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Realizing high-efficiency solar-driven CO2 reduction to chemicals and fuels requires high-performance photocatalysts with high utilization efficiency of solar light, efficient charge separation and transfer, and robust adsorption capacity for CO2. In this work, a tubular In2O3-C/CdIn2S4 (IOC/CIS) ternary heterojunction with an intimate interfacial contact was fabricated by pyrolysis of In-MIL-68 and subsequent solvothermal synthesis of CdIn2S4. The construction of a heterojunction promotes the separation and transfer efficiency of photogenerated carriers. The introduction of carbon not only accelerates the interfacial charge migration but also enhances light absorption and CO2 adsorption. The resulting 5IOC/CIS sample presents a remarkably improved photocatalytic CO2 reduction activity with a CO generation rate of 2432 μmol g-1 h-1, much higher than that of the In2O3/CdIn2S4 (IO/CIS) heterojunction (1906 μmol g-1 h-1). Furthermore, the type II charge transfer mechanism of the heterojunction was confirmed by the electron paramagnetic resonance characterization. This work provides new insight into the design and preparation of a highly efficient hollow heterojunction for photocatalytic applications.

The development of high-efficiency photocatalysts is of great importance to realize robust solar-driven CO₂ conversion; however, the low carrier separation efficiency and poor light absorption ability usually limit the performance of the photocatalysts. Herein, a hollow In₂S₃/polymeric carbon nitride (IS/CN) heterojunction was prepared via electrostatic self-assembly and in situ sulfidation under solvothermal conditions. The intimate interfacial contact between the IS and CN facilitates the construction of an effective heterojunction, as demonstrated by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM). The optimized IS/CN-5 sample exhibits a high CO evolution rate of 483.4 μmol g–¹ h–¹, which is 99 and 6 times as high as that of IS and CN, respectively. The improved charge separation and transfer efficiency, the hollow nanotube structure, and the enhanced CO₂ adsorption ability are the reasons for the excellent photocatalytic activity. Besides, a possible photocatalytic mechanism of CO₂ reduction by the IS/CN heterojunction was proposed on the basis of the band structures. This work provides an effective and facile strategy to construct hollow semiconductor heterojunctions for photocatalytic applications.

Heterogeneous catalysts with ultra-small clusters and atomically dispersed (USCAD) active sites have gained increasing attention in recent years. However, developing USCAD catalysts with high-density metal sites anchored in porous nanomaterials is still challenging. Here, through the template-free S-assisted pyrolysis of low-cost Fe-salts with melamine (MA), porous alveolate Fe/g-C3N4 catalysts with high-density (Fe loading up to 17.7 wt%) and increased USCAD Fe sites were synthesized. The presence of a certain amount of S species in the Fe-salts/MA system plays an important role in the formation of USCAD S-Fe-salt/CN catalysts; the S species act as a “sacrificial carrier” to increase the dispersion of Fe species through Fe-S coordination and generate porous alveolate structure by escaping in the form of SO2 during pyrolysis. The S-Fe-salt/CN catalysts exhibit greatly promoted activity and reusability for degrading various organic pollutants in advanced oxidation processes compared to the corresponding Fe-salt/CN catalysts, due to the promoted accessibility of USCAD Fe sites by the porous alveolate structure. This S-assisted method exhibits good feasibility in a large variety of S species (thiourea, S powder, and NH4SCN) and Fe salts, providing a new avenue for the low-cost and large-scale synthesis of high-density USCAD metal/g-C3N4 catalysts.

In this work, we proposed a facile and green method involving just two steps of dispersion and annealing to in-situ synthesize TiN/C composite materials. First, the nitrogen and titanium sources were combined by a complexing agent in the dispersion process, and then TiN/C composite materials were obtained by annealing the solid precursors from centrifuging the above solution in nitrogen atmosphere. High-density TiN nanoparticles with the size of ∼10 nm are dispersed uniformly on carbon matrix, and the composite has a high specific surface area up to 148 m2/g. When used as supercapacitor electrode materials, the composite exhibits relatively high specific capacitance of 159.0 F/g at 0.5 A/g, and good rate performance with specific capacitance of 96.0 F/g at 20 A/g. The current facile method could be a promising strategy for the low-cost and large-scale synthesis of metal nitride/carbon composite materials.

