Regulating redox sites for photocatalytic phenylcarbinol conversion and H2 production on lattice-matched Schottky junction.

Open AccessCCS ChemistryRESEARCH ARTICLE11 Apr 2022Slow Photon-Enhanced Heterojunction Accelerates Photocatalytic Hydrogen Evolution Reaction to Unprecedented Rates Jing Liu†, Yin-Hao Guo†, Zhi-Yi Hu†, Heng Zhao, Ze-Chuan Yu, Lihua Chen, Yu Li, Gustaaf Van Tendeloo and Bao-Lian Su Jing Liu† State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, 430070 Wuhan , Yin-Hao Guo† State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, 430070 Wuhan , Zhi-Yi Hu† State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, 430070 Wuhan Nanostructure Research Centre (NRC), Wuhan University of Technology, 430070 Wuhan , Heng Zhao State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, 430070 Wuhan , Ze-Chuan Yu School of Civil Engineering and Architecture, Wuhan University of Technology, 430070 Wuhan , Lihua Chen State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, 430070 Wuhan , Yu Li *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, 430070 Wuhan , Gustaaf Van Tendeloo Nanostructure Research Centre (NRC), Wuhan University of Technology, 430070 Wuhan EMAT, University of Antwerp, B-2020 Antwerp and Bao-Lian Su *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology, 430070 Wuhan Laboratory of Inorganic Materials Chemistry (CMI), University of Namur, B-5000 Namur https://doi.org/10.31635/ccschem.022.202101699 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail In photocatalysis, both the photogenerated charge separation and transport and the induced light utilization greatly influence performance. In this work, highly ordered [email protected] core-shell inverse opal ([email protected]) nanocomposites have been successfully designed as a model to couple the heterojunction system with the slow photon effect for photocatalytic H2 production. Theoretical calculations and experimentation provide direct evidence for the slow photon effect in the [email protected] nanocomposites. The type II heterojunction is responsible for promoting the migration and separation of photogenerated charges, and the slow photon effect is in charge of enhancing light harvesting in the [email protected] nanocomposites. This synergy of two functions gives rise to a significantly enhanced photocatalytic H2 production rate under simulated solar light for the [email protected] nanocomposites. The highest H2 production rate reaches 48.7 mmol g−1 h−1 under simulated solar light with the benchmark performance for all reported [email protected] composites. Our work provides proof-of-principle that coupling the heterojunction system with the slow photon effect can greatly enhance the photocatalytic activity of composite photocatalysts. Download figure Download PowerPoint Introduction Solar light utilization has been extended to limit global warming and decrease carbon emissions. Consequently, photocatalytic hydrogen generation enabled by semiconductors under light illumination has attracted increasing attention. In fact, this strategy has been widely explored as an environmentally friendly method for converting solar energy to stored chemical energy.1–3 Generally, the photocatalytic reaction involves the following steps: light harvesting, charge separation, transportation of photogenerated electrons and holes to the surface of the photocatalyst, and the redox reaction.4 Because the balance of the thermodynamics and kinetics of the photocatalytic reaction processes play the key role in the photocatalytic hydrogen generation efficiency, the single-component photocatalyst, owing to its low absorption of solar light and photocatalytic inefficiency, has hindered its commercial application. To overcome this obstacle, heterojunction photocatalytic water-splitting systems (including type I, type II, and type III heterojunctions, Z-scheme heterojunction, and S-scheme heterojunction systems) have been adopted because of their ability to accelerate the migration of photogenerated electrons and holes to various counterparts for reduction and oxidation reactions to prevent their recombination rate, and to prolong their lifetimes.4–16 Such heterojunction photocatalysts exhibit broadband light response and high hydrogen evolution rates.4,17–19 This internal charge-transfer process leads to a spatial separation of photogenerated electrons and holes, resulting in efficient electron transfer for H2 reduction when the conduction bands (CBs) of the composite photocatalyst couple favorably.2,13 Furthermore, the heterojunction system yields photogenerated carriers that benefit photocatalysis in terms of thermodynamic requirements.4,20,21 For the heterojunction system, the structural design is very important to make full use of the induced light. Hierarchically structural porous materials with high surface area, large pore volume, and interconnected hierarchical porosity of different length scales display significant structural advantages in electron and ion transport, and mass diffusion has roused widespread attention and applications.22–26 As a special hierarchically porous structure, three-dimensional ordered marcroporous (3DOM) structures as good light harvesters have given rise to considerable research activity. They allow deep penetration of light and lead to longer light pathways. They significantly improve induced light utilization efficiency. Previous work on single (TiO2, ZnO, BiVO4, etc.), binary (TiO2/CdS, TiO2/Au, TiO2/ BiVO4, etc.), and ternary (TiO2/BiVO4/ZnO, TiO2/Au/CdS, etc.) semiconductor-based composites with 3DOM structure show that the 3DOM structure can greatly improve the absorption and utilization of light and significantly enhance photocatalytic performance.17,22,27–32 Particularly, the inverse opal photonic crystal structures benefitting the slow photon effect have further exhibited highly enhanced photocatalytic activity.18,29,33–35 The slow photon effect generally occurs when the wavelength of blue and/or red edges of the photonic band gap (PBG) match the electronic band gap (EBG) of a semiconductor. When this happens, light propagates with extremely low group velocity, leading to a longer lifetime of the photons and a largely increased optical path length of the light wave in the material to promote the interaction between light and material.36–38 This greatly improves the photon