Photocatalytic H2O2 Production Research Articles

Metal-Organic Framework Templated Z-Scheme ZnIn2S4/Bi2S3 Hierarchical Heterojunction for Photocatalytic H2O2 Production from Wastewater.

Metal-organic framework derived materials received a lot of attention due to their significant benefits in photocatalytic reactions. In this work, a Z-scheme ZnIn2S4/Bi2S3 hierarchical heterojunction is first developed by a one-pot method using CAU-17 as a template. The specific preparation method endows an intimate interface contact between these two monomers, and CAU-17-derived Bi2S3 possesses a high surface area and porosity, resulting in an efficient charge separation and O2 capture. Thus, for photocatalytic H2O2 production from the O2 reduction reaction, the ZnIn2S4/Bi2S3 heterojunction can achieve an H2O2 yield of 995µmolL-1 in pure water and ambient air under visible light, 4.5 and 4 times that of ZnIn2S4 and Bi2S3, respectively. In addition, in tetracycline solution, ZnIn2S4/Bi2S3 can degrade tetracycline with a degradation rate of 95% by photocatalysis, and at the same time, a final H2O2 production yield of 1223µmolL-1 is reached. Similarly, high yields of H2O2 are also obtained from wastewater containing o-nitrophenol, acid golden yellow, or acid red, and these pollutants are effectively degraded. This work reveals the potential of metal-organic framework-derived materials in photocatalysis, as well as provides insights into H2O2 green synthesis and wastewater treatment.

Stepwise Protonation of Three-Dimensional Covalent Organic Frameworks for Enhancing Hydrogen Peroxide Photosynthesis.

Three-dimensional covalent organic frameworks (3D COFs), recognized for their tailorable structures and accessible active sites, offer a promising platform for developing advanced photocatalysts. However, the difficulty in the synthesis and functionalization of 3D COFs hinders their further development. In this study, we present a series of 3D-bcu-COFs with 8 connected porphyrin units linked by linear linkers through imine bonds as a versatile platform for photocatalyst design. The photoresponse of 3D-bcu-COFs was initially modulated by functionalizing linear linkers with benzo-thiadiazole or benzo-selenadiazole groups. Furthermore, taking advantage of the well-exposed porphyrin and imine sites in 3D-bcu-COFs, their photocatalytic activity was optimized by stepwise protonation of imine bonds and porphyrin centers. The dual protonated COF with benzo-selenadiazole groups exhibited enhanced charge separation, leading to an increased photocatalytic H2O2 production under visible light. This enhancement demonstrates the combined benefits of linker functionalization and stepwise protonation on photocatalytic efficiency.

Stepwise Protonation of Three‐Dimensional Covalent Organic Frameworks for Enhancing Hydrogen Peroxide Photosynthesis

Three‐dimensional covalent organic frameworks (3D COFs), recognized for their tailorable structures and accessible active sites, offer a promising platform for developing advanced photocatalysts. However, the difficulty in the synthesis and functionalization of 3D COFs hinders their further development. In this study, we present a series of 3D‐bcu‐COFs with 8 connected porphyrin units linked by linear linkers through imine bonds as a versatile platform for photocatalyst design. The photoresponse of 3D‐bcu‐COFs was initially modulated by functionalizing linear linkers with benzo‐thiadiazole or benzo‐selenadiazole groups. Furthermore, taking advantage of the well‐exposed porphyrin and imine sites in 3D‐bcu‐COFs, their photocatalytic activity was optimized by stepwise protonation of imine bonds and porphyrin centers. The dual protonated COF with benzo‐selenadiazole groups exhibited enhanced charge separation, leading to an increased photocatalytic H2O2 production under visible light. This enhancement demonstrates the combined benefits of linker functionalization and stepwise protonation on photocatalytic efficiency.

