Conjugated microporous polymers (CMPs) are a unique class of materials that combine extended π-conjugation with a permanently microporous skeleton. Since their discovery in 2007, CMPs have become established as an important subclass of porous materials. A wide range of synthetic building blocks and network-forming reactions offers an enormous variety of CMPs with different properties and structures. This has allowed CMPs to be developed for gas adsorption and separations, chemical adsorption and encapsulation, heterogeneous catalysis, photoredox catalysis, light emittance, sensing, energy storage, biological applications, and solar fuels production. Here we review the progress of CMP research since its beginnings and offer an outlook for where these materials might be headed in the future. We also compare the prospect for CMPs against the growing range of conjugated crystalline covalent organic frameworks (COFs).

Advances in Conjugated Microporous Polymers.

The presence of an excessive concentration of CO2 in the atmosphere needs to be curbed with suitable measures including the reduction of CO2 emissions at stationary point sources such as power plants through carbon capture technologies and subsequent conversion of the captured CO2 into non-polluting clean fuels/chemicals using photo and/or electrocatalytic pathways. Porous materials have attracted much attention for carbon capture and in the recent past; they have witnessed significant advancements in their design and implementation for CO2 capture and conversion. In this context, the emerging trends in major porous adsorbents such as MOFs, zeolites, POPs, porous carbons, and mesoporous materials for CO2 capture and conversion are discussed. Their surface texture and chemistry, and the influence of various other features on their efficiency, selectivity, and recyclability for CO2 capture and conversion are explained and compared thoroughly. The scientific and technical advances on the material structure versus CO2 capture and conversion provide deep insights into designing effective porous materials. The review concludes with a summary, which compiles the key challenges in the field, current trends and critical challenges in the development of porous materials, and future research directions combined with possible solutions for realising the deployment of porous materials in CO2 capture and conversion.

Emerging trends in porous materials for CO2 capture and conversion

The enrichment of radioactive iodine in the waste of nuclear industries threatens human health, and thus the efficient capture of iodine has attracted a great deal of attention in recent years. Porous organic polymers (POPs) and metal–organic frameworks (MOFs), new classes of porous materials, act as outstanding candidate adsorbent materials in this field due to their high surface areas, permanent tunable porosities, controllable structures, high thermal/chemical stabilities, versatility in molecular design and potential for post-synthetic modification. Herein, this review focuses on the research progress of these two types of porous materials for highly efficient iodine capture. We analyze and discuss some valid strategies for enhancing their iodine uptake, including increasing their surface area and pore volume, using organic building units with unique configurations and functions, introducing chemical functional groups to provide high-enthalpy binding sites, and further processing of POP and MOF materials. Indeed, there are many special structural and functional features found in porous POP and MOF materials, which make them unique and merit further exploration. Thus, we expect to see their usage grow as this field progresses.

Iodine capture in porous organic polymers and metal–organic frameworks materials

Three-dimensional porous coordination polymers, which are known as metal–organic frameworks (MOFs), have drawn considerable attention owing to their properties, such as highly crystalline and ordered structures, inorganic–organic-hybrid nature, tunability of chemical functionality, high porosity and surface area and moderate-to-high stability. Due to these properties, MOFs are applied extensively as probes for the detection of large varieties of organic molecules. In this line, different MOF-based instrumental and material-based methods along with different strategies have been developed to study and extend our information about the capabilities of MOFs as sensing probes for the detection of organic molecules as well as improving and developing their detection limits, selectivity and sensitivity toward specific analytes. Considering these points, we have presented and classified the content of this review based on the chemical structures of organic analytes in three categories, including (I) nitroaromatic explosives and energetic materials, (II) small organic molecules, such as solvents and volatile organic compounds, and (III) organic amines. For each group of these analytes, different material and instrumental methods using MOFs have been explained, with illustrations of remarkable examples. Finally, we compare the methods for the detection of each group of analytes and discuss which instrumentation is more effective for each group of analytes.

