| Summary: | The advance of the pharmaceutical industry has been determined as one of the factors that contributed to the ubiquitous presence of organic pharmaceuticals and heavy metals, particularly tetracycline (TC) and hexavalent chromium (Cr(VI)) in the environment, exposing the human and ecotoxicology to the unparallel impacts. Photocatalysis has emerged as an excellent method to remove a distinct range of organic and inorganic compounds due to its high efficiency and low energy consumption. Molybdenum oxide (MoO3) is a promising photocatalyst due to its excellent visible light response range and abundant of surface defects. Yet, it exhibits poor photocatalytic activity due to its low surface area and high recombination rate of photogenerated charges. Inspired by several developments of fibrous silica metal oxides which improved the surface area and accessibility of the active sites for enhanced photocatalytic activity, this research focused on the synthesis of fibrous silica molybdenum oxide (FSMo) for simultaneous photocatalytic removal of TC and Cr(VI). The FSMo catalyst was successfully synthesized via the microemulsion technique and subjected to several characterizations including X-ray diffraction, Fourier transform infrared, nitrogen adsorption-desorption, field emission scanning electron microscopy, transmission electron microscopy, ultraviolet-visible diffuse reflectance spectroscopy and photoluminescence. The FESEM analysis confirmed the successful fabrication of FSMo. The synthesized 10-FSMo demonstrated superior photocatalytic activity towards the removal of TC (74%) and Cr(VI) (69%) compared to the commercial MoO3, 46% and 55%, respectively, which can be attributed to its high surface area, narrow bandgap and low recombination of charges. The kinetic study of the catalyst indicated that the simultaneous photoredox of TC and Cr(VI) followed the pseudo-first-order Langmuir-Hinshelwood model. The mechanism of photocatalytic activity revealed that the active species for the removal of TC and Cr(VI) were electrons and holes, respectively. Stability studies showed that the 10-FSMo catalyst demonstrated only slight reduction (< 20 %) even after four cycles of experiments. The introduction of another pharmaceutical pollutant (ibuprofen) showed less than 20% reduction in removal efficiency of TC and Cr(VI). The optimization of simultaneous photoredox of TC and Cr(VI) using response surface methodology showed that 92.5% and 99.4% of the variabilities in the data were accounted for the model. The experimental values at optimized conditions (pH = 8.51, TC concentration = 11.8 mg L-1 and Cr(VI) concentration = 9.66 mg L-1) show 1.85% and 4.80% of error for removal of TC and Cr(VI) respectively, compared to the predicted values. These findings indirectly prove the potential use of the FSMo catalyst for wastewater treatment.
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