Optimization of methylene blue and povidone-iodine adsorption conditions on activated biochar from sunflower husk pyrolysis

anglais. Commercial activated carbons are mainly used in the adsorption process to remove pollutants from water and wastewater, however, due to their high costs, substitutes are currently being sought. Carbon materials obtained from activated biomass often show a high specific surface area (similar to that for activated carbons) due to a well-developed pore structure. In this study, activated biochar obtained from sunflower husks was tested for the adsorption of povidone-iodine (PVP-I) and methylene blue (MB). The biochar was prepared in the pyrolysis process (500°C) and chemically activated with K2 CO3 at a temperature of 800°C. The activation affected greatly the structural properties of the biochar – the specific surface area increased from 32.5 to 740.5 m2 /g, and the micropore and mesopore volume increased over 20 and 15 times, respectively. Also the iodine value changed from 89 to 495 mg/g. The physicochemical and granulometric properties as well as pH value of point of zero charge of the adsorbent surface were determined. The central composite design method was used to determine the optimal adsorption conditions (solution pH and adsorbent mass) in the initial concentration range 10–60 mg/dm3 for PVP-I and 30–250 mg/dm3 for MB. The maximum sorption capacity reaches 120 mg/g for MB and 5.6 mg/g for PVP-I. Sorption kinetics was investigated with use of several models. The times of half-saturation for these adsorbates are around 1 and 15 min, respectively. The detected Gibbs free energy change indicates the adsorption is spontaneous and thermodynamically favored. The adsorptive properties of the biochar obtained from waste sunflower husk are especially good for MB adsorption and acceptable with respect to PVP-I adsorption.

anglais. Adsorption; Sunflower husk; Pyrolysis; Chemical activation; Povidone-iodine; Methylene blue

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