Editorial

3 pages, 204 KiB

Open AccessEditorial

Nano-Photocatalytic Materials: Possibilities and Challenges

by José M. Doña-Rodríguez and Elisenda Pulido Melián

Nanomaterials 2021, 11(3), 688; https://doi.org/10.3390/nano11030688 - 09 Mar 2021

Cited by 9 | Viewed by 2280

Photocatalysis is one of the most promising processes within catalysis, due to its increasing potential and the possibility of its being combined with renewable solar energy [...] Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

Research

Jump to: Editorial, Review

16 pages, 3963 KiB

Open AccessArticle

Influence of Water on the Oxidation of NO on Pd/TiO₂ Photocatalysts

by M. J. Hernández Rodríguez, E. Pulido Melián, J. Araña, J. A. Navío, O. M. González Díaz, Dunia E. Santiago and J. M. Doña Rodríguez

Nanomaterials 2020, 10(12), 2354; https://doi.org/10.3390/nano10122354 - 27 Nov 2020

Cited by 6 | Viewed by 2091

Abstract

Two series of new photocatalysts were synthesized based on modification with Pd of the commercial P25 photocatalyst (EVONIK^®). Two techniques were employed to incorporate Pd nanoparticles on the P25 surface: photodeposition (series Pd-P) and impregnation (series Pd-I). Both series were characterized [...] Read more.

Two series of new photocatalysts were synthesized based on modification with Pd of the commercial P25 photocatalyst (EVONIK^®). Two techniques were employed to incorporate Pd nanoparticles on the P25 surface: photodeposition (series Pd-P) and impregnation (series Pd-I). Both series were characterized in depth using a variety of instrumental techniques: BET, DRS, XRD, XPS, TEM, FTIR and FESEM. The modified series exhibited a significant change in pore size distribution, but no differences compared to the original P25 with respect to crystalline phase ratio or particle size were observed. The Pd⁰ oxidation state was predominant in the Pd-P series, while the presence of the Pd²⁺ oxidation state was additionally observed in the Pd-I series. The photoactivity tests were performed in a continuous photoreactor with the photocatalysts deposited, by dip-coating, on borosilicate glass plates. A total of 500 ppb of NO was used as input flow at a volumetric flow rate of 1.2 L·min⁻¹, and different relative humidities from 0 to 65% were tested. The results obtained show that under UV-vis or Vis radiation, the presence of Pd nanoparticles favors NO removal independently of the Pd incorporation method employed and independently of the tested relative humidity conditions. This improvement seems to be related to the different interaction of the water with the surface of the photocatalysts in the presence or absence of Pd. It was found in the catalyst without Pd that disproportionation of NO₂ is favored through its reaction with water, with faster surface saturation. In contrast, in the catalysts with Pd, disproportionation took place through nitro-chelates and adsorbed NO₂ formed from the photocatalytic oxidation of the NO. This different mechanism explains the greater efficiency in NO_x removal in the catalysts with Pd. Comparing the two series of catalysts with Pd, Pd-P and Pd-I, greater activity of the Pd-P series was observed under both UV-vis and Vis radiation. It was shown that the Pd⁰ oxidation state is responsible for this greater activity as the Pd-I series improves its activity in successive cycles due to a reduction in Pd²⁺ species during the photoactivity tests. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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18 pages, 7595 KiB

Open AccessArticle

The Photocatalytic and Antibacterial Performance of Nitrogen-Doped TiO₂: Surface-Structure Dependence and Silver-Deposition Effect

by Abdul Wafi, Erzsébet Szabó-Bárdos, Ottó Horváth, Mihály Pósfai, Éva Makó, Tatjána Juzsakova and Orsolya Fónagy

Nanomaterials 2020, 10(11), 2261; https://doi.org/10.3390/nano10112261 - 15 Nov 2020

Cited by 12 | Viewed by 2798

Abstract

Catalysts for visible-light-driven oxidative cleaning processes and antibacterial applications (also in the dark) were developed. In order to extend the photoactivity of titanium dioxide into the visible region, nitrogen-doped TiO₂ catalysts with hollow and non-hollow structures were synthesized by co-precipitation (NT-A) and [...] Read more.

