Preferred metal oxides include titanium oxides such as rutile, titanium monoxide, titanium sesquioxide; silicon oxides, surfactant coated silica particles, zeolites, and surface treated derivatives thereof such as for example fluorinated silicas as described in PCT published patent application No. WO 99/03929; aluminum oxides, for example boehmite, pseudo-boehmite, bayerite, mixed oxides such as a