Photoreduction Activity Research Articles

Controllable Tuning of the Uranium Photoreduction and Hydrogen Evolution Activity on Znln2s4 Surface Domain Heteroaromatic Junction Via Al/Cu Co-Doping

Controllable Tuning of the Uranium Photoreduction and Hydrogen Evolution Activity on Znln2s4 Surface Domain Heteroaromatic Junction Via Al/Cu Co-Doping

Enhancement of Ti3C2 MXene on Au@Ag/TiO2 for the visible-light-driven photoreduction of nitroaromatics

Au@Ag/TiO2/Ti3C2 exhibits outstanding photoreduction activity at 0 °C because of the combination of efficient hot carrier generation and separation ability in one system.

Influence of plasmonic metals (Ag, Cu) on overall CO2 photoreduction activity of β-Ga2O3

Plasmonic metals can substantially promote the photo-activity of the conventional photocatalyst. Herein, we inserted Ag and Cu nanoparticles in β-Ga2O3 to photo reduce CO2 by water. The relative content of Ag and Cu governs the photo-activity. 2Ag: Cu/ β-Ga2O3 exhibits the optimum activity, which was 1.81, 1.57, 1.5 times higher than using pristine β-Ga2O3 for CO, H2, and CH4, respectively. Ag and Cu favored the production of CO and CH4, respectively. Bimetals improved the optical and electronic properties and increased the photocurrent responses by 8-folds. In situ DRIFTS for isotopic-labelled 13CO2 and ESR spectroscopy provided insight into the charge transfer mechanism and key intermediates. The molecular dynamics simulation indicates that bimetals induced hydrophobicity in β-Ga2O3 helped to populate CO2 molecules near the surface which slowly diffuse along the axial direction. Combining these findings, a plausible mechanism is given which could help in engineering catalysts for other solar energy applications.

A novel Z-scheme Bi4O5Br2 nanosphere/Bi2S3 nanorod heterojunction with rich oxygen vacancy enhanced the photoreduction of Cr (VI) based on efficient charge separation

The yield and effective separation of the photosensitive charge carriers are the main factors that can improve the photocatalytic efficiency of the semiconductors. Here, we proposed a novel Z-scheme Bi4O5Br2 nanosphere/Bi2S3 nanorod heterojunction containing oxygen vacancies (OVs), prepared by two steps synthesis, involving alcoholysis and anion exchange. The photocatalytic performance of Bi4O5Br2/Bi2S3 composites with different Bi2S3 content on Cr (VI) under Xe lamp irradiation was investigated. Compared with the pristine BiOBr, monophase Bi4O5Br2, and defect-free BiOBr/Bi2S3-2, Bi4O5Br2/Bi2S3 composites exhibited outstanding photoreduction activity. The optimal Bi4O5Br2/Bi2S3-2 composite reduced 91.3% Cr (VI) under neutral conditions within 80 min. The effects of catalyst dosage, chromium concentration, pH and added electrolyte were discussed in detail. The stability tests involving 5 cycles of photocatalytic experiments indicated that Bi4O5Br2/Bi2S3-2 maintained over 70% of its efficiency. The high-efficiency photocatalytic performance of Bi4O5Br2/Bi2S3-2 was attributed to excellent light-trapping ability and the efficient migration and separation of the carrier through a Z-scheme. The OVs on the surface captured the light-excited electrons to act on the photodegradation of Cr (VI). These results enriched the heterojunction engineering dealing with BiOBr and could provide new insights for solving the problem of Cr (VI) pollution in the environment.

Soluble Complexes of Cobalt Oxide Fragments Bring the Unique CO2 Photoreduction Activity of a Bulk Material into the Flexible Domain of Molecular Science.

The deposition of metal oxides is essential to the fabrication of numerous multicomponent solid-state devices and catalysts. However, the reproducible formation of homogeneous metal oxide films or of nanoparticle dispersions at solid interfaces remains an ongoing challenge. Here we report that molecular hexaniobate cluster anion complexes of structurally and electronically distinct fragments of cubic-spinel and monoclinic Co3O4 can serve as tractable yet well-defined functional analogues of bulk cobalt oxide. Notably, the energies of the highest-occupied and lowest-unoccupied molecular orbitals (HOMO and LUMO) of the molecular complexes, 1, closely match the valence- and conduction-band (VB and CB) energies of the parent bulk oxides. Use of 1 as a molecular analogue of the parent oxides is demonstrated by its remarkably simple deployment as a cocatalyst for direct Z-scheme reduction of CO2 by solar light and water. Namely, evaporation of an aqueous solution of 1 on TiO2-coated fluorinated tin oxide windows (TiO2/FTO), immersion in wet acetonitrile, and irradiation by simulated solar light under an atmosphere of CO2 give H2, CO, and CH4 in ratios nearly identical to those obtained using 20 nm spinel-Co3O4 nanocrystals, but 15 times more rapidly on a Co basis and more rapidly overall than other reported systems. Detailed investigation of the photocatalytic properties of 1 on TiO2/FTO includes confirmation of a direct Z-scheme charge-carrier migration pathway by in situ irradiated X-ray photoelectron spectroscopy. More generally, the findings point to a potentially important new role for coordination chemistry that bridges the conceptual divide between molecular and solid-state science.

