Engineering interfacial photo-induced charge transfer based on nanobamboo array architecture for efficient solar-to-chemical energy conversion

Accumulation of Long-Lived Photogenerated Holes at Indium Single-Atom Catalysts via Two Coordinate Nitrogen Vacancy Defect Engineering for Enhanced Photocatalytic Oxidation

Visible-light-driven photocatalytic oxidation by photogenerated holes has immense potential for environmental remediation applications. While the electron-mediated photoreduction reactions are often at the spotlight, active holes possess a remarkable oxidation capacity that can degrade recalcitrant organic pollutants, resulting in nontoxic byproducts. However, the random charge transfer and rapid recombination of electron-hole pairs hinder the accumulation of long-lived holes at the reaction center. Herein, a novel method employing defect-engineered indium (In) single-atom photocatalysts with nitrogen vacancy (Nv) defects, dispersed in carbon nitride foam (In-Nv-CNF), is reported to overcome these challenges and make further advances in photocatalysis. This Nv defect-engineered strategy produces a remarkable extension in the lifetime and an increase in the concentration of photogenerated holes in In-Nv-CNF. Consequently, the optimized In-Nv-CNF demonstrates a remarkable 50-fold increase in photo-oxidative degradation rate compared to pristine CN, effectively breaking down two widely used antibiotics (tetracycline and ciprofloxacin) under visible light. The contaminated water treated by In-Nv-CNF is completely nontoxic based on the growth of Escherichia coli. Structural-performance correlations between defect engineering and long-lived hole accumulation in In-Nv-CNF are established and validated through experimental and theoretical agreement. This work has the potential to elevate the efficiency of overall photocatalytic reactions from a hole-centric standpoint.

Oxygen vacancies synergistic cobalt phosphide electron bridge modulated bismuth oxychloride/carbon nitride Z-scheme junction for efficient carbon dioxide reduction coupled with tetracycline oxidation

Although great progress has been made with respect to electron bridges, the electron mobility of the state-of-the-art electron bridges is far from satisfactory because of weak electrical conductivity. To overcome the above issue, cobalt phosphide (CoP), as a model electron bridge, was modified by superficial oxygen vacancies (OVs) and embedded into a defective bismuth oxychloride/carbon nitride (BiO1-xCl/g-C3N4) Z-scheme heterojunction to obtain atomic-level insights into the effect of surface OVs on CoP electron bridges. Compared to BiO1-xCl/g-C3N4 and bismuth oxychloride/cobalt phosphide/carbon nitride (BiOCl/CoP/g-C3N4) composites, the defective bismuth oxychloride/cobalt phosphide/carbon nitride (BiO1-xCl/CoP/g-C3N4) heterojunction exhibited remarkable photocatalytic redox performance, indicating that the surface OVs-assisted CoP electron bridge effectively boosted electrical conductivity and yielded ultrafast electron transfer rates. The theoretical and experimental results demonstrate that the surface OVs play a critical role in improving the electrical conductivity of the CoP electron bridge, thereby accelerating electron mobility. This research provides insights into interfacial OVs-modified transition metal phosphide (TMP) electron bridges and their potential application in heterojunctions for energy crisis mitigation and environmental remediation.

Engineering Semi-Reversed Quantum Well Photocatalysts for Highly-Efficient Solar-to-Fuels Conversion

Semiconductor quantum wells (QWs) exhibit high charge-utilization efficiency for light-emitting applications due to their strong charge confinement effect. Inspired by this effect, herein, this work proposes a new idea to significantly improve the photo-generated charge separation for attaining a highly-efficient solar-to-fuels conversion process through "semi-reversing" the conventional QWs to confine only the photo-generated electrons. This electron confinement-improved charge separation is implemented in the well-designed model of the CdS/TiO2/CdS semi-reversed QW (SRQW) structure. The latter is fabricated by selectively assembling CdS quantum dots (QDs) onto the {101} facets (ultra-thin edge regions) of the TiO2 nanosheets (NSs). Upon light excitation, the photo-generated electrons of SRQW can be confined on the TiO2-{101} facets in the vicinity of the CdS/TiO2 hetero-interface. Thereby, the continuous multi-electron injection to the adsorbed reactants on the interfacial active-sites is significantly accelerated. Thus, the CdS/TiO2/CdS SRQW exhibits ≈35.7 and ≈56.0-fold enhancements on the photocatalytic activities for water and CO2 reduction, respectively, compared to those of pure TiO2. Correspondingly, its CH4-product selectivity is increased by ≈180%. This work provides a novel charge separation mechanism, which is of great importance for the design of the next-generation quantum-sized photocatalysts for solar-to-fuels conversion.

Schottky Junction and D-A1 -A2 System Dual Regulation of Covalent Triazine Frameworks for Highly Efficient CO2 Photoreduction

Covalent triazine frameworks (CTFs) are emerging as a promising molecular platform for photocatalysis. Nevertheless, the construction of highly effective charge transfer pathways in CTFs for oriented delivery of photoexcited electrons to enhance photocatalytic performance remains highly challenging. Herein, a molecular engineering strategy is presented to achieve highly efficient charge separation and transport in both the lateral and vertical directions for solar-to-formate conversion. Specifically, a large π-delocalized and π-stacked Schottky junction (Ru-Th-CTF/RGO) that synergistically knits a rebuilt extended π-delocalized network of the D-A1 -A2 system (multiple donor or acceptor units, Ru-Th-CTF) with reduced graphene oxide (RGO) is developed. It is verified that the single-site Ru units in Ru-Th-CTF/RGO act as effective secondary electron acceptors in the lateral direction for multistage charge separation/transport. Simultaneously, the π-stacked and covalently bonded graphene is regarded as a hole extraction layer, accelerating the separation/transport of the photogenerated charges in the vertical direction over the Ru-Th-CTF/RGO Schottky junction with full use of photogenerated electrons for the reduction reaction. Thus, the obtained photocatalyst has an excellent CO2 -to-formate conversion rate (≈11050 µmol g-1 h-1 ) and selectivity (≈99%), producing a state-of-the-art catalyst for the heterogeneous conversion of CO2 to formate without an extra photosensitizer.

