Simultaneous removal of metal ions and methyl orange by combined selective adsorption and photocatalysis

Abstract

The technology of the selective biosorption and photocatalysis were coupled to synthesize a double functional Chitosan-TiO₂ adsorbent (CTA). CTA can not only degrade organic pollutants but also adsorb metal ions simultaneously. It was interesting that the photocatalysis of CTA for methyl orange (MO) was promoted when MO was coexisted with metal ions. In the presence of Ni²⁺, the degradation ratio of MO gradually increased from 78.9 to 94.2% with the increasing of Ni²⁺ concentration from 50 to 150 mg L⁻¹; furthermore with the presence of Ag⁺, the degradation ratio for MO increased from 65.9 to 79.3%. At the same time the existence of MO had no obvious effect on the adsorption ability for metal ions. CTA can be reused more than 10 batches without losing its adsorption and degradation ability. XPS showed the binding energy of Ni²⁺ increased with Ni²⁺ initial concentration growing in a particular range. Higher binding energy of Ni will result in stronger OH• formation, so it has a positive influence on the photocatalysis of CTA. Scanning electron microscope (SEM) revealed that silver nanoparticles were found on the surface of CTA and in the solution of MO and Ag⁺, and the silver nanoparticles had promoter action on the degradation for MO. The results showed that the technology of biosorption and photocatalysis were synergistic when they were applied to the system of binary pollutants containing metal ions and MO. © 2010 American Institute of Chemical Engineers Environ Prog, 2010