Deciphering Z-scheme Charge Transfer Dynamics in Heterostructure NiFe-LDH/N-rGO/g-C3N4 Nanocomposite for Photocatalytic Pollutant Removal and Water Splitting Reactions

Susanginee Nayak,K M Parida

doi:10.1038/s41598-019-39009-4

Abstract

A series of heterostructure NiFe LDH/N-rGO/g-C3N4 nanocomposite were fabricated by combining calcinations-electrostatic self-assembly and hydrothermal steps. In this method, negatively charged N-rGO was electrostaticaly bonded to the self-assembled interface of n-n type g-C3N4/NiFe LDH hybrid. XRD and AFM results revealed successful formation of heterostructure nanocomposite due to the coupling effect of exfoliated NiFe LDH nanosheets with N-rGO and g-C3N4. Among the as synthesized heterostructure, CNNG3LDH performed superior photocatalytic activities towards 95 and 72% mineralization of RhB and phenol. Furthermore, CNNG3LDH could achieve the highest photocatalytic H2 evolution rate of 2508 μmolg−12h−1 and O2 evolution rate of 1280 μmolg−12h−1 under visible light irradiation. The CNNG3LDH possess lowest PL intensity, reduced arc of the Nyquist plot (43.8 Ώ) and highest photocurrent density (−0.97 mA cm−2) which revealed effective charge separation for superior photocatalytic activities. TRPL spectral results reveal the synergistic effect of layered component in CNNG3LDH for achievable higher life time of excitons of ~16.52 ns. In addition, N-rGO mediator based Z-scheme charge transfer mechanisms in CNNG3LDH were verified by the ESR and TA-PL studies. Enriched oxygen vacancy type defects in NiFe LDH and N-rGO mediated Z-scheme charge transfer mechanistic path strongly manifest the superior photocatalytic activities of the heterostructure materials.

Highlights

Www.nature.com/scientificreports heterostructure material with the synergistic effect of constituent semiconductor
The remarkable photocatalytic performances of the heterostructure towards mineralization of stable organic pollutants (Rhodamine B and Phenol) and visible light driven H2 and O2 productions was attributed to the outstanding synergistic coupling effects of (i) effective charge carrier migration and separation promoted by oxygen vacancies of exfoliated NiFe LDH nanosheets and further mediated by N-doped rGO, (ii) oxidation ability arising from NiFe LDH and (iii) superior reduction reaction activity due to g-C3N4
The dispersed aqueous solution of CNNG3LDH was quite stable in pH range of 5–9 and zeta potential value was found to be −40.4 mV at pH 7. These results reveal the wetting of negatively charged surface of heterostructure due to the introduction of electron rich N-rGO into C3N4/NiFe LDH (CNLDH) for superior photocatalytic reaction

Summary

Results and Discussions

In order to find out the origin of the high photocatalytic activity of the heterostructure CNNG3LDH nanocomposite in comparison to NiFe LDH, CN and CNLDH, LSV, EIS and M-S plots were taken into consideration to investigate the current generation, interfacial charge transfer rate at the electrode/ electrolyte interface and majority of carrier density with band edge potential of the material. In heterostructure CNNGxLDH nanocomposite, the incorporation of N-rGO into NiFe LDH nanosheets and CN attains Z-scheme mechanistic path, which restores the electrons and holes on their higher reduction and oxidation potentials of CN and LDH, respectively while extra excitons were recombined over N-rGO surface[64] These results an increase in degradation rate of 81% (CNNG1LDH) to 97% (CNNG3LDH) and decreases to 85% (CNNG5LDH) to 71% (CNNG7LDH) due to the black body radiation effect of N-rGO in the heterostructure CNNGxLDH. Based on ESR and TA-PL results, the photodegradation and corresponding mineralization of RhB and phenol over CNNG3LDH was justifiably follows Z-scheme mechanistic pathway

Conclusions

Author Contributions

Additional Information