A study on the photodegradation of organic pollutants using visible light-active Cu2O/WO3/TiO2nanocomposite photocatalyst / Jenny Chau Hui Foong

Jenny Chau , Hui Foong (2023) A study on the photodegradation of organic pollutants using visible light-active Cu2O/WO3/TiO2nanocomposite photocatalyst / Jenny Chau Hui Foong. PhD thesis, Universiti Malaya.

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Abstract

Textile dyeing wastewater becomes one of the root causes of environmental pollution. Photodegradation is considered the most promising approach due to its advantages, such as energy-saving, high performance, thorough degradation of organic compounds, and production of environment-friendly end products. Titanium dioxide (TiO2) is one of the photocatalysts that shows high photodegradation performance. However, the effectiveness of TiO2 is limited by the requirement of ultraviolet light excitation, wide band gap energy, and fast recombination of electron-hole pairs. In this study, a solar-responsive cuprous oxide (Cu2O)/tungsten oxide (WO3)/titanium dioxide (TiO2) ternary composite was successfully synthesized through an ultrasonic-assisted hydrothermal technique with varying weight% (wt.%) of WO3 and Cu2O and calcination temperature. Characterization techniques such as thermal gravimetric analysis (TGA), Raman, X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), UV-Vis, and zeta potential were used to study the morphological and crystalline structure of the synthesized Cu2O/WO3/TiO2 (CWT) composite. Next, a photoelectrochemical (PEC) study including electrochemical impedance spectrum (EIS), Mott-Schottky (MS), transient photocurrent, transient photovoltage, and linear sweep voltammetry (LSV) was used to explore the charge carrier characteristics. The formation of CWT ternary composite was proved to reduce the band gap of TiO2 effectively. The prepared 0.50CWT-500 composite exhibited the highest photodegradation activity (2.29 × 10−2 min−1) compared to the TiO2 (1.59 × 10−2 min−1) and 0.50WT composite (2.13 × 10−2 min−1) and 0.50CWT-500 showed complete mineralization in chemical oxygen demand (COD) reading towards 30 ppm of Reactive Black 5 (RB5) dye under 120 min of light irradiation. Effects of large surface area, small crystallite size, high pore volume and size, and low electron-hole pair recombination rate attributed to the superiority of 0.50CWT-500. Besides, 0.50CWT-500 could be reused, showing 80.51% of RB5 photodegradation in the fifth cycle. Scavenger study demonstrated that photogenerated hole (h+) was the main active species of 0.50CWT-500 to initiate the RB5 photodegradation and a direct Z-scheme heterojunction was proposed for the n-p-n junction of 0.50CWT-500 heterostructure. Cytotoxicity assessment determined the readings of half-maximal inhibitory concentration (IC50) were 1 ppm and 0.61 ppm (24 and 72 h of incubations) for the 0.50WT composite. The phytotoxicity study proved the safety of the treated RB5 dye solution. Last but not least, the prepared 0.50CWT-500 composite displayed a 92.50% acetaminophen (AMP) photodegradation % towards 1 ppm of AMP under 60 min of solar irradiation.

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