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Sensing organic analytes by metal–organic frameworks: a new way of considering the topic

The sharply rising level of atmospheric carbon dioxide resulting from anthropogenic emissions is one of the greatest environmental concerns nowadays. Capture and storage of carbon dioxide (CCS) from coal- or gas-burning power plants is an attractive route to reducing carbon dioxide emissions into the atmosphere. Porous organic polymers (POPs) have been recognized as a very promising candidate for carbon dioxide capture due to their low density, high thermal and chemical stability, large surface area, tunable pore size and structure, and facilely tailored functionality. In this review, we aim to highlight the POPs for CO2 capture and summarize the factors influencing CO2 capture capacity, such as surface area and pore structure, swellable polymers, heteroatomic skeleton and surface functionalized porous organic polymers.

Carbon dioxide capture in amorphous porous organic polymers

A series of novel triazine-containing pore-tunable carbon materials (NT-POP@800-1-6), which was synthesized via pyrolysis of porous organic polymers (POPs) without any templates. NT-POP@800-1-6 possess moderate BET surface areas of 475–736 m2 g−1, have permanent porosity and plenty of nitrogen units in the skeletons as effective sorption sites, and display relatively rapid guest uptake of 56–192 wt% in iodine vapour in the first 4 h. In addition, all the samples exhibit the outstanding CO2 adsorption capacity of 2.83–3.96 mmol g−1 at 273 K and 1.05 bar. Furthermore, NT-POP@800-1-6 show good selectivity ratios of 21.2–36.9 and 3.3–7.5 for CO2/N2 or CH4/N2, respectively. We believe that our new building block design provides a general strategy for the construction of triazine-containing carbon materials from various extended building blocks, thereby greatly expanding the range of applicable molecules.

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Template-free synthesis of porous carbon from triazine based polymers and their use in iodine adsorption and CO2 capture.

Porous cationic covalent triazine-based frameworks (CTFs) with imidazolium salts as tectons were prepared via ionothermal synthesis. The high-PF6 - -content CTF shows the CO2 adsorption of 44.7 cm3 g-1 and I2 capture capacity of 312 wt %. The influence of counterion species and contents on the porosities, CO2 adsorptions, and I2 capture capacities of the CTFs has been investigated.

Porous Cationic Covalent Triazine-Based Frameworks as Platforms for Efficient CO2 and Iodine Capture.

Conjugated microporous polymers with azide groups: a new strategy for postsynthetic fluoride functionalization and effectively enhanced CO2 adsorption properties.

A series of conjugated microporous polymers (CMPs) based on 1,3,6,8-tetrabromocarbazole (N4CMP-1-5) is synthesized via Suzuki cross-coupling or Sonogashira polycondensation. The porosity properties and surface area of these polymer networks can be finely tuned by using a linker with different geometries or strut length. These polymers show the Brunauer-Emmett-Tellerthe (BET) surface areas ranging from 592 to 1426 m2 g-1. The dominant pore sizes of the polymers on the basis of the different linker are located between 0.36 and 0.61 nm. Gas uptake increases with BET surface area and micropore volume, N4CMP-3 polymer can capture CO2 with a capacity of 3.62 mmol g-1 (1.05 bar and 273 K) among the obtained polymers. All of the polymers show high isosteric heats of CO2 adsorption (25.5-35.1 kJ mol-1), and from single component adsorption isotherms, IAST-derived ideal CO2/N2 (28.7-53.8), CO2/CH4 (4.6-5.2) and CH4/N2 (5.7-10.5) selectivity. Furthermore, N4CMPs exhibit the high CO2 adsorption capacity of 542-800 mg g-1 at 318 K and 50 bar pressure. These data indicate that these materials are a promising potential for clean energy application and environmental field.

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Chan Yao

Papers

Template-free synthesis of porous carbon from triazine based polymers and their use in iodine adsorption and CO2 capture.

Porous Cationic Covalent Triazine-Based Frameworks as Platforms for Efficient CO2 and Iodine Capture.

Conjugated microporous polymers with azide groups: a new strategy for postsynthetic fluoride functionalization and effectively enhanced CO2 adsorption properties.

Controlled synthesis of conjugated polycarbazole polymers via structure tuning for gas storage and separation applications

Thiophene-based conjugated microporous polymers: preparation, porosity, exceptional carbon dioxide absorption and selectivity