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

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.

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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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A novel thiol modified coal fly ash (CFA-SH) is successfully synthesized by a facile, efficient, and environmentally friendly process using 3-mercaptopropyltrimethoxysilane (MPTS). Various techniques have been used to characterize thoroughly the structure, the surface property, and the presence of the mercaptopropyl groups. The synthesized material proves to be an effective and selective adsorbent for removal of Hg 2+ and Cd 2+ ions from aqueous solution. The effect of time, pH, sample dose, speed, temperature, and metal ion concentrations were investigated thoroughly to optimize the sorption process. The kinetics data fitted in accordance with the pseudo-second-order model. It is also noticed that the Langmuir equation provides an accurate description of these sorption data, implying that monolayer sorption took place during adsorption. The quick and excellent uptake capacities (q m of 361.01 mg g −1 for Hg 2+ within 50 min at pH 8 and 106.38 mg g −1 for Cd 2+ within 60 min at pH 8) of the sorbent can be described on the basis of the hard and soft acid−base principle (HSAB) and electrostatic attraction. Moreover, both adsorbents and adsorbates can be reused using concentrated HCl. Finally, the low cost of the developed sorbent is also the prime point of interest in this experiment.

A single-step in situ synthetic method of sulfonic acid functionalized SBA-16 material with ordered large pores has been fabricated involving ammonium fluoride (NH 4 F), tetraethylorthosilicate (TEOS) in heptane, and 3-mercaptopropyltrimethoxysilane (MPTMS) in the presence of hydrogen peroxide (H 2 O 2 ) and Pluronic F127 (block copolymer) under mild acidic condition at room temperature. Due to the presence of numerous sulfonic acid groups on the surface, these materials show proficient adsorption capacities for dyes (q m = 365.46 mg g −1 for fuchsine basic, FB; q m = 217.87 mg g −1 for rhodamine 6G, R6G). Pseudo-second-order and intraparticle diffusion kinetics model as well as Langmuir isotherm model provided the best correlation with the obtained kinetic and isotherm data, respectively. Besides this, these materials prove to be efficient heterogeneous catalysts and show great catalytic activity toward Beckmann rearrangement of some oximes and esterification reaction. Moreover, these can be well regenerated in dilute acid solution and reused several times without causing any serious decrease of their adsorption capacity and catalytic activity. Finally, this work opens up a new vista of research in the direction of water treatment applications and in one-step in situ generation of solid acid catalyst at room temperature.

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