Electrospun Fe doped TiO2 fiber photocatalyst for efficient wastewater treatment

Water pollution caused by industrial wastewater is the most critical environmental problem in the world. Synthetic dyes are commonly used in various industries such as paper, plastic, printing, leather and textile for their ability to impact color. Complex composition, high toxicity and low biodegradability of dyes make them difficult to degrade which causes a substantial negative impact on overall ecosystems. To address this issue we synthesized TiO₂ fibers photocatalyst using the combination of sol-gel and electrospinning techniques to be used in the degradation of dyes which causes water pollution. We doped Fe in TiO₂ fibers to enhance the absorption in the visible region of the solar spectrum which will also help to increase the degradation efficiency. As synthesized pristine TiO₂ fibers and Fe doped TiO₂ fibers were analyzed using different characterization techniques such as X-ray diffraction, Scanning electron microscopy, Transmission electron microscopy, UV-Visible spectroscopy, X-ray photoelectron spectroscopy. 5% Fe doped TiO₂ fibers show excellent photocatalytic degradation activity for rhodamine B (99% degradation in 120 min). It can be utilized for degradation of other dye pollutants such as methylene blue, Congo red and methyl orange. It shows good photocatalytic activity (97%) even after 5 cycles of reuse. The radical trapping experiments reveals that holes, ^•O₂^- and ^•OH has a significant contribution in the photocatalytic degradation. Due to the robust fibrous nature of 5FeTOF the process of collection of photocatalysts was simple and without loss as compared to powder photocatalysts. This justifies our selection of electrospinning method of synthesis of 5FeTOF which is also useful for large scale production.

V-doped Ni2P nanoparticle grafted g-C3N4 nanosheets for enhanced photocatalytic hydrogen evolution performance under visible light

Exploring low-cost and highly active photocatalysts with noble metal-free cocatalysts is of great significance for photocatalytic hydrogen evolution under simulated sunlight irradiation. In this work, a novel V-doped Ni₂P nanoparticle loaded g-C₃N₄ nanosheet is reported as a highly efficient photocatalyst for H₂ evolution under visible light irradiation. The results demonstrate that the optimized 7.8 wt% V-Ni₂P/g-C₃N₄ photocatalyst exhibits a high hydrogen evolution rate of 271.5 μmol g^-1 h^-1, which is comparable to that of the 1 wt% Pt/g-C₃N₄ photocatalyst (279 μmol g^-1 h^-1), and shows favorable hydrogen evolution stability for five successive runs within 20 h. The remarkable photocatalytic hydrogen evolution performance of V-Ni₂P/g-C₃N₄ is mainly due to the enhanced visible light absorption ability, the facilitated separation of photo-generated electron-hole pairs, the prolonged lifetime of photo-generated carriers and the fast transmission ability of electrons.

Vacancy-Mediated Z-Scheme Heterostructure in SnO2-Decorated Spinel In3-xS4 with Boosted Photocatalytic Activity

The widespread application of dyes and heavy metals causes increasing environmental pollution. One effective way to mitigate environmental pollution is to use semiconductor photocatalysts for redox purification of pollutants. Heterostructured photocatalysts can reduce the electron-hole recombination rate and improve light utilization. In this work, a novel SnO₂/In_3-xS₄ composite with oxygen vacancy defect-mediated Z-scheme heterostructure is constructed for the first time by a one-pot method, in which SnO₂ ultrasmall nanocrystals are decorated on nanopetals of flower-like In_3-xS₄. Material analyses show that the as-built three-dimensional hierarchical architecture is able to essentially increase the specific surface area and thus the active sites of the products. More importantly, the formation of Z-scheme heterojunction between the oxygen vacancy-induced SnO₂ defect level and the In_3-xS₄ band structure not only promotes the separation of photogenerated charges but also makes them more reactive. Through the optimization of the composition ratio between the two phases, the visible-light-driven photocatalytic reaction rates of rhodamine B degradation and Cr(VI) reduction for the developed SnO₂/In_3-xS₄ composite photocatalyst are 12.8 and 6.3 times of bare In_3-xS₄ and 32.0 and 76.0 times of bare SnO₂, respectively. This work should provide a promising implication for designing new high-performance composite photocatalysts.

