Facile Synthesis of Mesoporous Reduced Graphene Oxide

Subscriber access provided by CORNELL UNIVERSITY LIBRARY

Article

Facile synthesis of mesoporous reduced graphene oxide microspheres with well-distributed Fe2O3 nanoparticles for photochemical catalysis Zehai Xu, Wanbin Li, Yufan Zhang, Zhen Xue, Xinwen Guo, and Guoliang Zhang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b01004 • Publication Date (Web): 16 Sep 2016 Downloaded from http://pubs.acs.org on September 20, 2016

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Industrial & Engineering Chemistry Research is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Industrial & Engineering Chemistry Research

Facile synthesis of mesoporous reduced graphene oxide microspheres with well-distributed Fe2O3 nanoparticles for photochemical catalysis

Zehai Xu a, Wanbin Li a, Yufan Zhang b, Zhen Xue a, Xinwen Guo c, Guoliang Zhang a *

a

Institute of Oceanic and Environmental Chemical Engineering, State Key Lab Breeding Base of Green Chemical

Synthesis Technology, Zhejiang University of Technology, Hangzhou 310014, China b

College of Engineering, University of California, Berkeley, CA 94720, USA

c

State Key Laboratory of Fine Chemicals, Department of Catalysis Chemistry and Engineering, Dalian University

of Technology, Dalian 116012, China

Tel/Fax: 86-571-88320863; E-mail: [email protected]

ABSTRACT: In this study, we report the fabrication of hollow reduced graphene oxide microspheres with well-distributed Fe2O3 nanoparticles (Fe-rGOS) via a spray-drying methodology. The L-ascorbic acid was employed to reduce graphite oxide (GO) and improve velocity of electrons transfer. Because of L-ascorbic acid and spray-drying procedure, the in situ Fe2O3 nanoparticles with a mean size of 5-10 nm were uniformly deposited on rGO support and the rGO migrated to the surface of the drop to form microspheres. The well dispersed nanoparticles not only generated more active sites and interface contact which was beneficial to enhance the stability of catalysts, but also acted as pillars between the rGO layers to achieve mesoporous structure. The formed mesoporous frameworks enhanced mass transfer in a large extent and led to the much better catalytic efficiency. Therefore, the prepared Fe-rGOS exhibited a remarkable photocatalytic activity in wide pH range and superior recyclability with low leaching

1

ACS Paragon Plus Environment


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

of iron ions.

Keywords: Graphene microspheres; Fe2O3 nanoparticles; Dispersion; Mesoporous structure; Photochemical catalysis

*

Corresponding author

1. Introduction Graphene, as a monolayer of an aromatic carbon into a two-dimensional (2D) structure, has attracted expanding interest for its unique properties such as remarkable electrical conductivity, large surface area, exceptional thermal, mechanical and optical properties,1-3 and has been applied in wide fields including energy storage, catalysts, drug delivery, sensors, antibacterials and etc.4-8 With rapid development of graphene, various macroscopic graphene structures such as porous films, flowers, foams and other complex architectures have been prepared by assembling graphene sheets due to their high flexibility.9-12 Recently, some researchers focus on designing the structure of graphene network and developing a series of 3D hollow graphene capsules and spheres.13-15 The hollow graphene spheres can not only inherit commendable properties from their bulk form, but also exhibit extra advantages in providing more free space between the spheres compared with 2D graphene sheets.16 More recently, graphene is considered to be an active material and play an important role in determining the catalytic properties of the metal-based graphene hybrids.17-19 Some studies have confirmed this action in the single-atom Pd nanoparticles grown on graphene for selective hydrogenation of 1,3-butadiene and in the activation of MoS2 and Fe3O4 nanoparticles by 2


Page 2 of 36

Page 3 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


graphene for catalytic decomposition of formic acid and oxygen reduction reaction (ORR).20-22 To achieve more desirable performance, the nanoparticles should be uniformly deposited on the surface of graphene. However, there are difficulties in the preparation process since the positions of nanoparticles fabricated are usually hard to control, especially for 3D metal-based graphene materials, which prevents the potentials from being fully realized. The spray-drying technique, which has been successfully explored in synthesis of functional nanoparticles or encapsulation of special core-shell structures in the field of chemical engineering and material science, may be a good choice.23-26 Because of its rapidity, mildness, scalability and low-cost, we expect that the atomized droplets generated during spray-drying process can be utilized to control the fabrication process precisely and thus promote the assembly of graphene microspheres on a large scale and the formation of mesoporous structure simultaneously. In general, the catalytic behavior of nanoparticles is highly dependent on particle size and dispersion quality, superior performance can be reflected by smaller particles. However, although several literatures have been reported for the fabrication of metal-based graphene nanocomposites through a spray-drying procedure,27-29 the nanoparticles prepared by these methods are over 50 nm in size and often suffer from aggregation, thus reducing their catalytic efficiency. The synthesis of well-distributed metal oxide nanoparticles with small size in mesoporous graphene support remains a big challenge. In this study, we report a facile route for fabricating mesoporous reduced graphene oxide spheres (rGOS) with uniform dispersion of nanoparticles through a spray-drying process. Our approach began with atomization of graphene aqueous suspension into a spray of droplets (Figure 1). A spherical structure can be formed by accumulating graphene sheets at the surface during the

3



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

spray-drying process. The presence of L-ascorbic acid and rapid spray-drying process led a significant increase of the dispersion of small nanoparticles, consequently improved their catalytic performance by generating more active sites and interface contact. More importantly, the nanoparticles intercalate with graphene layers to produce mesoporous frameworks, the mesoporous shell layer afforded a short diffusion pathway for both products and reactants and the sites for anchoring active species.30 The features presented here through nanocomposite catalysts demonstrate that developing graphene microspheres from atomized droplets can be an effective route for versatile purposes.

