Nanosilver particles (AgNP) were prepared by Tollens reduction reaction. The morphology of nano-silver and its stability in seawater were characterized by TEM and UV-Vis spectrophotometer. The results show that the nano-silver is spherical and the average particle size is 13 nm. Experiments show that the stability of nano-silver decreases with time and the stability in seawater is low. This study has important reference significance for the assessment of environmental hazards of nanosilver in environmental waters.
Since nano-silver particles (AgNP) have been widely used in recent years [1-6]. Previous literature has shown that nanosilver is inevitably discharged into the environment. Among them, a large amount of nano silver will be discharged and enter the ocean. Due to its spectral bactericidal properties, nano-silver emitted into the ocean will have a negative impact on microorganisms in the environment, which in turn affects the local ecological environment. As an effective antibacterial nanomaterial, the environmental toxicology of nanosilver has been widely studied [7-10], in which the toxicity of nanosilver is closely related to its stability in water. The literature indicates that the stability of nanosilver is often proportional to its toxicity. Therefore, it is important to study the stability of nano-silver particles in seawater for their risk assessment in the marine environment.
This study introduces the synthesis method of nanosilver. Due to its environmental friendliness, this method is widely used in the research field of nanosilver. The stability of nano-silver in seawater was studied by UV-Vis spectrophotometer.
1. Materials and methods 1.1 Reagents and instruments Silver nitrate (AR); D-maltose; ammonia water; NaOH (AR); deionized water; Bohai seawater water sample; UV-visible spectrophotometer.
1.2 Preparation of nano-silver Weigh 10-3 mol/L of AgNO3 and 0.01 mol/L of D-maltose into the reaction vessel, and slowly add NH4·H2O to a concentration of 5×10-3 mol/L. A certain amount of NaOH was added to the reaction system to raise the pH of the solution to 11.5. The obtained nanosilver was ultrafiltered by an ultrafiltration apparatus, and the nanosilver was washed with 1 L of deionized water to a neutral pH [7-9].
1.3 Stability of nano-silver in seawater Dissolve 10 mg/L of nano-silver in deionized water and seawater, and measure the peak of the spectrum with an ultraviolet-visible spectrophotometer within 24 hours.
2. Results and discussion 2.1 Characterization of nano-silver The characterization of the prepared nano-silver was carried out using a transmission electron microscope. The nano silver particles are spherical in shape. Characterization of the UV-visible absorption spectrum of nano-silver using an ultraviolet-visible spectrophotometer. The results show that the peak of the UV-visible spectrum of the nano-silver solution is around 400 nm, which is consistent with the literature results.
The stability of 2.2 nano-silver in deionized water and seawater is determined by the stability of nano-silver in deionized water and seawater. Experiments show that the stability of nano-silver in deionized water does not change significantly within 24 hours, but the spectral peak in seawater decreases with time. Figure 4 compares the spectral peaks of nanosilver in deionized water and seawater. The results show that the peak value of nanosilver in seawater is reduced by about 24%. The nano-silver in solution exists as a sol particle. In colloidal chemistry, the Shulze-Hardy rule shows that the stability of the sol particle is inversely proportional to the valence state of the counterion in its solution [10-12]. Wherein, the surface charge of the prepared nano silver is negatively charged, and therefore, the high valence cation in the water sample has a decisive influence on the stability of the nano silver. In seawater, the cations are mainly monovalent or divalent, of which Na+, K+, Ca2+, and Mg2+ are the most abundant cations in seawater [10, 11]. Since Ca2+ and Mg2+ are divalent, the two divalent cations can more effectively neutralize the negative charge on the surface of the nanosilver particles and thereby reduce the electron repulsion between the nanoparticles, thereby causing the aggregation effect between the nano silver particles. Becomes significant [9-12]. Therefore, due to the aggregation effect of nano-silver, the ultraviolet-visible spectral peak of nano-silver gradually decreases with time.
Studies have shown that nano-silver can be prepared by chemical reduction method, and the prepared nano-silver morphology is spherical and uniform in particle size distribution. The stability of nanosilver in seawater is lower than that in deionized water. The main reason for the stability of nanosilver is the cation content in seawater.