GREEN SYNTHESIS OF CO3O4/POLYANILINE NANOCOMPOSITES USING VERNONIA AMYGDALINA LEAF EXTRACT FOR PHOTOCATALYTIC DEGRADATION OF METHYLENE BLUE AND CONGO RED UNDER SOLAR IRRADIATION

Abstract

PANI, Co3O4 NPs, and Co3O4/PANI nanocomposites were successfully synthesized using a green synthesis method and applied for the photocatalytic degradation of Methylene blue (MB) and Congo red (CR). The synthesized materials were characterized using analytical techniques such as XRD, FT-IR, UV-Visible, and SEM. The FT-IR spectra of VA showed that the wavenumber absorption at 3470 cm-1 represented the hydroxyl (-OH) group, while at 2931 cm-1 characterized the C-H absorption. The peak observed at 1631 and 1402 cm−1 indicates C = C stretching and O-H bending of carboxylic acid, respectively. The band at 1173 cm−1 corresponds to the C-O stretching of an aromatic ester. The prominent absorption bands at 555 cm-1 and 648 cm-1 , attributed to the stretching vibrations of the metal-oxygen bond corresponding to (Co3+ - O) and (Co2+ - O) vibrations, respectively in NPs. A peak at 1628 cm-1 and 1401 cm-1 shows C=C, and C–N stretching vibration respectively. The characteristic band formed at 3368cm -1 corresponding to N–H stretching vibration of secondary amine and for pure PANI, The peak at 1622 cm−1 , 1404cm-1 is due to the C= C stretching vibration of the quinoid rings ((N=Q=N)) and benzenoid ring (N-B-N) respectively. Band at 1118 cm−1 is due to the C−N stretching of a secondary aromatic amine. XRD patterns revealed the crystalline sizes of the materials, with average particle sizes 19.25nm, 8.24nm, 11.03 for Co3O4 NPs, PANI powder, and NCs respectively. Morphological investigations indicated unique structures for each material. UVVisible spectra provided band gap energy values for the synthesized materials (1.69 and 3.93 for Co3O4 NPs; 1.57, 3.1 and 4.12 for PANI: 3.26, 3.80 and 5.3 for NCs). The photocatalytic degradation study demonstrated that Co3O4 NPs and Co3O4/PANI NCs efficiently degraded MB and CR under natural sunlight irradiation. The degradation efficiency was influenced by catalyst dose, initial concentration, pH, and exposure time. Maximum degradation percentages were achieved under optimized conditions for both dyes (93.69% in Co3O4/PANI NCS and 90.79% in Co3O4 NPs for CR and 91.66% in Co3O4/PANI NCs and 89.60% in Co3O4 NPs for MB). Co3O4/PANI NCs exhibited higher degradation efficiency than Co3O4 NPs due to interactions between inorganic semiconductors and conducting polymers. Kinetic studies revealed that MB followed pseudo zero-order kinetics, while CR degradation followed pseudo first-order kinetics with the R2 = 0.993 and 0.992 respectively