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jo urna l o f e nviro n mental scie nces 92 (2020) 1 e10              5

                                                               in Ag/Fe 2 O 3 NPs and Ag/Fe 2 O 3 NSs was more positive than that
                                                               in Ag/Fe 2 O 3 NCs. Several literatures had reported the similar
                                                               phenomenon (Wu et al., 2012; Hong et al., 2014). The increase
                                                               of the Ag 3d binding energy along with the increase of the Fe 2þ
                                                               content strongly supported the electron interaction from Ag to
                                                               Fe 2 O 3 . Such metal-support interaction could affect its catalytic
                                                               activity (Wu et al., 2009, 2012).
                                                                 To the best of our knowledge, the catalyst with larger
                                                               surface area probably showed better performance, mainly
                                                               due to moreactivesites.Thus, thenitrogen adsorption-
                                                               desorption isotherms of different samples were tested and
                                                               illustrated in Fig. 4. All the tested samples exhibited typical
                                                               IV adsorption isotherms with H 2 -type hysteresis loop, which
                                                               demonstrated that cylindrical channels were caused by ag-
                                                               gregates or agglomerates (Feng et al., 2016, 2017). Calculated
                                                               from the linear part of the BET plot, we found that the surface
                                                               area was slightly different, which followed the order of Ag/
                                                               Fe 2 O 3 NSs (45 m /g) > Ag/Fe 2 O 3 NCs (31 m /g) > Ag/Fe 2 O 3 NPs
           Fig. 4 e Nitrogen adsorption-desorption isotherms of Ag/  2
           Fe 2 O 3 NPs, Ag/Fe 2 O 3 NSs, and Ag/Fe 2 O 3 NCs. P/P 0 : relative  (28 m /g).
           pressure; STP: standard temperature and pressure.
                                                               2.2.  Catalytic activity
           Fig. 3c, the high resolution XPS spectra of Ag matched with the  The catalytic performance of the synthesized products was
           peaks of Ag 3d 5/2 and Ag 3d 3/2 , and the binding energy slightly  evaluated by the reduction of PNP by excess NaBH 4 as the
           differed for different samples. Higher binding energy meant  model reaction (Jiang et al., 2012, 2013). Thermodynamically,
           more positive charge of Ag. It was found that the charge of Ag  the reduction of PNP was favorable involving standard

           Fig. 5 e Ultraviolet-visible spectrophotometer (UV-Vis) spectra of p-nitrophenol (PNP) reduction with NaBH 4 using (a) Ag/
           Fe 2 O 3 NPs, (b) Ag/Fe 2 O 3 NSs, and (c) Ag/Fe 2 O 3 NCs, and (d) the rate constants (k) for PNP reduction on different Ag/Fe 2 O 3
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