Immobilization of Ag nanoparticles on NiFe2O4@TiO2@PDA: Multifunctional catalytic action toward the reduction of 4-Nitrophenol and photodegradation of methylene blue and ciprofloxacin

Freshwater, an essential commodity of life, is under threat by the presence of pernicious chemicals, such as 4nitrophenol (4-NP), organic azo dyes, and colorless antibiotic pollutants, leading to water pollution. It is an absolute necessity to transform these pernicious chemicals into benign compounds to mitigate water pollution and safeguard life on Earth. One such effort in the current work is the development of a recyclable, multifunctional, and heterogeneous NiFe2O4@TiO2@PDA-Ag magnetic nanocatalyst for the reduction of 4-NP to 4aminophenol (4-AP) and the photocatalytic degradation of methylene blue (MB) (an organic azo dye) and ciprofloxacin (CIP) (a colorless antibiotic pollutant) under irradiation with direct sunlight. Characterization of the developed catalyst was achieved using various spectroscopic and analytical methods (XRD, FTIR & UV-Vis spectroscopy, SEM, TEM, and XPS). The visible light active nature of the catalyst was confirmed by our UV-Vis spectroscopic data. The reduction of 4-NP to 4-AP with 97% conversion was achieved using the catalyst at room temperature in an aqueous medium in the presence of sodium borohydride (NaBH4) at a rate constant of 0.462 min-1. The photocatalytic degradation of MB and CIP was achieved using the catalyst under irradiation with direct sunlight, in which 96.5 and 68% degradation was observed with a degradation rate constant of 0.0483 and 0.0750 min-1 respectively. The presence of a magnetic NiFe2O4 core in the catalyst enables its recovery with the aid of the external magnet, its reusability was assessed and exhibited good efficacy up to five cycles. The magnetic nature of the catalyst was confirmed using vibrating sample magnetometry (VSM). The synthesis of a sole reusable magnetic catalyst suitable for the removal of three toxic pollutants under normal conditions adopting a facile methodology with excellent activity up to five cycles is rare and thus, the findings from the present work provide helpful information in wastewater treatment.

Automated summary

A recyclable, multifunctional, and heterogeneous NiFe2O4@TiO2@PDA-Ag magnetic nanocatalyst was developed for the reduction of 4-NP, degradation of methylene blue, and ciprofloxacin under sunlight. The catalyst exhibited efficient catalytic performance and good reusability for five cycles, providing useful insights for wastewater treatment.