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Evaluation of the influence of carbonaceous adsorbent surface chemistry on the adsorption process of pollutants


Author: Gînsari Irina
Degree:doctor of chemistry
Speciality: 02.00.04 - Physical chemistry
Year:2021
Scientific adviser: Raisa Nastas
doctor, associate professor (docent), Institute of Chemistry of the ASM
Institution: Institute of Chemistry of the ASM

Status

The thesis was presented on the 17 September, 2021
Approved by NCAA on the 22 December, 2021

Abstract

Adobe PDF document – 1.75 Mb / in romanian
Adobe PDF document – 1.74 Mb / in english

Thesis

CZU 543.54:[544.723:546.26](043.1)

Adobe PDF document 7.46 Mb / in romanian
214 pages

Keywords

activated carbons, modification, surface chemistry, adsorption, nitrite ions, co balt ions, strontium ions, kinetics, isotherms

Summary

ANNOTATION Ginsari Irina, „Evaluation of the influence of carbonaceous adsorbent surface chemistry on the adsorption process of pollutants”, PhD thesis in chemical sciences, Chisinau, 2021 Structure of the thesis. The thesis includes introduction, four chapters, general conclusions and recommendations, References contains 334 titles, total volume of 214 pages, 45 tables, 82 figures and 9 annexes. The obtained results have been published in 24 scientific papers. Keywords: activated carbons, modification, surface chemistry, adsorption, nitrite ions, co balt ions, strontium ions, kinetics, isotherms. Field of investigation: 114.01 – physical chemistry The purpose of the research consists in the modification of the surface chemistry and the correlation of carbonaceous adsorbents surface chemistry with their sorption and/or catalytic properties. Objectives of the thesis: ● modification of the activated carbon surface chemistry; ● evaluation of the physical-chemical characteristics (nitrogen sorption-desorption isotherms; thermal analysis; X-ray diffraction (XRD); scanning electron microscope coupled with an element analyser (SEM-EDX)); ● assessment of the surface chemistry (electrometric titrations, pHpzc, FTIR); ● evaluation of the redox properties (chemiluminescence method, ABTS radical cation method); ● elucidation of the particularities of interaction and/or specific sorption, the effect of porous structure and surface chemistry, in order to correlate the surface properties of carbon adsorbents with their sorbent and/or catalytic properties in order to improve the adsorption process of pollutants. Scientific novelty and originality consists in the elucidation of the particularities of specific interaction and/or sorption depending on the pH and surface chemistry of carbonaceous adsorbents. For the first time, mechanisms of adsorptions has been proposed for a broad pH interval, by considering the pH of the medium, the ionization degree of the groups (pHpzc) and the types of ions in solution. For the first time, the ABTS radical-cation method has been adapted for the evaluation of the redox properties of carbonaceous adsorbents (heterogeneous systems). A new and economical method of activated carbon oxidation with nitric acid/urea mixture has been proposed. The research hypothesis consists in modifying the surface chemistry of carbonaceous adsorbents by different methods: modification with chlorine ions, by oxidation (with nitric acid, with a mixture of nitric acid/urea) and impregnation with metals (copper and manganese oxides). The solved scientific problem consists in identifying the adsorption mechanisms of nitrite ions and bivalent metals on modified carbonaceous adsorbents depending on the surface chemistry and pH. The theoretical significance. The research results contribute to the development of scientific information regarding methods of the evaluation of carbon adsorbents surface chemistry. Also, this study correlates the surface properties of carbonaceous adsorbents with their sorbent and/or catalytic properties, in order to enhance the adsorption process of pollutants. The applicative value of the work. The applied research carried out in this thesis offers the possibility to evaluate the redox properties of carbon adsorbents by the ABTS cation-radical method, and, also to optimize the known methods of modifying activated carbons that contribute to decrease of their price. Implementation of scientific results. Modified carbonaceous adsorbents (oxidized with nitric acid and nitric acid/urea mixture) have been tested for nitrite ions removal from natural water. The ABTS radical-cation method, adapted for the evaluation of the redox properties in heterogeneous systems has been used in the research. Practical application possibilities: (i) of the oxidation method of activated carbons with nitric acid/urea mixture allows a production of an array of carbons at low prices; (ii) of carbonaceous adsorbents modified with chlorine ions as enterosorbents for adsorption/removal of nitrite ions from the digestive system.