Selective Photooxidation Research Articles

Novel of Poly(triazine imide) Composite for Selective Photooxidation

Novel of Poly(triazine imide) Composite for Selective Photooxidation

Photooxidation of Polyolefins to Produce Materials with In-chain Ketones and Improved Materials Properties.

Herein, we report a selective photooxidation of commodity postconsumer polyolefins to produce polymers with in-chain ketones. The reaction does not involve the use of catalyst, metals, or expensive oxidants, and selectively introduces ketone functional groups. Under mild and operationally simple conditions, yields up to 1.23 mol% of in-chain ketones were achieved. Installation of in-chain ketones resulted in materials with improved adhesion of the materials and miscibility of mixed plastics relative to the unfunctionalized plastics. The introduction of ketone groups into the polymer backbone allows these materials to react with diamines, forming dynamic covalent polyolefin networks. This strategy allows for the upcycling of mixed plastic waste into reprocessable materials with enhanced performance properties compared to polyolefin blends. Mechanistic studies support the involvement of photoexcited nitroaromatics in consecutive hydrogen and oxygen atom transfer reactions.

Optimizing the reaction pathway of methane photo-oxidation over single copper sites.

Direct photocatalytic conversion of methane to value-added C1 oxygenate with O2 is of great interest but presents a significant challenge in achieving highly selective product formation. Herein, a general strategy for the construction of copper single-atom catalysts with a well-defined coordination microenvironment is developed on the basis of metal-organic framework for selective photo-oxidation of CH4 to HCHO. We propose the directional activation of O2 on the mono-copper site breaks the original equilibrium and tilts the balance of radical formation almost completely toward •OOH. The synchronously generated •OOH and •CH3 radicals rapidly combine to form HCHO while inhibiting competing reactions, thus resulting in ultra-highly selective HCHO production (nearly 100%) with a time yield of 2.75 mmol gcat-1 h-1. This work highlights the potential of rationally designing reaction sites to manipulate reaction pathways and achieve selective CH4 photo-oxidation, and could guide the further design of high-performance single-atom catalysts to meet future demand.

Needle growth of Nb2O5 nanoparticles on BiOCl nanosheets to fabricate S-scheme heterojunction with oxygen vacancies for enhanced photooxidation of cyclohexane

The exploration of cost-efficient, environmentally friendly, and high-efficacy photocatalysts for the enhanced selective photooxidation of cyclohexane to KA oil (cyclohexanone (CHA-one) and cyclohexanol (CHA-ol)) is a pivotal challenge in the industrial realm. Herein, the present study focuses on the synthesis of needle-like S-scheme heterojunction photocatalysts with oxygen vacancies, which are achieved by the needle growth integration of nano-sized Nb2O5 particles onto the BiOCl nanosheets. Remarkably, the 40 % Nb2O5/BiOCl composites exhibited superior performance in the solvent-free photooxidation of cyclohexane at room-temperature and under atmospheric pressure. The production yield of KA oil was 180.3 μmol (CHA-one/CHA-ol molar ratio = 3.5), and exceptional selectivity towards KA oil, reaching up to 99.3 %. The enhanced photocatalytic efficiency in cyclohexane oxidation can be attributed to the unique S-scheme heterogeneous interfaces with specific nanoneedle morphology, which result in the enhanced photonic absorption, effective charge carrier separation, a high density of oxygen vacancies, and the exposure of the highly reactive (001) plane of BiOCl. The excellent interfacial charge separation and transfer pathways of S-scheme heterojunction are disclosed by the in-depth EPR analysis and DFT calculations. These insights highlight the significant potential of the needle-like Bi-based S-scheme heterojunction photocatalysts for the efficient photooxidation of saturated alkanes.

