Haiqiang Lu

Safe and facile hydrogenation of commercial Degussa P25 at room temperature with enhanced photocatalytic activity

In this paper, we developed a new safe and facile route to prepare black titania at room temperature for visible light photocatalysis. The commercial Degussa P25 was used as the starting material, and it was hydrogenated at 35 bar hydrogen and room temperature for up to 20 days. The resulting hydrogenated P25 was characterized by XRD, FT-IR, Raman, UV-Vis, TEM and photocatalysis tests under visible light in methanol solution. It was found that P25 powders under hydrogen treated for more than 15 days have a dark appearance, a crystalline-disordered core–shell structure, unique phase structure and good photocatalytic performance. The H2 evolution rates are 3.14, 3.56 and 3.94 mmol g−1 h−1 in 20% methanol solution for hydrogen treated P25 at 15, 17 and 20 days, respectively, which were largely higher than that with hydrogen treatment time less than 11 days. This work will provide a practical, green and facile method for the large scale synthesis of black titania at room temperature.

Facile synthesis of TaOxNy photocatalysts with enhanced visible photocatalytic activity

N-doped TaOxNy is prepared using ethylenediamine as the nitrogen source by a sol–gel method. The obtained samples are subsequently calcined at 500–900 °C. XRD analysis and XPS survey indicate the presence of immature TaO2 (Ta4+) in the N-doped TaOxNy sample sintered at 550 °C (TaOxNy-550), and the UV results show TaOxNy-550 has a rather strong absorption in the visible light region. The photocatalytic activities of TaOxNy are evaluated in hydrogen generation by water splitting and photodegradation of methyl orange. The N-doped TaOxNy sample sintered at 550 °C shows the highest H2 generation rate of 3.12 mmol g−1 h−1, and only 3.1% methyl orange is left after 90 min irradiation. Such photocatalytic activities are comparable to the conventional nitrogen-doped titania.

Adjusting phase transition of titania-based nanotubes via hydrothermal and post treatment

Titania-based nanotubes are prepared via hydrothermal and post treatment of titania with different anatase/rutile ratios. Commerical TiO2 P25 with an anatase/rutile ratio of 80/20 changes to sodium titanate, hydrogen titanate and anatase after hydrothermal treatment at 130 °C over 2 h, ion exchange by washing with water and calcination at 400 °C for 5 h. The final tubular structure has a lot of defects owing to a great quantity of dehydration. Pure rutile is more stable than P25. Lamellars exfoliate from (110) facets of rutile at 130 °C hydrothermal treatment to roll up into nanotubes. Only a small amount of rutile transfers to amorphous sodium titanate within 24 h, and it recrystallizes on the surface of nanotubes and results in a perfect tubular structure with a small amount of dehydration. The dissolution–recrystallization mechanism plays an important role in the composition and crystal structure of titania-based nanotubes.

Constructing Cd 0.5 Zn 0.5 S@ZIF-8 nanocomposites through self-assembly strategy to enhance Cr(VI) photocatalytic reduction

A novel and highly efficient photocatalyst of Cd0.5Zn0.5S@ZIF-8 nanocomposite has been developed by a facile self-assembly strategy. This is the first report on the application of CdxZn1-xS and metal-organic framework (MOF) nanocomposite as photocatalysts for the reduction of Cr(VI). The resulting Cd0.5Zn0.5S@ZIF-8 exhibited higher photocatalytic activity than that of pristine Cd0.5Zn0.5S and ZIF-8. Particularly, the CZS@Z60 composite with 60 wt% of ZIF-8 exhibited a photocatalytic activity that is about 1.6 times as high as that of Cd0.5Zn0.5S. The dominant reason for the improved photocatalytic reduction potential is proved to be the newly-formed interfacial SZn bonds that firmly connect Cd0.5Zn0.5S and ZIF-8 and substantially improve the separation efficiency of photo-excited electrons and holes. The newly-formed chemical bonds are confirmed by XPS analyses, and the prolonged lifetime of photo-excited electrons is evidenced by the electrochemical measurement of photocurrent, which shows that the photocurrent on Cd0.5Zn0.5S@ZIF-8 is much higher than that of Cd0.5Zn0.5S and ZIF-8. This study clearly demonstrates that the MOF-based composite nanomaterials hold great promises for applications in the field of environmental remediation and for design of novel photocatalytic materials.

Novel N-doped ZrO2 with enhanced visible-light photocatalytic activity for hydrogen production and degradation of organic dyes

Two new types of N-doped ZrO2 photocatalysts ZON and AZON have been synthesized using ethylenediamine as the nitrogen source by a facile and low-cost sol–gel method. The N-doped ZrO2 samples have been characterized using various techniques including X-ray diffraction (XRD), UV-Vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL) and N2 adsorption–desorption tests. The XRD analysis shows that the crystallinity of ZON samples calcined at 400–600 °C can be indexed to monoclinic ZrO2; while the AZON samples calcined at 400–550 °C only show amorphous diffraction patterns. The UV-Vis response of both N-doped ZrO2 samples can be extended to the visible light regime. The high resolution XPS spectra indicate that N element has been doped in the lattice of ZrO2. Visible-light photocatalytic reactions using the N-doped ZrO2 photocatalysts (i.e. ZON, AZON) calcined at 450 °C show the highest hydrogen production rate (2.12 mmol g−1 h−1) and best methylene orange degradation performance due to substitutional N-doping of the ZrO2. The novel N-doped ZrO2 materials are demonstrated to be very promising photocatalysts with enhanced visible-light photocatalytic activity. Our results provide useful insights into the development of novel photocatalytic materials for hydrogen production and degradation of organic wastes by narrowing the wide bandgap of semiconductors with high photocatalytic activity under UV-Vis light.