English

• 0.   Introduction

  Hydrogen peroxide has been used frequently as an eco-friendly chemical in industrial production, food preservation and environmental protection^[1-3]. It is of great significance to develop the method for accurate detection of hydrogen peroxide because H₂O₂ might be an intermediate for industrial processes and a by-product of chemical or biological reaction^[4-8]. Since traditional detecting techniques have shortcomings of high cost, time consuming and complex operation, electrochemical detection may be preferable due to its low consumption, fast response and simplicity^[9-12]. Although enzyme-based electrochemical sensors exhibit specific advantages, their application is limited by stability issues and high cost^[13-15]. Therefore, non-enzyme electrochemical sensors have become one of the research hotspots for H₂O₂ detection due to their high stability and no-dependency on temperature, ion concentration, pH and toxic chemicals^[16-19]. In recent years, various noble metal composites have been widely used in nonenzymatic sensor with the development of material preparation technology. Recent researches show that silver is the best conductive metal with good chemical properties^[20], catalytic properties^[21] and biocompatibility^[22]. Hence, it is widely used in the fields of electronics, chemical engineering, biomedicine, medicine, and daily necessities^[23]. Many methods have been used to prepare silver nanoparticles, such as template method^[24-25], wet chemical method^[26-27], electrochemical method^[28-29] and polyol method^[30]. However, the catalytic properties are often affected due to their tendency to agglomerate during preparation. Particle′s agglomeration is a key problem not to be ignored for the preparation of nano silver.

  In order to prepare highly dispersed nano silver, in this paper titanium dioxide (TiO₂) was introduced as carrier due to its excellent optical properties^[31], electrical properties^[32] and certain catalytic activity^[33]. The preparation method of titanium dioxide is simple and its morphology is highly controllable^[34-36]. It has attracted the more attention for electrochemical sensing and is often used as catalyst carrier^[37-38]. In this work, silver decorated TiO₂ microspheres (Ag-TiO₂ MS) were syn-thesized by one-pot solvothermal method. As shown in Fig. 1, an alcoholysis of tetrabutyl titanate (TBOT) was controlled in alcohol solvent to obtain TiO₂ micro-sphere and a reducing reaction of enol in vitamin C (VC) was performed with surrounding nano silver uniform dispersion during the high temperature and pressure. As a result, the one-pot reaction can still retain the metallic properties of silver. Herein, Ag-TiO₂ com-posite was provided for detecting H₂O₂. Combining this composite with other catalytic materials can promote new ideas for electrochemical sensors.

  Figure 1

  

  Figure 1.  Schematic illustration of one-pot solvothermal synthesis of finely-dispersed Ag-TiO₂MS

  下载: 全尺寸图片 幻灯片

  1.   Experimental

  1.1   Materials and reagents

  The reagents required in synthesis of Ag-TiO₂ MS were silver nitrate (AgNO₃, 99.8%), VC (99.7%) and TBOT (99.0%) purchased from Aladdin, China. The reagents used for electrochemical measurements included hydrogen peroxide (H₂O₂, 30%), urea (99. 0%), glucose (L-Glu, 98%) and lactose (Lac, 98%) that were purchased from Aladdin, China. Phosphate buffer solution (PBS, pH=7.0, 0.02 mol·L^-1) as supporting electrolyte was prepared with KH₂PO₄ and KOH (Sinopharm, China).

  1.2   One-pot synthesis of Ag-TiO₂ MS

  In a typical procedure, 30 mmol·L^-1 VC and 0.03 g AgNO₃ were dissolved in 70 mL absolute ethanol in a beaker with magnetic stirring, and then 8 mmol·L^-1 TBOT was added to form a transparent solution with brown color. Subsequently, the solution was transferred into 100 mL Teflon-line stainless steel autoclave (Microreactor, Yanzheng Instrument Ltd., Shanghai) and heated in an oven at 200 ℃ for 7 h. After the autoclave was cooled down to room temperature in air, the solid product (Ag-TiO₂ MS) was separated by centrifugation, washed with deionized water and absolute alcohol several times, and dried in vacuum at 60 ℃ for 6 h. TiO₂ microspheres (TiO₂ MS) can be synthesized by the same method just without adding AgNO₃.

  1.3   Preparation and characterization of Ag -TiO₂ MS electrode

  Prior to use, glassy carbon electrode (GCE, ϕ=3.0 mm, S=0.070 7 cm²) was polished with 300 and 50 nm aluminum oxide powders to a mirror-like, respectively, and then washed successively with acetone, ethanol and double-distilled water for several times. A homogeneous mixture was formed by adding 2.0 mg Ag-TiO₂ MS into 100 μL double-distilled water, 100 μL abso-lute ethanol and 10 μL Nafion (5%, w/w). The mixture was sonicated for 30 min. The preparation procedures of Ag-TiO₂ MS electrode as follows: 3.5 μL mixture was dropped on the surface of GCE and dried in ambi-ent air for 20 min.

  The morphology was examined by high resolution transmission electron microscopy (HR-TEM, 300 kV), high angle annular dark field scanning transmission electron microscopy (HAADF-STEM, 300 kV), coupled with energy dispersive X-ray spectrometer (EDX), using Cu Kα radiation and spherical-aberration corrected field-emission transmission electron microscope (Philips-FEI, Tecnai G2 F30 S-Twin). The oxidation states of chemical species were detected by X-ray photoelectron spectroscopy (XPS, Kratos Axis Ultra DLD) using a focused monochromatized Al Kα operated at 300 W. The binding energies were referenced to the C1s line at 284.6 eV from adventitious carbon.

