The plasma electrolytic oxidation (PEO) technique was used to prepare photocatalytic S-TiO coatings on Ti sheets; the incorporation of the S ions was possible from the electrolyte for modifying the structural and optics characteristics of the material. In this work, substrates of Ti (ASME SB-265 of 20 × 20 × 1 mm) were used in a PEO process in 10 min, using constant voltage pulses of 340 V with frequency of 1 kHz and duty cycles of 10% and of 30%. Solutions with HSO (0.1 M) and CHNS (52 and 79 mM) were used as electrolytes. X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy (EDS) were utilized to analyze the surface morphology, crystalline phase, and chemical composition of the samples. According to the results, the catalyst coatings had microporous structure and contained anatase-rutile TiO nanocrystalline mixture, until 73.2% rutile and 26.8% anatase in the samples grown with 30% duty cycle and the lowest concentration of CHNS. From the EDS measurements, the incorporation of sulfur ions to the coatings was 0.08 wt%. 99.5% reduction efficiency of Cr(VI)-EDTA with sunlight was observed after 2 h; it was determined by diphenyl carbazide spectrophotometric method. These coatings have potential for effective sunlight heterogeneous photoreduction of this toxic, cumulative, and non-biodegradable heavy metal that contaminates the soil and water and is a serious risk to sustainability, ecosystems, and human health.

Recibido 04-04-2017, aceptado 12-06-2017, versión final 25-07-2017.Artículo Investigación RESUMEN: Se implementó una fuente conmutada para ser utilizada en la técnica de Oxidación Electrolítica con Plasma (OEP). Los dispositivos electrónicos que se usaron son comunes y de bajo costo, lo que facilita la construcción del sistema. Se utilizó un microcontrolador de MICROCHIP para generar una señal digital con control de frecuencia y ciclo útil; también se usó un banco de condensadores y un puente de diodos para rectificar la alimentación suministrada directamente por la red eléctrica. El manejo de la potencia se hizo con transistores MOSFET en configuración "low side", la medición de la corriente se hizo con un sensor de Efecto Hall y los datos se enviaron a un computador mediante comunicación USB para ser visualizados a través de un algoritmo creado en LabVIEW. La fuente fue probada para crear microcavidades en láminas de titanio con el objetivo de formar nanoestructuras de dióxido de titanio.PALABRAS CLAVE: Fuente conmutada; oxidación electrolítica con plasma; ciclo útil; MOSFET.ABSTRACT: A switched-mode power supply was implemented for using in the Plasma Electrolytic Oxidation (PEO) technique. The electronic devices are inexpensive and ordinarily used, which facilitates the construction of the system. A MICROCHIP microcontroller was used for generating a digital signal with frequency and duty cycle control; a capacitor bank and a diode bridge were also used for rectifying the input signal from the electrical network. The management of the output voltage was made with an arrangement of MOSFET transistors in the "low side" configuration; the measurement of the current was made with a Hall Effect sensor and using the USB communication the data was sent to a computer for visualization with a LabVIEW algorithm. The power supply was tested for creating microcavities in a titanium sheet with the aim of forming nanostructures of titanium dioxide.