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Advanced Photocatalysts for Energy Conversion and Environmental Applications

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Photochemistry".

Deadline for manuscript submissions: closed (28 February 2023) | Viewed by 15272

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Special Issue Editor

Fujian Province University Key Laboratory of Green Energy and Environment Catalysis, Ningde Normal University, Ningde, China
Interests: metal–organic frameworks; environmental catalysis; chemical conversion of solar energy; dynamics of photogenerated carriers; interface engineering
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Photocatalysis is an advanced technique that transforms solar energy into sustainable fuels and oxidizes pollutants via the use of semiconductor photocatalysts. The main scientific and technological challenges for effective photocatalysis are the stability, robustness, and efficiency of semiconductor photocatalysts. For practical applications, the development of highly efficient and stable photocatalysts—crucial in energy conversion (i.e., hydrogen evolution, CO2 reduction, and oriented synthesis) and environmental remediation (i.e., air purification, antibacterial, and wastewater treatment)—is in high demand. This Special Issue plans to offer an opportunity for the publication of original research regarding the synthesis of novel photocatalytic materials and the application of them in energy conversion and environmental remediation.

Potential topics include, but are not limited to:

  • Photocatalytic performance;
  • Photocatalytic-semiconductor materials;
  • Metal-organic frameworks;
  • Mechanisms of the photocatalytic process;
  • Role of photocatalysts in the environment;
  • Role of photocatalysts in energy.

Dr. Ruowen Liang
Guest Editor

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • photocatalyst
  • nanomaterials
  • metal-organic frameworks
  • environment
  • energy

Published Papers (10 papers)

