MERCURY ADSORPTION ON BIOSORBENTS AND AN ANALYTICAL METHOD TO DETERMINE IONIC MERCURY USING SP-ICPMS

Author

Nur Shadia, Southern Illinois University CarbondaleFollow

Date of Award

12-1-2023

Degree Name

Master of Science

Department

Civil Engineering

First Advisor

FAKHRAEI, HABIBOLLAH

Abstract

Researching efficient removal techniques is essential due to the toxicity of heavy metals, even at low concentrations, and their pervasiveness in a variety of environmental settings. According to WHO, Mercury is one of the most dangerous pollutants for human health. It causes severe damage to the ecosystem and other living beings. But because of its favorable physical-chemical properties, it has been widely used in the industrial activities. Unfortunately, several rivers and aquifers are getting contaminated by this hazardous chemical and inevitably putting importance on how to solve this problem. Most importantly a cost effective and environmentally friendly methods are needed to get a sustainable solution to this contamination. In this study Pinecones and pecan shells were chosen because of its abundance in nature and they are completely free of cost to get. Though some of the studies has been performed to remove some heavy metals by utilizing these two agricultural waste materials, none of the previous study investigated this two-potential bio-sorbents for removing Mercury from water solutions. In addition, there is a chance that metals and other ions will coexist in the environment, which is a complicated situation where there would be a competition among the ions for active cites on the sorbent surface. This study presents the effective removal of Hg2+ at a trace level concentration through adsorption on the grounded pinecones (PC), pecan shells (PS) and Chemically modified pinecones (PC), and pecan shells (PS). The FTIR analysis showed the functional group present in each specimen and pHPZC of each sample was determined to understand the surface chemistry and reactivity of the materials. Chemical modification might result in the increased surface area, porosity, functional groups as compared to the unmodified samples. The factors affecting adsorption efficiency were pH, adsorbent dosage, ionic strength, contact time and metal concentration. The Hg2+ removal efficiency in aqueous solution was found 90-92% for PS and APC, 92-95% for APS, and 80-85% for PC at room temperature with 1 mg/mL dose and pH their optimum pH condition. However, for unmodified PC and PS, the adsorption efficiency was less for all situation as compared to the acid modified PC and PS. The base activated PC and PS were found to be less effective than even the unmodified materials. Thus, results indicate that modification of PC and PS with Nitric acid (HNO3) increases metal adsorption efficiency as compared to unmodified samples. Furthermore, all of the materials tested found to be following the Freundlich's adsorption isotherm in aqueous solutions. Besides, ionic mercury can be readily converted to organic mercury through methylation, and as organic mercury builds up in the food chain, it is very harmful to human health even at a low level. Thus, to provide appropriate protection, the US Environmental Protection Agency (EPA) has set the maximum contamination level of mercury in drinking water at 2.0 ppb. As a result, it becomes very crucial to invent a very sensitive and selective approach for monitoring the low concentration of Hg2+ in the environment. This study aims to create an incredibly sensitive assay for the detection and quantification of Hg2+ (aq) using the single-particle inductively coupled plasma mass spectrometry (spICP-MS). The well-known thymine (T)-Hg2+-T complex forms when AuNPs modified with single-stranded DNA are exposed to Hg2+ (aq) and this formation causes AuNPs to aggregate. By determining the overall reduction in the number of identified AuNPs or NP aggregates the degree of aggregation can quantified. This spICP-MS-based approach has been reported to obtain a substantially lower detection limit of 0.031 part-per-trillion (155 fM) and a larger (10,000-fold) linear range up to 1 ppb when compared to most other Hg assays that use the similar principle of aggregation-dispersion with DNA modified AuNPs. Besides, this approach showed low interference from the sample matrix. Considering the aforementioned advantages, this study focuses on quantifying aqueous Hg2+ using single stranded DNA-gold nanoparticles conjugates with the help of single-particle inductively coupled plasma mass spectrometry (spICP-MS).