Co-adsorption effect of Ir(III) complexes photosensitizers on CO 2 reduction photocatalysis of Ru(II)-Re(I) and polymeric carbon nitride Toshiya Tanaka 1 , Yusuke Kuramochi 2 , Osamu Ishitani 3 , Kazuhiko Maeda 1 1 Department of Chemistry, School of Science, Institute of Science Tokyo, Japan, 2 Department of Chemistry,Faculty of Science and Engineering, Kindai Universty, Japan, 3 Graduate School of Advanced Scinece and Engineering, Hiroshima University, Japan
Introduction Photocatalytic CO 2 reduction reactions have attracted significant attention as a potential solution to fossil fuel depletion and global warming. Among them, dinuclear complexes ( RuRe ), which combine Ru(II)(dmb) 3 2+ and fac -Re(I)(dmb)(CO) 3 (L) n + -type complexes, exhibit high CO 2 reduction activituy. 1 However, the photooxidative power of these complexes is limited. To address this limitation, a hybrid photocatalyst has been developed by adsorbing RuRe onto polymeric carbon nitride (PCN) powder modified with nanoparticulate anatase TiO 2 (Figure 1). This system can reduce CO 2 to CO using triethanolamine (TEOA) as a sacrificial electron donor, different from an analogous system without the solid component. Nevertheless, the photocatalytic activity is not satisfactory. Therefore, in this study, four different cyclometalated Ir complexes (Figure 2) were synthesized and co-adsorbed onto RuRe /TiO 2 /PCN to improve the photocatalytic activity. Result and Discussion Figure 2 shows the synthesized cyclometalated Ir(III) complexes. IrDP and IrTP were introduced a phosphonic acid linker directly with 1-phenyl-isoquinoline (piq) ligand. On the other hand, IrCDP and IrCTP have a methylene spacer between piq ligand and phosphonic acid linker. The Ir(III) complexes were adsorbed onto TiO 2 /PCN by dispersing theTiO 2 /PCN powder in a methanol/triethylamine (MeOH/TEA, 199:1 v/v) solution. Figure 3 shows the UV-vis diffuse reflectance spectra ofTiO 2 /PCN after adsorption of Ir(III) complexes, along with UV-vs absorption spectra of these Ir(III) complexes. The adsorption amount of IrDP , IrTP , IrCDP and IrCTP were estimated to be 14 mmol g -1 was adsorbed on all samples in the same manner. For photocatalytic reactions, 4 mg of each sample was dispersed in DMA-TEOA (4:1, v/v) 4 mL and the suspensions were irradiating at 405 nm LED light under CO 2 atmosphere. Figure 4 shows the photocatalytic reaction results of co-adsorption Ir(III) complexes after irradiating at 405 nm LED light for 20 h. Co-adsorption of IrDP and IrCDP with RuRe /TiO 2 /PCN enhanced CO production compared to the system without Ir(III) complexes. In contrast, the IrTP co-adsorbed system showed little differnce, and the IrCTP system showed only a slight improvement. The trend of photocatalytic activity in co-adsorption of Ir(III) compelxes will also be discussed in the poster presentation. References 1. Tamaki, Y.; Ishitani, O. ACS Catal. 2017 , 7 , 3394 2. Shizuno, M.; Kato, K; Nishioka, S.; Kanazawa, T.; Saito, D.; Nozawa, S.; Yamakata, A.; Ishitani, O.; Maeda, K. ACS Appl. Energy. Mater. 2022 , 5 , 9479
Figure 1. CO 2 reduction of RuRe / TiO 2 /PCN
Figure 2. Structure of cyclometalated Ir(III) photosensitizers
Figure 3. DRS of before and after adsorption on Ir(III) complexes and UV-vis absorption spectra of Ir(III) complexes in MeOH:TEA(199:1, v/v)
Figure 4. The result of photocatalytic reaction in DMA-TEOA (4:1, v/v) after irradiating at 405 nm at 20 h under CO 2 atmosphere
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