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Research

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16 pages, 4566 KiB  
Article
One-Pot Synthesis of N-Doped NiO for Enhanced Photocatalytic CO2 Reduction with Efficient Charge Transfer
Molecules 2023, 28(6), 2435; https://doi.org/10.3390/molecules28062435 - 07 Mar 2023
Cited by 3 | Viewed by 1244
Abstract
The green and clean sunlight-driven catalytic conversion of CO2 into high-value-added chemicals can simultaneously solve the greenhouse effect and energy problems. The controllable preparation of semiconductor catalyst materials and the study of refined structures are of great significance for the in-depth understanding [...] Read more.
The green and clean sunlight-driven catalytic conversion of CO2 into high-value-added chemicals can simultaneously solve the greenhouse effect and energy problems. The controllable preparation of semiconductor catalyst materials and the study of refined structures are of great significance for the in-depth understanding of solar-energy-conversion technology. In this study, we prepared nitrogen-doped NiO semiconductors using a one-pot molten-salt method. The research shows that the molten-salt system made NiO change from p-type to n-type. In addition, nitrogen doping enhanced the adsorption of CO2 on NiO and increased the separation of photogenerated carriers on the NiO. It synergistically optimized the CO2-reduction system and achieved highly active and selective CO2 photoreduction. The CO yield on the optimal nitrogen-doped photocatalyst was 235 μmol·g−1·h−1 (selectivity 98%), which was 16.8 times that of the p-type NiO and 2.4 times that of the n-type NiO. This can be attributed to the fact that the nitrogen doping enhanced the oxygen vacancies of the NiOs and their ability to adsorb and activate CO2 molecules. Photoelectrochemical characterization also confirmed that the nitrogen-doped NiO had excellent electron -transfer and separation properties. This study provides a reference for improving NiO-based semiconductors for photocatalytic CO2 reduction. Full article
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14 pages, 2891 KiB  
Article
CVD Growth of Hematite Thin Films for Photoelectrochemical Water Splitting: Effect of Precursor-Substrate Distance on Their Final Properties
Molecules 2023, 28(4), 1954; https://doi.org/10.3390/molecules28041954 - 18 Feb 2023
Cited by 2 | Viewed by 1243
Abstract
The development of photoelectrode materials for efficient water splitting using solar energy is a crucial research topic for green hydrogen production. These materials need to be abundant, fabricated on a large scale, and at low cost. In this context, hematite is a promising [...] Read more.
The development of photoelectrode materials for efficient water splitting using solar energy is a crucial research topic for green hydrogen production. These materials need to be abundant, fabricated on a large scale, and at low cost. In this context, hematite is a promising material that has been widely studied. However, it is a huge challenge to achieve high-efficiency performance as a photoelectrode in water splitting. This paper reports a study of chemical vapor deposition (CVD) growth of hematite nanocrystalline thin films on fluorine-doped tin oxide as a photoanode for photoelectrochemical water splitting, with a particular focus on the effect of the precursor–substrate distance in the CVD system. A full morphological, structural, and optical characterization of hematite nanocrystalline thin films was performed, revealing that no change occurred in the structure of the films as a function of the previously mentioned distance. However, it was found that the thickness of the hematite film, which is a critical parameter in the photoelectrochemical performance, linearly depends on the precursor–substrate distance; however, the electrochemical response exhibits a nonmonotonic behavior. A maximum photocurrent value close to 2.5 mA/cm2 was obtained for a film with a thickness of around 220 nm under solar irradiation. Full article
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14 pages, 6137 KiB  
Article
Surface Coordination of Pd/ZnIn2S4 toward Enhanced Photocatalytic Activity for Pyridine Denitrification
Molecules 2023, 28(1), 282; https://doi.org/10.3390/molecules28010282 - 29 Dec 2022
Cited by 2 | Viewed by 1280
Abstract
New surface coordination photocatalytic systems that are inspired by natural photosynthesis have significant potential to boost fuel denitrification. Despite this, the direct synthesis of efficient surface coordination photocatalysts remains a major challenge. Herein, it is verified that a coordination photocatalyst can be constructed [...] Read more.
