Eco-friendly novel adsorbents composed of hybrid compounds for efficient adsorption of methylene blue and Congo red dyes: Kinetic and thermodynamic studies

As a result of rapid modernization caused by industrial growth, drinking water is constantly polluted by various dyes. Hence, the health and environmental concerns associated with toxic dyes have received serious attention from communities around the world. In this work, novel adsorbents (Ti-Arg-TES and Ti-Tyr-C-APTMS) consisting of Ti/Si-alkoxides/amino acids with and without cellulose in 1:1:1 mol ratio were synthesized in methanol using sol-gel method. The synthesized novel organic-inorganic hybrid compounds as adsorbents were characterized by a combination of FTIR, XRD, SEM, EDS, BET, BJH, and other analysis methods. Then, their removal behaviors and possible mechanisms for methylene blue (MB) and Congo red (CR) dyes were systematically investigated. Batch adsorption experiments revealed that the adsorption process between these novel adsorbents and MB or CR dyes conformed to pseudo-second-order kinetics (R2 = 0.999 for MB, and R2 = 0.988 for CR) and both Langmuir (R2 = 0.970 for MB, and R2 = 0.955 for CR) and Freundlich (R2 = 0.953 for MB and CR) isotherm models, demonstrating a hybrid chemical/physical adsorption process. The maximum adsorption capacity was 57.14 mg/g for MB of Ti-Arg-TES and 83.05 mg/g for CR of Ti-Tyr-C-APTMS. Ti-Arg-TES and Ti-Tyr-C-APTMS adsorbents exhibited an excellent affinity for capturing MB and CR dyes from aqueous solution, respectively.