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jo urna l o f e nviro n mental scie nces 92 (2020) 1 e10              3

                                                               Fe 2 O 3 , the final silver deposited hematites were denoted as Ag/
                                                               Fe 2 O 3 NPs, Ag/Fe 2 O 3 NSs, and Ag/Fe 2 O 3 NCs, respectively.
                                                               1.4.  Catalytic activity

                                                               The catalytic activity of the as-prepared Ag/Fe 2 O 3 composites
                                                               was evaluated by reduction of PNP in the presence of NaBH 4 .
                                                               Briefly, 5 mmol of NaBH 4 was mixed with 50 mL PNP solution
                                                               (1 mmol/L) by stirring in a beaker, and 5 mg synthesized
                                                               catalyst was introduced into the mixture. Once the nano-
                                                               composite was added, 0.4 mL of the solution was taken out at
                                                               different time intervals, and diluted to measure ultraviolet-
                                                               visible (UV-Vis) absorption spectra (UV-Vis 2550, Shimadzu,
                                                               Japan) at 400 nm. The UV-Vis absorption could display the
                                                               amount of PNP in the solution, and thus monitored the reduc-
                                                               tion of PNP.

           Fig. 1 e X-ray powder diffraction patterns of Ag/Fe 2 O 3 NPs  1.5.  Characterization
           (nanoplates), Ag/Fe 2 O 3 NSs (nanospheres), and Ag/Fe 2 O 3
           NCs (nanocubes).                                    The crystalline structure and phase of the as-synthesized
                                                               samples were characterized by powder X-ray diffraction (XRD,
                                                               D8 ADVANCE, Brucker, Germany) patterns with Cu Ka radiation

                                                               (the wavelength l ¼ 1.54178 A) at 40 kV and 40 mA. Nitrogen
                                                               adsorption-desorption isotherm of the products was deter-
           washed with hexamethylene, deionized water and ethanol
                                                               mined at 77 K and the Brunauer-Emmett-Teller (BET, ASAP
           several times, respectively, and then dried at 40 C for 12 hr.

                                                               2460, Micromeritics, USA) surface area was obtained from the
                                                               linear part of the BET plot. The morphology and structure im-
           1.3.   Preparation of Ag/Fe 2 O 3
                                                               ages were got by the scanning electron microscope (SEM, JSM-
                                                               6700F, JEOL, Japan) and transmission electron microscope
           A simple hydrothermal method was applied to synthesize Ag/
                                                               (TEM, JEM-2100F, JEOL, Japan). The UV-Vis spectrum was
           Fe 2 O 3 . Typically, certain amount of Fe 2 O 3 was ultrasonically
                                                               collected by the Shimadzu UV-Vis 2550 spectrophotometer (UV-
           dispersed in 60 mL 50% (V/V)ethylene glycolaqueous solution.
                                                               Vis 2550, Shimadzu, Japan). X-ray photoelectron spectroscopy
           The calculated amount of AgNO 3 was then added rapidly to the
                                                               (XPS, EscaLab 250Xi, Thermo, USA) was performed to analyze
           above solution, and stirred vigorously for 1 hr. Then, the mixture
                                                               the surface composition. The Malvern zetasizer Nano ZS (Mal-
           solution was transferred to 100 mL Teflon-lined stainless steel
                                                               vern Instruments, UK) was used to measure the zeta potential
           autoclave and heated at 140 C for 12 hr. Upon cooling to room

                                                               of the samples. Inductively coupled plasma optical emission
           temperature, the product was collected, washed with water and
                                                               spectrometer (ICP-OES, Avio 500, PerkinElmer, USA) was
           ethanol, and dried overnight. According to different shapes of
                                                               applied to measure the element content.

           Fig. 2 e Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images of (a and d) Ag/Fe 2 O 3 NPs,
           (b and e) Ag/Fe 2 O 3 NSs, (c and f) Ag/Fe 2 O 3 NCs.
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