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In no event shall the Royal Society of Chemistry be held responsible for any errors or omissions in this Accepted Manuscript or any consequences arising from the use of any information it contains. www.rsc.org/crystengcomm Page 1 of 7 CrystEngComm Journal Name RSC Publishing ARTICLE Template free synthesis of hierarchically porous NaCoPO 4-Co 3O4 hollow microspheres and their Cite this: DOI: 10.1039/x0xx00000x application in electrocatalysts for glucose a a a a a Received 00th January 2012, Chengzhen Wei, Cheng Cheng, Junhong Zhao, Xin Yuan, Tingting Wu, Ying Accepted 00th January 2012 a a a,b Wang, Weimin Du and Huan Pang* DOI: 10.1039/x0xx00000x www.rsc.org/ Hierarchically porous NaCoPO 4-Co 3O4 hollow microspheres are successfully synthesized via a simple hydrothermal method and calcination in air. It is found that the as-prepared hierarchically porous NaCoPO 4-Co 3O4 hollow microspheres exhibit good catalytic activity toward the oxidation of glucose, it shows a fast amperometric response time of less than 5 s, and the detection limit is Manuscript estimated to be 0.125 µM. More importantly, compared with other normally co-existing electroactive species (such as ascorbic, uric acid and acid dopamine), the electrode modified with hierarchically porous NaCoPO 4-Co 3O4 hollow microspheres shows good selectivity. These results suggest that hierarchically porous NaCoPO 4-Co 3O4 hollow microspheres have promising application in electrocatalysts for quantitative determination of glucose with high sensitivity and selectivity. 1. Introduction glucose sensors usually suffer from the fatal drawback of poor stability due to the intrinsic nature of enzymes, which limit their In recent years, the design and synthesis of hollow wide applications. To overcome these problems, considerable Accepted micro/nanostructure materials with desired size, morphology and interest has been paid on development of non-enzymatic glucose composition have received considerable attention because of their sensor for practical applications. Recent research has shown that promising use in many fields such as sensor, energy storage, drug nanomaterials can be employed as electrocatalysts for the oxidation delivery and waste water treatment. 1-6 The success of these of glucose owing their novel physical and chemical properties, and applications strongly depends on the size of the hollow structure, and these nanomaterials also exhibit good performance for the detection also on the nanostructure of the shell. Above all, hierarchically of glucose. 19-24 The results demonstrate that nanostructured materials hollow spheres with the shell composed of nanosized building are potential candidates as the electrocatalysts materials for practical blocks (e.g., nanosheets, nanorods, or nanoparticles) should be of glucose monitoring. great importance for finding and making use of their novel Herein, We present that the synthesis of hierarchically porous properties, which could provide the advantages of both nanometer- NaCoPO 4-Co 3O4 hollow microspheres through hydrothermal route sized building blocks and micro- or submicrometer-sized and subsequent calcinations. Benefitting form hierarchically 7-10 assemblies. Moreover, porous materials are of great significance, NaCoPO 4-Co 3O4 hollow microspheres with porous structure, the because porous materials with high porosity and specific surface synthesized products were applied as electrocatalysts for the area are able to interact with liquids not only at the surface, but also oxidation of glucose. Cyclic voltammetry and amperometry were in the inner part of the bulk, and thus, porous materials generally used to evaluate the electrocatalytic activities of the hierarchically CrystEngComm exhibit enhanced chemical-physical performance over their solid porous NaCoPO 4-Co 3O4 hollow microspheres towards glucose. It is counterparts. 11-17 Therefore, preparation of hierarchically hollow found that the detection limit is estimated to be 0.125 µm. Moreover, spheres with porous has been a research hot spot. the electrode modified with hierarchically porous NaCoPO 4- It is no doubt that reliable and fast monitoring of glucose is vital Co 3O4 hollow microspheres is also highly selective to the target in clinical diagnostics, biotechnology, and the food industry. analyst. The hierarchically porous NaCoPO 4-Co 3O4 hollow Therefore, continuous efforts have been made to develop microspheres hold potential application in electrocatalysts for electrochemical glucose sensors. Over the past few years, the glucose. conventional glucose biosensors based on glucose oxidase (GOD) exhibits high sensitivity and selectivity. 