Tuning the lanthanum hydrolysis induced assembly process using long linear chains with -N⁺(CH₃)₃ groups for efficient phosphate removal

XL Li and YL Wang and SX Dong and CY Liu and SY Wang and WF Liu, CHEMICAL ENGINEERING JOURNAL, 451, 138713 (2023).

DOI: 10.1016/j.cej.2022.138713

Lanthanum composites are known for their specific interactions with phosphorus (ortho-P), which when combined with high-surface-charge matrix materials, makes them promising candidates for P adsorbents. Here, we have described an attempt to achieve an ideal lanthanum hydrolysis-induced assembly in a cellulose hydrogel network by regulating the spatial distribution of -N+(CH3)(3) groups on the polymer chains, thereby improving the dispersion of La(OH)(3) clusters in the matrices. A P adsorption capacity of 92.54 mg/g with a molar P/La ratio of 1.41 was observed in a composite consisting of 37.58 % -N+(CH3)(3) in a hydrogel, namely, lanthanum loaded cellulose cationic hydrogel (CCH@La). CCH@La exhibited a wide applicable scope of pH ranging from 3.0 to 9.0 and a good selectivity in the presence of co-existing substances. After five regeneration cycles, the adsorption amount of regenerated CCH@La still remained at 80.74 % of its maximum value. The maximum La(OH)(3) usage efficiency of CCH@La with -N+(CH3)(3) grafted polymer chains was estimated to be 2.01 folds of that in the -COO- grafted lanthanum loaded cellulose anionic hydrogel (CAH@La), underlining the role of tuning the space charge distribution for metal hydroxide dispersion in hydrogel systems. This allows for the synergistic effect of elec-trostatic attraction and La-P coordination produced by the ideally dispersed La(OH)(3) clusters in the network of hydrogels, thereby facilitating P adsorption. After adsorption, the main adsorbed P species in CCH@La were inner-sphere complex on the surface of La(OH)3 particles as well as the LaPO4.xH(2)O crystallite.

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