Visible Light-Driven Pure Water Splitting by a Nature-Inspired Organic Semiconductor-Based System

Fabricating intramolecular donor-acceptor system via covalent bonding of carbazole to carbon nitride for excellent photocatalytic performance towards CO2 conversion

Photocatalytic conversion of CO₂ into hydrocarbon fuels is an ideal technology of mitigating greenhouse effect caused by excessive emission of CO₂. However, the high recombination rate of electron-hole pairs and limited charge carriers transport speed constrained the catalytic performance of many semiconductor catalysts. In this contribution, a series of carbon nitride (g-CN) samples with intramolecular donor-acceptor (D-A) system were successfully prepared by introducing organic donor into their structures. Characterization results confirmed that carbazole was successful connected to the structure of g-CN via chemical bond. The formation of intramolecular D-A system greatly enlarged the light response region of g-CN-xDbc. In addition, a new charge transfer transition mode was formed in g-CN-0.01Dbc due to the incorporation carbazole, which enable it to use light with energy lower than the intrinsic absorption of g-CN. Meanwhile, the D-A structure led to the spatial separation of electrons and holes in g-CN-xDbc and significantly decreased the recombination rate of electron-hole pairs. The g-CN-0.01Dbc presented the best catalytic performance and the CO evolution rate was 9.6 times higher than that of g-CN. Moreover, the reaction was performed in water without any additive, which made it green and sustainable. DFT simulation confirmed the D-A structure and charge carrier migration direction in the prepared samples.

Nanoporous and nonporous conjugated donor-acceptor polymer semiconductors for photocatalytic hydrogen production

Conjugated polymers (CPs) as photocatalysts have evoked substantial interest. Their geometries and physical (e.g., chemical and thermal stability and solubility), optical (e.g., light absorption range), and electronic properties (e.g., charge carrier mobility, redox potential, and exciton binding energy) can be easily tuned via structural design. In addition, they are of light weight (i.e., mainly composed of C, N, O, and S). To improve the photocatalytic performance of CPs and better understand the catalytic mechanisms, many strategies with respect to material design have been proposed. These include tuning the bandgap, enlarging the surface area, enabling more efficient separation of electron-hole pairs, and enhancing the charge carrier mobility. In particular, donor-acceptor (D-A) polymers were demonstrated as a promising platform to develop high-performance photocatalysts due to their easily tunable bandgaps, high charge carrier mobility, and efficient intramolecular charge transfer. In this minireview, recent advances of D-A polymers in photocatalytic hydrogen evolution are summarized with a particular focus on modulating the optical and electronic properties of CPs by varying the acceptor units. The challenges and prospects associated with D-A polymer-based photocatalysts are described as well.

How to apply metal halide perovskites to photocatalysis: challenges and development

Semiconductor photocatalysts are widely used in environmental remediation and energy conversion processes that affect social development. These processes involve, for example, hydrogen production from water splitting, carbon dioxide reduction, pollutant degradation, and the conversion of raw organic chemical materials into high-value-added chemicals. Metal halide perovskites (MHPs) have become a new class of promising cheap and easy to manufacture candidate materials for use in photocatalytic semiconductors due to their advantages of high extinction coefficients, optimal band gaps, high photoluminescence quantum yields, and long electron-hole diffusion lengths. However, their unstable ion-bonded crystal structures (very low theoretical decomposition energy barriers) limit their widespread application. In this review, we introduce the physical properties of MHP materials suitable for photocatalysis, and MHP-based photocatalytic particle suspension systems, photoelectrode thin film systems, and photovoltaic-photo(electro)chemical systems. Then, numerous studies realizing efficient and stable photocatalytic water splitting, carbon dioxide reduction, organic conversion, and other reactions involving MHP materials were highlighted. In addition, we conducted rigorous analysis of the potential problems that could hinder progress in this new scientific research field, such as Pb element toxicity and material instability. Finally, we outline the potential opportunities and directions for photocatalysis research based on MHPs.

