Different Routes for Camellia Sinensis –Mediated Synthesis of Iron Oxide Nanoparticles: Structural, Thermal, and Magnetic Properties

ABSTRACT Green‐assisted iron oxide nanoparticles (NPs) were synthesized using Camellia sinensis extract (green tea, GT) at concentrations of 1%, 2%, 3%, 5%, and 10% w/v via three chemical routes: after‐synthesis (ASR), subsequent synthesis (SSR), and in situ synthesis (ISSR). Rietveld refined X ray diffractograms and transmission electron microcopy results confirmed mostly γ–Fe 2 O 3 NPs with mean sizes ranging from 8 to 25 nm depending on the synthesis route (Fe3O4 core was also observed in some of the ISSR samples). 57 Fe Mössbauer and magnetization data showed superparamagnetic behavior at 300 K for all NP ensembles. The saturation magnetization ( M S ) value roughly scaled with GT concentrations and, for the 1% of GT sample synthesized by the ISSR‐route, a 16% higher magnetization value (86 emu g −1 ) was found when compared to the one measured for the control sample (74 emu g −1 ), an effect attributed to the Fe 3 O 4 phase initially stabilized. Fourier transform infrared and UV–vis spectroscopies showed polyphenols from the GT on the NP surface, a result that agrees with the thermogravimetric data. The 15 K 57 Fe Mössbauer data indicated that these polyphenols bind to surface iron ions, favoring spin canting and the formation of a “magnetically dead layer” on the NP surface, an effect associated with the functional (─OH) groups of GT polyphenols. Our findings demonstrate that the different routes produce functionalized Fe‐oxide NPs with different crystallite sizes and polyphenol‐layer thicknesses by simply using Camellia sinensis extract.