Mancheng Zhang

Quaternized magnetic microspheres for the efficient removal of reactive dyes

In this paper, a novel quaternized magnetic resin, NDMP, was prepared and characterized. Two reactive dyes (RDs), Orange G (OG) and red RWO, were used as a small-molecular RD and large-molecular RD, respectively, to investigate their adsorption on NDMP. A common quaternized magnetic resin, MIEX, was selected for comparison. The adsorption kinetics of OG onto both resins and the adsorption kinetics of RWO onto NDMP followed pseudo-second-order kinetics, whereas the adsorption of RWO onto MIEX was better fitted by pseudo-first-order kinetics. The experimental data illustrated that the equilibrium adsorption amount of both RDs onto NDMP (1.9 mmol OG/g, 0.70 mmol RWO/g) was twice as large as that on MIEX (1.0 mmol OG/g, 0.35 mmol RWO/g). The Langmuir equation and the Freundlich model fit the isotherm data for OG and RWO adsorption, respectively. The adsorption of OG on the NDMP and MIEX resins declined in the presence of NaCl or Na₂SO₄. The effects of the salts on the adsorption of RWO were different. The recyclability of NDMP and MIEX were also evaluated. This work provides a reusable efficient adsorbent for the removal of RDs.

Preparation of a novel magnetic microporous adsorbent and its adsorption behavior of p-nitrophenol and chlorotetracycline

A novel method for fabricating hypercrosslinked magnetic polymer beads with improved acid resistance was developed. Magnetite nanoparticles were covered with tetraethoxysilane and vinyltriethoxysilane, followed by co-polymerization and post-crosslinking. The resulting M150 beads were highly stable at pH ≥ 2 and were superparamagnetic, with a saturation magnetization of 3.1 emu/g. M150 exhibited a specific surface area of 1022.4m(2)/g and an average pore width of 2.6 nm. The adsorption of p-nitrophenol and chlorotetracycline (CTC) onto M150 and the commercial non-magnetic resins NDA 150 and XAD-4 followed both pseudo-first-order and pseudo-second-order equations. M150 displayed much faster kinetics than the other resins because of its small particle size and abundant macropores. The adsorption isotherm of p-nitrophenol onto the three resins fitted the Freundlich equation (R(2)>0.98), whereas CTC adsorption was better described by the Langmuir isotherm. p-Nitrophenol adsorption was optimal at pH ≤ 4, whereas CTC adsorption was optimal at pH 5-6. All three sorbents showed high reusability for p-nitrophenol adsorption. XAD-4 demonstrated the highest reusability for CTC. The CTC adsorption capacities of M150 and NDA150 decreased by 12.42% and 20% after 10 adsorption-desorption cycles, respectively.

A magnetic sorbent for the efficient and rapid extraction of organic micropollutants from large-volume environmental water samples

A magnetic solid-phase extraction (MSPE) method based on a novel magnetic sorbent was proposed for the extraction of target compounds from large-volume water samples. First, magnetic hypercrosslinked microspheres (NAND-1) were prepared via membrane emulsification-suspension polymerization and post crosslinking reaction. To ensure that the Fe3O4 nanoparticles could completely pass through the membrane without blocking the pores, oleic acid was used to modify the Fe3O4 nanoparticles, which enhanced lipophilicity and monodispersity of the magnetite nanoparticles. The obtained NAND-1 microspheres exhibited super paramagnetic characteristics and excellent magnetic responsiveness with a saturation magnetization of 2.53 emu/g. In addition, a uniform particle size (~8 μm) and a large average surface area (1303.59 m(2)/g) were also observed, which were both beneficial for the extraction of the target compounds. Thus, NAND-1 has the potential to simultaneously exhibit good extraction efficiencies toward different types of organic micropollutants (OMPs), including triazines, carbamazepine and diethyl phthalate. The conditions of the MSPE based on NAND-1 were optimized by single factor and orthogonal design experiments. This MSPE method needed only a small amount of sorbent (50mg/L) for the extraction of OMPs from a large-volume aquatic sample (5L) and reached equilibrium in a short amount of time (30 min). Moreover, the solution volume, the pH, and the salinity had insignificant influences on the extraction of the eight target OMPs. Under the optimum conditions, the recoveries of the eight OMPs calculated by analyzing the spiked samples were from 91.7% to 99.4%. The NAND-1 could be recycled ten times and still achieve recoveries of the eight OMPs higher than 86%. The limits of detection of the eight OMPs ranged from 1.76 to 27.56 ng/L, and the limits of quantification were from 5.71 to 92.05 ng/L. These results indicated that the proposed method, based on the use of NAND-1 as a magnetic sorbent, has the advantages of convenience and high efficiency and can be successfully applied to analyze the OMPs in real water samples.

