A novel rapid synthesis of highly stable silver nanoparticle/carbon quantum dot nanocomposites derived from low-grade coal feedstock

Abstract

Silver nanoparticles/nanocomposites are gaining popularity for their unique features and wide-range of applications including bactericidal behaviour, sensing, and photocatalysis. In this report, a novel, single-step, sustainable, and low-cost fabrication of silver carbon quantum dot (Ag/CQD) nanocomposites by using coal-derived carbon quantum dots (CQDs) as a reductant and stabilizer having great potential for simple and quick synthesis of silver nanocomposites has been documented for the first time in this paper. The HRTEM image of the Ag/CQD nanocomposite depicts the crystalline nature with two distinct d-spacings of 0.22 and 0.24 nm attributed to the (100) and (110) in-plane of the graphitic core or aromatic carbon and d-spacings of 0.24 and 0.27 nm were also observed which are attributed to the (111) and (122) lattice planes of Ag. The size distribution histogram derived from the TEM image indicates the particles to be within 2–12 nm in diameter, complying with the Gaussian distribution. SAED patterns of the Ag/CQD nanocomposite showed concentric diffraction rings with the (111), (200), (220), and (311) lattice planes of the fcc-structured silver metal, which indicates the composition of silver nanoparticles. From the XPS deconvoluted Ag 3d spectrum of the nanocomposites, the binding energies of Ag 3d5/2 and Ag 3d3/2 at 367 and 373 eV can be observed, which indicates that the silver is present in the metallic zero valent [Ag(0)] oxidation state in the nanocomposite. Moreover, UV-vis spectra show a major absorption peak at 422.47 nm that contributes to surface plasmon resonance of the Ag/CQD nanocomposite. The nanocomposite shows a zeta potential of −9.91 mV, signifying their high stability. The effect of base and concentrations of the CQDs in the synthesis of Ag/CQD nanocomposites has also been studied. Oxygen possessing functional groups present on the CQD surface were observed to play a significant role in the reduction of Ag/CQD nanocomposites. In addition, the nanocomposite has promising bactericidal behaviour for both Gram-positive and -negative bacterial strains for application as an antibacterial material. The Ag/CQD nanocomposite shows a maximum inhibition against bacterial strain Rhodococcus soli with an inhibition zone diameter of 17 mm as compared to the other strains.