*3.6. XPS Analysis of PBN@SiO<sup>2</sup>*

XPS survey scans indicated the presence of Si, O, Fe, and C in blank PBN@SiO<sup>2</sup> and As, Si, O, Fe, and C in As(III)-PBN@SiO2. The peaks were assigned as follows: Fe 2p3/2— 708 eV; Fe 2p3/2—713 eV; Fe 2p1/2—722 eV; As(III) 3d—44.2 eV and As(IV) 3d—47 eV, respectively. The peak position of the Si 2p spectrum corresponds to a binding energy of 103.63 eV and shows the characteristics of Si(IV) in a SiO2-type compound [29].
