Preparation of high surface area activated carbon from waste-biomass of sunflower piths: Kinetics and equilibrium studies on the dye removal

Sunflower pith (SP), a vast agricultural waste is herein used as a precursor material for highly porous low density activated carbon production. Porosity and flake-like microstructure of the SP in its natural form are shown by micro-computed tomography (Micro-CT). Carbonization process turns the SP into thin, separated carbon flakes of 200 nm thickness. Two types of alkaline based chemical activation with KOH and NaOH are performed to yield SP based activated carbon (AC), K-SPAC and N-SPAC, respectively. Microstructural changes upon carbonization and activation process are elaborated by RAMAN, FTIR and SEM analyses. BET Surface area of the NaOH-activated N-SPAC was calculated as 2690 m2/g and was higher than KOH-activated K-SPAC with 2090 m2/g. Maximum adsorption capacity of N-SPAC was calculated as 965 mg/g whereas it was 580 mg/g for K-SPAC. Adsorption kinetic studies for N-SPAC revealed that at a low initial concentration of dye (500 mg/L), the pseudo first-order kinetic model was predictive. On the other hand, at high initial MB concentration (1000 mg/L), the results indicate that the adsorption kinetics follow the Elovich model with intraparticle diffusion as one of the rate-determining steps. In conclusion, overall results suggest that thanks to its highly porous microstructure, the SP is an alternative renewable AC precursor choice for dye removal applications

Catalytic synthesis of boron nitride nanotubes at low temperatures

KFeO2 is demonstrated for efficiency catalysing the formation of BN nanotubes (BNNT) by thermal chemical vapor deposition (TCVD). This alkali-based catalyst enables the formation of crystalline and high aspect ratio, multi-walled BNNTs at temperatures as low as 750°C, significantly lower than those typical of production by TCVD

AIR OXIDATION OF TURKISH BEYPAZARI LIGNITE .2. EFFECT OF DEMINERALIZATION ON STRUCTURAL CHARACTERISTICS IN OXIDATION REACTIONS AT 150-DEGREES-C

Demineralized (HCl/HF) samples of Beypazari lignite were oxidized in air at 150 degrees C for up 120 h in a ventilated oven. Elemental analyses, diffuse reflectance Fourier transform infrared (DRIFT), solid-state C-13 CP/MAS/TOSS NMR, and pyrolysis mass (PY-MS) spectroscopies as well as solvent swelling were used for the characterization of the oxidized and unoxidized samples. It was found that the removal of 90.1% of the mineral matter from Beypazari lignite facilitated the access of oxygen into the coal structure and permitted the occurrence of diffusion-controlled reactions. This was confirmed by the observation of linear relationships between the decrease in the intensity of aliphatic CH2 and CH3 groups, the increase of the O/H atomic ratio and the decrease in the aliphatic factor, and the square root of the duration of oxidation. It was observed from swelling measurements in pyridine before and after the oxidation that aryl esters and anhydrides, which were the major oxidation products, probably acted as covalent cross-links. Aliphatic groups oxidized more rapidly than aromatic structures and, in fact, methylenes oxidized more rapidly than methyls. The decrease in the intensity of the molecular ion series alkylphenols, alkyldihydroxybenzenes, alkylbenzenes, and alkylnaphthalenes arising from pyrolysis mass spectrometry of oxidized samples was approximately consistent with the corresponding increase in the intensity of CO2+, CH3COOH+, and CO+ molecular ions

AIR OXIDATION OF TURKISH BEYPAZARI LIGNITE .1. CHANGE OF STRUCTURAL CHARACTERISTICS IN OXIDATION REACTIONS AT 150-DEGREES-C

The oxidation of Beypazari lignite was carried out in air at 150-degrees-C for up to 168 h. Oxidized samples were withdrawn from a ventilated oven at different periods of time and characterized by elemental analysis, diffuse reflectance Fourier transform infrared (DRIFT), solid-state C-13 CP/MAS/TOSS NMR, and pyrolysis mass (Py-MS) spectroscopies. It was found that oxidation influenced the organic structure and the inorganics at different periods of the oxidation. Iron(II) sulfate was formed in 24 h, during which time there was almost no change of aliphatic CH2 and CH3 groups. After the formation of iron(II) sulfate, aliphatic CH2 and CH3 groups started to oxidize. Thus, the formation of iron(II) sulfate apparently prevented the oxidation of organic structure of Beypazari lignite during the first 24 h. The van Krevelen diagram (H/C vs O/C), the change of the O/H atomic ratio, and the rate of loss of aliphatic CH2 and CH3 groups showed the organic structure of Beypazari lignite to have continued in three stages. Aromatics seemed to be more stable than aliphatics during the oxidation process. The functional groups produced by the oxidation included ketones, carboxyls, and anhydrides but the major oxidation products were aryl esters. The abundance of CO2+, CO+, CH3COOH+, and SO2+ molecular ions increased in the pyrolysate of the oxidized sample whereas the molecular ions alkylphenols, dihydroxybenzenes, and alklynaphthalenes decreased after the oxidation

AIR OXIDATION OF TURKISH BEYPAZARI LIGNITE .3. CHANGE IN THE STRUCTURAL CHARACTERISTICS OF THE RESIDUE IN OXIDATION REACTIONS AT 150-DEGREES-C

Beypazari lignite was subsequently demineralized with HCl/HF and extracted by pyridine under supercritical conditions. The extracted residue was oxidized in air at 150-degrees-C for up to 120 h in a ventilated oven. Elemental analysis, diffuse reflectance Fourier transform infrared (DRIFT), solid-state C-13 CP/MAS/TOSS NMR, and pyrolysis mass (Py-MS) spectroscopic techniques were used for the structural characterization of the oxidized and unoxidized samples. It was found that the oxidation of the extracted residue proceeded in two consecutive stages. The rate of oxidation, as measured by changes in the concentrations of carboxyl and aliphatic CH2 and CH3 groups and in the O/H atomic ratio, was much faster in the initial than in the second stage. The removal of 90.1% of the mineral matter and 39.7% of the soluble material from the parent lignite facilitated the access of oxygen to the network structure which was relatively enriched in aromatic units by the supercritical fluid extraction. It was therefore easier to form aryl esters, alkyl esters, and anhydrides. Since aliphatic structures were relatively less in concentrations than aromatics, there was little change in the intensities of alkylbenzenes, alkylnaphthalenes, alkyldihydroxybenzenes, alkylphenols, and alkanes during oxidation. The higher intensities of CO2+ (m/z 44) and CH3COOH+ (m/z 60) molecular ions observed in Py-MS than CO+ (m/z 28) molecule ion indicated that more carboxyl-containing functional groups were formed by oxidation than carbonyl-containing groups. Aromatic structures in the organic network were not affected during oxidation. The oxidation pathway of the extracted residue was considered to lie between of the oxidation pathways of the parent and the demineralized Beypazari lignites