Achieving Enhanced Visible-Light-Driven Photocatalysis Using Type- II NaNbO 3 /CdS Core/Shell Heterostructures Sandeep Kumar, †,‡ Sunita Khanchandani, ‡ Meganathan Thirumal, † and Ashok K. Ganguli* ,‡,§ † Department of Chemistry, University of Delhi, New Delhi, Delhi 110007, India ‡ Department of Chemistry, Indian Institute of Technology, Hauz Khas, New Delhi, Delhi 110016, India § Institute of Nano Science & Technology, Habitat Centre, Phase-X, Sector-64, Mohali, Punjab 160062, India * S Supporting Information ABSTRACT: Expanding the light-harvesting range and suppressing the quick recombination of photogenerated charge carriers are of paramount significance in the field of photocatalysis. One possible approach to achieve wide absorption range is to synthesize type-II core/shell heterostructures. In addition, this system also shows great promise for fast separation of charge carriers and low charge recombination rate. Herein, following the surface functionalization method using 3-mercaptopropionic acid (MPA) as a surface functionalizing agent, we report on designing NaNbO 3 /CdS type-II core/shell heterostructures with an absorption range extending to visible range and explore the opportunity toward degradation of methylene blue (MB) dye as a model pollutant under visible light irradiation. Characterizations including X-ray diffraction (XRD), field- emission scanning electron microscopy (FESEM), UV-vis diffuse reflectance spectrum (DRS), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and Raman spectroscopy support the growth of CdS shell onto NaNbO 3 nanorods. The resulting core/shell heterostructures unveiled high surface areas, enhanced light harvesting, and appreciably increased photocatalytic activity toward MB degradation compared to individual counterparts and the photocatalytic standard, Degussa P25, under visible light irradiation. The remarkably enhanced photocatalytic activity of core/shell heterostructures could be interpreted in terms of efficient charge separation owing to core/shell morphology and resulting type-II band alignment between NaNbO 3 and CdS, which creates a step-like radial potential favoring the localization of one of the carriers in the core and the other in the shell. A plausible mechanism for the degradation of MB dye over NaNbO 3 /CdS core/ shell heterostructures is also elucidated using active species scavenger studies. Our findings imply that hydroxyl radicals (OH • ) play a crucial role in dictating the degradation of MB under visible light. This work highlights the importance of core/shell heterostructures in leading toward new paradigms for developing highly efficient and reusable photocatalysts for the destructive oxidation of recalcitrant organic pollutants. KEYWORDS: NaNbO 3 , CdS, photocatalysis, type-II band alignment, methylene blue, core/shell, heterostructures ■ INTRODUCTION Semiconductor photocatalysis has gained international emi- nence as a vanguard solution for the destructive oxidation of recalcitrant organic pollutants to mitigate the deterioration of environment. 1,2 Following the landmark work by Fujishima and Honda, 3 the semiconductor photocatalyst, TiO 2 , has received intense scrutiny owing to its unsurpassed stability and efficiency. This milestone research opens up a new chapter in the field of photocatalysis and attempts to outperform TiO 2 , having generated a large array of novel photocatalytic materials such as ZnO, SnO 2 , BiVO 4 , SrTiO 3 , NaNbO 3 , ZrO 2 , WO 3 , and so forth. 4-11 Among the explored semiconductor photocatalyst systems, perovskite based metal oxides 12-14 such as SrTiO 3 and NaNbO 3 have garnered noticeable attention in alleviating noxious pollutants and are touted as an environmentally benign and viable alternative to TiO 2 . In this regard, sodium niobate (NaNbO 3 ), an intriguing material with a typical pervoskite structure and rich pool of useful properties including good chemical stability, high crystallinity, low cost, abundance, and low environmental impact has spurred a great deal of scientific and technological interest. 15-17 Nevertheless, the prospect of efficient photocatalysis has not been reached primarily due to the wide band gap associated with NaNbO 3 that precludes significant activity under visible light. 18,19 Another daunting issue still remains with NaNbO 3 in suppressing the rapid recombination of photoexcited charge carriers. 20 Thus, strenuous efforts have been devoted to push the absorption onset of NaNbO 3 toward longer wavelengths and to accelerate Received: May 19, 2014 Accepted: July 15, 2014 Published: July 15, 2014 Research Article www.acsami.org © 2014 American Chemical Society 13221 dx.doi.org/10.1021/am503055n | ACS Appl. Mater. Interfaces 2014, 6, 13221-13233