Selective Design of Mesoporous Bi₂Se₃ Films with Orthorhombic and Rhombohedral Crystals

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.