The contamination of water and the environment caused by industrial, agricultural, and pharmaceutical pollutants has become a relevant global concern due to the adverse effects on health and the environment. Several toxic contaminants have been listed as priority contaminants (including 4-nitrophenol, methylene blue, and rhodamine 6G) by the U. S. Environmental Protection Agency and the World Health Organization, making it necessary to remove the maximum allowable level in commercial products. This project aligns with frontier research, and basic science is aimed at using bagasse of coffee powder for manufacturing biocompatible ecological metal nanoparticles catalysts with high efficiency. Besides being ecological, the proposed technology is scalable, economically viable, and easy to implement to reduce health risks.

Figure 1. (a) TEM (scale bar_20 nm), (b-d) HR-TEM (scale bars_2-5 nm), (e) FFT, and (f) the EDS mapping of CG-Ag₂O/Au-SiO₂ (scale bars_25 nm) revealing the presence of (g) Oxygen (O (Kα1)), (h) Silicon (Si (Kα1)), (i) Silver (Ag (Lα1)), (j) Gold (Au (Lα1)), (k) Carbon (Kα1_2) and (l) Nitrogen (Kα1_2), and DFT first principal studies for the catalytic systems Ag₂O (upper row) and Au (bottom row) optimized, bare systems (Ag₂O and Au), silica supported systems (Ag₂O/SiO₂, Au/SiO₂, N-Ag₂O/SiO₂, N-Au/SiO₂) and with presence of 4-nitrophenol onto supported systems (Ag₂O/SiO₂/4-NP, Au/SiO₂/4-NP, N-Ag₂O/SiO₂/4-NP, N-Au/SiO₂/4-NP).

 In this work, we successfully fabricated the Ag and Au nanocomposite onto the biogenic SiO2 using four reducing catalysts via a simple in situ synthesis protocol (Figure 1). Pyridinic nitrogen in green-fabricated Ag₂O/Au-SiO₂ effectively enhances the interfacial Au and N electron transfer. Further, it exhibited superior catalytic efficiency relative to chemically fabricated hybrids in marine water samples. The reusability assessments of green fabricated Ag₂O/Au-SiO₂ up to 15 cycles without much loss confirmed the remarkable stability of the fabricated catalyst. Notably, the CG-Ag₂O/Au-SiO₂ catalyst displays the highest activity parameter for Ag NPs reported to reduce 4-nitrophenol, methylene blue, and rhodamine 6G in marine water (Figure 2a, b).

Figure 2. (a) Schematic representation of the catalytic reduction of 4-nitrophenol to 4-aminophenol and degradation of methylene blue and rhodamine 6G to their non-toxic products using hybrids, (b) digital photographs under day light and the corresponding time-dependent UV-visible absorbance spectra of the catalytic degradation of mixed organic pollutants/dyes (4-nitrophenol, methylene blue, and rhodamine 6G) using CG-Ag₂O/Au-SiO₂ in marine water, and (c) TDOS results of the catalytic systems with 4-nitrophenol: Ag₂O/SiO₂/4-NP, N-Ag₂O/SiO₂/4-NP, Au/SiO₂/4-NP, and N-Au/SiO₂/4-NP.

The importance of pyridinic N in the Ag₂O and Au is also scrutinized through first-principles calculations (Figure 2c), which are performed to model the studied systems. The free energies, adsorption energies, charge transfer, and density of states calculations confirm the predominant role of N in Ag₂O-based systems for superior catalytic activity. As the doping with heteroatom changes the electronic structure and enhances the amount of charge at the adsorbent–adsorbate interface, DFT validates the tendency toward enhanced catalytic efficiencies via an N-Ag₂O and Au NPs surface. 

For more details, please check out our paper "Pyridinic N anchored Ag and Au hybrids for detoxification of Organic pollutants"

Link: https://www.nature.com/articles/s41545-022-00187-w

DOI: https://doi.org/10.1038/s41545-022-00187-w