Accelerated Charge Separation Research Articles

Improved carrier dynamics in nickel/urea-functionalized carbon nitride for ethanol photoreforming.

Photoreforming has been shown to accelerate the H2 evolution rate compared to water splitting due to thermodynamically favorable organic oxidation. In addition, the potential to simultaneously produce solar fuel and value-added chemicals is a significant benefit of photoreforming. To achieve an efficient and economically viable photoreforming process, the selection and design of an appropriate photocatalyst is essential. Carbon nitride is promising as a metal-free photocatalyst with visible light activity, high stability, and low fabrication cost. However, it typically exhibits poor photogenerated charge carrier dynamics, thereby resulting in low photocatalytic performance. Herein, we demonstrate improved carrier dynamics in urea-functionalized carbon nitride with in situ photodeposited Ni cocatalyst (Ni/Urea-CN) for ethanol photoreforming. In the presence of 1mM Ni2+ precursor, an H2 evolution rate of 760.5µmolh-1g-1 and an acetaldehyde production rate of 888.2µmolh-1g-1 were obtained for Ni/Urea-CN. The enhanced activity is ascribed to the significantly improved carrier dynamics in Urea-CN. The ability of oxygen moieties in the urea group to attract electrons and to increase the hole mobility via a positive shift in the valence band promotes an improvement in the overall carrier dynamics. In addition, high crystallinity and specific surface area of the Urea-CN contributed to accelerating charge separation and transfer. As a result, the electrons were efficiently transferred from Urea-CN to the Ni cocatalyst for H2 evolution while the holes were consumed during ethanol oxidation. The work demonstrates a means by which carrier dynamics can be tuned by engineering carbon nitride via edge functionalization.

Construction of rGO-coupled C3N4/C3N5 2D/2D Z-scheme heterojunction to accelerate charge separation for efficient visible light H2 evolution

As a fascinating two-dimensional (2D) conjugated polymer, graphitic carbon nitride (C3N4) has drawn broad attention as metal-free photocatalyst, but it’s further utilization is confined by the limited visible light harvesting and severe charge recombination. Herein, N-rich carbon nitride (C3N5) with an azo-linked two s-heptazine units, different from C3N4 with a tertiary N-atom linked three s-heptazines, is prepared for constructing a novel sandwich heterojunction composed of reduced graphene oxide (rGO)-coupled C3N5 and C3N4. The introduced rGO in C3N4/rGO/C3N5 heterojunction can accelerate the interfacial charge separation and promote a rGO-mediated solid-state Z-scheme mechanism with an obvious synergistic effect, whereby C3N4 and C3N5 serve as electron-rich and hole-rich reservoirs, respectively. The resultant 2D/2D heterojunction delivers efficient visible-light-responsive activity with H2 evolution rate of 319 μmol h−1, 5.6 and 2.7 times higher than that of C3N4 and C3N5 alone, respectively. This work presents a new concept to design highly efficient carbon nitride-based artificial photosynthetic system.

Interface Cd-N bond bridge accelerating charge separation to the enhanced visible light driven hydrogen production from water splitting on polyaniline@Cd-Zn-S photocatalyst

The key to the industrialization of eco-friendly hydrogen production from visible light driven water splitting is the development of photocatalyst with high performance and superior stability. Herein, a novel core-shell structure polyaniline@Cd-Zn-S (Cd/Zn = 0.8/0.2) nanorod photocatalyst with the shell thickness at ∼3 nm was constructed successfully. With polyaniline served as core, the construction of polyaniline@Cd-Zn-S reduced the charge transfer resistance and released reactive sites maximumly which could benefit the hydrogen production. The constructed polyaniline@Cd-Zn-S exhibited excellent photocatalytic hydrogen production efficiency and stability with the assistance of interface Cd-N bonds. The introduction of Cd-N bonds at the interface was inferred by both experimental and DFT simulated results. It served as the bridge between shell Cd-Zn-S and core polyaniline and promoted the directional transmission and efficient separation of photo generated charge carriers. Meanwhile, the improved directional transmission of photogenerated holes restricted photo corrosion effect of the Cd-Zn-S effectively and contributed to the photocatalytic stability. The hydrogen production without any cocatalyst increased more than 6 times to 721 μmol·h−1 after the construction of core-shell structure, and remain stable for 12 consecutive hours without photocatalytic performance reduction. This work proposed a new inspiring structural model for hetero junction construction of photocatalyst, and brought an interesting enlightenment to the development of eco-friendly hydrogen production technology.