Preparation of a novel anion exchange group modified hyper-crosslinked resin for the effective adsorption of both tetracycline and humic acid

A novel hyper-crosslinked resin (MENQ) modified with an anion exchange group was prepared using divinylbenzene (DVB) and methyl acrylate (MA) as comonomers via four steps: suspension polymerization, post-crosslinking, ammonolysis and alkylation reactions. The obtained resin had both a high specific surface area (793.34 m2·g−1) and a large exchange capacity (strong base anion exchange capacity, SEC: 0.74 mmol·g−1, weak base anion exchange capacity, WEC: 0.45 mmol·g−1). XAD-4 was selected as an adsorbent for comparison to investigate the adsorption behavior of tetracycline (TC) and humic acid (HA) onto the adsorbents. The results revealed that MENQ could effectively remove both TC and HA. The adsorption capacity of XAD-4 for TC was similar to that of MENQ, but XAD-4 exhibited poor performance for the adsorption of HA. The adsorption isotherms of TC and HA were well-fitted with the Freundlich model, which indicated the existence of heterogeneous adsorption through cation-π bonding and π-π interactions. The optimal solution condition for the adsorption of TC was at a pH of 5–6, whereas the adsorption of HA was enhanced with increasing pH of the solution.

Preparation of a permanent magnetic hypercrosslinked resin and assessment of its ability to remove organic micropollutants from drinking water

A rapid and effective method based on a novel permanent magnetic hypercrosslinked resin W150 was proposed for the removal of organic micropollutants in drinking water. W150 was prepared by suspension and post-crosslinking reaction and found to possess a high specific surface area of 1149.7 m2·g−1, a small particle size of 50 μm to 100 μm, and a saturation magnetization as high as 8 emu·g−1. W150 was used to eliminate nitrofurazone (NFZ) and oxytetracycline (OTC) from drinking water compared with commercial adsorbents XAD-4 and F400D. The adsorption kinetics of NFZ and OTC onto the three adsorbents well fitted the pseudo-second-order equation (r>0.972), and the adsorption isotherms were all well described by the Freundlich equation (r>0.851). Results showed that the reduction in adsorbent size and the enlargement in sorbent pores both accelerated adsorption. Moreover, the effect of particle size on adsorption was more significant than that of pore width. Given that the smallest particle size and the highest specific surface area were possessed by W150, it had the fastest adsorption kinetics and largest adsorption capacity for NFZ (180 mg·g−1) and OTC (200 mg·g−1). For the adsorbents with dominant micropores, the sorption of large-sized adsorbates decreased because of the inaccessible micropores. The solution pH and ionic strength also influenced adsorption.

Efficient and synergistic removal of tetracycline and Cu(II) using novel magnetic multi-amine resins

A series of magnetic multi-amine resins (MMARs, named E1D9-E9D1) was proposed for the removal of tetracycline (TC) and Cu(II) in sole and binary solutions. Results showed that the N content of the resins increased sharply from 1.7% to 15.49%, and the BET surface areas decreased from 1433.4 m2/g to 8.9 m2/g with methyl acrylate ratio increasing from E1D9 to E9D1. Their adsorption capacities for TC and Cu(II) could reach 0.243 and 0.453 mmol/g, respectively. The adsorption isotherms of TC onto MMARs transformed from heterogeneous adsorption to monolayer-type adsorption with DVB monomer ratio in resin matrix decrease, suggesting the dominant physical adsorption between TC and benzene rings. TC adsorption capacity onto E9D1 was higher than that onto E7D3 when the equilibrium concentration of TC exceeded 0.043 mmol/L because the electrostatic interaction between negatively charged groups of TC and protonated amines of adsorbents could compensate for the capacity loss resulting from BET surface area decrease. In the binary system, the electrostatic interaction between negatively charged TC-Cu(II) complex and protonated amines of adsorbents was responsible for the synergistic adsorption onto E7D3 and E9D1. The XPS spectra of magnetic resins before and after adsorption were characterized to prove the probable adsorption mechanisms. This work provides alternative adsorbent for the efficient treatment of multiple pollution with different concentrations of organic micropollutants and heavy metal ions.

Adsorption of HA Fractions with Different Molecular Weight on Magnetic Polyacrylic Anion Exchange Res

To investigate the effects of molecular weight (MW) on the adsorption by anion exchange resin, a commercial humic acid (HA) was fractionated into four sizes: HA1 ( 10,000 Da). The characterization reveals that aromaticity increases as the MW rises, while the negative charge follows the order HA3 > HA4 > HA2 > HA1. The adsorption maximum of HAs is 10.7, 18.8, 250, and 200 mg (total organic carbon, TOC)/g for HA1, HA2, HA3, and HA4, respectively. The results suggest that the effect of MW on adsorption is attributed to the different negative charge of HAs, and the effect of size exclusion is not observed.

Effect of Natural Organic Matter (NOM) with Different Molecular Size on Tetracycline Removal from Natural Aquatic Environment by Resin

To investigate the effects of molecular size on tetracycline removal by adsorption resin, two typical natural organic matters, humic acid (HA) and tannin acid (TA), with different molecular sizes were chosen to conduct the competitive experiment with tetracycline (TC). The results suggest that HA could slightly increase and TA would significantly decrease the adsorption capacity of XAD-4 resin for TC removing.