The hydrogen sulfide absorption capacity of zinc oxide doped with first-row transition-metal oxides (ca. 5% metal oxide loading) has been determined using a pulse reactor. The doped oxides were prepared either by impregnation of ZnO with t h e transition-metal nitrates or by coprecipitation of t h e transition-metal and zinc nitrates with ammonium/sodium carbonate. These absorbent precursors were then calcined to give the mixed oxides.Transmission electron microscopy studies of t h e impregnated and calcined absorbents revealed that the transition-metal oxides were finely dispersed over the ZnO a s y-Fe203, Co,O, and CuO from the respective nitrate salts of these metals. The basal planes were t h e predominant exposed faces of the hexagonal ZnO in all t h e absorbents, irrespective of whether t h e y were prepared by t h e coprecipitation or impregnation route. CuO and Co,O, were not seen as separate phases in the respective calcined coprecipitated absorbents, but t h e particle morphology was noticeably changed after sulfidation and crystalline ZnS was detected by electron diffraction. Oxides prepared by t h e coprecipitation route had higher surface areas and a greater capacity for H,S removal than their impregnated counterparts. Doping with iron salts had little effect on t h e H2S uptake of ZnO, irrespective of whether an impregnation or a coprecipitation route had been used, but doping with copper or cobalt salts resulted in a marked enhancement in t h e H,S uptake in each case.

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The preparation of transparent nanostructured TiO2 (anatase) membranes is described. Detailed characterization shows these membranes to be 50 μm thick nanoporous-nanocrystalline structures with associated values for porosity and surface roughness of 50% and 5000, respectively. Modification of these membranes by coadsorption of a ruthenium complex, bis[(4,4‘-dicarboxy-2,2‘-bipyridine)(4,4‘-dimethyl-2,2‘-bipyridine)ruthenium(II)] dichloride (I), and of a viologen, 1-ethyl-1‘-[(4-carboxy-3-hydroxyphenyl)methyl]-4,4‘-bipyridinium perchlorate (II), is also described. Detailed studies show that visible-light-induced electron transfer by electronically excited I to the conduction band of the nanostructured TiO2 membrane is followed by membrane mediated electron transfer to coadsorbed II. Detailed studies also show that, as a consequence of the rectifying properties of the semiconducting membrane, charge separation is long-lived. The possible significance of these findings for the development of a practical water splitting device is considered.

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