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Novel Photoactive Materials

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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Optical and Photonic Materials".

Deadline for manuscript submissions: closed (30 September 2018) | Viewed by 42506

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Prof. Dr. Maria Vittoria Diamanti

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Department of Chemistry, Materials and Chemical Engineering "Giulio Natta", Politecnico di Milano, Via Mancinelli 7, 20131 Milan, Italy
Interests: titanium dioxide; titanium anodizing: anodic oxidation, plasma electrolytic oxidation, TiO₂ nanotubes; TiO₂ coatings for photocatalysis, self-cleaning, corrosion resistance; self-cleaning materials for the built environment; interference colors in thin films
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Dear Colleagues,

Photoactivity represents the ability of a material, generally speaking a semiconductor, to become active when interacting with light. It can be declined in many ways, and several functionalities arising from this behavior of materials can be exploited, all leading to positive repercussions on our environment. There are three main classes of effects of photoactivity on our everyday life, all of which have been deeply investigated in the last few decades, allowing to develop more and more efficient materials and devices:

Energy production as a consequence of sunlight absorption, which is the principle of photovoltaic devices of all generations, be them silicon based, dye sensitized solar cells or thin films;
Environmental cleanup as a result of photocatalytic degradation of pollutants, both in gas phase and in liquid phase, which is currently exploited in air purification devices and water remediation reactors;
Cleaner and clearer surfaces thanks to photoinduced superhydrophilicity and related self-cleaning effects, which find relevant applications in building materials due to their lower requirements for maintenance and potentially higher durability.

All of them share a common point, that is, the interaction of a material with light, although many different materials are taken into account depending on the effect desired—from elemental semiconductors like silicon, to more complex compounds like CdTe or GaAs, to metal oxides like TiO₂ and ZnO. Given the broadness of the field, a huge number of works fall within this topic, and new areas of discovery are constantly explored.

You are all invited to submit a manuscript for this Special Issue, in the form of research papers, communications, or reviews.

Assoc. Prof. Maria Vittoria Diamanti

Guest Editor

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Keywords

photocatalysis
photovoltaics
self-cleaning
superhydrophilicity
semiconductor
metal oxide

Published Papers (12 papers)

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Editorial

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3 pages, 172 KiB

Open AccessEditorial

Special Issue: Novel Photoactive Materials

by Maria Vittoria Diamanti

Materials 2018, 11(12), 2553; https://doi.org/10.3390/ma11122553 - 15 Dec 2018

Cited by 3 | Viewed by 2007

Abstract

Photoactivity represents the ability of a material to activate when interacting with light. It can be declined in many ways, and several functionalities arising from this behavior of materials can be exploited, all leading to positive repercussions on our environment. There are several classes of effects of photoactivity, all of which have been deeply investigated in the last few decades, allowing researchers to develop more and more efficient materials and devices. The special issue “Novel Photoactive Materials” has been proposed as a means to present recent developments in the field; for this reason the articles included touch different aspects of photoactivity, from photocatalysis to photovoltaics to light emitting materials, as highlighted in this editorial. Full article

(This article belongs to the Special Issue Novel Photoactive Materials)

Research

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19 pages, 2347 KiB

Open AccessArticle

Stone/Coating Interaction and Durability of Si-Based Photocatalytic Nanocomposites Applied to Porous Lithotypes

by Marco Roveri, Francesca Gherardi, Luigi Brambilla, Chiara Castiglioni and Lucia Toniolo

Materials 2018, 11(11), 2289; https://doi.org/10.3390/ma11112289 - 15 Nov 2018

Cited by 10 | Viewed by 2360

Abstract

The use of hybrid nanocoatings for the protection of natural stones has received increasing attention over the last years. However, the interaction of these materials with stones and, in particular, its modification resulting from the blending of nanoparticles and matrices, are yet little explored. In this work, the interaction of two nanocomposite coatings (based on alkylalkoxysilane matrices and TiO₂ nanoparticles in water and 2-propanol) with two different porous stones is examined in detail by comparing their absorption behaviour and protection performance with those of the respective TiO₂-free matrices. It is shown that the protective effectiveness of both matrices is not negatively affected by the presence of TiO₂, as the desired water barrier effect is retained, while a significant photocatalytic activity is achieved. The addition of titania leads to a partial aggregation of the water-based matrix and accordingly reduces the product penetration into stones. On the positive side, a chemical interaction between titania and this matrix is observed, probably resulting in a greater stability of nanoparticles inside the protective coating. Moreover, although an effect of TiO₂ on the chemical stability of matrices is observed upon UV light exposure, the protective performance of coatings is substantially maintained after ageing, while the interaction between matrices and nanoparticles results in a good retention of the latter upon in-lab simulated rain wash-out. Full article

