Xuliang Zhang

Improved visible-light activities for degrading pollutants on TiO2/g-C3N4 nanocomposites by decorating SPR Au nanoparticles and 2,4-dichlorophenol decomposition path

It has been clearly demonstrated that the visible-light photocatalytic activities of g-C3N4 (CN) for degrading 2,4-dichlorophenol (2,4-DCP) and bisphenol A (BPA) could be improved by fabricating nanocomposites with a proper amount of nanocrystalline anatase TiO2. Interestingly, the visible-light activities of the amount-optimized nanocomposite could be further improved after decorating Au nanoparticles, with 5.11- and 3.1-time improvement respectively for 2,4-DCP and BPA compared to that of CN, even much higher than that of P25 TiO2 under UV-vis irradiation. Based on the transient-state surface photovoltage responses and photoelectrochemical measurements, it is confirmed that the exceptional visible-light activities of the fabricated Au-(TiO2/g-C3N4) nanocomposites are attributed to the extended visible-light response due to the surface plasmonic resonance (SPR) of decorated Au and its catalytic function, and to the enhanced charge separation by transferring electrons from CN and SPR Au to TiO2 in the nanocomposites. The highly promoted charge separation results in the effective availability of a large number of hydroxyl radicals (OH) participating in the photocatalytic oxidation process of 2,4-DCP. Furthermore, a possible mechanism of 2,4-DCP degradation is proposed according to the detailed analyses of produced intermediates. This work provides new idea for designing Au assisted nanocomposite photocatalysts for environmental remediation.

Exceptional performance of photoelectrochemical water oxidation of single-crystal rutile TiO2 nanorods dependent on the hole trapping of modified chloride

It is highly desired to effectively trap photogenerated holes for efficient photoelectrochemical (PEC) water oxidation to evolve O2 on oxide semiconductors. Herein, it is found for the first time mainly based on the time-resolved- and atmosphere-controlled- surface photovoltage responses that the modified chloride would effectively trap photogenerated holes so as to prolong the charge lifetime and hence promote charge separation of single-crystal rutile TiO2 nanorods. Its strong capacity to trap holes, comparable to the widely-used methanol and Co(II) phosphate, is well responsible for the exceptional photoactivities for PEC water oxidation to evolve O2 on rutile nanorods with a proper amount of chloride modified, about 2.5-time high as that on the resulting anatase nanoparticles, even 10-time if the surface area is considered. Moreover, it is suggested that the hole trapping role of chemically-adsorbed chloride is related to its lonely-pair electrons, and to the subsequently-produced intermediate Cl atoms with proper electronegativity for evolving O2. Interestingly, this finding is also applicable to the chloride-modified anatase TiO2. This work will provide a feasible strategy to design high-activity nanostructured semiconductor photoanodes for PEC water oxidation, even for overall water splitting.

Coupling of Nanocrystalline Anatase TiO2 to Porous Nanosized LaFeO3 for Efficient Visible-Light Photocatalytic Degradation of Pollutants

In this work we have successfully fabricated nanocrystalline anatase TiO2/perovskite-type porous nanosized LaFeO3 (T/P-LFO) nanocomposites using a simple wet chemical method. It is clearly demonstrated by means of atmosphere-controlled steady-state surface photovoltage spectroscopy (SPS) responses, photoluminescence spectra, and fluorescence spectra related to the formed OH− radical amount that the photogenerated charge carriers in the resultant T/P-LFO nanocomposites with a proper mole ratio percentage of TiO2 display much higher separation in comparison to the P-LFO alone. This is highly responsible for the improved visible-light activities of T/P-LFO nanocomposites for photocatalytic degradation of gas-phase acetaldehyde and liquid-phase phenol. This work will provide a feasible route to synthesize visible-light responsive nano-photocatalysts for efficient solar energy utilization.

Prolonged lifetime and enhanced separation of photogenerated charges of nanosized α-Fe2O3 by coupling SnO2 for efficient visible-light photocatalysis to convert CO2 and degrade acetaldehyde

To develop efficient visible-light photocatalysis on α-Fe2O3, it is highly desirable to promote visible-light-excited high-energy-level electron transfer to a proper energy platform thermodynamically. Herein, based on the transient-state surface photovoltage responses and the atmosphere-controlled steady-state surface photovoltage spectra, it is demonstrated that the lifetime and separation of photogenerated charges of nanosized α-Fe2O3 are increased after coupling a proper amount of nanocrystalline SnO2. This naturally leads to greatly improved photocatalytic activities for CO2 reduction and acetaldehyde degradation. It is suggested that the enhanced charge separation results from the electron transfer from α-Fe2O3 to SnO2, which acts as a proper energy platform. Based on the photocurrent action spectra, it is confirmed that the coupled SnO2 exhibits longer visible-light threshold wavelength (~590 nm) compared with the coupled TiO2 (~550 nm), indicating that the energy platform introduced by SnO2 would accept more photogenerated electrons from α-Fe2O3. Moreover, electrochemical reduction experiments proved that the coupled SnO2 possesses better catalytic ability for reducing CO2 and O2. These are well responsible for the much efficient photocatalysis on SnO2-coupled α-Fe2O3.

Dimension-matched plasmonic Au/TiO2/BiVO4 nanocomposites as efficient wide-visible-light photocatalysts to convert CO2 and mechanistic insights

Dimension (D)-matched plasmonic Au/TiO2/BiVO4 nanocomposites have been successfully constructed by first preparing BiVO4 nanoflakes via an ion exchange process from BiOCl nanosheets, followed by coupling (001) facet-exposed anatase TiO2 nanosheets and then modifying plasmonic Au nanorods. The well-designed 1D/2D/2D nanocomposites exhibit exceptional visible-light photocatalytic activities for CO2 conversion, and these nanocomposites indicate ∼30-fold and ∼60-fold enhancements compared to the resulting BiVO4 nanoflakes and the previously-reported BiVO4 nanoparticles, respectively. Based on steady-state surface photovoltage spectroscopy, transient-state surface photovoltage responses, wavelength-dependent photocurrent action spectra and fluorescence spectra related to the amount of produced ˙OH species, it is confirmed that the exceptional photocatalytic activity can be comprehensively ascribed to the following phenomena which result from the fabrication of 2D nanoflakes: increased specific surface area of BiVO4, coupling of TiO2 nanosheets to form a new proper-energy platform, which can accept photogenerated electrons from BiVO4 and plasmonic Au so as to greatly enhance the charge separation, and modified plasmonic Au with the extended wide-visible-light absorption to 660 nm, which can act as the co-catalyst for the transferred electrons to induce reduction reactions. Moreover, dimension matching in the fabricated nanocomposite is very favorable for photogenerated charge transfer and separation. Furthermore, isotope experiments of 13CO2 and D2O along with electrochemical measurements suggest that the produced H atoms are dominant active radicals, which can initiate the conversion of CO2.