Molecular sieves only allow molecules of a certain size (equal to, or less than the pore size) to pass through entry channels, whereas molecules larger than the pore size are excluded. Heating or dehydrating zeolites results in high void volumes, which impart to the zeolite the so called ‘‘molecular sieve’’ and adsorbent properties. These Si-O bonds are arranged in a three-dimensional structure of silicate tetrahedra, leading to the presence of open cavities in the form of channels and cages, which are usually occupied by H 2O molecules and extra-framework cations that are commonly exchangeable. These cavities result from the structural composition of zeolites, which is characterized by a framework of linked tetrahedra, each consisting of four O atoms surrounding a cation – usually Si. The water molecules that are lost on heating have been adsorbed in the pores and cavities (of dimensions ranging from 0.3 nm to 1.0 nm) present in the zeolites’ crystalline structure. He observed that upon heating this mineral steam was released, as water evaporated and the zeolite seemed to be boiling because of the rapid water loss. It was given to this type of substances in 1756, by a Swedish mineralogist named Axel Fredrik Cronstedt, who discovered them and their trait of intumescence. The word zeolite is formed from two Greek words “zeo” = boil & “lithos” = stone to mean boiling stones. Upon reaching the sea, the hot lava, water and the salt from the sea undergo reactions which, over the course of thousands of years, have led to the production of crystalline solids known as zeolites. In cases where such locations are on an island or near an ocean, the ejected lava and ash often flow into the sea. Volcanoes normally occur where tectonic plates are diverging or converging. When volcanoes erupt, magma (molten rock within the earth) breaks through the earth’s crust and flows out in form of lava accompanied by gases, dust and thick ash. Introduction Most natural zeolites are formed as a result of volcanic activity. These findings show that AC is a cost-effective material for achieving useful rates of oxygen reduction in air cathode MFCs.1. The coulombic efficiency ranged from 15% to 55%. Tests with the AC cathode produced a maximum power density of 1220 mW/m2 (normalized to cathode projected surface area 36 W/m3 based on liquid volume) compared to 1060 mW/m2 obtained by Pt catalyzed carbon cloth cathode. AC was cold-pressed with a polytetrafluoroethylene (PTFE) binder to form the cathode around a Ni mesh current collector. To further reduce the cost of MFC, an inexpensive activated carbon (AC) air cathode was tested as an alternative to a platinum-catalyzed electrode for oxygen reduction in a MFC. These findings demonstrate that cathodes can be constructed around metal mesh materials such as stainless steel, and that an inexpensive coating of PDMS can prevent water leakage and lead to improved coulombic efficiencies. The coulombic efficiency of the mesh cathodes reached more than 80%, and was much higher than the maximum of 57% obtained with carbon cloth. Two PDMS/carbon layers achieved the highest maximum power density of 1610 ± 56 mW/m2 (normalized to cathode projected surface area 47.0 ± 1.6 W/m3 based on liquid volume). Multiple PDMS/carbon layers were applied in order to optimize the performance of the cathode. Poly(dimethylsiloxane) (PDMS) was used as diffusion layer material, preventing water leakage, limiting oxygen transfer through the cathode and improving coulombic efficiency. Rather than adding a current collector to a cathode material such as carbon cloth, we constructed the cathode around the metal mesh itself, thereby avoiding the need for the carbon cloth or other supporting material. A new and simplified approach for making cathodes for microbial fuel cells (MFCs) was developed by using metal mesh current collectors and inexpensive polymer/carbon diffusion layers (DLs). Bruce Ernest Logan, Thesis Advisor/Co-AdvisorĪbstract: A microbial fuel cell (MFC) is a device for direct bioelectricity generation.Author: Zhang, Fang Graduate Program: Environmental Engineering Degree: Master of Science Document Type: Master Thesis Date of Defense: ApCommittee Members: