Structural, Optical and Electronic Properties of Photocatalysts Containing Metal Oxide Nanostructures

A special issue of Catalysts (ISSN 2073-4344). This special issue belongs to the section "Photocatalysis".

Deadline for manuscript submissions: closed (30 June 2022) | Viewed by 12330

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CENIMAT|i3N, Department of Materials Science, School of Science and Technology, NOVA University Lisbon, 2829-516 Caparica, Portugal
Interests: material characterization; production and structural characterization of oxide-based thin films; oxide-based nanostructures; solution synthesis routes; microwave synthesis; photocatalysis; sensors
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Special Issue Information

Dear Colleagues,

The design of photocatalysts takes into consideration way to achieve enhanced chemical stability and high surface area together with improved microstructure, a band gap suitable for the incident light source, and reusability characteristics. Metal oxides are largely investigated for use as photocatalysts, where several metal oxide materials have been reported in recent years. The most investigated examples are centered on being low cost, nontoxic, abundant, biocompatible, and highly stable and capable of generating charge carriers when exposed to radiation. Zinc oxide (ZnO), titanium dioxide (TiO2), tungsten oxide (WO3), copper oxide (CuO and Cu2O), nickel oxide (NiO), tin oxide (SnO and SnO2) have all these characteristics, and most can be easily produced.

The idea of growing metal oxide nanostructures on flexible substrates has been growing exponentially, and cellulose-based substrates have begun to appear as an interesting option, given their flexibility, inexpensiveness, light weight, low cost, environmentally friendly properties, and ease of handling. Hence, by integrating these photocatalytic nanostructures into paper substrates, the concept of photocatalytic paper is attained.

The present Special Issue of Catalysts will focus on the key features of ZnO, TiO2, WO3, NiO, and copper- and tin-based oxide nanostructures in addition to the growth of such nanostructures on cellulose-based substrates and their photocatalytic activity under UV, visible, and solar radiation. The photocatalysts can be employed for photocatalytic water splitting, CO2 reduction, and environmental remediation. The emphasis will be on the complete structural, optical, and electronic characterization of these nanostructures and the produced photocatalytic paper, closely linked to the final photocatalytic activity, with an overview on recent advances in the field. Also of interest to this Special Issue is the growth of metal oxides using chemical synthesis routes in which their environmentally friendly and low-cost characteristics are maintained.

Prof. Dr. Daniela Nunes
Guest Editor

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Keywords

  • Photocatalytic cellulose-based materials
  • Nanostructured metal oxide nanostructures (ZnO, TiO2, WO3, NiO, copper- and tin-based oxide materials)
  • Structural, optical, and electronic characterization
  • Low-cost and innovative production routes
  • Photocatalytic water splitting
  • CO2 reduction
  • environmental remediation

Published Papers (3 papers)

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Research

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21 pages, 6063 KiB  
Article
Synthesis, Structure, and Photocatalytic Activity of TiO2-Montmorillonite Composites
by Yonghui Zhang, Baoji Miao, Qiuling Chen, Zhiming Bai, Yange Cao and Basandorj Davaa
Catalysts 2022, 12(5), 486; https://doi.org/10.3390/catal12050486 - 26 Apr 2022
Cited by 12 | Viewed by 2043
Abstract
In the present study, TiO2-montmorillonite (MMT) composites were synthesized hydrothermally under variable conditions, including the TiO2/MMT mass ratio, reaction pH, reaction temperature, and dwelling time. These samples were determined by X-ray photoelectron spectrometry (XPS), ultraviolet–visible spectroscopy% (UV-Vis DRS), electrochemical [...] Read more.
In the present study, TiO2-montmorillonite (MMT) composites were synthesized hydrothermally under variable conditions, including the TiO2/MMT mass ratio, reaction pH, reaction temperature, and dwelling time. These samples were determined by X-ray photoelectron spectrometry (XPS), ultraviolet–visible spectroscopy% (UV-Vis DRS), electrochemical impedance spectroscopy (EIS), transient photocurrent responses, photoluminescence (PL) spectra, electron paramagnetic resonance (EPR), and N2 adsorption–desorption isotherms. The photocatalytic activity was evaluated as the ability to promote the visible-light-driven degradation of 30 mg/L of aqueous methylene blue, which was maximized for the composite with a TiO2 mass ratio of 30 wt% prepared at a pH of 6, a reaction temperature of 160 °C, and a dwelling time of 24 h (denoted as 30%-TM), which achieved a methylene blue removal efficiency of 95.6%, which was 4.9 times higher than that of pure TiO2. The unit cell volume and crystallite size of 30%-TM were 92.43 Å3 and 9.28 nm, respectively, with a relatively uniform distribution of TiO2 particles on the MMT’s surface. In addition, 30%-TM had a large specific surface area, a strong light absorption capacity, and a high Ti3+ content among the studied catalysts. Thus, the present study provides a basis for the synthesis of composites with controlled structures. Full article
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Review

