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Organic dyes, present in the aquatic environment, have negative effects on ecosystems. Attempts are being made to remove these dyes by using number of physico‐chemical methods. Out of all the methods, adsorption technique is the most economical and efficient technique. However, for this purpose, efficient and cost‐effective adsorbents are needed. In this paper processed neem leaf powder (NLP) has been used for methylene blue (MB) dye removal. NLP has been characterized by X‐ray diffraction, FTIR spectroscopic, and scanning electron microscopic techniques. Results have shown that NLP has crystalline character with number of functional groups. MB is removed by using NLP under different varying conditions such as NLP doses, varying MB concentration, and different pH. When fixed amount of NLP (0.2 g) is used, removal of MB increases with time and becomes almost constant after 40 min. Maximum MB removal is obtained at pH = 6.0. Adsorption isotherms and kinetic models are discussed and the data fitted well with Langmuir isotherm and pseudo second order kinetic models. Ab initio calculations have shown that nature of interaction depends on the orientation of groups and both type of adsorption is feasible in the present system. Results show that NLP is an effective adsorbent for removal of MB dye. [ABSTRACT FROM AUTHOR]

Organic dyes, present in the aquatic environment, have negative effects on ecosystems. Attempts are being made to remove these dyes by using number of physio‐chemical methods. Out of all the methods, adsorption technique is the most economical and efficient technique. For this purpose, efficient and cost‐effective adsorbents are needed. Neem leaf powder (NLP) containing Azadirachtin Indica, has been used for methylene blue (MB) dye removal. The interaction of dye on neem leaf containing Azadirachta indica plays an important role. Quantum mechanical calculations using density functional theory have been done in order to have an idea about interaction during adsorption. There is a possibility of both strong and weak interaction depending on the orientation of adsorbent and adsorbate. [ABSTRACT FROM AUTHOR]