Photocatalytic Energy Conversion Research Articles

Tailoring defects in In2S3/Zn0.3Cd0.7S heterojunctions for efficient photocatalytic CO2 conversion

Defect engineering is a highly effective approach to regulate the electronic structure of the catalyst surface, widely employed in the field of photocatalytic energy conversion. In this study, we have successfully synthesized a novel dual-defective In2S3/Zn0.3Cd0.7S (IS/ZCS) heterojunction structure via a self-assembly method, composed of Zn-vacancy-rich Zn0.3Cd0.7S (ZCS) and S-vacancy-rich In2S3 (IS). Under visible light illumination, 3% IS/ZCS sample exhibits remarkable photocatalytic performance in the synergistic reaction of CO2 reduction and 4-chlorobenzyl alcohol (Cl-PhCH2OH) oxidation with the CO yield significantly improved by a factor of 3.5 and 51 compared to that of ZCS and IS, respectively. The combined experimental data and theoretical calculations demonstrate that the dual-defective structure and Z-scheme transfer mode are the key factors behind the enhanced photocatalytic activity, providing more active sites and effectively improving the utilization of photogenerated charge carriers (PCCs). Moreover, the reaction pathway and catalytic mechanism of photocatalytic CO2 reduction were elucidated by the in-situ FTIR technique combined with DFT calculations, monitoring the intermediate and final products during the reaction period. Our results provide a powerful example of designing novel heterojunction photocatalysts with high activity and accelerating the separation of PCCs, with broad implications for the development of efficient photocatalytic systems.

A review on g-C3N4 decorated with silver for photocatalytic energy conversion

Artificial photocatalytic energy conversion is considered as the most potential strategy for solving the increasingly serious energy crisis and environmental pollution problems by directly capturing solar energy. Therefore, high efficiency photocatalyst has drawn significant research attention in recent years. Due to the excellent electronic, optical, structural, and physicochemical performances, silver-based g-C3N4 have become promising photocatalysts. This review emphasizes the recent progresses and challenges on g-C3N4 decorated with silver for photocatalytic energy conversion. The extensive use of g-C3N4 decorated with silver in diverse photocatalytic reactions, including hydrogen evolution, pollutant degradation and carbon dioxide reduction, is also fully introduced. In addition, we propose the perspectives of g-C3N4 decorated with silver on photocatalytic applications. We hope that this review will shed some light on the photocatalytic energy conversion of g-C3N4 decorated with silver.

Covalent Organic Framework/g-C3N4 van der Waals Heterojunction toward H2 Production.

Photocatalytic water splitting into H2 is the most economic and environmentally friendly strategy for H2 production, and rationally constructing a heterojunction retains enormous influence on a photocatalytic system. Herein, 2D/2D covalent organic framework/graphitic carbon nitride (COF/CN) van der Waals heterojunctions were readily prepared via an ultrasonic method for high-efficiency visible-light photocatalytic H2 production. The photocatalytic H2 production performance of optimized COF/CN composites can reach up to 449.64 μmol·h-1, which is approximately 5 times that of pure CN (89.08 μmol·h-1). The characterization and experimental studies reveal that the synergistic effect between COF and CN contributes to promoting the interfacial migration and spatial separation of photoinduced e--h+ pairs, further boosting the photocatalytic hydrogen production activity. This work may open a new window to design and fabricate effective heterojunction photocatalysts for photocatalytic energy conversion.

Engineered g-C3N5-Based Nanomaterials for Photocatalytic Energy Conversion and Environmental Remediation.

Photocatalysis plays a vital role in sustainable energy conversion and environmental remediation because of its economic, eco-friendly, and effective characteristics. Nitrogen-rich graphitic carbon nitride (g-C3N5) has received worldwide interest owing to its facile accessibility, metal-free nature, and appealing electronic band structure. This review summarizes the latest progress for g-C3N5-based photocatalysts in energy and environmental applications. It begins with the synthesis of pristine g-C3N5 materials with various topologies, followed by several engineering strategies for g-C3N5, such as elemental doping, defect engineering, and heterojunction creation. In addition, the applications in energy conversion (H2 evolution, CO2 reduction, and N2 fixation) and environmental remediation (NO purification and aqueous pollutant degradation) are discussed. Finally, a summary and some inspiring perspectives on the challenges and possibilities of g-C3N5-based materials are presented. It is believed that this review will promote the development of emerging g-C3N5-based photocatalysts for more efficiency in energy conversion and environmental remediation.

