Interfacial Charge Separation Research Articles

Tunning heterostructures interface of Cu2O@HKUST-1 for enhanced photocatalytic degradation of tetracycline hydrochloride

Cu2O is an attractive material for the architectural design of integrated nanomaterials in photocatalysis. Herein, a contrastive study was carried out to explore the influence of morphology/exposed Cu2O facets on the template growth process and the difference of fabricated composites in photocatalysis performance. A series of Cu2O@HKUST-1 with core–shell structure was developed via a self-confinement strategy, in which Cu2O nanocrystals with various shapes (cube, truncated octahedron and octahedron) act as self-confinement template to grow Cu-based metal–organic frameworks (HKUST-1) shell. It was revealed that the growth of HKUST-1 on Cu2O crystal depended on the original Cu2O crystal. The exposure of (111) facet in Cu2O was more favorable to the growth of HKUST-1 than (100) crystal plane. Optical and photoelectrochemical characterizations revealed that the cubic Cu2O@HKUST-1 exhibited the outstanding light response and most efficient interfacial charge transfer and separation among three types of composites. As a result, the degradation rates of tetracycline hydrochloride (TC-HCl) by cubic Cu2O@HKUST-1 under the visible light irradiation was 95.35% within 60 min, which was much higher than truncated octahedral Cu2O@HKUST-1 (78.81%) and octahedral Cu2O@HKUST-1 (66.58%). Mechanism explorations including radical capture experiments, electron paramagnetic resonance and band structure analysis showed that type II heterojunction was formed in cubic Cu2O@HKUST-1 and truncated octahedral Cu2O@HKUST-1, which was conducive to the separation and transfer of photo-generated carriers. However, type I heterojunction existed in octahedral Cu2O@HKUST-1 lead to the recombination of photocarriers. These findings revealed the interface-dependent photocatalytic performance in Cu2O@HKUST-1 and provided useful guidance for controllable construction of photocatalysts with heterojunction structure.

RGO-wrapped Ag-doped TiO2 nanofibers for photocatalytic CO2 reduction under visible light

The design of uniform graphene/noble-metal/semiconductor ternary nanocomposites without agglomeration or restacking of graphene for robust CO2 photoreduction is still challenging. This study demonstrates a strategy for fabricating reduced graphene oxide (rGO)-wrapped Ag/TiO2 nanofibers (NFs). Coaxial electrospinning with a negative electric potential resulted in core-shell NFs with aligned rGO wrapped around the entire fiber and Ag+ concentrated underneath the rGO layer. rGO-wrapped Ag/TiO2 NFs with a concentrated and uniformly distributed Ag layer on the TiO2 were then fabricated by subsequent thermal treatment. rGO monolayers and surface-concentrated Ag are beneficial for transporting and collecting photogenerated electrons for CO2 reduction as well as facilitating the light harvesting ability to extend the light response from the UV to visible region without shielding. Under visible light, rGO/Ag/TiO2 NFs with all these benefits exhibited 25-fold higher CO2 to CH4 photoreduction performance than bare TiO2 NFs, yielding 4.301 μmol gNF−1 of CH4 in 7 h. As wrapping rGO around the whole fiber increased the structural stability of the ternary nanocomposite, rGO/Ag/TiO2 NFs showed a consistent CO2 to CH4 photoreduction efficiency even after six cycles of testing for 17 h. The fabrication technique for rGO/Ag/TiO2 NFs presented in this study will contribute to the development of graphene/noble-metal/semiconductor ternary nanocomposites with high interfacial contact and charge separation for the efficient photoreduction of CO2 to CH4 under visible light.

Cr-Ti Mixed Oxide Molecular Cages: Synthesis, Structure, Photoresponse, and Photocatalytic Properties.

