Needle-like Mg-La bimetal oxide nanocomposites derived from periclase and lanthanum for cost-effective phosphate and fluoride removal: Characterization, performance and mechanism

Phosphate and fluoride are primary culprits of water eutrophication and skeleton fluorosis, respectively, severely threatening the security of aquatic lives and public health. To deal with the aqueous phosphate and fluoride pollution, PC@La nanocomposites were tailor-designed based on low-cost periclase and lanthanum salt via a facile urea hydrothermal method. Results from SEM, XRD, FTIR, XPS analysis revealed the PC@La-1.0 was constructed by Mg-La bimetal carbonated hydroxides with the three-dimensional needle-like nanostructure. Highly effective adsorption capacities for both phosphate (107.34 mg/g) and fluoride (63.11 mg/g) were achieved by PC@La-1.0. The adsorption was pH-dependent, and the optimal pH values for adsorption was 4.0-6.0. Over 80% of initial adsorption capacities remained after four adsorption-desorption cycles, indicating its satisfactory reusability. Superior adsorption selectivity for phosphate and fluoride was proven when co-existing with common ions and organics in solutions and real sewage. Mechanism analysis revealed that the unique structure of Mg-La bimetal carbonate hydroxide structure of PC@La-1.0 promoted an accumulative anion adsorption performance. Mg and La cations on PC@La-1.0 formed strong inner-sphere complexation with target phosphate and fluoride while the internal carbonate and hydroxyl groups contributed to adsorption via ion exchange. This study highlights the novel low-cost method to prepare promising candidates for efficient dephosphorization and defluorination from water.