Volatile Organic Compounds Adsorption Capacities of Zeolite/Activated Carbon Composites Formed by Electrostatic Self-Assembly

DC Liang and FQ Yu and Q Xie and QP Chen and Y Liu and YH Zheng and KP Zhu and ZJ Zhang and J Liu and X Zhu and JC Liu and ZH Zhu, ACS APPLIED MATERIALS & INTERFACES, 15, 38781-38794 (2023).

DOI: 10.1021/acsami.3c06686

Activated carbon (AC) is a broad-spectrum adsorbent but is flammableand has low adsorption capacities for polar and/or high-boiling volatileorganic compounds (VOCs), while zeolites exhibit high thermal stabilitybut poor adsorption of macromolecular and nonpolar VOCs. In this study,zeolite/AC composites were synthesized with the aim of obtaining broad-spectrum,efficient, and safe adsorbents for VOCs. Dimethyldiallyl-ammoniumchloride (DDA)-modified AC was used as a carrier for an in situ hydrothermalreaction enabling assembly with zeolites due to electrostatic attraction.Interface models were constructed for their phases, which revealedthe binding force and simulated the binding process. The adsorptionand flame resistance of the composites were evaluated. The resultsshowed that DDA effectively modified AC to give it a long-lastingpositive charge in solutions. High-silicon and pure- silicon zeolitesexhibited low negative charges or were even neutral; it was difficultto combine with the modified AC via electrostatic attractions. Instead,LTA zeolites with high aluminum contents and negative charges wereused, and the seed-induction method was used. Ethanol and ultrasonicdispersion were used to prevent agglomeration of the seeds and modifiedAC powder, so they were self-assembled electrostatically. Moreover,the crystallization time was extended and composites with high zeoliteloadings were successfully prepared. According to the model calculation,the binding energy between the zeolite and AC before and after theDDA modification were 324.97 and 1076.46 kcal mol(-1), respectively, and the distance between them was shortened by 2.7 & ANGS; after DDA treatment. As a result, AC and zeolite combinedmore closely and exhibited a stronger binding energy. The adsorptioncapacity for highly polar dichloromethane was improved by zeoliteloading on the AC, and the bed penetration time was doubled. However,impregnation with inorganic sodium enhanced the reactivities of theorganic components in the composite, and the ignition point was slightlyreduced. Furthermore, the electrostatic self-assembly method can expandto prepare the LTA zeolite/columnar AC composite from shaped AC, greatlyimproving its application prospects.

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