Atomically isolated Sb(CN)3 on sp2-c-COFs with balanced hydrophilic and oleophilic sites for photocatalytic C-H activation

Activation of carbon-hydrogen (C-H) bonds is of utmost importance for the synthesis of vital molecules. Toward achieving efficient photocatalytic C-H activation, our investigation revealed that incorporating hydrophilic C≡N-Sb(CN)3 sites into hydrophobic sp2 carbon-conjugated covalent organic frameworks (sp2-c-COFs) had a dual effect: It simultaneously enhanced charge separation and improved generation of polar reactive oxygen species. Detailed spectroscopy measurements and simulations showed that C≡N-Sb(CN)3 primarily functioned as water capture sites, which were not directly involved in photocatalysis. However, the potent interaction between water molecules and the Sb(CN)3-modified framework notably enhanced charge dynamics in hydrophobic sp2-c-COFs. The reactive species ·O2- and ·OH (ad) subsequently combined with benzyl radical, leading to the formation of benzaldehyde, benzyl alcohol, and lastly benzyl benzoate. Notably, the Sb(CN)3-modified sp2-c-COFs exhibited a 54-fold improvement in reaction rate as compared to pristine sp2-c-COFs, which achieved a remarkable 68% conversion rate for toluene and an 80% selectivity for benzyl benzoate.

Achieving High Selectivity in Photocatalytic Oxidation of Toluene on Amorphous BiOCl Nanosheets Coupled with TiO2

The inert C(sp³)-H bond and easy overoxidation of toluene make the selective oxidation of toluene to benzaldehyde a great challenge. Herein, we present that a photocatalyst, constructed with a small amount (1 mol %) of amorphous BiOCl nanosheets assembled on TiO₂ (denoted as 0.01BOC/TiO₂), shows excellent performance in toluene oxidation to benzaldehyde, with 85% selectivity at 10% conversion, and the benzaldehyde formation rate is up to 1.7 mmol g^-1 h^-1, which is 5.6 and 3.7 times that of bare TiO₂ and BOC, respectively. In addition to the charge separation function of the BOC/TiO₂ heterojunction, we found that the amorphous structure of BOC endows its abundant surface oxygen vacancies (Ov), which can further promote the charge separation. Most importantly, the surface Ov of amorphous BOC can efficiently adsorb and activate O₂, and amorphous BOC makes the product, benzaldehyde, easily desorb from the catalyst surface, which alleviates the further oxidation of benzaldehyde, and results in the high selectivity. This work highlights the importance of the microstructure based on heterojunctions, which is conducive to the rational design of photocatalysts with high performance in organic synthesis.

Temperature, Doping, and Chemical Potential Tuning Intrinsic Defects Concentration in Bi2MoO6: GGA + U Method

Using the GGA + U method, the formation energy and concentration of intrinsic defects in Bi₂MoO₆ are explored under different chemical conditions, with/without doping, from 120 to 900 K. We find that the intrinsic defect and carrier concentration can be deduced from the small range of calculated Fermi levels in the diagram of formation energy vs Fermi level under different conditions. Once the doping conditions or/and temperature are determined, the corresponding E_F is only limited to a special region in the diagram of formation energy vs Fermi level, from which the magnitude relationship of defects concentration can be directly derived from their formation energy. The lower the defect formation energy is, the higher the defect concentration is. With E_F moving under different doping conditions, the intrinsic defect concentration changes accordingly. At the same time, the highest electron concentration at the relative O-poor (point H_U) with only intrinsic defects confirms its intrinsic n-type behavior. Moreover, upon A^-/D⁺ doping, E_F moves closer to VBM/CBM for the increasing concentration of holes/electrons. The electron concentration can also be further improved after D⁺ doping, indicating that D⁺ doping under O-poor chemical growth conditions is positive to improve its photogenerated carriers. This provides us with a method to adjust the intrinsic defect concentration and deepens our knowledge about comprehension and application of the diagram of formation energy vs Fermi level.