Construction of a Z-scheme heterojunction for high-efficiency visible-light-driven photocatalytic CO2 reduction

The continuous growth of fossil fuel consumption and large amounts of CO2 emissions have caused global energy crisis and climate change. The employment of semiconductor photocatalysts to convert CO2 into value-added products has attracted extensive attention and research worldwide in recent years. However, it is difficult for a single-component semiconductor photocatalyst to achieve this goal efficiently due to its drawbacks, such as low quantum efficiency, limited surface area, limited number of active sites, the short lifetime of photogenerated carriers, poor long-term stability, and the weak redox ability of carriers. Fortunately, inspired by photosynthesis, the construction of an artificial Z-scheme heterojunction has brought a new dawn for the realization of this goal. The Z-scheme heterojunction has a high separation efficiency of electron-hole pairs with strong redox ability and a wide light response range. The abovementioned advantages make the Z-scheme heterojunction provide a great opportunity for the conversion of CO2 to value-added chemicals. This review concisely reports the progress of the Z-scheme heterojunction in the field of photocatalytic CO2 reduction in recent years, photocatalytic mechanism, choice of oxidation and reduction systems, strategies for improving efficiency, confirmation of the Z-scheme charge transport mechanism, problems and challenges, and the prospects for the future.

Panchromatic Ternary Polymer Dots Involving Sub-Picosecond Energy and Charge Transfer for Efficient and Stable Photocatalytic Hydrogen Evolution

Panchromatic ternary polymer dots (Pdots) consisting of two conjugated polymers (PFBT and PFODTBT) based on fluorene and benzothiadiazole groups, and one small molecular acceptor (ITIC) have been prepared and assessed for photocatalytic hydrogen production with the assistance of a Pt cocatalyst. Femtosecond transient absorption spectroscopic studies of the ternary Pdots have revealed both energy and charge transfer processes that occur on the time scale of sub-picosecond between the different components. They result in photogenerated electrons being located mainly at ITIC, which acts as both electron and energy acceptor. Results from cryo-transmission electron microscopy suggest that ITIC forms crystalline phases in the ternary Pdots, facilitating electron transfer from ITIC to the Pt cocatalyst and promoting the final photocatalytic reaction yield. Enhanced light absorption, efficient charge separation, and the ideal morphology of the ternary Pdots have rendered an external quantum efficiency up to 7% at 600 nm. Moreover, the system has shown a high stability over 120 h without obvious degradation of the photocatalysts.

Efficient Photocatalytic Overall Water Splitting Induced by the Giant Internal Electric Field of a g-C3 N4 /rGO/PDIP Z-Scheme Heterojunction

A graphitic carbon nitride/rGO/perylene diimide polymer (g-C₃ N₄ /rGO/PDIP) Z-scheme heterojunction is successfully constructed to realize high-flux charge transfer and efficient photocatalytic overall water splitting. A giant internal electric field in the Z-scheme junction is built, enabling the charge separation efficiency to be enhanced dramatically by 8.5 times. Thus, g-C₃ N₄ /rGO/PDIP presents an efficient and stable photocatalytic overall water splitting activity with H₂ and O₂ evolution rate of 15.80 and 7.80 µmol h^-1 , respectively, ≈12.1 times higher than g-C₃ N₄ nanosheets. Meanwhile, a notable quantum efficiency of 4.94% at 420 nm and solar-to-hydrogen energy-conversion efficiency of 0.30% are achieved, prominently surpassing many reported g-C₃ N₄ -based photocatalysts. Briefly, this work throws light on enhancing the internal electric field by interface control to dramatically improve the photocatalytic performance.

An efficient broad spectrum-driven carbon and oxygen co-doped g-C3N4 for the photodegradation of endocrine disrupting: Mechanism, degradation pathway, DFT calculation and toluene selective oxidation

In this study, a new type of carbon and oxygen co-doped g-C₃N₄ (PACN) was successfully synthesized by a one-step thermal polymerization method for the photodegradation of Bisphenol A (BPA) and selective oxidation of toluene to benzaldehyde. The degradation rate of BPA was 23.58 times higher than that of pristine g-C₃N₄ and the efficiency benzaldehyde formation rate without the need of any solvent increased to 5.43 times that of g-C₃N₄. At the same time, the band structure calculation of its simulated structure is performed by DFT, which shows that the introduction of oxygen linking band can adjust its band structure and obtain a smaller band gap. In addition, the PACN displays an enhanced photocatalytic degradation of BPA under the long wavelength (λ ≥ 550 nm) and NIR light irradiation (λ ≥ 760 nm), which indicates that the synthesized materials have a broad spectrum of photocatalytic activity. According to the results of secondary ion mass spectrometry (SIMS) and nuclear magnetic resonance spectroscopy (NMR), C atoms and O atoms were introduced into the original g-C₃N₄ skeleton. In addition, the intermediate products were detected by mass spectrometry (HPLC-MS), and the BPA degradation pathway was proposed. A feasible photocatalytic reaction mechanism was also proposed.

