Green synthesis of silver nanoparticles using Ocimum sanctum for efficient Congo red dye removal: a response surface...

Synthetic dyes, such as Congo red (CR), pose serious threats to human health and aquatic ecosystems because of their carcinogenicity and resistance to degradation, necessitating the development of efficient and eco-friendly remediation strategies. In this study, silver nanoparticles (AgNPs) were synthesized via a green method using Ocimum sanctum (holy basil) leaf extract and applied for CR dye removal from aqueous solutions. The adsorption process was optimized using response surface methodology (RSM) based on Box-Behnken design (BBD), evaluating the influence of key parameters including pH, AgNP dosage, initial dye concentration, contact time, and temperature. Under optimized conditions (pH 5, 0.4 g/L AgNPs, 50 mg/L dye, 50 °C, 60 min), a maximum removal efficiency of 93% was achieved. Characterization of AgNPs confirmed the presence of functional biomolecules, high crystallinity, and predominantly spherical morphology with an average particle size of 12.53 nm. Adsorption followed the Langmuir isotherm model, indicating monolayer coverage and pseudo-second-order kinetics, suggesting chemisorption, with a maximum adsorption capacity of 51.19 mg/g. Thermodynamic studies revealed that the process was spontaneous and exothermic. Moreover, desorption and reusability studies demonstrated an 85% removal efficiency after 10 cycles, highlighting the stability of the synthesized AgNPs. These findings underscore the potential of green-synthesized AgNPs as effective and sustainable adsorbents for the treatment of dye-contaminated wastewater.