Efficient Plasmonic Photocatalysts Research Articles

Rich Sulfur Vacancies and Reduced Schottky Barrier Height Synergistically Enable Au/ZnIn2S4 with Enhanced Photocatalytic CO2 Reduction into CO.

Constructing the plasmonic metal/semiconductor heterostructure with a suitable Schottky barrier height (SBH) and the sufficiently reliable active sites is of importance to achieve highly efficient and selective photocatalytic CO2 reduction into hydrocarbon fuels. Herein, we report Au/sulfur vacancy-rich ZnIn2S4 (Au/VSR-ZIS) hierarchical photocatalysts, fabricated via in situ photodepositing Au nanoparticles (NPs) onto the nanosheet self-assembled ZnIn2S4 (ZIS) micrometer flowers (MFs) with rich sulfur vacancies (VS). Density functional theory (DFT) calculations confirm that for the Au/VSR-ZIS system, the Au NPs serve as the reaction sites for H2O oxidation, and the VSR-ZIS MFs serve as those for CO2 reduction. The rich VS in the Au/VSR-ZIS hybrid can reduce its SBH so as to boost more hot electrons in the Au NPs across its Schottky barrier and then inject into the conduction band (CB) of the VSR-ZIS MFs. In addition, VS can also act as the electron sink to trap the photogenerated electrons, retarding the recombination of photogenerated carriers. The two merits effectively enhance the photogenerated electron density in the surface of VSR-ZIS MFs, availing CO2 photoreduction. In addition, the introduction of rich VS in the Au/VSR-ZIS hybrid can offer more active sites, benefiting the CO2 adsorption and accelerating the desorption of CO* from the surface of the photocatalyst. Therefore, under visible light illumination with no sacrificial reagent, the optimum photocatalyst (Au/VSR-ZIS-0.4) presents the enhanced and selective CO2 photoreduction into CO (8.15 μmol g-1h-1 and near 100%), which are superior to those of most of ZIS-based and plasmon-based photocatalysts. The photocatalytic activity is about 40.0-fold as high as that of the Vs-poor-ZIS (VSP-ZIS) MFs. This work contributes a viable strategy for designing highly efficient plasmonic photocatalysts by using the synergism of the anion vacancies and the optimized SBH induced by them.

Facile one-pot synthesis of plasmonic gold nanoparticles decorated porphyrin-metal organic framework for photocatalytic hydrogen evolution

Plasmonic metals and single-atom nanocomposites have recently gained attention for their enhancement of photocatalyst ability to harvest energy from visible light photons and consequently increase their photoactivity. Over the last decade, the functionalization of Au nanoparticles has been extensively studied to support photocatalytic processes such as hydrogen generation. Furthermore, porphyrin metal-organic frameworks (MOF) materials have demonstrated promising properties such as high crystallinity, surface area, and electron transfer to favor this reaction. Thus, herein Au@PCN(M) nanocomposite was designed by anchoring surface-modified Au nanoparticles into a porphyrin MOF (PCN(M)) where M represents single-atom transition metals (Pt and Co), these nanocomposites were synthesized by both one-pot and post-synthesis methods. Post-synthesis method displayed a higher yield in comparison to the one-pot method, which could be related to the higher crystallinity and metalation of Co and Pt species on PCN-222. Nevertheless, the obtained results for the one-pot method demonstrated that the developed approach is comparable in terms of performance and is promising for the synthesis of efficient plasmonic photocatalysts and their possibility of scale-up in the future.

CeVO4 nanoparticle coupled with Ag/AgBr as an efficient plasmonic photocatalyst for degradation of rhodamine B: Construction, characterization, and mechanism insight

The unique characteristics of the surface plasmon resonance effect significantly improve the utilization rate of solar energy and charge separation of narrow band-gap semiconductor materials. In this work, Ag/AgBr/CeVO4 plasmonic photocatalyst was synthesized by the microwave-assisted hydrothermal method, followed by in-situ precipitation and photoreduction process. The as-prepared Ag/AgBr/CeVO4-2.0 composite showed superior photocatalytic efficiency for degradation of rhodamine B (84.2% in 10 min), which was 1.45 and 84.2 times higher than that of Ag/AgBr and pristine CeVO4 nanoparticles (NPS, size 30–50 nm), respectively. Photoluminescence and photocurrent tests indicated the rapid transfer and separation of electron–hole pairs in this plasmonic system, which can be attributed to the localized surface plasmon resonance effect of Ag NPs. In investigations on band structure and radical quenching experiments, a Z-scheme photocatalytic system bridged by the Ag NPs was proposed. This research offers revealing insight into the design and fabrication of the CeVO4 plasmonic photocatalytic system for application in environment purification and remediation.