Rational modification of hydroxy-functionalized covalent organic frameworks for enhanced photocatalytic hydrogen peroxide evolution

Covalent organic frameworks (COFs), a class of flexibly tunable crystalline materials, have fascinating potential in photocatalytic hydrogen peroxide (H2O2) evolution under visible light irradiation. However, achieving efficient catalytic activity by tuning the composition of COFs and the linkages of building blocks is still a challenge. Herein, four imine-linked COFs with different numbers of hydroxy-functionalized are constructed to unveil the latent structure-activity relationship between the reversibility of bonding in supramolecular chemistry and the photocatalytic H2O2 performance. As the optimized material, TAPT-HTA-COF (1H-COF) containing single hydroxy group in aldehyde node exhibits a highest ordered structure and conjugation degree along and across the plane in the extended frameworks originating from the flexibly reversible iminol-to-ketoenamine tautomerism than others, which broadens the visible light absorption and accelerates the dissociation of photogenerated carriers in 1H-COF. These merits ensure that 1H-COF has the highest H2O2 yield (44.5 μmol L-1) and O2 two-electron reduction pathway among the four COFs under visible light irradiation (λ > 420 nm, 10 vol% isopropanol aqueous solution). At the same time, the long-range ordered framework of 1H-COF is well preserved during the photocatalytic H2O2 evolution process assisted by the proton-induced tautomerization. This work facilitates the design and development of COF-based photocatalysts in the evolution of H2O2.

Rational fabrication of cadmium-sulfide/graphitic-carbon-nitride/hematite photocatalyst with type II and Z-scheme tandem heterojunctions to promote photocatalytic carbon dioxide reduction

Artificial photosynthesis has become one of the most attractive strategies for lowering atmospheric carbon dioxide (CO₂) level and achieving the carbon balance; whereas, the fast electron-hole recombination and sluggish charge transfer in photocatalysts are themain stumbling blocks to the applications. Constructing semiconductor nano-heterostructures provides a promising strategy to accelerate the separation and transfer of photoinduced charge carriers for promoting the multielectron CO₂ reduction reaction. Herein, a CdS/g-C₃N₄/α-Fe₂O₃ three-component photocatalyst consisting of type II and Z-scheme tandem heterojunctions is skillfully fabricated via the solvothermal synthesis followed with photoinduced deposition. The CdS/g-C₃N₄/α-Fe₂O₃ tandem-heterojunction photocatalyst exhibits superior performance toward the conversion of CO₂ to fuels (CO and CH₄), compared with the single- and binary-component systems, owing to the favorable energy-level alignment, accelerated charge separation, facilitated water dissociation and sufficient reactive-hydrogen provision. The total consumed electron number of CdS/g-C₃N₄/α-Fe₂O₃ catalyst for CO₂ reduction is about 10.5 times that of pure g-C₃N₄. The photocatalytic mechanism is elucidated according to detailed characterizations and in-situ spectroscopy analyses. This work sheds light on the rational construction of heterojunction photocatalysts to promote the conversion of CO₂ to solar fuels, without using any sacrifice reagent or noble-metal cocatalysts.

Sulfur Vacancies Enriched 2D ZnIn2S4 Nanosheets for Improving Photoelectrochemical Performance

Vacancies engineering based on semiconductors is an effective method to enhance photoelectrochemical activity. Herein, we used a facile one-step solvothermal method to prepare sulfur vacancies modified ultrathin two-dimensional (2D) ZnIn2S4 nanosheets. The photon-to-current efficiency of sulfur vacancies modified ultrathin 2D ZnIn2S4 nanosheets is 1.82-fold than ZnIn2S4 nanosheets without sulfur vacancies and 2.04-fold than multilayer ZnIn2S4. The better performances can be attributed to the introduced sulfur vacancies in ZnIn2S4, which influence the electronic structure of ZnIn2S4 to absorb more visible light and act as the electrons trapping sites to suppress the recombination of photo-generated carriers. These results provide a new route to designing efficient photocatalyst by introducing sulfur vacancies.

2D/2D Bi2WO6/Protonated g-C3N4 step-scheme heterojunctions for enhancing the photodegradation of 17β-estradiol: promotional role of electrostatic interaction

A Bi2WO6/protonated g-C3N4 step-scheme heterojunction with an intimate interface though electrostatic interaction exhibited enhanced photodegradation of 17β-estradiol under visible light.

Effect of Morphology and Plasmonic on Au/ZnO Films for Efficient Photoelectrochemical Water Splitting

To improve photoelectrochemical (PEC) water splitting, various ZnO nanostructures (nanorods (NRs), nanodiscs (NDs), NRs/NDs, and ZnO NRs decorated with gold nanoparticles) have been manufactured. The pure ZnO nanostructures have been synthesized using the successive ionic-layer adsorption and reaction (SILAR) combined with the chemical bath deposition (CBD) process at various deposition times. The structural, chemical composition, nanomorphological, and optical characteristics have been examined by various techniques. The SEM analysis shows that by varying the deposition time of CBD from 2 to 12 h, the morphology of ZnO nanostructures changed from NRs to NDs. All samples exhibit hexagonal phase wurtzite ZnO with polycrystalline nature and preferred orientation alongside (002). The crystallite size along (002) decreased from approximately 79 to 77 nm as deposition time increased from 2 to 12 h. The bandgap of ZnO NRs was tuned from 3.19 to 2.07 eV after optimizing the DC sputtering time of gold to 4 min. Via regulated time-dependent ZnO growth and Au sputtering time, the PEC performance of the nanostructures was optimized. Among the studied ZnO nanostructures, the highest photocurrent density (Jph) was obtained for the 2 h ZnO NRs. As compared with ZnO NRs, the Jph (7.7 mA/cm2) of 4 min Au/ZnO NRs is around 50 times greater. The maximum values of both IPCE and ABPE are 14.2% and 2.05% at 490 nm, which is closed to surface plasmon absorption for Au NPs. There are several essential approaches to improve PEC efficiency by including Au NPs into ZnO NRs, including increasing visible light absorption and minority carrier absorption, boosting photochemical stability, and accelerating electron transport from ZnO NRs to electrolyte carriers.

