Microporous Organic Polymers Based on Hyper-Crosslinked Coal Tar: Preparation and Application for Gas Adsorption

Multifunctional porous β-cyclodextrin polymer for water purification

Keeping water clean is of vital significance for human health and environmental protection. In order to remove organic micro-pollutants and natural organic substances in water bodies and kill pathogenic microorganisms simultaneously, this study synthesized a multifunctional porous β-cyclodextrin polymer with a high specific surface area by introducing quaternary ammonium groups and rigid benzene rings, respectively, which was then polymerized with crosslinking agent-4,4'-bis (chloromethyl)-1,1'-biphenyl (BCMBP) in an ionic liquid system. The grafting of quaternary ammonium groups was beneficial for the removal of negative-charged humic acid (HA) and sterilization. The introduction of numerous rigid structures during benzylation and Friedel-Crafts alkylation reaction could significantly improve the porosity and specific surface area of the polymer, conducive to the exposure of cyclodextrin binding sites and contaminant adsorption. By changing the proportions of quaternization and benzylation, the structure and surface properties of the polymer could be adjusted, thus further regulating the adsorption performance. Compared with activated carbon, the polymer named BQCD-BP with a huge surface area of 1133 m² g^-1 prepared under optimized conditions showed outstanding adsorption performance and sterilization ability. The pseudo-second-order kinetic constant of BQCD-BP reached 1.2058 g·mg^-1·min^-1, which was approximately 50 times greater than that of activated carbon (0.0256 g·mg^-1·min^-1) under the same experimental condition. The adsorption capacity of BQCD-BP to HA was twice as high as that to AC, and the antibacterial ability of BQCD-BP was significant, achieving 90% at the dosage of 1g L^-1. Moreover, the adsorption process was hardly affected by the hydrochemical conditions, and the polymer was easy to regenerate. In addition, the excellent adsorption and antibacterial performance of the polymer were also identified by natural water treatment. COD was almost completely removed, and the removal efficiency of TP reached 92% after contact with BQCD-BP. The sterilization rate of BQCD-BP to viable bacteria in complex water bodies reached 82%. Undoubtedly, BQCD-BP is a potential multifunctional water treatment material with reasonable design in the actual water purification.

Microporous Carbon and Carbon/Metal Composite Materials Derived from Bio-Benzoxazine-Linked Precursor for CO2 Capture and Energy Storage Applications

There is currently a pursuit of synthetic approaches for designing porous carbon materials with selective CO₂ capture and/or excellent energy storage performance that significantly impacts the environment and the sustainable development of circular economy. In this study we prepared a new bio-based benzoxazine (AP-BZ) in high yield through Mannich condensation of apigenin, a naturally occurring phenol, with 4-bromoaniline and paraformaldehyde. We then prepared a PA-BZ porous organic polymer (POP) through Sonogashira coupling of AP-BZ with 1,3,6,8-tetraethynylpyrene (P-T) in the presence of Pd(PPh₃)₄. In situ Fourier transform infrared spectroscopy and differential scanning calorimetry revealed details of the thermal polymerization of the oxazine rings in the AP-BZ monomer and in the PA-BZ POP. Next, we prepared a microporous carbon/metal composite (PCMC) in three steps: Sonogashira coupling of AP-BZ with P-T in the presence of a zeolitic imidazolate framework (ZIF-67) as a directing hard template, affording a PA-BZ POP/ZIF-67 composite; etching in acetic acid; and pyrolysis of the resulting PA-BZ POP/metal composite at 500 °C. Powder X-ray diffraction, thermogravimetric analysis, scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller (BET) measurements revealed the properties of the as-prepared PCMC. The PCMC material exhibited outstanding thermal stability (T_d10 = 660 °C and char yield = 75 wt%), a high BET surface area (1110 m² g^–1), high CO₂ adsorption (5.40 mmol g^–1 at 273 K), excellent capacitance (735 F g^–1), and a capacitance retention of up to 95% after 2000 galvanostatic charge–discharge (GCD) cycles; these characteristics were excellent when compared with those of the corresponding microporous carbon (MPC) prepared through pyrolysis of the PA-BZ POP precursors with a ZIF-67 template at 500 °C.

Carbon dioxide adsorption based on porous materials

Global warming due to the high concentration of anthropogenic CO2 in the atmosphere is considered one of the world's leading challenges in the 21st century as it leads to severe consequences such as climate change, extreme weather events, ocean warming, sea-level rise, declining Arctic sea ice, and the acidification of oceans. This encouraged advancing technologies that sequester carbon dioxide from the atmosphere or capture those emitted before entering the carbon cycle. Recently, CO2 capture, utilizing porous materials was established as a very favorable route, which has drawn extreme interest from scientists and engineers due to their advantages over the absorption approach. In this review, we summarize developments in porous adsorbents for CO2 capture with emphasis on recent studies. Highly efficient porous adsorption materials including metal-organic frameworks (MOFs), zeolites, mesoporous silica, clay, porous carbons, porous organic polymers (POP), and metal oxides (MO) are discussed. Besides, advanced strategies employed to increase the performance of CO2 adsorption capacity to overcome their drawbacks have been discoursed.

