Cobalt Phthalocyanine Immobilized on Graphene Oxide: An Efficient Visible-Active Catalyst for the Photoreduction of Carbon Dioxide

New graphene oxide (GO)-tethered–CoII phthalocyaninecomplex [CoPc–GO] was synthesized by a stepwiseprocedure and demonstrated to be an efficient, cost-effectiveand recyclable photocatalyst for the reduction of carbondioxide to produce methanol as the main product. The developedGO-immobilized CoPc was characterized by X-raydiffraction (XRD), FTIR, XPS, Raman, diffusion reflection UV/Vis spectroscopy, inductively coupled plasma atomic emissionspectroscopy (ICP-AES), thermogravimetric analysis(TGA), Brunauer–Emmett–Teller (BET), scanning electron microscopy(SEM), and transmission electron microscopy (TEM).FTIR, XPS, Raman, UV/Vis and ICP-AES along with elementalanalysis data showed that CoII–Pc complex was successfullygrafted on GO. The prepared catalyst was used for the photocatalyticreduction of carbon dioxide by using water asa solvent and triethylamine as the sacrificial donor. Methanolwas obtained as the major reaction product along with theformation of minor amount of CO (0.82 %). It was found thatGO-grafted CoPc exhibited higher photocatalytic activitythan homogeneous CoPc, as well as GO, and showed goodrecoverability without significant leaching during the reaction.Quantitative determination of methanol was done byGC flame-ionization detector (FID), and verification of productwas done by NMR spectroscopy. The yield of methanolafter 48 h of reaction by using GO–CoPc catalyst in the presenceof sacrificial donor triethylamine was found to be3781.8881 mmolg 1 cat., and the conversion rate was foundto be 78.7893 mmolg 1cat.h 1. After the photoreduction experiment,the catalyst was easily recovered by filtration andreused for the subsequent recycling experiment without significantchange in the catalytic efficiency

本研究通过分步合成法制备了一种新型氧化石墨烯（graphene oxide, GO）锚定钴(II)酞菁配合物[CoPc–GO]，经验证其可作为高效、经济且可循环的光催化剂，用于二氧化碳还原反应，主产物为甲醇。所制备的GO负载型CoPc采用多种表征手段进行分析，包括X射线衍射（X-ray diffraction, XRD）、傅里叶变换红外光谱（FTIR）、X射线光电子能谱（XPS）、拉曼光谱、漫反射紫外-可见光谱、电感耦合等离子体原子发射光谱（inductively coupled plasma atomic emission spectroscopy, ICP-AES）、热重分析（TGA）、布鲁诺尔-埃米特-特勒比表面分析法（Brunauer–Emmett–Teller, BET）、扫描电子显微镜（SEM）以及透射电子显微镜（TEM）。FTIR、XPS、拉曼光谱、UV/Vis及ICP-AES表征结果结合元素分析数据证实，CoII–Pc配合物已成功接枝至GO表面。将所制备的催化剂用于以水为溶剂、三乙胺为牺牲剂的二氧化碳光催化还原反应，反应主产物为甲醇，同时伴随少量一氧化碳（0.82%）生成。研究发现，GO接枝型CoPc的光催化活性优于均相CoPc及纯GO，且具备良好的可回收性，反应过程中金属浸出量极低。采用气相色谱-火焰离子化检测器（GC-FID）对甲醇进行定量分析，并通过核磁共振波谱对产物进行了验证。在以三乙胺为牺牲剂的体系中，使用GO–CoPc催化剂反应48小时后，甲醇产率为3781.8881毫摩尔每克催化剂，催化转换速率为78.7893毫摩尔每克催化剂每小时。光催化还原实验结束后，可通过过滤法轻松回收催化剂，用于后续循环实验，且催化效率无显著下降。