Hong-Tao Fan

Use of polymer-bound Schiff base as a new liquid binding agent of diffusive gradients in thin-films for the measurement of labile Cu2+, Cd2+ and Pb2+

A new diffusive gradients in thin-films (DGT) device with solution of polymer-bound Schiff base (Py-PEI) derived from poly(ethyleneimine) and 2-pyridinecarboxaldehyde as the binding agent (Py-PEI DGT) was developed for measuring labile Cu(2+), Cd(2+) and Pb(2+) in waters. In synthetic solution, uptake percentages of Cu(2+), Cd(2+) and Pb(2+) by Py-PEI DGT were 99.2 ± 4.4%, 103.7 ± 4.8% and 98.7 ± 5.5% of the total metals, respectively. Performance of Py-PEI DGT was independent of pH 4-8.5 and ionic strength 1 × 10(-4)-0.1 mol L(-1). The uptake of labile metals showed agreement with the theoretical values of free ions in EDTA solution, and decreased with increase of humic acid (HA) and dissolved organic carbon (DOC) contents in water due to the complexation of HA and DOC with metals. DGT devices containing different liquid binding agents (Py-PEI, polyacrylate (PA) and poly(4-styrenesulfonate) (PSS)) were deployed in the same solution. The higher uptake percentages of Py-PEI DGT (13.2 ± 1.1, 26.5 ± 2.4 and 62.7 ± 3.2% of total Cu(2+), Cd(2+) and Pb(2+)) were obtained with respective to PSS DGT (6.7 ± 0.6, 9.2 ± 0.9 and 29.6 ± 2.7% of total above metals) and PA DGT (8.9 ± 0.9 and 16.2 ± 1.1% of total Cu(2+) and Cd(2+)) due to its relatively strong binding affinity with metals.

Application of poly (ethyleneimine) solution as a binding agent in DGT technique for measurement of heavy metals in water

A 0.050 mol L(-1) solution of poly (ethyleneimine) (PEI), had been used as a novel binding agent of diffusive gradients in thin-films (DGT) technique (PEI-DGT) for measuring the concentrations of labile Cu(2+), Cd(2+) and Pb(2+) in waters. The binding capacities of the PEI-DGT for Cu(2+), Cd(2+) and Pb(2+) were 11.8, 10.2 and 10.6 μmol L(-1), respectively. The performance of PEI-DGT was independence of pH in the range of 4-8 and ionic strength in the range from 1×10(-4) to 0.1 mol L(-1) (as NaNO3). PEI-DGT could measure 104.7±5.2% of the total concentration of Cd(2+) (0.500 mg L(-1)), 95.2±4.3% of the total Cu(2+) (0.500 mg L(-1)) and 99.2±3.4% of the total Pb(2+) (0.500 mg L(-1)) in synthetic solution. Effects of the ligands on the measurement of labile metals were also investigated in synthetic solutions containing the various concentrations of EDTA and humic acid. In EDTA solution, the concentrations of labile metals measured by PEI-DGT showed good agreement with the theoretical concentrations of free metal ions. In humic acid solution, the concentrations of labile metals measured by PEI-DGT decreased with the increase of the concentrations of humic acid. Several DGT devices with various binding agents, including PEI, sodium polyacrylate and poly(4-styrenesulfonate) solution, were used for the measurement of labile fractions of Cu(2+), Cd(2+) and Pb(2+) in the spiked waters and in mine wastewaters. The results showed that the concentrations of labile metal measured by DGT devices with different binding agents could be significantly different, indicating that the labile fractions of metals were dependent on the binding strength of the binding agents with metals. By choosing binding agents, the useful information on the speciation and bioavailability of the analytes can be provided.

Ion-imprinted silica adsorbent modified diffusive gradients in thin films technique: Tool for speciation analysis of free lead species

A new diffusive gradients in thin films (DGT) device, using Pb(II) ion-imprinted silica (IIS) as the binding agents and commercial cellulose acetate dialysis (CAD) membrane as the diffusion layer (CAD/IIS-DGT), has been developed and evaluated for sampling and measurement of free Pb(II) species. The CAD/IIS-DGT devices were successfully applied to the measurement of free Pb(II) species in synthetic solutions, in natural freshwaters and in industrial wastewaters. The CAD/IIS-DGT provides reliable results over pH range of 4.5-6.5 and a wide range of ionic strength from 1.0×10(-3) to 0.7 mol L(-1). The concentrations of the free Pb(II) species in synthetic solution containing different concentrations of ligands measured by CAD/IIS-DGT showed a good agreement with the value measured by Pb-ion selective electrode. Field deployments of the CAD/IIS-DGT devices allowed accurate measurements of the concentrations of free Pb(II) species.

