Enhanced phosphate removal by nano-lanthanum hydroxide embedded silica aerogel composites: Superior performance and insights into specific adsorption mechanism

Removal of phosphate from wastewater is a global crucial goal and grand challenge for resource recovery and eutrophication control. However, it represents a major application bottleneck in the phosphate-selective sorption system to enhance the selectivity towards phosphate and the stability of adsorbents. In this study, nano-lanthanum hydroxide was embedded inside the porous silica aerogel (SA) to synthesize a novel aerogel composite (LSA) for highly efficient and selective phosphate removal. La(OH)3 is expected to offer the specific binding sites toward phosphate, while the porous SA host serves as a “shield” with a protective network structure and supplies abundant non-specific sites. LSA possessed enhanced phosphate uptake even when competing anions coexisted at higher levels. Furthermore, LSA exhibited pH-independency due to its high pHpzc. LSA also performed the characteristics of high adsorption capacity, La utilization efficiency, and reusability. Specifically, the maximum Langmuir adsorption capacity of LSA-1/10 reached up to 153.8 mg P/g at pH 6.0. The exhausted LSA-1/10 could be effectively regenerated after 8 adsorption–desorption cycles. The underlying mechanism for such satisfactory performances of LSAs was revealed by XRD, STEM-EDS and XPS analysis. The predominant pathway for selective phosphate removal was confirmed to be the inner-sphere complexation between P and La, intriguingly, the formation of LaPO4·xH2O was detected. Moreover, LSAs were proved to be stable and exhibit no potential adverse effects on the ecosystem or human health. Overall, results proved LSA to be a promising sorbent for efficient phosphate capture in complex water remediation with the core features of preference and selectivity.