Biomimetic Donor–Acceptor Motifs in Conjugated Polymers for Promoting Exciton Splitting and Charge Separation

Triazine and Fused Thiophene-Based Donor-Acceptor Type Semiconducting Conjugated Polymer for Enhanced Visible-Light-Induced H2 Production

Conjugated polymers have attracted significant attention in the field of photocatalysis due to their exceptional properties, including versatile optimization, cost-effectiveness, and structure stability. Herein, two conjugated porous polymers, PhIN-CPP and ThIN-CPP, based on triazines, were meticulously designed and successfully synthesized using benzene and thiophene as building blocks. Based on UV diffuse reflection spectra, the photonic band gaps of PhIN-CPP and ThIN-CPP were calculated as 2.05 eV and 1.79 eV. The PhIN-CPP exhibited a high hydrogen evolution rate (HER) of 5359.92 μmol·g-1·h-1, which is 10 times higher than that of Thin-CPP (538.49 μmol·g-1·h-1). The remarkable disparity in the photocatalytic performance can be primarily ascribed to alterations in the band structure of the polymers, which includes its more stable benzene units, fluffier structure, larger specific surface area, most pronounced absorption occurring in the visible region and highly extended conjugation with a high density of electrons. The ΔEST values for PhIN-CPP and ThIN-CPP were calculated as 0.79 eV and 0.80 eV, respectively, based on DFT and TD-DFT calculations, which revealed that the incorporation of triazine units in the as-prepared CMPs could enhance the charge transfer via S1 ↔ T1 and was beneficial to the photocatalytic decomposition of H2O. This study presents a novel concept for developing a hybrid system for preparation of H2 by photocatalysis with effectiveness, sustainability, and economy.

Exploiting Photoinduced Atom Transfer Radical Polymerizations with Boron-Dopant and Nitrogen-Defect Synergy in Carbon Nitride Nanosheets

Graphitic carbon nitrides (g-C3N4) possess various benefits as heterogeneous photocatalysts, including tunable bandgaps, scalability, and chemical robustness. However, their efficacy and ongoing advancement are hindered by challenges like limited charge-carrier separation rates, insufficient driving force for photocatalysis, small specific surface area, and inadequate absorption of visible light. In this study, boron dopants and nitrogen defects synergy are introduced into bulk g-C3N4 through the calcination of a blend of nitrogen-defective g-C3N4 and NaBH4 under inert conditions, resulting in the formation of BCN nanosheets characterized by abundant porosity and increased specific surface area. These BCN nanosheets promote intermolecular single electron transfer to the radical initiator, maintaining radical intermediates at a low concentration for better control of photoinduced atom transfer radical polymerization (photo-ATRP). Consequently, this method yields polymers with low dispersity and tailorable molecular weights under mild blue light illumination, outperforming previous reports on bulk g-C3N4. The heterogeneity of BCN enables easy separation and efficient reuse in subsequent polymerization processes. This study effectively showcases a simple method to alter the electronic and band structures of g-C3N4 with simultaneously introducing dopants and defects, leading to high-performance photo-ATRP and providing valuable insights for designing efficient photocatalytic systems for solar energy harvesting.

Constructing an Asymmetric Covalent Triazine Framework to Boost the Efficiency and Selectivity of Visible-Light-Driven CO2 Photoreduction

The photocatalytic reduction of CO2 represents an environmentally friendly and sustainable approach for generating valuable chemicals. In this study, a thiophene-modified highly conjugated asymmetric covalent triazine framework (As-CTF-S) is developed for this purpose. Significantly, single-component intramolecular energy transfer can enhance the photogenerated charge separation, leading to the efficient conversion of CO2 to CO during photocatalysis. As a result, without the need for additional photosensitizers or organic sacrificial agents, As-CTF-S demonstrates the highest photocatalytic ability of 353.2 µmol g-1 and achieves a selectivity of ≈99.95% within a 4 h period under visible light irradiation. This study provides molecular insights into the rational control of charge transfer pathways for high-efficiency CO2 photoreduction using single-component organic semiconductor catalysts.

In situ synthesis of graphitic carbon nitride nanosheet/Ti3C2Tx MXene/TiO2 Z-scheme heterojunctions boosting charge transfer for full-spectrum driven photocatalytic sterilization

The development of a full-spectrum responsive photocatalytic germicide with excellent charge separation efficiency to harvest high antimicrobial efficacy is a key goal yet a challenging conundrum. Herein, graphitic carbon nitride nanosheet (PCNS)/Ti3C2Tx MXene/TiO2 (PMT) Z-scheme heterojunctions with robust interface contact were crafted by in situ interfacial engineering. The strong internal electrical field (IEF) from PCNS to TiO2, evinced by the Kelvin Probe Force Microscopy (KPFM) characterization, can obtain high charge separation efficiency with 73.99%, compared to Schottky junction PCNS/Ti3C2Tx (PM, 32.88%) and PCNS (17.70%). The Ti3C2Tx component can not only serve as a transfer pathway to accelerate the recombination of photoexcited electrons of TiO2 and holes of PCNS under the Ultraviolet-visible (UV-vis) light irradiation, but also replenish the photogenic electron concentrations to semiconductors in the near-infrared (NIR) light illumination. Meanwhile, the increased temperature due to the localized surface plasmon resonance (LSPR) can further boost the electronic activity to the generation of reactive oxygen species (ROS). Taken together, the PMT performs a high disinfection efficiency up to 99.40% under full solar spectrum illumination, 3.88 and 9.75 times higher than PCNS and TiO2, respectively, surpassing many reported Z-scheme heterojunctions. This work offers guidance for the design of Z-scheme heterojunction with the implanting of plasmons to secure excellent full-spectrum responsive photocatalytic sterilization performance.