Catalysts for visible-light-driven oxidative cleaning processes and antibacterial applications (also in the dark) were developed. In order to extend the photoactivity of titanium dioxide into the visible region, nitrogen-doped TiO₂ catalysts with hollow and non-hollow structures were synthesized by co-precipitation (NT-A) and sol–gel (NT-U) methods, respectively. To increase their photocatalytic and antibacterial efficiencies, various amounts of silver were successfully loaded on the surfaces of these catalysts by using a facile photo-deposition technique. Their physical and chemical properties were evaluated by using scanning electron microscopy (SEM), transmission electron microscopy–energy dispersive X-ray spectroscopy (TEM–EDS), Brunauer–Emmett–Teller (BET) surface area, X-ray diffraction (XRD), and diffuse reflectance spectra (DRS). The photocatalytic performances of the synthesized catalysts were examined in coumarin and 1,4-hydroquinone solutions. The results showed that the hollow structure of NT-A played an important role in obtaining high specific surface area and appreciable photoactivity. In addition, Ag-loading on the surface of non-hollow structured NT-U could double the photocatalytic performance with an optimum Ag concentration of 10⁻⁶ mol g⁻¹, while a slight but monotonous decrease was caused in this respect for the hollow surface of NTA upon increasing Ag concentration. Comparing the catalysts with different structures regarding the photocatalytic performance, silverized non-hollow NT-U proved competitive with the hollow NT-A catalyst without Ag-loading for efficient visible-light-driven photocatalytic oxidative degradations. The former one, due to the silver nanoparticles on the catalyst surface, displayed an appreciable antibacterial activity, which was comparable to that of a reference material practically applied for disinfection in polymer coatings. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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19 pages, 11161 KiB

Open AccessArticle

Automobile Exhaust Removal Performance of Pervious Concrete with Nano TiO₂ under Photocatalysis

by Guobao Luo, Hanbing Liu, Wenjun Li and Xiang Lyu

Nanomaterials 2020, 10(10), 2088; https://doi.org/10.3390/nano10102088 - 21 Oct 2020

Cited by 19 | Viewed by 2494

Abstract

The urban environment is facing serious problems caused by automobile exhaust pollution, which has led to a great impact on human health and climate, and aroused widespread concern of the government and the public. Nano titanium dioxide (TiO₂), as a photocatalyst, [...] Read more.

The urban environment is facing serious problems caused by automobile exhaust pollution, which has led to a great impact on human health and climate, and aroused widespread concern of the government and the public. Nano titanium dioxide (TiO₂), as a photocatalyst, can be activated by ultraviolet irradiation and then form a strong REDOX potential on the surface of the nano TiO₂ particles. The REDOX potential can degrade the automobile exhaust, such as nitrogen oxides (NO_x) and hydrocarbons (HC). In this paper, a photocatalytic environmentally friendly pervious concrete (PEFPC) was manufactured by spraying nano TiO₂ on the surface of it and the photocatalytic performance of PEFPC was researched. The nano TiO₂ particle size, TiO₂ dosage, TiO₂ spraying amount, and dispersant dosage were selected as factors to investigate the efficiency of photocatalytic degradation of automobile exhaust by PEFPC. Moreover, the environmental scanning electron microscope (ESEM) was used to evaluate the distribution of nano TiO₂ on the surface of the pervious concrete, the distribution area of nano TiO₂ was obtained through Image-Pro Plus, and the area ratio of nano TiO₂ to the surface of the pervious concrete was calculated. The results showed that the recommended nano TiO₂ particle size is 25 nm. The optimum TiO₂ dosage was 10% and the optimum dispersant dosage was 5.0%. The photocatalytic performance of PEFPC was best when the TiO₂ spraying amount was 333.3 g/m². The change in the photocatalytic ratio of HC and NO_x is consistent with the distribution area of nano TiO₂ on the surface of the pervious concrete. In addition, the photocatalytic performance of PEFPC under two light sources (ultraviolet light and sunlight) was compared. The results indicated that both light sources were able to stimulate the photocatalytic performance of PEFPC. The research provided a reference for the evaluation of automobile exhaust removal performance of PEFPC. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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11 pages, 5846 KiB