An Overview of the Photocatalytic Water Splitting over Suspended Particles

The conversion of solar to chemical energy is one of the central processes considered in the emerging renewable energy economy. Hydrogen production from water splitting over particulate semiconductor catalysts has often been proposed as a simple and a cost-effective method for large-scale production. In this review, we summarize the basic concepts of the overall water splitting (in the absence of sacrificial agents) using particulate photocatalysts, with a focus on their synthetic methods and the role of the so-called “co-catalysts”. Then, a focus is then given on improving light absorption in which the Z-scheme concept and the overall system efficiency are discussed. A section on reactor design and cost of the overall technology is given, where the possibility of the different technologies to be deployed at a commercial scale and the considerable challenges ahead are discussed. To date, the highest reported efficiency of any of these systems is at least one order of magnitude lower than that deserving consideration for practical applications.

Synthesis and enhanced photocatalytic activity of the flower-like CdS/Zn3(PO4)2 Z-scheme heteronanostructures

CdS/Zn3(PO4)2 Z-scheme heteronanostructures were prepared through a simple hydrothermal route and precipitation methods, and the efficiency for the photocatalytic degradation of MB solution can be improved greatly.

Fabrication of 2D/2D COF/SnNb2O6 nanosheets and their enhanced solar hydrogen production

2D TpPa-2-COF tightly decorated on the surface of SnNb₂O₆ nanosheets effectively increases the interface region, promotes separation of carriers and heightens charge utilization rate, thus achieving better solar H₂-production activity than bare SnNb₂O₆ and TpPa-2-COF.

In situ construction of a 2D/2D heterostructured ZnIn2S4/Bi2MoO6Z-scheme system for boosting the photoreduction activity of Cr(vi)

The direct 2D/2D Z-scheme heterostructures of ZnIn₂S₄/Bi₂MoO₆ were rationally constructed, exhibiting obviously enhanced photocatalytic activity for Cr(vi) reduction under visible light (λ ≥ 420 nm) irradiation.

Visible-light-promoted thiocyanation of sp2 C–H bonds over heterogeneous graphitic carbon nitrides

Mesoporous graphitic carbon nitride (mpg-C₃N₄) is developed as a practical heterogeneous photocatalyst for C–S bond formation.

Tunable Properties of Nature-Inspired N,N'-Alkylated Riboflavin Semiconductors

A series of novel soluble nature-inspired flavin derivatives substituted with short butyl and bulky ethyl-adamantyl alkyl groups was prepared via simple and straightforward synthetic approach with moderate to good yields. The comprehensive characterization of the materials, to assess their application potential, has demonstrated that the modification of the conjugated flavin core enables delicate tuning of the absorption and emission properties, optical bandgap, frontier molecular orbital energies, melting points, and thermal stability. Moreover, the thin films prepared thereof exhibit smooth and homogeneous morphology with generally high stability over time.

Integrated Z-Scheme Nanosystem Based on Metal Sulfide Nanorods for Efficient Photocatalytic Pure Water Splitting

Developing efficient metal sulfides for pure water splitting is a challenging topic in the field of photocatalysis. Herein, inspired by natural photosynthesis, an all-solid-state Z-scheme photocatalyst was constructed with Cd_0.9 Zn_0.1 S (CZS) for water reduction, red phosphorus (RP) for water oxidation, and metallic CoP as the electron mediator. RP@CoP core-shell nanostructures were uniformly attached on the CZS nanorods, which gave rise to multiple monodispersed nanojunctions. The integrated Z-scheme nanosystem exhibited an apparent quantum efficiency of 6.4 % at 420 nm for pure water splitting. Theoretical analysis and femtosecond transient absorption results revealed that the impressive performance was mainly due to efficient hole transfer of CZS, resulting from the intimate atomic contacts between CoP mediator and photocatalysts, together with favorable band alignment. Meanwhile, the multiple monodispersed Z-scheme nanojunctions could provide abundant reaction sites, which was also important for the boosted activity.

