Mesoporous CdS-pillared H2Ti3O7 nanohybrids with efficient photocatalytic activity

Heterostructured CdS-pillared H₂Ti₃O₇ nanohybrids were prepared by the self-assembly of exfoliated trititanate nanosheets and CdS nanosol particles under the electrostatic interactions. It was revealed that the present nanohybrids were mesoporous with specific surface areas of about 90 m² g⁻¹. The nanohybrids exhibited high photocatalytic activity and good recurrence stability in the H₂ evolution from water splitting. When the preparation molar ratio of H₂Ti₃O₇/CdS was 2:1, the nanohybrid reached a high H₂-evolution rate of 1523 μmol h⁻¹ g⁻¹ under a 300 W Xe lamp irradiation, which was 13 times higher than the bare CdS. Apart from the wider spectral responsive range, the superior photocatalytic performance of the nanohybrids was predominantly attributed to the efficient photogenerated charge separation between the trititanate nanosheets and the encapsulated CdS nanoparticles.     

SnO2-decorated multiwalled carbon nanotubes and Vulcan carbon through a sonochemical approach for supercapacitor applications

Multiwalled carbon nanotubes (MWCNTs) and Vulcan carbon (VC) decorated with SnO₂ nanoparticles were synthesized using a facile and versatile sonochemical procedure. The as-prepared nanocomposites were characterized by means of transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infra red spectroscopy. It was evidenced that SnO₂ nanoparticles were uniformly distributed on both carbon surfaces, tightly decorating the MWCNTs and VC. The electrochemical performance of the nanocomposites was evaluated by cyclic voltammetry and galvanostatic charge/discharge cycling. The as-synthesized SnO₂/MWCNTs nanocomposites show a higher capacity than the SnO₂/VC nanocomposites. Concretely, the SnO₂/MWCNTs electrodes exhibit a specific capacitance of 133.33 F g⁻¹, whereas SnO₂/VC electrodes exhibit a specific capacitance of 112.14 F g⁻¹ measured at 0.5 mA cm⁻² in 1 M Na₂SO₄.     

Physical,electrochemical and supercapacitive properties of activated carbon pellets from pre-carbonized rubber wood sawdust by CO2 activation

The physical and electrochemical properties of the activated carbon pellet electrodes have been investigated. Activated carbon pellets were prepared from single step carbonization process of pre-carbonized rubber wood sawdust at a temperature of 800 °C that followed with a CO₂ activation process at temperature in the range of 700–1000 °C. The BET characterization on the sample found that the surface area of the carbon pellet increased with the increasing of the activation temperature. The optimum value was as high as 683.63 m² g⁻¹. The electrical conductivity was also found to increase linearly with the increasing of the activation temperature, namely from 0.0075 S cm⁻¹ to 0.0687 S cm⁻¹ for the activation temperature in the range of 700–1000 °C. The cyclic voltammetry characterization of the samples in aqueous solution of 1 M H₂SO₄ also found that the specific capacitance increased with the increasing of the activation temperature. Typical optimum value was shown by the sample activated at 900 °C with the specific capacitance was as high as 33.74 F g⁻¹ (scan rate 1 mV s⁻¹). The retained ratio was as high as 32.72%. The activated carbon pellet prepared from the rubber wood sawdust may found used in supercapacitor applications.     

Rechargeability improvement of δ-type chemical manganese dioxide with the co-doping of Bi and Ni in alkaline electrolyte

δ-MnO₂ with the doping of Ni and Bi was prepared through a simple chemical precipitation/oxidation method. Its structure was confirmed by the X-ray diffraction tests. The results of cyclic voltammetry and galvanostatic charge–discharge tests showed that both the doping of Bi and Ni benefited the electrochemical activity of the MnO₂ electrode. Compared to the un-doped electrode, the Bi-doped one showed larger discharge capacity and the Ni-doped one showed higher discharge potential and better cycleability. With the co-doping of 5 wt% Bi and 10 wt% Ni, the discharge capacity of the MnO₂ electrode reached 252 mA h g^?1 at a 0.2C rate and 116 mA h g^?1 at a 1C rate, respectively. Its capacity remained in 105 mA h g^?1 after 50 cycles at a 1C rate, but the capacity of a commercial electrolytic MnO₂ electrode was only 37 mA h g^?1.     

