Rational Design Of Photocatalysts Research Articles

Unraveling Charge-Separation Mechanisms in Photocatalyst Particles by Spatially Resolved Surface Photovoltage Techniques.

The photocatalytic conversion of solar energy offers a potential route to renewable energy, and its efficiency relies on effective charge separation in nanostructured photocatalysts. Understanding the charge-separation mechanism is key to improving the photocatalytic performance and this has now been enabled by advances in the spatially resolved surface photovoltage (SRSPV) method. In this Review we highlight progress made by SRSPV in mapping charge distributions at the nanoscale and determining the driving forces of charge separation in heterogeneous photocatalyst particles. We discuss how charge separation arising from a built-in electric field, diffusion, and trapping can be exploited and optimized through photocatalyst design. We also highlight the importance of asymmetric engineering of photocatalysts for effective charge separation. Finally, we provide an outlook on further opportunities that arise from leveraging these insights to guide the rational design of photocatalysts and advance the imaging technique to expand the knowledge of charge separation.

CdS nanoparticles with highly exposed (1 1 1) facets decorated on Pt/TiO2 nanotubes for highly efficient photocatalytic H2 evolution

Photocatalytic water splitting is a prospective strategy to solve the shortage of human fossil fuel energy. In this work, we designed and synthesized the Pt as co-catalyst decorated on TiO2 nanotubes/metastable zinc-blende (ZB) CdS nanoparticles (NPs) with highly exposed (111) facets (HPTCA3) via the electrospinning-solvothermal and chemical deposition methods. The H2 evolution rate of HPTCA3 was 15025.38 μmol·g−1·h−1, which was about 111.3 and 2.4 times stronger than that of pure CdS power and Pt-TiO2/CdS hollow nanotubes (HPTC). The XRD patterns showed the presence of acetate promoted the growth of ZB CdS (111) crystal facets, and the photogenerated electrons were easily tended to accumulate on the CdS (111) facets, whichwas conducive to the transmission of electrons on the CdS and TiO2 interface. The type II heterojunction can broaden the visible light response range and accelerate the separation and transfer of photo-generated electrons and holes which can be supported by the Optical and Electrochemical characterizations. Band structure calculations and XPS spectrum indicated that the composite catalyst had an efficient electron transfer mechanism, which was beneficial for the spatial separation of photogenerated carriers. The work provides a rational photocatalyst design to improve the performance of photocatalytic splitting of water into hydrogen.

Rational Design of Photocatalysts for Controlled Polymerization: Effect of Structures on Photocatalytic Activities.

Over the past decade, the use of photocatalysts (PCs) in controlled polymerization has brought new opportunities in sophisticated macromolecular synthesis. However, the selection of PCs in these systems has been typically based on laborious trial-and-error strategies. To tackle this limitation, computer-guided rational design of PCs based on knowledge of structure-property-performance relationships has emerged. These rational strategies provide rapid and economic methodologies for tuning the performance and functionality of a polymerization system, thus providing further opportunities for polymer science. This review provides an overview of PCs employed in photocontrolled polymerization systems and summarizes their progression from early systems to the current state-of-the-art. Background theories on electronic transitions are also introduced to establish the structure-property-performance relationships from a perspective of quantum chemistry. Typical examples for each type of structure-property relationships are then presented to enlighten future design of PCs for photocontrolled polymerization.

Facet junction of BiOBr nanosheets boosting spatial charge separation for CO2 photoreduction

