Sustainable synthesis of a novel hydrothermally carbonized AuNPs-hydrochar nanocomposite for the photocatalytic degradation of cephalexin

Designing a simple, green, and, sustainable route to fabricate highly efficient photocatalysts is an important approach to promote the further development of the field of photocatalysis. So in the current study, an ecofriendly procedure for preparing a novel heterogeneous catalyst of gold hydrochar nanocomposite (AuNPs-hydrochar) using a common biological waste material of Typha domingensis old shoots is reported for the first time. Some interesting properties of AuNPs-hydrochar were revealed after being characterized such as the small particle size (35-65 nm) determined by scanning electron microscope (SEM), and surface plasmon resonance peaks (540 and 665 nm) detected by ultraviolet-visible spectroscopy (UV-VIS). The observed thermal stability by thermal gravimetric analysis (TGA) enabled AuNPs-hydrochar to be easily and efficiently applied as a photocatalytic material. Additionally, other techniques including Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and x-ray photoelectron spectroscopy (XPS) were used to fully characterize AuNPs-hydrochar. AuNPs-hydrochar composites with different ratios of AuNPs were prepared and tested in the current study. The photocatalytic degradation of cephalexin (CPL) using AuNPs-hydrochar resulted in almost 99% degradation under UV light using the optimum reaction conditions with an efficiency of 77% after five times of recycling. However, there was no observed efficiency at all under visible light. The high stability, recyclability, and applicability over a wide pH range of AuNPs-hydrochar were confirmed in this work.