Transformation-Optics-Designed Plasmonic Singularities for Efficient Photocatalytic Hydrogen Evolution at Metal/Semiconductor Interfaces.

Inspired by transformation optics, we propose a new concept for plasmonic photocatalysis by creating a novel hybrid nanostructure with a plasmonic singularity. Our geometry enables broad and strong spectral light harvesting at the active site of a nearby semiconductor where the chemical reaction occurs. A proof-of-concept nanostructure comprising Cu2ZnSnS4 (CZTS) and Au-Au dimer (t-CZTS@Au-Au) is fabricated via a colloidal strategy combining templating and seeded growth. On the basis of numerical and experimental results of different related hybrid nanostructures, we show that both the sharpness of the singular feature and the relative position to the reactive site play a pivotal role in optimizing photocatalytic activity. Compared with bare CZTS, the hybrid nanostructure (t-CZTS@Au-Au) exhibits an enhancement of the photocatalytic hydrogen evolution rate by up to ∼9 times. The insights gained from this work might be beneficial for designing efficient composite plasmonic photocatalysts for diverse photocatalytic reactions.

Enhanced interfacial charge transfer and photothermal effect via in-situ construction of atom co-sharing Bi plasmonic/Bi4O5Br2 nanosheet heterojunction towards improved full-spectrum photocatalysis

Constructing a plasmonic heterojunction photocatalyst is a prospective approach to improve full-spectrum photocatalytic performance. However, low interfacial charge transfer efficiency due to lattice mismatch severely limits its photocatalytic performance. Herein, a Bi atom co-sharing Bi/Bi4O5Br2 plasmonic heterojunctions were fabricated via in-situ reduction. Experimental characterizations and theoretical calculations demonstrate that the co-sharing Bi atom enables intimate contact in the heterointerface, significantly promoting interfacial charge transfer and separation. In addition, Bi metal's surface plasmon resonance effect extends the photoresponse to the near-infrared region and enhances the photothermal performances, significantly improving solar energy's utilization efficiency. By these prominent features, the optimized Bi/Bi4O5Br2 heterojunctions show that the photocatalytic degradation ratio of BPA reaches 100 % within 40 min under full-spectrum irradiation, which is about three times higher than that of Bi4O5Br2. Moreover, the photocatalytic efficiency was significantly increased by 7.5 times with the increase in temperature under NIR light irradiation due to the photothermal effect. This work offers new insights into the rational design of low-cost, highly efficient, and stable Bi-based plasmonic heterojunction photocatalysts for full solar spectrum utilization by integrating plasmonic nanostructures and photothermal effect.

In‐situ Integrated Plasmonic TiN@ZIF‐67 Composites for the Photoreduction of CO2into Solar Fuels: Insights into their Plasmonic Interaction and Mechanism

AbstractPlasmonic materials (PMs) essentially equip the photocatalysts to harvest energy from visible light photons. Interestingly, these PMs also support the photocatalysts, which has been realized upon the advent of non‐noble metals‐based PMs. In this context, this study reveals an interesting feature of TiN@ZIF‐67 plasmonic composite photocatalysts towards CO2reduction under solar irradiation. The composite is prepared via anin‐situand direct integration process, where the plasmonic TiN nanoparticles are surface‐modified using 3‐aminopropyl‐triethoxysilane/H‐Imidazole‐2‐carbaldehyde in the former and polyvinylpyrrolidone in the latter process to construct the 1H2ImCHO‐TiN@ZIF‐67 and TiN/PVP@ZIF‐67 composites, respectively. The structural and functional properties in these composites are confirmed using XRD and FTIR spectroscopy techniques. It is observed from the TEM images that the in‐situ integration leads to deep‐surface attachments of TiN on ZIF‐67, which exerted a major impact in the CO2photoreduction. The 1H2ImCHO‐TiN@ZIF‐67 shows the simultaneous production of ∼0.11 and 0.15 mmol g−1 h−1of methanol and ethanol, respectively; whereas, the TiN/PVP@ZIF‐67 produces only ∼0.31 mmol g−1h−1of methanol. The obtained results demonstrate that developed in‐situ synthetic approach is promising for the synthesis of efficient plasmonic photocatalysts and the product formation during CO2photoreduction can be dependent on how PMs are integrated with the host photocatalysts.

