Polymer-based heterojunction photocatalysts for environmental remediation and solar fuels: a review on interface...

Polymer-based heterojunction photocatalysis is a rapidly emerging paradigm in sustainable chemical engineering. It has appeared as a potential platform for tackling the concurrent global problems of environmental remediation and solar fuel production. These composite architectures overcome the inherent limitations of conventional photocatalysts, such as high carrier recombination rates, limited visible-light absorption, and poor catalyst reusability. This review aims to critically and comprehensively cover the basic photophysical and interfacial mechanisms that underpin polymer-based systems. We systematically monitor the entire photocatalytic cycle from the initial chromophore excitation and exciton generation on the polymer to state-of-the-art charge separation at donor-acceptor networks and Z-scheme heterojunction interfaces. Advanced synthesis and surface engineering techniques, such as chemical polymerization, nanostructuring, and green scalable synthesis pathways, are of particular interest, along with the strategic tuning of the Highest Occupied Molecular Orbital (HOMO) and Lowest Unoccupied Molecular Orbital (LUMO) boundary potentials in π-conjugated and metal-free frameworks to maximize the solar spectral utilization. In addition, critical chemical engineering applications involving the degradation of organic pollutants in the presence of sunlight, purification of ambient air, evolution of H₂ with the help of solar energy, and CO₂ reduction with the help of sunlight are presented in terms of structure-property-performance relationships of these emerging architectures. Finally, we summarize the current technical challenges for large-scale implementation and provide strategic analysis on the limitations of mass transport, operational stability in long periods, and scalable engineering design rules for future applications in environmental and energy fields at industrial scale.