Zhengfang Ye

Characterization and adsorption mechanism of Zn2+ removal by PVA/EDTA resin in polluted water.

Batch adsorption experiments were conducted using a PVA/EDTA resin as an adsorbent to adsorb Zn(II) ions from single component system in which experimental parameters were studied including solution pH, contact time, adsorbent dose and initial metal ions concentration. The equilibrium isotherms were determined at pH 6 under constant ionic strength and at different temperatures. The results showed that the maximum removal of Zn(II) (99.8%) with 1 g L(-1) of sorbent was observed at 40 mg L(-1) at an initial pH value of 6. Removals of about 60-70% occurred in 15 min, and equilibrium was attained at around 30 min. The equilibrium data for the adsorption of Zn(II) on PVA/EDTA resin was tested with various adsorption isotherm models among which three models were found to be suitable for the Zn(II) adsorption. In addition, the kinetic adsorption fitted well to the pseudo-second-order model and the corresponding rate constants were obtained. Thermodynamic aspects of the adsorption process were also investigated. Furthermore a higher desorption efficiency of Zn(II) from the PVA/EDTA resin using acid treatment was available by more than 95%.

Immobilization of nanoscale Fe0 in and on PVA microspheres for nitrobenzene reduction

In this study, nanoscale Fe(0) was immobilized in and on poly(vinyl alcohol) (PVA) microspheres by the inverse suspension crosslinked method. Two different sizes of Fe(0)/PVA microspheres were synthesized in the presence and absence of dispersant. The chelating action between Fe(2+) and PVA was identified by Fourier transform infrared and X-ray photoelectron spectroscopy. The morphology and distribution of the obtained Fe(0)/PVA microspheres were characterized by environmental scanning electron microscope, energy-dispersive X-ray spectrometry, and X-ray diffraction. Nanoscale Fe(0) particles were mostly dispersed over the surface of the microspheres. They were distributed more homogeneously on the surfaces of Fe(0)/PVA microspheres with diameter of 600-700 microm than those with diameter of 10-12 microm. The nitrobenzene (NB) reduction reactions followed pseudo-first-order kinetics. The normalized surface rate constants (k(SA)) values were determined to be 0.162 L h(-1)m(-2) for L-Fe(0)/PVA microspheres, 0.098 L h(-1)m(-2) for S-Fe(0)/PVA microspheres, and 0.023 L h(-1)m(-2) for nanoscale Fe(0) particles. Furthermore, with the analysis of the products by GC/MS, possible reductive pathways of NB by Fe(0)/PVA microspheres were suggested. The recovery rates of iron in microspheres were determined to be 81.17% for large Fe(0)/PVA and 60.31% for small Fe(0)/PVA.

Removal of Cr3+ from aqueous solution by biosorption with aerobic granules.

Aerobic granules were utilized as an effective biosorbent to remove Cr(3+) from aqueous solution. The results showed that the initial pH, contact time, and Cr(3+) concentration affected the biosorption process significantly. Both Freundlich and Langmuir isotherms were able to describe the equilibrium data reasonably with high correlation coefficients (R(2)>0.95) and pseudo-second-order model best fitted the biosorption process at experimental conditions. Moreover, Environmental Scanning Electronic microscope (ESEM), X-ray energy dispersion (EDX), and Fourier transform infrared (FTIR) analyses revealed that metal complexation, chemical precipitation, and ion exchange were involved in the removal of Cr(3+) with aerobic granules. Further analysis by a metal ion fraction test demonstrated that metal complexation could be the dominant mechanism of biosorption, whereas chemical precipitation and ion exchange appeared only to have minor role in the overall Cr(3+) biosorption process.

Preparation and adsorption performance of a novel bipolar PS-EDTA resin in aqueous phase.