Functionalized Linear Conjugated Polymer/TiO2 Heterojunctions for Significantly Enhancing Photocatalytic H2 Evolution

Conjugated polymers (CPs) have attracted much attention in recent years due to their structural abundance and tunable energy bands. Compared with CP-based materials, the inorganic semiconductor TiO2 has the advantages of low cost, non-toxicity and high photocatalytic hydrogen production (PHP) performance. However, studies on polymeric-inorganic heterojunctions, composed of D-A type CPs and TiO2, for boosting the PHP efficiency are still rare. Herein, an elucidation that the photocatalytic hydrogen evolution activity can actually be improved by forming polymeric-inorganic heterojunctions TFl@TiO2, TS@TiO2 and TSO2@TiO2, facilely synthesized through efficient in situ direct C-H arylation polymerization, is given. The compatible energy levels between virgin TiO2 and polymeric semiconductors enable the resulting functionalized CP@TiO2 heterojunctions to exhibit a considerable photocatalytic hydrogen evolution rate (HER). Especially, the HER of TSO2@TiO2 heterojunction reaches up to 11,220 μmol g-1 h-1, approximately 5.47 and 1260 times higher than that of pristine TSO2 and TiO2 photocatalysts. The intrinsic merits of a donor-acceptor conjugated polymer and the interfacial interaction between CP and TiO2 account for the excellent PHP activity, facilitating the separation of photo-generated excitons. Considering the outstanding PHP behavior, our work discloses that the coupling of inorganic semiconductors and suitable D-A conjugated CPs would play significant roles in the photocatalysis community.

Interfacial Self-assembly of Chiral Selenide Nanomembrane for Enantiospecific Recognition

Here, we report the synthesis of chiral selenium nanoparticles (NPs) using cysteine and the interfacial assembly strategy to generate a self-assembled nanomembrane on a large-scale with controllable morphology and handedness. The selenide (Se) NPs exhibited circular dichroism (CD) bands in the ultraviolet and visible region with a maximum intensity of 39.96 mdeg at 388 nm and optical anisotropy factors (g-factors) of up to 0.0013 while a self-assembled monolayer nanomembrane exhibited symmetrical CD approaching 72.8 mdeg at 391 nm and g-factors up to 0.0034. Analysis showed that a photocurrent of 20.97±1.55 nA was generated by the D-nanomembrane when irradiated under light while the L-nanomembrane generated a photocurrent of 20.58±1.36 nA. Owing to the asymmetric intensity of the photocurrent with respect to the handedness of the nanomembrane, an ultrasensitive recognition of enantioselective kynurenine (Kyn) was achieved by the ten-layer (10L) D-nanomembrane exhibiting a photocurrent for L-kynurenine (L-Kyn) that was 8.64-fold lower than that of D-Kyn, with a limit of detection (LOD) of 0.0074 nM for the L-Kyn, which was attributed to stronger affinity between L-Kyn and D-Se NPs. Noticeably, the chiral Se nanomembrane precisely distinguished L-Kyn in serum and cerebrospinal fluid samples from Alzheimer's disease patients and healthy subjects.

General Approach to Construct C-C Single Bond-Linked Covalent Organic Frameworks

C-C single bond-linked covalent organic frameworks (CSBL-COFs) are extremely needed because of their excellent stabilities and potential applications in harsh conditions. However, strategies to generate CSBL-COFs are limited to the acetylenic self-homocoupling Glaser-Hay reaction or post-synthetic reduction of vinylene-based COFs. Exploring new strategies to expand the realm of CSBL-COFs is urgently needed but extremely challenging. To address the synthetic challenges, we for the first time developed a general approach via the reaction between aromatic aldehydes and active methyl group-involving monomers with enhanced acidity, which realized the successful construction of a series of CSBL-COFs. As expected, the obtained CSBL-COFs exhibited outstanding chemical stability, which can stabilize in 6 M NaOH, 3 M HCl, boiling water, and 100 mg/mL NaBH4 for at least 3 days. It is important to mention that CSBL-COFs possess a large amount of ionic sites distributed throughout the networks; gentle shaking allowed our COFs to easily self-disperse as nanoparticles and suspend in water for at least 12 h without reprecipitating. As far as we know, such self-dispersed COFs with high water dispersity are rare to date, and few examples are mainly limited to the guanidinium- and pseudorotaxane-based COFs. Our work thus developed a family of self-dispersed COFs for potential applications in different sorts of fields. Our contribution would thus pave a new avenue for constructing a broader class of CSBL-COFs for their wide applications in various fields.

Strategies for Improving the Photocatalytic Hydrogen Evolution Reaction of Carbon Nitride-Based Catalysts

Due to the depletion of fossil fuels and their-related environmental issues, sustainable, clean, and renewable energy is urgently needed to replace fossil fuel as the primary energy resource. Hydrogen is considered as one of the cleanest energies. Among the approaches to hydrogen production, photocatalysis is the most sustainable and renewable solar energy technique. Considering the low cost of fabrication, earth abundance, appropriate bandgap, and high performance, carbon nitride has attracted extensive attention as the catalyst for photocatalytic hydrogen production in the last two decades. In this review, the carbon nitride-based photocatalytic hydrogen production system, including the catalytic mechanism and the strategies for improving the photocatalytic performance is discussed. According to the photocatalytic processes, the strengthened mechanism of carbon nitride-based catalysts is particularly described in terms of boosting the excitation of electrons and holes, suppressing carriers recombination, and enhancing the utilization efficiency of photon-excited electron-hole. Finally, the current trends related to the screening design of superior photocatalytic hydrogen production systems are outlined, and the development direction of carbon nitride for hydrogen production is clarified.

