Shijing Liang

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.

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.

Covalent Triazine-Based Frameworks as Visible Light Photocatalysts for the Splitting of Water.

Covalent triazine-based frameworks (CTFs) with a graphene-like layered morphology have been controllably synthesized by the trifluoromethanesulfonic acid-catalyzed nitrile trimerization reactions at room temperature via selecting different monomers. Platinum nanoparticles are well dispersed in CTF-T1, which is ascribed to the synergistic effects of the coordination of triazine moieties and the nanoscale confinement effect of CTFs. CTF-T1 exhibits excellent photocatalytic activity and stability for H2 evolution in the presence of platinum under visible light irradiation (λ ≥ 420 nm). The activity and stability of CTF-T1 are comparable to those of g-C3 N4 . Importantly, as a result of the tailorable electronic and spatial structures of CTFs that can be achieved through the judicial selection of monomers, CTFs not only show great potential as organic semiconductor for photocatalysis but also may provide a molecular-level understanding of the inherent heterogeneous photocatalysis.

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.

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).

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.

Layered indium chalcogenidoantimonates [Me2NH2]2In2Sb2S7-xSex (x = 0, 2.20, 4.20, 7) with tunable band gaps and photocatalytic properties

Two novel indium chalcogenidoantimonates and their quaternary mixed solid solutions with a layered structure of [In2Sb2S7-xSex]n2n− are successfully synthesized under mild solvothermal conditions. The compounds show a red-shift of their optical absorption edges and exhibit tunable photocatalytic activity for degradation of methyl orange (MO) with a shift of optical response from UV to the visible light region, as the proportions of Se increase.

Photocatalytic reduction of CO2 with H2O to CH4 over ultrathin SnNb2O6 2D nanosheets under visible light irradiation

Monolayer SnNb2O6 two-dimensional (2D) nanosheets with high crystallinity are prepared by an one-pot and eco-friendly hydrothermal method without any organic additives. For the first time, these SnNb2O6 nanosheets are applied to the photocatalytic reduction of CO2 with H2O to CH4 in the absence of co-catalysts and sacrificial agents under visible light irradiation. The structural features, morphology, photoabsorption performance, and photoelectric response have been investigated in detail. Results show the as-prepared SnNb2O6 samples with typical 2D nanosheets in the thickness of about 1 nm. Owing to the unique features of the nanosheets, the surface area, photoelectrical properties and the surface basicity of SnNb2O6 are greatly improved compared with the counterpart prepared by traditional solid state reaction. Furthermore, the adsorption capacity of CO2 on SnNb2O6 nanosheets is much higher than that of layered SnNb2O6. Thus, the photocatalytic activity of SnNb2O6 nanosheets for the reduction of CO2 is about 45 and 4 times higher than those of the references (layered SnNb2O6 and common N-doped TiO2), respectively. To understand the interactions between the CO2 molecule and the surface of the photocatalyst, and the reactive species in the reduction process, the intermediates have also been detected by in situ FTIR with and without visible light irradiation. Finally, a possible mechanism for the photocatalytic reduction of CO2 with H2O to CH4 on SnNb2O6 nanosheets is proposed. We believe this work will provide new opportunities for expanding the family of visible-light driven photocatalysts for the reduction of CO2.

Ultrathin HNb3O8 nanosheet: an efficient photocatalyst for the hydrogen production

A ultrathin HNb3O8 nanosheet was successfully prepared through a top-down approach. Atomic force microscopy (AFM) further confirmed that the thickness of the nanosheet was about 1.30 nm. The structure and the surface chemical state of the HNb3O8 nanosheet were well-characterized using X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), X-ray absorption fine structure (XAFS), Raman and X-ray photoelectron spectroscopy (XPS). The photocatalytic hydrogen evolution activity of the HNb3O8 nanosheet was about 4 times higher than that of layered HNb3O8 under ultraviolet irradiation. The enhanced activity was ascribed to the unique two-dimensional structure with a molecular thickness that leads to the effective separation of the photogenerated carriers. Moreover, a considerable variation in the photocatalytic hydrogen evolution activity of the HNb3O8 nanosheet was observed when suitable metals were loaded on the nanosheet via in situ photodeposition.