Preferential adsorption control: Ca-based LDO for regenerating used lubricating oil

Different Ca-based layered double oxides (LDO) were applied in the removal of contaminants in used lubricating oil as an alternative decolorant. CaAl-LDO and CaFeAl-LDO achieved much greater decoloration efficiency than the traditional decolorants, where 0.93 and 0.91 of the decoloration efficiency under the optimum conditions were obtained, respectively. The decoloration activity with CaFeAl-LDO ​> ​CaAl-LDO ​>> ​CaFe-LDO was revealed by both Density Functional Theory (DFT) calculations and experimental analysis. Ca12Al14O33 was shown to be the active component for decoloration. Fe3+ doped into CaAl-LDO could improve decoloration activity via a changed charge distribution of decolorant. High preferential adsorption activity, which originated from different charge distribution for contaminants instead of the oil components, contributed to outstanding decoloration performance. The activity depended on the adsorption intensity of contaminants, where the most of the active decolorant neither too strongly or weakly bound with the contaminants. The results of this study suggested the Ca based LDOs could be a potentially alternative decolorants for regenerating the used lubricating oil.