Preparation of Porous Nanostructures via the Epoxide Addition Method: A Study of pH and Gel Formation with Templating Prajan Divakar Marauo Davis, Geneva R. Peterson, Louisa J. Hope-‐Weeks Department of Chemistry and Biochemistry, Texas Tech University Lubbock, Texas 79409, U.S.A
Abstract: Recently, copper and zinc aerogels have been synthesized using the sol-‐gel method. The gels were prepared using different molar ratios of Cu:Zn and different copper salts. Characterization of the as-‐prepared aerogels involved Brunauer-‐Emmett-‐Teller, Barrett-‐Joyner-‐Halenda, and Powder X-‐ray Diffraction analyses. The Thermogravimetric analysis was then performed to obtain an aerogel containing copper metal and zinc oxide. Overall, the characterization process yielded unexpected results; the annealed aerogel contained large quantities of copper (II) oxide. In addition to the production of copper and zinc containing gels, a pH study of different manganese salt solutions with regard to the anion effect was investigated. Similar trends within the different metal salts regarding pH as a function of time were noted. The change in pH resulted from periodic additions of propylene oxide. Introduction: Porous nanostructures, also known as aerogels, are becoming more and more prevalent in commercial applications today. Their various uses make them especially attractive to research. In addition to requiring environmentally safe materials to produce, aerogels can be implemented as energy-‐storage devices, insulators and optical enhancers [1]. One of their common uses is for catalysis. The combination of copper and zinc oxide is one such aerogel that industries utilize in large scale amounts. These catalysts, however, are produced with alumina that improves their properties but is also financially demanding to produce and/or purchase. Sol-‐gel chemistry offers a solution to this problem with a cost-‐efficient and effective method of creating aerogels [2]. These aerogels may not only contain the substances required for a particular catalyst but also provide a large amount of surface area to facilitate reactions without the use of alumina. The unique properties of aerogels provide them with numerous pore sites within a monolith [3]. In addition, aerogels can be made with templates that can enhance gel properties, such as surface area and porosity, in an inexpensive and effective way. Silica and resorcinol-‐formaldehyde are two commonly used templates [4]. This report will further investigate the possibility of synthesizing copper and zinc oxide aerogels. In addition to the importance of copper and zinc containing aerogels, optimization is also a key component in developing aerogels with maximum efficiency. pH is one such factor that can alter the properties of an aerogel; therefore, another experiment investigating the effect of different anions in manganese salts (with periodic additions of epoxide) on the pH of gel solutions will be discussed in further detail [2]. Both these experiments can ultimately enhance the synthesis of aerogels and make them more beneficial for modern application. Experimental Method: The experimental structure of this entire report is twofold: to synthesize and study copper (Cu) and zinc (Zn) gels with Zn(NO3)2•6H2O and one of three different copper anions (CuBr2, CuCl2•2H2O, and Cu(NO3)2•3H2O) and to study the pH of different manganese salts with regard to the anion effect and the epoxide addition method. For the Cu/Zn gels, five different molar ratios of copper to zinc (1:1, 1:4, 1: 9, 4:1, and 9:1) were used, resulting in a total of fifteen different gels. The total number of moles of metal salts was kept constant at 6.60 mmoles. In this way, the amounts of solvent and epoxide were consistent, and the total volumes before gelation were identical. Preparation of Copper and Zinc Gels: Solution “A”: 1.00 mL of distilled water and 10.0 mL of dimethylforamide (DMF) were placed into a clean, dry beaker. The appropriate amounts of metal salts were then dissolved into the solution (see Table 1) [5]. Solution “B”: 0.792 g (7.20 mmols) of resorcinol were dissolved into a beaker of 10.0mL DMF and 0.910 mL of formaldeyhyde [5]. Since solid resorcinol is stored in a refrigerator, it may be necessary to crush chunks of the substance with a mortar and pestle to make dissolving easier. The amounts of solid in this experiment were measured with a Mettler Toledo digital balance, and the amounts of aqueous substances were measured out using appropriately numbered syringes. Table 1: Masses (g) of Metals Salts Required for Corresponding Molar Ratios of Cu:Zn
CuBr2
CuCl2• 2H2O
Cu(NO3)2• 3H2O
Zn(NO3)2• 6H2O
1 0.737 — 1
0.563
0.797
0.982
1 0.295 — 4
0.225
0.319
1.57
1 0.147 — 9
0.113
0.159
1.77
11