Utilization of Magonia pubescens extracts in the synthesis of rhodium NPs on Fe3O4@MgO support: A novel catalyst for 4-nitrophenol hydrogenation

Abstract

This study reports the development of three distinct nanoparticulate catalysts, each comprising a biosynthesized Fe3O4 nanoparticle magnetic core with an average diameter of 17 nm, showcasing superparamagnetic behavior. This magnetic core was further encased in a spherical magnesium oxide (MgO) layer through a bio-inspired strategy, leading to the Fe3O4@MgO support structure. Rhodium (Rh) nanoparticles, with diameters between 1.0 and 1.5 nm, were then fabricated to act as the main catalytic entities. These were subsequently affixed to the Fe3O4@MgO support, yielding Fe3O4@MgO-Rh, using three distinct methodologies. Remarkably, the bio-inspired processes employed for the creation of Fe3O4@MgO-Rh harnessed the infusion and extract from Magonia pubescens A St. Hil leaves, colloquially termed “Timbó”. These natural extracts played dual roles as reducing and stabilizing agents during the catalyst generation, leading to three variants: CI, CW, and CS. Comprehensive characterization of these catalysts was achieved using XPS, TEM, EDS, and VSM techniques. The ensuing evaluation involved the hydrogenation of 4-nitrophenol, which served to assess the efficiency and resilience of the bio-inspired catalysts vis-à-vis conventionally-produced counterparts. Notably, under benign conditions of a molecular H2 atmosphere (an ecologically sound hydrogen atom source) and moderate temperatures (60 °C), conversion rates exceeding 97 % were consistently observed for the substrate within a time frame of 0 to 15 min. For a more granular comparison of efficiency among the rhodium-centric catalysts, Turnover Frequency (TOF) and Total Turnover Number (TTON) computations were undertaken. Herein, the CI catalyst, originating from infusion, displayed a TTON value of 1263.24, underscoring its preeminence in 4-NF hydrogenation reactions. This was closely trailed by the CS catalyst, which boasted a TTON of 873.63, synthesized with a commercial surfactant.