Ling Wu

Multivalency Iodine Doped TiO2: Preparation, Characterization, Theoretical Studies, and Visible-Light Photocatalysis

Multivalency iodine (I(7)+/I(-)) doped TiO(2) were prepared via a combination of deposition-precipitation process and hydrothermal treatment. The as-prepared samples were characterized by X-ray diffraction, transmission electron microscopy, Brunauer-Emmett-Teller surface area, UV-vis diffuse reflectance spectra, X-ray photoelectron spectroscopy, surface photovoltage spectroscopy, and electric-field-induced surface photovoltage spectroscopy. The electronic structure calculations based on the density functional theory revealed that upon doping, new states that originated from the I atom of the IO(4) group are observed near the conduction-band bottom region of TiO(2), and the excitation from the valence band of TiO(2) to the surface IO(4-) is responsible for the visible-light response of the I-doped TiO(2). The as-prepared I-doped TiO(2) showed high efficiency for the photocatalytic decomposition of gaseous acetone under visible light irradiation (lambda > 420 nm). A possible mechanism for the photocatalysis on this multivalency iodine (I(7)+/I(-)) doped TiO(2) under visible light was also proposed.

Highly dispersed palladium nanoparticles anchored on UiO-66(NH2) metal-organic framework as a reusable and dual functional visible-light-driven photocatalyst

Proper design and preparation of high-performance and stable dual functional photocatalytic materials remains a significant objective of research. In this work, highly dispersed Pd nanoparticles of about 3-6 nm in diameter are immobilized in the metal-organic framework (MOF) UiO-66(NH₂) via a facile one-pot hydrothermal method. The resulting Pd@UiO-66(NH₂) nanocomposite exhibits an excellent reusable and higher visible light photocatalytic activity for reducing Cr(vi) compared with UiO-66(NH₂) owing to the high dispersion of Pd nanoparticles and their close contact with the matrix, which lead to the enhanced light harvesting and more efficient separation of photogenerated electron-hole pairs. More significantly, the Pd@UiO-66(NH₂) could be used for simultaneous photocatalytic degradation of organic pollutants, like methyl orange (MO) and methylene blue (MB), and reduction of Cr(vi) with even further enhanced activity in the binary system, which could be attributed to the synergetic effect between photocatalytic oxidation and reduction by individually consuming photogenerated holes and electrons. This work represents the first example of using the MOFs-based materials as dual functional photocatalyst to remove different categories of pollutants simultaneously. Our finding not only proves great potential for the design and application of MOFs-based materials but also might bring light to new opportunities in the development of new high-performance photocatalysts.

MIL-53(Fe) as a highly efficient bifunctional photocatalyst for the simultaneous reduction of Cr(VI) and oxidation of dyes

A bifunctional photocatalyst-Fe-benzenedicarboxylate (MIL-53(Fe)) has been synthesized successfully via a facile solvothermal method. The resulting MIL-53(Fe) photocatalyst exhibited an excellent visible light (λ≥ 420nm) photocatalytic activity for the reduction of Cr(VI), the reduction rate have reached about 100% after 40min of visible light irradiation, which has been more efficient than that of N-doped TiO2 (85%) under identical experimental conditions. Further experimental results have revealed that the photocatalytic activity of MIL-53(Fe) for the reduction of Cr(VI) can be drastically affected by the pH value of the reaction solution, the hole scavenger and atmosphere. Moreover, MIL-53(Fe) has exhibited considerable photocatalytic activity in the mixed systems (Cr(VI)/dyes). After 6h of visible light illumination, the reduction ratio of Cr(VI) and the degradation ratio of dyes have been exceed 60% and 80%, respectively. More significantly, the synergistic effect can also be found during the process of photocatalytic treatment of Cr(VI) contained wastewater under the same photocatalytic reaction conditions, which makes it a potential candidate for environmental restoration. Finally, a possible reaction mechanism has also been investigated in detail.

