Yunxuan Zhao

Effect of the molecular structure and surface charge of a bismuth catalyst on the adsorption and photocatalytic degradation of dye mixtures

[Bi6O6(OH)3](NO3)3·1.5H2O plates were prepared by a facile hydrothermal method. The effect of the pH value, hydrothermal temperature, reaction time, and concentration of Bi(III) ion and additives on the morphology and properties of the samples were investigated. The as-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET) surface area and UV-vis diffuse reflectance spectroscopy (UV-DRS). It was found that under ultraviolet light irradiation (≤420 nm), the sample prepared at pH = 0.72 displays a higher photocatalytic activity than those prepared at higher pH values, which has been mainly ascribed to the promoted oxygen adsorption at low pH values. Moreover, we investigated the effects of the molecular structure and surface charge on the adsorption and photocatalytic degradation of dye mixtures (methyl orange (MO)–methylene blue (MB) and MO–rhodamine B (RhB)). The results show that in the MB–MO mixture, the adsorption and degradation of both MO and MB are promoted greatly by electrostatic forces; while in the RhB–MO mixture, the degradation of RhB is greatly reduced by MO due to competitive adsorption. These findings help us to understand degradation processes for real wastewater samples containing more than one pollutant.

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.

NOVEL HIERARCHICAL NANORODS OF SILICON-DOPED Bi2O2CO3 AND ITS PHOTOCATALYTIC ACTIVITY

The silicon-doped Bi2O2CO3 nanorods with the interesting hierarchical structure are synthesized by a simple hydrothermal method. The samples are characterized by XRD, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), Ultraviolet-visible diffuse reflectance spectra (UV-DRS) and nitrogen sorption isotherms. It is found that with the increase of silicon content, the XRD peak of the sample significantly shifts toward a low diffraction angle and the particle morphologies change from nanosheets, nanoflowers to hierarchical nanorods. Moreover, the silicon-doped Bi2O2CO3 hierarchical nanorods exhibit improved photocatalytic degradation activities for different types of dyes under simulated solar light irradiation. The improved activity has been mainly attributed to the unique hierarchical nanorods structure and the formation of Si–O–Bi bonds.

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.

Controllable synthesis of “L”-shaped V2O5 and the improved adsorption capacity by fluorine

In this work, V2O5 with an interesting “L”-shape is successfully prepared by a simple hydrothermal method without using any surfactant or template. The formation mechanism of “L”-shaped V2O5 has been proposed. We have also investigated the effect of fluoride on the morphology, crystal structure and adsorption ability of the samples. The samples are characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) with select area electron diffraction (SAED), X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, UV-vis diffuse reflectance spectroscopy (UV-DRS), photoluminescence (PL) spectroscopy and N2 sorption isotherms. It is found that the addition of fluoride can restrain the formation of “L”-shaped V2O5, resulting in the high-energy {010} facets being exposed and an increased number of oxygen vacancies. Density functional theory (DFT) calculations and PL spectra further confirm the results above. As a result, F-doped V2O5 shows a significantly improved adsorption capacity for methylene blue (MB) compared to the undoped one. The adsorption kinetics follows well a pseudo-second-order model, with correlation coefficients (R) higher than 0.99.