Boosting hydrogen and oxygen evolution of porous CoP nanosheet arrays through electronic modulating with oxygen-anion-incorporation.

The exploration of earth-abundant single catalyst with high-efficiency bifunctional catalytic active sites for accelerated hydrogen and oxygen evolution reactions (HER and OER) is highly desirable but challenging. Herein, the synthesis of self-supported directional flake oxygen-incorporated cobalt phosphide arrays (O-CoP) with efficient bifunctional catalytic active sites was achieved by in situ oxidation followed by phosphorization of cobalt metal-organic framework nanosheet arrays (Co-MOF). By controlling the phosphating time, the P/O atomic ratio in the oxygen-incorporated cobalt phosphide could be adjusted, leading to the change of Co3+/Co2+ couples, and thus affecting the electronic environment of the cobalt active site. Benefiting from the tunable electronic structure and unique array architecture, the synthesized catalysts exhibited excellent electrocatalytic water decomposition for both HER and OER. Moreover, in the HER and OER couple system (HER||OER), the optimal O-CoP-40 catalyst delivers a low overpotential of only 1.54 V to obtain the 10 mA cm-2 and stably-running for 36 h. Theoretical calculations demonstrated that the electron-rich P-3p and O-2p orbitals could co-modulate the electronic environment of Co sites, which boosted water dissociation in the HER process and balanced the adsorption/desorption of intermediates in the OER pathway, resulting in a good overall water splitting. This research provides an effective strategy for the construction of efficient bifunctional phosphide electrocatalysts, as well as contributes to the understanding of anion incorporating to regulate the electronic structure of phosphides.

Selective separation of single-walled carbon nanotubes in aqueous solution by assembling redox nanoclusters.

The selective separation of soluble and individual single-walled carbon nanotubes (SWCNTs) in aqueous solution is a key step for harnessing the extraordinary properties of these materials. Manipulating the strong van der Waals intertube interactions between the SWCNT bundles is very important in selective separation, which is a long-standing challenge. Here we reported the ability of redox polyoxometalate clusters to modulate the intertube π-π stacking interaction through electron transfer and achieved the diameter-selective separation of SWCNTs in a surfactant aqueous solution. The large-diameter SWCNTs concentrated at ∼1.3-1.4 nm were selectively separated when ∼1 nm clusters encapsulated within the tube cavity, and the dispersion of subnanometer ∼0.7-0.9 nm SWCNTs was boosted when clusters were adsorbed on the outer surface of small-diameter nanotubes. The mechanism of diameter-selective separation of SWCNTs associated with the size-dependent interaction between cluster-tubes and the steric hindrance effect of clusters was revealed by optical absorption and Raman spectroscopy. This simple method thus enables the selective separation of individual high-quality SWCNTs in aqueous solutions without harsh sonication with the potential for other separation applications.

Host-Guest Molecular Interaction Enabled Separation of Large-Diameter Semiconducting Single-Walled Carbon Nanotubes.

Semiconducting single-walled carbon nanotubes (s-SWCNTs) with a diameter of around 1.0-1.5 nm, which present bandgaps comparable to silicon, are highly desired for electronic applications. Therefore, the preparation of s-SWCNTs of such diameters has been attracting great attention. The inner surface of SWCNTs has a suitable curvature and large contacting area, which is attractive in host-guest chemistry triggered by electron transfer. Here we reported a strategy of host-guest molecular interaction between SWCNTs and inner clusters with designed size, thus selectively separating s-SWCNTs of expected diameters. When polyoxometalate clusters of ∼1 nm in size were filled in the inner cavities of SWCNTs, s-SWCNTs with diameters concentrated at ∼1.3-1.4 nm were selectively extracted with the purity of ∼98% by a commercially available polyfluorene derivative. The field-effect transistors built from the sorted s-SWCNTs showed a typical behavior of semiconductors. The sorting mechanisms associated with size-dependent electron transfer from nanotubes to inner polyoxometalate were revealed by the spectroscopic and in situ electron microscopic evidence as well as the theoretical calculation. The polyoxometalates with designable size and redox property enable the flexible regulation of interaction between the nanotubes and the clusters, thus tuning the diameter of sorted s-SWCNTs. The present sorting strategy is simple and should be generally feasible in other SWCNT sorting techniques, bringing both great easiness in dispersant design and improved selectivity.

Interface engineering in CeO2 (111) facets decorated with CdSe quantum dots for photocatalytic hydrogen evolution.

