Novel synthesis of high-surface-area ordered mesoporous TiO2 with anatase framework for photocatalytic applications

Ordered mesoporous TiO₂ materials with an anatase frameworks have been synthesized by using a cationic surfactant cetyltrimethylammonium bromide (C₁₆TMABr) as a structure-directing agent and soluble peroxytitanates as Ti precursor through a self-assembly between the positive charged surfactant S⁺ and the negatively charged inorganic framework I^? (S⁺I^? type). The low-angle X-ray diffraction (XRD) pattern of the as-prepared mesoporous TiO₂ materials indicates a hexagonal mesostructure. XRD and transmission electron microscopy results and nitrogen adsorption–desorption isotherms measurements indicate that the calcined mesoporous TiO₂ possesses an anatase crystalline framework having a maximum pore size of 6.9 nm and a maximum Brunauer–Emmett–Teller specific surface area of 284 m² g^?1. This ordered mesoporous anatase TiO₂ also demonstrates a high photocatalytic activity for degradation of methylene blue under ultraviolet irradiation.     

Mesoporous TiO2 nano networks: Anode for high power lithium battery applications

Anatase phase mesoporous TiO₂ with I41/amd space group was synthesized via the urea assisted hydrothermal method. The existence of mono phasic TiO₂ sub-microspheres of uniform particle size (ca. 400 nm) encompassing an average crystallite size of 14 nm was demonstrated using the XRD, FE-SEM and TEM analysis. Surface area of ca. 116.49 m²/g along with a pore size of 7 nm was calculated using the BET and adsorption isotherm measurements which authenticated the mesoporous nature of the synthesized material. Suitable calcination temperature for the better electrochemical property was established via the optimization process. Accordingly, the mesoporous TiO₂ calcined at 400 °C displayed improved cycleability with excellent rate capability ever reported, even at 20 C-rate of discharge. The reason for the superior rate capability is corroborated to the highly mesoporous nature of the TiO₂ sub-microspheres that has imparted desirable surface area apposite for enhanced ionic and electronic diffusion.     

Superabsorbent polymer binder for achieving MnO2 supercapacitors of greatly enhanced capacitance density

One common dilemma encountered in designing a supercapacitor electrode is that the specific capacitance (C_s) of the active material decreases significantly as the active-material loading (mass area^? 1) increases. As a result, the geometric capacitance density (GCD; Farad area^? 1) of the electrode does not scale up linearly but gradually levels off with increasing loading. For MnO₂ supercapacitors, this problem has been solved to a great extent by introducing a superabsorbent polymer (SAP) binder, namely polyacrylic acid (PAA), to form composite particles with MnO₂. Other than acting as a binder to bound together MnO₂ particles, the SAP is believed to facilitate distribution of electrolyte throughout the active layer owing to its electrolyte-absorbing and swelling behaviors. The C_s of MnO₂ remains almost unchanged as the oxide loading varies over a wide range (1.5–6.5 mg cm^? 2) of heavy active-material loading. In addition, putting PAA throughout the entire active layer helps to magnify the specific interaction between PAA and MnO₂ that is known to enhance the capacitance of individual MnO₂ particles. The success in combining both high C_s and high active-material loading results in GCD of ca. 1.8–1.4 F cm^? 2 even under very high current densities (ca. 35–260 mA cm^? 2 or 5–40 A g^? 1-MnO₂).     

Mesoporous germanium as anode material of high capacity and good cycling prepared by a mechanochemical reaction

Mesoporous Ge was prepared by mechanochemical reaction of GeO₂ and Mg powders followed by an etching process with HCl solution. It was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and charge–discharge measurement. With a pore-distribution concentrated around 10 nm, the product presents a BET surface area of 49.98 m²/g. When using as an anode material for lithium ion battery, the mesoporous Ge exhibits a reversible capacity of 950 mA h/g and retains a capacity of 789 mA h/g after 20 cycles at a current density of 150 mA/g. The cycleability is significantly improved compared with non-porous Ge.     

Solar active nano-TiO2 for mineralization of Reactive Red 120 and Trypan Blue: 1st Nano Update

Nano-TiO₂ was synthesized by sol–gel method. The catalyst was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) images, transmission electron microscope (TEM), BET surface area measurement and DRS analysis. The formation of anatase phase nano-TiO₂ was confirmed by XRD measurements and its crystalline size is found to be 15.2 nm. SEM images depict the crystalline nature of prepared TiO₂. The BET surface area of prepared TiO₂ is found to be 86.5 m² g^?1 which is higher than that of commercially available TiO₂–P25. The photocatalytic activity of prepared anatase phase TiO₂ has been tested for the degradation of two azo dyes: Reactive Red 120 (RR 120) and Trypan Blue (TB) using solar light. The photocatalytic activity of nano-TiO₂ is higher than TiO₂–P25 under solar light. The mineralization of dyes has been confirmed by chemical oxygen demand (COD) measurements.     

