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Contradicting results about the origin of room temperature ferromagnetism (RTFM) from measurements on different forms of transition metal (TM)-doped ZnO nanostructured materials lead to strong debates on whether RTFM could be an intrinsic property to TM-doped ZnO or not. Through careful synthesis and extensive characterizations, we have excluded the extrinsic contaminations as the cause of RTFM. Our experimental study confirms that defects such as oxygen vacancies lie on surface of nanorods and are likely a source of RTFM. X-ray absorption and emission spectroscopy (XAS and XES) suggest that the doped Co ions, primarily in the divalent state, replace the Zn ions inside the tetrahedral without introducing Co clustering or Zn-related defects. Band gap narrowing upon Co doping is observed in both optical reflectance and O K-edge XAS/XES and is in agreement with the presence of oxygen vacancies and strong sp–d hybridization. Furthermore, such a trend can be nicely reproduced in GGA+U band structure calculations. Calculations also suggest that these oxygen vacancies are likely to congregate at low-energy (101) and (100) surfaces, instead of inside the bulk. Our findings highlight the importance of using the nanocrystalline surfaces to enhance the impurity concentrations and stabilize the ferromagnetism without post-sample annealing in an oxygen-deficient environment.

The catalytic wet oxidation of aqueous phenol over Mn–Ce–O mixed oxide catalysts was shown to be accompanied by undesirable formation of heavy polymers on the catalyst surface, leading to severe loss in catalytic activity and in mineralization selectivity. New potassium-doped Mn–Ce–O mixed oxide catalysts were developed and benchmarked for the destruction of concentrated phenolic (103ppm) synthetic wastewater at very mildconditions (110°C and 0.5 MPa O2pressure). Remarkable improvements in mineralization selectivity were attained. Complete removal of totalorganic pollution was achieved within 10–20 min and mineralization selectivity exceeding 95% was attained over fresh K–Mn–Ce–O catalyst. The leach-proof ability of the catalyst was confirmed from analysis of the treated waters. Detailed characterization of fresh and spent K-doped catalysts revealed drastic reduction in carbonaceous deposits on the catalyst surface, even after successive runs of non-regenerated catalyst samples. The catalyst surface was found to be active after the catalyst was reused thrice, though this time the TPO-detected surface carbonaceous species were far less than those in the nonpromoted Mn–Ce–O catalyst.