Microporous metal-organic frameworks against endocrine-disruptor bisphenol A: parametric evaluation and optimization

Electrospun of functionalized mesoporous UiO-66 as the selective coating of solid phase microextraction Arrow for the determination of nine alkylphenols

A solid-phase microextraction (SPME) Arrow and high-performance liquid chromatography-UV detector (HPLC-UV, detection at 225 nm) based method was developed for the selective determination of nine alkylphenols (APs) in milk. The functionalized mesoporous UiO-66 (4-meso-UiO-66) was utilized as the new coating material, which was synthesized by post-modification of pore-expanded UiO-66-NH2 by an esterification reaction with 4-pentylbenzoic acid. It was fully characterized by X-ray photoelectron spectroscopy (XPS), fourier transformation infrared spectrometry, nitrogen sorption-desorption test, scanning electron microscopy, transmission electron microscopy, and X-ray diffractometer. The characterization results showed the ester groups and benzene rings were introduced into the 4-meso-UiO-66, and the mesoporous structure was predominant in the 4-meso-UiO-66. The extraction mechanism of 4-meso-UiO-66 to APs is the synergistic effect of Zr-O electrostatic interaction and the size exclusion effect resulting from XPS, selectivity test, and nitrogen sorption-desorption test. The electrospinning technique was utilized to fabricate the 4-meso-UiO-66 coated SPME Arrow and polyacrylonitrile (PAN) was used as the adhesive. The mass rate of 4-meso-UiO-66 to PAN and the electrospinning time were evaluated. The extraction and desorption parameters were also studied. The linear range of this method was 0.2-1000 μg L-1 with a coefficient of determination greater than 0.9989 under the optimal conditions. The detection limits were 0.05-1 μg L-1, the inter-day and intra-day precision (RSD) were 2.8-11.5%, and the recovery was 83.6%-112%. The reusability study showed that the extraction performance of this new SPME Arrow could be maintained after 80 adsorption-desorption cycles. This method showed excellent applicability for the selective determination of APs in milk.

Adsorption and catalytic degradation of bisphenol A and p-chlorophenol by magnetic carbon nanotubes

Phenolic compounds are common industrial pollutants that seriously endangers water ecology and human health. Therefore, the development of efficient and recyclable adsorbents is of importance for wastewater treatment. In this research, HCNTs/Fe3O4 composites were constructed using co-precipitation way by loading magnetic Fe3O4 particles onto hydroxylated multi-walled carbon nanotubes (MWCNTs), showing excellent adsorption capacity for Bisphenol A (BPA) and p-chlorophenol (p-CP), and excellent catalytic ability of activating potassium persulphate (KPS) for degradation of BPA and p-CP. The adsorption capacity and catalytic degradation potential were evaluated for the removal of BPA and p-CP from solutions. The results showed that the adsorption took only 1 h to reach equilibrium and HCNTs/Fe3O4 had maximum adsorption capacities of 113 mg g-1 for BPA and 41.6 mg g-1 for p-CP at 303 K, respectively. The adsorption of BPA fitted well using the Langmuir, Temkin and Freundlich models while the adsorption of p-CP fitted well using the Freundlich and Temkin models. BPA adsorption on HCNTs/Fe3O4 was dominated by π-π stacking and hydrogen bonding forces. The adsorption included both the mono-molecular layer adsorption on the adsorbent surface and the multi-molecular layer adsorption on the non-uniform surface. The adsorption of p-CP on HCNTs/Fe3O4 was a multi-molecular layer adsorption on a dissimilar surface. The adsorption was controlled by forces such as π-π stacking, hydrogen bonding, partition effect and molecular sieve effect. Moreover, KPS was added to the adsorption system to initiate a heterogeneous Fenton-like catalytic degradation. Over a wide pH range (4-10), 90% of the aqueous BPA solution and 88% of the p-CP solution were degraded in 3 and 2 h, respectively. After three adsorption-regeneration or degradation cycles, the removal of BPA and p-CP remained up to 88% and 66%, indicating that HCNTs/Fe3O4 composite is cost-effective, stable and highly efficient to remove BPA and p-CP from solution.

Different strengthening effects of amino and nitro groups on the bisphenol A adsorption of an aluminum metal-organic framework in aqueous solution

In recent years, metal-organic frameworks (MOFs) have been employed in numerous applications for adsorption. Researchers synthesize new MOFs by various methods, including the introduction of functional groups. In this study, three different aluminum-based MOFs (with non-functionalized, amino-functionalized, nitro-functionalized) were produced by hydrothermal synthesis and used for investigating typical endocrine disrupting chemicals (EDCs), namely for bisphenol A (BPA) adsorption. We used several methods to characterize the MOFs and conducted batch adsorption experiments to investigate their adsorption properties, and explore the influence of different functional groups on adsorption materials. The specific surface area of Al-MOF-NH₂ is 6 times larger than that of Al-MOF according to the N₂ adsorption and desorption isotherms of the material, that is, the BET of Al-MOF, Al-MOF-NH₂, and Al-MOF-NO₂ were 109.68, 644.03, and 146.60 m²/g. Note that although the same synthesis method is used, pore size is greatly changed because of the different functional groups. Al-MOF and Al-MOF-NO₂ have more mesopores, and Al-MOF-NH₂ is mainly microporous. The BPA adsorption capacities of Al-MOF, Al-MOF-NH₂, and Al-MOF-NO₂ were 46.43, 227.78, and 155.84 mg/L. The outcomes can also be explained by the improved adsorption performance from the addition of amino functional groups. In this research, the adsorption isotherms and adsorption kinetics of the three Al-MOFs for BPA were also investigated to explain the different adsorption properties of various functional groups. The results show that the amino-functionalized materials have remarkable characterization morphologies, uniform particle distributions, appropriate particle sizes, excellent specific surface areas, and superior adsorption effects.

Pyridine-linked covalent triazine frameworks with bidirectional electron donor-acceptor for efficient organic pollution removal

Simultaneous regulation of adsorption and photocatalytic performance of covalent triazine frameworks (CTFs) to achieve efficient control of organic pollution in water is a promising strategy, but remains a formidable challenge. Herein, pyridine linkers were innovatively introduced into pristine CTF (p-CTF) and the bidirectional electron donor-acceptor (EDA) system of contaminant-to-pyridine and pyridine-to-triazine was constructed inside. Experimental results combined with theoretical calculations revealed that pyridine units with π-deficient properties performed as electron acceptors and electron donors in the adsorption and photocatalytic processes, respectively. This special structure provided a directional pathway for electron transfer, which endowed CTFs with excellent adsorption and photocatalytic properties. Compared to p-CTF, pyridine-linked CTF (M-CTF) showed a 16-fold increase in adsorption capacity for naphthalene (973.4 μmol·g^-1). Benefiting from the optimized light absorption and electron transfer form (n → π*transition), M-CTF exhibited high regeneration efficiency after adsorption of both bisphenol A (94 % after 4 cycles) and naphthalene (95 % after 4 cycles). Besides, the removal performance of organic micropollutants from natural water showed a great advantage thanks to the bidirectional EDA system. Overall, the present study provides new insights into the optimization of electronic structures for carbon-based environmental functional materials applied to organic pollution control in water.