Heterogeneous Photocatalysts Research Articles

SrNiO3 perovskite/CeO2 composites as heterogeneous photocatalysts for the 2-propanol oxidation in gas–solid regime

Both SrNiO3 perovskite and CeO2 are materials suitable for photocatalytic purposes. In this work, the preparation and physicochemical characterization of bare SrNiO3 and CeO2 along with composites where CeO2 was enriched with the perovskite from 15 to 70 % in mass of SrNiO3 in the composite are described. The materials have been used for the photocatalytic oxidation of 2-propanol in gas–solid regime in the presence of UV-LED or simulated solar irradiation. The solids were characterized by XRD, SEM/EDX, N2 adsorption/desorption and FTIR and UV–Vis diffuse reflectance spectroscopies. The composite containing 15 % w/w of SrNiO3 and 85 % w/w of CeO2 resulted the most active, giving rise the complete degradation of 2-propanol after 1.5 h or 6.0 h of irradiation by UV-LED and simulated solar light irradiation, respectively. Photocatalytic activity results are discussed considering the physical–chemical properties on the catalysts.

High photocatalytic activity of g-C3N4/CdZnS/MoS2 heterojunction for hydrogen production

In an effort to improve the light absorption efficiency of the photocatalyst, g-C3N4 nanosheets with visible light response have been prepared by roasting method, and the g-C3N4/CdZnS composite catalyst with 2D/0D architecture has been prepared by hydrothermal method after ultrasonic thinning. The g-C3N4/CdZnS/MoS2 composite catalyst with 2D/0D architecture has been synthesized by secondary hydrothermal method. TEM analysis proves that a close heterogeneous interface has been formed between g-C3N4 and CdZnS, and between CdZnS and MoS2. The ultraviolet diffuse reflectance spectrum shows that MoS2 has a wide light absorption range, which effectively enhances the light utilization ratio of the composite catalyst. The energy band structure diagram and photoelectrochemical test results show that a continuous stepped type II ternary heterojunction is formed among g-C3N4, CdZnS and MoS2, which promotes its separation of photogenerated charges. When the loading mass fraction of g-C3N4 and MoS2 is 4%, the hydrogen evolution rate of g-C3N4/CdZnS/MoS2 composite catalyst is 57.02 mmol g−1 h−1 under visible light, which is exceeding 20% that of g-C3N4/CdZnS and 4.79 times and 44.9 times higher than that of CdZnS and g-C3N4, respectively. The two-dimensional structure of g-C3N4 and MoS2 significantly improves the stability of the composite catalyst. This work offers feasible ways for ternary heterogeneous photocatalyst construction.

Linkage Conversion in Covalent Organic Frameworks: An Efficient Strategy to Promote Photocatalytic Organic Transformations

AbstractCovalent organic frameworks (COFs) are emerging as promising heterogeneous photocatalysts for organic transformations, owing to their fascinating optical properties, excellent recyclability, and customizable chemical structures. To maximize the photocatalytic activity of COFs, various strategies have been explored, including metal complexation, construction of donor‐acceptor structures, modification of functional groups, hybridization with inorganic semiconductors, and linkage conversion. Among these, linkage conversion has proved to be particularly effective, driving the production of numerous value‐added organic chemicals. In this concept article, we present a comprehensive overview of the latest advancements in linkage conversion and highlight the most enlightening examples that have adopted such a strategy to boost the photocatalytic capabilities of COFs for organic transformations. It is anticipated that this concept will assist researchers in designing novel COFs with multifunctional linkages, paving the way towards their broader application in organic synthesis.

