and possess abundant π-arene motifs with which p-orbitals on iodine can interact effectively via charge-transfer complexations. To mimic the conditions of a UNF reprocessing facility, gas-phase iodine capture experiments were performed under various conditions (dry/humid conditions and at 75 °C/25 °C). The maximum iodine uptake capacity of one of the materials (HPOP-4: 6.25 g/g at 75 °C and 4.35 g/g at 25 °C) is higher than several other iodine vapor adsorbents reported to date. The retention of trapped iodine by HPOPs at 25 °C is also quite remarkable with only 2–3% weight loss from iodine-loaded HPOPs, which makes HPOPs potential material for the storage/transportation of captured radioiodine. The results confirm desirable properties in HPOPs such as facile synthesis, high physiochemical stabilities, good moisture tolerance, rapid adsorption kinetics, and efficient reusability with low compromise in capture performance upon regeneration. These benefits render HPOPs as strong contenders for packing filters used for retaining radioiodine during cleaning either off-gas streams or annulus exhaust air (during “loss of coolant accident”)

Efficient Optoelectronic Sensing of HCl Vapor and Effective Iodine Capture/Storage by Hybrid Porous Organic Polymers Incorporating Triptycene and Phosphazene Motifs

A set of two unique hybrid POPs (HPOP-1 and HPOP-2) bearing triptycene and phosphazene units has been developed for their use as strategic materials capable of sensing HCl acid vapor and capturing/storing iodine. The materials were synthesized via the well-known Schiff base reaction, leading to the inclusion of ample imine linkages in the resultant HPOPs that were characterized thoroughly using various techniques. High thermal stability of HPOPs was evident from the TGA plots. The protonation of phosphazene and imine moieties in HPOPs, upon exposure to corrosive HCl vapors, acts like a chemical trigger that could be perceived not only by a “turn-on” fluorescence response but also by a color change visible to the unaided (naked) eye. The optical and electronic response of the HPOPs in the presence of HCl vapors is fully reversible using NH3 vapors as a chemical switch. These HPOPs were also found to be suitable for trapping iodine vapors and iodine species present in water or hexane solutions. This additional utility of HPOPs arises due to the presence of ample N, O, and P heteroatoms and imine linkages in the polymeric network. HPOPs can trap up to 4.90 g g–1 of iodine at 75 °C. The iodine removal efficiency at ambient temperature (25 °C) under dry as well as humid conditions is also quite promising, and performances are better than that of previously reported porous materials under similar experimental conditions. HPOPs can also efficiently remove iodine dissolved in water and hexane. All of these results indicate that HPOP-1 and HPOP-2 are potential materials for versatile environmental applications

Self-Assembly of Nanoscopic Coordination Cages Using a Flexible Tripodal Amide Containing Linker

Flexible, nanoscopic 3D cages containing the amide functionality were prepared via coordination-driven self-assembly from palladium(II) based 90° ditopic acceptor units and a tripod N,N‘,N‘ ‘-tris(3-pyridyl)trimesic amide. Both cages were characterized by NMR (31P, 1H) and electrospray ionization mass spectrometry. An MM2 force field simulation of one cage showed that the shape is likely pseudo trigonal bipyramidal with the diameter of the inner cavity of the cage about 1.9 nm

Self-Recognition in the Coordination Driven Self-Assembly of 2-D Polygons

Self-recognition in the transition-metal-mediated self-assembly of some 2-D polygons is presented. Prolonged heating of two or three organoplatinum reagents with 4,4‘-dipyridyl in aqueous acetone results in the predominant formation of a rectangle, triangle, and/or square. All mixtures are characterized with NMR and electrospray ionization mass spectrometry (ESIMS). Despite the potential for ill-defined oligomeric products, these mixed ligand systems prefer to self-assemble into discrete species

Self-Assembly of Three-Dimensional M₃L₂ Cages via a New Flexible Organometallic Clip

The simple combination of tritopic pyridine donor linkers with a new flexible acceptor “clip” in a 2:3 stoichiometric ratio generates three-dimensional M3L2 cages which possess large cavities in essentially quantitative yields

Synthesis of Triptycene-Based Organosoluble, Thermally Stable, and Fluorescent Polymers: Efficient Host–Guest Complexation with Fullerene

We report a facile synthesis of 2,6-diethynyltriptycene (DET) in high yield. Application of DET as monomer in polymer chemistry has been shown (for the first time) in syntheses of two novel polymers via Sonogashira cross-coupling reaction in high yield. The newly synthesized polymers were characterized by FT-IR, UV–vis absorption, and NMR spectroscopic techniques. The polymers prepared using DET have interesting properties such as high solubility in common organic solvents, high thermal stability [decomposition temperatures (<i>T</i>_d) > 495 °C], and high char yield (greater than 81% at 900 °C). Additionally, polymers are fluorescent. Host–guest interaction between triptycene-based polymers and fullerene (C₆₀) has been studied for the first time. Fluorescence quenching of our polymers by C₆₀ has been used to study the extent of (polymer·C₆₀) host–guest complex formation. Fluorescence quenching studies indicate binding constant for polymer·C₆₀ complexation on the order of 10⁵ M^–1

Pyrazine Motif Containing Hexagonal Macrocycles: Synthesis, Characterization, and Host–Guest Chemistry with Nitro Aromatics

The synthesis and characterization of cationic two-dimensional metallamacrocycles having a hexagonal shape and cavity are described. Both macrocycles utilize a pyrazine motif containing an organometallic acceptor tecton with platinum­(II) centers along with different donor ligands. While one macrocycle is a relatively larger [6 + 6], the other is a relatively smaller [2 + 2] polygon. A unique feature of the smaller ensemble is that it is an irregular polygon in which all six edges are not of equal length. Molecular modeling of these macrocycles confirmed the presence of hexagonal cavities. The ability of these π-electron rich macrocycles to act as potential hosts for relatively electron deficient nitroaromatics (DNT = 2,4-dinitrotoluene and PA = picric acid) has been studied using isothermal titration calorimetry (ITC) as a tool. Molecular dynamics simulation studies were subsequently performed to gain critical insight into the binding interactions between the nitroaromatic guest molecules (PA/DNT) and the ionic macrocycles reported herein

Self-Assembly of Neutral Platinum-Based Supramolecular Ensembles Incorporating Oxocarbon Dianions and Oxalate

Five neutral platinum-based macrocycles incorporating cyclic oxocarbondianions, squarate and croconate and their acyclic analogue, oxalate, have been synthesized in 90−95% yield via self-assembly. The combination of the diplatinum molecular clip with all three dianions afforded molecular rectangles, whereas a platinum-based 60° acceptor unit produced a supramolecular rhomboid with croconate ion but a triangle with squarate ion. In all cases, multinuclear NMR spectra were consistent with the formation of single highly symmetrical species. The three rectanglular and the rhomboid assemblies were characterized by single-crystal X-ray crystallography. The triangular species was characterized by FAB mass spectrometry

Facile Synthesis of Enantiopure Chiral Molecular Rectangles Exhibiting Induced Circular Dichroism

The facile syntheses of enantiopure molecular rectangles using 1,8-bis(trans-Pt(PEt3)2(NO3))anthracene and optically pure d- or l-tartrate are reported in high yields. These self-assembled macrocycles are unique examples where the phenomenon of induced chiral dichroism (ICD) has been observed in chiral metallosupramolecular assemblies