Improvement of photocatalytic activity in the degradation of 4-chlorophenol and phenol in aqueous medium using tin-modified TiO2 photocatalysts.

In this work, we present the synthesis of TiO2 photocatalysts modified with different % mol of tin using the sol-gel method. The materials were characterized using different analytical techniques. The Rietveld refinement, XPS, Raman and UV-Vis techniques confirm the substitution of tin in the TiO2 structural lattice due to changes in crystal lattice parameters, the low-energy shift of the Sn 3d5/2 orbital, generation of oxygen vacancies and the decreased band gap and increased BET surface area. The material with 1 mol% tin shows superior catalytic activity compared to the references for the degradation of 40 ppm 4-chlorophenol (3 hours of reaction) and 50 ppm phenol (6 hours of reaction). Reactions fit pseudo first order kinetics in both instances. The increase in photodegradation efficiency was attributed to the generation of energy levels below the TiO2 conduction band caused by the incorporation of 1% mol of tin, oxygen vacancies, and the heterojunction formed between the brookite-anatase-rutile, causing inhibition of the recombination of the electron (e-) and hole (h+) photogenerated species. The easy synthesis, low cost and increased photodegradation efficiency of the photocatalyst with 1 mol% tin have the potential to favor the remediation of recalcitrant compounds in water.

Cinética de la adsorción de fluoruro y arsénico usando nano-fibras de alúmina / Kinetics of the fluoride and arsenic adsorption using alumina nanofibers

Resumen En muchos países del mundo, incluido México, la presencia de elementos tóxicos, como el arsénico y flúor por encima de los niveles máximos permitidos en el agua potable (0.01 mg/L y 1.5 mg/L), respectivamente está generando problemas a la salud, como el cáncer y la fluorosis esquelética, respectivamente. El objetivo de este trabajo fue determinar la cinética del proceso de adsorción del fluoruro y arsénico en soluciones sintéticas, utilizando gamma alúmina (γ-Al2O3) para establecer si el proceso se desarrolla espontáneamente. Se sintetizó γ-Al2O3 nano-fibrilar, con alta área superficial /g), por precipitación homogénea, y se (352 m2 secó por espray. El nanomaterial adsorbente obtenido se usó para eliminar el fluoruro y el arsénico total de soluciones sintéticas. La morfología de la nano-fibra de γ-Al2O3 mesoporosa se analizó usando microscopía electrónica de transmisión y de barrido. El área superficial se determinó por adsorción-desorción a pH 7 de nitrógeno. Las isotermas de adsorción del proceso de remoción coincidieron con el modelo de Langmuir para ambos elementos. La γ-Al2O3 eliminó hasta 96 % de iones flúor y 92 % de arsénico total a pH 5, mientras que a pH 7 se alcanzó una remoción del 90 % y 94.2 % de fluoruro y arsénico, respectivamente. La cinética de remoción siguió el modelo de seudo-segundo orden, y el parámetro de equilibrio adimensional y la energía libre estándar de Gibbs confirmaron que el proceso se desarrolló espontáneamente. La gamma alúmina nano-fibrilar permitió la remoción natural y espontánea de arsénico y fluoruro presente en las soluciones utilizadas en este estudio.

Abstract In many countries of the world including Mexico, the presence of toxic elements such as arsenic and fluoride on the maximum levels permitted in drinking water (0.01 mg/L and 1.5 mg/L) is causing health problems such as cancer and skeletal fluorosis, respectively. For this reason, the objective of this work was to determine the kinetics of adsorption process of the fluoride and arsenic in synthetic water using gamma alumina (γ-Al2O3) and to determine whether the process develops spontaneously. Nanofiber γ-Al2O3 with high surface area was synthesized by homogeneous precipitation and spray dry method. This adsorbent nanomaterial was used to remove fluoride and total arsenic from synthetic water. Nanofiber morphology of the mesoporous γ-Al2O3 was analyzed by transmission and scanning electron microscopy. The high surface area (352 m2/g) was determined by nitrogen adsorption-desorption. The adsorption isotherms of the removal process concur by the Langmuir model for both toxic elements. γ-Al2O3 removes up to 96 % of fluoride ions and 92 % of total arsenic at pH5, while a removal of 90 % and 94.2 % at pH7 of fluoride and arsenic, respectively, is achieved. The removal kinetics follows the pseudo-second order model, and the dimensionless equilibrium parameter and Gibbs standard free energy confirm that the process is performed spontaneously. The gamma nano-fibrillar alumina is a good material for the natural and spontaneous removal of arsenic and fluoride present in synthetic water used in this study.