N-Doped SiO2/TiO2 mesoporous nanoparticles with enhanced photocatalytic activity under visible-light irradiation

Mesoporous nanocrystalline N-doped SiO2/TiO2 visible-light photocatalysts were prepared by treating SiO2/TiO2 xerogels in a flow of nitrogen gas bubbled through concentrated ammonia solution. Structural characterization and performance analysis results revealed that the addition of SiO2 remarkably altered the phase composition, specific surface area, microstructure, as well as the photocatalytic activity of N-doped TiO2. The presence of SiO2 in N-doped TiO2 particles suppressed the formation of rutile phase and the crystal growth of N-doped TiO2 particles during thermal calcinations. When weight ratio of SiO2/TiO2 was in 0.05-0.20, the N-doped SiO2/TiO2 exhibited higher photocatalytic activity than the N-doped TiO2, and optimum ratio was found to be 0.05. The enhanced photocatalytic activity could be attributed to the higher specific area, larger pore volume, and more surface hydroxyl groups in the catalyst.

CdS-decorated UiO–66(NH2) nanocomposites fabricated by a facile photodeposition process: an efficient and stable visible-light-driven photocatalyst for selective oxidation of alcohols

CdS nanorods have been successfully decorated on the surface of MOF (metal–organic framework) UiO–66(NH2) via a facile room-temperature photodeposition technique in a controlled manner. Electrochemical measurements indicate that the CdS photodeposition proceeds via the preferential reduction of Cd ions to Cd0 followed by chemical reaction with S8. The photocatalytic performances of the obtained CdS–UiO–66(NH2) nanocomposites have been evaluated by selective oxidation of various alcohol substrates using molecular oxygen as a benign oxidant. The results show that such CdS–UiO–66(NH2) nanocomposites exhibit considerable photocatalytic activity and stability, which may be due to the large specific surface area and the charge injection from CdS into UiO–66(NH2) leads to efficient and longer charge separation by reducing the recombination of electron–hole pairs. This work represents the first example of using MOFs not only as supports but also as electron providers to trigger the reaction for coupling MOFs with metal sulfides, thus fabricating novel MOF–CdS nanocomposite systems and improving their photocatalytic activity. It is hoped that our findings could offer useful information and open a new window for the design of novel MOF–semiconductor nanocomposites as efficient visible light driven photocatalysts.

Monolayer HNb3O8 for Selective Photocatalytic Oxidation of Benzylic Alcohols with Visible Light Response

Monolayer HNb3O8 2D nanosheets have been used as highly chemoselective and active photocatalysts for the selective oxidation of alcohols. The nanosheets exhibit improved photocatalytic activity over their layered counterparts. Results of in situ FTIR, DRS, ESR, and DFT calculations show the formation of surface complexes between the Lewis acid sites on HNb3O8 2D nanosheets and alcohols. These complexes play a key role in the photocatalytic activity of the material. Furthermore, the unique structural features of the nanosheets contributed to their high photocatalytic activity. An electron transition from the coordinated alcohol species to surface Nb atoms takes place and initiates the aerobic oxidation of alcohols with high product selectivity under visible light irradiation. This reaction process is distinct from that of classic semiconductor photocatalysis.

Microemulsion-mediated solvothermal synthesis of nanosized CdS-sensitized TiO2 crystalline photocatalystElectronic supplementary information (ESI) available: UV-visible absorption spectra, XRD patterns and EPR spectrum. See http://www.rsc.org/suppdata/cc/b3/b302418k/

Nanosized CdS-sensitized TiO2 nanocrystals were successfully prepared by a microemulsion-mediated solvothermal method. The effectiveness of the new photocatalyst was demonstrated by the decomposition of an organic compound and the formation of Ti3+ on TiO2 under visible-light irradiation.

