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4                           jour nal o f e nvironmental sciences 92 (2020) 1 e10


                                                              indexed to the standard diffraction pattern of hematite (JCPDS
          2.     Results and discussion
                                                              (Joint Committee on Powder Diffraction Standards) No. 33-
                                                              0664), which were corresponding to (012), (104), (110), (113),
          2.1.   Characterization of synthesized Ag/Fe 2 O 3
                                                              (024), (116), (214), (300), (200), respectively. In addition, other
                                                              peaks at 38.15 and 44.32 corresponded to the (111), and (200)


          The crystal and phase nature were determined by XRD. As
                                                              plane, respectively, which were characteristic peaks of the
          shown in Fig. 1, the evident diffraction peak at 24.18 , 33.18 ,  face centered cubic silver (JCPDS No. Ag 00-003-0921). The


          35.66 , 40.92 , 49.51 , 54.06 , 62.50 , 64.03 , and 75.48 , could be







                                                              peaks of silver and hematite simultaneously appeared indi-
                                                              cated that not only metallic Ag nanoparticles were grown on
                                                              the hematite, but also the phase of the hematite was
                                                              maintained.
                                                                The morphology and size of the synthesized products were
                                                              performed by SEM and TEM (Fig. 2). Fig. 2a demonstrates that
                                                              Fe 2 O 3 NPs were hexagon, whose mean width was ~140 nm,
                                                              and average thickness were ~16 nm. Fig. 2b illustrates the
                                                              images of Ag/Fe 2 O 3 NSs with spherical shape, and average
                                                              diameter of 40 nm. Fig. 2c shows Ag/Fe 2 O 3 NCs with size of
                                                              40 nm. From Fig. 2d, it could be clearly observed that silver
                                                              particles of about 30 nm were dispersed on the surface of
                                                              hematite NPs. From Fig. 2e and f, it was shown that the sizes of
                                                              Ag particles on the hematite NSs, and NCs were about 28 and
                                                              26 nm, respectively. The above images indicated that Ag was
                                                              successfully deposited on hematite nanoparticles. Moreover,
                                                              the size of Ag nanoparticles obtained from TEM agreed with
                                                              the result calculated from the XRD analysis through the for-
                                                              mula of Debye-Scherre, which were 33.2, 27.7 and 26.4 nm,
                                                              respectively. In the same synthesis process, the formation of
                                                              Ag nanoparticles with various sizes could be slightly influ-
                                                              enced by the morphology of the hematite.
                                                                XPS was employed to identify the surface element
                                                              composition of various catalysts. The survey XPS spectrum of
                                                              the prepared samples in Fig. 3a, showed the presence of C, O,
                                                              Fe and Ag. The high resolution XPS spectra of Fe 2p of all
                                                              synthesized Ag/Fe 2 O 3 samples are exhibited in Fig. 3b, and two
                                                              distinct peaks at 710.8 and 724.5 eV corresponding to Fe 2p 3/2
                                                              and Fe 2p 1/2 were observed. In addition, the shake-up satellite
                                                              located at 718.0 eV was the characteristic satellite peaks for a-
                                                              Fe 2 O 3 (Yang et al., 2011; Zhu et al., 2015; Zeng et al., 2017). The
                                                              binding energy at 709.9 and 711.3 eV fitted from the spectrum
                                                              of Fe 2p 3/2 were accordant with Fe 2þ  and Fe 3þ  species,
                                                              respectively (Dupin et al., 2000; Teng et al., 2003; Lu et al.,
                                                              2009), and the peak at 724.5 eV was assigned to Fe . There-
                                                                                                      3þ
                                                              fore, the content of Fe 2þ  can be measured by the atomic ratio
                                                                  2þ
                                                              of Fe /(Fe 2þ  þ Fe ), which follows an order of Ag/Fe 2 O 3
                                                                             3þ
                                                              NPs > Ag/Fe 2 O 3 NSs > Ag/Fe 2 O 3 NCs (Table 1). As shown in

                                                               Table 1 e Fitting results of Fe 2p XPS spectra of three
                                                               samples.
                                                               Sample        Binding      Relative   Fe /Fe 3þ
                                                                                                       2þ
                                                                           energy (eV)  percentage (%)
                                                               Ag/Fe 2 O 3 NPs  724.4      0.258       0.338
                                                                              711.3        0.490
                                                                              709.9        0.253
                                                               Ag/Fe 2 O 3 NSs  724.5      0.270       0.209
                                                                              711.6        0.557
                                                                              709.9        0.173
                                                               Ag/Fe 2 O 3 NCs  724.7      0.268       0.088
          Fig. 3 e X-ray photoelectron spectroscopy (XPS) spectra of          711.5        0.651
                                                                              709.8        0.082
          all samples: (a) survey spectrum, (b) Fe 2p, and (c) Ag 3d.
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