Open AccessArticle

A β-cyclodextrin Modified Graphitic Carbon Nitride with Au Co-Catalyst for Efficient Photocatalytic Hydrogen Peroxide Production

by Guifu Zuo, Yuqian Zhang, Shanshan Liu, Zhaoliang Guo, Qiannan Zhao, Gopalan Saianand, Liwei Feng, Lijuan Li, Wangze Li, Ning Zhang, Xianguang Meng and Vellaisamy A. L. Roy

Nanomaterials 2020, 10(10), 1969; https://doi.org/10.3390/nano10101969 - 04 Oct 2020

Cited by 14 | Viewed by 3402

Abstract

Photocatalytic hydrogen peroxide (H₂O₂) production has attracted considerable attention as a renewable and environment-friendly method to replace other traditional production techniques. The performance of H₂O₂ production remains limited by the inertness of graphitic carbon nitride (CN) [...] Read more.

Photocatalytic hydrogen peroxide (H₂O₂) production has attracted considerable attention as a renewable and environment-friendly method to replace other traditional production techniques. The performance of H₂O₂ production remains limited by the inertness of graphitic carbon nitride (CN) towards the adsorption and activation of O₂. In this work, a photocatalyst comprising of β-cyclodextrin (β-CD)-modified CN with supporting Au co-catalyst (Au/β-CD-CN) has been utilized for effective H₂O₂ production under visible light irradiation. The static contact angle measurement suggested that β-CD modification increased the hydrophobicity of the CN photocatalyst as well as its affinity to oxygen gas, leading to an increase in H₂O₂ production. The rate of H₂O₂ production reached more than 0.1 mM/h under visible-light irradiation. The electron spin resonance spectra indicated that H₂O₂ was directly formed via a 2-electron oxygen reduction reaction (ORR) over the Au/β-CD-CN photocatalyst. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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14 pages, 3585 KiB

Open AccessArticle

Preparation of a g-C₃N₄/UiO-66-NH₂/CdS Photocatalyst with Enhanced Visible Light Photocatalytic Activity for Tetracycline Degradation

by Hao Zhang, Jialiang Li, Xianglei He and Bo Liu

Nanomaterials 2020, 10(9), 1824; https://doi.org/10.3390/nano10091824 - 12 Sep 2020

Cited by 20 | Viewed by 3645

Abstract

A combination of calcination and hydrothermal processing was used to prepare a g-C₃N₄/UiO-66-NH₂/CdS photocatalyst, and the degradation of tetracycline (TC) over this material was assessed. The photocatalytic performance of this nanocomposite was approximately 4.4 and 2.3 times [...] Read more.

A combination of calcination and hydrothermal processing was used to prepare a g-C₃N₄/UiO-66-NH₂/CdS photocatalyst, and the degradation of tetracycline (TC) over this material was assessed. The photocatalytic performance of this nanocomposite was approximately 4.4 and 2.3 times those of CdS and g-C₃N₄, respectively, and was found to be affected by the CdS loading amount, the pH of the reaction solution and the initial TC concentration. This catalyst also exhibited stable performance over four consecutive reaction cycles. The highly enhanced photoactivity of the g-C₃N₄/UiO-66-NH₂/CdS is attributed to the introduction of CdS, which widens the range over which the material absorbs visible light and inhibits the recombination of electron–hole pairs. The results of this study suggest further applications for this material in the treatment of contaminated wastewater powered by solar energy. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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18 pages, 3540 KiB

Open AccessArticle

Removal of As(III) from Water Using the Adsorptive and Photocatalytic Properties of Humic Acid-Coated Magnetite Nanoparticles

by Phuong Pham, Mamun Rashid, Yong Cai, Masafumi Yoshinaga, Dionysios D. Dionysiou and Kevin O’Shea

Nanomaterials 2020, 10(8), 1604; https://doi.org/10.3390/nano10081604 - 15 Aug 2020

Cited by 7 | Viewed by 2942

Abstract

The oxidation of highly toxic arsenite (As(III)) was studied using humic acid-coated magnetite nanoparticles (HA-MNP) as a photosensitizer. Detailed characterization of the HA-MNP was carried out before and after the photoinduced treatment of As(III) species. Upon irradiation of HA-MNP with 350 nm light, [...] Read more.

