Nitrogen-doped multiwalled carbon nanotubes decorated with copper(I) oxide nanoparticles with enhanced capacitive properties

We report on the enhanced capacitive properties of a copper(I) oxide nanoparticle (Cu₂O NP)-decorated multiwalled carbon nanotube (MWCNT) forest with nitrogen (N) doping. A careful in situ solid-state dewetting and plasma doping method was developed that ensured homogeneous decoration and contamination-free Cu₂O NPs with N doping on the nanotube sidewalls. The morphology and structure of the hybrid materials were characterised by scanning electron microscopy, transmission electron microscopy, energy-dispersive spectroscopy, Raman spectroscopy and X-ray photoemission spectroscopy. The electrochemical performance of the hybrid materials was investigated by cyclic voltammetry and galvanostatic charge/discharge tests in a 0.1 M Na₂SO₄ electrolyte. The electrochemical tests demonstrated that the Cu₂O NP/N-MWCNT electrode exhibits a specific capacitance up to 132.2 F g^?1 at a current density of 2.5 A g^?1, which is 30% higher than that of the pure MWCNT electrode. Furthermore, the electrode could retain the specific capacitance at 85% stability over 1000 cycles. These observations along with the simple assembly method for the hybrid materials suggest that the Cu₂O NP/N-MWCNT could be a promising electrode for supercapacitor applications.     

Formation and Yield of Multi-Walled Carbon Nanotubes Synthesized via Chemical Vapour Deposition Routes Using Different Metal-Based Catalysts of FeCoNiAl,CoNiAl and FeNiAl-LDH

Multi-walled carbon nanotubes (MWCNTs) were prepared via chemical vapor deposition (CVD) using a series of different catalysts, derived from FeCoNiAl, CoNiAl and FeNiAl layered double hydroxides (LDHs). Catalyst-active particles were obtained by calcination of LDHs at 800 °C for 5 h. Nitrogen and hexane were used as the carrier gas and carbon source respectively, for preparation of MWCNTs using CVD methods at 800 °C. MWCNTs were allowed to grow for 30 min on the catalyst spread on an alumina boat in a quartz tube. The materials were subsequently characterized through X-ray diffraction, Fourier transform infrared spectroscopy, surface area analysis, field emission scanning electron microscopy and transmission electron microscopy. It was determined that size and yield of MWCNTs varied depending on the type of LDH catalyst precursor that is used during synthesis. MWCNTs obtained using CoNiAl-LDH as the catalyst precursor showed smaller diameter and higher yield compared to FeCoNiAl and FeNiAl LDHs.     

Synthesis and electrochemical properties of nanostructured nickel–cobalt oxides as supercapacitor electrodes in aqueous media

Co‐precipitation method was adopted in the preparation of nickel–cobalt oxides for potential application in supercapacitors. The formation of spinel nickel–cobalt oxide, NiCo₂O₄ started below 400 °C as confirmed by X‐ray diffraction analysis. Pure phase nickel cobaltite with cation ratio of 1:2 (Ni:Co) was obtained at calcination temperature of 400 °C. The spinel phase decomposed gradually until 700 °C. The calcination time for the formation of NiCo₂O₄ was found to be between 2 to 4 h. The particle size of the prepared sample studied by transmission electron microscopy showed a value of 9.47 nm. The electrochemical properties of the metal oxide were measured in various acidic, neutral and alkaline electrolyte systems (1.0 M HCl, 1.0 M KCl and 1.0 M KOH) by employment of cyclic voltammetry, galvanostatic charge–discharge test and electrochemical impedance spectroscopy. Ideal capacitor behaviour with the largest operating voltage of 1.0 V and good electrochemical stability were observed in NiCo₂O₄ using neutral KCl aqueous electrolyte. Meanwhile, the prepared sample displayed the highest surface redox activity in 1.0 M KOH alkaline electrolyte but showed the lowest electrochemical performance in acidic electrolyte. At the current density of 0.5 A g^?1, 1.0 M HCl, 1.0 M KCl and 1.0 M KOH gave specific capacitance values of 3.8, 41.9 and 249.8 F g^?1 respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Structure and Surface Transformations of Humic-Adsorbed Synthetic Hydrotalcite-Like Materials

