facile microwave assisted ionic liquid synthesis of sphere like biobr hollow and porous nanostructures with enhanced photocatalytic performance

Accepted Manuscript Facile microwave-assisted ionic liquid synthesis of sphere-like BiOBr hollow and porous nanostructures with enhanced photocatalytic performance Zhigang Chen, Jie Zeng, Jun Di, Dexiang Zhao, Mengxia Ji, Jiexiang Xia, Huaming Li PII: S2468-0257(16)30108-X DOI: 10.1016/j.gee.2017.01.005 Reference: GEE 50 To appear in: Green Energy and Environment Received Date: 28 November 2016 Revised Date: 20 January 2017 Accepted Date: 22 January 2017 Please cite this article as: Z Chen, J Zeng, J Di, D Zhao, M Ji, J Xia, H Li, Facile microwaveassisted ionic liquid synthesis of sphere-like BiOBr hollow and porous nanostructures with enhanced photocatalytic performance, Green Energy & Environment (2017), doi: 10.1016/j.gee.2017.01.005 This is a PDF file of an unedited manuscript that has been accepted for publication As a service to our customers we are providing this early version of the manuscript The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain ACCEPTED MANUSCRIPT Facile microwave-assisted ionic liquid synthesis of sphere-like BiOBr hollow and porous nanostructures with RI PT enhanced photocatalytic performance Zhigang Chen1,3*, Jie Zeng1, Jun Di2, Dexiang Zhao2, Mengxia Ji2, Jiexiang Xia2,*, Huaming Li2,*, Key Laboratory of Modern Agriculture Equipment and Technology, Ministry of Education, M AN U SC School of Environment and Safety Engineering,2 School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang, 212013, P R China *Corresponding author: Tel: +86-511-8879108; Fax: +86-511-88791108; EP TE D E-mail address: xjx@ujs.edu.cn; lhm@ujs.edu.cn AC C 1 ACCEPTED MANUSCRIPT Abstract In this work, two kinds of self-assembled hierarchical BiOBr microcrystals were RI PT rapidly synthesized through a simple microwave-assisted route in the presence of reactable ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br) These porous and hollow BiOBr microspheres were obtained via a facile solvothermal method with or without Polyvinyl Pyrrolidone (PVP), respectively During the SC synthetic process, ionic liquid [C16mim]Br played as solvent, reactant and template during the synthetic process at the same time Moreover, the BiOBr hollow and M AN U porous microspheres exhibited outstanding photocatalytic activities for the degradation of Rhodamine B (RhB) under visible light irradiation A possible photocatalytic mechanism was also discussed in detail It can be assumed that the higher photocatalytic activities of BiOBr porous microspheres materials could be ascribed to the novel structure, larger specific surface area, narrower band gap TE D structure and smaller particle size AC C EP Keywords: BiOBr; Photocatalytic; Ionic liquid; Microwave ACCEPTED MANUSCRIPT Introduction Semiconductor photocatalysis has been regarded as an efficient, green and promising solution in solving global environment and energy problems[1-4] As significant Bi III–VIA–VIIA ternary semiconductor compounds[5], bismuth oxyhalides RI PT BiOX (X = Cl, Br, I) belong to new types of prospective layer material for photocatalytic energy conversion and environmental decontamination considering their excellent physicochemical properties and low cost[6-8] Among these SC considerable properties of BiOX material, the open crystalline structures, the indirect-transition band-gap and the layered structure have attracted increasing morphologies of BiOX M AN U attention of researchers in the field of photocatalysis application[9-11] So far, a various nano/micro-structures, including nanoplates[12], [13] , nanobelts[14] and microspheres[15], [16], have been synthesized by numerous approaches to maximize their potency of photocatalytic degradation of pollutants Among the three kinds of BiOX, it is well acknowledged that BiOCl has the TE D largest band gap (Eg=3.4 eV), which makes its main light response range lie in the UV region The smallest band gap (Eg=1.8 eV) of BiOI means high recombination rate of photo generated electrons and holes, which greatly limits their applications[17–19] The bismuth oxybromide (BiOBr) semiconductor, shows the best EP photocatalytic oxidation and reduction activity under full light spectrum irradiation due to the befitting p-type indirect bandgap (Eg=2.8 eV)[20], which makes it a hotspot AC C to a great deal of researchers