absorption and conversion efficiency, as broadly evidenced and applied in various kinds of single semiconductors for enhanced photocatalytic activity.17,39 Since the heterojunction system plays a significant role in separating photogenerated electron-hole pairs and slow photon effect contributes a lot to enhancing light harvesting, binary/ternary inverse opal composites seldom provide evidence or theoretical calculations that reveal the slow photon effect in the inverse opal composites. Thus, it is worth systematically investigating and revealing the existence of the slow photon effect in inverse opal composites and demonstrating the advantages of coupling the slow photon effect with the heterojunction system in such an efficient solar-powered photocatalysis. Herein, we choose the very common semiconductors (ZnO, CdS) and report the construction of three-dimensional (3D) [email protected] core-shell inverse opal ([email protected]) nanocomposites as a photocatalyst model by coating CdS nanoparticles onto a ZnO inverse opal (ZnO-IO) open framework using the successive ion layer absorption and reaction (SILAR) method.19,29 To tune and monitor the slow photon effect, we tailor the macroporous sizes of the inverse opal nanocomposite to modulate the relative positions of PBG and EBG in the [email protected] composites, aiming to compare photocatalytic enhancement originating from the slow photons between the red edge and the blue edge.33,36 These results show that by coupling a heterojunction system with the slow photon effect, [email protected] films can enhance light absorption and facilitate the separation of photogenerated electrons and holes, resulting in significantly improved photocatalytic H2 production. This is the first evidence that the heterojunction system can synergistically be coupled with the slow photon effect in such a [email protected] photonic crystal heteronanostructure. The [email protected] nanocomposites demonstrate an unprecedented photocatalytic H2 production rate, proven to originate from the type II heterojunction system with ∼2.7× enhancement under simulated solar light. The slow photon effect enhances photocatalytic H2 production with ∼1.4× and 1.7× at the red and blue edges respectively, providing direct experimental evidence that the slow photon effect occurring at the blue edge can bring a higher photocatalytic enhancement than that in red edge.17,39,40 The highest H2 production rate for [email protected] reached 48.7 mmol g−1 h−1 under simulated solar light with the benchmark performance of ∼fivefold enhancement of [email protected] (10.5 mmol g−1 h−1). Experimental Methods Fabrication of ZnO inverse opal film Highly ordered and continuous ZnO-IO films coated on fluorine-doped tin oxide (FTO) substrate with different air sphere sizes were successfully prepared by a metal salt-based sol–gel infiltration according to our previous work.29 Three different-sized colloidal templates ranging from 230, 290, and 440 nm have been used in this work. After removing the templates by calcination, various ZnO-IO films with different pore sizes were obtained. The samples were then designated as ZnO-IO-230, ZnO-IO-290, and ZnO-IO-440, respectively. The synthesis process of ZnO-IO-3M was the same with ZnO-IO film except using the mixture of three colloidal spheres (230, 290, and 440 nm with the volume ratio of 1∶1∶1) as template. Fabrication of 3D [email protected] nanocomposites To obtain 3D [email protected], the CdS shell layer was coated on the ZnO-IO film by the SILAR technique, as in previous reports.41 Typically, the ZnO-IO film is successively immersed in solutions containing 0.5 M Cd(NO3)2 in ethanol for 5 min, to allow Cd2+ to adsorb onto the ZnO-IO film and is then rinsed with ethanol for 5 min to remove the excess Cd2+. The film was rinsed in a solution containing 0.5 M Na2S in methanol for 5 min, to allow S2− to adsorb onto the ZnO-IO film and to react with preadsorbed Cd2+ to form the desired CdS. The above procedure is termed a SILAR cycle, and the loading of CdS can be increased by repeating these assembly cycles. This immersion cycle was repeated eight times in this study. The final samples were designated as [email protected], [email protected], and [email protected], respectively. The [email protected] was synthesized via the same method to coat the same amount of CdS shell on the ZnO-IO-3M film. Characterizations The crystalline phase of the samples was examined by X-ray diffraction (XRD) with a Bruker D8 ADVANCE diffractometer (Karlsruhe, Germany) using Cu Kα radiation (λ = 1.54 Å) in the 2θ range of 20–70°. Field-emission scanning electron microscopy (FESEM) was performed on a Hitachi S-4800 electron microscope (Tokyo, Japan) equipped with an energy-dispersive spectroscopy facility to characterize the sample morphology and composition. The absorption spectra were collected with a UV2550 (SHIMADZU, Chukyo, Japan) UV–vis spectrometer. The reflection spectra were recorded using an Avaspec 2048/2 fiber-optic spectrometer (Beijing, China). Transmission electron microscopy (TEM) was carried out on an FEI Tecnai Osiris microscope (Massachusetts, United States), operated at 200 kV. The photocatalytic H2 production was performed with an online photocatalytic analysis system (Labsolar-6A, Beijing Perfectlight Technology Co., Ltd., Beijing, China). The gas products were analyzed periodically by an Agilent 7890A (California, United States) gas chromatograph (GC) with a thermal conductivity detector (TCD). Photocatalytic hydrogen reduction Typically, the photocatalytic H2 production was performed in a Pyrex reactor with an entry window of optical quartz glass (Labsolar-6A, Beijing Perfectlight Technology Co., Ltd., Beijing, China). One piece of the obtained [email protected] film coated on FTO substrate (geometrical area of each piece was 2 cm × 2 cm) was placed in the reaction cell with 100 mL of an aqueous solution containing 0.1 M Na2S and 0.1 M Na2SO3 as the sacrificial agents. The light source was irradiated under simulated solar light irradiation (250–780 nm, PLS-SXE-300DUV (Beijing, China) with an UV light intensity of 34 mW cm−2 and a visible light intensity of 158 mW cm−2, Beijing Perfectlight Technology Co., Ltd., Beijing, China). When under visible light irradiation, the light passed through a cutoff filter (λ > 420 nm). The amount of H2 produced was analyzed using on-line