Hydrotalcite-like material of Mg–Al-carbonate system (MACH) was prepared and its heat-treated product (MACHT) was obtained by calcination at 500°C, for 3 hours at atmospheric condition. The resulting materials were used as adsorbents for removal of humic substance (HS) from synthetic peat water (SPW) and natural peat water (NPW). Batch kinetic study showed that MACH or MACHT adsorb the humic substance with maximum adsorption capacities of around 15 mg of humic substance per g of adsorbent, when SPW was used compared to 78 mg/g when NPW was used. The humic substance uptake on MACH and MACHT from SPW and NPW followed the Langmuir model of adsorption. X-ray diffractograms showed that the layered structure of MACH collapsed when it was heated at 500°C and a new amorphous-like phase was observed. Due to the memory effect property of hydrotalcite, the regeneration of MACH from MACHT was observed when MACHT was treated with humic substance from SPW or NPW, and the basal spacing of around 7.9 Å was restored. The BET surface area increased by about a factor of 3, from 68.0 in MACH to 201.9 m²/g in MACHT, but the micropore surface area decreased by about 20%, from 12.3 in the former to 9.9 m²/g in the latter. Expulsion of water molecules and carbon dioxide from carbonate in the interlayer together with the formation of an amorphous-like phase was thought to be the reason for the increase of the BET surface area. The decrease in the micropore area is possibly due to collapse of the layered structure of MACH. The BET surface area for MACH and MACH-humic substance-adsorbed from SPW or NPW is similar. On the other hand, a high reduction in surface area was observed for MACHT-adsorbed humic substance from SPW or NPW, by about 80% in the latter compared to about 90% in the former when compared to MACHT. The regeneration of MACH from MACHT together with the adsorption of humic substances presumably contributed to a high reduction in surface area of humic substance-adsorbed MACHT samples     

Preparation and properties of zinc layered hydroxide with nitrate and phosphate as the counter anion,a novel control release fertilizer formulation

Journal of Porous Materials - New two-dimensional (2D) nanodelivery systems, namely Zinc layered hydroxide-nitrate (ZLN) and Zinc layered hydroxide-phosphate (ZLP) nanocomposites were successfully...     

Synthesis and Electrical Properties of Zn‐substituted Bismuth Copper Tantalate Pyrochlores

A complete substitutional solid solution, Bi_3.08Cu_1.84?xZn_xTa_3.08O_14.16: 0 ≤ x ≤ 1.84, was prepared by solid‐state reaction at temperature 950°C over 48 h. These thermally stable pyrochlores exhibited a remarkable transition from semiconducting to highly insulating behavior as their electrical conductivities varied by many orders of magnitude depending on the Zn concentration. The recorded activation energies increased from 0.40 to 1.40 eV, while the dielectric constants, ε′, and losses, tan δ, were in the range 50–70 and of order 10^?3–10^?2 at 1 MHz and ambient temperature, ~25°C, respectively.     

Effects of physicochemical parameters on the production of phenolic acids from palm oil mill effluent under liquid-state fermentation by Aspergillus niger IBS-103ZA

The present investigation is an effort to develop an environmentally friendly and cost-effective liquid-state fermentation process by introducing a new locally isolated fungal strain of Aspergillus niger (IBS-103ZA) for the production of phenolics from a new source, palm oil mill effluent (POME). Sucrose, manganese sulphate (MnSO₄) and temperature were identified as the most significant variables in improving phenolics production. Optimisation increased the total phenolic content from 856 ± 2.22 to 941 ± 3.72 GAE mg/l at 35.0 °C, 6.0% (w/v) sucrose, 2.7% (w/v) MnSO₄, and with other parameters fixed. The fermented extract (FE) with IC₅₀ value of 0.45 mg/ml showed the strongest antioxidant potency, compared to unfermented extract (UFE), with IC₅₀ of 1.13 mg/ml, and the synthetic antioxidant, BHT, with IC₅₀ of 0.63 mg/ml. The phenolic compounds were identified and quantified by HPLC.     