2. Experimental section 2.1 Chemical. The reactive brilliant red X-3B was purchased from Betapharma (Shanghai, China). All chemicals, such as hydrogen peroxide (H2O2, 30 %, w/w), alcohol, L-ascorbic acid, H2SO4, Fe(NO3)3·9H2O KMnO4, NaNO3 were of analytical grade and were purchased from Sinopharm chemical Reagent Co., China, and used without further purification unless otherwise noted. Deionized water was made by RO-EDI system with cations and anions measured by an IRIS Intrepid ICP and a Metrohm 861 Compact IC.

2.2 Preparation of graphite oxide. Graphite oxide was synthesized from natural graphite flakes using a modified Hummers method by the procedure described previously.31 2 g natural graphite flakes and 1 g NaNO3 were dispersed into H2SO4 in an ice-bath. 6 g KMnO4 was added into the suspension under stirring to prevent the temperature from exceeding 293 K. The suspension was kept in ice-bath for 120 min. The temperature was monitored by a thermometer. Then the suspension was heated to 308 K and maintained for 60 min. After that, 92 mL deionized water was

4


Page 4 of 36

Page 5 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


slowly poured into the mixture, the temperature of suspension was increased to 371 K and maintained for 40 min. Then the mixture was treated by 30% H2O2 solution. Finally, the product was rinsed with diluted HCl solution, collected and dried.

2.3 Preparation of rGOS and Fe-rGOS-SD and Fe-rGOS-IS catalysts. 0.2 g graphite oxide was exfoliated by ultrasonic treatment for 2 h in 100 mL water. The suspension was centrifuged at 4000 rpm for 10 min, there are almost no precipitate was collected, this indicated that the graphite oxide was exfoliated completely. Then 0.4 g L-ascorbic acid was added to 100 mL aqueous dispersion of GO under ultrasonic treatment for 2h. The suspension was injected in a mini spray dryer at a feed rate of 16.5 mL/min and heated to a certain temperature (The inlet and outlet temperatures were 553 K and 423 K, respectively) simultaneously, leading the suspension to evaporate. More opportunities were created for graphene sheets to interact with each other and move to the droplet surface beacuse of the enhancement of Brownian motion.32 Sequentially, a spherical shell was merged by accumulating graphene sheets at the surface. .After the completion of the spray-drying process, rGOS was collected. For Fe-rGOS, the difference was 0.04 g ferric nitrate added into the rGO suspension. After the spray-drying process, the collected powder was calcined at 200 oC, the resulting samples (Fe-rGOS prepared by spray-drying method) were abbreviated

as

Fe-rGOS-SD.

The

Fe-rGOS-IS

catalysts

were

performed

by

an

impregnating-solvothermal method. 0.2 g rGOS were dispersed in an 80 mL ethanol/water mixture (1:1, v/v). 0.04 g ferric nitrate was added in the solution and stirred at room temperature, then transformed into the Teflon-lined autoclave container and held at 353 K for 8 h. The collected black powers (Fe-rGOS prepared by impregnating-solvothermal method) were abbreviated as Fe-rGOS-IS.

5



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2.4 Characterization. The morphology of the prepared microspheres was evaluated using scanning electron microscope (SEM) measurements (Hitachi S-4800). Transmission electron microscopy (TEM) was prepared with an FEI Tecnai G2 F30 electron microscope operating at an accelerating voltage of 300 kV with energy dispersive X-ray spectroscopy (EDX). Nitrogen adsorption-desorption isotherms were obtained at 77 K through using an ASAP 2020 surface area and porosity analyzer (Micromeritics, USA). The X-ray diffraction (XRD) patterns of graphite oxide and fabricated microspheres were determined by using X’Pert PRO X-ray diffractometer with a step size of 0.02° for CuKα radiation (λ=1.5418 Å). Surface properties of the samples were examined by X-ray photoelectron spectroscopy (XPS). XPS experiments were carried out on a RAD upgraded PHI-5000C ESCA system (Perkin-Elmer) with Mg Kα radiation (hv = 1253.6 eV) and binding energies were calibrated by using at 10.0 kV and 20.0 mA, respectively. Thermogravimetric analysis (TGA) was performed on a TQ5000IR Analyzer at a heating rate of 5 o

C/min in air.

2.5 Degradation of dyes. The prepared catalysts were suspended in the aqueous solution of X-3B in a 500 ml glass batch reactor and shocked in darkness for 0.5 h to achieve the equilibrium adsorption of X-3B. A certain amount of hydrogen peroxide was added into the suspension, and then the external halogen lamp (maximum emission wavelength was about 480 nm) was switched on to initiate the reaction. The content of dye was measured by U-2910 digital spectrophotometer (Hitachi, Japan) after samples were filtered directly through a 0.45 µm microfiltration membrane. The content of hydrogen peroxide over the reaction time was determined colorimetrically by employing a UV-vis spectrophotometer (Hitachi, Japan) after complexation with titanium salt.33 Moreover, the iron concentrations in the solution after reaction were evaluated by 55B type AAS

6


Page 6 of 36

Page 7 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(Varian, USA) equipped hollow cathode Fe lamp (sensitive line, 248.3 nm slits, 0.4 nm operating current, 4 mA).

