Enhanced Solid-Phase Photocatalytic Degradation Activity of a Poly(vinyl chloride)-TiO2 Nanocomposite Film with Bismuth Oxyiodide

Incorporation of ultrathin porous metal-free graphite carbon nitride nanosheets in polyvinyl chloride for efficient photodegradation

Solid-phase photocatalytic degradation of waste plastics is one of the promising approaches to solve the "white pollution" problem. In this work, a low cost, metal-free, environmentally friendly organic photocatalyst, graphite carbon nitride (g-C₃N₄), was used for the first time to successfully enhance the photodegradation of polyvinyl chloride (PVC) under simulated sunlight from its visible light photocatalytic capability, while its organic nature and abundant surface functional groups were beneficial for its good dispersion in plastics. It was found that the ultrathin porous g-C₃N₄ nanosheet synthesized from urea (the UCN sample) had much stronger photodegradation effect in PVC/g-C₃N₄ composite films than its thick block counterpart synthesized with melamine (the MCN sample) due to its larger specific surface area, higher pore volume, and enhanced photogenerated charge carrier separation. With the incorporation of only 1 wt% UCN sample into PVC, its mechanical properties were largely enhanced with the tensile strength increase of ∼ 45% and the elongation at break increase of ∼ 72%, and its weight loss increased ∼ 58% after 120 h irradiation in the weather resistance test chamber. ^·O₂^- and h⁺ produced by the UCN sample were found as the main active species in the photocatalytic degradation of PVC to dechlorinate PVC and decompose its long-chain molecules into short-chain small molecules until its final degradation into CO₂ and H₂O under ideal conditions.

Adsorption properties and influencing factors of Cu(II) on polystyrene and polyethylene terephthalate microplastics in seawater

As an emerging contamination in the ocean, microplastics can act as effective vectors of pollutants, the ecological risks caused by the combined pollution of microplastics and other pollutants have attracted growing attention. In this work, Copper (Cu(II)) was chosen as the classic pollutant, polystyrene (PS) and polyethylene terephthalate (PET) pellets were used as the typical marine microplastics, the adsorption performance of Cu(II) on PS and PET beads was investigated by adsorption kinetics and isotherm experiments, and other influencing conditions, such as pH, salinity, coexisting heavy metals ions and aging treatment, were evaluated. The results indicated that the adsorption behavior of Cu(II) on PS and PET was spontaneous and endothermic in the simulated seawater environment, and the batch experimental data can be effectively described by pseudo-second-order model and Freundlich isothermal model. Besides, the adsorption capacity of microplastics for Cu(II) was the best at pH 7, the change of salinity had no obvious effect on the adsorption in the natural marine environment. Moreover, co-existence of lead (Pb(II)) exhibited evident impacts on Cu(II) sorption onto PS and PET, which confirmed the adsorption competition effect between them. Additionally, high temperature aging treatment of microplastics in different environments for different duration time could obviously affect the properties of microplastics. It was found that the microplastics after being exposed to high temperature environment in the air for 168 h showed relatively stronger adsorption amount for Cu(II). In summary, these findings suggested that electrostatic interaction and distributed diffusion mechanisms may be the main mechanisms of adsorption, while no new functional groups were generated after the adsorption, indicating that physisorption may dominate the adsorption performance of PS and PET pellets for Cu(II). This study provides supplementary insights into the role of microplastics as carriers of heavy metals in the marine environment.

Photocatalytic Degradation of Plastic Waste: A Mini Review

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.

Image analysis of PVC / TiO2 nanocomposites SEM micrographs

The present paper deals with image analysis of Scanning Electron Microscope (SEM) micrographs of PVC / TiO₂ nanocomposites prepared through solution casting technique at different wt% of TiO₂ nanofillers dispersed within the PVC matrix. The qualitative and quantitative dispersion of TiO₂ nanofillers is estimated through the proposed algorithm based on global threshold obtained from Otsu's method. The PVC-TiO₂- PVC molecular region map and TiO₂ nanofillers dispersion maps are obtained by background elimination technique with predefined threshold value and a global threshold value, respectively. The particle size distribution histograms are obtained in terms of TiO₂ nanofillers population versus available PVC/TiO₂ matrix areal spread. This study is carried out to correlate qualitative and quantitative dispersion of TiO₂ nanofillers within the PVC matrix with the variation of specimen properties accordingly.

High temperature depended on the ageing mechanism of microplastics under different environmental conditions and its effect on the distribution of organic pollutants

Microplastics, as an emerging class of pollutants has become a global concern, and is receiving increasing attention. Interestingly, microplastics are always in their ageing process when they enter the real environment. Our study investigated the ageing properties of polystyrene (PS) plastics in air, pure water and seawater environments at 75 °C. A two-dimensional (2D) Fourier transform infrared (FTIR) correlation spectroscopy (COS) analysis was used to better understand the ageing mechanism of the PS plastics. Based on the 2D-COS analysis, different ageing mechanisms were identified under different ageing conditions, such as an ageing sequence of aged-PS particle functional groups in air: 1601(CC) > 1050(C-O)>1453(C-H)>1493(C-H)>1375(C-OH)>1666(CO). Among the functional group changes, O-functional groups (C-O, C-OH and CO) were introduced during the ageing process. Moreover, for pristine PS particles, hydrophobicity was a major factor for the interaction between the microplastics and organic pollutants. For aged-PS particles, their adsorption capacities were significantly enhanced as the degree of ageing increased. The ageing degree of PS was highly responsible for increasing of the specific surface area and the increase in oxygen-containing surface groups. Furthermore, there was a significant enhancement in the adsorption affinity for antibiotic contaminants than for polycyclic aromatic hydrocarbon contaminants. Aged PS particles had little adsorption of polycyclic aromatic hydrocarbons, because the presence of oxygen-containing surface groups on the aged PS plastics might allow the formation of hydrogen bonds with the surrounding water molecules. Overall, a 2D-COS analysis was an effective method for understanding the ageing process of microplastics under different environmental conditions at high temperature. These results also clearly demonstrated the characteristics and mechanisms of the interaction between aged-microplastics and organic pollutants, which could be useful for understanding the environmental behavior of co-existing pollutants.