Ling Zan

The {001} facets-dependent high photoactivity of BiOCl nanosheets

BiOCl nanosheets (BiOCl NSs) were synthesized by hydrolyzing a hierarchical flowerlike molecular precursor (Bi(n)(Tu)(x)Cl(3n), Tu = thiourea). High photoactivity of {001} facets of BiOCl NSs was observed, and the mechanism was discussed.

Effect of graphitic carbon nitride microstructures on the activity and selectivity of photocatalytic CO2 reduction under visible light

Two kinds of graphitic carbon nitride (g-C3N4) were synthesized through a pyrolysis process of urea or melamine. It is found that the obtained g-C3N4, as photocatalysts, can reduce CO2 to organic fuels under visible light, and exhibit different photoactivity and selectivity on the formation of CH3OH and C2H5OH. The product derived from the urea (denoted as u-g-C3N4) shows a mesoporous flake-like structure with a larger surface area and higher photoactivity for the CO2 reduction than the non-porous flaky product obtained from melamine (denoted as m-g-C3N4). Moreover, using u-g-C3N4 as a photocatalyst can result in the formation of a mixture containing CH3OH and C2H5OH, while m-g-C3N4 only leads to the selective formation of C2H5OH. The present interesting findings could shed light on the design of efficient, eco-friendly and convenient photocatalysts and the tuning of their photoreactivity in the field of sustainable light-to-energy conversion.

Synthesis of highly symmetrical BiOI single-crystal nanosheets and their {001} facet-dependent photoactivity

Highly symmetrical BiOI single-crystal nanosheets (BiOI SCNs) with dominant exposed {001} facets (up to 95%) have been synthesized by annealing BiI3 and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, fast-Fourier transform pattern, UV-vis diffuse reflectance and photoluminescence. The thickness and the {001} facets percentage of BiOI SCNs can be tuned by changing the annealing temperature. The thermal decomposition process of BiI3 and the formation mechanism of BiOI SCNs were investigated. BiOI SCNs exhibit higher photoactivity (about 7 times) than irregular BiOI for degradation of Rhodamine B (RhB) dye under visible light irradiation. The {001} facets are the reactive facets of BiOI. The origin of {001} facets-dependent photoactivity is due to an improvement of the separation efficiency of photo-induced electrons and holes.

Synthesis of anatase TiO2 nanocrystals with {101}, {001} or {010} single facets of 90% level exposure and liquid-phase photocatalytic reduction and oxidation activity orders

Anatase TiO2 nanocrystals with {101}, {001} or {010} single facets of 90% level exposure were controllably synthesized from potassium titanate (PT) without fluorine and organic capping surfactants, and characterized by X-ray diffraction patterns (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and fast Fourier transformation (FFT). The liquid-phase photocatalytic reduction (O2˙− generation) and oxidation (˙OH generation) activity orders of anatase TiO2 facets are {001} > {101} > {010} upon removing facet synergetic effect and surface fluorine effect. UV-vis diffuse reflectance spectra (DRS) and photoluminescence (PL) spectra showed that absorbance edge order, and separation efficiency order of photoexcited holes and electrons are {001} > {101} > {010}, which explains the photocatalytic activity order well together with the atomic arrangement of different facets.

Bin(Tu)xCl3n: a novel sensitizer and its enhancement of BiOCl nanosheets’ photocatalytic activity

Bismuth complexes, Bin(Tu)xCl3n, were found to be photosensitizers for the first time. BiOCl nanosheets with inner Bin(Tu)xCl3n were synthesized and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, selected area electron diffraction, high-resolution transmission electron microscopy, UV-vis diffuse reflectance, Fourier transform infrared spectrometry, thermogravimetric analyses and photoluminescence. The as-synthesized BiOCl displayed high visible light (λ ≥ 420 nm) photocatalytic activity which was 112 and 13 times higher than P25 and BiOCl without Bin(Tu)xCl3n, for degrading RhB, respectively. The investigation of the photocatalytic mechanism demonstrated that Bin(Tu)xCl3n sensitized the BiOCl and resulted in unusually high visible light photocatalytic activity. The superoxide radical was the main active species in the photodegradation process. Furthermore, the concentration of the superoxide radical was quantized by the molecular probe nitroblue tetrazolium.

Dramatic visible light photocatalytic activity of MnOx–BiOI heterogeneous photocatalysts and the selectivity of the cocatalyst

Charge separation is very important for increasing the activity of semiconductor-based photocatalysts. Here we show that the main active species of BiOI are photo-induced holes, rather than ˙OH and O2˙−, under visible light irradiation. Based on this finding, the cocatalyst MnOx was used to enhance the transfer of the photo-induced holes, resulting in much higher photocatalytic activity, compared with the photocatalyst without MnOx. MnOx–BiOI heterogeneous nanostructure photocatalysts have been prepared by photo-deposition in Mn(NO3)2 solution, and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectroscopy. As-prepared MnOx–BiOI exhibited higher photoactivity than BiOI and Pt–BiOI for the degradation of Rhodamine B (RhB) dye under visible light irradiation. The PL spectrum showed that MnOx enhances the separation efficiency of the photo-induced electrons and holes of BiOI. Finally, BiOI was selectively combined with a deriving-hole-type cocatalyst to enhance the photocatalytic activity, and the reason for the cocatalyst selectivity is also discussed. This finding may be useful in bismuth-based photocatalysts to construct highly efficient solar energy conversion systems.

