Six kinds of 1,3,4-oxadiazole-functionalized fibers were prepared to evaluate the adsorption capacity for Hg 2+ . Finally, a functionalized fiber (PAN p-PMOD F) with the best adsorption performance was selected for further research. The PAN p-PMOD F fiber was characterized by infrared (IR), elemental analysis (EA), scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The PAN p-PMOD F shows excellent selectivity for mercury ions in a mixed heavy metal ion solution (Hg 2+ , Ni 2+ , Pb 2+ , Zn 2+ , Ag + , Co 2+ , Cr 3+ , Cu 2+ , and Cd 2+ ), and it can reduce the concentration of Hg 2+ to 44 ppb in the actual sewage, which is of great practical value for the treatment of mercury pollution. Furthermore, the adsorbed Hg 2+ can be desorbed completely by dilute HNO 3 and the PAN p-PMOD F can be reused many times with excellent recyclability.
The acid–base pairing and fabrication method was
herein
employed to construct acid–base bifunctional heterogeneous
catalysts. The boronic acid group was introduced into primary amine-functionalized
polyacrylonitrile fiber (PANEAF) via amide bond formation
to fabricate boronic acid-amine bifunctional PANFs as recyclable heterogeneous
catalysts by using the amino N atoms of PANEAF as anchoring
points. The so-obtained fiber catalysts PANEA–BA1F and PANEA–BA2F containing boronic acid groups
attached on benzene and pyridine rings, respectively, were employed
in the Henry reactions of aryl aldehydes with nitromethane. Catalytic
investigations showed that their performance had great correlation
with the change of boronic acid. PANEA–BA2F exhibited
a higher substrate selectivity than PANEA–BA1F,
and only the benzaldehydes with hydroxy, dimethylamino, and amide
groups were reactive, which showed preliminary substrate specificity
like enzyme catalysis. The in situ investigation with cyclododecane
as solvent by Raman and Fourier transform infrared spectroscopy (FT-IR)
analysis was conducted to clarify the catalytic difference. Moreover,
the uncommon reverse reactivity order of benzaldehydes in PANEA–BA1F-catalyzed condensation was explained.
A series of novel polyacrylonitrile fiber catalysts modified with different ratio of quaternary ammonium salt (QA) to tertiary amine (TA) were screened for heterogeneously catalyzed aza-Michael addition in water. The best catalyst was found to be PAN PQ-1 F with a QA:TA ratio of 1:1, which can lead to high yield, excellent selectivity of solvent and great recyclability under optimized conditions. The special microenvironment of hydrophilic inner layer and hydrophobic surface layer of PAN PQ-1 F is conducive to the leaving of the product and the high conversion of the reaction. Based on the fact that appropriate microenvironment combined with the catalytic sites promoted the reaction, cooperative effect of QA and TA in the microenvironment of PAN PQ-1 F catalyst was proposed.
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