(Invited) A Carbon Nanotube Binding Bis(pyrenylstyryl)Bodipy-C60 Nano Tweezer: Formation and Photoinduced Charge Separation in Supramolecular C60-Bodipy-SWCNT Triads

Electron donor-acceptor hybrids comprised of single-wall carbon nanotubes (SWCNT) are promising functional structures having direct applications in energy conversion schemes and molecular optoelectronics. For building such hybrids and exfoliation of SWCNTs, the p-stacking ability of large aromatic compounds such as pyrene is one of the commonly employed approaches. Often, the desired donor or acceptor entities are functionalized to carry one or more pyrene entities and allowed to interact with CNTs. As a suitable electron donor, BODIPYs stand out owing to their ease of structural modifications and rich spectral and redox properties. Consequently, several donor-acceptor conjugates comprised of BF2-chelated dipyrromethene, BODIPY, and the well-known electron acceptor, C60 have been developed. In the present study, we have newly synthesized a nano tweezer comprised of covalently linked BODIPY-C60 carrying two pyrenylstyryl arms, 1. Compound 1 is further allowed to interact with SWCNT(6,5) and SWCNT(7,6) to form the supramolecular C60-BODIPY-SWCNT triads. Upon spectral, electrochemical, and computational characterization, pump-probe spectroscopic studies covering a wide femto-to-millisecond time scale have been performed to establish the occurrence of photoinduced charge separation. The presence of CNT prolonged the lifetime of the charge-separated states revealing the success of the present molecular design strategy for energy harvesting applications. D’Souza, F.; Sandanayaka, A. S. D.; Ito, O. ‘SWNT-Based Supramolecular Nanoarchitectures with Photosensitizing Donor and Acceptor Molecules’ Phys. Chem. Letts. 2010, 1. 2586-2593.B. KC, G. N. Lim, and F. D’Souza, ‘Accelerated Charge Separation in Graphene Decorated Multi-Modular Tripyrene-Subphthalocyanine-Fullerene Donor-Acceptor Hybrids,’ Angew. Chem. Int. Ed. 2015, 54, 5088-5092.Barrejon, L. M. Arellano, F. D’Souza, F. Langa, ‘Bidirectional charge transfer in carbon-based hybrid nanomaterials’ Nanoscale, 2019, 11, 14978-14992. Figure 1

Plasmonic TiN nanobelts assisted broad spectrum photocatalytic H2 generation

The conversion of solar energy in a wide spectrum region to clean fuel, H2, remains a challenge in the field of photocatalysis. Herein, plasmonic TiN nanobelts, as a novel cocatalyst, were coupled with CdS nanoparticles to construct a 0D/1D CdS/TiN heterojunction. Utilization of the localized surface plasmon resonance (LSPR) effect generated from TiN nanobelts was effective in promoting light absorption in the near-infrared region, accelerating charge separation, and generating hot electrons, which can effectively improve the photocatalytic H2 generation activity of the 0D/1D CdS/TiN heterojunction over a wide spectral range. Furthermore, owing to the high metallicity and low work function, an ohmic-junction was formed between the CdS and TiN, favoring the transfer of hot electrons generated from TiN nanobelts the CdS nanoparticles, followed by the reaction with water to generate H2. Consequently, the 0D/1D CdS/TiN heterojunction demonstrated H2 generation activity even under light irradiation at 760 nm, while the pure CdS and Pt nanoparticles modified CdS presented no activity. This work opens a new insight into coupling plasmonic cocatalysts to realize full spectrum H2 production.