Galvanostatically deposited Fe: MnO2 electrodes for supercapacitor application

The present investigation describes the addition of iron (Fe) in order to improve the supercapacitive properties of MnO₂ electrodes using galvanostatic mode. These amorphous worm like Fe: MnO₂ electrodes are characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX), Fourier transform infrared spectroscopy (FTIR) and wettability test. The supercapacitive properties of MnO₂ and Fe: MnO₂ electrodes are investigated using cyclic voltammetry, chronopotentiometry and impedance techniques. It is seen that the supercapacitance increases with increase in Fe doping concentration and achieved a maximum of 173 F g^?1 at 2 at% Fe doping. The maximum supercapacitance obtained is 218 F g^?1 for 2 at% Fe: MnO₂ electrode. This hydrous binary oxide exhibited ideal capacitive behavior with high reversibility and high pulse charge–discharge property between ?0.1 and +0.9 V/SCE in 1 M Na₂SO₄ electrolyte indicating a promising electrode material for electrochemical supercapacitors.     

Controllable synthesis of layered Co–Ni hydroxide hierarchical structures for high-performance hybrid supercapacitors

A facile solvothermal method is developed for synthesizing layered Co–Ni hydroxide hierarchical structures by using hexamethylenetetramine (HMT) as alkaline reagent. The electrochemical measurements reveal that the specific capacitances of layered bimetallic (Co–Ni) hydroxides are generally superior to those of layered monometallic (Co, Ni) hydroxides. The as-prepared Co_0.5Ni_0.5 hydroxide hierarchical structures possesses the highest specific capacitance of 1767 F g⁻¹ at a galvanic current density of 1 A g⁻¹ and an outstanding specific capacitance retention of 87% after 1000 cycles. In comparison with the dispersed nanosheets of Co–Ni hydroxide, layered hydroxide hierarchical structures show much superior electrochemical performance. This study provides a promising method to construct hierarchical structures with controllable transition-metal compositions for enhancing the electrochemical performance in hybrid supercapacitors.     

Synthesis of MnO2 nanoparticles from sonochemical reduction of MnO4− in water under different pH conditions

MnO₂ was synthesized by sonochemical reduction of MnO₄⁻ in water under Ar atmosphere at 20 °C, where the effects of solution pH on the reduction of MnO₄⁻ were investigated. The obtained XRD results showed that poor crystallinity δ-MnO₂ was formed at pH 2.2, 6.0 and 9.3. When solution pH was increased from 2.2 to 9.3, the morphologies of δ-MnO₂ changed from aggregated sheet-like or needle-like structures to spherical nanoparticles and finally to cubic or polyhedron nanoparticles. After further irradiation, MnO₂ was readily reduced to Mn²⁺. It was confirmed that H₂O₂ and H atoms formed in the sonolysis of water acted as reductants for both reduction for MnO₄⁻ to MnO₂ and MnO₂ to Mn²⁺. The optimum irradiation time for the effective synthesis of MnO₂ was 13 min at pH 2.2, 9 min at pH 6.0, 8 min at pH 9.3, respectively.     

Cellulose-based carbon—A potential anode material for lithium-ion battery

A series of hard carbons was produced by the carbonization of microcrystalline cellulose powder in the temperature range of 950–1100 °C. The properties of the carbons were characterized using elemental analysis, X-ray diffraction and N₂ and CO₂ adsorption. The effect of heat-treatment temperature (HTT), pyrolytic carbon (PC) coating and discharging mode on the lithium insertion/deinsertion behavior of the carbons was assessed in a coin-type half-cell with metal lithium cathode. Increasing cellulose HTT modifies mostly carbon porosity, the surface area (S_DFT) decreases from about 500 to 167 m² g⁻¹. It is associated with lowering the reversible C_rev and irreversible C_irr capacities, but without improving relatively low (0.72) 1st cycle coulombic efficiency. Applying constant current (CC)+constant voltage (CV) discharging mode instead of conventional CC enhances the reversible capacity by 15–18%. PC coating is effective in reducing C_irr by ∼20% with a little change of C_rev. The best capacity parameters, C_rev of 458 mA h g⁻¹ and C_irr of 139 mA h g⁻¹, were measured for PC coated 1000 °C carbon. The prolonged cycling of full-cell assembled with anode of the carbon and commercial cathode revealed that after initial 20 cycles the capacity decay (0.029 mA h/cycle) is comparable to that of commercial cell with graphite-based anode.     