Zr‐MOF Nanosheets Featuring Benzothiadiazoles Enable Efficient Visible Light Driven Photooxidation of Sulfides and Amines

AbstractUltrathin zirconium‐based metal−organic framework (MOF) nanosheets, embedded with photochromic units, are expected to be highly efficient heterogeneous photocatalysts, thanks to their rich catalytic sites, short diffusion paths, and effective separation of photogenerated charge carriers. Herein, we reported the synthesis of novel Zr‐MOF nanosheets (Zr‐BTDB) through a solvothermal synthesis that integrates benzothiadiazole (BTz) as a photochromic moiety within the framework of MOF. The Zr‐BTDB nanosheets processes a [Zr12(μ3‐O)8(μ3‐OH)8(μ2‐OH)6] cluster with hcp topology. Importantly, Zr‐BTDB nanosheets exhibit excellent photocatalytic activity for the photooxidation of sulfides and amines at room temperature under blue light irradiation. Notably, these nanosheets maintain their photocatalytic activity and selectivity for up to five cycles without significant loss of activity and crystallinity. Systematical catalytic reactions revealed that the Zr‐BTDB nanosheets enable the generation of singlet oxygen (1O2) and superoxide radical (O2⋅−) under visible light irradiation, which is critical reactive oxygen species for the photooxidation of sulfides and benzylamines. Our work represents a straightforward route for the preparation of ultrathin, water stable, and visible‐light‐activated Zr‐MOF nanosheets, offering new potentials for the selective photooxidation of sulfides and amines in an eco‐friendly way.

Harnessing a Pd4 Water-Soluble Molecular Capsule as a Size-Selective Catalyst for Targeted Oxidation of Alkyl Aromatics.

Molecular hosts with functional cavities can emulate enzymatic behavior through selective encapsulation of substrates, resulting in high chemo-, regio-, and stereoselective product formation. It is still challenging to synthesize enzyme-mimicking hosts that exhibit a narrow substrate scope that relies upon the recognition of substrates based on the molecular size. Herein, we introduce a Pd4 self-assembled water-soluble molecular capsule [M 4 L 2] (MC) that was formed through the self-assembly of a ligand L (4',4‴'-(1,4-phenylene)bis(1',4'-dihydro-[4,2':6',4″-terpyridine]-3',5'-dicarbonitrile)) with the acceptor cis-[(en)Pd(NO3)2] [en = ethane-1,2-diamine] (M). The molecular capsule MC showed size-selective recognition towards xylene isomers. The redox property of MC was explored for efficient and selective oxidation of one of the alkyl groups of m-xylene and p-xylene to their corresponding toluic acids using molecular O2 as an oxidant upon photoirradiation. Employing host-guest chemistry, we demonstrate the homogeneous catalysis of alkyl aromatics to the corresponding monocarboxylic acids in water under mild conditions. Despite homogeneous catalysis, the products were separated from the reaction mixtures by simple filtration/extraction, and the catalyst was reused. The larger analogues of the alkyl aromatics failed to bind within the MC's hydrophobic cavity, resulting in a lower/negligible reaction outcome. The present study represents a facile approach for selective photo-oxidation of xylene isomers to their corresponding toluic acids in an aqueous medium under mild conditions.

Interface-regulated S-type core–shell PCN-224@TiO2 heterojunction for visible-light-driven generation of singlet oxygen for selective photooxidation of 2-chloroethyl ethyl sulfide

Selective oxidation of sulfur mustard gas (HD) to non-toxic sulfoxide by the visible-light-catalyzed generation of singlet oxygen (1O2) is a promising degradation strategy. Although PCN-224 can absorb visible light, it suffers from rapid electron-hole recombination and low redox capacity, which limits the performance of HD degradation. Titanium dioxide (TiO2) is an excellent photocatalyst but it lacks visible-light-activity in degrading HD. In this study, PCN-224@TiO2 heterojunction with S-type core–shell structure was synthesized by in-situ growth method to prolong the visible light absorption capacity of TiO2 and inhibit the rapid recombination of PCN-224. The interface formation and internal electric field were optimized by adjusting the Zr/Ti ratio to enhance the charge transfer, redox capacity, electron-hole separation, and visible light absorption. In this study, the formation of heterojunction composites based on Zr-O-Ti linkages is demonstrated by a series of characterization methods. It is demonstrated by experiments and theoretical calculations that PCN-224@TiO2 can generate nearly 100 % 1O2 under visible light conditions without a sacrificial agent, resulting in efficient and selective oxidation of 2-chloroethyl ethyl sulfide (CEES), a simulant of HD, to non-toxic sulfoxide form.