Recognition of Water-Induced Double-Edged Sword Effects in Photocatalytic Selective Oxidation of Toluene on Titanium Dioxide Clusters with Density Functional Theory Calculations

Recently, water promotion effects in the selective oxidation of benzyl alcohol to benzaldehyde have been experimentally recognized and identified. However, the effects of water on the photocatalytic selective oxidation of toluene into benzaldehyde remain elusive. In this work, the Ti₃O₉H₆ clusters in different solvents (water and toluene solvent) are used to study the water-induced effects in photocatalytic oxidation reactions in kinetics and thermodynamics using density functional theory (DFT) calculations. In addition, the influences of the OH groups on catalysts (Ti-OH bonds) from photocatalytic water splitting are also considered. The results clearly demonstrate the water-induced double-edged sword effects in the photocatalytic selective oxidation of toluene. We expect that our work can not only shed light on the mechanisms of photocatalytic selective oxidation of toluene into benzaldehyde and other activation reactions of sp³ C-H bonds but also design and modulate highly efficient photocatalysts.

Superoxide anion and singlet oxygen dominated faster photocatalytic elimination of nitric oxide over defective bismuth molybdates heterojunctions

Establishing an ideal photocatalytic system with efficient reactive oxygen species (ROS) generation has been regarded as the linchpin for realizing efficient nitric oxide (NO) removal and unveiling the ROS-mediated mechanism. In this work, a novel oxygen-deficient 0D/1D Bi_3.64Mo_0.36O_6.55/Bi₂MoO₆ heterojunctions (BMO-12-H) were successfully synthesized under the enlightenment of clarified crystal growth mechanism of bismuth molybdates. Because of the synergies between defect-engineering and heterojunction-construction, BMO-12-H demonstrated improved photoelectrochemical properties and O₂ adsorption capacity, which in turn facilitated the ROS generation and conversion. The enhancement of •O₂^- and ¹O₂ endowed BMO-12-H with strengthened NO removal efficiency (59%) with a rate constant of 12.6*10^-2 min^-1. A conceivable NO removal mechanism dominated by •O₂^- and ¹O₂ was proposed and verified based on the theoretical calculations and in-situ infrared spectroscopy tests, where hazardous NO was oxidized following two different exothermic pathways: the •O₂^--induced NO → NO₃^- process and the ¹O₂-induced NO → NO₂ → NO₃^- process. This work offers a basic guideline for accelerating ROS generation by integrating defect-engineering and heterojunction-construction, and provides new insights into the mechanism of efficient NO removal dominated by •O₂^- and ¹O₂.

Bismuth chromate (Cr2Bi3O11): a new bismuth-based semiconductor with excellent photocatalytic activity

A novel bismuth chromate material (Cr₂Bi₃O₁₁) was synthesized by a direct mixing method with higher photocatalytic activity in both organic pollutant detoxification and oxygen evolution. Cr₂Bi₃O₁₁ with a band gap of 2.20 eV could be activated by photons with a wavelength below 561 nm. This work not only provides an approach for the controllable synthesis of Cr₂Bi₃O₁₁, but also experimentally and theoretically shows its excellence and potential when applied in photocatalysis.

Modulating oxygen vacancies on bismuth-molybdate hierarchical hollow microspheres for photocatalytic selective alcohol oxidation with hydrogen peroxide production

