The temperature effect on the co-sequestration process receives little attention. Herein, kinetic and thermodynamic studies on the co-sequestration of Eu(III) and phosphate by γ-Al2O3 were investigated by batch experiments. The standard thermodynamic parameters (∆H0, ∆S0, and ∆G0), the activation thermodynamic parameters (∆H#, ∆S#, and ∆G#), and the activation energy (EA) for the co-sequestration process were obtained. Based on EA and ∆S# values, Eu(III) and phosphate co-sequestration is controlled by chemical reactions on γ-Al2O3 and by an associative mechanism. This work highlights the temperature effect on the co-sequestration of Eu(III) and phosphate in a geological environment.

By using the density functional theory (DFT) method, we theoretically investigated the structural, electronic and optical properties of functionalized MXenes with three different geometries, namely M2CT2-I, M2CT2-II and M2CT2-III (M = Ti, Zr, Hf; T = F, O, OH). Except for the M2CO2-II and M2CO2-III, there is no negative frequency in the phonon spectra of M2CT2 materials, which suggests the kinetic stabilities of these functionalized MXenes. The M2CT2-I materials with functional groups located above the opposite-side metal atoms have the largest cohesive energies, and thus, are energetically most favorable. Significantly, we found that all the energetically favorable M2CO2-I materials have not only suitable band gaps (0.92–1.75 eV), but also visible-light absorption, high redox potential of photo-induced holes, efficient separation of e−–h+ pairs, and exceptional carrier mobilities, implying the great possibility of Ti2CO2, Zr2CO2 and Hf2CO2 materials to be utilized as visible-light driven photocatalysts. Additionally, the Hf2CO2 materials with appropriate band edges could be used for photocatalytic water splitting. Our theoretical studies are valuable for further exploring the potential applications of MXenes, which are worthy of experimental investigation and confirmations.

•NiCo2O4@RGO nanocomposite was synthesized and employed as a CE in DSSC.•The DSSC equipped with NiCo2O4@RGO CE achieved the highest PCE of 6.17%.•The NiCo2O4@RGO CE gives a more stable catalytic activity for triiodide reduction.In this report, spinel NiCo2O4 nanobelts anchored on reduced graphene oxide (NiCo2O4@RGO) have been synthesized by a hydrothermal reduction process and used as counter electrode (CE) in dye-sensitized solar cells (DSSC). Without RGO, the NiCo2O4 nanobelts tend to aggregate and form sarciniform patterns. By introducing RGO, the NiCo2O4 nanobelts are dispersed on graphene sheets uniformly. The DSSC based on NiCo2O4 nanobelts CE achieves power conversion efficiency (PCE) of 5.20% and a higher PCE (6.17%) on NiCo2O4@RGO nanocomposite, which was comparable to the Pt CE (6.07%). The cyclic voltammetry tests (CV) analysis indicates that the NiCo2O4@RGO CE gives a more stable catalytic activity for triiodide reduction than NiCo2O4 CE does. Due to the existence of RGO, the composite possesses both higher efficiency and stability.NiCo2O4@RGO nanocomposite possesses a more stable catalytic activity as a counter electrode (CE) in dye-sensitized solar cell (DSSC).

•NiS and NiS2 hollow spheres were synthesized simultaneously.•The phase transformed from NiS into NiS2 with the sulfur contents increasing.•Both of them can substitute Pt as efficient CE catalyst of DSSCs.•NiS2 CE exhibits superior electrocatalytic activity than NiS CE.NiS and NiS2 hollow spheres were synthesized simultaneously by a facile solvothermal route without the help of any template or surfactant. The Ni/S molar ratio in the reactants plays a significant role in the formation of nickel sulfides with different stoichiometric ratio. The microstructures and morphologies of the NiS and NiS2 were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N2 adsorption–desorption isotherm measurements. In addition, the electrochemical performances of dye-sensitized solar cells based on these two types of nickel sulfides counter electrodes (CEs) were investigated in detail. It is found that NiS2 CE exhibit higher electrocatalytic activity than NiS CE for the reduction of triiodide. As a consequence, the DSSC with NiS2 CE generates higher power conversion efficiency (7.13%) than that with NiS CE (6.49%).

