Cobalt Oxide on Boron-Doped Graphitic Carbon Nitride as Bifunctional Photocatalysts for CO2 Reduction and Hydrogen Evolution.

In this work, the prepared cobalt oxide decorated boron-doped g-C3N4 (CoOx/g-C3N4) heterojunction exhibits remarkable activity in CO2 reduction (CO2RR), resulting in high yields of CH3COOH (∼383 µmol·gcatalyst-1) and CH3OH (∼371 µmol·gcatalyst-1) with 58% selectivity to C2+ under visible light. However, the same system leads to high H2 evolution (HER) by increasing the cobalt oxide content, suggesting that the selectivity and preference for the CO2RR or HER depend on oxide decoration. By comparing HER and CO2RR evolution in the same system, this work provides critical insights into the catalytic mechanism, indicating that the CoOx/g-C3N4 heterojunction formation is necessary to foster high visible light photoactivity.

Synthesis and characterization of cobalt nanoparticles for application in the removal of textile dye.

In this work, magnetic cobalt nanoparticles (CoNPs) were synthesized and applied to the removal of Remazol golden yellow RNL (RGY) from aqueous solutions and textile wastewater. The CoNPs were characterized and the Co content found in the CoNPs was 60.38% (m/m). The analysis of X-ray Diffraction (XRD) and Raman Spectroscopy indicated the presence of Co0 and CoO in the composition of the material, as confirmed by Thermogravimetric Analysis coupled to Mass Spectrometry (TG-MS). Images obtained by the Transmission Electron Microscope (TEM) showed that the CoNPs have sizes smaller than 10 nm, sphere morphology and high agglomeration capacity. The results obtained by nitrogen adsorption-desorption suggested that the nanomaterial presented a mesoporous characteristic, low specific surface area (15.70 m2 g-1) and a pore volume and pore diameter of 0.072 cm3 g-1 and 3.64 nm, respectively. CoNPs removed the RGY with high efficiency, reaching almost 100% removal in 30 min. The kinetic results showed that the reaction followed pseudo-second-order kinetics. Additionally, the removal process can be altered depending on the experimental condition. For instance, under acidic conditions, the reductive degradation prevailed, while in neutral or basic conditions, two simultaneous processes occur: reductive degradation and adsorption. Finally, CoNPs were applied to textile wastewater. The results showed high discoloration, reaching almost 88%. However, there was only a 32% decrease in chemical oxygen demand, showing that CoNPs are efficient at removing organic dyes from aqueous solutions.