High photocatalytic degradation activity of the polyvinyl chloride (PVC)-vitamin C (VC)-TiO2 nano-composite film.

A novel photodegradable polyvinyl chloride (PVC)-vitamin C (VC)-TiO(2) nano-composite film was prepared by embedding VC modified nano-TiO(2) photocatalyst into the commercial PVC plastic. The solid-phase photocatalytic degradation behavior of PVC-VC-TiO(2) nano-composite film under UV light irradiation was investigated and compared with those of the PVC-TiO(2) film and the pure PVC film, with the aid of UV-Vis spectroscopy, scanning electron microscopy (SEM), weight loss monitoring, and X-ray diffraction spectra (XRD). The results show that PVC-VC-TiO(2) nano-composite film has a high photocatalytic activity; the photocatalytic degradation rate of it is two times higher than that of PVC-TiO(2) film and fifteen times higher than that of pure PVC film. The optimal mass ratio of VC to TiO(2) is found to be 0.5. The mechanism of enhancing photocatalytic activity is attributed to the formation of a Ti(IV)-VC charge-transfer complex with five-member chelate ring structure and a rapid photogenerated charge separation is thus achieved.

Opposite photocatalytic activity orders of low-index facets of anatase TiO2 for liquid phase dye degradation and gaseous phase CO2 photoreduction

We firstly demonstrate the opposite photocatalytic activity orders of low-index facets of anatase TiO2 in the liquid phase for rhodamine B (RhB) photocatalytic degradation and in the gaseous phase for the photoreduction of CO2 to CH4. The photocatalytic activity order in the liquid phase for RhB photocatalytic degradation is revealed as {001} > {101} > {010}, whereas the photocatalytic activity order {010} > {101} > {001} is found in the gaseous phase for the photoreduction of CO2 to CH4. The atomic arrangement of the different facets, UV-vis diffuse reflectance spectra, photoluminescence spectra and attenuated total reflectance Fourier transform infrared spectroscopy analysis show that the photoactivity order in the gas phase for the photoreduction of CO2 to CH4 mainly depends on the CO2 molecule adsorption properties on the different exposed facets, and the separation efficiency of the photo-generated carriers determines the photoactivity order for the dye degradation reaction in the liquid phase. These findings also provide a new direction to design efficient photocatalysts and the tuning of their photoreactivity for environmental and energy applications.

Ag size-dependent visible-light-responsive photoactivity of Ag–TiO2 nanostructure based on surface plasmon resonance

Anatase TiO2 nanocrystals with regular polyhedron morphology and co-exposed {001} and {101} facets are prepared, and then ultrafine Ag nanoparticles (SAg NPs) with different sizes are loaded on those TiO2 facets (denoted as SAg–TiO2) through a novel in situ photoreduction approach. For comparison, Ag nanoparticles (PAg NPs) are also loaded on TiO2 facets (denoted as PAg–TiO2) by a traditional photodeposition method. The experimental results show that PAg NPs with a size of ∼20 nm only appeared on the {101} facets of TiO2, while SAg NPs with a much smaller size (1–6 nm) are highly dispersed on both {001} and {101} facets of TiO2. The size of Ag NPs plays an important role in surface plasmon resonance (SPR) effect and the photogenerated carrier separation process, and those Ag NPs loaded on TiO2 facets show size-dependent photoactivity for the RhB degradation. SAg–TiO2 with ultrafine SAg NPs on both {001} and {101} facets of TiO2 results in more substantial visible-light-responsive photoactivity and stability than PAg–TiO2 with larger Ag NPs on {101} facets of TiO2. Moreover, the RhB photodegradation reaction rate constant of SAg–TiO2 with Ag particle size of ∼1 nm is 10 and 21.3 times higher than that of PAg–TiO2 and the pristine TiO2, respectively.

Synthesis of multicomponent sulfide Ag2ZnSnS4 as an efficient photocatalyst for H2 production under visible light irradiation

Stannite-type multicomponent sulfide (Ag2ZnSnS4) nanoparticles with particle diameters of 100–200 nm were synthesized through a solvothermal treatment combined with a post-annealing process under N2 atmosphere. The obtained Ag2ZnSnS4 was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), UV-vis diffuse reflectance spectroscopy (DRS) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activities for hydrogen production of Ag2ZnSnS4 were evaluated under visible light (λ ≥ 420 nm) irradiation. It was found that the 1.0 wt% Pt-loaded Ag2ZnSnS4 displayed a photocatalytic hydrogen evolution activity of 580 μmol h−1 with a fairly good apparent quantum efficiency of 15.2% at 420 nm incident light irradiation.