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Cocatalysts play important roles in improving the activity and stability of most photocatalysts. It is of great significance to develop economical, efficient and stable cocatalysts. Herein, using Na2CoFe(CN)6 complex as precursor, a novel noble-metal-free FeCo@NGC cocatalyst (nano-FeCo alloy@N-doped graphitized carbon) is fabricated by a simple pyrolysis method. Coupling with g-C3N4, the optimal FeCo@NGC/g-C3N4 receives a boosted visible light driven photocatalytic H2 evolution rate of 42.2 μmol h−1, which is even higher than that of 1.0 wt% Pt modified g-C3N4 photocatalyst. Based on the results of density functional theory (DFT) calculations and practical experiment measurements, such outstanding photocatalytic performance of FeCo@NGC/g-C3N4 is mainly attributed to two aspects. One is the accelerated charge transfer behavior, induced by a photogenerated electrons secondary transfer performance on the surface of FeCo alloy nanoparticles. The other is related to the adjustment of H adsorption energy (approaching the standard hydrogen electrode potential) by the presence of external NGC thin layer. Both factors play key roles in the H2 evolution reaction. Such outstanding performance highlights an enormous potential of developing noble-metal-free bimetallic nano-alloy as inexpensive and efficient cocatalysts for solar applications.

On the basis of Landau-de Gennes theory, the fine structures of escaped concentric and ideal concentric configurations confined in nematic liquid crystal droplets were investigated. The escaped con...

The loading of noble-metal cocatalysts on photocatalysts can significantly increase the energy conversion efficiency from light to hydrogen (H2). However, the high cost of noble metals limits their practical application. Therefore, it is of great significance to explore alternative catalysts based on noble-metal-free materials. Herein, FeNi intermetallic compound nanoparticles wrapped with N-doped graphitized carbon (FeNi@NGC) are prepared by a facile pyrolysis approach. The FeNi@NGC is used as a novel cocatalyst of host photocatalysts, such as g-C3N4, to boost their photogenerated charge separation. In an aqueous solution containing triethanolamine and under visible-light irradiation, the optimized FeNi@NGC/g-C3N4 (FNC15) composite photocatalyst exhibits significantly increased PC activity with a H2 production rate of 2.696 mmol g−1 h−1, which is over 283 times that of primary g-C3N4 and even higher than that of 1.0 wt% Pt/g-C3N4. Furthermore, the FNC15 showed excellent stability and reusability. The apparent quantum yield (AQY) of the FNC15 composite photocatalyst reaches 24.78% and 7.28% at 400 nm and 420 nm, respectively. Notably, the FNC15 can promote photocatalytic overall water splitting with an H2 evolution rate of about 0.167 mmol g−1 h−1. Experimental analysis and DFT calculations are performed to investigate the mechanism of excellent PC H2 evolution. It appears that the FeNi@NGC loading on the surface of host photocatalysts can (i) boost the charge carrier separation and transfer because of the secondary charge transfer in the FeNi intermetallic compound and (ii) ameliorate the kinetics of H2 evolution on the surface of the photocatalyst and achieve obviously enhanced H2 generation. This work provides a new strategy for preparing efficient noble-metal-free cocatalysts for boosting photocatalytic H2 evolution.

On the basis of Landau–de Gennes theory and the finite-difference iterative method, spontaneous chiral structures in cylinders with degenerate planar boundary conditions are investigated. A...

In photocatalytic field, it is a significant challenge to synthesize cocatalyst with high performance, noble-metal free and facile methods to recycle. Herein, carbon layer coated Fe3C (Fe3C@C) nanoparticles were prepared by one-step method and for the first time utilized as highly efficient cocatalysts for improving visible-light-driven hydrogen evolution activity of g-C3N4. The photocatalytic hydrogen evolution rate of optimal Fe3C@C/g-C3N4 was about 27.2 times of bare g-C3N4 samples. Furthermore, the Fe3C@C/g-C3N4 composite catalyst showed excellent stability and reusability. The apparent quantum yield (AQY) of the optimized FeC@C/g- C3N4 reaches 0.501% and 0.124% at 400 nm and 420 nm, respectively. The AQY of the FeC@C/g- C3N4 is 26.2 times higher than that of g-C3N4 at 400 nm Fe3C@C has an extraordinary cocatalytic effect for g-C3N4 photocatalytic hydrogen evolution mainly due to three aspects: Firstly, the Fe3C acts as a trap to lure electrons because of its lower Fermi energy level and higher conductivity, which can increase the hydrogen production activity by trapping the photogenerated electrons produced by g-C3N4; Secondly, the coated carbon layer can provide chemical protection for Fe3C nanoparticles and promote the transfer of photogenic electrons, thus further improving the efficiency and stability of photocatalytic hydrogen production; Thirdly, the strong magnetic property of Fe3C@C nanoparticles gives Fe3C@C/g-C3N4 photocatalysts the advantages of low cost and high recovery efficiency. It is believed that this work provides a new strategy and possibility for the application of photocatalytic hydrogen production.

