Multifunctional property exploration: Bi4O5I2 with high visible light photocatalytic performance and a large nonlinear optical effect.

Exploration of the versatility of materials is very important for increasing the utilization of materials. Herein, we successfully prepared Bi4O5I2 powders via a facile solvothermal method. The Bi4O5I2 photocatalyst exhibited significantly higher photocatalytic activity as compared to the common BiOI photocatalyst in the degradation of methyl orange, methylene blue and rhodamine B under visible light irradiation. Especially, for the degradation of methyl orange, the photocatalytic activity of Bi4O5I2 is about 10 times that of BiOI. Moreover, Bi4O5I2 exhibits an extremely high second harmonic generation response of about 20 × KDP (the benchmark) estimated by the unbiased ab initio calculations. The coexisting multifunction of Bi4O5I2 is mainly because of the increased dipole moment due to the stereochemical activity of lone pairs that promotes separation and transfer of photogenerated carriers, then enhances the photocatalytic activity and results in a high second harmonic generation response. This indicates that Bi4O5I2 may have good potential applications in photocatalytic and nonlinear optical fields.

Charge transfer from internal electrostatic fields is superior to surface defects for 2,4-dichlorophenol degradation in K3-xNaxB6O10Br photocatalysts.

Both surface oxygen vacancies and bulk motivation in a semiconductor play very important roles in the photocatalytic process. To distinguish between the roles of bulk motivation and the surface state in a photocatalytic process, two different phases of K-B-O-B (KBB) photocatalysts with built-in electric field or surface oxygen vacancies were fabricated via the addition of different amounts of Na+ substitute. The crystal structure, band structure, reactive species and photocatalytic performance of two types of photocatalysts were systematically investigated. For the six studied photocatalysts, K3B6O10Br (KBB1), K2.87Na0.13B6O10Br (KBB2), and K2.33Na0.67B6O10Br (KBB3) with less Na+ content behaved as polar materials, while K1.7Na1.3B6O10Br (KBB4), K0.80Na2.20B6O10Br (KBB5), and Na3B6O10Br (KBB6) with more Na+ content behaved as nonpolar materials. Among them, KBB3 exhibited the best photocatalytic activity, which was about 1.15, 1.07, 1.4, 1.25, and 1.18 times that of the KBB1, KBB2, KBB4, KBB5 and KBB6 samples, respectively. During the degradation process of 2,4-dichlorophenol (2,4-DCP), the dominant reactive oxidation species was mainly ˙O2-, while the ˙OH and h+ played secondary roles. The oxygen vacancy concentration increased as the Na atoms increased for the polar materials, except for KBB1; the oxygen vacancy and the built-in electric field had a synergistic effect on the degradation process to nonpolar materials, with the main active species coming only from the high concentration of oxygen vacancies. Furthermore, the activity of KBB1 with only the built-in electric field was superior to that of KBB6 with surface oxygen vacancies, which further confirmed that for charge separation, the driving force from the bulk could provide more motivation than surface defects during the 2,4-DCP degradation process.