Facile construction of Fe3+/Fe2+ mediated charge transfer pathway in MIL-101 for effective tetracycline degradation

Semiconductor-based photocatalyst, whose efficiency distinctly hinges on the separation of photoinduced charge transfer within the interface of bulk structure, has incurred some intractable issues due to the existing energy barrier. Regulating the structure of MOF reasonably would feature an accelerated charge separation, and an effective utilization of photogenerated charges. Herein, a new type of MOF with both interior linker and metal valence modulation (m-MIL-101–1.0) is reported to boost photocatalytic activity owing to the formed charge migration pathway. At first, we introduced defective sites via CTAB, which acted as exposed sites for further reduction reaction. Then, NaBH4 was used to achieve metal valence regulation. Benefiting from the unique structure, the Fe3+/Fe2+ redox center was considered as a driving force to facilitate the charge transfer. It is properly considered that the activity improvement is attributed to the synergistic effect of both internal and external charge transfer channels. As a result, such m-MIL-101–1.0 has a higher activity than that of MIL-101 for photocatalytic degradation of tetracycline in water. We envision this interior configuration would be an ideal paradigm for tuning the activity of MOFs and extending the boundaries of MOF-based photocatalysts.

Precisely modifying Co2P/black TiO2 S-scheme heterojunction by in situ formed P and C dopants for enhanced photocatalytic H2 production

The construction of S-scheme heterojunction catalysts is promising for efficient photocatalytic hydrogen production, but the conscious modulation of S-scheme charge transfer has remained largely underdeveloped. Herein, P and C modified Co2P/black TiO2 S-scheme heterojunction photocatalyst (Co2P/PC-b-TiO2) is prepared by pyrolyzing a mixture of cobalt phosphonate and TiO2 under H2 atmosphere. The in situ formed P and C dopants can not only enhance the ratio of surface active O species to bulk O defects but also inhibit anatase-to-rutile phase transformation, thereby ensuring the high intrinsic activity. More importantly, the S-scheme heterojunction between PC-b-TiO2 and Co2P is modified by the incorporation of P and C, wherein the intimately coupled heterointerface and strong internal electric field can accelerate charge separation and migration and optimize the available redox potential. Accordingly, Co2P/PC-b-TiO2 displays dramatically ascendant photocatalytic hydrogen evolution performance and outstanding stability. This study provides guidance for elaborately modifying S-scheme heterojunctions through heteroatom doping and heralds a new paradigm for engineering advanced heterojunction catalysts.

Dysprosium doping in CdTe@CdS type II core/shell and cosensitizing with CdSe for photocurrent and efficiency enhancement in quantum dot sensitized solar cells

Quantum dot sensitized solar cells (QDSSCs) based on the II-VI QDs have become a promising and attractive technology due to their unique properties. However, the applications of the II-VI QDs, especially CdTe QDs, have still been restricted. Herein, a CdTe@Dy-doped CdS core/shell QDs cosensitized with CdSe QDs have been developed as a sensitizer in QDSSCs for enhancing the light-harvesting range and efficiency, accelerating charge separation, and suppressing charge recombination. The fabricated QDSSCs using TiO2/CdTe@Dy-doped-CdS/CdSe/ZnS photoanode exhibited the best short-circuit current (JSC = 20.08 mA/cm2) and power conversion efficiency (ƞ=8.26%) in comparison with that of other photoanodes comprising TiO2/CdTe, TiO2/CdTe@CdS, TiO2/CdTe@CdS/ZnS, TiO2/CdTe@CdS/CdSe/ZnS, and TiO2/CdTe@CdS/CdSe/Dy-Doped ZnS. As the obtained results from Diffuse Reflectance Spectroscopy, Photoluminescence, and Electrochemical Impedance Spectroscopy revealed, the CdTe/CdS type-II core/shell structure QDs leads to a wide absorption range, fast electron injection, and slower recombination rate because of the spatially indirect energy gap formation. Moreover, the presence of Dy cations in CdS crystal lattice boosts the charge transferring rate to the conduction band of TiO2. On the other hand, the cosensitizing of CdTe@Dy-doped CdS QDs with CdSe is advantageous not only to the electron injection and transferring but also to the hole-recovery from the valence band of QDs toward the electrolyte.