Graphitied carbon-coated bimetallic FeCu nanoparticles (FeCu@C) are fabricated by one-step method for the first time. The FeCu@C as novel cocatalysts of g-C3N4 for improving visible-light photocatalystic hydrogen evolution. The FeCu@C as the cocatalyst of g-C3N4 (FeCu@C/g-C3N4) possess better photocatalyst activity (7.22 μmol h−1) than that of Fe@C (2.51 μmol h−1) and Cu@C (5.36 μmol h−1) nanoparticles. The highest photocatalytic activity of FeCu@C/g-C3N4 can be attributed to the synergistic effect of the binary metals and the graphitied carbon layer. The bimetallic cocatalyst is not a simple combination of two metals, but a special electronic effect formed by the interaction between two metals. The Fe acts the catalytic activity center to capture photogenerated carries produced by g-C3N4, and agglomerates on the surface of FeCu alloys. Simultaneously, the coating of graphitied carbon layer can effectively enhance the stability of FeCu alloy and accelerate electron transfer. It is predicted that this work can provide new ideas and insights for the improvement of photocatalytic activity of semiconductors by non-precious alloy nanoparticles.

High performance, low cost and sustainable photocatalytic evolution of hydrogen is a promising energy supply alternative for modern society to resolve the depletion crisis of fossil fuel. The design of multi-heterojunction visible-light photocatalysts combined with electrochemical means is considered one of the most attractive options in recent years. In this work, a photoanode composed of top-opened ZnO/CdS/PbS nanotube arrays (ZnO/CdS/PbS ONTs) with multi-heterojunctions was synthesized via a three-step process, i.e. hydrothermal treatment, chemical bath deposition and successive ionic layer adsorption reaction (SILAR). This as-prepared photoanode exhibited remarkable photoelectrochemical activity under visible light irradiation. The photocurrent density and photoelectrochemical hydrogen evolution efficiency of the optimized ZnO/CdS/PbS ONTs reached up to 14.2 mA cm−2 and 5.5 mL cm−2 h−1 at 0.0 V vs. Ag/AgCl, respectively. The efficiency was 3.1 times that of top-closed ZnO/CdS nanotubes (1.8 mL cm−2 h−1). The experimental results suggest that the high photoelectrochemical activity can be ascribed to the inherent advantages of the structural and successive energy level relays design: on the one hand, the top-opened nanotube structure significantly enlarges surface area of the nanostructure, which facilitates efficient light absorption and rapid mass transport; on the other hand, the well-matched band energy edge of the multi-heterojunction interfaces literally build efficient electron highways to deliver electrons to reaction sites and reduce the recombination of photogenerated charge carriers.

Carbon-coated Cu-TiO2 nanocomposite (Cu-TiO2@C) was constructed using one-step method of thermal reduction. Their photocatalytic activity for hydrogen production from methanol aqueous solution was investigated. Under UV–vis light irradiation, the hydrogen yield of the 10 mg optimal Cu-TiO2@C reached 269.1 μmol h−1, which was very close to that of Pt@TiO2 (290.8 μmol h−1). The Cu-TiO2@C also displayed much higher photocatalytic stability in comparison with Cu-TiO2 without coated carbon layer. The nano-Cu as photocatalytic active site improve the efficiency of photoinduced carrier separation. The carbon layer with the ability to transfer photogenerated electrons faster and to adsorb hydroxyl radicals more easily, leading to a very significant increase the reaction rate. In addition, the carbon layer can also provide a chemical protection to the Cu nanoparticles and increase the stability of the photocatalysts. The Cu-TiO2@C photocatalyst with the low cost, enhanced photostability and photocatalytic activity is expected to be an excellent nanocomposite t in reforming of biomass or bio-derivatives field.

