Yanlong Yu

Structure of nitrogen and zirconium co-doped titania with enhanced visible-light photocatalytic activity.

Nitrogen and zirconium co-doped TiO2 (TiO2-N-x%Zr) photocatalysts were synthesized via a sol-gel method. The existing states of the dopants (N and Zr) and their corresponding band structures were investigated via XRD, Raman, BET, XPS, TEM, FT-IR, UV-vis DRS, and PL techniques. It was found that N existed only as a surface species (NOx) and Zr(4+) was doped in a substitutional mode; the doping of Zr(4+) ions and modification of N extended the absorption into the visible region and inhibited the recombination of electrons and holes. Moreover, the excess Zr(4+) ions existed as the ZrTiO4 phase when the content of Zr was sufficiently high, which could also contribute to the separation of the charge carriers. Therefore, the TiO2-N-x%Zr samples show enhanced visible-light photocatalytic activity compared with single-doped TiO2. These results offer a paradigm for the design and fabrication of optoelectronic functional materials such as solar cells and photocatalysts.

Efficient visible-light photocatalytic degradation system assisted by conventional Pd catalysis

Different approaches like doping and sensitization have been used to develop photocatalysts that can lead to high reactivity under visible-light illumination, which would allow efficient utilization of solar irradiation and even interior lighting. We demonstrated a conceptually different approach by changing reaction route via introducing the idea of conventional Pd catalysis used in cross-coupling reactions into photocatalysis. The –O–Pd–Cl surface species modified on Ni-doped TiO2 can play a role the same as that in chemical catalysis, resulting in remarkably enhanced photocatalytic activity under visible-light irradiation. For instance, Pd/Ni-TiO2 has much higher activity than N-TiO2 (about 3 ~ 9 times for all of the 4-XP systems) upon irradiation with wavelength of 420 nm. The catalytically active Pd(0) is achieved by reduction of photogenerated electrons from Ni-TiO2. Given high efficient, stable Pd catalysts or other suitable chemical catalysts, this concept may enable realization of the practical applications of photocatalysis.

Enhanced photocatalytic activity of TiO2–Cu/C with regulation and matching of energy levels by carbon and copper for photoreduction of CO2 into CH4

A novel copper and carbon co-modified TiO2 photocatalyst (TiO2–Cu/C) was prepared using a simple sol–gel method. The properties of the photocatalysts were investigated by XRD, Raman, BET, HRTEM, EDAX, XPS, absorption spectroscopy and PL techniques. It was revealed that copper was present as –O–Cu–O– species and carbon existed as elementary substance carbon nanoparticles on the surface of TiO2. Based on the experimental results, the band structure and electronic density of states of TiO2, TiO2–Cu and elementary substance carbon are predicted by theoretical calculations. The energy levels of the –O–Cu–O– species and the carbon nanoparticles were located above the valence band, which extends the absorption into the visible light region, facilitate the separation of photogenerated charge carriers and provide hole reactive sites on the surface. Thus, the photocatalytic activity of TiO2–Cu/C is much higher than that of pure TiO2, TiO2/C and TiO2–Cu for photoreduction of CO2 and H2O into CH4 under UV-light irradiation.

Enhanced photocatalytic activity of TiO2 activated by doping Zr and modifying Pd

A series of TiO2 photocatalysts introduced with Zr and Pd (TiO2–Zr–Pdx) are synthesized via a sol–gel method. It is revealed that Zr4+ ions are doped into TiO2 lattice in the substitutional mode and Pd2+ ions exist as –O–Pd–O– species on the surface of TiO2. The energy level of the substitutional doped Zr4+ ions and –O–Pd–O– surface species are located about 0.15 eV below the conduction band and 0.4 eV above the valence band, respectively. Moreover, the band structure of TiO2–Zr–Pdx can be further adjusted by changing the amount of Pd2+ ions. Owing to the synergistic effect of Pd and Zr, the response is extended into the visible region and the photogenerated charge carriers are separated effectively. Therefore, TiO2–Zr–Pdx samples exhibit improved photocatalytic activity, compared with TiO2–Zr and TiO2–Pd under both UV and Vis irradiation.

