Sunlight mediated improved photocatalytic degradation of carcinogenic benz[a]anthracene and benzo[a]pyrene by zinc oxide encapsulated hexacyanoferrate nanocomposite

Abstract

Polycyclic aromatic hydrocarbons (PAHs), pervasive plus priority emerging pollutants have the potential to destruct the bionetwork. Therefore, photocatalytic decay of toxic 4- and 5-ring membered PAHs, namely benz[a]anthracene (BaA) and benzo[a]pyrene (BaP), was explored in water. The nanocomposite of zinc hexacyanoferrate encapsulated with zinc oxide (ZnHCF@ZnO) was synthesized by Azadirachta indica mediated co-precipitation under normal conditions. Sunlight exposure caused a quick downfall in the concentration of PAH with composite exposing its eminent photo-activity. Encapsulation resulted in enhanced surface area (113 m2 g−1) and lesser band gap energy (2.2 eV) of nanocomposite owing to the synergism of semiconducting stuff of zinc oxide and intercalative properties of ZnHCF. At neutral pH, photo-degradation of PAHs (2 mg L−1) by optimum dose of catalyst followed first order kinetics and Langmuir isotherms (R2≥0.98; p ≤ 0.05). Slightly lower elimination of BaP (90%) than BaA (93%) might be due to its higher molecular weight and conjugation. Mechanism exploration revealed the involvement of “cation- π” interaction effectively between nanocomposite and PAHs (Xm =25.6 mg/g of BaA and 21.7 mg/g of BaP) than bared (ZnO and ZnHCF). Besides, it compacts the t1/2 value of BaA(0.35 h) and BaP (0.49 h) up to manifolds than its constituents (13–26 h). Smaller by-products like prop-2-en-1-ol, propionic acid and acrylic acid identified in GCMS, clearly supported electron excitement from encapsulated nanocomposite followed by OH (active species)based oxidation of PAHs. Particularly, the mineralization evaluation of PAHs through TOC analysis confirmed its conversion into H2O and CO2. Inclusive of the present study provides promising photo-catalyst with greater surface activity, low quantum yield with charge separation and reusable for ten cycles deprived of substantial loss of its action. Similar studies can be promoted to build up methods that can accurately predict the acceleration in the environment clean up strategies.