Advancements in heterogeneous photocatalysts: from classical semiconductors to cutting-edge S-scheme systems

Advancements in heterogeneous photocatalysts: from classical semiconductors to cutting-edge S-scheme systems

Precisely constructed core-shell organic/inorganic heterojunction for heightened photoreduction of Cr(VI): Synergy of reinforced interface interaction and high-speed carrier transfer

Photocatalysis technology has been widely studied for treating Cr(VI) pollution in water and constructing heterogeneous structures presents a compelling approach to enhance the efficiency of Cr(VI) treatment. Pitifully, solely utilizing heterostructure, especially random composites of heterogeneous photocatalysts, often falls short of effectively enhancing the separation efficiency of photogenerated carriers. Furthermore, most photocatalysts interact weakly with the Cr(VI) anions, greatly reducing the utilization efficiency of photogenerated carriers. Herein, pyridine-based conjugated imprinted polymer (CIP) photocatalyst was precisely coated on urchin-like TiO2 using an in-situ condensation approach, forming a compact core–shell structure of organic/inorganic heterojunction. On the one hand, the compact heterojunction structure of the core–shell effectively improved the separation efficiency of photogenerated carriers. On the other hand, CIP enhanced the adsorption between the photocatalyst and Cr(VI), effectively improving the utilization efficiency of photogenerated carriers. Due to the collaborative effects of selective adsorption and core–shell heterojunction photocatalysis, the photocatalyst demonstrated remarkable performance in eliminating Cr(VI). For high concentration Cr(VI) pollution of 100 ppm, complete elimination could be achieved within 90 min. This research presented an innovative and efficient approach for the precise synthesis of photocatalysts.

Heteroepitaxial MOF-on-MOF Photocatalyst for Solar-Driven Water Splitting.

Assembly of different metal-organic frameworks (MOFs) into hybrid MOF-on-MOF heterostructures has been established as a promising approach to develop synergistic performances for a variety of applications. Here, we explore the performance of a MOF-on-MOF heterostructure by epitaxial growth of MIL-88B(Fe) onto UiO-66(Zr)-NH2 nanoparticles. The face-selective design and appropriate energy band structure alignment of the selected MOF constituents have permitted its application as an active heterogeneous photocatalyst for solar-driven water splitting. The composite achieves apparent quantum yields for photocatalytic overall water splitting at 400 and 450 nm of about 0.9%, values that compare much favorably with previous analogous reports. Understanding of this high activity has been gained by spectroscopic and electrochemical characterization together with scanning transmission and transmission electron microscopy (STEM, TEM) measurements. This study exemplifies the possibility of developing a MOF-on-MOF heterostructure that operates under a Z-scheme mechanism and exhibits outstanding activity toward photocatalytic water splitting under solar light.

Selective Photocatalytic Oxidation of Thioethers to Sulfoxides Mediated by a Carbon Nanotube‐Porphyrin Nanohybrid

AbstractA heterogeneous photocatalyst was assembled through electrostatic immobilization of a cationic porphyrin at the surface of functionalized carbon nanotubes. The supra‐molecular nanohybrid catalyst was valorized in the aerobic photo‐oxidation of sulfides to the corresponding sulfoxides. The process operated selectively under visible light, with low catalytic loading, in water as the solvent, and the catalyst was readily recycled and reused.

Substituent Modulated Electronic Properties of Cu(I) Active Site in Metal–Organic Halides for Boosting Hydrogen Evolution Reaction†

Comprehensive SummaryDevelopment of heterogeneous molecular photocatalysts for promising light‐driven hydrogen evolution reaction (HER) is highly demanding but still challenging. Here, we report the blue‐greenish emitting dinuclear metal–organic halides as photocatalyst by incorporating site‐specific single copper(I) atoms that exhibit an efficient carbon‐negative H2 production. Interestingly, the electronic properties, including the spin and charge density of central Cu(I) active site, can be triggered by substituent modulation in metal–organic halides, which greatly affect the exciton dissociation kinetics and thus the HER reactivity. The optimized spin density in these heterogeneous photocatalysts drastically boosts the hydrogen production rate from 1250 to 3130 μmol·g–1·h–1. Our molecular strategy provides a platform that rationally facilitates electronic modulation of copper(I) atoms, tunes the macroscopic optoelectronic properties of photocatalysts and boosts carbon‐negative HER activity, extending the boundaries of conventional molecular‐based photocatalysts.

Earth-Abundant Recyclable Magnetic Iron Oxide Nanoparticles for Green-light Mediated C-H Arylation in Heterogeneous Phase.

