Jose Manuel Gatica

This study introduces an innovative hybrid approach combining salting-out and adsorption for the highly efficient removal of crystal violet (CV) dye from aqueous solutions. The method leverages high-ionic-strength brine discharge from the Complex of El-Outaya (CEO, ENASEL, Biskra, Algeria) and micro-mesoporous biochar derived from calves’ horn cores (BHC-800). Results demonstrate that both undiluted and diluted brine significantly enhance CV removal, while BHC-800, with a surface area of 258 m² g⁻¹, exhibits a maximum Langmuir adsorption capacity of 106.1 mg g⁻¹ (at 20 °C ± 2). Thermodynamic analysis confirms a spontaneous (ΔG° < 0) and exothermic (ΔH° = −0.86 kJ mol⁻¹) process, with increased interfacial disorder (ΔS° = 93.53 J mol⁻¹ K⁻¹). The synergistic effect of salting-out and adsorption achieved ~99.8% removal of CV at an initial concentration of 1000 mg L⁻¹. Furthermore, BHC-800 exhibited excellent reusability, maintaining high adsorption efficiency over multiple cycles. Economic assessment revealed operational costs of 0.45–0.89 US$ m⁻³ for 60% brine discharge. Biochar production costs were 0.076–0.18 US$ kg⁻¹, translating to 7.5–17.2 (10⁻⁴ US$) per gram of CV removed. This dual strategy not only offers an eco-friendly and cost-effective solution for dye-laden water but also promotes the valorization of saline effluents and animal byproducts, addressing critical environmental challenges in industrial wastewater treatment.

Air pollution, a major health concern, necessitates innovative solutions such as TiO₂-based photocatalytic building materials to combat its harmful effects. This study focuses on developing high-performance TiO₂ photocatalysts for NO_x removal in building applications, aiming to overcome the limitations of commercial TiO₂. These photocatalysts were synthesized via a hydrothermal method, with parameters such as synthesis time and post-treatment investigated to optimize their properties. Hydrothermal synthesis yielded TiO₂ nanoparticles with reduced aggregation and a high proportion of elongated particles with exposed {010} facets. This resulted in significantly enhanced photocatalytic activity compared to commercial P25 in methylene blue degradation and NO_x depollution. Subsequently, the optimized hydrothermal TiO₂ was successfully integrated into a silica sol–gel coating for application on building materials. The coated concrete demonstrated significantly higher NO_x removal efficiency and lower NO₂ release, achieving a 1.7-fold improvement in overall NO_x removal and significantly higher depolluting effectiveness compared to its P25 counterpart. These findings highlight the potential of hydrothermally synthesized TiO₂ with controlled morphology for the development of high-performance, environmentally friendly building materials with enhanced air purification capabilities.

How important is the support during the rational design of a catalyst? Herein, doped ceria (Zr; Pr and Tb) was used as an active support to prepare Pt catalysts (0.5 wt%) for glycerol selective oxidation. A thorough characterization of achieved catalytic systems showed that the nature of doping elements led to different physicochemical properties. The presence of surface Pr³⁺ and Tb³⁺ not only increased oxygen vacancies but also electron mobility, modifying the oxidation state of platinum particles. The redox properties of the catalyst were also affected, achieving a close interaction between the support and metal particles even in the form of Pt-O-Pr(Tb) solid solutions. Furthermore, the combination of medium-sized metal particle dispersion, strong metal–support interaction and a synergy between the amount of oxygen vacancies and Pt⁰, observed in the Pt/CeTb catalyst, led to a high turnover frequency (TOF) and increased selectivity to glyceric acid. Thus, the present study reveals how a simple structural modification of active supports, such as cerium oxide, by means of doping elements is capable of improving the catalytic performance during glycerol selective oxidation, avoiding the cumbersome methods of synthesis and activation treatments.

