Synthesis and interlayer modification of RbLaTa2O7

A layered semiconductor, lanthanum tantalum oxide was prepared by solid reaction at high temperature, and the processes for the modification of the interlayers by protonation, intercalation and pillaring were investigated. n-Butylamine could easily be intercalated into the interlayers of HLaTa₂O₇ to significantly enhance the interlayer distance, which facilitated the exchange of cation with n-butylamine. Finally, CdO pillars in the interlayer of lanthanum tantalum oxide were formed via calcinating at 500°C in air.     

ZnCr LDH nanosheets modified graphitic carbon nitride for enhanced photocatalytic hydrogen production

ZnCr layered double hydroxides (ZnCr LDH) nanosheets modified graphitic carbon nitride (g-C₃N₄) nanohybrids were fabricated via a self-assembly procedure through electrostatic interaction between these two components. Such 2D-2D inorganic-organic hybrid material was employed for photocatalytic hydrogen production under visible light for the first time. The physical and photophysical properties of the hybrid nanocomposites were investigated to reveal the effect of ZnCr LDH nanosheets on the photocatalytic activities of g-C₃N₄. It was found that 1 wt% ZnCr LDH nanosheets modified g-C₃N₄ was optimal for the formation of intimate interfacial contact. The visible light photocatalytic H₂ production activity over g-C₃N₄ was enhanced about 2.8 times after ZnCr LDH nanosheets modification. The significant enhancement in photocatalytic performance for ZnCr LDH/g-C₃N₄ heterojunction should be attributed to the promoted charge transfer and separation efficiency, resulting from the intimate interfacial contact and Type II band alignment between ZnCr LDH and g-C₃N₄.     

A review of intercalation composite phase change material: Preparation, structure and properties

This paper reviews preparation, structure and properties of the intercalation composite phase change material (PCM). The layered structure of clay and graphite is utilized to prepare the intercalation composite PCM. It is concluded that the preparation methods include liquid phase intercalation and melting intercalation. The thermal conductivity and flame retardancy of organic PCM are improved by intercalating organic PCM into montmorillonite (MMT) or graphite. The phase change properties of the intercalation composite PCM can be measured by differential scanning calorimetry (DSC) and T-history method.     

Vanadium-substituted porous manganese oxides with Li-ion intercalation properties

In this study, vanadium ions were substituted for manganese in the crystal lattice of synthetic cryptomelane, also denoted as OMS-2, via microwave field-assisted syntheses. Doping vanadium into the framework of mixed valence manganese oxide resulted in OMS-2 materials with modified composition, morphology, and electrical properties. Structural properties and morphology of synthesized materials were characterized by XRD and FESEM, respectively. Average oxidation state and resistivity measurements were also taken. The effect of framework doping of vanadium ions on lithium-ion intercalation properties of manganese oxides was investigated in Li-ion cathode half-cells.     

A review on bismuth-based composite oxides for photocatalytic hydrogen generation

Bismuth-based composite oxides are always considered the best visible-light photocatalysts for oxygen production. However, they are failed to photocatalytic reduce the hydrogen from water, due to their lower conduction band made up by Bi 6p and O 2p. Thus, it is significant to modulate their levels of the conduction and valence bands satisfying the redox potential for both H⁺/H₂ and O₂/H₂O, which will directly lead to discovering new visible-light materials for photocatalytic hydrogen generation. Recent years, some modified bismuth-based composite oxides have been reported to achieve photocatalytic hydrogen production. In this paper, a review of photocatalytic hydrogen generation by bismuth-based composite oxides is presented, mainly including energy band engineering, Z-scheme overall water splitting, and strategies for photocatalytic activity improvement.     

