Abstract
In this paper, a novel sulfonic acid containing magnetic methylene-based organosilica with core-shell structure (Fe3O4@OS-SO3H) is synthesized, characterized and its catalytic application is investigated for biodiesel production via esterification of carboxylic acids with alcohols. The Fe3O4@OS-SO3H was synthesized via co-condensation of tetraethyl orthosilicate (TEOS) and 1,2-bis(triethoxysilyl)methane (BTEM) around magnetite nanoparticles. The Fe3O4@OS-SO3H nanocatalyst was characterized by using FT-IR, PXRD, TGA, VSM, TEM and SEM techniques. The catalytic study showed that the Fe3O4@OS-SO3H nanocomposite can be used as an effective, powerful, selective and recyclable catalyst for the esterification of carboxylic acids with alcohols at 70 °C under solvent-free conditions. This nanocatalyst was recovered and reused several times without significant decrease in efficiency and stability.
Highlights
Fe3O4@OS was synthesized via co-condensation of tetraethyl orthosilicate (TEOS) and BTEM around Fe3O4@SiO2 NPs
The SH moieties of the latter material were oxidized in the presence of H2O2 to deliver the desired Fe3O4@OS-SO3H nanocatalyst (Scheme 1)
To show the exact role of supported sulfonic acids in the catalytic process, the activity of Fe3O4@OS-SH and Fe3O4@OS was studied and the result was compared with that of Fe3O4@OS-SO3H (Table 1, entry 4 vs. entries 7 and 8). Both sulfonic acid-free nanomaterials delivered no ester product under the same conditions as Fe3O4@OSSO3H, confirming that the esterification process is completely catalyzed by supported -SO3H moieties
Summary
The use of magnetic nanoparticles has received increasing attention in various industrial and medical applications, such as magnetic resonance imaging (Qiao et al, 2009; Liu et al, 2014; Ni et al, 2017), magnetic recording (Dai et al, 2010), drug delivery (Häfeli et al, 2009; Zhang J. et al, 2013), cancer treatment through magnetic hyperthermia (Lartigue et al, 2011; Kandasamy et al, 2018; Mejías et al, 2018), catalytic industry (Pourjavadi et al, 2012; Wang et al, 2013; Kainz and Reiser, 2014; Iglesias et al, 2015; Ghorbani-Vaghei and Izadkhah, 2018), and spintronic, optoelectronic, and electronic devices (Gandhi et al, 2018; Obeid et al, 2019). In continuation of the abovementioned studies, in this study, due to the importance of biodiesel fuels and magnetic organosilica NPs in the catalyst world, we have prepared and developed a novel sulfonic acid containing magnetic organosilica as an effective, powerful, recyclable, and reusable nanocatalyst in the esterification process to produce biodiesel products For this purpose, Fe3O4 and Fe3O4@SiO2 MNPs were first synthesized according to methods presented by us in previous research studies (Elhamifar et al, 2018; Neysi et al, 2019). H2O2 (35%, 5 mL) was added to the reaction vessel, for oxidation of SH groups to SO3H counterparts, and the resulting mixture was stirred at RT for 24 h After this process, the resulting product was collected by using a magnetic field and washed three times with H2O and EtOH. A pure ester product resulted after evaporation of the solvent
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