Effective photocatalysis processes with production of fewer toxic intermediates are highly desirable for air purification. In this study, titania/hydroxyapatite (TiO2/HAp) composites were synthesized by a facile hydrothermal method and employed to decontaminate nitric oxide (NO) in air under simulated solar light irradiation for the first time. It was found that the photocatalytic activity of the as-prepared TiO2/HAp composite (44.61%) was superior to those of the pristine components (TiO2: 38.57%, HAp: 36.73%) and mechanically mixed samples (35.36%). The TiO2/HAp composite with mass ratio of 3 : 1 (75% TiO2/HAp) exhibited the highest NO removal efficiency among them. Moreover, the toxic intermediate NO2 production was significantly inhibited over TiO2/HAp. These synergistically improved properties can be ascribed to the high separation efficiency and faster transfer of the photo-generated charge carriers as evidenced by the experimental results from photocurrent tests and electrochemical impedance spectroscopy (EIS). The results from temperature programmed desorption (TPD) confirmed that the 75% TiO2/HAp sample had stronger chemisorption for NO due to the increased concentration of surface OH groups. Furthermore, the electron spin resonance (ESR) characterization suggested that ˙O2− and ˙OH radicals were the major species involved for NO removal over TiO2/HAp composites. The five recycling tests suggested that the TiO2/HAp has superior photocatalytic stability. This study suggests that the combination of TiO2 with HAp is an effective approach for air purification.

•CQDs/BiOBr composites with OVs show high photocatalytic activity and stability.•The upconversion effect of CQDs can greatly improve O2− formation on BiOBr.•The upconversion effect can refresh the OVs on BiOBr for its long term stability.CQDs/BiOBr composites with oxygen vacancies were synthesized by a simple hydrolysis method at room temperature. The obtained composites exhibited much higher photocatalytic activity and stability than pure BiOBr under visible light. The upconversion effect of CQDs on BiOBr was studied by photoluminescence (PL) spectra, transient photocurrent (PC) responses measurements, electron spin resonance (ESR) analysis, reactive species scavenger experiments, and RhB and BPA degradation under monochromatic light irradiation. The results demonstrated that the upconversion effect of CQDs could improve O2− formation on BiOBr during photocatalytic process via more electron transfer in oxygen vacancies owing to the desirable long wavelength visible light and near infrared (NIR) light absorption property of CQDs. Moreover, the upconversion effect of CQDs could refresh the oxygen vacancies on BiOBr and therefore maintain the photocatalytic stability of BiOBr.

•BiOCl thin film on Bi plate was prepared.•Slow-releasing of Cl− plays an important role on preparing BiOCl thin film on Bi plate.•The BiOCl thin film showed excellent photocatalytic activity and stability.•A possible mechanism underlying the formation of BiOCl thin film had been proposed.A BiOCl thin film has been successfully synthesized on the Bi plate by a facile method at room temperature. Sodium hypochlorite (NaClO) was used as Cl source, in which Cl− was slow-released through redox reaction of NaClO by ethylene glycol (EG). The X-ray diffraction (XRD), scanning electron microscopy (SEM), diffuse reflection spectrometry (DRS) were employed to characterize the structure, morphology, and optical property of the as-prepared BiOCl thin film. The photocatalytic activity and stability of BiOCl thin film was evaluated by degradation of rhodamine B under both simulated solar light and visible light. The results indicated that as-prepared BiOCl thin film had excellent catalytic efficiency and good cycling performance towards photodegradation of RhB. Furthermore, a possible formation mechanism of BiOCl thin film on Bi plate had been proposed.

The BiPO4/BiOBr composites were successfully fabricated by a facile one-step hydrothermal method. The X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis diffuse reflection spectroscopy (DRS), photoluminescence (PL) and photocurrent (PC) measurements were employed to characterize the crystal structures, morphologies, optical properties, recombination of photo-generated electron–hole pairs, and electron–hole separation effect of the photocatalysts. BiPO4/BiOBr composites exhibited much higher photocatalytic activity for the degradation of RhB and MO dye than single BiOBr and BiPO4 under visible light and simulated sunlight irradiation, respectively. The results of PL and PC measurements demonstrated that the large enhancement of photocatalytic activity could be mainly ascribed to the surface junction of BiPO4/BiOBr composite which can effectively improve electron–hole separation speed during photocatalytic process.