Xiang-Bing Fan

An Exceptional Artificial Photocatalyst, Nih‐CdSe/CdS Core/Shell Hybrid, Made In Situ from CdSe Quantum Dots and Nickel Salts for Efficient Hydrogen Evolution

A novel hybrid Nih -CdSe/CdS core/shell quantum dot is a simple and exceptional artificial photocatalyst for H2 production from 2-propanol aqueous solution. Studies on the nature of the artificial photocatalyst and mechanism for H2 production demonstrate that the synthetic strategy is general and the artificial photocatalyst holds promise for light capture, electron transfer, and catalysis at the surface of the Nih -CdSe/CdS core/shell quantum dots, leading to a self-healing system for H2 evolution in harmony.

Photocatalytic hydrogen evolution from glycerol and water over nickel-hybrid cadmium sulfide quantum dots under visible-light irradiation.

Natural photosynthesis offers the concept of storing sunlight in chemical form as hydrogen (H2), using biomass and water. Herein we describe a robust artificial photocatalyst, nickel-hybrid CdS quantum dots (Nih-CdS QDs) made in situ from nickel salts and CdS QDs stabilized by 3-mercaptopropionic acid, for visible-light-driven H2 evolution from glycerol and water. With visible light irradiation for 20 h, 403.2 μmol of H2 was obtained with a high H2 evolution rate of approximately 74.6 μmol h(-1)  mg(-1) and a high turnover number of 38 405 compared to MPA-CdS QDs (mercaptopropionic-acid-stabilized CdS quantum dots). Compared to CdTe QDs and CdSe QDs, the modified CdS QDs show the greatest affinity toward Ni(2+) ions and the highest activity for H2 evolution. X-ray photoelectron spectroscopy (XPS), inductively-coupled plasma atomic emission spectrometry (ICP-AES), and photophysical studies reveal the chemical nature of the Nih-CdS QDs. Electron paramagnetic resonance (EPR) and terephthalate fluorescence measurements clearly demonstrate water splitting to generate ⋅OH radicals. The detection of DMPO-H and DMPO-C radicals adduct in EPR also indicate that ⋅H radicals and ⋅C radicals are the active species in the catalytic cycle.

Visible Light Catalysis-Assisted Assembly of Nih-QD Hollow Nanospheres in Situ via Hydrogen Bubbles

Hollow spheres are one of the most promising micro-/nanostructures because of their unique performance in diverse applications. Templates, surfactants, and structure-directing agents are often used to control the sizes and morphologies of hollow spheres. In this Article, we describe a simple method based on visible light catalysis for preparing hollow nanospheres from CdE (E = Te, Se, and S) quantum dots (QDs) and nickel (Ni(2+)) salts in aqueous media. In contrast to the well-developed traditional approaches, the hollow nanospheres of QDs are formed in situ by the photogeneration of hydrogen (H2) gas bubbles at room temperature. Each component, that is, the QDs, metal ions, ascorbic acid (H2A), and visible light, is essential for the formation of hollow nanospheres. The quality of the hollow nanospheres depends on the pH, metal ions, and wavelength and intensity of visible light used. Of the various metal ions investigated, including Cu(+), Cu(2+), Fe(2+), Fe(3+), Ni(2+), Mn(2+), RuCl5(2-), Ag(+), and PtCl4(2-), Ni(2+) ions showed the best ability to generate H2 and hollow-structured nanospheres under visible light irradiation. The average diameter and shell thickness of the nanospheres ranged from 10 to 20 nm and from 3 to 6 nm, respectively, which are values rarely reported in the literature. Studies using high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), inductively coupled plasma-mass spectroscopy (ICP-AES), and steady-state and time-resolved spectroscopy revealed the chemical nature of the hollow nanospheres. Additionally, the hollow-structured nanospheres exhibit excellent photocatalytic activity and stability for the generation of H2 with a rate constant of 21 μmol h(-1) mg(-1) and a turnover number (TON) of 137,500 or 30,250 for CdTe QDs or nickel, respectively, under visible light irradiation for 42 h.

Synthesis of Oligoparaphenylene-Derived Nanohoops Employing an Anthracene Photodimerization–Cycloreversion Strategy

The century-old yet synthetically underexplored anthracene photodimerization-cycloreversion reactions have been employed as the key steps to access highly strained aromatic hydrocarbons. Herein we report the chemical syntheses of oligoparaphenylene-derived nanohoops in five steps or less featuring a rigid dianthracene synthon. The newly synthesized nanohoops display intriguing experimental and computational properties.

