Radical-mediated photocatalytic dye degradation and antimicrobial properties of La2NiMnO6 nanoparticles

Abstract

This work focused to engineering double perovskite (DP) La₂NiMnO₆ (LNMO) nanoparticles (NPs) through the co-precipitation method and further calcined at 1000 °C. The flexibility in the multi-element structure of LNMO as a single-component system has been utilized to see the synergetic effect by tuning the band gap and hence redox potentials of radicals, which in turn enhances the electron and hole separation, and production of radicals, thus improving the efficacy of a photocatalyst. XRD confirms the phase purity of the LNMO NPs with a rhombohedral structure. FE-SEM and TEM analyses demonstrate the spherical morphology and uniform size distribution of the mesoporous particles having a size of ∼100 nm. LNMO NPs with a wide band gap E_g ∼ 3.56 eV (as evaluated by UV-vis analysis) were investigated for photocatalytic degradation of anionic methyl orange (MO) and cationic methylene blue (MB) dyes. An effective degradation of 84.57% for MO and 64.29% for MB was obtained in 60 min under UV irradiation. Radical trapping experiments performed with p-BQ, propanol, and ethanol as scavengers reveal the dominant role of superoxide (O₂˙⁻) radicals in the degradation of MO and MB. The reaction mechanism for degradation was explained based on the band edge potentials of CB (−0.34 eV) and VB (3.22 eV), and radical formation. Higher efficiency for MO is ascribed to the effective electrostatic attraction between the negatively charged surface of the LNMO NPs and positively charged MO dye molecules as established by the point of zero charge (pH_PZC = 8.43) of the LNMO NPs. The antimicrobial activity of LNMO NPs was also investigated against Gram-positive Bacillus subtilis, Gram-negative Escherichia coli bacteria, and Candida albicans (C. albicans), and Fusarium oxysporum as fungal pathogens. Maximum zone of inhibition (ZOI) of 31 mm and 32 mm was obtained for E. coli and B. subtilis, respectively, while 27 mm and 31 mm for Fusarium oxysporum and C. albicans, respectively.