Massive Intercalation of Urea in Montmorillonite

Abstract

Urea intercalated in montmorillonite (MMT) leads to considerable improvement of N efficiency in soils; however, there are no systematic approaches to elucidate the properties of urea intercalates within the interlayer space of swelling clays. This study focused on both the optimization of massive urea intercalation into MMT and the systematic characterization of urea-intercalated MMT (UCM). Anhydrous metal salts, which could allow optimal urea intercalation, were used for the first time to synthesize metal-urea complexes in a solid state. Massive intercalation of metal-urea complex into MMT was performed by simply mixing dehydrated MMT with a molten metal-urea complex containing excess urea at 105 ± 5°C. Successful complexation was confirmed by both the unique infrared spectra absorbance bands and the thermal behaviors of the coordinated urea molecules. The intercalation of metal-urea complexes into MMT was clearly demonstrated by a significant expansion of d(||,| spacing from 1.52 to 1.74 nm in Ca-UCM. as revealed by x-ray diffraction patterns. Infrared spectra also revealed that the intercalation of urea in the interlayer led to a distinct red shift in stretching vibration energy of the structural hydroxyl group of MMT from 3446 to 3483 cm" and from 3360 to 3400 cm" . Experimental urea loading capacity was estimated to be 33.7% urea. All the intercalated urea molecules were found to be quickly and completely released by water molecules through ligand exchange, maintaining their effectiveness as a N source for crop cultivation.

Metal-Urea-Montmorillonite Hybrid Incorporated with Citric Acid

“…Recently, we developed a new type of N fertilizer (hereafter referred to as MUCH) intercalating massive urea in interlayer space of montmorillonite (MMT). It showed a high N efficiency through smart suppression of ammonia volatilization without any changes in its inheritable character, fast effectiveness (Kim et al, 2011a;Kim et al, 2011b). Furthermore, we confirmed that physicochemical properties of soils were not significantly affected by MUCH treatment in sandy loam and clay loam soils on column experiment (Kim et al, 2011c).…”

“…Incorporation of citric acid into MUCH was confirmed by the existence of COO -symmetric stretching vibration at 1401 cm -1 as shown (Marchewaka and Pieraszko, 2003). Its IR spectrum also exhibited the red shift of >C=O and NH2 vibration energy and the blue shift of -C-N vibration energy as MUCH did (Kim et al, 2011a;Kim et al, 2011b). These IR bands are originated from urea molecules such as CO, NH2 and CN vibration energy at 1685, 1632 and 1468 cm -1…”

“…Significant differences were stated where P<0.05. In this study, the effect of Cit-MUCH was merely compared to that of MUCH because the effect of MUCH on decrease of NH3 volatilization was well proved by previous study (Kim et al, 2011b;Kim et al, 2011c).…”

“…Preparation and characterization of MUCH and Cit-MUCH Preparation of Cit-MUCH was attempted by the method slightly modified from the previous one (Kim et al, 2011a;Kim et al, 2011b), shown in Fig. 1.…”

“…3). The basal spacing peaks of MUCH and Cit-MUCH were about 1.74 nm, meaning that massive intercalation of urea into MMT was successful in both synthesized materials because intercalation of the guest into MMT leads to expansion of the interlayer space by its longitudinal dimension (Brigatti et al, 2006;Kim et al, 2011b). It was supposed that a slight increase in the basal spacing and new peak at 24.12º 2θ result from a change in urea arrangement of the complex.…”