Rapid template-free synthesis and photocatalytic performance of visible light-activated SnNb2O6 nanosheets

Visible light-activated SnNb2O6 nanosheets (NSs) with high surface area and small crystallites have been prepared by a microwave-assisted template-free hydrothermal method without exfoliation for the first time. This approach could be used to prepare the functional materials efficiently and extended to synthesizing two-dimensional nanosheet materials directly as well. The crystalline phases, photoabsorption performances, and surface areas and porosity of the samples are characterized by XRD, UV-vis diffuse reflectance spectroscopy (UV-vis DRS), and N2-adsorption. Results show that a hypsochromic shift of the photoabsorption edge is observed, which reflects an obvious quantum size effect. TEM images reveal SnNb2O6 nanosheets with a thickness of 1–4 nm versus several hundred nanometres in lateral size. Based on the experimental results, the formation mechanism of SnNb2O6 nanosheets is also studied and proposed, which reasonably follows a synergy interaction of reaction–crystallization and dissolution–recrystallization processes. Due to the unique morphology, larger surface area, smaller crystallites and stronger redox ability of the photogenerated hole–electron pair, these photocatalysts show much higher photocatalytic activities for the degradation of rhodamine B (RhB) compared with their counterparts prepared by the traditional solid-state reaction. The reaction rate is enhanced by over 4 times and the RhB molecule can be mineralized into CO2 and H2O over SnNb2O6 NSs. The decomposition mechanism of RhB over SnNb2O6 under visible light irradiation and the active species in the photocatalytic process have also been discussed.

One-Dimensional CdS/TiO2 Nanofiber Composites as Efficient Visible-Light-Driven Photocatalysts for Selective Organic Transformation: Synthesis, Characterization, and Performance

CdS/TiO2 heterojunction nanofibers have been successfully synthesized through the photodeposition of CdS on 1D TiO2 nanofibers that were prepared via a facile electrospinning method. The as-synthesized samples showed high photocatalytic activities upon selectively oxidizing a series of alcohols into corresponding aldehydes under visible light irradiation. TEM observations revealed that CdS was closely grown on the TiO2 nanofibers. Moreover, it was found that the CdS/TiO2 nanofibers that were photodeposited for 4 h exhibited the highest catalytic activity, with a conversion of 22% and a selectivity of 99%, which were much higher than those of commercial CdS. In addition, we also discuss the photoabsorption performance and the reaction mechanism of the photocatalytic oxidation of alcohols.

Catalytic Role of Cu Sites of Cu/MCM-41 in Phenol Hydroxylation

Four types of copper-containing MCM-41 mesoporous silicas were synthesized by the surface organometallic chemistry (SOMC) procedure (Cu/MCM-41-S), mechanical mixing (Cu/MCM-41-M), impregnation (Cu/MCM-41-I), and the hydrothermal technique (Cu/MCM-41-H). The resultant samples were characterized in detail by X-ray diffraction (XRD), N(2) physical adsorption, transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), temperature-programmed reduction (TPR), and infrared spectroscopy (IR) of NO adsorption. Catalytic behaviors of these samples for hydroxylation of phenol with H(2)O(2) were evaluated. The results revealed that depending on the preparation methods the samples contain different copper-oxo species and thus show different catalytic behaviors. Among these samples, the one prepared by SOMC contains a predominant amount of isolated Cu(2+) and exhibits the most excellent catalytic activity and selectivity. The amount of isolated copper species decreases in the order of Cu/MCM-41-S > Cu/MCM-41-H > Cu/MCM-41-I > Cu/MCM-41-M, while the amount of copper oxide clusters increases in a reversal order. The difference in the catalytic activity and product selectivity of these four samples could be rationally explained by the distinction of chemical states of copper species. The highly dispersed isolated Cu(2+) species are identified as the active sites in the phenol hydroxylation, while the nonisolated Cu(2+) clusters or oxide are responsible for the deep oxidation of primary product HQ and the decrease of product selectivity. The mechanism of the copper-catalyzed phenol hydroxylation was proposed.