Use of Visible Light Modulation Techniques in Urea Photocatalytic Degradation

Abstract

The aim of this work was to analyze the effect of visible LED dimming duty-cycle modulation techniques in a photocatalytic system for urea degradation using a visible light photocatalyst immobilized on macroscopic supports. For this reason, the effect of different LED dimming techniques was investigated and compared in terms of urea degradation together with ammonia and nitrate production during the irradiation time. The experimental results evidenced that using a visible LED dimming modulation with variable-peak variable-duty pulse-width modulation (PWM) allows to improve the photocatalytic degradation process, with respect to classical LED dimming with fixed-peak fixed-duty PWM, and influences the product's distribution of ammonia and nitrate in water. Therefore, the proof of concept herein proposed could be considered as preliminary potential results to be used in water recycling applications with a particular emphasis in recovery of urea photodegradation byproducts, such as ammonia, from wastewater that could be used as potential resources and an energy resource.

Catalytic Composite Systems Based on N-Doped TiO2/Polymeric Materials for Visible-Light-Driven Pollutant Degradation: A Mini Review

“…The methods for fixing N-doped TiO 2 particles on the chosen polymeric substrate can be developed starting from those studied for the immobilization of undoped TiO 2 . They may vary from simple, such as the solvent-casting method [46][47][48][49][50] or sol-gel techniques [58], to more complex, specialized and expensive methods, such as magnetron sputtering [59] and gelation of a catalyst in a polymeric substrate and subsequent extraction with supercritical CO 2 [55,56,60]. It is worth noting that the method for immobilizing N-doped TiO 2 on a polymeric support influences the photocatalytic activity, which also depends on the type of substrate and pollutant to be degraded.…”

“…Chemical-physical characterization results and visible-light-driven methylene blue degradation tests evidenced that the best performances are achieved when an optimal N-doped TiO 2 amount is dispersed in acetone to obtain a suspension that is dropped on the PS surface [46]. Starting from these preliminary results, N-doped TiO 2 was also immobilized on the surface of PS spheres and PS pellets in cylindrical shape by using the same preparation method [48][49][50]. The photocatalytic activity under visible light of such systems was evaluated in the methylene blue and urea degradation as well as in the inactivation of E. coli in real municipal wastewater, evidencing the stability of the obtained systems after several reuse cycles [48][49][50].…”

“…However, it must be considered that such systems can be activated only by UV light. Recent studies have been focused on the supporting provided to N-doped TiO 2 by various polymeric substrates, such as polyvinylidene fluoride (PVDF) [42], polypropylene (PP) [43], polytetrafluoroethylene (PTFE) [44], polyaniline (PANI) [45] and polystyrene (PS) [46][47][48][49][50]. Many authors reported that the coupling of semiconductors with polymers improves the photoactivity of N-doped TiO 2 for the degradation of water pollutants as well as for the inactivation of bacteria under visible-light irradiation (Table 2).…”

“…Starting from these preliminary results, N-doped TiO 2 was also immobilized on the surface of PS spheres and PS pellets in cylindrical shape by using the same preparation method [48][49][50]. The photocatalytic activity under visible light of such systems was evaluated in the methylene blue and urea degradation as well as in the inactivation of E. coli in real municipal wastewater, evidencing the stability of the obtained systems after several reuse cycles [48][49][50]. However, a photocatalytic activity lower than that observed for the powder forms of photocatalyst is generally observed [31].…”

Photocatalytic Oxidation of Urea on Surface-Modified Bi2WO6 with trans-4-Stilbenecarboxaldehyde

“…The accumulation of urea from urinary excretions becomes a problem in cities with a high population rate, where biodegradation is not sufficient to mitigate the associated ecological risks. − In fact, numerous investigations in recent years have focused on the development of heterogeneous photocatalysts powered by sunlight for effective environmental purification of wastewater. − In this sense, some efforts have been directed to the development of nanostructures based on Bi 2 WO 6 , which have revealed that they could function as excellent photocatalytic materials exhibiting enhanced activities for advanced oxidation of many contaminants. − However, despite the absorption of solar energy by these materials, an electron is promoted from the valence band to the conduction band (e CB – ), leaving an electronic deficiency in the valence band called a hole (h VB + ) (eq ). The recombination of the latter charge carriers can greatly decrease the overall efficiency of the solar to chemical energy conversion .…”