Vectorial Electron Transfer for Improved Hydrogen Evolution by Mercaptopropionic-Acid-Regulated CdSe Quantum-Dots–TiO2–Ni(OH)2 Assembly

A visible-light-induced hydrogen evolution system based on a CdSe quantum dots (QDs)-TiO2 -Ni(OH)2 ternary assembly has been constructed under an ambient environment, and a bifunctional molecular linker, mercaptopropionic acid, is used to facilitate the interaction between CdSe QDs and TiO2 . This hydrogen evolution system works effectively in a basic aqueous solution (pH 11.0) to achieve a hydrogen evolution rate of 10.1 mmol g(-1)  h(-1) for the assembly and a turnover frequency of 5140 h(-1) with respect to CdSe QDs (10 h); the latter is comparable with the highest value reported for QD systems in an acidic environment. X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, and control experiments demonstrate that Ni(OH)2 is an efficient hydrogen evolution catalyst. In addition, inductively coupled plasma optical emission spectroscopy and the emission decay of the assembly combined with the hydrogen evolution experiments show that TiO2 functions mainly as the electron mediator; the vectorial electron transfer from CdSe QDs to TiO2 and then from TiO2 to Ni(OH)2 enhances the efficiency for hydrogen evolution. The assembly comprises light antenna CdSe QDs, electron mediator TiO2 , and catalytic Ni(OH)2 , which mimics the strategy of photosynthesis exploited in nature and takes us a step further towards artificial photosynthesis.

Direct synthesis of all-inorganic heterostructured CdSe/CdS QDs in aqueous solution for improved photocatalytic hydrogen generation

Here we present a facile aqueous approach to synthesize heterostructured CdSe/CdS QDs with all-inorganic chalcogenide S2− ligands under mild conditions. High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and steady-state emission spectroscopy demonstrate that the heterostructured CdSe/CdS QDs with sulfur-rich surface composition are formed by heterogeneous nucleation of Cd2+ and S2− precursors on the CdSe QDs. After adsorption of small Ni(OH)2 clusters over the surface in situ, the CdSe/CdS–Ni(OH)2 photocatalyst enables H2 production efficiently with an internal quantum yield of 52% under visible light irradiation at 455 nm, up to an 8-fold increase of activity to that of spherical CdSe QDs–Ni(OH)2 under the same conditions. Femtosecond transient absorption spectroscopy, X-ray transient absorption (XTA) spectroscopy, steady-state and time-resolved emission spectroscopy show that the quasi-type-II band alignment in the CdSe/CdS heterostructure is responsible for the efficiency enhancement of light harvesting and surface/interfacial charge separation in solar energy conversion. The unprecedented results exemplify an easily accessible pattern of aqueous synthesis of all-inorganic heterostructured QDs for advanced photosynthetic H2 evolution.

Visible light-induced photochemical oxygen evolution from water by 3,4,9,10-perylenetetracarboxylic dianhydride nanorods as an n-type organic semiconductor

3,4,9,10-Perylenetetracarboxylic dianhydride (PTCDA) nanorods as an n-type organic semiconductor are utilized to construct a powder-based photocatalytic water oxidation system with cobalt oxide as a cocatalyst, which achieved an apparent quantum efficiency of 4.6 ± 0.3% under visible light irradiation at 410 nm.

Nonstoichiometric Cux Iny S Quantum Dots for Efficient Photocatalytic Hydrogen Evolution

Unlike their bulk counterpart, Cux Iny S quantum dots (QDs) prepared by an aqueous synthetic approach, show promising activity for photocatalytic hydrogen evolution, which is competitive with the state-of-the-art Cd chalcogen QDs. Moreover, the as-prepared Cux Iny S QDs with In-rich composition show much better efficiency than the stoichiometric ones (Cu/In=1:1).

Effect of electron transfer on the photocatalytic hydrogen evolution efficiency of faceted TiO2/CdSe QDs under visible light

Quantum dot (QD)/TiO2 composites are widely used materials in the field of photocatalysis. However, the influence of different exposed facets of TiO2 in composites on photocatalytic hydrogen evolution is rarely reported. In this work, CdSe QD–TiO2 composites with dominant {001} or {101} faceted anatase were synthesized and specifically characterized using X-ray powder diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Photocatalytic hydrogen evolution tests reveal that {001}-TiO2/CdSe QDs exhibit a 213.1- and 9.0-fold increase in photocatalytic activity compared to {001}-TiO2 and CdSe QDs, respectively. Notably, the photocatalytic activity of {001}-TiO2/CdSe QDs is 2.2 times higher than that of {101}-TiO2/CdSe QDs. Based on the results from UV-Vis diffuse reflectance spectroscopy, Brunauer–Emmett–Teller surface area testing, Mott–Schottky testing and steady-state and time-resolved emission spectroscopy, the main reason for enhanced photocatalytic activity is the faster electron transfer from CdSe QDs to {001}-TiO2 compared with to {101}-TiO2. This research on tailored facets in QD/TiO2 composites provides primary insights for the design of effective photocatalysts.

Direct synthesis of sulfide capped CdS and CdS/ZnS colloidal nanocrystals for efficient hydrogen evolution under visible light irradiation

CdS and CdS/ZnS colloidal nanocrystals (NCs) capped with inorganic sulfide (S2−) ligands were directly synthesized with no aid of organic ligands in water. The obtained CdS/ZnS-S2− NCs show a surprising activity for hydrogen evolution with a rate of 1.61 mmol mg−1 h−1 and an internal quantum yield of 54% under 465 nm light irradiation.