Weiming Wu

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.

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.

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.

An efficient cocatalyst of defect-decorated MoS2 ultrathin nanoplates for the promotion of photocatalytic hydrogen evolution over CdS nanocrystal

The defect degree of MoS2 ultrathin nanoplates are tailored easily via a facile one-pot hydrothermal method. The defect-rich MoS2 ultrathin nanoplates show excellent promotion of photocatalytic hydrogen evolution over CdS; 5.4 times as much as that of the CdS/Pt (1%), which arises from the dual-functional effect of the unique defect-decorated MoS2 ultrathin nanoplates.

A simple and highly efficient route for the preparation of p-phenylenediamine by reducing 4-nitroaniline over commercial CdS visible light-driven photocatalyst in water

Highly efficient photocatalytic reduction of 4-nitroaniline to p-phenylenediamine over a commercial CdS photocatalyst was observed under visible light irradiation (λ ≥ 420 nm) in water. The conversion of 4-nitroaniline and the selectivity of p-phenylenediamine were ∼100% and ∼98% after 9 min of visible light irradiation, respectively. The photoreduction efficiency of 4-nitroaniline over the CdS photocatalyst remained above 95% in the 5th cycle of testing. Its photocatalytic activity was much higher than those of nitrogen-doped TiO2 and commercial TiO2 photocatalysts. Further experimental results revealed that the ammonium formate and N2 atmosphere were indispensable for the photocatalytic reduction of 4-nitroaniline over the CdS photocatalyst. On the basis of the results of electron spin resonance, photoexcited electrons and ·CO2− radicals were detected in the present system. These species had strong reductive powers, and were therefore able to efficiently reduce 4-nitroaniline to p-phenylenediamine.

An architecture of CdS/H2Ti5O11 ultrathin nanobelt for photocatalytic hydrogenation of 4-nitroaniline with highly efficient performance

A CdS/H2Ti5O11 ultrathin nanobelt nanocomposite (CdTi) was fabricated successfully by a two-step process. It was confirmed by SEM and TEM/HRTEM that the highly dispersed CdS about 15 nm in size was firmly anchored on the ultrathin nanobelt. The as-prepared CdTi-5 with an optimal loading of 81.3% CdS converted 4-nitroaniline to p-phenylenediamine, giving almost 100% yield with a selectivity of about 98% in 3 min under visible light irradiation. Its photocatalytic activity was much higher than that of the bare CdS and P25/CdS composition. The highly efficient performance was attributed to the synergetic effects of the formed heterojunction between titanate, nanobelt and CdS as well as the unique features of the titanate nanobelt, which makes the photo-generated electron to transfer smoothly and promotes the separation of photo-induced carriers. Finally, based on the experimental results of Mott–Schottky, UV-vis DRS and EPR, a possible reaction mechanism for the hydrogenation of 4-nitroaniline over the CdTi was proposed.

Template-free synthesis of a CdSnO3⋅3H2O hollow-nanocuboid photocatalyst via a facile microwave hydrothermal method

A CdSnO3·3H2O hollow-nanocuboid photocatalyst was successfully synthesized via a facile template-free microwave hydrothermal method for the first time. The as-prepared samples were characterized by x-ray diffraction, UV-vis diffuse reflectance spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis and x-ray photoelectron spectroscopy. Moreover, samples prepared under different reaction times were analyzed by transmission electron microscopy to investigate the formation process of the CdSnO3·3H2O hollow-nanocuboids. Based on this result, a possible mechanism for the formation process was proposed. The sample prepared at 160 °C for 2 h at pH 11 exhibited the best photocatalytic activity and stability for the degradation of gaseous benzene under UV irradiation (λ = 254 nm) as compared with the other samples. The conversion and mineralization rates of benzene were about 12.5% and 67%, respectively. The mineralization rate was twice as high as that of commercial TiO2 (Degussa Co.). Furthermore, the excellent stability for the benzene decomposition was attributed to the positive charge on the catalyst surface, which was analyzed both by electron spin resonance and Zeta-potentials.

Highly efficient visible-light-induced photocatalytic hydrogenation of nitrobenzene to aniline in water

Highly efficient visible-light-induced photocatalytic hydrogenation of nitrobenzene to aniline in water was observed over a Bi2MoO6 photocatalyst under N2 atmosphere in the presence of (NH4)2C2O4 as a hole scavenger. 100% of the nitrobenzene was converted and the selectivity of aniline was ∼97% after 20 min of visible light irradiation (λ ≥ 400 nm). The Bi2MoO6 photocatalyst showed good catalytic stability for the hydrogenation of nitrobenzene. Further experimental results revealed that both (NH4)2C2O4 and the N2 atmosphere were indispensable for the photocatalytic hydrogenation of nitrobenzene to aniline over the Bi2MoO6 photocatalyst. On the basis of the electron spin resonance analysis results, photoinduced electrons of the Bi2MoO6 photocatalyst were found to be the main active species for the hydrogenation of nitrobenzene. Moreover, a mechanism was proposed to explain the visible-light-induced photocatalytic hydrogenation of nitrobenzene to aniline over the Bi2MoO6 photocatalyst.