GC (Agilent 7890A, California, United States) with TCD, using N2 as the carrier gas. The mass of photocatalyst on one piece of FTO was ∼1 mg. Photoelectrochemical measurements The photocurrent measurements in our experiments were performed on an electrochemical workstation (CHI 660D, Chenhua Instrument Co., Shanghai, China) in a standard three-electrode electrochemical cell with a Pt plate counter electrode and an Ag/AgCl reference electrode. And the electrolyte solution was performed using 0.1 M Na2S and Na2SO3, which was the same as with the sacrificial agents. The working electrodes with the exposed area of 1 × 1 cm2 were illuminated from the front side with solar light sources, the same as with the photocatalytic H2 production. All the [email protected] photoanodes were measured at 0.5 V external potential versus hydrogen electrode (RHE). Apparent quantum yields (AQY) are defined by the following equation because of a 2-electron process for H2 production in the [email protected] with the slow photon effect and type II heterojunction system. The energy density of irradiated solar light with 365 and 500 nm are 19 and 16 mW cm−2. AQY ( % ) = [ Number of the reacted electrons ] / [ Number of incident photons ] × 100 = [ Number of evolved hydrogen molecules × 2 ] / [ Number of incident photons ] × 100 Theoretical simulation of reflectance spectra The theoretical simulation of the reflectance spectra of [email protected] and [email protected] inverse opal films was calculated using the finite-difference time-domain (FDTD) method in the MEEP package.42 Computational details The density functional theory (DFT) calculation was performed by the Cambridge Sequential Total Energy Package. Generalized gradient approximation of the Perdew–Burke–Ernzerhof functional was used as the commutative correlation functional. The cutoff energy was set to 450 eV, and a 30 Å vacuum layer was constructed to eliminate the interaction between the periodic structures of the surface model. The Brillouin area was sampled at 2 × 2 × 1 K points. Results and Discussion Figure 1a illustrates the synthesis process for [email protected] nanocomposites. Figures 1b–1d present the FESEM images of the as-synthesized [email protected] films with different macroporous diameters. The hexagonal close-packed structure is well copied from the hexagonally packed colloidal crystal templates ( Supporting Information Figure S1). The obtained [email protected] films are highly ordered with continuous macroporous structure on a large scale ( Supporting Information Figure S2), similar to those of the ZnO-IO films ( Supporting Information Figure S3). The air-spheres of the ZnO-IO films are distributed uniformly, and the average pore diameter is ∼220, 260, and 380 nm, respectively ( Supporting Information Figure S3). After coating CdS nanoparticles on ZnO-IO structures, the average pore diameter for [email protected], [email protected], and [email protected] was ∼200, 240, and 360 nm. The thickness of the CdS shell was estimated at ∼10 nm via the SILAR method (Figures 1b–1d). SEM-electron dispersive X-ray spectroscopy (EDXS) results further show that the molar ratio of ZnO and CdS in all nanocomposites was close to 1∶1. Supporting Information Figure S4 presents the mapping images of [email protected] ( Supporting Information). These results demonstrate that we have successfully prepared well-ordered, large-area, high-structural quality [email protected] nanocomposites. These impressive core-shell inverse opal films would have an interesting influence on the photocatalytic H2 production based on our previous work for ZnO-IO film.29 Figure 1 | Schematic illustration and structural characterizations of [email protected] films. (a) Schematic illustration of the preparation of [email protected] films. The FESEM images of the as-prepared (b) [email protected] csIO-230, (c) [email protected] csIO-290, and (d) [email protected] csIO-440 heteronanostructures. Download figure Download PowerPoint A hexagonal wurtzite structure (JCPDS No. 079-0206) of the [email protected] films with different macroporous diameters and three strong diagnostic diffraction peaks at (10-10), (0002) and (10-11), respectively were observed based on the XRD patterns ( Supporting Information Figure S5). The diffraction peaks located at 37.76° and 51.75° belong to the FTO substrate. Three characteristic diffraction peaks at 26.46°, 43.89°, and 54.47° were ascribed to the (111), (220), and (222) crystal planes of cubic CdS (JCPDS No. 089-440), respectively. The broader diffraction peaks of cubic CdS implied that very small CdS nanoparticles were decorating the surface of ZnO-IO. Furthermore, the XRD results suggest that the CdS coating did not influence the crystalline phase of ZnO-IO film, indicating the successful synthesis of a heterojunction inverse opal structure. Since the only difference for these [email protected] films was the macroporous diameter, [email protected] was selected to demonstrate the morphological quality of the [email protected] structures. Figure 2a presents a typical TEM image of [email protected] structure, showing the stable core-shell inverse opal structure. Figure 2b presents the high-resolution transmission electron microscopy (HRTEM) image from the enlarged squared area in Figure 2a. The fast Fourier transform (FFT) from the whole area, clearly displayed the main zone axis of ZnO along [2-1-10] and verified the quasisingle crystal domains in the ZnO-IO framework, suggesting that the ZnO nanoparticles formed inverse opal structure with the same orientation (Figure 2b). These quasisingle crystal domains in this ZnO photonic crystal skeleton could improve the separation and the transport of photogenerated electrons and holes43 although details of the formation of such quasisingle crystal domains in inverse opal structure are not clear. However, the CdS (111) ring revealed that the CdS crystals coated on the surface of the framework had different orientations. Figure 2 | Compositional and structural characterizations of [email protected] film. (a) TEM images of low magnification. (b) HRTEM image of the area indicated in (a) and FFT image (inset). (c) Enlarged image of the area indicated in (b) and FFT image (inset). (d) HAADF-STEM image of one typical cell of inverse-opal structure and (e–h) the corresponding STEM-EDXS color maps in red box (d). Download figure