Understanding the mechanism of adsorption of CTAB and polylysine on silver nanoparticles and detection of Hg2+: Experimental and DFT study

Biosynthesis of silver nanospheres, kinetic profiling and their application in the optical sensing of mercury and chlorite ions in aqueous solutions

Pollution of water linked to microbial decontamination and extensive use of sodium chlorite (NaClO₂) as a disinfectant, especially in the face of the current COVID-19 situation, is a serious water pollution issue that needs to be addressed. In this context, an environmentally friendly and cost-effective method has been developed for the biomimetic synthesis of Ag nanospheres (Ag NSs) using aqueous extract of Piper nigrum for the detection of chlorite (ClO₂^-) and mercury (Hg²⁺) ions. The strong antioxidant properties of the biomolecules present in the Piper nigrum extract reduce silver ions (Ag⁺) to Ag⁰. After optimization of the formulation parameters, it was observed that 1 mL of piper nigrum extract was sufficient to reduce and stabilize 100 mL of 1.5 mM of Ag⁺ in 2.5 h at 30 °C. X-ray diffraction (XRD) pattern of Ag NSs revealed their crystalline nature and the characteristic Bragg's diffraction peaks confirmed their face cubic crystal (FCC) lattice. The characteristic reddish-brown color and absorption surface plasmon resonance (SPR) band at 435 nm confirmed the successful fabrication of Ag NSs. Kinetic analysis revealed a three-phase growth pattern involving nucleation, growth and stabilization. Transmission electron microscopy (TEM) and High-resolution transmission electron microscopy (HRTEM) micrograms, showed spherical NSs with narrow polydispersity with particle size ranging from 10 to 30 nm. The synthesized NSs were exposed to various metal ions and anions. The absorption intensity of Ag NSs quenched in the presence of mercury ions (Hg²⁺) among the cations and Chlorite ions (ClO₂^-) among the anions. The limit of detection (LOD) of 7.47 μM and 1.11 μM was evaluated from the calibration curve for Hg²⁺ and ClO₂^-, respectively. Based on these promising results, it is suggested that the method reported is a low-cost and one step biogenic protocol for the synthesis of Ag NSs and their employment for the detection of Hg²⁺ and ClO₂^-ions.

Selective adsorption of Pb2+ and Cu2+ on amino-modified attapulgite: Kinetic, thermal dynamic and DFT studies

Amino-modified attapulgite (M-ATP) was prepared to remove Pb²⁺ and Cu²⁺ from the aqueous solution. Fourier transform infrared spectroscopy (FT-IR) spectrums and X-ray powder diffraction (XRD) patterns revealed that a new Si-O-Si bond formed after modification. The result indicates that the graft reaction of ATP occurred at Si-O (2 0 0) tetrahedron crystal face. No matter whether in a single or binary heavy metal ion system, the adsorption experiments displayed that the equilibrium adsorption capacity of M-ATP towards Pb²⁺ was much higher than Cu²⁺, which indicated M-ATP more readily adsorbs the Pb²⁺. The selective adsorption mechanism of Pb²⁺ and Cu²⁺ on modified attapulgite was studied by density functional theory (DFT). The E_ads of Pb (- 2.01 eV) adsorbed on M-ATP is lower than Cu (- 1.79 eV) through the DFT calculation of adsorption energy (E_ads), which indicate that the Pb²⁺ adsorbed on M-ATP is more stable than Cu²⁺. Both adsorption experiments and theoretical calculations revealed that due to the stability of Pb²⁺ adsorption on M-ATP, Pb²⁺ is more readily adsorbed by M-ATP, and it is difficult for Cu²⁺ to exchange Pb²⁺ from M-ATP.