Mimicking natural thylakoid vesicles is an effective approach for facilitating photoabsorption and charge separation over photocatalysts. However, bulk materials cannot function well with a short photocarrier transport distance while thin-layers suffer from preparation difficulty due to the ease of structural collapse. Herein, inspired by natural thylakoid vesicles, a solid-state thermolysis templating method using the shape selectivity of MCM-41 and melamine precursor has been developed to assemble stable thin-shell g-C3N4 vesicles and their heterojunctions. The relatively narrow channel of MCM-41 allows the oligomerization of melamine inside the pore but inhibits its further polymerization into melon. With increasing temperature, oligomers begin to form and migrate out of the channel and polymerize selectively on the open-up outer surface into the vesicle structure. Single- and double-thin-shell g-C3N4 vesicles as well as their heterojunctions have successfully been fabricated through templating by MCM-41, hollow MCM-41 and MOx/MCM-41 (M = Ag, Fe, Co, Cu, and Ni) as evidenced by TEM. A uniform shell thickness can be precisely controlled from 17.5 to 42.1 nm. The tailored g-C3N4 vesicles exhibit enhanced photocatalytic activity and stability for the hydrogen evolution reaction which results from the enhanced photoabsorption and suppressed charge recombination. This new method is versatile for encapsulation of the secondary component including metals and metal oxides in g-C3N4.

Ultra-small metal clusters have attracted great attention owing to their superior catalytic performance and extensive application in heterogeneous catalysis. However, the synthesis of high-density metal clusters is very challenging due to their facile aggregation. Herein, one-step pyrolysis was used to synthesize ultra-small clusters and single-atom Fe sites embedded in graphitic carbon nitride with high density (iron loading up to 18.2 wt %), evidenced by high-angle annular dark field-scanning transmission electron microscopy, X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, and 57Fe Mossbauer spectroscopy. The catalysts exhibit enhanced activity and stability in degrading various organic samples in advanced oxidation processes. The drastically increased metal site density and stability provide useful insights into the design and synthesis of cluster catalysts for practical application in catalytic oxidation reactions.

Titanium based MOF materials NH2-MIL-125 was synthesized through solvothermal method. By increasing the concentration of the reactants, the morphology of NH2-MIL-125 can be controlled from circular plate to special polyhedron. Meanwhile, the polyhedron can be modulated from octahedron to rhombic dodecahedron through changing the titanium ester of the reactants from tetraethyl titanate to tetrabutyl titanate. This is the first time to obtain NH2-MIL-125 with rhombic dodecahedron morphology. The test of acetic acid as additive on morphology changes shows that the adsorption of additives on special facets shows a more significant impact on the morphology formation. The morphology control of NH2-MIL-125 based on the modulation of the type of titanium ester, reactants concentration, and the added acetic acid concentration were detailed exhibited and explained.

In this work, a facile polyvinylpyrrolidone (PVP) assisted solvothermal route using mixed solvents was reported to synthesize uniform quaternary chalcogenide Cu2FeSnS4 (CFTS) particles. PVP played a crucial role in tuning the shape and size of the resulted CFTS particles. Without PVP irregular shaped CFTS particles were obtained, however, quasi-spherical CFTS particles were produced by addition of PVP. The average particle sizes of particles were in the range of ~ 360 to ~ 230 nm. Moreover, the photodegradation of Rhodamine-B (RhB) with CFTS particles under visible light was investigated and optimized in terms of PVP concentration, catalyst dosage, dye concentration and pH of the solution. The quenching experiments for reactive species indicates that both hydroxyl and superoxide radicals play roles in the photodegradation. The stability of the as-prepared CFTS particles was demonstrated by reusing it in five consecutive degradation cycles.