in recent years Besides the intrinsic crystal structure, the photocatalytic performance of a specific semiconductor is closely related to its particle size, morphology and dimensionality[4], [21] While these parameters significantly depend on their synthesis routes[22-24] For example, Xiang et al prepared microsphere structure Bi2WO6/BiOI heterojunction photocatalyst via a chemical etching method[25] Zhang et al synthesized BiOBr nanosheets via a hydrolysis process exhibiting a selective visible-light photocatalytic behavior as the activity over RhB[26] Feng et al synthesized mesoporous BiOBr 3-D microspheres with remarkably high photocatalytic activity in ethanol-mediated condition[27] Guo et al ACCEPTED MANUSCRIPT employed a facile in situ crystallization approach at room temperature to synthesized core-satellites structured BiOBr-CdS highly efficient photocatalyst[28] Huang et al developed a facile room-temperature precipitation method to prepare multiple heterojunctions with tunable photocatalytic reactivity in full-range BiOBr−BiOI RI PT composites[5] Though these BiOBr photocatalysts synthesized via above conventional routes have considerable photocatalytic activities, these synthesis methods are time-consuming for researchers especially in the field of synthetic chemistry where trial-and-error experiments take much of their energies Encouragingly, microwave SC heating has pushed the limits of fast chemical reactions time in minutes since microwave heating process is able to heat target molecules efficiently without heating [30] Therefore, bottom-up microwave-assisted method offers M AN U the entire reactor[29], many unique capabilities, for instance, relatively higher reaction rate, higher yield and energy saving [31], [32] As the novel green media, ionic liquids have been frequently reported in literature recently[33-37] The importance of ionic liquids in the field of inorganic TE D materials synthesis has been realized in terms of their excellent properties such as high thermal stability, wide temperature range for liquid state, low interfacial tension and high ionic conductivity[38], [39] Moreover, many ionic liquids, especially those EP based on imidazolium and quaternary ammonium salts, are chemically very similar to the types of organic cations that are commonly used as structure-directing agents or templates in the preparation of unique morphology of inorganic materials[40], [41] AC C Furthermore, ionic liquids are excellent solvents for absorbing microwaves irradiation because of their large numbers of positive ions with high polarizability and ionic conductivity Therefore, the use of microwave heating in ionic liquids for the synthesis of ideal inorganic materials has apparent advantages over other solvents[42], [43] So far, many various morphologies of inorganic materials prepared by ionic liquid assisted microwave synthesis route have been reported, including N–B–F-tri-doped TiO2[43], nanoparticle sizes Gd4F3[44], g-C3N4/BiOBr porous microspheres[45], hexagonal platelet-like Bi2Te3 crystals[46], CuS quantum dots[47] and so on ACCEPTED MANUSCRIPT Based on above studies, a novel ionic liquid assisted microwave synthesis route for the fast controlled synthesis of hollow and porous sphere-like BiOBr within 20 has developed It can be demonstrated that the ionic liquid [C16mim]Br had a significant influence on the morphology of BiOBr and played important roles as RI PT solvent, reactant, template and microwave-absorbing agent at the same time The obtained hollow and porous BiOBr both have satisfactory photocatalytic activities in the degradation of RhB under visible light This method has some obvious advantages: the process is fast, high yield and environmental friendly; the reaction can be SC performed under atmospheric pressure in a microwave oven; the morphology of BiOBr can be easily controlled It is believed that this environmental friendly route M AN U can be developed into a general way to synthesize other nanomaterials Experimental section 2.1 Material and sample preparation TE D Bismuth nitrate [Bi(NO3)3·5H2O], polyvinylpyrrolidone(PVP K30), ethylene glycol (EG) and absolute ethanol were of analytical grade and used without further purification The ionic liquid 1-hexadecyl-3-methylimidazolium bromide EP ([C16mim]Br, 99%) was purchased from Shanghai Chengjie Chemical Co., Ltd 2.2 Preparation of hollow BiOBr microspheres AC C