View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Archive Ouverte en Sciences de l'Information et de la Communication Cobalt Phthalocyanine Immobilized on Graphene Oxide: An Efficient Visible-Active Catalyst for the Photoreduction of Carbon Dioxide Pawan Kumar, Arvind Kumar, Bojja Sreedhar, Bir Sain, Siddharth Ray, Suman Jain To cite this version: Pawan Kumar, Arvind Kumar, Bojja Sreedhar, Bir Sain, Siddharth Ray, et al.. Cobalt Phthalocya- nine Immobilized on Graphene Oxide: An Efficient Visible-Active Catalyst for the Photoreduction of Carbon Dioxide. Chemistry - A European Journal, Wiley-VCH Verlag, 2014, 20, pp.6154 - 6161. 10.1002/chem.201304189. hal-01456553 HAL Id: hal-01456553 https://hal.archives-ouvertes.fr/hal-01456553 Submitted on 5 Feb 2017 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. DOI: 10.1002/chem.201304189 Full Paper & Heterogeneous Catalysis Cobalt Phthalocyanine Immobilized on Graphene Oxide: An Efficient Visible-Active Catalyst for the Photoreduction of Carbon Dioxide Pawan Kumar,[a] Arvind Kumar,[b] Bojja Sreedhar,[c] Bir Sain,[a] Siddharth S. Ray,[b] and Suman L. Jain*[a] Abstract: New graphene oxide (GO)-tethered–CoII phthalo- was obtained as the major reaction product along with the cyanine complex [CoPc–GO] was synthesized by a stepwise formation of minor amount of CO (0.82%). It was found that procedure and demonstrated to be an efficient, cost-effec- GO-grafted CoPc exhibited higher photocatalytic activity tive and recyclable photocatalyst for the reduction of carbon than homogeneous CoPc, as well as GO, and showed good dioxide to produce methanol as the main product. The de- recoverability without significant leaching during the reac- veloped GO-immobilized CoPc was characterized by X-ray tion. Quantitative determination of methanol was done by diffraction (XRD), FTIR, XPS, Raman, diffusion reflection UV/ GC flame-ionization detector (FID), and verification of prod- Vis spectroscopy, inductively coupled plasma atomic emis- uct was done by NMR spectroscopy. The yield of methanol sion spectroscopy (ICP-AES), thermogravimetric analysis after 48 h of reaction by using GO–CoPc catalyst in the pres- (TGA), Brunauer–Emmett–Teller (BET), scanning electron mi- ence of sacrificial donor triethylamine was found to be croscopy (SEM), and transmission electron microscopy (TEM). 3781.8881 mmol gÀ1 cat., and the conversion rate was found FTIR, XPS, Raman, UV/Vis and ICP-AES along with elemental to be 78.7893 mmolgÀ1cat.hÀ1. After the photoreduction ex- analysis data showed that CoII–Pc complex was successfully periment, the catalyst was easily recovered by filtration and grafted on GO. The prepared catalyst was used for the pho- reused for the subsequent recycling experiment without sig- tocatalytic reduction of carbon dioxide by using water as nificant change in the catalytic efficiency. a solvent and triethylamine as the sacrificial donor. Methanol Utilization of carbon dioxide as a sustainable C1 building block photoreduction of CO2, but their quantum yields and selectivi- has emerged as an important area of research in last two dec- ties of products are low.[2–3] In the recent years, photocatalytic ades mainly due to the concurrently problems of global warm- systems, including transition-metal complexes, such as ruthe- ing, as well as depletion of fossil fuels.[1] The effective use of nium(II) polypyridine carbonyl complex, cobalt(II) trisbipyridine, clean and abundant solar energy might provide a viable ap- cobalt(III) macrocycles, rhenium and iridium complex with proach to solve the problems of energy and environmental a photosensitizer have emerged to be efficient catalytic sys- crisis by a photocatalytic reduction of carbon dioxide to valu- tems to reduce CO2 with relatively high quantum yield and able chemicals. Although a number of improved catalytic sys- high selectivity of products.[4] However, the difficult recovery tems, such as nanosized titanium oxide, titanium oxide doped and non-recycling ability of a homogeneous complex make with transition metals, noble metals, and mixed with another these systems less attractive. To overcome these problems, im- metal oxide have been emerged as potent catalysts for the mobilization of homogeneous metal complexes to solid sup- port is an obvious way to combine the advantages of homoge- [a] P. Kumar, Dr. B. Sain, Dr. S. L. Jain neous catalysts, for example, high reactivity, selectivity, and Chemical Sciences Division, CSIR-Indian Institute of Petroleum heterogeneous catalysts, such as facile recovery and recycling Mohkampur, Dehradun 248005 (India) of the catalyst.