Green synthesis of Ce^sup 3+^ rich CeO^sub 2^ nanoparticles and its antimicrobial studies

Cerium oxide nanoparticles (CeO2-np) with Ce3+ rich surfaces were synthesized by ecofriendly route using tannic acid. XRD and SAED patterns confirm the cubic structure of CeO2-np. A semi-quantitative XPS analysis revealed the presence of 34 % Ce3+ ions. Tannic acid not only mediates the CeO2-np synthesis, but also helps in reduction of surface states from Ce4+ to Ce3+ Oxygen vacancies were evidenced from XPS and photoluminescence studies. The synthesized nanoparticles showed good antimicrobial activity towards both gram positive (Bacillus subtitis) and gram negative (Escherichia coli) bacteria. The toxicity of CeO2-np towards tested bacteria is due to production of Reactive oxygen species (ROS). The presence of Ce3+ ions and rich surface oxygen vacancies may lead to excellent production of ROS and simultaneously causing cell wall damage. Present findings show that tannic acid assisted CeO2-np with obtained properties acts as good antibacterial agent.