Nanoparticles of Cs₃Bi₂Br₉ Decorated on H₂Ti₃O₇ Nanotubes for the Photocatalytic Oxidation of Hydroxymethylfurfural to 2,5-Furandicarboxaldehyde

Herein, the successful construction of heterostructure Cs3Bi2Br9/H2Ti3O7 (CBB/HTiO-NT) consisting of nanoparticles of lead-free halide perovskite Cs3Bi2Br9 (CBB) on hydrogen titanate nanotubes (H2Ti3O7, HTiO-NT) is reported. The application of this heterostructure was intensively investigated in the photocatalytically induced selective oxidation of hydroxymethylfurfural (HMF) to 2,5-furandicarboxaldehyde (FDC) and of benzyl alcohol (BnOH) to benzoic acid (BzA). The weight % (wt %) of CBB nanoparticles was optimized, and the resulting optimal CBB/HTiO-NT heterostructure was deeply analyzed. Comprehensive analysis of the morphology and structure demonstrated the successful combination of HTiO-NT and CBB in CBB/HTiO-NT heterostructures. If the CBB content is too low, it is not stable, potentially because it decomposes at the interface with HTiO-NT. The 30 wt % CBB/HTiO-NT heterojunction exhibited the most efficient photooxidation of HMF and BnOH, with selectivity of 87% for FDC and 81% for BzA, respectively, in an organic solution irradiated by blue light. Analysis of optical and photoelectrochemical properties revealed that the inclusion of CBB nanoparticles into HTiO-NT led to enhanced mobility of charge carriers and improved photocatalytic efficiency. The oxidative characteristics and rate of charge carrier migration in the CBB/HTiO-NT heterostructure were enhanced by the geometry and tubular structure of HTiO-NT, thereby promoting the formation of superoxide (·O2–) radicals. Furthermore, scavenger experiments have demonstrated the essential role of the photogenerated species, specifically h+, e–, and ·O2–, in the process of HMF photooxidation. Consequently, a plausible chemical pathway for the photocatalytic oxidation of HMF to FDC was presented. However, additional improvement of the stability of the composite material is necessary. The present study offers a potential approach to improve photocatalytic conversions to value-added chemicals by utilizing CBB/HTiO-NT-based photocatalysts.