THE USE OF MXENE COMPOSITES IN WATER TREATMENT APPLICATIONS: PHOTOCATALYTIC DEGRADATION OF ORGANIC DYES AND ADSORPTION OF HEAVY METALS

Abstract

More sustainable water supply requires new technical advancements. The treatment of wastewater to the point that it can be reused eliminates the need to extract fresh water from natural resources. The utilization of novel nanomaterials with improved properties is an important area of focus for wastewater reclamation innovation. The two-dimensional titanium carbide Ti3C2Tx was the first transition metal carbide (MXene) discovered and has large surface area, hydrophilic behavior, plenty of surface functional groups and high conductivity. These properties make Ti3C2Tx MXene as an attractive platform for preparing composites for different wastewater treatment applications, in addition to its ease of tuning and ability to be functionalized and modified. In this research work, novel Ti3C2Tx MXene-based photocatalyst and adsorbent materials with improved properties were synthesized and investigated for specific water remediation applications, namely; (1) the photocatalytic degradation of organic dyes, and (2) the adsorption of heavy metals from aqueous solutions. The first study of this thesis explores the synthesis of Ti3C2Tx MXene photocatalysts decorated respectively with silver and palladium nanoparticles, using a simple hydrothermal treatment method. The synthesized photocatalysts were fully characterized and tested for the photocatalytic degradation of methylene blue (MB) and rhodamine B (RhB) under ultraviolet and solar light irradiation. The photocatalysis kinetics, the effect of catalyst to dye ratio and irradiation time have also been analyzed. A significant improvement in the photocatalytic performances was observed for all synthesized MXene composites when compared to pristine MXene, with a superior degradation efficiency achieved for AgNPs/TiO2/Ti3C2Tx. A possible photodegradation mechanism is proposed at the end of this study, emphasizing MXene's important role in acting as an electron reservoir for photogenerated electrons from TiO2 nanoparticles when exposed to light, resulting in an increase in O2•- radical formation and improved organics degradation. The second study of this thesis explores the potential for the simultaneous removal of Co(II), Cr(VI), Cu(II), Ni(II) and Pb(II) ions from aqueous solutions by Ti3C2Tx MXene/biopolymers (MCL) composites prepared via a simple facile treatment using chitosan and lignosulfonate as renewable and biodegradable reactants. The physicochemical characterization of obtained adsorbents demonstrated that chitosan-lignosulfonate formed nanospheres and were overlaying on the surface of MXene, endowing it with a variety of surface functionalities, high specific surface area and antioxidant characteristics. The adsorption performance of MCL was optimized by altering its compositions and dosage against a single Cu(II) solute. Additionally, the competitive adsorption in multi-metals system revealed that MCL had a substantial difference in adsorption affinity toward various heavy metal ions; the MCL removal efficiency for the quinary-metal ions adsorption followed a trend of Pb(II) > Cr(VI) ≈ Cu(II) > Ni(II) ≈ Co(II) in neutral pH conditions. Detailed adsorption characteristics of MCL including adsorption kinetics, isotherms, thermodynamics, and recyclability were investigated. The predicted adsorption mechanism is proposed at the end of this study, demonstrating that electrostatic interactions dominate the adsorption behavior of MCL adsorbents toward heavy metal ions, with ion exchange processes actively participating.

Date of Award	2022
Original language	American English
Awarding Institution	HBKU College of Science and Engineering