The solvothermal reaction of titanium isopropoxide and chromate in the presence of benzoate produced two novel host-guest clusters encapsulating Cs+ or H3O+, (H3O)@Ti7Cr14 and Cs@Ti7Cr14. The most remarkable feature is that the Ti7O7 ring is concentrically embraced by a Cr14O14 ring to form a rigid Ti7Cr14 host. ESI-MS and 133Cs NMR revealed that the overall framework structures are preserved, whereas the benzoate ligands on the two clusters may be labile in solutions. Both (H3O)@Ti7Cr14 and Cs@Ti7Cr14 exhibit good UV-vis light-responsive properties and photocatalytic activities, with absorption edges extending up to 780 nm. Cs@Ti7Cr14 is an effective visible-light-responsive photocatalyst in both the heterogeneous methylene dye degradation and homogeneous CO2 cycloaddition reaction under mild conditions like room temperature and 1 bar of CO2. According to the mechanism studies, Cs+, as a rigid guest, can significantly improve the photogenerated charge separation efficiency of the Ti7Cr14 host, thereby improving its interface charge separation properties, photocurrent, and photocatalytic activities. Our findings not only provide new members of heterometallic titanium oxide clusters to enrich the metal oxide cluster family but also open up new possibilities for their photoresponses, which may play an important role in solar energy harvesting for sustainable chemistry.

Construction of Ag: ZnIn2S4/Bi2S3 Z-scheme heterojunctions for boosting interfacial charge separation and photocatalytic degradation of TC

The construction of Z-scheme heterostructures is one of the most effective strategies to improve photocatalytic efficiency. In this study, Ag+ doped ZnIn2S4/Bi2S3 composite nanosphere materials with different mass fractions of Bi2S3 were successfully synthesized by the solvothermal method. Systematic studies showed that the construction of heterogeneous structures and Ag+ doping could extend the optical absorption edge and provide more active sites. More importantly, it was shown by photoelectrochemical and PL spectroscopy tests that Ag: ZnIn2S4/Bi2S3 has strong visible light absorption and photocarrier transfer capability. In addition, the Z-scheme mechanism of Ag: ZnIn2S4/Bi2S3 was investigated by electron spin response (ESR) and active substance capture experiments, which confirmed that both superoxide radicals(O−2) and hydroxyl radicals(OH) were involved in the photocatalytic reaction. The results showed that the optimized Ag: ZnIn2S4/2.5%Bi2S3 degraded TC by 89.7%, 1.87 times higher than the original ZnIn2S4. This work provides a promising method for the construction of Z-scheme heterojunctions based on ZnIn2S4.

TiO2-modified g-C3N4 nanocomposite for photocatalytic degradation of organic dyes in aqueous solution

In the current study, a direct S-scheme titanium dioxide/graphitic carbon nitride (TiO2/g-C3N4) heterojunction structure was fabricated via simultaneous calcination of TiO2 precursors and g-C3N4. Guava leaf extract was utilized as a reductant for TiO2 production through a green synthetic method, and g-C3N4 was prepared by thermal decomposition of melamine. The pristine and nanocomposite photocatalysts were characterized by XRD, FTIR, BET, TGA, HRTEM, UV–vis DRS, and PL to elucidate their physicochemical properties. The photocatalytic activity of synthesized photocatalysts was examined through the degradation of rhodamine B (RhB) and methylene blue (MB) dyes under simulated solar light irradiation. The nanocomposite exhibited commendable photocatalytic performances with 96% degradation efficiency of RhB attained in 120 min and 95% degradation efficiency of MB achieved in 150 min. The enhanced photocatalytic activities were attributable to visible light-harvesting characteristics and the formation of an S-scheme heterojunction system between two catalysts which promotes interfacial charge separation efficiency and longer charge carrier lifespan. After 4 consecutive cycles, the degradation efficiencies of both RhB and MB remained above 85%. According to the trapping experiments, OH• and O2•− radicals were critical in the degradation of RhB, while h+ and O2•− radicals were dominant in the degradation of MB. The nanocomposite was also tested for elution of actual water pollutants by combining two dyes, and above 90% degradation efficiencies were achieved for both dyes after 240 min.