A method for measurement of free cadmium species in waters using diffusive gradients in thin films technique with an ion-imprinted sorbent

A diffusive gradients in thin films (DGT) device for the analysis of free Cd(II) species, based on Cd(II) ion-imprinted sorbent (IIS) as the binding agents and commercial polyethersulfone membrane (PES) as diffusion layer, was developed (PES/IIS-DGT). DGT time-series experiments showed that the mass of free Cd(II) species accumulated by PES/IIS-DGT was linear vs. time (R(2)xa0=xa00.9953) and the concentration of free Cd(II) species by PES/IIS-DGT was in good agreement with the total dissolved concentrations of free Cd(II) species in simple synthetic solutions where free ionic species dominated. PES/IIS-DGT performance was independent in the range of pH 4.5-7.5 and ionic strength range from 1.0xa0×xa010(-3) to 0.7xa0molxa0L(-1). The measurement of free Cd(II) species in synthetic solution containing different concentrations of ligands by PES/IIS-DGT showed an excellent agreement with the value measured by Cd(II) ion selective electrodes (Cd-ISE), indicating that PES/IIS-DGT method is more suitable than Cd-ISE for the measurement of low concentration of free Cd(II) species due to the enrichment of IIS for the analytes.

Sampling of dissolved inorganic SbIII by mercapto-functionalized silica-based diffusive gradients in thin-film technique

The mercapto-functionalized silica (MPS) diffusive gradients in thin-film (DGT) devices, for the first time, were characterized by the determination of dissolved inorganic SbIII. The performance of MPS–DGT was assessed by (1) determining the diffusion coefficient of SbIII in polyethersulfone membrane, (2) assessing the uptake efficiency and digestion efficiency of MPS for SbIII, (3) investigating the effect of pH, ionic strength (as NaNO3) and foreign ions on the performance of MPS–DGT for SbIII species, and (4) assessing the validation of MPS–DGT for the measurement of dissolved inorganic SbIII in spiked water samples. The diffusion coefficient of SbIII measured in the PES membrane by a diffusion cell was (3.05 ± 0.09) × 10−6 cm2 s−1. There was a tendency toward higher adsorption affinity for SbIII compared with SbV. Mass vs. time measurements of MPS–DGT at pH 6 (0.01 mol L−1 NaNO3) demonstrated a linear uptake of SbIII (R2 = 0.9973). The performance of MPS–DGT was independent of ionic strength (0.001–0.7 mol L−1 NaNO3 at pH 5) and pH (3–8, 0.01 mol L−1 NaNO3) for the measurement of SbIII. The presence of foreign ions (such as CaII, MgII, CdII, ZnII, CuII, AsIII and SbV) has no significant influence on the uptake of SbIII by MPS–DGT. MPS–DGT can quantitatively measure the concentration of dissolved inorganic SbIII in spiked etching wastewater. In spiked natural freshwater, the concentration of dissolved inorganic SbIII obtained by MPS–DGT is significantly lower than the concentration of added SbIII due to the presence of natural organic matter (8.7 mg C L−1) which would have complexed a fraction of the added SbIII and thereby changed the speciation of added SbIII. The MPS–DGT device can potentially be used as a tool for speciation measurements of SbIII in aqueous environments.

Equilibrium, isotherm, kinetic and thermodynamic studies for removal of tetracycline antibiotics by adsorption onto hazelnut shell derived activated carbons from aqueous media

Hazelnut shell, an agricultural waste, was used to prepare activated carbons by phosphoric acid activation. Hazelnut shell derived activated carbon (HSAC) was characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy and N2 adsorption/desorption isotherms, and was used as an adsorbent for the removal of three tetracycline (TC) antibiotics (tetracycline (TC), oxytetracycline (OTC), and chlortetracycline (CTC)) from aqueous solution. Batch adsorption studies were carried out by varying the initial concentrations of TCs, pH of solution, ionic strength of solution, contact time and temperature. 20xa0min was required to attain equilibrium. There was no significant influence of ionic strength in a range from 0.0001 to 1 mol L−1 and pH in the range of 4–8 on the uptakes of TCs by the HSAC. The maximum adsorption capacities of the HSAC followed the sequence OTC (321.5 mg g−1) > CTC (313.5 mg g−1) > TC (302.9 mg g−1). The data fitted well with the pseudo-second-order kinetic and Langmuir models. The intraparticle diffusion model indicated that the adsorption of TCs on the HSAC was controlled by both intraparticle diffusion and external mass transfer. Under the test temperature and pressure, the thermodynamic constants revealed that the adsorption of TCs onto the HSAC was spontaneous and endothermic. The HSAC had relatively high potential for the removal of TCs from aqueous solution.

In situ synthesis of layered double hydroxides on γ-Al2O3 and its application in chromium(VI) removal

Mg-Al layered double hydroxides (LDHs) adsorbent was synthesized in situ on γ-Al2O3 for the removal of Cr(VI) from aqueous solution. The material was characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electronic microscopy and thermogravimetry and differential thermal analysis. Compared to the LDHs powder, the calcined LDHs sorbent prepared in situ on γ-Al2O3 had higher specific surface area and was easy to recover and reuse. The adsorptive capacity for removing Cr(VI) from aqueous solution was resulting from the memory effect of LDHs based on the XRD results. Both the pseudo-second-order kinetic model and the Langmuir model fit the experimental data well. Furthermore, the adsorbent exhibits excellent sorption-regeneration performances.