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Fluorescent graphene quantum dots (GQDs) are nanomaterials which possess unique properties that show great potential in different applications. In this work, GQDs were synthesized using graphene oxide (GO) as precursor via thermal treatment at high temperature. The obtained GQDs were highly fluorescent and were suitable for the determination of heavy metal ions. X-ray diffraction, FTIR spectroscopy, and UV visible spectroscopy confirm the formation of GQDs. TEM images show that formed GQDs have size ranging from 2 to 10 nm. Emission profile of aqueous GQDs was taken by exciting GQDs at different wavelength. The intensity of GQDs remains the same for 4-5 months. Furthermore, as prepared, GQDs were used for selective recognition of Fe 3+ , Pb +2 , and Cr 3+ from the bunch of different metal ions in aqueous media. Lower limit of detection obtained for Fe 3+ , Cr 3+ and Pb 2+ using GQDs were 50, 100 and 100 nM, respectively, which indicates that the GQDs can be utilized as a promising material for sensing of the heavy metal ions. Graphical abstract., (© 2020. Springer-Verlag GmbH Germany, part of Springer Nature.)

Graphene quantum dots (GQDs) have been prepared from graphene oxide (GO) and characterized by standard analytical techniques. The size of the prepared GQDs ranges from 2-10 nm. Aqueous dispersion of GQDs exhibited excitation-dependent emission behavior. Emission intensity of the aqueous dispersion found stable for the examined duration of about four months. GQDs exhibited selective recognition of Fe3+ and Cr3+ out of various common ions such as alkali, alkaline-earth and transition metal ions in aqueous medium through fluorescence quenching. The lower limit of detection of Fe3+ is 1 μM and that of Cr3+ is 4 μM. [ABSTRACT FROM AUTHOR]

The advancement in membrane-based separation technologies offers advantages over traditional ways. Recovery of acid from acidic waste stream is an important issue to be solved by greener route. Diffusion dialysis using anion exchange membranes (AEMs) is an energy-intensive and environment friendly process to be taken forward. Herein, we report the eco-friendly route for chloromethylation of polysulfone using chloromethyl ethyl ether (CMEE). Effect of chloromethyl ethyl ether concentration, reaction temperature, and reaction time are investigated to get maximum tethered chloromethyl group and high yield of product. Series of chloromethylated polysulfone membranes are prepared with different concentrations of graphene quantum dots (GQDs) followed by quaternization using trimethylamine. The prepared membranes are characterized by their water content, transport properties, and stabilities. Composite membranes show enhanced water uptake, ion exchange capacity, and mechanical stability compared to that of pristine membrane. Interestingly, to address the environmental impact of acids present in industrial waste, AEMs are employed for acid recovery from model waste at higher concentrations of acid and salt using diffusion dialysis. For prepared membranes, 35.5–47.5% acid recovery has been achieved in presence of metal ions. SCE-1.0 (1.0 wt % GQD/ QPSU) membrane shows the highest acid recovery (47.5%) among the membranes. Composite membranes suggest their potential utility in acidic effluent treatment via diffusion dialysis. Image 1 • Polysulfone/GQD composite AEMs have been synthesized successfully. • Composite membranes show good ionic conductivity with stability. • AEMs showed its application in acid recovery by diffusion dialysis. [ABSTRACT FROM AUTHOR]