Increasing electron density by surface plasmon resonance for enhanced photocatalytic CO2 reduction

The photocatalytic CO2 reduction reaction is a multi-electron process, which is greatly affected by the surface electron density. In this work, we synthesize Ag clusters supported on In2O3 plasmonic photocatalysts. The Ag–In2O3 compounds show remarkedly enhanced photocatalytic activity for CO2 conversion to CO compared to pristine In2O3. In the absence of any co-catalyst or sacrificial agent, the CO evolution rate of optimal Ag–In2O3-10 is 1.56 μmol/g/h, achieving 5.38-folds higher than that of In2O3 (0.29 μmol/g/h). Experimental verification and DFT calculation demonstrate that electrons transfer from Ag clusters to In2O3 on Ag–In2O3 compounds. In Ag–In2O3 compounds, Ag clusters serving as electron donators owing to the SPR behaviour are not helpful to decline photo-induced charge recomnation rate, but can provide more electron for photocatalytic reaction. Overall, the Ag clusters promote visible-light absorption and accelerate photocatalytic reaction kinetic for In2O3, resulting in the photocatalytic activity enhancement of Ag–In2O3 compounds. This work puts insight into the function of plasmonic metal on enhancing photocatalysis performance, and provides a feasible strategy to design and fabricate efficient plasmonic photocatalysts.

New Insights of Charge Transfer at Metal/Semiconductor Interfaces for Hot-Electron Generation Studied by Surface-Enhanced Raman Spectroscopy.

Plasmonic nanostructures with hot spots are very efficient in generating energetic (hot) electrons to realize light-driven chemical reactions. This effect primarily originates from high electric fields with nonuniform distribution in the hot-spot area. However, charge-transfer (CT) at plasmonic nanostructure interfaces and its effect on hot-electron generation have not been explored in detail. Here, a series of semiconductor/metal interfaces, with continuously adjustable energy-band structures, were constructed by the assembly of CdxZn1-xS supports and Au nanoparticles (NPs) interconnected with p-aminothiophenol (PATP) molecules. The plasmon-mediated oxidation of PATP embedded in CdxZn1-xS/PATP/45 nm-Au NP molecular junctions was systematically investigated using gap-mode-liked surface-enhanced Raman spectroscopy (SERS). Combining in situ SERS studies with energy-level analysis, interfacial CT was found to be a primary determinant of hot-electron-induced oxygen activation on large Au NP surfaces. This study provides a new perspective on the hot-electron generation mechanism to facilitate the rational design of efficient plasmonic photocatalysts.

Boosting the photocatalytic nitrogen reduction to ammonia through adsorption-plasmonic synergistic effects

Ammonia is one of the most essential chemicals in the modern society but its production still heavily relies on energy-consuming Haber-Bosch processes. The photocatalytic reduction of nitrogen with water for ammonia production has attracted much attention recently due to its synthesis under mild conditions at room temperature and atmospheric pressure using sunlight. Herein, we report a high-performance Au/MIL-100(Cr) photocatalyst, comprising MIL-100(Cr) and Au nanoparticles in photocatalytic nitrogen reduction to ammonia at ambient conditions under visible light irradiation. The optimized photocatalyst (i.e., 0.10Au/MIL-100(Cr)) achieved the excellent ammonia production rate with 39.9 µg gcat−1 h−1 compared with pure MIL-100(Cr) (2.73 µg gcat−1 h−1), which was nearly 15 times that on pure MIL-100(Cr). The remarkable activity could be attributed to the adsorption-plasmonic synergistic effects in which the MIL-100(Cr) and Au are responsible to the strong trapping and adsorption of N2 molecules and photo-induced plasmonic hot electrons activating and decomposing the N2 molecules, respectively. This study might provide a new strategy for designing an efficient plasmonic photocatalyst to improve the photocatalytic performance of N2 fixation under visible light irradiation.

