Robust Photocatalytic H2O2 Production by Octahedral Cd3(C3N3S3)2 Coordination Polymer under Visible Light

Ag Atom Induces Microstrain Environment around Cd Sites to Construct Diatomic Sites for Almost 100% CO2-to-CO Electroreduction

Deeply understanding how local microstrain environment around diatomic sites influences their electronic state and adsorption is crucial for improving electrochemical CO2 reduction (eCO2R) reaction; however, precise engineering of the atomic microstrain environment is challenging. Herein, we fabricate Ag-CdTMT electrocatalysts with AgN2S2-CdN2S2 diatomic sites by anchoring Ag to the nodes of CdTMT (TMT = 2,4,6-trimercaptotriazine anion) coordination polymers. The Ag-CdTMT catalysts achieve approximately 100% Faradaic efficiency for CO reduction with an industrial level current density (∼200 mA cm-2 in H-cell). The embedded Ag atoms induce the formation of Ag-Cd diatomic sites with local microstrain, stretching Cd-N/S bonds, and reinforcing electron localization at Cd sites. The microstrain engineering and adjacent Ag atoms synergistically reduced Cd 4d-C 2p antibonding orbital occupancy for intensifying *COOH adsorption as the rate-determining step. This study provides novel insights into customizing the electronic structure of diatomic sites through strain engineering.

Inhibiting Photo-Oxidation and Enhancing Visible-Light-Driven Photocatalytic Water Oxidation over Covalent Organic Frameworks Through the Coordination of Cobalt with Bipyridine

Photocatalytic water splitting using covalent organic frameworks (COFs) is a promising approach for harnessing solar energy. However, challenges such as slow kinetic dynamics in the photocatalytic oxygen evolution reaction (OER) and COFs' self-oxidation hinder its progress. In this study, an enamine-based COF coordinated is introduced with cobalt dichloride, CoCl2 (CoCl2-TpBPy). The coordination of cobalt ions with bipyridines in CoCl2-TpBPy enhances charge-carrier separation and migration, leading to effective photocatalytic OER. Under visible light irradiation, CoCl2-TpBPy achieves a notable OER rate of up to 1 mmol·g-1·h-1, surpassing the reported organic semiconductor analogs. Additionally, CoCl2-TpBPy shows minimal nitrogen evolution compared to TpBPy and ethanol-treated TpBPy (E-TpBPy), indicating cobalt plays a pivotal role in improving charge utilization and minimizing photo-oxidation. In situ X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) analyses revealed that Co(IV) species are key to the high OER efficiency. This work highlights Co(IV) species in the efficient OER and inhibiting photo-oxidation of CoCl2-TpBPy.

Engineering of CdS-chain arrays assembled through S⋯S interactions in 1D semiconductive coordination polymers

One-dimensional (1D) Cd(II) coordination polymers [Cd(x-SPhOMe)2]n (x = ortho, meta, and para; HSPhOMe = methoxybenzenethiol) containing inorganic 1D (-Cd-S-)n chains were synthesized. Among these, the KGF-31 polymer bearing para-SPhOMe featured a three-strand chain structure assembled via interchain S⋯S interactions and exhibited high photoconductivity and longevity.

Surface-active site modulation of the S-scheme heterojunction toward exceptional photocatalytic performance

Heterojunction photocatalysts have shown their immense capability in enhancing photogenerated charge carrier separation. Yet, the intrinsic scarcity of active sites in semiconductor components of heterojunction photocatalysts limits their potential for photocatalysis being used in practical applications. Herein, we employ a non-noble metal cocatalyst (i.e., NiS) for modulating a S-scheme heterojunction photocatalyst consisting of Cd₃(C₃N₃S₃)₂ (CdCNS) and CdS. It is revealed that the formation of the CdCNS/CdS S-scheme heterojunction can enable optimal photogenerated charge carrier utilization efficiency and optimized redox capability. More importantly, the meticulous loading of NiS can play multiple roles in enhancing the photocatalytic performance of the CdCNS/CdS photocatalyst, including endowing it with abundant surface-active sites and acting as a photogenerated electron acceptor. As a result, the optimized NiS-loaded CdCNS/CdS attains an excellent hydrogen production rate of 38.17 mmol g^-1 h^-1, to reach a quantum efficiency of 29.02% at 420 nm. The results reported in this work provide an interesting insight into the important roles of surface-active site modulation in optimizing photocatalytic performances.

