Interactions of urea surfaces with water as relative humidity obtained from dynamic vapor sorption experiments, in situ single-particle Raman spectroscopy, and ab initio calculations

Authors: EISA, MOHAMED - Lehigh University; RAGAUSKAITE, DOVILE - Lehigh University; SHI, JINGMING - Lehigh University; SHIMIZU, SEISHI - University Of York; BUCKO, TOMAS - Lehigh University; Williams, Clinton; BALTRUSAITIS, JONAS - Lehigh University

Submitted to: ACS Earth and Space Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2023
Publication Date: 9/18/2023
Citation: Eisa, M., Ragauskaite, D., Shi, J., Shimizu, S., Bucko, T., Williams, C.F., Baltrusaitis, J. 2023. Interactions of urea surfaces with water as relative humidity obtained from dynamic vapor sorption experiments, in situ single-particle Raman spectroscopy, and ab initio calculations. ACS Earth and Space Chemistry. 7(10):2139-2153. https://doi.org/10.1021/acsearthspacechem.3c00210.
DOI: https://doi.org/10.1021/acsearthspacechem.3c00210

Interpretive Summary: Nitrogen fertilizer is needed to maintain optimal yield and food production. Applied nitrogen is also very labile and significant portions of applied nitrogen are not used by the crop and lost to the environment. Urea is a common nitrogen fertilizer. Wetting and dissolution of urea is the the first step to understanding transformation and eventual loss of applied nitrogen. Increased understanding of urea transformations is necessary to provide predictive models of urea transformation kinetics and loss. A study was conducted to measure the adsorption kinetics of water onto urea and the resulting structural changes that lead to eventual dissolution. Water sorption was shown to adhere to the Guggenheim-Anderson-de Boer model and sorption rates increased with increasing relative humidity. Results will be used to improve kinetic models of urea dissolution and transformations.

Technical Abstract: Urea is a critical nitrogen carrier molecule that is abundant in the environment due to the anthropogenic activity to enhance crop growth. Intrinsic link between its high solubility and volatilization to lose reactive nitrogen species and CO2, especially under excessive RH conditions suggest that urea hydrolysis initiated decomposition reaction can be affecting global nitrogen balance. A fundamental analysis of water as RH adsorption on urea particle surfaces was performed using a combination of Dynamic Vapor Sorption experiments, in situ single particle Raman spectroscopy and ab initio calculations. DVS data acquired exhibited three RH adsorption regimes with urea with 74% RH dramatically changing adsorbate-urea interactions from monolayer to multilayer induced deliquescence. Several empirical kinetic models were utilized to understand RH interaction with urea surfaces and Guggenheim-Anderson-de Boer model provided a good description of the adsorption at <60 % RH values while a Van Campen model was used to fit the data acquired during the urea crystal deliquescence. The experimental water sorption rate using Van Campen model showed a gradual rise from 0.02 mg/min at 80% to 0.08 mg/min at 95% in agreement with the Van Campen's model of increasing trend albeit at higher rates ranging from 0.03 mg/min at 80% to 0.1 mg/min at 95%. In situ Raman spectroscopy combined with optical images of a single particle showed that urea 1009 cm-1 peak FWHM can provide in depth information on the transient phenomena taking place on the urea particle surface as well as in partially liquefied environment. Finally, DFT results suggested Wulff reconstruction of single urea crystal be depended on the presence of the higher crystalline planes particular, the (111) facet became significant together with (101) and (110) while in the presence of bulk H2O (101) became the dominant facet.