Synthesis , Characterization And Crystallographic Features Of Zirconium Molybdo-Pyrophosphate As A Composite Material

A three inorganic ion exchange materials zirconium phosphate,zirconium molybdateand zirconium molybdo-pyrophosphate have been synthesized under identical conditions. Structures of these materialswere established by chemical analysis,X-ray diffraction, thermogravimetric and differential thermal analyses,fourier transform infrared spectroscopy and Xray fluorescence analysis.From the data obtained the synthesized materials can be written as (Zr1.15PO4.8.3H2O)for zirconium phosphate with an amorphous structure and (Zr1.18Mo6.7.2H2O) and(Zr1.7MoPO7.2.3H2O) for zirconium molybdate and zirconium molybdo-pyrophosphate, respectively, with the semicrystalline structures. The data obtained from X-ray peak broadening analysis was used to evaluate the crystallite size and lattice strain by Scherer’ formula and Williamson-Hall (W.H) analyses. The chemical stability of these materials has been investigated in water and acidic media.The ion exchange capacity of zirconium molybdo-pyrophosphate for Pb and Cd ions have been studied at different heating temperatures.


1-INTRODUCTION
A good deal of interest has grown in the last decades in synthetic inorganic ionexchangers becauseof their greater resistance to high radiation and high temperature,which isof great importance in the nuclear technology[1]. Inorganic ionexchangers have been widely used for the removal of heavytoxic metals from wastewater [2].The water pollution also arises due to the increasing use of copper, iron, zinc, lead and cadmium in many industries [3]. The heavy metals when present in water are injurious to the health.Thus, by synthesizing new inorganic cation-exchangers, having affinity and selectivity for a particular metal ion, one can separate the undesired metalfrom effluents.Zirconium molybdopyrophosphate (ZMPP) ion exchanger dried at 50 0Cwas used in the removal of 134 Cs, 60 Co and 152,154 Eu radioisotopes from radioactive liquid waste solutionswith the selectivity Cs(I) >Eu(III) > Co(II) [4]. In this work three inorganicion exchangers based onphosphate and molybdate anions such as zirconium phosphate,zirconium molybdate and zirconium molybdo-pyrophosphate were studied.These components were found to show relatively increased ionexchange capacity and selectivity. The present paper describes the synthesis of inorganic ion exchange materials in different volume ratios.Chemical stability,crystallite size and lattice strain was investigated. The empirical formulas, structures and the ion-exchange capacities of the product materials were conducted. and sodium molybdate(Na2MoO4) to tetra sodium pyrophosphate (Na4P2O4)with volumetric ratio Zr:MO:P equal to 2:1:1 at constant stirring and room temperature. After complete addition precipitation was occurred and then the reaction mixtures were overnight standing.The precipitates were filtered and washed several times with deionized water. The precipitate was dried at 50 • C in an electric oven, grained and sieved for different mesh sizes and stored at room temperature.

2.3-CHEMICAL STABILITY
The stability ofzirconium phosphate(ZP), zirconium molybdate (ZM) and zirconium molybdo pyrophosphate(ZMPP) in various media such as H2O,HCl and HNO3 were studied by mixing 0.05gm of the solid with 5 ml of the desired solution using a batch factorequal 100ml.g -1 in a shaker thermostat at 25±1 0 C for 72 hours. The concentration of the acid was varied between 0.1to 6 M. After 3 days the solution was separated by centrifugation and the solutions analyzed by atomic absorption spectrometer (ASS) for determination of the metal ion concentration in solution.

2.4-CAPACITY MEASUREMENTS
Repeated batch equilibration of 30 ppm metal Chloride solution(Pb +2 and Cd +2 ) with solid material in V/m ratio100 ml/g was carried out for the capacity evaluation.The mixture was shaken in a shaker thermostat at 25±1 0 C.After overnight standing the solid was separated and the concentration of the metal ion was measured by atomic absorption spectrometer(ASS).The capacity value was calculated by Equation ( 1): (1) Where Co is the initial concentration of solution (mg/l),V is the solution volume (ml) and m is the weight of the exchanger (g) [6,7].