Recent Advances in Black TiO2 Nanomaterials for Solar Energy Conversion.

Titanium dioxide (TiO2) nanomaterials have been widely used in photocatalytic energy conversion and environmental remediation due to their advantages of low cost, chemical stability, and relatively high photo-activity. However, applications of TiO2 have been restricted in the ultraviolet range because of the wide band gap. Broadening the light absorption of TiO2 nanomaterials is an efficient way to improve the photocatalytic activity. Thus, black TiO2 with extended light response range in the visible light and even near infrared light has been extensively exploited as efficient photocatalysts in the last decade. This review represents an attempt to conclude the recent developments in black TiO2 nanomaterials synthesized by modified treatment, which presented different structure, morphological features, reduced band gap, and enhanced solar energy harvesting efficiency. Special emphasis has been given to the newly developed synthetic methods, porous black TiO2, and the approaches for further improving the photocatalytic activity of black TiO2. Various black TiO2, doped black TiO2, metal-loaded black TiO2 and black TiO2 heterojunction photocatalysts, and their photocatalytic applications and mechanisms in the field of energy and environment are summarized in this review, to provide useful insights and new ideas in the related field.

Advances in Piezoelectric Polarization Enhanced Photocatalytic Energy Conversion

Advances in Piezoelectric Polarization Enhanced Photocatalytic Energy Conversion

Neoteric advances in affordable photocatalytic energy conversion and storage with perovskites nanocrystals: A review

Environmental issues caused by energy crisis and its simultaneous demand are the factors driving researchers to explore the studies related to photocatalysis over the globe thus new pathways have come to light in order to store and convert solar energy. However, the conventional materials for the job including metal oxides and sulfides, with the passage of time, are diminishing and are being replaced by their best alternatives such as perovskites and their derivatives. The halide and oxides, with basic composition ABX3, are most famous among all the perovskites to be used in energy harvesting. The proclaimed supremacy of perovskite photocatalysts with their inherent potential to combat the energy crisis has been the compelling motive for the current article. As nano-structuring offers manifold features such as porosity, surface area, charge carrier mobility, and confinement. These characteristics contribute to their potential applications in batteries, solar cells, DSSCs, reduction of carbon dioxide, and thermoelectricity. The foregoing literature is devoid of comprehensive discussion on flexile and dynamic nano-structuring of parovskites concerning CO2 reduction and thermoelectric utilities. Therefore, perovskites derivatives, mainly halide and oxides have been summarized in the article to provide optimization in energy devices on basis of their structure, morphology, and composition control.

Graphitic carbon nitride nanosheets as promising candidates for the detection of hazardous contaminants of environmental and biological concern in aqueous matrices.

Monitoring of pollutant and toxic substances is essential for cleaner environment and healthy life. Sensing of various environmental contaminants and biomolecules such as heavy metals, pharmaceutics, toxic gases, volatile organic compounds, food toxins, and pathogens is of high importance to guaranty the good health and sustainable environment to community. In recent years, graphitic carbon nitride (g-CN) has drawn a significantamount of interest as a sensor due to its large surface area and unique electrochemical properties, low bandgap energy, high thermal and chemical stability, facile synthesis, nontoxicity, and electron rich property. Furthermore, the binary and ternary nanocomposites of graphitic carbon nitride further enhance their performance as a sensor making it a cost effective, fast, and reliable gadget for the purpose, and opens a wide area of research. Numerous reviews addressing a variety of applications including photocatalytic energy conversion, photoelectrochemicaldetection, and hydrogen evolution of graphitic carbon nitride have been documented to date. But a lesser attention has been devoted to the mechanistic approaches towards sensing of variety of pollutants concerned with environmental and biological aspects. Herein, we present the sensing features of graphitic carbon nitride towards the detection of various analytes including toxic heavy metals, pharmaceuticals, phenolic compounds, nitroaromatic compounds, volatile organic molecules, toxic gases, and foodborne pathogens. This review will undoubtedly provide future insights for researchers working in the field of sensors, allowing them to investigate the intriguing graphitic carbon nitride material as a sensing platform that is comparable to several other nanomaterials documented in the literature. Therefore, we hope that this study could reveal some intriguing sensing properties of graphitic carbon nitride, which may help researchers better understand how it interacts with contaminants of environmental and biological concern. Graphitic carbon nitride Nanosheets as Promising Analytical Tool for Environmental and Biological Monitoring of Hazardous Substances.

