The Catalytic Activity of Carob Extract-Capped Silver Nanoparticles in the Remediation of Recalcitrant Nitroaromatics

Nitroaromatic compounds are highly stable pollutants in the aquatic environment, posing serious health risks due to their mutagenic, carcinogenic, and toxic nature. In this study, the catalytic reduction of four organic pollutants (o-aminonitrobenzene, p-nitrophenol, 2,4-dinitrophenol, and 1,2-diamino-4-nitrobenzene) to corresponding aminobenzenes was achieved using sodium borohydride (NaBH₄, the reducing agent) and carob extract-capped silver nanoparticles (cc-AgNPs; the catalyst) under ambient conditions. The silver catalyst, cc-AgNPs, was biosynthesized, adopting an eco-friendly green synthesis approach in which carob (Ceratonia silique L.) pod water extract was used as a reducing and capping agent. The cc-AgNPs were characterized using various techniques, including Ultraviolet-visible (UV-vis) spectroscopy, Fourier Transform Infrared spectrometer (FT-IR), Transmission Electron Microscopy (TEM), zeta size and potential measurements. The UV-vis spectra of cc-AgNPs showed a characteristic surface plasmon resonance peak at 422–425 nm. Analysis of the FT-IR spectrum confirmed that the cc-AgNPs were coated with carob extract. Zeta potential measurement indicated that the surface charge of the catalyst was negative (-21.4 ± 0.7 mV). Based on TEM results, the average size of the cc-AgNPs was 33–43 nm. cc-AgNPs reduced the nitroaromatics to aminobenzene derivatives in < 1 min. in the presence of the reductant NaBH₄. The study revealed that cc-AgNPs are effective in catalytic hydrogenation of nitroaromatics. The cc-AgNPs can be used in environmental remediation to eliminate persistent nitroaromatics and convert them into valuable amino benzene precursors. These precursors can then potentially be used to produce various organic compounds for applications in the pharmaceutical, organic synthesis, and dye production industries.