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13 pages, 2277 KiB

Open AccessArticle

Single-Step Process for Titanium Surface Micro- and Nano-Structuring and In Situ Silver Nanoparticles Formation by Ultra-Short Laser Patterning

by Dante Maria Aceti, Emil Filipov, Liliya Angelova, Lamborghini Sotelo, Tommaso Fontanot, Peyman Yousefi, Silke Christiansen, Gerd Leuchs, Stanislav Stanimirov, Anton Trifonov, Ivan Buchvarov and Albena Daskalova

Materials 2022, 15(13), 4670; https://doi.org/10.3390/ma15134670 - 3 Jul 2022

Cited by 2 | Viewed by 2706

Abstract

Ultra-short laser (USL)-induced surface structuring combined with nanoparticles synthesis by multiphoton photoreduction represents a novel single-step approach for commercially pure titanium (cp-Ti) surface enhancement. Such a combination leads to the formation of distinct topographical features covered by nanoparticles. The USL processing of cp-Ti in an aqueous solution of silver nitrate (AgNO₃) induces the formation of micron-sized spikes surmounted by silver nanoparticles (AgNPs). The proposed approach combines the structuring and oxidation of the Ti surface and the synthesis of AgNPs in a one-step process, without the use of additional chemicals or a complex apparatus. Such a process is easy to implement, versatile and sustainable compared to alternative methodologies capable of obtaining comparable results. Antimicrobial surfaces on medical devices (e.g., surgical tools or implants), for which titanium is widely used, can be realized due to the simultaneous presence of AgNPs and micro/nano-structured surface topography. The processed surfaces were examined by means of a scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and Raman spectroscopy. The surface morphology and the oxidation, quality and quantity of AgNPs were analyzed in relation to process parameters (laser scanning speed and AgNO₃ concentration), as well as the effect of AgNPs on the Raman signal of Titanium oxide. Full article

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16 pages, 3280 KiB

Open AccessFeature PaperArticle

Photocatalytic Reduction of Nitrates and Combined Photodegradation with Ammonium

by Francesco Conte, Veronica Pellegatta, Alessandro Di Michele, Gianguido Ramis and Ilenia Rossetti

Catalysts 2022, 12(3), 321; https://doi.org/10.3390/catal12030321 - 11 Mar 2022

Cited by 3 | Viewed by 2770

Abstract

Bare titania and metal-promoted TiO₂ catalysts were employed in the treatment of nitrates, which are ubiquitous pollutants of wastewater. The results show that the process can be carried out under visible light (from a white light LED lamp) and, in the best case, 23.5% conversion of nitrate was obtained over 4 h with full selectivity towards N₂ by employing 0.1 mol% Ag/TiO₂ prepared by flame spray pyrolysis. Moreover, the performance was worse when testing the same catalysts with tap water (11.3% conversion), due to the more complex composition of the matrix. Finally, it was found that photoreduction of nitrate can be effectively performed in combination with photo-oxidation of ammonium without loss in the activity, opening up the possibility of treating highly polluted wastewater with a single process. The latter treatment employs the two contaminants simultaneously as electron and holes scavengers, with very good selectivity, in a completely new process that we may call Photo-Selective Catalytic Reduction (Photo-SCR). Full article

(This article belongs to the Special Issue 10th Anniversary of Catalysts—Feature Papers in Photocatalysis)

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15 pages, 3809 KiB

Open AccessArticle

Photocatalytic Reduction of CO₂ over Iron-Modified g-C₃N₄ Photocatalysts

by Miroslava Edelmannová, Martin Reli, Kamila Kočí, Ilias Papailias, Nadia Todorova, Tatiana Giannakopoulou, Panagiotis Dallas, Eamonn Devlin, Nikolaos Ioannidis and Christos Trapalis

Photochem 2021, 1(3), 462-476; https://doi.org/10.3390/photochem1030030 - 13 Nov 2021

Cited by 4 | Viewed by 2845

Abstract

Pure g-C₃N₄ sample was prepared by thermal treatment of melamine at 520 °C, and iron-modified samples (0.1, 0.3 and 1.1 wt.%) were prepared by mixing g-C₃N₄ with iron nitrate and calcination at 520 °C. The photocatalytic activity of the prepared materials was investigated based on the photocatalytic reduction of CO₂, which was conducted in a homemade batch reactor that had been irradiated from the top using a 365 nm Hg lamp. The photocatalyst with the lowest amount of iron ions exhibited an extraordinary methane and hydrogen evolution in comparison with the pure g-C₃N₄ and g-C₃N₄ with higher iron amounts. A higher amount of iron ions was not a beneficial for CO₂ photoreduction because the iron ions consumed too many photogenerated electrons and generated hydroxyl radicals, which oxidized organic products from the CO₂ reduction. It is clear that there are numerous reactions that occur simultaneously during the photocatalytic process, with several of them competing with CO₂ reduction. Full article

(This article belongs to the Special Issue Feature Papers in Photochemistry)

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13 pages, 3051 KiB

Open AccessEditor’s ChoiceArticle

Novel Photocatalytic NH₃ Synthesis by NO₃⁻ Reduction over CuAg/TiO₂

by Ryota Kato, Mai Furukawa, Ikki Tateishi, Hideyuki Katsumata and Satoshi Kaneco

ChemEngineering 2019, 3(2), 49; https://doi.org/10.3390/chemengineering3020049 - 8 May 2019

Cited by 13 | Viewed by 5513

Abstract

The highly effective reaction system was investigated for the photocatalytic ammonia synthesis from the reduction of nitrate ions by using the semiconductor photocatalyst, Cu and Ag doped on TiO₂ (CuAg/TiO₂) at room temperature under UV light irradiation (max. 352 nm). In this study, CuAg/TiO₂ gave the high efficiency and the selectivity for the ammonia synthesis by the photoreduction of nitrate in the presence of methanol as a hole scavenger. For the evaluation of the photocatalytic activity over CuAg/TiO₂, various TiO₂ samples, such as standard TiO₂, Cu/TiO₂, and Ag/TiO₂, were evaluated in the same procedure. The chemical properties were investigated by XRD, TEM, XPS, PL, and DRS. We examined the optimum conditions for the experimental factors and the important issues, including the effect of the molar ratio of Cu and Ag onto TiO₂, the optimization of the CuAg amount loaded on TiO₂, the influence of the loading amount of the catalyst on the reduction of nitrate ions, the exploration of the optimum hole scavenger, and the reusability of the optimum photocatalyst. The very efficient conversion of nitrate ions (95%) and the highest selectivity (86%) were achieved in the reaction with the optimum conditions. Here, we reported the process that nitrate ions can efficiently be reduced, and ammonia can be selectively synthesized over CuAg/TiO₂. Full article

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