(Invited) In Situ spectroscopy of Electrochemical and Photoelectrochemical Interfaces

We explore various aspects of electrochemistry and photoelectrochemistry using in situ spectroscopy of electrode (metal) and photoelectrode (semiconductor) interfaces under electrochemical working conditions. Using sum frequency generation (SFG) spectroscopy, we measure the voltage dependence of the orientation of D2O molecules at a graphene electrode surface, which enables us to extract the free energy orienting potential of interfacial water.1 In particular, we measure the “free OD” feature in the spectra, which corresponds to the topmost water molecule that is rotated up out of the bulk water solution and is, therefore, not hydrogen bonded. Using transient absorption spectroscopy (TAS), we measure the lifetime of hot electrons photoexcited in plasmon resonant nanostructures.5 In a similar study, we use transient reflectance spectroscopy (TRS) to measure the photoexcited carrier dynamics in a GaP/TiO2 photoelectrode, as well as the electrostatic field dynamics at this semiconductor-liquid interface in situ under various electrochemical potentials.2 Here, the electrostatic fields at the surface of the semiconductor are measured via Franz−Keldysh oscillations (FKO). These spectra reveal that the nanoscale TiO2 protection layer enhances the built-in field and charge separation performance of GaP photoelectrodes. Using surface enhanced Raman scattering (SERS) spectroscopy, we monitor local electric fields via Stark-shifts of nitrile-functionalized silicon photoelectrodes.6 By monitoring Stark shifts in graphene-enhanced Raman spectroscopy (GERS), we measure local electric fields and local charge densities at monolayer graphene electrode surfaces.3 Lastly, we measure the stacking dependence of monolayer WSe2/MoSe2 heterostructures and observe resonant excitation of interlayer excitons for photocatalytic energy conversion.4 Montenegro, A., C. Dutta, M. Mammetkuliev, H.T. Shi, B.Y. Hou, D. Bhattacharyya, B.F. Zhao, S.B. Cronin and A.V. Benderskii, Asymmetric response of interfacial water to applied electric fields. Nature, 594, 62 (2021).Xu, Z.H., B.Y. Hou, F.Y. Zhao, Z. Cai, H.T. Shi, Y.W. Liu, C.L. Hill, D.G. Musaev, M. Mecklenburg, S.B. Cronin and T.Q. Lian, Nanoscale TiO2 Protection Layer Enhances the Built-In Field and Charge Separation Performance of GaP Photoelectrodes. Nano Letters, 21, 8017-8024 (2021).Shi, H.T., B.F. Zhao, J. Ma, M.J. Bronson, Z. Cai, J.H. Chen, Y. Wang, M. Cronin, L. Jensen and S.B. Cronin, Measuring Local Electric Fields and Local Charge Densities at Electrode Surfaces Using Graphene-Enhanced Raman Spectroscopy (GERS)-Based Stark-Shifts. ACS Applied Materials & Interfaces, 11, 36252-36258 (2019).Chen, J., C.S. Bailey, D. Cui, Y. Wang, B. Wang, H. Shi, Z. Cai, E. Pop, C. Zhou and S.B. Cronin, Stacking Independence and Resonant Interlayer Excitation of Monolayer WSe2/MoSe2 Heterostructures for Photocatalytic Energy Conversion. ACS Applied Nano Materials, DOI:10.1021/acsanm.9b01898 (2020).Yu Wang, Yi Wang, Indu Aravind, Zhi Cai, Lang Shen, Boxin Zhang, Bo Wang, Jihan Chen, Bofan Zhao, Haotian Shi, Jahan M. Dawlaty, and Stephen B. Cronin. In Situ Investigation of Ultrafast Dynamics of Hot Electron-Driven Photocatalysis in Plasmon-Resonant Grating Structures. Journal of the American Chemical Society. DOI: 10.1021/jacs.1c12069 (2022).Haotian Shi, Ryan T. Pekarek, Ran Chen, Boxin Zhang, Yu Wang, Indu Aravind, Zhi Cai, Lasse Jensen, Nathan R. Neale, and Stephen B. Cronin. Monitoring Local Electric Fields using Stark Shifts on Napthyl Nitrile-Functionalized Silicon Photoelectrodes. The Journal of Physical Chemistry C, 124, 17000-17005 (2020).