Download PowerPoint Figure 2b also displays the ∼10 nm thickness of CdS located on the surface of ZnO, consistent with the SEM observations. The enlarged image of a zone on the surface presents the CdS crystal along the [10-1] zone axis (Figure 2c), further revealing the CdS polycrystalline coat on the ZnO-IO framework. Figures 2d–2h present the CdS distribution on the ZnO-IO framework via high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) and STEM- STEM-EDXS images on the randomly selected regions of [email protected] The uniform distribution of Zn, Cd, and S throughout the [email protected] was clearly observed, showing the homogeneous distribution of CdS nanocrystallites on the ZnO-IO structure and intimate contact interface between the CdS and ZnO phases. These results confirm that the CdS nanocrystals were successfully coated onto the ZnO-IO framework to form a core-shell inverse opal structure. And the intimate contact interface is also expected to bring efficient electron transfer and high separation effect. It is well documented that reflectance spectra reflect the morphological quality of the inverse opal photonic crystal structure and the judgment criteria for the occurrence of slow photon effects.17,18,36 The theoretical simulation of the reflectance spectra of [email protected] inverse opal films with 230 and 290 nm templates has been performed to feature the experimental spectral observations (Figures 3a–3d). The FDTD method was implemented by using the MEEP package to calculate the optical response of the ZnO-CdS inverse opal system.42,44 Reflectance spectra with wavelengths ranging from 250 nm to 1000 nm were obtained. In the FDTD simulation, and the system was periodic and of along the The two with thickness to the wavelength of the at the and the two vacuum to and thickness the and one material layer which the thickness was times the diameter, and in the The material layer the inverse opal system used in the which was constructed following the cubic with its surface to the Materials were by the that ZnO was by a with to and CdS of wave source was placed in the vacuum and two were placed at the between the vacuum layer and the on both Reflectance was calculated by the the of the two For [email protected] and [email protected], the calculated reflectance peaks were and nm. In both the reflectance to longer wavelengths as the was as expected from the photonic crystal structure of the films. the were located the electronic band edge of CdS blue in Figure which evidence of the existence of the slow photon effect. It is then expected that the occurrence of the slow photon effect on the red edge of [email protected] and on the blue edge of [email protected] bring high enhancement in light absorption and photocatalytic H2 Figure | Theoretical simulation of reflectance of the material layer in the FDTD simulation in three side regions with higher than 1 and regions are the is to (d) Theoretical simulation of reflectance spectra of [email protected] and [email protected] inverse opal films using FDTD and the blue is the of CdS. and UV–vis absorption spectra and reflectance spectra of [email protected] with different macroporous diameters. The the electronic absorption band of CdS. Download figure Download PowerPoint UV–vis and the reflectance spectra of these [email protected] films were performed in to the relative between the reflection and the absorption of the obtained [email protected] composites from an experimental of (Figures and UV–vis was performed to the electronic structures and the optical absorption of these [email protected] films (Figure The strong absorption at wavelength in the nm range the absorption of hexagonal ZnO, showing its UV absorption After coating the CdS crystal shell on the surface of the ZnO macroporous framework, the absorption edge was extended to nm, the of CdS. This indicated that both UV light and visible light were by the [email protected] films. This is very for the utilization of solar light for hydrogen production. It also that the the of the the higher the light absorption for these This is because the enhances light and the optical path length of the light the inverse opal structure, its optical absorption For a high quality photonic crystal structure, the PBG can be by the and/or the average This is revealed by the reflectance spectra of the [email protected] and ZnO-IO films. the CdS the PBG of located at nm ( Supporting Information Figure After the CdS shell the of reflection peaks of [email protected] located at nm (Figure showing a of nm to the high average of the composites of ZnO = and CdS = This to the PBG red edge of [email protected] the electronic band of CdS nm). When the was increased to 290 nm, the corresponding reflection from nm ( Supporting Information Figure to nm. The PBG blue edge side of [email protected] then with the electronic band of CdS (Figure the red and blue edges of the PBG the occurrence of the slow photon The PBG of [email protected] was further from nm ( Supporting Information Figure to nm its PBG was at nm, the electronic wavelength of CdS (Figure the band reflection the light absorption to decrease the photocatalytic activity of [email protected] because of the of the slow photon the measured reflectance of [email protected] and [email protected] were in good with calculated spectra measured reflectance peaks were and nm, and the calculated reflectance peaks were and nm, (Figure the that were observed on the red edge of [email protected] and the blue edge of [email protected] reflectance were also in the calculated experimentation and theoretical calculations provide direct evidence of the existence of the slow photon on the red edge of [email protected] and the blue edge of [email protected], which can bring high enhancement for photocatalytic H2 Photocatalytic H2 generation was performed to show the slow photon effect in [email protected] using 0.1 M Na2S and Na2SO3 as sacrificial (Figure [email protected] and [email protected] exhibited significant enhancement of photocatalytic H2 production with the hydrogen amount of and mmol g−1 in 5 respectively under visible light irradiation (λ > 420 However, the [email protected] low photocatalytic H2 production with the hydrogen amount of only mmol g−1 in 5 This difference in H2 production for these samples originate from the slow photon effect that at the red