Understanding on the photogenerated charge separation from a microscopic level remains a challenge and is highly desirable as it provides a cornerstone for designing high-performance photocatalysts. Herein, facet engineering is chosen as a tool to reveal the relationship between the charge separation/transfer and crystal structure. A series of BiOBr nanosheets with dominantly exposed facet of (001) or (010) as well as different lateral facet exposure ratios are constructed via adjusting pH value during the hydrothermal process. It is found that exposure of anisotropic crystal facets allows the separative transfer of photogenerated electrons and holes onto the lateral facets and dominantly exposed facets, respectively, which is attributed to the junction formed between distinct facets (i.e., facet junction). In the case of BiOBr-5 with (010)/(102) facet junction, the electron transfer rate (kET) and efficiency (ηET) are 3.658 × 106s−1 and 54.09%, which are superior than the counterpart of BiOBr-1 with (001)/(110) facet junction. The fast electron transfer rate and high transfer efficiency of BiOBr-5 result in the high CO evolution rate from CO2 photoreduction under artificial sunlight. Our work may bring some new insights into the mechanism of facet junction and rational design of photocatalysts with high performance for solar energy storage in future.

2D Pentagonal Pd‐Based Janus Transition Metal Dichalcogenides for Photocatalytic Water Splitting

Janus transition metal dichalcogenides (TMDs), which differ from their conventional counterparts by exhibiting two different layers of chalcogenides and an asymmetric out‐of‐plane structural configuration, are theorized to exhibit a relatively wide variety of properties. Herein, the structural, electronic, and optical properties of three Janus Pd‐based TMD monolayers (PdSSe, PdSTe, and PdSeTe) are investigated through comprehensive density functional theory calculations. The most stable ground‐state configurations of these Janus TMD monolayers correspond to the unique pentagonal configuration instead of the common 1T or 2H phases. The monolayers are semiconductors with moderate bandgaps (2.06–2.21 eV) and anisotropic optical absorption properties. By exhibiting suitable band edge positions with respect to the redox potentials of water, they can simultaneously facilitate the hydrogen and oxygen evolution reactions as water‐splitting photocatalysts. In addition, the effects of uniaxial and biaxial strains on the optoelectronic properties of the monolayers are investigated, and it is determined that the application of strain reduces their bandgaps and causes a redshift of their optical absorption spectra, thereby allowing them to harvest ultraviolet and visible photons more effectively. An insight on the intrinsic properties of 2D Pd‐based Janus TMDs is provided, which elucidates the rational design of photocatalysts for water splitting.

Single-Atom Fe-N4 sites promote the triplet-energy transfer process of g-C3N4 for the photooxidation

Polymeric carbon nitride materials show intriguing prospects in numerous light-to-energy conversion applications, but seldom studies focus on their triplet energy transfer, leading to the insufficient lifetime for the photochemical process. Inspired by the porphyrin molecular photocatalyst, single-atom sites (Fe-N4) as triplet sensitizing sites were fabricated in g-C3N4 for the preparation of Fe-g-C3N4, which processes a long-lived triplet emissive state (τPH = 4.93 μs). But under realistic condition for the large-scale production of catalyst, single atoms are inevitable to sinter, resulting in the formation of other metal species. Therefore, the photooxidation of 1,5-dihydroxynaphthalene (1,5-DHN) and the photocatalytic E-Z Isomerization of stilbene were selected as the model reactions to evaluate the influence of various Fe species on the triplet energy transfer. It was found that Fe-N4 sites promote the triplet energy transfer process, while Fe nanoclusters (Fe0) promote the electron transfer and inhibit triplet energy transfer. This finding provides guidance for the rational design of photocatalysts to efficiently improve triplet energy transfer process and its application.

Novel g-C3N4/C/Fe2O3 Composite for Efficient Photocatalytic Reduction of Aqueous Cr(VI) under Light Irradiation

Research on the rational design of photocatalysts for efficient hexavalent chromium (Cr(VI)) reduction from Cr(VI)-containing wastewater has attracted widespread attention. In this paper, a novel g...

Molecular-Level Insights on the Facet-Dependent Degradation of Perfluorooctanoic Acid.