(This article belongs to the Special Issue Novel Photoactive Materials)

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20 pages, 5419 KiB

Open AccessFeature PaperArticle

Photoactive ZnO Materials for Solar Light-Induced Cu_xO-ZnO Catalyst Preparation

by Magdalena Brzezińska, Patricia García-Muñoz, Agnieszka M. Ruppert and Nicolas Keller

Materials 2018, 11(11), 2260; https://doi.org/10.3390/ma11112260 - 13 Nov 2018

Cited by 16 | Viewed by 3222

Abstract

In this work, the solar light-induced redox photoactivity of ZnO semiconductor material was used to prepare Cu_xO-ZnO composite catalysts at room temperature with a control of the chemical state of the copper oxide phase. Cu₂^(I)O-ZnO and Cu^(II)O-ZnO composite catalysts were prepared by using Cu(acac)₂ in tetrahydrofuran-water and Cu(NO₃)₂ in water as metallic precursor, respectively. Prior to the implementation of the photon-assisted synthesis method, the most efficient photoactive ZnO material was selected from among different ZnO materials prepared by the low temperature polyol and precipitation methods with carbonates and carbamates as precipitation agents. The photocatalytic degradation of the 4-chlorophenol compound in water under simulated solar light was taken as a model reaction. The ZnO support materials were characterized by X-ray diffraction (XRD), surface area and porosimetry measurements, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and the synthesis method strongly influenced their photoactivity in terms of 4-chlorophenol degradation and of total organic carbon removal. The most photoactive ZnO material was prepared by precipitation with carbonates and calcined at 300 °C, benefitting from a high specific surface area and a small mean crystallite size for achieving a complete 4-chlorophenol mineralization within 70 min of reaction, with minimum Zn²⁺ released to the solution. Besides thermal catalysis applications, this work has opened a new route for the facile synthesis of Cu₂O-ZnO heterojunction photocatalysts that could take place under solar light of the heterojunction built between the p-type semi-conductor Cu₂O with direct visible light band gap and the ZnO semiconductor phase. Full article

(This article belongs to the Special Issue Novel Photoactive Materials)

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17 pages, 2550 KiB

Open AccessArticle

Tetranuclear Oxo-Titanium Clusters with Different Carboxylate Aromatic Ligands: Optical Properties, DFT Calculations, and Photoactivity

by Maciej Janek, Aleksandra Radtke, Tadeusz M. Muzioł, Maria Jerzykiewicz and Piotr Piszczek

Materials 2018, 11(9), 1661; https://doi.org/10.3390/ma11091661 - 08 Sep 2018

Cited by 16 | Viewed by 3886

Abstract

Titanium(IV) oxo-clusters of the general formula (Ti₄O₂(OⁱBu)₁₀(O₂CR’)₂) (R’ = C₁₃H₉ (1), PhCl (2), PhNO₂ (3)) were studied in order to estimate [...] Read more.

Titanium(IV) oxo-clusters of the general formula (Ti₄O₂(OⁱBu)₁₀(O₂CR’)₂) (R’ = C₁₃H₉ (1), PhCl (2), PhNO₂ (3)) were studied in order to estimate their potential photoactivity. The structure of the resulting tetranuclear Ti(IV) oxo-complexes was then determined via single crystal X-ray diffraction, infrared and Raman spectroscopy, and electron spin resonance (ESR). An analysis of diffuse reflectance spectra (DRS) allowed for the assessment of band gap values of (1)–(3) microcrystalline samples complexes. The use of different carboxylate ligands allowed the band gap of tetranuclear Ti(IV) oxo-clusters to be modulated in the range of 3.6 eV–2.5 eV. Density functional theory (DFT) methods were used to explain the influence of substitutes on band gap and optical activity. Dispersion of (1)–(3) microcrystals in the poly(methyl methacrylate) (PMMA) matrixes enabled the formation of composite materials for which the potential photocatalytic activity was estimated through the study on methylene blue (MB) photodegradation processes in the presence of UV light. The results obtained revealed a significant influence of carboxylate ligands functionalization on the photoactivity of synthesized tetranuclear Ti(IV) oxo-complexes. Full article

(This article belongs to the Special Issue Novel Photoactive Materials)

