Hualei Zhou

In-built Tb4+/Tb3+ redox centers in terbium-doped bismuth molybdate nanograss for enhanced photocatalytic activity

A series of terbium-doped Bi2MoO6 with different Tb contents were synthesized using a hydrothermal method. The crystalline structure, surface area, morphology, chemical state and optical properties were analyzed in detail. The photocatalytic activity of the samples was evaluated by degradation of organics under visible light irradiation. The results indicated that doping of terbium ions could obviously improve the photocatalytic activity of Bi2MoO6, which was attributed to the generation of Tb4+/Tb3+ redox centers in terbium-doped Bi2MoO6. The photoluminescence (PL) spectroscopy, photocurrent measurement and active species trapping experiments suggest that the recombination of photo-generated electron–hole pairs was efficiently restrained by a trapping–releasing process between the Tb4+ and Tb3+ ions.

Novel In2S3/ZnWO4 heterojunction photocatalysts: facile synthesis and high-efficiency visible-light-driven photocatalytic activity

Novel heterojunction photocatalysts In2S3/ZnWO4 were prepared by a hydrothermal and surface-functionalized method, and the optimized In2S3/ZnWO4 ratio was tuned to explore their visible-light photocatalytic activity for rhodamine B (RhB) degradation. The heterojunction structure formed by the In2S3 nanoparticles grew on the primary ZnWO4 nanorods. Remarkably, In2S3/ZnWO4 composites exhibited much higher photocatalytic activity than that of the individual In2S3 and ZnWO4. The enhanced activity could be attributed to the strong visible-light absorption and the effective separation and transportance of the photogenerated charges. Moreover, the main active species for the degradation of RhB were also investigated. Then, a possible reaction mechanism for the excellent photocatalytic activity of the In2S3/ZnWO4 composites was proposed.

Substitution of Ce(III,IV) ions for Bi in BiVO4 and its enhanced impact on visible light-driven photocatalytic activities

Bi1−xCexVO4+δ (0 ≤ x ≤ 0.3) solid solution photocatalysts were synthesized by substitution of Ce for Bi in the BiVO4 lattice using the hydrothermal method. X-ray diffraction, Raman spectroscopy and high-resolution transmission electron microscopy revealed that the crystal phase transformed from the monoclinic phase to the tetragonal phase, probably due to the substitution of cerium ions in the Bi3+ positions. UV-vis diffuse reflectance spectroscopy was used to investigate the absorption range and band gap of the photocatalysts. The photocatalytic activities of the prepared samples were examined by studying the degradation of MB and phenol under visible-light irradiation and the best performance was attained for the sample with a cerium content of 20 at% (Bi0.8Ce0.2VO4+δ). The results of photoluminescence spectroscopy and photocurrent measurement demonstrated that the recombination of photogenerated charges was greatly depressed and the photocatalytic activity was improved by the substitution of Ce for Bi in BiVO4. Furthermore, the proposed mechanism of the enhanced photocatalytic activity was discussed.

Preparation, characterization of Mo, Ag-loaded BiVO4 and comparison of their degradation of methylene blue

Two types of metal-loaded visible-light-driven photocatalysts, Mo-BiVO4 and Ag-BiVO4, were synthesized by wet impregnation method. Material poperties were characterized by UV-vis diffuse reflectance spectroscopy, X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy and low temperature nitrogen adsorption-desorption. Photocatalytic activity of the obtained materials was investigated through degrading methylene blue (MB) solution under visible-light irradiation. The results reveal that both metal loaded-BiVO4 catalysts have monoclinic scheelite structure. Mo and Ag exist as oxides on the surface of the particles. The changes of absorption in visible-light region, band gap (Eg) and specific surface area (ABET) caused by loading Ag are more obvious than those caused by loading Mo. But the isoelectric point of Ag-BiVO4 decreases less than that of Mo-BiVO4 does. Both catalysts show higher photocatalytic activity than pure BiVO4, resulting in the significantly improved efficiency of degradation of MB. And the degradation efficiency of these two metal-loaded BiVO4 photocatalysts is similar to each other. However, mechanisms of such enhancement are different. The decrease of isoelectric point helps Mo-BiVO4 improve the degradation efficiency. As for Ag-BiVO4, the augmentation of absorption in visible-light region as well as the abatement of Eg plays more important roles.

In situ preparation of novel heterojunction BiOBr/BiVO4 photocatalysts with enhanced visible light photocatalytic activity

Heterojunction photocatalysts BiOBr/BiVO4 were in situ synthesized through acid etching coupled with a hydrothermal process, and the optimized BiOBr/BiVO4 ratio was tuned to explore their visible-light photocatalytic activity for MB degradation. Remarkably, BiOBr/BiVO4 composites exhibited higher visible-light photocatalytic ability compared with single BiVO4 and BiOBr alone. The charge-separation process was interpreted based on the energy band structure. The heterojunction formed between BiVO4 and BiOBr, that effectively promotes the separation of photo-induced electrons and holes, is responsible for the improved photocatalytic activity.

