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基于煤矸石的气凝胶复合材料制备及其光降解活性研究

作者:完美论文网  来源:www.wmlunwen.com  发布时间:2019/9/3 10:02:01  

摘要:以工业固体废弃物煤矸石为原材料,制备出高比表面积、低导热率的SiO2气凝胶粉末和具有光降解活性的SiO2-TiO2复合气凝胶,既提供了固体废弃物煤矸石综合治理的新途径,又降低了气凝胶的生产成本,实现了煤矸石的高附加值利用,并为硅基气凝胶提供了更为廉价的硅源材料。

通过碱溶活化、酸浸除杂和湿法提取工艺制备出硅酸钠溶液,为后续试验提供优质的硅前体。采用“一锅”法结合环境压力干燥快速制备出具有高比表面积的疏水性SiO2气凝胶粉末,较传统溶胶-凝胶法相比可缩短气凝胶的制备周期。以四氯化钛(TiCl4)为钛前体,采用溶胶-凝胶法制备SiO2-TiO2复合湿凝胶,经表面改性(TMCS)和溶剂(正己烷)交换后可实现在常温常压条件下干燥制备出具有光降解活性的SiO2-TiO2复合气凝胶,并以其为骨料制备出具有光降解活性的气凝胶砂浆,进一步探讨气凝胶复合砂浆的物理、力学和光催化性能,取得如下结论。

(1)通过单一变量法分析了Na2CO3与煤矸石质量比、NaOH浓度、固液比、反应温度和反应时间对硅酸钠溶液的模数和SiO2浸取率的影响,通过混合煅烧和酸浸能有效去除Al、Ca和Fe等杂质,去除率分别为94.3%、95.6%和91%,干燥后的煤矸石酸渣中SiO2含量可达95.9%。研究表明,最佳煅烧质量比、NaOH浓度、固液比、反应温度和反应时间分别为0.6、0.5 mol/L、1:20、90℃和90 min,所制备的硅酸钠溶液模数为3.1,SiO2的浸取率92.2%。采用“一锅”法简化了合成与改性工艺,并制备出具有多孔结构的疏水性SiO2气凝胶粉末,其比表面积为748.53 m2/g,密度低至0.18 g/cm3,导热系数低至0.033 W·m-1·K-1,平均孔径在7.04 nm,孔体积约为2.64 cm3/g,是一种具有高比表面的纳米介孔材料。

(2)以TiCl4为钛源,自制硅酸钠溶液为硅源,采用溶胶-凝胶法结合常压干燥工艺制备出具有光催化性能的SiO2-TiO2复合气凝胶,分析了TiO2含量和煅烧温度对复合气凝胶的合成、结构和光催化性能的影响。结果表明,最佳TiO2含量和煅烧温度分别为40%和500℃,最优条件下制备的SiO2-TiO2复合气凝胶比表面积为589.15 m2/g,煅烧后的复合气凝胶呈亲水性,增大了其与甲基橙溶液的接触面积,通过吸附和光催化氧化对甲基橙溶液的降解率可达95.3%,重复使用四次后其降解效果仍可达70.33%。

(3)以SiO2-TiO2复合气凝胶为骨料,水泥为胶凝材料制备具有光降解活性的气凝胶,分析了不同气凝胶取代率对复合砂浆的物理、抗压强度、抗折强度和光催化性能的影响。结果表明,随着气凝胶取代率的增大,气凝胶砂浆的密度、抗折强度和抗压强度均在减小,但光催化效果逐渐增加,当气凝胶取代率为60%时,砂浆的密度为1196 kg/m3,抗折、抗压强度分别为9.6 MPa和0.9 MPa,气凝胶砂浆在紫外光条件下48 h对甲基橙的综合降解效果为70.6%。

In this paper, industrial solid waste coal gangue is used as raw material, SiO2 aerogel powders with high specific surface and SiO2-TiO2 composite aerogels with photodegradation activity were prepared. This route not only provides a new way for comprehensive treatment of solid waste coal gangue, but also reduces the production cost of aerogels, what realize the high value utilization of coal gangue and provides a cheaper source of silicon for silicon-based aerogels. Sodium silicate solution was prepared by mixing calcination of Na2CO3, impurity removal of H2SO4 and leaching of NaOH, which provides high quality silicon precursors for subsequent experiments. The hydrophobic SiO2 aerogel powder with high specific surface area was rapidly prepared by "one pot" method and dried under ambient pressure condition. This method can reduce the industrial production cost of silica aerogels and realize high value-added utilization of solid waste. SiO2-TiO2 composite wet-gel was prepared by sol-gel method using TiCl4 as titanium source and sodium silicate solution as silicon source. After surface modification and solvent exchange, SiO2-TiO2 composite aerogels with photodegradation activity were prepared by drying at atmospheric pressure. The effects of TiO2 content and calcination temperature on the structure and photocatalytic properties of the aerogels were analyzed to determine the optimal process.

The effects of the quality ratio of Na2CO3 and coal gangue, NaOH concentration, solid-liquid ratio, heating temperature and heating time on the modulus of sodium silicate solution and the leaching rate of SiO2 were analyzed by single variable method. The impurities such as Al, Ca and Fe can be effectively removed by mixed calcination and acid leaching. The removal rates were 94.3%, 95.6% and 91%. The content of SiO2 in gangue acid residue can reach 95.9%. The results show that the optimum mass ratio, NaOH concentration, solid-liquid ratio, heating temperature and heating time were 0.6, 0.5 mol/L, 1:20, 90 C and 90 min. The modulus of sodium silicate solution was 3.1 and the leaching rate of SiO2 can reach 92.2%. The specific surface area of aerogel is 748 m2/g, the density is about 0.18 g/cm3, the thermal conductivity is 0.033 W·M-1·K-1, the average pore size is 7.04 nm, and the pore volume is about 2.64 cm3/g, which is a typical mesoporous material.

SiO2-TiO2 composite aerogels with photocatalytic properties were prepared by sol-gel method combined with atmospheric drying technology using TiCl4 as titanium source and sodium silicate solution as silicon source. The effects of TiO2 content and calcination temperature on the synthesis, structure and photocatalytic properties of the composite aerogels were analyzed. The results show that the optimum TiO2 content and calcination temperature were 40% and 500℃. The SiO2-TiO2 composite aerogel has a specific surface area of 589.15 m2/g. The composite aerogels show hydrophobicity after calcination. The degradation rate of methyl orange solution can reach 95.3% by adsorption and photocatalytic oxidation, and the degradation effect can reach 70.33% after four times of reuse.

The aerogels composite mortar with photodegradation activity were prepared by using SiO2-TiO2 aerogel as aggregate and cement as cementitious material. The effects of different aerogel substitution rates on the physical, compressive strength, flexural strength and photocatalytic properties of the composite mortar were analyzed. The results show that the density, flexural strength and compressive strength of aerogel mortar decreased with the increase of aerogel substitution rate, but the photocatalytic effect gradually increased. When the aerogel substitution rate is 60%, the density of mortar is 1196 kg/m3, the flexural strength and compressive strength is 9.6 MPa and 0.9 MPa. The comprehensive degradation effect of aerogel composite mortar in 48 h under UV irradiation can reach 70.6%.

关键词:煤矸石;SiO2气凝胶粉末;SiO2-TiO2复合气凝胶;光催化降解;气凝胶砂浆

oal gangue; SiO2 aerogel powder; SiO2-TiO2 aerogel; photocatalytic activity; aerogel composite mor

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