Linear electronic relationship of surface functionalized fly ash and substituted phenols on bactericidal activity with the computational study

Abstract Fly ash is a solid waste by‐product obtained from coal‐burning power plants. It is a silico‐aluminate material with an admixture of several metal oxides, which finds an application in geopolymers, zeolites, cement, catalysts, etc. The present article aims to assess the antibacterial activity of fly ash and substituted phenols against Escherichia coli and Staphylococcus in broth and agar cultures, respectively. High‐Temperature Activated Fly Ash (TAFA) shows significant bactericidal activity against gram positive (+) and negative (−) bacteria as compared to Mechanically Activated Fly Ash (MAFA) and Waste Polyethylene Coated Fly Ash (WPCFA), which attribute to the augmentation of mullite phase (lacking charge balancing cation) of fly ash at high temperature. These modified fly ash (TAFA, MAFA, and WPCFA) were characterized by Fourier Transform Infra Red (FT‐IR), Scanning Electron Microscope (SEM), and X‐Ray Diffraction (XRD) techniques. The substituted phenols further explored the significance of charge on the antibacterial properties. The para‐substituted phenols with groups having (+) mesomeric effect M > (−) I Inductive effect and ortho substituents with (+) I effect shows a linear electronic relationship with antibacterial properties with gram (+) bacteria, owing to charge augmentation at oxygen atom of phenoxide ion due to electronic effects. Further, the bactericidal efficacy was less significant on gram (−) bacteria. Small energy gap ( E gap ) values corroborated the chemical reactivity of phenols and substituted phenols. The antimicrobial potential of phenol/substituted phenols can be correlated with global descriptors. Molecular Electrostatic Potential (MEP) maps obtained through Density Functional Theory (DFT) indicate the nucleophilic centers in the molecular structure.