Microwave oven (SINEOMAS-I) was used to perform synthesis of BiOBr hollow microspheres, the details were as follows: mmol of Bi(NO3)3·5H2O was dissolved into 20 ml EG solution containing stoichiometric amounts of ionic liquid [C16mim]Br After stirring for 30 min, the mixed homogeneous solution was transferred to a 100 mL microwave reaction bottle in the microwave reactor and heated for 20 at 160 °C and then cooled down to room temperature Temperature was monitored by an infrared temperature sensor The final product was separated by centrifugation, washed with distilled water and absolute ethanol for several times respectively, and dried under vacuum at 50 °C for 12 h before further ACCEPTED MANUSCRIPT characterizations 2.3 Preparation of porous BiOBr nanospheres architectures The porous BiOBr nanospheres were prepared similarly via Microwave-assisted RI PT synthesis procedure, the details were as follows: mmol of Bi(NO3)3·5H2O was dissolved into 20 mL EG solution containing stoichiometric amounts of ionic liquid [C16mim]Br and 0.1 g polyvinylpyrrolidone (PVP K30) After stirring for 30 min, the mixed homogeneous solution was transferred to a 100 mL microwave reaction bottle SC in the microwave reactor and heated for 20 at 160 °C and then cooled down to room temperature The final product was separated by centrifugation, washed with M AN U distilled water and absolute ethanol for several times respectively, and dried under vacuum at 50 °C for 12 h before further characterizations 2.4 Characterization X-ray powder diffraction (XRD) analysis was carried out on a Shimadzu TE D XRD-600 X-ray diffractometer with high-intensity Cu-Kα (λ = 1.54 Å) radiation Structural information for the samples was obtained via a Fourier transform spectrophotometer (FT-IR, Nexus 470, Thermo Electron Corporation) by using the EP standard KBr disk method The field emission scanning electron microscopy (SEM) measurements were carried out with a field-emission scanning electron microscope (JEOL JSM-7001F) equipped with an energy-dispersive X-ray spectroscope (EDS) AC C operating at an acceleration voltage of 10 kV Transmission electron microscopy (TEM) micrographs were obtained using a JEOL-JEM-2010 microscope (JEOL, Japan) operating at 200 kV The nitrogen adsorption–desorption isotherms at 77 K were investigated using a TriStar II 3020 Surface Area and Porosity Analyzer (Micromeritics Instrument Corporation, USA) Diffuse reflectance spectra (DRS) was measured in the range of 200 to 800 nm by using a UV-vis spectrophotometer (Shimadzu UV-2450, Japan) BaSO4 was used as the reflectance standard material Photocurrent measurements were performed on an electrochemical workstation (CHI 660B, Chenhua Instrument Company, Shanghai, China) ACCEPTED MANUSCRIPT 2.5 Photocatalytic activity measurement Photocatalytic activity of hollow BiOBr and porous BiOBr samples was evaluated by the degradation of RhB under visible light irradiation Experiments were carried out in a cylindrical Pyrex vessel (100 mL) by means of a 300 W Xe lamp with RI PT a UV cutoff filter (λ > 400 nm) as the visible light source Aeration was performed using an air pump to ensure a constant supply of oxygen and full mixing of the solution In a typical run, 0.02 g of BiOBr powder was dispersed into 100 mL of RhB (10 mg L−1) solution Whereafter, the suspensions were magnetically stirred for 30 SC in the dark to establish an adsorption/desorption equilibrium Then the Pyrex photocatalytic reactor was exposed to visible light irradiation with maximum M AN U illumination time up to 105 Furthermore, all experiments were performed at 30 °C via a circulating water system to prevent thermal catalytic effects During every irradiation time interval (15 min), mL suspension was sampled from the reactor cell, the photocatalyst powders were separated by centrifuge to obtain RhB supernatant liquid, which was analyzed with a UV-Vis spectrophotometer (UV-2450, Shimadzu) TE D at the maximal absorption wavelength (553 nm) of RhB 2.6 Photoelectrochemical measurements EP To investigate the transition of photogenerated electrons in hollow BiOBr and porous BiOBr materials, the photocurrents were measured with an electrochemical AC C analyzer (CHI660B, Chen Hua Instruments, Shanghai, China) in a standard three-electrode system, which employed a platinum wire as counter electrode, a saturated Ag/AgCl electrode as the reference electrode, an indium tin