Photosensitization of TiO2 nanosheets with ZnIn2S4 for enhanced visible photocatalytic activity toward hydrogen production

TiO2 nanosheet is a fruitful paradigm for a wide variety of photocatalytic applications due to its characteristics of high photoactivity, robust stability, and environmental friendliness. However, its pragmatic utilization for visible light photocatalytic energy conversion still remains challenging owing to the wide bandgap. Herein, a 2D/3D TiO2/ZnIn2S4 nanostructure was purposively constructed via a microwave-assisted synthesis, with ZnIn2S4 functioned as a photosensitizer to overcome the lack of visible light response capacity for TiO2. The optimal TiO2/ZnIn2S4 sample exhibits an excellent photocatalytic H2 evolution activity with a rate of 1167.38 μmol/g/h under visible light illumination, far beyond that of pristine TiO2 nanosheet (6.78 μmol/g/h) and ZnIn2S4 (378.51 μmol/g/h). The enhanced photocatalytic performance can be attributed to synergy effects of the extended visible light response, compatible band alignment, and fast charge carrier separation. The in situ irradiated X-ray photoelectron spectroscopy (XPS) was used to systematically study the transfer behavior of photo-induced electrons; the results highlighted that the flow direction of photoexcited charges is from ZnIn2S4 to TiO2 nanosheets due to the strong interfacial contact. Then both ZnIn2S4 and TiO2 nanosheets can act as the active sites for proton reduction, which therefore boosts the hydrogen production under visible irradiation. This work opens a new venue for the development of flexible photosensitization systems for solar-driven energy conversion.

A comparative experimental and theoretical study on the structural and optical properties of ZnO synthesized at room temperature using an ultrasonication technique

AbstractIn the present article we report a comparative experimental and theoretical study on the structural and optical properties of ZnO. First principle calculations were carried out using density functional theory (DFT) to study the electronic structure of ZnO. The direct‐type band gap was found in the ZnO's typical estimated energy band structure in the Brillouin zone path G‐G or in the middle of the Γ k‐point grid. To develop UV/ZnO/O2/H2O2 system for photodegradation of organic contaminants in an aqueous system, zinc oxide (ZnO) nanostructures were synthesized using an ultrasonication process at ambient temperature. To test the photocatalytic activity of synthesized nanostructures, we used phenol red (PR) dye as a test substrate. We found that ZnO nanostructures photo‐degraded PR dye at a rate of over 90% under ultraviolet light irradiation, converting photonic energy into chemical energy (photocatalytic energy conversion) that can be used for water purification. To explore the structural, optical, morphological, and compositional characteristics of synthesized ZnO nanostructures, various techniques including powder X‐ray diffraction, Fourier‐transform infrared spectroscopy, UV‐visible spectroscopy, scanning electron microscopy, and energy dispersive X‐ray spectroscopy were used.

Photoluminescent and photocatalytic behaviour of zinc oxide nanostructures synthesized through the room temperature ultrasonication method.

