沉淀法合成三硅酸镁粉体的孔结构及吸附性能

以Na2O.nSiO2和Mg(NO3)2为原料,经沉淀法合成得到三硅酸镁。采用BET、吡啶吸附和亚甲基蓝吸附等表征手段,考察了不同加料顺序和不同活化方法对样品孔道结构、表面酸性及吸附性能的影响。结果表明,滴定顺序对样品的表面织构有明显影响,Mg(NO3)2溶液滴入Na2O.nSiO2溶液合成的样品为微孔材料,主要为3 nm以下的微孔,比表面积达568.93 m2/g,孔容为0.3524 cm3/g;Na2O.nSiO2溶液滴入Mg(NO3)2溶液合成的样品为大孔材料,比表面积为179.40 m2/g,孔容为0.8350 cm3/g;各样品孔径均呈多峰分布;煅烧和酸化均可提高样品的表面酸量;各样品的亚甲基蓝吸附量与表面织构规律并不完全相同,表明孔道结构并不是影响样品吸附性能的唯一因素,酸活性位点的数量、强弱以及种类对样品的吸附性能均有一定影响。

Porous structure and adsorption properties of magnesium trisilicate synthesised by a precipitation method

Magnesium trisilicate was synthesized by precipitation using Na_2 O·nSiO_2 and Mg(NO_3)_2 as raw materi-als.The precipitate was heated at 450℃ or activated by H_2 SO_4,after which the samples were characterized by BET,pyridine adsorption and methylene blue adsorption to check the effect of method of mixing,calcination and a-cidic activation on the porous structure,surface acidity and adsorption properties.The results showed that the sam-ple which was synthesized by addition of Mg(NO_3)_2 to the sodium silicate solution was mieroporous with a specific surface area of 568.93 m~2/g,a pore capacity of 0.3542 cm~3/g and exhibited a multimodal pore width distribution in the 1-3 nm and 0.7-0.9 nm micropore regions.The sample which was synthesized by addition of the sodium sili-cate solution to Mg(NO_3)_2 solution was mesoporous with a specific surface area of 179.40 m~2/g and a pore capacity of 0.8350 cm~3/g.Calcination and acidic activation increased the surface acidity,reduced the specific surface area and changed the distribution of pore width.The porous structure and the quantity,type and strength of surface a-cidity all affect the adsorption properties of the material.