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

Abstract

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 electrostatic 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·xH2O crystallite.