Rapid growth in economy and society currently relies on fossil fuels heavily, leading to serious concern on energy sustainability and environmental pollution. This has aroused increasing interest in solar energy, which is the most abundant and green energy source. However, it remains a significant challenge in storing and harnessing solar energy due to its diurnal and seasonal fluctuation along with uneven distribution. Moreover, its energy density is relatively low; and the energy supply from traditional solar cells is time-varying. Consequently, it is difficult to synchronize the generation and usage of electricity from solar cells. In contrast, photocatalytic water splitting can convert solar energy to chemical energy, which can be stored in the form of hydrogen, an ideal energy carrier that is characteristic of cleanness and operational convenience. Also, photocatalytic CO2 reduction can transform greenhouse gas to valuable fuels. Furthermore, photocatalytic degradation of organic pollutants can decontaminate air, water, and soil. Additionally, photocatalytic disinfection and sterilization can reduce human exposure to pathogens and toxins. Therefore, photocatalysis has received extensive attention globally, becoming the hotspot and frontier across several fields, including chemistry, materials science, energy and environment engineering. In this special issue (Part 1), 2 progress reports, 12 review articles and 15 research articles have been published. Classified based on applications, 8 papers concern with hydrogen evolution, 7 papers involve CO2 reduction, 2 articles deal with pollutant decomposition, and 11 papers are related to nitrate reduction, nitrogen fixation, organic synthesis, syngas synthesis, NADH (nicotinamide adenine dinucleotide) regeneration and so on. From the materials perspective, 8 papers discuss C3N4, 4 articles involve CdS, 3 paper concern with conjugated polymers, other papers cover TiO2, CdSe, CoMn alloy, PbI2/CuI, silicon, metal-organic frameworks (MOFs), perovskite oxides, Bi2MoO6 and so on. Photocatalytic H2 production is of great interest from both theoretical and practical viewpoints because of its potential application in converting solar energy into storable chemical energy. Herein, Zhen and Xue (solr.202000440) have reviewed surface functionalization of polymeric carbon nitride at atomic and molecular levels for photocatalytic H2 production and CO2 reduction applications. Then, Yu et al. have (solr.202000372) reported enhanced photocatalytic H2 production activity of g-C3N4, which are prepared by one-step crystallization and cyano-group modification. Yang and co-workers (solr.202000414) have presented the fabrication of 2D/2D CdS/MXene Schottky heterojunctions by electrostatic self-assembly and solvothermal method and their application in high-efficiency photocatalytic hydrogen production. Tang and colleagues (solr.202000281) have reported the molecular cobalt catalysts grafted on a conjugated microporous polymer for high-efficiency H2 production. Zhao et al. (solr.202000415) have prepared a CdS/MoS2 nanooctahedron heterostructure with a tight interface for enhanced photocatalytic H2 evolution and biomass upgrading. Wu's group (solr.202000474) have reported a per-6-thiol-cyclodextrin engineered [FeFe]-H2ase mimic/CdSe quantum dot assembly for effective photocatalytic H2 evolution. Xu et al. (solr.202000486) have synthesized a lignin-modified g-C3N4 nanoarchitecture with an ultrathin layered topography for efficient photocatalytic H2 production. Finally, Kwon et al. (solr.202000411) have reported a self-assembly between the CdS quantum dots and the RuO2/reduced graphene oxide nanosheets, showing enhanced photocatalytic H2 production activity. Nowadays, there is increasing interest in solutions to the increasing CO2 level in the atmosphere. Photocatalytic reduction of CO2 into storable solar fuels is an appealing strategy to simultaneously overcome both environmental problems and energy crisis. In this special issue, Wang's group (solr.202000443) has firstly discussed the active sites of catalysts for CO2 activation and conversion. Then, Liang et al. (solr.202000478) have summarized recent research progress in g-C3N4 and its composite photocatalysts for CO2 reduction. Huang's group (solr.202000430) has reviewed junction engineering for photocatalytic and photoelectrocatalytic CO2 reduction. Zhang et al. (solr.202000387) have demonstrated an all-earth-abundant photothermal silicon platform for CO2 catalysis with nearly 100% sunlight absorption ability. Jia's group (solr.202000313) has reported anchoring single-atom Ru on CdS, showing enhanced CO2 capture and charge accumulation for highly selective photothermocatalytic CO2 reduction to solar fuels. Xiang et al. (solr.202000351) have prepared an ultrathin S-scheme heterojunction based on few-layer g-C3N4 and monolayer Ti3C2Tx MXene for photocatalytic CO2 reduction. Finally, Zhang's group (solr.202000326) has reported an ultraviolet-visible-near-infrared responsive Cu2-xS/g-C3N4 composite photocatalyst and its photocatalytic CO2 reduction performance. It worth noting that significant efforts have been made to prepare high-performance photocatalysts for environment remediation including air purification, hazardous waste removal, water purification, and etc. Herein Xu et al. (solr.202000416) have fabricated a g-C3N4/NH2-UIO-66 composite photocatalyst with enhanced photocatalytic removal efficiency for hexavalent chromium. Zhu's group (solr.202000453) has reported the enhanced photocatalytic phenol degradation activity in the presence of g-C3N4/PDI (perylenetetracarboxylic diimide). Janáky and co-workers (solr.202000418) have reported the preparation of PbI2/CuI nanocomposite electrode and its solar photoelectroreduction of nitrate ions. Peng's group (solr.202000487) has summarized updated research progresses in photocatalytic nitrogen-fixation reaction over semiconductors. Su and colleagues (solr.202000444) have surveyed recent advance in the rational harnessing of photoexcited hole-electron pairs in semiconductor photocatalysts, and the application in oxidative and reductive synthetic transformations for chemical and pharmaceutical production. Ouyang's group (solr.202000488) has reported the fabrication of CoMn alloy using a metal-segregation method and its enhanced photothermal conversion of syngas to light olefins. Qian and Zhang (solr.202000489) have commented the recent advance in the conjugated microporous polymers in visible light promoted chemical transformations such as water splitting, CO2 reduction, organic photoredox reactions, and etc. Chen and colleague (solr.202000442) have reviewed the current research status of Bi2MoO6-based photocatalysts and their surface/interface modification strategies and applications. Dong and co-workers (solr.202000419) have reviewed the synthesis strategy, interfacial effect and photocatalytic application of perovskite nanocrystals-based heterostructure photocatalysts. Hao and Li (solr.202000454) have reviewed visible-light initiated synergistic/cascade reactions over metal-organic frameworks. Ma's group (solr.202000397) has highlighted the 2D/2D Z-Scheme heterojunctions for photocatalytic application. Wang et al. (solr.202000392) have reviewed two-dimensional silicon (2D Si) for catalysis and photocatalysis applications. Liu's group (solr.202000339) has summarized the key developments of conjugated photocatalytic systems for NADH (nicotinamide adenine dinucleotide) regeneration. As the guest editors, we thank all the authors for their prompt response to the paper call and their valuable contribution to this special issue. All the manuscripts were refereed through rigorous peer-review processes. We greatly appreciate the timely and conscientious evaluation of manuscripts by the reviewers. Last but not least, we are grateful to Dr. Lulu Ma, Editor of Solar RRL, for her tremendous support and dedication. Jiaguo Yu received his B.S. and M.S. in chemistry from Central China Normal University and Xi'an Jiaotong University, respectively; his Ph.D. in Materials Science from Wuhan University of Technology (WUT). In 2000, he became a Professor at WUT. His research interests include photocatalysis, adsorption, supercapacitor, electrocatalysis, formaldehyde removal and so on. He is Foreign Member of Academia Europaea (The Academy of Europe) (2020), Foreign Fellow of the European Academy of Sciences (2020) and Fellow of the Royal Society of Chemistry (2015). Tierui Zhang is currently Professor at the Technical Institute of Physics and Chemistry, Chinese Academy of Sciences. He obtained his Ph.D. degree in Chemistry from Jilin University, China in 2003. He worked as a postdoctoral fellow in the labs of Prof. Markus Antonietti, Prof. Charl F.J. Faul, Prof. Hicham Fenniri, Prof. Z. RyanTian, Prof. Yadong Yin, and Prof. Yushan Yan. His current scientific interests focus on catalyst nanomaterials for energy conversion. Nianqiang Wu is currently Armstrong-Siadat Endowed Professor in Materials Science at University of Massachusetts Amherst, USA. He has received his Ph.D. degree in Materials Science and Engineering from Zhejiang University, China. Dr. Wu is Fellow of the Electrochemical Society (FECS) and Royal Society of Chemistry (FRSC). His research interest lies in: 1) photocatalysts and photoelectrochemical cells, 2) electrochemical energy storage, and 3) biosensing, microfluidics and photodynamic therapy.