Physicochemical properties of pine-derived bio-chars modified by metal oxides and their performance in the removal of NO

Pine-derived bio-chars have been prepared at different temperatures with and without KOH chemical activation. Three metal oxides (V₂O₅, MnO and CuO) were loaded on this chars by incipient-wetness impregnation method respectively. Pine wood pellets were characterized by thermogravimetric, and pine-chars samples were characterized by SEM-EDS, XRD, N₂ physisorption and FTIR. Activity test for the selective catalytic reduction of NO with NH₃ was also carried out in dry simulated flue gas at fixed temperature 160 °C. The results show that pretreatment with KOH and carbonization at 600 °C seems to be the best method for pine-chars preparation. Active metal oxides are well distributed on the surface of carbon support and are partly reduced by carbon during preparation. The mesopores disappear in V- and Mn-containing samples, and V-addition could decrease the amount of micropores as well. At the fixed temperature 160 °C, the active metal oxides have an order of CuO > V₂O₅ >> MnO_x >> Non-modified sample on the NO reduction activity. Pine-chars modified by CuO seems to be the best option in this research.     

Facile layer-by-layer self-assembly of 2D perovskite niobate and layered double hydroxide nanosheets for enhanced photocatalytic oxygen generation

Photocatalytic O₂-generation reaction is recognized as a crucial step in water splitting and has drawn great attention of researchers. In this work, a hetero-layered composite photocatalyst was successfully prepared by a facile self-assembly method based on electrostatic interaction between oppositely charged Zn/Cr-layered double hydroxide (Zn/Cr-LDH) and lead niobate nanosheets. The layer-by-layer stacking of Zn/Cr-LDH and HPb₂Nb₃O₁₀ nanosheets was beneficial for rapid migration of photo-induced charge carriers inside the photocatalyst because of large contact area. In the meantime, Zn/Cr-LDH and HPb₂Nb₃O₁₀ components exhibited suitable energy-band alignment, which led to efficient separation of photo-induced charge carriers. The composite photocatalyst showed enhanced photocatalytic O₂-generation activity under visible-light irradiation without loading cocatalyst. Briefly, this work expanded the applications of AB₂Nb₃O₁₀-based materials in photocatalytic energy conversion and proved that constructing composites based on electrostatic self-assembly of complementary 2D materials is a promising strategy for development of more efficient photocatalysts.     

Recent progress and challenges in photocatalytic water splitting using layered double hydroxides (LDH) based nanocomposites

The worldwide energy demand is steadily increasing and estimated to be doubled by the year 2050 due to a continuous hike in economies and population. A large part of the global energy requirement procures using traditional energy sources such as fossil fuels, which are non-renewable. Also, their excessive consumption imparts negative impacts on the environment by CO₂, and CO emissions, which constantly increase the average global temperature. Therefore, the need for a more reliable, sustainable, inexpensive, renewable and environmentally-friendly form of energy is imperative. From these perspectives, hydrogen energy is emerging as one of the most promising alternatives to overcome rising energy demand with a zero-carbon footprint.Herein, various layered double hydroxides (LDH) nanocomposite owing to their attractive physicochemical properties and synergistic effect with other materials in the field of hydrogen production are reviewed. Why the class of LDHs materials is critical and their ideographic properties which make them promising materials in the field of water splitting via photocatalysis and electrocatalysis are also discussed. The synthetic methods of LDHs based nanocomposites fabrication are summarized. Various challenges and strategies from the viewpoint of a different method of hydrogen production through LDHs are reported. Additionally, multiple techniques like surface plasmon resonance (SPR), heterojunction formation, and doping with co-catalyst to increase the efficiency for photocatalytic hydrogen production are also presented. Hopefully, this review will help the readers explore highly efficient, inexpensive and stable LDH catalysts toward photocatalytic water splitting.     

Recent advancements of layered double hydroxide heterojunction composites with engineering approach towards photocatalytic hydrogen production: A review

