Cs₃Bi₂Br₉/g-C₃N₄ Direct Z-Scheme Heterojunction for Enhanced Photocatalytic Reduction of CO₂ to CO

Abstract

Lead-free halide perovskite derivative Cs 3 Bi 2 Br 9 has recently been found to possess optoelectronic properties suitable for photocatalytic CO 2 reduction reactions to CO. However, further work needs to be performed to boost charge separation for improving the overall efficiency of the photocatalyst. This report demonstrates the synthesis of a hybrid inorganic/organic heterojunction between Cs 3 Bi 2 Br 9 and g-C 3 N 4 at different ratios, achieved by growing Cs 3 Bi 2 Br 9 crystals on the surface of g-C 3 N 4 using a straightforward antisolvent crystallization method. The synthesized powders showed enhanced gas-phase photocatalytic CO 2 reduction in the absence of hole scavengers of 14.22 (±1.24) μmol CO g −1 h −1 with 40 wt % Cs 3 Bi 2 Br 9 compared with 1.89 (±0.72) and 5.58 (±0.14) μmol CO g −1 h −1 for pure g-C 3 N 4 and Cs 3 Bi 2 Br 9 , respectively. Photoelectrochemical measurements also showed enhanced photocurrent in the 40 wt % Cs 3 Bi 2 Br 9 composite, demonstrating enhanced charge separation. In addition, stability tests demonstrated structural stability upon the formation of a heterojunction, even after 15 h of illumination. Band structure alignment and selective metal deposition studies indicated the formation of a direct Z-scheme heterojunction between the two semiconductors, which boosted charge separation. These findings support the potential of hybrid organic/inorganic g-C 3 N 4 /Cs 3 Bi 2 Br 9 Z-scheme photocatalyst for enhanced CO 2 photocatalytic activity and improved stability.

A g-C3N4/rGO/Cs3Bi2Br9 mediated Z-scheme heterojunction for enhanced photocatalytic CO2 reduction

“…5c and d), the crystals were hexagonal in shape with a lattice spacing of approximately 4.2 Å corresponding to the (102) plane and similar to previously reported values in the literature. 15,47 In contrast, TEM micrographs of BGCN (Fig. S3†) and 2EGCN (Fig.…”

“…45 The displayed peaks proved the crystalline nature of the semiconductor with peaks at 13.1, 16.1, 22.4, 27.2, 27.4, 31.9, 35.8, 39.4, and 45.5° (2 θ ) corresponding to the planes (100), (101), (102), (003), (201), (202), (212), and (220), respectively. 15,46 The addition of BGCN, EGCN, BGCN/rGO, and EGCN/rGO did not largely affect the crystalline structure of CBB. However, taking a closer look at the region between 26 and 28.5° (2 θ ) where the (003) and (201) peaks of CBB coincide with the (002) peak of GCN, a deconvolution showed that the ratio of the CBB peaks had changed suggesting a suppressed preferential growth in the presence of a secondary material during the synthesis (Fig.…”

“…11,12 This arrangement gives CBB its unique perovskite-like structure and optoelectronic properties and offers a non-toxic and stable alternative to lead-based perovskites. 13–15…”

“…The enhanced production was due to the formation of a direct Z-scheme configuration where photogenerated charges in the semiconductors were spatially separated, keeping CBB as the reduction site and GCN as the oxidation site. 15 …”

Perovskite Paradigm Shift: A Green Revolution with Lead-Free Alternatives in Photocatalytic CO2 Reduction

“…Inspired by biomimetic artificial photosynthesis, the concept of Z-scheme photocatalytic systems was first proposed by Bard in 1979 . Despite having the same band structure configuration as a Type-II heterojunction, the Z-scheme heterojunction has a distinctly different charge-transfer mechanism, following an exclusive Z-shape charge carrier pathway (Figure d) to promote electron–hole pair separation. ,,, There are different types of Z-scheme heterojunctions, and their detailed respective working principles are available from various literature reports. ,, Notably, the direct Z-scheme heterojunction has been extensively investigated in photocatalysis, especially in CO 2 photoreduction of high energy demand, owing to the well-preserved redox ability of each constituent in the composite in addition to the spatially separation of reduction and oxidation sites. ,,, Typically, the LFHPs are utilized as the reduction site by hybridization with a semiconductor with lower lying CB and VB. As a prevalent Bi-based oxidation photocatalyst, i.e., Bi 2 WO 6 , has been investigated for Z-scheme heterostructure formation with LFHPs such as Cs 3 Bi 2 Br 9 , Cs 3 Bi 2 I 9 , and Cs 2 AgBiBr 6 , in which all these Bi-based Z-scheme heterojunction architectures were shown to exhibit better photocatalytic CO 2 reduction performance.…”