A facile synthetic strategy for mesoporous crystalline copper–polyaniline composite

A facile and novel strategy for preparing mesoporous crystalline copper–polyaniline composite is reported wherein the reaction is carried out at room temperature using copper nitrate as the oxidizing agent and methanol as the solvent. The composite obtained as a precipitate has been characterized using UV–visible absorption spectroscopy (UV–vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption–desorption method, Barrett–Joyner–Halenda (BJH) method, Brunauer–Emmett–Teller method (BET) and thermogravimetric analysis (TGA). The XRD studies in conjunction with the BJH method reveals that the composite has crystalline nature with a mesoporous structure and has a diameter of 3.5 nm. The specific surface area of copper–polyaniline composite is estimated to be as high as 63.2 m² g^?1 using the BET surface area plot. The characterization of the filtrate indicates the presence of pernigraniline with a very small weight percent of copper.     

Structural characterization and activation energy of NiTiO3 nanopowders prepared by the co-precipitation and impregnation with calcinations

In this paper, we report on the formation of novel hexagonal NiTiO₃ nanopowders synthesized by the impregnation or co-precipitation methods through the thermal decomposition reaction of the precursors. The decomposition course was followed using differential thermal analysis (DTA) and thermogravimetric analysis (TGA) techniques. The intermediate decomposition products as well as the formed titanate were characterized using X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) spectroscopy. XRD patterns of the precursors calcined at 1000 °C showed the formation of the single ilmenite-type rhombohedral structure only with the impregnated precursor, while with the precipitated NiTiO₃ powders one it indicates the presence of some NiO and TiO₂ impurities. Transmission electron microscopy (TEM) exhibited loosely agglomerated hexagonal particles with uniform morphology having a size around 61 nm. The Brunauer-Emmett-Teller (BET) surface area measurements showed a type III isotherm with calculated surface area of 152 m²/g. The plot of ln σ_ac vs. temperature as a function of frequency indicates a semiconducting behavior with ferroelectric phase transition at 605 K. The calculated activation in the ferroelectric region is 0.93 eV suggests the predominance of hopping conduction mechanism. Kinetic analysis of TG data according to different integral methods showed that in the NiC₂O₄·2H₂O–TiO₂ precursor, the water molecules are coordinately bounded and the presence of TiO₂ reduces the activation energy needed to the oxalate decomposition reaction.     

Assembly of NaTaO3 porous microspheres via imperfect oriented attachment mechanism

Spongy-like NaTaO₃ mesoporous microspheres are assembled from nanoparticles via imperfect oriented attachment. Study shows that the NaTaO₃ spongy microspheres with the diameters of ～1 μm are composed of the fundamental building blocks of ～50 nm NaTaO₃ nanospheres. The high-resolution transmission electron microscopy further reveals that these fundamental building blocks are assembled from primary building blocks of ～10 nm NaTaO₃ nanocrystals. The pore diameters of these spongy microspheres are ca. 30 nm and the Brunauer–Emmett–Teller (BET) surface area is calculated to be 57.8 m² g^?1. This interesting ternary alkali metal composite oxide of NaTaO₃ spongy microspheres with high specific surface area and strong stability will be favorable for their practical application in photocatalysis. This synthesis route may throw light on the fabrication of the binary or ternary porous metal oxides by geometrical stacking of the nanobuilding blocks via imperfect oriented attachment.     

A binder-free thin film anode composed of Co2 +-intercalated buserite grown on carbon cloth for oxygen evolution reaction

We present a binder-free catalytic anode for highly efficient and stable oxygen evolution reaction in alkaline media. The catalyst consists of a thin film of buserite-type layered manganese dioxide (MnO₂) intercalated with Co^2 + ions, resulting from electrodeposition of the layered MnO₂ film with tetrabutylammonium (Bu₄N⁺) ions on a carbon cloth, followed by ion-exchange of the initially incorporated Bu₄N⁺ with Co^2 + in solution. The electrode is capable to produce a current density of 10 mA cm^− 2 at an overpotential (η) of 377 mV with a Tafel slope of 48 mV dec^− 1, much superior to the layered MnO₂ without Co^2 +.     

