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Recent advances in surface‐enhanced Raman scattering (SERS) on semiconductor substrates offer this technology improved selectivity on top of other advantages, such as cost efficiency. However, the enhancement factor (EF) based on the semiconductors is still low compared with the noble metal substrates. Here, a new strategy of developing the semiconductor substrates based on aerogels is proposed for the first time. According to the modified Herzberg–Teller coupling rule, TiO2 aerogels are selected as the control object because of their large tunability. The surface area, amorphousness, and surface oxygen vacancy densities of TiO2 aerogels are regulated synergically. Due to the tuning of band structure, including band gap and defect band, multiresonant interband charge transfer (CT) pathways are generated and enhanced CT efficiency. A strong, intrinsically activated SERS effect is generated. Amorphous TiO2 aerogel with the highest surface oxygen vacancies shows a significant EF of 2.42 × 107, and TiO2 aerogels afford the large surface area and more active sites, which is conducive to promoting the adsorption of molecules. The aerogel‐based SERS is demonstrated to have wide applicability for ultrasensitive detection of explosives and organic dyes. The aerogel nanomaterials demonstrated here open a way for the construction of low‐cost and high‐sensitivity SERS substrate materials. [ABSTRACT FROM AUTHOR]

The construction of heterojunctions is usually considered as a common strategy to improve charge separation and transfer during the photocatalytic hydrogen evolution reaction (HER) process. Originating from the surficial electrical characteristic of Ti3C2 nanosheets and 2D UiO‐66, a novel 2D/2D Ti3C2/UiO‐66 composite is facilely constructed by the electrostatic self‐assembly process for HER. Higher photocatalytic HER efficiency (265.2 μmol h−1 g−1) is achieved for 2D/2D composites compared to both, pristine 3D UiO‐66 (15.89 μmol h−1 g−1) and 2D UiO‐66 (30.2 μmol h−1 g−1), respectively. The formation of a 2D/2D Ti3C2/UiO‐66 Schottky junction is beneficial for photoinduced electron–hole separation and charge transfer. More exposed active sites stemming from the maintained 2D morphology are simultaneously induced, which is also preferable for HER. Experimental and theoretical analysis reveals the prominent performance attributed to effective charge separation and accelerated electron migration from 2D UiO‐66 to Ti3C2 nanosheets with higher electrochemcial active surface area. Herein, a new route for the construction of efficient photocatalytic systems is provided. [ABSTRACT FROM AUTHOR]

Copper-doped α-MnO2 (Cu-α-MnO2) nanowires were synthesized with various amounts of Cu2+ via a hydrothermal method. Based on the XRD and XPS data, the substitution of larger Cu2+ ions in place of Mn3+ (0.645 Å) or Mn4+ ions (0.530 Å) result in the expansion in the lattice and increase of the amount of Mn3+. The electrocatalytic results indicate that the Cu-α-MnO2 shows superior ORR activity than that of the pristine α-MnO2 due to the decreases in the charge transfer resistance and enhance the kinetic rate. In addition, the Mg-air battery using Cu-α-MnO2 (Cu: Mn = 1:4) displays a maximal peak power density of 73.4 mW cm−2 and high discharge voltage. This finding provides an effective and cheap method to improve electrocatalyst for Mg-air batteries. [ABSTRACT FROM AUTHOR]

Photoanodes in quantum-dot-sensitized solar cells are essential to the process of light collection and charge transfer. In this paper, three-dimensional inverse opal (ZnO@ZIF-8 3D IO) photoanode is fabricated via a self-assembled opal template method. The synthesized photoanode has completely connected pores with extended diameter, thus promoting the permeability of QDs and electrolyte. Meanwhile, the light trapping ability and charge transfer process can be enhanced due to the slow photon and multi-scattering effect of the regularly interconnected macroporous array structure. ZIF-8 shell coated on the surface of ZnO IO not only provides high porosity but also serves as a protective passivation layer to reduce the carriers recombination occurred at the interfacial. In order to investigate the charge transport mechanism of ZnO @ ZIF-8 IO, cascaded CdS/CdSe quantum dots were used as sensitizers. Benefiting from the IO structure and ZIF-8 modification, the photoelectric conversion efficiency of solar cells based on ZnO@ZIF-8 IO can reach 1.75% (1.71 ± 0.04%), almost twice of that of the solar cells based on ZnO IO photoanode (0.81 ± 0.05%). [ABSTRACT FROM AUTHOR]