A NiS co-catalyst decorated Zn3In2S6/g-C3N4 type-II ball-flower-like nanosphere heterojunction for efficient photocatalytic hydrogen production

Promoting the separation of photogenerated electron-hole pairs and enhancing the charge carrier transfer are critical in photocatalysis. In our work, a ball-flower-like NiS/Zn₃In₂S₆/g-C₃N₄ photocatalyst fabricated by a hydrothermal method exhibited superior performance for photocatalytic water splitting. The optimized 2.0% NiS/Zn₃In₂S₆/g-C₃N₄ rivaled noble metal based Pt/g-C₃N₄ and showed an apparent quantum efficiency (AQE) of 24.3% at 420 nm, with a H₂ yield of 4.135 mmol g^-1 h^-1, which was 30.4 and 9.51 times that of pure g-C₃N₄ and binary Zn₃In₂S₆/g-C₃N₄ composites, respectively. The experimental and characterization results suggested that the heterojunction formed between Zn₃In₂S₆/g-C₃N₄ and the decorating NiS co-catalyst cooperatively suppressed the electron-hole recombination and facilitated the charge carrier transfer, thus resulting in significant improvement of the H₂ evolution performance. Moreover, the increased specific surface area and the enhanced visible-light absorption also contributed to superior water splitting performance. The prepared ternary catalytic system with the heterojunction and non-noble metal co-catalyst has great potential as an alternative to noble metals for achieving cost-efficient water splitting systems.

Synthesis of Ni modified Au@CdS core-shell nanostructures for enhancing photocatalytic coproduction of hydrogen and benzaldehyde under visible light

The development of visible light responsive photocatalysts for simultaneous production of hydrogen (H₂) fuel and value-added chemicals is greatly promising to solve the energy and environmental issues by improving the utilization efficiency of solar energy. Herein, the three-component Ni/(Au@CdS) core-shell nanostructures were constructed by the hydrothermal synthesis followed with photodeposition. The intimate integration of plasmonic Au nanospheres and visible-light responsive CdS shells modified with Ni cocatalyst facilitated the generation and separation of electron-hole pairs as well as reduced the overpotential of hydrogen evolution. The Ni/(Au@CdS) photocatalyst exhibited excellent performance toward the selective transformation of benzyl alcohol under anaerobic conditions, and the yields of H₂ and benzaldehyde reached up to 3882 and 4242 μmol·g^-1·h^-1, respectively. The apparent quantum efficiency (AQE) was determined to be 4.09% under the irradiation of 420 nm. The systematic studies have verified the synergy of plasmonic effect and metal cocatalyst on enhancing the photocatalysis. This work highlights the desirable design and potential application of plasmonic photocatalysts for solar-driven coproduction of H₂ fuel and high-value chemicals.

Carbon Nitride-Based Ruthenium Single Atom Photocatalyst for CO2 Reduction to Methanol

With increasing concerns for global warming, the solar-driven photocatalytic reduction of CO₂ into chemical fuels like methanol is a propitious route to enrich energy supplies, with concomitant reduction of the abundant CO₂  stockpiles. Herein, a novel single atom-confinement and a strategy are reported toward single ruthenium atoms dispersion over porous carbon nitride surface. Ruthenium single atom character is well confirmed by EXAFS absorption spectrometric analysis unveiling the cationic coordination environment for the single-atomic-site ruthenium center, that is formed by Ru-N/C intercalation in the first coordination shell, attaining synergism in N-Ru-N connection and interfacial carrier transfer. From time resolved fluorescence decay spectra, the average carrier lifetime of the RuSA-mC₃ N₄ system is found to be higher compared to m-C₃ N₄ ; the fact uncovering the crucial role of single Ru atoms in promoting photocatalytic reaction system. A high yield of methanol (1500 µmol g^-1 cat. after 6 h of the reaction) using water as an electron donor and the reusability of the developed catalyst without any significant change in the efficiency represent the superior aspects for its potential application in real industrial technologies.

Synthesis of EDTA-bridged CdS/g-C3N4 heterostructure photocatalyst with enhanced performance for photoredox reactions

Photocatalytic reactions represent a kind of green and sustainable chemical processes for organic transformations, but the efficiency is limited by the severe recombination and/or inadequate redox potentials of photoinduced charge carriers in photocatalysts. To address these issues, herein, the CdS-EDTA/g-C₃N₄ heterostructures were designed according to Z-scheme photocatalytic mechanism and synthesized by the hydrothermal growth of CdS on g-C₃N₄ nanoflakes with assistance of EDTA chelating agent. EDTA played multiple roles in the formation of CdS-EDTA/g-C₃N₄ heterostructure photocatalysts, such as controlling the morphology of CdS nanostructures, linking CdS and g-C₃N₄ together, and boosting the charge transfer between two semiconductors. The optimized CdS-EDTA/g-C₃N₄(10%) photocatalyst exhibited much higher activities toward the selective reduction of nitrophenol and the selective oxidation of benzyl alcohol, than those of CdS/g-C₃N₄ heterostructures without EDTA. The enhanced photocatalysis of CdS-EDTA/g-C₃N₄ can be ascribed to the efficient separation and suitable photoredox potentials of photoexcited charge carriers in the EDTA-bridged Z-scheme system. This work provides the inspiration for exploring inexpensive organic electron mediators for constructing all-solid-state Z-scheme photocatalysts and demonstrates the enhanced performance of Z-scheme photocatalysts for photoredox reactions of organic transformations.