3. Results and discussion In order to improve velocity of electrons transfer which can enhance the catalytic performance, the first procedure in this method is the reduction of GO. There are many effective reductants, such as hydrazine hydrate, sodium borohydride, L-ascorbic acid (L-AA) and etc, can be employed in various chemical reactions. In this study, we selected L-AA, known as Vitamin-C, since L-AA have mildly reductive ability and is endowed with nontoxic property.34,35 The surface properties of GO and rGOS were evaluated by XPS measurement. As depicted in Figure 2, the XPS of GO shows four types of disparate chemical states of carbons, which are situated at 284.7 (C-C), 286.1 (C-O), 286.9 (C-O-C) and 288.5 eV (C=O).36,37 As expected, the proportions of the oxygen functional groups decreased significantly after the reduction process of GO by L-AA. The shifts of C-O and C=O in the binding energies (BE) (Figure 2b) compared to GO suggest a different chemical state.38 It is worth to note that a small quantity of oxygen functional groups were still remained to maintain the hydrophilicity of graphene. SEM images of dried powders (Figure 3a-3d) reveal the spherical structure. It can be observed that although all spheres have some creases, the surface of Fe-rGOS-SD exhibits more smooth, which is may due to the enlargement of adhesion between layers after introducing tiny nanoparticles. The average size of Fe-rGOS-SD (2.4±0.2 µm) is smaller than that of rGOS (3.3±0.3 µm), which is similar to the reported literatures.39,40 According to basic atomization theory, viscosity estimates the ability of the fluid to resist deformation through shear stress. When the viscosity of suspension was enhanced, the change of air-liquid velocity would cause high

7



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

frictional forces on the liquid surface, inducing the deformation and generation of large droplets. Therefore, the small size of Fe-rGOS-SD can be attributed to the decrement in viscosity in the formation of spheres during spray drying process. As shown in Figure 3d and inserted image, these superstructures are hollow, and the thickness of the outer shell is uniformly around 100-150 nm created by Fe2O3 nanoparticles and rGO sheets. Moreover, the split hollow sphere allows the light to enter into their interior by multiple refractions, which can make full use of the light source. TEM images of rGOS (Figure S1, Supporting Information) reveal that hollow spheres are formed with rGO multilayer and numerous folds and creases can be observed for typical rGO spheres. The light portion of rGO sphere demonstrates the existence of the hollow interior structure. This result also indicates that the shell is thick enough to keep the spherical form during spray drying process. The rGOS serves as a novel support that is uniformly modified by many small Fe2O3 nanoparticles with a mean size of 5-10 nm in Figure 3e and 3f. The elemental mapping spectra for the Fe-rGOS-SD (Figure 3g) demonstrate that all elements including Fe are observed and the Fe2O3 nanoparticles are uniformly distributed on the surface of the modified rGOS. On the contrary, nanoparticles aggregate seriously in the Fe-rGOS-IS, which is hard to observe any particles (Figure S2, Supporting Information). High-resolution TEM (HRTEM) images in Figure 3f exhibit clear lattice fringes of samples. The lattice distance of 0.25 nm corresponds to (110) crystal planes of α-Fe2O3 (JCPDS no 33-0664).41 This reveals that the spray-drying strategy is of benefit to improve the compatibility and dispersion of nanoparticles. More importantly, the well dispersed nanoparticles encapsulated within the graphene layers will effectively increase their interface contact, thus can obviously promote the catalytic or electrochemical activity of hybrids. Furthermore, the nitrogen adsorption/desorption isotherms and

8


Page 8 of 36

Page 9 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


pore size distribution curve were employed to determine the specific surface area and pore size distribution of Fe-rGOS-SD, rGOS, Fe-rGOS-IS and Fe-P25. As depicted in Figure 4, rGOS and Fe-rGOS-IS exhibited low surface areas with nonporous nature while Fe-P25 demonstrated a surface area (54.2 m2/g) with nonuniform pore size distribution. However, it is worth to note that a mesoporous structure with a specific surface area of 90.3 m2/g and an average pore size of about 4.1 nm was revealed for Fe-rGOS-SD, it is possible that the in situ Fe2O3 nanoparticles act as pillars that intercalate and stack between graphene layers during the spray-drying process, consequently increased with additional mesoporosity, this phenomenon is similar to the reported literature.42 The formed mesoporous structure may greatly increase the mass transfer and lead to the much better catalytic efficiency.43 To analyze the crystal structures of graphene microspheres and Fe-rGOS-SD, further characterization by XRD was conducted and the resulted patterns are presented in Figure 5. It can be seen that the XRD patterns of rGOS are typical of graphite oxide after reduction procedure. As is apparent from the pattern of graphite oxide (inserted graph of Figure 5), the strong (001) peak situated at 2θ =10.2o (d-spacing ~8.672Å) completely vanishes in the patterns of rGOS, confirming that the graphite oxide has been exfoliated and reduced.44 The pattern of as-obtained rGOS shows a broad (002) peak at 2θ of 23.3o (d-spacing ~3.818Å). The results also confirm the existence of graphene as multiple layers because of the presence of (002) diffraction peak in the rGOS.45 The interactions between rGO and Fe2O3 and surface chemical structure of the Fe-rGOS microspheres were investigated. Figure 6a shows the O 1s XPS spectrum of the prepared samples, which can be resolved into three peaks. The peak of Fe-rGOS-SD at 531.4 eV is assigned to Fe–O

9



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

corresponding to the oxygen in Fe2O3 nanoparticles and the peak at 532.7 eV in Fe-rGOS-SD should be attributed to the formation of Fe–O–C bond between graphene and Fe2O3 nanoparticles, which was also consistent with the results in previous literatures that the BE of Fe–O–C bond can be situated in the range of 531–533 eV.46 Moreover, The BE of Fe 2p for Fe-rGOS-SD was observed around 723.1 and 710.8 eV, which was distributed to the spectra of Fe 2p1/2 and Fe 2p3/2, respectively (Figure 6b). Both peak position and separation were characteristic of Fe2O3.47,48 As mentioned above, graphene can act as a unique support for the growth of active nanomaterials, such as metal oxide or metal nanoparticles. Although metal-based graphene materials have been proposed for use in energy storage, catalysts, antibacterials and sensors, nanoparticles frequently suffer from agglomeration and dissolution during the preparation of composites. The dispersion and positional fixation of nanoparticles on graphene spheres are key points in overcoming this obstacle. In order to enhance the performance, we should improve the dispersion of nanoparticles in rGOS support. Herein, the GO and L-AA solution was initially mixed uniformly, and then rGO was decorated with metal ions. L-AA led an interaction between nanoparticles and support and then increased the nanoparticles dispersion. Besides, as it was very rapid during the spray-drying process of the hydrosol, the water evaporated with the increase of temperature and the droplets lessened simultaneously. The rGO sheets collided and interacted with each other more frequently and moved up to the liquid/air interface.32 Therefore, the Fe2O3 nanoparticles in prepared Fe-rGOS-SD possess excellent the dispersion. Compared with the process using traditional impregnating-solvothermal method (Figure 7b), the nanoparticles were facilitated to be fixed between two layers or embedded into the inner rGO layer through