g-C3N4 has been widely investigated in photocatalytic water splitting, even though they still suffer low specific surface area and high carrier recombination. Here Co-doped g-C3N4 (Co–C3N4) has been successfully synthesized under an argon atmosphere to 550 °C for 4 h via pyrolysis of an organic–inorganic hybrid precursor which was pre-prepared through the hydrothermal procedure. The Co–C3N4 possesses a higher specific surface area of 82 m2/g, which is 16.4 times as high as that of the bulk g-C3N4. On the other hand, the in situ Co doping can extend the light absorption region to visible light and greatly improve the charge transfer rate. Both the changes in surface area and optical property are beneficial to the photocatalytic reaction. The Co–C3N4 photocatalyst with the optimal ratio of cyanuric acid to melamine for 1:40 exhibited an excellent H2 production rate of 741.6 µmol g−1 h−1 under Xe lamp irradiation. The possible formation mechanism of tubular Co–C3N4 is proposed. Meanwhile, designing unique organic–inorganic hybrid structures may open up a new way for excellent photocatalytic water splitting. [ABSTRACT FROM AUTHOR]

Here, we present a novel TU series based on Ti 3 C 2 nanosheets modified UiO-66-NH 2 with Schottky junction for photocatalytic H 2 evolution. • Ti 3 C 2 nanosheets were integrated with UiO-66-NH 2 for enhanced photocatalytic HER activity. • TU series displayed superior photocatalytic H 2 evolution activity and stability. • Spatial separation and transfer of charge carriers was realized by the Schottky junction. • Ti 3 C 2 nanosheets with functional groups possessed abundant active sites. • DFT calculations revealed O-TC possessed the most positive Fermi level and lowest ΔG H*. As newly-developing non-noble metallic co-catalysts, MXenes have attracted intensive attention as an ideal candidate to promote the photocatalytic H 2 -production activity. In this study, Ti 3 C 2 nanosheets prepared by intercalation were further attached to porous MOFs (UiO-66-NH 2) via one-pot hydrothermal method to form face-to-face intimate contact. The obtained TU10 presented the highest photocatalytic H 2 -evolution rates in TU series, exceeding that of pure UiO-66-NH 2 by approximately 8 times. The speculation revolving about enhanced photocatalytic H 2 -production performance was proposed as the presence of exposed active sites at the edge of Ti 3 C 2 nanosheets and spatial separation and transfer of charge carriers introduced by the Schottky junction at TU series interface, which accumulated the photo-induced electrons on the surface of Ti 3 C 2 nanosheets and improved its electron-donating ability. The DFT calculations revealed that O-terminated Ti 3 C 2 possessed the most positive Fermi level and the lowest Gibbs free energy (|ΔG H* | = 0.08 ≈ 0). This work may provide new insights for constructing MXenes/MOFs structure based on Schottky junction effect to achieve high photocatalytic H 2 -production performance. [ABSTRACT FROM AUTHOR]

