The response surface methodology has been extended to study the adsorption of malachite green dye (MG) on Indian Neem leaf powder (NLP), Azadirachta indica. The study was experimented by varying the solution concentration from 10 to 100 mg/l. The removal percentage of MG was determined by spectrophotometer at wavelength of 618 nm. Design Expert 11.0 was used as a tool to study the optimal conditions of MG adsorption (applying 2-factorial interaction model of central composite design) and

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... ion of interaction effects of different operating parameters including pH, time, solute concentration, temperature and adsorbent dosage. Numerical optimization helped to identify the optimal conditions for achieving the targeted dye removal of 95.493% when the pH, time, solute concentration, temperature and adsorbent amount were set at the range of 6.868, 36.4 min, 27.899 mg/l, 308.477 K, and 4.3475 g/l respectively. The experimental results indicate that the maximum adsorption capacity of NLP depends on various operating parameter like, pH, dye concentration, particle size of adsorbents and it's activation. It was noted that adsorption capacity of the NLP increases from 33.33 to 66.72 mg/g when it was activated with dilute HCl. The higher correlation coefficient value (R 2 ) of Langmuir isotherm 0.996 and lower p value (0.01203) indicate the fitness of the response surface 2FI model developed. Kinetic studies displayed the suitability of pseudo second order reaction for this adsorption process. The thermodynamic study show that the sorption process is exothermic and spontaneous in nature. It was observed that the adsorbent NLP in the form of fine powder are very effective for the removal of MG from its aqueous solution. The satisfactory values of regression coefficients at different temperature, and fittings of adsorption isotherms indicate that Indian NLP is a promising adsorbent for treatment of textile dyes. Abbreviations NLP Neem leaf powder (adsorbent) MG Malachite green (treatable dye) BOD Biological oxygen demand COD Chemical oxygen demand SEM Scanning electron microscope EDX Energy dispersive X-ray 1 3 117 Page 2 of 18 h Initial sorption rate = k 2 ·Q 2 (mg/g min) and k 2 (g/g min) ΔS Entropy (J/mol K) ΔH Enthalpy (kJ/mol) ΔG Gibb's Energy (kJ/mol) Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.