Photocatalytic selective oxidation of alcohols into high value-added carbonyl compounds accompanied by producing hydrogen peroxide (H₂O₂) is undoubtedly a more efficient solar energy conversion strategy with high atom economy. Herein, we have developed an efficient photocatalyst of bismuth-molybdate (Bi₂MoO₆) hierarchical hollow microspheres with tunable surface oxygen vacancies (OVs) for promoting the photocatalytic selective alcohol oxidation with H₂O₂ production. The effect of surface OVs on the photocatalytic efficiency is studied systematically by comparing the performance of different photocatalysts. The benzaldehyde and H₂O₂ production rates over the OV-rich Bi₂MoO₆ photocatalyst reach up to 1310 and 67.2 μmol g^-1 h^-1, respectively, which are 2.3 and 4.0 times those generated from the OV-poor Bi₂MoO₆ hollow microspheres. The roles of various active radicals in the photocatalytic reaction are probed by a series of controlled experiments and in situ ESR measurements, revealing that both superoxide radical (•O₂^-) and carbon-centered radical are the key active intermediates. The introduction of surface OVs on Bi₂MoO₆ hollow microspheres accelerates the separation and transfer of photo-generated charge carriers as well as enhances the adsorption and activation of reactant molecules, thereby greatly promoting the photocatalytic selective oxidation of alcohols along with H₂O₂ production. This work not only demonstrates a facile strategy for the preparation of high-efficiency photocatalysts by simultaneous modulations of morphology and surface defects, but also offers insight into developing the dual-functional photocatalytic reactions for the full utilizations of photoinduced electrons and holes.

Oxygen-deficient bismuth molybdate nanocatalysts: Synergistic effects in boosting photocatalytic oxidative coupling of benzylamine and mechanistic insight

Herein, bismuth molybdate (Bi₂MoO₆) nanocatalysts containing oxygen vacancies (OVs) are found to considerably promote the photocatalytic performance toward oxidative coupling of benzylamine to N-benzylidenebenzylamine under visible light irradiation. The structure-activity relationship for this interesting catalyst is revealed for the first time. The oxygen-deficient Bi₂MoO₆ nanoplatelets (BMO-NPs) are synthesized using ethylene glycol-ethanol solvent mixture as a reaction medium in solvothermal method. A comparison with hydrothermally prepared Bi₂MoO₆ square-like sheets (BMO-SHs) suggests that the nanoplatelets are much smaller in size and contain higher amount of OVs. Benzylamine conversion over the BMO-NPs is ca. 4.0 times higher than that over the BMO-SHs and ca. 3.8 and ca. 34.6 times higher than that over the commercial benchmark TiO₂ P25 and BiVO₄ catalysts, respectively. The BMO-NPs achieve more than 80% product yield within 2 h of irradiation regardless of substituents of benzylamine derivatives. The enhanced activity of BMO-NPs is due to synergistic roles of high surface-to-volume ratio and OVs, providing enlarged active area, extended light absorption range and improved charge separation and transfer efficiency as evidenced from UV-vis DRS, BET surface area, photocurrent response, electrochemical impedance spectroscopy, and time-resolved fluorescence decay measurements. EPR-trapping and radical scavenging experiments indicate O₂^- as a main active species rather than ¹O₂ and a plausible imine formation mechanism via O₂^--assisted charge transfer is proposed accordingly. The work offers an alternative facile preparation method to design efficient semiconductor photocatalysts and for the first time reveals a possible benzylamine coupling mechanism over the oxygen-deficient Bi₂MoO₆ nanocatalyst.

Recent Advances in Heterogeneous Photo-Driven Oxidation of Organic Molecules by Reactive Oxygen Species

The photo-driven oxidation of organic molecules into corresponding high-value-added products has become a promising method in chemical synthesis. This strategy can drive thermodynamically non-spontaneous reactions and achieve challenging thermocatalytic processes under ambient conditions. Reactive oxygen species (ROS) are not only significant intermediates for producing target products via photoinduced oxidation reactions but also contribute to the creation of sustainable chemical processes. Here, the latest advances in heterogeneous photo-driven oxidation reactions involving ROS are summarized. The major types of ROS and their generation are introduced, and the behaviors of various ROS involved in photo-driven processes are reviewed in terms of the formation of different bonds. Emphasis is placed on unraveling the reaction mechanisms of ROS and establishing strategies for their regulation, and the remaining challenges and perspectives are summarized and analyzed. This Review is expected to provide an in-depth understanding of the mechanisms of ROS involved in photo-driven oxidation processes as an important foundation for the design of efficient catalysts. Clarifying the role of ROS in oxidation reactions has important scientific significance for improving the atomic and energy efficiency of reactions in practical applications.