A magnetically isolable iron oxide nanoparticles is introduced as an efficient heterogeneous photocatalyst for non-directed C-H arylation employing aryl diazonium salts as the aryl precursors. This first-row transition metal-based photocatalyst revealed versatile activities and is applicable to a wide range of substrates, demonstrating brilliant efficacy and superior recyclability. Detailed catalytic characterization describes the physical properties and redox behavior of the Fe-catalyst. Adequate control experiments helped to establish the radical-based mechanism for the C-H arylation.

Photocatalytic degradation of antibiotics by N-doped carbon nanoflakes-nickel ferrite composite derived from algal biomass

This work reports the synthesis of nickel ferrite (NiFe) nanoparticles, N-doped mesoporous carbon nanoflakes (NCF) and novel nickel ferrite-carbon nanoflakes (NiFe@NCF) nanocomposite using solvothermal method. NCF was derived from a cyanobacterial consortium consisting of Anabaena, Lyngbya and Weistiellopsis, rich in carbon and nitrogen. The synthesized nanoparticles were used as heterogeneous photocatalyst for degradation of two harmful water pollutants, ciprofloxacin (CIP) and levofloxacin (LEV). 99.91% LEV and 98.86% CIP were degraded within 50 and 70 min of visible light irradiation using NiFe@NCF following pseudo first order kinetics. This improved efficiency of the nanocomposite may be attributed to its higher surface area, reduction of band gap (from 2.42 to 2.19 eV), more active sites as well as charge carrier mobility with decreasing agglomeration tendency of the magnetic nickel nanoparticles upon being embedded on NCF. N-doping improves light harvesting property, retards charge recombination and extends as well as delocalises ᴨ-conjugated system resulting in enhanced photocatalytic activity. The scavenging experiments and EPR analysis reveal that O2−• and •OH are the main active species taking part in the degradation process. The material performs well within a wide range of pH and can be effectively used up to 5 repetitive cycles. A feasible photocatalytic degradation mechanism of the antibiotics against NiFe@NCF nanocomposite is also put forwarded along with their possible degradation pathways from LCMS studies.

NPh3-Mediated WO3-Photocatalyzed Semiheterogeneous Hydroxylation of Aryl and Alkyl Boronic Acids.

With an inexpensive and commercially available WO3 semiconductor as the heterogeneous photocatalyst, a catalytic amount of NPh3 as the single-electron donor, and ambient air as the single-electron acceptor and oxygen source, the semiheterogeneous photocatalytic hydroxylation of alkyl and aryl boronic acids was developed. A broad range of hydroxylated compounds can be obtained in excellent yields.

Zr‐MOF nanosheets featuring benzothiadiazoles enable efficient visible light driven photooxidation of sulfides and amines

Ultrathin 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.

Porous Organic Polymers (POPs) Based on Acridone as Heterogeneous Photocatalysts for Oxidative Dimerization and Cyclocondensation Reactions

AbstractPorous organic polymers (POPs) are emergent tailor‐made materials, which can be accessed by covalent polymerization of diligently designed molecular building blocks in a bottom‐up fashion. Acridone, a well‐known chromophore that undergoes intersystem crossing (ISC) with near‐unity quantum yield akin to benzophenone, was structurally elaborated into a building block and subjected to Friedel‐Crafts polyalkylation to afford a series of POPs, namely, Ac‐MePOP, Ac‐OMePOP, and Ac‐CBPOP. These POPs exhibit remarkable porosity and significant absorption in the visible region. Of the three polymers, Ac‐CBPOP with the highest BET surface area of ca. 1027 m2/g is shown to serve as an excellent heterogeneous photocatalyst for visible light‐mediated oxidative transformations, that is, oxidative coupling of benzylamines to imines and cyclocondensation of o‐phenylenediamines with aldehydes to benzimidazoles under oxygen atmosphere. It is further shown that Ac‐CBPOP can be reused for several reaction cycles without any loss of catalytic activity with its stability intact. Mechanistic studies show that 1O2 serves as the key reactive oxygen species, formed by the energy transfer from Ac‐CBPOP to 3O2, in the photocatalytic oxidation reactions. The results demonstrate the development of stable photocatalytic POP materials with tailor‐made properties by a bottom‐up covalent polymerization of programmed molecular building blocks.

