Comparing defect-assisted interfacial charge transfer in CdS/PSA and CdS/ TiO₂-NTAs nanoheterojunctions for enhanced photodegradation and biosensing

Firstly, oxygen vacancy defects are intentionally introduced in the preparation process of TiO2 nanotube arrays (TiO2-NTAs) and porous silicon arrays (PSA) films through the anodic oxidation method after annealing treatment, as expected. Then, CdS/TiO2-NTAs and CdS/PSA heterostructures are successfully fabricated using the electrodeposition method, incorporating abundant surface vacancy defects. The crafted CdS/TiO2-NTAs nano-heterojunctions presented elevated photoelectrochemical (PEC) performances and sensing activities compared with that of CdS/PSA, validating by photodegradation and PEC biosensing tests, which mainly ascribed to the synergistic effect between the promoted carriers separation efficiency and boosted surface active sites induced by vacancies defects. Furthermore, a comparative and comprehensive interfacial charge transfer mechanism and qualitative dynamic processes for CdS/TiO2-NTAs and CdS/PSA type-II nanoheterojunctions are proposed, revealing an enlarged staggered band offset between CdS and TiO2-NTAs. The evaluation of this band offset was conducted using nanosecond time-resolved transient photoluminescence and steady photoluminescence spectra, respectively. Following this scheme, the photodegradation rate for CdS/TiO2-NTAs nanocomplex toward degradation of MO was 92.8% and 1.06 times than that of CdS/PSA; while the PEC biosensing performance for CdS/TiO2-NTAs showed a detection range 0 - 600 mu M and limit of detection of 2.3 mu M, with a sensitivity of 456 mA cm(- 2) M (-1).