Master Thesis : Synergistic visible-light photocatalysis by ZnO nanohybrids immobilized on activated halloysite for textile dyes degradation (including an introduction to research methodology)

Abstract

This study wanted to address the water pollution caused by textile azo dyes and synthesized advanced photocatalytic composite materials based on clay-supported ZnO nano hybrids for enhanced photocatalytic degradation of azo dyes, along with establishing their synergistic relationship. Due to the limited visible-light activity of ZnO in photocatalysis, different pure, metal-doped, and modified materials were synthesized,d and ZnO nanoparticles were successfully immobilized into them to form binary and ternary photocatalytic composite materials, i.e., ZnO nano hybrids, and tested for enhanced photocatalytic degradation of reactive black 5 (RB5) azo dyes in synthetic solution. Specifically, raw halloysite was modified by chemical treatment, and an activated clay (AC) was produced. Then, graphitic carbon nitride (g-C3N4) was synthesized and modified with Fe metal doping to form Fe/g-C3N4. After that, ZnO nanoparticles were synthesized using a precipitation process, and 4 different composite materials were formed, particularly [Fe/g-C3N4]/AC, ZnO/AC, [Fe/g-C3N4]/Zn, O, and [Fe/g-C3N4]/ZnO/AC. Then, 6 different analytical tests were carried out, namely SEM, XRD, DRS, Nitrogen adsorption-desorption, XP, S, and zeta potential for assessing the surface morphology, surface texture, crystal structure, optical properties, and surface charge, etc. of 8 synthesized materials. To evaluate the photocatalytic performance of 8 sample materials, photocatalytic experiments were carried out in the photocatalytic reactor for the degradation of RB5 azo dye under Visible light. The initial and residual concentrations of the dye were noted after 0, 2, 4, 6, and 8 h, and the RB5 degradation percentage was calculated. It was observed that the ternary composite [Fe/g-C3N4]/ZnO/AC is the best sample, showing a removal of 70% within 2 h, ending with the complete degradation of the azo dye after 8 h. For this sample, the RB5 degradation kinetic law was also determined, and a probable mechanism of RB5 dye degradation was proposed. To conclude, binary and ternary heterojunction composite materials like [Fe/g-C3N4]/ZnO and [Fe/g-C3N4]/ZnO/AC can enhance the photocatalytic performance of pure ZnO for the degradation of azo dyes, overcoming the barrier of limited visible light activity.