Fabrication of Z-Scheme Heterojunction g-C₃N₄/Yb³⁺-Bi₅O₇I Photocatalysts with Enhanced Photocatalytic Performance under Visible Irradiation for Hg⁰ Removal

Abstract

Constructing a heterojunction and designing a band gap are effective methods to promote the efficiency of a photocatalyst and solar energy utilization. In this work, g-C 3 N 4 /Yb 3+ -Bi 5 O 7 I nanostructured photocatalysts were successfully prepared using a hydrothermal method with glycol as a solvent and a calcination method, and the performance of the photocatalysts containing different amounts of g-C 3 N 4 was studied. A series of characterizations confirmed the successful complexation of g-C 3 N 4 nanosheets with Bi 5 O 7 I, and Yb 3+ was successfully doped into the lattice of Bi 5 O 7 I. g-C 3 N 4 and Yb 3+ have a synergistic effect on expanding the photoresponse range of CYB(g-C 3 N 4 /Yb 3+ -Bi 5 O 7 I) composite photocatalysts. As expected, CYB samples have wonderful photocatalytic performance and stability in the removal of Hg 0 , among which CYB-20 has the highest removal efficiency, reaching 79%. Yb 3+ with upconversion characteristics can convert infrared light into visible light and form new energy levels in Bi 5 O 7 I. g-C 3 N 4 and Bi 5 O 7 I form a Z-scheme heterojunction to improve the photocatalytic performance of Bi 5 O 7 I. Besides, the electron and hole transmission paths and the catalytic mechanism of the photocatalysts are also proposed. This work offers a new approach to construct a photocatalyst system for pollutant emission control with a wide wavelength range of sunlight, which may be helpful to develop environmentally benign functional materials.

Advanced Two-Dimensional Heterojunction Photocatalysts of Stoichiometric and Non-Stoichiometric Bismuth Oxyhalides with Graphitic Carbon Nitride for Sustainable Energy and Environmental Applications

“…The results of scavenger studies and electron spin resonance spectroscopy confirmed that • O 2 − was the primary active species, which could only have been generated if the transfer mechanism was based on the Z-scheme heterojunction [107]. The visible light photocatalytic oxidation of hazardous gas-phase mercury (Hg 0 ) to divalent mercury (Hg 2+ ) for its easy removal was reported using g-C 3 N 4 /Bi 5 O 7 I nanosheets doped with Yb 3+ [108]. As observed from Figure 6a, the mercury removal efficiency of g-C 3 N 4 /Bi 5 O 7 I doped with Yb 3+ was 79.01% and 42.02%, respectively, under visible and near infrared light radiation, while the efficiency under near infrared light was just 13.3% without Yb 3+ doping.…”

“…(a) Mercury removal efficiency under visible and near infrared light excitation in the presence of g-C 3 N 4 /Yb 3+ -Bi 5 O 7 I (CYB) and g-C 3 N 4 -Bi 5 O 7 I (g-CNB) as photocatalysts, (b) schematic depicting the mechanism of charge transfer in the Z-scheme heterojunction g-C 3 N 4 /Yb 3+ -Bi 5 O 7 I during the photocatalytic oxidation of Hg 0 . Reprinted from Ref [108]. with permission from American Chemical Society.…”

Polymorphism and Visible-Light-Driven Photocatalysis of Doped Bi2O3:M (M = S, Se, and Re)

“…The parameter n defines the type of electron transfer in the semiconductor with n = 4 for indirect allowed and n = 1 for direct allowed electronic transitions. 127 Plotting (αhν) 2/n against hν provides the corresponding Tauc plot, and a linear regression line is used to determine the band-gap energy E g . The band-gap energy is usually determined from diffuse reflectance spectra; by applying the Kubelka−Munk function, 128,129 these data can be transformed into the corresponding absorption spectra: 130…”

“…The band-gap determination of the semiconductors was carried out via the approach of Tauc et al using optical absorbance data . After further development by Davis and Mott, the “Tauc model” is based on an energy-dependent absorption coefficient α expressed by the following formula: − where α is the absorption coefficient, h is the Planck constant, ν is the photon frequency, E g is the band-gap energy, and A is a proportionality constant. The parameter n defines the type of electron transfer in the semiconductor with n = 4 for indirect allowed and n = 1 for direct allowed electronic transitions .…”

“…After further development by Davis and Mott, the “Tauc model” is based on an energy-dependent absorption coefficient α expressed by the following formula: − where α is the absorption coefficient, h is the Planck constant, ν is the photon frequency, E g is the band-gap energy, and A is a proportionality constant. The parameter n defines the type of electron transfer in the semiconductor with n = 4 for indirect allowed and n = 1 for direct allowed electronic transitions . Plotting (α h ν) 2/ n against h ν provides the corresponding Tauc plot, and a linear regression line is used to determine the band-gap energy E g .…”