We hope the reviewer understand the experimental deficiencies at the stage of the present experiments. We deeply appreciate the comment raised by the reviewer. Thank you very much. However, we regret that we were not able to investigate the XPS analysis due to pandemic situation, which could definitely give us additional information about the elemental confirmation.
First of all, authors have to attach a EDX mapping images before/after sorption of chromium ions. And the authors are strongly recommended to add XPS spectra to this section of revised manuscript. The XPS method is much more sensitive and more accurately determines changes in the chemical composition of samples.