Porous walnut-like LaOCO derived from metal-organic frameworks for arsenate removal: A study of kinetics, isotherms, and mechanism.

Exploration of renewable materials for efficient elimination of arsenic from water is highly imperative. Herein, one kind of novel porous walnut-like LaOCO composite is reported for the first time, fabricated via direct pyrolysis of La-MOFs at 550 °C under the air atmosphere. The as-synthesized material predominantly consists of LaOCO, featuring micrometer-scale walnut-like morphology and an abundant mesoporous structure. Adsorption experiments demonstrated that a pseudo-second-order model with a high correlation coefficient (0.9976-0.9988) can depict this adsorption process in a good manner and indicates chemical adsorption. Analysis of the isotherms further revealed that this adsorption is a monolayer and homogeneous process, with an excellent adsorption capacity (210.1 As mg/g), as calculated from the Langmuir model. Thermodynamic parameters indicated this adsorption process to be a spontaneous and endothermic, with a positive change in entropy. By characterization results, it can be deduced that the anion-exchange interaction (i.e. carbonate is prone to being replaced by arsenate) and inner-sphere complexation were both responsible for arsenate removal. A broad working pH range (3.0-9.0) and a good cyclic performance (removal rate is above 90% for the fourth cycle) as well as an excellent adsorption capacity make this adsorbent a promising arsenic scavenger.