Preparation of Pt/γ-Bi2MoO6 Photocatalysts and Their Performance in α-Alkylation Reaction under Visible Light Irradiation

Bi(NO3)3·5H2O and (NH4)6Mo7O24·4H2O were used as precursors to synthesize flaky γ-Bi2MoO6 samples by a hydrothermal method, and Pt/γ-Bi2MoO6 samples with different mass fractions were prepared by an NaBH4 reduction method. Alpha alkylation of benzyl alcohol and acetophenone with photocatalysts under visible light irradiation was performed, and the activity of 4 wt % Pt/γ-Bi2MoO6 (γ-Bi2MoO6 was prepared by a nitric acid method, pH = 9, and reaction temperature 180 °C) was the best. The photocatalytic reaction conditions were optimized by changing various kinds of variables, such as the type of catalyst, solvent, and base, and the amount of base, catalyst, and reactant. The optimal conditions for the organic reaction were 75 mg 4 wt % Pt/γ-Bi2MoO6, 6 mL n-heptane, 1.2 mmol NaOH, 1 mmol acetophenone, and 3 mmol benzyl alcohol. Under the optimal reaction conditions, the effects of different light wavelengths and light intensities on the reaction were measured, and the cycling ability of the photocatalyst was tested. After five cycles, the photochemical properties of the catalyst were relatively stable. Finally, the active substances were identified (such as electrons (e-), holes (h+), hydroxyl radicals (•OH), and superoxide radicals (•O2-).

Structural-Phase Catalytic Redox Reactions in Energy and Environmental Applications

The structure-property engineering of phase-based materials for redox-reactive energy conversion and environmental decontamination nanosystems, which are crucial for achieving feasible and sustainable energy and environment treatment technology, is discussed. An exhaustive overview of redox reaction processes, including electrocatalysis, photocatalysis, and photoelectrocatalysis, is given. Through examples of applications of these redox reactions, how structural phase engineering (SPE) strategies can influence the catalytic activity, selectivity, and stability is constructively reviewed and discussed. As observed, to date, much progress has been made in SPE to improve catalytic redox reactions. However, a number of highly intriguing, unresolved issues remain to be discussed, including solar photon-to-exciton conversion efficiency, exciton dissociation into active reductive/oxidative electrons/holes, dual- and multiphase junctions, selective adsorption/desorption, performance stability, sustainability, etc. To conclude, key challenges and prospects with SPE-assisted redox reaction systems are highlighted, where further development for the advanced engineering of phase-based materials will accelerate the sustainable (active, reliable, and scalable) production of valuable chemicals and energy, as well as facilitate environmental treatment.

Modifications of heterogeneous photocatalysts for hydrocarbon C–H bond activation and selective conversion

This feature article summarizes the recent progress in the modification of heterogeneous photocatalysts for photocatalytic hydrocarbons’ C–H bond activation.

Modulation of Bi2 MoO6 -Based Materials for Photocatalytic Water Splitting and Environmental Application: a Critical Review

Highly active photocatalysts driving chemical reactions are of paramount importance toward renewable energy substitutes and environmental protection. As a fascinating Aurivillius phase material, Bi₂ MoO₆ has been the hotspot in photocatalytic applications due to its visible light absorption, nontoxicity, low cost, and high chemical durability. However, pure Bi₂ MoO₆ suffers from low efficiency in separating photogenerated carriers, small surface area, and poor quantum yield, resulting in low photocatalytic activity. Various strategies, such as morphology control, doping/defect-introduction, metal deposition, semiconductor combination, and surface modification with conjugative π structures, have been systematically explored to improve the photocatalytic activity of Bi₂ MoO₆ . To accelerate further developments of Bi₂ MoO₆ in the field of photocatalysis, this comprehensive Review endeavors to summarize recent research progress for the construction of highly efficient Bi₂ MoO₆ -based photocatalysts. Furthermore, benefiting from the enhanced photocatalytic activity of Bi₂ MoO₆ -based materials, various photocatalytic applications including water splitting, pollutant removal, and disinfection of bacteria, were introduced and critically reviewed. Finally, the current challenges and prospects of Bi₂ MoO₆ are pointed out. This comprehensive Review is expected to consolidate the existing fundamental theories of photocatalysis and pave a novel avenue to rationally design highly efficient Bi₂ MoO₆ -based photocatalysts for environmental pollution control and green energy development.