Insight into the enhanced visible-light photoreduction of aqueous Cr(VI) by assembled Fe3O4/LDO/BiOBr composites

We synthesized Fe3O4/LDO/BiOBr composites (Fe3O4/ZnAl-layered double oxide/bismuth oxybromide) by hydrothermal self-assembly and calcination treatment. The UV–visible diffuse reflectance spectra showed that Fe3O4/LDO/BiOBr had a significant redshift and enhanced visible-light absorption ability. Fe3O4/LDO/BiOBr demonstrated excellent photoreduction activity in response to Cr(VI), and the photocatalytic efficiency for 50 mg/L Cr(VI) was 98% within 30 min by Fe3O4/LDO/BiOBr-1.5. The improved behavior of Fe3O4/LDO/BiOBr for Cr(VI) was attributed to the construction of electron transfer path and efficient separation of photogenerated carriers. Fe3O4 acted as the electron-bridge between LDO and BiOBr, which accelerated the carrier transfer speed and reduced the interface resistance. The transient photocurrent response and electron transfer rate of Fe3O4/LDO/BiOBr-1.5 were 5.3 and 2.2 times greater than those of BiOBr, respectively. Fe3O4/LDO/BiOBr-1.5 also exhibited favorable durability and reusability, potential application in real Cr(VI) wastewater, and easy recovery ability from solutions under an external magnetic field. This study provided a ternary assembled Fe3O4/LDO/BiOBr for efficient photoreduction of high concentrations of Cr(VI) by effective solar light harvesting, which expanded the application of LDO-based catalysts in future wastewater treatment devices.

Photo-Driven Reduction of Carbon Dioxide: A Sustainable Approach Towards Achieving Carbon Neutrality Goal

The photo-driven reduction of carbon dioxide (CO2) into green and valuable solar fuels could be a promising solution to simultaneously address energy- and environmental-related problems. This approach could play an integral role in achieving a sustainable energy economy by closing the carbon cycle and allowing the storage and transportation of intermittent solar energy within the chemical bonds of hydrocarbon molecules. This Perspective discusses the latest technological advancements in photo-driven CO2 conversion via various pathways, namely photocatalysis, photoelectrocatalysis and photovoltaic-integrated systems. In addition to providing an outlook on unresolved issues concerning the said technologies, this Perspective also spotlights new trends and strategies in the structural engineering of materials to meet the demands for prominent CO2 photoreduction activity as well as spearhead the ground-breaking advances in the field that lead to the translation of CO2 photo-driven technologies from the laboratory to industrial-scale applications.

Removal of U(VI) from aqueous solution via photoreduction over Fe3O4/g-C3N4 composite under visible light irradiation

Herein, Fe3O4/g-C3N4 composites with different proportions were prepared to remove U(VI) from wastewater through photocatalytic reduction. The morphology, composites, and magnetism of the Fe3O4/g-C3N4 composites were measured. The characterization results showed that Fe3O4 nanoparticles were well distributed on the surface of g-C3N4, resulting in the good magnetism and corresponding excellent separation ability of the composites. The U(VI) removal efficiency of the composites with different ratios of Fe3O4 and g-C3N4 was also determined. It was found that Fe3O4/g-C3N4 with an Fe content of 14% showed the highest U(VI) removal efficiency of 98.7% after 25 min. The photocatalytic reaction rate constant was 0.161 min−1, which was 2.9 times that of pure g-C3N4 and 2.4 times that of pure Fe3O4. In addition, after five reaction cycles, the composite showed high photoreduction activity and magnetic properties.