Simultaneously Achieving Fast Intramolecular Charge Transfer and Mass Transport in Holey D-π-A Organic Conjugated Polymers for Highly Efficient Photocatalytic Pollutant Degradation

Simultaneously realizing efficient intramolecular charge transfer and mass transport in metal-free polymer photocatalysts is critical but challenging for environmental remediation. Herein, we develop a simple strategy to construct holey polymeric carbon nitride (PCN)-based donor-π-acceptor organic conjugated polymers via copolymerizing urea with 5-bromo-2-thiophenecarboxaldehyde (PCN-5B2T D-π-A OCPs). The resultant PCN-5B2T D-π-A OCPs extended the π-conjugate structure and introduced abundant micro-, meso-, and macro-pores, which greatly promoted intramolecular charge transfer, light absorption, and mass transport and thus significantly enhanced the photocatalytic performance in pollutant degradation. The apparent rate constant of the optimized PCN-5B2T D-π-A OCP for 2-mercaptobenzothiazole (2-MBT) removal is ∼10 times higher than that of the pure PCN. Density functional theory calculations reveal that the photogenerated electrons in PCN-5B2T D-π-A OCPs are much easier to transfer from the donor tertiary amine group to the benzene π-bridge and then to the acceptor imine group, while 2-MBT is more easily adsorbed on π-bridge and reacts with the photogenerated holes. A Fukui function calculation on the intermediates of 2-MBT predicted the real-time changing of actual reaction sites during the entire degradation process. Additionally, computational fluid dynamics further verified the rapid mass transport in holey PCN-5B2T D-π-A OCPs. These results demonstrate a novel concept toward highly efficient photocatalysis for environmental remediation by improving both intramolecular charge transfer and mass transport.

Water-soluble conjugated polymers for bioelectronic systems

Bioelectronics is an interdisciplinary field of research that aims to establish a synergy between electronics and biology. Contributing to a deeper understanding of bioelectronic processes and the built bioelectronic systems, a variety of new phenomena, mechanisms and concepts have been derived in the field of biology, medicine, energy, artificial intelligence science, etc. Organic semiconductors can promote the applications of bioelectronics in improving original performance and creating new features for organisms due to their excellent photoelectric and electrical properties. Recently, water-soluble conjugated polymers (WSCPs) have been employed as a class of ideal interface materials to regulate bioelectronic processes between biological systems and electronic systems, relying on their satisfying ionic conductivity, water-solubility, good biocompatibility and the additional mechanical and electrical properties. In this review, we summarize the prominent contributions of WSCPs in the aspect of the regulation of bioelectronic processes and highlight the latest advances in WSCPs for bioelectronic applications, involving biosynthetic systems, photosynthetic systems, biophotovoltaic systems, and bioelectronic devices. The challenges and outlooks of WSCPs in designing high-performance bioelectronic systems are also discussed.

Poly(ionic liquid)s for Photo-Driven CO2 Cycloaddition: Electron Donor-Acceptor Segments Matter

CO₂ cycloaddition with epoxides is a key catalytic procedure for CO₂ utilization. Several metal-based catalysts with cocatalysts are developed for photo-driven CO₂ cycloaddition, while facing difficulties in product purification and continuous reaction. Here, poly(ionic liquid)s are proposed as metal-free catalysts for photo-driven CO₂ cycloaddition without cocatalysts. A series of poly(ionic liquid)s with donor-acceptor segments are fabricated and their photo-driven catalytic performance (conversion rate of 83.5% for glycidyl phenyl ether) outstrips (≈4.9 times) their thermal-driven catalytic performance (17.2%) at the same temperature. Mechanism studies confirm that photo-induced charge separation is promoted by the donor-acceptor segments and can accelerate the CO₂ cycloaddition reaction. This work paves the way for the further use of poly(ionic liquid)s as catalysts in photo-driven CO₂ cycloaddition.

In Situ Modification of Multi-Walled Carbon Nanotubes with Polythiophene-Based Conjugated Polymer for Information Storage

One-dimensional multi-walled carbon nanotubes (MWNTs) have unique electrical properties, but they are not solution-processable, which severely limits their applications in microelectronic devices. Therefore, it is of great significance to improve the solubility of MWNTs and endow them with new functions by chemical modification. In this work, MWNTs were in situ functionalized with poly[(1,4-diethynyl-benzene)-alt-(3-hexylthiophene)] (PDHT) via Sonogashira-Hagihara polymerization. The obtained material PDHT-g-MWNTs was soluble in conventional organic solvents. By sandwiching a PDHT-g-MWNTs film between Al and ITO electrodes, the fabricated Al/PDHT-g-MWNTs/ITO electronic device exhibited nonvolatile rewritable memory behavior, with highly symmetrical turn-on/off voltages, a retention time of over 10⁴ s, and durability for 200 switching cycles. These findings provide important insights into the development of carbon nanotube-based materials for information storage.

