Selective CO 2 adsorption in a porphyrin polymer with benzimidazole linkages† Venkata S. Pavan K. Neti, a Jun Wang, b Shuguang Deng b and Luis Echegoyen * a A new nanoporous porphyrin-based benzimidazole linked polymer, PBILP, was synthesized. The use of porphyrin monomers as molecular building units led to the formation of a rigid amorphous network that has a moderate surface area (S BET ¼ 557 m 2 g 1 ). The CO 2 adsorption ability of PBILP is 12.1 wt% (2.76 mmol g 1 ) and it has a CO 2 /CH 4 selectivity of 7.2 at 273 K/1 bar and a CO 2 /N 2 selectivity of 72 at 273 K/1 bar. The synthesis of nitrogen rich microporous materials has gained signicant attention due to their potential as solid adsorbents for CO 2 capture. These microporous materials include, but are not limited to, metal–organic frameworks (MOFs), 1 zeolitic imidazolate frameworks (ZIFs), 2 and hypercross-linked microporous polymers (BILPs, POPs, etc.). 3–6 The key strategy to develop new and efficient POPs mainly relies on the design of nitrogen rich building blocks that possess high surface areas. In fact, many examples of new ligands and link- ages have expanded the versatility of the resulting functional microporous materials. These materials have found a wide variety of applications in gas storage and separation, 3–6 hetero- geneous catalysis, 6j etc. POPs and their membranes are best suited for selective gas adsorption and gas separation applica- tions due to their physical, chemical, high temperature and pressure stabilities, and their resistance towards moisture, and basic and acidic conditions. 4a,5a Recently, Hupp and Nguyen et al. reported an Al-porphyrin based POP for supercritical CO 2 processing and for the degradation of nerve agents. 6d El-Kaderi et al. developed benzimidazole-linked polymers (BILPs), 5a azo- linked polymers (ALPs), 5e and Zhang et al. reported imine linked polymers (ILPs), 4b and Uyama et al. reported N-doped activated carbon monoliths for selective CO 2 capture. Some advantages of porous polymers over activated carbons are higher CO 2 /N 2 selectivity and efficient and reversible capture of CO 2 . On the other hand, advantages of the micro- and meso- porous activated carbons over the porous polymers are the low cost of the raw material and the high CO 2 uptake. The selective CO 2 adsorption in these frameworks over CH 4 or N 2 is believed to arise as a consequence of CO 2 -framework interactions through R–N(d  )–C(d + )O 2 . In order to expand the BILP chemistry to porphyrins, we focused on carboxaldehyde based porphyrin, specically meso- tetra-(4-phenylformyl) porphyrin (TCPP, 1), and benzene- 1,2,4,5-tetramine (BTA, 2). We have prepared a porphyrin benzimidazole linked polymer (PBILP) containing poly- benzimidazole linkages as shown in Scheme 1. Part of the motivation behind this work is to demonstrate the capture of high amounts of CO 2 in a metalloporphyrin porous polymer. In the future we want to convert the captured CO 2 to poly- carbonates or other polymers, similar to a report using cobalt- porphyrins to effect this catalytic transformation. 7a High nitrogen and cobalt content of PBILP can be used for selective CO 2 adsorption and also for catalytic transformations. In this report, we describe the synthesis and characterization of PBILP and the selective CO 2 adsorption properties. The synthesis of PBILP was accomplished by the condensation reaction between 1 and 2, which is similar to a BILP synthesis reported by El- Kaderi et al. with a slight modication (see ESI†). 5a Compound 1 was synthesized following a similar literature procedure. 7b A homogeneous solution of 1 was added drop-wise to the suspension of 2 in N,N 0 -dimethylformamide (DMF) over 4 h while stirring at the 30  C, followed by stirring at room temperature for 12 h. The reaction yielded a purple suspension which was bubbled with O 2 , and then heated at 130  C for 36 h. The slow addition of 1 to 2 yielded the PBILP in a 60% yield as a purple solid. The resulting purple polymeric solid was unam- biguously characterized by spectral and analytical methods. The PBILP was designed to possess a 2D network structure arising from the four benzimidazole-linkages (Scheme 1). It is well known that during the course of polymerization, planar a Department of Chemistry, University of Texas at El Paso, El Paso, TX 79968, USA. E-mail: echegoyen@utep.edu; Fax: +1-915-747-8807; Tel: +1-915-747-7573 b Department of Chemical Engineering, New Mexico State University, Las Cruces, NM 88003, USA † Electronic supplementary information (ESI) available: Experimental details, Fig. S1–S7. See DOI: 10.1039/c4ra15086d Cite this: RSC Adv. , 2015, 5, 10960 Received 23rd November 2014 Accepted 8th January 2015 DOI: 10.1039/c4ra15086d www.rsc.org/advances 10960 | RSC Adv. , 2015, 5, 10960–10963 This journal is © The Royal Society of Chemistry 2015 RSC Advances COMMUNICATION Published on 08 January 2015. Downloaded by The University of Texas at El Paso (UTEP) on 10/06/2015 21:23:40. View Article Online View Journal | View Issue