br X ray di raction XRD
X-ray diﬀraction (XRD) analysis displayed that all MCDIONs had the typical diﬀraction peaks of ION and MnCO3 (Fig. 2A), implying that MnCO3 was successfully integrated into IONs. The compositions of IONs and MCDIONs were investigated by Fourier transform infrared (FT-IR) spectroscopy. As shown in Fig. S3A, all samples had similar curves. The peaks at 586 cm−1 could be attributed to typical Fe-O stretching vi-bration. The peaks at 1048 and 1638 cm−1 were assigned to -C-N stretching vibration and -N-H bending vibration, demonstrating the existence of PEI chains in these particles .