A novel mechanism for visible-light degradation of phenol by oxygen vacancy Bi2MoO6 homojunction

Homojunctions formed between two same semiconductors can notably facilitate charge transfer and separation. It is mainly used in solar cells to improve power conversion efficiency, and there is great potential for its application in photo-catalytic wastewater degradation. Herein, we designed an oxygen vacancy of Nanorods/Nanosheets Bi2MoO6 homojunction photo-catalyst, prepared by calcining pure Bi2MoO6 at high temperature and annealing it at the ambient temperature. Various characterization methods analyzed the chemical ingredient, microstructure, and optical characteristics. They are degrading phenol during visible illumination to survey the photo-catalytic performance of the homojunction. Density function theory (DFT) and other characterization methods demonstrate that the enhanced activity of the photo-catalyst is the efficient interfacial charge transfer and separation induced by the internal electric field and oxygen vacancies in the homojunction. This work provides a new strategy for constructing a novel homojunction to treat phenol wastewater.

High interfacial charge separation in visible-light active Z- scheme g-C3N4/MoS2 heterojunction: Mechanism and degradation of sulfasalazine

Examination of highly proficient photoactive materials for the degradation of antibiotics from the aqueous solution is the need of the hour. In the present study, a 2D/2D binary junction GCM, formed between graphitic-carbon nitride (g-C3N4) and molybdenum disulphide (MoS2), was synthesized using facile hydrothermal method and its photo-efficacy was tested for the degradation of sulfasalazine (SUL) from aqueous solution under visible-light irradiation. Morphological analysis indicated the nanosheets arrangement of MoS2 and g-C3N4. The visible-light driven experiments indicated that 97% antibiotic was degraded by GCM-30% within 90 min which was found to be quite high than pristine g-C3N4 and MoS2 at solution pH of 6, GCM-30% dose of 20 mg, and SUL concentration of 20 mgL−1. The degradation performance of GCM-30% was selectively improved due to enhanced visible-light absorption, high charge carrier separation, and high redox ability of the photogenerated charges which was induced by the effective Z-scheme 2D/2D heterojunction formed between g-C3N4 and MoS2. The reactive radicals as determined by the scavenging study were •O2−, and h+. A detailed degradation mechanism of SUL by GCM-30% was also predicted based on the detailed examination of the band gaps of g-C3N4 and MoS2.

Solid-state Z-scheme assisted hydrated tungsten trioxide/ZnIn2S4 photocatalyst for efficient photocatalytic H2 production

Efficient water splitting for H2 evolution over semiconductor photocatalysts is highly attractive in the field of clean energy. It is of great significance to construct heterojunctions, among which the direct Z-scheme nanocomposite photocatalyst provides effective separation of photo-generated carriers to boost the photocatalytic performance. Herein, Z-scheme hydrated tungsten trioxide/ZnIn2S4 is fabricated via an in-situ hydrothermal method where ZnIn2S4 nanosheets are grown on WO3⋅xH2O. The close contact between WO3⋅0.5H2O and WO3⋅0.33H2O as well as ZnIn2S4 improve the charge carrier separation and migration in the photocatalyst, where the strong reducing electrons in the conduction band of ZnIn2S4 and the strong oxidizing holes in the valence band of WO3⋅0.33H2O are retained, leading to enhanced photocatalytic hydrogen production. The obtained WO3⋅xH2O/ZnIn2S4 shows an excellent H2 production rate of 7200 μmol g−1 h−1, which is 11 times higher than pure ZnIn2S4. To the best of our knowledge, this value is higher than most of the WO3-based noble metal-free semiconductor photocatalysts. The improved stability and activity are attributed to the formation of the Z-scheme heterojunction, which can markedly accelerate the interfacial charge separation for surface reaction. This work offers a promising strategy towards the design of an efficient Z-scheme photocatalyst to suppress electron–hole recombination and optimize redox potential.

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.