Nanoplatform-based cascade engineering for cancer therapy

Various therapeutic techniques have been studied for treating cancer precisely and effectively, such as targeted drug delivery, phototherapy, tumor-specific catalytic therapy, and synergistic therapy, which, however, evoke numerous challenges due to the inherent limitations of these therapeutic modalities and intricate biological circumstances as well. With the remarkable advances of nanotechnology, nanoplatform-based cascade engineering, as an efficient and booming strategy, has been tactfully introduced to optimize these cancer therapies. Based on the designed nanoplatforms, pre-supposed cascade processes could be triggered under specific conditions to generate/deliver more therapeutic species or produce stronger tumoricidal effects inside tumors, aiming to achieve cancer therapy with increased anti-tumor efficacy and diminished side effects. In this review, the recent advances in nanoplatform-based cascade engineering for cancer therapy are summarized and discussed, with an emphasis on the design of smart nanoplatforms with unique structures, compositions and properties, and the implementation of specific cascade processes by means of endogenous tumor microenvironment (TME) resources and/or exogenous energy inputs. This fascinating strategy presents unprecedented potential in the enhancement of cancer therapies, and offers better controllability, specificity and effectiveness of therapeutic functions compared to the corresponding single components/functions. In the end, challenges and prospects of such a burgeoning strategy in the field of cancer therapy will be discussed, hopefully to facilitate its further development to meet the personalized treatment demands.

A Metal-Free Oxygenated Covalent Triazine 2-D Photocatalyst Works Effectively from the Ultraviolet to Near-Infrared Spectrum for Water Oxidation Apart from Water Reduction

Solar-driven water splitting is highly desirable for hydrogen fuel production, particularly if water oxidation is effectively sustained in a complete cycle and/or by means of stable and efficient photocatalysts of main group elements, for example, carbon and nitrogen. Despite extensive success on H₂ production on polymer photocatalysts, polymers have met with very limited success for the rate-determining step of the water splitting-water oxidation reaction due to the extremely slow "four-hole" chemistry. Here, the synthesized metal-free oxygenated covalent triazine (OCT) is remarkably active for oxygen production in a wide operation window from UV to visible and even to NIR (up to 800 nm), neatly matching the solar spectrum with an unprecedented external quantum efficiency (even 1% at 600 nm) apart from excellent activity for H₂ production under full arc irradiation, a big step moving toward full solar spectrum water splitting. Experimental results and DFT calculations show that the oxygen incorporation not only narrows the band gap but also causes appropriate band-edge shifts. In the end, a controlled small amount of oxygen in the ionothermal reaction is found to be a promising and facile way of achieving such oxygen incorporation. This discovery is a significant step toward both scientific understanding and practical development of metal-free photocatalysts for cost-effective water oxidation and hydrogen generation over a large spectral window.

Grafting Molecular Cobalt-oxo Cubane Catalyst on Polymeric Carbon Nitride for Efficient Photocatalytic Water Oxidation

In this work, we have successfully constructed a cobalt-oxo (Co^III ₄ O₄ ) cubane complex on polymeric carbon nitride (PCN) through pyridine linkage. The covalently grafted Co^III ₄ O₄ cubane units were uniformly distributed on the PCN surface. The product exhibited greatly enhanced photocatalytic activities for water oxidation under visible-light irradiation. Further characterizations and spectroscopic analyses revealed that the grafted Co^III ₄ O₄ cubane units could effectively capture the photogenerated holes from excited PCN, lower the overpotential of oxygen evolution reaction (OER), and serve as efficient catalysts to promote the multi-electron water oxidation process. This work provides new insight into the future development of efficient photocatalysts by grafting molecular catalysts for artificial photosynthesis.

Recent Progresses on Metal Halide Perovskite-Based Material as Potential Photocatalyst

Recent years have witnessed an incredibly high interest in perovskite-based materials. Among this class, metal halide perovskites (MHPs) have attracted a lot of attention due to their easy preparation and excellent opto-electronic properties, showing a remarkably fast development in a few decades, particularly in solar light-driven applications. The high extinction coefficients, the optimal band gaps, the high photoluminescence quantum yields and the long electron–hole diffusion lengths make MHPs promising candidates in several technologies. Currently, the researchers have been focusing their attention on MHPs-based solar cells, light-emitting diodes, photodetectors, lasers, X-ray detectors and luminescent solar concentrators. In our review, we firstly present a brief introduction on the recent discoveries and on the remarkable properties of metal halide perovskites, followed by a summary of some of their more traditional and representative applications. In particular, the core of this work was to examine the recent progresses of MHPs-based materials in photocatalytic applications. We summarize some recent developments of hybrid organic–inorganic and all-inorganic MHPs, recently used as photocatalysts for hydrogen evolution, carbon dioxide reduction, organic contaminant degradation and organic synthesis. Finally, the main limitations and the future potential of this new generation of materials have been discussed.