Nitrogen‐Rich Carbon Dot‐Mediated n→π* Electronic Transition in Carbon Nitride for Superior Photocatalytic Hydrogen Peroxide Production

AbstractSolar‐driven synthesis of hydrogen peroxide (H2O2) through photocatalysis stands out as a promising avenue for sustainable energy generation, marked by environmental friendliness and industrial feasibility. However, the inherent limitations of carbon nitride (CN) in photocatalytic H2O2 production significantly impede their performance. Herein, a novel 0D/2D carbon dots‐modified CN nanosheet heterojunction (CDsMCN) is introduced, synthesized through a hydrothermal‐calcination tandem strategy induced by CDs derived from melamine. This innovative technique enhances the n→π* electronic transition in CDsMCN, accelerating the separation efficiency of electron‐hole pairs, boosting oxygen adsorption, and promoting a highly selective 2e− ORR. Comparative to pristine CN, CDs10MCN exhibited a remarkable tenfold increase in H2O2 production, reaching an impressive 1.48 mmol L−1. Furthermore, CDs10MCN demonstrates exceptional stability, maintaining its catalytic efficiency at the initial level over four consecutive cycles. The notable achievement of a molar selectivity of H2O2 ≈80% at an onset potential of 0.6 V (vs RHE) underscores its exceptional ability to produce the desired product selectively. Advanced in situ characterization together with DFT calculations revealed that the ultrathin CDs10MCN nanosheet heterojunction with enhanced n→π* electronic transition improves its optical properties, reduces bandgap, facilitates fast charge migration, and increases photocatalytic H2O2 performance, thereby serving as a promising candidate for advanced catalytic applications.

Molecularly Tunable Heterostructured Co-polymers Containing Electron-deficient and -rich Moieties for Visible-light and Sacrificial-agent-free H2O2 Photosynthesis.

As an alternative to hydrogen peroxide (H2O2) production by complex anthraquinone oxidation process, photosynthesis of H2O2 from water and oxygen without sacrificial agents is highly demanded. Herein, a covalently connected molecular heterostructure is synthesized via sequential C-H arylation and Knoevenagel polymerization reactions for visible-light and sacrificial-agent-free H2O2 synthesis. The subsequent copolymerization of the electron-deficient benzodithiophene-4,8-dione and the electron-rich biphenyl (B) and p-phenylenediacetonitrile (CN) not only expands the π-conjugated domain but also increases the molecular dipole moment, which largely promotes the separation and transfer of the photoinduced charge carriers. The optimal heterostructured BTDB-CN0.2 manifested an impressive photocatalytic H2O2 production rate of 1920 μmol g-1 h-1, which is 2.2 and 11.6 times that of BTDB and BTDCN. As revealed by the femtosecond transient absorption (fs-TA) and theoretical calculations, the linkage serves as a channel for the rapid transfer of photogenerated charge carriers, enhancing the photocatalytic efficiency. Further, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) uncovers that the oxygen reduction reaction occurs through the step one-electron pathway and the mutual conversion between C=O and C-OH with the anchoring of H+ during the catalysis favored the formation of H2O2. This work provides a novel perspective for the design of efficient organic photocatalysts.

Understanding the effect of multiple configurations in polymeric carbon nitride for efficient solar-driven hydrogen peroxide photosynthesis

A oxygen and potassium co-doped polymeric carbon nitride (O/K-PCNs) was simply constructed by an acid gas cutting strategy for photocatalytic H2O2 generation. The effect of each accompanied configurations on photosynthesis of H2O2 was systematically analyzed. The C–O–C structure formed by O doping is capable of decreasing K ions incorporated energy barrier, thus remarkably improving the content of crucial K active sites. Dual heteroatom sites synergistically enhance O2 adsorption and surface ORR by a bridge K–O–O–C model. Moreover, the accompanied cyano defect and poly(heptazine imide) is responsible for improving in-plane and interlayer carriers separation, respectively. The optimal O/K-PCNs exhibits 60-fold higher photocatalytic H2O2 production rate than pure PCN. A positive correlation between the H2O2 production rate and the K heteratoms content was established. This work clarifies role of multiple configurations in PCN, especially O-containing groups, providing a new insight for design heteroatoms-doped materials for solar energy conversion.