Integration of plasmonic effect and S-scheme heterojunction into gold decorated carbon nitride/cuprous oxide catalyst for photocatalysis

A plasmonic Step-scheme heterojunction Au/g-C 3 N 4 /Cu 2 O photocatalyst was fabricated for the degradation of pollutants and energy generation . The removal of pollutants (oxytetracycline hydrochloride , OTH) and hydrogen evolution experiments showed that the catalyst had satisfactory stability and perfect photocatalytic performance. Among these catalysts, the 4-Au/g-C 3 N 4 /Cu 2 O displays the highest catalytic performance with the OTH removal efficiency as high as 94.8%. For the catalytic H 2 evolution, the 4-Au/g-C 3 N 4 /Cu 2 O reveals the optimal H 2 generation rate (552.6 μmol g −1 . h −1 ), which is about 13.4 times higher than that of the bare Cu 2 O sample. The satisfactory photocatalytic performance can be attributed to the efficient interfacial charge separation, the high light absorption capacity induced by localized surface plasmon resonance (LSPR) of Au nanoparticles , and the formation of Step-scheme heterojunction retaining strong photocatalytic oxidation and reduction capability. The charge density difference was also calculated to verify the existence of the built-in electric field, which was the driving force for the formation of Step-scheme heterojunction structure. • Step-scheme Au/g-C 3 N 4 /Cu 2 O was synthesized for oxytetracycline hydrochloride degradation and hydrogen generation. • Internal electric field will assist charge transfer. • The charge density difference between g-C 3 N 4 and Cu 2 O was calculated. • A plasmonic Step-scheme photocatalytic mechanism was proposed based on the experiments and simulations.

In-situ fabrication of Bi2S3/BiVO4/Mn0.5Cd0.5S-DETA ternary S-scheme heterostructure with effective interface charge separation and CO2 reduction performance

• Bi 2 S 3 /BiVO 4 /Mn 0.5 Cd 0.5 S-DETA ternary heterostructure is obtained. • The heterostructure exhibited excellent photocatalytic CO 2 reduction and stability. • Mechanism of charge transfer and separation in S-scheme heterojunction is proposed. • S-scheme photocatalytic mechanism is discussed. Exploring new and efficient photocatalysts to boost photocatalytic CO 2 reduction is of critical importance for solar-to-fuel conversion. In this study, through the in-situ growth method, a series of S-scheme mechanism Bi 2 S 3 /BiVO 4 /Mn 0.5 Cd 0.5 S-DETA nanocomposites with good photocatalytic activity were synthesized. The extremely small size of Mn 0.5 Cd 0.5 S-DETA nanoparticles provides more active sites for photocatalytic reactions. In order to solve the serious shortcomings of sulfide photo-corrosion, BiVO 4 were introduced as oxidation catalyst to consume too many holes and improve the stability of the material. In addition, the in-situ growth method produces the reduction cocatalyst Bi 2 S 3 during the BiVO 4 and Mn 0.5 Cd 0.5 S-DETA recombination process, thereby improving the efficiency of charge transfer at their interface contact. The ternary composite unveils a higher CO 2 -reduction rate (44.74 μmol g −1 h −1 ) comparing with pristine BiVO 4 (14.11 μmol g −1 h −1 ). The enhanced photocatalytic CO 2 reduction performance is due to the special interface structure of the S-scheme Bi 2 S 3 /BiVO 4 /Mn 0.5 Cd 0.5 S-DETA photocatalyst, which facilitates the charge separation at the interface and improves its photocatalytic activity and stability. .

Highly active Cs2SnCl6/C3N4 heterojunction photocatalysts operating via interfacial charge transfer mechanism

In this study, a novel lead-free perovskite heterojunction Cs2SnCl6/C3N4 composite was constructed and applied for photocatalytic NO purification. After design optimization, the Cs2SnCl6/C3N4 heterojunction exhibit excellent and stable photocatalytic NO purification ability under visible-light irradiation, which is significantly better than pristine Cs2SnCl6 and C3N4. Combined in-situ DRIFTS and electron spin resonance spin-trapping, the mechanism of Cs2SnCl6/C3N4 photocatalytic NO removal was revealed. Under visible-light irradiation, the photo-generated electrons on the conduction band of C3N4 would spontaneously migrate to the CB of Cs2SnCl6, leaving holes (h+) on the valence band of C3N4, contributing to efficiently segregated charge carriers and improved photocatalytic NO purification. Density functional theory calculations also revealed the directional electron transfer at the C3N4 and Cs2SnCl6 interface, in which the charge was migrated from C3N4 to Cs2SnCl6 induced by the internal electric field. This research sheds fresh light on the fabrication of Cs2SnCl6/C3N4 heterojunctions as well as its effective interfacial charge separation.

