Redução de CO2 em eletrodo semicondutor modificado com complexo de aspirinato de cobre

The chemical reduction of CO2 to fuels offers a way of recycling carbon dioxide and produces interesting products with energetic applications. In the present study, a copper (II) aspirinate complex photoelectrode was synthesized, characterized and examined for the photoelectrocatalytic response in CO2 reduction. Thin films of copper (II) aspirinate on the nanotube Ti/TiO2 surface is easily obtained after treatment with spin coating technique (400 rpm/1 min and 4000 rpm/30 s), with 1.0 x 10-2 mol L-1 [Cu2(asp)4] complex in DMSO. The Ti/TiO2 nanotubes (NTs) were obtained applying 30 V during 50 h in titanium plate (in a solution of 0.25 wt% NH4F with glycerol and water 90:10, v/v %)1, followed the calcination step (450 oC – 1 h). The morphological characterization was carried out by Field Emission Gun-Scanning Electron Microscopy (FEG-SEM) with a JEOL 7500F Microscope. The photoelectrochemical experiments were performed in a 500 mL glass cell with two compartments with cooling system (10oC), where the Ti/TiO2-[(Cu)2Asp4] working electrode was irradiated with UV-Vis light (125 W high pressure mercury lamp) inserted in a central quartz bulb, Ag/AgCl (KCl 3 mol L-1) electrode was used as reference, and the counter electrode consisted of a 70TiO2/30RuO2 DSA® plate, in 0.1 mol L-1 sodium sulfate solution medium. Before the experiment, the sodium sulfate solution was bubbled with CO2 (gas) over 1 h. The applied potential during the photoelectrocatalysis was -0.35 V, during 2 h. Methanol generated as product from CO2 photoelectroreduction were detected and quantified by gas chromatography (GC-FID model 2010 Shimadzu) using a solid-phase microextraction technique (SPME). Also, experiments of photocurrent responses in light on-off process at applied voltage were performed, and the results demonstrate that the Ti/TiO2-[Cu2(asp)4] showed good photoresponses and reproducible for different on-off cycles under the light on and light off conditions. The Ti/TiO2-[Cu2(asp)4] sample exhibited higher photocurrents than that of Ti/TiO2-NTs samples under UV-Vis irradiation. During the photoelectrocatalysis, under -0.35 V, the CO2 photoreduction produced methanol (concentration = 0.89 mmol L-1), in 0.1 mol L-1 Na2SO4 pH=6, and in this reaction the charge was around 6.4 C. The results show that the Ti/TiO2- [Cu2(asp)4] electrode can be a good strategy to increase the CO2 conversion to methanol when compared to common system based on Ti/TiO2 nanotubes, due electron mediator effect.