Microfludically-generated lanthanum hydroxide cross-linked chitosan microspheres for phosphate removal

doi:10.11949/0438-1157.20220501

Abstract

Abstract:

Lanthanum hydroxide [La(OH)₃] cross-linked chitosan (CS) microspheres (La-CS-M) were prepared based on microfluidic technology. The compositions and structures of La-CS-M were characterized by various means. The performance and mechanism of its adsorption and removal of phosphate in water were explored. The results showed that La(OH)₃ was successfully loaded within La-CS-M. Compared with the cross-linked chitosan spheres (La-CS) prepared by traditional dropping method, the surface and interior of La-CS-M were porous with an volumetric mean particle size of 415.8 μm, porosity of 89.22%, average pore size of 960.0 nm, and pH_pzc of about 6.5. La-CS-M maintained a high adsorption capacity in a wide pH range from 3.0 to 10.0, and the presence of $C O 3 2 -$ had a more negative effect on phosphate adsorption compared to Cl^-, $N O 3 -$ , $S O 4 2 -$ and humic acid (HA). The adsorption kinetic data and isotherm results were well fitted with pseudo-second-order model and Langmuir model, achieving a maximum adsorption capacity of 56.48 mg/g at pH 6.0. Combined with XPS characterization and adsorption data, it could be deducted that the adsorption mechanism of La-CS-M involved electrostatic adsorption and formation of inner sphere complex (through coordination exchange or Lewis acid-base interaction). After phosphate adsorption, La-CS-M could be desorbed by 2.5 mol/L NaOH solution, exhibiting good reproducibility and adsorption stability.

Key words: lanthanum hydroxide, chitosan microspheres, microfluidic, preparation, adsorption, wastewater

摘要：

基于微流控技术制备了氢氧化镧[La(OH)₃]交联壳聚糖（CS）微球（La-CS-M），并对其组成和结构进行表征，探究了微球吸附去除水中磷酸盐的性能和机理。结果表明，La-CS-M成功负载了La（OH）₃，与传统滴落法制备的氢氧化镧交联壳聚糖球（La-CS）相比，其表面和内部具有疏松多孔结构，其体积平均粒径为415.8 μm，孔隙率为89.22%，平均孔径为960.0 nm，pH_pzc约为6.5。La-CS-M在宽pH范围内（3.0~10.0）均保持较高吸附量， $C O 3 2 -$ 对La-CS-M吸附性能影响较Cl^-、 $N O 3 -$ 、 $S O 4 2 -$ 以及腐殖酸（HA）明显。吸附动力学数据符合准二级动力学模型，等温吸附数据符合Langmuir模型且在pH=6.0时最大吸附量为56.48 mg/g。结合XPS表征和吸附数据推测La-CS-M的吸附机理涉及静电吸附和形成内层配合物（通过配位交换或Lewis酸碱作用）。吸附磷酸盐后La-CS-M可通过2.5 mol/L NaOH溶液实现脱附，具有良好的再生性和吸附稳定性。

关键词: 氢氧化镧, 壳聚糖微球, 微流控, 制备, 吸附, 废水

CLC Number:

X 703

Chengwei LI, Huayong LUO, Mingxuan ZHANG, Peng LIAO, Qian FANG, Hongwei RONG, Jingyin WANG. Microfludically-generated lanthanum hydroxide cross-linked chitosan microspheres for phosphate removal[J]. CIESC Journal, 2022, 73(9): 3929-3939.

李承威, 骆华勇, 张铭轩, 廖鹏, 方茜, 荣宏伟, 王竞茵. 氢氧化镧交联壳聚糖微球的微流控制备及其除磷性能[J]. 化工学报, 2022, 73(9): 3929-3939.

Figures/Tables 12

Fig.1 Schematic diagram of microfludically-generated lanthanum hydroxide cross-linked chitosan microspheres

Fig.2 Digital image of freeze-dried La-CS-M (a), SEM images of La-CS-M before (b) and after (c) phosphate adsorption, optical image of La-CS-M (d), digital (e) and SEM (f) images of freeze-dried La-CS

Fig.3 XRD pattern of La-CS-M (a), FTIR spectra of CS and La-CS-M before and after phosphate adsorption (b), particle size distribution of La-CS-M (c) and the pH at point of zero charge (pHpzc) of La-CS-M (d)

Table 1 The pore characteristics and La loading capacities of chitosan microspheres

吸附剂	孔隙度/%	平均孔径/nm	La负载量/%(质量)
La-CS-M	89.22	960.0	36.26
La-CS	87.86	473.9	37.99

Fig.4 Effect of pH on phosphate adsorption onto La-CS (a), effect of pH on phosphate adsorption onto La-CS-M (b), and species of phosphate in different pH (c)

Fig.5 Effects of co-existing ions (a) and humic acid (HA) (b) on phosphate adsorption

Fig.6 Fitting curves of kinetic models (a) and intraparticle diffusion model (b) for phosphate adsorption onto La-CS-M,and adsorption isotherms (c)

Table 2 Kinetic and isotherm modeling parameters for phosphate adsorption onto La-CS-M

模型	参数	数值
准一级动力学模型	q_e/(mg/g)	50.95
	k₁/min^-1	6.75×10^-3
	R²	0.923
准二级动力学模型	q_e/(mg/g)	57.43
	k₂/(g/(mg·min))	1.52×10^-4
	R²	0.969
颗粒内扩散模型	k_1d/(mg/(g·min^0.5))	1.89
	C₁	4.82
	R²	0.989
	k_2d/(mg/(g·min^0.5))	0.57
	C₂	33.97
	R²	0.918
Langmuir模型	q_max/(mg/g)	56.48
	k_L/(L/mg)	0.40
	R²	0.980
Freundlich模型	k_F/(mg/g)(L/mg)^1/ⁿ	23.15
	n	4.11
	R²	0.962

Table 3 Comparison of maximum phosphate adsorption capacity （qmax） based on Langmuir model between La-CS-Mand other La-loaded adsorbents

吸附剂	磷酸盐浓度/(mg/L)	pH	温度/℃	q_max/(mg/g)	文献
La-CS-M	5~50	6.0±0.1	25	56.48	本研究
包埋滑石粉的海藻酸镧凝胶	2.5~50.0	4	25	16.034	[5]
水合氧化镧改性的硅藻土	10~100	5.60	25	58.70	[25]
氢氧化镧改性介孔稻壳生物炭	5~100	6.6	25	41.22~45.62	[24]
MgFe₂O₄-生物炭基海藻酸镧珠	5~50	5.3±0.3	25±1	27.68	[29]
包埋氢氧化镧的聚乙烯醇/海藻酸铝凝胶球	0~50	4.0	25	7.86	[10]
掺杂氢氧化镧的活性炭纤维	10~70	—	室温	15.3	[26]

Fig.7 The regenerability (a) and adsorption stability (b) of La-CS-M

Fig.8 XPS full spectrum of La-CS-M before and after phosphate adsorption (a), and the high resolution spectra of O 1s (b),La 3d (c) and P 2p (d)

Fig.9 Adsorption mechanisms of phosphate adsorption onLa-CS-M in different pH conditions

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