  1.4   Electrochemical measurement of H₂O₂

  Electrochemical measurements were performed on an Ivium potentiostat in N₂-satruated 0.02 mol·L^-1 PBS (pH 7.0), with or without H₂O₂, using a three-elec-trode cell with the Ag-TiO₂ MS electrode as working electrode, a Pt foil counter electrode, and a Ag/AgCl reference electrode. The electrochemical impedance spectroscopy (EIS) was measured by applying amplitude of 5.0 mV over the frequency ranging from 10⁵ to 10^-2 Hz. For electrochemically sensing H₂O₂, the sensitivity, stability, reproducibility and antiinterfering activity studies were also performed in N₂-saturated 0.02 mol·L^-1 PBS (3.0 mL, pH 7.0) using chronoamperome-try at -0.3 V.

  2.   Results and discussion

  2.1   Characterization of Ag-TiO₂ MS

  Fig. 2 shows a typical SEM image of the TiO₂ MS and Ag-TiO₂ MS. As shown in Fig. 2a, the average size of TiO₂ MS was hundred nanometers but not uniform. The inset of Fig. 2a showed a rough TiO₂ MS with a diameter of about 250 nm. As shown in Fig. 2b, the layers of material superimposed on the surface of Ag-TiO₂ MS and the surface roughness of the spheres was improved by Ag modification. The average diameter of each sphere was about 200~300 nm. In addition, it can be found that some spheres twined together, which may be related to the growth process of Ag-TiO₂ MS. By changing the reaction time, we found that the adhesion phenomenon was gradually obvious with the increase of solvent heat time during the growth of TiO₂ MS (Fig.S1).

  Figure 2

  

  Figure 2.  SEM images of TiO₂ MS (a) and Ag-TiO₂ MS (b)

  下载: 全尺寸图片 幻灯片

  XPS spectra was further used to confirm the surface chemical composition and oxidation state. Fig. 3 shows the high resolution XPS spectra of Ti2p, O1s, Ag3d and Ag MVV for Ag-TiO₂ MS. Ti2p spectra can be divided into Ti2p_1/2 and Ti2 p_3/2 peaks, and the peaks at 463.7 and 457.9 eV can be assigned to Ti—O bonds. The O1s XPS spectrum for Ag-TiO₂ MS at 530.2 eV is ascribed to Ti—O bonds. The Ag3d XPS spectrum of Ag-TiO₂ MS shows peaks at 368.0 and 374.0 eV, corresponding to the Ag3d_5/2 and Ag3d_3/2, respectively. The Auger parameter (α′), which is defined as the sum of the kinetic energy of the Auger electron (α_{Ag M4 VV}) and the binding energy of the core level Ag3d_5/2 (α_Ag3d5/2), can be calculated by the equation of α′ =α_{Ag M4 VV}+α_Ag3d5/2^[39]. The characteristic peak appeared in the Ag M₄VV XPS spectrum at 358.0 eV and the α′ was calculated to be 726.0 eV, which is ascribed to Ag⁰ in Ag-TiO₂ MS.

  Figure 3

  

  Figure 3.  XPS spectra of Ag-TiO₂ MS

  下载: 全尺寸图片 幻灯片

  XRD patterns of TiO₂ MS and Ag-TiO₂ MS are shown in Fig. 4. It can be seen that TiO₂ MS might be amorphous and this can be confirmed by the selected area electron diffraction (SAED, Fig. S2). Four diffraction peaks with 2θ values of 38.1°, 44.3°, 64.4° and 77.4° can be assigned to (111), (200), (220) and (311) planes of face-centered cubic (fcc) Ag.

  Figure 4

  

  Figure 4.  XRD patterns of TiO₂ MS and Ag-TiO₂ MS

  下载: 全尺寸图片 幻灯片

  Fig. 5a and 5d show the TEM images of TiO₂ MS and Ag-TiO₂ MS, which reveal the detailed structure of the spherical morphology. Both in TiO₂ MS and Ag-TiO₂ MS, there was no obvious lattice stripe of TiO₂, which indicates that it mainly exists in amorphous form. However, Ag⁰ were grown on the surface of Ag-TiO₂ MS. These Ag nanoparticles (Ag NPs) had highly crystalline and the lattice spacing was determined to be 0.236 nm, which is attributed to (111) plane of Ag (Fig. 5f).

  Figure 5

  

  Figure 5.  TEM images of TiO₂ MS (a~c) and Ag-TiO₂ MS (d~f)

  Inset shows the magnified image with clear lattice fringes

  下载: 全尺寸图片 幻灯片

  Furthermore, the composition of TiO₂ MS and Ag-TiO₂ MS was confirmed by EDX. Fig. 6 illustrated that the TiO₂ MS included Ti, O elements and the Ag-TiO₂ MS included Ti, O, and Ag elements, suggesting that TiO₂ MS and Ag-TiO₂ MS were successful by one-pot synthesis method. In addition, Fig. 7 is the HAADF -STEM images and the corresponding EDX mappings of TiO₂ MS and Ag-TiO₂ MS. Obviously, it proved that the distribution of Ti, O and Ag elements was relatively homogenous, and Ag⁰ was highly dispersed on the sur-face of TiO₂ MS.