10


Page 10 of 36

Page 11 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


spray-drying process (Figure 7a). In order to obtain more details concerning distribution and metal content of samples, XPS and thermal gravity analysis (TGA) were carried out. In this case, we took Fe-rGOS-SD and Fe-rGOS-IS for comparison. The actual contents of surface Fe concentration in Fe-rGOS-SD was analyzed by XPS and the surface atomic percent was only 0.50 at% (Figure 7c), which indicated that only a little quantity of iron atoms were deposited on the surface of microspheres, while higher percentage (1.02 at%) of ferric atoms was detected by XPS in Fe-rGOS-IS. The mass percent of Fe content on the surface of Fe-rGOS-SD and Fe-rGOS-IS was calculated at 2.04 wt% and 4.16 wt%, respectively. Figure 7d shows the TGA results of the rGOS, Fe-rGOS-SD and Fe-rGOS-IS according to the time of heat treatment. A slight weight loss of two samples occurred below 100 oC due to the release of physically adsorbed water, and the mass loss above this temperature was due to the disintegration of carbon structures and the reserved oxygen functional groups.49 The total residue of rGOS, Fe-rGOS-SD and Fe-rGOS-IS were also investigated under air, in which almost 0.21 wt%, 7.78 wt% and 6.25 wt% of the overall weight were left, respectively. As a further confirmation, the remnant of Fe-rGOS was α-Fe2O3 which was characterized by XRD analysis (Figure S3, Supporting Information). Fe contents were calculated at 5.23 wt% and 4.23 wt% for Fe-rGOS-SD and Fe-rGOS-IS, respectively. The results indicated that more Fe2O3 nanoparticles can be loaded through spray-drying method. While nanoparticles mainly deposited on the surface of Fe-rGOS-IS, the majority of nanoparticles in Fe-rGOS-SD were fixed between layers or inside the interior. Figure 8a exhibits the efficiency of different catalytic conditions for the photodegradation of dye. Because of the better dispersion of Fe2O3 nanoparticles and the existence of mesoporous

11



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 12 of 36

structure, a large interface was created between small Fe2O3 nanoparticles and rGO layers, which accelerated the rate of interfacial electron transfer. Therefore, the prepared Fe-rGOS-SD exhibited much better performance compared with Fe-rGOS-IS. The results elucidated that the size and location of the Fe2O3 nanoparticles play an significant role in determining the catalytic properties of the catalysts. In the presence of hydrogen peroxide, the behaviors of rGO microspheres, Fe3+, Fe2O3, Fe-P25 in catalytic oxidation process were also evaluated. The concentration of Fe3+ was the same as what was mentioned above. Although commercial P25 is a prominent support in photocatalytic field, it is worth noting that Fe-rGOS-SD was 16% higher than P25 nanoparticles as support of ferric oxides in the presence of H2O2 due to the reduction of GO which increases the velocity of electron transfer of rGOS supports and more active sites in catalysts with large surface area. Furthermore, the photocatalytic activity can be also evaluated by the decomposition efficiency of H2O2. As for the sample of Fe-rGOS-SD, the graph Figure 8b depicted that more H2O2 decomposed over the reaction time compared to the other catalysts, thus abundant hydroxyl radicals were generated to destroy the dye molecules, consequently promoting the catalytic performance. The kinetics of the photodegradation of rGOS, Fe2O3 NPs, Fe-P25, Fe-rGOS-SD and Fe-rGOS-IS were fitted to a pseudofirst-order kinetics (eq1) and a combined first-order kinetics model (eq2), the formula is as follow:

C = C 0 exp(−kt )

C = C1 exp(−kt ) + C 2 exp(−kt )

(1) (2)

where C represents the dye concentration (mg L-1), C0 is the initial dye concentrations of first-order reaction (mg L-1); k is the reaction rate coefficient (min-1) and t is the time (min), C1

12


Page 13 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


and C2 are the initial dye concentrations of two independent first-order reactions (mg L−1), and k1 and k2 are the reaction rate constants (min−1), respectively. The rate constants of rGOS and Fe2O3 NPs fitted by pseudo-first-order kinetics were 0.00068 and 0.00203 min-1 (Table 1), respectively, while Fe-rGOS-SD exhibited the highest activity among all samples in the presence of hydrogen peroxide, the rate constant was improved to 0.03945 min-1, which is approximately five times greater than that of Fe-rGOS-IS (0.00812 min-1) and three times greater than that of Fe-P25 (0.01281 min-1). The high photocatalytic behavior for degradation of X-3B under light irradiation can be explained from the scheme (inset image of Figure 8a). When the small nanoparticles were uniformly fixed on the surface of graphene sheets, those photogenerated electrons in conduction band (CB) were induced to transfer to rGO, causing to the separation of hole-electron. The rGO can applied as an electron collector and transporter to lengthen the lifetime of the charge carriers, thus enhancing the photocatalytic activity. The recycling tests were taken out to determine the reusability and stability of Fe-rGOS-SD. As apparent from the Figure 9, Fe-rGOS-SD catalyst exhibited excellent stability, since more than 95% color was removed under visible light irradiation over five cycles. The leaching of iron ions during the reaction process remained below 0.35 mg L-1 in all the cycles (Figure S4, Supporting Information). The superior stability of Fe-rGOS-SD is due to the fact that the rapid spray-drying process and the presence of L-ascorbic acid could make Fe2O3 nanoparticles uniformly deposited and firmly adhere with rGO sheets to restrain the leaching of iron ions. In this case, it not only prevents the support from collapsing, but also retains more metal oxide particles to keep prominent photocatalytic performance. SEM images confirmed the uniform Fe-rGOS-SD without breakage after multiple uses in catalysis (Figure 10a), while Fe-rGOS-IS easily disorganized