Visible light promoted aerobic selective photo-oxidation of cyclohexene on LaCoxCu1−xO3 catalyst

Visible light promoted aerobic selective photo-oxidation of cyclohexene on LaCoxCu1−xO3 catalyst

Highly selective oxidation of biomass-derived alcohols and aromatic alcohols to aldehydes over Ti3C2-TiO2 nanocomposites under visible light

Ti3C2Tx is a two-dimensional (2D) material belonging to the MXenes family. It has a unique combination of functional features that make it appropriate for a wide range of fascinating applications, including supercapacitors, batteries, strain sensors, photocatalysis, and more. In this study, we report a synthesis of Ti3C2-TiO2 nanocomposites with tight interfacial contact that has been successfully fabricated by in situ development of TiO2 nanoparticles (NPs) on the surface of Ti3C2Tx nanosheets (NSs) via a simple and cost-effective hydrothermal process. The catalysts are well characterized by various sophisticated techniques, including X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), Brunauer-Emmett-Teller (BET), CHI660E electrochemical workstation, and HRTEM. The photocatalytic performance of pure Ti3C2Tx, Ti3C2-TiO2 (MT1), and Ti3C2-TiO2 (MT5) nanocomposites was evaluated by highly selective photo-oxidation of biomass-derived furfuryl alcohol (FA), cinnamyl alcohol, vanillin alcohol, and various aromatic alcohols to the corresponding aldehyde with >99% selectivity for all the alcohol substrates under visible light (385–740 nm). Photocatalytic oxidation results revealed that Ti3C2-TiO2 (MT5) has superior photocatalytic activity than Ti3C2-TiO2 (MT1) and pure Ti3C2Tx NSs. The exceptional photocatalytic activity was attributed to the composite's unique morphology and characteristics.

Highly Selective Photooxidation of Benzyl Alcohol to Benzaldehyde by Bi–Mo/g-C3N4 in Aqueous Solution

Highly Selective Photooxidation of Benzyl Alcohol to Benzaldehyde by Bi–Mo/g-C₃N₄ in Aqueous Solution

G-C3N4 nanosheets coupled with CoSe2 as co-catalyst for efficient photooxidation of xylose to xylonic acid

Photocatalysis has emerged as an effective approach to sustainably convert biomass into value-added products. CoSe2 is a promising non-precious, efficient cocatalyst for photooxidation, which can facilitate the separation of photogenerated electron–holes, increase the reaction rates, and enhance photocatalytic efficiency. In this work, we synthesized a stable and efficient photocatalysis system of CoSe2/g-C3N4 through attaching CoSe2 on g-C3N4 sheets, with a yield of 50.12% for the selective photooxidation of xylose to xylonic acid. Under light illumination, the photogenerated electrons were prone to migrating from g-C3N4 to CoSe2 due to the higher work function of CoSe2, resulting in the accelerated separation of photogenerated electron–holes and the promoted photooxidation. Herein, this study reveals the unique function of CoSe2, which can significantly promote oxygen adsorption, work as an electron sink and accelerate the generation of ·O2−, thereby improving the selectivity toward xylonic acid over other by-products. This work provides useful insights into the design of selective photocatalysts by engineering g-C3N4 for biomass high-value utilization.

