Synthesis and evaluation of the oil removal potential of 3-bromo-benzimidazolone polymer grafted silica gel

Abstract

This work reports the synthesis of 3-bromo-benzimidazolone using melt condensation, its polymerization and functionalization on silica which was extracted from diatomaceous earth in our previous work. The synthesized compounds were characterized using FTIR, NMR, SEM-EDS and TEM. The FTIR and NMR spectra of the synthesized benzimidazolones showed the compounds to have several functional groups: A band due to Si–O–C at 1085.41 cm⁻¹, a broad band at 3380 cm⁻¹ and chemical shifts: positive distortionless enhancement by polarization transfer (DEPT) ¹³C peaks (indicating lack of CH₂ and CH₃ groups), ¹H NMR – 11.053 ppm (N–H), 7.086 ppm (Ar-H); ¹³C NMR – 155.34 ppm (CO), 101.04 ppm (C–Br) characteristic of benzimidazolones. SEM-EDS of the functionalized silica showed a rough irregular morphology with Si and O as the major elements. Carbon was also present indicating that silica was successfully functionalized with 3-bromo-benzimidazolone and TEM showed interconnected smear-like particles arranged irregularly. The functionalized silica was then applied in the treatment of oily wastewater and factors like initial oil concentration, adsorption dosage and time were optimized using the central composite design of response surface methodology in the design expert software. The amount of oil adsorbed was obtained by quantifying the total organic carbon using TOC test kits. Results showed that the optimum conditions for oil removal were 6650 mg L⁻¹ oil concentration, with adsorbent dosage of 0.004 g and a contact time of 16 h. Under these conditions, the percentage adsorption was 97.9% with a desirability of 0.99. The materials were therefore seen to be applicable to field wastewaters.