**Acknowledgements**

This work was supported by The World Academy of Sciences for the Advancement of Science in developing countries (TWAS) under Research Grant No. 12-169 RG/CHE/AF/AC-G UNESCO FR: 3240271320 for which grateful acknowledgment is made. AAA is also grateful to the Royal Society of Chemistry for personal research grant. The assistance of Professor J-G. Mao of Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, in the XRD and SEM analyses is gratefully acknowledged.
