This review article highlights recent progress in use of green precursors for synthesis of carbon-dots and their applications in fluorescence-based sensing and bioimaging.

Herein, we report a multitasking Cu-MOF/rGO hybrid, fabricated by simple ultra-sonication of slow diffusion driven Cu-MOF crystals with chemically synthesized reduced graphene oxide (rGO). The molecular structure of the Cu-MOF was authenticated by single crystal X-ray studies. The prepared materials have been probed by various physicochemical characterization techniques. Due to the positive synergistic effects between Cu-MOF crystals and rGO nanosheets, the newly synthesized Cu-MOF/rGO hybrid delivers high charge storage efficiency (685.33 F g⁻¹ at 1.6 A g⁻¹), high energy (137.066 W h kg⁻¹) and power density (4800.04 W kg⁻¹) and excellent rate ability (retains 71.01% of its initial capacitance at 8 A g⁻¹). Furthermore, the long cycle life (91.91% after 1000 cycles) of this hybrid indicates its high stability on the electrode surface. Additionally, the electrode modified with the Cu-MOF/rGO hybrid performs exceptionally towards the electrochemical detection of nitrite in a wide dynamic linear range of 3–40 000 μM (R² = 0.99911), with a notable detection limit of 33 nm and a high sensitivity of 43.736 μA μM⁻¹ cm⁻². The versatility of the Cu-MOF/rGO modified electrode can be observed by distinguished selectivity in the presence of some common interfering species and also ability to detect nitrite in real samples.

A new cobalt based inclined polycatenated metal–organic framework, {[Co₄(FcDCA)₄(bpy)₄(H₂O)₆]·11H₂O}_n [FcDCA = 1,1′-ferrocene dicarboxylic acid and bpy = 4,4′-bipyridyl] (1), has been designed and synthesized in a facile manner. 1 can be simplified as a 2D + 2D → 3D inclined polycatenation class with Doc1/1, as authenticated by single crystal X-ray studies. Further, 1 was employed as a modifier for a glassy carbon electrode (1-GCE) without using any binders to explore its supercapacitor performance. Detailed electrochemical investigations carried out using 1-GCE reveal a specific capacitance of 446.8 F g⁻¹ at a current density of 1.2 A g⁻¹, with an excellent cycle life of ∼88.37% (after 800 cycles). Moreover, a high rate performance was also observed for 1-GCE (it retains 81% of its initial capacitance up to a high current density of 10 A g⁻¹), which endorsed its good stability on the electrode surface. The results were found to be superior than those for {[Co(bpy)_1.5(NO₃)₂]}_n (2), highlighting the role of the presence of FcDCA in 1. Additionally, the notable adsorption and desorption properties of 1 towards selected Chicago Sky Blue (CSB) and Congo Red (CR) dyes confirms the candidature of 1 as a potential dye adsorbing agent.

Two-dimensional (2D) mixed metal–organic frameworks (M-MOFs) have emerged as promising energy storage materials in the MOF family. Herein, we report the facile, room temperature synthesis of a Na/Zn-based bimetallic MOF, [NaZn₂(μ₂-BTC)₂(μ₂-O)₂(Azopy)(H₂O)₂]_n (1, where BTC = trimesic acid and Azopy = 4,4′-azopyridine), grown through a slow diffusion technique. The crystal structure of 1 reveals the ratio of Zn(II) to Na(I) metal ions to be 2 : 1, and the overall framework exhibits a 2D layered structure. In light of the poor conductivity of MOFs, and also to take full advantage of this 2D MOF for supercapacitor use, we assembled a unique robust heterostructure of 1 with another 2D material, i.e. reduced graphene oxide (2), using a simple-yet-effective ultra-sonication assisted approach. Electrochemical analyses reveal the notable specific capacitance (435.2 F g⁻¹ at 1.6 A g⁻¹) of the formed heterostructure (3), with exceptional cycling efficiency (no observed loss up to 4000 cycles in the absence of any binders). The obtained encouraging results were attributed to synergistically enhanced contributions from each participating 2D material and the formation of a robust heterostructure due to the proper stacking of the two different layered 2D materials. The results exceed those of related state-of-the-art structures and suggest the promising nomination of 2D MOFs and their heterostructures for application in the emerging world of next-generation supercapacitors.