Facile synthesis and characterization of copper oxalate/cobalt oxalate/manganese oxalate and copper oxide/cobalt manganese oxide/manganese oxide as new nanocomposites for efficient photocatalytic degradation of malachite green dye

Scientists seek to synthesize new catalysts with simple methods to treat water pollution from organic dyes using photocatalytic degradation technology. In this technology, when light falls on the catalyst, the produced hydroxyl free radicals convert the dye into non-toxic gases such as CO₂ and H₂O. So, in this work, copper oxalate/cobalt oxalate/manganese oxalate (Abbreviated as P₁) and copper oxide/cobalt manganese oxide/manganese oxide (Abbreviated as P₂) new nanocomposites were fabricated via precipitation of Cu²⁺/Co²⁺/Mn²⁺ solution using oxalic acid and ignition of precipitate at 550 °C for 4 hrs, respectively. Some tools, involving X-ray diffraction (XRD), UV–vis spectrophotometer, energy dispersive X-ray spectroscopy (EDX), nitrogen gas sorption analyzer, transmission electron microscope (TEM), and field emission scanning electron microscope (FE-SEM), were used for characterizing the fabricated nanocomposites. The EDX spectra confirmed that the P₁ composite consist of C (26.28 %), oxygen (46.66 %), manganese (7.27 %), cobalt (7.59 %), and copper (12.20 %). Also, the P₂ composite consist of oxygen (8.23 %), manganese (31.34 %), cobalt (27.19 %), and copper (33.24 %). A transmission electron microscope shows that the P₁ and P₂ composites consist of polyhedral and spherical shapes with an average diameter of 28.13 and 14.37 nm, respectively. The BET surface area, average pore size, and total pore volume of the P₁ composite are 29.0725 m²/g, 2.0749 nm, and 0.0302 cc/g, respectively. Besides, the BET surface area, average pore size, and total pore volume of the P₂ composite are 58.1088 m²/g, 1.6087 nm, 0.0467 cc/g, respectively. 60 mg of the synthesized nanocomposites completely decompose 60 mL of 15 mg/L of malachite green dye solution within 20 min in the presence of hydrogen peroxide and UV light. The synthesized catalysts outperformed many other catalysts published in previous studies.     

Fabrication and electrochemical performance of nickel ferrite nanoparticles as anode material in lithium ion batteries

Nano-sized nickel ferrite (NiFe₂O₄) was prepared by hydrothermal method at low temperature. The crystalline phase, morphology and specific surface area (BET) of the resultant samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and nitrogen physical adsorption, respectively. The particle sizes of the resulting NiFe₂O₄ samples were in the range of 5–15 nm. The electrochemical performance of NiFe₂O₄ nanoparticles as the anodic material in lithium ion batteries was tested. It was found that the first discharge capacity of the anode made from NiFe₂O₄ nanoparticles could reach a very high value of 1314 mAh g⁻¹, while the discharge capacity decreased to 790.8 mAh g⁻¹ and 709.0 mAh g⁻¹ at a current density of 0.2 mA cm⁻² after 2 and 3 cycles, respectively. The BET surface area is up to 111.4 m² g⁻¹. The reaction mechanism between lithium and nickel ferrite was also discussed based on the results of cycle voltammetry (CV) experiments.     

Synthesis of Co-containing mesoporous carbon foams using a new cobalt-oxo cluster as a precursor

A novel trinuclear cobalt-oxo cluster 2[Co₃O(Ac)₆(H₂O)₃]·H₂O (Co-OXO) has been obtained and characterized by X-ray single-crystal diffraction and elemental analysis. The structure of Co-OXO displays 3D supramolecular networks through hydrogen bonds and generates boron nitride (bnn) topology. Co-OXO was further used as a precursor to synthesize Co-containing mesoporous carbon foams (Co-MCFs), which exhibit highly ordered mesostructure with specific surface area of 614 m² g^?1 and uniform pore size of 2.7 nm. Charge–discharge tests show that the specific discharge capacitance of Co-MCFs is 7% higher than that of the MCFs at the current density of 100 mA g^?1, and 26% higher than that of MCFs at the current density of 3 A g^?1. The electrochemical behaviors of Co-MCFs are obviously improved due to the improved wettability, increased graphitization degree and the pseudo-capacitance through additional faradic reactions arising from cobalt.     