Sulfur-Decorated Hyper-Cross-Linked Coal Tar: A Microporous Organic Polymer for Efficient and Expeditious Mercury Removal

Hyper-cross-linked microporous organic polymers are a class of porous materials that have captured widespread attention owing to their high surface areas and wide range of monomeric sources. Balancing economy with performance is the initial hurdle when designing effective hyper-cross-linked microporous organic polymers. Herein, we demonstrated an inexpensive sulfurated solvent-knitted hyper-cross-linked microporous polymer scaffold, named sulfur-decorated hyper-cross-linked coal tar (CTHP-SES), utilizing coal tar as an aromatic monomer with numerous positions for potential chelation of toxic metals, particularly mercury, from water. The resulting material illustrated selective adsorption of mercury from both water (1037 mg g^-1) and the gas phase (416 mg g^-1) with rapid kinetics (183.67 mg min^-1 g^-1), good recyclability (4 runs), and excellent stability under both strong basic and acidic conditions. CTHP-SES was able to reduce the concentration of the Hg(II) solution from 1 mg L^-1 to 32 μg L^-1 after 10 min due in part to the promising distribution coefficient (K_d = 2.371 × 10⁶ mL g^-1). These results show that CTHP-SES offers a promising and practical platform to cope with a variety of environmental contaminations.

Preparation of Porous Carbon Materials Derived from Hyper-Cross-Linked Asphalt/Coal Tar and Their High Desulfurization Performance

The development of simple and highly effective desulfurization technology is attracting more and more interest in both industrial and academic fields. Here, a new family of precursors was prepared based on hyper-cross-linked asphalt and coal tar building blocks. Thanks to the preintroduced porous structure, the precursors were converted into carbons with high surface area and large micropore volume via a uniform carbonization process. The synergistic effects of high surface area, abundant microporous structure, and the introduced polar functional groups endow the carbon materials with high desulfurization performance. The results of repeated experiments show that the adsorption capacities of five carbonized samples are higher than 40 mg S g^-1, and the theoretical maximum adsorption capacity reaches 44.7 mg S g^-1. Particularly, the adsorption equilibrium of all the carbonized samples can be reached in 5 min. Moreover, the recycle adsorption performance was also studied. Toluene exhibits the best elution effect among three eluents (iso-octane, para-xylene, and toluene) and the adsorption capacity remains 89% of the initial adsorption capacity after two adsorption-desorption cycles. It is believed that both innocent treatment of byproducts from petroleum industry and their high-value application for deep desulfurization in liquid hydrocarbon fuels benefit environmental protection and sustainable development.

Postfunctionalization of Porous Organic Polymers Based on Friedel-Crafts Acylation for CO2 and Hg2+ Capture

Melamine-based porous organic polymers (POPs) are promising for gas uptake and water treatment because of their unique and tunable porosity, high nitrogen (N) content, and high Brunauer-Emmett-Teller (BET) surface area (S_BET). However, it is difficult to construct ketone-based POPs by the Friedel-Crafts acylation reaction. Herein, the ketone-based POPs were postfunctionalized with melamine (MA) by the Schiff-based reaction and the rigid triazine rings of MA were embedded in the polymer chains as rigid cross-linkers, resulting in the polymers with high S_BET (555 m²·g^-1) and total pore volume (0.72 cm³·g^-1). Moreover, plentiful imine, amino, and triazine functionalities were inserted in the polymers, providing the polymers with high N content of 41.83 wt %. The resulting polymers were promising for CO₂ capture (145 mg·g^-1; 273 K, 1.0 bar) and Hg²⁺ removal (372 mg·g^-1). This study offers a universal strategy to construct melamine-based POPs from various ketone-functionalized HCPs via a simple postfunctionalization.

Synthesis of Porous Organic Polymers with Tunable Amine Loadings for CO2 Capture: Balanced Physisorption and Chemisorption

The cross-coupling reaction of 1,3,5-triethynylbenzene with terephthaloyl chloride gives a novel ynone-linked porous organic polymer. Tethering alkyl amine species on the polymer induces chemisorption of CO₂ as revealed by the studies of ex situ infrared spectroscopy. By tuning the amine loading content on the polymer, relatively high CO₂ adsorption capacities, high CO₂-over-N₂ selectivity, and moderate isosteric heat (Q_st) of adsorption of CO₂ can be achieved. Such amine-modified polymers with balanced physisorption and chemisorption of CO₂ are ideal sorbents for post-combustion capture of CO₂ offering both high separation and high energy efficiencies.

PDMS-coated hypercrosslinked porous organic polymers modified via double postsynthetic acidifications for ammonia capture

Double postsynthetic acidifications of a hypercrosslinked polymer afforded record high NH₃ adsorption capacity per surface area. Its PDMS coating provided an 40-fold enhancement of low-pressure NH₃ adsorption capacity and hydrophobicity.

A hypercrosslinked porous organic polymer was modified by post-oxidation and post-sulfonation to obtain a porous platform with a high density of acidic groups. Such an acidified material exhibits record high NH₃ adsorption capacity per surface area, fast adsorption rate, and recyclability at low desorption temperature. Noticeably, the coating of the polymer with PDMS represents a facile and efficient route to enable both a significant improvement of low-pressure NH₃ adsorption capacity (∼40-fold enhancement; from 0.04 to 1.41 mmol g^–1) with respect to the non-modified polymer at 500 ppm and hydrophobicity associated with the selective sorption of NH₃ over water vapor (hydrophilic for the non-coated material). This material is easy to prepare, cost-effective, and scalable to mass production.