  Figure 6

  

  Figure 6.  EDX spectra of (a) TiO₂ MS and (b) Ag-TiO₂ MS

  下载: 全尺寸图片 幻灯片

  Figure 7

  

  Figure 7.  HAADF-STEM images and the corresponding EDX mappings of (a) TiO₂ MS and (b) Ag-TiO₂ MS

  下载: 全尺寸图片 幻灯片

  2.2   Electrochemical performance of Ag-TiO₂ MS for H₂O₂

  Cyclic voltammetry (CV) was employed to characterize the electrochemical behavior of the electrode. Fig. 8 shows the CV curves of TiO₂ MS and Ag-TiO₂ MS electrodes in 0.02 mol·L^-1 PBS (pH 7.0) with and with-out 1 000 μmol·L^-1 H₂O₂ at scan rates of 20 mV·s^-1. Compared with TiO₂ MS, Ag-TiO₂ MS electrode showed a reduction peak at around -0.4 V, suggesting the strong reduction ability of Ag-TiO₂ MS for H₂O₂.

  Figure 8

  

  Figure 8.  CVs of TiO₂ MS (black curves) and Ag-TiO₂ MS (red curves) electrodes in 0.02 mol·L^-1 PBS (pH 7.0) with (solid curves) or without (dotted curves) 1 000 μmol·L^-1 H₂O₂ at 20 mV·s^-1

  下载: 全尺寸图片 幻灯片

  The electrochemical performance of Ag-TiO₂ MS electrode towards H₂O₂ reduction was further examined via changing the H₂O₂ concentrations (Fig. 9) and scan rates (Fig. 10). As seen in Fig. 9b, the increase of H₂O₂ concentration led to a regular increase in the reduction peak current in Ag-TiO₂ MS electrodes. Compared with Fig. 9a, it was no obvious response to hydrogen peroxide for TiO₂ MS electrode, indicating that the Ag-TiO₂ MS electrodes have good electrocatalytic activity and an application prospect as a sensor after loading with Ag.

  Figure 9

  

  Figure 9.  CVs of TiO₂/MS (a) and Ag-TiO₂/MS (b) electrodes at 20 mV·s^-1 with adding different concentrations of H₂O₂

  下载: 全尺寸图片 幻灯片

  Figure 10

  

  Figure 10.  CVs of Ag-TiO₂ MS electrode in the presence of 2 000 μmol·L^-1 H₂O₂ at different the scan rates

  下载: 全尺寸图片 幻灯片

  The kinetic parameters were further calculated by the relation graph of H₂O₂ concentration and scan rates (Fig. 10). In the irreversible process, the diffusion coefficient (D₀) and reaction rate constant (k₀) were calculated using the Eq.1 and Eq.2^[40].

  ${I_{\rm{p}}} = 2.99 \times {10^5}{n^{3/2}}{\alpha ^{1/2}}A{c_0}{D_0}^{1/2}{v^{1/2}} $

  (1)

  ${I_{\rm{p}}} = 0.227nFA{c_0}{k_0}\exp [ -\alpha F({E_{\rm{p}}} -{E_{1/2}})/(RT)] $

  (2)

  Where I_p is the peak current (A), n is the number of electrons, F is Faraday constant, A is the area of the electrode (cm²), c₀ is the concentration of H₂O₂ (mol·L^-1), E_p is the peak potential (V), E_1/2 is the half-wave peak potential (V), α is the charge transfer coefficient, v is the scan rate (V·s^-1). The concentration of H₂O₂ was 2 000 μmol·L^-1 and the electroactive surface area for Ag-TiO₂ MS was 0.070 7 cm². Eq.3 is built by evalu-ating the logarithm of Eq.2.

  ${\rm{In}}\;{I_{\rm{p}}} = -\alpha F({E_{\rm{p}}} -{E_{1/2}})/(RT) + \ln (0.227nFA{c_0}{k_0}) $

  (3)

  The linear relationship of I_p and v^1/2 for Ag-TiO₂ MS electrode was I_p=120.07v^1/2+4.992 (R²=0.996) (Fig. 11a). The calculated D₀ value on Ag-TiO₂ MS elec-trode was 1.96×10^-5 cm·s^-1.

  Figure 11

  

  Figure 11.  (a) Relationship of I_p and v^1/2 and (b) relationship of ln I_p and (E_p-E_1/2) for Ag-TiO₂ MS electrode

  下载: 全尺寸图片 幻灯片

  The relationship of ln I_p and (E_p-E_1/2) for Ag-TiO₂ MS was ln I_p=-15.897(E_p-E_1/2)-12.117 (R²=0.996). The calculated k₀ value on Ag-TiO₂ MS electrode was 1.45× 10^-3 cm·s^-1.

  In order to illustrate the effect of the loaded silver, EIS of TiO₂ MS and Ag-TiO₂ MS electrodes were carried out. The obtained Nyquist plots are shown in Fig. 12 and the constant phase angle element (CPE) replaces the electrode double layer capacitance in the equivalent circuit diagram. Two typical semicircles can be observed at high frequency range and the low frequency region, respectively. Based on the equivalent circuit, charge-transfer resistance (R_ct) can be deter-mined from the diameter of the left most semicircle, and the polarization resistance (R_p) can be determined from the diameter of the second semicircle. The param-eters obtained from the fitting curves of EIS are shown in Table 1. The ohmic serial resistance (R_s) can be obtained by the intercept on the real axis at high frequency. The R_ct of TiO₂ MS and Ag-TiO₂ MS electrodes were 726 and 613 Ω, and the R_p were 291.5 and 28.34 kΩ, respectively. Obviously, the R_ct and R_p of Ag-TiO₂ MS were lower than that of TiO₂ MS, which conformed that Ag-TiO₂ MS has better electronic conductivity and electrochemical reaction rate.

