Functional impacts of carbon-based nanomaterials in the performance of heterostructure photocatalysts for the remediation of pharmaceutical pollutants in wastewater- A review

The toxicity, persistence, and recalcitrance of pharmaceutically active compounds (PhACs) in wastewater to conventional treatment methods are attributable to their chemical stability, low biodegradability, and structural complexity. However, studies have identified photocatalytic treatment in advanced oxidation processes (AOPs) as a panacea for these targeted pollutants. The review evaluates the unique dimensions of carbon-based nanomaterials (CBNMs) coupled with metals, metal oxides and metal-organic frameworks to form heterostructure photocatalysts. It assessed their functional role in the hybrid photocatalysts. The findings revealed that CBNMs act as electron sinks to capture photogenerated excitons (e - -h + ). This is due to their π−conjugation and lower bandgap properties, which significantly improve the redox processes during photocatalytic degradation of pollutants in wastewater. Also, the study revealed that various structural dimensions of CBNMs coupled with semiconductors act as electron mediators, inducing accelerated charge transfer and a unique shift of absorption edge to higher wavelength for rapid visible photon absorption. The study specifically presents 2D reduced graphene oxide and 1D carbon nanotubes (CNTs) with bandgap narrowing potentials, structural stability and superior electron delocalization among other CBNMs applied in heterostructure development. Also, the use of a heteroatom doping strategy refines the electronic structure of CBNMs, which creates the premise for prolonged photoinduced carrier lifetime. In addition, a desired charge carrier mechanism of Z-Scheme and the recent S-scheme was accomplished with the formed heterostructure, with photodegradation performance of over 95%. This presents a suitable pathway for advanced treatment techniques for the recalcitrant pharmaceutical pollutants in wastewater. • Photocatalytic degradation of persistent pharmaceutically active compounds • Carbon-based nanomaterials (CBNMs) in heterostructure fabrication • Development of heterojunctions with CBNMs and photocatalytic materials • Photocatalytic efficiency of heterostructure photocatalysts