We present a controllable synthesis of ternary hierarchical hollow sphere, assembling by numerous particle-like Cu2MoS4, via a facile hydrothermal method. By adding graphene oxides (GO) in the reaction process, Cu2MoS4/reduced graphene oxide (RGO) heterostructures were obtained with enhanced photocurrent and photocatalytic performance. As demonstrated by electron microscopy observations and X-ray characterizations, considerable interfacial contact was achieved between hierarchical Cu2MoS4 hollow sphere and RGO, which could facilitate the separation of photoinduced electrons and holes within the hybrid structure. In comparison with the pure Cu2MoS4 hollow sphere, the obtained hybrid structures exhibited significantly enhanced light absorption property and the ability of suppressing the photoinduced electron–holes recombination, which led to significant enhancement in both photocurrent and efficiency of photocatalytic methyl orange (MO) degradation under visible light (λ > 420 nm) irradiation.

A nanocomposite of SnS2 nanoparticles with reduced graphene oxide (SnS2@RGO) had been successfully synthesized as a substitute conventional Pt counter electrode (CE) in a dye-sensitized solar cell (DSSC) system. The SnS2 nanoparticles were uniformly dispersed onto graphene sheets, which formed a nanosized composite system. The effectiveness of this nanocomposite exhibited remarkable electrocatalytic properties upon reducing the triiodide, owning to synergistic effects of SnS2 nanoparticles dispersed on graphene sheet and improved conductivity. Consequently, the DSSC equipped with SnS2@RGO nanocomposite CE achieved power conversion efficiency (PCE) of 7.12%, which was higher than those of SnS2 nanoparticles (5.58%) or graphene sheet alone (3.73%) as CEs and also comparable to the value (6.79%) obtained with pure Pt CE as a reference.Keywords: counter electrode; DSSC; nanocomposites; SnS2@RGO

•Structural phase transition was applied to the fabrication of counter electrodes.•Tin (IV) sulfide transformed into tin (II) sulfide after an annealing process.•By introducing the reduced graphene oxide, the nanocomposite exhibited excellent performance.•A superior power conversion efficiency of 7.47% was achieved.Annealing is an important process for fabricating counter-electrodes of dye-sensitized solar cells. Along with the annealing process, however, structural phase transitions sometimes occur, which have significantly effect on the performance of the electrodes and cells, but is often ignored. Here, we report such a phase transition in which tin (IV) sulfide is transformed into tin (II) sulfide after annealing in an argon atmosphere. The precursor and final product are respectively fabricated together with reduced graphene to form nanocomposites that are subsequently used as the counter-electrodes. It is found that the power conversion efficiency of dye-sensitized solar cell with the counter-electrode made of tin (II) sulfide and reduced graphene oxide nanocomposites achieves 7.47%. The efficiency is much higher than that (5.30%) of a device using tin (IV) sulfide and reduced graphene oxide nanocomposites as counter-electrode and is even comparable to the value (7.75%) of a cell with conventional platinum as counter-electrode.

The origin of the photoactivity in graphitic carbon nitride (g-C3N4) and the strategies for improving its photocatalytic efficiency were systematically investigated using first-principles computations. We found that g-C3N4 composed of tri-s-triazine units (g-CN1) is preferable in photocatalysis, owing to its visible-light absorption and appropriate band edge potentials. Despite the benefit of nanocrystallization of g-CN1, excessively minimized and passivated g-CN1 nanosheets (g-CN1NSs) should be inhibited, due to the intensely broadened band gaps in these structures. C- or N-vacancies in g-CN1NSs lead to gap states and smaller band widths, which should also be restrained. Compared with C substitution in B doped g-CN1NSs, N-substitution is favourable for enhancing the photoactivity of g-CN1NSs, due to the red-shift light absorption and the absence of gap states within this structure. Both WTe2 coupled and CdSe cluster loaded g-CN1NSs have decreased band gaps and directly separated carriers, which are beneficial to promote the photoactivity of g-CN1NSs. Among these modified g-CN1NS photocatalysts, WTe2 coupled g-CN1NSs are more preferable, as a result of their smaller band gap, free gap states and more rapid migration of excitons.

