1. Fe-Al binary Oxide Nano-Sorbent: Synthesis, Characterization and Phosphate Sorption Behavior Tofik Ahmed, Abi.M.Taddesse, Tesfahun Kebede, Girma Goro Haramaya University, College of Natural and Computational Sciences, Haramaya, Ethiopia
Introduction
Results (continued)
Results (continued)
Phosphorous removal using efficient treatment processes such as adsorption is important for the control of eutriphication [1]. There is a paucity of information related to the synthesis, characterization and sorption property studies of Fe-Al binary mixed oxide at nano-scale for phosphate removal from wastewater. The objectives of this work were to a) synthesize and characterize Fe-Al binary mixed oxide nano-sorbent, b) identify the combined effect of alumina and calcinations temperature that resulted to the nano-sized particle with better specific surface area, and c) study the phosphate sorption behavior of the selected as-synthesized nano sorbent
The adsorption data fitted well to both Langmuir (R2=0.999) and Freundlich (R2=0.998) isotherms for a wide range of adsorbate concentrations. Therefore, all the adsorbents and adsorbates followed the Langmuir and Freundlich isotherms. Values of the equilibrium parameter (RL) from Langmuir isotherm and n values from the Freundlich isotherm have indicated that the adsorption process is favorable.
The EDX (Figure 2a) results showed that the adsorbent mainly contained the elements O, Fe, and Al indicating the composition of mixed metal oxides. Chemical composition analysis revealed that Fe and Al oxides were the components of the adsorbent supporting the EDX result. From SEM image the predominant population of particles indicate the formation of the binary oxide (Figure 2b). TEM image shows spherical particles with average particle size of 16 nm roughly conforming with the result calculated from Dbye Scherere Equation(Figure 2c). The peaks at 1042 cm-1, 1076 cm-1, and cm-1 could be grounds for judging the visibility of phosphate adsorption onto nano–sized iron aluminum mixed oxide sorbent.
The spectra of 10Al300 display a number of peaks before and after adsorption. The new peaks appeared in Figure 12 at cm-1, cm-1 , cm-1 and at cm-1 can be attributed to possible adsorption of phosphate. Accordingly, the peaks at 1042 cm-1 and cm-1 can be bands to phosphated iron. Furthermore, the peak at cm-1 is evidently representing the existence of P-O vibration.
Materials and Methods
Gel evaporation method [2] was followed to synthesize nano sized Fe-Al binary oxide. The percentage of aluminum considered was 0%, 10% and 30%. The powders obtained were calcined at three different temperature: 300 oC, 600 oC and 900 oC. From the nine samples prepared, the nanomaterials with the highest specific surface area was selected for further characterization (XRD, SEM/EDX, TEM, FTIR, FAAS) and subsequent sorption property study.
The phosphate sorption process was found to be spontaneous and endothermic from the negative and positive values of ∆G and ∆H respectively. The positive value of ∆S showed the increased randomness at the solid/solution interface (Table 1). Furthermore, Phosphate desorbability was observed to increase with increasing pH indicating that relatively favorable conditions for repeatability of the process at higher pH values
Results
The results indicate that introducing alumina could delay the crystallization of iron oxide during calcination. Crystal transformation of iron oxide from maghemite to hematite is also delayed due to increased alumina. Increasing the calcinations temperature enhances the transformation of maghemite to hematite. The avarage crystallite size of the as-obtained materials was calculated using Dbye Scherere Equation and ranged between 20 to 40 nm (Figure 1a-c)
The surface area calculated using Sear’s method evidenced that the sample with 10% Al subjected to 300 0C exhibited the highest surface area (119 m2/g). This was selected for further characterization and sorption behavior study.
Conclusion
The results suggested that the nanosized Fe–Al binary mixed oxide could be successfully applied for adsorbing phosphate and controlling the phosphorous pollution in aqueous solution.
The optimized parameters for maximum phosphate adsorption were: pH=4, dose=0.1g, agitation speed= 140 rpm, contact time=12h and initial phosphate concentration = 20 mg/L. Having all these parameters optimized this study has entitled 99.86% efficiency of phosphate ion removal from aqueous solution.
This adsorbent, with large adsorption capacity and high selectivity, is a very promising adsorbent for the removal of phosphate ions from aqueous solutions.
Figure 2: EdX spectrum(a), SEM Image(b) and TEM image © of selected as synthesized powder.
Maximum phosphate adsorption was obtained at pH=4, dose=0.1g, agitation speed= 140 rpm, contact time=12h and initial phosphate concentration = 20 mg/L. Having all these parameters optimized this study has entitled 99.86% efficiency of phosphate ion removal from aqueous solution. The effect of co-existing anions on the adsorption of phosphate was also studied and no significant effect on the efficiency of the nano-sorbent was observed due to competing ions such as fluoride
Figure 1:XRD patterns of (a) samples calcined at 300oC with various content of aluminium, (b) samples calcined at 600 oC with various content of aluminium, and (c) samples calcined at 900 oC with various content of aluminum.
The authors would like to thank Haramaya University for the financial assistance. The University of Cape Town, Physics Department is also acknowledged for characterizing the samples using XRD,SEM/EDX and TEM.