Adsorption of Reactive Red 195 from aqueous medium using Lotus (Nelumbo nucifera) leaf powder chemically modified with dimethylamine: characterization, isotherms, kinetics, thermodynamics, and mechanism assessment

Lotus leaf powder (LLP) was chemically modified with dimethylamine (DMA) to achieve a tertiary amine type powder, named DMA-LLP, and used as an adsorbent for the removal of Reactive Red 195 (RR 195) from the aqueous medium. DMA-LLP was characterized using field emission-scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), Brunauer-Emmett-Teller (BET), point of zero charge (pH(PZC)), and fourier transform infrared (FTIR) spectroscopy. The kinetic data exhibited a good correlation coefficient (R-2 > 0.9916) for the pseudo-second-order model. To evaluate the equilibrium data at different temperatures, the non-linear Langmuir and Freundlich isothermal models were used. The Langmuir model best described the equilibrium data (R-2 > 0.9931). The maximum adsorption uptake from the Langmuir model, q(max), was 131.5 mg/g (pH = 2.0, C-o = 300 mg/L, dosage = 0.03 g/30 mL, and T = 298 K). The pH(PZC) of DMA-LLP was found to be 5.5. The obtained thermodynamic parameters demonstrated the spontaneous and endothermic nature of the adsorption. The regeneration findings indicate that DMA-LLP could be used up to five times, with maximum removal of 72% achieved after the fifth cycle. Thus, we conclude that the DMA-LLP was an efficient adsorbent for removing RR 195 from the aqueous environment. NOVELTY STATEMENT In the modern era, dyes are inevitable and their surging usage leads to colossal contamination of aqueous streams, thereby threatening both the land and aquatic species. One among such dye is anionic Reactive Red 195 (RR 195), and traceable even at minute concentrations of aqueous streams, posing a severe threat to living species. Moreover, RR 195 is highly recalcitrant offering resistance to biodegradation due to the presence of an azo (-N=N-) group within its structure. Thus, there is a definite need to address the issue of eliminating RR 195 from industrial wastewater effluents. In lieu of this, the primitive objective of this study is to test the effectiveness of the natural adsorbent lotus leaf (Nelumbo nucifera) for the selective sorption of RR 195 from the aqueous stream. Although ample literature is available on the direct utilization of lotus leaf as adsorbent, yet no study was performed on the chemical modification (dimethylamine) of the aforementioned adsorbent. Hence, an attempt has been made in this direction to add a new sorbent into the adsorbents database.

Automated summary

The study focuses on the chemical modification of lotus leaf powder to create a tertiary amine type powder named DMA-LLP, which proved to be an effective adsorbent for removing Reactive Red 195 (RR 195) from aqueous environments. The Langmuir model best described the adsorption equilibrium data, and thermodynamic parameters showed the spontaneous and endothermic nature of the adsorption process. Regeneration findings indicated that DMA-LLP could be reused up to five times with a maximum removal rate of 72% achieved after the fifth cycle.