Oxygen adsorption on Au clusters and a rough Au(111) surface: The role of surface flatness, electron confinement, excess electrons, and band gap

It has been shown recently that while bulk gold is chemically inert, small Au clusters are catalytically active. The reasons for this activity and its dramatic dependence on cluster size are not understood. We use density functional theory to study O2 binding to Au clusters and to a Au(111) surface modified by adsorption of Au clusters on it. We find that O2 does not bind to a flat face of a planar Au cluster, even though it binds well to its edge. Moreover, O2 binds to Au clusters deposited on a Au(111) surface, even though it does not bind to Au(111). This indicates that a band gap is not an essential factor in binding O2, but surface roughness is. Adding electrons to the surface of a Au(111) slab, on which one has deposited a Au cluster, increases the binding energy of O2. However, adding electrons to a flat Ausurface has no effect on O2binding energy. These observations have a simple explanation: in clusters and in the rough surface, the highest occupied molecular orbital (HOMO) is localized and its charge density sticks out in the vacuum. This facilitates charge transfer into the π* orbital of O2, which induces the molecule to bind to gold. A flat face of a cluster or a flat bulk surface tends to delocalize the HOMO, diminishing the ability of the surface to bind O2. The same statements are true for the LUMO orbital, which is occupied by the additional electron given to the system to charge the system negatively

Water supply and sanitation services in small towns in rural–urban transition zones: The case of Bushenyi-Ishaka Municipality, Uganda

Small towns lag behind cities in drinking water and sanitation access globally. Closing this gap requires developing service models for areas with both urban and rural characteristics. This study assessed Bushenyi-Ishaka, a municipality in Uganda situated at the rural–urban transition, with a focus on service ladder indictors. Data sources included household interviews (n = 500) and water quality samples from sources and storage containers. Households in more urban (as compared to rural) cells were more likely to use improved water sources (including piped water on-premises), make regular payments for water, rely on shared sanitation facilities, and make use of manual sludge emptying services. Most households (72%) used an unlined pit latrine not intended for emptying and reuse. These findings suggest that small town servicing models should prioritize non-sewered sanitation management, including incentives for safe excreta containment and disposal opportunities. This study also highlights a need for integrated services models to expand rural–urban water and sanitation coverage

Water supply and sanitation services in small towns in rural–urban transition zones: The case of Bushenyi-Ishaka Municipality, Uganda

Small towns lag behind cities in drinking water and sanitation access globally. Closing this gap requires developing service models for areas with both urban and rural characteristics. This study assessed Bushenyi-Ishaka, a municipality in Uganda situated at the rural–urban transition, with a focus on service ladder indictors. Data sources included household interviews (n = 500) and water quality samples from sources and storage containers. Households in more urban (as compared to rural) cells were more likely to use improved water sources (including piped water on-premises), make regular payments for water, rely on shared sanitation facilities, and make use of manual sludge emptying services. Most households (72%) used an unlined pit latrine not intended for emptying and reuse. These findings suggest that small town servicing models should prioritize non-sewered sanitation management, including incentives for safe excreta containment and disposal opportunities. This study also highlights a need for integrated services models to expand rural–urban water and sanitation coverage