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56 pages, 15253 KiB  
Review
Cerium-, Europium- and Erbium-Modified ZnO and ZrO2 for Photocatalytic Water Treatment Applications: A Review
by Elisa Gaggero, Paola Calza, Erik Cerrato and Maria Cristina Paganini
Catalysts 2021, 11(12), 1520; https://doi.org/10.3390/catal11121520 - 14 Dec 2021
Cited by 12 | Viewed by 3073
Abstract
In the last decades photocatalysis has become one of the most employed technologies for the implementation of the so-called Advanced Oxidation Processes (AOPs) for the removal of harmful pollutants from wastewaters. The materials identified as the best photocatalysts are transition metal oxides, in [...] Read more.
In the last decades photocatalysis has become one of the most employed technologies for the implementation of the so-called Advanced Oxidation Processes (AOPs) for the removal of harmful pollutants from wastewaters. The materials identified as the best photocatalysts are transition metal oxides, in which the band structure allows charge carrier separation upon solar irradiation. The photoinduced charge carrier can thus cause oxidative and reductive redox reactions at the surface, inducing the formation of the radical species able to initiate the AOPs. Despite the great advantages of this process (non-toxic, cheap and environmentally clean), the main drawback lies in the fact that the most efficient semiconductors are only able to absorb UV irradiation, which accounts for only 5% of the total solar irradiation at the Earth’s surface and not enough to generate the required amount of electron-hole pairs. On the other hand, many efforts have been devoted to the sensitization of wide band gap transition metal oxides to visible light, which represents a higher percentage (almost 45%) in the solar electromagnetic spectrum. Among all the strategies to sensitize transition metal oxides to visible irradiation, doping with lanthanides has been less explored. In this regard, lanthanides offer a unique electronic configuration, consisting in 4f orbitals shielded by a 5s5p external shell. This occurrence, coupled with the different occupation of the localized 4f orbitals would provide an astounding opportunity to tune these materials’ properties. In this review we will focus in depth on the modification of two promising photocatalytic transition metal oxides, namely ZnO and ZrO2, with cerium, europium and erbium atoms. The aim of the work is to provide a comprehensive overview of the influence of lanthanides on the structural, optical and electronic properties of the modified materials, emphasizing the effect of the different 4f orbital occupation in the three considered doping atoms. Moreover, a large portion of the discussion will be devoted to the structural-properties relationships evidencing the improved light absorption working mechanism of each system and the resulting enhanced photocatalytic performance in the abatement of contaminants in aqueous environments. Full article
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30 pages, 7540 KiB  
Review
Metal Oxide-Based Photocatalytic Paper: A Green Alternative for Environmental Remediation
by Daniela Nunes, Ana Pimentel, Rita Branquinho, Elvira Fortunato and Rodrigo Martins
Catalysts 2021, 11(4), 504; https://doi.org/10.3390/catal11040504 - 16 Apr 2021
Cited by 42 | Viewed by 6410
Abstract
The interest in advanced photocatalytic technologies with metal oxide-based nanomaterials has been growing exponentially over the years due to their green and sustainable characteristics. Photocatalysis has been employed in several applications ranging from the degradation of pollutants to water splitting, CO2 and [...] Read more.
The interest in advanced photocatalytic technologies with metal oxide-based nanomaterials has been growing exponentially over the years due to their green and sustainable characteristics. Photocatalysis has been employed in several applications ranging from the degradation of pollutants to water splitting, CO2 and N2 reductions, and microorganism inactivation. However, to maintain its eco-friendly aspect, new solutions must be identified to ensure sustainability. One alternative is creating an enhanced photocatalytic paper by introducing cellulose-based materials to the process. Paper can participate as a substrate for the metal oxides, but it can also form composites or membranes, and it adds a valuable contribution as it is environmentally friendly, low-cost, flexible, recyclable, lightweight, and earth abundant. In term of photocatalysts, the use of metal oxides is widely spread, mostly since these materials display enhanced photocatalytic activities, allied to their chemical stability, non-toxicity, and earth abundance, despite being inexpensive and compatible with low-cost wet-chemical synthesis routes. This manuscript extensively reviews the recent developments of using photocatalytic papers with nanostructured metal oxides for environmental remediation. It focuses on titanium dioxide (TiO2) and zinc oxide (ZnO) in the form of nanostructures or thin films. It discusses the main characteristics of metal oxides and correlates them to their photocatalytic activity. The role of cellulose-based materials on the systems’ photocatalytic performance is extensively discussed, and the future perspective for photocatalytic papers is highlighted. Full article
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