Catalytic Aerobic Oxidation of C(sp3 )-H Bonds

Oxidation reactions are a key technology to transform hydrocarbons from petroleum feedstock into chemicals of a higher oxidation state, allowing further chemical transformations. These bulk-scale oxidation processes usually employ molecular oxygen as the terminal oxidant as at this scale it is typically the only economically viable oxidant. The produced commodity chemicals possess limited functionality and usually show a high degree of symmetry thereby avoiding selectivity issues. In sharp contrast, in the production of fine chemicals preference is still given to classical oxidants. Considering the strive for greener production processes, the use of O₂ , the most abundant and greenest oxidant, is a logical choice. Given the rich functionality and complexity of fine chemicals, achieving regio/chemoselectivity is a major challenge. This review presents an overview of the most important catalytic systems recently described for aerobic oxidation, and the current insight in their reaction mechanism.

Facile Formation of Bi2O2CO3/Bi2MoO6 Nanosheets for Visible Light-Driven Photocatalysis

Bi2O2CO3/Bi2MoO6 heterojunction catalysts were prepared by treating Bi2MoO6 sheets with aqueous NaHCO3 solutions at room temperature. All the Bi2O2CO3/Bi2MoO6 heterojunctions exhibited higher activities than pristine Bi2MoO6 in the photocatalytic degradation of rhodamine B (RhB), methyl orange, and ciprofloxacin under visible-light irradiation, and the most active photocatalyst was found to be the one with a C/Bi molar ratio of ∼1/2.3. Relevant samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, N2 adsorption-desorption, Fourier transform infrared spectroscopy, and UV-vis spectroscopy. The higher activity of Bi2O2CO3/Bi2MoO6 than pristine Bi2MoO6 is explained by the enhanced separation and transfer of photogenerated electron/hole pairs, as verified by transient photocurrent densities, photoluminescence spectroscopy, and electrochemical impedance spectroscopy. Photogenerated holes (h+) and superoxide radical anions (•O2 -) were found to be the main active species. The good reusability of Bi2O2CO3/Bi2MoO6 was testified by cycling degradation of RhB and tetracycline hydrochloride.

Selective aerobic oxidation of alkyl aromatics on Bi2MoO6 nanoplates decorated with Pt nanoparticles under visible light irradiation

Pt/Bi2MoO6 nanoplates are efficient photocatalysts for the selective oxidation of saturated C-H bonds in alkyl aromatics under visible light illumination using O2 as an oxidant. This study opens a new window for direct C-H functionalization through the photocatalytic method based on cheap Bi2MoO6 semiconductor materials.

Surface defect-mediated efficient electron-hole separation in hierarchical flower-like bismuth molybdate hollow spheres for enhanced visible-light-driven photocatalytic performance

It is desirable to develop an efficient visible-light-driven photocatalyst for practical application to degrade highly-noxious pollutants. Herein, the hydrogenation hierarchical flower-like Bi₂MoO₆ hollow spheres (H-BMO-X, where X represents the different hydrogen calcination temperatures) have been successfully fabricated by a solvothermal-surface hydrogenation process. The as-prepared nano-photocatalyst H-BMO-300 clearly exhibits a photocatalytic reaction apparent rate constant k for high-noxious pollutants by ∼3-times higher than pristine Bi₂MoO₆. Moreover, the resultant H-BMO-300 sample with a narrow bandgap of ∼2.70 eV possesses surface oxygen vacancy defects. Based on the scanning Kelvin probe and surface photovoltage spectroscopy, it is deduced that the photocatalytic activities are attributed to the surface oxygen vacancy of H-BMO-X favoring the electron-hole pair's separation. The enhanced photocatalytic performance can be ascribed to the synergistic effect of surface defects favoring efficient electron-hole separation and the hollow hierarchical structure benefiting the utilization of visible light, which provides more surface-active sites. This work provides a viable route to perceptibly enhance the photocatalytic activities of H-BMO-300 for environmental remediation with good mineralization properties.