Z-Scheme Photocatalytic Systems for Solar Water Splitting

As the world decides on the next giant step for the renewable energy revolution, scientists have begun to reinforce their headlong dives into the exploitation of solar energy. Hitherto, numerous attempts are made to imitate the natural photosynthesis of plants by converting solar energy into chemical fuels which resembles the "Z-scheme" process. A recreation of this system is witnessed in artificial Z-scheme photocatalytic water splitting to generate hydrogen (H2). This work outlines the recent significant implication of the Z-scheme system in photocatalytic water splitting, particularly in the role of electron mediator and the key factors that improve the photocatalytic performance. The Review begins with the fundamental rationales in Z-scheme water splitting, followed by a survey on the development roadmap of three different generations of Z-scheme system: 1) PS-A/D-PS (first generation), 2) PS-C-PS (second generation), and 3) PS-PS (third generation). Focus is also placed on the scaling up of the "leaf-to-tree" challenge of Z-scheme water splitting system, which is also known as Z-scheme photocatalyst sheet. A detailed investigation of the Z-scheme system for achieving H2 evolution from past to present accompanied with in-depth discussion on the key challenges in the area of Z-scheme photocatalytic water splitting are provided.

Heterogeneous photoredox flow chemistry for the scalable organosynthesis of fine chemicals

Large-scale photochemical synthesis of high value chemicals under mild conditions is an ideal method of green chemical production. However, a scalable photocatalytic process has been barely reported due to the costly preparation, low stability of photosensitizers and critical reaction conditions required for classical photocatalysts. Here, we report the merging of flow chemistry with heterogeneous photoredox catalysis for the facile production of high value compounds in a continuous flow reactor with visible light at room temperature in air. In the flow reactor system, polymeric carbon nitrides, which are cheap, sustainable and stable heterogeneous photocatalysts, are immobilized onto glass beads and fibers, demonstrating a highly flexible construction possibility for devices of the photocatalytic materials. As an example of the production of high value chemicals, important chemical structures such as cyclobutanes, which are basic building blocks for many pharmaceutical compounds, like magnosalin, are synthesized in flow with high catalytic efficiency and stability.

In situ preparation of Bi2S3 nanoribbon-anchored BiVO4 nanoscroll heterostructures for the catalysis of Cr(vi) photoreduction

Novel Bi₂S₃ nanoribbon-anchored BiVO₄ nanoscroll heterostructures were fabricated, showing enhanced photocatalytic activity for Cr(vi) reduction under UV-visible light illumination.

Improving the photocatalytic hydrogen production of SrTiO3 by in situ loading ethylene glycol as a co-catalyst

Ethylene glycol, as a cocatalyst, is supported on the surface of SrTiO₃, which greatly promotes the photocatalytic reaction efficiency.

Water Oxidation Catalysts for Artificial Photosynthesis

Water oxidation is the primary reaction of both natural and artificial photosynthesis. Developing active and robust water oxidation catalysts (WOCs) is the key to constructing efficient artificial photosynthesis systems, but it is still facing enormous challenges in both fundamental and applied aspects. Here, the recent developments in molecular catalysts and heterogeneous nanoparticle catalysts are reviewed with special emphasis on biomimetic catalysts and the integration of WOCs into artificial photosystems. The highly efficient artificial photosynthesis depends largely on active WOCs integrated into light harvesting materials via rational interface engineering based on in-depth understanding of charge dynamics and the reaction mechanism.

Recent Progress and Approaches on Carbon-Free Energy from Water Splitting

Sunlight is the most abundant renewable energy resource, providing the earth with enough power that is capable of taking care of all of humanity's desires-a hundred times over. However, as it is at times diffuse and intermittent, it raises issues concerning how best to reap this energy and store it for times when the Sun is not shining. With increasing population in the world and modern economic development, there will be an additional increase in energy demand. Devices that use daylight to separate water into individual chemical elements may well be the answer to this issue, as water splitting produces an ideal fuel. If such devices that generate fuel were to become widely adopted, they must be low in cost, both for supplying and operation. Therefore, it is essential to research for cheap technologies for water ripping. This review summarizes the progress made toward such development, the open challenges existing, and the approaches undertaken to generate carbon-free energy through water splitting.