  Figure 12

  

  Figure 12.  Nyquist plots of Ag-TiO₂ MS, TiO₂ MS and GCE electrodes

  下载: 全尺寸图片 幻灯片

  Table 1

  

  Table 1.  Parameters obtained from the fitting curves of EIS in Fig. 12

  下载: 导出CSV

  Sample	Rs/Ω	Rct/Ω	Rp/kΩ
  Ag-TiO2 MS	126.9	613	28.34
  TiO2 MS	133.9	726	291.5
  GCE	135.4	675	138.9

  In conclusion, hydrogen peroxide can be adsorbed by nano silver in neutral medium^[41], the cathodic reaction process may be shown as fllows:

  $\begin{array}{*{20}{l}} {{\rm{Ag -Ti}}{{\rm{O}}_{\rm{2}}}{\rm{ + }}{{\rm{H}}_{\rm{2}}}{{\rm{O}}_{\rm{2}}}{\rm{ + }}{{\rm{e}}^ -} \to {\rm{Ti}}{{\rm{O}}_{\rm{2}}}{\rm{ -Ag -O}}{{\rm{H}}_{{\rm{ad}}}}{\rm{ + O}}{{\rm{H}}^ -}} \end{array} $

  (4)

  ${\rm{Ti}}{{\rm{O}}_{\rm{2}}}{\rm{ -Ag -O}}{{\rm{H}}_{{\rm{ad}}}}{\rm{ + }}{{\rm{e}}^{\rm{ -}}} \to {\rm{ O}}{{\rm{H}}^{\rm{ -}}}{\rm{ + Ag -Ti}}{{\rm{O}}_{\rm{2}}} $

  (5)

  ${\rm{O}}{{\rm{H}}^{\rm{ -}}}{\rm{ + }}{{\rm{H}}^{\rm{ + }}} \to {{\rm{H}}_{\rm{2}}}{\rm{O}} $

  (6)

  Successful loading of nano silver will make the reaction step 4 and 5 easier to perform, which provide higher electrochemical reaction rates for catalytic reactions and effectively improve the electrical conductivity of the material.

  2.3   Detection performance of Ag-TiO₂ MS towards H₂O₂

  Amperometric response (I-t, the relation between current and time) curves were performed with the successive addition H₂O₂ into a stirring electrochemical cell containing 3 mL PBS (0.02 mol·L^-1, pH 7.0) at an optimized potential of -0.3 V (Fig. 13). For Ag-TiO₂ MS electrode, each response current step showed a downward trend between 0.1 to 102 μmol·L^-1 and an upward trend between 478 to 699 μmol·L^-1. It is clear that the response current can remain stable only in the intermediate concentration range.

  Figure 13

  

  Figure 13.  I-t curve of Ag-TiO₂ MS in 0.02 mol·L^-1 PBS (pH 7.0) with the successive adding H₂O₂

  下载: 全尺寸图片 幻灯片

  Fig. 14 presents the linear fitting relationships between the current response and H₂O₂ concentration. The current responses as functions of H₂O₂ concentration can be represented by three different linear equations, which are valid at different concentration ranges. The linear regression equations of Ag-TiO₂ MS were I=2.21×10^-4c_H2O2+0.278 (R²=0.979) for c_H2O2=0.1~102 μmol·L^-1, I=5.41×10^-4c_H2O2+0.240 (R²=0.997) for c_H2O2= 102~478 μmol·L^-1 and I=1.234×10^-3c_H2O2-0.109 (R²= 0.985) for c_H2O2=478~699 μmol·L^-1. The limit of detection (LOD) was determined by using the equation LOD= 3S_B/b, where b is the slope of the calibration curve and S_B is the standard deviation of the blank solution. The LOD (S/N=3) of Ag-TiO₂ MS sensor was calculated to be 0.04 μmol·L^-1. Meanwhile the obtained sensitivity of Ag-TiO₂ MS was 3.13×10^-3 μA·L·μmol^-1·cm^-2.

  Figure 14

  

  Figure 14.  I-c_H2O2 linear fitting results for Ag-TiO₂ MS

  下载: 全尺寸图片 幻灯片

  Compared with several previous reports, as shown in Table 2, the as -prepared sensors exhibited the low-est detection limit with good linear range and the fast-current response towards H₂O₂, which it can be attribut-ed to the special properties of Ag -TiO₂ MS. In the com-posite, the metallic oxide plays a significant as sub-strate material. Therefore, the good electron transfer efficiency of the Ag-TiO₂ MS may lead to the short response time.

  Table 2

  

  Table 2.  Comparison of H₂O₂ sensors reported previously with Ag-TiO₂ MS sensor

  下载: 导出CSV

  Sensor	cH2O2/(μmol·L-1)		Reference
  	Linear range	Detection limit
  Prussian blue-TiO2	1.5~90	1.5	[42]
  Thionin/DNA/nano-TiO2	50~22 300	50	[43]
  TiN	20~3 000	250	[44]
  AgNPs-TiO2 nanowires	100~60 000	1.7	[45]
  Cu2O/TiO2/sepiolite electrode	20~2 360	1.7	[46]
  Cu2O/TiO2 nanotubes array	500~80 00	90.5	[47]
  Pd0.7Au0.3/carbon nanotube	1~19 000	0.3	[48]
  Fe3O4/graphene oxide/pristine graphene	0.5~277	0.09	[49]
  Au@Ag nanorods	0~100	3.2	[50]
  Au-Ag/Co3O4 nanofibers	0.05~5 000	0.01	[51]
  CuCo2O4 hollow microspheres	10~8 900	0.75	[52]
  Graphene nanosheets@FeOOH	0.25~1 200	0.08	[53]
  AuNPs-NH2/Cu-metal-organic framework	5~850	1.2	[54]
  Co3N nanowire/Ti mesh	0.1~2 500	0.05	[55]
  Ag/Sn3O4/GCE	0.8~52 000	0.8	[56]
  Pt/C-CeO2	10~30 000	2	[57]
  BiVO4/TiO2	5~200	5	[58]
  Ag-TiO2 MS	0.1~102	0.04	This work

