Recyclable printed circuit boards and alkali reduction wastewater: approach to a sustainable copper-based metal-organic framework

Printed circuit board (PCB) waste contains a high concentration of copper (Cu) leftover from the processing. Another, alkali reduction (AR) wastewater, is considerably produced with a main component of 1,4-benzenedicarboxylic acid (H₂BDC) in textile manufacturing. For the sake of environmental sustainability, it is of great significance to recover useful waste sources for reforming into valuable materials. Herein, in this study, for the first time, we report a facile pathway to produce a Cu-based metal-organic framework (CuBDC) in a quantitative yield of 75.45% synthesized by completely using the leaching solutions of PCB and AR wastewater as precursors instead of commercial chemicals. Under a simple stirring condition at room temperature, the as-obtained CuBDC from the wastewater exhibits typical laminar shapes of pure CuBDC crystals. In addition, the wastewater derived CuBDC products were examined with crystalline phase purity, porosity, coordination chemistry, and functional groups. Notably, these characteristics accord well with the concept of high-purity CuBDC. Moreover, the optimal conditions for CuBDC fabrication from PCB and AR wastewater were designed. Lastly, CuBDC from the recycled sources showed high adsorption capacity (5.75 cm³·g^-1) and ideal selectivity (10.85) toward CO₂ for CO₂/CH₄, which is unexpectedly outperforming the pure CuBDC. Also in terms of materials cost, the economic feasibility was evaluated. Overall, this work offers a green synthesis pathway for the preparation of sustainable CuBDC by using PCB and AR wastewater.