Synthesis of 1-(Pyrrol-2-yl) imine modified silica as a new sorbent for the removal of hexavalent chromium from water

The water pollution is a big problems faced by the countries of the world, without exception. One of the most important and toxic heavy metals in wastewater is chromium. The major problem here is to detect the concentration of hexavalent chromium and try to remove it by adsorption. The product 1-(Pyrrol-2-yl) imine modified silica was successfully prepared by immobilizing 1H-pyrrole-2-carbaldhyde on silica gel previously doped with 3-aminopropyltrimethoxysilane. The modified surface shows good thermal stability determined by (TGA). The FTIR and UV results confirmed that the pyrrole-2-carbaldhyde units have been immobilized at the surface of the modified silica gel. SEM images of the modified polysiloxane surface showed tough and porous nature, indicating that the materials present good characteristics to be used as an adsorbent. The synthesized SiNPr was investigated as an adsorbent for removal of Cr (VI). The adsorption experiments were conducted for a wide range of solution pH, adsorbent dosage, temperature, initial concentration and contact time. It was observed that the percentage removal of Cr(VI) increased with an increase of initial concentration until 20 mg/L, while it decreased with increase in solution pH, contact time, adsorbent dose and temperature. Over 86% removal efficiency of Cr (VI) was achieved after 5 min, at solution pH around 4, 25°C temperature, 0.01 g weight of dose and initial concentration of 20 mg/L Cr(VI) solution. The adsorption of Cr (VI) on the (Si-NPr) was optimized under acidic conditions and at room temperature. Cr (VI) adsorption using (Si-NPr) can be described using pseudo second order and Freundlich isotherm model. The amount of Cr(VI) adsorbed per unit mass of (Si-NPr) obtained by pseudo second order model, Qe calc (2.469) were in consistent with the experimental value, Qe exp (2.782) indicate the pseudo second order model better represented the adsorption kinetics. The Langmuir maximum adsorption capacity Qm is 13.05 mg/g, at 25°C, and pH 4 and 0.03 weight of adsorbent dose. The RL value (0.48) at 25 °C) indicates that the adsorption of Cr (VI) on (Si-NPr) is favorable. From Freundlich isotherm model parameters, value of 1/n=0.9863 while n=1.0139 indicating that the adsorption of Cr (VI) on (Si-NPr) is favorable. The adsorption data suited with Langmuir and Freundlich, but Freundlich adsorption model was found to have the highest regression value and the best suit. The fact that the Freundlich model is a good fit to the experimental adsorption data suggests physical adsorption as well as a heterogeneous distribution of active sites on the adsorbent surface The negative ∆G° values (-4.224 to -1.775 kJ/mol) indicate that the adsorption is favorable and spontaneous at studied temperatures. The negative value of ∆H° (-26.1 kJ/mol) reflects an exothermic adsorption and indicates that the adsorption is favored at low temperature. A negative value of ΔS (-0.075) suggests that the adsorption process involves an associative mechanism. The adsorption leads to order through the formation of an activated complex between the adsorbate and adsorbent. Also a negative value of ΔS reflects that no significant change occurs in the internal structures of the adsorbent during the adsorption process. The results of the present study exhibit that the prepared compound has a negative biological activity against Staphylococcus aurous, Pseudomonas aeruginosa, and Escherichia coli. (Si-NPr) is a good effective adsorbent for the removal of Cr (VI) from the wastewater and can be reused for many times.