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The phase junction of TiO2 nanoparticles plays an essential role in improving photocatalytic activity. Mixed phase brookite–rutile TiO2 nanoparticles with different phase compositions were synthesized through a hydrolysis method using nitric acid of different concentrations. The bi-crystalline phase was characterized by X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and Brunauer–Emmett–Teller (BET), UV-vis diffuse reflectance spectroscopy (DRS) and Photoluminescence (PL) analysis. Photoelectrochemical properties were investigated by transient photocurrent density (TPR) and electrochemical impedance spectroscopy (EIS). XRD and Raman results revealed that the brookite content increased in the sample when increasing the HNO3 concentration. The prepared mixed-phase TiO2 nanoparticles have mesopores with large surface areas ranging from 48.81 to 89.95 m2 g−1. UV-vis spectra showed a redshift of absorption edge from 398 nm to 408 nm with increasing brookite content. The optical band gaps which were obtained from the UV-vis spectra were decreased with increasing brookite content. Photoluminescence results showed that the sample prepared with 5.0 M nitric acid (BCTi-4) showed the lowest emission due to the electron–hole recombination. Furthermore, BCTi-4 revealed the highest photocurrent density of 6 μA cm−2 and the smallest Rct values of 3.30 kΩ. The photocatalytic properties of prepared samples were evaluated by the degradation of methylene blue under UV and visible light irradiation. The BCTi-4 exhibited the highest degradation rate that completely degraded methylene blue after 3 hours of UV irradiation and 36 hours under visible light irradiation. This was attributed to the synergetic effect of phase junction of brookite and rutile, which reduces the recombination of photoexcited electron–hole pairs and the optimal ratio of brookite and rutile. [ABSTRACT FROM AUTHOR]

The phase junction of TiO2 nanoparticles plays an essential role in improving photocatalytic activity. Mixed phase brookite–rutile TiO2 nanoparticles with different phase compositions were synthesized through a hydrolysis method using nitric acid of different concentrations. The bi-crystalline phase was characterized by X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and Brunauer–Emmett–Teller (BET), UV-vis diffuse reflectance spectroscopy (DRS) and Photoluminescence (PL) analysis. Photoelectrochemical properties were investigated by transient photocurrent density (TPR) and electrochemical impedance spectroscopy (EIS). XRD and Raman results revealed that the brookite content increased in the sample when increasing the HNO3 concentration. The prepared mixed-phase TiO2 nanoparticles have mesopores with large surface areas ranging from 48.81 to 89.95 m2 g−1. UV-vis spectra showed a redshift of absorption edge from 398 nm to 408 nm with increasing brookite content. The optical band gaps which were obtained from the UV-vis spectra were decreased with increasing brookite content. Photoluminescence results showed that the sample prepared with 5.0 M nitric acid (BCTi-4) showed the lowest emission due to the electron–hole recombination. Furthermore, BCTi-4 revealed the highest photocurrent density of 6 μA cm−2 and the smallest Rct values of 3.30 kΩ. The photocatalytic properties of prepared samples were evaluated by the degradation of methylene blue under UV and visible light irradiation. The BCTi-4 exhibited the highest degradation rate that completely degraded methylene blue after 3 hours of UV irradiation and 36 hours under visible light irradiation. This was attributed to the synergetic effect of phase junction of brookite and rutile, which reduces the recombination of photoexcited electron–hole pairs and the optimal ratio of brookite and rutile. [ABSTRACT FROM AUTHOR]

The application of TiO 2 nanoparticles in the photocatalytic treatment of chemically or biologically contaminated water is an attractive, albeit unoptimized, method for environmental remediation. Here, TiO 2 nanoparticles with mixed brookite/rutile phases were synthesized and calcined at 300-1100 °C to investigate trends in photocatalytic performance. The crystallinity, crystallite size, and particle size of the calcined materials increased with calcination temperature, while the specific surface area declined significantly. The TiO 2 phase composition varied: at 300 °C, mixed brookite/rutile phases were observed, whereas a brookite-to-anatase phase transformation occurred above 500 °C, reaching complete conversion at 700 °C. Above 700 °C, the anatase-to-rutile phase transformation began, with pure rutile attained at 1100 °C. The optical band gaps of the calcined TiO 2 nanoparticles decreased with rising calcination temperature. The mixed anatase/rutile phase TiO 2 nanoparticles calcined at 700 °C performed best in the photocatalytic degradation of methylene blue owing to the synergistic effect of the crystallinity and phase structure. The photocatalytic virus inactivation test demonstrated excellent performance against the MS2 bacteriophage, murine norovirus, and influenza virus. Therefore, the mixed anatase/rutile phase TiO 2 nanoparticles calcined at 700 °C may be considered as potential candidates for environmental applications, such as water purification and virus inactivation., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)