Effect of nickel and rGO on the photocatalytic properties of Co3􀀀 xNixO4 prepared with citric acid and CTAB

Abstract

This work summarizes the research about Co3􀀀 xNixO4 x = 0.0 (0%), 0.01 (1%), and 0.04 (4%) conducted with the addition of reduced graphene oxide, rGO, using two routes: with citric acid R1 (C₆H₈O₇, CA) and cetyltrimethylammonium R2 (C19H42BrN, CTAB) by sol-gel technique. The results show that the composite material ¿with rGO¿ enhanced the photocatalytic degradation of methylene blue (MB). According to the results, incorporating rGO into samples with low Ni concentrations of 1% and 4% and processed at 400 ◦C with R1, significantly increased their specific surface area to 31.372 m2.g-1 and 84.743 m2.g-1, respectively. The XRD technique shows the formation of pure cobalt spinel without associated secondary phases and with complete insertion of Ni into the structure. The presence of CA allows the formation of the oxide at lower temperatures. The results of the magnetic tests suggest that the samples obtained by the two synthesis routes present a paramagnetic behavior. The use of CTAB permits the formation of nanoparticles with low agglomeration. TEM images indicate that the sizes of the nanoparticles obtained in the synthesis are less than 20 nm. Thus, based on Raman spectroscopy, the vibrational modes corresponding to the Co3-xNixO4 structure were studied, identifying a broadening and displacement of the peaks with the addition of Ni. Moreover, the disappearance of the peaks corresponding to rGO and attributed to the coating of Co3-xNixO4 graphene nanoparticles was observed. The adsorption isotherms show the behavior of a mesoporous textured material. The diffuse reflectance indicates that R2 with a 1.72 eV value obtained the material with the smallest gap. In addition, the process identified that the existence of reduced graphene oxide increases the material's specific surface area, which plays a crucial role in MB degradation, outperforming the 4% Ni sample that degraded 39.65% in a two-hour treatment.