A Smart Adsorbent with Ability of Environmentally Friendly Regeneration for p-Nitrophenol Removal in Aqueous Solution

Efficient removal of p-nitrophenol from water by imidazolium ionic liquids functionalized cellulose microsphere

Removing p-nitrophenol (PNP) from water resources is crucial due to its significant threat to the environment and human health. Herein, imidazolium ionic liquids with short/long alkyl chain ([C2VIm]Br and [C8VIm]Br) modified cellulose microspheres (MCC-[C2VIm]Br and MCC-[C8VIm]Br) were synthesized by radiation method. To examine the impact of adsorbent hydrophilicity on adsorption performance, batch and column experiments were conducted for PNP adsorption. The MCC-[C2VIm]Br and MCC-[C8VIm]Br, with an equivalent molar import amount of ionic liquids, exhibited maximum adsorption capacities of 190.84 mg/g and 191.20 mg/g for PNP, respectively, and the adsorption equilibrium was reached within 30 min. Both adsorbents displayed exceptional reusability. Integrating the findings from XPS and FTIR analyses, and AgNO3 identification, the suggested adsorption mechanism posited that the adsorbents engaged with PNP through ion exchange, hydrogen bonds and π-π stacking. Remarkably, the hydrophobic MCC-[C8VIm]Br exhibited superior selectivity for PNP than the hydrophilic MCC-[C2VIm]Br, while had little effect on adsorption capacity and rate. MCC-[C8VIm]Br-2 with high grafting yield increased the adsorption capacity to 327.87 mg/g. Moreover, MCC-[C8VIm]Br-2 demonstrated efficient PNP removal from various real water samples, and column experiments illustrated its selective capture of PNP from groundwater. The promising adsorption performance indicates that MCC-[C8VIm]Br-2 holds potential for PNP removal from wastewater.

Poly(2-vinylpyridine)/MCM-41 Composites with Micropores and Switchable Mesopores for the Removal of Cr(VI)

Porous structure design and reversible regulation of pore size during adsorption-desorption are crucial to the removal of pollutants in water such as Cr(VI). In this paper, micropores and switchable mesopores were constructed on MCM-41 to further improve adsorption-desorption performance of Cr(VI) via the confinement effect of micropores and opening and closing of mesopores. 2-Vinylpyridine was introduced and polymerized into the pores and on the pore mouth of MCM41 modified by C═C group (AM41) under the irradiation of ultraviolet light. The obtained samples (PM41) possessed mesopores (2.73 nm) and micropores (1.36 nm), where mesopores could open or close under different pH and micropores showed the confinement effect because their pore size is close to Cr(VI) diameter (0.87 nm). Compared with MCM-41, the introduction of poly(2-vinylpyridine) enhanced obviously its adsorptive ability and it trapped most of the Cr(VI) (99%) in solution, 12 times higher than that of the parent sample. The change of pore size is favorable to the cycle performance, and after 3 times recycling, the removal rate of Cr(VI) by PM41-20 remained above 88%. Langmuir isotherm showed a better data correlation than the Freundlich model. Cr(VI) in solution was removed by electrostatic interaction between the pyridine group and Cr(VI) and the confinement effect from micropores.

Thermosensitive poly(N-isopropylacrylamide)-grafted magnetic-cored dendrimers for benzene uptake

A series of thermosensitive and magneto-responsive dendrimers was synthesized based on magnetic-cored dendrimers (MCD) and carboxylic end-capped poly(N-isopropylacrylamide) (PNIPAM) to obtain PNIPAM-g-MCD. Thermo-response profiles of the PNIPAM-g-MCD from dynamic light scattering within the temperature range of 25-45 °C indicated that the lower critical solution temperature (LCST) of the PNIPAM-g-MCD was 32 °C. The physical size of the PNIPAM-g-MCD decreased as the temperature increased above the LCST. The initial hydrodynamic size of the PNIPAM-g-MCDs at 25 °C was 298.6 nm and reached 226.4 nm at 45 °C upon heating. Adsorption of benzene onto the PNIPAM-g-MCD at 25 °C was assessed, and the results showed that hydrophobic benzene was included within the internal cavities of lipophilic PNIPAM-g-MCD to maintain a thermodynamically stable state. Entrapment effects of the PNIPAM-g-MCD were confirmed at 45 °C, and the removal efficiency of benzene increased considerably to 50% when benzene was adsorbed, and the entrapment process was added. The shrunken PNIPAM terminal groups aggregated and trapped benzenes within the cavities of PNIPAM-g-MCD to prevent escape into the aqueous solution. Un-trapped benzene was removed through coalescence with PNIPAM-g-MCD because hydrophobic interactions prevailed with increasing temperature. PNIPAM-g-MCD were also able to form emulsions below the LCST and disrupted emulsions above the LCST in oil-water emulsions.