Simultaneously tailor band structure and accelerate charge separation by constructing novel In(OH)3-TiO2 heterojunction for enhanced photocatalytic water reduction

The convenient modification of transition metal and the simultaneous adjustment of energy band are effective measures to improve the photocatalytic activity of titanium dioxide but remains challenging in photocatalytic hydrogen evolution field. Herein, In(OH)3-TiO2 heterostructures were constructed by solid-state synthetic strategy under room temperature for tuning the band structure and accelerating the photoexcited charge separation to enhance the photocatalytic activity for hydrogen evolution. By the quantified modification of In(OH)3, the obtained In(OH)3-TiO2 delivers an appreciable photocatalytic activity and stability for hydrogen evolution, which is 15.7 folds superior to commercial P25. Due to the narrowed band gap, the increased charge carrier density, the restrained recombination rate of photoexcited electron-hole pairs and the accelerated photogenerated charge separation, the In(OH)3-TiO2 heterostructures thereby achieve the boosted photocatalytic hydrogen evolution performance. This work provides a feasible strategy to enhance the photocatalytic hydrogen evolution of TiO2 via tuning the band gap and accelerating the photoinduced charge separation.

Efficient charge transfer and CO2 photoreduction of hierarchical CeO2@SnS2 heterostructured hollow spheres with spatially separated active sites

Heterostructured hybrids with hollow configuration and efficient charge separation are very promising for CO2 photoreduction. This study demonstrates the design and fabrication of hierarchical double-shelled CeO2@SnS2 hollow spheres with spatially separated active sites (MnOx/CeO2@SnS2/Ni2P DSHSs) for efficient CO2 photoreduction. In this catalyst system, MnOx and Ni2P cocatalysts are selectively anchored on the CeO2 and SnS2 shells, respectively, forming spatially separated active sites. The confinement effect of outer-surface SnS2 nanosheets offers more opportunities for Ni2P cocatalyst to react with CO2 molecules. Owing to the desired hierarchical double-shelled hollow architecture and spatially-separated cocatalysts, the MnOx/CeO2@SnS2/Ni2P DSHSs possess the advantages of abundant spatially-separated active sites, enhanced visible-light harvesting, and accelerated charge separation. As expected, the optimized MnOx/CeO2@SnS2/Ni2P DSHSs sample exhibits remarkable CO2 photoreduction activity. The CO yield and selectivity reach 29.67 μmol g−1 h−1 and 90.1%, respectively, which are remarkably higher than the control samples. This study demonstrates a promising strategy to construct well-defined hierarchical hybrid catalysts for maximizing CO2 photoreduction performance.

Steering Unit Cell Dipole and Internal Electric Field by Highly Dispersed Er atoms Embedded into NiO for Efficient CO2 Photoreduction

AbstractThe weak internal electric field over antiferromagnetic materials makes it difficult to facilitate charge migration to the surface, leading to low performance for CO2 photoreduction. The asymmetry and polarization refinement structure can induce an intensive internal electric field. Herein, n‐type NiO is synthesized with highly dispersed erbium atoms doping (Er/NiO1−x) via a molten salt method to accelerate charge separation and transfer. The doping of Er atoms can distort the unit cell of NiO to alter the symmetry and enhance the polarization and internal electric field, in favor of efficient separation of charges. In addition, the highly dispersed erbium‐doped n‐type NiO can largely boost the adsorption and activation of CO2, and weaken the energy barrier for CO2 photoreduction reaction. Benefiting from the unique features, an optimal doping ratio (≈2%) with erbium atoms achieves a remarkable elevation in carrier separation efficiency and excellent CO2 photoreduction performance with a CO yield of 368 µmol g−1 h−1 in the Ru(byp)32+/ethanolamine electron‐agent generating system, which is 26.3‐fold and 3.9‐fold relative to traditional NiO and n‐type NiO, respectively. The obtained Er/NiO1−x photocatalyst and the unit cell dipole governing the internal electric field opens a new window for CO2 photoreduction in antiferromagnetic materials.

Constructing Z-scheme carbon-rich carbon nitride/TiO2 photocatalyst for improved photocatalytic activity

A carbon-rich polymeric carbon nitride/TiO2 photocatalyst was prepared by self-assembling for photodegradation of pollutant. The model pollutant, rhodamine B, was almost completely decomposed by the photocatalyst within 10 min of white light irradiation. The radical trapping experiment suggested the photogenerated electrons, photogenerated holes and hydroxyl radicals are the predominant active species for RhB removal, which also demonstrated the migration of charge carriers followed the Z-scheme transfer path. Beside, the enhanced light harvesting ability and accelerated charge separation are also beneficial to the highly efficient photocatalytic activity. This work provides a simple method to construct Z-scheme photocatalyst.

