Chengsi Pan

New type of BiPO4 oxy-acid salt photocatalyst with high photocatalytic activity on degradation of dye.

A high photocatalytic BiPO(4) with a novel nonmetal oxy acid structure is synthesized by a hydrothermal method. BiPO(4) photocatalyst has an optical indirect band gap of 3.85 eV. In a comparison of BiPO(4) with that of TiO(2) (P25, Degussa), it is found that the photocatalytic activity of BiPO(4) is twice that of TiO(2) (P25, Degussa) for the degradation of methylene blue (MB) dye, while the BET surface of BiPO(4) is just one tenth of that of P25. Both the high position of the valence band and the high separation efficiency of electron-hole pairs result in the high photocatalytic activity. The inductive effect of PO(4)(3-) helps the e(-)/h(+) separation, which plays an important role in its excellent photocatalytic activity. It may extend to the synthesis of other inorganic nonmetal salts of oxy photocatalysts with suitable band gap and high activity for the environmental purification of organic pollutants in aqueous solution.

Enhancement of photocatalytic activity of Bi2WO6 hybridized with graphite-like C3N4

Bi2WO6 photocatalyst was hybridized by graphite-like C3N4via facile chemisorption. After hybridization with C3N4, the photocatalytic activity of Bi2WO6 was obviously enhanced. A C3N4/Bi2WO6 photocatalyst hybridized with monolayer C3N4 exhibited the highest photocatalytic activity which was 68.9% higher than that of pure Bi2WO6. The enhanced photocatalytic activity of the C3N4/Bi2WO6 photocatalysts could be attributed to the synergetic effect between C3N4 and Bi2WO6. The photogenerated holes on the valence band of Bi2WO6 could transfer to the highest occupied molecular orbital of C3N4via the well developed interface, causing rapid photoinduced charge separation and enhancing the photocatalytic activity.

Size-controlled synthesis of BiPO4 nanocrystals for enhanced photocatalytic performance

Well dispersed BiPO4 nanocrystals with a diameter of ∼9 nm are synthesized in oleic acid (OA) and bis(2-ethylhexyl) phosphate (BEHP) media by a high-temperature hydrolysis reaction. OA absorbed on the surface of the nanocrystals helps make a monodispersion. In this reaction, the diameters of the as prepared BiPO4 nanocrystals can be controlled from 9 nm to 250 nm by changing the OA/BEHP ratio (v/v). The roles of BEHP and OA during the formation of the nanocrystals and for tuning the grain size of the particles have been discussed, and a possible formation mechanism of the nanocrystals is proposed. BiPO4 nanocrystals with a diameter of ∼9 nm after OA removal show the highest activity for degradation of methylene blue solution in the UV region, which is also nearly twice the reported activity of BiPO4, and 2.6 times higher than that of P25. The high Brunauer–Emmett–Teller (BET) surface, large band gap, surface effect, and short mobility distance for carriers to the surface are recognized as the key factors for the high photocatalytic activity of nanocrystals.

Effects of distortion of PO4 tetrahedron on the photocatalytic performances of BiPO4

Three kinds of crystal phase BiPO4 (HBIP, nMBIP and mMBIP) were selectively synthesized by a hydrothermal method. The governed factors for the formation of three crystal phase of BiPO4 were both on the acidity of the solution and reaction temperature. The BiPO4 with nMBIP phase structure showed higher activity for degradation of MB solution under UV irradiation than HBIP and mMBIP. The catalytic activity per surface area activity of nMBIP (3.8×105 h−1 m−2) was about ten times higher than that of P25(1.4×104 h−1 m−2). The BiPO4 with nMBIP structure exhibited the highest activity due to the most distorted PO4 tetrahedron. The induce effect of the dipole moment derived from the distorted PO4 tetrahedron promoting the separation of e−/h+ pairs and further benefited for the photocatalytic reaction. This correlation may help to design and develop other oxoacid salt photocatalysts with high activity.

A review of BiPO4, a highly efficient oxyacid-type photocatalyst, used for environmental applications

Semiconductor photocatalysts used for environmental applications have attracted a lot of attention due to their ability to completely convert pollutants into CO2 and H2O. For a simple and economical treatment, more efficient photocatalysts are highly desired compared to widely used TiO2. A non-metallic oxyacid type photocatalyst, BiPO4, was first discovered by the authors group and is now commonly accepted as a superior photocatalyst compared to TiO2 in the UV region. Because of its excellence, this paper has reviewed the recent progress on BiPO4, specifically on the efforts from the authors group, including the preparation as well as the modification methods involved in activity enhancement. The description of the physical properties and typical degradation pathways of the photocatalyst are also given for better comprehension of the origin of its high activity. Furthermore, as a represented non-metallic oxyacid photocatalyst, research into BiPO4 will offer guidelines for designing effective photocatalysts of the same type for environmental applications.

Influence of ZnWO4 nanorod aspect ratio on the photocatalytic activity

ZnWO4 nanorod photocatalysts with various aspect ratios were synthesized by a hydrothermal method. The aspect ratio of the ZnWO4 nanorods was governed by the hydrothermal temperature and pH value. ZnWO4 nanorod photocatalysts showed highly efficient photocatalytic activity for the degradation of methylene blue under ultraviolet light irradiation. The photocatalytic activity and the effective separation of photogenerated electron–hole pairs were promoted by the increasing aspect ratio of the ZnWO4 nanorods. The amount of electron donors in the ZnWO4 increased with the aspect ratio of ZnWO4, which was in good agreement with photocurrent results. The enhancement of photocurrent density and photocatalytic activity resulted from the reduction of charge-transfer resistance and capacitive reactance, which were deduced by the high aspect ratio of ZnWO4 nanorods.

Controllable synthesis of Fe5(PO4)4(OH)3·2H2O as a highly efficient heterogeneous Fenton-like catalyst

Fe5(PO4)4(OH)3·2H2O has been successfully synthesized by a simple hydrothermal process. The effects of hydrothermal temperature and pH value on the morphologies and sizes of the Fe5(PO4)4(OH)3·2H2O particles were investigated. The Fe5(PO4)4(OH)3·2H2O photocatalyst showed lower photocatalytic activity for the degradation of methylene blue under visible light irradiation. But the heterogeneous Fenton-like Fe5(PO4)4(OH)3·2H2O with H2O2 showed highly efficient photocatalytic activity in the photocatalytic decomposition of methylene blue. Effective electron transfer from the visible light-excited dyes to Fe(III), which leads to regeneration of Fe(II) and an easy cycle of Fe(III)/Fe(II), results in much faster degradation and mineralization of methylene blue in the photo-Fenton reaction under visible light irradiation.