Three-dimensional bandgap-tuned Ag2S quantum dots/reduced graphene oxide composites with enhanced adsorption and photocatalysis under visible light

Abstract

The pursuit of photodegrading environmental pollutants while efficiently utilizing solar energy remains a pivotal endeavor. Herein, Ag₂S quantum dots (QDs)/reduced graphene oxide (rGO) composites with Ag₂S QDs dispersed on porous stereoscopic rGO-based network were synthesized through a facile hydrothermal process without the addition of any other reducing agent or cross-linker. The as-obtained composites exhibited enhanced adsorption and photocatalysis performance under visible light because of the individual and synergistic effects. The hierarchically stereoscopic structure led to outstanding adsorption ability due to large specific surface area and spongy nature, which facilitated connection between the contaminants and the photocatalytic sites. The incorporation of rGO also suppressed the recombination of electron–hole pairs in the semiconductor and favored the separation from wastewater. Ag₂S QDs, whose properties were influenced by quantum size effect, displayed a widened bandgap of 1.82 eV rather than initial 0.92 eV, attributing to stronger redox potential to degrade organic pollutants while efficiently absorbing the visible portion of solar light. With methyl orange as the model pollutant, the comprehensively optimized sample obtained at 150 °C exhibited adsorption capacity of 260 mg g⁻¹ at 25 °C and photodegradation rate 7.8 times that of commercial TiO₂ nanoparticles under visible light. Phenol was also analyzed to remove the influence of photosensitization of dyes. Our investigation gives a new insight into the design and fabrication of narrow band semiconductor/rGO composites with enhanced adsorption and photocatalysis.