Wenwen Liu

Enhanced performance of doped BiOCl nanoplates for photocatalysis: understanding from doping insight into improved spatial carrier separation

The spatial carrier separation of semiconductor photocatalysts with different crystal facets has been utilized for improving photocatalytic efficiency. However, the efficiency of spatial carrier separation is restricted in these facet-based semiconductor photocatalysts. Herein, we aim to steer spatial separation of photoexcited carriers by implementing a doping strategy and select BiOCl nanoplates as a model photocatalyst to investigate spatial carrier separation and photocatalytic performance. High-resolution transmission electron microscopy shows that doped BiOCl single crystalline nanoplates have (001) crystal facets on their top and bottom surfaces, while they have (110) crystal facets at their four side surfaces. The photoelectrochemical results show that doping enhances the separation efficiency of the photoexcited carriers. Meanwhile, the phenomenon that the valence band decreases gradually while photocatalytic degradation efficiency increases with increasing dopant concentration implies that the increase of photocatalytic efficiency originates from the effective separation of the photoexcited carriers. Furthermore, photodeposition results of BiOCl and doped BiOCl nanoplates indicate an enhanced spatial separation of photoexcited electrons and holes between (001) and (110) crystal facets. The doped BiOCl nanoplates exhibit significant efficiency for pollutant degradation under visible light. The results obtained demonstrate the rational design of spatial carrier separation with different crystal orientations for more efficient solar-driven photocatalytic conversion.

Simple and facile ultrasound-assisted fabrication of Bi2O2CO3/g-C3N4 composites with excellent photoactivity

Bi2O2CO3/g-C3N4 (BOC/CN) composites photocatalyst was fabricated via a facile ultrasonic-assisted method. The crystal structure, morphology, optical and photocatalytic properties of the as-prepared samples were characterized by various analytical techniques. The results indicated that the Bi2O2CO3 nanoflakes grew on the surface of the g-C3N4 nanosheets, forming closely contacted interfaces between the Bi2O2CO3 and the g-C3N4 component. BOC/CN composites with 50wt% of g-C3N4 showed the optimal photoactivity for the degradation of RhB under visible light, which was approximately 2.2 times higher than that of pure g-C3N4 and 7 times of pure Bi2O2CO3, respectively. The enhanced performance of the BOC/CN composites was mainly attributed to a synergistic effect including the accelerated separation and migration of photogenerated charge carriers, demonstrated by Photoluminescence (PL), electrochemical impedance spectra (EIS) and photocurrent density. Finally, a possible photocatalytic mechanism was proposed based on the experimental results. It is expected that such a facile route method could provide new insights into fabricating other g-C3N4-based composite photocatalysts for environmental remediation.

In situ formation of carbon encapsulated nanosheet-assembled MoSe2 hollow nanospheres with boosting lithium storage

Carbon encapsulated nanosheet-assembled MoSe2 hollow nanospheres were in situ fabricated via a facile hydrothermal treatment and subsequent annealing treatment. When evaluated as anode material for lithium-ion batteries, the MoSe2/C hybrid hollow spheres manifest prodigious cycling stability (a high reversible capacity of 795mAhg-1 after 250 cycles at 0.2Ag-1 and 744mAhg-1 after 300 cycles at 1Ag-1) and compelling rate capability (370mAhg-1 even at a high current density of 10Ag-1) compared to the bare MoSe2 hollow nanospheres. The impressive lithium storage properties of the as-prepared MoSe2/C nanocomposites can be attributed to the introduction of glucose-derived conductive carbon and the design of hollow structure, which facilitates fast electron and ion transfer, relieves the stress caused by volume variation upon cycling and improves the electric conductivity. Such remarkable electrochemical performances together with universal approach endow this material with potential application for next generation lithium-ion batteries.

Facet and morphology dependent photocatalytic hydrogen evolution with CdS nanoflowers using a novel mixed solvothermal strategy

As the highest energy facet of wurtzite CdS, (0 0 2) facet is well worth investigating toward the contribution in photocatalytic hydrogen (H2) evolution. In this study, flower-like CdS with highly preferred (0 0 2) facet was fabricated through a low temperature mixed-solvothermal strategy. The mixted-solvent of diethylenetriamine (DETA) and ethyl alcohol (EtOH) was used to inhibit the growth of (1 0 0) and (1 0 1) facets. For comparison, porous flower-like, belt-like and net-like CdS samples with different preferred degrees of (0 0 2) facet were controllably synthesized by the addition of H2O in different proportions. The preferred orientation degrees of (0 0 2) facet were qualitative proved by the mathematical fitting of XRD patterns. As expected, the flower-like CdS exhibited the highest photocatalytic activity on H2 evolution under visible light without any co-catalyst. Meanwhile, the photocatalytic H2 production increased with the increasement of exposed (0 0 2) facet, which suggested that (0 0 2) facet of CdS played a critical role in improving the photocatalytic activity. Moreover, the growth mechanisms of CdS with various morphologies were investigated and proposed in detail.