Lattice-matched in-situ construction of 2D/2D T-SrTiO3/CsPbBr3 heterostructure for efficient photocatalysis of CO2 reduction

The elaborate regulation of heterostructure interface to accelerate the interfacial charge separation is one of practicable approaches to improve the photocatalytic CO2 reduction performance of halide perovskite (HP) materials. Herein, we report an in-situ growth strategy for the construction of 2D CsPbBr3 based heterostructure with perovskite oxide (SrTiO3) nanosheet as substrate (CsPbBr3/SrTiO3). Lattice matching and matchable energy band structures between CsPbBr3 and SrTiO3 endow CsPbBr3/SrTiO3 heterostructure with an efficient interfacial charge separation. Moreover, the interfacial charge transfer rate can be further accelerated by etching SrTiO3 with NH4F to form flat surface capped with Ti−O bonds. The resultant 2D/2D T-SrTiO3/CsPbBr3 heterostructure exhibits an impressive photocatalytic activity for CO2 conversion with a CO yield of 120.2 ± 4.9 µmol g−1 h−1 at the light intensity of 100 mW/cm2 and water as electron source, which is about 10 and 7 times higher than those of the pristine SrTiO3 and CsPbBr3 nanosheets, surpassing the reported halide perovskite-based photocatalysts under the same conditions.

Tailoring Charge Separation at Meticulously Engineered Conjugated Polymer/Perovskite Quantum Dot Interface for Photocatalyzing Atom Transfer Radical Polymerization.

In stark contrast to conventional organic ligand-capped counterparts, the ability to create stable metal halide perovskite nanocrystals strongly tethered with conjugated polymers (CPs) represents an important endeavor toward tailoring charge carrier dynamics at their interface that critically underpins applications of this unique class of all semiconducting, organic-inorganic nanomaterials for optoelectronics. This, however, has yet to be largely explored. Herein, we report, for the first time, the unraveling of efficient charge separation at judiciously designed CP/perovskite quantum dot (QD) interface for photoinduced atom transfer radical polymerization (p-ATRP). Such scrutiny is rendered by in situ crafting an array of monodisperse, highly stable, CP-ligated perovskite QDs with precisely controlled dimensions of each constituent via capitalizing on unimolecular, amphiphilic starlike block copolymers as nanoreactors. The intimate and permanent surface tethering of CPs imparts remarkable thermal, photo, and polar solvent stabilities of CP-ligated perovskite QDs. More importantly, they manifest efficient interfacial charge separation with a profound dependence on the length of ligated CPs and the size of perovskite QDs. The outstanding structural stabilities and charge separation characteristic enable CP-ligated perovskite QDs as robust photocatalysts for p-ATRP of a wide selection of monomers with stable and controllable reaction kinetics, also depending crucially on the length of CPs and the size of perovskite QDs. In principle, an exciting variety of CP-ligated, uniform perovskite QDs with virtually unlimited material choice of both markedly improved stabilities and tunable electronic band alignments can be readily accessed by exploiting the amphiphilic starlike block copolymer nanoreactor strategy for use in photodetectors, sensors, and LEDs, among other areas.

(Invited) In Situ Time-Resolved Probe of Charge Carrier Dynamics at Planar Semiconductor Photoelectrode/Liquid Interface

