The present work reports the synthesis of zeolites from two metakaolins, one derived from the white kaolin and the other derived from the red kaolin, found in a deposit in the city of São Simão (Brazil). The metakaolins were prepared by calcination of the kaolins at 600 °C; zeolite A was obtained after alkali treatment of the metakaolins with NaOH. The resulting solids were characterized by powder X-ray diffraction, thermal analysis, scanning electron microscopy, and nitrogen adsorption/desorption at −196 °C, which confirmed formation of zeolite A. The zeolites were applied as adsorbents to remove methylene blue, safranine, and malachite green from aqueous solutions. The zeolites displayed high adsorption capacity within short times (between one and five minutes); q_t was 0.96 mg/g. The equilibrium study showed that the zeolites had higher adsorption capacity for malachite green (q_e = 55.00 mg/g) than for the other two cationic dyes, and that the Langmuir isotherm was the model that best explained the adsorption mechanism.

Two titania photocatalysts have been prepared using the sol–gel method using TiCl₄ as a precursor, and two different alcohols, namely, ethanol or propanol (Et or Pr). The main aim of this work was to study the effect of the nature of the alcohol on the chemical, structural and photocatalytic properties for paracetamol photodegradation of the final solids. The TiCl₄/alcohol molar ratio to obtain the corresponding alkoxides (TiEt and TiPr) was 1/10. These alkoxides were calcined at 400 °C to prepare the oxide catalysts (named as TiEt400 and TiPr400). Powder X-ray diffraction (PXRD) of the original samples showed the presence of anatase diffraction peaks in sample TiPr, while TiEt is a completely amorphous material. Contrary to commercial TiO₂-P25, the PXRD diagrams of the calcined samples showed anatase as the exclusive crystalline phase in both solids. The specific surface area (S_BET) of sample TiPr400 was larger than that of sample TiEt400, and both larger than that of TiO₂-P25. The three solids have been tested in the photodegradation of paracetamol in aqueous solution. It has been established that the alcohol used influences the properties and catalytic activity of the final oxides. The synthesized solids exhibit a higher activity than commercial TiO₂-P25, because of their structural characteristics and larger S_BET.

Three series of layered double hydroxides (LDH) with a hydrotalcite-like structure and composition corresponding to [Mg₄Al₂(OH)₁₂(CO₃)]·3H₂O have been prepared from a common batch by applying three different aging procedures, namely, stirring at room temperature, hydrothermal treatment, and microwave-hydrothermal treatment. It has been found that the tested properties of the samples (mainly related to their crystallinity) are considerably improved by using the microwave-hydrothermal treatment. Shorter times are also evinced than in the other two aging treatments; however, if the microwave-hydrothermal treatment is too far extended, incipient destruction of the particles is observed.

A Zn,Al layered double hydroxide (LDH), with the hydrotalcite structure and the mixed oxide obtained upon its calcination at 650 °C, was tested in the adsorption and photocatalytic degradation of 4-Nitrophenol in aqueous solution. The Zn,Al LDH was fast and easily obtained by the coprecipitation method. Hydrothermal treatment under microwave irradiation was applied to compare the effect of the ageing treatment on the photocatalytic behavior. The efficiency of the synthetized solids was compared to that of a commercial ZnO. The ageing treatment did not improve the performance of the original samples in the degradation of 4-nitrophenol. The activity of the synthetized solids tested exceeded that observed for the reaction with commercial ZnO. The photocatalytic performance of the original non-calcined hydrotalcite is similar to that of commercial ZnO. The calcined hydrotalcite showed a better performance in the adsorption-degradation of the contaminant than ZnO, and its reusability would be possible as it recovered the hydrotalcite-like structure during the reaction.

The modification of bentonite with Al–Fe species from different concentrated precursors at both stages: (i) the preparation of the (Al/Fe)-mixed pillaring solution and (ii) intercalation itself, was studied at lab scale. The final solids were characterized by X-ray fluorescence (XRF), X-ray diffraction (XRD), Cationic Exchange Capacity (CEC), textural analyses by nitrogen adsorption–desorption at 77 K, and hydrogen-temperature programmed reduction (H₂-TPR). Finally, the modified clays were assessed as active materials in the Catalytic Wet Peroxide Oxidation (CWPO) of phenol under very mild conditions through 1.0 h of reaction: T = 25.0 °C ± 0.1 °C, pH = 3.7, ambient pressure (76 kPa), and 0.5 g catalyst per dm³. Metal hydrolysis by the dissolution of elemental aluminium (final Total Metal Concentration TMC = 4.62 mol dm⁻³) achieved the best results, decreasing the volume of solution per mass unit of clay required to successfully expand the layered starting mineral by a factor of close to 75, in comparison with the widespread conventional preparation using highly diluted Al-based pillaring solutions. Even in the absence of any solvent for the clay dispersion, the intercalating/pillaring method was shown to be favourable, as a novel strategy promoting the process intensification and subsequent preparation of Al/Fe- and other Al-based pillared clays at larger scales. The best catalyst prepared from concentrated precursors exhibited 79.1% phenol conversion, 19.3% TOC mineralization, and pretty low iron leaching (0.037 mg Fe dm⁻³; ∼0.12% w/w) in such a short catalytic assessment; all these results were quite comparable or even exceeded those exhibited by the catalyst prepared from dilute precursors.

A montmorillonite has been intercalated with Al³⁺ polycations, using concentrated solutions and clay mineral dispersions. The reaction has been assisted by microwave radiation, yielding new intercalated solids and leading to Al-pillared solids after their calcination at 500 °C. The solids were characterized by elemental chemical analysis, X-ray diffraction, FTIR spectroscopy, thermal analyses, and nitrogen adsorption. The evolution of the properties of the materials was discussed as a function of the preparation conditions. Microwave treatment for 2.5 min provided correctly pillared solids.