13



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

when undergoes washing and redispersion (Figure 10b). These results strongly suggest that Fe2O3 nanoparticles were firmly fixed on the support of rGOS, this can be attributed to the formation of Fe-O-C bond which was also beneficial to elevate the stability of spheres,50 as evidenced by the XPS analysis. Furthermore, the effects of pH on the catalytic activity of Fe-rGOS were presented (Figure S5, Supporting Information), the prepared Fe-rGOS exhibited a remarkable photocatalytic performance in wide pH range of 4-10.

4. Concluding remarks In this study, we have proposed a spray-drying process to fix Fe2O3 nanoparticles on the reduced graphene oxide and form nanocomposite microspheres. The L-ascorbic acid was employed to reduce GO and improve velocity of electrons transfer simultaneously. The Fe2O3 nanoparticles have uniform dispersion in microspheres due to the rapid spray-drying process and the presence of L-ascorbic acid. Moreover, additional mesoporosity was produced through employing tiny Fe2O3 nanoparticles as pillars to intercalate between graphene layers during the spray-drying process. The well-distributed Fe2O3 nanoparticles in the mesoporous frameworks of rGOS can generate more active sites and interface contact, therefore achieved high visible light photocatalytic performance and excellent recycling efficiency This work would open up new strategies for using the rGOS as a highly efficient catalyst support for different applications.

Associated content Supporting Information

Supporting Information (SI) available: TEM images of rGOS and Fe-rGOS-IS , XRD patterns of remnant in TG analysis, Iron leaching in the solution of different cycles，Relative concentration of

14


Page 14 of 36

Page 15 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


X-3B as a function of time obtained at different pH values in the presence of Fe-rGOS-SD catalyst. This material is available free of charge via the Internet at http://pubs.acs.org.

Author Information Corresponding Author: Tel/Fax: 86-571-88320863; E-mail: [email protected]

Acknowledgements This work was supported by the National Natural Science Foundation of China (Grant Nos. 21236008 and 21476206), Fujian Provincial Department of Ocean (Grant No.2014-06) and Taishan Scholarship Blue Industry Program from Shandong Provincial Government (Grant No. 2014008). G.Z. specially thanks Fujian Provincial Government for the Minjiang Scholarship. A patent application related to this work has been filed.

Literature Cited (1) Mukherjee, R.; Thomas, A. V.; Krishnamurthy, A.; Koratkar, N. Photothermally reduced graphene as

high-power anodes for lithium-ion batteries. ACS Nano, 2012, 6, 7867-7878.

(2) Criado, A.; Melchionna, M.; Marchesan, S.; Prato, M. The Covalent functionalization of graphene on

substrates. Angew. Chem. Int. Ed. 2015, 54, 10734-10750.

(3) Xiang, Q.; Cheng, B.; Yu. J. Graphene-based photocatalysts for solar-fuel generation. Angew. Chem. Int. Ed.,

2015, 54, 11350-11366.

(4) Wang, G. H.; Hilgert, J.; Richter, F. H.; Wang, F.; Bongard, H. J.; Spliethoff, B.; Weidenthaler, C.; Schüth, F.

Platinum-cobalt

bimetallic

nanoparticles

in

hollow

carbon

nanospheres

for

hydrogenolysis

of

5-hydroxymethylfurfural. Nat Mater. 2014, 13, 293-300.

(5) Zitolo, A.; Goellner, V.; Armel, V.; Sougrati, M. T.; Mineva, T.; Stievano, L.; Fonda, E.; Jaouen, F.

Identification of catalytic sites for oxygen reduction in iron and nitrogen-doped graphene materials. Nat Mater. 15



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

2015, 14, 937.

(6) Chen, X. J.; Dai, Y. Z.; Guo, J.; Liu, T. H.; Wang, X. Y. Novel magnetically separable reduced graphene oxide

(RGO)/ZnFe2O4/Ag3PO4 nanocomposites for enhanced photocatalytic performance toward 2,4-dichlorophenol under visible light. Ind. Eng. Chem. Res. 2016, 55, 568-578.

(7) Xing, F.; Meng, G. X.; Zhang, Q.; Pan, L. T.; Wang, P.; Liu, Z. B.; Jiang, W. S.; Chen, Y.; Tian, J. G.

Ultrasensitive flow sensing of a single cell using graphene-based optical sensors. Nano Lett. 2014, 14, 3563-3569.

(8) Tu, Y. S.; Lv, M.; Xiu, P.; Huynh, T.; Zhang, M.; Castelli, M.; Liu, Z. R.; Huang, Q.; Fan, C. H.; Fang, H. P.;

Zhou, R. H. Destructive extraction of phospholipids from Escherichia coli membranes by graphene nanosheets.

Nat. Nanotech, 2013, 8, 594-601.

(9) Huang, K.; Liu, G.; Lou, Y.; Dong, Z.; Shen, J.; Jin, W. A graphene oxide membrane with highly selective

molecular separation of aqueous organic solution. Angew. Chem., Int. Ed., 2014, 53, 6929-6932.

(10) Li, Y.; Chen, J.; Huang, L.; Li, C.; Hong, J. D.; Shi, G. Highly compressible macroporous graphene monoliths

via an improved hydrothermal process. Adv. Mater. 2014, 26, 4789-4793.

