Advanced Dye Sorbents from Combined Stereolithography 3D Printing and Alkali Activation of Pharmaceutical Glass Waste

Upcycling waste derived glass into high-performance photocatalytic scaffolds by alkali activation and direct ink writing

Novel and eco-friendly solutions are extensively needed for wastewater treatment. This work capitalizes on the combination of waste vitrification and additive manufacturing to produce an efficient photocatalyst for the specific purpose. Fine powders of waste-derived glass, containing Fe3O4 inclusions, by simple suspension (for a solid loading of 65 wt %) in alkaline solution (5 M NaOH), were transformed into pastes for direct ink writing. 3D-printed reticulated scaffolds were stabilized by the progressive hardening of a zeolite-like gel, formed by glass/solution interaction, at nearly room temperature. The printed scaffolds were successfully tested for the removal of methylene blue, realized by combining the high sorption capacity of the gel with the catalytic activity of magnetite inclusions, under UV light. A complete degradation of methylene blue is achieved by 90 min exposure, comparing favorably with other reported photocatalytic materials, requiring from 60 to 360 min. The photocatalytic activity was tested for several cycles, with no significant degradation. In other words, a waste-derived material can be reused for multiple times, to remediate wastewaters, with evident benefits on waste minimization.

Utilization of Foamed Glass as an Effective Adsorbent for Methylene Blue: Insights into Physicochemical Properties and Theoretical Treatment

This study reports a potential approach for the valorization of glass waste (GW) that is mainly composed of amorphous silica to prepare lightweight foamed glass (FG). The preparation of FG was achieved by mixing sodium hydroxide with GW powder followed by sintering at a temperature of 800 °C. As-synthesized FG was characterized and applied as an effective adsorbent for the removal of hazardous organic water contaminants, in particular, methylene blue (MB) dye. FG exhibited porosity of 91%, bulk density of 0.65 g/cm³, compressive strength of 4 MPa, and thermal conductivity of 0.27 W/m·K. Theoretical treatment indicated that a monolayer model with one energy site was the best in fitting the removal of MB molecules. The number of MB molecules per active site (n) ranged from 2.20 to 1.70, suggesting vertical orientation and a multi-molecular adsorption mechanism. The density of FG receptor sites (D_M) increased with the temperature, and this parameter played a vital role in the adsorption process. The adsorption capacity (Q_sat) increased from 255.11 to 305.58 mg/g, which signifies endothermic interactions. MB adsorption on FG was controlled by physical forces such as electrostatic interactions (i.e., the adsorption energies were <20 kJ/mol). The results of this study prove the feasibility of glass waste as an effective and low-cost adsorbent for water remediation.