Light driven Aspergillus niger-ZnS nanobiohybrids for degradation of methyl orange

Abstract

Inorganic-microbial hybrid systems have potential to be sustainable, efficient and versatile chemical synthesis platforms by integrating the light-harvesting properties of semiconductors with microbial cells. Here, we demonstrate light-driven photocatalytic semiconducting Aspergillus niger cells-ZnS nanoparticles for enhanced removal of the dye methyl orange. Chemically synthesized ZnS nanoparticles exhibited a zinc blende pattern in X-ray diffraction, had a dimension of 20-90 nm with a band gap (E_bg) of 3.4 eV at 1.83 × 10¹⁸ photons/second. Biologically synthesized ZnS nanoparticles of 40-90 nm showed a hexagonal pattern in the X-ray powder diffraction spectra with an E_bg 3.7 eV at 1.68 × 10¹⁸ photons/second. At a methyl orange (MO) concentration of 100 mg/L, dosage of 0.5 × 10⁵ mol catalyst and pH 4, a 97.5% and 98% removal efficiency of MO was achieved in 90 min and 60 min for, respectively, chemically and biologically synthesized ZnS nanobiohybrids in the presence of UV-A light. The major degradation products of photocatalysis for chemically synthesized ZnS nanobiohybrids were naphtholate (C₁₀H₇O m/z 143) and hydroquinone (C₉H₅m/z 113). For the biologically synthesized ZnS nanobiohybrids, the degradation products were hydroquinone (C₉H₅m/z 113) and 2-phenylphenol (C₁₂H₁₀O m/z 170).

Keywords: Aspergillus niger; Methyl orange; Nanobiohybrid; Photocatalysis; ZnS nanoparticles.