Abstract The annealed Ti 3 C 2 T x MXenes retained original layered morphology and gave rise to the formation of TiO 2 is anticipated to achieve improved photocatalytic hydrogen evolution performance as a noble-metal-free co-catalyst. In this work, a novel Ti 3 C 2 /TiO 2 /UiO-66-NH 2 hybrid was rationally designed for the first time by simply introducing annealed Ti 3 C 2 T x MXenes over water-stable Zr-MOFs (UiO-66-NH 2) precursors via a facile hydrothermal process. As expected, the rationally designed Ti 3 C 2 /TiO 2 /UiO-66-NH 2 displayed significantly improvement in photocatalytic H 2 performance (1980 μmol·h−1·g−1) than pristine UiO-66-NH 2 under simulated sunlight irradiation. The excellent photocatalytic HER activity can be attributed to the formation of multi-interfaces in Ti 3 C 2 /TiO 2 /UiO-66-NH 2 , including Ti 3 C 2 /TiO 2 /UiO-66-NH 2 , Ti 3 C 2 /TiO 2 and Ti 3 C 2 /UiO-66-NH 2 interfaces, which constructed multiple pathways at the interfaces with Schottky junctions to accelerate the separation and transfer of charge carriers and endowed the accumulation of photo-generated electrons on the surface of Ti 3 C 2. This work expanded the possibility of porous MOFs for the development of efficient photocatalytic water splitting using annealed MXenes. Graphical abstract Image 1 Highlights • Ti 3 C 2 /TiO 2 /UiO-66-NH 2 was obtained by introducing annealed Ti 3 C 2 T x over Zr-MOFs. • Ti 3 C 2 /TiO 2 /UiO-66-NH 2 presented superior photocatlytic H 2 -production activity. • Three types of contact interfaces with Schottky junctions were depicted. • The enhanced charge transfer efficiency was investigated in detail. [ABSTRACT FROM AUTHOR]

[Display omitted] • A charge transfer medium was introduced in situ at the interface. • Rapid extracting of photoinduced electrons. • Efficient charge carrier separation/transfer. Interfacial charge transfer resistance is one of the main limiting factors for realizing high photocatalytic efficiency of heterostructures system. Herein, an activated carbon layer is successfully introduced between the interface of polymer carbon nitride (CN) and TiO 2 heterostructure (CNP-x) as charge transfer medium by in situ pyrolysis carbonization method. Because of the lower spatial resistance of the crystalline/amorphous interface and the fast carrier transportation character of activated carbon, the efficiency of TiO 2 in extracting photoinduced electrons from CN was significantly improved. That is, the separation/transport of photocarriers in CNP-x heterostructure is accelerated, and the recombination time of photogenerated electrons and holes is prolonged. The CNP-1 exhibits a H 2 evolution rate of 1298.5 μmol h−1 with apparent quantum yield (AQY) of 34.5 %, 20.3 % and 12.6 % at 365 nm, 380 nm and 400 nm, respectively. This work offers a novel and unique strategy to promote interface charge separation and transport of CN-based heterostructures by accurately introduction charge transfer medium. [ABSTRACT FROM AUTHOR]

Low photocurrent density of hematite (α-Fe 2 O 3) originating from the inherent defects usually hinders its application in photoelectrochemical (PEC) water oxidation. In this paper, the synergetic effect of increase of oxygen vacancies and in-situ constructing heterojunction by coating MOFs on the α-Fe 2 O 3 nanoarrays gives rise to the boosted photocurrent of α-Fe 2 O 3 from 0.25 mA/cm2 to 2.1 mA/cm2 at 1.23 V (vs. RHE). The results showed that the appropriate energy band structure engineered by the presence of MOFs layer not only facilitated the PEC water oxidation, but also enhanced the light absorption performance. With inducing oxygen vacancies in further, the intrinsic conductivity of photoanode can be well ameliorated. The value of carrier density is improved one order higher to promote charge transfer between the interfaces and raise the carrier separation efficiency as a result. • The constructed MOFs heterojunction by CVD method regulates the band structure. • Induced oxygen vacancy improves the intrinsic conductivity of α-Fe 2 O 3. • The synergistic effect increased photocurrent density by about 10 times. [ABSTRACT FROM AUTHOR]

One of the key strategies to go beyond the limited hydrogen production efficiency during photocatalytic process is to increase effective charge carrier concentration participating hydrogen evolution reaction (HER). Herein, considering organic luminescent materials as "photo-excited electron factory" with large numbers of exited carriers under light irradiation, 2-Fluorene-4,5-diphenylimidazole/CdS (FI/CdS) S-scheme heterojunction was constructed to modulate charge transfer via extracting abundant of photoexcited electrons in FI as luminescent quenching process. The impeded charge recombination in FI/CdS S-scheme heterojunction gave rise to 6 orders of magnitude higher in carriers concentration and 7.8 times higher in H 2 evolution rate for CF20 (9.67 × 1026 cm−3, 5.28 mmol h−1 g−1) than that of pure CdS (2.69 × 1020 cm−3, 0.68 mmol h−1 g−1). It demonstrates that quenching photo-excited electrons in luminescent component through synergistic organic-luminescent/semiconductor interaction could be a creative and prominent strategy to enhance photocatalytic performance. [ABSTRACT FROM AUTHOR]

