Pillared Layer Double Hydroxides

Pillared LDHs which possess empty interlayer/inter-pillar space are desirable but unlike pillared clays are difficult to prepare. The difficulty is largely due to the affinity of the layers for the carbonate anion; if CO2 is present during synthesis, the carbonate is preferentially incorporated and once in the interlayer it is held tenaciously and not easily replaced. Most of the pillaring strategies employ a CO2-free environment and make use of the fact that Cl" or NO3" anions are easier to displace. Thus the Cl" or NO3" LDH is prepared, usually under nitrogen, and these anions are then replaced with larger polyoxometalate anions such as, for example, V10Of8~, TagO^OH7", NbgO^OH7". Another approach has relied on the use of LDH initially synthesized with large intercalated organic anions, for example the terephthalate dianion (Figure 8) as the interlayer species. The organic anion is then displaced by the polyoxometalate species. As in clays, the pillaring of LDHs results in an increase in surface area and pore volume. The increases are however lower than in pillared clays. This is due to the high layer charge in LDHs which leads to a high pillar density which in some cases yields materials in which the pillars are 'stuffed' into the LDH and do not exist as isolated discrete pillars. An example is polyvanadate-intercalated LDH which has a surface area of ca. 35m2g"1 compared to 25 m2 g"1 for the unpil-lared material. True pillaring does occur as in the case of Zn2Al[a-SiV3W9O40] which exhibits a surface area of 155 m2g"1.

Solar Panel Basics

Solar Panel Basics

Global warming is a huge problem which will significantly affect every country in the world. Many people all over the world are trying to do whatever they can to help combat the effects of global warming. One of the ways that people can fight global warming is to reduce their dependence on non-renewable energy sources like oil and petroleum based products.

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