  2.4   Selectivity, reproducibility, repeatability and storage stability of Ag-TiO₂ MS electrodes

  Fig. 15a is the long-term stability chart of Ag-TiO₂ MS electrode. The electrodes were stored at room temperature and exposed to air before use. After one month, the current response of the sensor to H₂O₂ decreased by 17.9%. By analysis of SEM, XRD, TEM and XPS (Fig. S3, S4, S5, S6), it can be seen that the catalytic performance of the Ag-TiO₂ MS electrode was decreased due to the weakening of crystalline surface strength and the destruction of the morphological struc-ture. Fig. 15b is the I-t curve of Ag-TiO₂ MS in 0.02 mol·L^-1 PBS (pH 7.0) for selective studies. 500 μmol· L^-1 H₂O₂, L-Glu, VC, urea and Lac were added successively. The results showed that the addition of H₂O₂ caused a significant current response, and further addition of interfering substances did not have an obvious reaction, indicating that Ag-TiO₂ MS has good selectivi-ty and sensitivity for H₂O₂.

  Figure 15

  

  Figure 15.  (a) Normalized response of Ag-TiO₂ MS toward 100 μmol·L^-1 H₂O₂ in PBS (pH 7.0) at -0.3 V in 30 days; (b) I-t curve of Ag-TiO₂ MS in 0.02 mol·L^-1 PBS (pH 7.0) for selective studies with adding 500 μmol·L^-1 H₂O₂, L-Glu, VC, urea and Lac; (c) Reproducibility studies with adding 500 μmol·L^-1 H₂O₂; (d) Repeatability studies with adding 500 μmol·L^-1 H₂O₂

  下载: 全尺寸图片 幻灯片

  Ag-TiO₂ MS electrodes were prepared in parallel to evaluate the electrocatalytic activity sensor reproduc-ibility for H₂O₂. After calculation, 5 electrodes were subsequently prepared under the same conditions, and the relative standard deviation of current response was only 2.0% (Fig. 15c). The same electrode was repeated-ly measured for 5 times, and the relative standard devi-ation of response was 3.7% (Fig. 15d).

  3.   Conclusions

  In summary, Ag-TiO₂ MS were successfully synthesized by one-pot method. Serving as a H₂ O₂ detection electrode, Ag-TiO₂ MS presents excellent nonenzymatic H₂O₂ sensing performance in terms of wide linear range and reliable stability. It is believed that the Ag-TiO₂ MS presents broad applications in the development of nonenzymatic H₂O₂ electrochemical sensors and the immobilization of finely dispersed silver on TiO₂ microsphere paves an effective way to construct H₂O₂ detection electrode. The Ag-TiO₂ MS material can be further modified in subsequent research, such as high-temperature renitriding into titanium nitride to enhance its stability for better application in electrochemical sensors.

  
  Acknowledgements: This work was supported by the Natural Science Foundation of Zhejiang Province, China (Grant No.LY17B050006) and the National Key Research and Develop-ment Plan (Grant No.2017YFB0307503). Supporting information is available at http://www.wjhxxb.cn
  
• 1. [1]

     Chen W, Cai S, Ren Q Q, Wen W, Zhao Y D. Analyst, 2012, 137: 49-58 doi: 10.1039/C1AN15738H

  2. [2]

     Rodrigo A B S, Rodrigo H O M, Eduardo M R, Rodrigo A A M. Food Chem. , 2012, 133(1): 200-204 doi: 10.1016/j.foodchem.2012.01.003

  3. [3]

     Sekar N K, Gumpu M B, Ramachandra B L, Nesakumar N, Sankar P, Babu K J, Krishnan U M, Rayappan J B B. J. Nanosci. Nanotechnol. , 2018, 18(6): 4371-4379 doi: 10.1166/jnn.2018.15259

  4. [4]

     Wu T T, Englehardt J D. Environ. Sci. Technol. , 2012, 46(4): 2291-2298 doi: 10.1021/es204250k

  5. [5]

     Anastasia S I, Anna D M, Sergey V A, Konstantin A S. Food Chem. , 2019, 283: 431-436 doi: 10.1016/j.foodchem.2019.01.051

  6. [6]

     Li J M, Shah A M. J. Am. Soc. Nephrol. , 2003, 14: 221-226 doi: 10.1097/01.ASN.0000077406.67663.E7

  7. [7]

     Huang B K, Sikes H D. Redox Biol. , 2014, 2: 955-962 doi: 10.1016/j.redox.2014.08.001

  8. [8]

     Li M, Gao H F, Wang X F, Wang Y F, Qi H L, Zhang C X. Microchim. Acta, 2017, 184(2): 603-610 doi: 10.1007/s00604-016-2051-9

  9. [9]

