Similar to the development tendency of CuSbS
2, it also needs to adopt efficient strategies to improve the charge separation efficiency of CuPbSbS
3, aiming to enhance the photocatalytic performance. Recently, our group has successfully designed the BiTiO
3/CuPbSbS
3 heterostructure photocatalyst and realized the efficient piezo-photocatalytic degradation of RhB, which not only greatly enhanced the charge separation of bare CuPbSbS
3 but successfully broaden the photocatalytic application of CuPbSbS
3 from PHE to PD [
144]. Concretely, the ferroelectric materials, with the structure feature of non-centrally symmetric, possess the unique property of spontaneous polarization. At the same time, the corresponding polarization direction can be reversed by the mechanical force or external electric field [
145-
152]. Typically, the BiTiO
3 with perovskite structure has achieved the most promising research progress in the exploration of ferroelectric materials due to its unique feature of natural piezoelectric and pyroelectric [
153-
157]. By tuning the mechanical force or temperature at the junction interface of the BiTiO
3-based heterostructure, the synergistic effect between BiTiO
3 and semiconductor photocatalysts can realize the enhancement of charges optoelectronic process. Specifically, the spontaneous polarizations of BiTiO
3 can generate an internal built-in electric field and thus provide an effective route for the construction with semiconductor photocatalyst with piezo/pyro-photoelectron effect, which has been demonstrated by the representative heterostructures of BaTiO
3/TiO
2 [
158], BaTiO
3/MoO
3 [
159], BaTiO
3/Ag
2O [
160], and BaTiO
3/C [
155]. Taking the consideration of the unique semiconductor properties of CuPbSbS
3, it is speculated that the heterostructure of BaTiO
3/CuPbSbS
3 can also achieve a promising photocatalytic performance. As shown in
Fig. 6a, on the basis of the BDCA-synthesized CuPbSbS
3, the BiTiO
3/CuPbSbS
3 heterostructure photocatalyst was further obtained through a conventional hydrothermal process. Based on the characterization of SEM and TEM, the CuPbSbS
3 nanoflakes tightly attach on the surface of BiTiO
3 nanorods, which is visually exhibited in the dashed ellipse
Fig. 6a. In the heterostructure of BiTiO
3/CuPbSbS
3, the synergistic effect between the piezoelectricity feature of BiTiO
3 and semiconductor properties of CuPbSbS
3 can greatly improve the degradation-participating photogenerated holes density. Specifically, as shown in
Figs. 6b and
c, in the heterostructure of BiTiO
3/CuPbSbS
3, the BiTiO
3 can generate a piezoelectric field under the ultrasound, which is tending to perpendicular to the BiTiO
3 direction. Therefore, the photogenerated electrons and holes in CuPbSbS
3 can be effectively separated into opposite directions. Specifically, during the PD process, the reaction between the free charges and environment media can generate four major reactive oxygen species, namely hydroxyl radicals (
•OH), hydrogen peroxide (H
2O
2), superoxide anion radical (
•O
2−), and singlet oxygen (
1O
2) [
161,
162]. The corresponding PD reactions can be concluded as:
•O
2− + e
− + 2H
+ → H
2O
2; H
2O
2 + e
− → OH
− +
•OH. Among them, the
1O
2 possesses extremely short lifetime, which is the excited state of O
2. Therefore, the
1O
2 is generally absent in any PD reaction due to the easy quench [
163]. In this case, the high density photogenerated holes, along with the
•OH and
•O
2‒ directly participate in RhB degradation. Finally, under the further simulated solar light irradiation, the piezo-photocatalytic degradation rate of RhB by BiTiO
3/CuPbSbS
3 heterostructure photocatalyst reached nearly 90.56% in only 0.5 h, along with a promising
k value of 9.33 × 10
−2 min
−1.