Economia circular aplicada à resíduos vegetais: nanopartículas metálicas aplicadas como catalisadores em sistemas alternativos de energia

Abstract

Nanotechnology research proposes innovations and possibilities for studies to solve problems in society, as one of the main goals from an ecological point of view is the reduction of Greenhouse Gas (GHG) emissions. Thus, green chemistry emerges, justifying the use of less toxic reagents, incorporating them with plant extracts and chemical applications. The project aims to synthesize, characterize, and evaluate the electrocatalytic efficiency of nickel nanoparticles supported on carbonaceous materials in the ethanol oxidation process. For the synthesis, fragments of the L. ferrea fruit were used were washed, ground and dried. 0,75 g of the material was placed in 100 mL of H2O and stirred for 24 hours. In the synthesis of NiNPs, 1,4 mL of the extract was used, 3,6 mL of water H2O and 50 mL of a 0,1 mmol L-1 NiCl2 solution were added at pHs ,0, 8.0, 9.0, 10 and 12. For in-situ and ex-situ adsorption, masses of 0,25 g; 0,50 g; 0,75 g; and 1,0 g were stirred with 50 mL NiCl2 1x10-3 mol L-1 for 10 min and adding 1,4 mL of extract and 3,6 ml H2O at the mentioned pH. In the phytochemical, alkaline hydroxides at 0,1% NaOH were used, in tannin CH3OH, 2% FeCl3 and 2% gelatin were used, for saponin 0,1 M NaOH, in terpenes 0,1% of (CH3CO)2O (m/v), H2SO4 at 0,01% (v/v) and 3 ml of CHCl3, and alkaloids 2 ml at 1% of heated HCl. 50 NiCl2 at 1x10-4 mol L-1 was mixed with activated carbon (tucumã and commercial) Vulcan xc-72R brand, and masses 0,25 g, 0,50 g, 0,75 g and 1,0 g, 1,4 mL of extract and 3,6 mL of (H2O), pH 7,0, were added. The mixture was filtered and read on the UV/Vis spectrophotometer. The filtered material was washed and dried at 80 °C. The electronic spectrum showed absorption maxima at 228, 270, and 363 nm, typical of flavonoids. At pH 7,0, peaks were observed at 326 nm in the first hour, shifting to 308 nm in the fifth hour. At pH 8,0, in the first hour, wavelengths ranged from 243 nm to 328 nm. At pH 9,0, the reduction of Ni²⁺ ions occurred at different rates. At pH 10 absorption maxima were observed at 250, 287, and 325 nm, while at pH 12, a peak at 213 nm was observed. At 25ºC, the best results occurred with 0,7 (a.u.) and 320 to 350 (nm) compared to 45ºC and 65ºC. Successes with the in-situ and ex-situ adsorption method, at concentrations of 0,25 g, 0,50 g, 0,75 g and 1,0 g of activated carbon (commercial and tucumã), highlighting the masses of 0,75 g and 1,0 g. In voltammetry, ex-situ method, the currents increase with pH (13-14). In the ex-situ method, by allowing the prior formation of NiNPs, particles with greater crystallinity, less interaction, less definition of redox peaks, and lower anodic current are generated. The in-situ curves show a higher current at pH (11-13). In the ex-situ tucumã charcoal method, there is a more pronounced peak current at pH 11, with lower reproducibility, but a significant electrochemical response at pH 13-14, with defined peaks and high currents. In cyclic voltammetry with anchored NiNPs and a scan speed of 10 mV s-1, ethanol oxidation is favored at pH 13 and 14, with a higher anodic current density. At pH 7,0 and 9,0, there is lower activity, similar to that observed with the commercial support, as the highest anodic responses occur at pH 13 and 14. In the ex-situ, there are defined oxidation peaks for concentrations of 0,5 to 1,0 mol L⁻¹ of ethanol, anticipating alcoholic oxidation from 0,1 V. Thus, the current maximums between 0,8 and 1,0 V indicate efficiency in electro-oxidation, in the in-situ method, highlighting the concentrations of 0,7 and 1,0 mol L⁻¹, which present higher current and defined oxidation peaks, above 0,2 V. In the ex-situ method, tucumã obtained low concentrations (0,1 and 0,3 mol L⁻¹) promoting anticipation of alcoholic oxidation, with lower current intensity. However, the concentration of 0,3 mol L⁻¹ shows a current growth, without the formation of a defined oxidation peak. The higher concentrations (0,5 to 1,0 mol L⁻¹) present peaks of 0,7 and 0,9 V, with those of 0,7 and 1,0 mol L⁻¹ being more prominent. The NiNPs/AC catalyst, C. tucumã in-situ, the concentrations of 0,7 and 1,0 mol L⁻¹ stand out, with anticipation of ethanol electro-oxidation and defined oxidation peaks. Therefore, the 1,0 mol L⁻¹ ethanol solution obtained better electro-oxidation and stability. Thus, chronoamperometry stands out, with currents of 0,001 mA for Ni/C ex-situ, 0,0021 mA for Ni/C in-situ, 0,018 mA for Ni/AC ex-situ and 0,0134 for Ni/AC in-situ.