Dual enhancement of photooxidation and photoreduction activity by coating CdS nanoparticles on lignin-based biomass carbon with irregular flower-like structure

Dual enhancement of photooxidation and photoreduction activity by coating CdS nanoparticles on lignin-based biomass carbon with irregular flower-like structure

Enhancing Nb2O5 activity for CO2 photoreduction through Cu nanoparticles cocatalyst deposited by DC-magnetron sputtering

Herein we demonstrate that the deposition of a small loading of Cu nanoparticles (0.51 wt %) by DC-magnetron sputtering over niobium oxide (Nb2O5) increases its photocatalytic activity for the reduction of carbon dioxide (CO2) into methane (CH4), methanol (CH3OH), acetone (CH3COCH3), acetic acid (CH3COOH), isopropanol (CH3CH(OH)CH3) and formate (HCOO−). The improvement in the CO2 photoreduction of the Nb2O5/Cu can be attributed mainly to a reduction in the recombination rate of the electron-holes pairs photogenerated due to the electron trapping by Cu species as observed by the photoluminescence analysis, high dispersion of Cu, and high specific surface area of material even after addition Cu.

Surface Local Polarization Induced by Bismuth‐Oxygen Vacancy Pairs Tuning Non‐Covalent Interaction for CO2 Photoreduction

AbstractThe inefficient charge separation and lack of active sites have been regarded as the main obstacles limiting the CO2 photoreduction efficiency. It is highly desirable but challenging to create a local polarization field to accelerate charge separation and build reactive sites for CO2 reduction dynamics. Herein, atomic level bismuth‐oxygen vacancy pairs are engineered into Bi24O31Br10 (BOB) atomic layers to create a local polarization field. It facilitates photogenerated electrons to migrate from BOB to vacancy pair sites and favors the activation of CO2 molecules. Simultaneously, it works as reactive sites to tune the non‐covalent interaction of intermediates and optimizes the reaction process. The vacancy pairs tuned surface atomic structures enable the formation of a highly stable Bi−C−O−Bi intermediate state and consecutive Bi−C−O intermediate, thus changing the rate‐determining step from CO* formation to COOH* formation. Benefiting from these features, the VBiO‐BOB delivers a 20.9‐fold CO2 photoreduction activity enhancement relative to highly crystalline BOB in pure water with highly stability. This work provides new insights for the design of a vacancy pair to create local polarization and tune the non‐covalent interaction.

Metal-Free Catalysis: A Redox-Active Donor-Acceptor Conjugated Microporous Polymer for Selective Visible-Light-Driven CO2 Reduction to CH4.

Achieving more than a two-electron photochemical CO2 reduction process using a metal-free system is quite exciting and challenging, as it needs proper channeling of electrons. In the present study, we report the rational design and synthesis of a redox-active conjugated microporous polymer (CMP), TPA-PQ, by assimilating an electron donor, tris(4-ethynylphenyl)amine (TPA), with an acceptor, phenanthraquinone (PQ). The TPA-PQ shows intramolecular charge-transfer (ICT)-assisted catalytic activity for visible-light-driven photoreduction of CO2 to CH4 (yield = 32.2 mmol g-1) with an impressive rate (2.15 mmol h-1 g-1) and high selectivity (>97%). Mechanistic analysis based on experimental results, in situ DRIFTS, and computational studies reveals that the potential of TPA-PQ for catalyzing photoreduction of CO2 to CH4 was energetically driven by photoactivated ICT upon surface adsorption of CO2, wherein adjacent keto groups of PQ unit play a pivotal role. The critical role of ICT for stimulating photocatalysis is further illustrated by synthesizing another redox-active CMP (TEB-PQ), bearing triethynylbenzene (TEB) and PQ, that shows 8-fold lesser activity for photoreduction toward CO2 to CH4 (yield = 4.4 mmol g-1) as compared to TPA-PQ. The results demonstrate a novel concept for CO2 photoreduction to CH4 using an efficient, sustainable, and recyclable metal-free robust organic photocatalyst.

Remarkable CO2 photoreduction activity using TiO2 nanotube arrays under favorable photothermal conditions driven by concentrated solar light

The photoreduction of carbon dioxide (CO2) to solar fuels is meaningful in many fields relevant to CO2 emission control, solar energy conversion and storage, carbon-neutral fuel production, CO2 conversion, and carbon cycle closure. The CO2 photoreduction on TiO2 nanotube arrays using concentrated sunlight under favorable photothermal conditions is considered in this work. TiO2 is a typical catalyst for the process while the reaction rate is still kept at rather poor level, partly because of the mild reaction conditions employed. In this study, the TiO2 photocatalyst was shaped as nanotube arrays and the current process limitations were tackled by raising the incident light intensity and reaction temperature by using concentrating solar light (concentration ratio between 200 and 800), while jointly increasing the achievable H2O and CO2 partial pressure. The results showed that the rate of CO2 photoreduction on the TiO2 nanotube array was increased by hundred times. The use of concentrated solar light heightens the hydrocarbons production rate to thousand μmol g−1 h−1 and enriches hydrocarbons products to CH4, C2H4, and C2H6. The favorable effects on enhancing the catalyst performance were ascribed to the intensification of reaction conditions. This noticeable breakthrough may represent an important step forward in the deployment of CO2 photoreduction technologies.