Enhanced boron adsorption onto synthesized MgO nanosheets by ultrasonic method

MgO nanosheets with high adsorption performance were fabricated by an ultrasonic method. It was revealed that, nest-like MgO was formed from the magnesium salt solution precipitation and further calcination. Then the nest-like MgO was exfoliated by ultrasonic waves to obtain MgO nanosheets with approximately a lateral of 200–600 nm and a thickness of 10 nm. Adjusting the ultrasonic time and power, the specific surface areas of MgO nanosheets could be tuned in a range of 79–168 m²/g. The synthesized MgO nanosheets were used as adsorbents to remove boron from aqueous solution, and the maximum boron adsorption capacity of these MgO nanosheets reached 87 mg g⁻¹. The high uptake capability of the MgO nanosheets makes it potentially adsorbent for the removal of boron from wastewaters.     

Ultrasonic assisted-Fenton-like degradation of nitrobenzene at neutral pH using nanosized oxides of Fe and Cu

Ultrasonic-assisted heterogeneous Fenton reaction was used for degradation of nitrobenzene (NB) at neutral pH conditions. Nano-sized oxides of α-Fe₂O₃ and CuO were prepared, characterized and tested in degradation of NB (10 mg L⁻¹) under sonication of 20 kHz at 25 °C. Complete degradation of NB was effected at pH 7 in presence of 10 mM H₂O₂ after 10 min of sonication in presence of α-Fe₂O₃ (1.0 g L⁻¹), (k = 0.58 min⁻¹) and after 25 min in case of CuO (k = 0.126 min⁻¹). α-Fe₂O₃ showed also effective degradation under the conditions of 0.1 g L⁻¹ oxide and 5.0 mM of H₂O₂, even though with a lower rate constant (0.346 min⁻¹). Sonication plays a major role in enhancing the production of hydroxyl radicals in presence of solid oxides. Hydroxyl radicals-degradation pathway is suggested and adopted to explain the differences noted in rate constants recorded on using different oxides.     

Characterization of nanoporous carbon fibrous materials obtained by chemical activation of plane tree seed under ultrasonic irradiation

An ultrasonic irradiation was applied for the impregnation by chemical agents in the chemical activation process of new type of active carbon precursor. Plane tree seed, due to the unique fibrous structure and low cost is a promising eco-friendly raw material for the preparation of activated carbon materials. Ultrasonic irradiation was used for the impregnation step allowing the chemical activation by different agents: potassium or sodium hydroxide, hydrogen peroxide and pyrogallol. The porous structures were examined by nitrogen adsorption/desorption isotherms at 77 K and electrochemically by cyclic voltammetry. The textures of these materials were observed by scanning electron microscopy. The application of ultrasonic irradiation in the impregnation step increased surface area of the final material more than two times in comparison to the material which impregnation in the activation process was by conventional stirring. Ultrasonic irradiation enhances the chemical activation process and the activated carbon fibrous materials with nanoporous structure were obtained by impregnation of seeds with alkaline hydroxides. Total surface areas of these samples were 976 m² g⁻¹ and 1130 m² g⁻¹. These fibers have total specific capacitance as high as 125 F g⁻¹ and 53 F g⁻¹ which major fraction in both cases originate from internal micropores structure.     

Spray pyrolyzed NiO–C nanocomposite as an anode material for the lithium-ion battery with enhanced capacity retention

NiO–C nanocomposite was prepared by a spray pyrolysis method using a mixture of Ni(NO₃)₂ and citric acid solution at 600 °C. The microstructure and morphology of the NiO–C composite were characterized by means of X-ray diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) mapping, and thermogravimetric analysis (TGA). The results showed that the NiO nanoparticles were surrounded by amorphous carbon. Electrochemical tests demonstrated that the NiO–C nanocomposites exhibited better capacity retention (382 mAh g^− 1 for 50 cycles) than that of pure NiO (141 mAh g^− 1 for 50 cycles), which was also prepared by spray pyrolysis using only Ni(NO₃)₂ as precursor. The enhanced capacity retention can be mainly attributed to the NiO–C composite structure, composed of NiO nanoparticles surrounded by carbon, which can accommodate the volume changes during charge–discharge and improve the electrical conductivity between the NiO nanoparticles.     

