Metal-organic hybrid: Photoreduction of CO 2 using graphitic carbon nitride supported heteroleptic iridium complex under visible light irradiation Anurag Kumar a, b , Pawan Kumar a, b , Rajnikant Borkar c , Amit Bansiwal c , Nitin Labhsetwar c , Suman L. Jain a, * a Chemical Sciences Division, CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun 248005, India b Academy of Scientiﬁc and Industrial Research (AcSIR), New Delhi 110001, India c CSIR-National Environmental Engineering Research Institute (CSIReNEERI), Nehru Marg, Nagpur 440020, India article info Article history: Received 14 May 2017 Received in revised form 11 July 2017 Accepted 23 July 2017 Available online 25 July 2017 Keywords: Visible light Photocatalysis Hybrid material Graphitic carbon nitride CO 2 reduction abstract A novel heteroleptic iridium complex supported on graphitic carbon nitride was synthesized and used for photoreduction of carbon dioxide under visible light irradiation. The methanol yield obtained after 24 h irradiation was 9934 mmol g 1 cat (TON 1241 with respect to Ir) by using triethylamine (TEA) as a sacriﬁcial donor, which was signiﬁcantly higher as compared to the semiconductor carbon nitride 145 mmol g 1 cat under identical conditions. The presence of triethylamine was found to be vital for the higher methanol yield. After the reaction, the photocatalyst could easily be recovered and reused for subsequent six runs without signiﬁcant loss in photo activity. © 2017 Elsevier Ltd. All rights reserved. 1. Introduction Photoreduction of carbon dioxide to energy rich chemicals using solar energy is an area of tremendous importance in view of providing alternative energy source as well as to mitigate concen- tration of CO 2 in atmosphere [1,2]. Photocatalytic CO 2 reduction using a semiconductor based photocatalyst under mild reaction conditions has been appeared to be a potential approach for CO 2 conversion due to its simplicity and potential scalability for prac- tical applications [3]. However, most of the semiconductors re- quires ultra-violet light due to large band gap and provide poor efﬁciency and conversion to the desired product. For the efﬁcient utilization of solar light which comprises 5% UV and 45% visible light, a photocatalyst that is able to harvest visible light is desired [4,5]. Due to large band gap, most of the semiconductor photo- catalysis suffers from the drawback of poor visible light absorption and faster electron-hole recombination which resulted to the poor conversion efﬁciency and selectivity [6]. Unlike to these semiconductor photocatalysts, molecular complexes of transition metals such as Ir, Ru(II) or Re(II) bipyridyl complexes possess good visible light absorbance and long lived excited states; hence they provide better electron transfer which resulted to the more efﬁ- cient reduction of CO 2 [7e9]. In addition, in metal complexes, metal centre can bind with CO 2 , which in turn provide higher CO 2 con- centration and higher conversion efﬁciency [10,11]. Despite of several advantages, molecular complexes suffer from the inherent disadvantages of homogeneous catalysis of difﬁcult recovery and non-recyclability. Thus, combining a visible light responsive semiconductor with molecular photocatalyst to make the system heterogeneous seems to be a straight forward approach for carrying out the CO 2 reduction. In this regard, recently our group has developed a number of CO 2 reduction systems by using organic semiconductors such as graphene oxide/reduced graphene oxide in combination of transition metal complexes for carrying out CO 2 reduction under visible light irradiation [12e15]. A signiﬁcant improvement due to the better charge separation efﬁciency was observed in hybrid photocatalysts and they provided higher con- version/yield of methanol than the individual components with the added beneﬁts of facile recovery and recyclability for several runs * Corresponding author. E-mail address: suman@iip.res.in (S.L. Jain). Contents lists available at ScienceDirect Carbon journal homepage: www.elsevier.com/locate/carbon http://dx.doi.org/10.1016/j.carbon.2017.07.080 0008-6223/© 2017 Elsevier Ltd. All rights reserved. Carbon 123 (2017) 371e379