Abstract
Polyaluminum chloride (PAC) is an inorganic polymer material that has the advantages of a simple preparation process and special electronic structure. It is considered to be the most efficient and widely used flocculation material for water treatment. In this work, PAC has been used as a Lewis acid catalyst in interdisciplinary fields because of its polynuclear Al–O cation structure. Further, its catalytic mechanism in green organic synthesis has been studied in detail by using the multicomponent Biginelli reaction as the probe. The effect of solvent on the self-assembly and aggregation process of PAC materials was investigated using optical microscopy, UV-Vis spectrophotometry, particle size analysis, XPS, IR, SEM and HR-TEM. The results show that the PAC materials have different morphological characteristics in different solvents. The Al–O–Al cations were transformed in the ethanol solvent to form new multi-nuclear cation aggregates Alb, which could be used as inorganic micro–nano reactors with unique synergistic catalysis in catalytic reactions. This is the first time the role of PAC in the Biginelli reaction has been analyzed with a liquid in situ infrared instrument, which provided favorable evidence for the speculated reaction mechanism. The PAC–ethanol system is, therefore, considered to be a green, efficient (best yield >99%), economic and recyclable catalyst for catalyzing organic synthesis reactions. The development and utilization of PAC materials in organic synthesis will bring new vitality to this cheap material, which is widely used in industries.
Highlights
Polyaluminum chloride (Al2Cln(OH)6Àn, PAC) is currently the most commonly used occulant for water treatment in industrial production, with its usage reaching up to 3000–4000 tons per day.[1,2,3,4,5] It has been reported that polyaluminum chloride can exist in three different forms in aqueous solutions: monomer (Ala), fast reaction colloid (Alb) and slow reaction colloid (Alc).[6]
The Al–O–Al cations were transformed in the ethanol solvent to form new multi-nuclear cation aggregates Alb, which could be used as inorganic micro–nano reactors with unique synergistic catalysis in catalytic reactions
In order to explore the microscopic mechanism of the self-assembled Alb aggregates and other particles in the PAC–ethanol system, we used an optical microscope and particle size analyzer to study the morphology of PAC in different solvents, and the results are shown in Fig. 1 and S3.† Fig. 1(a1–a3) is the optical image of PAC material in an aqueous solution; it can be seen that the PAC material rst formed round vesicles a er coming in contact with water, and quickly dissolved in water
Summary
Polyaluminum chloride (Al2Cln(OH)6Àn, PAC) is currently the most commonly used occulant for water treatment in industrial production, with its usage reaching up to 3000–4000 tons per day.[1,2,3,4,5] It has been reported that polyaluminum chloride can exist in three different forms in aqueous solutions: monomer (Ala), fast reaction colloid (Alb) and slow reaction colloid (Alc).[6].
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