The interfaces of heterostructures have been widely studied in the field of photocatalytic H2 evolution reaction (HER). In the present study, the CdSe QDs/CeO2(111) heterostructures were synthesized by wet chemistry method. The CdSe QDs/CeO2(111)-0.075 showed higher photocatalytic H2 evolution with 283.32 µmol g-1h-1, because of the enhanced light absorbance intensity and edge, lower recombination, higher separation and transfer, as well as longer lifetime of the photogenerated carrier. Density functional theory (DFT) calculations further confirmed that the enhanced HER activity of CdSe QDs/CeO2(111) heterostructures is resulted from a stronger water adsorption, a lower energy barrier of water dissociation and a more optimal free energy of hydrogen adsorption than CdSe and CeO2. The strategy of construction heterostructures provides a promising pathway for enhancing the performance of photocatalytic H2 evolution as well as other catalytic reactions.

Sodium borohydride-assisted synthesis of strontium substituted lanthanum cobaltate with in-situ generated cobaltosic oxide: Towards enhanced oxygen evolution reaction in alkaline media.

Based on the intrinsic behaviour of doped Co-based perovskite to generate the second phase of Co3O4, a novel strategy was developed to synthesize a hybrid catalyst consisting of La1-xSrxCoO3-δ (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) and in-situ generated Co3O4 in the presence of NaBH4. When x increased to 1.0, a well-designed integration (SrCoO2.5@Co3O4) was obtained which displayed the optimal OER activity with an overpotential of 330 mV at 10 mA cm-2, a small Tafel slope of 66.7 mV dec-1 and terrific durability in alkaline media. This excellent performance can be attributed to the auxiliary of the in-situ generated Co3O4 for SrCoO2.5 which modifies the chemical states of Co cations, compensates for the unsatisfactory electrical conductivity of SrCoO2.5 while preserves oxygen vacancies, boosts the content of lattice oxygen and exposes more active sites. This work is expected to provide a new mind to design effective electrocatalysts towards water splitting.

Green Approach for Metal Oxide Deposition at an Air-Liquid-Solid Triphase Interface with Enhanced Photocatalytic Activity.

Bioinspired superhydrophobic substrates have been used in many scientific and technological areas. These substrates can trap atmosphere-linked air pockets at the solid-liquid interface, offering an opportunity to address the oxygen-deficit problem in many reaction systems. Herein, we addressed the oxygen-deficit problem in metal oxide electrochemical deposition by using a triphase electrode possessing an air-liquid-solid joint interface. Oxygen in the interface is directly available from the air phase for sufficient OH- production via oxygen cathodic reaction, thereby offering us a green approach to fabricate two-dimensional mesoporous ZnO nanoarrays over a wide range of current densities. Further, because metal oxides are deposited at the triphase interface, sufficient O2, a natural electron scavenger required in photocatalytic reaction to suppress the recombination of photogenerated electron-hole pairs, can be directly supplied, and we demonstrated their enhanced photocatalytic reaction kinetics in water remediation. The present work highlights a powerful interface-engineering strategy for fabricating metal oxides with unprecedented photocatalytic ability.

One-pot nitridation route synthesis of SrTaO2N/Ta3N5 type II heterostructure with enhanced visible-light photocatalytic activity.

Rationally and skillfully constructing semiconductor heterostructured photocatalysts, benefited from the facilitated the carrier separation and transfer, have attracted intensive attention and been demonstrated as a manageable and effective strategy to develop high-performance photocatalysts. Herein, a novel SrTaO2N/Ta3N5 heterostructured photocatalyst were fabricated by one-pot nitridation of Sr2Ta2O7/Ta2O5 precursor under ammonia flow. The as-prepared SrTaO2N/Ta3N5 is a type-II heterostructure with an intimate interface contact, and the photocatalytic hydrogen production over the optimized heterostructure SrTaO2N(0.1)/Ta3N5 is about 14.1 times higher than that of individual SrTaO2N. The experimental results suggest that the formation of type-II heterostructure and intimate interface contact between Ta3N5 and SrTaO2N accelerates the separation and transfer of electrons and holes under visible light irradiation, consequently contribute to the improved hydrogen production rate. Moreover, we highlight that one-pot nitridation has the great potential to apply as an underlying general strategy of designing and fabricating other types of high-efficiency tantalum oxynitride-based heterostructured photocatalysts.

Boosted electrocatalytic activity of nitrogen-doped porous carbon triggered by oxygen functional groups.

