A. P.  Bhirud, Sathaye, S. D., Waichal, R. P., Nikam, L. K., and Kale, B. B., ?Eco-friendly, highly stable and efficient nanostructured p-type N-doped ZnO photocatalyst for environmentally benign solar hydrogen production?, Green Chemistry, vol. 14, no. 10, pp. 2790-2798, 2012.