Redox-Active Tin Metal-Organic Framework with a Thiolate-Based Ligand

Metal-organic frameworks (MOFs) and coordination polymers composed of thiolates as coordinating functional groups are interesting materials with unique optical and electronical properties. Herein, we report the preparation of KGF-4 and KGF-10, two Sn-MOF crystal structures with bonds between Sn and thiolate. KGF-10 was isolated as a pure phase and found to exhibit redox properties and a semiconducting band structure, as confirmed by first-principles (density functional theory) calculations.

Influence of calcination temperature on photocatalytic H2O2productivity of hierarchical porous ZnO microspheres

Photocatalytic production of H₂O₂from water and atmospheric oxygen has been recognized as a green and sustainable chemical process, due to the abundance of raw materials and sustainable solar energy. Herein, flower-like hierarchical ZnO microspheres were prepared by hydrothermal method followed by calcination at different temperatures, and their photocatalytic performance in H₂O₂production was examined under simulated sunlight irradiation. The calcination temperature plays a vital role in the structure, morphology, and surface area of the final ZnO products as well as their optical and electrochemical properties, which are determining factors in their photocatalytic activity. The ZnO calcined at 300 °C (Zn-300) exhibits the highest activity and optimal stability, showing productivity of 2793μmol l^-1within 60 min of irradiation, which was 6.5 times higher than that of uncalcined ZnO precursor. The remarkable photocatalytic activity is attributed to enhanced light utilization, large surface area, abundant exposed active sites, improved separation efficiency, and prolonged carrier lifespan. Moreover, the results from cycling experiments indicate the as-prepared ZnO samples exhibit good stability and long-time performance. This work provides useful information for the preparation of hierarchical ZnO photocatalysts.

Carbon Dot-Triggered Photocatalytic Degradation of Cellulose Acetate

Chemical modification of biopolymers, before use in thermoplastic applications, can reduce the susceptibility to open environment degradation. We demonstrate carbon dots (CDs) as green photocatalytic triggers that can render the common cellulose derivative, cellulose acetate (CA), degradable under open environment relevant conditions. CD-modified cellulose acetate (CA + CD) films were subjected to UV-A irradiation in air and simulated sea water, and the degradation process was mapped by multiple spectroscopic, chromatographic, and microscopy techniques. The addition of CDs effectively catalyzed the deacetylation reaction, the bottleneck preventing biodegradation of CA. The photocatalytically activated degradation process led to significant weight loss, release of small molecules, and regeneration of cellulose fibers. The weight loss of CA + CD after 30 days of UV-A irradiation in air or simulated sea water was 53 and 43%, respectively, while the corresponding values for plain CA films were 12 and 4%. At the same time the weight average molar mass of CA + CD decreased from 62,000 to 11,000 g/mol and 15,000 g/mol during UV-A irradiation in air and simulated sea water, respectively, and the degree of substitution (DS) decreased from 2.2 to 1.6 both in air and in water. The aging in water alone did not affect the weight average molar mass, but the DS was decreased to 1.9. Control experiments confirmed the generation of hydrogen peroxide when aqueous CD dispersion was subjected to UV-A irradiation, indicating a free radical mechanism. These results are promising for the development of products, such as mulching films, with photocatalytically triggered environmental degradation processes.

Disulfide polymer grafted polypropylene/polyethylene filter media for selective cadmium removal

Heavy metal pollution caused by stormwater runoff has triggered a demand for effective heavy metal sorbents. Effective heavy metal removal using conventional stormwater runoff treatment processes that employ filtration mechanisms as primary removal mechanisms is difficult. Therefore, we attempt to improve cadmium removal performance by attaching disulfide polymer (DiS-COP) containing soft bases, thiols, onto the surface of polypropylene/polyethylene (PP/PE) fiber media, which is widely used for stormwater runoff treatment. Material characterization demonstrated that DiS-COP was successfully grafted and grown on the surface of PP/PE (Dis-PP/PE). The batch and continuous flow adsorption capacities of Dis-PP/PE were 81.1 mg/g and 2.33 mg/g, respectively, which is 40 times higher than those of pristine PP/PE. Applicability of DiS-PP/PE at pH 6-8 was demonstrated, and effects of calcium and humic acid on cadmium adsorption were investigated. Calcium marginally affected cadmium adsorption, which can be explained using the Hard and soft (Lewis) acids and bases theory (HSAB), but cadmium removal efficiency decreased owing to humic acid (HA)-Cd complex formation and agglomeration in the presence of organic material. In a breakthrough test, the adsorption column exhibited complete cadmium uptake over 24 h until it reached the breakthrough point. Therefore, heavy metal adsorption performance of PP/PE was successfully enhanced by grafting DiS-COP on its surface.