oxide (ITO) glass as working electrode, respectively Hollow BiOBr and porous BiOBr modified electrode were prepared by a simple casting method as follows: mg of the as-prepared sample was dispersed in 0.5 mL ethanol and 0.5 mL EG to produce a suspension, in which 20 µL of the resulting colloidal dispersion was then dip-coated onto a fixed area (0.5 × cm2) of ITO glass electrode and dried under oven at 55 °C for h A 500 W Xe arc lamp was utilized as the photosource The electrolyte solution ACCEPTED MANUSCRIPT for the photocurrent measurements was phosphate buffered saline (0.1 mol L−1, pH = 7.0) Results and discussion RI PT 3.1 XRD analysis The crystal structure of the hollow BiOBr and porous BiOBr microspheres were ascertained by powder XRD instrument and showed in Fig All the diffraction SC peaks in the patterns can distinctly indicate that two kinds of samples both possess pure phase and tetragonal structure of BiOBr with lattice parameter a = b = 3.915 Å, c M AN U = 8.076 Å, which were consistent with the reported values (JCPDS Card No.73-2061) The good crystallinities of the BiOBr samples were directly proved with the intense and narrow diffraction peaks No clear differences of XRD patterns were found between the two BiOBr samples, excepting the diffraction peaks of porous BiOBr samples synthesized with [C16mim]Br and PVP were slightly broader than the TE D hollow BiOBr synthesized with [C16mim]Br, which was consistent with the reported data[48] Moreover, the pseudo-average crystal size of the BiOBr samples were calculated based on Scherrer’s Equation D=Kλ/(βcosθ), where K is constant, λ is EP X-ray wavelength, β is a half high width of the diffraction peak and θ is diffraction angle Based on the Scherrer’s Equation, the average grain sizes of porous and hollow BiOBr materials were determined to be ca 12.8 and 16.0 nm, respectively It can AC C conservatively concluded that hollow and porous BiOBr samples consist of nano-sized crystal particles It agreed well with the results observed with SEM as described later 3.2 FT-IR analysis The FT-IR spectra of samples in the range of 480-4000 cm-1 were showed in Fig These spectra were taken so as to identify the functional groups in the synthesized sample Generally, tetragonal BiOBr contains numerous alternating [Bi2O2]2+ layers and Br- layers[49], [50] In the FT-IR spectra of as-prepared samples, the characteristic ACCEPTED MANUSCRIPT peaks at 517 cm−1 and 720 cm-1 were attributed to the vibrations of Bi–O bonds in BiOBr, which were accordance with the stretching vibration of the bonds in tetragonal BiOX (X = Cl, Br and I)[51] In addition, the peak at 1600 cm−1 was assigned to the bending vibrations of the free water molecules, and the broad absorption peak at about RI PT 3300 cm−1 was associated with the O-H stretch of the intermolecular hydrogen bonds or molecular water[52] It could be attributed to the absorbed H2O on the surface of the BiOBr materials No characteristic peaks of imidazolium C–H stretching of the ionic liquid were observed in FT-IR spectra It can be assumed that the ionic liquid can be SC removed completely from the surface of the material by washing with deionized water 3.3 SEM ,TEM and EDS analysis M AN U and alcohol The morphology and microstructures of the BiOBr obtained by using ionic liquid [C16mim]Br microwave-assisted synthesis at 160 °C for 20 were investigated by SEM and TEM observation As shown in Figure 3a, these uniform and compact TE D BiOBr microspheres with diameters ranging from ca 1.0 to 1.5 µm could be observed Higher magnification microscopy image (Fig 3b) showed that each delicate sphere-like BiOBr was constructed of numerous agminated nanosheets with tens of EP nanometers in thickness These nanosheets were highly directed to grow from one center (crystal nucleus) to all directions, developing into a self-assembled BiOBr spheroidal architectures It can suggest that the individual nanosheets formed and simultaneously AC C grown and were connected together by ionic liquid [C16mim]Br ,which had aggregation behaviors and constitution of micelles in solution[53], [54] A representative TEM image (Fig 3c, d) further confirmed that the obtained BiOBr product is a fluff spheroidal morphology At the same time, it was interesting to find that there were dark periphery and relatively bright center of BiOBr microspheres in TEM image, confirming that as-prepared BiOBr samples were