Ru and RuOx decorated carbon nitride for efficient ammonia photosynthesis

Photocatalytic ammonia synthesis is a promising strategy for sustainable development compared to the energy-intensive industrial Haber-Bosch approach. Herein, a ternary heterostructure that consists of ruthenium species and carbon nitride (C₃N₄) was rationally explored for ammonia photosynthesis. Compared to the small ammonia yield from the g-C₃N₄ and Ru/g-C₃N₄ system, the Ru/RuO₂/g-C₃N₄ system represents 6 times higher activity with excellent stability under full-spectrum irradiation. Such an enhancement is not only due to efficient transfer of electrons and holes to Ru and RuO₂, respectively, facilitating both the reduction and oxidation reaction, but also taking advantage of Ru for N[triple bond, length as m-dash]N activation.

Design and synthesis of robust Z-scheme ZnS-SnS2 n-n heterojunctions for highly efficient degradation of pharmaceutical pollutants: Performance, valence/conduction band offset photocatalytic mechanisms and toxicity evaluation

Petal-like ZnS-SnS₂ heterojunctions with Z-scheme band alignment were prepared by one-pot solvothermal strategy. The optimal (1:1) ZnS-SnS₂ can degrade 93.46 % of tetracycline and remove 73.9 % COD of pharmaceutical wastewater under visible-light irradiation due to the efficient production of H, O₂^-, h⁺ and OH. The toxicity evaluation by ECOSAR prediction and the growth of E. coli indicates efficient toxicity reduction of tetracycline by photocatalysis and the non-toxicity of ZnS-SnS₂. The attacked sites on tetracycline by reactive species were analyzed according to Fukui index, and two degradation pathways of tetracycline were inferred via the identification of intermediate products. Tetracycline degradation efficiency and the energy consumption in different water bodies were compared, and it was found that the electrical energy per order (EE/O) was the lowest in Ganjiang River. The valence band offset (ΔE_VBO) and conduction band offset (ΔE_CBO) of ZnS-SnS₂ were 1.02 eV and 0.22 eV, respectively. The probable photocatalytic mechanism of ZnS/SnS₂ heterojunctions with Z-scheme band alignment based on ΔE_VBO and ΔE_CBO was first presented.

Enhanced photoelectrochemical activity of α-Fe2O3/TiO2 nanoheterojunction by controlling hydrodynamic conditions

Interfacial heterostructuring has appeared to be an efficient strategy to address the efficiency and applicability of the photocatalysts in solar energy conversion. Herein, we developed one-dimensional (1D) α-Fe₂O₃/TiO₂ nanoheterojunction arrays for enhanced photoelectrochemical (PEC) activity. α-Fe₂O₃ nanotubes were firstly prepared via anodization under controlled hydrodynamic conditions to increase the efficiency. 1D α-Fe₂O₃/TiO₂ nanoheterojunction arrays were then prepared through a hydrothermal treatment and a subsequent annealing process. A controlled anodization by modulating the hydrodynamic conditions, added a fine coating of TiO₂ overlayer, to finally give an optimized composition and geometry for improved light absorption and spatial charge separation efficiency. Consequently, the optimized α-Fe₂O₃ generated a photocurrent of 0.07 mA cm^-2 (3.5 times higher than that of pristine α-Fe₂O₃), and the as-obtained α-Fe₂O₃/TiO₂ nanoheterojunction exhibited a photocurrent intensity of 0.12 mA cm^-2 (about 6 times higher than that of pristine α-Fe₂O₃). A long-term stability can also be ensured. The well-controlled architectures provides a guideline for synthesis of advanced nanomaterials.

Band structure engineering of polymeric carbon nitride with oxygen/carbon codoping for efficient charge separation and photocatalytic performance

The high charge recombination efficiency and weak visible-light absorption of polymeric carbon nitride (CN) severely suppress its photocatalytic performance. To overcome these defects, oxygen/carbon codoped CN (OCN) was prepared firstly using acrylamide as the additive. OCN exhibits much enhanced visible light absorption, charge separation and transfer, and thus photoactivity in hydrogen production and environmental remediation. OCN exhibits a ~6-fold higher photocatalytic hydrogen production rate (~2626 μmol h^-1 g^-1) than CN, comparable to most of nonmetal-doped CN, and an apparent quantum yield of ~16.3% (420 nm). OCN is also much better at producing singlet oxygen than CN. The significantly enhanced charge separation for OCN arises from the O/C codoping structure which forms an impurity level above the valence band edge in the bandgap, i.e., works as a hole-capture center. This work affords a simple and effective strategy to synthesize modified CN for photoactivity enhancement, clarifies the doping mechanism, and may guide research on other nonmetal doped organic semiconductor photocatalysts.

Light-Induced Formation of MoOxSy Clusters on CdS Nanorods as Cocatalyst for Enhanced Hydrogen Evolution