A comparative perspective of electrochemical and photochemical approaches for catalytic H2O2 production

Recent advances in the design, preparation, and applications of different catalysts for electrochemical and photochemical H₂O₂ production are summarized, and some invigorating perspectives for future developments are also provided.

Semiconductive Nature of Lead-Based Metal-Organic Frameworks with Three-Dimensionally Extended Sulfur Secondary Building Units

Recently, metal-organic frameworks (MOFs) composed of sulfur secondary building units (sulfur-SBUs) have attracted significant attention as unique electronic materials with high conductivities and photo- and electrocatalytic properties. Herein we report the crystal structure of KGF-1, an example of a Pb-MOF composed of three-dimensionally extended sulfur-SBUs that displays molecular sieving behavior, visible-light absorption, and a semiconductor band structure and is a hydrogen-evolution photocatalyst.

Recent Strategies for Hydrogen Peroxide Production by Metal-Free Carbon Nitride Photocatalysts

Hydrogen peroxide (H2O2) is a chemical which has gained wide importance in several industrial and research fields. Its mass production is mostly performed by the anthraquinone (AQ) oxidation reaction, leading to high energy consumption and significant generation of wastes. Other methods of synthesis found in the literature include the direct synthesis from oxygen and hydrogen. However, this H2O2 production process is prone to explosion hazard or undesirable by‑product generation. With the growing demand of H2O2, the development of cleaner and economically viable processes has been under intense investigation. Heterogeneous photocatalysis for H2O2 production has appeared as a promising alternative since it requires only an optical semiconductor, water, oxygen, and ideally solar light irradiation. Moreover, employing a metal-free semiconductor minimizes possible toxicity consequences and reinforces the sustainability of the process. The most studied metal‑free catalyst employed for H2O2 production is polymeric carbon nitride (CN). Several chemical and physical modifications over CN have been investigated together with the assessment of different sacrificial agents and light sources. This review shows the recent developments on CN materials design for enhancing the synthesis of H2O2, along with the proposed mechanisms of H2O2 production. Finally, the direct in situ generation of H2O2, when dealing with the photocatalytic synthesis of added-value organic compounds and water treatment, is discussed.

Efficient Hydrogen Peroxide Generation Utilizing Photocatalytic Oxygen Reduction at a Triphase Interface

Photocatalytic oxygen reduction has garnered attention as an emerging alternative to traditional anthraquinone oxidation process to synthesize H₂O₂. However, despite great efforts to optimize photocatalyst activity, the formation rate has been largely limited by the deficient accessibility of the photocatalysts to sufficient O₂ in water. Here we boost the reaction by reporting an air-liquid-solid triphase photocatalytic system for efficient H₂O₂ generation. The triphase system allows reactant O₂ to reach the reaction interface directly from the ambient atmosphere, greatly increasing the interface O₂ concentration, which in turn simultaneously enhanced the kinetics of formation constant and suppressed the unwanted electron-hole recombination and the kinetics of H₂O₂ decomposition reaction. Compared with a conventional liquid-solid diphase reaction system, the triphase system enables an increase in H₂O₂ formation by a factor of 44. The triphase system is generally applicable to fundamentally understand and maximize the kinetics of semiconductor-based photocatalytic oxygen reduction for H₂O₂ generation.

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A triphase photocatalytic system is developed for efficient H₂O₂ generation

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Sufficient interface oxygen is provided

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The formation rate is enhanced

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The unwanted electron-hole recombination and H₂O₂ decomposition rates are suppressed

Selective removal of heavy metal ions by disulfide linked polymer networks

Heavy metal contaminated surface water is one of the oldest pollution problems, which is critical to ecosystems and human health. We devised disulfide linked polymer networks and employed as a sorbent for removing heavy metal ions from contaminated water. Although the polymer network material has a moderate surface area, it demonstrated cadmium removal efficiency equivalent to highly porous activated carbon while it showed 16 times faster sorption kinetics compared to activated carbon, owing to the high affinity of cadmium towards disulfide and thiol functionality in the polymer network. The metal sorption mechanism on polymer network was studied by sorption kinetics, effect of pH, and metal complexation. We observed that the metal ions-copper, cadmium, and zinc showed high binding affinity in polymer network, even in the presence of competing cations like calcium in water.

