Nitrate adsorption characteristics of synthesized allophanes with various chemical compositions

• Published in: Clay minerals Vol. 57; no. 3-4; pp. 223 - 229
• Main Author: Ohashi, Fumihiko
• Format: Journal Article
• Language: English; French; German; Spanish
• Published: Middlesex Cambridge University Press 01.09.2022
• Subjects: Adsorption; Aluminium; Aluminum; Aluminum silicates; Anion exchanging; Anions; Cavitation; Chemical composition; Chemical synthesis; Environmental impact; Gases; Groundwater; Hydrothermal reactions; Nitrates; Nitrogen; Porous materials; Reagents; River networks; Silicates; Surface chemistry; X rays; X-ray diffraction
• ISSN: 0009-8558; 1471-8030
• DOI: 10.1180/clm.2022.39

Abstract Allophane-related aluminium silicates with various chemical compositions were synthesized using a hydrothermal reaction with inorganic reagents as starting solutions. The X-ray diffraction traces of the synthesized allophanes showed broad reflections centred at 0.34 and 0.23 nm, which were attributed to the imogolite-like structure of the allophanes. Energy-dispersive X-ray measurements confirmed that the Al-rich materials were synthesized as targeted. The specific surface area of the synthesized allophanes was 313–500 m 2 g –1 , which is greater than that of a natural allophane (248 m 2 g –1 ). The amount of nitrate adsorbed on the synthesized allophanes tended to increase as the Al content increased. The maximum amount of nitrate adsorbed was 2.07 mmol g –1 at pH ~2, which was comparable to that of a common anion-exchange material. A possible adsorption mechanism for nitrate at lower pH levels is the weak NO 3 – interaction of the positively charged surface of Al-OH 2 + sites.