Photocatalytic removal of gaseous ethanol, acetaldehyde and acetic acid: from a fundamental approach to real cases

Abstract

The photocatalytic oxidation of volatile organic compounds (VOCs) has been extensively investigated. With respect to water treatment, photocatalytic degradation of air pollutants is still less understood, but this has not prevented photocatalytic building materials and air purifiers to reach the market. Here, we provide a selective overview of the current understanding on VOC photocatalytic oxidation, focusing on ethanol, acetaldehyde, and acetic acid. Among the main indoor pollutants, these molecules are also oxidation intermediates of numerous VOCs. Their adsorption at the photocatalyst surface is first presented, based on theoretical and experimental evidence. Reaction intermediates are discussed, comparing proposed reaction mechanisms. The role of the photocatalyst features in directing adsorption and oxidation phenomena is highlighted, encompassing both TiO2 and emerging photocatalysts. We then critically discuss gaps in our knowledge, such as the effect of air humidity, multi-pollutant interactions and deactivation pathways. Finally, attempts to model VOC degradation in realistic conditions are reviewed.

Noble Metal Promoted TiO2 from Silver-Waste Valorisation: Synergism between Ag and Au

“…Ethanol was almost completely converted already after 1 h of UV irradiation, forming acetaldehyde as the main oxidation product, and ethylene, which can be formed by a parallel pathway of dehydration (Figure 2), as reported by Nadeem et al [20]. No other intermediates were detected: on these grounds and based on previous literature reports [24], acetaldehyde can be assumed to be further converted to CO2, as reported in Figure 2.…”

“…However, while it showed ethanol degradation and acetaldehyde formation, the degradation of the latter required a longer irradiation time compared to the metal-modified sample here reported. It should be considered that acetaldehyde is far more toxic and more stable to degradation compared to ethanol [24].…”

Ultradeep Removal of Acetaldehyde from Ethanol through Catalytic Hydrogenation with Highly Dispersed Ag Nanoparticles Supported on Phenyl-Modified SiO2

“…Removal of AA from the environment has attracted people’s attention. Physical and chemical technologies including adsorption, catalytic oxidation, membrane separation, and biological treatment were developed for the elimination of dilute AA from a large volume of gas. − Among these methods, adsorption and catalytic oxidation are two kinds of commonly involved technologies. For adsorption, it is usually applied to remove AA with a lower concentration (ppm or subppm), which possesses the advantages of low cost, simple operation procedure, and a high utilization ratio. , For example, carboxymethyl cellulose-foam-supported HKUST-1@graphdiyne (HK@GDY/CMC-B) was designed with a high thermal conductivity and directional channels to enhance its adsorption/desorption efficiency of AA.…”

“…The obtained HK@GDY/CMC-B exhibited an excellent acetaldehyde adsorption capacity of up to 11.0 mmol g –1 in AA vapor ( C 0 = 7.8 mg m –3 , T = 298 K) . Due to its low energy consumption and potential utilization under sunlight, photocatalytic oxidation degradation (PCOD) also proved to be a powerful method for the removal of indoor acetaldehyde. ,,, With H–Zr 0.1 Ti 0.9 O 2 @U6N as the catalyst and being operated under UV–vis stimulation, 98% of AA (gaseous AA, ∼1000 ppm) could be decomposed in 20 min …”

Ultrasound waves at the service of photocatalysis: From sonochemical synthesis to ultrasound-assisted and piezo-enhanced photocatalysis

“…In a polluted and energy-starving world, photocatalysis is a much-needed technology that has the potential to revolutionize environmental protection, green chemistry, and renewable energy by making use of light to activate reactions of pollutant degradation, selective synthesis, water splitting, and CO 2 reduction. Nevertheless, despite the huge amount of research over the last decades, real-life photocatalysis applications are few and mostly limited to the small-scale treatment of contaminants [1]. Current photocatalytic technologies suffer from limited solar energy utilization, high recombination rate, and low mobility of photo-induced carriers, which curb the process efficiency and result in increased energy costs needed for lamp irradiation.…”