Rice husk, a byproduct of rice production, poses significant environmental challenges due to disposal issues, while the emission of volatile organic compounds into the atmosphere further exacerbates these concerns. This study addresses both problems by exploring the potential of texturally enhanced SiO₂, derived from Uruguayan rice husk, as a catalytic support for manganese oxides in the combustion of volatile organic compounds. SiO₂ was synthesized from rice husk ash using a sustainable, acid-free pretreatment method, yielding a notably high silica purity of 96.5%—a level comparable to or exceeding previously reported values, highlighting the high silica quality inherent in Uruguayan rice husk. The catalytic activity was evaluated using acetone as a model volatile organic compound, achieving up to 90% conversion with 30 wt.% manganese oxide at 300 °C, with CO₂ as the primary product. Furthermore, a 24 h stability test demonstrated consistent performance, maintaining a conversion rate of around 95.6 ± 2.5%. These findings suggest that high-purity SiO₂ derived from Uruguayan rice husk, with its sustainability benefits, offers an effective solution for acetone removal when supporting an active phase such as manganese oxides, addressing both rice husk disposal and volatile organic compound emissions.

Rice husk, a byproduct of rice production, presents significant environmental challenges due to its disposal, while the emission of volatile organic compounds into the atmosphere poses additional concerns. This study addresses these issues by exploring the potential of texturally modified SiO₂ derived from Uruguayan rice husk as a catalytic support for manganese oxides in volatile organic compounds combustion. SiO₂ was synthesised from rice husk ash using a sustainable, acid-free pretreatment method, yielding a notably high silica purity of 96.5%—a level comparable to or exceeding those reported in previous studies, and underscoring the high silica quality inherent in Uruguayan rice husk. The catalytic performance of the catalysts was evaluated using acetone as a model of volatile organic compound, achieving up to 90% conversion with 30 wt.% manganese oxide at 300 °C, primarily yielding CO₂. Furthermore, a 24-hour stability test indicated consistent conversion, maintaining around 95.6 ± 2.5%. These findings suggest that Uruguayan rice husk-derived SiO₂, with its high purity and sustainability benefits, offers an effective solution for acetone removal when supporting an active phase such as manganese oxides, addressing both rice husk disposal and volatile organic compounds emissions.

A copper–iron-based catalyst has been prepared by a low-temperature co-precipitation and sonication method. The material shows catalytic activity in the acyloxylation reaction of 1,4-dioxane and cyclohexene under microwave irradiation.

Exhausted TWCs subjected to chemical/thermal treatments were used as a support of MnO_x catalysts for the total combustion of acetone. The so-prepared new devices were characterized by using adherence tests, elemental and thermal analyses, XRD, N₂ physisorption, and SEM-EDS. Incorporation of only 2.6 wt.% of the active phase (Mn₂O₃ and Mn₃O₄) to the recycled honeycomb considerably improved the catalytic response, achieving at 250 °C a 60% increase in acetone conversion with respect to the spent autocatalyst. The following procedure is proposed as a simple way to provide the TWC devoid of noble metals a second life in the VOCs’ oxidation field.

Single-phase oxygen stoichiometric LaMnO₃ and doped La_0.8A_0.2MnO₃ (A = Ca, Sr, Ba) perovskites have been prepared by a simple one-step auto-combustion method. Cation-deficient LaMnO_3+δ and La_0.8A_0.2MnO_3+δ were obtained by calcination of the former samples in air at 750 °C. The samples were characterized by X-ray powder diffraction, X-ray photoelectron spectroscopy, temperature-programmed reduction, temperature-programmed oxygen desorption, and N₂ physisorption in order to apply them as catalysts in the complete catalytic oxidation of acetone as a model volatile organic compound. The studied phases show the expected orthorhombic and rhombohedral perovskite crystal structures. Catalytic experiments performed with all the samples show measurable activity already at 100 °C. At 200 °C, doped La_0.8A_0.2MnO₃ samples show higher activity than undoped LaMnO_3, with increasing conversion with larger A-cation size. Calcined samples also show higher activity than as-prepared ones making La_0.8Ba_0.2MnO_3+δ the best catalyst at this temperature. All doped samples show >95% acetone conversion at T ≥ 250 °C with a weak dependence on the sample processing or A cation doping. The collected evidence confirms that the most important factors for the catalytic activity of these oxides are the Mn⁴⁺/Mn³⁺ molar ratio on the surface of the samples and the cation-deficiency of the bulk perovskite structure. In addition, increasing the symmetry of the bulk crystal structure appears to have an additional favourable effect. Despite the observation of the presence of surface carbonates, we show that it is possible to use the as-prepared samples without further thermal treatment with good results in the oxidation of acetone.