3-RESULTS AND DISCUSSION
The scope of this work is the attempt to synthesize composites with high chemical stability and high selectivity for some pollutants and heavy metals [8].The exchangers zirconium phosphate (ZP), zirconium molybdate (ZM) and zirconium molybdo pyrophosphate (ZMPP) were synthesized with complete characterization for elucidation the structure and the chemical formula of the composites. The chemical stability of ZP, ZM and ZMPP were studied in water, nitric acid and hydrochloric acid and the data showed high stability to chemical attack.The composites are stable in HNO3 and HCl solutions up to 3 M acid solutions. X-ray diffraction patterns of ZP, ZM and ZMPP are represented in Figs.(1,2,3). Figures 2 and 3 show that the composites ZM and ZMPP have semi crystallinenature while ZP has the amorphousstructure. The XRD pattern of ZMPP heated at different heating temperatures 50 0 C,200 0 C,400 0 C,600 0 C,850 0 C and after saturated by 30ppm of Pb +2 and Cd +2 ions show that ZMPP have amorphous structure up to 600 0 C and crystallinity increased at 600 0 C,850 0 C .The Bragg angle 2θ and the full width at half maximum β(FWHM) were determined to evaluate thecrystalline size and lattice strain for the material.From Debe-Scherrer,s formula; D=(K.λ) / β.Cos θ (2) Where D is the effective average crystalline size,Kis the shape factor (0.9), λ is the wavelength of Cu-Kα radiation in A 0 , θ is the Bragg diffraction angle and the β is the measured full width at half maximum(FWHM).The lattice strain induced in powders due to crystal imperfection and distortion was calculated using Hall equation with the formula [9,10]. βCos θ / λ = 1/D + (ε. Sin θ) / λ (3) where εis the effective strain.By substitution in equation2 from equation1 about the value of (ε), equation 3 becomes; (β.Cos θ)/ λ={ (β.Cos θ)/(K. λ) }+{( ε. Sin θ)/ λ} (4) By multiplying both sides of equation 3 in aconstant value λ / (β.Cos θ) and rearrangement we get on; ε= β/4tan θ (5) From equation 2 and 5 it was confirmed that the peak width from crystalline size varies as 1/ Cos θ strain varies as tan θ.The sum of the equations 2 and 5. β = {K. λ/ D Cos θ} +4 ε. tan θ (6) Byrearranging the above equation, we get; β Cos θ={K. λ/ D} +4 ε sinθ (7) The above equations are Williamson-Hall,s (W-H) equations. By plots relation between (4sin θ)along xaxis and (β Cos θ)along y-axis and from the linear fit of the data,the crystalline size was estimated from the y-intercept,and the lattice strain (ε), from the slope of the fit was calculated and the results represented in Table(1). The data in Table(1)indicated that opposite order with and the lattice strain of ZMPP heated at different crystalline size heating temperatures before and after saturation by 30ppm of Pb +2 and Cd +2 ions. The data in Table(1)show that the lattice strain (ε) before saturation > (ε) after saturation by Pb +2 ion > (ε) after saturation by Cd +2 ion.This order shows that opposite order with crystalline size [11]. IR spectrums of the composites were represented in Figs. (4,5 and 6).From Figs.(4 and 5) we found that broad and sharp peak in the range 3600-3200 and ~1620 cm -1 ,which assigned to the stretching and bending modes of water molecules [12]. In Fig.(4) a band in the region 1050 cm -1 may be due to the presence of P-O stretching   [13]. In Fig.6we found that broad and sharp peak in the range 3600-2600 and ~1600 cm -1 , which assigned to free and interstitial water molecules.The peaks at 880 and 740 cm -1 due to Zr-O bond. The peak at 500 due to Mo-O bond and characterized to molybdategroup [14]. TGA and DTA of ZP, ZM and ZMPP composites are represented in Figs. (7)(8)(9) respectively. In figure (7) two endothermic peaks are appeared for ZP. The first at 91.860C due to dehydration of free water [7] and the second peak at 587 o C due to start of condensation due to removal of lattice water from the material [1]. Figure  (8) indicate 3 endothermic peaks at 121, 376.6 and 585.6 o C for ZM. The first peak at 121 o C may be due to removal of external water molecules and second peak at 376.6 o C may be due to dehydration of interstitial water [7] and the last peak at 585.6 o C due to the crystallization of ZrO2 and MoO3 to form ZrOMoO4. Figure (9) indicate two endothermic peaks at 150 o C and 596 o C for ZMPP. The first peak at 150 o C due to removal of external water molecules and the other peak at 596 o C due to formation of pyrophosphate phase [7].An exothermic peak at 629 o C were appeared due to the crystallization of ZMPP. From TG curves in figures (7-9), the water content was calculated from the calcination of the composites at 850 0 C.The data indicated that the weight loss of ZP, ZM and ZMPP were equal 20.4% ,10.52% ,11.3%, respectively. These values were used in calculation of the number of the water molecules in the composite material using the equation6 [6,15]; 18n=

3.1-EFFECT OF HEATING TEMPERATURE ON THE APPARENT CAPACITY OF ZMPP COMPOSITE
Thermal treatment of zirconiummolybdo pyrophosphate was investigated by measuring the capacity of the composite at different heating temperatures that accompany the change in the structural behaviuor.The capacity in mg/g was measured by batch technique using batch factor 100ml/g and metal ion concentration 30ppm.The data of capacity was represented in table (2) and showed that, generally, the original zirconium molybdo pyrophosphate composite dried at 50 o C are selective for Pb 2+ and Cd 2+ ions. Water molecules play important roles as exchangeable active sites,on heating at 200 o C,600 o C and 850 o C the capacity of zirconium molybdo pyrophosphate decreased which may be attributed by in the early stage of the heating only water molecules present in the cavity of the exchanger will be lost (cavity water),and by increasing the heating temperature the water molecules present in the structure will be lost during condensation(condensation water)leading to shrinkage in the cavity and channels of the exchanger at higher temperatures.This shrinkagein the structure leading to some strike difficulties and decrease in the number of the exchangeable active sites of the exchanger [12].