Transport of N-CD and Pre-Sorbed Pb in Saturated Porous Media.

Salahaddin Kamrani,Mosleh Kamrani,Mohammed Baalousha,Vahab Amiri

doi:10.3390/molecules25235518

Abstract

Carbon dots (CDs) are a new type of nanomaterials of the carbon family with unique characteristics, such as their small size (e.g., <10 nm), high water solubility, low toxicity, and high metal affinity. Modification of CDs by Nitrogen functional groups (N-CDs) enhances their metal adsorption capacity. This study investigated the influences of pH (4, 6, and 9), ionic strength (1, 50, and 100 mM), and cation valency (Na+ and Ca2+) on the competitive adsorption of Pb to quartz and N-CD surfaces, the transport and retention of N-CDs in saturated porous media, and the capacity of N-CDs to mobilize pre-adsorbed Pb in quartz columns. Pb adsorption was higher on N-CDs than on quartz surfaces and decreased with increases in ionic strength (IS) and divalent cations (Ca2+) concentration. N-CD mobility in quartz columns was highest at pH of 9- and 1-mM monovalent cations (Na+) and decreased with decreases in pH and increases in ionic strength and ion valency. N-CDs mobilized pre-adsorbed Pb from quartz due to the higher adsorption affinity of Pb to N-CD than to quartz surfaces. These findings provide valuable insights into the transport, retention, and risk assessment of lead in the presence of carbon-based engineered nanoparticles.

Highlights

Carbon dots (CDs), a new member of the carbon-based engineered nanoparticles, are widely used in many applications, including sensors, cell imaging, photocatalysis, metal detection, organophosphate pesticide detection, light-emitting devices, energy storage devices, and organic photovoltaics [1,2,3].Carbon Dot (CD) have important properties, such as high surface area and high metal affinity and sorption capacity, due to the abundance of surface functional groups, such as carboxylic, phenolic, and hydroxyl groups [4].Functional groups on the surfaces of carbon nanoparticle play important roles in the removal of heavy metals from aqueous media [5]
The overall objective of this study is to investigate the impact of pH, ionic strength, and valency on the fate and transport of nitrogenfunctionalized functionalized carbon dots (N-CDs) in saturated porous media
Carbon dots were synthesized from citric acid using a simple, one-step polymerization reaction method according to the method reported elsewhere [14]

Summary

Introduction

CDs have important properties, such as high surface area and high metal affinity and sorption capacity, due to the abundance of surface functional groups, such as carboxylic, phenolic, and hydroxyl groups [4]. Functional groups on the surfaces of carbon nanoparticle play important roles in the removal of heavy metals from aqueous media [5]. The interactions between surface functional groups and the heavy metals can directly or indirectly affect the adsorption mechanisms, such as electrostatic interaction, surface complexation, ion exchange, physical adsorption, and precipitation [6]. Nitrogenation is a widely used approach to generate nitrogen-containing functional groups (e.g., -NH2 , -NH, -C=N, and -C-N) on the surfaces of carbon-based materials [1]

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