Ruowen Liang

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.

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.

Preparation of MIL-53(Fe)-Reduced Graphene Oxide Nanocomposites by a Simple Self-Assembly Strategy for Increasing Interfacial Contact: Efficient Visible-Light Photocatalysts

In this work, MIL-53(Fe)-reduced graphene oxide (M53-RGO) nanocomposites have been successfully fabricated by a facile and efficient electrostatic self-assembly strategy for improving the interfacial contact between RGO and the MIL-53(Fe). Compared with D-M53-RGO (direct synthesis of MIL-53(Fe)-reduced graphene oxide nanocomposites via one-pot solvothermal approach), M53-RGO nanocomposites exhibit improved photocatalytic activity compared with the D-M53-RGO under identical experimental conditions. After 80 min of visible light illumination (λ ≥ 420 nm), the reduction ratio of Cr(VI) is rapidly increased to 100%, which is also higher than that of reference sample (N-doped TiO2). More significantly, the M53-RGO nanocomposites are proven to perform as bifunctional photocatalysts with considerable activity in the mixed systems (Cr(VI)/dyes) under visible light, which made it a potential candidate for industrial wastewater treatment. Combining with photoelectrochemical analyses, it could be revealed that the introduction of RGO would minimize the recombination of photogenerated electron-hole pairs. Additionally, the effective interfacial contact between MIL-53(Fe) and RGO surface would further accelerate the transfer of photogenerated electrons, leading to the enhancement of photocatalytic activity of M53-RGO toward photocatalytic reactions. Finally, a possible photocatalytic reaction mechanism is also investigated in detail.

Electrostatically derived self-assembly of NH2-mediated zirconium MOFs with graphene for photocatalytic reduction of Cr(VI)

Novel photocatalysts RGO-UiO-66(NH2) were synthesized via an electrostatically derived self-assembly of UiO-66(NH2) with graphene, followed by hydrothermal reduction. Such nanocomposites exhibit enhanced photocatalytic activity for the reduction of Cr(VI) compared with the pristine UiO-66(NH2).

M@MIL-100(Fe) (M = Au, Pd, Pt) nanocomposites fabricated by a facile photodeposition process: Efficient visible-light photocatalysts for redox reactions in water

Proper design and preparation of high-performance and stable dual functional photocatalytic materials remains a significant objective of research. In this work, highly dispersed noble-metal nanoparticles (Au, Pd, Pt) were immobilized on MIL-100(Fe) (denoted M@MIL-100(Fe)) using a facile room-temperature photodeposition technique. The resulting M@MIL-100(Fe) (M = Au, Pd, and Pt) nanocomposites exhibited enhanced photoactivities toward photocatalytic degradation of methyl orange (MO) and reduction of heavy-metal Cr(VI) ions under visible-light irradiation (λ ≥ 420 nm) compared with blank-MIL-100(Fe). Combining these results with photoelectrochemical analyses revealed that noble-metal deposition can effectively improve the charge-separation efficiency of MIL-100(Fe) under visible-light irradiation. This phenomenon in turn leads to the enhancement of visible-light-driven photoactivity of M@MIL-100(Fe) toward photocatalytic redox reactions. In particular, the Pt@MIL-100(Fe) with an average Pt particle size of 2 nm exhibited remarkably enhanced photoactivities compared with those of M@MIL-100(Fe) (M = Au and Pd), which can be attributed to the integrative effect of the enhanced light absorption intensity and more efficient separation of the photogenerated charge carrier. In addition, possible photocatalytic reaction mechanisms are also proposed.

Strategies for engineering metal-organic frameworks as efficient photocatalysts

Abstract Environmental pollution and energy deficiency represent major problems for the sustainability of the modern world. Photocatalysis has recently emerged as an effective and environmentally friendly technique to address some of these sustainability issues, although the key to the success of this approach is dependent on the photocatalysts themselves. Based on their attractive physic chemical properties, including their ultrahigh surface areas, homogeneous active sites and tunable functionality, metal-organic frameworks (MOFs) have become interesting platforms for the development of solar energy conversion devices. Furthermore, MOFs have recently been used in a wide variety of applications, including heterogeneous photocatalysis for pollutant degradation, organic transformations, hydrogen production and CO2 reduction. In this review, we have highlighted recent progress towards the application of MOFs in all of these areas. We have collected numerous reported examples of the use of MOFs in these areas, as well as providing some analysis of the key factors influencing the efficiency of these systems. Moreover, we have provided a detailed discussion of new strategies that have been developed for enhancing the photocatalytic activity of MOFs. Finally, we have provided an outlook for this area in terms of the future challenges and potential prospects for MOFs in photocatalysis.

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.