Jianyu Han

Post-synthesis modification of a metal–organic framework to construct a bifunctional photocatalyst for hydrogen production

To construct photocatalytically active MOFs, various strategies have recently been developed. We have synthesized and characterized a new metal–organic framework (MOF-253-Pt) material through immobilizing a platinum complex in 2,2′-bipyridine-based microporous MOF (MOF-253) using a post-synthesis modification strategy. The functionalized MOF-253-Pt serves both as a photosensitizer and a photocatalyst for hydrogen evolution under visible-light irradiation. The photocatalytic activity of MOF-253-Pt is approximately five times higher than that of the corresponding complex. The presence of the short Pt⋯Pt interactions in the framework was revealed with extended X-ray absorption fine structure (EXAFS) spectroscopy and low temperature luminescence. These interactions play an important role in improving the photocatalytic activity of the resulting MOF.

Recent progress in g-C3N4 based low cost photocatalytic system: activity enhancement and emerging applications

Graphitic C3N4 (g-C3N4) has continuously attracted attention since it was reported as a metal-free semiconductor for water splitting. However, its ability to evolve hydrogen from water is significantly dependent on the use of noble metal co-catalyst, mainly Pt. In recent years, good progress has been achieved in developing co-catalysts containing earth abundant elements only for constructing low cost and efficient g-C3N4 based photocatalytic systems. Besides, exfoliation of bulk g-C3N4 into two dimensional g-C3N4 nanosheets offers large surface area and exposed active sites, which are beneficial for activity enhancement. Furthermore, oxygen evolution and CO2 photoreduction over g-C3N4 have gained increasing interests due to the demand to achieve overall water splitting and conversion of CO2 into chemicals and fuels. In this mini-review, we will briefly summarize the latest research works on g-C3N4 based photocatalytic systems during the last three years with emphasis on the progress achieved in enhancing the hydrogen evolution activity of g-C3N4 by loading noble metal free co-catalysts, exfoliating bulk g-C3N4 into nanosheets, and applying the g-C3N4 system in photocatalytic O2 evolution and CO2 reduction.

Bio-inspired organic cobalt(II) phosphonates toward water oxidation

The development of artificial photosynthesis systems that can efficiently catalyze water oxidation to generate oxygen remains one of the most important challenges in solar energy conversion to chemical energy. In photosystem II (PSII), the Mn4CaO5 cluster adopts a distorted coordination geometry and every two octahedra are linked by di-μ-oxo (edge-shared) or mono-μ-oxo (corner-shared) bridges, which is recognized as a critical structure motif for catalytic water oxidation. These structural features provide guidance on the design and synthesis of new water oxidation catalysts. Herein we synthesized a new layered organic cobalt phosphonate crystal, Co3(O3PCH2–NC4H7–CO2)2·4H2O (1) and demonstrate it as a heterogeneous catalyst for water oxidation. Its catalytic activity was compared to those of cobalt phosphonates with different structures (2–4) in terms of O2 evolution rate and O2 yield under the same reaction conditions. The compound with both mono- and di-μ-oxo bridged octahedral cobalt displays superior catalytic activity. In contrast, the presence of only mono-μ-oxo bridged cobalt in the structure results in lower O2 yield and O2 evolution rate. Further structural analysis reveals that the presence of a longer Co–N bond induces a distorted dissymmetry coordination geometry, and consequently facilitates water oxidation. These results provide important insight into the design of water oxidation catalysts.

A crystalline Cu–Sn–S framework for high-performance lithium storage

In order to address the increasing demands for clean energy, it is highly desirable to explore new electrode materials to improve the efficiency of lithium ion batteries (LIBs). In this work, we report the successful synthesis of a crystalline (H3O)2(enH2)Cu8Sn3S12 material via a surfactant-thermal strategy. The crystal structure analysis shows that the as-prepared chalcogenide has 3D interconnected channels occupied by disordered H2en2+ and H3O+. Taking advantage of porous structures and H2en2+ and H3O+ as stabilizers, (H3O)2(enH2)Cu8Sn3S12 has been explored as an anode material for lithium ion batteries. Our results exhibit a high capacity of 563 mA h g−1 at a current density of 0.1 A g−1 after 100 cycles. In addition, outstanding cycling properties are demonstrated with only 7.2% capacity loss from the 5th to 100th cycle. Our research could provide insight into the exploration of crystalline ternary thiostannate for lithium ion batteries in the future.

CdS quantum dots and tungsten carbide supported on anatase–rutile composite TiO2 for highly efficient visible-light-driven photocatalytic H2 evolution from water

Developing efficient photocatalysts with noble-metal-free co-catalysts for visible-light-driven photocatalytic H2 evolution from water is appealing yet remains challenging. Herein, by supporting CdS QDs with diameters smaller than 5 nm and tungsten carbide (WC) on TiO2, a CdS/WC/TiO2 photocatalyst was fabricated for visible-light-driven photocatalytic H2 evolution from aqueous solution containing lactic acid as an electron donor. The optimal H2 evolution rate on CdS/WC/TiO2 (624.9 μmol h−1) is comparable to the H2 evolution rate on CdS/Pt/TiO2 (636.2 μmol h−1), indicating that WC is a good candidate to substitute Pt as the co-catalyst. Formation of an anatase–rutile composite TiO2 with a rutile content of 68.7% makes great contribution to the efficient H2 evolution on CdS/WC/TiO2. The rutile–anatase composite TiO2 promotes the separation of the photogenerated electron–hole pairs and thereby benefits the efficient H2 evolution reaction. The present work is expected to be helpful in designing efficient noble-metal-free photocatalysts for H2 evolution from visible-light-driven photocatalytic water splitting.

Metal–organic framework immobilized cobalt oxide nanoparticles for efficient photocatalytic water oxidation

Water oxidation reactions driven by visible light play an important role in solar fuel production. Recently, catalysts based on earth abundant elements, such as cobalt oxides, have been studied extensively. Out of many factors, the catalyst particle size certainly affects the photocatalytic activity. To reduce the catalyst particle size below 5 nm without encountering agglomeration, a practical approach is to adopt a proper substrate to immobilize the catalyst nanoparticles. Herein, we utilized MIL-101, a highly porous and robust metal–organic framework (MOF), to immobilize cobalt oxide nanoparticles by a simple and facile method involving double solvent impregnation followed by a mild heat treatment. With cobalt loading in the range of 1.4–4.9 wt%, ultra small cobalt oxide nanoparticles (2–3 nm) have been successfully immobilized in the cages of MIL-101 with a good dispersion and narrow size distribution. Photocatalytic and electrochemical studies have indicated that the resultant cobalt oxide nanoparticles embedded in the MOF are highly efficient and stable water oxidation catalysts. A high turnover frequency (TOF) of 0.012 s−1 per cobalt atom and oxygen yield of 88% were obtained under the optimized conditions in the [Ru(bpy)3]2+–Na2S2O8 system. The MIL-101 support plays the roles of confining the size of catalyst nanoparticles and promoting charge transfer, leading to an enhanced photocatalytic performance.