Novel and noble-metal-free CdIn2S4/MoB Schottky heterojunction photocatalysts with efficient charge separation for boosting photocatalytic H2 production

A binary dumbbell visible light driven photocatalyst for simultaneous hydrogen production with the selective oxidation of benzyl alcohol to benzaldehyde

Photocatalytic hydrogen evolution by heterojunction photocatalysts is considered an effective way to address environmental and energy crises. In this work, a novel ZnCoP/CdLa 2 S 4 Schottky heterojunction was prepared via a physical mixing method assisted by water bath heating and used to enhance the efficiency of photocatalytic hydrogen production . Owing to the higher work function and metallic conductivity of ZnCoP , the photoinduced electrons can transfer from CdLa 2 S 4 to ZnCoP through the ZnCoP/CdLa 2 S 4 interface, which suppresses the recombination of photoinduced electrons and holes. Moreover, the Schottky heterojunction formed at the interface between ZnCoP and CdLa 2 S 4 inhibits electron backflow from ZnCoP to CdLa 2 S 4 , which further promotes the separation of electron-hole pairs. Meanwhile, the ZnCoP/CdLa 2 S 4 heterojunction exhibited enhanced visible light absorption compared to CdLa 2 S 4 . In addition, ZnCoP acts as an electron acceptor and hydrogen evolution active site. The synergistic effect of the tight ZnCoP/CdLa 2 S 4 interface, the higher work function and metallic conductivity of ZnCoP, and the formation of Schottky junctions significantly enhance the photocatalytic hydrogen production evolution performance of CdLa 2 S 4 . When the amount of ZnCoP was 30 wt% (wt%, mass fraction), the 30ZCP/CLS composite showed the highest photocatalytic performance, and the hydrogen production rate reached 10.26 mmol·g −1 ·h −1 under visible light irradiation and with Na 2 S and Na 2 SO 3 as sacrificial agents, which was 7.7 times that of CdLa 2 S 4 . Combined with the activity data and characterization results, a potential mechanism for photocatalytic hydrogen production over ZnCoP/CdLa 2 S 4 Schottky heterojunctions was proposed. In this work, a novel ZnCoP/CdLa 2 S 4 Schottky heterojunction was prepared for enhancing the photocatalytic hydrogen evolution performance.