Sonochemically synthesized MnO2 nanoparticles as electrode material for supercapacitors

In this study, manganese oxide (MnO₂) nanoparticles were synthesized by sonochemical reduction of KMnO₄ using polyethylene glycol (PEG) as a reducing agent as well as structure directing agent under room temperature in short duration of time and characterized by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Scanning electron microscope (SEM), Transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) analysis. A supercapacitor device constructed using the ultrasonically-synthesized MnO₂ nanoparticles showed maximum specific capacitance (SC) of 282 Fg⁻¹ in the presence of 1 M Ca(NO₃)₂ as an electrolyte at a current density of 0.5 mA cm⁻² in the potential range from 0.0 to 1.0 V and about 78% of specific capacitance was retained even after 1000 cycles indicating its high electrochemical stability.     

Rapid preparation of high electrochemical performance LiFePO4/C composite cathode material with an ultrasonic-intensified micro-impinging jetting reactor

A joint chemical reactor system referred to as an ultrasonic-intensified micro-impinging jetting reactor (UIJR), which possesses the feature of fast micro-mixing, was proposed and has been employed for rapid preparation of FePO₄ particles that are amalgamated by nanoscale primary crystals. As one of the important precursors for the fabrication of lithium iron phosphate cathode, the properties of FePO₄ nano particles significantly affect the performance of the lithium iron phosphate cathode. Thus, the effects of joint use of impinging stream and ultrasonic irradiation on the formation of mesoporous structure of FePO₄ nano precursor particles and the electrochemical properties of amalgamated LiFePO₄/C have been investigated. Additionally, the effects of the reactant concentration (C = 0.5, 1.0 and 1.5 mol L⁻¹), and volumetric flow rate (V = 17.15, 51.44, and 85.74 mL min⁻¹) on synthesis of FePO₄·2H₂O nucleus have been studied when the impinging jetting reactor (IJR) and UIJR are to operate in nonsubmerged mode. It was affirmed from the experiments that the FePO₄ nano precursor particles prepared using UIJR have well-formed mesoporous structures with the primary crystal size of 44.6 nm, an average pore size of 15.2 nm, and a specific surface area of 134.54 m² g⁻¹ when the reactant concentration and volumetric flow rate are 1.0 mol L⁻¹ and 85.74 mL min⁻¹ respectively. The amalgamated LiFePO₄/C composites can deliver good electrochemical performance with discharge capacities of 156.7 mA h g⁻¹ at 0.1 C, and exhibit 138.0 mA h g⁻¹ after 100 cycles at 0.5 C, which is 95.3% of the initial discharge capacity.     

Engineering birnessite-type MnO2 nanosheets on fiberglass for pH-dependent degradation of methylene blue

We construct hierarchical MnO₂ nanosheets @ fiberglass nanostructures via one-pot hydrothermal method without any surfactants. The morphology and structure of MnO₂-modified fiberglass composites are examined by focus ion beam scanning electron microscopy (FIB/SEM), X-Ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR). The birnessite-type MnO₂ nanosheets are observed to grow vertically on the surface of fiberglass. Furthermore, the birnessite-type MnO₂-fiberglass composites exhibit good ability for degradation of methylene blue (MB) in different pH levels. In neutral solution (pH 6.5–7.0), it achieves a high removal rate of 96.1% (2 h, at 60 °C) in the presence of H₂O₂; and in acidic environment (pH 1.5), 96.8% of MB solution (20 mg/L, 100 mL) is decomposed by oxidation within only 5 min. In principles, the rational design of MnO₂ nanosheets-decorated fiberglass architectures demonstrated the suitability of the low-cost MnO₂-modified fiberglass nanostructure for water treatment.     

Structure,stability and electrical properties of the La(2−x)SrxMnO4±δ solid solution series

Single phase materials of the La_(2−x)Sr_xMnO_4±δ (0.6 ≤ x ≤ 2.0) solid solution series were prepared via solid state reaction. The structure of each material was examined at room temperature and determined to be tetragonal for all phases examined. An expansion in lattice volume was observed on increasing lanthanum content. The stability and thermal expansion of each member of the solid solution series was determined via the use of in situ high temperature X-ray diffraction. It was found that all materials remained stable up to a temperature of 800 °C. Thermal expansion coefficients were found to be in the region of 15 × 10^− 6 K^− 1 for La_(2−x)Sr_xMnO_4±δ compounds where x > 1.4. The electrical conductivity of each phase was also determined over a similar temperature range with a maximum value of ∼6 Scm^− 1 at 900 °C for the x = 1.8 phase.     

