Pengfei Tan

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.

Facile fabrication of novel porous graphitic carbon nitride/copper sulfide nanocomposites with enhanced visible light driven photocatalytic performance.

In this work, a novel organic-inorganic heterostructured photocatalyst: porous graphitic carbon nitride (g-C3N4) hybrid with copper sulfide (CuS) had been synthesized via a precipitation-deposition method at low temperature for the first time. UV-vis spectroscopy revealed the porous g-C3N4/CuS nanocomposites showed a strong and broad visible light absorption. Furthermore, the g-C3N4/CuS nanocomposites showed higher photocatalytic activity in the photodegradation of various organic dyes than that of pure g-C3N4 and CuS, and the selected sample of g-C3N4/CuS-2 exhibited the best photocatalytic activity under visible light. The good photocatalytic activity could be ascribed to the matching of the g-C3N4 and CuS band gap energies. Besides, photoluminescent spectra and photoelectrochemical measurements also proved that the CuS/g-C3N4 could greatly enhance the charge generation and suppress the charge recombination of photogenerated carriers. According to the experimental result, a possible photocatalytic mechanism has been proposed. Due to the high stability, the porous g-C3N4/CuS could be applied in the field of environmental remediation. Our work highlights that coupling semiconductors with well-matched band energies provides a facile way to improve the photocatalytic activity.

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.

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.

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.

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.

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.

Manganese oxide at cadmium sulfide (MnOx@CdS) shells encapsulated with graphene: A spatially separated photocatalytic system towards superior hydrogen evolution

Exploring novel, high-efficiency and durable catalysts is of vital importance to expedite current research on photocatalytic H2 evolution and address the energy and environmental issues. Herein, we rationally designed and synthesized a novel MnOx@CdS@GR photocatalyst with spatially separated dual co-catalysts for efficient visible-light-driven hydrogen production activity. In this spatially separated photocatalytic system, reduced graphene oxide (GR) and MnOx nanoparticles were anchored on the outer and inner surfaces of CdS shells acting as electron and hole collectors, respectively. The composition, microstructure and optical properties of the samples were thoroughly investigated. Photoluminescence spectra and photocurrent response as well as electrochemical impedance spectra were employed to reveal the separation and transfer ability of photo-generated charge carriers in the spatially separated MnOx@CdS@GR catalyst. Benefit from the synergistic effect including boosted light absorption capacity, enlarged specific surface area and increased separation and transfer efficiency of electron/hole pairs, the MnOx@CdS@GR exhibited superior H2 evolution performance, and the optimized H2-evolution rate reached a value of 5.45 mmol h-1 g-1, which is approximately 7.2 times than that of bare CdS. Moreover, this novel catalyst also displayed a long-term stability without apparent debasement in H2 evolution activity. Finally, the photocatalytic mechanism was proposed and discussed.