On-Demand Regulation of Photoreversible Color Switching for Rewritable Paper and Transient Information Encryption.

The achievement of photoreversible color switching systems (PCSS) has offered great opportunities for fundamental studies and practical applications. However, the development of PCSS that possessing highly reversible cyclability and on-demand regulation of recoloration process remains a grand challenge. Herein, we report a hydrazine-mediated self-doping strategy for the synthesis of alkaline Ti3+ self-doped TiO2-x nanoparticles, enabling the TiO2-x nanoparticles/methylene blue based PCSS with long photoreversible cyclability and rapid color switching rate. The Ti3+ species as internal sacrificial electron donors significantly improve the photoreductive activity of TiO2-x nanoparticles, which results in fast decoloration rate and long cycling number of the PCSS. Simultaneously, the alkaline property of TiO2-x nanoparticles enhances the oxidation kinetics of the PCSS to dramatically accelerate the recoloration rate. Moreover, the PCSS can be integrated elaborately with biodegradable agarose to form flexible color switching films, which exhibit long-waited on-demand regulation of recoloration rate in a wide range. By taking advantage of photoreversible color switching and time-resolved color changing process, we demonstrate their potential application in self-erasing rewritable paper and transient optical information encryption. This work represents a new strategy for the future development of PCSS and their advanced applications.

Highly selective CO2 capture and photoreduction over porous carbon nitride foams/LDH monolith

Sunlight-driven photocatalytic CO2 into useful carbon compounds is an ideal way to mitigate the greenhouse effect. However, this strategy is limited by poor light absorption and rapid photoexcited electron-hole recombination of traditional photocatalysts. Here, a g-C3N4 (CN) foam/LDH heterojunction monolith (NCF) was fabricated by growing NiFe-LDH in situ on the porous CN foam substrate. The composite had good air permeability and light transmittance, which improves light-harvesting, CO2 capture, and interfaces charge transfer of the NCF. The results show that the NCF catalyst has good CO2 adsorption performance (1.52 mmol g−1) and enhanced CO2 photoreduction activity (55.1 μmol g-1h−1), which is ∼ 10 times higher than that of pure LDHs powder. Furthermore, the practical applicability of the NCF monolith with different thicknesses is illustrated via the CO2 photoreduction test for the first time. This work could shed light on the development of dual-functional materials for efficient capture and photoreduction of CO2.

In2S3-NiS co-decorated MoO3@MoS2 composites for enhancing the solar-light induced CO2 photoreduction activity

In2S3-NiS co-decorated MoO3@MoS2 (INS/MoO3@MoS2) heterojunctions were prepared in nonthermal plasma via the in-situ sulfurization for enhancing the solar-light photocatalytic conversion of CO2 into CH4 and CO at 423 K. In contrast with hexagonal h-MoO3 nanorods, CH4 and CO yields were enhanced by h-MoO3@MoS2 and In2S3/MoO3@MoS2, while the increased CH4 yield and decreased CO yield were obtained by INS/MoO3@MoS2 and NiS/MoO3@MoS2. The optimal 3-INS/MoO3@MoS2 with a nominal NiS-In2S3 content of 5.0 wt% and a In/Ni molar ratio of 2:1 exhibited the best photoreduction activity of CO2, of which CH4 and CO yields were 49.11 and 6.19 μmol g−1 h−1, respectively. It's ascribed to the tight interface for enhancing the visible-light absorption capacity and reinforcing the transfer and separation of charge carriers. S-rich sites and O vacancies were favorable for the adsorption and photoreduction of reactants on the bulks surface. The nonthermal plasma induced in-situ sulfurization was thus a promising route to fabricate metal sulfides-based heterojunctions.

