Zhonghua Hu

Novel activation process for preparing highly microporous and mesoporous activated carbons

Abstract An improved ZnCl 2 -chemical activation method is proposed to produce highly porous activated carbons. The novel process can produce either microporous carbons or mesoporous carbons from lignocellulosic materials, such as coconut shells and palm seeds. The porosity of the resultant activated carbons was characterized by nitrogen adsorption isotherms at 77 K. The BET-surface area of the carbons can be over 2400 m 2 /g; the mesopore content (ratio of mesopore volume to total pore volume) is 71%. Furthermore, the activated carbon from palm seeds possesses mesopore content as high as 94%. Thermogravimetric analysis (TGA) was used to monitor the course of pyrolysis of coconut shell and ZnCl 2 -impregnated coconut shell. The adsorptive properties for phenol and dyes were tested.

Preparation of high-surface-area activated carbons from coconut shell

Abstract High-surface-area activated carbons were prepared by chemical activation of coconut shell with KOH as active agent. The influence of activation parameters on the final products was studied by varying the KOH-to-shell ratio, activation temperature and pre-heat temperatures. The samples were characterized by nitrogen adsorption isotherms at 77xa0K. The surface area and pore volume of the carbons were estimated by BET, the Langmuir equation and the t-plot method. Pre-treatment at 600°C favored the product with good yield, high surface area and granular form. The BET surface area and pore volume were as high as 2451xa0m2/g and 1.21xa0cm3/g, respectively. The activated carbons exhibited a much higher adsorption capacity for phenol, 4-chlorophenol and 4-nitrophenol from aqueous solution than did a commercial activated carbon.

Mesoporous high-surface-area activated carbon

Coconut shells and palm seeds have been used as raw materials to obtain activated carbons with high surface area by simultaneous treatment with zinc chloride and carbon dioxide as the physical and chemical agents, respectively. Both the surface area and the mesopore content could be tuned by controlling the experimental parameters, viz., ZnCl2-to-raw material ratio, duration of exposure to the carbon dioxide atmosphere and temperature of activation. In particular, ZnCl2-to-shell ratios above 1 yielded high surface areas, and ratios above 2 resulted in high mesopore content. The adsorption capacity and nature of the porosity were investigated by adsorption experiments using adsorbates with different molecular sizes (viz., phenol, methylene blue and erythrosine red). The capacities of the mesoporous activated carbons were much higher than those of microporous carbons for larger adsorbates, confirming the presence of large amounts of mesopores in the former. The measured adsorption capacities for the prepared samples conformed to the expectations based on micropore and mesopore area and volume estimations.

Chromium adsorption on high-performance activated carbons from aqueous solution

The adsorption of Cr(VI) from aqueous solutions by commercial and lab-made high surface area (HSA)-activated carbons was investigated. Physiochemical factors such as equilibrium time, temperature and solution pH that affect the magnitude of Cr(VI) adsorption were studied. The HSA-activated carbons showed high performance for Cr removal, and their adsorption capacity is several times larger than that of commercial carbons. Both micropores and mesopores have important contribution on the adsorption. However, desorption is more dependent on the mesoporosity of activated carbons. Therefore, regeneration is easier for the carbon with high mesoporosity. As a result, the adsorption capacity of mesoporous carbon could be recovered over 97%, whereas 54% for highly microporous carbon.

Degradation of methyl orange by composite photocatalysts nano-TiO2 immobilized on activated carbons of different porosities.

Composite photocatalysts TiO(2) immobilized on granular activated carbons with different porosities (TiO(2)/AC) were prepared by a novel approach, dip-hydrothermal method using peroxotitanate as precursor. The TiO(2)/AC composites were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and the nitrogen absorption. Their photocatalytic activity was evaluated by degradation of methyl orange (MO). The results showed that nano-TiO(2) particles of anatase type were well deposited on the activated carbon surface. The porosity of activated carbon had significant influence on the adsorption, the amount of TiO(2) deposited on the external surface of AC and the activity of composite photocatalysts. The composite TiO(2)/AC made from proper mesoporosity AC exhibited higher catalytic activity than the mixture of powdered TiO(2) with AC. Furthermore, the mechanism of synergistic effect of AC adsorption and TiO(2) photocatalysis was discussed.

Study on the treatment of copper-electroplating wastewater by chemical trapping and flocculation

Sodium diethyldithiocarbamate (DDTC) is used as a trapping agent and poly-ferric sulphate and polyacrylamide are used as flocculants to treat copper-electroplating wastewater. The influences on the precipitation and flocculation of Cu2+ cation are studied in details, such as the amount of complex copper (EDTA and NH4Cl are used as coordination agents), the addition of DDTC, poly-ferric sulphate and polyacrylamide (PAM) and pH of the solution. In addition, the influences on the trapping copper by different agents such as DDTC, diethylammonium diethyldithiocarbamate (DDC) and ammonium pyrrolidinedithiocarbamate (APDC) are studied as well. The results show that the dosage of DDTC depends only on the content of complex copper, but not on the total amount of copper in the wastewater. When the molar ratio of DDTC to Cu is between 0.8 and 1.2, Cu removal efficiency could be higher than 99.6%. Poly-ferric sulphate and PAM have little effects on the Cu removal, but they have significant effects on the flocculating volume, precipitation rate and nephelometric of the upper clean water.

