Molecular modelling of a biochar–ZnO–CuO nano-biofertilizer: adsorption simulation for optimized nutrient delivery

Abstract

Amid growing concerns regarding the safety, efficacy, and environmental impact of conventional fertilizers, nanotechnology-based alternatives—particularly nano-biofertilizers—have emerged as promising solutions. In this study, we optimized a conceptualized biochar (CBC) structure (with formula: C₆₀H₃₉NO₁₃ and molar mass: 981.97 g mol⁻¹), building on both our ongoing research and existing literature. Molecular dynamics (MD) simulations were employed to investigate biochar adsorption interactions with zinc oxide (ZnO) and copper oxide (CuO) nanonutrients (NNs), as single and co-adsorbates. Quantitative computational analysis revealed that the CBC molecule exhibits structural stability, with a heat of formation of −226.45 kcal mol⁻¹, a total energy of −12,586.15 eV, and an ionization potential of 8.37 eV. Additional evaluations—including COSMO sigma profiling, UV-Vis spectral analysis, and frontier molecular orbital (HOMO–LUMO) mapping—gave deeper insight into CBC molecular properties. Distinct spatial separation of these orbitals across different functional groups underscores biochar's chemical stability, despite a small HOMO–LUMO energy gap (ΔE_gap = 0.058106 eV). Adsorption simulations demonstrated energetically favorable interactions between both NNs and CBC, with a higher affinity for CuO over ZnO (average rigid adsorption energy: −17.64 vs. −14.15 eV). The average structural deformation energy associated with ZnO compared to CuO in the adsorption process (−687.68 eV vs. −6.38 eV) shows different mechanisms or sites of adsorption, respectively. In the co-presence of both nanonutrients, energy parameters were modulated, indicating a positive synergy. These findings offer foundational insights into the molecular properties and thermodynamic behavior of biochar in nanonutrient adsorption. However, recognizing that real world factors such as soil cation exchange capacity, pH, microbiome, and humidity also influence these adsorption interactions, the study discusses their potential effects and recommends the need for further research to bridge theoretical models with empirical data, optimize nanoformulations, assess ecological impacts, and evaluate the economic viability of biochar-based nanofertilizers for sustainable agricultural applications.