hollow microspheres structures Similar findings were also reported in the previous literature[49], which concluded that ionic liquid [C16mim]Br played an essential part in the construction of hollow BiOBr microspheres since the BiOBr microspheres ACCEPTED MANUSCRIPT advantage of porous BiOBr catalysts, which could increase the quantity of excited active species (h+) bringing about more efficiently photocatalytic process Moreover, the prorous structure of the BiOBr photocatalysts could initiate multiple scattering of visible light, which means that the improvement of light utilization and increase of RI PT photogenerated e- and h+ hole density Last but no the least, the layer structure of prorous BiOBr could provide large space to separate and transfer the hole-electron pair efficiently Accordingly, the enhanced photocatalytic decomposition ability of the SC contaminants was owing to the synergistic effect of above multiple factors Conclusions M AN U In summary, BiOBr hollow microsphere and porous nanosphere structures have been fast controlled and prepared via a new ionic liquid assisted microwave synthesis route, which is a rapid, reliable, high-yielding, template-free and environment-friendly route Experiments results indicated that both the ionic liquid and the microwave heating method play important roles in the formation of BiOBr TE D hollow microsphere and porous nanosphere structures The average diameter of flower-like hollow microspheres and BiOBr porous nanospheres was 1.0–1.5 µm and µm, respectively Furthermore, both samples exhibited excellent photocatalytic EP degradation of RhB The higher photocatalytic activities of BiOBr porous nanospheres might be ascribed to its novel structures, large surface area, smaller AC C particle size and band gap As demonstrated by this successful example, the ionic liquid assisted microwave synthesis method may also be a promising route for a fast and large scale synthesis of other elemental and compound nanostructures This will open up a new feasibility for fast controlled production of a variety of 3D nanostructures in high yields Acknowledgment This work was financially supported by the National Natural Science Foundation 15 ACCEPTED MANUSCRIPT of China (No 21476098, 21471069 and 21576123), the Doctoral Innovation Fund of Jiangsu Province (KYZZ16_0340), the Science and Technology support program of Zhenjiang (SH2014018) and the Natural Science Foundation of Jiangsu Province RI PT (BK2012717) References [1] H Tong, S Ouyang, Y Bi, N Umezawa, M Oshikiri, and J Ye, “Nano-photocatalytic Materials: Possibilities and Challenges,” Adv Mater., 24 (2012) SC 229 Science Bulletin, 60 (2015) 1791 M AN U [2] D.T Yue, X.F Qian and Y.X Zhao, “Photocatalytic remediation of ionic pollutant,” [3] Y.F Zhao, B Zhao, J.J Liu, G.G Chen, R Gao, S Y Yao, M.Z Li, Q.H Zhang, L Gu, J.L Xie, X D Wen, L.Z Wu, C H Tung, D Ma and T Zhang, “Oxide-Modified Nickel Photocatalysts for the Production of Hydrocarbons in Visible Light,” Angew Chem Int Edit., 55 (2016) 4215 TE D [4] Y.F Zhao, X.D Jia, G I N Waterhouse, L.Z Wu, C.H Tung, D O'Hare and T Zhang, “Layered double hydroxide nanostructured photocatalysts for renewable energy production,” Adv Energy Mater., (2016) 7824 EP [5] H.W Huang, X Han, X.W Li, S.C Wang, P K Chu and Y.H Zhang, “Fabrication of Multiple Heterojunctions with Tunable Visible-Light-Active AC C Photocatalytic Reactivity in BiOBr-BiOl Full-Range Composites Based on Microstructure Modulation and Band Structures,” ACS Appl Mater Interfaces, (2015) 482 [6] G G Briand and N Burford, “Bismuth Compounds and Preparations with Biological or Medicinal Relevance,” Chem Rev., 99 (1999) 2061 [7] M Shang, W Wang, and L Zhang, “Preparation of BiOBr lamellar structure with high photocatalytic activity by CTAB as Br source and template,” J Hazard Mater., 167 (2009) 803 [8] J Di, J.X Xia, M.X Ji, B Wang, S Yin, Q Zhang, Z.G Chen, H.M Li, “Carbon 16 ACCEPTED MANUSCRIPT Quantum Dots Modified BiOCl Ultrathin Nanosheets with Enhanced Molecular Oxygen Activation Ability for Broad Spectrum Photocatalytic Properties and Mechanism Insight,” ACS Appl Mater Interfaces, (2015) 20111 [9] J Di, J.X Xia, M.X Ji, L Xu, S Yin, Z.G Chen, H.M Li, “Bidirectional RI PT acceleration of carrier separation spatially via N-CQDs/atomically-thin BiOI nanosheets nanojunctions for manipulating active species in a photocatalytic process,” J Mater Chem A, (2016) 5051 [10] J Wang, Y Yu, and L Zhang, “Highly efficient photocatalytic removal of SC sodium pentachlorophenate with Bi3O4Br under visible light,” Appl Catal B Environ., 136 (2013) 112 M AN U [11] S Shenawi-Khalil, V Uvarov, S Fronton, I Popov, and Y Sasson, “A Novel Heterojunction BiOBr/Bismuth Oxyhydrate Photocatalyst with Highly Enhanced Visible Light Photocatalytic Properties,” J Phys Chem., 116 (2012) 11004 [12] J Jiang, K Zhao, X Xiao, and L Zhang, “Synthesis and Facet-Dependent Photoreactivity of BiOCl Single-Crystalline Nanosheets,” J Am Chem Soc., 134 TE D (2012) 4473 [13] D.J Mao, X.M Lü, Z.F Jiang, J.M Xie, , X.F Lu, W Wei, A.M S.Hossain., “Ionic liquid-assisted hydrothermal synthesis of square BiOBr nanoplates with highly EP efficient photocatalytic activity,” Mater Lett., 118 (2014) 154 [14] H Deng, J Wang, Q Peng, X Wang, and Y Li, “Controlled Hydrothermal Synthesis of Bismuth Oxyhalide Nanobelts and Nanotubes,” Chem.-Eur J., 11 (2005) AC C 6519 [15] J Di ,J.X Xia, Y.P Ge, L Xu, H Xu, J Chen M.Q He, H.M Li, “Facile fabrication and enhanced visible light photocatalytic activity of few-layer MoS2 coupled BiOBr microspheres,” Dalton Trans., 43 (2014) 15429 [16] J Zhang, J.X Xia, S Yin, H.M Li, H Xu, M.Q He, L.Y Huang, Q Zhang, “Improvement of visible light photocatalytic activity over flower-like BiOCl/BiOBr microspheres synthesized by reactable ionic liquids,” Colloids Surf Physicochem Eng Asp Mar., 420 (2013) 89 [17] J Li, Y Yu, and L Zhang, “Bismuth oxyhalide nanomaterials: layered structures 17 ACCEPTED MANUSCRIPT meet photocatalysis,” Nanoscale, (2014) 8473 [18] J Jiang, X Zhang, P Sun, and L Zhang, “ZnO/BiOI Heterostructures: Photoinduced Charge-Transfer Property and Enhanced Visible-Light Photocatalytic Activity,” J Phys Chem C, 115 (2011) 20555 RI PT [19] J Jiang, L Zhang, H Li, W He, and J J Yin, “Self-doping and surface plasmon modification induced visible light photocatalysis of BiOCl,” Nanoscale, (2013) 10753 [20] L Ye, Y Su, X Jin, H Xie, and C Zhang, “Recent advances in BiOX (X = Cl, SC Br and I) photocatalysts: synthesis, modification, facet effects and mechanisms,” Environ Sci Nano 1(2014) 90 M AN U [21] Y.F Zhao, G.B Chen, T Bian, C Zhou, G.I.N Waterhouse, L.Z Wu, C.H Tung, L.J Smith, D O'Hare, and T Zhang, “Defect- rich ultrathin znal-layered double hydroxide nanosheets for efficient photoreduction of co2 to co with water,” Adv Mater, 27 (2015) 7824 [22] C Deng and H Guan, “Fabrication of hollow inorganic fullerene-like BiOBr (2013) 119 TE D eggshells with highly efficient visible light photocatalytic activity,” Mater Lett., 107 [23] J Li, L Zhang, Y Li, and Y Yu, “Synthesis and internal electric field dependent EP photoreactivity of Bi3O4Cl single-crystalline nanosheets with high {001} facet exposure percentages,” Nanoscale, (2014) 167 [24] J Di, J.X Xia, S Yin, H Xu, L Xu, Y.G Xu, M.Q He, H.M Li, “Preparation of g-C3N4/BiOI AC C sphere-like photocatalysts via a reactable ionic liquid for visible-light-driven photocatalytic degradation of pollutants,” J Mater Chem A, (2014) 5340 [25] Y Xiang, P Ju, Y Wang, Y Sun, D Zhang, and J Yu, “Chemical etching preparation of the Bi2WO6/BiOI p–n heterojunction with enhanced photocatalytic antifouling activity under visible light irradiation,” Chem Eng J., 288 (2016) 264 [26] D Zhang, J Li, Q Wang, and Q Wu, “High {001} facets dominated BiOBr lamellas: facile hydrolysis preparation and selective visible-light photocatalytic activity,” J Mater Chem A, (2013) 8622 18 ACCEPTED MANUSCRIPT [27] Y Feng, L Li, J Li, J Wang, and L Liu, “Synthesis of mesoporous BiOBr 3D microspheres and their photodecomposition for toluene,” J Hazard Mater 192 (2011) 538 [28] Y X Guo, H.G Huang, Y He, N Tian, T Zhang, P K Chu, Q An, and Y.H RI PT Zhang, “In situ crystallization for fabrication of a core-satellite structured BiOBr-CdS heterostructure with excellent visible-light-responsive photoreactivity,” Nanoscale, (2015) 11702 [29] Y.J Zhu and F Chen, “Microwave-Assisted Preparation of Inorganic SC Nanostructures in Liquid Phase,” Chem Rev., 114 (2014) 6462 [30] S P Gubin, Ed., Magnetic nanoparticles Weinheim: Wiley-VCH, 2009 M AN U [31] R S Varma and V V Namboodiri, “An expeditious solvent-free route to ionic liquids using microwaves,” Chem Commun., (2001) 643 [32] R S Varma and V V Namboodiri, “Solvent-free preparation of ionic liquids using a household microwave oven,” Pure Appl Chem., 73 (2009) 73 [33] A Rehman