In situ synthesis of p-n (BiO)₄CO₃(OH)₂/Bi₂O₂CO₃ internal polarized heterojunction for improved visible light photocatalytic performance

Abstract

P-n type (BiO) 4 CO 3 (OH) 2 /Bi 2 O 2 CO 3 internal polarized heterojunction was prepared via an in situ photosynthesis method and characterized using x-ray diffraction (XRD), scanning electron microscopy (SEM),UV-vis diffuse reflectance spectra (UV-vis DRS) and surface photovoltage (SPV).The results indicate that phase transition process of β-Bi 2 O 3 →Bi 2 O 2 CO 3 →(BiO) 4 CO 3 (OH) 2 can be regulated by controlling the photosynthesis time. With increasing of reaction time, CO 3 2− in Bi 2 O 2 CO 3 structures is replaced by polar OH − , and the two-dimensional (2D) heterostructure of (BiO) 4 CO 3 (OH) 2 /Bi 2 O 2 CO 3 is fabricated. The photocatalytic activities of the junction were investigated by degradation of tetrachlorophenol (4-CP) under the visible light illumination. The enhanced photocatalytic activity of (BiO) 4 CO 3 (OH) 2 /Bi 2 O 2 CO 3 has been attributed to the synergetic effect between intrinsic internal electric field (IEF) and charge separation for a photocatalyst with p-n heterojunction structures. Moreover, h + and ·OH are proved working as the main active species for the degradation performence. It shows great potential in application for wastewater treatment.

Structural, Optical and Photocatalytic Activity of α-Bi2O3/Bi2O2CO3/(BiO)4CO3(OH)2 Ternary Multi-heterojunction Nanoflakes Synthesized via Submerged DC Electrical Discharge in Urea Solution

“…The tetragonal β-Bi 2 O 3 and body centered cubic γ-Bi 2 O 3 are metastable phases, which formed at high temperature and can be stabilize down to room temperature or transform to α-Bi 2 O 3 at high cooling rates 22,23 . In addition, thermal transformation of α-Bi 2 O 3 and β-Bi 2 O 3 to (BiO) 2 CO 3 and (BiO) 4 CO 3 (OH) 2 were reported previously 24,25 . Bismuth oxides including α-Bi 2 O 3 , β-Bi 2 O 3 , γ-Bi 2 O 3 and δ-Bi 2 O 3 as well as (BiO) 2 CO 3 and (BiO) 4 CO 3 (OH) 2 show photocatalytic activity 19,22,25−28 .…”

“…Hence, the e ciency should not decline noticeably with each cycle. The degradation e ciency of the recovered α- and Bi 2 O 2 CO 3 will move upward or downward to lineup the Fermi level of the multi-heterojunction structure 25 . Under visible light irradiation, the photogenerated electrons on the conduction band of component with less negative edge potential will transfer to upper CB, while the holes in the valence band with more positive edge potential are likely to transfer opposite position 70 .…”

“…IEF is a factor in improving photocatalytic activity by means of simplifying transformation and separation of the photo generated carriers. The alternative layer structure of (Bi 2 O 2 ) 2+ uorite ake and (MO 6 ) 2− perovskite layers in bismuth-based binary metal oxides form IEF that enhanced separation e ciency of photo generated charge carriers 25,36 .Bismuth subcarbonate with (BiO) 2 CO 3 chemical formula is a n-type photocatalyst and has shown photocatalytic performance in decomposition of pollutants in wastewater and polluted air 14 , 37,38 . The electronic structure of (BiO) 2 CO 3 is comprised of hybridized O 2p and Bi 6p orbitals in conduction band and O 2p, Bi 6p and C 2p orbitals in valence band 14 .…”

“…The electronic structure of (BiO) 2 CO 3 is comprised of hybridized O 2p and Bi 6p orbitals in conduction band and O 2p, Bi 6p and C 2p orbitals in valence band 14 . The structure of (BiO) 2 CO 3 is composed of (Bi 2 O 2 ) 2+ slabs that are intertwined by means of CO 3 2− layers, which lead to IEF and improve photocatalytic performance 25,39 . However, the photocatalytic application of (BiO) 2 CO 3 under the solar spectrum is limited due to the wider band gap between 2.8 eV and 3.5 eV and lower charge separation e ciency 25,39,40 preparation by one-pot in-situ growth were reported elsewhere 25,39,45−48 .…”

“…The structure of (BiO) 2 CO 3 is composed of (Bi 2 O 2 ) 2+ slabs that are intertwined by means of CO 3 2− layers, which lead to IEF and improve photocatalytic performance 25,39 . However, the photocatalytic application of (BiO) 2 CO 3 under the solar spectrum is limited due to the wider band gap between 2.8 eV and 3.5 eV and lower charge separation e ciency 25,39,40 preparation by one-pot in-situ growth were reported elsewhere 25,39,45−48 . Compared with several conventional techniques for nanostructures synthesis, DC electrical arc discharge in liquid provides a straightforward, exible and cost-effective method for mass production nanomaterials without environmental footprints.…”