Zailun Liu

Photocatalytic Performances of Ag3PO4 Polypods for Degradation of Dye Pollutant under Natural Indoor Weak Light Irradiation.

It is still a big challenge for Ag3PO4 to be applied in practice mainly because of its low stability resistant to photo corrosion, although it is an efficient photocatalyst. Herein, we have mainly investigated its activity and stability under indoor weak light for the degradation of dye pollutants. It is amazing that under indoor weak light irradiation, rhodamine B (RhB) can be completely degraded by Ag3PO4 polypods after 36 h, but only 18% of RhB by N-doped TiO2 after 120 h. It is found that under indoor weak light irradiation, the degradation rate (0.08099 h(-1)) of RhB over Ag3PO4 polypods are 46 times higher than that (0.00173 h(-1)) of N-doped TiO2. The high activity of Ag3PO4 polypods are mainly attributed to the three-dimensional branched nanostructure and high-energy {110} facets exposed. After three cycles, surprisingly, Ag3PO4 polypods show a high stability under indoor weak light irradiation, whereas Ag3PO4 have been decomposed into Ag under visible light irradiation with an artificial Xe light source. This natural weak light irradiation strategy could be a promising method for the other unstable photocatalysts in the degradation of environmental pollutants.

Controllable synthesis of uniform BiOF nanosheets and their improved photocatalytic activity by an exposed high-energy (002) facet and internal electric field

To date, it still remains a big challenge to develop a new photocatalyst for photocatalysis technologies. Herein, a BiOF photocatalyst with a regular nanosheet shape has been, for the first time, prepared by a simple hydrothermal method. The samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible diffuse reflectance spectroscopy (UV-DRS), electrochemistry impede spectroscopy (EIS) and nitrogen sorption isotherms. Also, ab initio density functional theory (DFT) calculations have been carried out to give insight into the energy band and electronic structures of BiOF. Furthermore, rhodamine B (RhB) is chosen as the representative dye pollutant to evaluate the photocatalytic activity of BiOF. The results show that the uniform BiOF nanosheets grow preferentially along the [110] and [100] orientation, and 75.4% of the (002) facets are exposed. After 60 min of ultraviolet light irradiation (<420 nm), 79.3% of RhB is degraded by BiOF, while only 33.7% of RhB is degraded by the commercial rutile TiO2. The apparent kinetic rate constant (0.02534 min−1) of BiOF is 3.88 times higher than (0.00652 min−1) rutile TiO2. Moreover, the calculation results demonstrate that the high-energy (002) facets are more active than the low-energy (020) and (200) facets. For the layered BiOF there is an internal electric field (IEF) perpendicular to the [Bi2O2]2+ slabs and fluorine anionic slabs, which is favorable for the efficient separation of the photogenerated electrons and holes. It is the synergetic effect of the surface structure and bulk IEF that greatly improves the activity of the BiOF nanosheets. We expect that bulk IEF adjustment is another new strategy to develop new, efficient photocatalysts for layered materials.

Fully Understanding the Photochemical Properties of Bi2O2(CO3)1–xSx Nanosheets

The photochemical properties of crystal facets with obviously distinct atomic and geometric structures have been studied widely to date. However, little work has been performed for two or more facets with very similar atomic and geometric structures. Herein, we mainly report the photochemical properties of {001} and {100} facets of Bi2O2(CO3)1-xSx with very similar atomic and geometric structures. The simulation and experimental results show that over {100} facets, sulfur prefers to substitute for the carbonate anion, leading to the formation of an interesting serpentine internal electric field that greatly inhibits the charge recombining of electrons and holes, which has rarely been demonstrated; over {001} facets, however, sulfur preferentially adsorbs in oxygen vacancies, which greatly reduces the surface energy of {001} facets, leading to 80% of the high-energy {001} facets exposed. As a result, the photochemical properties of nanosheets have been greatly improved. This study could help us to fully understand the photochemical properties of semiconductors.

Facile synthesis of Cu2PO4OH hierarchical nanostructures and their improved catalytic activity by a hydroxyl group

One- and three-dimensional (1D, 3D) Cu2PO4OH hierarchical architectures have been successfully prepared by a facile hydrothermal method, mainly through adjusting the precursor concentrations. A possible splitting mechanism is proposed to understand the evolution from 1D to 3D hierarchical architectures. Besides, through experiments and density functional theory (DFT) calculations, we find that copper hydroxyphosphate (Cu2PO4OH) shows an excellent catalytic activity for the degradation of rhodamine B (RhB). This has been mainly ascribed to the contribution of hydroxyl groups contained in Cu2PO4OH, which favours to form more hydroxyl radicals. Moreover, both partial density of states (PDOS) and total density of states (TDOS) have confirmed that the conduction band (CB) is affected by part of the O 2p orbitals of the hydroxyls; thus the hydroxyl group is responsible for the increased band gap and the positive VB of Cu2PO4OH. This study suggests that new photocatalysts or photoelectric materials can be developed through introducing hydroxyl groups.

In situ hydrothermal fabrication of a MnO2@CoMoO4@Ni nanohybrid electrode and ultrahigh energy density of ASCs

It still remains a big challenge to fabricate a high-energy-density supercapacitor (SC). Herein, an in situ hydrothermal method is developed to fabricate the high-performance MnO2@CoMoO4@Ni electrode, in which the high capacitance of MnO2 and the high electrical conductivity of CoMoO4 nanowires are fully utilized through the closely-contacted core@shell nanostructure. Amazingly, a flexible AC@Ni//MnO2@CoMoO4@Ni asymmetric supercapacitor (ASC) has been fabricated, which delivers an ultrahigh energy density (2.63 mW h cm−3) at a power density of 4 mW cm−3; after being charged for 10 s, the device assembled in series by two ASCs can efficiently power 15 light emitting diodes (LEDs, 5 mm-diameter red) for more than 5 minutes. Moreover, the ASC still retains 91.28% capacitance after 10000 cycles. We hold that a hybrid nanostructure from a high-energy-density material with a high-electric-conductivity material is a promising strategy to acquire high-performance SCs.

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.

Electrochemical properties of novel titania nanostructures.

In this study, the supercapacitive properties of six new TiO2 nanostructures-including nanodishes, three-layer nanosheets, ancient Chinese coins, single-layer nanosheets, hollow nanocubes, and commercial rutile TiO2 are investigated mainly by cyclic voltammetry, chronopotentiometry, and electrochemical impedance spectroscopy. The results show that among them, the TiO2 nanodishes have the highest discharging capacitance at 1792 mFg(-1), which is 6.4 and 1.5 times higher than that of TiO2 single-layer nanosheets and commercial rutile TiO2, respectively. We found that the electrochemical properties of the TiO2 samples are predominated primarily by the high-energy facets exposed, instead of by the Brunauer-Emmett-Teller area. An important and previously unknown finding of our work is that the electrochemical properties of electrode materials can be improved by controlling the high-energy facets.

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.