ABSTRACT
BACKGROUND: Due to the extensive use of phosphates in industry, agriculture and households, the phosphate - γ-alumina interactions are important for understanding its detrimental contribution to eutrophication in lakes and rivers. In situ Fourier transform infrared (FTIR) spectroscopy can provide more detailed information on the adsorbate-adsorbent interaction and the formation of hydrogen bonds. RESULTS: In situ ATR-FTIR spectroscopy was used to identify phosphate complexes adsorbed within the three-dimensional network of mesoporous γ-alumina at pH 4.1 and 9.0. The integrated intensity between 850 cm-1 and 1250 cm-1 was used as a relative measure of the amount of adsorbed phosphate. The integrated intensity proved to be about 3 times higher at pH 4.1 as compared with the corresponding intensity at pH 9.0. The adsorption of phosphate at the two pH conditions could be well described by the Langmuir adsorption isotherm at low concentrations and the empirical Freundlich adsorption isotherm for the whole concentration range, viz. 5 - 2000 µM. CONCLUSIONS: From the band shape of infrared spectra at pH 4.1 and pH 9.0, it was proposed that the symmetry of the inner-sphere surface complex formed between phosphate and γ-alumina was C1 at the lower pH value, whilst the higher value (9.0) implied a surface complex with C2v or C1 symmetry. The difference in adsorbed amount of phosphate at the two pH values was ascribed to the reduced fraction of ≡ AlOH2+ surface sites and the increased fraction of ≡ AlO- sites upon increasing pH from 4 to 9.
ABSTRACT
In this paper, the surface stoichiometry, acid-base properties as well as the adsorption of xanthate at ZnS surfaces were studied by means of potentiometric titration, adsorption and solution speciation modeling. The surface proton binding site was determined by using Gran plot to evaluate the potentiometric titration data. Testing results implied that for stoichiometric surfaces of zinc sulfide, the proton and hydroxide determine the surface charge. For the nonstoichiometric surfaces, the surface charge is controlled by proton, hydroxide, zinc and sulfide ions depending on specific conditions. The xanthate adsorption decreases with increasing solution pH, which indicates an ion exchange reaction at the surfaces. Based on experimental results, the surface protonation, deprotonation, stoichiometry and xanthate adsorption mechanism were discussed.
ABSTRACT
Pore size adjustable mesoporous silica was synthesized by adsorption of varying amounts of sodium dodecyl benzenesulfonate at the surface of silica activated by zinc ion via a novel surface charge reversal route. The pore size and volume can be adjusted from 5.9 to 13.76 nm and 0.88 to 1.08 cm(3) g(-1), respectively, with increasing the SDBS concentration from 0.77 to 3.08 mmol L(-1). Adsorption of Zn(2+) as a function of pH and N(2) adsorption/desorption isotherms demonstrated that the metal ions such as Zn(2+) could be readily removed with dilute nitric acid without apparent collapse of the pore structure at the proper range of SDBS concentration.
ABSTRACT
In this paper, mesoporous alumina with different pore sizes and wall crystalline structures was synthesized at calcination temperatures over 550 degrees C. The characterization of the samples calcined at 550, 800, 1100, and 1300 degrees C, respectively, was performed using TEM, XRD, FTIR, TG/DTA, and N2 adsorption/desorption techniques. The correlation between pore size and wall crystalline structure on calcination temperature was systematically investigated.