Boosting 2e− oxygen reduction reaction in garland carbon nitride with carbon defects for high-efficient photocatalysis-self-Fenton degradation of 2,4-dichlorophenol

Photocatalytic two-electron oxygen reduction reaction (2e-ORR) has been regarded as a promising strategy to solve the disadvantage of Fenton technology (constant addition of H2O2). Herein, a photocatalysis-self-Fenton system was constructed on garland g-C3N4 with carbon defects (GCN-PSFs) for pollutants degradation. Carbon defects in the obtained GCN not only accelerate charge separation but also improve 2e- ORR. As expected, the apparent rate constant for 2,4-DCP degradation by GCN-PSFs enhances to 0.070 min−1, which is 5.4, 3.3 and 2.6 times as that of BCN, BCN-PSFs and GCN. The capture experiments and electron spin resonance indicate that the high activity is attributed to abundant ∙OH radicals, which are formed from the in-situ produced H2O2. Density functional theory (DFT) calculation confirms that the carbon defects in GCN is favorable for photocatalytic 2e- ORR to H2O2. This work provides a new insight for high-efficient degradation of organic pollutants by PSFs.

Rationally constructed ZnCdS-HDCs@In2S3-HNRs double-hollow heterojunction with promoted light capture capability for photoelectrochemical biosensing

The construction of novel heterojunction is regarded as an operative scheme to promote the transport of photogenerated carriers and reduce electron-hole pair recombination to enhance the photoelectrochemical (PEC) performances. Herein, ZnCdS hollow dodecahedral nanocages (ZnCdS-HDCs) and In2S3 hollow nanorods (In2S3-HNRs), which were derived from two different of metal-organic frameworks (MOFs) by solvothermal sulfidation method and were constructed an original double-hollow heterostructure ZnCdS-HDCs@In2S3-HNRs. The intrinsic mechanism of In2S3-HNRs benefiting from unique morphology to boost the photochemical properties under visible light irradiation was illustrated. Meanwhile, the mechanism of the novel type II heterojunction with staggered matching levels was revealed, which could effectively restrict electron-hole pair reassociation separation, and accelerated charge separation and transfer. Therefore, based on the excellent PEC performance of ZnCdS- HDCs@In2S3-HNRs double-hollow heterostructure, a signal-off PEC biosensor platform without labeled was constructed for the detection of CA15-3, which manifested acceptable specificity, reproducibility and stability. Additionally, the expected PEC biosensors showed a linear response range from 1.0 × 10−5 to 10 U·mL−1 in addition to an ultralow detection limit of 3.78 × 10−6 U·mL−1. This study innovatively constructed and prepared a new double-hollow heterojunction material with superior PEC nature for the application of PEC biosensing, which exhibits a broad application prospect.

PtS quantum dots/Nb2O5 nanosheets with accelerated charge transfer for boosting photocatalytic H2 production

PtS quantum dot cocatalysts/Nb2O5 nanosheets showed abundant active sites and accelerated charge separation, leading to excellent photocatalytic H2 evolution performance.

Ternary 0d/2d/3d Photocatalyst Constructed by AU Clusters Ti3c2tx and Tio2 Based on Strong Interfacial Interaction and Accelerating Charge Separation for Efficiently Hydrogen Production

Ternary 0d/2d/3d Photocatalyst Constructed by AU Clusters Ti3c2tx and Tio2 Based on Strong Interfacial Interaction and Accelerating Charge Separation for Efficiently Hydrogen Production

In situ growth of 2D/3D Bi2MoO6/CeO2 heterostructures toward enhanced photodegradation and Cr(VI) reduction