Photoelectrochemistry is a promising approach for converting solar energy to storable chemical energy in chemical fuels. The efficiency of photoelectrochemcial devices depends critically on efficient transfer of charge carrier across the electrode liquid interface and the efficiency and selectivity of the catalytic reaction on electrode surface. Although transient absorption spectroscopy is a powerful tool for probing interfacial dynamics in high surface area electrodes, it is often not applicable on planar electrodes because the observed signal is often dominated by carrier dynamics in the bulk. In this talk, we discuss our recent effort in developing in situ time-resolved linear and nonlinear spectroscopic tools that can be used to probe carrier dynamics and reactions at planar electrode/liquid interfaces, focusing on transient reflection spectroscopy and electric field induced second harmonic generation (EFISH) spectroscopy. Compared to transient absorption, transient reflection spectroscopy is more sensitive to surface carrier density that can be more directly correlated to catalysis. We showed that transient reflectance change can be used to follow charge carrier dynamics and their amplitude can be directly correlated to efficiency of initial interfacial charge separation on p-GaP single crystals protected by TiO2 ALD layer. Our finding suggests that IPCE is determined by the product of the efficiency of initial ultrafast (< hundreds of ps) charge separation across the GaP/TiO2 interface and the efficiency of water reduction reaction on the slower time scale. Key loss pathways that limit these efficiencies are discussed. In a second approach, we showed the EFISH signal in a n-doped single crystal TiO2 can be used to probe the accumulation of photogenerated carriers at surface states and these trapped carriers are responsible for the water oxidation reaction.

Self-Assembled Zeolitic Imidazolate Framework/CdS Hollow Microspheres with Efficient Charge Separation for Enhanced Photocatalytic Hydrogen Evolution.

Enhanced interfacial charge separation is of great importance to high-efficiency photocatalytic hydrogen production. Herein, we successfully fabricated novel ZIF-67/CdS hollow sphere (HS) and ZIF-8/CdS HS heterostructures through an in situ self-assembly process, in which ZIF-67 and ZIF-8 are closely coated on CdS HSs to form "double-shell"-like structures. This hierarchical heterostructure with porous outer layers on the surface of CdS HSs can expose accessible active sites and possess close contact. Upon visible-light illumination, the optimal proportion of ZIF-67/CdS HS displays a hydrogen generation rate of 1721 μmol g-1 h-1, which is 11.9 and 3.1 times higher than that of a pure CdS HS (145 μmol g-1 h-1) and ZIF-8/CdS HS (555 μmol g-1 h-1), respectively. The proposed photocatalytic mechanism is explored: ZIF-8/CdS HS follows the type-II mechanism, and ZIF-67/CdS HS follows the Z-scheme mechanism. The reason for the higher photocatalytic activity of ZIF-67/CdS HS is that ZIF-67 not merely with a porous structure facilitates the diffusion of H2 gas, but with a well-matched band structure promotes charge transfer and separation.

Enhanced visible light response of Ag/SnO2 nanostructure enables high-efficiency photocatalytic hydrogen evolution

Construction of synergistic photocatalysis system is regarded as an important concept for effectively utilizing solar energy. Herein, Ag nanoparticles decorated SnO2 flower-like structure is designed and fabricated to synergistically realize efficient hydrogen production from water splitting. According to the results of density functional theory simulations and corresponding experimental analyses, it is identified that interfacial charge coupling of composite system intrinsically facilitate the efficient interfacial charge migration and separation. Moreover, introducing Ag nanoparticles not only expands response range of incident light for SnO2 through LSPR effect but also reduces the hydrogen adsorption free energy in the catalytic process. Eventually, contributed by the enhanced interaction between reactants and catalysts and optimized carrier behavior, Ag/SnO2 exhibits a faster hydrogen production rate than SnO2. The research method designed in this paper may provide a new idea for research of photocatalyst for photocatalytic hydrogen evolution.

Synergy of Adsorption and Plasmonic Photocatalysis in the Au-CeO2 Nanosystem: Experimental Validation and Plasmonic Modeling.

