Topotactic conversion of BiOCOOH to coherent Bi2MoO6/Bi2O2CO3 heterojunctions with atomic-level interfacial integration toward synergistic photocatalytic redox catalysis

In-situ construction of a Type-I Bi 2 MoO 6 /Bi 2 O 2 CO 3 heterojunction via temperature-mediated topotactic transformation. • Optimized BCM-2 achieved near-complete synergistic removal of RhB and Cr(VI) within 90 min, outperforming individual components. • Unveiled an anomalous charge-transfer mechanism circumventing intrinsic limitations of conventional Type-I heterojunctions. The simultaneous elimination of recalcitrant organic pollutants and toxic heavy metals from industrial effluents demands photocatalytic platforms with synergistic redox capabilities. Herein, we report a topotactic phase-transformation strategy that exploits BiOCOOH nanosheets as a sacrificial topographic template to construct an atomically coherent Bi 2 MoO 6 /Bi 2 O 2 CO 3 (BCM) heterojunction through precision hydrothermal temperature modulation (160 °C). Unlike conventional exogenous deposition routes that generate mechanically contacted, defect-laden interfaces, the thermally driven in-situ nucleation of Bi 2 O 2 CO 3 from the [Bi 2 O 2 ] 2+ structural units of BiOCOOH promoted by DMF-derived carbonate species, ensures lattice-commensurate phase boundaries with negligible interfacial defects, as confirmed by HRTEM-resolved interplanar spacings of 0.196 nm and 0.338 nm across a continuous interface. Despite a nominal Type-I (straddling-gap) band alignment, the BCM-2 composite harbors a pronounced internal electric field (IEF) established by spontaneous interfacial charge redistribution (from Bi 2 O 2 CO 3 to Bi 2 MoO 6 ), supported by XPS binding energy shifts (Bi 4f: +0.2 eV; Mo 3d: −0.1 eV). This IEF induces asymmetric band bending that deviates from conventional Type-I carrier co-localization, spatially directing photogenerated electrons to the strong-reduction-potential conduction band of Bi 2 O 2 CO 3 (−0.61 eV vs. NHE) and holes to the oxidizing valence band of Bi 2 MoO 6 (1.80 eV vs. NHE), a charge-transfer topology mechanistically analogous to the step-scheme (S-scheme) mechanism. Radical trapping and ESR experiments confirm ⋅ O 2 − and h + as the dominant reactive species, fully consistent with this carrier-separation model. The synergy of electrostatic Cr(VI) pre-concentration on the positively charged Bi 2 O 2 CO 3 surface and IEF-mediated efficient carrier separation delivers 100% degradation of Rhodamine B (20 mg/L) and 93.19% reduction of Cr(VI) (30 mg/L) within 60 min under visible-light irradiation (λ > 420 nm, 300 mW cm −2 ), far surpassing the physically mixed counterpart. Exceptional recyclability over four cycles with negligible activity loss further underscores the structural robustness of the topotactic interface. This work demonstrates the potential of topotactic phase transformation as a strategy for controlling heterojunction interfaces through local structural inheritance and promoting S-scheme-like charge-transfer behavior for photocatalytic environmental remediation. Download: Download high-res image (318KB) Download: Download full-size image