Surface engineering is an efficient way to enhance photoabsorption, promote charge separation and boost photocatalysis. Herein, sulfur-doped holey g-C3N4 nanosheets have been prepared through a universal self-templating approach with thiocyanuric acid as the single-precursor. By subtly controlling the feeding amount of precursor, the synthesized sulfur-doped holey g-C3N4 nanosheets exhibit excellent visible-light driven photocatalytic hydrogen production activity. The optimized catalyst presents a hydrogen evolution rate of 6225.4 μmol g−1h−1, with an apparent quantum yield of 10 % at 420 nm. Comprehensive characterizations and theoretical calculations suggest that the enhanced photocatalysis is attributed to the synergy of the enlarged surface area, the negatively-shifted conduction band, and the narrowed bandgap due to sulfur-doping and ultra-thin two-dimensional topology. This work highlights the importance of controlling the precursor dosage and inducing sulfur doping into the polymer, providing a promising and reliable strategy to simultaneously regulate the nanostructural and electronic structure of g-C3N4 for highly efficient photocatalysis.

Ordered mesoporous graphitic carbon nitrides were prepared by directly condensing the uniform mixtures of melamine and KIT-6. After removal of the KIT-6 sacrificial template, the carbon nitrides were characterized with TEM, N2 physical adsorption, XRD, FT-IR, XPS, UV–vis and PL spectrometries, and tested for their RhB photocatalytic degradation activity. Together, these characterizations confirmed the as-prepared tunable mesoporous materials with enhanced charge separation efficiency and superior photocatalytic performance. Compared with a conventional bulk g-C3N4, ordered mesoporous g-C3N4 exhibits a larger specific surface area of 279.3 m2/g and a pore size distribution about 4.0 nm and 13.0 nm. Meanwhile, the reduced bandgap energy of 2.77 eV and lower photogenerated electron-hole pair recombination frequency were evidenced by UV–Vis and PL spectra. The RhB photocatalytic degradation activity maximizes with a mass ratio of KIT-6/melamine of 80% (KCN80), and the kinetic constant reaches 0.0760 min−1 which is 16 times higher than that of the bulk sample. Reusability of KCN80 was demonstrated by a lack of evident deactivation after three consecutive reaction periods. The direct condensation of the KIT-6 and melamine mixture does not require pre-casting of the precursor into the pore system of the templates. Owing to its high product yield, improved SBET, reduced bandgap energy and limited charge recombination, the facile-prepared ordered mesoporous g-C3N4 is a practical candidate for further modification.

With the assistance of inorganic salt, graphitic carbon nitride nanosheets were prepared with increased mesoporous surface area for promoting the photocatalytic performance compared with the one without. Series of photocatalysts with different mass ratio of NH4NO3/melamine were prepared and characterized by XRD, FT-IR, XPS, TEM, SEM, N2 physical adsorption, UV–vis and PL spectrometries. Photocatalytic degradation of RhB under visible light irradiation (λ>420 nm) was applied to evaluate catalytic properties. The catalytic activity maximizes at an intermediate NH4NO3/melamine ratio at 0.15, giving a maximum performance, RhB totally being degraded within 30 min and kinetic constant reaching 0.167 min−1 that is 4.5 times as high as that on BCN. The NH4NO3 assisted procedure is a facile, repeatable, environmental friendly, and efficient method for preparing g-C3N4 nanosheets with high photocatalytic performance.