Perfluorooctanoic acid (PFOA) has raised significant health concerns due to its high ecotoxicological risks and difficulties in removal by conventional water treatment process. Previous studies have demonstrated that photocatalytic techniques exhibit great potential in PFOA removal. However, the underlying mechanism of the degradation process has not been fully understood, particularly the contribution of the facet effects of catalysts. In this study, a combination of experiments and first-principles calculations were conducted to shed light on the facet-dependence of the interfacial interactions and oxidation during the PFOA degradation process. We proved that the interfacial interaction was essential in initiating the hole-dominated degradation process, and the {110}R3̅c facet of hexagonal In2O3 features the strongest interaction with PFOA. The overall defluorination rate was mainly controlled by the hole-dominated oxidation processes under UV irradiation, which were further attributed to the electronic structures and reaction site distributions of different In2O3 surfaces. This study provides molecular-level insights on the facet-dependent PFOA catalytic degradation process, which can guide the rational design of photocatalysts to achieve superior decontamination efficiency.

Atomically Dispersed Iron Metal Site in a Porphyrin-Based Metal-Organic Framework for Photocatalytic Nitrogen Fixation.

The rational design of photocatalysts for efficient nitrogen (N2) fixation at ambient conditions is important for revolutionizing ammonia production and quite challenging because the great difficulty lies in the adsorption and activation of the inert N2. Inspired by a biological molecule, chlorophyll, featuring a porphyrin structure as the photosensitizer and enzyme nitrogenase featuring an iron (Fe) atom as a favorable binding site for N2via π-backbonding, here we developed a porphyrin-based metal-organic framework (PMOF) with Fe as the active center as an artificial photocatalyst for N2 reduction reaction (NRR) under ambient conditions. The PMOF features aluminum (Al) as metal node imparting high stability and Fe incorporated and atomically dispersed by residing at each porphyrin ring promoting the adsorption and the activation of N2, termed Al-PMOF(Fe). Compared with the pristine Al-PMOF, Al-PMOF(Fe) exhibits a substantial enhancement in NH3 yield (635 μg g-1cat.) and production rate (127 μg h-1 g-1cat.) of 82% and 50%, respectively, on par with the best-performing MOF-based NRR catalysts. Three cycles of photocatalytic NRR experimental results corroborate a stable photocatalytic activity of Al-PMOF(Fe). The combined experimental and theoretical results reveal that the Fe-N site in Al-PMOF(Fe) is the active photocatalytic center that can mitigate the difficulty of the rate-determining step in photocatalytic NRR. The possible reaction pathways of NRR on Al-PMOF(Fe) were established. Our study of porphyrin-based MOF for the photocatalytic NRR will provide insight into the rational design of catalysts for artificial photosynthesis.

Improved charge separation and carbon dioxide photoreduction performance of surface oxygen vacancy-enriched zinc ferrite@titanium dioxide hollow nanospheres with spatially separated cocatalysts

Here, we describe the fabrication of surface oxygen vacancy-enriched ZnFe2O4@TiO2 double-shell hollow heterostructure nanospheres (ZnFe2O4@H-TiO2-x) coupled with spatially separated CoOx and Au-Cu bimetallic cocatalysts. The ZnFe2O4@TiO2 heterojunction and spatially separated dual cocatalysts can significantly promote the separation of photoinduced charge carriers. Combined with the unique hollow double-shell heterostructure characteristics and improved surface state properties, the hybrid nanospheres can efficiently adsorb and activate CO2 molecules. These advantages cause the optimized catalyst to exhibit remarkably higher gas-phase photocatalytic CO2 reduction activity than the control CoOx/ZnFe2O4/Au-Cu and ZnFe2O4@H-TiO2-x double-shell hollow nanospheres loaded with a single cocatalyst. Meanwhile, the Au-Cu bimetal effect boosts the CO2 conversion rate and CH4 selectivity. The optimized hybrid catalyst with a Au/Cu ratio of 1:1 provides a CH4 yield of 21.39 μmol g−1 h−1 with 93.8% selectivity. This work provides a rational photocatalyst design to improve CO2 conversion and CH4 selectivity.

