Abstract
In this study, a series of TiO2 nanotubes (NTs) were synthesized employing electrochemical anodization of titanium foil in an ionic liquid solution containing a mixture of glycerol and choline chloride, acting as electrolyte. The as-synthesized TiO2 NTs were calcined at 350, 450, or 550 °C for a 2 h duration to investigate the influence of calcination temperature on NTs formation, morphology, surface properties, crystallinity, and subsequent photocatalytic activity for visible light photodegradation of gaseous formaldehyde (HCHO). Results showed that the calcination temperature has a significant effect on the structure and coverage of TiO2 NTs on the surface. Freshly synthesized TiO2 NTs showed better-ordered structure compared to calcined samples. There was significant pore rupture with increasing calcination temperature. The transformation from anatase to rutile phase appeared after calcination at 450 °C and the weight fraction of the rutile phase increased from 19% to 36% upon increasing the calcination temperature to 550 °C. The band gaps of the TiO2 NTs were in the range from 2.80 to 2.74 eV, shifting the active region of the materials to visible light. The presence of mixed anatase–rutile TiO2 phases in the sample calcined at 450 °C showed enhanced photoactivity, which was confirmed by the 21.56 mg∙L−1∙g−1 removal of gaseous formaldehyde under 120 min of visible light irradiation and displayed enhanced quantum yield, ∅HCHO of 17%.
Highlights
Indoor air pollution is one of the major worldwide human health concerns related to volatile organic compounds (VOCs) since it can lead to sick building syndromes such as headache and fatigue
It can be observed that almost the whole surface is covered by TiO2 NTs and is denser than other samples that were calcined 3a.t1d. iCffhearreancttetreimzaptieornaotuf trhees.TAiOs2foNratnhoetuTbieOs 2 NTs calcined at 350, 450, and 550 °C, obvious changes can be seen from Figure 4b–d
Mixed anatase–rutile phase TiO2 nanotubes were successfully fabricated via electrochemical anodization of titanium foil in this study
Summary
Indoor air pollution is one of the major worldwide human health concerns related to volatile organic compounds (VOCs) since it can lead to sick building syndromes such as headache and fatigue. VOCs such as formaldehyde, toluene, and chloroform are the most commonly investigated airborne contaminants [1]. Formaldehyde (HCHO) is considered as one of the most hazardous VOCs because long-term exposure to it causes adverse effects on human health such as eye irritation, breathing difficulties, and skin irritation [2,3]. The World Health Organization (WHO) guidelines for indoor air HCHO concentration is 0.08 ppm. Nielsen et al [4] reported that the maximum HCHO concentration in a house inhabited by asthmatics in Boston was 162 μg/m3 while for homes in Japan the maximum concentration was 58 μg/m3, the value can increase to 220 μg/m3 in the summer. It is crucial to eliminate this chemical substance in order to improve indoor air quality and to comply with stringent environmental regulations
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