Photocatalytic hydrogen production has been considered as one of the most promising alternatives for providing clean, sustainable, and renewable energy sources. Tremendous investigation and efforts have been devoted to increase the efficiency of the solar to energy conversion of a photocatalyst. Layered double hydroxide (LDH) received scientific attention for its excellent compositional flexibility and controllable morphology, leading to the facile incorporation of the metal species into their layered structure. The unique multi-structure and the tunability of its band gap make LDH more prominent in the field of photocatalysis. This article highlights the recent developments in the fabrication of LDH-based photocatalyst nanocomposites and the engineering approaches for augmenting their photocatalytic hydrogen production efficiency. The thermodynamics and challenges in photocatalytic water splitting are deliberated to understand the pathways to construct efficient semiconductor photocatalysis system. The efficiency enhancement of LDH-based photocatalysts are comprehensively discussed by giving special attention to the heterojunction engineering of type I, type II, p-n junction, Z-scheme, S-scheme, and R-scheme. Fabrication of the hybrid LDH nanocomposites through band gap engineering and metal loading are summarised. The architectural and morphological tuning of LDH-based composite through the construction of the novel core-shell structure and layer-by-layer nanosheets are also demonstrated. Finally, the future recommendations are outlined to provide insights for their development in the photocatalysis field.     

Optical properties of metal oxides based nanofluids

The purpose of this research is to experimentally investigate optical behavior of alumina and titania nanofluids. In this study, classical theories such as, Rayleigh, Maxwell–Garnett and Lambert–Beer's approaches are used for analytical analysis. The effect of surfactant on stability of nanofluids has been examined. Experiment is conducted for two volume concentrations of 0.1% to 0.3% v/v for the optical properties. Both experimental and analytical analyses were used to obtain these properties of nanofluids. Extinction coefficient and refractive index of TiO₂ nanofluids are found higher than Al₂O₃ nanofluids in visible region of light for all concentrations. Results of this work will be very helpful in analyzing direct absorption solar collectors using alumina and titania nanofluids.     

Crystalline-to-amorphous transformation of tantalum-containing oxides for a superior performance in unassisted photocatalytic water splitting

Crystalline tantalum-containing oxides are usually taken as the advanced photocatalysts for water splitting. How about the amorphous counterparts? In this work, a transformation of crystalline Na₂Ta₂O₆ (CNa₂Ta₂O₆) to amorphous TaO_x (Am-TaO_x) was achieved by a facial hydrothermal method. We proposed a transformation mechanism based on nucleation-dissolution -recrystallization and further intensified the influence of base concentration on the composition, crystallinity, and morphology (CCM) as confirmed by XRD, TEM, EDS. N₂-physisorption, Raman, IR, and XPS analysis. It is found that when comparing to the crystalline counterparts, amorphous samples possessed higher surface area, abundant surface hydration layers and H⁺ adsorption, showing an unassisted photocatalytic water splitting with a rate of 70 ± 7 μmol g^?1 h^?1, much larger than that of 15 ± 1 μmol g^?1h^?1 of CNa₂Ta₂O₆, 11 ± 1 μmol g^?1h^?1 of crystalline Ta₂O₅ (CTa₂O₅), 30±2 μmol g^?1h^?1 of mixture with crystalline Ta₂O₅ and amorphous Na_xTa_yO_z (CTa₂O₅/Am-Na_xTa_yO_z), and even 4.6 × 10^?4 μmol g^?1h^?1 for commercial TiO₂. This observation is beneficial from the short diffusion paths of amorphous state for charge carriers, amount of catalytic sites, and stronger reducing ability. These findings develop a novel and efficient pathway towards synthesizing the different CCM of tantalum-containing compounds under hydrothermal conditions and could open opportunities for further investigating the photocatalytic property of tantalum-containing materials.     

Research progress of metal oxides as anode materials for lithium ion capacitors

锂离子电容器是一种介于超级电容器和锂离子电池之间的新型储能器件,具有高能量密度、高功率密度以及长循环寿命等优点,在电动汽车、轨道交通、智能电网、可移动电子设备等领域具有非常广泛的应用前景。金属氧化物具有脱/嵌锂能力优异,理论比容量普遍较高,而且自然资源丰富、环境友好的优点,是一类理想的锂离子电容器负极材料,但电子导电率不高,脱/嵌锂过程中不可逆体积畸变较大,影响了其商业化的应用。本文综述了金属氧化物负极材料的制备方法,并分析了其作为锂离子电容器负极材料的电化学性能与优缺点,最后展望了金属氧化物负极材料未来的发展方向。     

Photodeposition of AuNPs on metal oxides: Study of SPR effect and photocatalytic activity

