Synthesis and application of natural asphalt sulfonic acid (NA-SO3H) as a novel and reusable carbonaceous super adsorbent for rapid decolorization of aqueous dye solutions

Abstract

This research involves functionalizing solid natural asphalt through sulfonation in the presence of H2SO4. The resulting product, known as mildly sulfonated natural asphalt sulfonic acid (ms-NA-SO3H), was investigated and confirmed by SEM, DRS, EDX, BET, CHNOS, and FT-IR analyses. The FT-IR spectrum of ms-NA-SO3H displays distinctive absorption peaks related to the presence of asymmetric and symmetric stretching modes of SO2, which are associated with SO vibrations. These findings confirm the successful sulfonation of natural asphalt. The SEM images illustrated that the surface of natural asphalt appears relatively smooth, with minimal porosity except for occasional cracks. Conversely, the external surface of the ms-NA-SO3H adsorbent exhibits irregular pores, compared to natural asphalt. In the next step, the porous heterogeneous bituminous has been used for the decolorization of methylene blue, and methyl orange solutions. Variation of removal percent versus dye concentration showed functionalization surface groups of natural asphalt with SO3H groups have provided high activated sites for color removal from the aqueous environment. Various parameters such as solution pH, contact time, adsorbent dosage, and initial dye concentration, were examined. The results of surface adsorption analysis at different concentrations revealed that the adsorption behavior on the adsorbent could be accurately described by the Langmuir isotherm and the pseudo-second-order kinetic model. The rapid removal and high adsorption capacity of the modified asphalt indicate its efficiency in the surface adsorption processes. The reusability of the ms-NA-SO3H adsorbent was studied via a physical adsorption mechanism, using ethanol or dimethyl formamide. Obtained results showed the prepared modified asphalt is a simple, efficient, cost-effective, and environmentally friendly candidate for different pollution removal.