Next-Generation Metal-Free Photocatalysts: Multifunctional Covalent Organic Polymer Nanostructures for Visible-Light-Driven Water Remediation and Efficient CO₂ Capture

Abstract

The rapid escalation of industrial effluents, greenhouse gas emissions, and energy demands necessitates the development of sustainable materials capable of addressing environmental pollution and carbon management simultaneously. Conventional metal-based photocatalysts, though effective under laboratory conditions, suffer from critical drawbacks such as photo-corrosion, high cost, toxicity, and limited visible-light absorption. To overcome these limitations, the present study introduces a new class of metal-free multifunctional photocatalysts based on covalent organic polymer (COP) nanostructures, designed for visible-light-driven water remediation and efficient CO₂ capture. The proposed nanostructures are synthesized through a controlled bottom-up polymerization route, integrating donor–acceptor (D–A) linkages within an extended π-conjugated framework to enhance light harvesting, exciton separation, and surface reactivity. Structural and spectroscopic analyses, including XRD, FTIR, BET, UV–Vis DRS, PL, and XPS, confirm the successful formation of highly porous, thermally stable, and photoactive COPs with a narrow bandgap in the visible spectrum. The optimized polymer exhibited exceptional photocatalytic performance in degrading organic pollutants such as methylene blue and tetracycline under simulated solar irradiation, achieving over 96% degradation efficiency within 60 minutes while maintaining stability over multiple cycles. Kinetic modeling revealed pseudo-first-order behavior governed by •OH and •O₂⁻ radical pathways, consistent with efficient charge migration and suppressed recombination. Simultaneously, the high surface area and nitrogen-rich framework of the COP enabled enhanced CO₂ uptake of 3.8 mmol g⁻¹ at 298 K, attributed to strong physisorption and tunable pore architecture. Mechanistic investigations demonstrate that the synergistic interaction between conjugated donor–acceptor segments facilitates long-range charge separation, improving both photocatalytic and adsorption capabilities. The multifunctional performance of the proposed COP photocatalyst outperforms many state-of-the-art metal-based systems, establishing its potential for sustainable wastewater treatment and carbon management under ambient conditions. Furthermore, the study provides a scalable and eco-friendly pathway for fabricating robust, recyclable, and low-cost photocatalysts without reliance on critical metals. Overall, this research highlights a next-generation approach to environmental nanotechnology, where metal-free covalent organic polymer nanostructures act as a unified platform for visible-light-induced pollutant degradation and selective CO₂ capture. The findings pave the way for integrating organic semiconductor design principles with green chemistry to develop advanced multifunctional materials for future photocatalytic, carbon sequestration, and energy conversion applications.