Kaisheng Zhang

Removal of cobalt ions from aqueous solution by an amination graphene oxide nanocomposite

A newly designed amination graphene oxide (GO-NH2), a superior adsorption capability to that of activated carbon, was fabricated by graphene oxide (GO) combining with aromatic diazonium salt. The resultant GO-NH2 maintained a high surface area of 320 m(2)/g. When used as an adsorbent, the GO-NH2 demonstrated a very quick adsorption property for the removal of Co(II) ions, more than 90% of Co(II) ions could be removed within 5 min for dilute solutions at 0.3g/L adsorbent dose. The adsorption capability approaches 116.35 mg/g, which is one of the highest capabilities of todays materials. The thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggested that the Co(II) ions adsorption on GO-NH2 was a spontaneous process. Considering the superior adsorption capability, the GO-NH2 filter membrane was fabricated for the removal of Co(II) ions. Membrane filtration experiments revealed that the removal capabilities of the materials for cobalt ions depended on the membranes thickness, flow rate and initial concentration of Co(II) ions. The highest percentage removal of Co(II) exceeds 98%, indicating that the GO-NH2 is one of the very suitable membrane materials in environmental pollution management.

Performance of novel hydroxyapatite nanowires in treatment of fluoride contaminated water

Novel ultralong hydroxyapatite (HAP) nanowires were successfully prepared for fluoride removal for the first time. The fluoride adsorption on the HAP nanowires was studied on a batch mode. The results revealed that the adsorption data could be well described by the Freundlich model, and the adsorption kinetic followed the pseudo-second-order model. The maximum of adsorption capacity was 40.65 mg/g at pH 7.0 when the fluoride concentration is 200mg/L. The thermodynamic parameters suggested that the adsorption of fluoride was a spontaneous endothermic process. The FT-IR, XPS and Zeta potential analysis revealed that both anion exchange and electrostatic interactions were involved in the adsorption of fluoride. Furthermore, the HAP nanowires were made into HAP membrane through a simple process of suction filtration. Membrane filtration experiments revealed that the fluoride removal capabilities depended on the membrane thickness, flow rate and initial concentration of fluoride. The as-prepared membrane could remove fluoride efficiently through continues filtration. The filtered water amount could reach 350, 192, and 64 L/m(2) when the fluoride concentrations were 4, 5 and 8 ppm, respectively, using the HAP membrane with only 150 μm thickness. The as-synthesized ultralong HAP nanowires were thus demonstrated to be very effective and biocompatible adsorbents for fluoride removal from contaminated water.

Wide pH range for fluoride removal from water by MHS-MgO/MgCO3 adsorbent: Kinetic, thermodynamic and mechanism studies

A novel environment friendly adsorbent, micro-nano hierarchical structured flower-like MgO/MgCO3 (MHS-MgO/MgCO3), was developed for fluoride removal from water. The adsorbent was characterized and its defluoridation properties were investigated. Adsorption kinetics fitted well the pseudo-second-order model. Kinetic data revealed that the fluoride adsorption was rapid, more than 83-90% of fluoride could be removed within 30 min, and the adsorption equilibrium was achieved in the following 4 h. The fluoride adsorption isotherm was well described by Freundlich model. The maximum adsorption capacity was about 300 mg/g at pH=7. Moreover, this adsorbent possessed a very wide available pH range of 5-11, and the fluoride removal efficiencies even reached up to 86.2%, 83.2% and 76.5% at pH=11 for initial fluoride concentrations of 10, 20 and 30 mg/L, respectively. The effects of co-existing anions indicated that the anions had less effect on adsorption of fluoride except phosphate. In addition, the adsorption mechanism analysis revealed that the wide available pH range toward fluoride was mainly resulted from the exchange of the carbonate and hydroxyl groups on the surface of the MHS-MgO/MgCO3 with fluoride anions.

