İNŞaat mühendiSLİĞİ anabiLİm dali

The Removal of Organic Pollutants From Natural Waters By Adsorptıon on Carbon Nanomaterıals
In this study, the effect of different NOM preloading conditions on the adsorption of two organic compounds (OCs), Phenanthrene (PNT) and Trichloroethylene (TCE), by pristine single–walled carbon nanotube (SWNT), pristine multi–walled carbon nanotube (MWNT), pristine graphene nanosheet (GNS), graphene oxide nanosheet (GO), and two coal based granular activated carbons (GACs ) were investigated. This study composed of three major sections. In the first section, the characterization of studied adsorbents was evaluated. For that purpose, various characterization methods have been used to determine physico-chemical properties of adsorbents such as fourier transform infrared (FTIR), BET surface areas, pore volumes, pore size distributions, zeta potential, and oxygen content. Furthermore, surface morphology of the adsorbents was also analyzed by scanning electron microscope (SEM). In the second section of the study, first of all, the adsorption of PNT and TCE by six different adsorbents (SWNT, MWNT, GNS, GO and GACs) in distilled-deionized water (DDW) were investigated. Afterwards, all the adsorbents were preloaded with four different NOM solutions containing three different humic acid solutions (isolated) and one surface water to elucidate the effect of NOM preloading on adsorption of OCs. The results from non-preloaded (DDW) and NOM preloaded conditions were also compared. The comparison of PNT and TCE adsorption capacities of adsorbents in four different NOM solutions revealed that the lowest adsorption capacities were observed for adsorbents in which preloaded with surface water. The adsorption capacity of adsorbents were altered depending on the types of background water, absorbate, and adsorbent. Besides, it is concluded that the physicochemical characteristics of NOMs (i.e., hydrophobic or hydrophilic fractions, dissolved organic carbon contents, Ca2+ concentrations, and SUVA254 values.) may affect the adsorption capacity of adsorbents. Also, the results of experiments were modelled according to commonly used isotherm models as Freundlich (FM), Langmuir (LM), Langmuir-Freundlich (LFM) and Polanyi-Manes (PMM). As a result, according to regression coefficient (r2) and root-mean-square deviation (RMSE) values, the suitability of isotherm models varied depending on the type of the adsorbent, OCs , and characteristics of natural water. Due to the fact that, this suggested that PNT and TCE were adsorbed on adsorbent surfaces homogeneously as well as heterogeneously. According to single point adsorption descriptors (Kd), it has been found that the adsorption of PNT and TCE molecules were reduced in the presence of NOM molecules due to the blockage of pores. Additionally, adsorption results of all studied adsorbents for PNT was higher than TCE in the single solute conditions due to their distinct molecular properties. In the last section of study, adsorption kinetics of OCs (PNT and TCE) by six different adsorbents were examined in one hydrophobic (HPO), one hydrophilic (HPI) and distilled-deionized water (DDW). The results of experiments were evaluated depending on commonly used kinetic models as pseudo first order model (PFOM), pseudo second order model (PSOM Type 1–5), intraparticle diffusion model (ĠPDM) and external particle diffusion models (EPDM). Among the all studied kinetics models, PSOM Type–1 (r2: 0.978–1) provided good fitting for the kinetic data. This result showed that there might be a chemical interaction between PNT, TCE and adsorbents. As for the investigation of diffusion based models, the results exhibited that the data fitted well with EPDM (r2: 0.917–0.999).This finding suggested that PNT and TCE more dominantly attached to the pore surface of the adsorbent.
All in all, the observed high adsorption capacities of carbon nanomaterials as much as granular activated carbons suggested that they can be used as an alternative adsorbents instead of granular activated carbons. The results of DDW experiments were shown that the adsorption mechanisms of OCs by GNSs, CNTs, and GACs strongly related with the molecular configuration and structure of OCs. According to results of NOM preloading experiments, it was also determined that the adsorption of OCs affected by pHpzc, oxygen content, pore and adsorbent surface area as well as molecular size and hydrophobicity of the adsorbate. Additionally, the results also revealed that the adsorption of organic compounds also affected by physicochemical properties of NOMs.