A crystalline organic hybrid thiogallate containing high content of amino groups for efficient Cr(VI) removal

Amino groups are effectual adsorption sites for removal of Cr(VI) from wastewater. Accordingly, adsorbents containing more amino groups are more likely to achieve high Cr(VI) adsorption capacities. Numerous crystalline organic hybrid metal sulfides possess high content of organic amines, implying their great potential for Cr(VI) adsorption. However, these compounds have never been employed as adsorbents to eliminate Cr(VI) from wastewater. Here we reported the first application of a crystalline organic hybrid thiogallate [enH₂][Ga₄S₇(en)₂] (EGS) for Cr(VI) adsorption. The structure of EGS features a two-dimensional [Ga₄S₇(en)₂]_n^2n– layer, where the unprotonated en molecules are anchored on the layer. In addition, abundant biprotonated [enH₂]²⁺ molecules are resided in the interlayer. The high content of en results in a high N content of 12.20 % in EGS. Consequently, EGS exhibited outstanding Cr(VI) adsorption capacity of 442.2 mg·g⁻¹ at 298 K, 560.3 mg·g⁻¹ at 308 K, and 675.0 mg·g⁻¹ at 318 K, much higher than that of most organic–inorganic hybrid composites. Dynamics and thermodynamics studies were performed to reveal the Cr(VI) adsorptive behavior of EGS. Our study shows that crystalline organic hybrid metal sulfides are promising adsorbents for Cr(VI) elimination.