Effect of photodeposition of AuNPs (gold nanoparticles) on TiO₂, CeO₂, Cu₂O and Fe₃O₄ supports has been illustrated on sacrificial donor based hydrogen evolution. The synthesized samples were characterized by diffuse reflectance spectroscopy (DRS), and transmission electron microscopy (TEM). Highest photocatalytic activity was exhibited by Au/TiO₂ followed by Au/Fe₃O₄, Au/CeO₂ and Au/Cu₂O. Au/TiO₂ under optimized conditions has shown significantly high photocatalytic activity under both UV–visible and visible radiation. Au/TiO₂ shows hydrogen evolution rate of 920 μmol h⁻¹ and 32.4 μmol h⁻¹ under UV–visible and visible radiation, respectively. Significant enhancement in hydrogen evolution rate under visible light is very encouraging and may be attributed to polydispersed nature of AuNPs wherein larger particles facilitate light absorption and the smaller function as catalytic sites. Further studies are in progress to study the influence of various parameters on photocatalytic activity of Au/TiO_2.     

Growth and properties of solvothermally derived highly crystalline Cu2ZnSnS4 nanoparticles for photocatalytic and electrocatalytic applications

This work reports the photocatalytic and electrocatalytic applications of solvothermally derived Cu₂ZnSnS₄ (CZTS) nanoparticles. The synthesized material was applied for the photocatalytic degradation of Rhodamine B (RhB), a carcinogenic dye. The nanoparticles degrade 83% of RhB in the presence of visible light (589 nm) illumination. A negligible fall in the degradation percentage after 3 photocatalytic cycles and post catalytic properties demonstrate the excellent photostability of the nanostructure. The electrocatalytic performance of CZTS for hydrogen evolution reaction (HER) through water splitting and charge storage reveals their potential applications for efficient electrochemical energy systems. The nanoparticles show excellent electrocatalytic performance for HER as indicated by the low Tafel slope. The Linear Sweep Voltametry (LSV) plot performed after 1000 cyclic voltammetry (CV) cycles shows negligible loss of current confirming the good stability of the nanostructure. Chronoamperometry (CA) performed at constant potential shows negligible loss of current for 12 h, which confirms that the synthesized CZTS is a potential and durable candidate for electrochemical applications. The material is highly stable in both the processes; electrocatalysis as well as photocatalysis.     

Synthesis,characterization and photocatalytic evaluation of potassium hexatitanate (K2Ti6O13) fibers

Potassium hexatitanate has been barely studied as a photocatalytic material for the hydrogen production from water splitting. The aim is to synthesize and characterize K₂Ti₆O₁₃ fibers in order to evaluate their photocatalytic activity. Materials were characterized by XRD, BET, UV–Vis and SEM. Fibers were produced with sizes varying from 12 to 35 μm in length and 260–530 nm in diameter, as well as with a specific surface area of 4.1 m²/g and 2.3 m²/g for a heat treatment at 900 °C (C21) and 1000 °C (C22), respectively. Band gap energies for these titanates fall within the visible spectrum 3.23 eV (C21) and 3.28 eV (C22), respectively. Maximum hydrogen production was achieved by (C21) with 2387 μmolH₂/gcat, while the lowest production was observed for sample (C22) with 1538 μmolH₂/gcat at 8 h of irradiation. Crystals of K₂Ti₆O₁₃ exhibited high photocatalytic activity and they can be considered as potential photocatalysts for H₂ production.     

Optical and structural properties of the sol-gel-prepared ZnO thin films and their effect on the photocatalytic activity

ZnO thin films were obtained by the sol-gel method, using the dip-coating procedure. Glass slides were used as substrates. The sintering temperature (T_s) was varied in the range of 200-600 °C in intervals of 50 °C, in an open atmosphere. Films with 1 and 5 coatings were prepared for each T_s. An increase of the grain size from 10 to 34 nm as the T_s increased was observed from X-ray diffraction measurements. The thickness of the films prepared starting from five coatings, decreased by 36% when T_s increased, and denser films were obtained. This result was corroborated with the refractive index values, calculated from the UV-Vis transmission spectra. The films were tested as a photocatalyst by the photobleaching of methylene blue in an aqueous solution under UV light exposure during 5 h. The photocatalytic activity (PA) increased with T_s, around 72% for the films with one coating and 66% for those with five coatings. The samples with one coating and a T_s=500 °C showed the best PA. However, the glass substrate had a negative effect on the PA for T_s>500 °C, even when the surface morphology of the samples showed an increase in roughness when T_s increased. The observed negative effect can be due to the presence of an amorphous compound formed by Si, Zn and O at the glass-ZnO interface.     