18 However, these enzymatic This journal is © The Royal Society of Chemistry 2013 J. Name ., 2013, 00 , 1-3 | 1 CrystEngComm Page 2 of 7 ARTICLE Journal Name 2. Experimental microspheres with a diameter of about 5-8 µm. The microspheres with rough surface are interconnected. As shown in the Fig. 1b, the 2.1 Materials synthesis microsphere is constructed by nanosheets with smooth surface and All the reagents used were of analytical grade and used without the thickness is about 30 nm (the inset in Fig. 1b). A typical broken further purification. Hierarchically porous NaCoPO 4-Co 3O4 hollow microsphere is shown in Fig. 1c, which reveals the hollow interior of microspheres were successfully prepared via combining a the hierarchical microspheres. The hollow nature of the as-prepared hydrothermal route and calcination treatment in air process. In a hierarchical microspheres can also be further proved by transmission typical synthesis experiment, 0.110 g cobalt (II) chloride electron microscopy. It was found that the contrast between the hexahydrate, 0.846 g sodium tartaric and 0.15 g sodium central portion and the edge of the hierarchical microspheres pyrophosphate were added into 20.0 mL H 2O and stirred for 30 min. strongly confirms the formation of hollow nature (Fig. 1d). The mixture solution was then transferred into a 35 mL Teflon-lined stainless steel autoclave and heated at 200 ºC for 24 h. After being cooled to room temperature, the resulting precipitate were obtained by centrifugation and washed with ethanol and water for three times, and then dried at 50 ºC for 12 h. Subsequently, the products were further calcined at 550 °C for 30 min at a heating rate of 1°C min -1 in air to obtain hierarchically porous NaCoPO 4-Co 3O4 hollow microspheres. 2.2 Preparation of the hierarchically porous NaCoPO 4-Co 3O4 hollow microspheres/GC . The glassy carbon (GC) electrode (3 mm diameter) was polished using a polishing cloth with alumina slurry (1.0, 0.3, and 0.05 mm in Manuscript sequence), and rinsed fully with deionized H 2O and ethanol solution, then allowed to dry at room temperature. To prepare the GC electrode modified with the hierarchically porous NaCoPO 4-Co 3O4 hollow microspheres material, an aqueous dispersion of the -1 NaCoPO 4-Co 3O4 (1 mg mL ) was prepared, and then the suspension (5 µL) was cast onto the surface of the pretreated GC electrode. The solvent was allowed to evaporate at room temperature, leaving the hierarchically porous NaCoPO 4-Co 3O4 hollow microspheres material immobilized on the GC electrode surface. 2.3 Materials characterization Accepted The phase and compositions of the samples were examined via X- Fig. 1 FESEM (a-c) and TEM (d) images of the precursor 3D ray diffraction (XRD) on a Rigaku-Ultima Ш with Cu Kα radiation hierarchical hollow microspheres. (λ= 1.5418 Å). The morphologies and microstructures of the products were characterized using a field-emission scanning electron In this work, sodium tartaric plays an important role in the microscope (FESEM, JEOL JSM-6701F), transmission electron preparation of the hierarchically hollow microspheres precursors. microscope (TEM, JEOL-2010). The surface area, pore size, and Without adding sodium tartaric, the as-prepared sample with urchin- pore size distribution of the samples were determined by Brunauer- like morphology can be obtained (Fig. S1, ESI†). FTIR spectra of sodium tartaric and hierarchically hollow microspheres precursors Emmett-Teller (BET) N 2 adsorption/desorption and Barett-Joyner- -1 Halenda (BJH) methods on a Micromimetrics ASAP2020 are shown in Fig. S2. The peaks at 2974 and 2929 cm are assigned -1 physisorption analyzer. Electrochemical measurements were to the stretching vibration of C-H. The band at 1610 cm is assigned -1 conducted on a CHI 660D electrochemical station (CH Instruments, to the C=O. The peak at 1380 cm is attributed to the stretching Shanghai, China), a three-compartment electrochemical cell vibration of the C-O. We therefore concluded that sodium tartaric containing a modified GC electrode