A novel chelating resin containing many amino and carboxyl functional groups, PS-EDTA resin, was prepared from chloromethylated polystyrene bead by reacting with ethylenediamine and chloroacetate in aqueous phase in sequence. The structure of PS-EDTA resin was characterized by means of infrared spectroscopy, scanning electron microscopy, surface area analysis and thermogravimetry. Adsorption behavior of the resin for Ag (I) ions in aqueous solutions was investigated by batch experiments. The results indicated that the adsorption removal of PS-EDTA resin for Ag (I) could achieve more than 99.9% at pH values of 5.0 with an initial Ag (I) concentration of 60.0mg/L within 2h. The maximum removal capacity of PS-EDTA toward Ag (I) was found to be almost 3314.97 mg/g at 25 degrees C. In addition, adsorption kinetic data were described by pseudo-second-order equation and the equilibrium data fitted very well with the Freundlich model. It was found that the PS-EDTA resin had excellent adsorption properties for Ag (I), so it should be a promising composite adsorbent with application in the recovery of Ag (I) ions from aqueous environment.

Novel chelating resin with cyanoguanidine group: useful recyclable materials for Hg(II) removal in aqueous environment.

A novel chelating resin containing cyanoguanidine moiety has been successfully prepared by the functionalizing reaction of a macroporous bead based on chloromethylated copolymer of styrene-divinylbenzene (CMPS) with dicyandiamide (DCDA) in the presence of phase transfer catalyst. The Fourier transform-infrared spectra (FT-IR) and scanning electron microscopy (SEM) were employed in the characterization of the resulting chelating resin, meanwhile, the adsorption properties of the resin for Hg(II) were investigated by batch and column methods. The results indicated that the resin displayed a marked advantage in Hg(II) binding capacity, and the saturated adsorption capacity estimated from the Langmuir model was dramatically up to 1077 mg g(-1) at 45 °C. Furthermore, it was found that the resin was able to selectively separate Hg(II) from multicomponent solutions with Zn(II), Cu(II), Pb(II) and Mg(II). The desorption process of Hg(II) was tested with different eluents and the ratio of the highest recovery reached to 96% under eluting condition of 1M HCl+10% thiourea. Consequently, the resulting chelating resin would provide a potential application for treatment process of Hg(II) containing wastewater.

Organic pollutants removal from 2,4,6-trinitrotoluene (TNT) red water using low cost activated coke.

We treated 2,4,6-trinitrotoluene (TNT) red water from the Chinese explosive industry with activated coke (AC) from lignite. Since the composition of TNT red water was very complicated, chemical oxygen demand (COD) was used as the index for evaluating treatment efficiency. This study focused on sorption kinetics and equilibrium sorption isotherms of AC for the removal of COD from TNT red water, and the changes of water quality before and after adsorption were evaluated using high performance liquid chromatography, UV-Vis spectra and gas chromatography/mass spectroscopy. The results showed that the sorption kinetics of COD removal from TNT red water onto AC fitted well with the pseudo second-order model. The adsorption process was an exothermic and physical process. The sorption isotherm was in good agreement with Redlich-Peterson isotherm. At the conditions of initial pH = 6.28, 20 degrees C and 3 hr of agitation, under 160 g/L AC, 64.8% of COD was removed. The removal efficiencies of 2,4-dinitrotoluene-3-sulfonate (2,4-DNT-3-SO3-) and 2,4-dinitrotoluene-5-sulfonate (2,4-DNT-5-SO3-) were 80.5% and 84.3%, respectively. After adsorption, the acute toxicity of TNT red water reduced greatly, compared with that of unprocessed TNT red water.

Selective removal for Pb2+ in aqueous environment by using novel macroreticular PVA beads

Batch sorption experiments were conducted using macroreticular poly(vinyl alcohol) (MR-PVA) beads as a adsorbent to adsorb Pb(II) from both single component system and multi-metal solution in which experimental parameters were studied including solution pH, contact time, adsorbent dose, initial concentration of metal ions and ionic strength. The equilibrium isotherms were determined at pH 6 under constant ionic strength and at different temperatures. The results showed that the maximum adsorption capacity of Pb(II) (213.98 mg g(-1)) with 1 g L(-1) of adsorbent was observed at 300 mg L(-1) at an initial pH value of 6.0 under temperature of 288 K. Removals of about 60% occurred in 30 min, and equilibrium was attained at around 150 min. The equilibrium data for the adsorption of Pb(II) on MR-PVA beads was tested with various adsorption isotherm models among which three models were found to be suitable for the Pb(II) adsorption. In addition, the kinetic adsorption fitted well to the pseudo-second-order model and the corresponding rate constants were obtained. Thermodynamic aspects of the adsorption process were also investigated.