(11) Li, X.; Zhang, G.; Bai, X.; Sun, X.; Wang, X.; Wang, E.; Dai, H. Highly conducting graphene sheets and

Langmuir-Blodgett films. Nat. Nanotech, 2008, 3, 538-542.

(12) Lee, S. H.; Kim, H. W.; Hwang, J. O.; Lee, W. J.; Kwon, J.; Bielawski, C.; Ruoff, R. S.; Kim, S. O.

Three-dimensional self-assembly of graphene oxide platelets into mechanically flexible macroporous carbon films.

Angew. Chem. Int. Ed. 2010, 49, 10084.

(13) Vickery, J. L.; Patil, A. J.; Mann, S.Fabrication of graphene-polymer nanocomposites with higher-order

three-dimensional architectures. Adv Mater. 2009, 21, 2180-2184.

(14) Sohn, K.; Na, Y. J.; Chang, H.; Roh, K. M.; Jang, H. D.; Huang, J. Oil absorbing graphene capsules by

capillary molding. Chem Commun. 2012, 48, 5968-5970.

16


Page 16 of 36

Page 17 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(15) Li, W. B.; Zhang, Y. F.; Xu, Z. H.; Yang, A. S.; Meng, Q.; Zhang, G. L. Self-assembled graphene oxide

microcapsules with adjustable permeability and yolk-shell superstructures derived from atomized droplets. Chem.

Commun., 2014, 50, 15867-15869.

(16) Shao, Q. G.; Tang, J.; Lin, Y. X.; Zhang, F. F.; Yuan, J. S.; Zhang, H.; Shinya, N.; Qin, L. Synthesis and

characterization of graphene hollow spheres for application in supercapacitors. J. Mater. Chem. A, 2013, 1,

15423-15428.

(17) Cui, X. J.; Li, Y.; Bachmann, S.; Scalone, M.; Surkus, A. E.; Junge, K.; Topf, C.; Beller, M. Synthesis and

characterization of iron-nitrogen-doped graphene/core-shell catalysts: efficient oxidative dehydrogenation of

N-Heterocycles. J. Am. Chem. Soc. 2015, 137, 10652-10658.

(18) Chen, F.; Surkus, A. E.; He, L.; Pohl, M. M.; Radnik, J.; Topf, C.; Junge, K.; Beller, M. Selective catalytic

hydrogenation of heteroarenes with N-graphene-modified cobalt nanoparticles (Co3O4-Co/NGr@ α-Al2O3). J. Am. Chem. Soc. 2015, 137, 11718−11724. (19) Duan, J.; Chen, S.; Dai, S.; Qiao, S. Shape control of Mn3O4 nanoparticles on nitrogen-doped graphene for enhanced oxygen reduction activity. Adv. Func. Mater, 2014, 24, 2072-2078.

(20) Yan, H.; Cheng, H.; Yi, H.; Lin, Y.; Yao, T.; Wang, C.; Li, J.; Wei, S.; Lu, J. Single-atom Pd-1/graphene

catalyst achieved by atomic layer deposition: remarkable performance in selective hydrogenation of 1, 3-Butadiene.

J. Am. Chem. Soc. 2015, 137, 10484−10487. (21) Koroteev, V. O.; Bulushev, D. A.; Chuvilin, A. L.; Okotrub, A. V.; Bulusheva, L. G. Nanometer-sized MoS2 clusters on graphene flakes for catalytic formic acid decomposition. ACS Catal. 2014, 4, 3950-3956.

(22) Wu, Z. S.; Yang, S.; Sun, Y.; Parvez, K.; Feng, X.; Müllen, K. 3D nitrogen-doped graphene aerogel-supported

Fe3O4 nanoparticles as efficient eletrocatalysts for the oxygen reduction reaction. J. Am. Chem. Soc. 2012, 134, 9082−9085.

17



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

(23) Carne-Sanchez, A.; Stylianou, K. C.; Carbonell, C.; Naderi, M.; Imaz, I.; Maspoch, D. Protecting

metal-organic framework crystals from hydrolytic degradation by spray-dry encapsulating them into polystyrene

microspheres. Adv. Mater. 2015, 27, 869-873.

(24) Wu, Z. X.; Wu, W. D.; Liu, W. J.;.Selomulya, C.; Chen, X. D.; Zhao, D. Y. A General "surface-locking"

approach toward fast assembly and processing of large-sized, ordered, mesoporous carbon microspheres. Angew.

Chem., Int. Ed., 2013, 52, 13764-13758.

(25) Ma, J.; Fang, Z.; Yan, Y.; Yang, Z.; Gu, L.; Hu, Y.; Li, H.; Wang, Z.; Huang, X. Novel large-scale synthesis of

a C/S nanocomposite with mixed conducting networks through a spray drying approach for Li-S batteries. Adv

Energy Mater. 2015, 5, 1500046.

(26) Sanchez, A. C.; Imaz, I.; Sarabia, M. C.; Maspoch, D. A spray-drying strategy for synthesis of nanoscale

metal-organic frameworks and their assembly into hollow superstructures. Nat Chem. 2013, 5, 203-211.

(27) Zhou, G. W.; Wang, J.; Gao, P.; Yang, X.; He Y. S.; Liao, X. Z.; Yang, J.; Ma, Z. F. Facile spray drying route

for the three-dimensional graphene-encapsulated Fe2O3 nanoparticles for lithium ion battery anodes. Ind. Eng. Chem. Res. 2013, 52,1197-1204.

(28) Jia, H.; Kloepsch, R.; He, X.; Badillo, J. P.; Winter, M.; Placke, T. One-step synthesis of novel mesoporous

threedimensional GeO2 and its lithium storage properties. J. Mater. Chem. A, 2014, 2, 17545-17550. (29) Gan, L.; Guo, H.; Wang, Z.; Li, X.; Peng, W.; Wang, J.; Huang, S.; Su, M. A facile synthesis of

graphite/silicon/graphene spherical composite anode for lithium-ion batteries. Electrochim. Acta. 2013, 104,

117-123.

