Suvendu Karak

Selective Molecular Sieving in Self‐Standing Porous Covalent‐Organic‐Framework Membranes

Self-standing, flexible, continuous, and crack-free covalent-organic-framework membranes (COMs) are fabricated via a simple, scalable, and highly cost-effective methodology. The COMs show long-term durability, recyclability, and retain their structural integrity in water, organic solvents, and mineral acids. COMs are successfully used in challenging separation applications and recovery of valuable active pharmaceutical ingredients from organic solvents.

Constructing Ultraporous Covalent Organic Frameworks in Seconds via an Organic Terracotta Process

Research on covalent organic frameworks (COFs) has recently gathered significant momentum by the virtue of their predictive design, controllable porosity, and long-range ordering. However, the lack of solvent-free and easy-to-perform synthesis processes appears to be the bottleneck toward their greener fabrication, thereby limiting their possible potential applications. To alleviate such shortcomings, we demonstrate a simple route toward the rapid synthesis of highly crystalline and ultraporous COFs in seconds using a novel salt-mediated crystallization approach. A high degree of synthetic control in interlayer stacking and layer planarity renders an ordered network with a surface area as high as 3000 m2 g-1. Further, this approach has been extrapolated for the continuous synthesis of COFs by means of a twin screw extruder and in situ processes of COFs into different shapes mimicking the ancient terracotta process. Finally, the regular COF beads are shown to outperform the leading zeolites in water sorption performance, with notably facile regeneration ability and structural integrity.

Pore surface engineering in porous, chemically stable covalent organic frameworks for water adsorption

Herein, we have explored the possibility of a class of covalent organic frameworks (COFs) as water adsorbing materials. We have selected, synthesized 12 chemically stable functionalized Schiff base COFs and thoroughly studied their water uptake behaviour. Further, a deep understanding was developed with these COFs towards the effects of condensation pressure of water and hydrophilic/hydrophobic groups present in the COF pores on water absorption capacity and ultimately, their recyclability. Among all reported COFs, TpPa-1 shows the highest water uptake of 30 wt% (368 cm3 g−1; 17 mmol g−1) at P/P0 = 0.3, which is also comparable with the recently reported carbon materials and few well known MOFs. This study also reveals that the overall water uptake of COFs can be tuned systematically based on chemical functionality and pore size in a wider window of relative pressures.

CCDC 1578181: Experimental Crystal Structure Determination

Related Article: Saibal Bera, Amit Chakraborty, Suvendu Karak, Arjun Halder, Soumyajyoti Chatterjee, Subhadeep Saha, and Rahul Banerjee|2018|Chem.Mater.|30|4755|doi:10.1021/acs.chemmater.8b01698

Interlayer Hydrogen-Bonded Covalent Organic Frameworks as High-Performance Supercapacitors

Covalent organic frameworks (COFs) have emerged as promising electrode materials in supercapacitors (SCs). However, their insoluble powder-like nature, poor capacitive performance in pristine form, integrated with inferior electrochemical stability is a primary concern for their long-term use in electrochemical devices. Keeping this in perspective, herein we report a redox active and hydrogen bonded COF with ultrahigh stability in conc. H2SO4 (18 M), conc. HCl (12 M) and NaOH (9 M). The as-synthesized COF fabricated as thin sheets were efficiently employed as a free-standing supercapacitor electrode material using 3 M aq. H2SO4 as an electrolyte. Moreover, the pristine COF sheet showcased outstanding areal capacitance 1600 mF cm-2 (gravimetric 169 F g-1) and excellent cyclic stability (>100 000) without compromising its capacitive performance or Coulombic efficiency. Moreover, as a proof-of-concept, a solid-state supercapacitor device was also assembled and subsequently tested.

Convergent Covalent Organic Framework Thin Sheets as Flexible Supercapacitor Electrodes

Flexible supercapacitors in modern electronic equipment require light-weight electrodes, which have a high surface area, precisely integrated redox moieties, and mechanically strong flexible free-standing nature. However, the incorporation of the aforementioned properties into a single electrode remains a great task. Herein, we could overcome these challenges by a facile and scalable synthesis of the convergent covalent organic framework (COF) free-standing flexible thin sheets through solid-state molecular baking strategy. Here, redox-active anthraquinone (Dq) and π-electron-rich anthracene (Da) are judiciously selected as two different linkers in a β-ketoenamine-linked two-dimensional (2D) COF. As a result of precisely integrated anthraquinone moieties, COF thin sheet exhibits redox activity. Meanwhile, π-electron-rich anthracene linker assists to improve the mechanical property of the free-standing thin sheet through the enhancement of noncovalent interaction between crystallites. This binder-free strategy offers the togetherness of crystallinity and flexibility in 2D COF thin sheets. Also, the synthesized porous crystalline convergent COF thin sheets are benefited with crack-free uniform surface and light-weight nature. Further, to demonstrate the practical utility of the material as an electrode in energy-storage systems, we fabricated a solid-state symmetrical flexible COF supercapacitor device using a GRAFOIL peeled carbon tape as the current collector.

Construction of highly crystalline ultraporous covalent organic frameworks in seconds

Covalent organic frameworks (COFs) have concerned substantial deal of recognition to the researchers because of its summoned inordinate scientific attention owing to its diverse applications such as catalysis, gas storage, sensing and optoelectronics. The conventional synthetic route for obtaining such ordered covalent networks is the connection of symmetrical building blocks through covalent bonds. However, tedious synthetic procedures, longer reaction time combined with the usage of toxic solvents and poor yield appears to be the bottleneck towards their greener fabrication, thereby limiting their possible potential applications. In this regard, we have introduced the simplest route via molecular organization approach towards the exceptionally rapid synthesis of highly crystalline, ultraporous COFs in seconds. The as-synthesized COFs ranked at the top among all reported two-dimensional COFs in terms of BET surface area till date. Accounting crystallography, we have detailed the molecular level fundamentals of COF crystallization and control over layered planarity and interlayer stacking. In addition, processing such porous, crystalline materials into various geometric shapes of industrial importance faces inadequacy due to the intricate problems like insolubility, grain boundaries as well as the difficulties in bulk scale synthesis. In this regard, we have further explored the possibility of industrial-scale (kg/h) synthesis of COFs and in situ processing them into different shapes (beads, cylinders, tube etc.) and sculpture mimicking the Terracotta Process by keeping their potentiality intact. The shapes outperformed the conventional zeolites and other MOFs in dehumidification performance. [1] Karak, S. et al. (2017). J. Am. Chem. Soc., DOI: 10.1021/jacs.6b08815. [2] Kandambeth, S. et al. (2012). J. Am. Chem. Soc., 134, 19524-19527. [3] Kandambeth, S. et al. (2016). Adv. Mater., DOI: 10.1002/adma.201603945.