NH2-MIL-125(Ti) is a promising microporous MOF material which has potential applications in photocatalytic and catalytic oxidation reactions. In this work, a facile surfactant assistant synthetic method was employed to obtain hierarchical NH2-MIL-125 with the mesoporosity for photocatalytic degradation of organic dyes. The as-prepared NH2-MIL-125 showed excellent dye removal efficiency due to the combination of improved adsorption and photodegradation. Compared with the microporous NH2-MIL-125, the adsorption capacity of organic dyes increased 28% on hierarchical NH2-MIL-125 and the photodegradation rate approximately increased 2.4 times according to the structure with abundant mesopores and macropores. The morphology of hierarchical NH2-MIL-125 can also be modulated from tetragonal plates to truncated bipyramids and octahedrons, and the obtained catalyst shows similar enhanced photodegradation performance.

Magnetic porous Fe3O4/C/Cu2O composites were prepared by a simple two-step process. Porous Fe3O4/C was synthesized via calcining iron tartrate precursor and then Cu2O was composited with Fe3O4/C by a precipitation-reduction method. The as-prepared samples were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS) elemental mapping. Results show that Fe3O4/C has porous nanorod structure, which is composed of numerous small nanoparticles of about 50nm. Fe3O4 and carbon are uniformly distributed in the Fe3O4/C/Cu2O composite and Cu2O is dispersed on the surface of Fe3O4/C. Fe3O4/C/Cu2O composite exhibits excellent photo-Fenton catalytic performance for the degradation of methylene blue (MB) under visible light irradiation and neutral pH conditions, and MB (100mg/L) could be almost completely removed within 60min. The composite shows good recyclability and could be conveniently separated by an applied magnetic field. These results demonstrate that the Fe3O4/C/Cu2O composite is a powerful Fenton-like catalyst for degradation of organic pollutants from wastewater.

MnC2O4 precursor was prepared by a precipitation method, and then porous MnO@C composites were obtained by mixing MnC2O4 precursor with different amounts of glucose and sintering at different temperatures. The influences of carbon content and crystallinity on the electrochemical performance of MnO@C were investigated. Galvanostatic charge–discharge test results showed that the MnO@C sample “1.2,700” has the largest specific capacity among all samples, which can reach high specific discharge capacity of 1691 mAh g−1 at the current density of 100 mA g−1 after 200 cycles. Even at the high current density of 1600 mA g−1, a remarkable discharge capacity of ∼630 mAh g−1 can still be delivered, demonstrating a good rate capability. The excellent electrochemical performance can be ascribed to porous structure, good crystallinity and proper amount of carbon coating. This facile method can be applied to the large-scale synthesis of high performance transition metal oxide@carbon composite electrode materials.

The spherical shape, uniform size and small degree of agglomeration of the particles play crucial roles in promoting the practical applications of the phosphor powders. In this paper, the novel Eu3+ -doped cerium lutetium Ce2LuO5.5 composite nanopowders with a cubic fluorite structure were prepared via a typical solution combustion route, and their internal structure, surface morphology as well as luminescence properties were investigated. The Eu3+ could substitute in either Lu3+ or Ce4+ sites and the existence of oxygen vacancy was confirmed in the composite by X-ray diffraction and Raman spectra techniques. Without the addition of surfactant, most of the as-prepared particles were bound together, and the luminescence was very weak even after a sintering process. Assisted with appropriate polyvinyl alcohol (PVA) surfactant in the combustion reaction and a subsequent heat-treatment process, the bound-particles were evidently separated and seemed to be nearly spherical shape. The particle size could be controlled to 30–120 nm and the luminescence was enhanced by adjusting the subsequent sintering temperature. Excited with 466 nm blue light, the nanopowders exhibited characteristic 5D0 → 7FJ (J = 0–4) emission transition of Eu3+ and showed enhanced red luminescence as Eu3+ occupied Ce4+ site rather than Lu3+ site. The maximum emission was obtained as 40 mol% Eu substitutes Ce in the composite. Due to the coincidence of 466 nm excitation light with the emission of InGaN chips in white light-emitting diodes, the surface-morphology improved Eu-doped Ce2LuO5.5 phosphor nanopowders have a potential application in solid state lighting fields.

