Simultaneous removal of methylene blue, copper Cu(II), and cadmium Cd(II) from synthetic wastewater using fennel-based adsorbents

Abstract This work looked into viability of using fennel-based adsorbents to simultaneously eliminate cadmium, methylene blue, and copper from water solution. Phosphoric acid (H3PO4) and calcium hydroxide (Ca(OH)2) solutions were applied to the untreated fennel seeds (PFS) to yield H3FS and CaFS, respectively. The presence of –OH, –C–O–C–, and –C=O functional groups on the surface of the adsorbents was confirmed by FTIR results. XRD and UV–Vis results established hydrolysis of cellulose from fennel seeds. According to studies on time and kinetics, the adsorption process was relatively quick in the first 60 min. Furthermore, isotherm models showed that the results fit Langmuir model more closely. This finding indicated that uptake takes place on uniform active sites on adsorbent surfaces. Studies on thermodynamics showed that the adsorption procedure was advantageous and practicable. PFS, H3FS, and CaFS had maximum Cu(II) adsorption capacities of 7.208, 5.504, and 5.791 mg/g. It was 2.274, 5.021, and 12.3 mg/g for Cd(II) by PFS, H3FS, and CaFS. PFS, H3FS, and CaFS could adsorb MB to a maximum of 11.114, 4.071, and 18.468 mg/g. Reusability studies of the adsorbents were also evaluated and the results suggested that the adsorbents can be recycled a number of times.