Spherical mesoporous silica designed for the removal of methylene blue from water under strong acidic conditions.

This work proposes a novel technology for environmental remediation based on mesoporous silica spheres, which were successfully synthesized by the solvothermal method using the cetyltrimethylammonium bromide as a structuring agent. The adsorbent was designed to remove cationic dyes at strong acidic conditions. The surface was modified by a careful thermal treatment aiming at the condensation of silanol to siloxane groups. The adsorbent was characterized by XRD, SEM, FTIR, N2 adsorption/desorption and the equilibrium technique to determine the pHpzc. The kinetic of the adsorption followed a pseudo-second-order model and the process was ruled by physical forces. The isotherms were fitted to Freundlich and Temkin models, indicating that the physisorption occurred with multilayer formation, with the interaction adsorbate-adsorbate being relevant to the whole process. The adsorption capacity was approximately 60 mg g-1 and the adsorbents performance in the fast-contact system showed removal of 65%wt. of a 93 mg L-1 methylene blue (MB) solution in a single application.

Nanoflakes of chloride zinc-iron-aluminum-based layered double hydroxides obtained from industrial waste: a green approach to mass-scale production.

A greener technology aiming at a smarter industrial waste treatment is proposed to produce chloride iron-zinc-aluminum layered double hydroxides (LDHs). Waste Pickling Acid (WPA) and sodium aluminate (NaAlO2) from secondary sources were meticulously mixed under mild experimental conditions using a sodium hydroxide solution as a pH-regulator. A set of characterization techniques (XRD, SEM, TGA, FTIR, AAS and adsorption-desorption of N2) indicated the formation of highly-dispersed nanoflake crystallites with textural characteristics and thermal stability similar to syntheses with high-quality chemicals. An interesting discussion on chemical composition and M2+/M3+ molar ratio is presented. Although the co-precipitation synthesis was conducted without control of environmental CO2, complete intercalation of the chloride anion was achieved, making these particles more favorable for further anion exchange applications. The experimental variables temperature of reaction and WPA/NaAlO2 volume ratio showed the strongest influence on the LDHs crystallinity and porosity. LDHs architected with iron and zinc have the potential to be applied in systems for removing sulfur gases for cleaner energy production, e.g. in the refining process of biogas to produce biomethane.

Removal and Extraction of Carboxylic Acids and Non-ionic Compounds with Simple Hydroxides and Layered Double Hydroxides.

Carboxylic acids are an important natural component as a final product or intermediates for syntheses. They are produced in plants, animals and also as products from biotechnological processes. This review presents the use of single hydroxide particles and layered double hydroxides as alternative adsorbents to remove carboxylic acids from liquid media. The proposal to use hydroxide particles is based on its affinity to adsorb or intercalate carboxylic acids. Besides, the change in properties of the adsorbate-sorbate product evinces that this intermediate can be used as a vehicle to transport and release carboxylic acids. Additional examples will also be presented to prove that layered hydroxides are capable of removing non-ionic compounds from wine, milk and tomato. The use of layered compounds to remove active ingredients could reduce the number of separations steps, costs and reduce or eliminate solvents, thus encouraging the design of industrial processes of separation using hydroxides particles.

In-Situ Direct Synthesis of HKUST-1 in Wool Fabric for the Improvement of Antibacterial Properties.

The use of Metal-Organic Frameworks (MOF) such as HKUST-1 in textiles is an alternative with regard to the development of technologies that are increasingly seeking for functionalities, mainly in the fields of health and hygiene, named biofunctional fabrics. However, the application of the MOF under the surface of the wool fiber can lead to a low durability finish due to its low fixation. Thus, this project aims to perform the direct synthesis of HKUST in the wool fiber, so that a product with good washing durability can be obtained. The purpose of this study was to incorporate metal-organic frameworks, composed of copper and trimesic acid, into woolen fabrics, to improve the antibacterial properties. The synthesis was performed directly in the wool fabric, at time intervals of 24 and 48 h. The resulting fabrics were characterized by Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), X-Ray Diffractometry (XRD), Fourier Transform Spectroscopy Infrared-Attenuated Total Reflectance (FTIR-ATR), and colorimetric analysis (CIElab), and the Antimicrobial Activity Test (American Association of Textile Chemist and Colourists - AATCC Test Method 61-2007-2A) was performed. The results suggested that the application produced textiles with antibacterial properties, showing activity against Escherichia coli.

Selective oxidation catalysts obtained by immobilization of iron(III) porphyrins on thiosalicylic acid-modified Mg-Al layered double hydroxides.

Nitrate-intercalated Mg-Al layered double hydroxides (LDHs) were synthesized and exfoliated in formamide. Reaction of the single layer suspension with thiosalicylic acid under different conditions afforded two types of solids: LDHA1, in which the outer surface was modified with the anion thiosalicylate, and LDHA2, which contained the anion thiosalicylate intercalated between the LDH layers. LDHA1 and LDHA2 were used as supports to immobilize neutral (FeP1 and FeP2) and anionic (FeP3) iron(III) porphyrins. For comparison purposes, the iron(III) porphyrins (FePs) were also immobilized on LDH intercalated with nitrate anions obtained by the co-precipitation method. Chemical modification of LDH facilitated immobilization of the FePs through interaction of the functionalizing groups in LDH with the peripheral substituents on the porphyrin ring. The resulting FePx-LDHAy solids were characterized by X-ray diffraction (powder) and UV-Vis and EPR spectroscopies and were investigated as catalysts in the oxidation of cyclooctene and cyclohexane. The immobilized neutral FePs and their homogeneous counterparts gave similar product yields in the oxidation of cyclooctene, suggesting that immobilization of the FePs on the thiosalicylate-modified LDHs only supported the catalyst species without interfering in the catalytic outcome. On the other hand, in the oxidation of cyclohexane, the thiosalicylate anions on the outer surface of LDHA1 or intercalated between the LDHA2 layers influenced the catalytic activity of FePx-LDHAy, leading to different efficiency and selectivity results. FeP1-LDHA2 performed the best (29.6% alcohol yield) due to changes in the polarity of the surface of the support and the presence of FeP1. Interestingly, FeP1 also performed better in solution as compared to the other FePs. Finally, it was possible to recycle FeP1-LDHA2 at least three times.

First insight into catalytic activity of anionic iron porphyrins immobilized on exfoliated layered double hydroxides.

Mg-Al layered double hydroxide (LDH) intercalated with glycinate anions was synthesized through co-precipitation and exfoliated in formamide and the single-layer suspension was reacted with aqueous iron porphyrin solutions (Fe(TDFSPP) and Fe(TCFSPP)). The obtained materials were characterized by X-ray powder diffraction, UV-vis, and electron paramagnetic resonance and investigated in the oxidation reaction of cyclooctene and cyclohexane using iodosylbenzene as oxidant. The iron porphyrin seems to be immobilized at the surface of the glycinate intercalated LDH. The catalytic activities obtained in heterogeneous media for iron porphyrin, Fe(TDFSPP), was superior to the results obtained under homogeneous conditions, but the opposite effect was observed on the Fe(TCFSPP), indicating that, instead of the structural similarity of both iron porphyrins (second-generation porphyrins), the immobilization of each one produced different catalysts. The best catalytic activity of the Fe(TDFSPP)/Gly-LDH, compared to Fe(TCFSPP)/Gly-LDH, can be explained by the easy access of the oxidant and the substrate to the catalytic sites in the former, probably located at the surface of the layered double hydroxide pillared with glycinate anions. A model for the immobilization and a mechanism for the oxidation reaction will be discussed.