Title : 
  Normalized FT - IR - spectra of pH - dependend phosphorus adsorption on goethite 
 Abstract_text_1 : 
  Normalized FT - IR - spectra of pH - dependend phosphorus adsorption on goethite . 
 Abstract_text_2 : 
  P adsorption was investigated on synthetic and commercially available goethite ( 99 % , Alfa Aesar ) . The composition and crystallinity was confirmed by X - ray diffraction analyses with an Empyrean powder diffractometer ( PANalytical ) with Cu Kα radiation ( λ=0.15418 nm ) . The determination of the d - values and the verification of the calculated lattice parameter were performed using the XPowder software . The specific surface area of 17.2 m2 g-1 was determined with an Autosorb-1 ( Quantachrome ) using a five - point BET measurement and N2 . The point of zero charge ( PZC ) was determined using potentiometric titration , which was 8.8 for pure goethite without adsorbed P. P adsorption on goethite was studied in a batch setup at the pH values of 4 , 6 , 8 , 10 , and 12 . Therefore , goethite sample material ( 5 g ) for the respective pH steps was adjusted to pH 4 , 6 , 8 , 10 , or 12 , respectively , in ultrapure water with 0.01 M HCl ( pH 4 ) , or 0.1 M to 5 M KOH ( pH 6 to 12 ) using a Potentiometric Compact Titrator G20S and combined DGi115 - SC pH electrode ( Mettler - Toledeo ) under continuous stirring . For P adsorption , 0.5 g of goethite and 40 ml of a 0.15 mmol l-1 KH2PO4 , solution , adjusted to pH 4 , 6 , 8 , 10 , or 12 as well , were mixed to achieve a solid - solution ratio of 1:80 . The goethite- KH2PO4 mixture was shaken horizontally at 150 motions min-1 for 24 h. The P concentration in the solution was determined after reaction times of 2 , 24 , 48 , and 168 h. The samples have been centrifuged for 15 min at 3500 rpm and the clear supernatant was filtrated by using P - poor Whatmann 512 ½ filters . The concentrations of P and Fe were determined using inductively coupled plasma atomic emission spectroscopy ( ICP - AES ) . Under real conditions in the soil , an influence of the P sorption on the pH is to be expected . Therefore , the pH change was taken into account both at the beginning and at the end of the adsorption experiments . The pH change was measured in a reference experiment that was treated exactly under the same conditions as P adsorption experiment . The amount of adsorbed P was referred to both the initial and the final pH. For FT - IR spectroscopic measurements , the solid goethite samples after an adsorption time of 2 and 168 h were dried for 24 h at 40 ° C , and stored in a desiccator . The samples were analyzed without further treatment prior to FT - IR measurements . IR spectroscopic analyses were carried out by measurement of the absorbance in the FT - IR Drift mode ( Tensor 27 HTS - XT , Bruker ) and a wavenumber range from 400 to 4000 cm-1 . The spectrum of each treatment was created by generate the average of the 2 replicated samples by using the software Essential FTIR ® ( Operant LLC ) , where each sample included 40 scans . For evaluation , all spectra together were truncated in the range 1300 to 800 cm-1 , baseline corrected , and normalized with respect to the highest absorbance . After 2 h adsorption time , the amount of adsorbed P was 0.52 µmol m-2 at pH 4 , 0.65 µmol m-2 for pH 6 , 0.58 µmol m-2 for pH 8 , 0.29 µmol m-2 for pH 10 , and 0.14 µmol m-2 for pH 12 . Considering the initial pH , P adsorption on goethite after an adsorption time of 168 h was highest for pH 8 , yielding a P surface coverage of 0.75 µmol m-2 after a reaction time of 168 h , followed by pH 6 with 0.72 µmol m-2 , and pH 4 with 0.68 µmol m-2 . The extent of adsorption decreased from pH 8 to 10 with 0.58 µmol m-2 and was lowest for pH 12 with 0.18 µmol m-2 . The solution pH decreased for the initial pH 4 to 3.9 . , and for the initial pH of 6 , the final pH was 5.0 . For initial pH values 8.0 and 10.0 , the corresponding final pH values were 6.7 and 7.6 , respectively . At initial pH 12.0 , the decrease of the solution pH weakened with a final pH of 11.6 . Research domain : Soil Sciences Research question : How does the solution - pH affect the amount and binding motiv of adsorbed phosphorus on the goethite surface ? 
 Keywords : 
  Soil , Fourier transforms , goethite , phosphorus , absorbance , FT - IR spectrsocopy , goethite , phosphorus , adsorption , absorbance , opendata , Boden , Phosphor , Adsorption , Spektroskopie