Mu Li,Feiyun Sun,Wentao Shang,Xiaolei Zhang,Wenyi Dong,Tongzhou Liu,Wen Pang
Understanding the mechanism by which perfluorochemicals (PFCs) adsorbed on carbonaceous surface is eventually important to the design and process optimization of effective PFCs removal technologies . In this study, the possible binding mechanism of six different PFCs onto carbonaceous surface was investigated by means of first principles quantum mechanical methods based on density functional theory (DFT) calculation and wave function analysis. The adsorption process fitted well with pseudo-second-order kinetic indicated that chemical bonding could not be underestimated. The results indicate that there were monolayer adsorption, electrostatic and hydrophobic interactions existed in PFCs adsorption process. DFT results suggested that the adsorption of PFCs on carbonaceous surface was one chemisorption process that accompanied by Van der Waals interactions. As there was different head functional groups in PFOS and PFOA, their adsorption capacity mainly controlled by the availability of active sites that was occupied by PFCs. The variation of chain length of PFBS and PFOS also take a certain responsible for different adsorption paths, due mainly to their hydrophobic effect. The obtained results from wave function and DFT analysis give in-depth understanding of PFCs adsorption on carbonaceous surface and help to their effectively removal.
Conventional polyamide-based interface polymerized nanofiltration (NF) membranes exhibit trade-off characteristics between water permeability and salt selectivity . The introduction of nanomaterial interlayers into thin-film composite (TFC) membranes is expected to overcome the limitation. Herein, a novel membrane was constructed via coating a polyvinyl alcohol (PVA) interlayer on the PES supporting film. Trace amounts of MXene nanosheets were used to form a barrier to avoid the occupancy of large pores by PVA. Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), Raman spectra , water contact angle (WCA), zeta potential , and other characterizations were used to evaluate the chemical and physical properties of the prepared membranes. Due to the PVA hydrophilicity , the composite membranes achieved higher hydrophilicity. Besides, the electronegativity enhancement and roughness improvement facilitate the film to have better application prospects. At the lab scale, the optimized membranes achieved a high-water flux of 22.8 L m⁻ 2 h⁻ 1 bar⁻ 1 and a 94.5% MgSO 4 rejection. The typical kinds of PFCs , including PFOA, PFOS , PFHxA and PFBA, were quantitatively evaluated and analyzed by electrostatic interaction. The excellent performance was maintained in the case of environmental changes owing to the stableness of the PVA interlayer. This study provides a new avenue for fabricating robust NF membranes for actual production.
Guanhong Liu,Brittney Ashley Stewart,Kai Yuan,Siyuan Ling,Meng Zhang,Guangju Wang,Kuangfei Lin
The adsorption-desorption performance of perfluorooctanoic acid (PFOA), one of the environmentally persistent pollutants which is refractory to degrade in soil, was investigated and reported. The adsorption-desorption process of PFOA was firstly conducted using different fractions (sand, coarse silt and fine silt) of soil collected from Shanghai, China. More than 50% of PFOA (2.0 mg/L) could be adsorbed by soils while only less than 10% of which could be desorbed once contamination occurs. The kinetics and particle diffusion rates of PFOA in different fractions of soil were calculated and analyzed in detail. Apart from this, the retention of short-chained PFCs , which can be generated as degradation products of PFOA, were also measured. In single solute systems, the adsorption of pollutants in soils dramatically increased as the chain length of PFCs grew longer. Similarly, in mixed solutions, preferential adsorption of longer-chained PFCs over shorter chains in soils were sited, attributable to the stronger hydrophobicity of the pollutants. However, the desorption of them performed in reverse, where the desorption rates of longer-chained PFCs were far lower than those of shorter ones. Furthermore, influencing factors including pH, temperature and co-existing matters were studied during the adsorption process. After comprehending the adsorption behavior of PFOA in soil fractions, the situation of the adsorption of PFOA in various soils chosen from nine provinces in China was investigated and compared. There was an obvious discrepancy, whether it be from the rate or the amount of adsorption of PFOA (approximately 10%), in the nine different soils. Finally, a multiple linear regressive equation was employed to sort influencing parameters which are prone to affect the adsorption of PFOA in soils, the contribution of these are provided in order of relevance. These results demonstrate the adsorption performance and behavior of PFOA and PFCs in different soils, which can be utilized as a scientific reference for maximizing remediation of PFOA polluted sites in the future.
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