Contents lists available at ScienceDirect Molecular Catalysis journal homepage: www.elsevier.com/locate/mcat Mesoporous covalent organic framework: An active photo-catalyst for formic acid synthesis through carbon dioxide reduction under visible light Priyanka Sarkar a , Sk. Riyajuddin b,1 , Anjan Das a,1 , Arpita Hazra Chowdhury a , Kaushik Ghosh b , Sk. Manirul Islam a, * a Department of Chemistry, University of Kalyani, Kalyani, Nadia, West Bengal, India b Institute of Nano Science and Technology, Mohali, 160062 India ARTICLE INFO Keywords: Photocatalysis Covalent organic framework Carbon dioxide Formic acid Photoreductions ABSTRACT We demonstrate the photocatalytic reduction of CO 2 into HCOOH using mesoporous Covalent Organic Framework (COF) as the active photocatalyst, Co(dmg) 2 as co-catalyst with Triethanolamine (TEOA) as sacri- fcial electron source under atmospheric pressure. Greater than 125 TON is achieved with 10 mg catalyst. The reaction cycle is dependent on the use of co-catalyst, Co(dmg) 2 and sacrifcial electron donor (TEOA). The reaction does not occur in the absence of light (445 nm) and can readily be controlled by light intensity alter- nation. We also demonstrate that a TON of 36 can be obtained with use of sunlight using the catalytic cycle. These results open the door to an entirely new class of protocol for photocatalytic reduction of CO 2 using COF and Co(dmg) 2 as co-catalyst under visible light. 1. Introduction Increasing environmental concerns in recent years for global warming, climate change, and ocean acidifcation are motivating re- searchers around the world for developing efcient and green strategies to capture, store, and utilize CO 2 [1–5]. Again, in the viewpoint of chemistry, CO 2 is one of most abundant, inexpensive and renewable carbon feedstock for producing value-added organic compounds and fuels [6–17]. So, the research on chemical transformations of CO 2 into fuels and essential chemicals are increasing day by day to reduce the CO 2 concentration in the atmosphere. Driving reactions by using a sustainable, green and eco-friendly process is a great challenge for modern scientifc community [18–20]. Consequently, it has become imperative for chemists to fnd new technologies capable of trans- forming undesirable CO 2 to useful chemicals, which are energetically efcient. One of the best means is the use of solar energy for the pho- tochemical reduction of CO 2 in terms of abundant and sustainable source of energy [21–30]. There are reports available for the photo reduction of CO 2 using metal oxide, such as TiO 2 under UV radiation [31–35] and also chemical reduction of CO 2 to formic acid [36,37]. However, the majority of the sun's rays fall under the visible-IR range, which is not enough to photoreduce CO 2 with these materials limiting their applicability and scalability. Thus, photoactive materials that are able to reduce CO 2 under visible light are an imminent and currently unavoidable need. In this context, covalent organic frameworks (COFs) have recently emerged as a new class of photoactive materials for light-induced CO 2 reduction [38–42]. Although, COFs are similar to related polymeric carbon nitrides, they modular, versatile and have easy tunable elec- tronic properties, structure, crystallinity and porosity. Additionally COFs are completely composed of light elements, which are earth- abundant leading to synthetically versatile heterogeneous photo- catalysis [43–45]. The highly efcient light harvesting and charge transport capability of COFs presumably arises from the π-electron conjugation in plane together along with the possibility of axial charge transport in the stacking direction by the overlap of π-orbitals [46–49]. However, it is highly surprising that despite their enormous potential, COFs have hardly been explored as visible light active photocatalysts for the production of solar fuels. Recently some work on photocatalytic reduction of CO 2 to fuels and various chemicals using COFs as active photocatalysts have been reported [39]. Herein, we report a novel mesoporous COF with high surface area (600 m²/g), strong crystallinity and robust stability, and along with Cobalt-(dmg) 2 Co-catalysts it exhibits excellent heterogeneous photo- catalytic performances for CO 2 reduction under visible-light irradiation. The efciency of the photocatalytic protocol is seen very high in terms https://doi.org/10.1016/j.mcat.2019.110730 Received 3 September 2019; Received in revised form 22 November 2019; Accepted 27 November 2019 ⁎ Corresponding author. E-mail address: manir65@redifmail.com (S.M. Islam). 1 authors contributed equally Molecular Catalysis xxx (xxxx) xxxx 2468-8231/ © 2019 Elsevier B.V. All rights reserved. Please cite this article as: Priyanka Sarkar, et al., Molecular Catalysis, https://doi.org/10.1016/j.mcat.2019.110730