(30) Li, Y.; Shi, J. Hollow-structured mesoporous materials: chemical synthesis, functionalization and applications.

Adv Mater. 2014, 26, 3176-3205.

(31) Hummers, W. S.; Offeman, R. E. Preparation of graphitic oxide. J. Am. Chem. Soc. 1958, 80, 1339.

18


Page 18 of 36

Page 19 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(32) Chen, C.; Yang, Q. H.; Yang, Y.; Lv, W.; Wen, Y.; Hou, P. X.; Wang, M.; Cheng, H. M. Self-assembled

free-standing graphite oxide membrane. Adv. Mater. 2009, 21, 3007–3011.

(33) DeLaat, J.; Gallard, H. E. Inorganic and organic byproducts of the reactions between chlorite, activated

carbon, and phenolic compounds. Environ. Sci. Technol. 1999, 33, 2726-2732.

(34) Zhang, J.; Yang, H.; Shen, G.; Cheng, P.; Zhang, J.; Guo, S. Reduction of graphene oxide via L-ascorbic acid.

Chem. Commun., 2010, 46, 1112-1114.

(35) Dar, R. A.; Giri, L.; Karna, S. P.; Srivastava, A. K. Performance of palladium nanoparticle-graphene

composite as an efficient electrode material for electrochemical double layer capacitors. Electrochim. Acta. 2016,

196, 547-557.

(36) Yin, H.; Zhao, S.; Wan, J. ; Tang, H.; Chang, L.; He, L.; Zhao, H.; Gao, Y.; Tang, Z. Three-dimensional

graphene/metal oxide nanoparticle hybrids for high-performance capacitive deionization of saline water. Adv.

Mater, 2013, 25, 6270-6276.

(37) Yan, Y.; Kuila, T.; Kim, N. H. ; Ku, B. C. ; Lee, J. H. Effects of reduction and polystyrene sulfate

functionalization on the capacitive behaviour of thermally exfoliated graphene. J. Mater. Chem. A, 2013, 1,

5892-5901.(38) Long, D. ; Li, W.; Qiao, W. ; Miyawaki, J.; Yoon, S. H.; Mochida, I. Ling, L. Graphitization

behaviour of chemically derived graphene sheets. Nanoscale, 2011, 3, 3652-3656.

(39) Murtaza, Q.; Stokes, J.; Ardhaoui, M. Experimental analysis of spray dryer used in hydroxyapatite thermal

spray powder. J. Therm. Spray. Technol. 2012, 21, 936-974.

(40) Petit, J.; Méjean, S.; Accart, P.; Galet, L.; Schuck, P.; Floch-Fouéré, C. L.; Delaplace, G.; Jeantet, R. A

dimensional analysis approach for modelling the size of droplets formed by bi-fluid atomisation. J. Food. Eng.

2015, 149, 237-247.

(41) Zhang, G.; Qin, L.; Wu, Y.; Xu, Z.; Guo, X. Iron oxide nanoparticles immobilized to mesoporous NH2-SiO2

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

spheres by sulfonic acid functionalization as highly efficient catalysts. Nanoscale, 2015, 7, 1102-1109.

(42) Jayaramulu K, Datta KKR, Rçsler C, Petr M, Otyepka M, Zboril R, Fischer, R. A. Biomimetic

superhydrophobic/superoleophilic highly fluorinated graphene oxide and ZIF-8 composites for oil-water

separation. Angew. Chem. Int. Ed. 2015, 54, 1178-82.

(43) Karger, J.; Valiullin, R. Mass transfer in mesoporous materials: the benefit of microscopic diffusion

measurement. Chem. Soc. Rev. 2013, 42, 4172-4197.

(44) Zhu,C. Z.; Guo, S. J.; Fang, Y. X.; Dong, S. J. Reducing sugar: new functional molecules for the green

synthesis of graphene nanosheets. ACS Nano, 2010, 4, 2429-2437.

(45) Lei, Z.; Lu, L.; Zhao, X. S. The electrocapacitive properties of graphene oxide reduced by urea. Energy

Environ Sci. 2012, 5, 6391-6399.

(46) Zhou, J.; Song, H.; Ma, L.; Chen, X. Magnetite/graphene nanosheet composites: interfacial interaction and its

impact on the durable high-rate performance in lithium-ion batteries. RSC Advances, 2011, 1, 782-791.

(47) Qin, L.; Pan, X. X.; Wang, L.; Sun, X. P.; Zhang, G. L.; Guo, X. W. Facile preparation of mesoporous TiO2(B) nanowires with well-dispersed Fe2O3 nanoparticles and their photochemical catalytic behavior. Appl. Catal., B, 2014, 150-151, 533-44.

(48) Xu, Z.; Huang, C.; Wang, L.; Pan, X.; Qin, L.; Guo. X.; Zhang, G. Sulfate functionalized Fe2O3 nanoparticles on TiO2 nanotube as efficient visible light-active photo-Fenton catalyst. Ind. Eng. Chem. Res. 2015, 54, 4593−4602.

(49) Jin, L.; Yang, K.; Yao, K.; Zhang, S. ; Tao, H.; Lee, S. T.; Liu, Z.; Peng, R. Functionalized graphene oxide in

enzyme engineering: a selective modulator for enzyme activity and thermostability. ACS Nano, 2012, 6,

4864-4875.

(50) Zubir, N. A.; Yacou, C. Motuzas, J.; Zhang, X.; Zhao, X. S.; Costa, J. C. D. The sacrificial role of graphene

20


Page 20 of 36

Page 21 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


oxide in stabilising a Fenton-like catalyst GO-Fe3O4. Chem. Commun., 2015, 51, 9291-9293.