Acute toxicity evaluation of explosive wastewater by bacterial bioluminescence assays using a freshwater luminescent bacterium, Vibrio qinghaiensis sp. Nov.

The compositions of explosive wastewater generated from TNT (2,4,6-trinitrotoluene) purification stage were characterized by using UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), high performance liquid chromatograph (HPLC) and gas chromatograph/mass spectroscopy (GC/MS). The acute toxicity was evaluated by bacterium bioluminescence assay using a freshwater luminescent bacterium (Vibrio qinghaiensis sp. Nov.) and a marine luminescent bacterium (Photobacterium phosphoreum). The results showed that the wastewaters biodegradability was poor due to the high amount of chemical oxygen demand (COD). The main organic components were dinitrotoluene sulfonates (DNTS) with small amount of TNT, dinitrotoluene (DNT), mononitrotoluene (MNT) and other derivatives of nitrobenzene. It was highly toxic to luminescent bacteria P. phosphoreum and V. qinghaiensis sp. Nov. After reaction time of 15 min, the relative concentration of toxic pollutants (expressed as reciprocal of dilution ratio of wastewater) at 50% of luminescence inhibition ratio was 5.32×10(-4) for P. phosphoreu, while that was 4.34×10(-4) for V. qinghaiensis. V. qinghaiensis is more sensitive and suitable for evaluating the wastewaters acute toxicity than P. phosphoreum. After adsorption by resin, the acute toxicity can be greatly reduced, which is helpful for further treatment by biological methods.

A facile one-step electrochemical strategy of doping iron, nitrogen, and fluorine into titania nanotube arrays with enhanced visible light photoactivity.

Highly ordered iron, nitrogen, and fluorine tri-doped TiO2 (Fe, (N, F)-TiO2) nanotube arrays were successfully synthesized by a facile one-step electrochemical method in an NH4F electrolyte containing Fe ions. The morphology, structure, composition, and photoelectrochemical property of the as-prepared nanotube arrays were characterized by various methods. The photoactivities of the samples were evaluated by the degradation of phenol in an aqueous solution under visible light. Tri-doped TiO2 showed higher photoactivities than undoped TiO2 under visible light. The optimum Fe(3+) doping amount at 0.005M exhibited the highest photoactivity and exceeded that of undoped TiO2 by a factor of 20 times under visible light. The formation of N 2p level near the valence band (VB) contributed to visible light absorption. Doping fluorine and appropriate Fe(3+) ions reduced the photogenerated electrons-holes recombination rate and enhanced visible light photoactivity. The X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) results indicated the presence of synergistic effects in Fe, N, and F tri-doped TiO2, which enhanced visible light photoactivity. The Fe, (N, F)-TiO2 photocatalyst exhibited high stability.

Nitrogen-doped perovskite-type La2Ti2O7 decorated on graphene composites exhibiting efficient photocatalytic activity toward bisphenol A in water

Nitrogen-doped lanthanum titanate decorated on graphene sheets (GR/N-doped La2Ti2O7) used as photocatalyst was prepared by a two-step process. To synthesize GR/N-doped La2Ti2O7, La2Ti2O7 was initially developed under heat treatment in NH3 and subsequently decorated on GR by hydrothermal processing. The resulting GR/N-doped La2Ti2O7 was characterized by scanning electron microscopy, transmission electron microscopy, atomic force microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Characterization results indicated that N-doped La2Ti2O7 was approximately 6-8 nm thick with single-crystalline perovskite structure and chemically attached onto GR nanosheets by the formation of TiN bond, TiC bond, and oxynitrides. The application of GR/N-doped La2Ti2O7 composites to bisphenol A decomposition exhibits high photocatalytic efficiency under irradiation compared with pure La2Ti2O7 materials. This finding was due to the synergistic effect of great adsorption, enhanced light absorption, efficient charge separation and transfer processes in the presence of GR, and reduced band gap energy because of N doping. This study provides new insights into the fabrication and practical application of high-performance photocatalysts in wastewater treatment.