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.
Santos et al. (Fri,) studied this question.