Captions for Tables 21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Table 1. Kinetic Parameters for Heterogeneous Oxidation of X-3B

Table 1. Kinetic Parameters for Heterogeneous Oxidation of X-3B 22


Page 22 of 36

Page 23 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Substrate degradation System

Pseudo-first-order k (min-1) R2

k1 (min-1)

Combined first-order k2 (min-1)

R2

rGOS-H2O2

0.00068

0.8783

0.00062

0.00062

0.8955

Fe-rGOS-SD

0.00423

0.9966

0.01005

0.00806

0.9912

Fe-rGOS-SDH2O2

0.03945

0.9993

0.14622

0.03895

0.9999

Fe-P25-H2O2

0.01281

0.9931

0.02138

0.01715

0.9995

Fe-rGOS-ISH2O2

0.00812

0.9648

0.01428

0.00961

0.9982

Fe-P25

0.00663

0.9718

0.02567

0.00661

0.9947

Fe2O3-H2O2

0.00203

0.8987

0.00235

0.00235

0.9573

H2O2

0.00022

0.8209

/

/

/

photolysis

0.00005

0.7165

/

/

/

Captions for Figures 23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1. Scheme depicting the spray-drying procedure for pure rGOS and Fe-rGOS formation. Within a droplet, the suspension containing graphene sheets (purple), ferric ions (red) and reductant (blue bar) is concentrated to the liquid/air interface and nanoparticles (yellow) crystallize into spheres. Figure 2. XPS survey spectra: C1s spectra of the synthesized GO (a) and rGOS (b). Figure 3. SEM images of rGOS (a, c) and Fe-rGOS-SD (b, d) at different magnification. The inset graphs of (a and b) are the size distribution of rGOS and Fe-rGOS-SD microspheres TEM images of Fe-rGOS-SD (e, f) at different magnification, and a mechanically broken hollow superstructure showing the internal cavities and the thickness of its wall (inserted graph). Element distributions maps of Fe-rGOS-SD determined by EDX (g). Figure 4. Adsorption/desorption isotherms and BJH pore size distribution for Fe-rGOS-SD. Figure 5. XRD patterns of (a) graphite, (b) rGOS, (c) Fe-rGOS-SD and (d) Fe-rGOS-IS. The inset graph is XRD pattern of graphite oxide. Figure 6. XPS survey spectra: O1s spectra of the synthesized Fe-rGOS-SD (a), Fe2p spectra of the synthesized Fe-rGOS-SD (b). Figure 7. Scheme of dispersion state of nanoparticles via spray-drying method with aid of reductant (a) and impregnating-solvothermal method (b). Element atomic percentage of Fe-rGOS-SD and Fe-rGOS-IS (c). TG curves of rGOS, Fe-rGOS-SD and Fe-rGOS-IS (d). Figure 8. (a) Relative concentration of X-3B as a function of time at different

24


Page 24 of 36

Page 25 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


procedure (T = 298 K, Ccat. = 0.2 g L−1, CX-3B = 100 mg L−1, CH2O2 =5.0 mmol L−1, pH = 6.0): (a) direct photolysis (b) rGOS-H2O2 (c) Fe3+-H2O2 (d) rGOS (e) Fe-rGOS-SD (f) Fe-rGOS-SD-H2O2 (g) Fe-P25-H2O2 (h) Fe-rGOS-IS-H2O2 (i) Fe-P25 (j) Fe2O3-H2O2 (k) Fe-rGOS-IS. Inset graph exhibits possible mechanism of heterostructured Fe-rGOS for degradation of X-3B under light irradiation. (b) Comparison the consumption of H2O2 in the presence of different catalysts. Figure 9. Reusability of catalyst after subsequent reactions (T = 298 K, Ccat. = 0.2 g L−1, CX-3B = 100 mg L−1, CH2O2 =5.0 mmol L−1, pH = 6.0). Figure 10. SEM images of catalyst Fe-rGOS-SD (a) and Fe-rGOS-IS (b) after multiple uses in catalysis.

25



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 1

26


Page 26 of 36

Page 27 of 36

(a)

GO

rGOS

C-C (284.7)

Intensity

C=O (288.4)

280

285

(b)

C-C (284.6) C-O (286.1) C-O-C (286.9)

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


290

C-O (286.4) C=O (289.5)

295

280

Binding Energy(eV)

285

290

Binding Energy(eV)

Figure 2

27


295


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 3

28


Page 28 of 36

300

Fe-rGOS-SD rGOS Fe-rGOS-IS Fe-P25

0.10 0.08

200 150

3

250

Pore Volume (cm g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Quantity Absorbed(cm3/g STP)

Page 29 of 36

0.06 0.04 0.02 0.00 0

10 20

100

30 40 50 60 70 80 Pore Width (nm)

50 0 0.0

0.2

0.4

0.6

0.8 0

Relative Pressure(P/P )

Figure 4

29


1.0


Intensity

Graphite oxide

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 30 of 36

d 10

20

30

40

2theta 2thea(degree)

c

b a 10

20

30

40

2theta(degree)

Figure 5

30


50

60

O 1s

(a)

Fe-O (531.4)

C-O-Fe (532.7) C-OH/C-O-C (533.8)

Intensity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


528

530

532

534

536

538

540

Binding Energy(eV)

(b)

Fe 2p 710.8 723.1

Intensity

Page 31 of 36

700

705

710

715

720

725

730

Binding Energy(eV)

Figure 6

31


735


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 7

32


Page 32 of 36

Page 33 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 8

33



1.0 First

Second

Third

Fourth

Fifth

0.8

0.6

C/Co

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 34 of 36

0.4

0.2

0.0 0

150

300

450

Time(min)

Figure 9

34


600

750

Page 35 of 36

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Figure 10

35



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

For Table of Contents Only

36


Page 36 of 36

Facile Synthesis of Mesoporous Reduced Graphene Oxide

Recommend Documents