Dye discharge from industrial textile effluent is hazardous to the environment. Hence, the removal of dye has become important as it affects both human and aquatic life, even if it is present in minimal amounts. In comparison to the physio‐chemical technique, photocatalytic degradation of the dye using nanoparticles that are generated biologically provides a feasible method for the breakdown of environmental pollutants. Unlike other metal oxides, Copper oxide nanoparticles (CuONPs) have attracted the attention of many researchers due to their potential to act as photocatalyst and also because of their enormous surface area. Euphorbia antiquorum (triangular spurge) is a common thorny succulent found all over peninsular India, primarily in dry areas. The aqueous extract of the selected plant was employed to synthesis CuONPs, which were then analyzed using SEM‐EDX, FTIR, XPS, and XRD. The present study describes how CuONPs derived from the extract of E. antiquorum degrade major commercial dyes such as Congo Red (CR), Coomassie Brilliant Blue (CBB R‐250 dye, and Reactive Black (RB). The photocatalytic degradation efficiency of synthesized CuONPs has been demonstrated for a wide range of dyes used in the textile industry. Dye degradation of RB using synthesized CuONPs showed 93% efficiency.

Quercetin is known for potent biomedical applications and selective purification of quercetin is the need of the hour. To achieve selective adsorption of quercetin, we have prepared chitosan resin grafted with quercetin. Chitosan is a polysaccharide that is derived from chitin. The shells of shrimp, crabs, and lobster are crucial for the extraction of chitin. After cellulose, chitin was the second most abundant polysaccharide and chitosan was derived by deacetylation of chitin. Chitosan was justified to be a better bio‐adsorbent because of its low cost and outstanding chelating efficiency. Chitosan was covalently cross‐linked to improve its mechanical stability. Herein, Quercetin grafted chitosan resin (QICR) was prepared, where adsorption occurs by hydrophobic interaction between 2‐phenyl‐chromones structure in resin and quercetin in bulk solution. Prepared QICR was characterized using Fourier Transform Infrared Spectroscopy (FTIR) for confirmation of quercetin grafted in chitosan. The porosity of the prepared resin was confirmed by Brunauer‐Emmett‐Teller (BET) and Scanning Electron Microscopy (SEM) analysis. The adsorption capacity of QICR was calculated for both static and dynamic modes and it was found to be approximately equal. The equilibrium data obtained from the adsorption studies were analyzed for isotherm models. Prepared QICR fits better with Langmuir adsorption isotherm with an R2 value of 0.98. Quercetin adsorption was analyzed for kinetic studies, in which pseudo‐second order describes the adsorption. The desorption capacity of quercetin was also calculated in dynamic mode. The present study reveals that prepared QICR would be a better choice for the selective adsorption of quercetin.