Adsorptive performance of sunflower seed ash as a novel biosorbent for the elimination of Congo red from aqueous solution

This study investigated the adsorption of an azo dye called Congo red from aqueous solution. Ash prepared from sunflower seed waste was used as the adsorbent. Brunauer–Emmett–Teller (BET), Scanning electron microscopy (SEM), and Fourier-Transform Infrared spectroscopy (FT-IR) analyses were performed to characterize the prepared adsorbent. Based on the results of BET, the specific active surface area was about 102 m2/g, and the results of SEM indicated that the adsorbent surface had a very fine porosity that could be attributed to the presence of cellulosic materials in the adsorbent structure. In this study, the effect of the initial concentration of Congo red dye (10-50 mg/L), the concentration of adsorbent (1-5 g/L), and the processing time (10-240 min) on the rate of Congo red dye removal was investigated. The results showed that the highest percentage of dye removal, i.e., 92%, was achieved at a dye concentration of 50 mg/L, an adsorbent concentration of 3 g/L, and a processing time of 180 min. Under these conditions, the amount of adsorbed dye per gram of the adsorbent was 15.5 mg/g. In addition, pseudo-first order and pseudo-second order kinetic models were also used for modeling. The modeling results indicated that the pseudo-second order model had a higher level of accuracy. Finally, washing adsorbent with different solvents (one molar sodium hydroxide, double distilled water, and ethanol) was investigated, the results indicated that the adsorbent washed with one molar sodium hydroxide had a proper performance after five times of reuse.