Engineering BiOBrxI1−x solid solutions with enhanced singlet oxygen production for photocatalytic benzylic C[sbnd]H bond activation mediated by N-hydroxyl compounds

The aerobic, selective oxidation of hydrocarbons via CH bond activation is still a challenge. This work shows the achievement of the room temperature visible light driven photocatalytic activation of benzylic CH bonds with N-hydroxysuccinimide over BiOBrxI1-x (0 ≤ x ≤ 1) solid solutions, whose valance bands were engineered through varying the ratio of bromide to iodide. The optimal BiOBr0.85I0.15 catalyst exhibited over 98% conversion ratio of ethylbenzene, which was about 3.9 and 8.9 times that of pure BiOBr and BiOI, respectively. The excellent photocatalytic activity of BiOBr0.85I0.15 solid solution can be ascribed to the orbital hybridization of the valence band containing both Br 4p and I 5p orbitals, which could promote photo-induced charge carrier separation and improve the generation of singlet oxygen. This work shed some light on the rational design of photocatalysts for targeted organic transformation.

Coproduction of hydrogen and lactic acid from glucose photocatalysis on band-engineered Zn1-xCdxS homojunction

SummaryPhotocatalytic transformation of biomass into value-added chemicals coupled with co-production of hydrogen provides an explicit route to trap sunlight into the chemical bonds. Here, we demonstrate a rational design of Zn1-xCdxS solid solution homojunction photocatalyst with a pseudo-periodic cubic zinc blende (ZB) and hexagonal wurtzite (WZ) structure for efficient glucose conversion to simultaneously produce hydrogen and lactic acid. The optimized Zn0.6Cd0.4S catalyst consists of a twinning superlattice, has a tuned bandgap, and displays excellent efficiency with respect to hydrogen generation (690 ± 27.6 μmol·h−1·gcat.−1), glucose conversion (~90%), and lactic acid selectivity (~87%) without any co-catalyst under visible light irradiation. The periodic WZ/ZB phase in twinning superlattice facilitates better charge separation, while superoxide radical (⋅O2-) and photogenerated holes drive the glucose transformation and water oxidation reactions, respectively. This work demonstrates that rational photocatalyst design could realize an efficient and concomitant production of hydrogen and value-added chemicals from glucose photocatalysis.

Rational construction of plasmonic Z-scheme Ag-ZnO-CeO2 heterostructures for highly enhanced solar photocatalytic H2 evolution

Rational design of photocatalyst with wide solar-spectrum absorption, negligible electron-hole recombination, and maximized redox potential is an essential prerequisite for achieving commercial-scale photocatalytic H2 production. This contribution combines surface plasmon resonance and Z-scheme charge transport in a single photocatalyst (Ag-ZnO-CeO2 heterostructure) aiming to improve its performance for photocatalytic H2 production. The Ag-ZnO-CeO2 heterostructure is fabricated via sunlight-driven combustion and deposition approaches. The successful construction is confirmed by several characterization techniques. The Z-scheme configuration is verified by in situ irradiated XPS and ESR analyses. Ag plays dual rules as an electron mediator to facilitate the Z-scheme charge transport and plasmonic material to maximize the light absorption in the visible region. The designed photocatalyst exhibits significantly enhanced photocatalytic activity for H2 production (18345 μmol h−1 g−1) under simulated sunlight irradiation. This work offers the opportunity of constructing efficient Z-scheme photocatalyst from wide bandgap semiconductors with full-visible light response, suppressed electron-hole recombination, and optimized redox potential.

In situ investigation of hot-electron-induced Suzuki−Miyaura reaction by surface-enhanced Raman spectroscopy

The palladium-catalyzed Suzuki−Miyaura cross coupling reaction is one of the most useful methods for forming carbon—carbon bonds. In addition to traditional thermal activation, plasmonic photocatalysts can also promote this reaction under light illumination. However, it is still debated whether hot electron transfer or localized thermal heating is the main driving force of this reaction. Herein, we utilize in situ surface-enhanced Raman spectroscopy to characterize the Suzuki–Miyaura reaction on the surface of Au@Pd nanoparticles. We exclude the possibility that plasmon-induced heating drives the reaction, and we confirm the hot-electron mechanism by demonstrating a linear relationship between the reaction rate and laser power. Based on these results, we propose that the hot-electron transfer mechanism is the primary route for the plasmon-driven heterogeneous Suzuki−Miyaura cross coupling reaction. These results may help the rational design of photocatalysts.