Metal and metal-oxide particles are commonly photodeposited on photocatalysts by reduction and oxidation reactions, respectively, consuming charges that are generated under illumination. This study reveals that amorphous MoO_xS_y clusters can be easily photodeposited at the tips of CdS nanorods (NRs) by in situ photodeposition for the first time. The as-prepared MoO_xS_y-decorated CdS samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma (ICP) to determine the composition and the possible formation pathways of the amorphous MoO_xS_y clusters. The MoO_xS_y-tipped CdS samples exhibited better hydrogen evolution performance than pure CdS under visible-light illumination. The enhanced activity is attributed to the formation of intimate interfacial contact between CdS and the amorphous MoO_xS_y clusters, which facilitates the charge separation and transfer. Through time-resolved photoluminescence (TRPL) measurements, it was clearly observed that all MoO_xS_y-decorated CdS samples with different loadings of MoO_xS_y showed a faster PL decay when compared to pure CdS, resulting from the effective trapping of photogenerated electrons by the MoO_xS_y clusters. Kelvin probe force microscopy (KPFM) was further used to study the surface potentials of pure CdS NRs and MoO_xS_y-decorated CdS NRs. A higher surface potential on MoO_xS_y-decorated CdS NRs was observed in the dark, indicating that the loading of MoO_xS_y resulted in a lower surface work function compared to pure CdS NRs. This contributed to the effective electron trapping and separation, which was also reflected by the increased photoelectrochemical response. Thus, this study demonstrates the design and facile synthesis of MoO_xS_y-tipped CdS NRs photocatalysts for efficient solar hydrogen production.

Crystal-Amorphous Core-Shell Structure Synergistically Enabling TiO2 Nanoparticles' Remarkable SERS Sensitivity for Cancer Cell Imaging

Exploring novel surface-enhanced Raman scattering (SERS) active materials with high detection sensitivity, excellent biocompatibility, low biotoxicity, and good spectral stability is urgently required for efficacious cancer cell diagnosis. Herein, black TiO₂ nanoparticles (B-TiO₂ NPs) with crystal-amorphous core-shell structure are successfully developed. Remarkable SERS activity is derived from the synergistic effect of the promising crystal-amorphous core-shell structure. Abundant excitons can be generated by high-efficiency exciton transitions in the crystal core, a feature that provides sufficient charge source. Significantly, the novel crystal-amorphous heterojunction enables the efficient exciton separation at the crystal-amorphous interface, which can effectively facilitate charge transfer from the crystal core to the amorphous shell and results in exciton enrichment at the amorphous shell. Kelvin probe force microscopy (KPFM) confirms the Fermi level of the amorphous layer shifting to a relatively low position compared to that of the crystal core, allowing efficient photoinduced charge transfer (PICT) between the amorphous shell and probe molecules. The first-principles density functional theory (DFT) calculations further indicate that the amorphous shell structure possesses a narrow band gap and a relatively high electronic density of state (DOS), which can effectively promote vibration coupling with target molecules. Moreover, MCF-7 drug-resistant (MCF-7/ADR) breast cancer cells can be quickly and accurately diagnosed based on the high-sensitivity B-TiO₂-based SERS bioprobe. To the best of our knowledge, this is the first time the crystal-amorphous core-shell heterojunction enhancement of the TiO₂-molecule PICT process, which widens the application of semiconductor-based SERS platforms in precision diagnosis and treatment of cancer, has been investigated.

Charge separation and molecule activation promoted by Pd/MIL-125-NH2hybrid structures for selective oxidation reactions

The Pd/MIL-125-NH₂hybrid photocatalyst exhibits great advantages in charge separation and molecule activation, with sufficient generation of both superoxide radical and singlet oxygen toward selective oxidation of organic molecules.

Nanostructured hexagonal ReO3 with oxygen vacancies for efficient electrocatalytic hydrogen generation

We report oxygen vacancies (OVs) rich hexagonal ReO₃ nanostructured electrocatalysts for efficient hydrogen generation. Through a simple argon plasma exposure, OVs are introduced into the ReO₃ nanoparticles (NP) and nanosheets to enhance electrocatalytic activities with decreasing overpotentails from 157 mV and 178 mV to 138 mV and 145 mV at the current density of 10 mA cm^-2, respectively. As-processed OVs rich ReO₃ NP exhibit a good stability during electrochemical measurements for 20 h in acidic electrolyte. The huge active surface area, abundant OVs and excellent conductivity contribute to the performance according to the experimental data. Further theoretical calculations show that the abundant OVs adsorb H with lower Gibbs free energy facilitating hydrogen evolution.

Two-dimensional bimetallic phosphide ultrathin nanosheets as non-noble electrocatalysts for a highly efficient oxygen evolution reaction

Highly efficient non-noble metal oxygen evolution reaction (OER) catalysts are urgently needed for the practical application of electrochemical energy technology. Herein, we report two-dimensional (2D) bimetallic phosphide (Co1-xFexP) ultrathin nanosheets as new OER catalysts. The two-dimensional (2D) morphology of the nanosheets and the synergistic effect between different transition-metal elements made contributions to the OER catalysis. By optimizing the doping ratio of the Fe atoms, the Co0.8Fe0.2P nanosheets showed the best OER performance with a small overpotential of 270 mV versus a rotating hydrogen electrode at a current density of 10 mA cm-2 and low Tafel slope of 50 mV dec-1 in an alkaline electrolyte. Moderate iron doping improved the degree of oxidation at the surface of CoP nanosheets and preserved the conductive and chemically stabilizing host, thereby enhancing the OER activity. Our findings could aid the rational design of novel non-layered 2D nanomaterial OER catalysts.

Efficient photoredox conversion of alcohol to aldehyde and H2 by heterointerface engineering of bimetal-semiconductor hybrids

Controllable and precise design of bimetal- or multimetal-semiconductor nanostructures with efficient light absorption, charge separation and utilization is strongly desired for photoredox catalysis applications in solar energy conversion. Taking advantage of Au nanorods, Pt nanoparticles, and CdS as the plasmonic metal, nonplasmonic co-catalyst and semiconductor respectively, we report a steerable approach to engineer the heterointerface of bimetal-semiconductor hybrids. We show that the ingredient composition and spatial distribution between the bimetal and semiconductor significantly influence the redox catalytic activity. CdS deposited anisotropic Pt-tipped Au nanorods, which feature improved light absorption, structure-enhanced electric field distribution and spatially regulated multichannel charge transfer, show distinctly higher photoactivity than blank CdS and other metal-CdS hybrids for simultaneous H2 and value-added aldehyde production from one redox cycle.

