Preparation of fly ash-TiO2-metal hybrid composites for adsorption and photocatalytic applications

Abstract

Abstract: Chapter-1

This chapter provides an overview of adsorption and semiconductor photocatalysis as effective strategies for wastewater treatment, with a focus on fly ash–TiO₂–metal–zeolite hybrid materials. It discusses the environmental impact of industrial effluents and the drawbacks of conventional remediation technologies. The chapter highlights the role of fly ash as an inexpensive, porous support, its functionalization with TiO2 to enhance photocatalytic activity, and subsequent performance improvements achieved through metal doping and zeolite incorporation. A critical review of recent studies illustrates how these components work synergistically to broaden light absorption, enhance charge separation, and improve catalyst durability for degrading dyes. Methods for material synthesis, structural and optical characterization, and performance evaluation are summarized. The chapter concludes by identifying existing research gaps and emphasizing the need for advanced hybrid composites capable of achieving superior efficiency under visible and solar light irradiation. Chapter-2

This study emphasizes the need to achieve both high photocatalytic efficiency and strong adsorption capacity in a catalyst to ensure complete removal of fuchsine blue dye (FB) from wastewater. In this work, TiO2 and fly ash–TiO2 composites (0.5–5wt%) were prepared using a sol–gel method combined with wet impregnation, and their performance was evaluated for combined processes of adsorption and photocatalytic breakdown of fuchsin blue dye. The materials were characterized using XRD, UV–DRS, SEM, EDS, Raman spectroscopy, and N₂ adsorption analysis. Adsorption and degradation experiments were conducted to evaluate the effects of pH (2–10), adsorbent dosage (1–9 mg), contact time (30–180 min), and initial dye concentration (5–30 mg/L) on FB dye removal efficiency. Among the tested samples, the 5 wt% fly ash–TiO2 composite exhibited the highest adsorption capacity of 20.32 mg/g and achieved 76% FB dye removal. These results indicate that adsorption occurs primarily through monolayer coverage on a homogeneous surface, in agreement with the Langmuir isotherm, and governed by pseudo-first-order kinetics. Under UV irradiation, the same 5wt% fly ash–TiO2 composite reached a maximum photocatalytic degradation of 88% after 180 minutes, following pseudo-first-order kinetics. The catalyst demonstrated excellent reusability, maintaining its dye removal performance consistent over five consecutive cycles. Chapter-3 In this study, copper (Cu) photo-deposited fly ash-TiO2 composites (FT-Cu0.5-2) with Cu content ranging from 0.5 to 2wt% were synthesized to evaluate their adsorption and photocatalytic activity toward the photodegradation of fuchsin blue (FB) dye under visible light as well as natural sunlight. Structural characterization was performed using X-ray diffraction (XRD) and diffuse reflectance spectroscopy (DRS), while morphological and surface chemical analyses were carried out through high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and N₂ adsorption Brunauer-Emmett-Teller (BET) analysis. These confirmed the successful fabrication of fly ash-TiO2 (FT) and Cu-modified composites (FT-Cu0.5-2). Copper nanoparticles, with sizes in the range between 7 and 17 nm, were uniformly distributed on the FT composite surface. The impact of various adsorption parameters, including FB dye concentration, adsorbent dose, solution pH, and contact duration, was systematically investigated. Following 180 minutes of adsorption in the dark, the 1wt% Cu-loaded FT composite (FT-Cu1) showed the highest dye removal efficiency of 77% and fitted well to the Langmuir adsorption model. A notable enhancement in photocatalytic activity was observed for FT-Cu1, which achieved 92% FB degradation under sunlight and 94% under visible light, compared to the unmodified FT catalyst with only 68% and 71% removal, respectively. This enhancement in removal efficiency is attributed to the synergistic interaction between Cu, fly ash, and TiO2 components. The presence of Cu improved the efficient separation of photogenerated charge carriers and expanded visible light absorption by introducing intermediate energy states within the TiO2 bandgap. The degradation pathway of FB dye was elucidated via trapping experiments using hole scavengers and detection of intermediate species through High-Resolution Mass Spectrometry (HRMS). Additionally, the FT-Cu composite exhibited strong photostability and could be reused effectively, maintaining approximately 83% degradation efficiency after five consecutive cycles, demonstrating its potential for sustainable treatment of organic contaminants. Chapter-4 In this work, copper photo-deposited fly ash–TiO₂ (FT-Cu1) composites were modified with ZSM-5 zeolite at loadings of 1%, 3%, and 5% by weight, designated as 1ZFT-Cu1, 3ZFT-Cu1, and 5ZFT-Cu1, respectively. These composites were investigated for their capability to adsorb and photo-catalytically degrade crystal violet (CV) dye under visible and solar light exposure. Characterization techniques, including UV-Vis diffuse reflectance spectroscopy (DRS), field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), and BET surface area analysis, revealed that the addition of ZSM-5 enhanced crystallinity, minimized particle aggregation, and increased visible light absorption by the composites. Among the samples, the 3wt% ZSM-5-loaded composite (3ZFT-Cu1) exhibited the best photocatalytic performance, achieving dye removal efficiencies of 98% under visible light and 95% under solar irradiation, using a catalyst dosage of 5 mg, initial dye concentration of 5 mg/L, a contact time of 180 minutes, and solution pH 9. The adsorption process fitted well with the Freundlich isotherm model, indicating multilayer adsorption, while the degradation kinetics followed a pseudo-first-order rate. The superior activity is credited to the synergistic interaction of copper doping, the porous structure of ZSM-5, and the fly ash support, which collectively enhanced light absorption and dye uptake. The 3ZFT-Cu1 composite also showed commendable stability, retaining 84% of its degradation efficiency after five cycles of reuse. Free radical trapping studies using hole scavengers elucidated the photocatalytic degradation pathway of CV dye, highlighting the composite’s effectiveness under visible light for potential wastewater treatment applications