Porous Organic Polymers: An Emerged Platform for Photocatalytic Water Splitting

Porous organic polymers (POPs), known for its high surface area and abundant porosity, can be easily designed and constructed at the molecular level. The POPs offer confined molecular spaces for the interplay of photons, excitons, electrons and holes, therefore featuring great potential in catalysis. In this review, a brief summary on the recent development of some current state-of-the-art POPs for photocatalytic water splitting and their design principles and synthetic strategies as well as relationship between structure and photocatalytic hydrogen or oxygen evolution performance are presented. Future prospects including research directions are also proposed, which may provide insights for developing POPs for photocatalytic water splitting with our expectations

Effect of Tea Polyphenols on the Melt Grafting of Glycidyl Methacrylate onto Polypropylene

It is considered to be one of the most effective strategies to prepare functionalized polypropylene (PP) materials via the melt grafting of polar monomers onto PP chains. However, the grafting efficiency of functional monomers is generally low. To achieve a high grafting efficiency, we explored the effect of tea polyphenols (C), which are good free radical scavengers, on the melt grafting of glycidyl methacrylate (GMA) onto PP chains initiated by dicumyl peroxide (DCP). Specifically, 0.5~3 wt% of tea polyphenols (C) were introduced to the PP/DCP/GMA melt blending system. The morphology, melt flow rate (MFR), thermal and mechanical properties of tea polyphenols (C) incorporated PP/DCP/GMA blends were investigated systematically. The results showed that the proper amount of tea polyphenols (C) (0.5~2 wt%) promoted the grafting of GMA. Unexpectedly, the PP backbone suffered from more severe degradation with the addition of tea polyphenols (C). The phenomena were ascribed to the reaction between phenolic hydroxyl groups of tea polyphenols (C) and epoxy groups of grafted GMA, which was revealed by the FTIR results. In addition, according to DSC and the tensile test, the co-grafting of GMA and tea polyphenols (C) improved the crystallization ability, yield strength and Young’s modulus of the PP matrix

Microporous organic polymers as CO2 adsorbents : advances and challenges

Microporous organic polymers (MOPs) with internal pores less than 2 nm have potential use in gas separation, sensing, and storage, in the form of membranes, monoliths, fibers, or adsorbent granules. These covalently bonded polymers are being formed by reacting with rigid organic monomers, and MOPs have lately been studied for capturing CO2 from gas mixtures in the form of membranes and adsorbents. Especially, the potential of MOPs in the processes of carbon capture and storage has been in the focus and small pore MOPs are preferred for regular separation processes but larger pores could be suitable if cryogenic processes would be used. Recent studies (2014 – mid 2019) on the potential use of MOPs as CO2 adsorbents and, to some degree, CO2-selective membranes are reviewed

D-π-A conjugated polymer dyes-covered TiO2 compact layers for enhancing photovoltaic performance of dye-sensitized solar cells

Three donor-conjugated units (triphenylamine (TPA)) and phenothiazine (PTZ))-side chain acceptor (cyanoacrylic acid (CAA)) donor-π-acceptor (D-π-A) conjugated polymers with different conjugated units (thiophen and/or 3, 4-ethylenedioxythiophene) were rationally designed and synthesized. The electronic properties and energy levels could be effectively tuned via methodically altering the conjugated units of the resulted polymers (PTPAPTZ, PTPAPTZ-1 and PTPAPTZ-2). Regulating the molecular orbital energy levels can be considered as a direct and effective method to get bathchromic and broad spectra shifts in polymer dyes. Photoelectrochemical cells based on the dye sensitized solar cells (DSSCs) format were fabricated putting the polymers as sensitizers. Device based on PTPAPTZ-2 exhibits a power conversion efficiency of 4.71% with short circuit photocurrent density of 10.8 mA·cm, overrating all polymer DSSCs previously disclosed

Phthalazinone structure-based covalent triazine frameworks and their gas adsorption and separation properties

In this work, new classes of phthalazinone-based covalent triazine frameworks (PHCTFs) were prepared by ionothermal synthesis from two full rigid dicyano building blocks with rigid, thermostable and asymmetric N-heterocycle-containing structures. The surface and internal morphologies of PHCTFs were examined by FE-SEM and TEM. The resultant microporous polymers, PHCTFs, exhibited BET specific surface areas up to 1845 m(2) g(-1) and a moderately narrow pore size distribution. According to the sorption measurements, the CO2 uptake can be up to 17.1 wt% (273 K/1 bar) and the H-2 uptake can be up to 1.92 wt% (77 K/1 bar). Moreover, the initial slopes of the single component gas adsorption isotherms in the low pressure range were used as the gas separation ratios. The obtained polymer networks possess satisfactory CO2/N-2 selectivity performance up to 52 and CO2/CH4 selectivity up to 12. Combining the relationship of the structure and performance, it can be concluded that a twisted and non-coplanar topology conformation can be used to improve the porosity of microporous organic polymers. At the same time, the nitrogenand oxygen-rich characteristics of the phthalazinone core endow the networks with a strong affinity for CO2 and thereby high CO2 adsorption capacity. So the pore structure and chemical composition may play very important roles on the adsorption properties of small gas molecules

