Experimental research data

Description

Experimental data on adsorption of urea by modified biochar

Steps to reproduce

Adsorption trials, encompassing kinetic, isothermal, and thermodynamic studies, were performed in batch mode using 100 mL Erlenmeyer flasks. Each flask contained a mixture of 0.020 g of the solid adsorbent and 40.0 mL of aqueous urea solution, which was agitated on an orbital shaker set to 150 rpm. For the kinetic evaluations, the experiments were carried out at 25℃ with an initial urea concentration (C0) of 100 mg L-1, and samples were collected at regular intervals between 2 and 360 min. The equilibrium adsorption isotherms were established by varying the initial urea concentration from 25 to 600 mg L-1 at 25℃, with a contact time of 4 h to guarantee saturation. Thermodynamic behaviors were investigated at three different temperatures (15, 25, and 35℃) using a fixed C0 of 100 mg L-1. The concentration of unadsorbed urea in the aqueous phase was determined utilizing the p-DMAB colorimetric assay (Zhang et al., 2026). The mathematical determination of the equilibrium adsorption capacity (Qe) is detailed in Equation (1) of Text S1 (Section 1) in the Supplementary Material. Furthermore, the comprehensive formulations for the kinetic models (pseudo-first-order, pseudo-second-order, and intraparticle diffusion; see Eqs. S1–S3, Text S1 Section 1), isotherm models (Langmuir and Freundlich; see Eqs. S4–S5, Text S1 Section 2) (Li et al., 2022), and thermodynamic calculations (see Eqs. S6–S9, Text S1 Section 3) (Huangfu et al., 2023) are explicitly provided in the Supplementary Material. The nutrient release dynamics were simulated employing a custom PVC column setup (50 cm height, 2.6 cm internal diameter) filled with 60–80 mesh quartz sand, adapted from a previous methodology with slight adjustments (Askarizadeh et al., 2023). In this configuration, the specific sample (either unmodified urea or the biochar-based slow-release fertilizer) was embedded between a 20 cm basal layer and a 5 cm upper layer of quartz sand. The dynamic leaching process was initiated by introducing 70 mL of deionized water into the column at 12-hour intervals until the urea was fully depleted. The nitrogen content in the collected leachate was spectrophotometrically measured following the p-DMAB protocol outlined in Section 2.6. To better comprehend the controlled-release mechanisms, the cumulative release profiles were mathematically simulated using four distinct empirical models: Weibull (Askarizadeh et al., 2023), Double-exponential (Jin et al., 2017), Logistic (Usta & Incecayir, 2022), and Zero-order platform (Danielak et al., 2025). The explicit mathematical expressions governing these four release models are documented in Equations (2) through (5) of Text S1 (Section 6) in the Supplementary Material.

Institutions

• Anhui Agricultural University

  Anhui, Hefei

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