2D photocatalysts with tuneable supports for enhanced photocatalytic water splitting

Sustainable hydrogen production is attracting increasing attention and visible-light-driven water splitting is considered as one of the most promising approaches for hydrogen evolution and solar energy storage. Different materials have been screened at mild conditions in recent decades and 2-dimensional (2D) layered materials are considered good candidates for the photocatalytic water splitting reaction. 2D single layer MoS2 has shown its potential in various catalytic systems, and has also been used in photocatalytic water splitting reaction recently. However, current studies of MoS2 monolayers give low intrinsic activity, preventing it from practical applications. This is attributed to the rapid recombination of the photo-excited charge carriers at room temperature, resulting in poor quantum efficiency (QE). Herein, a state-of-the-art strategy to prolong the exciton lifetimes is reported, which is achieved by combining the 2D MoS2 nanosheets with solid state polar-faceted supports. The charge separation process can be facilitated by the strong local polarisation introduced by the polar-faceted supports, and tuned by changing the supports with different surface polarities. Polar oxide surface is the exposure of oxygen-terminated high energetic facet, which is known to give a net dipole moment perpendicular to its surface. Such variation in the surface properties of the support to the above metal would lead to a difference in metal-support interaction(s). The resulting composite structures show great enhancement toward the visible-light-driven photocatalytic water splitting reaction, giving hydrogen and oxygen evolution in a stoichiometric 2:1 ratio at elevated temperatures from pure water. Photocatalytic performances are improved by the prolonged exciton lifetimes and exceptional hydrogen evolution activity of 2977 μmol g−1 h−1 with impressive QEs are obtained over Ru-doped MoS2 nanosheets on polar ceria support, which is among the best of the reported results of similar catalytic systems to date. More excitingly, the linear relationship between the exciton lifetimes and strength of the local polarisation is also observed, indicating that the rational design of photocatalysts can be simply achieved via engineering their local polarisation by incorporation of polar-faceted materials.

Fabrication of molybdenum doped carbon nitride nanosheets for efficiently photocatalytic water splitting

Rational design of photocatalyst with efficient performance in water splitting is highly desired for solar energy utilization. In this work, a simple and facile strategy was developed to synthesize Mo doped graphic carbon nitride (g-C3N4) by a two-step thermal treatment process. As obtained product exhibits sheet-like morphology with porous structure, and the formation mechanism could be ascribed to the exfoliation effect in thermal environment. Photocatalytic property investigation reveals that Mo doped g-C3N4 nanosheets present greatly improved hydrogen evolution rate of 1.6 mmol g−1 h−1 under visible light, which is about 9.4 times higher than that of pristine g-C3N4. The improved performance could be well attributed to its enhanced visible light absorption, well suppressed carrier recombination and greatly increased specific surface area. Accordingly, our work provides a promising and straight forward way to develop advanced photocatalyst with high efficiency for renewable energy generation.

Photocatalytic syngas synthesis from CO2 and H2O using ultrafine CeO2-decorated layered double hydroxide nanosheets under visible-light up to 600 nm

The rational design of photocatalyst that can effectively reduce CO2 under visible light (λ > 400 nm), and simultaneously precise control of the products syngas (CO/H2) ratio is highly desirable for the Fischer-Tropsch reaction. In this work, we synthesized a series of CeO2-decorated layered double hydroxides (LDHs, Ce-x) samples for photocatalytic CO2 reduction. It was found that the selectivity and productivity of CO and H2 from photoreduction of CO2 in conjunction with Ru-complex as photosensitizer performed an obvious “volcano-like” trend, with the highest point at Ce-0.15 and the CO/H2 ratio can be widely tunable from 1/7.7 to 1/1.3. Furthermore, compared with LDH, Ce-0.15 also drove photocatalytic CO2 to syngas under 600 nm irradiation. It implied that an optimum amount of CeO2 modifying LDH promoted the photoreduction of CO2 to syngas. This report gives the way to fully utilize the rare earth elements and provides a promising route to enhance the photo-response ability and charge injection efficiency of LDH-based photocatalysts in the synthesis of syngas with a tunable ratio under visible light irradiation.