1,3,5-Triazine-Based Microporous Polymers with Tunable Porosities for CO₂ Capture and Fluorescent Sensing

The synthetic control over pore structure remains highly desirable for porous organic frameworks. Here, we present a competitive chemistry strategy, i.e., a systematical regulation on Friedel–Crafts reaction and Scholl coupling reaction through tuning the ratios of monomers. This leads to a series of spirobifluorene-based microporous polymers (Sbf-TMPs) with systematically tuned porosities and N content. Unlike the existing copolymerization strategy by which the synthesized polymers exhibit a monotonic change tendency in the porosities, our networks demonstrate an unusually different trend where the porosity increases first and then decreases with the increasing Ph/Cl ratios for the monomers. This is mainly ascribed to the completion of coexisting reaction routines and the different “internal molecular free volumes” of the repeating units. The as-made networks feature tunable capacities for CO₂ adsorption over a wide range and attractive CO₂/N₂ selectivities. Moreover, these donor–acceptor type frameworks exhibit selective and highly sensitive fluorescence-on or fluorescence-off properties toward volatile organic compounds, which implies their great potential in fluorescent sensors

Facile Preparation of Dibenzoheterocycle-Functional Nanoporous Polymeric Networks with High Gas Uptake Capacities

A consolidated ionothermal strategy was developed for the polymerization of thermally unstable nitriles to construct high performance materials with permanent porosity, and carbazole, dibenzofuran, and dibenzothiophene were separately introduced into covalent triazine-based networks to investigate the effects of heterocycles on the gas adsorption performance. Three nitriles, namely 3,6-dicyanocarbazole, 3,6-dicyanodibenzofuran, and 3,6-dicyanodibenzothiophene, were designed and synthesized, which were readily converted to heat-resistant intermediates at a moderate temperature and then polymerized to create highly porous poly­(triazine) networks instead of the traditional one-step procedure. This documents an improved strategy for the successful construction of heterocyclic-functional triazine-based materials. The chemical structures of monomers and polymers were confirmed by ¹H NMR, FTIR, and elemental analysis. Such polymers with high physical–chemical stability and comparable BET surface areas can uptake 1.44 wt % H₂ at 77 K/1 bar and 14.0 wt % CO₂ at 273 K/1 bar and present a high selectivity for gas adsorption of CO₂ (CO₂/N₂ ideal selectivity up to 45 at 273<i>K</i>/1.0 bar). The nitrogen- and oxygen-rich characteristics of carbazole and dibenzofuran feature the networks strong affinity for CO₂ and thereby high CO₂ adsorption capacity. This also helps to thoroughly understand the influence of pore structure and chemical composition on the adsorption properties of small gas molecules

Metalated Mesoporous Poly(triphenylphosphine) with Azo Functionality: Efficient Catalysts for CO₂ Conversion

Mesoporous poly­(triphenylphosphine) with azo functionality (<b>poly­(PPh</b>_<b>3</b><b>)-azo</b>) is reported, which was synthesized via oxidative polymerization of P­(<i>m</i>-NH₂Ph)₃ at ambient conditions. This kind of polymer could strongly coordinate with metal ions (e.g., Ru³⁺) and could reduce Ag⁺ in situ to metallic form. The resultant metalated <b>poly­(PPh</b>_<b>3</b><b>)-azo</b> (e.g., <b>poly­(PPh</b>_<b>3</b>)<b>-azo-Ag</b> or <b>-Ru</b>) were discovered to be highly efficient catalysts for CO₂ transformation. <b>Poly­(PPh</b>_<b>3</b><b>)-azo-Ag</b> showed more than 400 times higher site-time-yield (STY) for the carboxylative cyclization of propargylic alcohols with CO₂ at room temperature compared with the best heterogeneous catalyst reported. <b>Poly­(PPh</b>_<b>3</b><b>)-azo-Ru</b> also exhibited good activity for the methylation of amines with CO₂. It was demonstrated that the high performances of the catalysts originated from the cooperative effects between the polymer and the metal species. In addition, both catalysts showed good stability and easy recyclability, thus demonstrating promising potential for practical utilization for the conversion of CO₂ into value-added chemicals