Despite the potential of hexagonal boron carbon nitride (h-BCN) with a unique graphite-like structure in the field of photocatalysis, the serious photocarrier recombination caused by disordered charge transfer has limited its practical application. In this work, we propose a conceptual design of in-plane heterostructures consisting of graphene sheet and non-phase-separated borocarbonitride (G sheet –BCN) with micro π-conjugated heterointerface for directional utilization of disorder charge. The obtained G 150 –BCN exhibits 10 times longer carrier decay lifetime (16.82 ns) and 3.7 times higher CO yield (51.14 μmol g−1 h−1) than pristine BCN. It was confirmed by systematical characterizations and theoretical calculations that the micro π-conjugated heterointerface enables the directional transport of photo-induced electrons from BCN to graphene domains, resulting in enhanced carrier separation and CO 2 reduction efficiency. This work developed a unique synthetic route to the design and construction of heterojunction with proper interface and rational electronic structure for efficient separation of photoexcited charges. [Display omitted] • A conceptual design of in-plane Graphene sheet –BCN heterostructure was proposed. • The different work functions of two domains generated interfacial charge gradient. • The micro π-conjugated heterointerface enables directional utilization of disorder charge. • The carrier separation and CO 2 reduction efficiency was significantly enhanced. • The mechanism of photocatalytic performance enhancement has been proposed. [ABSTRACT FROM AUTHOR]

Photoelectrodes based on reduced TiO 2 are being extensively studied in the search for photocatalytic materials that can perform solar-driven water splitting and renewable hydrogen production. To date, substantial efforts have been devoted to understanding the microscopic mechanisms that underlie their photoelectrochemical (PEC) behavior, but this is a critical missing input to the Ti 3 d carriers that govern the PEC activity. In this study the single and co-doping (N, H) in anatase TiO 2 are prepared for PEC hydrogen production. The codoped photocathode delivers much better PEC performance from the enhanced solar light response and a fast electron pathway. Soft x-ray spectroscopy including x-ray absorption (XAS) and photoelectron spectroscopy (XPS) has been used to investigate the location and occupation of the defect levels from doping, through which the relevant engineered electronic properties in doped TiO 2 are determined. It is shown that co-doping effectively produce the substitutional nitrogen in comparison with single doping. The Ti3+ defect states promoted by doping introduces localized Ti 3 d -derived states below Fermi level (E F), resulting in a large reduction (approximately 1 eV) in the band gap of co-doped TiO 2. The progressive production of oxygen vacancies eventually causes a surface band upward-bending induced electron transfer mechanism critical for charge separation. The present insights into defect chemistry and its determination to the electronic structure of co-doped TiO 2 provide important guidance for using TiO 2 in electrocatalysis and optoelectronics. We employed a joint x-ray absorption and photoelectron spectroscopic experiments to probe the electronic structure of TiO 2 upon doping. The result supports the importance of defect states in a band gap reduction and promotion of charge transfer for enhanced solar-driven PEC water splitting of co-doped TiO 2. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Co(OH) 2 confined in MIL-100 nanosheets is prepared. • Cobalt acetate colloid is adopted to realize confinement of Co(OH) 2. • Oxygen vacancies are induced by the incorporation of Co(OH) 2. • The nanointerface interaction of Co(OH) 2 /MIL-100 regulates the electronic structure of Fe atoms. • Co(OH) 2 /MIL-100 exhibits superior water splitting activity with the overpotential of 1.62 V. Exploring cost-effective and advanced bifunctional electrocatalysts is crucial for overall water splitting. Confinement engineering integrates electronic structure and interface transfer for synergistic cooperation between active sites and carriers, thus realizing enhanced electrocatalytic performance. Herein, Co(OH) 2 confined MIL-100 nanosheets are grown on nickel foam (Co(OH) 2 /MIL-100) by cobalt acetate colloid. The confinement effect guarantees the highly dispersed Co(OH) 2 in MIL-100. The two-dimensional nanosheet arrays of Co(OH) 2 /MIL-100 provide sufficient active sites and rich channels for facilitated ion/electron transportation. The characterizations and theoretical calculation prove that the strong coupling between Co(OH) 2 and MIL-100 induces oxygen vacancies and highly active Fe3+ species to promote charge transfer and regulate the d-band center. As a result, the intermediate adsorption strength is optimized, which is beneficial to boost the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) process. The Co(OH) 2 /MIL-100 exhibits competitive OER and HER overpotentials of 260 mV and 160 mV at 50 mA cm−2 in alkaline electrolyte, respectively. Furthermore, the two-electrode electrolyzer equipped with Co(OH) 2 /MIL-100(+) || Co(OH) 2 /MIL-100(-) displays a low operation potential of 1.62 V (50 mA cm−2) and maintains high stability for 20 h. Thus, this work offers a novel colloid-assisted confinement strategy to simultaneously tailor the electronic structure and active sites for highly efficient electrocatalysts. [ABSTRACT FROM AUTHOR]

