Adsorption mechanism of Cr(VI) onto GO/PAMAMs composites

Han Liu,Fan Zhang,Zhiyuan Peng

doi:10.1038/s41598-019-40344-9

Abstract

Graphene oxide/polyamidoamine dendrimers (GO/PAMAMs) composites were used to remove Cr(VI) from simulated effluents, the adsorption kinetics and thermodynamics of Cr(VI) onto GO/PAMAMs were systematically investigated. The results showed that the optimum pH value was 2.5, the removal percentage reached 90.7% for 30 mg/L of Cr(VI) within 120 min. The adsorption process was well described by pseudo-second-order kinetic model. The maximum adsorption capacities of Cr(VI) onto GO/PAMAMs were found to be 131.58, 183.82 and 211.42 mg/g at 293.15, 303.15 and 313.15 K, respectively, which were calculated from the Langmuir model equation. The adsorption thermodynamic parameters indicate that the adsorption of Cr(VI) onto GO/PAMAMs is a spontaneous endothermic process. The XPS analysis reveals the adsorption and removal mechanism of Cr(VI) on GO/PAMAMs that first the Cr(VI) binds to the protonated amine of GO/PAMAMs, then Cr(VI) be reduced to Cr(III) with the assistance of π-electrons on the carbocyclic six-membered ring of GO in GO/PAMAMs, and then Cr(III) was released into solution under the electrostatic repulsion between the Cr(III) and the protonated amine groups.

Highlights

Chromium is widely used in the industries of leather-tanning[1], mining, textile dyeing, manufacturing processes of anti-corrosion agents and pigments[2], which means that it’s unavoidable to generate large amounts of chromium-containing wastewater
Hou Wang et al.30. fabricated a novel ternary magnetic composites consisted of reduced graphene oxide, polypyrrole (Ppy) and Fe3O4 nanoparticles (Ppy-Fe3O4), the Ppy-Fe3O4/rGO nanohybrid exhibited excellent adsorption performance for Cr(VI), the maximum adsorption capacity for Cr(VI) onto Ppy-Fe3O4/rGO reached 293.3 mg/g, which was much higher than that of Fe3O4/rGO, the adsorption mechanism was through both electrostatic attraction and ion exchange, XPS analysis revealed that Cr(VI) was reduced to low poisonous Cr(III) by nitrogen species of Ppy
It was found that the Graphene oxide (GO)/PAMAMs had relatively fluffy and foam-like structures, which certainly provide good platform for heavy metal adsorption

Summary

Results and Discussion

When the initial Cr(VI) concentration reached 180 mg/L, the adsorption capacity is almost no increasing, which means the adsorption reached saturation This could be interpreted that when the concentration of Cr(VI) is lower than 180 mg/L, there are adequate amine groups and adsorption sites on the surface of GO/PAMAMs for removing of Cr(VI). The adsorption equilibrium data on PAMAMs/GO were fitted with the Langmuir and Freundlich isotherm models at 293.15, 303.15 and 313.15 K and listed in Fig. 6 and Table 2. The R2 value of Langmuir isotherm is closer to

This work

Conclusions

Additional Information