Effective collection of hydrophobic organic pollutants in water with aluminum hydroxide and hydrophobically modified polyacrylic acid

A Study on the Dilational Modulus Measurement of Polyacrylic Acid Films at Air-Water Interface by Pendant Bubble Tensiometry

The dilational modulus (E) of polymer films has been commonly measured using the oscillating ring/bubble/drop methods with an external force, and often without specifying the state of the adsorbed film. This study explores an approach where E was determined from the relaxations of surface tension (ST) and surface area (SA) of natural perturbations, in which ST and SA were monitored using a pendant bubble tensiometer. The E of the adsorbed film of PAA (polyacrylic acid) was evaluated for aqueous solutions at CPAA = 5 × 10-4 g/cm3, [MW = 5, 25, and 250 (kDa)]. The E (=dγ/dlnA) was estimated from the surface dilational rate (dlnA/dt) and the rate of ST change (dγ/dt) of the bubble surface from the natural perturbation caused by minute variations in ambient temperature. The data revealed that (i) a considerable time is required to reach the equilibrium-ST (γeq) and to attain the saturated dilational modulus (Esat) of the adsorbed PAA film, (ii) both γeq and Esat of PAA solutions increase with MW of PAA, (iii) a lower MW solution requires a longer time to reach its γeq and Esat, and (iv) this approach is workable for evaluating the E of adsorbed polymer films.

Deciphering the transformation mechanism of substituted polycyclic aromatic hydrocarbons on Al(III)-montmorillonite: An experimental and density functional theory study

The researches on transformation of polycyclic aromatic hydrocarbons (PAHs) on clay minerals modified by metal ions have received increasing attention. However, the transformation of PAHs with electron-withdrawing or electron-donating substitutional groups on clay minerals is not well understood currently. In this study, the degradation of anthracene (ANT) with different substituents (including -CH₃, -CHO, -Br, -OMe, and -NO₂) on Al(III)-montmorillonite (MMT) was investigated in the dark. The results showed that aromatic compounds were degraded with the rate constants (k_obs) of 0.004-0.141 d^-1. Moreover, ANT with electron-donating substituents (e.g., -CH₃, -OMe) had a higher transformation rate than that with electron-withdrawing substituents (e.g., -Br, -NO₂). The reactive oxygen species (ROS) quenching experiments indicated that ROS played a significant role in the transformation of ANT and ANT derivatives. Density functional theory (DFT) calculations revealed that the reactivity of single substituted PAHs was highly correlated with their ionization potential (IP), the energy of highest occupied molecular orbital (E_HOMO), the energy of lowest unoccupied molecular orbital (E_LUMO), and electronegativity (ζ), while independent of hardness (η). This study provides novel insights into predicting the reactivity of PAHs derivatives, and lays a fundamental basis for better understanding the fate of substituted PAHs in soils.