Yaoguang Yu

Facile Approach to Synthesize g-PAN/g-C3N4 Composites with Enhanced Photocatalytic H2 Evolution Activity

Novel composites consisting of graphitized polyacrylonitrile (g-PAN) nanosheets grown on layered g-C3N4 sheets were synthesized through a facile one-step thermal condensation of PAN and melamine for the first time. Photoluminescence spectroscopy and the photoelectrochemical measurements reveal that g-PAN nanosheets act as effective electron transfer channels to facilitate charge carrier separation in g-PAN/g-C3N4 composites. The g-PAN/g-C3N4 composites exhibit significantly enhanced visible-light photocatalytic performance for H2 evolution over pristine g-C3N4. The 5.0 wt % g-PAN/g-C3N4 composite has optimal H2 evolution rate of 37 μmol h(-1), exceeding 3.8 times over pristine g-C3N4. We have proposed a possible mechanism for charge separation and transfer in the g-PAN/g-C3N4 composites to explain the enhanced photocatalytic performance.

Hierarchical architectures of porous ZnS-based microspheres by assembly of heterostructure nanoflakes: lateral oriented attachment mechanism and enhanced photocatalytic activity

Hierarchical ZnS-based microspheres with porous structures are successfully synthesized via a facile “one pot” route without using any templates or surfactants. These microspheres are aggregations composed of wurtzite/sphalerite heterostructure nanoflakes. Interestingly, due to the doping with In, the dipole field direction of ZnS-based nanoparticles changes. As a result, the formation of heterostructure nanoflakes are found to follow a lateral oriented attachment (LOA) mechanism and a subsequent phase transformation process rather than the oriented attachment (OA) mechanism reported in previous literatures. This discovery would provide a convenient method in constructing 2D anisotropic structures and might offer a new insight to the growth process of ZnS-based materials. Furthermore, photocatalytic activities for water splitting are investigated under visible-light irradiation (λ > 400 nm) and an enhanced photocatalytic activity (the initial rate for H2 evolution is up to 3.7 mmol h−1 with a concentration of photocatalyst of 45 mg L−1) is achieved, attributable to the particular heterostructure of 2D nanoflakes, the porous structure of 3D microspheres and the large specific area of as-prepared photocatalyst powders.

ZIF-8 derived carbon (C-ZIF) as a bifunctional electron acceptor and HER cocatalyst for g-C3N4: construction of a metal-free, all carbon-based photocatalytic system for efficient hydrogen evolution

A ZIF-8 derived carbon (C-ZIF)/g-C3N4 composite was constructed for the first time through facile thermal condensation of a zeolitic imidazolate framework (ZIF-8) and melamine. The obtained C-ZIF/g-C3N4 composite exhibited an obviously enhanced photocatalytic H2 production rate compared to pure g-C3N4 under visible light irradiation. The 1 wt% C-ZIF/g-C3N4 composite without loading the Pt co-catalyst showed 36.2 times higher H2 evolution rate than that of pure g-C3N4, which is even 2.8 times higher than that of Pt/g-C3N4 (the state-of-the-art g-C3N4-based photocatalyst). It was revealed by photoluminescence spectroscopy, time-resolved fluorescence spectroscopy and electrochemical impedance spectroscopy that the formed C-ZIF and g-C3N4 junction could promote quick charge carrier separation and transfer. The C-ZIF not only acted as an effective electron acceptor, but also functioned as an efficient hydrogen evolution reaction (HER) cocatalyst to promote photocatalytic hydrogen evolution. Our work provides an effective way for the development of metal-free, all carbon-based photocatalysts for H2 evolution.

Preparation of 1D cubic Cd0.8Zn0.2S solid-solution nanowires using levelling effect of TGA and improved photocatalytic H2-production activity

The one-dimensional (1D) cubic Cd0.8Zn0.2S solid-solution nanowires are first prepared by the “levelling effect” of thioglycolic acid (TGA) in a solvothermal process. It exhibits the enhanced transfer and separation efficiency of carriers to improve the photocatalytic H2-production activity. TGA not only serves as the sulphur source but also plays a template medium agent role. Furthermore, no TGA selectivity for diverse solvents to prepare 1D Cd0.8Zn0.2S solid solutions suggests that it also may be extended to the preparation of other 1D metal sulphide solid solutions in diverse solvents.

