Enhanced adsorption capacity of activated carbon over thermal oxidation treatment for methylene blue removal: kinetics, equilibrium, thermodynamic, and reusability studies.

Activated carbon (AC) is an effective and inexpensive adsorbent material for dye removal, but it cannot always be used repeatedly. Furthermore, the adsorbed dyes with toxicity usually remain on its surface. In this study, a thermal air oxidation process was used to modify the surface of AC and decompose adsorbed methylene blue (MB). The behavior of this process on spent AC was investigated using TGA-DTA, while the degradation of MB before and after the regeneration process was analyzed using a carbon, hydrogen, nitrogen, sulfur (CHNS) analyzer. It was discovered that thermal air oxidation could promote the formation of oxygenated functional groups on AC produced from steam-activated carbon coconut shell (SACCS), which when treated at 350 °C (denoted as SACCS-350), demonstrated an adsorption capacity 2.8 times higher than the non-air-oxidized AC (SACCS). The key parameters for the MB adsorption of SACCS and SACCS-350, such as kinetics, equilibrium, and thermodynamics, were compared. Moreover, the SACCS-350 could be reused at least 3 times for the adsorption of MB. Based on these results, thermal air oxidation treatment could successfully improve the adsorption performance of AC and regenerate spent AC through a reasonable and environmentally friendly process compared to other regeneration methods.

Improving the Bio-Oil Quality via Effective Pyrolysis/Deoxygenation of Palm Kernel Cake over a Metal (Cu, Ni, or Fe)-Doped Carbon Catalyst.

Waste palm kernel cake (WPKC) is being utilized as a biomass feedstock for the sustainable production of catalysts/supports and bio-oil fuels. Herein, metal (Cu, Ni, and/or Fe)-doped carbon catalysts were prepared using conventional impregnation and pyrolysis methods. The physicochemical properties of the as-prepared catalysts were analyzed. According to the obtained results, the catalyst acidity was highly increased with the increase in the metal loading amount on a carbon support, leading to a better performance for deoxygenation/aromatization. A maximum yield of bio-oil from WPKC pyrolysis was achieved up to ∼60% under optimum conditions determined via statistical designs. From the results of bio-oil compositions, 15%Ni loading on activated carbon exhibited the best performance of about 72% for the production of hydrocarbon compounds. Monoaromatic hydrocarbons such as benzene, toluene, and xylenes (BTXs) could be reduced via condensation and polymerization with the increase of the Ni-loading amount. Moreover, the catalytic performance of the selected 15%Ni-carbon catalyst was also compared with those of commercial catalysts zeolite and alumina, and the results showed that the 15% metal-doped carbon catalyst presented much better stability/reusability for five times with less reduction of the hydrocarbon yield in the upgraded bio-oil. This research provided an eco-friendly strategy for the low-cost production of bio-oil fuel with a high quality/yield from waste biomass pyrolysis.

Environmental surface chemistries and adsorption behaviors of metal cations (Fe3+, Fe2+, Ca2+ and Zn2+) on manganese dioxide-modified green biochar.

The facile preparation and modification of low-cost/efficient adsorbents or biochar (CP) derived from the carbonization of palm kernel cake (lignocellulosic residue) has been studied for the selective adsorption of various metal cations, such as Fe3+, Fe2+, Ca2+ and Zn2+, from aqueous solution. The CP surface was modified with KMnO4 (CPMn) and HNO3 (CPHNO3) in order to improve the adsorption efficiency. The physicochemical properties of the as-prepared adsorbents were investigated via BET, pHpzc, FT-IR, Boehm titration, TG-DTG, XRD and SEM-EDS techniques. The surfaces of all adsorbents clearly demonstrated negative charge (pHpzc > pH of the mixture solution), resulting in a high adsorption capacity for each metal cation. Fe2+ was found to be more easily adsorbed on modified CP than the other kinds of metal cations. Synergistic effects between the carboxylic groups and MnO2 on the surface of CPMn resulted in better performance for metal cation adsorption than was shown by CPHNO3. The maximum adsorption capacities for Fe3+, Fe2+, Ca2+ and Zn2+ using CPMn, which were obtained from a monolayer adsorption process via Langmuir isotherms (R 2 > 0.99), were 70.67, 68.60, 5.06 and 22.38 mg g-1, respectively. The adsorption behavior and monolayer-physisorption behavior, via a rapid adsorption process as well as single-step intra-particle diffusion, were also verified and supported using Dubinin-Radushkevich, Redlich-Peterson and Toth isotherms, a pseudo-second-order kinetic model and the Weber-Morris model. Moreover, the thermodynamic results indicated that the adsorption process of metal cations onto the CPMn surface was endothermic and spontaneous in nature. This research is expected to provide a green way for the production of low-cost/efficient adsorbents and to help gain an understanding of the adsorption behavior/process for the selective removal of metal ions from wastewater pollution.

An Effective Heterogeneous Catalyst of [BMIM]3 PMo12 O40 for Selective Sugar Epimerization.

The development of heterogeneous catalysts for the epimerization of sugars has received much less attention than that for the isomerization of sugars. To date, molybdates are the most effective catalysts for the epimerization of sugars, although they lack stability toward hydrolysis of their active sites in water. To solve the issue of the formation of a highly water-soluble heteropolyblue (PMored ) for phosphomolybdates (PMos) in aqueous reaction systems, herein, a 1-butyl-3-methylimidazolium phosphomolybdate ([BMIM]3 PMo12 O40 ) was synthesized through an ion-exchange method. This catalyst was effective and selective for the C2-epimerization of sugars under mild reaction conditions (<100 °C; 1-2 h) with good water-tolerant properties. The reaction was confirmed to occur in a heterogeneous manner and no leaching of PMored was detected by means of UV/Vis spectroscopy. Moreover, the catalyst can be simply separated by filtration and reused for at least eight cycles without a drop in catalytic activity. XRD, FTIR, and X-ray photoelectron spectroscopy measurements indicate that the catalyst is stable under the reaction conditions. In a comparison of the catalytic activity and surface wettability with those of other PMo salts, that is, 1-ethyl-3-methylimidazolium phosphomolybdate ([EMIM]3 PMo12 O40 ), 1-hexyl-3-methylimidazolium ([HexMIM]3 PMo12 O40 ), [choline]3 PMo12 O40 , and cetyltrimethylammonium phosphomolybdate ([CTA]3 PMo12 O40 ), it is found that [BMIM]3 PMo12 O40 has more appropriate hydrophobic-hydrophilic balance, which should be responsible for better catalytic activity and stability.

Preparing hydrophobic nanocellulose-silica film by a facile one-pot method.

Hydrophobic nanocellulose-silica film was successfully prepared by a facile one-pot method using tetraethoxysilane (TEOS) and dodecyl triethoxylsilane (DTES). Morphological characterization of the hydrophobic nanocellulose-silica (NC-SiO2-DTES) film showed well self-assembled DTES modified silica spherical nanoparticles with the particle sizes in the range of 88-126nm over the nanocellulose film. The hydrophobicity of the NC-SiO2-DTES film was achieved owing to the improvement of roughness of the nanocellulose film by coating dodecyl- terminated silica nanoparticles. An increase in DTES loading amount and reaction time increased the hydrophobicity of the film, and the optimum condition for NC-SiO2-DTES film preparation was achieved at DTES/TEOS molar ratio of 2.0 for 8h reaction time. Besides, the NC-SiO2-DTES film performed superoleophilic property with octane and hexadecane contact angles of 0°. It also showed an excellent hydrophobic property over all pH values ranged from 1 to 14.