     Nitinaivinij K, Parnklang T, Thammacharoen C, Ekgasit S, Wongravee K. Anal. Methods, 2014, 6(24): 9816-9824 doi: 10.1039/C4AY02339K

  10. [10]

      Gimeno P, Bousquet C, Lassu N, Maggio A F, Lempereur L. J. Pharm. Biomed. Anal. , 2015, 107: 386-393 doi: 10.1016/j.jpba.2015.01.018

  11. [11]

      Kawde A N, Aziz M, Baig N, Temerk Y. J. Electroanal. Chem. , 2015, 740: 68-74 doi: 10.1016/j.jelechem.2015.01.005

  12. [12]

      Ensafi A A, Abarghoui M M, Rezaei B. Sens. Actuators B, 2014, 196: 398-405 doi: 10.1016/j.snb.2014.02.028

  13. [13]

      Updike S J, Hicks G P. Nature, 1967, 214(5092): 986 doi: 10.1038/214986a0

  14. [14]

      Santos A, Macías G, Ferré-Borrull J, Pallares J, Marsal L F. ACS Appl. Mater. Interfaces, 2012, 4(7): 3584-3588 doi: 10.1021/am300648j

  15. [15]

      Amor-Gutiérrez O, Rama E C, Costa-García A, Fernandez-Abedul M T. Biosens. Bioelectron. , 2017, 93: 40-45 doi: 10.1016/j.bios.2016.11.008

  16. [16]

      吕雪义, 刘俊果, 朱艳艳. 无机化学学报, 2020, 36(9): 1675-1682 https://www.cnki.com.cn/Article/CJFDTOTAL-DLXB201502001.htmLÜ X Y, LIU J G, ZHU Y Y. Chinese J. Inorg. Chem. , 2020, 36(9): 1675-1682 https://www.cnki.com.cn/Article/CJFDTOTAL-DLXB201502001.htm

  17. [17]

      Zaibudeen A W, Philip J. Sens. Actuators B, 2018, 255: 720-728 doi: 10.1016/j.snb.2017.08.065

  18. [18]

      Liu F Y, Peng W, Zhang Q Q, Wang Z Y, Liu Y Y, Zheng Z K, Qin X Y, Zhang X Y, Dai Y, Li L, Huang B B. Anal. Bioanal. Chem. , 2018, 410: 7663-7670 doi: 10.1007/s00216-018-1380-4

  19. [19]

      Baghayeri M, Alinezhad H, Tarahomi M, Fayazi M, Ghanei-Motlagh M, Maleki B. Appl. Surf. Sci. , 2019, 478: 87-93 doi: 10.1016/j.apsusc.2019.01.201

  20. [20]

      Gholami M, Koivisto B. Appl. Surf. Sci. , 2019, 467: 112-118

  21. [21]

      褚有群, 王玲巧, 黄章烤, 徐颖华, 赵峰鸣. 无机化学学报, 2020, 36(3): 555-556 https://www.cnki.com.cn/Article/CJFDTOTAL-DLXB201502001.htmCHU Y Q, WANG L Q, HUANG Z K, XU Y H, ZHAO F M. Chinese J. Inorg. Chem. , 2020, 36(3): 555-556 https://www.cnki.com.cn/Article/CJFDTOTAL-DLXB201502001.htm

  22. [22]

      Qin X Y, Lu W B, Luo Y L, Lu W B, Chang G H, Asiri A M, Al-Youbi A O, Sun X P. Electrochim. Acta, 2012, 74: 275-279 doi: 10.1016/j.electacta.2012.04.094

  23. [23]

      Alrub A M. Surf. Sci. , 2019, 681: 70-75 doi: 10.1016/j.susc.2018.11.005

  24. [24]

      Li C H, Jamison A C, Rittikulsittichai S, Lee T C, Lee T R. ACS Appl. Mater. Interfaces, 2014, 6: 19943-19950 doi: 10.1021/am505424w

  25. [25]

      Wang L, Yang W T, Zhu W, Guan X G, Xie Z G, Sun Z M. Inorg. Chem. , 2014, 53: 11584-11588 doi: 10.1021/ic501657p

  26. [26]

      Zhai A X, Cai X H, Du B. Trans. Nonferrous Met. Soc. China, 2014, 24(5): 1452-1457 doi: 10.1016/S1003-6326(14)63212-X

  27. [27]

      Singh J, Tripathi N, Mohapatra S. Nano-Struct. Nano-Objects, 2019, 18: 92-99

  28. [28]

      Li B E, Hao J Z, Min Y, Xin S G, Guo L T, He F, Liang C Y, Wang H S, Li H P. Mater. Sci. Eng. C, 2015, 51: 80-86 doi: 10.1016/j.msec.2015.02.036

  29. [29]

      Sahyar B Y, Kaplan M, Ozsoz M, Celik E, Otles S. Bioelectrochemistry, 2019, 130: 107327 doi: 10.1016/j.bioelechem.2019.107327

  30. [30]

      Li W, He Y, Xu J, Wang W Y, Zhu Z T, Liu H. J. Alloys Compd. , 2019, 803: 332-340 doi: 10.1016/j.jallcom.2019.06.257

  31. [31]

      Xia L, Yang Y, Cao Y, Liu B, Li X X, Chen X Y, Song H, Zhang X M, Gao B, Fu J J. Surf. Coat. Technol. , 2019, 365: 237-241 doi: 10.1016/j.surfcoat.2018.06.033

  32. [32]