Enhancement of photocatalytic activity in Tb/Eu co-doped Bi2MoO6: the synergistic effect of Tb–Eu redox cycles

Tb/Eu co-doped Bi2MoO6 photocatalysts were successfully synthesized by a hydrothermal method, and their photocatalytic activity for the degradation of Rhodamine B (RhB) under visible light irradiation was researched. An obvious red-shift of the optical absorption edge for the co-doped samples was observed as compared to the single or non-doped Bi2MoO6. Raman spectra displayed the influence of Tb and Eu ions in the material structure, and the mixed valence states of Tb and Eu ions in the lattice of Bi2MoO6 were verified by XPS. The results of photoluminescence spectroscopy and photocurrent measurement demonstrated that the recombination of photogenerated electron–hole pairs was tremendously depressed by the synergistic effect of Tb–Eu redox cycles in the Tb/Eu co-doped Bi2MoO6 photocatalyst and the photocatalytic activity was improved. Furthermore, the proposed mechanism of the enhanced photocatalytic activity was discussed.

Modification and investigation of silica particles as a foam stabilizer

As a solid foam stabilizer, spherical silica particles with diameters ranging from 150 to 190 nm were prepared via an improved Stöber method and were subsequently modified using three different silane coupling agents to attain the optimum surface hydrophobicity of the particles. Fourier transform infrared (FTIR) spectra and the measured contact angles were used to characterize the surface properties of the prepared particles. The foam stability was investigated by the foam drainage half-life and the expansion viscoelastic modulus of the liquid film. The results demonstrate that all of the modified silica nanoparticles effectively improve the foam stability. The surface hydrophobicity of the modified particles is found to be a key factor influencing the foam stability. The optimum contact angle of the particles lies in the approximate range from 50° to 55°. The modifier molecular structure used can also influence the stabilizing foam property of the solid particles. The foam system stabilized by (CH3)2SiCl2-modified silica particles exhibits the highest stability; its drainage half-life at maximum increases by 27% compared to that of the blank foam system and is substantially greater than those of the foam systems stabilized by KH570- and KH550-modified particles.

Role of the surface chemistry of activated carbons in dye removal from aqueous solution

Commercial activated carbons were modified by a series of chemical or physical treatments using H2O2, NH3, and heating under N2 flow without notably changing their pore structures. The resultant carbons were characterized by N2 adsorption and Bohem titration and then used to remove Ponceau 4R, methyl orange and brilliant blue from aqueous solutions. Surface chemistry was found to play a significantly different role in removing these three compounds. The removal of anionic Ponceau 4R increases with increasing carbon surface basicity due to the predominant dispersive interaction mechanism. In contrast, surface chemistry has little effect on the removal of anionic methyl orange, which can be explained by two parallel mechanisms involving electrostatic and dispersive interactions due to the basic amine group in a dye molecule. The influence of surface chemistry on the removal of amphoteric brilliant blue dye can also be ignored due to a weak interaction between the carbons and dye molecules, which is resulted from strong cohesive energy from electrostatic forces inside amphoteric dye molecules.

Transition metal-doped amorphous molybdenum sulfide/graphene ternary cocatalysts for excellent photocatalytic hydrogen evolution: Synergistic effect of transition metal and graphene

Though amorphous molybdenum sulfide (MoSx) is considered a promising H2 evolution cocatalyst, its intrinsic activity and charge transfer efficiency are still unsatisfactory. To overcome these drawbacks, transition metal-doped (Fe, Co, or Ni) amorphous MoSx/graphene ternary nanocomposites were designed and fabricated using a one-step solvothermal method. Their structure, morphology, and properties were characterized. The metal-doped MoSx nanoparticles were well distributed on the graphene sheets in the ternary composites. Metal doping greatly enhanced the intrinsic activity of amorphous MoSx, and the integration of graphene notably promoted the separation of photoinduced carriers. The photocatalytic H2 evolution with amorphous MoSx as cocatalyst has been substantially improved under the synergistic effect of the transition metal and graphene. The H2 evolution rate of Co-doped amorphous MoSx/graphene composites reached 11.45 mmol·h-1·g-1 at the Co:Mo molar ratio of 2:3, which is 64% higher than that of Co-doped MoSx, 21 times that of undoped MoSx/graphene, and 127 times that of pure MoSx. This study would supply an efficient strategy and a new vision for developing excellent noble-metal-free photocatalysts for photocatalytic hydrogen production.