Jinhong Bi

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.

Template-free hydrothermal synthesis and photocatalytic performances of novel Bi2SiO5 nanosheets.

Orthorhombic Bi(2)SiO(5) nanosheets with thicknesses of 10-20 nm were first synthesized by a template-free hydrothermal synthesis process using Bi(NO(3))(3) and different Si sources as raw materials. The as-prepared samples were characterized by X-ray diffraction, Brunauer-Emmett-Teller (BET) surface area analysis, UV-vis diffuse reflectance spectroscopy, scanning electron microscopy, high-resolution transmission electron microscopy, and a photoluminescence technique with terephthalic acid. The results showed that different precursors led to samples with different morphologies, particle sizes, and BET surface areas. As a novel photocatalyst, the photocatalytic performances of Bi(2)SiO(5) samples were evaluated by the photocatalytic degradation of salicylic acid and gaseous benzene. The results revealed that the sample obtained from Na(2)SiO(3) as a precursor exhibited higher activity than that from (C(2)H(5)O)(4)Si due to its biscuit-like morphology, a smaller particle size, and a higher BET surface areas.

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.

Sulfur-doped covalent triazine-based frameworks for enhanced photocatalytic hydrogen evolution from water under visible light

Here, we show for the first time that the photocatalytic activity of covalent triazine-based frameworks (CTFs) can be efficiently improved using a facile sulfur-doping approach. The sulfur-doped CTFs show superior photocatalytic activity and stability in hydrogen evolution from water under visible light irradiation over pristine CTFs and g-C3N4. The significantly improved catalytic efficiency was attributed to sulfur-doping in the frameworks, which results in enhanced adsorption of visible light, reduced recombination of free charge carriers, and rapid separation and transportation of photogenerated electron–holes.

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.

Hydrothermal synthesis and performance of a novel nanocrystalline Pb2Sn2O6 photocatalyst

A novel nanocrystalline Pb(2)Sn(2)O(6) photocatalyst was prepared successfully for the first time by a hydrothermal process at 180 degrees C for 12 h. The samples were characterized by an x-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), surface area (BET) and ultraviolet-visible (UV-vis) spectroscopes. The results showed that the pH value played an important role in controlling the phase formation and crystallite sizes of the Pb(2)Sn(2)O(6). A single phase could be obtained at a pH>/=9. A possible reaction mechanism in the hydrothermal process was also proposed. The average particle size for the sample prepared at pH = 13 was only about 9 nm, and the BET surface area was as large as 76.7 m(2) g(-1). The N(2) adsorption-desorption isotherms and pore size distribution curve demonstrate a mesoporous structure with a narrow pore size distribution. As a novel photocatalyst, the prepared Pb(2)Sn(2)O(6) samples exhibit powerful photocatalytic activity for the decomposition of methyl orange under 365 nm UV light irradiation. Furthermore, it was found that the degradation process may be initiated directly by photogenerated holes rather than commonly sensed hydroxyl radicals.

Constructing a MoS₂ QDs/CdS Core/Shell Flowerlike Nanosphere Hierarchical Heterostructure for the Enhanced Stability and Photocatalytic Activity.

MoS2 quantum dots (QDs)/CdS core/shell nanospheres with a hierarchical heterostructure have been prepared by a simple microwave hydrothermal method. The as-prepared samples are characterized by XRD, TEM, SEM, UV-VIS diffuse reflectance spectra (DRS) and N2-sorption in detail. The photocatalytic activities of the samples are evaluated by water splitting into hydrogen. Results show that the as-prepared MoS2 QDs/CdS core/shell nanospheres with a diameter of about 300 nm are composed of the shell of CdS nanorods and the core of MoS2 QDs. For the photocatalytic reaction, the samples exhibit a high stability of the photocatalytic activity and a much higher hydrogen evolution rate than the pure CdS, the composite prepared by a physical mixture, and the Pt-loaded CdS sample. In addition, the stability of CdS has also been greatly enhanced. The effect of the reaction time on the formations of nanospheres, the photoelectric properties and the photocatalytic activities of the samples has been investigated. Finally, a possible photocatalytic reaction process has also been proposed.

Engineering a highly dispersed co-catalyst on a few-layered catalyst for efficient photocatalytic H2 evolution: a case study of Ni(OH)2/HNb3O8 nanocomposites

How to control the size and dispersity of co-catalysts and enhance the interaction between the catalyst and co-catalysts are open issues in catalysis. In this work, we have developed a novel approach to solve the aforementioned problems by utilizing the interlayered spatial steric inhibition effect of layered materials and the self-assembly of 2D nanosheets. A Ni(OH)2-modified few-layered HNb3O8 photocatalyst is taken as a typical example. SEM and TEM results show that the co-catalyst Ni(OH)2 with an ultrasmall size has been uniformly dispersed on the HNb3O8 layers through our method. However, the samples prepared by a traditional deposition method exhibit a heterogeneous Ni(OH)2 modification with a large size. That is, our method could provide a larger number of surface active sites. Furthermore, due to the confined interlayer region of the layered HNb3O8, a very strong interaction between Ni(OH)2 and HNb3O8 is achieved. As a result, the photogenerated charge carriers have been separated efficiently and the lifetime of the charge carrier is prolonged. Thus, the photocatalytic activities of our Ni(OH)2/HNb3O8 samples are greatly enhanced. The optimal H2 evolution rate of our sample is about 15.7 times higher than that of the sample prepared by a traditional co-catalyst modification method. This work highlights an efficient strategy for obtaining a highly dispersed co-catalyst, which might help to guide the way toward the development of highly efficient co-catalyst-modified photocatalyst systems.

Design and Synthesis of TiO2 Hollow Spheres with Spatially Separated Dual Cocatalysts for Efficient Photocatalytic Hydrogen Production

TiO2 hollow spheres modified with spatially separated Ag species and RuO2 cocatalysts have been prepared via an alkoxide hydrolysis–precipitation method and a facile impregnation method. High-resolution transmission electron microscopy studies indicate that Ag species and RuO2 co-located on the inner and outer surface of TiO2 hollow spheres, respectively. The resultant catalysts show significantly enhanced activity in photocatalytic hydrogen production under simulated sunlight attributed to spatially separated Ag species and RuO2 cocatalysts on TiO2 hollow spheres, which results in the efficient separation and transportation of photogenerated charge carriers.

MoS2 Quantum Dots-Modified Covalent Triazine-Based Frameworks for Enhanced Photocatalytic Hydrogen Evolution

MoS2 quantum dots (QDs)-modified covalent triazine-based framework (MoS2 /CTF) composites are synthesized through an in situ photodeposition method. MoS2 QDs are well distributed and stabilized on the layers of CTFs by coordination of the frameworks to MoS2 . The QDs-sheet interactions between MoS2 and CTFs facilitate interfacial charge transfer and separation. As a consequence, the composites exhibit outstanding photocatalytic activity and stability for hydrogen evolution under visible light irradiation (λ≥420 nm), that exceed those over pristine CTFs and MoS2 -modified g-C3 N4 (MoS2 /g-C3 N4 ) composite, making them promising materials for solar energy conversion.