Synthesis of platelet-like BiVO4 using hyperbranched polyethyleneimine for the formation of heterojunctions with Bi2O3

Surface structures of nanoparticles (NPs) designed at the atomic level are vital to enhance the catalytic performance and stability of NPs. In this work, we report the engineering of plate-like and platelet-like BiVO4 NPs for the formation of heterojunctions with Bi2O3. The morphology and size of NPs were observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Raman spectroscopy, SAED and powder X-ray diffraction (XRD) were carried out to show the structural composition and they confirmed monoclinic phases for both BiVO4 and Bi2O3. BiVO4 NPs notoriously have low surface area and pore volume, thus HPEI was incorporated to improve these properties. Brunuer-Emmett-Teller (BET) technique was used to characterize the surface area (S-BET) of the photocatalysts and S-BET was increased by 88% after the addition of 0.15 mM HPEI during synthesis. Diffuse reflectance spectroscopy was used to elucidate the optical properties of NPs and a blueshift in the heterojunctions was observed due to the incorporation of Bi2O3. Tuning of {010} monoclinic BiVO4 was achieved after the addition of 0.5 M NaCl which resulted in plate-like morphologies showing improved optical and electronic properties. Uniform platelet-like BiVO4 NPs were synthesized successfully after the addition of 0.15 mM HPEI, and this also induced impaired dispersion and size reduction. The calculated band positions of BiVO4 and Bi2O3 in the heterojunctions were well positioned for carrier charge separation, which was confirmed by the flat band potentials that were 0.553, - 0.47, - 0.70 and - 0.77 V for Bi2O3, p-BiVO4, 0.15HPEI-0.5NaCl-BiVO4-Bi2O3 and 0.5NaCl-BiVO4.