Molecularly Tunable Heterostructured Co‐polymers Containing Electron‐deficient and ‐rich Moieties for Visible‐light and Sacrificial‐agent‐free H2O2 Photosynthesis

As an alternative to hydrogen peroxide (H2O2) production by complex anthraquinone oxidation process, photosynthesis of H2O2 from water and oxygen without sacrificial agents is highly demanded. Herein, a covalently connected molecular heterostructure is synthesized via sequential C−H arylation and Knoevenagel polymerization reactions for visible‐light and sacrificial‐agent‐free H2O2 synthesis. The subsequent copolymerization of the electron‐deficient benzodithiophene‐4,8‐dione and the electron‐rich biphenyl (B) and p‐phenylenediacetonitrile (CN) not only expands the π‐conjugated domain but also increases the molecular dipole moment, which largely promotes the separation and transfer of the photoinduced charge carriers. The optimal heterostructured BTDB‐CN0.2 manifested an impressive photocatalytic H2O2 production rate of 1920 μmol g‐1 h‐1, which is 2.2 and 11.6 times that of BTDB and BTDCN. As revealed by the femtosecond transient absorption (fs‐TA) and theoretical calculations, the linkage serves as a channel for the rapid transfer of photogenerated charge carriers, enhancing the photocatalytic efficiency. Further, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) uncovers that the oxygen reduction reaction occurs through the step one‐electron pathway and the mutual conversion between C=O and C−OH with the anchoring of H+ during the catalysis favored the formation of H2O2. This work provides a novel perspective for the design of efficient organic photocatalysts.

Insight into bay-/end-substituted perylene diimide and its S-scheme heterojunction for enhanced photocatalytic H2O2 production under visible-light irradiation

Here, 1D bis(N-carboxymethyl) peryleneimide (H2PDI), 0D 1,6,7,12-tetrachloro-bis(N-carboxymethyl) peryleneimide (4Cl-H2PDI), and 2D 4Cl-H2PDI/graphene quantum dot (4Cl-H2PDI/GQD) nanostructures are synthesized and carefully analyzed. The effect of bay-/end-substitution and S-scheme heterojunction of PDI-based materials as main catalysts on the photocatalytic H2O2 evolution is first studied through the oxygen reduction reaction (ORR). Under the visible-light irradiation (> 420 nm), 4Cl-H2PDI and 4Cl-H2PDI/GQD as photocatalysts exhibit the ∼7 and ∼16 times H2O2 evolution rate than H2PDI (1059.6 vs. 2484.0 vs. 160.0 µM g−1 h−1), respectively. The systematical experiments reveal that 4Cl-H2PDI and 4Cl-H2PDI/GQD should prefer a two-step single-electron ORR process, while H2PDI may involve a 4e‒ water oxidation and one-step 2e‒ ORR process. Further experiments confirm that the bay-substitution and GQD doping of H2PDI can promote the generation, transportation, and separation of photogenerated electrons and holes, and prolong the carrier lifetime. This work provides insight into PDI-based photocatalytic H2O2 production.

All-organic heterojunctions used for the excellent photocatalytic H2O2 synthesis: The key role of bay-position Cl in PDI

Melem is the basic structural unit of g-C3N4. When directly utilized as a photocatalyst, the separation efficiency of photogenerated electron-hole pairs is low. In this study, we constructed a Melem-based all-organic heterojunction (PICN) by reacting the -NH2 at the terminal of the Melem unit with the anhydride of PDA. The photocatalytic efficiency for H2O2 production of the heterojunction is 4.2 times that of CN. Introducing -Cl at the bay position of PDI further enhances the photocatalytic H2O2 production efficiency by 1.6 times. This enhancement is attributed to the introduction of -Cl, which not only broadens the UV–visible light absorption range of the sample but also improves the interface electron transfer efficiency between Melem and PDICl. Moreover, the introduction of -Cl can also reduce the overpotential of the O2 reduction reaction on the surface of the sample. These novel findings may provide insights for the design of organic heterojunction photocatalysts.