Modification of Polymeric Carbon Nitride with Au-CeO2 Hybrids to Improve Photocatalytic Activity for Hydrogen Evolution

The construction of a multi-component heterostructure for promoting the exciton splitting and charge separation of conjugated polymer semiconductors has attracted increasing attention in view of improving their photocatalytic activity. Here, we integrated Au nanoparticles (NPs) decorated CeO2 (Au-CeO2) with polymeric carbon nitride (PCN) via a modified thermal polymerization method. The combination of the interfacial interaction between PCN and CeO2 via N-O or C-O bonds, with the interior electronic transmission channel built by the decoration of Au NPs at the interface between CeO2 and PCN, endows CeAu-CN with excellent efficiency in the transfer and separation of photo-induced carriers, leading to the enhancement of photochemical activity. The amount-optimized CeAu-CN nanocomposites are capable of producing ca. 80 μmol· H2 per hour under visible light irradiation, which is higher than that of pristine CN, Ce-CN and physical mixed CeAu and PCN systems. In addition, the photocatalytic activity of CeAu-CN remains unchanged for four runs in 4 h. The present work not only provides a sample and feasible strategy to synthesize highly efficient organic polymer composites containing metal-assisted heterojunction photocatalysts, but also opens up a new avenue for the rational design and synthesis of potentially efficient PCN-based materials for efficient hydrogen evolution.

Copper-Bridged Tetrakis(4-ethynylphenyl)ethene Aggregates with Photo-Regulated 1 O2 and O2 .- Generation for Selective Photocatalytic Aerobic Oxidation

Active species regulation is a key scientific issue that essentially determines the selectivity and activity of a photocatalyst. Herein, Cu^I -bridged tetrakis(4-ethynylphenyl)ethene aggregates (T₄ EPE-Cu) with photo-regulated ¹ O₂ and O₂ ^.- generation were demonstrated for selective photocatalytic aerobic oxidation. In this system, transient photovoltage combined with the density functional theory calculations confirmed that Cu-alkynyl was the main oxygen activation site. The adsorbed O₂ tends to produce O₂ ^.- because of the potential well effect of Cu-alkynyl under high-energy light excitation. But under low-energy light, O₂ tends to produce ¹ O₂ via resonance energy transfer with Cu-alkynyl. For α-terpinene oxidation, the ratios of ¹ O₂ products to O₂ ^.- products can be controlled from 1.3 (380 nm) to 10.7 (600 nm). Furthermore, T₄ EPE-Cu exhibited ultrahigh photocatalytic performance for Glaser coupling and benzylamine oxidation, with a conversion and selectivity of over 99 %.

Carbon Nitride Photocatalysts with Integrated Oxidation and Reduction Atomic Active Centers for Improved CO2 Conversion

Single-atom active-site catalysts have attracted significant attention in the field of photocatalytic CO₂ conversion. However, designing active sites for CO₂ reduction and H₂ O oxidation simultaneously on a photocatalyst and combining the corresponding half-reaction in a photocatalytic system is still difficult. Here, we synthesized a bimetallic single-atom active-site photocatalyst with two compatible active centers of Mn and Co on carbon nitride (Mn₁ Co₁ /CN). Our experimental results and density functional theory calculations showed that the active center of Mn promotes H₂ O oxidation by accumulating photogenerated holes. In addition, the active center of Co promotes CO₂ activation by increasing the bond length and bond angle of CO₂ molecules. Benefiting from the synergistic effect of the atomic active centers, the synthesized Mn₁ Co₁ /CN exhibited a CO production rate of 47 μmol g^-1  h^-1 , which is significantly higher than that of the corresponding single-metal active-site photocatalyst.

Promoted Electron Transfer and Surface Absorption by Single Nickel Atoms for Photocatalytic Cross-Coupling of Aromatic Alcohols and Aliphatic Amines under Visible Light

The preparation of imines has drawn increasing attention as they are fundamental intermediates in the production of pharmaceuticals, agricultures, and fine chemicals. Nevertheless, current approaches for imines synthesis mainly focus on thermally driven reactions which always involve the consumption of high price noble metal catalysts, expensive ligands, strong base, and harsh reaction conditions. Herein, we demonstrate single atom nickel anchored on polymeric carbon nitride (Ni-SA@PCN) in Ni-N₄ structure for visible light-promoted crossed coupling between aromatic alcohols and aliphatic amines. As expected, the Ni atoms dispersed carbon nitride demonstrates an obviously improved charge separation and transfer as reflected in UV-vis, fluorescence intensity and lifetime, photocurrent density, and electrochemical impedance characterizations. More impressively, the density functional theory (DFT) calculations also reveals that the presence of Ni atoms can dramatically accelerate the absorption of reactive substrates on the surface of PCN. The decreased absorption energy from -0.51 to -3.35 eV, associated with increased O═O bond length from 1.226 to 1.371 Å indicates a huge advantage of single Ni atom on oxygen activation. As a result, the obtained Ni-SA@PCN photocatalyst shows a prominent catalytic efficiency in imines formation with a reaction conversion of 73% and selectivity of >99%. Lastly, the photocatalytic reactions displays an excellent compatibility with various imines being achieved with high yield.

Unveiling the charge transfer dynamics steered by built-in electric fields in BiOBr photocatalysts

Construction of internal electric fields (IEFs) is crucial to realize efficient charge separation for charge-induced redox reactions, such as water splitting and CO₂ reduction. However, a quantitative understanding of the charge transfer dynamics modulated by IEFs remains elusive. Here, electron microscopy study unveils that the non-equilibrium photo-excited electrons are collectively steered by two contiguous IEFs within binary (001)/(200) facet junctions of BiOBr platelets, and they exhibit characteristic Gaussian distribution profiles on reduction facets by using metal co-catalysts as probes. An analytical model justifies the Gaussian curve and allows us to measure the diffusion length and drift distance of electrons. The charge separation efficiency, as well as photocatalytic performances, are maximized when the platelet size is about twice the drift distance, either by tailoring particle dimensions or tuning IEF-dependent drift distances. The work offers great flexibility for precisely constructing high-performance particulate photocatalysts by understanding charge transfer dynamics.

