2022-08-30
Professor Wang Yili and his research group from the College of Environmental Science and Engineering has made new progress in the field of lanthanum matrix composite adsorption for phosphorus removal, and the research paper entitled "Tuning the lanthanum hydrolysis induced assembly process using long linear chains with –N+(CH3)3 groups for efficient phosphate removal" were published in the Top Journal of Chemical Engineering (Q1, IF = 16.744). The first author of the paper is Li Xiaolin, a doctoral student from the College of Environmental Science and Engineering and the signature unit of the first author is Beijing Forestry University. The main information of this paper is as follows:
Excessive phosphorus emissions have been recognized as a global problem which causes serious threats to human health and the sustainability of aquatic ecosystems due to water quality degradation and biodiversity loss. In recent years, lanthanide composites have been widely studied for their specific interactions with phosphorus (ortho-P) which makes them promising candidates for P adsorbents when combined with high-surface-charge matrix materials. The paper 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.
The paper has demonstrated a satisfactory adsorption ability of CCH@La for P removal. Through functional charge group design, CCH@La with an ideal La(OH)3 dispersion showed a remarkable P adsorption affinity because of its abundant La–O binding sites and electrostatic interactions. The zeta potential of CCH@La was 26.71 mV at pH 7.0, and the adsorption capacity reached 92.54 mg P/g with the molar P/La ratios of 1.41. The adsorption process was pH-dependent but a relative high adsorption amount (>72 mg P/g) could be realized in a wide pH range of 3.0–9.0. Besides, good selectivity for P was confirmed in the presence of co-existing substances (Cl?, NO3?, SO42?, HCO3? and HA). After five regeneration cycles, approximately 20 % loss of adsorption capacities implied the reusability of CCH@La. The high density of long linear chains with –N+(CH3)3 groups in CCH@La could prompt La unit transport from high-nuclearity clusters to low-nuclearity clusters, thereby decreasing the LJ potential of the particle pairwise interaction and improving the dispersion of La(OH)3. The good dispersion of La(OH)3 nanoparticles in the hydrogel exposed more La–O sites to P, leading to an ideal adsorption efficiency. The adsorption mechanism analysis unveiled that the superior adsorption efficiency was strongly attributed to the synergy effect of the enhanced La–P inner-sphere complexation produced by ideal dispersion of La(OH)3 clusters and the electrostatic attraction exerted by the cationic groups. After adsorption, the main adsorbed P species in CCH@La were inner-sphere complex on the surface of La(OH)3 particles and LaPO4·xH2O crystallite. This study provides new insights into the coordinated regulation of charge distribution and La(OH)3 dispersion in P adsorbent design and it also demonstrates the potential application of CCH@La in dephosphorization for water treatment.
This work was supported by the National Key Research and Development Program of China (No. 2017YFC0505303), the National Natural Science Foundation of China (Nos. 51978054 and 52170122) and Beijing Municipal Education Commission through the Innovative Transdisciplinary Program “Ecological Restoration Engineering” (No. GJJXK210102).
Paper link: https://doi.org/10.1016/j.cej.2022.138713.
