Abstract
It is essential and important to determine the adsorption mechanism as well as removal efficiency when using an adsorption technique to remove toxic heavy metals from wastewater. In this research, the removal efficiency and mechanism of chromium removal by a silica-based nanoparticle were investigated. A PEI-silica nanoparticle was synthesized by a one-pot technique and exhibited uniformly well-dispersed PEI polymers in silica particles. The adsorption capacity of chromium ions was determined by a batch adsorption test, with the PEI-silica nanoparticle having a value of 183.7 mg/g and monolayer sorption. Adsorption of chromium ions was affected by the solution pH and altered the nanoparticle surface chemically. First principles calculations of the adsorption energies for the relevant adsorption configurations and XPS peaks of Cr and N showed that Cr(VI), [HCrO4]− is reduced to two species, Cr(III), CrOH2+ and Cr3+, by an amine group and that Cr(III) and Cr(VI) ions are adsorbed on different functional groups, oxidized N and NH3+.
Highlights
The term “heavy metals” refers to metals with specific gravities of approximately 4.0 or higher, which are distributed mostly in rock and soil
We investigated combinatorial configurations of three adsorbates (Cr, CrOH, and HCrO4) and four adsorption sites (−N =, −NH−, −NH2, −NH3) based on the X-ray photoelectron spectroscopy (XPS) spectra
Experiments with various initial pH values (2 to 4) were conducted under controlled conditions and found that the removal efficiency of the PEI-silica nanoparticles was affected by the solution pH, and the highest removal efficiency of chromium occurred at a pH of 4
Summary
The term “heavy metals” refers to metals with specific gravities of approximately 4.0 or higher, which are distributed mostly in rock and soil. Cr(III) is an essential human dietary element and, Cr(VI) occurs naturally in nature from the erosion of chromium deposits These can be produced by anthropogenic emissions, such as industrial processes. The US EPA and the EU established the permissible emission standards for Cr(III) and Cr(VI) as a total chromium amount of 0.1 mg/L in 19916 For these reasons, studies on reducing the amount of chromium below the effluent water quality standard are very important issues. Silica is superior to the other materials mentioned above because of its high porosity, large surface area and great number of functionalities[28,29] For these reasons, a great amount of research on silica as Cr(VI) adsorbents has been carried out[30,31,32,33,34,35,36,37,38]. The preparation of silica adsorbents consists of two stages, including the synthesis of porous silica and the attachment of functional groups for Cr(VI) adsorption onto the silica surface
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