尿素改性核桃壳多孔碳的制备及其对碘的去除

Urea-modified walnut shell porous carbon and its removal of iodine

摘要:

以农业废弃物核桃壳为碳基体，通过尿素辅助氢氧化钾活化法制备了一种高碘捕获性能的多孔炭材料（WS-Urea）。该材料具有超高的比表面积（3395.97 cm2/g）和微孔体积（1.39 cm3/g），在气态碘捕获实验中，WS-Urea对碘6 h的捕获量可达3161 mg/g 。经过制备条件的优化，在m(核桃壳):m(KOH):m(尿素)=1:1.5:3、活化温度为900 ℃的条件下制备的多孔炭，其对碘的捕获量达到最大值，为6248 mg/g。气态碘捕获后的多孔炭表征结果表明，多孔炭中的微孔结构对碘的物理吸附起主导作用，而以羟基为主的化学吸附则起次要作用，这导致部分被捕获的碘发生了电荷转移 ，以聚阴离子的形式存在。 在环己烷的碘吸附实验中，,0.4 g/L的多孔炭对100 mg/L的碘溶液在90min内的去除率达到86.62%，动力学和等温线模型拟合结果表明，吸附过程主要为物理吸附，且以单层吸附为主。热力学分析结果表明，吸附是放热且自发的过程。

Abstract:

A high-performance porous carbon material for iodine capture was prepared using agricultural waste walnut shells as a carbon matrix through urea-assisted potassium hydroxide activation. This porous carbon exhibits an ultra-high specific surface area (3395.97 cm2/g) and micropore volume (1.39 cm3/g). In gaseous iodine capture experiments, it can achieve an iodine uptake of 3161 mg/g within 6 hours. After optimizing the preparation conditions, including a preparation temperature of 900 ℃ and a mass ratio of walnut shell: potassium hydroxide: urea of 1:1.5:3, the maximum iodine capture capacity reached 6248 mg/g. Characterization of the porous carbon after gaseous iodine capture revealed that the microstructure predominantly facilitates physical adsorption of iodine, while chemical adsorption, mainly by hydroxyl groups, plays a secondary role. This results in partial charge transfer of captured iodine, leading to the formation of polyanions. In the iodine adsorption experiments conducted in a cyclohexane medium, porous carbon at a dosage of 0.4 g/L demonstrated an efficient removal rate of 86.62% for an initial iodine concentration of 100 mg/L over a period of 90 minutes. The kinetic and isotherm studies suggest that the mechanism of adsorption was predominantly physiosorption, consistent with monolayer formation on the adsorbent surface. Furthermore, thermodynamic analysis indicated that the adsorption process was exothermic and proceeded spontaneously.