Ag nanocubes-decorated ammonium hydroxide-treated carbon nitride to improve photocatalytic H2O2 production and fuel cell performance

A novel photocatalyst is designed by surface modification and cocatalyst loading of graphitic carbon nitride (g-C3N4) with ammonium hydroxide and silver nanocubes (AgNCs), respectively. The synergistic effect of the modification in the intralayer of g-C3N4 and surface plasmon resonance (SPR) bands of AgNCs significantly enhances the migration and separation efficiency of photo-induced charge carriers. A nickel mesh coated with photocatalyst and the carbon paper loaded with pristine g–C3N4–mixed iron phthalocyanine (FeIIPc) used as the photoanode and cathode, respectively, are constructed for the self-powered photoelectrochemical cell, which exhibits the maximum power density of 0.74 mW cm−2. The AHCN/AgNCs-based cell reveals approximately a 3.1-times enhancement in maximum power density compared with the pristine g–C3N4–based cell. In addition, the photocatalytically generated H2O2 (chemical energy) can be stored in water, and then used as fuel by the connection of two electrodes in the dark. After the fuel cell is operated for 12 h, the specific capacitance retention rate still maintains as high as 57.2 %, which is the greatest retention rate in comparison with the previously reported H2O2 fuel cell systems. Our work offers a feasible opinion on how to improve the visible light utilization of semiconductors by tuning the intralayer properties and loading plasmonic metal.

Regulation of d-band center of TiO2 through fluoride doping for enhancing photocatalytic H2O2 production activity

Titanium dioxide (TiO2) has received extensive attention for photocatalytic hydrogen peroxide (H2O2) production, with the d-band center related to the adsorption performance, which affects the photocatalytic reaction process. Herein, an ingenious strategy to lower the antibonding-orbital occupancy in the Ti 3d orbital by fluoride ion (F−) doping is proposed, with density functional theory calculations predicting that F-doping into TiO2 induces a non-uniform charge distribution and enables an upshift of the d-band center in F/TiO2. This manipulation provides accessible active centers with favorable d-band energy levels, which can improve the charge-transfer behavior, strengthen the interaction between the adsorbed oxygen and the photocatalyst, and reduce the adsorption energy of oxygen, eventually promoting the photocatalytic H2O2 production rate. The experimental results further confirm that a lower antibonding-orbital occupancy can intensify the adsorption of atomic oxygen at the Ti sites. Electron paramagnetic resonance experiment reveals that the presence of F− ions in the lattice induces the formation of Ti3+ centers that localize the extra electron needed for charge compensation. Femtosecond transient absorption (fs-TA) spectroscopy suggests that photogenerated electrons are transferred from the conduction band of F/TiO2 to the Ti3+ surface states and surface F− ions, expediting the separation of electrons and holes. Consequently, with F− doping in TiO2, the photocatalytic H2O2 production yields improved from 277 to 467 μmol·g−1·h−1, with ethanol as a sacrificial reagent. This study provides a new strategy for regulating the d-band center to optimize the adsorption strength between the photocatalyst and oxygen atoms and achieve enhanced photocatalytic H2O2 production performance.

Photocatalytic H2O2 production and fuel cell performance based on PDI nanobelts enhanced by surface plasmon resonance of gold nanoparticles

The photocatalytic hydrogen peroxide (H2O2) fuel cell represents an innovative self-powered apparatus amalgamating the production and conversion of H2O2 to supply electricity. Using efficient photocatalyst as photoanode to realize two-electron water oxidation to produce H2O2 is considered as a key factor to improve the performance of fuel cell. In this study, perylene imide nanobelts decorated with gold nanoparticles (Au/PDI) were synthesized and subsequently employed as the photoanode to construct a photocatalytic H2O2 fuel cell. This cell can produce H2O2 under irradiation and store it, subsequently utilizing the stored H2O2 to generate electricity in the absence of light. The maximum power density of Au/PDI-based cell could reach 1.07 mW·cm−2 under AM 1.5G solar light, which has around 1.7 times enhancement compared to PDI-based cell. Meanwhile, a specific capacitance of 5661 mF·cm−2 was obtained after 3 h irradiation. After operating the cell for 12 h, the specific capacitance remained at 50.2% of its initial value. It is indicated that PDI-based photocatalysts hold considerable promise in water oxidation for H2O2 production. The incorporation of noble nanometals has shown effective enhancement in photocatalytic H2O2 production through the localized surface plasmon resonance (LSPR) effects, thereby enriching the photoanode materials designed for H2O2 fuel cell application.