Effect of Nanoparticle Size on Plasmon-Driven Reaction Efficiency.

Hot electron chemistry is of paramount significance because of its applicability to photocatalytic reactions, solar energy conversion, and waste decomposition. The nonradiative decay of excited plasmons in gold nanoparticles (AuNPs) generates highly energetic nonthermal electrons and holes that can induce chemical reactions when transferred to nearby molecules. In this study, we explore the relationship between AuNP size (26-133 nm) and the plasmon-induced reaction yield. To isolate the size from other structural parameters, we prepare perfectly round gold nanospheres (AuNSs) with narrow size distributions. The use of a nanoparticle-on-mirror configuration, in which the reactant molecules (4-mercaptobenzoic acid) are positioned in nanogaps between the AuNSs and a Au film, promotes the generation of hot carriers and allows the highly sensitive detection of the reaction products (benzenethiol) using surface-enhanced Raman spectroscopy. We show that the reaction yield increases as the AuNS size increases up to 94 nm and then decreases for larger AuNSs. This peculiar Λ-shaped size-dependent reactivity can be explained by considering both the plasmonic absorption efficiency of AuNSs and the decay rate of plasmons via electron-surface scattering. The product of the calculated absorption cross section and the inverse of the AuNS size reproduces our experimental results remarkably well. These findings will contribute to the design of highly efficient plasmonic photocatalysts and photovoltaic devices.

In situ SERS monitoring of plasmon-driven catalytic reaction on gap-controlled Ag nanoparticle arrays under 785 nm irradiation

Plasmon-enhanced photocatalysis has attracted considerable attention due to its low energy consumption and high energy throughput. Surface-enhanced Raman scattering (SERS) is a highly sensitive and label-free nondestructive tool to investigate plasmon-driven photocatalytic reactions. Herein, we present a facile method to fabricate gap-controlled Ag nanoparticle (NP) arrays with uniform and high-density distribution of hot spots, which can be employed as both efficient plasmonic photocatalysts and stable SERS platforms. The plasmon-driven catalytic reaction of 4-nitrobenzenethiol (4NBT), which transforms it into p, p′-dimercaptoazobenzene (DMAB), is detected by using an in situ SERS technique at the excited wavelength of 785 nm. According to the temperature and laser power density dependent photocatalytic reaction rates observed on the Ag NP arrays, we quantitatively determined that the reductive coupling of 4NBT is more likely to occur as the gap decreases. The finite-difference time-domain (FDTD) simulation results demonstrate that the plasmonic hot spots are significantly enhanced with a decrease in gap, which in turn reduces activation energy. The gap-controlled Ag NP arrays are efficient for both promotion and detection of plasmon-driven catalytic reactions, and may pave a pathway for implementing efficient plasmonic photocatalytic platforms.

Ag-Au Core-Shell Triangular Nanoprisms for Improving p-g-C3N4 Photocatalytic Hydrogen Production.

Ag–Au core–shell triangular nanoprisms (Ag@Au TNPs) have aroused extensive research interest in the field of hydrogen evolution reaction (HER) due to their strong plasmon effect and stability. Here, Ag@Au TNPs were fabricated by the galvanic-free replacement method. Then, we loaded them on protonated g-C3N4 nanoprisms (P–CN) by the electrostatic self-assembly method as an efficient plasmonic photocatalyst for HER. The hydrogen production rate of Ag@Au TNPs/P–CN (4.52 mmol/g/h) is 4.1 times higher than that of P–CN (1.11 mmol/g/h) under simulated sunlight irradiation, making it the most competitive material for water splitting. The formed Schottky junction helps to trap the hot electrons generated from Ag@Au TNPs, and the well-preserved tips of the Ag@Au TNPs can effectively generate an electromagnetic field to inhibit the photogenerated electron–holes pairs recombination. This study suggests that the rational design of Ag@Au TNPs by the galvanic-free replacement method is an effective co-catalyst for HER and boosting the additional combination of plasmonic metals and catalyst metals for the enhancement to HER.

