Chendong Shuang

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.

Characterization of Dissolved Organic Matter in Municipal Wastewater Using Fluorescence PARAFAC Analysis and Chromatography Multi-Excitation/Emission Scan: A Comparative Study

Dissolved organic matter (DOM) in municipal wastewater was mainly characterized using high-performance liquid chromatography (HPLC) and size exclusion chromatography (HPSEC) with multi-excitation/emission fluorescence scan. Meanwhile, fluorescence excitation-emission-matrix combined with parallel factor analysis (EEM-PARAFAC) was also applied. Compared with chromatography fluorescence fingerprints, the EEM-PARAFAC model could not reflect the variety of DOM species with similar fluorescence but different physicochemical properties. The chromatography results showed that the protein-like species were variable among different municipal wastewater treatment plants, some of which are in combination with humic-like species; while there were two major humic-like species fractionated by hydrophilicity and molecular weight (MW), which are also the major contributors to UV absorbance at 254 nm. It was also identified that the relatively hydrophilic humic fractions were slightly larger than the relatively hydrophobic humic fractions. In all the investigated wastewater treatment plants, the relatively hydrophilic and larger MW humic fraction mainly contributed to the fluorescence intensity of humic-like EEM-PARAFAC components. As well as facilitating interpretations of EEM-PARAFAC components, the HPLC/HPSEC fluorescence fingerprints also contributed to a better understanding of fluorescent DOM species in municipal wastewater.

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.

Enhanced adsorption and antifouling performance of anion-exchange resin by the effect of incorporated Fe3O4 for removing humic acid

The application of anion-exchange resins (AERs) is limited by fouling, which increases the fresh resin dosage, regeneration frequency, and amount of regeneration effluent. In this study, five AERs with different Fe3O4 amounts was prepared by increasing the amount of Fe3O4 added to 100 g of monomer mixture for suspension polymerization from 0 g to 40 g. Results showed considerably improved pore volume and hydrophilicity of the resin with increased Fe3O4 content, leading to significantly enhanced adsorption and desorption of humic acid. A method of developing novel resins with enhanced adsorption and antifouling abilities by incorporating Fe3O4 was then proposed. The adsorbent structure resulting from the incorporated inorganic particles was found to be important in determining the adsorption behavior of a hybrid adsorbent.

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.

Rapid removal of copper with magnetic poly-acrylic weak acid resin: Quantitative role of bead radius on ion exchange

A novel magnetic weak acid resin NDMC was self-synthesized for the removal of Cu(2+) from aqueous solutions. NDMC showed superior properties on the removal of Cu(2+) compared to commercial resins C106 and IRC-748, which was deeply investigated by adsorption isotherms and kinetic tests. The equilibrium adsorption amount of Cu(2+) onto NDMC (267.2mg/g) was almost twice as large as that onto IRC-748 (120.0mg/g). The adsorption kinetics of Cu(2+) onto the three resins fitted well with the pseudo-second-order equation. The initial adsorption rate h of NDMC was about 4 times that of C106 and nearly 8 times that of IRC-748 at the initial concentration of 500mg/L. External surface area was determined to be the key factor in rate-controlling by further analyzing the adsorption thermodynamics, kinetics parameters and physicochemical properties of the resins. NDMC resin with the smallest bead radius possessed the largest external surface and therefore exhibited the fastest kinetics. The adsorption amount of Cu(2+) onto NDMC was not influenced as the concentration of Na(+) increased from 1.0 to 10.0mM/L. Dilute HCl solution could effectively desorb Cu(2+). NDMC demonstrated high stability during 10 adsorption/desorption cycles, showing great potential in the rapid removal of Cu(2+) from wastewater.