New surface coordination photocatalytic systems that are inspired by natural photosynthesis have significant potential to boost fuel denitrification. Despite this, the direct synthesis of efficient surface coordination photocatalysts remains a major challenge. Herein, it is verified that a coordination photocatalyst can be constructed by coupling Pd and CTAB-modified ZnIn2S4 semiconductors. The optimized Pd/ZnIn2S4 showed a superior degradation rate of 81% for fuel denitrification within 240 min, which was 2.25 times higher than that of ZnIn2S4. From the in situ FTIR and XPS spectra of 1% Pd/ZnIn2S4 before and after pyridine adsorption, we find that pyridine can be selectively adsorbed and form Zn⋅⋅⋅C-N or In⋅⋅⋅C-N on the surface of Pd/ZnIn2S4. Meanwhile, the superior electrical conductivity of Pd can be combined with ZnIn2S4 to promote photocatalytic denitrification. This work also explains the surface/interface coordination effect of metal/nanosheets at the molecular level, playing an important role in photocatalytic fuel denitrification. Full article
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12 pages, 3977 KiB  
Article
In Situ Fabrication of N-Doped ZnS/ZnO Composition for Enhanced Visible-Light Photocatalytic H2 Evolution Activity
Molecules 2022, 27(23), 8544; https://doi.org/10.3390/molecules27238544 - 04 Dec 2022
Cited by 2 | Viewed by 1429
Abstract
For achieving the goal of peaking carbon dioxide emissions and achieving carbon neutrality, developing hydrogen energy, the green and clean energy, shows a promising perspective for solving the energy and ecological issues. Herein, firstly, we used the hydrothermal method to synthesize the ZnS(en) [...] Read more.
For achieving the goal of peaking carbon dioxide emissions and achieving carbon neutrality, developing hydrogen energy, the green and clean energy, shows a promising perspective for solving the energy and ecological issues. Herein, firstly, we used the hydrothermal method to synthesize the ZnS(en)0.5 as the precursor. Then, ZnS/ZnO composite was obtained by the in situ transformation of ZnS(en)0.5 with heat treatment under air atmosphere. The composition, optical property, morphology, and structural properties of the composite were characterized by X-ray photoemission spectroscopy (XPS), Ultraviolet-visible absorption spectra (Uv-vis Abs), Scanning electron microscopy (SEM) and Transmission electron microscopy image (TEM). Moreover, the content of ZnO in ZnS/ZnO was controlled via adjustment of the calcination times. The visible-light response of ZnS/ZnO originated from the in situ doping of N during the transformation of ZnS(en)0.5 to ZnS/ZnO under heat treatment, which was verified well by XPS. Photocatalytic hydrogen evolution experiments demonstrated that the sample of ZnS/ZnO-0.5 h with 6.9 wt% of ZnO had the best H2 evolution activity (1790 μmol/h/g) under visible light irradiation (λ > 400 nm), about 7.0 and 12.3 times that of the pure ZnS and ZnO, respectively. The enhanced activities of the ZnS/ZnO composites were ascribed to the intimated hetero-interface between components and efficient transfer of photo-generated electrons from ZnS to ZnO. Full article
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12 pages, 5253 KiB  
Article
M-Carboxylic Acid Induced Formation of New Coordination Polymers for Efficient Photocatalytic Degradation of Ciprofloxacin
Molecules 2022, 27(22), 7731; https://doi.org/10.3390/molecules27227731 - 10 Nov 2022
Cited by 1 | Viewed by 898
Abstract
Four new 2–3D materials were designed and synthesized by hydrothermal methods, namely, {[(L1·Cu·2H2O) (4,4-bipy)0.5] (β-Mo8O26)0.5·H2O} (1), {[(L1·Cu)2·(4,4-bipy)] (Mo5O16)} (2), {Co(L1)2}n [...] Read more.
Four new 2–3D materials were designed and synthesized by hydrothermal methods, namely, {[(L1·Cu·2H2O) (4,4-bipy)0.5] (β-Mo8O26)0.5·H2O} (1), {[(L1·Cu)2·(4,4-bipy)] (Mo5O16)} (2), {Co(L1)2}n (3), and {[(L1)2][β-Mo8O26]0.5·5H2O} (4). [L1=5-(4-aminopyridine) isophthalic acid]. The degradation of ciprofloxacin (CIP) in water by compounds 1–4 was studied under visible light. The experimental results show that compounds 1–4 have obvious photocatalytic degradation effect on CIP. In addition, for compound 1, the effects of temperature, pH, and adsorbent dosage on photocatalytic performance were also investigated. The stability of compound 1 was observed by a cycle experiment, indicating that there was no significant change after three cycles of CIP degradation. Full article
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15 pages, 4972 KiB  
Article
Modification of Polymeric Carbon Nitride with Au–CeO2 Hybrids to Improve Photocatalytic Activity for Hydrogen Evolution
Molecules 2022, 27(21), 7489; https://doi.org/10.3390/molecules27217489 - 03 Nov 2022
Cited by 2 | Viewed by 1016
Abstract
The construction of a multi-component heterostructure for promoting the exciton splitting and charge separation of conjugated polymer semiconductors has attracted increasing attention in view of improving their photocatalytic activity. Here, we integrated Au nanoparticles (NPs) decorated CeO2 (Au–CeO2) with polymeric [...] Read more.