Atomically unraveling the dependence of surface microstructure on plasmon-induced hydrogen evolution on Au/SrTiO3

Strong light-matter interaction and coupled catalytic surface in plasmonic photocatalysts offer a unique opportunity for solar-to-chemical energy conversion. The interface/surface engineering is significant strategy to modulate the performance of plasmon-induced water splitting. This situation motivates the demand of a plasmonic heterostructure with well-defined atomic surface structures but identical bulk structure for plasmon-induced water splitting. In this work, using Au/SrTiO3 as a prototype, we found that altering the Ti-terminated and Sr-terminated surface of SrTiO3 gives rise to a remarkable difference in plasmon-induced hydrogen evolution activity. The efficiency of charge separation at the Sr-terminated surface is inferior compared with which at the Ti-terminated structure, while the reaction kinetics of Sr-terminated surfaces is faster than the counterpart, thus leading to a high plasmon-induced hydrogen evolution performance at Au/ SrTiO3 with surfaces of Sr-termination. Modulation of the interface/surface structure of Au/SrTiO3 changes not only charge separation but surface catalysis in plasmonic photocatalysts, where the catalysis process dominates the final photocatalytic performance. This work paves a way to design efficient plasmonic photocatalysts for solar-to-chemical energy conversion.

Ag/AgCl as an efficient plasmonic photocatalyst for greenhouse gaseous methane oxidation

In this work, quasi-cube Ag/AgCl plasmonic photocatalyst was synthesized by a simple co-precipitation method and in situ photo-reduction process. The synthesized Ag/AgCl shows high efficiency and good stability in the complete oxidation of nonpolar greenhouse gas methane under the simulated sunlight irradiation. Systematic experiments and finite-difference time-domain (FDTD) simulated calculations were employed to explore the reasons for the appreciable performance improvement, and results showed that the surface plasmonic resonance (SPR) effect of Ag nanoparticles can generate strong electric field which would induce the polarization of methane molecules, hence enhancing the adsorption of methane. This work provides a new idea for exploration of other plasmonic photocatalysts in the field of nonpolar gaseous molecules photo-oxidation.

Interfacial Modulation with Aluminum Oxide for Efficient Plasmon‐Induced Water Oxidation

AbstractPlasmon‐induced photocatalysts hold great promise for solar energy conversion owing to their strong light‐harvesting ability and tunable optical properties. However, the complex process of interfacial extraction of hot carriers and the roles of metal/semiconductor interfaces in plasmonic photocatalysts are still not clearly understood. Herein, the manipulation of the interface between a plasmon metal (Au) and a semiconductor (rutile TiO2) by introducing an interfacial metal oxide (Al2O3) is reported. The resulting Au/Al2O3/TiO2 exhibits remarkable enhancement in photocatalytic water oxidation activity compared with Au/TiO2, giving an apparent quantum efficiency exceeding 1.3% at 520 nm for photocatalytic water oxidation. Such an interfacial modulation approach significantly prolongs the lifetime of hot carriers in the Au/TiO2 system, which conclusively improves the utilization of hot carriers for plasmon‐induced water oxidation reaction upon irradiation. This work emphasizes the essential role of the interfacial structure in plasmonic devices and provides an alternative method for designing efficient plasmonic photocatalysts for solar energy conversion.

Design and synthesis of porous M-ZnO/CeO2 microspheres as efficient plasmonic photocatalysts for nonpolar gaseous molecules oxidation: Insight into the role of oxygen vacancy defects and M=Ag, Au nanoparticles

In this paper, porous microsphere M-ZnO/CeO2 (M = Ag, Au) plasmonic photocatalyst was prepared through a simple hydrothermal method and in situ photo-deposition. This photocatalyst shows excellent stability and high efficiency in the complete mineralization of nonpolar gaseous molecules (CH4 and C2H4) under the simulated sunlight. The appreciable performance improvements are caused by the formation of heterojunctions and oxygen vacancy defects, the surface plasmon resonance (SPR) of noble metal nanoparticles as well as the 3D porous microsphere structures. Especially in this work, we systematically studied the effect of concentration changes of oxygen vacancy defects on photocatalytic performance by XPS, EPR and Raman characterization. Furthermore, a possible mechanism of photo-oxidation reaction in plasmonic photocatalyst system is discussed below. This study provides new inspiration for designing other plasmonic photocatalysts to remove nonpolar gaseous molecules.

