The influence of salt in the formation of carboxylic functionalized mesoporous silica

Sammanfattning: Popular summary This master thesis was focused on the influence of salt, such as NaCl and CaCl2, in the formation of carboxylic functionalized mesoporous silica materials. Mesoporous silica materials are one type of porous materials with a pore size between 2 and 5 nm (1݊݉ = 0.000000001 ݉ ). The walls of the pores in this kind of materials consist of silicon dioxide, which is called silica (sand). The mesoporous silica materials, or rather the mesoporous silica particles, are formed by amphiphilic molecules, a kind of molecule with one part that loves water and one part that hates water, and a silica source. Within the group of amphiphilic molecules, surfactants are mostly used. The surfactants are molecules with positive or negative charged head groups, which love water, and long organic tails, that hate water. Examples of surfactants in our daily life are shampoo and detergent. When the surfactants have been dissolved in water, the tails that hate water will get together and only leave the charged head groups outside in contact with the water. In this case, the grouped surfactants can form different shapes with the tails inside and the head groups on the surface of the shapes. The silica source will build up walls around these shapes. Accordingly, the “mesopores” of the materials are filled with surfactants during their creation. When the surfactants are removed, the mesopores arise, and the mesoporous materials with silica walls are formed. The networks of mesopores are often well ordered in various structures. When adding acid or salt into the formation mixture of mesoporous silica materials, the structure or the shape of the materials (particles) can sometimes be changed. The process is like baking, when adding different things, such as baking powder or salt, the shape or the texture of the pastries can be changed. In the work of this thesis, a surfactant with positive charged head group was used. Moreover, one kind of molecule consists of a negative part and a silicon part was added in the mixture. The negative part of this molecule is called carboxylic group, which is the major component of vinegar. In the mixture, this molecule will be in contact with the surfactant head group via the carboxylic part and in contact with the silica source via the silicon part. After the formation, when the surfactants are removed, the carboxylic groups will remain within the pores, therefore, carboxylic functionalized mesoporous silica (CFMS) materials are formed. Addition of acid can change the structures of the CFMS materials. The shapes of the particles can change depending on the structure. In this work we show that addition of salt can change the structures and the shapes of the CFMS particles. Additionally, the particle sizes increase when the amount of salt increases. Some of the CFMS particles have interesting and well-defined shapes, as shown in Figure 1. This means that salts can be used as control chemicals in the formation.