Carbon Electrode Material with High Densities of Energy and Power

Abstract Activated carbon (AC) samples as electrode materials were prepared by means of simultaneous physical-chemical activation using walnut shells as precursors. The porosity and surface chemistry of the resultant AC samples were studied by the nitrogen adsorption at 77 K, and FTIR spectrum. The testing supercapacitors were assembled with resultant carbon electrode and electrolyte of 6 mol·L −1 KOH solution. Their electrochemical properties were investigated by charge-discharge of constant current, cyclic voltammogram, impedance spectrum and so on. The results showed that the capacitor had low inner resistance, low leakage current, high stability, and capacitance retainability. The specific capacitance of AC increased with increasing BET specific surface area. The specific capacitance of the AC sample with a specific area of 1197 m 2 ·g −1 could be as high as 292 F·g −1 . At a discharge current of 80 mA, the corresponding specific energy density, power density, and maximum power of the supercapacitor are 7.3 Wh·kg −1 , 770 W·kg −1 , and 5.1 W·g −1 , respectively.

Facile synthesis and characterization of high-performance NiMoO4 · xH2O nanorods electrode material for supercapacitors

One-dimensional NiMoO4xa0·xa0xH2O nanorods were synthesized by a facile template-free hydrothermal method as a potential electrode material for supercapacitors. The influences of reaction temperature, reaction time, and nickel source on the properties of resultant samples were investigated. Electrochemical data reveal that the as-synthesized one-dimensional NiMoO4xa0·xa0xH2O nanorod superstructures can deliver a remarkable specific capacitance (SC) of 1131xa0Fxa0g−1 at a current density of 1xa0Axa0g−1 and remain as high as 914xa0Fxa0g−1 at 10xa0Axa0g−1 in a 6xa0M KOH aqueous solution. Moreover, there is only 6.2xa0% loss of the maximum SC after 1000 continuous charge–discharge cycles at the high current density of 10xa0Axa0g−1. Such outstanding electrochemical performance may be owing to the unique one-dimensional hierarchical structures, which can facilitate the electrolyte ions and electrons to easily contact the NiMoO4 nanorod building blocks and then allow for sufficient faradaic reactions to take place, even at high current densities.

Novel 3D flower-like CoNi2S4/carbon nanotube composites as high-performance electrode materials for supercapacitors

Novel 3D flower-like CoNi2S4/carbon nanotube composites with a porous structure were designed through a facile precursor transformation approach as electrode materials for supercapacitors. The resulting samples are characterized by X-ray diffraction, Raman spectra, energy dispersive spectroscopy, field emission scanning electron microscopy, transmission electron microscopy, and nitrogen adsorption–desorption. Their electrochemical performance was investigated by means of cyclic voltammetry, galvanostatic charge–discharge, impedance spectra and cycle life. By selecting carbon nanotubes as the conductive support for the growth of CoNi2S4, the as-obtained CoNi2S4/carbon nanotube composites displayed an ultrahigh specific capacitance of 2094 F g−1 at 1 A g−1 and a good rate capability (72% capacity retention at 10 A g−1). These results above suggest the great potential of the unique flower-like CoNi2S4/carbon nanotube composites in the development of high-performance electrode materials for supercapacitors.

A novel synthesis of size-controllable mesoporous NiMoO4 nanospheres for supercapacitor applications

A novel hydrothermal emulsion method is proposed to synthesize mesoporous NiMoO4 nanosphere electrode material. The size of sphere-shaped NiMoO4 nanostructure is controlled by the mass ratio of water and oil phases. Nickel acetate tetrahydrate and ammonium heptamolybdate were used as nickel and molybdate precursors, respectively. The resultant mesoporous NiMoO4 nanospheres were characterized by X-ray diffraction, N2 adsorption and desorption, scanning electron microscopy, and transmission electron microscopy. The electrochemical performances were evaluated by cyclic voltammetry (CV), cyclic chronopotentiometry (CP), and electrochemical impedance spectroscopy (EIS) in 6xa0M KOH solution. The typical mesoporous NiMoO4 nanospheres exhibit the large specific surface area of 113xa0m2xa0g−1 and high specific capacitance of 1443xa0Fxa0g−1 at 1xa0Axa0g−1, an outstanding cyclic stability with a capacitance retention of 90xa0% after 3000xa0cycles of charge-discharge at a current density of 10xa0Axa0g−1, and a low resistance.