Renewable biomass-derived carbon-supported g-C3N4 doped with Ag for enhanced photocatalytic reduction of CO2

Constructing noble metal-doped g-C3N4/carbon composites is a feasible route to overcome the intrinsic drawbacks of pristine g-C3N4 for enhanced activity of CO2 photoreduction. Herein, a novel Ag-doped g-C3N4/biomass-derived carbon composite with hollow bird's nest-like (Ag-g-C3N4/BN-C) is designed and prepared via a simple yet effective one-step pyrolysis method. In the Ag-g-C3N4/BN-C, the highly-dispersed Ag nanoparticles (20–30 nm) with the surface plasmon resonance (SPR) effect act as a significant cocatalyst not only to efficiently trap the photogenerated electrons from g-C3N4 to boost the separation of photogenerated electron-hole pairs but also to produce additional active “hot electrons”, while the conductive quasi-spherical hollow structure of BN-C doubles the specific surface area with multiple reflections of light, providing abundant active sites and more utilization efficiency of light energy. As a result, the Ag-g-C3N4/BN-C exhibits a remarkably enhanced CO evolution rate of 33.3 μmol·g−1·h−1 without addition of any sacrificial reagents and photosensitizers, superior to those of both the pristine g-C3N4 and many reported g-C3N4-based counterparts. The findings of this work demonstrate a good indication for integrating g-C3N4 with SPR-dependence noble metal and renewable biomass-derived carbon for enhanced CO2 photoreduction, which may be extended to modify other semiconductor materials for more photocatalytic applications with enhanced activity.

Promoting photocatalytic CO2 reduction to CH4 via a combined strategy of defects and tunable hydroxyl radicals

A well-designed photocatalyst with excellent activity and selectivity is crucial for photocatalytic CO2 conversion and utilization. TiO2 is one of the most promising photocatalysts. However, its excessive surface oxidation potential and insufficient surface active sites inhibit its activity and photocatalytic CO2 reduction selectivity. In this work, highly dispersed Bi2Ti2O7 was introduced into defective TiO2 to adjust its oxidation potential and the generation of radicals, further inhibiting reverse reactions during the photocatalytic conversion of CO2. Moreover, an in situ topochemical reaction etching route was designed, which achieved defective surfaces, a contacted heterophase interface, and an efficient electron transfer path. The optimized heterophase photocatalyst exhibited 93.9% CH4 selectivity at a photocatalytic rate of 6.8 μmol·g−1·h−1, which was 7.9 times higher than that of P25. This work proposes a feasible approach to fabricating photocatalysts with well-designed band structures, highly dispersed heterophase interfaces, and sufficient surface active sites to effectively modulate the selectivity and activity of CO2 photoreduction by manipulating the reaction pathways.

BiOBr/NiO S‐Scheme Heterojunction Photocatalyst for CO2 Photoreduction

Artificial photosynthesis by CO2 photoreduction is an ideal channel for mitigating the greenhouse effect and energy crises. Nevertheless, its efficiency is still low due to severe charge recombination and sluggish kinetics. Herein, an S‐scheme BiOBr/NiO heterojunction, composed of two kinds of p‐type semiconductors, exhibits enhanced CO2 photoreduction activity. Enhanced light absorption and specific surface area are attributable to NiO nanosheets with hierarchical porous structures. Results from in situ irradiated X‐ray photoelectron spectroscopy and work function calculation manifest that the photoexcited electrons transfer from BiOBr to NiO via the S‐scheme mechanism. And charge separation and a strong redox ability are simultaneously realized. In situ diffuse reflectance infrared Fourier transform spectra unveil complex intermediates in CO2 photoreduction. This work presents a novel understanding for the CO2 photoreduction mechanism of S‐scheme heterojunctions built by p‐type semiconductors by integrating in situ monitoring techniques with density functional theory calculation.

In situ construction of Sn-doped structurally compatible heterojunction with enhanced interfacial electric field for photocatalytic pollutants removal and CO2 reduction

Fabrication of heterojunction photocatalysts is a promising strategy for achieving spatial charge separation, for which the interfacial electric field is the linchpin. However, the current density of interfacial electric field still have room for enhancement. In this study, we first demonstrated the regulation of interfacial electric field between bismuth semiconductors assisted by stannum (Sn) doping, raising the surface charge transfer efficiency from 27.25 % of BiOBr/BiOIO3 to 38.08 % of Sn-BiOBr/BiOIO3 composite. Correspondingly, the visible-light induced degradation rates towards tetracycline, 2, 4-chlorophenol and Rhodamine B exhibited 4.2-, 4.7- and 31.5-fold increase, respectively. Meanwhile, the CO2 photoreduction activity was also improved. The density functional theory calculation results unveiled that the Sn2+/Sn4+ redox couple could cause charge redistribution at interface and a distinctly unidirectional interfacial electric field with the direction from BiOIO3 to Sn-BiOBr was formed. This study provides a universal strategy for the design of bismuth-containing heterojunction with tunable interfacial electric field.