Photocatalytic Degradation of Plastic Waste: A Mini Review

Abstract

Plastic waste becomes an immediate threat to our society with ever-increasing negative impacts on our environment and health by entering our food chain. Sunlight is known to be the natural energy source that degrades plastic waste at a very slow rate. Mimicking the role of sunlight, the photocatalytic degradation process could significantly accelerate the degradation rate thanks to the photocatalyst that drastically facilitates the photochemical reactions involved in the degradation process. This mini review begins with an introduction to the chemical compositions of the common plastic waste. The mechanisms of photodegradation of polymers in general were then revisited. Afterwards, a few photocatalysts were introduced with an emphasis on titanium dioxide (TiO2), which is the most frequently used photocatalyst. The roles of TiO2 photocatalyst in the photodegradation process were then elaborated, followed by the recent advances of photocatalytic degradation of various plastic waste. Lastly, our perspectives on the future research directions of photocatalytic plastic degradation are present. Herein, the importance of catalytic photodegradation is emphasized to inspire research on developing new photocatalysts and new processes for decomposition of plastic waste, and then to increase its recycling rate particularly in the current pandemic with the ever-increasing generation of plastic waste.

Microbial abilities to degrade global environmental plastic polymer waste are overstated

“…UV light treatment is commonly applied to pre-treat PE (Zahra et al 2010, Montazer et al 2018 and PP plastics prior to degradation experiments (Jeyakumar et al 2013, Aravinthan et al 2016. The saturated bonds in the C-C backbone of such homochain polymers are broken down through photoinitiated chain-scission and crosslinking reactions, a process that can be accelerated by the presence of chemical impurities and structural abnormalities (Lee and Li 2021). Chemical bonds in the main polymer chain are broken by the energy of light, followed by β-scission propagation and free radical reactions, resulting in polymer fragmentation into a diversity of smaller chain lengths and therefore a reduced molecular weight (Yousif and Haddad 2013).…”

Microplastics in the Marine Environment: A Review of Their Sources, Formation, Fate, and Ecotoxicological Impact

“…Chemical pollutants are present in the atmosphere (e.g., sulfur dioxide, nitrogen dioxide, ozone, and volatile organic compounds) and the marine environment (e.g., acidity and salinity). The atmospheric pollutants can directly degrade the plastics or catalyze the radical formation by photochemical reactions leading to plastic degradation [73]. Sulfur dioxide and nitrogen dioxide can enhance the formation of ozone in the atmosphere, as a result of UV excitation and photochemical reaction with oxygen [74].…”

Prospects of TiO2-based photocatalytic degradation of microplastic leachates related disposable facemask, a major COVID-19 waste

“…The underpinnings of photocatalytic degradation (PCD) are photocatalysts with strong redox potential. Semiconductor materials such as TiO 2 , ZnO, WO 3 , g-C 3 N 4 , CdS, SnO 2 ZrO 2 , BiVO 4 , and ZnS are employed as a photocatalysts in the PCD of organic contaminants (Lee and Li, 2021;Sharma et al, 2021). Once the absorbed energy of the photon (E) exceeds the semiconductor's band gap energy, electrons (e − ) in the valence band (VB) are transported to the conduction band (CB), and hence positive holes (h + ) are created in the VB, resulting in the dissociation of electron-hole pairs.…”

“…For PCD, anatase and rutile forms of TiO 2 are often used. Brookite forms are rarely utilized due to their unstable nature (Lee and Li, 2021). Iron oxide semiconductors are unstable because of their rapid photocathodic reactions and the resulting corrosive materials.…”