Abstract: This study demonstrated the impacts of the synthesis methods on the textural structures, chemical properties, and Hg⁰ capture capability of the MnO_x system. Compared with the samples synthesized using the precipitation (PR) and hydrothermal (HT) methods, the adsorbent prepared via the sol-gel (SG) technique gave the best performance. At 150 °C, ca. 90% Hg⁰ removal efficiency was reached after 7.5 h for MnO_x prepared by the SG method, ca. 40% higher than that of the other two methods. The specific surface area of the adsorbent synthesized via the SG technique (23 m²/g) was almost double that of the adsorbent prepared by the HT method (12 m²/g) and three times that of the one prepared by the PR method (7 m²/g). The presence of plentiful acid sites from the SG method facilitated the physisorption of Hg⁰, making more Hg⁰ available to be oxidized to HgO by the redox sites and thus giving the adsorbent prepared by the SG method the highest Hg⁰ removal efficiency. The strong oxidative ability accelerated the oxidation of the physically adsorbed Hg⁰ to HgO, which explained the higher Hg⁰ removal efficiency of the sample prepared using the HT method than that of the one synthesized by the PR technique. During the whole Hg⁰ removal cycles, chemisorption dominated, with the initial adsorption stage and the external mass-transfer process playing important roles.

Key words: Synthesis methods; Hg⁰ capture; MnO_x; Acidity; Oxidative ability

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