A Photosensitive Cationic Macrocycle Based on Triphenylamine as Photocatalysts for Selective Photooxidation of Phosphines, Styrenes, and Hydroazobenzenes

A Photosensitive Cationic Macrocycle Based on Triphenylamine as Photocatalysts for Selective Photooxidation of Phosphines, Styrenes, and Hydroazobenzenes

Benzothiadiazole-functionalized Zr-MOF nanosheets enable visible-light mediated photocatalytic oxidation of sulfides in water

Ultrathin metal-organic frameworks (MOFs) nanosheets incorporating photochromic units are highly efficient heterogeneous photocatalysts, thanks to their highly exposed catalytic sites, short diffusion pathways, and efficient separation of photo-generated carriers. Herein, we report on the solvothermal synthesis of photoactive benzothiadiazole (BTz) functionalized Zr-MOF nanosheets (Zr-BTDB-NS), which are constructed from Zr12 nodes linked by nine BTDB2− (BTDB = 4,4′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzoate) ligands. The Zr-BTDB-NS exhibited superior photocatalytic activity towards the aerobic oxidation of a broad range of sulfides to their corresponding sulfoxides under visible light irradiation in water at room temperature, even in a gram-scale. The Zr-BTDB-NS can be efficiently recycled and reused for seven cycles without a decrease in conversion or selectivity. Detailed mechanism studies revealed that the Zr-BTDB-NS generates singlet oxygen (1O2) and superoxide radical (O2–) reactive oxygen species under visible light irradiation, which are responsible for the oxidation of sulfides into their corresponding sulfoxides. The simplicity of the synthetic approach as well as the diversity of photoactive organic units hold great promise for designing ultrathin, water-stable, and photoactive Zr-MOF nanosheets. This work will also be of added value for selective photooxidation of sulfides under green and mild conditions.

Guest-Regulated Generation of Reactive Oxygen Species from Porphyrin-Based Multicomponent Metallacages for Selective Photocatalysis.

The development of novel materials for highly efficient and selective photocatalysis is crucial for their practical applications. Herein, we employ the host-guest chemistry of porphyrin-based metallacages to regulate the generation of reactive oxygen species and further use them for the selective photocatalytic oxidation of benzyl alcohols. Upon irradiation, the sole metallacage (6) can generate singlet oxygen (1O2) effectively via excited energy transfer, while its complex with C70 (6⊃C70) opens a pathway for electron transfer to promote the formation of superoxide anion (O2⋅-), producing both 1O2 and O2⋅-. The addition of 4,4'-bipyridine (BPY) to complex 6⊃C70 forms a more stable complex (6⊃BPY) via the coordination of the Zn-porphyrin faces of 6 and BPY, which drives fullerenes out of the cavities and restores the ability of 1O2 generation. Therefore, benzyl alcohols are oxidized into benzyl aldehydes upon irradiation in the presence of 6 or 6⊃BPY, while they are oxidized into benzoic acids when 6⊃C70 is employed as the photosensitizing agent. This study demonstrates a highly efficient strategy that utilizes the host-guest chemistry of metallacages to regulate the generation of reactive oxygen species for selective photooxidation reactions, which could promote the utilization of metallacages and their related host-guest complexes for photocatalytic applications.

Guest‐Regulated Generation of Reactive Oxygen Species from Porphyrin‐Based Multicomponent Metallacages for Selective Photocatalysis

AbstractThe development of novel materials for highly efficient and selective photocatalysis is crucial for their practical applications. Herein, we employ the host‐guest chemistry of porphyrin‐based metallacages to regulate the generation of reactive oxygen species and further use them for the selective photocatalytic oxidation of benzyl alcohols. Upon irradiation, the sole metallacage (6) can generate singlet oxygen (1O2) effectively via excited energy transfer, while its complex with C70 (6⊃C70) opens a pathway for electron transfer to promote the formation of superoxide anion (O2⋅−), producing both 1O2 and O2⋅−. The addition of 4,4′‐bipyridine (BPY) to complex 6⊃C70 forms a more stable complex (6⊃BPY) via the coordination of the Zn‐porphyrin faces of 6 and BPY, which drives fullerenes out of the cavities and restores the ability of 1O2 generation. Therefore, benzyl alcohols are oxidized into benzyl aldehydes upon irradiation in the presence of 6 or 6⊃BPY, while they are oxidized into benzoic acids when 6⊃C70 is employed as the photosensitizing agent. This study demonstrates a highly efficient strategy that utilizes the host‐guest chemistry of metallacages to regulate the generation of reactive oxygen species for selective photooxidation reactions, which could promote the utilization of metallacages and their related host‐guest complexes for photocatalytic applications.