A molecular-gap device for specific determination of mercury ions

Specific determination/monitoring of trace mercury ions (Hg2+) in environmental water is of significant importance for drinking safety. Complementarily to conventional inductively coupled plasma mass spectrometry and atomic emission/absorption spectroscopy, several methods, i.e., electrochemical, fluorescent, colorimetric, and surface enhanced Raman scattering approaches, have been developed recently. Despite great success, many inevitably encounter the interferences from other metal ions besides the complicated procedures and sophisticated equipments. Here we present a molecular-gap device for specific determination of trace Hg2+ in both standardized solutions and environmental samples based on conductivity-modulated glutathione dimer. Through a self-assembling technique, a thin film of glutathione monolayer capped Au nanoparticles is introduced into 2.5 μm-gap-electrodes, forming numerous double molecular layer gaps. Notably, the fabricated molecular-gap device shows a specific response toward Hg2+ with a low detection limit actually measured down to 1 nM. Theoretical calculations demonstrate that the specific sensing mechanism greatly depends on the electron transport ability of glutathione dimer bridged by heavy metal ions, which is determined by its frontier molecular orbital, not the binding energy.

Performance of a novelly-defined zirconium metal-organic frameworks adsorption membrane in fluoride removal.

A novelly-defined adsorption membrane for rapid removal of fluoride from drinking water was prepared. Both zirconium metal-organic frameworks (Zr-MOFs) adsorbent and membrane with large specific surface area of 740.28m2/g were used for fluoride removal for the first time. For adsorption technique, fluoride adsorption on Zr-MOFs was studied on a batch mode. The adsorption data could be well described by Langmuir isotherm model while the adsorption kinetic followed pseudo-second-order model. The maximum of adsorption capacity was 102.40mg/g at pH 7.0 when the initial fluoride concentration was 200mg/L. The FT-IR and XPS analyses of Zr-MOFs revealed that both surface hydroxyl groups and Zr(IV) active sites played important roles in fluoride adsorption process. The as-prepared Zr-MOFs adsorbent was suitable for practical treatment of drinking water and regeneration by sodium hydroxide solution (3wt%). For membrane experiments, Zr-MOFs membrane supported on Alumina substrate could remove fluoride efficiently through dynamic filtration. The fluoride removal capability of Zr-MOFs membrane depended on flow rate and initial concentration of fluoride. The fluoride removal abilities of Zr-MOFs membrane with 20μm thickness could reach 5510, 5173, and 4664L/m2 when fluoride concentrations were 5, 8 and 10mg/L, respectively. This study indicated that Zr-MOFs membrane could be developed into a very viable technology for highly effective removal of fluoride from drinking water.

High efficient removal of fluoride from aqueous solution by a novel hydroxyl aluminum oxalate adsorbent.

A novel adsorbent, hydroxyl aluminum oxalate (HAO), for the high efficient removal of fluoride from aqueous solution was successfully synthesized. The adsorbent was characterized and its performance in fluoride (F(-)) removal was evaluated for the first time. Kinetic data reveal that the F(-) adsorption is rapid in the beginning followed by a slower adsorption process; 75.9% adsorption can be achieved within 1min and only 16% additional removal occurred in the following 239min. The F(-) adsorption kinetics was well described by the pseudo second-order kinetic model. The calculated adsorption capacity of this adsorbent for F(-) by Langmuir model was 400mgg(-1) at pH 6.5, which is one of the highest capabilities of todays materials. The thermodynamic parameters calculated from the temperature-dependent isotherms indicate that the adsorption reaction of F(-) on the HAO is a spontaneous process. The FT-IR spectra of HAO before and after adsorbing F(-) show adsorption mechanism should be hydroxyl and oxalate interchange with F(-).

Development of a nanosphere adsorbent for the removal of fluoride from water.

A new uniform-sized CeCO3OH nanosphere adsorbent was developed, and tested to establish its efficiency, using kinetic and thermodynamic studies, for fluoride removal. The results demonstrated that the CeCO3OH nanospheres exhibited much high adsorption capacities for fluoride anions due to electrostatic interactions and exchange of the carbonate and hydroxyl groups on the adsorbent surface with fluoride anions. Adsorption kinetics was fitted well by the pseudo-second-order model as compared to a pseudo-first-order rate expression, and adsorption isotherm data were well described by Langmuir model with max adsorption capacity of 45mg/g at pH 7.0. Thermodynamic examination demonstrated that fluoride adsorption on the CeCO3OH nanospheres was reasonably endothermic and spontaneous. Moreover, the CeCO3OH nanospheres have less influence on adsorption of F(-) by pH and co-exiting ions, such as SO4(2-), Cl(-), HCO3(-), CO3(2-), NO3(-) and PO4(3-), and the adsorption efficiency is very high at the low initial fluoride concentrations in the basis of the equilibrium adsorption capacities. This study indicated that the CeCO3OH nanospheres could be developed into a very viable technology for highly effective removal of fluoride from drinking water.