      Zheng L X, Dong Y C, Bian H D, Lee C, Lu J, Li Y Y. Electrochim. Acta, 2016, 203: 257-264 doi: 10.1016/j.electacta.2016.04.049

  33. [33]

      Arunachalam M, Yun G, Ahn K S, Seo W S, Jung D S, Kang S H. Int. J. Hydrogen Energy, 2018, 43(34): 16458-16467 doi: 10.1016/j.ijhydene.2018.07.043

  34. [34]

      Zhao F M, Yan F, Qian Y, Chu Y Q, Ma C A. Int. J. Electrochem. Sci. , 2012, 7(12): 12931-12940

  35. [35]

      Chang B Y S, Huang N M, An'amt M N, Marlinda A R, Norazriena Y, Muhamad M R, Harrison I, Lim H N, Chia C H. Int. J. Nanomed. , 2012, 7: 3379-3387

  36. [36]

      Ding S J, Huang F Q, Mou X L, Wu J J, Lu X J. J. Mater. Chem. , 2011, 21(13): 4888-4892 doi: 10.1039/c0jm03628e

  37. [37]

      Wang S L, Qian H H, Hu Y, Dai W, Zhong Y J, Chen J F, Hu X. Dalton Trans. , 2013, 42(4): 1122-1128 doi: 10.1039/C2DT32040A

  38. [38]

      Zhao S D, Chen J R, Liu Y F, Jiang Y, Jiang C G, Yin Z L, Xiao Y G, Cao S S. Chem. Eng. J. , 2019, 367: 249-259 doi: 10.1016/j.cej.2019.02.123

  39. [39]

      Zhao F M, Zhou M L, Wang L Q. J. Electroanal. Chem. , 2019, 833: 205-212 doi: 10.1016/j.jelechem.2018.11.050

  40. [40]

      Bard A J, Faulkner L R. Electrochemical Methods Fundamentals and Applications. New York: John Wiley & Sons Inc, 2001.

  41. [41]

      Lim S P, Shahid M M, Rameshkumar P, Huang N M, Che L M. J. Mater. Sci. -Mater. Electron. , 2020, 31(8): 6017-6026 doi: 10.1007/s10854-020-03153-9

  42. [42]

      Chu Z Y, Shi L, Liu Y, Jin W Q, Xu N P. Biosens. Bioelectron. , 2013, 47: 329-334 doi: 10.1016/j.bios.2013.03.023

  43. [43]

      Lo P H, Ashok Kumar S, Chen S M. Colloids Surf. B, 2008, 66: 266-273 doi: 10.1016/j.colsurfb.2008.07.003

  44. [44]

      Xie Z, Liu X X, Wang W P, Liu C, Li Z C, Zhang Z J. Nanoscale Res. Lett. , 2014, 9: 105-109 doi: 10.1186/1556-276X-9-105

  45. [45]

      Qin X Y, Lu W B, Luo Y L, Chang G H, Asiri A M, Al-Youbi A O, Sun X P. Electrochim. Acta, 2012, 74: 275-279 doi: 10.1016/j.electacta.2012.04.094

  46. [46]

      Yan P, Zhong L, Wen F X, Tang A D. J. Electroanal. Chem. , 2018, 827: 1-9 doi: 10.1016/j.jelechem.2018.08.030

  47. [47]

      Wen X, Long M, Tang A D. J. Electroanal. Chem. , 2017, 785: 33-39 doi: 10.1016/j.jelechem.2016.12.018

  48. [48]

      Alal O, Caglar A, Kivrak H, Sahin O. Electroanalysis, 2019, 31(9): 1646-1655 doi: 10.1002/elan.201900140

  49. [49]

      Cai L L, Hou B J, Shang Y Y, Xu L, Zhou B, Jiang X N, Jiang X Q. Chem. Phys. Lett. , 2019, 736: 136797 doi: 10.1016/j.cplett.2019.136797

  50. [50]

      Chen Q G, Lin T R, Huang J L, Chen Y, Guo L Q, Fu F F. Anal. Methods, 2018, 10(5): 504-507 doi: 10.1039/C7AY02819A

  51. [51]

      Zhang Y T, Deng D M, Zhu X L, Liu S, Zhu Y, Han L, Luo L Q. Anal. Chim. Acta, 2018, 1042: 20-28 doi: 10.1016/j.aca.2018.07.065

  52. [52]

      Cheng D, Wang T, Zhang G X, Wu H M, Mei H. J. Alloys Compd. , 2020, 819: 153014 doi: 10.1016/j.jallcom.2019.153014

  53. [53]

      Chen X R, Gao J, Zhao G Q, Wu C. Sens. Actuators B, 2020, 313: 128038 doi: 10.1016/j.snb.2020.128038

  54. [54]

      Dang W J, Sun Y M, Jiao H, Xu L, Lin M. J. Electroanal. Chem. , 2020, 856: 113592 doi: 10.1016/j.jelechem.2019.113592

  55. [55]

      Xie F Y, Cao X Q, Qu F L, Asiri A M, Sun X P. Sens. Actuators B, 2018, 255: 1254-1261 doi: 10.1016/j.snb.2017.08.098

  56. [56]

      Tian L L, Xia K D, Hu W P, Zhong X H, Chen Y L, Yang C, He G G, Su Y Y, Li L. Electrochim. Acta, 2017, 231: 190-199 doi: 10.1016/j.electacta.2017.02.052

  57. [57]

      Uzunoglu A, Ipekci H H. J. Electroanal. Chem. , 2019, 848: 113302 doi: 10.1016/j.jelechem.2019.113302

