Combined experimental and molecular dynamics removal processes of contaminant phenol from simulated wastewater by polyethylene terephthalate microplastics

ABSTRACT

Microplastics (MPs) and phenolics are pollutants found ubiquitously in freshwater systems. MPs oftentimes serve as a vector for pollutants across ecosystems and are now being explored as alternative adsorbents for pollutant removal. This strategy would reflect the ‘reuse’ of an existing waste stream into a potentially useful product while at the same time helping to minimize plastic waste in the marine environment. In this study, the adsorption of phenol onto pristine (Pr-PET), modified (Mod-PET), and aged (Ag-PET) Polyethylene Terephthalate (PET) microplastics was examined experimentally and theoretically. Kinetics, isotherms, and thermodynamics models were used to investigate the adsorption process while Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations were employed to investigate molecular level alterations. The result showed that the Ag-PET MPs had the best removal efficiency due larger surface area and the adsorption occurred in a pseudo-second-order manner, showing that the rate of phenol adsorption is directly proportional to the number of surface-active sites on the surface of PET MPs while the intraparticle diffusion defined rate-limiting step. However, the maximum monolayer adsorption capacity followed Mod-PET (38.02 mg/g) > Ag-PET (8.08 mg/g) > Pr-PET (6.84 mg/g). The adsorption process proceeded spontaneously and thermodynamically favourable. GCMC-MD simulations revealed that PET MPs are capable of successfully adsorbing the phenol molecule through Van der Waals and electrostatic interactions and can be adopted as novel adsorbents for phenol removal in aqueous solutions.

GRAPHICAL ABSTRACT

KEYWORDS:

• Adsorption
• dynamics
• interaction mechanisms
• kinetics
• simulation

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The authors confirm that the data supporting the findings of this study are available within the article and its supplementary materials.

Additional information

Funding

This study was partially supported by the Special Funds for Innovative Area Research [No.20120015, FY 2008-FY2012] and Basic Research (B) [No. 24310005, FY2012-FY2014; No.18H03384, FY2017-FY2020] of Grant-in-Aid for Scientific Research of Japanese Ministry of Education, Culture, Sports, Science and Technology (MEXT) and the Steel Foundation for Environmental Protection Technology of Japan [No. C-33, FY 2015-FY 2017].