Amino- or carboxylate-functionalised SBA-15 acts as a selective adsorbent and shows enhanced adsorption capacity for toxic dyes.

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Polyethylenimine-based modified coal fly ash (CFA-PEI) is synthesized by the wet impregnation method. The material was found to be an excellent adsorbent for removal of cationic (Malachite Green; MG) and anionic (Reactive Red 2; RR2) dyes from aqueous solution. CFA-PEI was characterized by various sophisticated instruments such as FTIR spectroscopy, 13 C MAS NMR spectroscopy, XRD, elemental analysis, Brunauer−Emmett−Teller (BET) isotherm, TGA, FESEM, and HRTEM. The FTIR spectra reveal that the N-containing functional group is introduced on the surface of CFA-PEI, which plays a vital role in the removal of these dyes. The adsorption behavior of the CFA-PEI toward toxic dyes is evaluated by investigating the effect of solution pH, contact time, solution temperature, adsorbent dose, and concentration of dye solution. The obtained adsorption isotherm and the kinetics data of both MG and RR2 are in compliance with the Langmuir adsorption isotherm and pseudo-second-order kinetics, respectively. Moreover, excellent adsorption capacity on CFA-PEI of dyes (q m : 174.83 mg/g for MG and 316.75 mg/g for RR2) is attributed to various factors (H-bonding, electrostatic interaction). CFA-PEI also has high regeneration capacity toward these dyes from aqueous solution. Finally, the advantage of the adsorbent lies in its low cost.

The removal of toxic dyes (Methyl Violet, MV; Congo Red, CR; and Malachite Green, MG, respectively) from water using Si-MCM-41 functionalized with aspartic acid (APA), polyethylenimine (PEI), and βcyclodextrin (β-CD) developed through new facile synthetic routes is reported here. The successful functionalizations of Si-MCM-41 were examined by means of TGA, solid-state 13 C CP MAS NMR spectra, FTIR, XRD, nitrogen sorption, FESEM, and TEM. Beside this, the sorption behavior of those sorbents using sorbates is determined by considering some factors like the pH of the medium, contact time, temperature of the medium, concentration of the dye medium, sorbent dose, and agitation speed. The kinetics data fitted a pseudo-second-order model. It is noticed that the Langmuir equation yields an accurate description of these sorption data, implying that monolayer adsorption took place in all sorption processes. The proficient sorption capacities of these adsorbents (q m = 374.89 mg g −1 for MV on Si-MCM-41−APA, q m = 458.72 mg g −1 for CR on Si-MCM-41−PEI, and q m = 561.45 mg g −1 for MG on Si-MCM-41−β-CD) can be described from the viewpoint of both hydrogen bonding and electrostatic interactions between the sorbents and sorbates. Moreover, both sorbents and sorbates can be recycled and reused after a regeneration process.

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