Doping level effect on visible-light irradiation W-doped TiO2–anatase photocatalysts for Congo red photodegradation

A series of W-modified TiO₂ (W–TiO₂) photocatalysts were synthesized by a simple sol–gel method. The new photocatalysts were characterized by X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis-diffuse reflectance spectroscopy (DRS), and Brunauer, Emmett and Teller (BET) surface area analyzer. The photoactivity of the W–TiO₂ photocatalysts was evaluated by the photocatalytic oxidation of Congo red (CR) dye. It was found that the average size of the prepared photocatalysts is 10 nm. Moreover, they have high surface areas (∼ 216 m² g⁻¹) and their light-absorption extends to the visible region compared to pure TiO₂. The effects of W-loading and of the calcination temperature of the prepared photocatalysts on their photocatalytic activity were also studied. The obtained results show that the W_0.5–TiO₂ photocatalyst calcined at 350 °C is much highly photoactive than non-doped or highly doped TiO₂. The enhanced photocatalytic activity of the weakly doped TiO₂ may be attributed to the increase in the charge separation efficiency and the presence of surface acidity on the W_0.5–TiO₂ photocatalyst.     

Structural and magnetic properties of orthorhombic LixMnO2

Rietveld refinement of the crystal and magnetic structures of Li_xMnO₂ (x = 0.98, 1.00, 1.02) are performed using neutron and X-ray measurements. A significant structural disorder due to the presence of manganese ions in lithium positions (Mn_Li) and lithium ions in manganese ones (Li_Mn) is found to be a common feature of Li_0.98MnO₂, Li_1.00MnO₂, and Li_1.02MnO₂.An essential anisotropy of the thermal-expansion coefficients of the lithium manganese oxides is observed in the temperature range of 1.5–300 K. Furthermore, the distortion of the oxygen octahedral environment around the manganese ions decreases when the temperature lowers. This is attributed to the strong exchange interactions between parallel exchange-coupled Mn chains. First-principles calculations of the effective exchange-interaction parameters in Li₁₆Mn₁₆O₃₂ confirm the essential antiferromagnetic interactions between the chains. In addition, a hypothetical (Li₁₅Mn)Mn₁₆O₃₂ structure where a lithium atom located between the Mn double layers is replaced by a manganese atom is considered. The calculations reveal that the presence of such defects results in appearance of a ferromagnetic component that agrees with the magnetic measurements.     

Synthesis and characterization of nanocrystalline tin oxide by sol–gel method

Nanocrystalline SnO₂ particles have been synthesized by a sol–gel method from the very simple starting material granulated tin. The synthesis leads a sol–gel process when citric acid is introduced in the solution obtained by dissolving granulated tin in HNO₃. Citric acid has a great effect on stabilizing the precursor solution, and slows down the hydrolysis and condensation processes. The obtained SnO₂ particles range from 2.8 to 5.1 nm in size and 289–143 m² g⁻¹ in specific surface area when the gel is heat treated at different temperatures. The particles show a lattice expansion with the reduction in particle size. With the absence of citric acid, the precursor hydrolyzes and condenses in an uncontrollable manner and the obtained SnO₂ nanocrystallites are comparatively larger in size and broader in size distribution. The nanocrystallites have been characterized by means of TG-DSC, FT-IR, XRD, BET and TEM.     

Preparation of palladium membranes from the reaction of Pd(C3H3)(C5H5) with H2: wet-impregnated deposition

A new technique to prepare a palladium membrane for high-temperature hydrogen permeation was developed: Pd(C₃H₃)(C₅H₅) an organometallic precursor reacted with hydrogen at room temperature to decompose into Pd crystallites. This reaction together with sintering treatment under hydrogen and nitrogen in sequence resulted in the formation of dense films of pure palladium on the surface of the mesoporous stainless steel (SUS) support. Under H₂ atmosphere the palladium membrane could be sintered at 823 K to form a skin layer inside the support pores. The hydrogen permeance was 5.16×10⁻² cm³ cm⁻² cm Hg⁻¹ s⁻¹ at 723 K. H₂/N₂ selectivity was 1600 at 723 K.     