Facile synthesis, structural and optical properties of Au-TiO2 plasmonic nanohybrids for photocatalytic applications

In this study, we conducted the room temperature synthesis of Au-TiO2 plasmonic nanohybrids with Au nanoparticles chemically attached to the TiO2 nanostructures. We systematically examined the effects of modifying the nanostructured TiO2 with Au nanoparticles based on their structural and optical properties. Transmission electron microscopy showed that the Au nanoparticles were uniformly attached to the TiO2 nanostructures. X-ray diffraction analysis confirmed the presence of Au nanoparticles on the TiO2 nanostructures. Ultraviolet–visible diffuse reflectance spectroscopy study of the Au-TiO2 nanostructures detected a peak at 554 nm due to the surface plasmon resonance of the Au nanoparticles. The photocatalytic efficiency of the Au-TiO2 plasmonic nanohybrids increased with the attachment of more Au nanoparticles to TiO2 nanostructures. The superior photodegradation activity of the Au-TiO2 nanohybrids can be attributed to the creation of Schottky junctions and the efficient utilization of sunlight. The as-synthesized Au-TiO2 plasmonic nanohybrids degraded organic dyes comprising methylene blue (MB), methyl orange (MO), a mixture of MO and MB, and 4-nitrophenol in water under sunlight. The most efficient Au-TiO2 plasmonic nanohybrids exhibited degradation efficiencies of 94% with MB, 85% with MO, and 87% with the mixture of MO and MB in only 20 min under irradiation by sunlight. The photocatalytic activity of the Au-TiO2 nanohybrids was 3.3 times greater than that of the pristine TiO2. A mechanism is proposed to explain the superior photocatalytic activity of the Au-TiO2 plasmonic nanohybrids. In this study, we demonstrated a facile method for the development of highly efficient plasmonic photocatalysts.

In situ exsolution of silver nanoparticles on AgTaO3-SrTiO3 solid solutions as efficient plasmonic photocatalysts for water splitting

Starting from two wide band gap semiconductors AgTaO3 and SrTiO3, we managed to reduce the band gap by forming their solid solutions, i.e. (AgTaO3)1-x(SrTiO3)x (0.0 ≤ x ≤ 1.0). These solid solutions all adopt cubic perovskite structure similar to SrTiO3 and high temperature phase of AgTaO3, suggesting that SrTiO3 is helpful to stabilize AgTaO3 in its high temperature cubic phase. Substantial improvements over photocatalytic hydrogen production were realized in these solid solutions which clearly outperform their parent compounds AgTaO3 and SrTiO3. In-situ exolution of silver nanoparticles at the surface of solid solutions (x = 0.2) substantially strengthen the visible light absorption due to localized surface plasmons of these silver nanoparticles. This contributes to further improvements on both photocatalytic hydrogen and oxygen production under visible light illumination (λ ≥ 400 nm). Apparent quantum efficiency as high as ˜ 2.02% and ˜ 0.11% was achieved at solid solutions (x = 0.2) decorated with silver nanoparticles for full range (λ ≥ 250 nm) and visible light (λ ≥ 400 nm) illumination respectively. Photoelectrochemical analysis suggests that solid solutions own a better charge separation conditions than their parent compounds. Furthermore, the band edge positions of solid solutions (x = 0.2) lie approximately in the middle between AgTaO3 and SrTiO3, being ideal for solar water splitting reactions.