Doping mechanism of Zn2+ ions in Zn-doped TiO2 prepared by a sol–gel method

A series of Zn doped TiO2 is prepared via a sol–gel method by changing the concentration of Zn ions and calcination temperature. To investigate the existing states of introduced Zn, the transformation of existing states and the phase transition for the Zn doped TiO2 samples, high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) techniques are applied. The existing states of Zn2+ ions and the transformation of existing states (O–Zn–Cl and ZnTiO3) in Zn doped TiO2 are closely related to the calcination temperature and concentration of introduced Zn ions, as well as the phase transition temperature from anatase to rutile. This work can be helpful for a better realization about the doping mechanism of Zn2+ ions in Zn doped TiO2.

Synthesis of TiO2-N/SnO2 heterostructure photocatalyst and its photocatalytic mechanism

A series of TiO2-N/SnO2X heterostructure photocatalysts were synthesized by a hydrolysis-deposition method. The structure, existing states of N and SnO2 heterostructure at the interface of TiO2-N/SnO2X were studied by EADX, XRD, Raman, FT-IR, XPS, and HRTEM. The band structure is investigated by both theoretical calculation and experiment characterization. It was found that the introduction of NOx surface species and SnO2 nanoparticles would enhance the absorption in visible region, increase reactive oxidative species and separate photogenerated electrons and holes efficiently. Therefore, the photocatalytic activity is improved significantly for TiO2-N/SnO2X, compared with TiO2-N and TiO2 under visible and UV light irradiation. This work may offer a new strategy to fabricate new photocatalyst with high photocatalytic performance.

The band structure and photocatalytic mechanism for a CeO2-modified C3N4 photocatalyst

A series of CeO2-modified C3N4 (C3N4/CeO2X%) heterostructure photocatalysts was synthesized via a hydrothermal method. Their band structure was studied via theoretical calculation and experimental characterization. The behavior of charge carriers was investigated via absorption spectra, PL, and time-resolved PL decay curves. It was found that the modification of CeO2 on C3N4 matched the energy band, enhanced absorption in the visible region, separated photogenerated electrons and holes. Owing to the modification of CeO2 on C3N4, the photocatalytic performance was significantly improved as compared to that of C3N4. This study may offer a new strategy to fabricate and design a band structure of a new photocatalyst with high photocatalytic performance.

TiO2–Pd/C composited photocatalyst with improved photocatalytic activity for photoreduction of CO2 into CH4

A novel Pd-modified TiO2 photocatalyst composited with carbon nanoparticles (TiO2–Pd/C) was synthesized via a sol–gel method. Characterized by XRD, Raman, BET, HRTEM, EDAX, XPS, absorption spectra and PL techniques, the introduced Pd existed as unique O–Pd–O species, and C existed as the substance carbon nanoparticles on the surface of TiO2, behaving as a composited photocatalyst on a nanoscale. Based on the experimental results and theoretical calculations, it was found that the introduction of O–Pd–O surface species and the carbon nanoparticles extend the absorption into the visible light region and facilitate the separation of photogenerated charge carriers, resulting in a much better photocatalytic activity of the photo-reduction of CO2 into CH4, than would be achieved with TiO2–Pd and TiO2/C samples.

Doping and transformation mechanisms of Fe3+ ions in Fe-doped TiO2

A series of Fe-doped TiO2 samples with different concentrations of Fe3+ ions annealed at different temperatures were prepared using a sol–gel method. For Fe-doped TiO2, the existing states of Fe3+, the transformation of these existing states and the phase transition are investigated. It is revealed that the existing states of Fe3+ and the transformation of these existing states (substitutional Fe3+, α-Fe2O3 and Fe2TiO5) are closely related to the annealing temperature and the concentration of Fe3+. The anatase–rutile (A–R) transition is promoted by the substitutionally doped Fe in the TiO2 lattice. In addition, the Fe-doped TiO2 with a high calcination temperature (800 °C) and high doping concentration (x > 20) shows obvious ultrasonic piezoelectric catalytic activity for the reduction of CO2 to CH4. This work may be useful in understanding the doping mechanisms of Fe-doped TiO2, and the fabrication of new catalytic materials.

Corrigendum: Efficient visible-light photocatalytic degradation system assisted by conventional Pd catalysis

This corrects the article DOI: 10.1038/srep09561.