Author

Nadhem Ismail

Date of Award

December 2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemical Engineering

First Advisor

Ali Alshami

Abstract

Inorganic crystallization, referred to as mineral scaling, have been posing tremendous operational challenges to water-based industries over the years. Multiple recent initiatives have focused on developing sustainable and highly effective antiscalants/scale inhibitors; however, most of the investigated antiscalants have demonstrated low scaling ion tolerance and unknown scale inhibitor-mineral crystal interaction. Engineered soft materials, particularly Quantum Dots (QDs) and biopolymer-based formulations, are among the most desirable solutions since they both solve critical environmental issues and offer insights into the inhibition mechanism. This dissertation reports on the development and performance evaluation of three distinct soft materials-based formulations; Carboxyl-Silicon Quantum Dots (CSiQDs), Carboxymethylcellulose grafted Polyacrylate (CMC-PAA), and multi-functionality Carbon Dots (QDs) based formulations. Carboxyl-Silicon Quantum Dots (CSiQDs) was synthesized and tested, for the first time, against gypsum scaling. Abundant carboxyl groups in the surface of SiQDs was confirmed by different characterization techniques such as XPS, and zeta-potential. The water dispersibility and solubility was promoted upon functionalization as confirmed by Dynamic Light Scattering (DLS) and TEM images. The developed material’s performance was superior to the recently reported nano-photonic formulations at different testing conditions, giving the same efficiency at substantially lower dosages. The inhibition mechanism was elucidated via live crystals monitoring through confocal microscopy and supported by post-test SEM and XRD. The developed inhibitor worked by threshold inhibition through interfering with the nucleation and crystal growth steps. In the second approach that involved Carboxymethyl Cellulose (CMC) based formulation, three formulations of different grafted chains, different lengths and chemistries were developed. The formulations structural properties and grafting was confirmed by FTIR, and NMR. The grafting fostered the thermal stability of the developed formulations as confirmed by TGA analysis. The efficacy of the grafted products, especially CMC-g-PAA was superior to bare CMC by at least 20% in all dosages. CMC-g-PAA was also effective in RO skids pilot plant system for inorganic scaling but was not as effective for biofouling as revealed by autopsy results of RO membranes used in the study. Finally, in the third approach (multi-functionality Carbon Dots Based Formulations), four (4) CQDs based formulations were developed; carboxyl-carbon dots (CQDs), nitrogen-doped carbon dots (NCQDs), arginine-doped carbon dots (Arg-CQDs), and phosphonic acid-functionalized carbon quantum dots (PCQDs). The chemical structure and morphology of the formulations was confirmed via FTIR and high resolution TEM, respectively. Zeta-potential results confirmed the negatively charge surface in case of CQDs and positively charged surface for NCQDs, and Arg-CQDs formulations. Antiscaling results revealed a very good performance of PCQDs, followed by CQDs, while NCQDs had the lowest ranking in terms of antiscaling performance. Key advantages of the developed soft-materials based technologies in this dissertation include better concentration control in industrial applications, better elucidation of scale inhibition mechanisms through the scaling process, and the ability to use antiscalant visualizations on scale cores due to the fluorescence properties of the developed materials (i.e. QDs).

Available for download on Saturday, January 17, 2026

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