Nowadays, for environmental remediation, photocatalytic process involving graphene-based semiconductors is considered a very promising oxidation process for water treatment. In the present study, nanocomposite (Cu/Ni/rGO) has been synthesized by Dypsis lutescens leaf extract. Characterization of the sample was carried out by UV-visible spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Different parameters like contact time, nanocatalyst amount, dye concentration, effect of temperature. and pH factor were optimized to examine the maximum removal efficiency for dyes rhodamine B and alizarine R with and without visible light source. In both cases, i.e., with or without light, maximum removal was observed at 20 mg of nanocatalyst for 5 ppm concentration of both dyes at 45 °C temperature and pH 10 for rhodamine B and pH 4 for alizarine R, respectively with a 20 min contact time. Maximum removal of dyes 93% rhodamine B and 91% alizarine R were observed under a tungsten lamp as compared to without a tungsten lamp, i.e., 78% of RhB and 75% of AR from mixture solution of these dyes. To assess the rate of reaction, spontaneity, and nature of reaction thermodynamics, kinetics and adsorption isotherms were studied. Thermodynamic values indicated that both dyes depicted endothermic and spontaneous degradation processes. Isotherm data fitted best to a Freundlich isotherm, while results of kinetic studies of both dyes followed the pseudo 2nd order kinetic equation. In the end, scavenging radical studies concluded that hydroxyl radicals were the main active specie involved in the photocatalytic degradation process, and regeneration experiments resulted that Cu/Ni/rGO nanocomposites were re-utilized for about four times.

In this study, leaves of Polyalthia longifolia were utilised as carbon source for the synthesis of carbon dots by ultrasonication. UV-visible spectrum of prepared carbon dots exhibited two absorption peaks at 225 nm and 260 nm, respectively. Fourier transform spectrum of carbon dots exhibited the different functional groups at absorption peak values of 1650 cm⁻¹, 2989 cm⁻¹, 1471 cm⁻¹, 1762 cm⁻¹ and 1126 cm⁻¹, respectively. X-ray diffraction analysis of carbon dots showed the amorphous nature of carbon dots with peak values at 31.38º and 40.93º, respectively. Raman spectrum of synthesised carbon dots illustrated two peaks at 1362 cm⁻¹ and 1510 cm⁻¹. These prepared carbon dots were then employed for photocatalytic removal of congo red dye and methylene blue dye under visible light source. The maximum removal of methylene blue dye was achieved at pH 8, at a dye concentration of 5 mg/L in a time interval of 60 min. In the case of congo red dye, maximum degradation was observed in acidic medium at a pH of 6 with 5 mg/L dye concentration in a time interval of 90 min. Further kinetic models of zero order, first order, second order, parabolic diffusion and modified Freundlich were applied to dye photocatalytic studies. It can be observed that methylene blue dye degradation by carbon dots followed parabolic diffusion model while congo red dye depicted closed correlation with both parabolic diffusion and modified Freundlich kinetic models.

In the recent work, synthesis of cobalt nanoparticles (CoNPs) was carried out by using whole plant extract of Catharanthus roseus. The average particle size of CoNPs calculated by XRD studies was found to be 27.08 nm. In assessment of antioxidant activity, DPPH radical scavenging percentage values of 37.05% and 79.19% were observed at 125 µg/ml and 1000 µg/ml nanoparticle concentration respectively. CoNPs exhibit greater growth inhibition percentage against gram negative bacteria in comparison to gram positive bacteria. In hemolytic assay, prepared nanoparticles depicted hemolysis rate of 1.53%. The surface of green synthesized CoNPs was modified with cetyltrimethylammonium bromide (CTAB) as a cationic surface modifier. Furthermore, the unmodified and modified CoNPs were studied for degradation of toxic alizarin red S dye in aqueous media. Best dye degradation results were observed at pH 6 with nanoparticle dosage of 10 mg and at lower concentration value of dye.