Preparation and electrochemical properties of mesoporous Co3O4 crater-like microspheres as supercapacitor electrode materials

Mesoporous Co₃O₄ microspheres with unique crater-like morphology were obtained by utilizing the mesoporous silica material MCM-41 as a template. The analysis results of N₂ adsorption–desorption measurement indicate that the product has a large Brunauer–Emmett–Teller (BET) surface area of 60 m² g⁻¹ and a narrow pore size distribution centering around 3.7 nm. Its electrochemical properties were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements. The findings reveal that this novel morphology material has a smaller inner resistance of about 0.4 Ω and a higher onset frequency of 550 Hz. This material can provide a high specific capacitance of 102 F g⁻¹ and a large capacity retention of 74% in 500 continuous cycles test at a sweep rate of 3 mV s⁻¹. More significantly, the mass loading of electroactive species can reach as large as 2 mg cm⁻², which is one order of magnitude larger than common amount used.     

Ultrasonically assisted removal of Congo Red,Phloxine B and Fast green FCF in ternary mixture using novel nanocomposite following their simultaneous analysis by derivative spectrophotometry

In this study dependency of simultaneous adsorption of Congo Red (CR), Phloxine B (BP) and Fast green FCF (FG) onto CuS/ZnS nanocomposites loaded on activated carbon (CuS/ZnS-NCs-AC) to pH, adsorbent mass, sonication time and initial dyes concentration were modeled and optimized, while CuS/ZnS-NCs-AC was identified by XRD, FESEM and EDS analysis. CR, PB and FG concentration determination were undertaken by first and second order derivative spectrophotometry in ternary mixture. According to central composite design (CCD) based on desirability function (DF), the best experimental conditions was set as pH 6.0, 0.02 g CuS/ZnS-NCs-AC, 5 min sonication time, 15 mg L⁻¹ for PB and 10 mg L⁻¹ for other dyes. Conduction of experiments to above conditions lead to highest dyes removal efficiency of 99.72, 98.8 and 98.17 for CR, PB and FG, respectively. The adsorption data efficiently fitted by Langmuir isotherm model, while the order of maximum adsorption capacity (Q_max) for PB (128.21 mg g⁻¹) > CR (88.57 mg g⁻¹) > FG (73.40 mg g⁻¹) is related to their different structure and charges. Kinetics of process was efficiently explained according to pseudo-second-order kinetic in cooperation of Weber and Morris based on intraparticle diffusion.     

Inorganic polymer phosphazene disulfide as cathode material for rechargeable lithium batteries

Novel inorganic network polymer phosphazene disulfide [(NPS₂)₃]_n was synthesized by a solution cross-link method. IR and element content analysis confirmed the polymer's molecular structure. The polymer has an average particle size of d_0.5 = 7.7 μm and the specific surface area is 57.4 m² g^− 1. TG/DTA analysis showed that [(NPS₂)₃]_n underwent a decomposition reaction from 200 to 300 °C. When used as cathode material in lithium batteries, its initial discharge capacity was 459.1 mAh g^− 1, which is almost 93.5% of theoretical specific capacity (490.9 mAh g^− 1). After 30 charge–discharge cycles, the discharge capacity of [(NPS₂)₃]_n stabilized at approximately 400.1 mAh g^− 1 which revealed an excellent cyclic ability. Therefore [(NPS₂)₃]_n is of great potential as cathode material for secondary lithium batteries.     

Rapid synthesis of LiCr0.15Mn1.85O4 by glycine–nitrate method

LiCr_0.15Mn_1.85O₄ spinel has been successfully synthesized by glycine–nitrate method (GNM). The presence of pure spinel phase was confirmed by long term XRPD measurements and the Rietveld structural refinement. Lattice parameter was estimated to be 8.2338 Å. Average particle size of prepared powder material is below 500 nm. The BET surface area is 9.6 m² g^− 1. As a cathode material for lithium batteries LiCr_0.15Mn_1.85O₄ shows initial discharge capacity of 110 mA h g^− 1 and capacity retention of 83% after 50 cycles.