Lijuan Shen

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.

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.

A Clean and General Strategy To Decorate a Titanium Metal–Organic Framework with Noble-Metal Nanoparticles for Versatile Photocatalytic Applications

We demonstrate a facile and general approach for the fabrication of highly dispersed Au, Pd, and Pt nanoparticles (NPs) on MIL-125(Ti) without using extra reducing and capping agents. Noble-metal NP formation is directed by an in situ redox reaction between the reductive MIL-125(Ti) with Ti(3+) and oxidative metal salt precursors. The resulting composites function as efficient 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.

Morphology-controlled synthesis and efficient photocatalytic performances of a new promising photocatalyst Sr0.25H1.5Ta2O6·H2O

A new photocatalyst Sr0.25H1.5Ta2O6·H2O (HST) with high surface area was successfully prepared by a facile and mild hydrothermal reaction using Ta2O5·nH2O as a precursor. TEM images revealed that their different morphologies, from nanoplate to nanopolyhedron, were formed under different pH values of the reactive solutions. The formation mechanism of HST was also studied and proposed. Growth of HST nanocrystallites followed a reaction-crystallization model. By analyzing the results of XRD, DRS, XPS, electrochemistry and theoretical calculation, the crystal and electronic structural characterizations of HST was established. Compared with isostructural Sr0.4H1.2Nb2O6·H2O (HSN), the Ta 5d orbitals were the main contribution to the bottom of the conduction band of HST, inducing the energy level more negative while the top of valence band, which was dominated by O 2p states, remained almost unchanged. Due to the more suitable electronic band structure and various morphologies, the photocatalyst showed superior photocatalytic activities for water splitting to generate H2 and for degrading benzene as compared with HSN. The rate of H2 evolution and the conversion ratio of benzene were 81 times and 4 times higher than that of TiO2 (Degussa P25), respectively. The proposed mechanisms for photocatalytic reactions based on the experimental results were discussed.