Abstract
The textural properties and surface chemistry of different activated carbons, prepared by the chemical activation of olive stones, have been investigated in order to gain insight on the NO2 adsorption mechanism. The parent chemical activated carbon was prepared by the impregnation of olive stones in phosphoric acid followed by thermal carbonization. Then, the textural properties and surface chemistry were modified by chemical treatments including nitric acid, sodium hydroxide and/or a thermal treatment at 900 °C. The main properties of the parent and modified activated carbons were analyzed by N2-adsorption, scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR) techniques, in order to enlighten the modifications issued from the chemical and thermal treatments. The NO2 adsorption capacities of the different activated carbons were measured in fixed bed experiments under 500 ppmv NO2 concentrations at room temperature. Temperature programmed desorption (TPD) was applied after adsorption tests in order to quantify the amount of the physisorbed and chemisorbed NO2. The obtained results showed that the development of microporosity, the presence of oxygen-free sites, and the presence of basic surface groups are key factors for the efficient adsorption of NO2.
Highlights
Nitrogen oxides (NOx ) are among the most pollutant gases and largely contribute to acid rain formation and the depletion of the ozone layer
The Temperature programmed desorption (TPD)-MS experiment carried out on sample A is carried out on sample A is characterized by the presence of CO2 emissions, which are attributed to characterized by the presence of CO emissions, which are attributed to the presence of acidic groups the presence of acidic groups such2 as carboxylic, lactone, and anhydride
2 on the different activated carbons was examined in a fixed bed reactor at ambient lignocellulosic biomass precursors
Summary
Nitrogen oxides (NOx ) are among the most pollutant gases and largely contribute to acid rain formation and the depletion of the ozone layer. Nowicki et al [19] studied the effect of the treatment with urea to modify the textural properties and the acid–base character of the activated carbon surfaces They showed that the choice of the activation and modification procedure of coniferous tree sawdust produces activated carbons with high nitrogen dioxide adsorption capacity (reaching 69 mg NO2 /g in wet conditions). The results showed that a wet oxidation treatment can increase the amount of surface oxygen groups on the carbon surface, resulting in the enhancement of NO adsorption These observations were confirmed by Bashkova et al [25] in the removal of NO2 by wood-based activated carbons modified with urea and thermally treated at 950 ◦ C. Such an approach permits the correlation of the adsorption performances and mechanisms (physisorption, chemisorption) to the different properties of the activated carbons
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