Highly efficient photocatalytic hydrogen evolution and simultaneous formaldehyde degradation over Z-scheme ZnIn2S4-NiO/BiVO4 hierarchical heterojunction under visible light irradiation

Simultaneous hydrogen production with the selective oxidation of benzyl alcohol to benzaldehyde by a noble-metal-free photocatalyst VC/CdS nanowires

Photocatalytic Methane Conversion: Insight into the Mechanism of C(sp ³ )–H Bond Activation

Visible light photocatalytic H(2) production from water splitting using solar light is of great importance from the viewpoint of solar energy conversion and storage. In this study, a novel visible-light-driven photocatalyst multiwalled carbon nanotube modified Cd(0.1)Zn(0.9)S solid solution (CNT/Cd(0.1)Zn(0.9)S) was prepared by a simple hydrothermal method. The prepared samples exhibited enhanced photocatalytic H(2)-production activity under visible light. CNT content had a great influence on photocatalytic activity and an optimum amount of CNT was determined to be ca. 0.25 wt%, at which the CNT/Cd(0.1)Zn(0.9)S displayed the highest photocatalytic activity under visible light, giving an H(2)-production rate of 78.2 μmol h(-1) with an apparent quantum efficiency (QE) of 7.9% at 420 nm, even without any noble metal cocatalysts, exceeding that of pure Cd(0.1)Zn(0.9)S by more than 3.3 times. The enhanced photocatalytic activity was due to CNT as an excellent electron acceptor and transporter, thus reducing the recombination of charge carriers and enhancing the photocatalytic activity. Furthermore, the prepared sample was photostable and no photocorrosion was observed after photocatalytic recycling. Our findings demonstrated that CNT/Cd(0.1)Zn(0.9)S composites were a promising candidate for the development of high-performance photocatalysts in photocatalytic H(2) production. This work not only shows a possibility for the utilization of low cost CNT as a substitute for noble metals (such as Pt) in the photocatalytic H(2)-production but also for the first time shows a significant enhancement in the H(2)-production activity by using metal-free carbon materials as effective co-catalysts.

