Enhanced adsorption of phosphate by flower-like mesoporous silica spheres loaded with lanthanum

• Flower-like mesoporous silica loaded with La was used for P adsorption.
• It showed a maximum adsorption capacity of 44.8 mg P/g at 25 °C.
• Its adsorption was pH-dependent and little affected by competitive ions.
• It exhibited superior La utilization efficiency compared to literature.

Monodispersed flower-like mesoporous silica spheres doped with lanthanum were synthesized via a facile method and explored as novel adsorbents for efficient phosphate adsorption for the first time. The synthesized adsorbents possessed a flower-like structure, especially with unique mesoporous channels featuring with small inner pores and wide outer pores. By raising lanthanum loading, the surface areas and pore volumes of resulting adsorbents were observed to continuously decrease, accompanied with gradually increasing pore sizes; that led to a dramatic improvement in phosphate adsorption from water. By taking cost effectiveness for practical application into consideration, the adsorbent with a theoretical La/Si molar ratio of 0.1 possessed a promising performance as compared to the literature ever reported, thanks to the large outer mesopores likely minimizing the diffusion problem caused by the pore blocking when LaPO4 nanorods formed during adsorption. In the kinetic study, its phosphate adsorption followed the pseudo-second-order equation better, suggesting chemisorption. Meanwhile, superior phosphate adsorption capacities were achieved within the pH range of 3.0 and 6.0; and almost unaffected by the presence of F−, Cl−, NO3−, and SO42−SO42−.

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