Synthesis of high efficient and stable plasmonic photocatalyst Ag/AgNbO3 with specific exposed crystal-facets and intimate heterogeneous interface via combustion route

Abstract The efficiency and stability of plasmonic photocatalysts that closely related with microstructure characteristics are intensively studied for practical applications. Here, a plasmonic photocatalyst Ag/AgNbO3 was successfully synthesized by a facile combustion method, and systematically characterized by XRD, XPS, DRS, SEM, TEM and photocurrent techniques. The photocatalytic activity of Ag/AgNbO3 as a function of Ag vs Nb contents are assessed toward Rhodamine B (RhB) and tetracycline (TC) degradation under the visible-light. At an optimal Ag content, the greatest photocatalytic efficiency of as-prepared Ag/AgNbO3 on photodegradation of RhB (0.0447 min−1) was 2 times higher than that of currently reported solvents routes (0.0213 min−1). Meanwhile, the experimental and theoretical studies were conducted to examine the photocatalytic efficiency and stability of the as-prepared photocatalysts, the results show that the photocatalytic efficiency and stability are related with the SPR effect, ferroelectric polarization, specific exposed crystal-facets and interfacial crystallinity. This work may also provide new ideas for the design and preparation of other highly efficient and stable plasmonic photocatalysts.

Enhanced visible light photocatalytic performance and reaction mechanism on Ag/AgCl-LaCO<sub>3</sub>OH nanorods composite

Air pollution has become a focused issue worldwide with the rapid development of industry. As one of the major air pollutants, nitric oxide (NO) could cause to serious atmospheric problems, such as acid rain, haze and photochemical smog. Photocatalysis as a green technology has received increasing attention, because it has represented greatly potential application over the late decades. As a novel photocatalyst, LaCO3OH possesses relatively negative conduction band and positive valence band edges, which can be enable to sufficient potential for photocatalytic air decomposition. But the band gap of LaCO3OH (4.1 eV) allows only a small portion of solar spectrum in the ultraviolet (UV) light region to be absorbed. To extend the light absorption spectra into the visible light region, the combination of narrow band gap Ag/AgCl with the wide band gap LaCO3OH to build heterojunction could utilize abundant solar light. Noble metal nanoparticles (NPs) showed strong visible light absorption due to surface Plasmon resonance effect (SPR). In particular, silver NPs show SPR in the visible region, which has been utilized to develop efficient plasmonic photocatalysts. In this study, a three-component Ag/AgCl-LaCO3OH nanorod photocatalyst has been fabricated successfully through a chemical precipitation treatment and applied to photocatalytic NO removal. The as-prepared samples were characterized by XRD, SEM, TEM, XPS, UV-vis DRS, PL and ESR. The photocatalytic NO oxidation process was monitored by in situ DRIFTS. The results indicated that the visible-light harvesting and the photogenerated carrier separation can be enhanced simultaneously, which could result from introduction of Ag/AgCl into LaCO3OH (LCO) nanorod photocatalyst. Under visible-light irradiation, the photogenerated electron-hole pairs separation is promoted by the plasma resonance (SPR) effect of the metallic Ag0. The hot electrons would be transferred to the defect level endowed by the oxygen vacancies of the LCO. Subsequently, the electron can be transferred to the surface of LCO, captured by O2 to form ·O2− radicals, which plays a dominant role in the photocatalytic NO oxidation. In addition, the holes would be transferred to the surface of AgCl, and interact with Cl− to transform Cl0, which can directly participate in the oxidation of NO. Furthermore, Cl0 can be reduced to Cl− and react with Ag+ to forming AgCl, avoiding the photocorrosion of AgCl effectively. Meanwhile, the effect of the mol ratio of Ag/AgCl on the photocatalytic performance was also evaluated. The optimized Ag/AgCl-LCO (mol ratio at 75%) nanorods demonstrated a high NO removal ratio of 54.0%, which far exceeding that of the individual LCO (3.1%) or Ag/AgCl (18.0%) photocatalyst. Moreover, the in situ FT-IR spectra was used to dynamically monitor the intermediate toxic by-products, in combination with the active species, and further reveal the mechanism of photocatalytic NO oxidation from the molecular level. The reaction mechanism can be described as Ag + visible light → e−+h+, e−+O2→ ·O2−, h++AgCl→Cl0+Ag+, ·O2−+NO→NO3−, Cl0+ NO→NO3−+Cl−, NO+2·OH→NO2+H2O, NO2+·OH→NO3−+H+ and Cl−+Ag+→AgCl. The present work could provide navel perspectives for advancing the photocatalysis efficiency, offer a new insight of the photocatalytic reaction mechanism and promote large-scale environmental decontamination applications of plasma-based semiconductor composites.