Combination of Na-modified zeolite and anion exchange resin for advanced treatment of a high ammonia–nitrogen content municipal effluent

In this study, the exchange equilibrium and kinetic experiments of ammonia-nitrogen on the Na-form zeolite were conducted. The results indicated that the presence of humic acid have a negative effect on the equilibrium exchange capacity but have limited influence on the equilibrium time except shorten the sole intra-particle diffusion control time. The exchange equilibrium data could be well fitted by Freundlich model in the absence of humic acid but Langmuir model in the presence of humic acid. While the exchange kinetic data could be well described by pseudo-second-order kinetic model in both situations. An anion exchange resin exhibited high removal efficiency to humic acid and dissolved organic matter through kinetic results and fluorescence excitation-emission matrix (EEM) spectroscopy results. The use of the anion exchange resin prior to the Na-form zeolite improved the ammonia-nitrogen removal efficiency from 78% to 95% and increased the treatment volume of the Na-form zeolite from 51 BV (bed volume) to 76 BV. Both the resin and the Na-form zeolite could be successfully regenerated by the combination of alkaline and sodium chloride. Complete elution of ammonia-nitrogen was achieved when the mass percentage of sodium chloride and alkaline was 10% and 0.6% respectively.

Dissolved organic matter removal using magnetic anion exchange resin treatment on biological effluent of textile dyeing wastewater

This study investigated the removal of dissolved organic matter (DOM) from real dyeing bio-treatment effluents (DBEs) with the use of a novel magnetic anion exchange resin (NDMP). DOMs in two typical DBEs were fractionized using DAX-8/XAD-4 resin and ultrafiltration membranes. The hydrophilic fractions and the low molecular weight (MW) (<3kDa) DOM fractions constituted a major portion (>50%) of DOMs for the two effluents. The hydrophilic and low MW fractions of both effluents were the greatest contributors of specific UV254 absorbance (SUVA254), and the SUVA254 of DOM fractions decreased with hydrophobicity and MW. Two DBEs exhibited acute and chronic biotoxicities. Both acute and chronic toxicities of DOM fractions increased linearly with the increase of SUVA254 value. Kinetics of dissolved organic carbon (DOC) removal via NDMP treatment was performed by comparing it with that of particle active carbon (PAC). Results indicated that the removal of DOC from DBEs via NDMP was 60%, whereas DOC removals by PAC were lower than 15%. Acidic organics could be significantly removed with the use of NDMP. DOM with large MW in DBE could be removed significantly by using the same means. Removal efficiency of NDMP for DOM decreased with the decrease of MW. Compared with PAC, NDMP could significantly reduce the acute and chronic bio-toxicities of DBEs. NaCl/NaOH mixture regenerants, with selected concentrations of 10% NaCl (m/m)/1% NaOH (m/m), could improve desorption efficiency.

Effect of the chemical structure of anion exchange resin on the adsorption of humic acid: behavior and mechanism.

Polystyrenic (PS) anion-exchange resin and polyacrylic (PA) anion-exchange resin were used to investigate the effect of resin chemical structure on the adsorption of humic acid (HA). Due to the rearrangement of HA to form layers that function as barricades to further HA diffusion, PS resin exhibited 12.4 times slower kinetics for the initial adsorption rate and 8.4 times for the diffusion constant in comparison to that of the PA resin. An HA layer and a spherical cluster of HA can be observed on the surface of the PS and PA resins after adsorption, respectively. The considerable difference in HA adsorption between the PS and PA resins was due to the difference in molecule shape for interaction with different resin structures, which can essentially be explained by the hydrophobicity and various interactions of the PS resin. A given amount of HA occupies more positively charged sites and hydrophobic sites on the PS resin than were occupied by the same amount of HA on the PA resin. Increased pH resulted in an increase of HA adsorption onto the PA resin but a decrease in adsorption onto PS resin, as the non-electrostatic adsorption led to electrostatic repulsion between the HA attached to the resin and the HA dissolved in solution. These results suggest higher rates of adsorption and higher regeneration efficiency for interaction of HA with more hydrophilic anion exchange materials.

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.