  58. [58]

      Derbali M, Othmani A, Kouass S, Touati F, Dhaouadi H. Mater. Res. Bull. , 2020, 125: 110771 doi: 10.1016/j.materresbull.2020.110771

• 

  Figure 1  Schematic illustration of one-pot solvothermal synthesis of finely-dispersed Ag-TiO₂MS

  下载: 全尺寸图片 幻灯片
  

  Figure 2  SEM images of TiO₂ MS (a) and Ag-TiO₂ MS (b)

  下载: 全尺寸图片 幻灯片
  

  Figure 3  XPS spectra of Ag-TiO₂ MS

  下载: 全尺寸图片 幻灯片
  

  Figure 4  XRD patterns of TiO₂ MS and Ag-TiO₂ MS

  下载: 全尺寸图片 幻灯片
  

  Figure 5  TEM images of TiO₂ MS (a~c) and Ag-TiO₂ MS (d~f)

  Inset shows the magnified image with clear lattice fringes

  下载: 全尺寸图片 幻灯片
  

  Figure 6  EDX spectra of (a) TiO₂ MS and (b) Ag-TiO₂ MS

  下载: 全尺寸图片 幻灯片
  

  Figure 7  HAADF-STEM images and the corresponding EDX mappings of (a) TiO₂ MS and (b) Ag-TiO₂ MS

  下载: 全尺寸图片 幻灯片
  

  Figure 8  CVs of TiO₂ MS (black curves) and Ag-TiO₂ MS (red curves) electrodes in 0.02 mol·L^-1 PBS (pH 7.0) with (solid curves) or without (dotted curves) 1 000 μmol·L^-1 H₂O₂ at 20 mV·s^-1

  下载: 全尺寸图片 幻灯片
  

  Figure 9  CVs of TiO₂/MS (a) and Ag-TiO₂/MS (b) electrodes at 20 mV·s^-1 with adding different concentrations of H₂O₂

  下载: 全尺寸图片 幻灯片
  

  Figure 10  CVs of Ag-TiO₂ MS electrode in the presence of 2 000 μmol·L^-1 H₂O₂ at different the scan rates

  下载: 全尺寸图片 幻灯片
  

  Figure 11  (a) Relationship of I_p and v^1/2 and (b) relationship of ln I_p and (E_p-E_1/2) for Ag-TiO₂ MS electrode

  下载: 全尺寸图片 幻灯片
  

  Figure 12  Nyquist plots of Ag-TiO₂ MS, TiO₂ MS and GCE electrodes

  下载: 全尺寸图片 幻灯片
  

  Figure 13  I-t curve of Ag-TiO₂ MS in 0.02 mol·L^-1 PBS (pH 7.0) with the successive adding H₂O₂

  下载: 全尺寸图片 幻灯片
  

  Figure 14  I-c_H2O2 linear fitting results for Ag-TiO₂ MS

  下载: 全尺寸图片 幻灯片
  

  Figure 15  (a) Normalized response of Ag-TiO₂ MS toward 100 μmol·L^-1 H₂O₂ in PBS (pH 7.0) at -0.3 V in 30 days; (b) I-t curve of Ag-TiO₂ MS in 0.02 mol·L^-1 PBS (pH 7.0) for selective studies with adding 500 μmol·L^-1 H₂O₂, L-Glu, VC, urea and Lac; (c) Reproducibility studies with adding 500 μmol·L^-1 H₂O₂; (d) Repeatability studies with adding 500 μmol·L^-1 H₂O₂

  下载: 全尺寸图片 幻灯片

  Table 1.  Parameters obtained from the fitting curves of EIS in Fig. 12

  Sample	Rs/Ω	Rct/Ω	Rp/kΩ
  Ag-TiO2 MS	126.9	613	28.34
  TiO2 MS	133.9	726	291.5
  GCE	135.4	675	138.9

  下载: 导出CSV

  Table 2.  Comparison of H₂O₂ sensors reported previously with Ag-TiO₂ MS sensor

  Sensor	cH2O2/(μmol·L-1)		Reference
  	Linear range	Detection limit
  Prussian blue-TiO2	1.5~90	1.5	[42]
  Thionin/DNA/nano-TiO2	50~22 300	50	[43]
  TiN	20~3 000	250	[44]
  AgNPs-TiO2 nanowires	100~60 000	1.7	[45]
  Cu2O/TiO2/sepiolite electrode	20~2 360	1.7	[46]
  Cu2O/TiO2 nanotubes array	500~80 00	90.5	[47]
  Pd0.7Au0.3/carbon nanotube	1~19 000	0.3	[48]
  Fe3O4/graphene oxide/pristine graphene	0.5~277	0.09	[49]
  Au@Ag nanorods	0~100	3.2	[50]
  Au-Ag/Co3O4 nanofibers	0.05~5 000	0.01	[51]
  CuCo2O4 hollow microspheres	10~8 900	0.75	[52]
  Graphene nanosheets@FeOOH	0.25~1 200	0.08	[53]
  AuNPs-NH2/Cu-metal-organic framework	5~850	1.2	[54]
  Co3N nanowire/Ti mesh	0.1~2 500	0.05	[55]
  Ag/Sn3O4/GCE	0.8~52 000	0.8	[56]
  Pt/C-CeO2	10~30 000	2	[57]
  BiVO4/TiO2	5~200	5	[58]
  Ag-TiO2 MS	0.1~102	0.04	This work

  下载: 导出CSV
•