The oxidation of highly toxic arsenite (As(III)) was studied using humic acid-coated magnetite nanoparticles (HA-MNP) as a photosensitizer. Detailed characterization of the HA-MNP was carried out before and after the photoinduced treatment of As(III) species. Upon irradiation of HA-MNP with 350 nm light, a portion of the As(III) species was oxidized to arsenate (As(V)) and was nearly quantitatively removed from the aqueous solution. The separation of As(III) from the aqueous solution is primarily driven by the strong adsorption of As(III) onto the HA-MNP. As(III) removals of 40–90% were achieved within 60 min depending on the amount of HA-MNP. The generation of reactive oxygen species (•OH and ¹O₂) and the triplet excited state of HA-MNP (³HA-MNP*) was monitored and quantified during HA-MNP photolysis. The results indicate ³HA-MNP* and/or singlet oxygen (¹O₂) depending on the reaction conditions are responsible for converting As(III) to less toxic As(V). The formation of ³HA-MNP* was quantified using the electron transfer probe 2,4,6-trimethylphenol (TMP). The formation rate of ³HA-MNP* was 8.0 ± 0.6 × 10⁻⁹ M s⁻¹ at the TMP concentration of 50 µM and HA-MNP concentration of 1.0 g L⁻¹. The easy preparation, capacity for triplet excited state and singlet oxygen production, and magnetic separation suggest HA-MNP has potential to be a photosensitizer for the remediation of arsenic (As) and other pollutants susceptible to advanced oxidation. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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24 pages, 8691 KiB

Open AccessArticle

Assessing the Photocatalytic Degradation of Fluoroquinolone Norfloxacin by Mn:ZnS Quantum Dots: Kinetic Study, Degradation Pathway and Influencing Factors

by Jyoti Patel, Ajaya K. Singh and Sónia. A. C. Carabineiro

Nanomaterials 2020, 10(5), 964; https://doi.org/10.3390/nano10050964 - 18 May 2020

Cited by 38 | Viewed by 3477

Abstract

Norfloxacin (NOFX), a broadly used fluoroquinolone antibiotic, has been a subject of great concern in the past few years due to its undesirable effect on human beings and aquatic ecosystems. In this study, novel Mn doped ZnS (Mn:ZnS) quantum dots (QDs) were prepared [...] Read more.

Norfloxacin (NOFX), a broadly used fluoroquinolone antibiotic, has been a subject of great concern in the past few years due to its undesirable effect on human beings and aquatic ecosystems. In this study, novel Mn doped ZnS (Mn:ZnS) quantum dots (QDs) were prepared through a facile chemical precipitation method and used as photocatalysts for NOFX degradation. Prior to photodegradation experiments, morphological and optical parameters of the QDs were examined through transmission electron microscopy, scanning electron microscopy, energy dispersive X-ray analysis, Fourier transform infrared spectroscopy, ultraviolet-visible spectroscopy, fluorescence spectroscopy, Brunauer–Emmett–Teller analysis, and differential thermal and thermogravimetric analyses. Mn:ZnS QDs exhibited excellent properties of photodegradation, not only under UV irradiation but also in sunlight, which induced NOFX to photodegrade. The utmost photodegradation efficiency was obtained under optimal conditions (25 mL of NOFX, 15 mg/L, pH 10, 60 min UV irradiation, 60 mgs QDs), adopting first order kinetics. In addition, hydroxyl radicals produced by the conduction band electrons were found to be the primary reason dominating the transformation of NOFX in basic conditions, while holes, oxygen atoms, as well as the doped metal (Mn) enhanced the degradation. The QDs showed excellent reusability and stability in four repeated cycles. Finally, four different pathways were predicted, derived from the identified intermediates, with piperazinyl ring transformation being the primary one. It is expected that the synthesized Mn:ZnS QDs could be utilized as efficient photocatalytic materials for energy conversion and ecological remediation. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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18 pages, 3109 KiB