The development of high-performance, low-price and durable doped carbon-based materials as multifunctional oxygen reduction reaction and oxygen evolution reaction catalysts is of great significance for the sustainable energy conversion devices. Adopting zinc zeolitic imidazolate framework and graphitic carbon nitride as nitrogen-sources and templates, we herein design a facile route to fabricate an oxygen (6.11%) functionalized and heavy nitrogen (23.54%) doped porous carbon (NOC-800) with high graphitization degree, high surface area and total pore volume. Electrochemical measurements indicate that as-obtained NOC-800 sample has satisfactory multifunctional oxygen-involving electrocatalytic properties in alkaline media, showing an onset and half-wave potential of -0.141 and -0.249 V vs. Ag/AgCl for oxygen reduction and an overpotential of 377 and 448 mV at 10 and 50 mA cm-2 for electrocatalytic oxygen evolution, respectively, even comparable to commercial RuO2 catalyst and majority of present mainstream metal-free catalysts. Moreover, the desirable stability of NOC-800 catalyst for both oxygen reduction and oxygen evolution reaction is also demonstrated. Combined with the analysis and discussion of the physicochemical characterization and electrochemical measurements, it is proposed and highlighted that oxygen functional groups introduced into nitrogen-doped carbon profitably contributes to high-efficiency overall oxygen-involving electrocatalytic activities.

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.

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.

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.

Controlling shape anisotropy of hexagonal CdS for highly stable and efficient photocatalytic H2 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. What's 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.

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.

C-S bond induced ultrafine SnS2 dot/porous g-C3N4 sheet 0D/2D heterojunction: synthesis and photocatalytic mechanism investigation.

The construction of novel heterojunctions is precisely deemed to be an effective strategy to facilitate photo-generated carrier separation and boost charge utilization efficiency, leading to much enhanced photocatalytic activities. Herein, in situ of growing ultrafine SnS2 nanoparticles on a porous g-C3N4 sheet (SnS2/g-C3N4) 0D/2D heterojunction was achieved via a low-temperature solvothermal process. Combined with various characterization techniques, it is revealed that SnS2 dots with a diameter of 3 nm distribute evenly on the surface of the g-C3N4 substrate with strong C-S bonds. The photocatalytic activities are evaluated by the degradation of Rhodamine B (RhB) under visible light irradiation, showing a much enhanced photodegradation efficiency of 96.8% over 105 min irradiation and an enhanced reaction rate constant (k = 3.3% min-1, 8.25 and 8.05 times that of pure g-C3N4 and SnS2). The improved photocatalytic activities could be ascribed to the efficient electron-hole separation of porous g-C3N4, which is caused by the ultrafine SnS2 dots linked with the g-C3N4 substrate through C-S bonds. Therefore, the recombination efficiency is decreased. In addition, reactive active species trapping experiments prove that the superoxide radical (˙O2-) and holes (h+) are the main active species in this photocatalytic system. The photodegradation mechanism of the SnS2/g-C3N4 heterojunction is analyzed and demonstrated in detail.

Well-organized migration of electrons for enhanced hydrogen evolution: Integration of 2D MoS2 nanosheets with plasmonic photocatalyst by a facile ultrasonic chemical method.

The construction of a plasmonic photocatalyst is an efficient way to suppress detrimental electrons-holes recombination and extend the spectral range of light absorption in semiconductors. However, the facilitation effect in the aspect of electrons-holes separation is great limited as the lack of a driving force compelled the electrons or holes migration to surface catalytic sites makes them flow randomly in semiconductors. In this work, we confirm that the integration of MoS2 nanosheets formed two dimensional (2D) layered heterojunction with C3N4 with Au-C3N4 plasmonic photocatalyst can further enhance electrons-holes separation through the formation of Au-C3N4-MoS2 nanostructure by a facile ultrasonic chemical method. The integrated MoS2 nanosheets extract the electrons not only from C3N4 due to a building up of 2D layered heterojunction but also from plasmonic Au via a "pipe" played by C3N4. The electrons "pump" role of the 2D MoS2 nanosheets makes electrons flow randomly turn into the well-organized migration direction, promoting the electrons-holes more efficient separation and lifetime prolongation. Meanwhile, MoS2 nanosheets also increase the light absorption of the photocatalyst owing to its inherent strength of the narrower band gap. Enabled by integration of 2D MoS2 nanosheets, the hydrogen production rate is 2.08 times higher than that of its counterpart Au-C3N4. This work highlights a new window to employ 2D layered heterojunction for enhanced photocatalytic hydrogen evolution performance.

Simple and facile ultrasound-assisted fabrication of Bi(2)O2CO(3)/g-C(3)N(4) 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.