The construction of a multi-component heterostructure for promoting the exciton splitting and charge separation of conjugated polymer semiconductors has attracted increasing attention in view of improving their photocatalytic activity. Here, we integrated Au nanoparticles (NPs) decorated CeO2 (Au–CeO2) with polymeric carbon nitride (PCN) via a modified thermal polymerization method. The combination of the interfacial interaction between PCN and CeO2 via N-O or C-O bonds, with the interior electronic transmission channel built by the decoration of Au NPs at the interface between CeO2 and PCN, endows CeAu–CN with excellent efficiency in the transfer and separation of photo-induced carriers, leading to the enhancement of photochemical activity. The amount-optimized CeAu–CN nanocomposites are capable of producing ca. 80 μmol· H2 per hour under visible light irradiation, which is higher than that of pristine CN, Ce–CN and physical mixed CeAu and PCN systems. In addition, the photocatalytic activity of CeAu–CN remains unchanged for four runs in 4 h. The present work not only provides a sample and feasible strategy to synthesize highly efficient organic polymer composites containing metal-assisted heterojunction photocatalysts, but also opens up a new avenue for the rational design and synthesis of potentially efficient PCN-based materials for efficient hydrogen evolution. Full article
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19 pages, 4856 KiB  
Article
Designing a 0D/1D S-Scheme Heterojunction of Cadmium Selenide and Polymeric Carbon Nitride for Photocatalytic Water Splitting and Carbon Dioxide Reduction
Molecules 2022, 27(19), 6286; https://doi.org/10.3390/molecules27196286 - 23 Sep 2022
Cited by 4 | Viewed by 1632
Abstract
Constructing photocatalysts to promote hydrogen evolution and carbon dioxide photoreduction into solar fuels is of vital importance. The design and establishment of an S-scheme heterojunction system is one of the most feasible approaches to facilitate the separation and transfer of photogenerated charge carriers [...] Read more.
Constructing photocatalysts to promote hydrogen evolution and carbon dioxide photoreduction into solar fuels is of vital importance. The design and establishment of an S-scheme heterojunction system is one of the most feasible approaches to facilitate the separation and transfer of photogenerated charge carriers and obtain powerful photoredox capabilities for boosting photocatalytic performance. Herein, a zero-dimensional/one-dimensional S-scheme heterojunction composed of CdSe quantum dots and polymeric carbon nitride nanorods (CdSe/CN) is created and constructed via a linker-assisted hybridization approach. The CdSe/CN composites exhibit superior photocatalytic activity in water splitting and promoted carbon dioxide conversion performance compared with CN nanorods and CdSe quantum dots. The best efficiency in photocatalytic water splitting (10.2% apparent quantum yield at 420 nm irradiation, 20.1 mmol g−1 h−1 hydrogen evolution rate) and CO2 reduction (0.77 mmol g−1 h−1 CO production rate) was achieved by 5%CdSe/CN composites. The significantly improved photocatalytic reactivity of CdSe/CN composites primarily originates from the emergence of an internal electric field in the zero-dimensional/one-dimensional S-scheme heterojunction, which could greatly improve the photoinduced charge-carrier separation. This work underlines the possibility of employing polymeric carbon nitride nanostructures as appropriate platforms to establish highly active S-scheme heterojunction photocatalysts for solar fuel production. Full article
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14 pages, 3727 KiB  
Article
CdS Nanocubes Adorned by Graphitic C3N4 Nanoparticles for Hydrogenating Nitroaromatics: A Route of Visible-Light-Induced Heterogeneous Hollow Structural Photocatalysis
Molecules 2022, 27(17), 5438; https://doi.org/10.3390/molecules27175438 - 25 Aug 2022
Cited by 1 | Viewed by 1309
Abstract
Modulating the transport route of photogenerated carriers on hollow cadmium sulfide without changing its intrinsic structure remains fascinating and challenging. In this work, a series of well-defined heterogeneous hollow structural materials consisting of CdS hollow nanocubes (CdS NCs) and graphitic C3N [...] Read more.
Modulating the transport route of photogenerated carriers on hollow cadmium sulfide without changing its intrinsic structure remains fascinating and challenging. In this work, a series of well-defined heterogeneous hollow structural materials consisting of CdS hollow nanocubes (CdS NCs) and graphitic C3N4 nanoparticles (CN NPs) were strategically designed and fabricated according to an electrostatic interaction approach. It was found that such CN NPs/CdS NCs still retained the hollow structure after CN NP adorning and demonstrated versatile and remarkably boosted photoreduction performance. Specifically, under visible light irradiation (λ ≥ 420 nm), the hydrogenation ratio over 2CN NPs/CdS NCs (the mass ratio of CN NPs to CdS NCs is controlled to be 2%) toward nitrobenzene, p-nitroaniline, p-nitrotoluene, p-nitrophenol, and p-nitrochlorobenzene can be increased to 100%, 99.9%, 83.2%, 93.6%, and 98.2%, respectively. In addition, based on the results of photoelectrochemical performances, the 2CN NPs/CdS NCs reach a 0.46% applied bias photo-to-current efficiency, indicating that the combination with CN NPs can indeed improve the migration and motion behavior of photogenerated carriers, besides ameliorating the photocorrosion and prolonging the lifetime of CdS NCs. Full article
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Review

