Yongjin Ma

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.

Rational design and preparation of few-layered MoSe2 nanosheet@C/TiO2 nanobelt heterostructures with superior lithium storage performance

A heterostructure of MoSe2 nanosheets decorated on C/TiO2 nanobelts was successfully fabricated through a facile hydrothermal process with the assistance of glucose. Ultrathin MoSe2 nanosheets fully covered on TiO2 nanobelts were coupled with carbon components as strong skeletons, which possess high contact surface area, efficient electronic transport frameworks and sufficient void spaces. As expected, the MoSe2@C/TiO2 heterostructures exhibit remarkable cycling stability (discharge capacity of 987.4 mA h g−1 after 100 cycles at a current density of 500 mA g−1) and rate capability (retained capacity of 860 mA h g−1 even at a current rate of 3000 mA g−1) as anode materials in lithium-ion batteries. The excellent electrochemical performance can be attributed to the structural advantages of MoSe2@C/TiO2 heterostructures, enabling great potential as anode materials in lithium-ion batteries.

Sulphur and nitrogen dual-doped mesoporous carbon hybrid coupling with graphite coated cobalt and cobalt sulfide nanoparticles: Rational synthesis and advanced multifunctional electrochemical properties

Doping-type carbon matrixes not only play a vital role on their electrochemical properties, but also are capable of suppressing the crush and aggregation phenomenon in the electrode reaction process for pristine metallic compound. Herein, graphite coated cobalt and cobalt sulfide nanoparticles decorating on sulphur and nitrogen dual-doped mesoporous carbon (Co@Co9S8/S-N-C) was fabricated by a combined hydrothermal reaction with pyrolysis method. Benefited from g-C3N4 template and original synthetic route, as-obtained Co@Co9S8/S-N-C possessed high specific surface area (751.7m2g-1), large pore volume (1.304cm3g-1), S and N dual-doped component and relative integrated graphite skeleton, as results it was developed as decent oxygen reduction electro-catalyst and ultra-long-life Li-ion battery anode. Surprisingly, compared with commercial Pt/C, it displayed a higher half-wave potential (0.015V positive) and lower Tafel slop (66mVs-1), indicating its superior ORR activities. Moreover, the ultra-long-life cyclic performances were revealed for lithium ion battery, exhibiting the retention capacities of 652.1mAhg-1 after 610 cycles at 0.2Ag-1, 432.1 and 405.7mAhg-1 at 5 and 10Ag-1 after 1000 cycles, respectively. We propose that the synergistic effect of structure and chemical component superiorities should be responsible for the remarkable electrochemical behaviors of the Co@Co9S8/S-N-C.

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.

Multiple active components, synergistically driven cobalt and nitrogen Co-doped porous carbon as high-performance oxygen reduction electrocatalyst

Developing durable and efficient doped-type carbon electrocatalysts with diverse heteroatoms or transition metals for oxygen reduction reaction (ORR) has captured increasing attention for their incredible electrocatalytic properties. However, compared to multiple-atom-doped carbon matrix, the introduction of single-type atoms into carbon skeletons provides little benefit to enhancing ORR activity. On the basis of this consideration, we successfully fabricated a cobalt (Co) and nitrogen (N) dual-doped porous carbon (Co@C-N) hybrid with multiple active sites by a facile strategy of combined hydrothermal reaction with thermolysis. As a comparison, porous nitrogen-doped carbon (C@N) was obtained by a similar method. Electrochemical tests confirm that the Co@C-N-120-900 exhibits the best ORR performance in alkaline media with the positive onset potential (Eonset) of 0.956 V vs. RHE (only 12 mV more negative than Pt/C), the high half-wave potential (E1/2) of 0.851 V vs. RHE (24 mV more positive than 20 wt% Pt/C), superior selectivity (a four-electron-dominant process), and smaller Tafel slope (57 mV dec−1). Meanwhile, as-synthesized Co@C-N-120-900 catalyst shows greater durability and significantly greater methanol tolerance than Pt/C catalyst. Our experiments indicate that the better overall ORR performance for Co@C-N-120-900 could be caused by the synergistic effect of multiple active components (single Co atom, Co–Nx and plentiful pyridinic-N), high BET specific surface area (1080 m2 g−1) and porous structures. Thus, the Co@C-N-120-900 catalyst is expected to be a cost-efficient and promising electrocatalyst in the field of the sustainable energy application, and this work might provide some directions for fabricating advanced energy storage materials.