Spongelike CuInS2 3D microspheres were synthesized through a solvothermal method employing CuCl, InCl3, and thiourea as Cu, In, and S sources, respectively, and PVP as surfactant. The as-prepared products have regular spherical shapes with diameters of 0.8–3.7 μm, the spheres consisted of small nanosheets, which are composed of small nanoparticles. As an important solar cell material, its photovoltaic property was also tested and the results showed a solar energy conversion efficiency of 3.31%. With the help of reduced graphene, its conversion efficiency could be further increased to 6.18%. Compared with conventional Pt material used in counter electrodes of solar cells, this new material has an advantages of low-cost, facile synthesis and high efficiency with graphene assistance.Keywords: counter electrodes; CuInS2; graphene assisted; microspheres; photovoltaic property; power conversion efficiency;

Porous bismuth sulfide–carbon (Bi2S3–C) composite microspheres were synthesized via a facile solvothermal route and served as a low-cost counter electrode material for Pt-free dye-sensitized solar cells (DSSCs). The electrochemical performance analysis indicates that the Bi2S3–C electrode has lower charge transfer resistance at the electrolyte/electrode interface, smaller Nernst diffusion impedance of iodide in electrolyte and higher catalytic ability than the bare Bi2S3 electrode. After optimization of the content of carbon, the DSSC with the Bi2S3–C counter electrode exhibited an excellent power conversion efficiency of 6.72%, which is comparable to that of the Pt-based DSSC (6.74%).

3D cubic microporous In2O3 has been successfully obtained by calcining the as-synthesized cube In(OH)3–InOOH precursor at 300 °C for 2 hours. X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) were employed to clarify the structures and morphologies of both the cubic In(OH)3–InOOH precursor and cubic In2O3. The formation mechanisms of the In(OH)3–InOOH precursor and cubic In2O3 were investigated. As an important semiconductor photocatalytic material, its photocatalytic properties have been tested. Under the irradiation of UV light, the cubic microporous In2O3 exhibits excellent photocatalytic properties to degrade eosin B (EB), which presents ∼95% degradation of EB after 3 hours and the degradation rates is 10.5 times that of commercial In2O3 powder. The high separation efficiency of electron–hole pairs results in high photocatalytic activity. Furthermore, the photoluminescent properties of the cubic microporous In2O3 have been investigated as well.

•SnS2 nanoparticles are synthesized via a solvothermal method by changing solvent concentration, which obtained the similar hexagonal SnS2 nanoparticles with a smaller size, and the mean diameter is in the range of 5–10 nm.•With the decrease of EG dosage in initial stage, the intensity of (001) plane is intensified.•The highest conversion efficiency of our materials achieved 6.3%, while the efficiency of Pt based was 6.67%.•Our dye-sensitized solar cell offered lower interface resistance between the electrolyte and the counter electrode.In this paper, we focused on synthesizing hexagonal SnS2 nanoparticles with perfect crystallinity as a replacement of Pt catalyst conventionally used in the counter electrode (CE) of a dye-sensitized solar cell (DSSC). When the conditions of the initial reaction were changed, the SnS2 nanoparticles growth along the (001) facet with various preferred orientations was obtained. The highest power conversion efficiency (PCE) of our materials achieved 6.3%, while the efficiency of Pt based was 6.67%. From the electrochemical impedance spectroscopy analysis, we found that our dye-sensitized solar cell offers lower interface resistance between the electrolyte and the counter electrode. Our work obtained the DSSC with the power-conversion efficiency and stable property, and it also provided routes for preparing low-cost DSSC using inorganic nanostructure as CE.

•Nickel sulfide hollow spheres have been prepared by a one-step hydrothermal method with no template.•A hollow structure provides a higher electrolyte absorption, which could be used as counter electrode in dye-sensitized solar cells.•The DSSC consisted of hollow NiS CE showed a PCE of 6.9% which is comparable to that of Pt CE (6.75%).NiS has a high conductivity and excellent catalytic properties. Furthermore, a hollow structure provides a higher electrolyte absorption, which could be used as counter electrode in dye-sensitized solar cells. In this paper, NiS hollow spheres have been prepared by a traditional one-step hydrothermal method. The dye-sensitized solar cell with NiS hollow spheres as a counter electrode yielded a preferable power conversion efficiency of 6.90%, which was comparable to that of platinum (6.75%) as counter electrode.