Hydrogen peroxide production in pure water on a pyrrole-containing hydrothermal carbon photocatalyst

Herein, a pyrrole-containing hydrothermal carbon (N-SHTC) was developed by a simple one-step hydrothermal carbonization approach using starch and nitric acid as starting reactants. The introduction of nitric acid promoted the dehydration and carbonization of starch and led to the synthesis of N-SHTC at lower hydrothermal temperature, and also resulted in the incorporation of N into the furan structure to form pyrrole units. The charge transfer efficiency of N-SHTC was significantly improved due to the introduced pyrrole units as potential electron acceptor. With no scavengers or O2 bubbling, N-SHTC exhibited a H2O2 production rate of 1132 μmol g-1 h-1 in pure water under visible light. Notably, the H2O2 photoproduction performance of N-SHTC was further enhanced in the presence of metal salt ions due to the strengthened electron-withdrawing property of pyrrole units caused by the metal salt ions. These merits enabled N-SHTC the potentially practical applications in photocatalytic production of H2O2.

High-concentration hydrogen peroxide production by solar interfacial catalysis

Solar-driven catalytic synthesis of H2O2 is an ideal alternative to the anthraquinone method, but current photocatalysts still suffer from low activity and inefficient solar energy utilization. Here we presented an economic and efficient solar interfacial catalysis system (SICS) that incorporated photothermal–photocatalytic materials into commercial sponge to simultaneously generate the required heat and carriers for H2O2 production. We demonstrated its superiority over conventional particulate photocatalysis (PC) in photocatalytic H2O2 production. The SICS, located at the air–water interface, remarkably improve the activities of photocatalysts by efficient utilization of solar-converted heat. The produced H2O2 from SICS was reserved in the sponge and resulted in an ultrahigh concentration of 46 mM for per gram catalyst after 1 h solar irradiation. As thus, our application experiments confirmed that the SICS presented great advantages in organic pollutant (e.g. phenol and tetracycline) degradation compared with conventional PC. This work paves a new way for the industrialization of solar-driven catalysis.

Enhancing the crystallinity of covalent organic frameworks to achieve improved photocatalytic hydrogen peroxide production under ambient conditions

Photocatalytic production of hydrogen peroxide (H2O2) presents a promising strategy for environmental remediation and energy production. However, achieving clean and efficient H2O2 production under ambient conditions without organic sacrificial agents remains challenging. Enhancing the low crystallinity of covalent organic frameworks (COFs) can promote the separation and transmission of photo-generated carriers, thereby boosting their photocatalytic performance. Herein, we introduce a novel synthetic approach by substituting traditional acetic acid catalysts with organic base catalysts to enhance the crystallinity of β-ketoenamine-linked COF, TpBD-COF. Compared to TpBD-COF-A synthesized using acetic acid catalysts, TpBD-COF-B, synthesized with organic base catalysts, exhibited advancements including increased absorption intensity in the visible spectrum, reduced photoluminescence intensity, enhanced photo-generated carrier separation performance, and a 2.1-fold increase in photocatalytic H2O2 production. Under visible light irradiation, TpBD-COF-B achieved a photocatalytic H2O2 production rate of 533 µmol h−1 g−1 using only air and water, without the need for organic sacrificial agents. Furthermore, TpBD-COF-B also exhibited good performance in long-term catalytic production experiments, tests with actual water bodies, and cyclic usage experiments. This study offers a strategy for enhancing the crystallinity of COFs to improve their photocatalytic activity, with promising applications in clean energy production and environmental remediation.

Optimizing photocatalytic H2O2 production through morphology-controlled supramolecular self-assembly of porous carbon nitride nanotubes via C6N6 rings

Optimizing photocatalytic H2O2 production through morphology-controlled supramolecular self-assembly of porous carbon nitride nanotubes via C6N6 rings

Oxygen-enriched carbon quantum dots from coffee waste: Extremely active organic photocatalyst for sustainable solar-to-H2O2 conversion