A water-soluble type II photosensitizer for selective photooxidation reactions of hydroazaobenzenes, olefins, and hydrosilanes in water

A water-soluble type II photosensitizer with excellent water solubility was utilized for selective photooxidation reactions of hydroazaobenzenes, olefins, and hydrosilanes in water.

Customizing the synergy of reactive oxygen species and photoactive charges on Bi2O2CO3/ZnIn2S4 for the selective photooxidation transformation of 5-hydroxymethylfurfural

Customizing the synergy of reactive oxygen species and photoactive charges on Bi2O2CO3/ZnIn2S4 for the selective photooxidation transformation of 5-hydroxymethylfurfural

Photocatalytic activity of colloidal Bi–Si-based nanoparticles prepared by laser synthesis in liquid

A combination of laser ablation and laser irradiation by focused laser beam in liquid is used to prepare the Bi- and Si-based nanocolloids in water in a Bi:Si molar ratio of 12:1. The composition, structure, morphology, and optical properties of the obtained nanostructures are studied. The synthesized composite nanostructures are shown to consist mainly of bismuth oxycarbonate Bi2(CO3)O2 and bismuth silicate Bi12SiO20. The materials are tested in the decomposition of the model dye rhodamine B, including the stability of the catalyst and the opportunity of its regeneration by laser irradiation as well as in phenol decomposition when excited by LED with a wavelength of 375 nm. The opportunity to use the Bi–Si-based colloidal nanostructures for the selective photooxidation of 5-(hydroxymethyl)furfural is considered.

Partial Thermal Condensation Mediated Synthesis of High-Density Nickel Single Atom Sites on Carbon Nitride for Selective Photooxidation of Methane into Methanol.

Direct selective transformation of greenhouse methane (CH4) to liquid oxygenates (methanol) can substitute energy-intensive two-step (reforming/Fischer-Tropsch) synthesis while creating environmental benefits. The development of inexpensive, selective, and robust catalysts that enable room temperature conversion will decide the future of this technology. Single-atom catalysts (SACs) with isolated active centers embedded in support have displayed significant promises in catalysis to drive challenging reactions. Herein, high-density Ni single atoms are developed and stabilized on carbon nitride (NiCN) via thermal condensation of preorganized Ni-coordinated melem units. The physicochemical characterization of NiCN with various analytical techniques including HAADF-STEM and X-ray absorption fine structure (XAFS) validate the successful formation of Ni single atoms coordinated to the heptazine-constituted CN network. The presence of uniform catalytic sites improved visible absorption and carrier separation in densely populated NiCN SAC resulting in 100% selective photoconversion of (CH4) to methanol using H2O2 as an oxidant. The superior catalytic activity can be attributed to the generation of high oxidation (NiIII═O) sites and selective C─H bond cleavage to generate •CH3 radicals on Ni centers, which can combine with •OH radicals to generate CH3OH.

In-plane implanting carbon rings into carbon nitride to intrigue nonradical photodegradation

Photocatalysis has emerged as a prevailing and clean technology for water purification. In this work, we developed a facile approach for fabricating in-plane carbon/carbon nitride heterojunctions (CN-PDs) that induced 100 % photodegradation of naproxen under visible light irradiation in a nonradical manner. Experimental and simulation results collectively revealed that the incorporated carbon rings in carbon nitride (CN) significantly accelerate the charge dynamics of excitons, leading to a higher concentration of hot carriers. In addition, a lower intersystem crossing energy barrier was observed for the unique nanostructure compared to pristine CN, enabling an efficient energy-transfer-mediated oxygen activation to selectively generate singlet oxygen. An optimized composition of carbon rings (CN-PDs0.1) enhanced the photodegradation of naproxen compared to CN. This study established the structure-activity relationships in selective photooxidation. The findings will benefit advanced design of high-performance nonmetal photocatalysts for organic wastewater treatment.