Wenhao Gu

A simple post-synthesis conversion approach to Zn(OH)F and the effects of fluorine and hydroxyl on the photodegradation properties of dye wastewater

In this work, Zn(OH)F is prepared by an initiative, simple post-synthesis method, in which the molar ratio of F/Zn (RF) was varied to investigate the effect of the NH4F amounts added on the samples. Further, we have mainly investigated their energy bands and photochemical properties. Under UV light irradiation (λ£420nm), the samples (RF=0,1,2) show the high degradation activities of methylene blue (MB) dye, namely, 80% of MB can be degraded after 8min. It is found that the hydroxyl and fluorine have greatly down shifted the conduction band (CB, 0.99eV) and valence band (VB, 4.17eV) of Zn(OH)F, compared with ZnO (CB=-0.31eV, VB=2.89eV), but with the nearly same band gap. For the degradation of MB dye, the main oxidative species are holes and hydroxyl radicals for ZnO and Zn(OH)F, respectively. This study suggests that this simple post-synthesis fluorination approach could be extended to develop the other photocatalysts; moreover, we can facilely tune the band structure and photocatalytic activity by introducing or removing hydroxyl and fluorine, which could benefit to develop new photocatalysts.

Investigation on the effect of an anion layer on photocatalytic activity: carbonate vs. oxalate

In a layer structure, the influence of an anion layer on the photochemical property is still unknown. In this study, we mainly investigated the photochemical properties of Bi2O2CO3 and Bi(C2O4)OH. It has been found that although they have similar layer structures, Bi2O2CO3 shows activities 1.15 and 2.48 times higher than those of Bi(C2O4)OH for the degradation of phenol and rhodamine B (RhB) under UV light irradiation (λ ≤ 400 nm), respectively; these high activities have been mainly attributed to their different anion layers. For Bi2O2CO3, CO32− ions connect with one another to form a linked anion layer, whereas the alternating [Bi2O2]2+ and CO32− layers are completely separate; however, for Bi(C2O4)OH, C2O42− ions do not link with each other, whereas oxygen bridges are formed between the [Bi2O2]2+ and C2O42− layers. The results demonstrate that an internal electric field (IEF) is favored by the separate [Bi2O2]2+ and CO32− layers, which can greatly improve the charge separation rate. In contrast, the oxygen bridges between the [Bi2O2]2+ and C2O42− layers do not favor the formation of an IEF, resulting in a low charge separation rate. This finding suggests that layer semiconductors with completely separate cation and anion layers can be developed as efficient photocatalysts.

Na0.5Ce0.5MoO4 as a new light absorption material to efficiently degrade RhB under visible light irradiation

It still remains a big challenge to develop an efficient visible light responsive photocatalyst for the full utilization of solar energy. In this work, Na0.5Ce0.5MoO4 has been developed as a new, high visible light absorption medium and a high electron-conducting material. It has greatly improved the visible light absorbance and the charge separation and transfer rates of the Na0.5Ce0.5MoO4/MoO3 heterojunction. Amazingly, the activity of Na0.5Ce0.5MoO4 (10%)/MoO3 is 6.4 times higher than that of MoO3 for the photodegradation of RhB under visible light irradiation (λ ≥ 420 nm). We expect that Na0.5Ce0.5MoO4 could be applied to prepare other excellent visible light heterojunction photocatalysts to fully utilize solar energy.