Molecular Design of Covalent Triazine Frameworks with Anisotropic Charge Migration for Photocatalytic Hydrogen Production

Covalent triazine frameworks (CTFs) represent promising polymeric photocatalysts for photocatalytic hydrogen production with visible light. However, the separation and transfer of charges in CTFs are isotropic because of the uniform distribution of donor-acceptor motifs in the skeleton. Herein, to achieve the anisotropic charge carrier separation and migration, thiophene (Th) or benzothiadiazole (BT) unit is selected as the dopant to modify the molecular structure of CTF-based photocatalysts. Both theoretical and experimental studies reveal that the incorporation of Th or BT units induces the anisotropic charge carrier separation and migration at the interface of CTFs. The optimized polymer manifests a much enhanced photocatalytic activity for photocatalytic hydrogen production with visible light, and thus this study provides a useful tool to design conjugated polymer photocatalysts at the molecular level for solar energy conversion.

Advances in preparation, mechanism and applications of graphene quantum dots/semiconductor composite photocatalysts: A review

Due to the low efficiency of single-component nano materials, there are more and more studies on high-efficiency composites. As zero dimensional (0D) non-metallic semiconductor material, the emergence of graphene quantum dots (GQDs) overcomes the shortcomings of traditional photocatalysts (rapid rate of electron-hole recombination and narrow range of optical response). Their uniqueness is that they can combine the advantages of quantum dots (rich functional groups at edge) and sp² carbon materials (large specific surface area). The inherent inert carbon stabilizes chemical and physical properties, and brings new breakthroughs to the development of benchmark photocatalysts. The photocatalytic efficiency of GQDs composite with semiconductor materials (SCs) can be improved by the following three points: (1) accelerating charge transfer, (2) extending light absorption range, (3) increasing active sites. The methods of preparation (bottom-up and top-down), types of heterojunctions, mechanisms of photocatalysis, and applications of GQDs/SCs (wastewater treatment, energy storage, gas sensing, UV detection, antibiosis and biomedicine) are comprehensively discussed. And it is hoped that this review can provide some guidance for the future research on of GQDs/SCs on photocatalysis.

Semiconducting Polymers for Oxygen Evolution Reaction under Light Illumination

Sunlight-driven water splitting to produce hydrogen fuel has stimulated intensive scientific interest, as this technology has the potential to revolutionize fossil fuel-based energy systems in modern society. The oxygen evolution reaction (OER) determines the performance of overall water splitting owing to its sluggish kinetics with multielectron transfer processing. Polymeric photocatalysts have recently been developed for the OER, and substantial progress has been realized in this emerging research field. In this Review, the focus is on the photocatalytic technologies and materials of polymeric photocatalysts for the OER. Two practical systems, namely, particle suspension systems and film-based photoelectrochemical systems, form two main sections. The concept is reviewed in terms of thermodynamics and kinetics, and polymeric photocatalysts are discussed based on three key characteristics, namely, light absorption, charge separation and transfer, and surface oxidation reactions. A satisfactory OER performance by polymeric photocatalysts will eventually offer a platform to achieve overall water splitting and other advanced applications in a cost-effective, sustainable, and renewable manner using solar energy.

Construction of metal (Mn, Ce, Eu)-containing species in CN nanocomposites with photo-responsive oxidase-mimicking activity for multi-antioxidant discrimination

On the basis of three M-CN nanocomposites with photo-oxidase activity, a colorimetric sensor is proposed for the pattern recognition of antioxidants.

Charge-transfer regulated visible light driven photocatalytic H2 production and CO2 reduction in tetrathiafulvalene based coordination polymer gel

The much-needed renewable alternatives to fossil fuel can be achieved efficiently and sustainably by converting solar energy to fuels via hydrogen generation from water or CO₂ reduction. Herein, a soft processable metal-organic hybrid material is developed and studied for photocatalytic activity towards H₂ production and CO₂ reduction to CO and CH₄ under visible light as well as direct sunlight irradiation. A tetrapodal low molecular weight gelator (LMWG) is synthesized by integrating tetrathiafulvalene (TTF) and terpyridine (TPY) derivatives through amide linkages and results in TPY-TTF LMWG. The TPY-TTF LMWG acts as a linker, and self-assembly of this gelator molecules with Zn^II ions results in a coordination polymer gel (CPG); Zn-TPY-TTF. The Zn-TPY-TTF CPG shows high photocatalytic activity towards H₂ production (530 μmol g^-1h^-1) and CO₂ reduction to CO (438 μmol g^-1h^-1, selectivity > 99%) regulated by charge-transfer interactions. Furthermore, in situ stabilization of Pt nanoparticles on CPG (Pt@Zn-TPY-TTF) enhances H₂ evolution (14727 μmol g^-1h^-1). Importantly, Pt@Zn-TPY-TTF CPG produces CH₄ (292 μmol g^-1h^-1, selectivity > 97%) as CO₂ reduction product instead of CO. The real-time CO₂ reduction reaction is monitored by in situ DRIFT study, and the plausible mechanism is derived computationally.

