In the work "the multi-mechanisms and interlayer configurations of metoprolol uptake on montmorillonite", published in Chemical Engineering Journal, montmorillonite are used as an adsorbent for the uptake of metoprolol under various experimental conditions. The results are interesting but the authors has made a mistake when assessing the speciation of metoprolol. This beta-blocker is mostly neutral rather than zwitterionic for pH values up to pK(a1). This mistake may induce confusion and false conclusions for the readers of Chemical Engineering Journal unfamiliar with such organic contaminants, especially when assessing the impact of pH on the adsorption mechanisms of metoprolol onto clay minerals.