In the present article we report the synthesis of zinc oxide (ZnO) nanostructures at room temperature using an ultrasonication technique to study their photoluminescent and photocatalytic behaviour. Synthesized nanomaterial showed a strong near band edge ultraviolet (UV) light emission and red emission, thereby finding its use in photoluminescent materials. We developed a UV/ZnO/O2 /H2 O2 system for the photodegradation of organic pollutants in an aqueous system. We used synthesized nanostructures to photodegrade phenol red (PR) dye to check their photocatalytic activity. The ZnO nanostructures photodegraded more than 90% of the PR dye under UV light irradiation in which photonic energy is converted to chemical energy (photocatalytic energy conversion), thereby exploitable for water purification applications. Synthesized ZnO nanostructures were characterized using powder X-ray diffraction, Fourier transform infrared spectroscopy, UV-visible light spectroscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy to investigate their structural, optical, morphological, and compositional properties, respectively.

Controlled photoinduced electron transfer from g-C3N4 to CuCdCe-LDH for efficient visible light hydrogen evolution reaction

Ample visible-light response and efficient charge transfers in semiconductor heterojunction are still enslaved to the limited photocatalytic water splitting. In most cases, the rational design of hybrid composites tune in atomic level interaction led to remarkable stability and superior activity. Here, this work is a systematic investigation of metal ion substitution in the LDH and LDH/g-C3N4 hybrid composites for hydrogen evolution reaction (HER) under visible light. The construction of heterostructure not only facilitates the charge separation and transfer owing to the formed heterojunction through band gap engineering and tunable optical properties which are inherited from morphology of as grown CuCdCe-LDH over the exfoliated g-C3N4 but also provides plenty of surface active sites due the increased surface area photostability. The CuCdCe-LDH/g-C3N4 exhibits superior HER rate of 3.5 mmolg−1h−1 with AQY of 5.78% over their binary counterparts. The density functional theory calculations also suggest that the HER activity of CuCdCe-LDH is substantially enhanced by coupling with g-C3N4 the electrochemical results leading to high photocurrent response. The high photocatalytic activity of the composite was due to efficient photoexcited charge transfer process and the synergistic effect between CuCdCe-LDH and g-C3N4. These finding will open scopes for designing inexpensive high performance materials for broad applications of photocatalytic energy conversion.

Oxidation co-catalyst modified In2S3 with efficient interfacial charge transfer for boosting photocatalytic H2 evolution

Constructing an efficient co-catalyst/photocatalyst system for charge separation boosting photocatalytic hydrogen generation is a vital challenge. Herein, highly-dispersed PdS nanoparticles (NPs) acting as an efficient hole co-catalyst has been decorated on the ultrathin In2S3 nanosheets. The strong interactions between PdS and In2S3 via Pd–S–In bonds enable an intimate interface junction. Due to the high capacity of PdS for the hole capture with the assistance of internal electric field, the photogenerated charge carriers are not only separated effectively, the semiconductor photocatalyst In2S3 is also protected from the photo-oxidation. As expected, a remarkable H2 production rate of 142.27 μmol/h has been achieved for 3PdS/In2S3 nanocomposite, which is 149.8 times higher than that of the pristine In2S3 nanosheets, and 13.3 times superior to the In2S3 decorated with a reductive co-catalyst Pt. This work provides a new insight into the co-catalyst modification engineering for an efficient photocatalytic energy conversion.

Mixed Metal Sulfides for the Application of Photocatalytic Energy Conversion

Mixed Metal Sulfides for the Application of Photocatalytic Energy Conversion

Electrospun Semiconductor‐Based Nano‐Heterostructures for Photocatalytic Energy Conversion and Environmental Remediation: Opportunities and Challenges

Harvesting solar energy to drive the semiconductor photocatalysis offers a promising tactic to address ever‐growing challenges of both energy shortage and environmental pollution. Design and synthesis of nano‐heterostructure photocatalysts with controllable components and morphologies are the key factors for achieving highly efficient photocatalytic processes. One‐dimensional (1D) semiconductor nanofibers produced by electrospinning possess a large ratio of length to diameter, high ratio of surface to volume, small grain sizes, and high porosity, which are ideally suited for photocatalytic reactions from the viewpoint of structure advantage. After the secondary treatment of these nanofibers through the solvothermal, gas reduction, in situ doping, or assembly methods, the multi‐component nanofibers with hierarchical nano‐heterostructures can be obtained to further enhance their light absorption and charge carrier separation during the photocatalytic processes. In recent years, the electrospun semiconductor‐based nano‐heterostructures have become a “hot topic” in the fields of photocatalytic energy conversion and environmental remediation. This review article summarizes the recent progress in electrospinning synthesis of various kinds of high‐performance semiconductor‐based nano‐heterostructure photocatalysts for H2 production, CO2 reduction, and decomposition of pollutants. The future perspectives of these materials are also discussed.

