Abstract An advanced model is applied to analytically explore the adsorption mechanism of Indigotine blue dye (IBD) onto a CoFe2O4/chitosan magnetic composite (CoFe2O4/CMC). Contrary to the classical adsorption models, the model is defined starting from the statistical physics theory and it is a generalized model containing numerous parameters having a defined physical meaning. Experimental evidences based on equilibrium data at four temperatures (298−328 K) are analyzed for a useful analytical interpretation. The analysis of the data via the advanced model indicates that the number of IBD linked per CoFe2O4/CMC active site (n) varied from 3.65 to 3.83, also demonstrating that the orientation (adsorption geometry) of the IBD dye on CoFe2O4/CMC surface is angled and affected by the temperature. Based on these values, it can be deduced that the adsorption mechanism at all the investigated temperatures is a multi-molecular process. It is also demonstrated that an increment in the temperature leads to a positive evolution of the adsorption capacity (Qsat) from 224.81 mg/g at T = 298 K to 289.87 mg/g at T = 328 K, testifying that the adsorption process is overall endothermic. This theoretical evidence is corroborated by the estimation of the adsorption energies ( Δ E 1 a and Δ E 2 a ), which indicated that physical interactions between IBD molecules and the CoFe2O4/CMC receptor sites and among IBD-IBD molecules take place. Finally, three thermodynamic parameters are determined for a further insight into the interpretation of the adsorption mechanism. The adsorption configurational entropy (Sad) evolution allows confirming the occurrence of different adsorbed layers (NC = 1+N2), while the Gibbs adsorption free energy (Gad) confirmed that the process is spontaneous.

中文翻译：

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CoFe2O4/壳聚糖磁性复合材料吸附靛蓝染料的理论分析模型

摘要 应用先进的模型来分析探索靛蓝染料 (IBD) 在 CoFe2O4/壳聚糖磁性复合材料 (CoFe2O4/CMC) 上的吸附机制。与经典吸附模型相反，该模型是从统计物理理论出发定义的，它是一个广义模型，包含许多具有定义物理意义的参数。分析了基于四个温度 (298-328 K) 下的平衡数据的实验证据，以获得有用的分析解释。通过高级模型对数据的分析表明，每个 CoFe2O4/CMC 活性位点 (n) 连接的 IBD 数量从 3.65 到 3.83 不等，这也表明 IBD 染料在 CoFe2O4/CMC 表面上的取向（吸附几何）角度和温度的影响。基于这些值，可以推断出在所有研究温度下的吸附机制是一个多分子过程。还表明，温度升高导致吸附容量（Qsat）从 T = 298 K 时的 224.81 mg/g 增加到 T = 328 K 时的 289.87 mg/g，证明吸附过程是整体的吸热的。吸附能（ΔE 1 a 和Δ E 2 a ）的估计证实了这一理论证据，这表明IBD分子与CoFe2O4/CMC受体位点之间以及IBD-IBD分子之间发生了物理相互作用。最后，确定了三个热力学参数，以进一步了解吸附机制的解释。