Open AccessArticle

Influence of Semiconductor Morphology on Photocatalytic Activity of Plasmonic Photocatalysts: Titanate Nanowires and Octahedral Anatase Nanoparticles

by Zhishun Wei, Maya Endo-Kimura, Kunlei Wang, Christophe Colbeau-Justin and Ewa Kowalska

Nanomaterials 2019, 9(10), 1447; https://doi.org/10.3390/nano9101447 - 11 Oct 2019

Cited by 16 | Viewed by 2593

Abstract

Octahedral anatase particles (OAP) with eight exposed and thermodynamically most stable (101) facets were prepared by an ultrasonication-hydrothermal (US-HT) reaction from potassium titanate nanowires (TNW). The precursor (TNW) and the product (OAP) of US-HT reaction were modified with nanoparticles of noble metals (Au, [...] Read more.

Octahedral anatase particles (OAP) with eight exposed and thermodynamically most stable (101) facets were prepared by an ultrasonication-hydrothermal (US-HT) reaction from potassium titanate nanowires (TNW). The precursor (TNW) and the product (OAP) of US-HT reaction were modified with nanoparticles of noble metals (Au, Ag or Pt) by photodeposition. Samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), scanning transmission electron microscopy (STEM) and time-resolved microwave conductivity (TRMC). The photocatalytic activity was investigated in three reaction systems, i.e., anaerobic dehydrogenation of methanol and oxidative decomposition of acetic acid under UV/vis irradiation, and oxidation of 2-propanol under vis irradiation. It was found that hydrogen liberation correlated with work function of metals, and thus the most active were platinum-modified samples. Photocatalytic activities of bare and modified OAP samples were much higher than those of TNW samples, probably due to anatase presence, higher crystallinity and electron mobility in faceted NPs. Interestingly, noble metals showed different influence on the activity depending on the semiconductor support, i.e., gold-modified TNW and platinum-modified OAP exhibited the highest activity for acetic acid decomposition, whereas silver- and gold-modified samples were the most active under vis irradiation, respectively. It is proposed that the form of noble metal (metallic vs. oxidized) as well as the morphology (well-organized vs. uncontrolled) have a critical effect on the overall photocatalytic performance. TRMC analysis confirmed that fast electron transfer to noble metal is a key factor for UV activity. It is proposed that the efficiency of plasmonic photocatalysis (under vis irradiation) depends on the oxidation form of metal (zero-valent preferable), photoabsorption properties (broad localized surface plasmon resonance (LSPR)), kind of metal (silver) and counteraction of “hot” electrons back transfer to noble metal NPs (by controlled morphology and high crystallinity). Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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12 pages, 3705 KiB

Open AccessArticle

Photocatalytic Activity of TiO₂ Nanofibers: The Surface Crystalline Phase Matters

by Hongnan Zhang, Ming Yu and Xiaohong Qin

Nanomaterials 2019, 9(4), 535; https://doi.org/10.3390/nano9040535 - 03 Apr 2019

Cited by 24 | Viewed by 3310

Abstract

The crystal phases and surface states of TiO₂ can intrinsically determine its performance in the applications of photocatalysis. Here, we prepared TiO₂ nanofibers with different crystal phase contents by electrospinning followed via calcination at different temperatures. The TiO₂ nanofibers were [...] Read more.

