Platinum Metals Review - Volume 42, Issue 3, 1998

No industrial process is 100 per cent efficient and the generation of waste, both organic and inorganic, is an unavoidable reality. The recycling of waste is becoming increasingly important as concerns about the environment and the availability of resources come more to the fore, but there remain many waste streams which are not yet suitable for recovery of their reusable content, on the grounds of cost or practicality. Historically, the disposal of such wastes has been either via incineration or release into the environment after neutralisation or immobilisation, in a landfill site or into a drain or sewer, or the like. These options are becoming more restricted as regulations tighten and public perception of any but the most benign discharges worsens. This paper sets out reasons for using electrochemical oxidation with a ruthenium electro-catalyst to provide an effective and environmentally friendly alternative to other technologies. Electrochemical oxidation can effect mineralisation of toxic organic species with minimal generation of secondary waste and efficient recovery of the ruthenium mediator and is particularly suited for the treatment of highly chlorinated and aromatic compounds.

The creation of systems that are capable of performing molecular-scale operations is currently under extensive investigation, particularly in the emerging field of nanotechnology. Towards this end, we have been actively involved in the construction and study of the properties of metallo-based assemblies based on electron-deficient cyclophanes and donor-acceptor [2]catenanes. Metallic moieties, such as [Ru(bipy)2 (L)]⁶⁺ and [Os(bipy)2(L)]⁶⁺, where bipy = 2,2′-bipyridyl and L= tetracationic cyclophane ligand, form an integral part of the molecular structures of these assemblies and in these specific cases create photoactive complexes. The photoinduced electron transfer reactions which occur within these molecules have been extensively studied, especially in relation to the corresponding processes found in natural photosynthetic reaction centres. Here, we present a short review on relevant aspects of this work as well as the potential use of metal-based cyclophanes as binders for aromatics.

The first two parts of this paper on titanium-based electrodes concentrated on the development of coatings comprising noble metals and their oxides suitable for use in chloride-bearing electrolytes. This concluding part deals with similar types of electrodes which act as counter electrodes in commercial processes where the product is made on the cathode. Many electrolytes in this category involve sulfuric acid, which means that oxygen evolves at the anodes. Applications for which these electrodes are used range from those operating at very high current density, such as electrogalvanising, to others at much lower current density, such as impressed current cathodic protection of rebar in concrete.