COLLOIDAL QUANTUM DOTS-ASSISTED HYBRID PHOTOCATALYST FOR WASTEWATER TREATMENT

Abstract

Water pollution from toxic organic dyes and industrial effluents poses a severe threat to ecosystems and human health, underscoring the urgent need for sustainable, efficient wastewater treatment technologies. Among various approaches, photocatalysis has emerged as a promising technique for pollutant degradation due to its cost-effectiveness and environmental compatibility. However, the performance of conventional photocatalysts is hindered by several critical limitations, including poor light absorption capability, toxicity of heavy-metal-based catalysts, rapid e⁻/h⁺ recombination, and limited recyclability. This thesis aims to overcome these challenges by developing eco-friendly colloidal Quantum Dots (QDs) based nanohybrids integrated with one-dimensional (1D) and zero-dimensional (0D) nanomaterials to achieve efficient charge separation, broadened light absorption, and improved photocatalysis. Furthermore, the influence of external stimuli, including magnetic fields (MF), electric fields, and piezoelectric effects, was investigated to enhance the photocatalytic degradation efficiency of toxic pollutants. Firstly, a novel Cu:Zn-In-Se2 QDs decorated Fe3O4 nanorods mesoporous films were employed for the photocatalytic degradation of methylene blue (MB) under the influence of an external MF. The optimized hybrid nanohybrid photocatalyst achieved a remarkable 99.96% degradation efficiency, representing a 49% improvement over the control Fe3O4 photocatalyst (67.01%). This enhanced performance was attributed to the synergistic effect of the broad light absorption of Cu:Zn-In-Se2 QDs/Fe3O4 and the efficient carrier dynamics facilitated by the Lorentz force in the presence of the MF. Additionally, the toxicity of treated methylene blue (MB) water was evaluated using Brassica oleracea (kale) as a model plant system. Plants irrigated with treated water exhibited superior growth compared to those irrigated with MB-contaminated water, confirming the reduced toxicity of the treated water and demonstrating its potential for safe agricultural reuse and sustainable wastewater management. Secondly, a hybrid photocatalyst composed of Mn:CuInSe2 QDs integrated with a mesoporous TiO2 film photoanode was developed and evaluated for the simultaneous photoelectrochemical degradation of Rhodamine B (RhB) and hydrogen generation. The optimized hybrid Mn:CuInSe2 QDs/TiO2 nanohybrid photocatalyst achieved a remarkable 93.31% degradation efficiency of RhB at an external bias of 1.4 V and a photocurrent density of ~4 mA cm-2 at 0.8V vs RHE. The results highlight the potential of Mn:CuInSe2 QDs/TiO2 nanohybrid as a dual-function photocatalyst for efficient and fast wastewater treatment and clean fuel production. Thirdly, the piezoelectric degradation of pollutants was investigated using ZnSnO3-based nanomaterials, demonstrating the capability of piezo-catalysis to degrade organic contaminants effectively. Overall, this research provides new insights into the design of novel eco-friendly Cu:ZnInSe2 QDs/ZnSnO3 nanohybrid photocatalysts and presents external-vibrational-stress-assisted photocatalysis for efficient environmental remediation and renewable energy generation.