The crystal phases and surface states of TiO₂ can intrinsically determine its performance in the applications of photocatalysis. Here, we prepared TiO₂ nanofibers with different crystal phase contents by electrospinning followed via calcination at different temperatures. The TiO₂ nanofibers were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectrometry, transmission electron microscopy (TEM), and photocatalytic performance testing. The results showed that the phases of TiO₂ nanofibers were layered, that surface crystal phase transition rate was faster than that of internal layers contributed the difference in the ratio of anatase and rutile in the outer and inner layer of TiO₂ nanofibers. The TiO₂ nanofibers obtained at 575 °C had the best photocatalytic activity, taking only 25 min to degrade Rhodamine B. At 575 °C, the rutile content of the sample surface was about 80 wt.%, while the internal rutile content was only about 40 wt.%. Subsequently, we prepared two different structures of anatase–rutile core-shell TiO₂ nanofibers. The core-shell structure can be clearly seen by TEM characterization. The photocatalytic activity of two kinds of core-shell TiO₂ nanofibers was tested. The results showed that the photocatalytic activity was close to that of the pure phase TiO₂ nanofibers, which corresponded with the surface phase. This further proves that the photocatalytic activity of the material is mainly affected by its surface structure. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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13 pages, 4286 KiB

Open AccessArticle

Highly Hydrophilic TiO₂ Nanotubes Network by Alkaline Hydrothermal Method for Photocatalysis Degradation of Methyl Orange

by Jin Yang, Jun Du, Xiuyun Li, Yilin Liu, Chang Jiang, Wenqian Qi, Kai Zhang, Cheng Gong, Rui Li, Mei Luo and Hailong Peng

Nanomaterials 2019, 9(4), 526; https://doi.org/10.3390/nano9040526 - 03 Apr 2019

Cited by 34 | Viewed by 4755

Abstract

High-density and highly cross-coated anatase TiO₂ nanotubes networks have been successfully prepared on the surface of Ti foil by alkaline hydrothermal using NaOH and Ti foil as the precursors. The nanotubes networks were analyzed using X-ray diffraction (XRD), energy dispersive X-ray spectrometer [...] Read more.

High-density and highly cross-coated anatase TiO₂ nanotubes networks have been successfully prepared on the surface of Ti foil by alkaline hydrothermal using NaOH and Ti foil as the precursors. The nanotubes networks were analyzed using X-ray diffraction (XRD), energy dispersive X-ray spectrometer (EDX), transmission electron microscope (TEM), scanning electron microscopy (SEM), optical contact angle tester, and ultraviolet (UV) fluorescence spectrophotometer, respectively. The results showed that the nanotubes network with diameters of 30–50 nm were obtained on the Ti foil surface. The morphology of the nanotubes network possessed the three-dimensional network structure, The TiO₂ nanotubes network grew along the (101) direction of the tetragonal anatase crystal. The morphology and crystal phase of the TiO₂ nanotubes network were better at the conditions of NaOH concentration 7–10 mol/L and temperature 160–170 °C. The best contact angle of TiO₂ nanotubes network after UV-light irradition was only 5.1 ± 2.9°. Under the irradiation of mercury lamp, the nanotubes network exhibited excellent photocatalytic performance and the degradation ratio of methyl orange solution reached to 80.00 ± 2.33%. Thus, the anatase TiO₂ nanotubes network has great potential in applications for pollution photocatalytic degradation. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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11 pages, 2785 KiB

Open AccessArticle

Powder and Nanotubes Titania Modified by Dye Sensitization as Photocatalysts for the Organic Pollutants Elimination

by Julie J. Murcia, Elsa G. Ávila-Martínez, Hugo Rojas, Jairo Cubillos, Svetlana Ivanova, Anna Penkova and Oscar H. Laguna

Nanomaterials 2019, 9(4), 517; https://doi.org/10.3390/nano9040517 - 02 Apr 2019

Cited by 15 | Viewed by 3310

Abstract

In this study, titanium dioxide powder obtained by the sol-gel method and TiO₂ nanotubes, were prepared. In order to increase the TiO₂ photoactivity, the powders and nanotubes obtained were modified by dye sensitization treatment during the oxide synthesis. The sensitizers applied [...] Read more.