Graphene-like h-BN/CdS 2D/3D heterostructure composite as an efficient photocatalyst for rapid removing rhodamine B and Cr(Ⅵ) in water

Graphene-like boron nitride (h-BN) has the large surface area. The h-BN/CdS composite was successfully synthesized by one-step hydrothermal method. In this work, the physical structure, morphology, optic and electronic property of the h-BN/CdS photocatalyst were characterized and explored via XRD, SEM, TEM, XPS, UV–vis DRS, EIS and transient photocurrent. The heterojunction between h-BN and CdS could enhance the efficiency of charge transfer and significantly suppress the recombination of electrons and holes. The photocatalytic performance of the h-BN/CdS composite was evaluated by degrading rhodamine B (RhB) and photocatalytic reducing Cr (Ⅵ) ion, respectively. Moreover, 1.0 wt% h-BN/CdS composite could effectively inhibit the agglomeration of CdS nanospheres, which displayed the optimum photocatalytic activity under visible light irradiation. Meanwhile, 1.0 wt% h-BN/CdS composite had outstanding feature in recycling stability. The results indicated that two-dimensional (2D) h-BN as a substrate of CdS nanospheres was beneficial to prolong photoexcited electrons lifetime. The heterostructure interfaces of the h-BN/CdS composites resulted in photocatalytic performance promotion. However, the excessive h-BN caused the serious aggregation of CdS nanospheres. This work showed a facile method for the rational design of photocatalyst via optimizing their structure and surface.

AgSCN/AgCl/FeOCl nanosheets heterojunction with novel interface structure and excellent photocatalytic performance

Abstract To develop a photocatalyst with novel structure and high performance, a Z-scheme AgSCN/AgCl/FeOCl heterojunction has been successfully prepared by the in-situ synthesis and anion exchange method for the first time. The photocatalytic activity and photo-Fenton catalytic activity of the AgSCN/AgCl/FeOCl nanosheets for the degradation of ibuprofen are 40.7 times and 4.1 times higher than that of FeOCl, respectively. The interfacial structure of the AgSCN/AgCl/FeOCl heterojunction photocatalyst accelerated the separation of the photogenerated electron-hole pairs. The core-shell structure of AgSCN/AgCl effectively suppressed the photocorrosion. This study provides a new approach to the rational design of photocatalysts for emerging environmental applications.

Elucidating the predominant role of crystal disorders in hierarchical photocatalysts governing their charge carrier separation and associated activity in photocatalytic water treatment

The superiority of a hierarchical photocatalyst for water treatment applications is mostly rationalized in terms of two features: light harvestability and adsorption capability. Not only a conclusive evidence to support these claims is missing, knowledge on the ‘key material property’ governing photocatalyst performance is also unclear. Herein, a hierarchical BiOBr photocatalyst was studied in comparison with its plate-like counterpart. Found from the photocatalytic water treatment experiments, the hierarchical BiOBr exhibited three times faster reaction kinetics compared to the plate-like BiOBr. While light harvestability and adsorption capability of the two structures was not significantly different, a ca. 36% higher photocurrent and a ca. 16% longer charge carrier lifetime observed in hierarchical BiOBr demonstrated its superior charge carrier separability. Compared to other material properties, crystal disorders were found to predominantly influence the photocatalytic activity, which was verified through Raman spectroscopy, high resolution transmission electron microscopy, and X-ray diffraction analyses. The findings provide an insight into the role of crystallographic disorders in hierarchical photocatalysts which is a useful advancement towards the pursuit of rational photocatalyst design particularly for interfacial photocatalytic water treatment applications.