MnCO3 precursors with different morphologies were crystallized using three kinds of surfactants as soft templates, i.e., cation surfactant cetyl trimethyl ammonium bromide (CTAB), anion surfactant sodium dodecyl sulfate (SDS) and neutral poly(vinyl pyrrolidone) (PVP). When PVP was used, the reaction manner was changed from only stirring at room temperature to a hydrothermal route. Under hydrothermal conditions, different ethanol/water ratios and sources of CO32− (NaHCO3 and urea) were used. Porous cubic, regular spherical and nut-like spherical Mn2O3 samples can be obtained by a simple post-annealing process. The correlation between the morphology of Mn2O3 and its performance as an anode material for Li-ion batteries was evaluated. The nut-like spherical Mn2O3 sample has the best cycling performance, with a specific discharge capacity of 925 mA h g−1 at a current density of 100 mA g−1 after 180 cycles. The sample composed of cubes and spheres has superior rate performance. The specific discharge capacity decreases with increasing current density from ~872 mA h g−1 at 100 mA g−1 to ~361 mA h g−1 at 2000 mA g−1.

Homogeneous flower-like OMS-2 particles were successfully prepared in a short time of merely 4 h using a hydrothermal method under a MnSO4–K2S2O8–K2SO4–H2SO4 system. The flower-like OMS-2 particles with a diameter of around 2 μm were composed of uniform slender cryptomelane rods several hundred nanometers in length when the pH of the precursor solution was 0.18 and the solution was treated at 443 K. XRD and SEM characterization techniques demonstrated that formation of flower-like OMS-2 involved three stages including formation of fiber-like OMS-2, flower-like pyrolusite-type MnO2 and flower-like OMS-2 with decreasing pH value from 4.08 to 0.18. In the case of reaction time, the redox reaction between Mn2+ and S2O82− was accomplished within the initial 1 h, and the highly crystallized uniform flower-like particles were obtained at 4 h.

Nanocrystalline spinel LiMn2O4 and layered LiCo1−xMnxO2 (x = 0–0.15) cathode materials were synthesized by a rapid combustion route in combination with an annealing treatment using common filter paper as the template and ethanol as the fuel. The structure, morphology and electrochemical properties of the materials were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), galvanostatic charge–discharge test, cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The spinel LiMn2O4 annealed at 750 °C shows excellent cycling stability (capacity retention is 92% after 200 cycles), high coulombic efficiency (>99%) and good rate capability. The layered LiCoO2 shows high initial capacity (168.9 mAh g−1) and good rate capability, but its capacity retention is only 74% after 80 cycles owing to the nanosize effect. After doping a small quantity of Mn (x = 0.05), the cycling performance of the Mn-doped sample was significantly improved compared with that of the pristine LiCoO2 (capacity retention is 87% after 80 cycles).

Crystalline Co3O4 and Co(OH)(2) were synthesized using Co(NO3)(2) as a precursor by conventional-hydrothermal and microwave-hydrothermal routes, respectively. The Co3O4 phase showed cubic morphologies while the beta-Co(OH)(2) phase exhibited plate-like shapes. The electrochemical performances of Co3O4 and Co(OH)(2) phases were evaluated as electrode materials for lithium-ion battery anodes, cathodes and supercapacitors. Both Co3O4 and Co(OH)(2) phases showed pseudocapacitive performances in Li2SO4 and KOH electrolytes. The Co3O4 and Co(OH)(2) phases were found to be more promising as anodes than as cathodes in lithium-ion batteries. The Co(OH)(2) electrodes showed higher specific capacitances than those of Co3O4 materials. (C) 2014 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