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11 pages, 2126 KiB

Open AccessArticle

First-Principles Investigation on the Electronic and Mechanical Properties of Cs-Doped CH₃NH₃PbI₃

by Dongyan Liu, Shanshan Li, Fang Bian and Xiangying Meng

Materials 2018, 11(7), 1141; https://doi.org/10.3390/ma11071141 - 05 Jul 2018

Cited by 21 | Viewed by 3726

Abstract

Methylammonium lead iodide, CH₃NH₃PbI₃, is currently a front-runner as light absorber in hybrid solar cells. Despite the high conversion efficiency, the stability of CH₃NH₃PbI₃ is still a major obstacle for commercialization application. In this work, the geometry, electronic structure, thermodynamic, and mechanical property of pure and Cs-doped CH₃NH₃PbI₃ have been systematically studied by first-principles calculations within the framework of the density functional theory (DFT). Our studies suggest that the (CH₃NH₃)⁺ organic group takes a random orientation in perovskite lattice due to the minor difference of orientation energy. However, the local ordered arrangement of CH₃NH₃⁺ is energetic favorable, which causes the formation of electronic dipole domain. The band edge states of pure and Cs-doped CH₃NH₃PbI₃ are determined by (PbI₆)⁻ group, while A-site (CH₃NH₃)⁺ or Cs⁺ influences the structural stability and electronic level through Jahn–Teller effect. It has been demonstrated that a suitable concentration of Cs can enhance both thermodynamic and mechanical stability of CH₃NH₃PbI₃ without deteriorating the conversion efficiency. Accordingly, this work clarifies the nature of electronic and mechanical properties of Cs-doped CH₃NH₃PbI₃, and is conducive to the future design of high efficiency and stable hybrid perovskite photovoltaic materials. Full article

(This article belongs to the Special Issue Novel Photoactive Materials)

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17 pages, 3760 KiB

Open AccessArticle

New Insights on the Photodegradation of Caffeine in the Presence of Bio-Based Substances-Magnetic Iron Oxide Hybrid Nanomaterials

by Davide Palma, Alessandra Bianco Prevot, Marcello Brigante, Debora Fabbri, Giuliana Magnacca, Claire Richard, Gilles Mailhot and Roberto Nisticò

Materials 2018, 11(7), 1084; https://doi.org/10.3390/ma11071084 - 26 Jun 2018

Cited by 32 | Viewed by 4000

Abstract

The exploitation of organic waste as a source of bio-based substances to be used in environmental applications is gaining increasing interest. In the present research, compost-derived bio-based substances (BBS-Cs) were used to prepare hybrid magnetic nanoparticles (HMNPs) to be tested as an auxiliary in advanced oxidation processes. Hybrid magnetic nanoparticles can be indeed recovered at the end of the treatment and re-used in further water purification cycles. The research aimed to give new insights on the photodegradation of caffeine, chosen as marker of anthropogenic pollution in natural waters, and representative of the contaminants of emerging concern (CECs). Hybrid magnetic nanoparticles were synthetized starting from Fe(II) and Fe(III) salts and BBS-C aqueous solution, in alkali medium, via co-precipitation. Hybrid magnetic nanoparticles were characterized via X-ray diffraction (XRD), thermo-gravimetric analysis (TGA) and Fourier transform infrared (FTIR) spectroscopy. The effect of pH, added hydrogen peroxide, and dissolved oxygen on caffeine photodegradation in the presence of HMNPs was assessed. The results allow for the hypothesis that caffeine abatement can be obtained in the presence of HMNPs and hydrogen peroxide through a heterogeneous photo-Fenton mechanism. The role of hydroxyl radicals in the process was assessed examining the effect of a selective hydroxyl radical scavenger on the caffeine degradation kinetic. Full article

(This article belongs to the Special Issue Novel Photoactive Materials)

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13 pages, 3757 KiB

Open AccessFeature PaperArticle

Understanding the Influence of Interface Morphology on the Performance of Perovskite Solar Cells

by Manuel Salado, Laura Calió, Lidia Contreras-Bernal, Jesus Idígoras, Juan Antonio Anta, Shahzada Ahmad and Samrana Kazim

