Efficient Removal of Co(2+) from Aqueous Solution by 3-Aminopropyltriethoxysilane Functionalized Montmorillonite with Enhanced Adsorption Capacity

To achieve a satisfactory removal efficiency of heavy metal ions from wastewater, silane-functionalized montmorillonite with abundant ligand-binding sites (-NH(2)) was synthesized as an efficient adsorbent. Ca-montmorillonite (Ca-Mt) was functionalized with 3-aminopropyl triethoxysilane (APTES) to obtain the APTES-Mt products (APTES(1.0CEC)-Mt, APTES(2.0CEC)-Mt, APTES(3.0CEC)-Mt, APTES(4.0CEC)-Mt) with enhanced adsorption capacity for Co(2+). The physico-chemical properties of the synthesized adsorbents were characterized by spectroscopic and microscopic methods, and the results demonstrated that APTES was successfully intercalated into the gallery of Ca-Mt or grafted onto the surface of Ca-Mt through Si-O bonds. The effect of solution pH, ionic strength, temperature, initial concentrations and contact time on adsorption of Co(2+) by APTES-Mt was evaluated. The results indicated that adsorption of Co(2+) onto Ca-Mt, APTES(1.0CEC)-Mt and APTES(2.0CEC)-Mt can be considered to be a pseudo-second-order process. In contrast, adsorption of Co(2+) onto APTES(3.0CEC)-Mt and APTES(4.0CEC)-Mt fitted well with the pseudo-first-order kinetics. The adsorption isotherms were described by the Langmuir model, and the maximum adsorption capacities of APTES(1.0CEC)-Mt, APTES(2.0CEC)-Mt, APTES(3.0CEC)-Mt and APTES(4.0CEC)-Mt were 25.1, 33.8, 61.6, and 61.9 mg·g(-1), respectively. In addition, reaction temperature had no impact on the adsorption capacity, while both the pH and ionic strength significantly affected the adsorption process. A synergistic effect of ion exchange and coordination interactions on adsorption was observed, thereby leading to a significant enhancement of Co(2+) adsorption by the composites. Thus, APTES-Mt could be a cost-effective and environmental-friendly adsorbent, with potential for treating Co(2+)-rich wastewater.