The aqueous lithium-ion batteries using LiMn2O4 as cathode materials are considered to be one of the most promising stationary power sources for large-scale energy storage devices. In the present work, LiMn2O4 rods were successfully synthesized by using hydrothermal reaction to produce beta-MnO2 rods as precursor followed by its solid-state lithiation. The influences of the solid-state reaction conditions on the final products were investigated and the electrochemical performances were tested in Li2SO4 aqueous electrolyte. The results show that LiMn2O4 rods can be obtained at 700 degrees C for 8 h (Sample A) and at 900 degrees C for 3 h (Sample B), respectively. Sample A exhibits superior electrochemical performances. The discharge capacities are 92.5, 92.9, 93.5 and 96.8 mAh g(-1) at 1000, 500, 200 and 100 mA g(-1), respectively. They are nearly constant between the high current density of 1000 and 200 mA g(-1), demonstrating its high rate capability. In addition, sample A exhibits good cycling performance with only a total capacity loss of 5.4% after 200 cycles. (c) 2013 Elsevier B.V. All rights reserved.

Thermal decomposition of stearic acid gel was employed to study the phase evolution of BaTiO3 nanoparticles by thermal gravimetric analysis, X-ray diffraction, Fourier transform infrared, and UV−vis diffuse reflectance spectra. The calcined process of stearic acid gel consisted of a series of oxidation and combustion reactions in air, accompanied by strong exothermal effects. When the stearic acid gel was calcined in air, some organic-Ba was easily transformed into BaCO3 crystallites even at low calcined temperatures, while the organic-Ti, combining with the rest of the organic-Ba could only form the intermediate phase BaTi2O5 instead of TiO2 crystallites, which reacted with BaCO3 to form BaTiO3 nanoparticles. The intermediate phase BaTi2O5 existed very shortly in the calcined process and was successfully identified in the current work.

Lithium niobate (LiNbO3, LN) crystallites were successfully synthesized by soft-chemistry synthesis methods of sol–gel and hydrothermal process, respectively. It has been found that pure LiNbO3 powders could be prepared at about 600 and 240 °C by sol–gel and hydrothermal routes, respectively. X-ray diffraction (XRD), infrared spectra (IR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to further investigate the quality of the obtained LiNbO3 powders by both synthesis routes. The present work shows that the hydrothermal method is superior to the sol–gel method since it may facilely obtain high purity, better crystallinity and uniform morphology lithium niobate powders.

LiMn2O4 rods are prepared by hydrothermal preparation of β-MnO2 precursor rods from MnSO4 and NaClO3 (autoclave, 150 °C, 10 h) followed by lithiation in ethanolic LiOH solution and calcination in air (700 °C, 8 h for sample A, or 900 °C, 3 h, sample B).

Lithium niobate (LiNbO3, LN) crystallites were successfully synthesized by soft-chemistry synthesis methods of sol–gel and hydrothermal process, respectively. It has been found that pure LiNbO3 powders could be prepared at about 600 and 240 °C by sol–gel and hydrothermal routes, respectively. X-ray diffraction (XRD), infrared spectra (IR), scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were used to further investigate the quality of the obtained LiNbO3 powders by both synthesis routes. The present work shows that the hydrothermal method is superior to the sol–gel method since it may facilely obtain high purity, better crystallinity and uniform morphology lithium niobate powders.

Iron oxide@C composites and lithium ferrites were synthesized by a cotton-template method as anode materials for Li-ion batteries. α-Fe2O3@C composites with 3-D porous hollow secondary structures were prepared by directly burning the cotton containing the iron salt (FeCl3 or Fe(NO3)3) in air, and the Fe3O4@C composites with similar structures were obtained by annealing α-Fe2O3@C under a N2 atmosphere. α-LiFeO2 and α-LiFe5O8 particles with sizes of 100–500 nm were also prepared using a similar method. Electrochemical measurements showed that all these samples demonstrated good electrochemical performances as Li-ion battery anodes, especially α-Fe2O3@C derived from Fe(NO3)3, which delivers a high reversible capacity of 990 mA h g−1 at 100 mA g−1 after 50 cycles. Both the porous hollow secondary structure and the suitable amount of amorphous carbon are significant for the electrochemical performances of the iron oxide@C composites. Such a method is simple, rapid and inexpensive and may facilitate the preparation of other high performance electrode materials with porous hollow structures.