Controlling shape anisotropy of hexagonal CdS for highly stable and efficient photocatalytic H 2 evolution and photoelectrochemical water splitting

Photocorrosion and low solar conversion efficiency hindered widely applications of CdS in photocatalytic (PC) H2 evolution and photoelectrochemical (PEC) water splitting. Hence, this work reports the shape anisotropy of hexagonal CdS possesses highly stable and efficient PC H2 evolution and PEC water splitting by simply mixed diethylenetriamine (DETA) and deionized water (DIW) solvothermal. Here we demonstrate that the shape of hexagonal CdS plays an important role in their PC activity. The CdS-Nanorod yields optimal 5.4 mmol/g/h PC H2 production and photocurrent density 2.63 mA/cm2 at open circuit potential (OCP). The enhanced performance is attributed to the effective separation and transport of the photogenerated electron-hole pairs, which were verified by PL and transisent absorbance. Moreover, hexagonal CdS-Nanorod shows long-term PC H2 production and highly stable photocurrent density. As compared with CdS-Nanosphere, the hexagonal CdS-Nanorod exhibits 27 times and 19.2 times in H2 production and photocurrent density, respectively. Whats more, STH efficiency of hexagonal CdS-Nanorod is 3.23% and an impressive applied bias photon-to-current efficiency (ABPE) is 2.63% at 0.134 V (vs. RHE). Temperature is also explored and reported. The possible mechanism of PC H2 evolution and PEC water spiltting are proposed for CdS-Nanorod. This work may provide a promising strategy to fabricate efficient PC and PEC systems for solar-to-fuel energy conversion.

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.

Phase Transformation Synthesis of Strontium Tantalum Oxynitride-Based Heterojunction for Improved Visible Light-Driven Hydrogen Evolution

Tantalum oxynitride-based materials, which possess narrow band gaps and sufficient band energy potentials, have been of immense interest for water splitting. However, the efficiency of photocatalytic reactions is still low because of the fast electron-hole recombination. Here, a Sr2Ta2O7- xN x/SrTaO2N heterostructured photocatalyst with a well-matched band structure was in situ constructed by the nitridation of hydrothermal-prepared Sr2Ta2O7 nanosheets. Compared to Sr2Ta2O7- xN x and pure SrTaO2N, the Sr2Ta2O7- xN x/SrTaO2N heterostructured photocatalyst exhibited the highest rate of hydrogen evolution, which is ca. 2.0 and 76.4 times of Sr2Ta2O7- xN x and pure SrTaO2N, respectively, under the similar reaction condition. The enhanced performance arises from the formation of suitable band-matched heterojunction-accelerated charge separation. This work provides a promising strategy for the construction of tantalum oxynitride-based heterojunction photocatalysts.

Boosting charge transfer via molybdenum doping and electric-field effect in bismuth tungstate: Density function theory calculation and potential applications

Regulating internal electronic structure of photocatalysts via elements doping holds huge potential in tuning efficient charge transfer and boosting high-performance. Herein, molybdenum embedded bismuth tungstate (Bi2WO6) is employed to explore the electronic structures and various performances via the assistance of experimental verification and density function theory (DFT) simulation. The band structures and Mo ions doping behaviors of Bi2MoxW1-xO6 are systematically measured. Doping can induce the distortion of intrinsic electric density and internal electric-field, resulted in efficient charge transfer of Bi2Mo0.4W0.6O6. It exhibits much efficient photocatalytic activities under visible-light irradiation, also manifests huge potential as an anode material in lithium-ion batteries (LIBs) which is rarely reported before. This work may provide insights in the development of bismuth-based semiconductors in energy related applications.

Enhanced Visible Light Photocatalytic Degradation by Mn3O4/CeO2 Heterojunction: a Z-Scheme System photocatalyst

A Z-scheme system Mn3O4/CeO2 heterojunction was fabricated via a simple one-step hydrothermal method and further applied for photocatalytic Rhodamine B (RhB) degradation. In this work, the Mn3O4 nanoparticle was uniformly deposited on CeO2 nanorod surface, which formed a typical heterojunction. The presence of Mn3O4 in the Mn3O4/CeO2 heterojunction was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) verified that Mn was in the form of Mn3+ and Mn2+ in Mn3O4 nanoparticle. Noticeably, the Mn3O4/CeO2 heterojunction exhibited excellent photocatalytic activity for RhB degradation. The drastically enhanced photocatalytic performance could be attributed to improved light harvesting, efficient separation of the photo-generated electron–hole pairs and stronger electronic conductivity. Moreover, the photocatalytic mechanism was also explored on the Mn3O4/CeO2 heterojunction. This novel Mn3O4/CeO2 heterojunction was proved to have great potential for the degradation of organic contaminants in water.