Photoinduced Carrier Dynamics at the Interface of Black Phosphorus and Bismuth Vanadate

Two-dimensional (2D) heterostructures of black phosphorus (BP)/bismuth vanadate (BVO) have attracted much attention due to their potential uses in photocatalytic water splitting. However, the interfacial photoinduced electron- and hole-transfer dynamics are not explored computationally. Herein, we have used density functional theory (DFT) calculations and DFT-based fewest-switches surface-hopping dynamics simulations to investigate the light-driven electron and hole dynamics taking place at the interface of BP and the BVO(010) surface. Our results show that the BP monolayer is adsorbed on BVO(010) via van der Waals interaction. Upon irradiation, the electron transfer takes place from BP to BVO(010) within 500 fs but with two distinct processes. In the first phase, the electron transfer proceeds adiabatically and is mainly driven by atomic motions. In the second phase, the electron transfer decays very slowly. The hole-transfer dynamics from BVO(010) to BP exhibits a similar ultrafast decay in the first stage followed by a slow decay; however, there is a comparable amount of hole trapped in a BP state due to a large energy gap from its higher state. These insights may be useful for the design of novel photocatalytic water-splitting materials.

Collective excitation of plasmon-coupled Au-nanochain boosts photocatalytic hydrogen evolution of semiconductor

Localized surface plasmon resonance (LSPR) offers a valuable opportunity to improve the efficiency of photocatalysts. However, plasmonic enhancement of photoconversion is still limited, as most of metal-semiconductor building blocks depend on LSPR contribution of isolated metal nanoparticles. In this contribution, the concept of collective excitation of embedded metal nanoparticles is demonstrated as an effective strategy to enhance the utilization of plasmonic energy. The contribution of Au-nanochain to the enhancement of photoconversion is 3.5 times increase in comparison with that of conventional isolated Au nanoparticles. Experimental characterization and theoretical simulation show that strongly coupled plasmonic nanostructure of Au-nanochain give rise to highly intensive electromagnetic field. The enhanced strength of electromagnetic field essentially boosts the formation rate of electron-hole pair in semiconductor, and ultimately improves photocatalytic hydrogen evolution activity of semiconductor photocatalysts. The concept of embedded coupled-metal nanostructure represents a promising strategy for the rational design of high-performance photocatalysts.

Plasmonic effect offers a valuable opportunity to improve the efficiency of semiconductor, photocatalysts. Here, the authors show that the collective excitation of plasmonic metal, nanoparticles is more favorable for enhancing the utilization of plasmonic energy by, semiconductors.

Electron Deficient Monomers that Optimize Nucleation and Enhance the Photocatalytic Redox Activity of Carbon Nitrides

Polymeric carbon nitride (PCN) is usually synthesized from nitrogen-rich monomers such as cyanamide, melamine, and urea, but is rather disordered in many cases. Now, a new allotrope of carbon nitride with internal heterostructures was obtained by co-condensation of very electron poor monomers (for example, 5-amino-tetrazole and nucleobases) in the presence of mild molten salts (for example, NaCl/KCl) to mediate the polymerization kinetics and thus modulate the local structure, charge carrier properties, and most importantly the HOMO and LUMO levels. Results reveal that the as-prepared NaK-PHI-A material shows excellent photo-redox activities because of a nanometric hetero-structure which enhances visible light absorption and promotes charge separation in the different domains.

Synergy of Dopants and Defects in Graphitic Carbon Nitride with Exceptionally Modulated Band Structures for Efficient Photocatalytic Oxygen Evolution