Solar-driven artificial photosynthesis offers a promising avenue for hydrogen peroxide (H2O2) generation, an efficient and economical replacement for current methods. The efficiency and selectivity hurdles of the two-electron oxygen reduction reaction (ORR) in solar-to- H2O2 conversion are substantial barriers to large scale production. In this manuscript, a simple biomass-assisted synthesis was performed to produce oxygen-enriched carbon quantum dots (OE-CQDs) from spent coffee waste, acting as an efficient photocatalyst for solar-powered H2O2 production. OE-CQDs can stabilize and store light-generated electrons effectively, boosting charge separation and enhancing photocatalytic performance with longevity. The maximal photocatalytic H2O2 production was achieved viz the utilization of OE-CQDs with generation rate of 356.86 μmol g-1 h-1 by retaining 80% activity without any external sacrificial donors. The outstanding performance of synthesized OE-CQDs under light exposure at wavelength (λ) of 280 nm has been ensured by the quantum yield value of 9.4% upon H2O2 generation. The combinatorial benefits of OE-CQDs with their authentic crystalline structure and oxygen enrichment, is expected to be enhancing the ORR activity through accelerating charge transfer, and optimizing oxygen diffusion. Consequently, our eco-friendly method holds considerable promise for creating highly efficient, metal-free photocatalysts for artificial H2O2 production.

Photocatalytic coproduction of hydrogen peroxide and Aldehydic/Keto acid on carbon nitride

Photocatalytic H2O2 production is emerging as an alternative technology to contribute H2O2-based advanced oxidation applications. However, the present reaction systems rarely consider the selective oxidation of sacrificial agent along with oxygen reduction reaction. Herein, we design a reaction system by using hydroxycarboxylic acids as additives to boost photocatalytic H2O2 production. More importantly, hydroxycarboxylic acids could simultaneously be dehydrogenated into aldehydic/keto acids with high selectivity. Lactic acid as one of the typical hydroxycarboxylic acids reveals the feasibility of this hypothesis, delivering 6.56 mM/h of H2O2 generation along with > 70 % pyruvic acid selectivity. The universality of this reaction system is demonstrated by using other hydroxycarboxylic acids. This works sheds new light on coupling H2O2 generation with value-added chemicals production by mild photocatalytic approach.

Pyridine-Based Covalent Organic Frameworks with Pyridyl-Imine Structures for Boosting Photocatalytic H2O2 Production via One-Step 2e- Oxygen Reduction.

Bipyridine-based covalent organic frameworks (COFs) have emerged as promising contenders for the photocatalytic generation of hydrogen peroxide (H2O2). However, the presence of imine nitrogen alters the mode of H2O2 generation from an efficient one-step two-electron (2e-) route to a two-step 2e- oxygen reduction pathway. In this work, we introduce 3,3'-bipyridine units into imine-based COF skeletons, creating a pyridyl-imine structure with two adjacent nitrogen atoms between the pyridine ring and imine linkage. This unique bipyridine-like architecture can effectively suppress the two-step 2e- ORR process at the single imine-nitrogen site, facilitating a more efficient one-step 2e- pathway. Consequently, the optimized pyridyl-imine COF (PyIm-COF) exhibits a remarkable H2O2 production rate of up to 5850 μmol h-1 g-1, nearly double that of pristine bipyridine COFs. This work provides valuable insight into the rational design of functionalized COFs for enhanced H2O2 production in photocatalysis.

Oxygen vacancies rich polyoxometalate for haloperoxidase mimic involved antibiofouling on self-provided H2O2 from photocatalysis

Biofouling significantly impacts marine environments and economies through pollution and economic loss. Artificial nanozymes, resembling haloperoxidase, are highly effective in combating biofouling due to their ability to facilitate the conversion of Br− to HBrO, thereby inhibiting the survival and proliferation of microorganisms. However, this process necessitates the presence of H2O2. To achieve haloperoxidase mimicry in biofouling prevention without external H2O2, a bifunctional polyoxometalate (POM) with abundant oxygen vacancies has been developed. This compound simultaneously exhibits haloperoxidase mimicry and photocatalytic H2O2 generation. Theoretical analyses suggest that oxygen vacancies elevate the d-band center, improving the adsorption of H2O2 and Br-, and thus enhancing haloperoxidase mimicry. The POM compound demonstrates notable H2O2 production capabilities, with a rate of 1.77 mmol·h−1·g−1, attributed to oxygen vacancies facilitating electron-hole pair separation. This advancement allows for haloperoxidase mimic biofouling prevention without the need for added H2O2. This study not only elucidates the structure–activity relationship in haloperoxidase mimicry and photocatalytic H2O2 production but also presents an effective and eco-friendly method for biofouling prevention.