Insights into the efficient charge separation and transfer efficiency of La,Cr-codoped SrTiO3 modified with CoP as a noble-metal-free co-catalyst for superior visible-light driven photocatalytic hydrogen generation

The exploration of non-noble-metal-based photocatalysts with high efficiency and durability toward hydrogen evolution is vitally necessary to meet the challenges of the global energy and environmental crisis. In this work, we prepared noble-metal-free cobalt phosphide (CoP) as an efficient co-catalyst on La,Cr-codoped SrTiO3 (La,Cr:SrTiO3) to form a novel photocatalyst with enhanced H2 evolution activity. It was evidenced that the introduction of CoP led to a remarkable improvement in the photocatalytic H2 evolution activity of La,Cr:SrTiO3, and the content of CoP in the composite had an important influence on the photocatalytic activity. The optimized La,Cr:SrTiO3/CoP (4 wt%) composite exhibited a catalytic H2 evolution rate of 198.4 μmol h−1 g−1, which was nearly 27 and 15 times higher than that of La,Cr:SrTiO3 and CoP, even slightly higher than that of La,Cr:SrTiO3/Pt (0.5 wt%). More importantly, this novel photocatalyst also showed a long-term stability without noticeable activity degradation. Based on the results of UV–vis diffuse reflectance spectroscopy, photoluminescence spectra, photocurrent response, and electrochemical impedance spectra, we ascribed the enhanced H2 evolution performance of the La,Cr:SrTiO3/CoP to a synergistic effect including the broadened visible-light response range, accelerated photogenerated charge separation and transfer efficiency. It is believed that our present work throws light on the rational design of novel, high-performance, visible-light-driven hybrid photocatalysts based on non-noble-metal elements.

Intimate contacted two-dimensional/zero-dimensional composite of bismuth titanate nanosheets supported ultrafine bismuth oxychloride nanoparticles for enhanced antibiotic residue degradation

Constructing a two-dimensional/zero-dimensional (2D/0D) composite with matched crystal structure, suitable energy band structure as well as intimate contact interface is an effective way to improve carriers separation for achieving highly photocatalytic performance. In this work, a novel bismuth titanate/bismuth oxychloride (Bi4Ti3O12/BiOCl) composite consisting of 2D Bi4Ti3O12 nanosheets and 0D BiOCl nanoparticles was constructed for the first time. Germinating ultrafine BiOCl nanoparticles on Bi4Ti3O12 nanosheets can provide abundant contact interface and shorten migration distance of photoinduced carriers via two-step synthesis contained molten salt process and facile chemical transformation process. The obtained Bi4Ti3O12/BiOCl 2D/0D composites exhibited enhanced photocatalytic performance for antibiotic tetracycline hydrochloride degradation. The rate constant of optimal Bi4Ti3O12/BiOCl composite was about 4.4 times higher than that of bare Bi4Ti3O12 although Bi4Ti3O12/BiOCl composite appeared lesser photoabsorption. The enhanced photocatalytic performance can be mainly ascribed to matched crystal structure, suitable energy band structure and intimate contact interface between Bi4Ti3O12 nanosheets and ultrafine BiOCl nanoparticles as well as unique 2D/0D composite structure. Besides, a probable degradation mechanism on the basis of active species trapping experiments, electrochemical impedance spectroscopy, photocurrent responses and energy band structures was proposed. This work may be stretched to other 2D/0D composite photocatalysts construction, which is inspiring for antibiotic residue treatment.

Novel two-dimensional Bi4V2O11 nanosheets: controllable synthesis, characterization and insight into the band structure

In this work, a stable EDTA–Bi complex formed by the chelation of bismuth ions and ethylenediaminetetraacetic acid (EDTA) under alkaline conditions was adopted to controllably prepare novel two-dimensional (2D) Bi4V2O11 nanosheets via a facile hydrothermal method. It is proved that the phases of the product will change with the variation of the amount of EDTA and the pH value of the precursor solution. The fabricated Bi4V2O11 has a uniform sheet-like structure with a thickness of 1.26 nm. Based on the experimental results, we provide a reasonable nucleation and growth mechanism for Bi4V2O11 nanosheets, which could give some suggestions on the synthesis of other 2D Bi-based materials. On the basis of Mott–Schottky plots and UV-vis diffuse reflectance spectra, we demonstrate that the as-obtained Bi4V2O11 is an n-type semiconductor and possesses a better light-harvesting ability in comparison with monoclinic BiVO4. In addition, the corresponding conduction band potential and valence band potential of the Bi4V2O11 nanosheets are ascertained as well.