Electronic structure greatly determines the band structures and the charge carrier transport properties of semiconducting photocatalysts and consequently their photocatalytic activities. Here, by simply calcining the mixture of graphitic carbon nitride (g-C₃ N₄ ) and sodium borohydride in an inert atmosphere, boron dopants and nitrogen defects are simultaneously introduced into g-C₃ N₄ . The resultant boron-doped and nitrogen-deficient g-C₃ N₄ exhibits excellent activity for photocatalytic oxygen evolution, with highest oxygen evolution rate reaching 561.2 µmol h^-1 g^-1 , much higher than previously reported g-C₃ N₄ . It is well evidenced that with conduction and valence band positions substantially and continuously tuned by the simultaneous introduction of boron dopants and nitrogen defects into g-C₃ N₄ , the band structures are exceptionally modulated for both effective optical absorption in visible light and much increased driving force for water oxidation. Moreover, the engineered electronic structure creates abundant unsaturated sites and induces strong interlayer C-N interaction, leading to efficient electron excitation and accelerated charge transport. In the present work, a facile approach is successfully demonstrated to engineer the electronic structures and the band structures of g-C₃ N₄ with simultaneous introduction of dopants and defects for high-performance photocatalytic oxygen evolution, which can provide informative principles for the design of efficient photocatalysis systems for solar energy conversion.

A Critical Review on Energy Conversion and Environmental Remediation of Photocatalysts with Remodeling Crystal Lattice, Surface, and Interface

Solar energy is a renewable resource that can supply our energy needs in the long term. A semiconductor photocatalysis that is capable of utilizing solar energy has appealed to considerable interests for recent decades, owing to the ability to aim at environmental problems and produce renewal energy. Much effort has been put into the synthesis of a highly efficient semiconductor photocatalyst to promote its real application potential. Hence, we reviewed the most advanced methods and strategies in terms of (i) broadening the light absorption wavelengths, (ii) design of active reaction sites, and (iii) control of the electron-hole (e^--h⁺) recombination, while these three processes could be influenced by remodeling the crystal lattice, surface, and interface. Additionally, we individually examined their current applications in energy conversion (i.e., hydrogen evolution, CO₂ reduction, nitrogen fixation, and oriented synthesis) and environmental remediation (i.e., air purification and wastewater treatment). Overall, in this review, we particularly focused on advanced photocatalytic activity with simultaneous wastewater decontamination and energy conversion and further enriched the mechanism by proposing the electron flow and substance conversion. Finally, this review offers the prospects of semiconductor photocatalysts in the following three vital (distinct) aspects: (i) the large-scale preparation of highly efficient photocatalysts, (ii) the development of sustainable photocatalysis systems, and (iii) the optimization of the photocatalytic process for practical application.

Dimension-Matched Zinc Phthalocyanine/BiVO4 Ultrathin Nanocomposites for CO2 Reduction as Efficient Wide-Visible-Light-Driven Photocatalysts via a Cascade Charge Transfer

Cascade charge transfer was realized by a H-bond linked zinc phthalocyanine/BiVO₄ nanosheet (ZnPc/BVNS) composite, which subsequently works as an efficient wide-visible-light-driven photocatalyst for converting CO₂ into CO and CH₄ , as shown by product analysis and ¹³ C isotopic measurement. The optimized ZnPc/BVNS nanocomposite exhibits a ca. 16-fold enhancement in the quantum efficiency compared with the reported BiVO₄ nanoparticles at the excitation of 520 nm with an assistance of 660 nm photons. Experimental and theoretical results show the exceptional activities are attributed to the rapid charge separation by a cascade Z-scheme charge transfer mechanism formed by the dimension-matched ultrathin (ca. 8 nm) heterojunction nanostructure. The central Zn²⁺ in ZnPc could accept the excited electrons from the ligand and then provide a catalytic function for CO₂ reduction. This Z-scheme is also feasible for other MPc, such as FePc and CoPc, together with BVNS.

Photocatalytically active ladder polymers

Conjugated ladder polymers (cLaPs) are introduced as organic semiconductors for photocatalytic hydrogen evolution from water under sacrificial conditions. Starting from a linear conjugated polymer (cLiP1), two ladder polymers are synthesized via post-polymerization annulation and oxidation techniques to generate rigidified, planarized materials bearing dibenzo[b,d]thiophene (cLaP1) and dibenzo[b,d]thiophene sulfone subunits (cLaP2). The high photocatalytic activity of cLaP1 (1307 μmol h-1 g-1) in comparison to that of cLaP2 (18 μmol h-1 g-1) under broadband illumination (λ > 295 nm) in the presence of a hole-scavenger is attributed to a higher yield of long-lived charges (μs to ms timescale), as evidenced by transient absorption spectroscopy. Additionally, cLaP1 has a larger overpotential for proton reduction and thus an increased driving force for the evolution of hydrogen under sacrificial conditions.