A biocompatible and novelly-defined Al-HAP adsorption membrane for highly effective removal of fluoride from drinking water

A biocompatible and novelly-defined adsorption membrane for rapid removal of fluoride was prepared. Both adsorption and membrane techniques were used in this research. Al(OH)3 nanoparticles modified hydroxyapatite (Al-HAP) nanowires were developed and made into Al-HAP membrane. The adsorption data of Al-HAP adsorbent could be well described by Freundlich isotherm model while the adsorption kinetic followed pseudo-second-order model. The maximum of adsorption capacity was 93.84mg/g when the fluoride concentration was 200mg/L. The adsorption mechanism was anion exchanges and electrostatic interactions. The contribution rates of HAP nanowires and Al(OH)3 nanoparticles in fluoride removal were 36.70% and 63.30%, respectively. The fixed-bed column test demonstrate that the Al-HAP was biocompatible and in a good stability during the process of water treatment. The fluoride removal abilities of Al-HAP membrane with 0.3mm thickness could reach 1568L/m2 when fluoride concentrations were 5mg/L. This study indicated that the Al-HAP membrane could be developed into a very viable technology for highly effective removal of fluoride from drinking water.

Performance and mechanism of hierarchically porous Ce–Zr oxide nanospheres encapsulated calcium alginate beads for fluoride removal from water

Hierarchically porous Ce–Zr oxide nanosphere encapsulated calcium alginate millimeter-sized beads (CZ-CABs) were synthesized by using a sol–gel templating technique. Their defluoridation performance, including static and dynamic adsorption, was systematically evaluated. The adsorption kinetic followed the pseudo-second-order model. The adsorption isotherm could be divided into two distinct regions depending on the fluoride concentrations, and the CZ-CABs exhibited a Langmuir–Freundlich maximum fluoride adsorption capacity of 137.6 mg g−1 under neutral conditions. Such a specific adsorption isotherm indicated that various mechanisms were involved in the fluoride adsorption depending on fluoride concentrations, which were further demonstrated by FTIR and XPS analyses. The effect of pH and co-existing anions on fluoride adsorption was studied. Furthermore, column adsorption experiments were conducted, and the results showed a high efficiency of the CZ-CABs for the removal of fluoride from water on a continuous flow basis.

EDTA-Fe(III) Fenton-like oxidation for the degradation of malachite green

Industrial waste, urban sewage and aquaculture have led to severely increased grades of environment pollutants such as dyes, pesticides and fertilizer. The use of technologies for purifying contaminated waters can be difficult and toxic due to the anti-photolysis, anti-oxidation and anti-bio-oxidation characteristics of organic pollutants, and there is therefore a significant need for new approaches. Here, we report methods of Fenton oxidation and EDTA-Fe(III) Fenton-like oxidation which can be used to degrade malachite green (MG: a dye and antibiotic-like substance) from contaminated water. Compared with the degradation rate (59.34%) of the Fe(III)/H2O2 Fenton process, the EDTA-Fe(III) Fenton-like oxidation got a better degradation rate (92.7%) at neutral pH conditions. By conducting a series of parallel controlled experiments (changing parameters such as the reactant concentration, temperature, and pH), we report the relationships between the degradation effect and different parameters, and we fitted their pseudo first order kinetic curves. Furthermore, we repeated to adjustment of the concentrations of MG in solutions to test the cycle performance and catalytic activities of EDTA-Fe(III)/H2O2 system and it showed good repeatability in the first five rounds and all of them keep the degradation efficiencies greater than 80%. By conducting comparative spin-trapping electron paramagnetic resonance (EPR) experiments, we showed indirectly that the OH contributes to the degradation of MG. Additionally, the results of the EPR experiments showed that EDTA contributes to the generation of OH in the EDTA-Fe(III)/H2O2 Fenton-like system. By conducting total organic carbon (TOC) analysis experiments, we found that EDTA was also oxidized to some extent during the degradation of MG. In all, the findings of this work widen the range of the optimal pH values up to neutral condition for degradation of MG by use of EDTA-Fe(III) Fenton-like system. And this system could be used as one approach for the degradation of organic pollutants at neutral conditions and provide some initial information regarding EDTA-Fe(III) Fenton-like oxidations. Its significant for the expansion of the homogenous Fenton-like family and its application in the field of water treatment.