Adsorption-mediated water treatment leaves adsorbents as secondary pollutants in the environment. However, photocatalysis aids in decomposing the contaminant into its nontoxic forms. In this context, we demonstrate an adsorption-photocatalysis pairing in Au-CeO2 nanocomposites for a total methylene blue (MB) removal from water. We synthesized Au-CeO2 through the citrate (cit) reduction method at different Au loading and studied its adsorption capacity with kinetics and thermodynamic models. We observe that the high adsorption capacity of Au-CeO2 is primarily because of the presence of Ce3+ states in CeO2 and citrate ligands on Au NPs. The Ce3+ states interact and transfer their electrons to supported Au NPs, rendering a negative charge over Au. The negatively charged Au surface and the carboxyl (-COO-) group of citrate ligands mediate an electrostatic interaction/adsorption of cationic MB. The total removal of MB is expedited under white light and lasers. A control experiment with Au NPs shows less adsorption-photocatalysis. The size of Au NPs and Au-CeO2 interfacial interaction is responsible for the surface plasmon resonance spectral position at 550-600 nm. Linear sweep voltammetry (LSV) and plasmonic field simulation show surface plasmon-driven photocatalysis in Au-CeO2. LSV shows a 3-fold higher photocurrent density in Au-CeO2 than colloidal Au NPs under white light. The simulated electric field intensity in Au-CeO2 is maximum at SPR excitation and the closest interfacial separation (d = 0 nm). The plasmon-driven photocatalysis in colloidal Au NPs is mainly due to the interaction of hot electrons with the adsorbed MB molecule. Notably, near-field light concentration, hot electrons, and interfacial charge separation are responsible for excellent MB removal in the Au-CeO2 nanosystem. The total MB removal through adsorption-photocatalysis pairing is 99.3% (Au-CeO2), 30.7% (Au NPs), and 13% (CeO2).

G‐C3N4/SnS2 van der Waals Heterostructures Enabling High‐Efficiency Photocatalytic Hydrogen Evolution

AbstractVan der Waals (vdW) heterojunction has played an essential role in effectively utilizing solar energy for sustainable hydrogen production. Herein, a 2D/2D g‐C3N4/SnS2 photocatalyst with vdW heterojunction is developed by self‐assembly contacting SnS2 hexagonal nanoplates and g‐C3N4 nanosheets. A reasonable Type‐II charge transfer mechanism based on the vdW heterostructure is proposed and verified by hydroxyl radical generation test. Photocatalysts with vdW heterostructure enable high‐efficiency H2 production under the visible light illumination, of which the optimized rate is about seven times higher than that of SnS2. Experimental analysis and corresponding density functional theory simulation jointly identify that enhanced photocatalytic activity is ascribed to the optimized behavior of photogenerated carriers and promotional interaction between reactants with catalysts. Specifically, charge redistribution and staggered band structure of the heterojunction intrinsically facilitate the efficient interfacial charge migration and separation. Diminished free energy of surface hydrogen adsorption reveals the easier hydrogen adsorption‐desorption for a composite system from the viewpoint of thermodynamics. This work may be attractive for the implementation of rationally synthesizing catalysts for efficient photocatalytic water splitting.

Photoinduced charge separation at Zn-Pd/TiO2 hybrids interface for enhanced electrochemical and photocatalytic activity

One dimensional nanostructures based hybrids have proven to be potent for photocatalytic applications. The hybrids having modified interface play a vigorous role in enrichment of photocatalytic activity by electronic interaction. Electronic interaction at interface occurs by the formation of electronic barriers (Ohmic/Schottky) that affects the transport of charge carriers and hence photocatalytic activity. The present work reports the switching of role play between Ohmic and Schottky barriers using different hybrids in order to have enhancement in photocatalytic activity. In order to form hybrids, metal nanoparticles (Pd and Zn) and bimetallic nanoparticles (ZnPd) are chosen to study the modification of interface by XPS and UPS. The analysis revealed that Pd and ZnPd crafted TiO2 nanorods (TiO2 NR) shows the formation of Schottky barrier with upward band bending at interface. Similarly, Zn crafted TiO2 NR shows the Ohmic barrier with downward band bending at interface. The band bending in hybrids is accredited to interfacial electronic interaction and charge separation at interface. The modified hybrids are studied for electrochemical analysis using cyclic voltammetry. It is analyzed that higher electrical conductivity is present in ZnPd/TiO2 NR, facilitates the transport of charge carriers. The improved charge separation at interface of ZnPd/TiO2 NR leads to enhanced photocatalytic activity in comparison to Pd/TiO2 NR and Zn/TiO2 NR.