Ag and MOFs-derived hollow Co3O4 decorated in the 3D g-C3N4 for creating dual transferring channels of electrons and holes to boost CO2 photoreduction performance

The rapid recombination of photoinduced charge carriers and low selectivity are still challenges for the CO₂ photoreduction. Herein, we proposed that ZIF-67-derived Co₃O₄ hollow polyhedrons (CoHP) were embedded into NaCl-template-assisted synthesized 3D graphitic carbon nitride (NCN), subsequently, loading Ag by photo-deposition as efficient composites (CoHP@NCN@Ag) for CO₂ photoreduction. This integration simultaneously constructs two heterojunctions: p-n junction between Co₃O₄ and g-C₃N₄ and metal-semiconductor junction between Ag and g-C₃N₄, in which Co₃O₄ and Ag serve as hole (h⁺) trapping sites and electron (e^-) sinks, respectively, achieving spatial separation of charge carriers. The donor-acceptor structure design of NCN realize a good photogenerated e^--h⁺ separation efficiency. The mesoporous structure of hollow Co₃O₄ facilitate gas-diffusion efficiency, light scattering and harvesting. And the introduction of plasmonic Ag further strengthens the light-harvesting and charge migration. Benefiting from the rational design, the optimized ternary heterostructures exhibit a high CO₂-CO yield (562 μmol g^-1), which is about 4-fold as high as that of the NCN (151 μmol g^-1). Moreover, the conjectural mechanism was systematically summarized. We hope this study provides a promising strategy for designing efficient g-C₃N₄ systems for the CO₂ photoreduction.

Photocatalytic Air Purification Using Functional Polymeric Carbon Nitrides

The techniques for the production of the environment have received attention because of the increasing air pollution, which results in a negative impact on the living environment of mankind. Over the decades, burgeoning interest in polymeric carbon nitride (PCN) based photocatalysts for heterogeneous catalysis of air pollutants has been witnessed, which is improved by harvesting visible light, layered/defective structures, functional groups, suitable/adjustable band positions, and existing Lewis basic sites. PCN-based photocatalytic air purification can reduce the negative impacts of the emission of air pollutants and convert the undesirable and harmful materials into value-added or nontoxic, or low-toxic chemicals. However, based on previous reports, the systematic summary and analysis of PCN-based photocatalysts in the catalytic elimination of air pollutants have not been reported. The research progress of functional PCN-based composite materials as photocatalysts for the removal of air pollutants is reviewed here. The working mechanisms of each enhancement modification are elucidated and discussed on structures (nanostructure, molecular structue, and composite) regarding their effects on light-absorption/utilization, reactant adsorption, intermediate/product desorption, charge kinetics, and reactive oxygen species production. Perspectives related to further challenges and directions as well as design strategies of PCN-based photocatalysts in the heterogeneous catalysis of air pollutants are also provided.

Synergy of Iron Doping and Cyano Groups for Enhanced Photocatalytic Hydrogen Production over C3 N4

Improving the insufficient carrier separation dynamics is still of significance in carbon nitride (C₃ N₄ ) research. Extensive research has been devoted to improving the carrier separation efficiency through a single strategy, while ignoring the synergistic enhancement effect produced by coupling two or more conventional strategies. Herein, we reported the fabrication of cyano group-containing Fe-doped C₃ N₄ porous materials via direct co-calcination of iron acetylacetonate and melamine for synergistically improving the photocatalytic performance. Iron acetylacetonate can promote the generation of cyano groups and form Fe-doping in C₃ N₄ , thereby increasing the visible-light absorption and reactive sites. Further, the internal donor-acceptor system formed by cyano groups and Fe-doped sites promoted charge carrier separation and inhibited the radiation recombination of e^- -h⁺ pairs. The optimized photocatalytic activity of Fe-CN-2 sample was 4.5 times of bulk C₃ N₄ (BCN).

Donor-Acceptor Conjugated Heptazine Polymers with Highly Efficient Photocatalytic Degradations towards Tetracyclines

Photocatalysis is an efficient and green technology in the environmental protection. Due to the high charge separation and transfer, donor-acceptor (D-A) conjugated polymers attract much attention for their photocatalytic degradations towards organic pollutants. Herein, the authors reported three novel D-A conjugated polymers, named as HPBP, HPTP, and HPF, with heptazine moieties as electron acceptors, while biphenyl, terphenyl, or fluorene moieties as electron donors, respectively, which indeed exhibit a highly efficient photocatalytic degradation towards tetracyclines upon the visible-light irradiation. Among them, the photocatalytic performance of HPF is especially noticeable with the degradation rate up to 87% within 30 min, almost 11 times in comparison to those of pristine g-C₃ N₄ , which is mainly attributed to its high crystallinity and conjugation. For their photocatalytic mechanism, the •O₂ ^- radical anions are regarded as the active species.

Modulating Local Charge Distribution of Carbon Nitride for Promoting Exciton Dissociation and Charge-Induced Reactions

The sustainable light can generate reduction and oxidation centers in situ through the generation of photoexcited electrons and holes in the presence of photocatalyst. However, the photoexcited electrons and holes have huge Coulombic attraction and high exciton binding energy due to the weak screening effect and dielectric properties in many low-dimensional conjugated polymers, such as carbon nitride. Reducing the exciton binding energy of carbon nitride and promoting the conversion of excitons into free charge carriers are necessary for improving the activity of photocatalytic reactions but still very challenging. Here, by introducing amino-cyano functional groups into carbon nitride, it is demonstrated that excitons can be effectively dissociated into electrons and holes by finely controlling the charge distribution of heptazine ring. It is found that carbon nitride with heptazine rings of positive charge distribution can greatly reduce the exciton binding energy to 24 from 71 meV. Compared with heptazine ring having negative charge distribution, heptazine ring with positive charge distribution can increase photocatalytic hydrogen production of carbon nitride by up to ten times. This work provides an easy way to promote the dissociation of excitons in carbon nitride by regulating the charge distribution.

