[Analysis of XPS in the Removal of Cr(Ⅵ) from Groundwater with rGO-nZⅥ].

Iron nanoparticles are widely used in heavy metal ions removal from water, but because of the characteristics of easily aggregation and transference in the groundwater, remediation effect was reduced. GO with a negative charge containing oxygen-containing functional groups on the surfaces of graphene, are widely used for the removal of heavy metal ions from water, but it has little on remediating hexavalent chromium (Cr2O2-7, CrO2-4) with negatively charged electrons. Therefore, rGO-nZⅥ was synthesized via liquid phase reduction method to overcome the aggregation and transference of FeO, changing the negative charged Cr2O2-7 or CrO2-4 to positive charged Cr3+. The material behavior characteristics of Cr(Ⅵ) removal were discussed. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to test the prepared rGO-nZⅥ. Results indicated that nZⅥ was successfully loaded on the surface of GO, and the shape of the particles was approximate ball and the granular diameter ranged from 20 to 100 nm. Removal efficiency of Cr(Ⅵ) (40 mg·L-1) from water was nearly 100% within 24 h using rGO-nZⅥ. X-ray photoelectron spectroscopy (XPS) analyses using the XPSPEAK41 program indicated that FeO firstly reduced negatively charged Cr(Ⅵ) to positively charged Cr(Ⅲ) by providing electron, then the chromium in the solution can be removed as chromium hydroxide (Cr(OH)3) by a hydrolysis precipitation process. As the reaction progress, materials charges were changing, which benefited adsorpting Cr(Ⅵ). After 24 h reaction, the residual nZⅥ loading on rGO-nZⅥ remained, which showed the potential of sequentially remediating contamination. The results showed important theoretical value and practicability.