Sonochemistry synthesis of nanocrystals embedded in a MoO3–CdS core–shell photocatalyst with enhanced hydrogen production and photodegradation

CdS nanocrystals embedded in MoO3–CdS core–shell nanospheres have been successfully synthesized by a sonochemistry method at room-temperature and normal pressure without using any templates or surfactants. The unique core–shell nanostructures play a key role which results in a large increase in the photocatalytic activity for hydrogen production and photodegradation. In particular, the rate of MoO3–CdS core–shell photocatalytic hydrogen yield reached 5.25 mmol h−1 g−1 and exhibited a high apparent yield (28.86% at 420 nm) of hydrogen production without noble metal co-catalysts. Moreover, the MoO3–CdS core–shell composites also showed a very high decomposition rate of Rhodamine B (RhB) under the irradiation of visible-light (λ > 400 nm).

Doping La into the depletion layer of the Cd0.6Zn0.4S photocatalyst for efficient H2 evolution

We report a novel strategy for the enhancement of photocatalytic H2 evolution by doping La into the depletion layer of Cd0.6Zn0.4S (CZS: x% La). The apparent quantum yield of the CZS: 2% La photocatalyst at 350 nm is up to 93.3%, which is extremely high for solar water splitting even compared with the noble metal cocatalyst systems. This work may contribute to the design and construction of materials with outstanding capability for charge separation and hence improve the properties of the materials for various applications.

A facile approach to construct BiOI/Bi5O7I composites with heterostructures: efficient charge separation and enhanced photocatalytic activity

A series of BiOI/Bi5O7I composite photocatalysts with heterostructures was successfully synthetized through a facile hydrothermal method. Attributed to the heterostructure between BiOI and Bi5O7I, photogenerated electrons and holes can be separated efficiently. The photocatalytic activity of the as-prepared samples was evaluated through the MO degradation reaction. The removal rate of MO was up to 93% after 40 min under visible light (λ ≥ 400 nm) irradiation, while the photocatalytic activity showed no decay after 3 cycles. Furthermore, the photocatalytic mechanism of MO degradation over the BiOI/Bi5O7I composite photocatalyst was investigated by taking TA, H2O2 and EDTA as probes. The experimental results indicate that the enhanced photocatalytic performance is attributed to the synergistic effect of photogenerated holes and superoxide radicals. The excellent activity and photostability reveal that the BiOI/Bi5O7I composite photocatalyst is a promising visible-light-response photocatalyst with potential applications in the field of water treatment.

Controllable synthesis of In2O3 octodecahedra exposing {110} facets with enhanced gas sensing performance

In2O3 octodecahedra have been successfully prepared by annealing the 18-facet In(OH)3 precursor. The as-prepared In2O3 polyhedra inherit the morphology of the In(OH)3 precursor and expose twelve {110} and six {100} facets. Gas sensing tests show that octodecahedron-based In2O3 sensor exhibits a sensitivity of 610 to 1000 ppm ethanol, which is 2.3-fold and 5.5-fold enhancement compared with cube- and particle-based sensor, respectively. The XPS results demonstrate that the {110} and {100} facets of In2O3 octodecahedra provided more oxygen vacancies than either the cubes exposing only {100} facets or the irregular particles. More oxygen vacancies would contribute to the enhancement of gas sensing performance. The crystal facet analysis of In2O3 octodecahedra show that high energy {110} facets could be easier to form oxygen vacancy than that of {100} facets, which could be the main reason for high gas sensing property. This finding will open a door to the design of high performance gas sensor, and the results are also beneficial to other fields such as energy conversion, environmental protection.

Synthesis of metal oxide nanosheets through a novel approach for energy applications

This work describes an ultra-facile and generalized route to synthesize metal oxide nanosheets including TiO2, Fe2O3, Co3O4, ZnO, and WO3 with large area. Compared with conventional routes, the route here is ultra-facile to prepare scalable metal oxide nanosheets for energy applications.

Hierarchical Zn3V3O8/C composite microspheres assembled from unique porous hollow nanoplates with superior lithium storage capability

Fabricating hollow/porous structures and coating carbon on their surfaces are two effective strategies to improve the electrochemical properties of electrode materials for lithium-ion batteries (LIBs). In this work, we report the successful synthesis of novel hierarchical Zn3V3O8/C microspheres assembled from unique porous hollow nanoplates via a facile reverse microemulsion method and a subsequent annealing process. Notably, the PVP assisted heterogeneous contraction effect plays an important role in the formation of the distinctive hollow structure in the constituent nanoplates during the annealing process. Impressively, the resulting Zn3V3O8/C composite shows excellent electrochemical performance with a large capacity (912 mA h g−1 at 0.4 A g−1), excellent rate behavior (410 mA h g−1 at 3.2 A g−1) and cycling stability (756 mA h g−1 at 1.6 A g−1 after 500 cycles) when evaluated as the anode material for LIBs. The superior electrochemical performance of the as-synthesized Zn3V3O8/C microspheres can be attributed to the existence of carbon on the surface and, in particular, the unique porous hollow nanoplate structure.