Materials 2018, 11(7), 1073; https://doi.org/10.3390/ma11071073 - 25 Jun 2018

Cited by 17 | Viewed by 3835

Abstract

In recent years, organo-halide perovskite solar cells have garnered a surge of interest due to their high performance and low-cost fabrication processing. Owing to the multilayer architecture of perovskite solar cells, interface not only has a pivotal role to play in performance, but also influences long-term stability. Here we have employed diverse morphologies of electron selective layer (ESL) to elucidate charge extraction behavior in perovskite solar cells. The TiO₂ mesoporous structure (three-dimensional) having varied thickness, and nanocolumns (1-dimensional) with tunable length were employed. We found that a TiO₂ electron selective layer with thickness of about c.a. 100 nm, irrespective of its microstructure, was optimal for efficient charge extraction. Furthermore, by employing impedance spectroscopy at different excitation wavelengths, we studied the nature of recombination and its dependence on the charge generation profile, and results showed that, irrespective of the wavelength region, the fresh devices do not possess any preferential recombination site, and recombination process is governed by the bulk of the perovskite layer. Moreover, depending on the type of ESL, a different recombination mechanism was observed that influences the final behavior of the devices. Full article

(This article belongs to the Special Issue Novel Photoactive Materials)

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9 pages, 2618 KiB

Open AccessArticle

Sol-Gel Hydrothermal Synthesis and Visible Light Photocatalytic Degradation Performance of Fe/N Codoped TiO₂ Catalysts

by Hsu-Hui Cheng, Shiao-Shing Chen, Sih-Yin Yang, Hui-Ming Liu and Kuang-Shan Lin

Materials 2018, 11(6), 939; https://doi.org/10.3390/ma11060939 - 03 Jun 2018

Cited by 29 | Viewed by 3829

Abstract

Using Ti(OC₄H₉)₄ as a precursor, Fe(NO₃)₃⋅9H₂O as the source of iron, and NH₄NO₃ as the source of nitrogen, an Fe/N codoped TiO₂ catalyst was prepared using a sol-gel [...] Read more.

Using Ti(OC₄H₉)₄ as a precursor, Fe(NO₃)₃⋅9H₂O as the source of iron, and NH₄NO₃ as the source of nitrogen, an Fe/N codoped TiO₂ catalyst was prepared using a sol-gel hydrothermal method. The as-prepared powders were characterized using X-ray powder diffraction, electron spectroscopy for chemical analysis, Fourier-transform infrared spectroscopy, and ultraviolet-visible spectrophotometry. Fe and N codoping resulted in decreased crystallite size and increased specific surface area. Results of the photocatalytic degradation of acid orange 7 (AO7) in a continuous-flow fluidized-bed reactor indicated that the maximum decolorization (more than 90%) of AO7 occurred with the Fe/N-TiO₂ catalyst (dosage of 20 g/L) when a combination of visible light irradiation for 10 h HRT (hydraulic retention time), and a heterogeneous system was used. The AO7 degradation efficiency was considerably improved by increasing the hydraulic retention time from 2.5 to 10 h or by reducing the initial AO7 concentration from 300 to 100 mg/L. The reaction rate increased with the light intensity and the maximum value occurred at 35 mW/cm²; moreover, the efficiency of the AO7 degradation increased when the pH decreased with maximum efficiency at pH 3. Full article

(This article belongs to the Special Issue Novel Photoactive Materials)

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12 pages, 7033 KiB

Open AccessArticle

Synthesis and Broadband Spectra Photocatalytic Properties of Bi₂O₂(CO₃)_1−xS_x

by Junping Ding, Huanchun Wang, Haomin Xu, Lina Qiao, Yidong Luo, Yuanhua Lin and Cewen Nan

Materials 2018, 11(5), 791; https://doi.org/10.3390/ma11050791 - 14 May 2018

Cited by 7 | Viewed by 3380

Abstract

High efficiency photocatalyst Bi₂O₂(CO₃)_1−xS_x was synthesized conveniently with chemical bath precipitation using Bi₂O₂CO₃ as the precursor. The microstructures of the samples are systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS) and UV-Vis spectroscopy; the optical and photocatalytic properties are carefully tested as well. The content of S, which was tuned through the controlling of the precipitation process, was verified to have an intense effect over the photocatalytic properties. A nearly saturated S ratio and the best photocatalytic performance were observed in specimens with the most S content. Our study reveals that, with negligible influence of the morphology and crystal structure, Bi₂O₂(CO₃)_1−xS_x possessed a broadened optical absorption regionfromultraviolet to visible light, and enhanced photocatalytic activity in comparison to precursor Bi₂O₂CO₃ in photocatalytic degradation of Congo Red aqueous solution. Full article

(This article belongs to the Special Issue Novel Photoactive Materials)

