绿色回收废旧二硅化钼中含钼相的微观结构演变及其光催化机制

Molybdenum is a key role metal in human life and industry. In recent years, the world’s molybdenum demand has been driven by soaring steel production, particularly in China. With the rapid growing demand for molybdenum metal and ceaseless exploitation of all the mineral resources of molybdenum in the world, primary mineral supplies are becoming more and more insufficient to meet demands, resulting in increasing exploitation of secondary sources. Among secondary resources, spent molybdenum disilicide (MoSi2) is undoubtedly very important and contains 63 wt. % of molybdenum. Unfortunately, it is difficult to find reports of the recovery of molybdenum from spent MoSi2. Thus, this proposals show a novel, simple and direct process to treat spent MoSi2 to prepare MoO3, and the photocatalytic properties of the synthesized MoO3 will be discussed. .A well-known, yet unresolved, phenomenon occurring during low temperature oxidation is “MoSi2 pest”, which leads to disintegration of the material (i.e. destruction of the compound into powder). Typically, the pest phenomenon is not beneficial for the application of MoSi2 parts, however, this proposals use the pest phenomenon to convert spent MoSi2 to MoO3 and SiO2 as follows: MoSi2+O2→MoO3+SiO2. The thermodynamic conditions, kinetic and structural macrokinetics characteristics of MoSi2 pest oxidation will be investigated, and the microstructural evolution will be studied by XRD, SEM and TEM, etc. Then the phase containing Mo transformation mechanism will be discussed, and the physical model will be founded..Based on a high vapour pressure of a Mo-bearing species in equilibrium with MoO3 in air, MoO3 can be recovered from the pest product of MoSi2 by thermal evaporation and condensation. The phase composition, microstructure and dislocation of the recycled MoO3 will be investigated by XRD, SEM and HRTEM, and the optical properties will measured by FTIR and Raman. The growth process will be proposed for the formation of the recycled MoO3, and then the uniform morphology of the recycled MoO3 will prepared in future experiment..MoO3, as a wide band gap n- type semiconductor, is one of the most intriguing transition metal oxides. As catalyst material, MoO3, has attractive prospects in photocatalysis field and it can be used in environmental pollution control due to good adsorption properties for dyeing agent molecules. However, there are few reports on the photocatalytic properties of recycled MoO3. In present proposals, the photocatalytic properties of recycled MoO3 to degrade organic dyes such as methylene blue, methyl orange and phenol will be determined from the band gap structure, electron-hole pairs and recyclability and a possible photocatalytic mechanism is suggested..This work will develop the theories and methods of the recovery molybdenum from spent MoSi2 and other spent materials containing molybdenum, which is strong beneficial to the sustainable development of molybdenum resources.

面向钼资源短缺和有机污染物治理的重大需求，针对大量废旧二硅化钼得不到科学利用的问题，在申请人前期研究的基础上，提出以三氧化钼的形式绿色回收废旧二硅化钼中钼的新思想，揭示含钼相的组织演变规律，并把回收产物应用于有机污染物降解领域，探明相关降解机制。基于二硅化钼存在Pest现象的逆向思维，实现废旧二硅化钼中钼的环境友好性分离，通过热力学计算、动力学规律和结构宏观动力学特征分析，明确钼元素的迁移过程，澄清含钼相的转化机制。基于三氧化钼高温蒸汽压较高的现象，提出通过蒸发-冷凝工艺以三氧化钼的形式回收钼，阐明三氧化钼的形核条件和长大机理，构建三氧化钼形态控制的物理模型，实现回收产物的精确设计。从物料特征、能带结构、电子空穴复合几率、重复利用等方面探明三氧化钼对有机污染物的光催化降解规律，建立结构、形态和性能之间的关系。为促进稀有金属钼的绿色循环利用、发展光催化降解材料提供必要的理论依据和技术支持。

MoSi2是一种在800-1800℃广泛使用的电热元件材料，同时也是一种抗氧化涂层材料，此外还是一种潜在的高温结构材料，因而MoSi2在航空航天、高温烧结等工业领域和实验室研究方面获得普遍应用，每年产生大量废弃MoSi2；MoSi2中的Mo是过渡族难熔稀有金属，Mo的氧化物MoO3是一种半导体，具有电致变色、光催化降解等特性，因而本项目针对大量废旧MoSi2得不到科学利用的问题，基于MoSi2存在低温Pest现象的逆向思维，提出以MoO3的形式绿色回收废旧MoSi2中Mo的新思想。研究了MoSi2的Pest氧化以及热蒸发回收MoO3的最佳工艺条件，明确了Mo元素的迁移过程和MoO3的形成机制；探明了MoO3对亚甲基蓝的光催化降解规律。结果表明：500℃氧化180min可以使MoSi2完全转化为MoO3和无定形SiO2的混合物；950℃对氧化产物进行热蒸发，可以实现MoO3和SiO2的完全分离，XRD、XPS、FT-IR、Raman、TEM、HRTEM等分析表明回收产物为α-MoO3，UV-Vis结果显示回收MoO3的带隙为2.96eV；以回收MoO3作为光催化剂，对20mg/L亚甲基蓝溶液进行降解，暗处理30 min的吸附降解率达到42.15%，光照60 min其降解率达到99.25%，自由基捕获实验表明MoO3主要靠产生·OH降解染料。与市售MoO3试剂相比，回收MoO3具有更好的光催化活性。以回收的MoO3和Fe2O3为原料制备了Fe2(MoO4)3，同样展示了良好的光催化性能。本项目以废旧MoSi2为原料，基于MoSi2和MoO3的本征物理与化学特性，发展了一种低温氧化和高温热蒸发的绿色回收工艺，进而把回收产物MoO3应用于有机污染物的光催化降解领域，是一种从固废到环境治理的综合过程，其成果对于促进含钼资源的绿色综合利用、发展光催化降解材料与技术具有重要的科学意义和应用价值。