Photosystem II-based biomimetic assembly for enhanced photosynthesis

Photosystem II (PSII) is a fascinating photosynthesis-involved enzyme, participating in sunlight-harvest, water splitting, oxygen release, and proton/electron generation and transfer. Scientists have been inspired to couple PSII with synthetic hierarchical structures via biomimetic assembly, facilitating attainment of natural photosynthesis processes, such as photocatalytic water splitting, electron transfer and ATP synthesis, in vivo. In the past decade, there has been significant progress in PSII-based biomimetic systems, such as artificial chloroplasts and photoelectrochemical cells. The biomimetic assembly approach helps PSII gather functions and properties from synthetic materials, resulting in a complex with partly natural and partly synthetic components. PSII-based biomimetic assembly offers opportunities to forward semi-biohybrid research and synchronously inspire optimization of artificial light-harvest micro/nanodevices. This review summarizes recent studies on how PSII combines with artificial structures via molecular assembly and highlights PSII-based semi-natural biosystems which arise from synthetic parts and natural components. Moreover, we discuss the challenges and remaining problems for PSII-based systems and the outlook for their development and applications. We believe this topic provides inspiration for rational designs to develop biomimetic PSII-based semi-natural devices and further reveal the secrets of energy conversion within natural photosynthesis from the molecular level.

Surface modification induced construction of core-shell homojunction of polymeric carbon nitride for boosted photocatalytic performance

Surface modification has been considered a simple and effective strategy to enhance the photocatalytic activity of polymeric carbon nitride (CN), but resultant difference of energy band structures between the modified surface layer and the unmodified inside in the sample has always been neglected. Herein, maleoyl-modified CN (MaCN) was simply prepared via a dehydration reaction between CN and maleic acid, and exhibits enhanced charge separation, optical absorption, and thus photocatalytic hydrogen evolution activity, relative to the bulk CN. The surface modification causes variation of the band structure, suggesting the difference of band levels between the surface layer with maleoyl-modification and the inside without any modification in MaCN, and the surface layer and the inside with matched band levels form type-II core-shell homojunction to enhance the charge separation. This work expounds a conceptual framework of core-shell homojunction in surface-modified CN photocatalysts.

Insight into the influence of donor-acceptor system on graphitic carbon nitride nanosheets for transport of photoinduced charge carriers and photocatalytic H2 generation

The rapid recombination of photogenerated charges is one of the main restriction for promoting the photocatalytic H₂ generation of graphitic carbon nitride (CN) material. Herein, donor-acceptor (D-A) system was introduced into CN nanosheets by oxygen and/or phenyl doping (DA-CN) strategy to facilitate the transport of photoinduced charge carriers and H₂ generation. Experimental and theoretical results revealed that the nanosheet structure of DA-CN shortened the photoexcited charges transport length to the surface, and the D-A system embedded in DA-CN provided the dipole-induced internal electric field for charges transport. As a consequence, compared with pristine CN, DA-CN samples performed the improved transport of photogenerated charges and photocatalytic H₂ evolution. Notably, DA-CN-OP (oxygen and phenyl co-doping) with the strongest dipole-induced internal electric field originated from D-A system displayed the highest photocatalytic H₂ evolution rate at 7.394 mmol g^-1h^-1, which was 7.67 times as that of pristine CN (0.964 mmol g^-1h^-1). This work not only provides a simple strategy to construct highly efficient CN nanosheet photocatalyst with D-A system, but also promote the deep insight into the effect of molecular dipole originated from D-A system on the transport of photoinduced charge carriers and photocatalytic activity for CN material.

Asymmetric Acceptor-Donor-Acceptor Polymers with Fast Charge Carrier Transfer for Solar Hydrogen Production

Construction of local donor-acceptor architecture is one of the valid means for facilitating the intramolecular charge transfer in organic semiconductors. To further accelerate the interface charge transfer, a ternary acceptor-donor-acceptor (A₁ -D-A₂ ) molecular junction is established via gradient nitrogen substituting into the polymer skeleton. Accordingly, the exciton splitting and interface charge transfer could be promptly liberated because of the strong attracting ability of the two different electron acceptors. Both DFT calculations and photoluminescence spectra elucidate the swift charge transfer at the donor-acceptor interface. Consequently, the optimum polymer, N₃ -CP, undergoes a remarkable photocatalytic property in terms of hydrogen production with AQY_405 nm =26.6 % by the rational design of asymmetric molecular junctions on organic semiconductors.

Cascade Reactions by Nitric Oxide and Hydrogen Radical for Anti-Hypoxia Photodynamic Therapy Using an Activatable Photosensitizer

Organelle-targeted activatable photosensitizers are attractive to improve the specificity and controllability of photodynamic therapy (PDT), however, they suffer from a big problem in the photoactivity under both normoxia and hypoxia due to the limited diversity of phototoxic species (mainly reactive oxygen species). Herein, by effectively photocaging a π-conjugated donor-acceptor (D-A) structure with an N-nitrosamine substituent, we established a unimolecular glutathione and light coactivatable photosensitizer, which achieved its high performance PDT effect by targeting mitochondria through both type I and type II (dual type) reactions as well as secondary radicals-participating reactions. Of peculiar interest, hydrogen radical (H^•) was detected by electron spin resonance technique. The generation pathway of H^• via reduction of proton and its role in type I reaction were discussed. We demonstrated that the synergistic effect of multiple reactive species originated from tandem cascade reactions comprising reduction of O₂ by H^• to form O₂^•-/HO₂^• and downstream reaction of O₂^•- with ^•NO to yield ONOO^-. With a relatively large two-photon absorption cross section for photoexcitation in the near-infrared region (166 ± 22 GM at 800 nm) and fluorogenic property, the new photosensitizing system is very promising for broad biomedical applications, particularly low-light dose PDT, in both normoxic and hypoxic environments.

The effect of indium doping on the hydrogen evolution performance of g-C3N4 based photocatalysts

Doping graphite carbon nitride (g-C₃N₄) with indium ions in an unique quasi-interlayer fashion is effective to improve its visible light photocatalytic performance towards hydrogen evolution via water splitting.