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14 pages, 5432 KiB

Open AccessArticle

Facile Synthesis and Characterization of Ag₃PO₄ Microparticles for Degradation of Organic Dyestuffs under White-Light Light-Emitting-Diode Irradiation

by Chi-Shun Tseng, Tsunghsueh Wu and Yang-Wei Lin

Materials 2018, 11(5), 708; https://doi.org/10.3390/ma11050708 - 30 Apr 2018

Cited by 21 | Viewed by 3247

Abstract

This study demonstrated facile synthesis of silver phosphate (Ag₃PO₄) photocatalysts for the degradation of organic contaminants. Ag₃PO₄ microparticles from different concentrations of precursor, AgNO₃, were produced and characterized by scanning electron microscopy, powder X-ray diffraction, and UV–visible diffuse reflectance spectroscopy. Degradation rates of methylene blue (MB) and phenol were measured in the presence of microparticles under low-power white-light light-emitting-diode (LED) irradiation and the reaction rate followed pseudo-first-order kinetics. The prepared Ag₃PO₄ microparticles displayed considerably high photocatalytic activity (>99.8% degradation within 10 min). This can be attributed to the microparticles’ large surface area, the low recombination rate of electron–hole pairs and the higher charge separation efficiency. The practicality of the Ag₃PO₄ microparticles was validated by the degradation of MB, methyl red, acid blue 1 and rhodamine B under sunlight in environmental water samples, demonstrating the benefit of the high photocatalytic activity from Ag₃PO₄ microparticles. Full article

(This article belongs to the Special Issue Novel Photoactive Materials)

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14 pages, 31039 KiB

Open AccessFeature PaperArticle

Photocatalytic Activity of Nanotubular TiO₂ Films Obtained by Anodic Oxidation: A Comparison in Gas and Liquid Phase

by Beatriz Eugenia Sanabria Arenas, Alberto Strini, Luca Schiavi, Andrea Li Bassi, Valeria Russo, Barbara Del Curto, Maria Vittoria Diamanti and MariaPia Pedeferri

Materials 2018, 11(4), 488; https://doi.org/10.3390/ma11040488 - 24 Mar 2018

Cited by 13 | Viewed by 3723

Abstract

The availability of immobilized nanostructured photocatalysts is of great importance in the purification of both polluted air and liquids (e.g., industrial wastewaters). Metal-supported titanium dioxide films with nanotubular morphology and good photocatalytic efficiency in both environments can be produced by anodic oxidation, which avoids release of nanoscale materials in the environment. Here we evaluate the effect of different anodizing procedures on the photocatalytic activity of TiO₂ nanostructures in gas and liquid phases, in order to identify the most efficient and robust technique for the production of TiO₂ layers with different morphologies and high photocatalytic activity in both phases. Rhodamine B and toluene were used as model pollutants in the two media, respectively. It was found that the role of the anodizing electrolyte is particularly crucial, as it provides substantial differences in the oxide specific surface area: nanotubular structures show remarkably different activities, especially in gas phase degradation reactions, and within nanotubular structures, those produced by organic electrolytes lead to better photocatalytic activity in both conditions tested. Full article

(This article belongs to the Special Issue Novel Photoactive Materials)

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8 pages, 1916 KiB

Open AccessArticle

Growth and Brilliant Photo-Emission of Crystalline Hexagonal Column of Alq₃ Microwires

by Seokho Kim, Do Hyoung Kim, Jinho Choi, Hojin Lee, Sun-Young Kim, Jung Woon Park and Dong Hyuk Park

Materials 2018, 11(4), 472; https://doi.org/10.3390/ma11040472 - 22 Mar 2018

Cited by 14 | Viewed by 3597

Abstract

We report the growth and nanoscale luminescence characteristics of 8-hydroxyquinolinato aluminum (Alq₃) with a crystalline hexagonal column morphology. Pristine Alq₃ nanoparticles (NPs) were prepared using a conventional reprecipitation method. Crystal hexagonal columns of Alq₃ were grown by using a surfactant-assisted self-assembly technique as an adjunct to the aforementioned reprecipitation method. The formation and structural properties of the crystalline and non-crystalline Alq₃ NPs were analyzed with scanning electron microscopy and X-ray diffraction. The nanoscale photoluminescence (PL) characteristics and the luminescence color of the Alq₃ single NPs and their crystal microwires (MWs) were evaluated from color charge-coupled device images acquired using a high-resolution laser confocal microscope. In comparison with the Alq₃ NPs, the crystalline MWs exhibited a very bright and sharp emission. This enhanced and sharp emission from the crystalline Alq₃ single MWs originated from effective π-π stacking of the Alq₃ molecules due to strong interactions in the crystalline structure. Full article

(This article belongs to the Special Issue Novel Photoactive Materials)

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