Heterostructured Hybrid rGO@α‐MnO<sub>2</sub>/rGO@δ‐MnO<sub>2</sub> Nanoflower: An Efficient Catalyst for Aerobic Solvent‐Free <i>N</i>‐Alkylation Reactions and Energy Storage Material
Haribandhu Chaudhuri, Niranjan Karak
Abstract
Abstract A new reduced graphene oxide (rGO) based bi‐phasic crystal of MnO 2 , namely α‐MnO 2 nanorods and δ‐MnO 2 nanoflakes containing heterostructured hybrid nanoflower rGO@α‐MnO 2 /rGO@δ‐MnO 2 has been fabricated through a facile hydrothermal method followed by annealing treatment. The successful synthesis of the hybrid material was studied by XRD, Raman, BET, FESEM with EDX, FTIR and TEM analyses. An efficient N ‐alkylation reaction of substituted aromatic amines with aromatic alcohols was carried out under solvent‐free aerobic conditions in the presence of catalytic amount of rGO@α‐MnO 2 /rGO@δ‐MnO 2 . The catalyst shows excellent activity in terms of high yields (up to 98 %), short reaction time (10 h) along with a simple work‐up process. The spent material can be regenerated several times without causing any serious decrease in catalytic activity. Moreover, cyclic voltammetry (CV), galvanostatic charge‐discharge (GCD), and cyclic stability techniques were executed to evaluate the performances of rGO@α‐MnO 2 , rGO@δ‐MnO 2 , and rGO@α‐MnO 2 /rGO@δ‐MnO 2 as energy storage materials. Among all those materials, rGO@α‐MnO 2 /rGO@δ‐MnO 2 exhibited a proficient specific capacitance, C S (267 F/g at 1 A/g) along with excellent cycling ability (∼83 % retention up to 10000 cycles). The superb electrochemical performance of rGO@α‐MnO 2 /rGO@δ‐MnO 2 might be ascribed to the combination of bi‐phasic α‐MnO 2 and δ‐MnO 2 with rGO sheets, resulting in a flower‐like structure.