and X Zeng, “Ionic Liquids as Green Solvents and Electrolytes for TE D Robust Chemical Sensor Development,” Acc Chem Res., 45 (2012) 1667 [34] G Chatel, J F B Pereira, V Debbeti, H Wang, and R D Rogers, “Mixing ionic liquids-‘simple mixtures’ or ‘double salts’,” Green Chem., 2051, 16 (2014) EP 2051 [35] J Di, J.X Xia, S Yin, H Xu, M.Q He, H.M Li, L Xu, Y.P Jiang, “A g-C3N4/BiOBr visible-light-driven composite: synthesis via a reactable ionic liquid AC C and improved photocatalytic activity,” RSC Adv., 19624, (2013) 19624 [36] J Dupont and J D Scholten, “On the structural and surface properties of transition-metal nanoparticles in ionic liquids,” Chem Soc Rev., 39 (2010) 1780 [37] J.X Xia, Y.Y Ge, J Di, L Xu, S Yin, Z.G Chen, P.J Liu, H.M Li, “Ionic liquid-assisted strategy for bismuth-rich bismuth oxybromides nanosheets with superior visible light-driven photocatalytic removal of bisphenol-A,” J Colloid Interface Sci., 473 (2016) 112 [38] Z.G Chen, H.J Ma, J.X Xia, J Zeng, J Di, S Yin, L Xu, H.M Li., “Ionic liquid-induced strategy for FeWO4 microspheres with advanced visible light 19 ACCEPTED MANUSCRIPT photocatalysis,” Ceram Int., 42 (2016) 8997 [39] J A Dahl, B L S Maddux, and J E Hutchison, “Toward Greener Nanosynthesis,” Chem Rev., 107 (2007) 2228 [40] J Wu, N Li, L Zheng, X Li, Y Gao, and T Inoue, “Aggregation Behavior of RI PT Polyoxyethylene (20) Sorbitan Monolaurate (Tween 20) in Imidazolium Based Ionic Liquids,” Langmuir, 24 (2008) 9314 [41] J Łuczak, M Paszkiewicz, A Krukowska, A Malankowska, and A Zaleska-Medynska, “Ionic liquids for nano- and microstructures preparation Part 2: SC Application in synthesis,” Adv Colloid Interface Sci., 227 (2016) [42] R Martínez-Palou, “Microwave-assisted synthesis using ionic liquids,” Mol M AN U Divers., 14 (2010) [43] F Li et al., “Ionic-liquid-assisted synthesis of high-visible-light-activated N–B–F-tri-doped mesoporous TiO2 via a microwave route,” Appl Catal B Environ., 144 (2014) 442 [44] P S Campbell, C Lorbeer, J Cybinska, and A.-V Mudring, “One-Pot Synthesis TE D of Luminescent Polymer-Nanoparticle Composites from Task-Specific Ionic Liquids,” Adv Funct Mater., 23 (2013) 2924 [45] M.Q He, D.X Zhao, J.X Xia, L Xu, J Di, H Xu, S Yin, H.M Li, “Significant EP improvement of photocatalytic activity of porous graphitic-carbon nitride/bismuth oxybromide microspheres synthesized in an ionic liquid by microwave-assisted processing,” Mater Sci Semicond Process., 32 (2015) 117 AC C [46] G Ji, Y Shi, L Pan, and Y Zheng, “Effect of ionic liquid amount (C8H15BrN2) on the morphology of Bi2Te3 nanoplates synthesized via a microwave-assisted heating approach,” J Alloys Compd., 509 (2011) 6015 [47] G R Chaudhary, P Bansal, and S K Mehta, “Recyclable CuS quantum dots as heterogeneous catalyst for Biginelli reaction under solvent free conditions,” Chem Eng., 243 (2014) 217 [48] J.X Xia, S Yin, H.M Li, H Xu, Y Yan, and Q Zhang, “Self-Assembly and Enhanced Photocatalytic Properties of BiOI Hollow Microspheres via a Reactable Ionic Liquid,” Langmuir, 27 (2011) 1200 20 ACCEPTED MANUSCRIPT [49] L Zhao, X Zhang, C Fan, Z Liang, and P Han, “First-principles study on the structural, electronic and optical properties of BiOX (X=Cl, Br, I) crystals,” Phys B Condens Matter., 407 (2012) 3364 [50] J Di, J.X Xia, M.X Ji, B Wang, S Yin, Q Zhang, c, Z.G Chen, H.M Li, RI PT “Advanced photocatalytic performance of graphene-like BN modified BiOBr flower-like materials for the removal of pollutants and mechanism insight,” Appl Catal B Environ., 183 (2016) 254 [51] I Ardelean, S Cora, and D Rusu, “EPR and FT-IR spectroscopic studies of SC Bi2O3–B2O3–CuO glasses,” Phys B Condens Matter., 403 (2008) 3682 [52] K Nakamoto, Infrared Spectra of Inorganic and Coordination Compound, 4th M AN U edn, Wiley, New York, 1986 [53] J.X Xia, S Yin, H M Li, H Xu, L Xu, and Y.G Xu, “Improved visible light photocatalytic activity of sphere-like BiOBr hollow and porous structures synthesized via a reactable ionic liquid,” Dalton Trans., 40 (2011) 5249 [54] H Cheng, B Huang, Z Wang, X Qin, X Zhang, and Y Dai, “One-Pot TE D Miniemulsion-Mediated Route to BiOBr Hollow Microspheres with Highly Efficient Photocatalytic Activity,” Chem - Eur J., 17 (2011) 8039 [55] B M Pirzada, O Mehraj, N A Mir, M Z Khan, and S Sabir, “Efficient visible photocatalytic activity and enhanced stability of BiOBr/Cd(OH)2 EP light heterostructures,” New J Chem., (2015) 7153 [56] L Shang, B