One-pot solvothermal synthesis of MoS2-modified Mn0.2Cd0.8S/MnS heterojunction photocatalysts for highly efficient visible-light-driven H2 production

Morphology and defects design in g-C3N4 for efficient and simultaneous visible-light photocatalytic hydrogen production and selective oxidation of benzyl alcohol

Modification of twin crystal Cd0.5Zn0.5S photocatalyst with up-conversion nanoparticles for efficient photocatalytic H2-production

Photocatalytic processes offer promising solutions for environmental remediation and clean energy production, yet their efficiency under the visible light spectrum remains a significant challenge. Here, we report a novel silver–graphene (Ag-G) modified TiO2 (Ag-G-TiO2) nanocomposite photocatalyst that demonstrates remarkably enhanced photocatalytic activity for both dye wastewater degradation and hydrogen production under visible and UV light irradiation. Through comprehensive characterization and performance analysis, we reveal that the Ag-G modification narrows the TiO2 bandgap from 3.12 eV to 1.79 eV, enabling efficient visible light absorption. The nanocomposite achieves a peak hydrogen production rate of 191 μmolesg−1h−1 in deionized (DI) water dye solution under visible light, significantly outperforming unmodified TiO2. Intriguingly, we observe an inverse relationship between dye degradation efficiency and hydrogen production rates in dye solutions with tap water versus DI water, highlighting the critical role of water composition in photocatalytic processes. This work not only advances the understanding of fundamental photocatalytic mechanisms but also presents a promising photocatalyst for solar-driven environmental remediation and clean energy production. The Ag-G-TiO2 nanocomposite’s enhanced performance across both visible and UV spectra, coupled with its dual functionality in dye degradation and hydrogen evolution, represents a significant step towards addressing critical challenges in water treatment and sustainable energy generation. Our findings highlight the complex interplay between light absorption and reaction conditions, offering new insights for optimizing photocatalytic systems. This research paves the way for developing more efficient and versatile photocatalysts, potentially contributing to the global transition towards sustainable technologies and circular economy in waste management and energy production.

Designing an efficient hybrid structure photocatalyst for photocatalytic decomposition and hydrogen (H2) evolution has been considered a great choice to develop renewable technologies for clean energy production and environmental remediation. Enhanced charge transfer (CT) based on the interaction between a noble metal and a semiconductor is a crucial factor influencing the movement of photogenerated electron-hole pairs. Herein, we focus on the recent advances related to plasmon-enhanced noble metals and the semiconductor nature to drive the photocatalytic H2 production and photodegradation of the organic dye rhodamine B (RhB) under UV and visible light irradiation. Specifically, the combination of concerted catalysis and green nanoengineering strategies to design ZnO-based composite photocatalysts and their decoration with metallic Ag have been realized by the radio frequency (RF) sputtering technique at room temperature. This simultaneity enhances the interface coupling between Ag and ZnO and reduces the energy threshold. The creation of charge transfer in the heterojunction and Schottky barrier changes the photoelectronic properties of the as-synthesized Al-doped ZnO (AZO); afterward, these effects promote the migration, transportation, and separation of photoinduced charge carriers and enhance the light-harvesting efficiency. As a result, the as-synthesized AZO-20 hybrid nanostructure exhibits a photocurrent density of 2.5 mA/cm2 vs Ag/AgCl, which is improved by almost 12 times compared with that of bare ZnO (0.2 mA/cm2). The hydrogen evolution rates of AZO-20 were ∼38 and ∼24 μmol/h under UV and visible light exposure, which are almost five- and tenfold higher than those of pristine ZnO, respectively. Additionally, the RhB degradation efficacies of the obtained AZO-20 were greater than almost 97 and 82% under UV and visible light illumination, respectively. The achieved apparent rate constant for the photocatalytic RhB decomposition was 0.014 min-1, indicating that it is 14-fold than that in pristine ZnO (0.001 min-1). Heterostructure AZO photocatalysts possess excellent practical stability in the water-splitting reaction and photocatalytic RhB decomposition, posing as promising candidates in practical works for pollution and energy challenges.

TiO2 nanosheets with exposed {001} facets co-modified by AgxAu1−x NPs and 3D ZnIn2S4 microsphere for enhanced visible light absorption and photocatalytic H2 production