In this study, titanium dioxide powder obtained by the sol-gel method and TiO₂ nanotubes, were prepared. In order to increase the TiO₂ photoactivity, the powders and nanotubes obtained were modified by dye sensitization treatment during the oxide synthesis. The sensitizers applied were Quinizarin (Q) and Zinc protoporphyrin (P). The materials synthesized were extensively characterized and it was found that the dye sensitization treatment leads to modify the optical and surface properties of Titania. It was also found that the effectiveness of the dye-sensitized catalysts in the phenol and methyl orange (MO) photodegradation strongly depends on the dye sensitizer employed. Thus, the highest degradation rate for MO was obtained over the conventional Q-TiO₂ photocatalyst. In the case of the nanotubes series, the most effective photocatalyst in the MO degradation was based on TiO₂-nanotubes sensitized with the dye protoporfirin (ZnP). Selected catalysts were also tested in the phenol and MO photodegradation under visible light and it was observed that these samples are also active under this radiation. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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12 pages, 3466 KiB

Open AccessArticle

Microstructures and Photodegradation Performance toward Methylene Orange of Sputtering-Assisted Decoration of ZnFe₂O₄ Crystallites onto TiO₂ Nanorods

by Yuan-Chang Liang and Yen-Chen Liu

Nanomaterials 2019, 9(2), 205; https://doi.org/10.3390/nano9020205 - 05 Feb 2019

Cited by 10 | Viewed by 2879

Abstract

In this study, TiO₂–ZnFe₂O₄ (ZFO) core-shell nanorods with various ZFO crystallite thicknesses were synthesized through sputtering-deposited ZFO thin films onto the surfaces of TiO₂ nanorods. By coupling the ZFO narrow bandgap oxide with TiO₂, an [...] Read more.

In this study, TiO₂–ZnFe₂O₄ (ZFO) core-shell nanorods with various ZFO crystallite thicknesses were synthesized through sputtering-deposited ZFO thin films onto the surfaces of TiO₂ nanorods. By coupling the ZFO narrow bandgap oxide with TiO₂, an enhanced photodegradation efficiency of methylene orange under irradiation was achieved. Structural analyses revealed that ZFO crystallites fully covered the surfaces of the TiO₂ nanorods. The sputtering-deposited ZFO crystallites on the head region of the composite nanorods were markedly thicker than those covering the lateral region of the composite nanorods. The coverage of ZFO crystallites on the TiO₂ nanorods led to an improved light harvesting, a decrease in the hole–electron recombination rate, as well as the enhanced photodegradation activity of the TiO₂–ZFO heterostructures under irradiation. The optimized ZFO thickness on the head region of the composite nanorods was approximately 43 nm on average and that at the lateral region of the composite nanorods was 15 nm, which exhibited superior photodegradation ability to methylene orange and retained a stable photodegradation efficiency of approximately 97% after cycling tests. The results herein demonstrate that sputtering deposition of ZFO crystallite with tunable thickness is a promising approach to designing TiO₂–ZFO composite nanorods with various ZFO coverage sizes and to adjust their photodegradation ability toward organic dyes. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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14 pages, 4520 KiB

Open AccessArticle

Sol-gel Syntheses of Photocatalysts for the Removal of Pharmaceutical Products in Water

by Artium Belet, Cédric Wolfs, Julien G. Mahy, Dirk Poelman, Christelle Vreuls, Nathalie Gillard and Stéphanie D. Lambert

Nanomaterials 2019, 9(1), 126; https://doi.org/10.3390/nano9010126 - 20 Jan 2019

Cited by 19 | Viewed by 4761

Abstract

A screening study on seven photocatalysts was performed to identify the best candidate for pharmaceutical products degradation in water. Photocatalysts were deposited as thin films through a sol-gel process and subsequent dip-coating on glass slides. The efficiency of each photocatalyst was assessed through [...] Read more.

