# A Comparative Study on ZrO2- and MgO-Based Sulfonic Acid Materials for the Reactive Adsorption of o-Xylene

## TL;DR

This study compares two sulfonic acid materials for removing o-xylene, a harmful VOC, showing that their performance depends on how the acid groups are attached to the support.

## Contribution

The paper reveals how the anchoring mechanism of sulfonic acid groups on ZrO2 and MgO affects their reactivity for o-xylene removal.

## Key findings

- SZO, with covalently bonded sulfonic acid groups, achieved ≥91.3% removal efficiency for o-xylene.
- SMO's ion-paired sulfonic acid groups did not participate in the sulfonation reaction with o-xylene.
- SZO showed a high adsorption capacity of 38.59 to 82.07 mg/g for o-xylene at 130–150 °C.

## Abstract

The recovery and abatement of volatile organic compounds (VOCs) have received increasing attention due to their significant environmental and health impacts. Supported sulfonic acid materials have shown great potential in converting aromatic VOCs into their non-volatile derivatives through reactive adsorption. However, the anchoring state of sulfonic acid groups, which is closely related to the properties of the support, greatly affects their performance. In this study, two supported sulfonic acid materials, SZO and SMO, were prepared by treating ZrO2 and MgO with chlorosulfonic acid, respectively, to investigate the influence of the support properties on the anchoring state of sulfonic acid groups and their reactive adsorption performance for o-xylene. The supports, adsorbents, and adsorption products were extensively characterized, and the reactivity of SZO and SMO towards o-xylene was systematically compared. The results showed that sulfonic acid groups are anchored on the ZrO2 surface through covalent bonding, forming positively charged sulfonic acid sites ([O1.5Zr-O]δ−-SO3Hδ+) with a loading of 3.6 mmol/g. As a result, SZO exhibited excellent removal efficiency (≥91.3%) and high breakthrough adsorption capacity (ranging from 38.59 to 82.07 mg/g) for o-xylene in the temperature range of 130 –150 °C. In contrast, sulfonic acid groups are anchored on the MgO surface via ion-paired bonding, leading to the formation of negatively charged sulfonic acid sites ([O0.5Mg]+:OSO3H−), which prevents their participation in the electrophilic sulfonation reaction with o-xylene molecules. This work provides new insights into tuning and enhancing the performance of supported sulfonic acid materials for the resource-oriented treatment of aromatic VOCs.