Tong, H.J Yu, G I N Waterhouse, C Zhou, Y.F Zhao, M Tahir, AC C L.Z Wu, C H Tung and T Zhang, “CdS nanoparticle-decorated Cd nanosheets for efficient visible light-driven photocatalytic hydrogen evolution”, Adv Energy Mater., (2016) 1501241 [57] J.X Xia, J Di, S Yin, H.M Li, Li Xu, Y.G Xu, C.Y Zhang, H.M Shu, “Improved visible light photocatalytic activity of MWCNT/BiOBr composite synthesized via a reactable ionic liquid,” Ceram Int., 40 (2014) 4607 [58] J Xia, S Yin, H Li, H Xu, L Xu, and Q Zhang, “Enhanced photocatalytic activity of bismuth oxyiodine (BiOI) porous microspheres synthesized via reactable ionic liquid-assisted solvothermal method,” Colloids Surf Physicochem Eng Asp., 21 ACCEPTED MANUSCRIPT 387 (2011) 23 [59] Q L Yuan, Y Zhang, H Y Yin, Q L Nie and W W Wu, Rapid, simple and low-cost fabrication of BiOBr ultrathin nanocrystals with enhanced visible light photocatalytic activity, J Exp Nanosci., 11 (2016) 359-369 RI PT [60] Y Huo, J Zhang, M Miao, and Y Jin, “Solvothermal synthesis of flower-like BiOBr microspheres with highly visible-light photocatalytic performances,” Appl AC C EP TE D M AN U SC Catal B Environ., 111 (2012) 334 22 ACCEPTED MANUSCRIPT Figure caption: Fig XRD patterns of BiOBr samples of: (a) hollow BiOBr; (b) porous BiOBr Fig FT-IR spectra of BiOBr samples: (a) hollow BiOBr,; (b) porous BiOBr Fig BiOBr microspheres structures: (a, b) the high magnification SEM images; (c, RI PT d) TEM image of the hollow BiOBr microspheres; (e) EDS images of hollow BiOBr Fig (a, b) SEM (c) EDS images of the porous BiOBr microspheres structures Fig (a) Hollow BiOBr and Porous BiOBr samples of UV-vis diffuse reflectance spectra (DRS); (b) direct band gap of hollow BiOBr and porous BiOBr nanospheres SC Fig Nitrogen absorption–desorption isotherms of porous and hollow BiOBr samples M AN U Fig Transient photocurrent response for the porous BiOBr and hollow BiOBr microspheres with and without irradiation in 0.1mol L-1 PBS solution (pH =7) under visible light irradiation Fig Photodegradation of RhB with different structure BiOBr under visible-light irradiation TE D Fig Comparison of photocatalytic activities of the microwave porous BiOBr catalysts for the degradation of RhB with or without adding EDTA-2Na and TBA under visible light irradiation EP Fig 10 A schematic illustration of RhB degradation over microwave porous BiOBr AC C microspheres under visible light irradiation 23 ACCEPTED MANUSCRIPT RI PT SC b (032) (220) (124) (020) (014) (211) (212) (112) a (002) (011) (001) (012) Intensity (a u.) (110) Hollow BiOBr Porous BiOBr JCPDS Card No.73-2061 20 30 40 50 60 70 80 M AN U 10 2-Theta (degree) TE D Hollow BiOBr Porous BiOBr a b 4000 -1 720cm 517cm -1 AC C EP Absorbance (a.u.) Fig 3200 2400 1600 -1 Wavenumber (cm ) Fig 24 800 M AN U SC RI PT ACCEPTED MANUSCRIPT 600 (e) Si 400 300 TE D Intensity (a.u.) 500 Bi Bi 200 Br 100 O Br AC C EP Energy (KeV) Fig 25 ACCEPTED MANUSCRIPT 2500 (c) Bi Si 2000 Bi 1500 RI PT Intensity Br 1000 Br Bi Bi Energy (KeV) 1.2 (a) EP 0.2 TE D Absorbance 0.8 0.4 Hollow BiOBr Porous BiOBr 1.0 0.6 M AN U Fig SC 500 O AC C 0.0 200 300 400 500 600 700 Wavelength (nm) 26 800 ACCEPTED MANUSCRIPT RI PT 0.5 Hollow BiOBr Porous BiOBr (b) 0.0 2.0 2.4 2.6 2.8 3.0 M AN U 2.2 SC 1/2 1.0 (α Ephoton) 1.5 Ephoton (eV) TE D 100 EP Porous BiOBr Hollow BiOBr 80 60 AC C Quantity Absorbed (cm /g STP) Fig 40 20 0.0 0.2 0.4 0.6 Relative Pressure (P/P0) Fig 27 0.8 1.0 ACCEPTED MANUSCRIPT 0.03 0.02 0.01 0.00 40 80 120 160 Time (s) 240 M AN U Fig 200 SC RI PT Photocurrent (µA) Porous BiOBr Hollow BiOBr TE D 1.0 Blank Hollow BiOBr Porous BiOBr 0.6 EP C/C0 0.8 AC C 0.4 0.2 0.0 15 30 45 60 Time (min) Fig 28 75 90 105 ACCEPTED MANUSCRIPT 1.0 BiOBr C4H10O+BiOBr 0.8 RI PT EDTA+BiOBr C/C0 0.6 0.4 0.0 15 30 45 60 75 90 M AN U Time (min) SC 0.2 AC C EP TE D Fig Fig 10 29 105 ...ACCEPTED MANUSCRIPT Facile microwave- assisted ionic liquid synthesis of sphere- like BiOBr hollow and porous nanostructures with RI PT enhanced photocatalytic performance Zhigang Chen1,3*,... image of the hollow BiOBr microspheres; (e) EDS images of hollow BiOBr Fig (a, b) SEM (c) EDS images of the porous BiOBr microspheres structures Fig (a) Hollow BiOBr and Porous BiOBr samples of. .. caption: Fig XRD patterns of BiOBr samples of: (a) hollow BiOBr; (b) porous BiOBr Fig FT-IR spectra of BiOBr samples: (a) hollow BiOBr, ; (b) porous BiOBr Fig BiOBr microspheres structures: (a,