The construction of semiconductor-based photocatalysts has attracted more and more attention due to their great potential for the utilization of solar light. In our work, a heterostructure by in situ integration of bismuth molybdate nanosheets and ceria microspheres (Bi2MoO6/CeO2) was successfully fabricated and used for effective photocatalytic degradation of pollutants and Cr(VI) reduction. The chemical compositions, microstructures, and optical properties of obtained nanocomposites were investigated by various characterization. The optimized Bi2MoO6/CeO2 showed more superior degradation rate for RhB and tetracycline than the most Bi2MoO6-based photocatalysts previously reported, and exhibited superb removal rates of 98.4% for Cr(VI) reduction within 90 min, which was much higher than those of pristine Bi2MoO6 and CeO2. A typical type–II photocatalytic mechanism was put forward by considering active species capture experiments, EPR, and XPS analysis, which was beneficial to adjust the bandgap structure and accelerate charge separation. This present work manifests that Bi2MoO6/CeO2 nanocomposites with excellent photocatalytic properties have a vast application prospect in wastewater remediation.

Type-Ⅰ hetero-junction of BiOI-BiO2-x anchored on Ni foam accelerating charge separation and transfer for efficiently purifying hazardous wastewater

About 70 mg of BiOI-BiO2-x powder was attached to Ni foam. Compared to BiOI/Ni foam and BiO2-x/Ni foam, the BiOI-BiO2-x/Ni foam exhibited distinctly enhanced photocatalytic activity for removing RhB from water. Among them, the BiOI-BiO2-x = 1:3/Ni foam demonstrated the optimal photocatalytic activity. Around 97% of RhB was decomposed over BiOI-BiO2-x = 1:3/Ni foam under 7 h irradiation of a 300 W xenon lamp, which was 47.5 times that over BiOI/Ni foam and 1.3 times that over BiO2-x/Ni foam, respectively. The degradation rate constant (k) of RhB over BiOI-BiO2-x = 1:3/Ni foam was 71.8 times that over BiOI/Ni foam and 2.6 times that over BiO2-x/Ni foam, respectively. The removal rates of TOC and TON in the BiOI-BiO2-x = 1:3/Ni foam solution were approximately 50% and 29%, respectively. Photo-induced electrons and holes flowed from BiOI to BiO2-x and then photo-generated electrons of BiO2-x further transferred to Ni foam. The separation efficiency of carriers in BiOI-BiO2-x = 1:3/Ni foam was greatly improved, thereby enhancing its photocatalytic activity. In addition, the improved photocatalytic activity of BiOI-BiO2-x = 1:3/Ni foam was ascribed to its strong adsorption capacity. The mainly active species for RhB degradation were holes (h+) and superoxide radicals (·O2–).

Ag3PO4-TiO2-Carbon nanofiber Composite: An efficient Visible-light photocatalyst obtained from electrospinning and hydrothermal methods

In this contribution, we synthesized Ag3PO4-TiO2 NPs assembled carbon nanofibers (Ag3PO4-TiO2-CNFs) photocatalyst by the combination of electrospinning and hydrothermal processes. The photocatalyst was characterized by various techniques such as SEM, TEM, XRD, UV, PL, etc. The morphological examination by SEM and TEM revealed a uniform distribution of the Ag3PO4 NPs over the TiO2-CNFs surface. Compared to TiO2 NFs, the loading of Ag3PO4 NPs into the TiO2-CNFs composite enhances its absorbance to the visible light region and offers a route with low resistance for charge separation. The photocatalytic performance of the Ag3PO4-TiO2-CNFs composite was studied by a methylene blue (MB) degradation test under visible light irradiation. It was observed that the Ag3PO4-TiO2-CNFs composite exhibited significantly enhanced photocatalytic performance as compared to the pristine Ag3PO4 NPs and TiO2 NFs. The Ag3PO4-TiO2-CNFs composite eliminated the entire MB dye within 10 min of visible light irradiation. Also, the reusability test indicated that the photocatalyst possesses excellent stability. The high photocatalytic activity is attributed to the increased surface area, enhanced visible light response, accelerated charge separation, and dye adsorption property of the composite material. Furthermore, the photocatalyst showed good antibacterial property against Escherichia coli (E. coli) bacteria. The excellent dyes removal ability and the good antibacterial property of the as-prepared Ag3PO4-TiO2-CNFs photocatalyst show the potentiality of the material in wastewater treatment.

FeOOH photo-deposited perylene linear polymer with accelerated charge separation for photocatalytic overall water splitting

FeOOH photo-deposited perylene linear polymer with accelerated charge separation for photocatalytic overall water splitting