Synthesis of Al-substituted mesoporous silica coupled with CdS nanoparticles for photocatalytic generation of hydrogen

Aluminum-substituted mesoporous silica (Al-HMS) molecular sieve coupled with CdS nanoparticles (CdS/Al-HMS) were prepared by template assembly, ion-exchange and sulfuration routes. The XRD and TEM results indicated that the assembly of less than 2 wt% CdS nanoparticles in the porous channels of Al-HMS didn't significantly affect the wormhole-like mesoporous framework structure of Al-HMS, whereas the porous channels of Al-HMS were filled up by CdS nanoparticles after loading of 21 wt% CdS. The diffuse reflectance UV–visible spectra exhibited that the absorption edge was gradually blue-shifted with decrease in CdS content due to the quantum confinement effect. The CdS/Al-HMS sample loaded 0.99 wt% Ru showed the highest H₂ evolution at a rate of 13.23 mL h⁻¹ with an apparent quantum yield of 5.92% at 420 nm by photocatalytic degradation of formic acid under visible light irradiation.     

Noble metal free efficient photocatalytic hydrogen generation by TaON/CdS semiconductor nanocomposites under natural sunlight

Tantalum oxynitride have narrow band gap and its band potentials are suitable for visible light induced hydrogen generation. However, due to fast electron-hole recombination, the efficiency of photocatalytic hydrogen evolution reaction is very low. Herein, we have synthesized semiconductor heterojunction photocatalyst, i.e., TaON/CdS with suitable band positions by a simple precipitation method. Ratio between two semiconductors is optimized to obtain maximum hydrogen evolution. XRD, XPS and TEM analysis demonstrate the formation of heterojunction between these semiconductors. Among the synthesized catalysts, 3% TaON/CdS heterostructure exhibits the highest hydrogen evolution activity with H₂ production rate of 7.5 mmol h⁻¹ under natural solar light, whereas the rate is 11 mmol h⁻¹ under the visible light generated by xenon (Xe) lamp without the addition of any noble metal as the co-catalyst. The CdS and 3% TaON/CdS nanomaterials show an AQE of 5.1% and 12.2%, respectively. Combination of Mott-Schottky, UPS and DR UV–visible spectroscopy studies revealed the formation of S scheme semiconductor heterojunction between these nanomaterials with valence, conduction band positions, i.e., 1.46, −0.78 eV for CdS and 2.19, −0.66 eV for TaON, respectively. These band positions help in efficient e-h pair separation to produce hydrogen from water.     

Photoactive semiconducting metal oxides: Hydrogen gas sensing mechanisms

The use of photactive nano materials in gas sensors is a promising and novel strategy to enhance key sensing properities including sensitivity, selectivity, durability and improved manufacture costs and power consumption. Photoactive gas sensors can also be used as an alternative to thermal heating gas sensing processes. This review article provides an overview of hydrogen gas sensing mechanisms exhibited by different semiconducting metal oxides (SMOx) and their derivatives under Ultra-Violet (UV) and visible light conditions while examining tunable gas sensing properties and unique morphological properties. Most of the materials discussed have been newly developed and show promise for hydrogen gas sensing under photoactive conditions at room temperature. In addition, we explore the dependence of the sensing properties on the width of electron depletion layer, the effect of heterojunction as well as the effect of modifications of the sensing material/s (including varying the photoactive SMOx materials, SMOx functionalized with noble metals (as dopants), graphene-based materials and natural derivatives). Finally, advantages and limitations of the sensing properties are summarized to enhance further development of SMOx materials and their derivatives towards hydrogen gas sensing.