Abstract Owing to insufficient active sites, strongly bound excitons and insufficient optical absorption, polymer semiconductors have only shown mild activity as potential candidates for photocatalysis. A g-C 3 N 4 with improved optical absorption capacity, charge transfer performance and porosity was successfully prepared by a one-step NH 4 Cl-assisted route. Interaction of melamine with NH 4 Cl preparation of Porous g-C 3 N 4 (CN-xy) with active functional groups modified pore wall shown to result in highly crystalline species with a maximum π-π layer stacking distance of heptazine units of 0.321 nm, decreases the optical band gap from 2.80 to 2.13 eV and maximum surface area reached 56.485 m2 g−1. The balanced improvement of the multiple defects of g-C 3 N 4 makes the photocatalytic degradation of RhB and the photocatalytic hydrogen production efficiency 4 and 5 times higher than the pristine g-C 3 N 4 , respectively. Graphical abstract Unlabelled Image Highlights • One-step in suit inducing. • Amino and cyano modified porous g-C 3 N 4. • Trade-off in all aspects. • Forming an electronic transmission path for D-π-A. [ABSTRACT FROM AUTHOR]

A unique heterostructure is developed based on a 3D photoactive semiconductor and a 0D Cu 2 O QDs for superb photocatalytic reduction CO 2 into CO. It reported a novel and simple method to prepare a 3D g-C 3 N 4 foam with micron-sized porous structures using ultrastable foam as a soft template for the first time. Moreover, Cu 2 O QDs are loaded onto 3D g-C 3 N 4 foam through a simple photodeposition strategy. Systematically characterization demonstrated that g-C 3 N 4 foam not only act as an excellent carrier for Cu 2 O QDs, but also greatly improve the photocatalytic performance by enhancing CO 2 adsorption and gas transfer. Simultaneously, the rationally designed g-C 3 N 4 foam/Cu 2 O QDs exhibited notablely enhancement in photocatalytic performance with 3.9 times and 11 times higher than that of g-C 3 N 4 foam and bulk g-C 3 N 4 powder. The excellent photocatalytic activity can be attributed to the unique porous structure and the synergistic effect between g-C 3 N 4 foam and Cu 2 O QDs, which can speed up the transfer of charge carriers and urged the cumulation of photo-generated electrons on the Cu 2 O QDs. Our work provides new ideas for constructing 0D/3D hierarchical photocatalytic systems, which may provide guidance on designing efficient photocatalysts to maximize photocatalyst kinetics. Unlabelled Image • Cu 2 O QDs modified 3D g-C 3 N 4 foam was facilely synthesized. • Photocatalytic reduction CO 2 was enhanced by excellent CO 2 adsorption performance. • Synergistic effect between g-C 3 N 4 foam and Cu 2 O QDs was proposed in this system. [ABSTRACT FROM AUTHOR]