Cd3(C3N3S3)2 coordination polymer/graphene nanoarchitectures for enhanced photocatalytic H2O2 production under visible light

For a long time, there has been global concern over the environment and energy problems. Recently, the problems, which have brought about serious effect on the global living condition, have been in the "spotlight" and given impetus to the universal's efforts to head for the same direction: stem the worst warming and strive for the renewable energy source. Hydrogen peroxide (H₂O₂) is undoubtedly a good choice, which holds the promise as a clean, efficient, safe and transferrable energy carrier. Octahedral coordination polymer, Cd₃(C₃N₃S₃)₂, was found to be a robust photocatalyst for H₂O₂ generation under visible light irradiation. To further improve the H₂O₂ generation efficiency, adhering the octahedron to reduced graphene (rGO) was applied as the strategy herein. The study shows that by adhering Cd₃(C₃N₃S₃)₂ to rGO, the formation of H₂O₂ is 2.5-fold enhanced and its deformation is concurrently suppressed. This work not only demonstrates the effectiveness of adhering Cd₃(C₃N₃S₃)₂ polymer to rGO for the improvement of the polymer's photocatalytic performance, but also proposes a general way for the fabrication of graphene/coordination compound hybrids for maximizing their synergy.

Development of semi-continuous chemo-enzymatic terpene epoxidation: combination of anthraquinone autooxidation and the lipase-mediated epoxidation process

Novel combination of anthraquinone process and lipase-mediated epoxidation in a semi-continuous approach, exclusively for monoterpenes.

Dual function photocatalysis of cyano-bridged heteronuclear metal complexes for water oxidation and two-electron reduction of dioxygen to produce hydrogen peroxide as a solar fuel

Hydrogen peroxide was produced from oxygen and water via visible-light irradiation of polymeric heteronuclear cyano-bridged complexes with the 2,2′-bipyridine ligand (bpy) (M^II[Ru^II(CN)₄(bpy)]; M^II = Ni^II, Fe^II and Mn^II).

Solar-Driven H2 O2 Generation From H2 O and O2 Using Earth-Abundant Mixed-Metal Oxide@Carbon Nitride Photocatalysts

Light-driven generation of H2 O2 only from water and molecular oxygen could be an ideal pathway for clean production of solar fuels. In this work, a mixed metal oxide/graphitic-C3 N4 (MMO@C3 N4 ) composite was synthesized as a dual-functional photocatalyst for both water oxidation and oxygen reduction to generate H2 O2 . The MMO was derived from a NiFe-layered double hydroxide (LDH) precursor for obtaining a high dispersion of metal oxides on the surface of the C3 N4 matrix. The C3 N4 is in the graphitic phase and the main crystalline phase in MMO is cubic NiO. The XPS analyses revealed the doping of Fe(3+) in the dominant NiO phase and the existence of surface defects in the C3 N4 matrix. The formation and decomposition kinetics of H2 O2 on the MMO@C3 N4 and the control samples, including bare MMO, C3 N4 matrix, Ni- or Fe-loaded C3 N4 and a simple mixture of MMO and C3 N4 , were investigated. The MMO@C3 N4 composite produced 63 μmol L(-1) of H2 O2 in 90 min in acidic solution (pH 3) and exhibited a significantly higher rate of production for H2 O2 relative to the control samples. The positive shift of the valence band in the composite and the enhanced water oxidation catalysis by incorporating the MMO improved the light-induced hole collection relative to the bare C3 N4 and resulted in the enhanced H2 O2 formation. The positively shifted conduction band in the composite also improved the selectivity of the two-electron reduction of molecular oxygen to H2 O2 .

Air activation by a metal-free photocatalyst for “totally-green” hydrocarbon selective oxidation

We demonstrate that polytriazine imide (PTI) is an efficient photocatalyst for cyclohexane selective oxidation using air and water without any other oxidants, initiators and solvents.