Softening gold for elastronics

Gold, one of the noble metals, has played a significant role in human society throughout history. Gold's excellent electrical, optical and chemical properties make the element indispensable in maintaining a prosperous modern electronics industry. In the emerging field of stretchable electronics (elastronics), the main challenge is how to utilize these excellent material properties under various mechanical deformations. This review covers the recent progress in developing "softening" gold chemistry for various applications in elastronics. We systematically present material synthesis and design principles, applications, and challenges and opportunities ahead.

Facile synthesis of bimodal macroporous g-C3N4/SnO2 nanohybrids with enhanced photocatalytic activity

It is of vital importance to construct highly interconnected, macroporous photocatalyst to improve its efficiency and applicability in solar energy conversion and environment remediation. Graphitic-like C₃N₄ (g-C₃N₄), as an analogy to two-dimensional (2D) graphene, is highly identified as a visible-light-responsive polymeric semiconductor. Moreover, the feasibility of g-C₃N₄ in making porous structures has been well established. However, the preparation of macroporous g-C₃N₄ with abundant porous networks and exposure surface, still constitutes a difficulty. To solve it, we report a first facile preparation of bimodal macroporous g-C₃N₄ hybrids with abundant in-plane holes, which is simply enabled by in-situ modification through thermally treating the mixture of thiourea and SnCl₄ (pore modifier) after rotary evaporation. For one hand, the formed in-plane macropores endow the g-C₃N₄ system with plentiful active sites and short, cross-plane diffusion channels that can greatly speed up mass transport and transfer. For another, the heterojunctions founded between g-C₃N₄ and SnO₂ consolidate the electron transfer reaction to greatly reduce the recombination probability. As a consequence, the resulted macroporous g-C₃N₄/SnO₂ nanohybrid had a high specific surface area (SSA) of 44.3 m²/g that was quite comparable to most nano/mesoporous g-C₃N₄ reported. The interconnected porous network also rendered a highly intensified light absorption by strengthening the light penetration. Together with the improved mass transport and electron transfer, the macroporous g-C₃N₄/SnO₂ hybrid exhibited about 2.4-fold increment in the photoactivity compared with pure g-C₃N₄. Additionally, the recyclability of such hybrid could be guaranteed after eight successive uses.

Cross-linked bond accelerated interfacial charge transfer in monolayer zinc indium sulfide (ZnIn2S4)/reduced graphene oxide (RGO) heterostructure for photocatalytic hydrogen production with mechanistic insight

By separating the photo-excited charge carriers, the cross-linked bonds enabled the monolayer ZnIn₂S₄/RGO heterostructure to produce more H₂.

Ultrathin BiOCl Single-Crystalline Nanosheets with Large Reactive Facets Area and High Electron Mobility Efficiency: A Superior Candidate for High-Performance Dye Self-Photosensitization Photocatalytic Fuel Cell

Strong dye adsorption and fast electron transfer are of crucial importance to achieve high conversion efficiency of dye self-photosensitization photocatalytic fuel cells (DSPFCs). In this study, we have experimentally achieved the enhanced cell performance in ultrathin BiOCl{010} (BOC(010)-U) nanosheets and provide an idea to investigate the relationship between the physical structure and the chemical performance of semiconductor materials. Experimental phenomenon showed that the exposed areas of highly active {010} facets were remarkably enhanced with the decrease of the BiOCl thickness. The large area of {010} facets with abundant active sites and open channel characteristic were exposed to facilitate photosensitization process, and the atomically thin structure was designed to speed up electron transfer. By employing 40 mL of 5 mg/L rhodamine B as fuel, it was found that the BOC(010)-U photoanode exhibited superior photovoltaic performance and photocatalytic degradation activity than other materials in the DSPFC system, whose J_sc and V_oc were measured to be 0.00865 mA/cm² and 0.731 V, respectively. Besides, about 72% color removal efficiency and 10.77% Coulombic efficiency were obtained under visible light irradiation for 240 min. The experimental results and multiple characterizations demonstrated that the strong dye adsorption ability and efficient charge migration were responsible for the sustaining generation of photocurrent and enhancement of pollutants degradation activity.

Ordered-Disordered BaZrO3-δ Hollow Nanosphere/Carbon Dot Hybrid Nanocomposite: A New Visible-Light-Driven Efficient Composite Photocatalyst for Hydrogen Production and Dye Degradation

Perovskites form an interesting class of photocatalytic compounds because of their chemical stability and exotic chemistry. Although barium zirconates have been known for a long time, their photocatalytic study in the literature is very limited. Herein, we have studied the effect of structural disorder, oxygen vacancies and carbon dots (CDs) on photocatalytic activity of BaZrO_3-δ (BZO) hollow nanospheres. High alkaline conditions during hydrothermal synthesis lead to the formation of disordered states as well as oxygen vacancies in BZO and create midgap states within the band gap of BZO. The midgap states further shift its absorption onset toward visible light and their presence and effects have been proved by ultraviolet-visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and electron spin resonance analysis. A composite that consists of CDs shows upconversion photoluminescence and charge-carrier transfer properties to enhance the light absorption of a photocatalyst and its activity. The photocatalytic efficiency of the compounds were examined by H₂ evolution and the degradation of methylene blue (MB) dye. In this study, loading of 3 wt% CDs on BZO shows the highest hydrogen evolution efficiency (670 μmol/h/g) with an apparent quantum yield of ∼4% and the highest MB dye degradation efficiency (∼90%) among all synthesized composites. The synergistic effect of increased visible light absorption along with enhanced photogenerated charge-carrier transfer efficiency in the presence of CDs and oxygen vacancies in BZO contributes to the enhanced photocatalytic efficacy of hybrid nanomaterials under visible light irradiation.

