Waste to wastewater treatment: Graphene quantum dots embedded poly(ethylene terephthalate) membranes for efficient phenol removal

Efficient waste management strategies are essential for addressing environmental degradation and advancing sustainable development. Utilizing waste materials in wastewater treatment presents a promising avenue toward this goal. This study investigates the use of waste carton paper and waste plastic bottles in composite membranes for treating wastewater containing phenol as a contaminant. It introduces a unique approach by utilizing waste carton paper as a bio-source for the synthesis of graphene quantum dots (GQDs) and incorporating them as nanofillers in polyethylene terephthalate (PET) membranes derived from recycled plastic bottles. Furthermore, this study addresses the performance and stability of GQDs-PET membranes for smaller dissolvable organics such as phenol in semi-pilot UF systems. An array of characterizations was performed to confirm the successful application of waste carton paper as a bio source for synthesizing GQDs and to study their effect on the PET membrane structure and properties. The pore size, porosity and wetting properties of the GQDs-PET membranes could be flexibly modulated by regulating the contents of the GQDs. The performance stability of fabricated membranes was evaluated using a continuous operating semi-pilot scale cross-flow ultrafiltration (UF) setup. The optimal GQDs-PET membrane showed a higher water flux (24 L/m 2 .hr.bar) than the pristine PET membrane (9.9 L/m 2 .hr.bar) and demonstrated enhanced removal performance for phenol, ∼ 94 %, under alkaline feed conditions (pH 9.5) for more than 4 h. The stable phenol removal performance of the GQDs-PET membrane for a longer time can be attributed to the electrostatic repulsions between the membrane surface and phenoxide ion at a higher pH induced by GQDs in the PET membrane structure. These results revealed that the as-prepared GQDs-PET composite membranes possessed great potential for actual wastewater advanced treatment and purification. Additionally, this work supports sustainable development and circular economy principles by repurposing waste plastic bottles and carton paper for efficient wastewater treatment applications. • Application of waste carton paper and plastic bottles for wastewater treatment. • Waste carton paper is a suitable biosource for synthesis of GQDs. • GQDs improved hydrophilicity and removal performance of PET membrane.