In-situ exploration of divergent methane coupling pathways in dry and aqueous environments on silver and palladium heteropolyacid-titania photocatalysts

Methane, abundant but inert, contributes significantly to greenhouse gases, primarily through combustion, which emits vast amounts of CO2. Photocatalytic methane coupling at ambient temperature offers a method to convert it into ethane, a more versatile hydrocarbon. This study examines selective methane-to-ethane coupling using heterogeneous photocatalysts comprising silver and palladium salts dispersed on titania. Through a combination of ex-situ and in-situ techniques along with DFT simulations, distinct mechanisms and active phases in these catalysts are revealed. In silver catalysts, dispersed cationic Ag+ species are crucial for methane activation, while in palladium catalysts, palladium primarily exists in metallic form during coupling. Water strongly enhances coupling rates with both catalysts. DFT modeling identified methane adsorption sites, suggesting methane activation via •OH radicals, experimentally supported by EPR under in-situ conditions.

Improving charge separation capability of CdS/Bi/Ti3C2Tx nanocomposites for efficient photocatalytic oxidative organic transformations

The development of new strategies to improve the separation of photogenerated carriers is crucial for enhancing photocatalytic efficiency of heterogeneous photocatalysts. Here, we have successfully constructed CdS/Bi/Ti3C2Tx nanocomposites with high electron-hole separation efficiency through coupling Bi and Ti3C2Tx on CdS nanorods. The average emission lifetime of the CdS/Bi/Ti3C2Tx nanocomposites can be up to ca. 6.74 ns, which realizes efficient heterogeneous photocatalysis for oxidative hydroxylation of arylboronic acids and coupling of amines with high yields. The photocatalytic rates are ∼15250 μmol·g−1·h−1 for 4-cyanophenol production and ∼12125 μmol·g−1·h−1 for (E)-N-benzyl-1-phenylmethanimine production, which are twice and three-fold higher than those (∼7500 and ∼4000 μmol·g−1·h−1) of the CdS nanorods, respectively. The high photocatalytic efficiency can be ascribed to the strong electron-hole separation capacity by migrating electrons into Bi and Ti3C2Tx from CdS nanorods. In addition, the CdS/Bi/Ti3C2Tx nanocomposites also have satisfactory sustainable recycling and reuse properties. This work provids a new strategy for constructing heterogeneous metal/semiconductor nanophotocatalysts with strong electron-hole separation capacity for high-efficient light-driven organic transformations.

Tailoring a decatungstate-incorporated metal-organic framework for light-driven [3+2] cyclization of phenols with olefins

Photocatalytic oxidative [3+2] cycloaddition of phenol-olefin is an economy and green strategy to synthesize 2,3-Dihydrobenzofurans (2,3-DHBs) compared with the thermal catalysis with noble metals under harsh conditions. Thus, it is urgent to design noble metal-free heterogeneous photocatalyst that combined single-electron transfer (SET) and hydrogen-atom transfer (HAT) dual function. Decatungstate [W10O32]4− is considered as an ecofriendly photocatalyst for HAT and SET, but it is commonly used in homogeneous catalysis. Herein, we report CuW10-TIPA as a white-light-activated heterogeneous photocatalyst for synthesizing 2,3-dihydrobenzofurans via [3+2] cycloaddition of phenols with olefins, a crucial step in relevant pharmaceutical structural motifs. The coordination bonds between Cu(I) and TIPA, strong H-bonds between TIPA and [W10O32]4− and anion∙∙∙π interactions between [W10O32]4− and TIPA dramatically promote the separation of photoinduced electron-hole and facilitate the charge transfer among each component. Our approach is characterized by its mildness, scalability, and recyclability. We delve into the discussion on [W10O32]4− anions-mediated C-H bond activation via the HAT pathway, with the cooperation of the photosensitizer TIPA and Cu(I), which enhances absorption in the visible region and narrows the energy band.

