Facile synthesis of vaterite CaCO₃ microspheres from carbon capture and solid waste utilization towards microwave absorption and dye wastewater adsorption

Mineralization of CO₂ to minerals like calcium carbonate (CaCO₃) has been considered as an effective approach to combat global warming. In this paper, Ca²⁺ ions were firstly extracted from waste carbide slag, and then facilely transformed to vaterite CaCO₃ via disperse bubbling carbonization method assisted with an air stone. By optimizing the reaction conditions, highly mono-dispersed vaterite CaCO₃ microspheres (VCMs) were obtained. These microspheres consisted of aggregated CaCO₃ nanocrystals, bearing a mesoporous structure. As a proof-of-concept, these mesoporous microspheres were utilized for dye adsorption and electromagnetic (EM) microwave absorption. For the former, the VCMs were used to adsorb Congo red, yielding a fast adsorption time of 9 min and a high adsorption capacity of 138.77 mg/g. For the latter, EM microwave dielectric parameters were measured, and dye-adsorbed VCMs exhibited better microwave-absorption performance with a minimum reflection loss of −43.2 dB, about 3 times of pristine vaterite. To the best of our knowledge, this is the first report of solid-waste-derived VCMs as microwave absorbent and dye adsorbent. Considering the low-cost, eco-friendly and facile preparation and effective utilization of VCMs, our work provides a promising strategy for large-scale carbon capture, solid waste utilization, and treatment of microwave and wastewater pollution.