Spatially isolated silver in graphitic carbon nitride matrix by Ag-supramolecular mixture pyrolysis for promoting 4-nitrophenol reduction

The wastewater treatment of 4-nitrophenol (4-NP) is necessary due to its harmful effects on the environment and human. In this study, two low-cost and efficient catalysts were synthesized via ammonium hydroxide-treated Agsupramolecular as precursor followed by pyrolysis. The structure and morphology of Ag@MCN-x catalysts with different Ag content were confirmed by FT-IR, XRD, SEM, TEM, XPS and N-2 adsorption-desorption isotherms. Benefiting from the well-dispersed Ag NPs with 3.36 nm diameters and efficient electronic transfer between Ag and MCN, the porous pinecone-like Ag@MCN-2 presented excellent catalytic activity toward reduction of 4-NP with 100 % conversion under very low Ag loading (0.69 wt%). The rate constant (kapp) of Ag@MCN-2 could reach 0.0315 min(-1). Significantly, the obtained catalyst possessed superior reusability and the conversion was maintained at nearly 100 % after six cycles. Meanwhile, the morphology and crystalline of Ag@MCN-2 after reuse, acquired by XRD, SEM and TEM, were remained well. Compared with other catalysts prepared by conventional step-by-step method, Ag@MCN-2 has distinguishing features, such as its excellent reusability, high dispersion of metal, small size of Ag nanoparticles, low-cost raw materials, and easy preparation. This work provides new insights into designing suitable catalyst for rapid conversion of 4-nitrophenol pollutant.