Determining roles of in-situ measured surface potentials of phase controlled synthesized MnO2 nanostructures for superficial adsorption

Adsorption is one of options for environmental remediation. Current works focused on designing nanostructures, and ex-situ measured specific area and zeta potential were main descriptors for the adsorption performance, leaving the materials’ intrinsic features irrelevant to adsorption. Herein, to investigate the adsorption performance and adsorbent inherent characteristics, an in-situ measurement of zeta potential was presented by taking MnO2 adsorbing methylene blue (MB) as an example. The performance was randomly related between ex-situ measured specific areas and zeta potentials of MnO2, but the in-situ measured MnO2 zeta potentials in 10 and 100 mg·L−1 MB solutions both showed nonlinear hyperbolic relationship with the performance, confirming the significant role of in-situ zeta potentials. Furthermore, adsorption enhancement in low pH conditions was observed, for Mn(IV) oxidability promoted by acidic solutions, where MB redox was oxidized to the positively charged oxidized form, facilitating adsorption onto negatively charged MnO2. The adsorption performance of MnO2 with considerably low specific area was comparable to reported nanostructured metal oxide adsorbents, showing the importance of surface zeta potentials and oxidability. An insight into the adsorption affecting factors within the inherent features of adsorbents was presented through in-situ measured zeta potentials and pH dependent adsorption.