Development and characterization of silver modified novel graphitic-carbon nitride (Ag-ZnO/C3N4) coupled with metal oxide photocatalysts for accelerated degradation of dye-based emerging pollutants

Industrial wastewater undesirably affects aquatic life and the environment. One of the main sources of aquatic pollution is organic dyes, which are discharged into the mainstream water without any treatment. Therefore, organic dyes and their derivatives must be degraded by heterogeneous photocatalysts before discharge into wastewater. In this study, we synthesized three different photocatalysts using a low-cost material, i.e., melamine (as a ground material). The photocatalysts, pristine graphitic-carbon nitride (g-C3N4), coupled with zinc oxide (ZnO/C3N4), and modified with a silver (Ag-ZnO/C3N4), were synthesized by the calcination of melamine, following a hydrothermal process. The novel synthesized photocatalysts were characterized by different electro-analytical techniques such as X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Fourier Transform Infra-red (FT-IR), and Thermogravimetric analysis (TGA). The XRD results reveal the crystalline nature of the synthesized photocatalysts, which increases further with silver modification. TEM analysis discloses that the average particle sizes of ZnO and Ag NPs were 3–5 nm and 20–22 nm, respectively. Where the g-C3N4 displays a 2-D sheet-like structure. The photocatalysts were deeply investigated to study the degradation of organic dyes under UV light for Bromophenol Blue (BBP) and Methylene Blue (MB). Effects of different parameters such as contact time, Dye dose, photocatalyst dose, and pH were also investigated. In all three photocatalysts, Ag-ZnO/C3N4 was the most effective, showing high degradation for both dyes; BPB showed 99.2 percent degradation, whereas in MB the maximum degradation was 97.3 percent. The maximum degradation observed in the pH study was different for both dyes, BPB shows high degradation at pH-1 with 96.8 percent degradation, whereas in MB the maximum degradation is observed at pH-14 with 99.3 percent. The kinetics of the dyes BPB and MB, which follow pseudo-first-order kinetics, were also calculated. In short, the results revealed that the novel g-C3N4 photocatalysts were extremely active in the degradation of target organic dyes, which encourages more work on the degradation of these pollutants from wastewater.