Effects of La_2O_3 addition on microstructure development and physical properties of harder ZTA-CeO_2 composites with sustainable high fracture toughness

The influence of La_2 O_3 inclusion(0-3 wt%) on the micro structure,phase formation and mechanical properties of zirconia toughed alumina(ZTA) added with 5.0 wt% CeO_2 was investigated.ZTA CeO_2 composites were sintered at 1600℃ for 4 h.The microstructure,phase formation,density,fracture toughness and hardness properties were characterised through FESEM,Microscopy Image Analysis Software and XRD diffractometer,Archimedes principle and Vickers indentation technique,respectively.The XRD,image processing and FESEM reveal the existence of LaAl_(11)O_(18).The addition of La_2 O_3 incites the sintering,microstructure refinement,densification of ZTA-CeO_2 matrix and phase transformation.Hence,the hardness of ZTA-CeO_2 ceramics is increased rapidly based on refinement of Al_2 O_3 grains,densification of ZTA-CeO_2 composites and porosity reduction.It is observed that the fracture toughness is enhanced through in situ formation of elongated LaAl_(11)O_(18) grains.The addition of 0.7 wt% La_2 O_3 culminated in the achievement of the optimum findings for density(4.41 g/cm3),porosity(0.46%),hardness(1792 HV) and fracture toughness(8.8 MPa·m~(1/2)).Nevertheless,excess La_2 O_3 is proven to be detrimental as it displays poor mechanical properties due to the poor compactness of numerous LaAl_(11)O_(18) grains,coarsening of Al_2 O_3 grains and decline in density.     

The Effect of Single, Binary and Ternary Anions of Chloride, Carbonate and Phosphate on the Release of 2,4-Dichlorophenoxyacetate Intercalated into the Zn–Al-layered Double Hydroxide Nanohybrid

Intercalation of beneficial anion into inorganic host has lead to an opportunity to synthesize various combinations of new organic–inorganic nanohybrids with various potential applications; especially, for the controlled release formulation and storage purposes. Investigation on the release behavior of 2,4-dichlorophenoxyacetate (2,4-D) intercalated into the interlayer of Zn–Al-layered double hydroxide (ZAN) have been carried out using single, binary and ternary aqueous systems of chloride, carbonate and phosphate. The release behavior of the active agent 2,4-D from its double-layered hydroxide nanohybrid ZANDI was found to be of controlled manner governed by pseudo-second order kinetics. It was found that carbonate medium yielded the highest accumulated release of 2,4-D, while phosphate in combination with carbonate and/or nitrate speeds up the release rate of 2,4-D. These results indicate that it is possible to design and develop new delivery system of latex stimulant compound with controlled release property based on 2,4-D that is known as a substance to increase latex production of rubber tree, Hevea brasiliensis.     

Numerical simulation of underground seasonal cold energy storage for a 10 MW solar thermal power plant in north-western China using TRNSYS

This paper aims to explore an efficient, cost-effective, and water-saving seasonal cold energy storage technique based on borehole heat exchangers to cool the condenser water in a 10 MW solar thermal power plant. The proposed seasonal cooling mechanism is designed for the areas under typical weather conditions to utilize the low ambient temperature during the winter season and to store cold energy. The main objective of this paper is to utilize the storage unit in the peak summer months to cool the condenser water and to replace the dry cooling system. Using the simulation platform transient system simulation program (TRNSYS), the borehole thermal energy storage (BTES) system model has been developed and the dynamic capacity of the system in the charging and discharging mode of cold energy for one-year operation is studied. The typical meteorological year (TMY) data of Dunhuang, Gansu province, in north-western China, is utilized to determine the lowest ambient temperature and operation time of the system to store cold energy. The proposed seasonal cooling system is capable of enhancing the efficiency of a solar thermal power plant up to 1.54% and 2.74% in comparison with the water-cooled condenser system and air-cooled condenser system respectively. The techno-economic assessment of the proposed technique also supports its integration with the condenser unit in the solar thermal power plant. This technique has also a great potential to save the water in desert areas.