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24 pages, 3358 KiB  
Review
Advances in Bi2WO6-Based Photocatalysts for Degradation of Organic Pollutants
Molecules 2022, 27(24), 8698; https://doi.org/10.3390/molecules27248698 - 08 Dec 2022
Cited by 10 | Viewed by 1897
Abstract
With the rapid development of modern industries, water pollution has become an urgent problem that endangers the health of human and wild animals. The photocatalysis technique is considered an environmentally friendly strategy for removing organic pollutants in wastewater. As an important member of [...] Read more.
With the rapid development of modern industries, water pollution has become an urgent problem that endangers the health of human and wild animals. The photocatalysis technique is considered an environmentally friendly strategy for removing organic pollutants in wastewater. As an important member of Bi-series semiconductors, Bi2WO6 is widely used for fabricating high-performance photocatalysts. In this review, the recent advances of Bi2WO6-based photocatalysts are summarized. First, the controllable synthesis, surface modification and heteroatom doping of Bi2WO6 are introduced. In the respect of Bi2WO6-based composites, existing Bi2WO6-containing binary composites are classified into six types, including Bi2WO6/carbon or MOF composite, Bi2WO6/g-C3N4 composite, Bi2WO6/metal oxides composite, Bi2WO6/metal sulfides composite, Bi2WO6/Bi-series composite, and Bi2WO6/metal tungstates composite. Bi2WO6-based ternary composites are classified into four types, including Bi2WO6/g-C3N4/X, Bi2WO6/carbon/X, Bi2WO6/Au or Ag-based materials/X, and Bi2WO6/Bi-series semiconductors/X. The design, microstructure, and photocatalytic performance of Bi2WO6-based binary and ternary composites are highlighted. Finally, aimed at the existing problems in Bi2WO6-based photocatalysts, some solutions and promising research trends are proposed that would provide theoretical and practical guidelines for developing high-performance Bi2WO6-based photocatalysts. Full article
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25 pages, 3199 KiB  
Review
Photocatalytic Water Splitting: How Far Away Are We from Being Able to Industrially Produce Solar Hydrogen?
Molecules 2022, 27(21), 7176; https://doi.org/10.3390/molecules27217176 - 23 Oct 2022
Cited by 6 | Viewed by 2588
Abstract
Solar water splitting (SWS) has been researched for about five decades, but despite successes there has not been a big breakthrough advancement. While the three fundamental steps, light absorption, charge carrier separation and diffusion, and charge utilization at redox sites are given a [...] Read more.
Solar water splitting (SWS) has been researched for about five decades, but despite successes there has not been a big breakthrough advancement. While the three fundamental steps, light absorption, charge carrier separation and diffusion, and charge utilization at redox sites are given a great deal of attention either separately or simultaneously, practical considerations that can help to increase efficiency are rarely discussed or put into practice. Nevertheless, it is possible to increase the generation of solar hydrogen by making a few little but important adjustments. In this review, we talk about various methods for photocatalytic water splitting that have been documented in the literature and importance of the thin film approach to move closer to the large-scale photocatalytic hydrogen production. For instance, when comparing the film form of the identical catalyst to the particulate form, it was found that the solar hydrogen production increased by up to two orders of magnitude. The major topic of this review with thin-film forms is, discussion on several methods of increased hydrogen generation under direct solar and one-sun circumstances. The advantages and disadvantages of thin film and particle technologies are extensively discussed. In the current assessment, potential approaches and scalable success factors are also covered. As demonstrated by a film-based approach, the local charge utilization at a zero applied potential is an appealing characteristic for SWS. Furthermore, we compare the PEC-WS and SWS for solar hydrogen generation and discuss how far we are from producing solar hydrogen on an industrial scale. We believe that the currently employed variety of attempts may be condensed to fewer strategies such as film-based evaluation, which will create a path to address the SWS issue and achieve sustainable solar hydrogen generation. Full article
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