Nanoparticles of\nCs<sub>3</sub>Bi<sub>2</sub>Br<sub>9</sub> Decorated on H<sub>2</sub>Ti<sub>3</sub>O<sub>7</sub> Nanotubes\nfor the Photocatalytic Oxidation of Hydroxymethylfur

Herein, the successful construction of heterostructure\nCs<sub>3</sub>Bi<sub>2</sub>Br<sub>9</sub>/H<sub>2</sub>Ti<sub>3</sub>O<sub>7</sub> (CBB/HTiO-NT) consisting of nanoparticles of lead-free\nhalide\nperovskite Cs<sub>3</sub>Bi<sub>2</sub>Br<sub>9</sub> (CBB) on hydrogen\ntitanate nanotubes (H<sub>2</sub>Ti<sub>3</sub>O<sub>7</sub>, HTiO-NT)\nis reported. The application of this heterostructure was intensively\ninvestigated in the photocatalytically induced selective oxidation\nof hydroxymethylfurfural (HMF) to 2,5-furandicarboxaldehyde\n(FDC) and of benzyl alcohol (BnOH) to benzoic acid (BzA). The weight\n% (wt %) of CBB nanoparticles was optimized, and the resulting optimal\nCBB/HTiO-NT heterostructure was deeply analyzed. Comprehensive analysis\nof the morphology and structure demonstrated the successful combination\nof HTiO-NT and CBB in CBB/HTiO-NT heterostructures. If the CBB content\nis too low, it is not stable, potentially because it decomposes at\nthe interface with HTiO-NT. The 30 wt % CBB/HTiO-NT heterojunction\nexhibited the most efficient photooxidation of HMF and BnOH, with\nselectivity of 87% for FDC and 81% for BzA, respectively, in an organic\nsolution irradiated by blue light. Analysis of optical and photoelectrochemical\nproperties revealed that the inclusion of CBB nanoparticles into HTiO-NT\nled to enhanced mobility of charge carriers and improved photocatalytic\nefficiency. The oxidative characteristics and rate of charge carrier\nmigration in the CBB/HTiO-NT heterostructure were enhanced by the\ngeometry and tubular structure of HTiO-NT, thereby promoting the formation\nof superoxide (·O<sub>2</sub><sup>–</sup>) radicals. Furthermore,\nscavenger experiments have demonstrated the essential role of the\nphotogenerated species, specifically h<sup>+</sup>, e<sup>–</sup>, and ·O<sub>2</sub><sup>–</sup>, in the process of HMF\nphotooxidation. Consequently, a plausible chemical pathway for the\nphotocatalytic oxidation of HMF to FDC was presented. However, additional\nimprovement of the stability of the composite material is necessary.\nThe present study offers a potential approach to improve photocatalytic\nconversions to value-added chemicals by utilizing CBB/HTiO-NT-based\nphotocatalysts.