Desenvolvimento de materiais mesoporosos baseados em sílica oriunda de biomassa para utilização como sistema remediador de hidrocarbonetos policíclicos aromáticos

Abstract

This work describes the synthesis and characterization of mesoporous materials from the use of amorphous silica extracted from rice husk ashes (RHAs), as well as the preparation of mixed matrix membranes (MMMs) using the mesoporous materials as filler materials to be used in the remediation of the polycyclic aromatic hydrocarbons (PAHs). The mesoporous materials were synthesized by the hydrothermal method and the MMMs by casting. It was possible to observe that the acid treatment did not alter the molecular structure of the RHSs, as well as there was an increase in the percentage of SiO2 in the thermal stability. The RHAs presented an amorphous silica nature, with the characteristics of a fine powder of white color, with type IV isotherms and H1 type hysteresis, and high surface area values. The hydrothermal method was efficient in the synthesis of the mesoporous materials, which presented TGA curves and characteristic bands of the formation of the amorphous condensed silica framework, typical of mesoporous materials of the M41S family, with high surface area. The casting method was efficient for the preparation of the MMMs, which showed a good dispersion of the mesoparticles incorporated, small-angle ordering and a small increase in the Tg values of the MMMs with the incorporation of the MCM−41−NH2 (CCA). The adsorption tests showed that there was an increase in the adsorbed amount (qe) with the increase of the initial concentration of the HPAs, adsorbent amount, contact time, and temperature, however pH variation was not significant. The adsorption kinetics was relatively fast and followed the non-linear pseudo-second order model, and the isotherms obtained were more adequate to the theoretical Langmuir model. The values of qe found for the mixture of HPAs Naf, B[b]F, B[k]F, and B[a]P were in the same order of magnitude for all adsorbent materials tested: Naf < B[a]P < B[k]F < B[b]F due to the hydrophobic effect. The transport properties were more influenced by the incorporation of the MCM−41−NH2 (RHA) into PSf−Ac than the addition of the PABA−MCM−41 (RHA) in PES, as the best results of the rate of permeation, rate of retention, and percentage of removal were obtained for the MMMs based on PSf, however the pure PSf and PES membranes presented similar results.