Selective adsorption of phosphate in water using lanthanum-based nanomaterials: A critical review

In recent years, lanthanum-based nanomaterials (La-NMs) are selected as an efficient nano-adsorbent for phosphate removal because La³⁺ has a strong affinity with oxygen-donor atoms from phosphate. Additionally, there are a broad interest and literature base for the effect of different synthesis optimization and environmental parameters on the adsorption performance of La-NMs. A considerable amount of research has also investigated the regeneration and application of La-NMs to real wastewater in a laboratory scale. Based on the literature survey, it was found that La-NMs are often produced via co-precipitation and hydrothermal methods. Moreover, phosphate's adsorption process and behavior onto La-NMs are described well with the pseudo-second-order model and Langmuir model. The interaction mechanism between phosphate and La-NMs are dominated by ligand exchange, surface complexation and electrostatic attraction. Furthermore, phosphate could easily desorb from La-NMs due to the weak H-bonding interaction between phosphate and the H-bond acceptor groups on the surface of La-NMs. Despite the wealth of literature available in this area, there is a lack of systematic review to evaluate the gaps in the use of La-NMs to eliminate phosphate in water. In this review, we mainly summarize and discuss the role and the effect of the synthesis techniques on the physicochemical properties and the adsorption behavior of La-NMs. The possible adsorption mechanism, regeneration efficiency, and the application of La-NMs to the real environmental samples are also presented and highlighted.