[5] In this context, a number of homogeneous Fax: (+ 91)135-2660202 E-mail: [email protected] photoredox complexes have been supported to various sup- [b] A. Kumar, Dr. S. S. Ray ports, such as TiO2, organic polymers, ion-exchange resins. Analytical Sciences Division, CSIR-Indian Institute of Petroleum However, in most of the cases, noncovalent attachment of the Mohkampur, Dehradun 248005 (India) metal complex to support materials renders to the leaching of [c] Dr. B. Sreedhar the active species during the reaction.[6] Inorganic and Physical Chemistry Division Metallophthalocyanines and their derivatives have been CSIR-Indian Institute of Chemical Technology Hyderabad, 500607, Andhra Pradesh (India) widely used as photosensitizers for various applications in a va- Supporting information for this article is available on the WWW under riety of fields due to their unique properties, such as excellent http://dx.doi.org/10.1002/chem.201304189. semiconductivity, photoconductivity, thermal, and chemical Chem. Eur. J. 2014, 20, 6154 – 6161 6154 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Full Paper stability. Most of the studies conducted to date on metal vide great potential as a support material for various cata- [13] phthalocyanines for photocatalytic reduction of CO2 were per- lysts. Prior to the immobilization, the GO was treated with formed either in homogeneous solution or by supporting chloroacetic acid to convert the epoxy groups into carboxy [7] them to other semiconductor materials, such as TiO2. In this (COOH) groups, which were subsequently used for the grafting context, Zhou et al.[8] reported the use of in situ synthesized of CoPc to the GO surface. The schematic representation of TiO2/CoPc nanocomposite for the photocatalytic reduction of the synthesis of CoPc immobilized on GO (GO–CoPc) is shown carbon dioxide to formic acid, formaldehyde, and methanol. in Scheme 1. Graphene oxide (GO), an oxidized form of grapheme, has The morphology and structure of as-prepared GO and GO– emerged to be a promising material, particularly as a precursor CoPc catalyst was investigated by scanning electron microsco- to prepare reduced GO (rGO), chemically functionalized gra- py (SEM) and transmission electron microscopy (TEM). As pre- phene, and grapheme-based composite materials.[9,10] Very re- sented in Figure 1b, the SEM image of GO–CoPc shows twisted cently, Hsu et al.[11] have reported GO as a promising photocat- alyst for the conversion of CO2 to methanol with the conver- sion rate of 0.172 mmolgÀ1 cat.À1 hÀ1 under visible light. Herein, we describe the successful synthesis of covalently anchored cobalt phthalocyanine to the GO, its characterization, and use for the photocatalytic reduction of the carbon dioxide to methanol with improved product yield and selectivity. The oxygen functionalities on GO are targeted for stable and effi- cient anchoring of CoPc catalyst on nanosheets of GO through covalent attachment. The prepared catalyst exhibited higher photocatalytic activity under visible-light irradiation and gave Figure 1. SEM image of a) GO and b) GO-CoPc. methanol with improved yield and selectivity. The quantitative and qualitative determination of the methanol formation was performed by GC and 1H NMR spectroscopy. and crumpled nanosheets in an agglomerated phase with lot of wrinkled features of GO–CoPc catalyst. The TEM images shown in Figure 2a and b also reveal the nanoscopic features Synthesis and characterization of catalyst with layered structure of GO–CoPc catalyst (Figure S1 in the GO was obtained from the oxidation of graphite with KMnO4 Supporting Information). The TEM image of carboxylic group [12] and H2SO4 following the literature procedure. High specific (COOH) containing GO before immobilization of CoPc is shown surface area of GO along with easily accessible ample oxygen in Figure 2c. The dark spots in the TEM image (Figure 2c) are functionalities decorated on both side of GO nanosheets pro- probably due to the COOH functionalities located on the sur- Scheme 1. Synthesis of GO-grafted CoPc. Chem. Eur. J. 2014, 20, 6154 – 6161 www.chemeurj.org 6155 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Full Paper broad diffraction of graphite (002) at 2q value of approximately 268 appeared, indicating that exfoliation of the layered CoPc– GO was obtained.[15] The porosity characteristics of the samples were investigated by measuring the N2 adsorption/desorption isotherms at 77 K (Figure 4). Total pore volume and surface area of synthesized Figure 2. TEM image of a) GO; b) GO-CoPc; c) GO-COOH; and d) SAED pat- tern of GO-CoPc. face of GO. Selected area electron diffraction pattern of GO– CoPc shows that material was amorphous in nature (Fig- ure 2d). XRD patterns were used to study the changes in structure (Figure 3). The XRD spectrum of GO shown in Figure 3a gives characteristic diffraction peak at 10.88 (001), corresponding to a GO interlayer spacing of approximately 0.74 nm.[14] After im- mobilization of CoPc, this peak disappeared, and another Figure 4.