Caffeine Adsorption on a Thermally Modified Bentonite: Adsorbent Characterization, Experimental Design, Equilibrium and Kinetics

Colloids and Interfaces Pub Date : 2024-04-15 DOI:10.3390/colloids8020026

J. A. Quintero-Jaramillo, Javier Ignacio Carrero, N. R. Sanabria-González

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Abstract

Caffeine is a chemical compound found in various products such as coffee, tea, and energy drinks; therefore, it is common in wastewater and surface water. The present study investigated caffeine adsorption on a thermally modified bentonite-type clay. The effects of the heat treatment of the adsorbent over the temperature range of 60–500 °C, as well as the initial pH of the solution, stirring speed, and contact time, on the removal of caffeine were analyzed. The adsorbent was characterized by XRF, XRD, FT–IR, thermal analysis (TGA–DSC), and N2 physisorption at 77 K. The response surface methodology (RSM) based on a central composite design (CCD) was used to evaluate and optimize the adsorption of caffeine in aqueous solution. The maximum adsorption capacity of caffeine obtained with the Langmuir model was 80.3 ± 2.1 mg/g (0.41 ± 0.01 mmol/g) at 25 °C under equilibrium conditions (initial pH = 8.0, stirring speed = 400 rpm, contact time = 120 min). A kinetic study showed that the pseudo-second-order and Elovich models adequately describe the adsorption process. Bentonite thermally modified at 400 °C can be considered a low-cost adsorbent with potential application for removing caffeine in aqueous media.

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咖啡因在热改性膨润土上的吸附：吸附剂特性、实验设计、平衡与动力学

咖啡因是一种存在于咖啡、茶和能量饮料等各种产品中的化合物，因此在废水和地表水中很常见。本研究调查了热改性膨润土型粘土对咖啡因的吸附情况。研究分析了在 60-500 °C 温度范围内对吸附剂进行热处理以及溶液初始 pH 值、搅拌速度和接触时间对咖啡因去除率的影响。采用基于中心复合设计（CCD）的响应面方法（RSM）对水溶液中咖啡因的吸附进行了评估和优化。在 25 °C 的平衡条件下（初始 pH = 8.0，搅拌速度 = 400 rpm，接触时间 = 120 分钟），利用 Langmuir 模型得到的咖啡因最大吸附容量为 80.3 ± 2.1 mg/g（0.41 ± 0.01 mmol/g）。动力学研究表明，伪二阶模型和埃洛维奇模型能充分描述吸附过程。在 400 °C 下进行热改性的膨润土可被视为一种低成本吸附剂，有望用于去除水介质中的咖啡因。

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Colloids and Interfaces

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