A co-precipitation method was employed to prepare Eu3+-doped gadolinium tungstate and Y3Al5O12:Ce fluorescent powders. Eu3+-doped gadolinium tungstate phosphors can be effectively excited both by ultraviolet light at 395 nm and blue light at 465 nm and emit remarkably intense red emission at 613 nm with near line spectrum. Ce3+-doped YAG can also efficiently absorb this blue light and produce a broad band of luminescence centering at 540 nm. The red fluorescent powder and yellow fluorescent phosphor were then mixed together at different weight ratios. It is found that the emission spectra of the blended phosphors excited with blue light at 465 nm is the superposition of the two phosphors, which means that the mixture’s emission can be tuned by controlling the weight ratios. These results demonstrated the possibility of using the blended phosphors to increase the color-rendering properties of white LEDs.Graphical abstractHighlights► Eu3+-doped gadolinium tungstate phosphors have been successfully synthesized. ► 40 mol% Eu3+ doped Gd6WO12:Eu3+excited by blue light shows excellent red emission. ► The blended phosphors mixed YAG:Ce with Gd6WO12:Eu3+ show white light with warm tune. ► The blended phosphors could increase the color-rendering properties of white LEDs.

Bi2Te3 nanosheets were prepared by the solvothermal method. The XRD diffraction patterns indicated that all the samples had a single hexagonal lattice structure. Both scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to characterize their size, morphology, and microstructure. The fabricated Bi2Te3 nanosheets showed obvious preferred growth orientations along the aa- and bb-axes. Based on experimental results for the typical thickness of the nanosheets, a possible phenomenological mechanism for the formation of the Bi2Te3 nanosheets was proposed considering the competition between gravity and Van der Waals forces.Highlights► The solvothermal method was adopted and hexagonal Bi2Te3 nanosheets were obtained. ► The possible growth mechanism of the hexagonal Bi2Te3 nanosheets was discussed. ► The optical properties of the Bi2Te3 samples were researched.

Mesoporous structure and carbon coating are two important techniques for improving electrode performance for Li ion batteries. The combining of these two techniques in one system offers a new strategy for producing new high-performance electrode materials. Here, we demonstrate a two-step method for preparing carbon coated mesoporous β-In2S3 microspheres. The mesoporous β-In2S3 microspheres were synthesized through a solvothermal route, with the assistance of surfactant poly(vinyl pyrrolidone). After treating with glucose in a hydrothermal condition and calcinating under an inert atmosphere, mesoporous β-In2S3@C microspheres were obtained. Electron microscope and nitrogen absorption studies showed that the sample maintained microsphere morphology and mesoporous structure after carbon treating, but an amorphous carbon layer with a thickness of 8 nm could be found on the surface. Both β-In2S3 and β-In2S3@C mesoporous microspheres exhibited remarkable Li storage performance at the initial charge and discharge cycle. Compared with reported β-In2S3 microspheres without porous structure, the mesoporous β-In2S3 microspheres showed limited improvement on electrode performance. Furthermore, the carbon coating greatly improved the Li intercalation–deintercalation cycling behaviour. The specific capacity of mesoporous β-In2S3@C microspheres was almost unchanged after the 5th cycle and was more than three times higher than that of mesoporous β-In2S3 microspheres after 50 cycles. We suggested that the mesoporous structure and carbon coating together exhibited a better “buffering” effect for compensating volume changes and enhancing the reversibility of electrode reactions.

Electrical transport properties of a heteroepitaxial p–n junction made of charge-ordered La7/16Ca9/16MnO3 (LCMO) and 0.5 wt% Nb doped SrTiO3 (SNTO) were studied. The junction displayed highly rectifying current–voltage characteristics over a temperature range from 85 to 280 K. The slope of the diffusion voltage vs temperature shows two evident changes, which can be respectively associated to the paramagnetic to ferromagnetic and ferromagnetic to antiferromagnetic (charge ordering ) magnetic transitions of LCMO. Two distinct electronic transport mechanisms are also discerned around the charge ordering temperature (TCO); thermally assisted tunneling at temperatures lower than TCO and diffusion/recombination at higher temperatures.

