Montmorillonite induced assembly of multi-element doped g-C3N4 nanosheets with enhanced activity for Rhodamine B photodegradation

Abstract

Montmorillonite (Mt) nanosheets have been widely used as supporter to disperse and enhance the functional materials (e.g., g-C3N4 (CN)). Herein, a new insight into the inducer role of Mt. in structure-tuning of CN at nano- and molecular scales were researched. Results showed that the pores and interlayers of Mt. induced the spatial-confined polymerization of precursors urea (U)/melamine (M), obtaining the highly dispersed CN nanosheets; simultaneously, the Al/Mg–OH groups and interlayer Na cations of Mt. induced the self O, Na, Mg, Al elements from Mt. to dope into the CN framework. It is found that the advantage of urea in nanostructure construction of CN nanosheets for the CN-U/Mt. composite with larger specific surface area, and the superiority of melamine in multi-element doping for CN-M/Mt. with a narrowed band gap. Therefore, the optimal CN-UM/Mt. composite showed the highest activity for Rhodamine B (RhB) photodegradation with a reaction time of 60 min and an apparent rate constant of 0.053 min−1, which is better than most other g-C3N4/clay minerals composites. The enhanced activity could be owing to the high adsorption of Mt., large specific surface area of CN nanosheets, and the adjusted band structure originated from the comprehensive effects of CN nanosheets, nonmetal O- and metal cations doping induced by Mt., enabling a narrowed band gap with strengthened visible-light adsorption and an enhanced photogenerated carrier separation efficiency. Furthermore, in terms of the semiconductor mechanism, it showed more reactive oxygen species of 1O2 (main) and •O2− (secondary) for effective RhB degradation, but without the typical holes. This work indicates the great potential of Mt. as an inducer in structure tuning of g-C3N4 for efficient photocatalytic purification.