A screening study on seven photocatalysts was performed to identify the best candidate for pharmaceutical products degradation in water. Photocatalysts were deposited as thin films through a sol-gel process and subsequent dip-coating on glass slides. The efficiency of each photocatalyst was assessed through the degradation of methylene blue first, and then, through the degradation of 15 different pharmaceutical products. Two main types of synthesis methods were considered: aqueous syntheses, where the reaction takes place in water, and organic syntheses, where reactions take place in an organic solvent and only a stoichiometric amount of water is added to the reaction medium. Photocatalysts synthesized via aqueous sol-gel routes showed relatively lower degradation efficiencies; however, the organic route required a calcination step at high temperature to form the photoactive crystalline phase, while the aqueous route did not. The best performances for the degradation of pharmaceuticals arose when Evonik P25 and silver nanoparticles were added to TiO₂, which was synthesized using an organic solvent. In the case of methylene blue degradation, TiO₂ modified with Evonik P25 and TiO₂ doped with MnO₂ nanoparticles were the two best candidates. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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Review

Jump to: Editorial, Research

22 pages, 2344 KiB

Open AccessReview

The Influence of Photoactive Heterostructures on the Photocatalytic Removal of Dyes and Pharmaceutical Active Compounds: A Mini-Review

by Alexandru Enesca and Luminita Andronic

Nanomaterials 2020, 10(9), 1766; https://doi.org/10.3390/nano10091766 - 07 Sep 2020

Cited by 20 | Viewed by 3126

Abstract

The diversification of pollutants type and concentration in wastewater has underlined the importance of finding new alternatives to traditional treatment methods. Advanced oxidation processes (AOPs), among others, are considered as promising candidate to efficiently remove organic pollutants such as dyes or pharmaceutical active [...] Read more.

The diversification of pollutants type and concentration in wastewater has underlined the importance of finding new alternatives to traditional treatment methods. Advanced oxidation processes (AOPs), among others, are considered as promising candidate to efficiently remove organic pollutants such as dyes or pharmaceutical active compounds (PhACs). The present minireview resumes several recent achievements on the implementation and optimization of photoactive heterostructures used as photocatalysts for dyes and PhACs removal. The paper is focused on various methods of enhancing the heterostructure photocatalytic properties by optimizing parameters such as synthesis methods, composition, crystallinity, morphology, pollutant concentration and light irradiation. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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24 pages, 4016 KiB

Open AccessReview

Advances and Challenges in Developing Efficient Graphene Oxide-Based ZnO Photocatalysts for Dye Photo-Oxidation

by Asim Ali Yaqoob, Nur Habibah binti Mohd Noor, Albert Serrà and Mohamad Nasir Mohamad Ibrahim

Nanomaterials 2020, 10(5), 932; https://doi.org/10.3390/nano10050932 - 12 May 2020

Cited by 95 | Viewed by 6882

Abstract

The efficient remediation of organic dyes from wastewater is increasingly valuable in water treatment technology, largely owing to the tons of hazardous chemicals currently and constantly released into rivers and seas from various industries, including the paper, pharmaceutical, textile, and dye production industries. [...] Read more.

The efficient remediation of organic dyes from wastewater is increasingly valuable in water treatment technology, largely owing to the tons of hazardous chemicals currently and constantly released into rivers and seas from various industries, including the paper, pharmaceutical, textile, and dye production industries. Using solar energy as an inexhaustible source, photocatalysis ranks among the most promising wastewater treatment techniques for eliminating persistent organic pollutants and new emerging contaminants. In that context, developing efficient photocatalysts using sunlight irradiation and effectively integrating them into reactors, however, pose major challenges in the technologically relevant application of photocatalysts. As a potential solution, graphene oxide (GO)-based zinc oxide (ZnO) nanocomposites may be used together with different components (i.e., ZnO and GO-based materials) to overcome the drawbacks of ZnO photocatalysts. Indeed, mounting evidence suggests that using GO-based ZnO nanocomposites can promote light absorption, charge separation, charge transportation, and photo-oxidation of dyes. Despite such advances, viable, low-cost GO-based ZnO nanocomposite photocatalysts with sufficient efficiency, stability, and photostability remain to be developed, especially ones that can be integrated into photocatalytic reactors. This article offers a concise overview of state-of-the-art GO-based ZnO nanocomposites and the principal challenges in developing them. Full article

(This article belongs to the Special Issue Nano‐Photocatalytic Materials: Possibilities and Challenges)

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