Biomolecular l-tryptophan as a hole mediator anchored on g-C3N4 exhibits remarkably enhanced photocatalytic H2 evolution

A novel g-C₃N₄-based composite coupled with levorotatory-tryptophan restrains the recombination of photogenerated holes and electrons, exhibiting enhanced photocatalytic H₂ production.

Construction of a 3D/2D g-C3N4/ZnIn2S4 hollow spherical heterostructure for efficient CO2 photoreduction under visible light

The 3D/2D g-C₃N₄/ZnIn₂S₄ hollow spherical heterostructure can greatly increase visible light absorption and improve the efficiency of photo-generated electron migration and conversion, resulting in an excellent CO generation rate.

Facile synthesis of the Z-scheme graphite-like carbon nitride/silver/silver phosphate nanocomposite for photocatalytic oxidative removal of nitric oxides under visible light

In this study, a novel ternary Z-scheme Graphite-like Carbon Nitride (g-C₃N₄)/Silver (Ag)/Silver Phosphate (Ag₃PO₄) photocatalyst was designed and prepared using a two-step method (sodium chloride (NaCl) template-assisted strategy plus selective deposition). Its photocatalysts performance against removing 400 ppm of Nitric Oxides (NOx) was then investigated. We found 50 wt% g-C₃N₄/Ag/Ag₃PO₄(AP-CN 2:1) catalyst removes up to 74% of NO in 90 min under the illumination of visible light (>420 nm), which is respectively 3.5 and 1.8 times higher than using g-C₃N₄ or Ag₃PO₄, alone. This improved performance was attributed to the formation of Z-scheme g-C₃N₄/Ag/Ag₃PO₄ heterojunction, driven by the built-in electric field across the g-C₃N₄/Ag/Ag₃PO₄ interface. These separated the electron-hole but enhanced the original strong oxidation and reduction performance of related components. The superior performance is also attributed to the improved surface area, enhanced hydrophilicity (H₂O₂) and better visible-light-harvesting capability of the composite compound. More importantly, the AP-CN 2:1 sample maintained a NO removal rate of more than 73% even after four rounds of recycling. The photocatalytic oxidation removal mechanism was evaluated using the radical-capture experiments, electron spin resonance (ESR) and ion-exchange high-performance liquid chromatography (HPLC) analysis. The findings of this work offer a simple but effective design of a highly reactive and practical ternary Z-scheme heterojunction photocatalysts for the removal of toxic NO.

An All-Organic D-A System for Visible-Light-Driven Overall Water Splitting

Direct water splitting over photocatalysts is a prospective strategy to convert solar energy into hydrogen energy. Nevertheless, because of the undesirable electron accumulation at the surface, the overall water-splitting efficiency is seriously restricted by the poor charge separation/transfer ability. Here, an all-organic donor-acceptor (D-A) system through crafting carbon rings units-conjugated tubular graphitic carbon nitride (C-TCN) is proposed. Through a range of characterizations and theoretical calculations, the incorporation of carbon rings units via continuous π-conjugated bond builds a D-A system, which can drive intramolecular charge transfer to realize highly efficient charge separation. More importantly, the tubular structure and the incorporated carbon rings units cause a significant downshift of the valence band, of which the potential is beneficial to the activation for O₂ evolution. When serving as photocatalyst for overall water splitting, C-TCN displays considerable performance with H₂ and O₂ production rates of 204.6 and 100.8 µmol g^-1 h^-1 , respectively. The corresponding external quantum efficiency reaches 2.6% at 405 nm, and still remains 1.7% at 420 nm. This work demonstrates that the all-organic D-A system conceptualized from organic solar cell can offer promotional effect for overall water splitting by addressing the charge accumulation problem rooted in the hydrogen evolution reaction.

Phenyl-Bridged Graphitic Carbon Nitride with a Porous and Hollow Sphere Structure to Enhance Dissociation of Photogenerated Charge Carriers and Visible-Light-Driven H2 Generation

Graphitic carbon nitride (CN) suffers from rapid recombination of photoexcited charges due to the existing highly symmetrical tri-s-triazine ring and long charge diffusion path, resulting in moderate photocatalytic activity. The bridged phenyl embedded in the CN structure was used to reduce the symmetry of the tri-s-triazine ring. In addition, the CN material was constructed with a porous and hollow sphere structure to shorten the diffusion path of charge carriers. Herein, simple thermal polymerization of a trimesic acid-doped melamine-cyanuric acid (MCA) supramolecular was employed to construct phenyl-bridged graphitic carbon nitride (Ph-CN-MCA) with a hollow sphere structure composed of porous nanosheets for visible-light catalytic H₂ evolution. The porous and hollow sphere-structured Ph-CN-MCA possessed increased degree of polymerization, more negative conduction band potential, enlarged Brunauer-Emmett-Teller (BET) surface area, and shortened charge diffusion path. In addition, bridged phenyl embedded in the Ph-CN-MCA structure not only accelerated the dissociation of photogenerated carriers but also narrowed the band gap and extended the visible-light absorption. Further, the separated highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of Ph-CN-MCA facilitated the spatial dissociation of photogenerated charges, which was also confirmed by theoretical calculations. As a consequence, compared with the reference CN-MA catalyst prepared from melamine, Ph-CN-MCA showed approximately 48.42 times the photocatalytic H₂ evolution under visible-light irradiation. The developed synthetic method herein highlights that phenyl-bridged graphitic carbon nitride with a porous and hollow sphere structure could provide an efficient platform to boost the dissociation of photoexcited charge carriers and photocatalytic H₂ evolution.