Based on Landau-de Gennes theory, electric field-induced structure transition of negative nematic liquid crystals in submicron-confined cylinder cells was investigated. The easy orientation of the weak anchoring conditions on the cylindrical side surface was prescribed along the radial direction. When we kept the cell gap d unchanged and gradually increased the voltage U, system showed an unexpected structure transition. At a critical value of U = Uc, two-dimensional (2D) local order reconstruction occurred in the system. Meanwhile, when we kept the ratio of U/d unchanged and gradually decreased the d, biaxiality layer gradually moved from the central axis to the cylindrical side surface and disappeared when d is under nanoscale. Furthermore, Uc decreased when the anchoring energy on the side surface increased. Keywords: Negative nematics, Submicron cylinder cells, Local order reconstruction, Landau-de Gennes theory, Relaxation iterative method

The electric field-induced structural transition of domain walls in nanoconfined nematic liquid crystal systems was investigated on the basis of Landau–de Gennes theory. Two models of nanoconfined domain wall systems were established as splay–bend and twist wall systems under Freedericksz transitions with two different rotation directions under the effect of electric field E/E0. Results showed that two structural transition processes occur in both models. Pincement transition occurs under a critical external field Ec1/E0. In pincement transition, walls change into two squeezed symmetric surface defects with opposite charges. Surface defects spread along the direction of the substrates and attain surface order reconstruction states as E/E0 is enhanced to Ec2/E0. The increment in cell gap d from the nanoscale to the microscale will not affect Ec2/E0 in both models.

Oxygen functional groups are often overlooked in most carbon coated co-catalyst for photocatalytic hydrogen evolution, and its influences on proton reduction are not been well considered. In this work, a noble-metal-free co-catalyst CuNi alloy nanoparticle wrapped in a carbon layer containing oxygen-containing functional groups (CuNi@C O) was designed and synthesized. Under visible light irradiation, the photocatalytic H2 evolution rate of CuNi@C O/g-C3N4 was 2.36 mmol g−1 h−1, which was higher than that of Pt co-catalyst at the same conditions. Density functional theory calculations and mechanistic studies indicate that the H adsorption free energy on the CuNi@C O was more suitable for hydrogen evolution than that of Pt, where the C O groups on the carbon layer surface modulated the work function of CuNi alloy. It is believed that the understanding the function of surface C O group can broaden the research directions of photocatalyst modification and improve the activity of photocatalytic hydrogen evolution.

Nanostructured silicon has been intensively investigated as a high capacity Li-ion battery anode. However, the commercial introduction still requires advances in the scalable synthesis of sophisticated Si nanomaterials and electrodes. Moreover, the electrode degradation due to volume changes upon de-/lithiation, low areal electrode capacity, and application of large amounts of advanced conductive additives are some of the challenging aspects. Here we report a Si electrode, prepared from direct deposition of Si nanoparticles on a current collector without any binder or conducting additives, that addresses all of the above issues. It exhibits an excellent cycling stability and a high capacity retention taking advantages of what appears to be a locally protective, yolk-shell reminiscent, solid electrolyte interphase (SEI) formation. Cycling an electrode with a Si nanoparticle loading of 2.2 mg cm−2 achieved an unrivalled areal capacity retention, specifically, up to 4.2 mAh cm−2 and ~ 1.5 mAh cm−2 at 0.8 mA cm−2 and 1.6 mA cm−2, respectively.

Within Landau–de Gennes theory, we modeled a system consisting of two anti-connected hybrid alignment nematics (HAN). Our numerical simulation results indicated the occurrence of four states denoted as I, II, III and IV. The states undergo a structure transition as a function of the cell gap d. For d [Formula: see text] d0, where d0 is the maximum value for the structure transition to occur, state I and II are bistable, whereas state III and IV are metastable and quadruply degenerate. We found that d0 = 15[Formula: see text], where [Formula: see text] is the biaxial characteristic coherence length. When d[Formula: see text] [Formula: see text] d [Formula: see text] d0, where d[Formula: see text] = 7[Formula: see text] and d[Formula: see text] is the critical cell gap for order reconstruction (OR), continuous inversion walls appear both in state III and IV. We first found that the structure transition from inversion walls to defect walls occurs with decreasing d from the submicron to nanoscale. During this process, quadruply degenerate states in state III and IV transformed into doubly degenerate states. Meanwhile, states I and II remained bistable. When d = d[Formula: see text], all states reached a new type of OR pattern with two biaxial walls cross-linked with each other by a novel approach; i.e., from defect walls to OR.