Single-atom catalysts for photocatalytic energy conversion

<h2>Summary</h2> Artificial photocatalytic energy conversion represents a highly intriguing strategy for solving the energy crisis and environmental problems by directly harvesting solar energy. The development of efficient photocatalysts is the central task for pushing the real-world application of photocatalytic reactions. Due to the maximum atomic utilization efficiency and distinct advantages of outstanding catalytic activity, single-atom catalysts (SACs) have emerged as promising candidates for photocatalysts. In the current review, recent progresses and challenges on SACs for photocatalytic energy conversion systems are presented. Fundamental principles focusing on charge separation/transfer and molecular adsorption/activation for the single-atom photocatalysis are systemically explored. We outline how the isolated reactive sites facilitate the photogenerated electron–hole transfer and promote the construction of efficient photoactivation cycles. The widespread adoption of SACs in diverse photocatalytic reactions is also comprehensively introduced. By presenting these advances and addressing some future challenges with potential solutions related to the integral development of photocatalysis over SACs, we expect to shed some light on the forthcoming research of SACs for photocatalytic energy conversion.

Vacancy-modified g-C3N4and its photocatalytic applications

As an emerging semiconductor-based catalyst, g-C3N4has attracted significant attention for visible light-driven photocatalytic energy conversion, synthesis of chemicals, and environmental remediation.

MoS2–ZnO nanocomposites for photocatalytic energy conversion and solar applications

ZnO is a large-band-gap semiconductor with promising photocatalytic properties. The high bandgap (Egap) of ZnO, on the other hand, restricts its application in solar-driven photocatalysis since it can only respond to UV light that makes up just 5% of the full solar spectrum. Apart from this, it also suffers from the problem of fast charge recombination. During the last few years, great attention has been paid to increase the efficiency of ZnO in solar-driven photocatalysis, by increasing light-harvesting span or charge separation efficiency. It has been reported that when ZnO is coupled with MoS2 (Low Egap semiconductor), its light-harvesting span extends to most of the solar spectrum due to the synergic adsorption of two dissimilar Egap semiconductors. Furthermore, MoS2–ZnO nanocomposites also show decreased charge recombination and fast interfacial charge transfer. In this article, we have reviewed the wide solar applications of MoS2–ZnO nanocomposites and the mechanisms of these photo-induced reactions.

In situ growth of g-C3N4 on clay minerals of kaolinite, sepiolite, and talc for enhanced solar photocatalytic energy conversion

The clay mineral/g-C3N4 composites were prepared through a simple one-pot synthesis with acid-treated clay minerals and melamine as precursors. Three typical clay minerals, e.g., kaolinite, sepiolite, and talc, were adopted as photocatalyst carriers. Notably, the acid-treated clay minerals coupled with g-C3N4 in three different ways. The kaolinite/g-C3N4 composite, in particular, proceeded with an intercalation reaction due to the in situ growth of g-C3N4 within the layers of acid-treated kaolinite, leading to the expansion of kaolinite layers and a prominently large specific surface area of 61.9 m2 g−1. The resultant composites were used in photocatalytic H2 generation by water splitting and CO2 reduction, exhibiting superior photocatalytic performance to the g-C3N4. Among the obtained composites, the optimized kaolinite/g-C3N4 showed the best photocatalytic activities, e.g. 3.03 μmol g−1 h−1 of CO evolution and 385 μmol g−1 h−1 of H2 evolution, compared with merely 0.91 μmol g−1 h−1 of CO evolution and 96.4 μmol g−1 h−1 of H2 evolution for bare g-C3N4. The superior performance of kaolinite/g-C3N4 can be ascribed to the large specific surface area and better distribution of g-C3N4, which can enhance the light absorption, increase the number of active sites and favor the charge separation.