MoS2 Quantum Dots@TiO2 Nanotube Arrays: An Extended-Spectrum-Driven Photocatalyst for Solar Hydrogen Evolution

TiO₂ nanotube arrays (TiO₂ NTAs) decorated with molybdenum disulfide quantum dots (MoS₂ QDs) were synthesized by a facile electrodeposition method and used as a composite photocatalyst. MoS₂ QDs/TiO₂ NTAs showed enhanced photocatalytic activity compared with pristine TiO₂ NTAs for solar light-promoted H₂ evolution without adding any sacrificial agents or cocatalysts. The photocatalytic activity was influenced by the amount of MoS₂ QDs coated on TiO₂ NTAs. The optimal composition showed excellent photocatalytic activity, achieving H₂ evolution rates of 31.36, 5.29, and 1.67 μmol cm^-2  h^-1 corresponding to ultraviolet (UV, λ<420 nm), visible (Vis, λ≥420 nm), and near-infrared (NIR, λ>760) illumination, respectively. The improved photocatalytic activity was attributed to the decreased bandgap and the surface plasmonic properties of MoS₂ QDs/TiO₂ NTAs, which promoted electron-hole pair separation and the absorption capacity for Vis and NIR light. This study presents a facile approach for fabricating MoS₂ QDs/TiO₂ NTA heterostructures for efficient photocatalytic H₂ evolution, which will facilitate the development of designing new photocatalysts for environment and energy applications.

Faster Electron Injection and More Active Sites for Efficient Photocatalytic H2 Evolution in g-C3 N4 /MoS2 Hybrid

Herein, the structural effect of MoS₂ as a cocatalyst of photocatalytic H₂ generation activity of g-C₃ N₄ under visible light irradiation is studied. By using single-particle photoluminescence (PL) and femtosecond time-resolved transient absorption spectroscopies, charge transfer kinetics between g-C₃ N₄ and two kinds of nanostructured MoS₂ (nanodot and monolayer) are systematically investigated. Single-particle PL results show the emission of g-C₃ N₄ is quenched by MoS₂ nanodots more effectively than MoS₂ monolayers. Electron injection rate and efficiency of g-C₃ N₄ /MoS₂ -nanodot hybrid are calculated to be 5.96 × 10⁹ s^-1 and 73.3%, respectively, from transient absorption spectral measurement, which are 4.8 times faster and 2.0 times higher than those of g-C₃ N₄ /MoS₂ -monolayer hybrid. Stronger intimate junction between MoS₂ nanodots and g-C₃ N₄ is suggested to be responsible for faster and more efficient electron injection. In addition, more unsaturated terminal sulfur atoms can serve as the active site in MoS₂ nanodot compared with MoS₂ monolayer. Therefore, g-C₃ N₄ /MoS₂ nanodot exhibits a 7.9 times higher photocatalytic activity for H₂ evolution (660 µmol g-¹ h^-1 ) than g-C₃ N₄ /MoS₂ monolayer (83.8 µmol g^-1 h^-1 ). This work provides deep insight into charge transfer between g-C₃ N₄ and nanostructured MoS₂ cocatalysts, which can open a new avenue for more rationally designing MoS₂ -based catalysts for H₂ evolution.

IR-Driven Ultrafast Transfer of Plasmonic Hot Electrons in Nonmetallic Branched Heterostructures for Enhanced H2 Generation

The ultrafast transfer of plasmon-induced hot electrons is considered an effective kinetics process to enhance the photoconversion efficiencies of semiconductors through strong localized surface plasmon resonance (LSPR) of plasmonic nanostructures. Although this classical sensitization approach is widely used in noble-metal-semiconductor systems, it remains unclear in nonmetallic plasmonic heterostructures. Here, by combining ultrafast transient absorption spectroscopy with theoretical simulations, IR-driven transfer of plasmon-induced hot electron in a nonmetallic branched heterostructure is demonstrated, which is fabricated through solvothermal growth of plasmonic W₁₈ O₄₉ nanowires (as branches) onto TiO₂ electrospun nanofibers (as backbones). The ultrafast transfer of hot electron from the W₁₈ O₄₉ branches to the TiO₂ backbones occurs within a timeframe on the order of 200 fs with very large rate constants ranging from 3.8 × 10¹² to 5.5 × 10¹² s^-1 . Upon LSPR excitation by low-energy IR photons, the W₁₈ O₄₉ /TiO₂ branched heterostructure exhibits obviously enhanced catalytic H₂ generation from ammonia borane compared with that of W₁₈ O₄₉ nanowires. Further investigations by finely controlling experimental conditions unambiguously confirm that this plasmon-enhanced catalytic activity arises from the transfer of hot electron rather than from the photothermal effect.

Near-infrared-driven Cr(vi) reduction in aqueous solution based on a MoS2/Sb2S3 photocatalyst

A novel MoS₂/Sb₂S₃ composite with enhanced near-infrared photocatalytic efficiency was fabricated.