**Author details**

Dilek Duranoğlu\* and Ulker Beker

\*Address all correspondence to: dduran@yildiz.edu.tr

Chemical Engineering Department, Yıldız Technical University, Istanbul, Turkey

### **References**

:30 mg/L)

and Cr2p3/2 orbitals, there are two separate

**Figure 10.** XPS spectrum(Cr 2p1/2 and Cr 2p3/2 orbitals) of Cr(VI) exhausted activated carbon (at pH 2 and *C*<sup>i</sup>

bands for both orbitals (Figure 10). Significant bands appeared at binding energies of 577.0– 578.0 eV for Cr2p3*/*2 and at binding energies of 586.0–588.0 eV for Cr2p1*/*2 orbital. They correspond to trivalent chromium. CrO3 was characterized by higher binding energies; 580.0– 580.5 eV and 589.0–590.0 eV, since the hexavalent form draws electrons more strongly than

XPS showed that 86% of adsorbed chromium is in Cr(III) form. In other words, some of Cr(VI) adsorbed directly while a significant amount of Cr(VI) adsorbed to the surface after reducing the trivalent form during the adsorption process. Although original carbon surface is not suitable to adsorb cations, carbon surface is oxidized as a result of reduction reaction, and oxidized carbon surface is more attractive for Cr(III) cations than the former situation. Nevertheless, a little amount of Cr(III) was released into the aqueous phase due to electrostatic

Adsorption of Cr(VI) onto activated carbon derived from different biomass waste materials, have been reviewed and the factors that influenced the Cr(VI) adsorption were discussed by using both literature and experimental data. Peach stone, one of the biomass waste materials, was used as an activated carbon precursor. Prepared activated carbons showed high Cr(VI) adsorption capacity. Cr(VI) adsorption was strongly pH-dependent and superior at low pH. Freundlich model well expressed Cr(VI) adsorption. Adsorption kinetics followed the pseudo

repulsion between the positively charged groups and Cr(III) ions at pH 2.

second-order kinetic model which consists of chemisorption.

According to the XPS results corresponding Cr2p1*/*<sup>2</sup>

the trivalent form [51].

298 Desalination Updates

**4. Conclusion**


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