Comparative study on the urea removal by different nanoporous materials

Ultrahigh and kinetic-favorable adsorption for recycling urea using corncob-derived porous biochar

Insufficient attention has been given to the recycling of excess urea despite its potential detrimental effects on soil nutrient equilibrium, geological structure, and crop health. In this study, corncob-derived porous biochar (CPB), which is rich in surface functional groups, was prepared from biomass corncob in two steps as an adsorbent to remove urea from wastewater. Compared with the typical carbonization and activation processes, this process resulted in a higher yield of CPB and an ultrahigh adsorption capacity for urea. Response surface analysis was utilized to determine the optimal carbonization conditions, which were found to be 500 °C for 6 h with a heating rate of 15 °C/min. The exceptional adsorption capability of CPB can be ascribed to its porous structure and significant presence of oxygen-containing functional groups, which facilitate a synergistic interaction of physisorption and chemisorption. This adsorption phenomenon aligns with the Harkins-Jura isotherm model and adheres to pseudo-second order kinetics. CPB demonstrates potential as an adsorbent for the elimination of urea from wastewater in an economical and effective fashion.

In silico screening of nanoporous materials for urea removal in hemodialysis applications

The design of miniaturized hemodialysis devices, such as wearable artificial kidneys, requires regeneration of the dialysate stream to remove uremic toxins from water. Adsorption has the potential to capture such molecules, but conventional adsorbents have low urea/water selectivity. In this work, we performed a comprehensive computational study of 560 porous crystalline adsorbents comprising mainly covalent organic frameworks (COFs), as well as some siliceous zeolites, metal organic frameworks (MOFs) and graphitic materials. An initial screening using Widom insertion method assessed the excess chemical potential at infinite dilution for water and urea at 310 K, providing information on the strength and selectivity of urea adsorption. From such analysis it was observed that urea adsorption and urea/water selectivity increased strongly with fluorine content in COFs, while other compositional or structural parameters did not correlate with material performance. Two COFs, namely COF-F6 and Tf-DHzDPr were explored further through Molecular Dynamics simulations. The results agree with those of the Widom method and allow to identify the urea binding sites, the contribution of electrostatic and van der Waals interactions, and the position of preferential urea-urea and urea-framework interactions. This study paves the way for a well-informed experimental campaign and accelerates the development of novel sorbents for urea removal, ultimately advancing on the path to achieve wearable artificial kidneys.

Poly(β-cyclodextrin)-Activated Carbon Gel Composites for Removal of Pesticides from Water

Pesticides are widely used in agriculture to increase and protect crop production. A substantial percentage of the active substances applied is retained in the soil or flows into water courses, constituting a very relevant environmental problem. There are several methods for the removal of pesticides from soils and water; however, their efficiency is still a challenge. An alternative to current methods relies on the use of effective adsorbents in removing pesticides which are, simultaneously, capable of releasing pesticides into the soil when needed. This reduces costs related to their application and waste treatments and, thus, overall environmental costs. In this paper, we describe the synthesis and preparation of activated carbon-containing poly(β-cyclodextrin) composites. The composites were characterized by different techniques and their ability to absorb pesticides was assessed by using two active substances: cymoxanil and imidacloprid. Composites with 5 and 10 wt% of activated carbon showed very good stability, high removal efficiencies (>75%) and pesticide sorption capacity up to ca. 50 mg g-1. The effect of additives (NaCl and urea) was also evaluated. The composites were able to release around 30% of the initial sorbed amount of pesticide without losing the capacity to keep the maximum removal efficiency in sorption/desorption cycles.