Selective Design of Mesoporous Bi2Se3 Films with Orthorhombic and Rhombohedral Crystals

Abstract

Materials with the same chemical composition can exhibit distinct properties depending on their crystal phases. Here, the synthesis of two types of mesoporous Bi₂Se₃ films at different reduction potentials is reported and their application in electrochemical glucose sensing. Mesoporous Bi₂Se₃ is synthesized by incorporating block copolymer micelle assemblies into the deposition solution and applying a reduction potential. To characterize the crystal phases accurately, Bi₂Se₃ films are heat-treated at 200 °C for 1 h in a nitrogen atmosphere. The results reveal that the Bi₂Se₃ films synthesized under different conditions exhibit clearly distinct phases: rhombohedral (R-Bi₂Se₃) and orthorhombic (O-Bi₂Se₃). The R-Bi₂Se₃-8 nm, featuring 8 nm pores and synthesized at a more negative reduction potential, outperforms its nonporous counterpart, achieving a glucose sensing sensitivity of 0.143 µA cm^-2 µM^-1 and a detection limit of 6.2 µM at pH 7.4 in 0.1 M phosphate-buffered saline solution. In contrast, the O-Bi₂Se₃, prepared at a relatively positive potential, exhibits no glucose-sensing activity. The inactivity of O-Bi₂Se₃ for glucose oxidation is likely due to the energetically unfavorable intermediates, as predicted by density functional theory calculations. These findings underscore the critical role of crystal phase control in porous nanomaterials and pave the way for developing innovative porous systems.

Keywords: bismuth selenides; crystal phase; electrochemical glucose sensing; mesoporous materials; soft templating method.

Figure 1

a) Schematic illustration of the electrodeposition of mesoporous Bi₂Se₃ films and the difference in crystal phase depending on the deposition conditions. b–d,f–h) Top‐view SEM images of (b–d) R‐Bi₂Se₃ films synthesized at −0.06 V and (f–h) O‐Bi₂Se₃ films synthesized at 0.00 V. (b,f) R‐Bi₂Se₃‐non and O‐Bi₂Se₃‐non prepared in the absence of polymer. c,g) R‐Bi₂Se₃‐8 nm and O‐Bi₂Se₃‐8 nm synthesized using PS₅₀₀₀‐b‐PEO₂₅₀₀. d,h) R‐Bi₂Se₃‐12 nm and O‐Bi₂Se₃‐12 nm synthesized using PS₉₀₀₀‐b‐PEO₃₅₀₀. e,i) Cross‐sectional SEM images of e) R‐Bi₂Se₃‐8 nm and i) O‐Bi₂Se₃‐8nm.

Figure 2

a,b) Schematic illustration of the atomic arrangement in (a) rhombohedral Bi₂Se₃ and (b) orthorhombic Bi₂Se₃. c) XRD patterns of R‐Bi₂Se₃‐8 nm and O‐Bi₂Se₃‐8 nm films deposited on ITO glass.

Figure 3

a,d) XRD patterns of (a) R‐Bi₂Se₃ and (d) O‐Bi₂Se₃ films annealed at 200 °C for 1 h under nitrogen gas, with a heating rate of 1 °C min⁻¹. b,e) HRTEM images and c,f) corresponding SAED patterns of the annealed b,c) R‐Bi₂Se₃ and e,f) O‐Bi₂Se₃ films, respectively.

Figure 4

a) Schematic illustration of the electrochemical glucose detection experiment using mesoporous Bi₂Se₃ films. b) ECSA analysis of Bi₂Se₃ films with 8 nm pores, 12 nm pores, and nonporous structures in different crystal phases. c) Current response of R‐Bi₂Se₃ films during continuous titration of glucose solution in 0.1 M PBS (pH 7.4) at a constant potential of 0.1 V. d) Current density plot as a function of glucose concentration, demonstrating the sensing performance.

Figure 5

a–d) Optimized D‐glucose adsorption configurations shown from the side and top views, along with their corresponding ELF maps, on different Bi₂Se₃ surfaces: (a) O(100), (b) R(001)_Se1, (c) R(001)_Se2, and (d) R(001)_Bi. Green, purple, cyan, red, and white spheres represent Bi, Se, C, O, and H atoms, respectively. e) Schematic representation of the glucose electrooxidation reaction to gluconolactone (C₆H₁₀O₆). f) Calculated Gibbs free energy profiles for D‐glucose oxidation on O(100) (navy stepped line), R(001)_Se1 (blue stepped line), R(001)_Se2 (green stepped line), and R(001)_Bi (red stepped line) at 0.911 V versus reversible hydrogen electrode. The numbers (in eV) indicate the free energy levels relative to the initial state (^* + C₆H₁₂O₆). Side views and ELF plots of the *C₆H₁₁O₆ and *C₆H₁₀O₆ intermediates are also shown. White arrows in the ELF plots highlight the covalent bond formation between *C₆H₁₁O₆ and the surface.