TEMPO/O2 Synergistically Mediated BiBrO-Photocatalyzed Decarboxylative Phosphorylation of N-Arylglycines.

With both TEMPO and O2 (in air) as the homogeneous redox mediators, BiBrO as the heterogeneous semiconductor photocatalyst, the first example of semi-heterogeneous photocatalytic decarboxylative phosphorylation of N-arylglycines with diarylphosphine oxides was established. A series of α-amino phosphinoxides were efficiently synthesized.

Toward Functionality and Deactivation of Metal-Single-Atom in Heterogeneous Photocatalysts.

Single-atom heterogeneous catalysts (SAHCs) provide an enticing platform for understanding catalyst structure-property-performance relationships. The 100% atom utilization and adjustable local coordination configurations make it easy to probe reaction mechanisms at the atomic level. However, the progressive deactivation of metal-single-atom (MSA) with high surface energy leads to frequent limitations on their commercial viability. This review focuses on the atomistic-sensitive reactivity and atomistic-progressive deactivation of MSA to provide a unifying framework for specific functionality and potential deactivation drivers of MSA, thereby bridging function, purpose-modification structure-performance insights with the atomistic-progressive deactivation for sustainable structure-property-performance accessibility. The dominant functionalization of atomically precise MSA acting on properties and reactivity encompassing precise photocatalytic reactions is first systematically explored. Afterward, a detailed analysis of various deactivation modes of MSA and strategies to enhance their durability is presented, providing valuable insights into the design of SAHCs with deactivation-resistant stability. Finally, the remaining challenges and future perspectives of SAHCs toward industrialization, anticipating shedding some light on the next stage of atom-economic chemical/energy transformations are presented.

Core-shell ZnO@FeNi-MOF/BC nanoreactor photocatalyzed efficient selective oxidation—Size exclusion effects and nonradical pathways domination

Modulating the catalytic activity of heterogeneous photocatalysts and simultaneously achieving selective and deep mineralization of refractory pollutants remains challenging. To solve this problem, we synthesized ZnO@FeNi-MOF/biomass waste-derived porous carbon (BC) nanoreactor and constructed a photocatalytic and peroxymonosulfate (PMS) activation synergistic tandem catalytic system. The core–shell structure of ZnO@FeNi-MOF leverages the size exclusion effects to enhance the selectivity towards micropollutants. Additionally, the constructed S-scheme heterogeneous interface serves as the reactive oxygen species generator. Highly porous and conductive BC serves as an excellent co-catalyst and a trap for pollutants. The nonradical pathway-dominated system further improves oxidative selectivity. We revealed typical antibiotics’ mineralization and detoxification pathways by experimental means and theoretical calculations. Furthermore, the long-term stable operation of the fixed bed continuous flow device shows high potential for engineering application. The research presents a viable approach for a tandem hybrid catalytic system that effectively and selectively eliminates organic contaminants.

From insoluble to processable: Aminic solvent dissolution of donor–acceptor conjugated network polymers for fabrication of photocatalytic thin film

Conjugated network polymers (CNPs) have gained considerable attention as heterogeneous photocatalysts, however, their limited solubility in solvents poses a significant challenge in employing CNPs for photoreactors. Herein, we report the chemical dissolution of CNPs in aminic solvents to enhance solution processability. The CNPs, synthesized via the Knoevenagel polycondensation, were dissolved into corresponding polymer inks, forming thin films on various substrates through mild heating. Residual functional groups on the CNP surface provided latent reactive sites for liquid amines, facilitating structural disentanglement and dissolution without hindering the π-conjugation. The resulting polymer films on FTO electrodes exhibited broader light absorbance and > 2-fold enhanced photoresponse compared to CNP powder films. Photocatalytic production of H2O2 using the large-area polymer film (254.4 cm2) demonstrated sustained activity with a production rate of 0.21 mM H2O2 h−1 over 14 h without sacrificial agents. These findings lay the groundwork for applying CNP photocatalysts in chemical, optical, and electronic applications.