The origin of the photoactivity in graphitic carbon nitride (g-C3N4) and the strategies for improving its photocatalytic efficiency were systematically investigated using first-principles computations. We found that g-C3N4 composed of tri-s-triazine units (g-CN1) is preferable in photocatalysis, owing to its visible-light absorption and appropriate band edge potentials. Despite the benefit of nanocrystallization of g-CN1, excessively minimized and passivated g-CN1 nanosheets (g-CN1NSs) should be inhibited, due to the intensely broadened band gaps in these structures. C- or N-vacancies in g-CN1NSs lead to gap states and smaller band widths, which should also be restrained. Compared with C substitution in B doped g-CN1NSs, N-substitution is favourable for enhancing the photoactivity of g-CN1NSs, due to the red-shift light absorption and the absence of gap states within this structure. Both WTe2 coupled and CdSe cluster loaded g-CN1NSs have decreased band gaps and directly separated carriers, which are beneficial to promote the photoactivity of g-CN1NSs. Among these modified g-CN1NS photocatalysts, WTe2 coupled g-CN1NSs are more preferable, as a result of their smaller band gap, free gap states and more rapid migration of excitons.

Mesoporous structure and carbon coating are two important techniques for improving electrode performance for Li ion batteries. The combining of these two techniques in one system offers a new strategy for producing new high-performance electrode materials. Here, we demonstrate a two-step method for preparing carbon coated mesoporous β-In2S3 microspheres. The mesoporous β-In2S3 microspheres were synthesized through a solvothermal route, with the assistance of surfactant poly(vinyl pyrrolidone). After treating with glucose in a hydrothermal condition and calcinating under an inert atmosphere, mesoporous β-In2S3@C microspheres were obtained. Electron microscope and nitrogen absorption studies showed that the sample maintained microsphere morphology and mesoporous structure after carbon treating, but an amorphous carbon layer with a thickness of 8 nm could be found on the surface. Both β-In2S3 and β-In2S3@C mesoporous microspheres exhibited remarkable Li storage performance at the initial charge and discharge cycle. Compared with reported β-In2S3 microspheres without porous structure, the mesoporous β-In2S3 microspheres showed limited improvement on electrode performance. Furthermore, the carbon coating greatly improved the Li intercalation–deintercalation cycling behaviour. The specific capacity of mesoporous β-In2S3@C microspheres was almost unchanged after the 5th cycle and was more than three times higher than that of mesoporous β-In2S3 microspheres after 50 cycles. We suggested that the mesoporous structure and carbon coating together exhibited a better “buffering” effect for compensating volume changes and enhancing the reversibility of electrode reactions.

By using the density functional theory (DFT) method, we theoretically investigated the structural, electronic and optical properties of functionalized MXenes with three different geometries, namely M2CT2-I, M2CT2-II and M2CT2-III (M = Ti, Zr, Hf; T = F, O, OH). Except for the M2CO2-II and M2CO2-III, there is no negative frequency in the phonon spectra of M2CT2 materials, which suggests the kinetic stabilities of these functionalized MXenes. The M2CT2-I materials with functional groups located above the opposite-side metal atoms have the largest cohesive energies, and thus, are energetically most favorable. Significantly, we found that all the energetically favorable M2CO2-I materials have not only suitable band gaps (0.92–1.75 eV), but also visible-light absorption, high redox potential of photo-induced holes, efficient separation of e−–h+ pairs, and exceptional carrier mobilities, implying the great possibility of Ti2CO2, Zr2CO2 and Hf2CO2 materials to be utilized as visible-light driven photocatalysts. Additionally, the Hf2CO2 materials with appropriate band edges could be used for photocatalytic water splitting. Our theoretical studies are valuable for further exploring the potential applications of MXenes, which are worthy of experimental investigation and confirmations.