Kinetic, isotherm and thermodynamic investigations of phosphate adsorption onto core-shell Fe3O4@LDHs composites with easy magnetic separation assistance.

In this study, three different magnetic core-shell Fe3O4@LDHs composites, Fe3O4@Zn-Al-, Fe3O4@Mg-Al-, and Fe3O4@Ni-Al-LDH were prepared via a rapid coprecipitation method for phosphate adsorptive removal. The composites were characterized by XRD, FTIR, TEM, VSM and BET analyses. Characterization results proved the successful synthesis of core-shell Fe3O4@LDHs composites with good superparamagnetisms. Batch experiments were conducted to study the adsorption efficiency of phosphate. Optimal conditions for the phosphate adsorption were obtained: 0.05 g of adsorbent, solution pH of 3, and contact time of 60 min. Proposed mechanisms for the removal of phosphate species onto Fe3O4@LDHs composites at different initial solution pH were showed. The kinetic data were described better by the pseudo-second-order kinetic equation and KASRA model. The adsorption isotherm curves showed a three-region behavior in the ARIAN model. It had a good fit with Langmuir model and the maximum adsorption capacity followed the order of Fe3O4@Zn-Al-LDH>Fe3O4@Mg-Al-LDH>Fe3O4@Ni-Al-LDH. Thermodynamic analyses indicated that the phosphate adsorption process was endothermic and spontaneous in nature. The three Fe3O4@LDHs composites could be easily separated from aqueous solution by the external magnetic field in 10s. These novel magnetic core-shell Fe3O4@LDHs adsorbents may offer a simple single step adsorption treatment option to remove phosphate from water without the requirement of pre-/post-treatment for current industrial practice.

[Synthesis and characterization of CTMAB and PDMDAAC modified organobentonite].

The natural bentonite was purified and changed to sodium form by NaCl via exchange reaction. Their characteristics, such as swelling volume, swelling value, colloid valence, ethylene blue adsorbed and cation exchange capacity, were measured. The results indicate that the property of Na-bentonite is better than that of natural bentonite. Using cetyltrimethylammonium bromide (CTMAB) and homopolymer of dimethyldiallyammomium chloride (PDMDAAC) as organo-intercalating reagents, two organic modified bentonites were prepared and characterized by Fourier transform infrared (FTIR), X-ray powder diffraction (XRD) and BET surface area. The XRD results showed that the CTMAB-bentonite and PDMDAAC-bentonite had typical X-ray diffraction peaks, and the d001 values increased to 1.89 and 1.45 nm, respectively. Combined with the results of FTIR, the modified reagents had been intercalated to the layer of bentonite. The BET areas, pore volumes and average pore diameters of the two organo-bentonites were decreased as compared to that of Na-bentonite.

Removal of o-nitrobenzoic acid by adsorption on to a new organoclay: montmorillonite modified with HDTMA microemulsion.

A new organoclay, consisting of montmorillonite modified by a hexadecyl trimethyl ammonium (HDTMA) microemulsion, was synthesized, characterized and used as an adsorbent for the removal of o-nitrobenzoic acid from aqueous solution. Adsorption kinetics, isotherms and effects of operating variables, such as adsorbent dosage, ionic strength and initial solution pH, were also investigated. The results of Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) analysis and BET surface area determination indicated that HDTMA molecules had entered into the interlayer of the montmorillonite. The optimized experimental conditions for the adsorption of o-nitrobenzoic acid by montmorillonite modified by HDTMA microemulsion were 0.5 g adsorbent dosage, 0.4 mL of 0.1 mol lbL(-1) CaCl2 solution, initial solution pH of 6.0 and contact time of 6 h. The adsorption isotherms of o-nitrobenzoic acid fitted the Langmuir model well (R2 = 0.9880). The adsorption kinetics data fitted the pseudo-second-order equation (R2 = 0.9999). These above results indicate that montmorillonite modified by an HDTMA microemulsion can be used as adsorbent for o-nitrobenzoic acid because of its high adsorption capacity and low cost.

Adsorption of phosphate from aqueous solution by hydroxy-aluminum, hydroxy-iron and hydroxy-iron-aluminum pillared bentonites.

Phosphorus removal is important for the control of eutrophication, and adsorption is an efficient treatment process. In this study, three modified inorganic-bentonites: hydroxy-aluminum pillared bentonite (Al-Bent), hydroxy-iron pillared bentonite (Fe-Bent), and mixed hydroxy-iron-aluminum pillared bentonite (Fe-Al-Bent), were prepared and characterized, and their phosphate adsorption capabilities were evaluated in batch experiments. The results showed a significant increase of interlayer spacing, BET surface area and total pore volume which were all beneficial to phosphate adsorption. Phosphate adsorption capacity followed the order: Al-Bent>Fe-Bent>Fe-Al-Bent. The adsorption rate of phosphate on the adsorbents fits pseudo-second-order kinetic models (R(2)=1.00, 0.99, 1.00, respectively). The Freundlich and Langmuir models both described the adsorption isotherm data well. Thermodynamic studies illustrated that the adsorption process was endothermic and spontaneous in nature. Finally, phosphate adsorption on the inorganic pillared bentonites significantly raised the pH, indicating an anion/OH(-) exchange reaction.

[Study on fluorescence spectral behavior of trimethoxyphenylflurone with gallium in microemulsion].

In the present paper, the fluorescence spectral behavior of gallium with trimethoxyphenylflurone (TM-PF) in microemulsion was studied. In the buffer medium of HAc-NaAc at pH 4.95, the fluorescence intensity is in proportion to the concentration of gallium (III) in the range of 0-0.045 microg x mL(-1). The CTMAB microemulsion was efficiently used to enhance the sensibility and stability of the system, and the limits of detection were 1.2 ng x mL(-1). The coexistent metal ions can be separated and gallium can be enriched by the extraction of butyl acetate, greatly improving the selectivity and sensibility of the system. The method possesses high sensitivity as well as high selectivity. It can be used to determine trace amount of gallium in ore samples successfully.