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Chemistry in Wastewater Treatment
Published in Sreedevi Upadhyayula, Amita Chaudhary, Advanced Materials and Technologies for Wastewater Treatment, 2021
Sonali Sengupta, Chandan Kumar Pal
Phosphorous, which comes to the surface water from fertilizer, must be removed from wastewater. Phosphorous in the form of phosphate PO4−3 can be easily removed by using alum or sodium aluminate. Aluminum combines with phosphate to form aluminum phosphate AlPO4. Optimum pH for removal of phosphate by aluminum is 5.5–6.5. Except aluminum, other cations, such as iron and calcium can also be used to remove phosphate from water. Iron, in the form of either ferric phosphate (pH 7–8) or ferrous phosphate (pH 4.5–5), and calcium in the form of hydroxyapatite (pH < 9.5) remove phosphate (1).
NMR Spectroscopy of Bulk Oxide Catalysts
Published in Alexis T. Bell, Alexander Pines, NMR Techniques in Catalysis, 2020
Aluminium phosphate, A1PO4, is a well-known catalyst and catalyst support, which is generally prepared by neutralizing acidic solutions containing stoichiometric amounts of Al3+ and P043− ions. Precipitations conducted off-stoichiometry have resulted in novel aluminophosphates, which have activity in acid-catalyzed isomerization and dehydration reactions. Figure 17a shows that the rate constants of such reactions increase strongly with increasing P/Al ratio, especially as the ratio exceeds the stoichiometric value of 1.0. Figure 17b reveals that this increase is correlated with the appearance of downfield shifted resonances in the 1H MAS-NMR spectra (6.0 and 9.7 ppm), signifying the presence of highly acidic P-OH groups at the surface [81]. Enhanced Bronsted acidity associated with such species has also been discussed in conjunction with 1H and 31P MAS-NMR studies of PCl3− and H3PO4-modified silica surfaces [82] and with calcined zirconium phosphate-based catalysts [83].
Systems Based on AlP
Published in Tomashyk Vasyl, Ternary Alloys Based on III-V Semiconductors, 2017
An amorphous aluminum phosphate approximating the composition 2Al2O3⋅P2O5 (Al4P2O11) was precipitated from Na pyrophosphate and AlCl3 in aqueous solution (Stone et al. 1956). The precipitate was washed free of chlorides and dried at room temperature to yield a white powder that contained 35.8% total H2O.
On structure and oxidation behaviour of non-stoichiometric amorphous aluminium phosphate coating
Published in Surface Engineering, 2019
Aluminium phosphate with chemical composition of AlPO4 is a well-known ceramic material with low density (2.56 g cm−3 for berlinite), high melting temperature (1800°C), and high hardness (6.5 Mohs) [1]. It is also chemically compatible with most widely used ceramic materials including silicon carbide, alumina, mullite, and silica over a moderate range of temperatures [2]. However, stoichiometric aluminium phosphate is isostructural with silica and undergoes similar polymorphic transformations (quartz-type, tridymite, and cristobalite). In fact, its use as a high temperature ‘engineering ceramic’ material is limited primarily because of the phase transformations which involve large molar volume changes [3]. Therefore, synthesis of non-stoichiometric and amorphous aluminium phosphate with no allotropic volume changes which is stable at the elevated temperatures appears advantageous as it skips the aforementioned drawbacks and provides unique properties arising from the amorphous structure such as superior corrosion and oxidation resistance [4].