Nanorods of transition metal oxalates: A versatile route to the oxide nanoparticles

A versatile route has been explored for the synthesis of nanorods of transition metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates using reverse micelles. Transmission electron microscopy shows that the as-prepared nanorods of nickel and copper oxalates have diameter of 250 nm and 130 nm while the length is of the order of 2.5 μm and 480 nm, respectively. The aspect ratio of the nanorods of copper oxalate could be modified by changing the solvent. The average dimensions of manganese, zinc and cobalt oxalate nanorods were 100 μm, 120 μm and 300 nm, respectively, in diameter and 2.5 μm, 600 nm and 6.5 μm, respectively, in length. The aspect ratio of the cobalt oxalate nanorods could be modified by controlling the temperature.The nanorods of metal (Cu, Ni, Mn, Zn, Co and Fe) oxalates were found to be suitable precursors to obtain a variety of transition metal oxide nanoparticles. Our studies show that the grain size of CuO nanoparticles is highly dependent on the nature of non-polar solvent used to initially synthesize the oxalate rods. All the commonly known manganese oxides could be obtained as pure phases from the single manganese oxalate precursor by decomposing in different atmospheres (air, vacuum or nitrogen). The ZnO nanoparticles obtained from zinc oxalate rods are ～55 nm in diameter. Oxides with different morphology, Fe₃O₄ nanoparticles faceted (cuboidal) and Fe₂O₃ nanoparticles (spherical) could be obtained.     

Charge storage mechanism of MnO2 cathodes in Zn/MnO2 batteries using ionic liquid-based gel polymer electrolytes

Cathode reactions in Zn/MnO₂ batteries using aqueous electrolytes have been usually interpreted by the reduction of Mn^4 + to Mn^3 + while protons and/or cations penetrate inside the cathode. However, until now, the MnO₂ storage charge mechanism using a non-aqueous gel polymer electrolyte (GPE) has not been investigated. In this work, ionic liquid-based GPEs including BMIM Tf and ZnTf₂ have been employed in Zn/MnO₂ batteries. Different states of charge of MnO₂ cathodes used in Zn/IL-GPE/MnO₂ batteries have been analyzed by XPS and EDX techniques. XPS analysis showed that Mn^4 + is reduced during the discharge process at the same time as Zn^2 + cations are incorporated into the cathode. Besides, Zn^2 + cations insertion is accompanied by triflate anions.     

Structural characterization of dodecyltrimethylammonium (DTMA) bromide modified sepiolite and its adsorption isotherm studies

In this study, dodecyltrimethylammonium (DTMA) bromide was used to modify natural sepiolite via an ion exchange reaction to form DTMA-sepiolite. Sepiolite and DTMA-sepiolite were then characterized by using Brunauer–Emmett–Teller (BET), elemental analysis, XRD, FT-IR, thermogravimetric (TG) and zeta potential analysis techniques. The BET surface area of sepiolite significantly decreased from 152.14 m² g^–1 to 88.63 m² g^–1, after the modification, due to the coverage of the pores of sepiolite. DTMA was located onto sepiolite according to the differential thermogravimetric (dTG) peaks of DTMA-sepiolite. XRD results confirmed the interaction between DTMA⁺ cations and sepiolite. FT-IR spectra indicated the existence of DTMA functional groups on sepiolite surface. After the characterization was accomplished, adsorption isotherm studies of naphthalene, which is the first member of the polycyclic aromatic hydrocarbons (PAHs), were carried out. The maximum adsorption capacity of DTMA-sepiolite for naphthalene was determined from Langmuir isotherm equation at pH 6 and 20 °C as 1.88 × 10^–4 mol g^?1 or 24.09 mg g^?1.     

Kinetics and mechanism of the reduction of colloidal MnO2 by glycyl-leucine in the absence and presence of surfactants

The kinetics of the reduction of water-soluble colloidal manganese dioxide by glycyl-leucine (Gly-Leu) has been investigated in the presence of perchloric acid both in aqueous as well as micellar media at 35 °C. The study was carried out as functions of [MnO₂], [Gly-Leu] and [HClO₄]. The first-order-rate is observed with respect to [MnO₂], whereas fractional-order-rates are determined in both [Gly-Leu] and [HClO₄]. Addition of sodium pyrophosphate and sodium fluoride enhanced the rate of the reaction. Further, the use of surfactant micelles is highlighted as, in favourable cases, the micelles help the redox reactions by bringing the reactants into a close proximity due to hydrogen bonding. While the ionic surfactants SDS and CTAB have not shown any effect on the reaction rate, the nonionic surfactant TX-100 has catalytic effect which is explained in terms of the mathematical model proposed by Tuncay et al. (1999). The Arrhenius and Eyring equations are valid for the reaction over the range of temperatures used and different activation parameters (E_a, ΔH^#, ΔS^# and ΔG^#) have been evaluated. Kinetic studies show that the redox reaction between MnO₂ and Gly-Leu proceeds through a mechanism combining one- and two-electron pathways: Mn(IV) → Mn(III) → Mn(II) and Mn(IV) → Mn(II). On the basis of the observed results, a possible mechanism has been proposed and discussed.