Near-Infrared-Driven Selective Photocatalytic Removal of Ammonia Based on Valence Band Recognition of an α-MnO2/N-Doped Graphene Hybrid Catalyst

Near-infrared (NIR)-response photocatalysts are desired to make use of 44% NIR solar irradiation. A flower-like α-MnO₂/N-doped graphene (NG) hybrid catalyst was synthesized and characterized by X-ray diffraction spectroscopy, transmission electron microscopy, Raman spectroscopy, UV-vis-NIR diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. The flower-like material of α-MnO₂/NG was oval-shaped with the semi major axis of 140 nm and semi minor axis of 95 nm and the petal thickness of 3.5-8.0 nm. The indirect band gap was measured to be 1.16 eV, which is very close to 0.909 eV estimated by the first-principles calculation. The band gap can harvest NIR irradiation to 1069 nm. The coupling of α-MnO₂ with NG sheets to form α-MnO₂/NG can significantly extend the spectrum response up to 1722 nm, improving dramatically the photocatalytic activity. The experimental results displayed that the α-MnO₂/NG hybrid catalyst can recognize ammonia in methyl orange (MO)-ammonia, rhodamine B (RHB)-ammonia, and humic acid-ammonia mixed solutions and selectively degrade ammonia. The degradation ratio of ammonia reached over 93.0% upon NIR light irradiation in the mixed solutions, while those of MO, RHB, and humic acid were only 9.7, 9.4, and 15.7%, respectively. The products formed during the photocatalytic process were followed with ion chromatography, gas chromatography, and electrochemistry. The formed nitrogen gas has been identified during the photocatalytic process. A valence band recognition model was suggested based on the selective degradation of ammonia via α-MnO₂/NG.

Internal Polarization Modulation in Bi2 MoO6 for Photocatalytic Performance Enhancement under Visible-Light Illumination

A built-in electric field from polarization inside polar photocatalysts could provide the driving force for photogenerated electrons and holes to move in opposite directions for better separation to improve their photocatalytic performance. The photocatalytic performance of a polar photocatalyst of Bi₂ MoO₆ has been enhanced through the precise control of its structure to increase internal polarization. DFT calculations predicted that a shortened crystal lattice parameter b in Bi₂ MoO₆ could induce larger internal polarization, which was achieved by the modulation of the pH of the reaction solution during a solvothermal synthetic process. A series of Bi₂ MoO₆ samples were created with reaction solutions of pH≈1, 4, and 8; the crystal lattice parameter b was found to decrease gradually with increasing solution pH. Accordingly, these Bi₂ MoO₆ samples demonstrated a gradually enhanced photocatalytic performance with decreasing crystal lattice parameter b, as demonstrated by the photocatalytic degradation of sulfamethoxazole/phenol and disinfection of Staphylococcus aureus bacteria under visible-light illumination due to improved photogenerated charge-carrier separation. This study demonstrates an innovative design strategy for materials to further enhance the photocatalytic performance of polar photocatalysts for a broad range of technical applications.

Plasmonic resonance enhanced photoelectrochemical aptasensors based on g-C3N4/Bi2MoO6

An in-depth exploration associated with localized surface plasmon resonance between g-C₃N₄/Bi₂MoO₆ and gold nanoparticles has been conducted for highly efficient photoelectrochemical aptasensors under ultraviolet and visible light irradiation.

Highly improved visible-light-induced photocatalytic performance over BiOI/Ag2CO3 heterojunctions

The heterojunctions between BiOI and Ag₂CO₃ obviously improved visible-light-driven photocatalytic activity compared with separate BiOI and Ag₂CO₃ particles.

Defect state of indium-doped bismuth molybdate nanosheets for enhanced photoreduction of chromium(vi) under visible light illumination

The construction of defect states is an effective method for regulating the energy band structure of photocatalytic semiconductor materials.