Conversion Of Benzylamine Research Articles

Visible‐Light Photocatalytic and Photo‐bactericidal Activity of Ni‐CuWO4/OTiO2 Composite†

Comprehensive SummaryA series of nickel‐doped copper tungstate/oxygen‐rich TiO2 heterojunction‐constructed composites of xNi‐CuWO4/OTiO2 were successfully prepared to demonstrate the enhancement of the visible‐light photoactivity through promoting the photogenerated charge carrier separation efficiency. Of all these composites, 0.2Ni‐CuWO4/OTiO2 exhibits excellent and stable visible light photoactivity for the photooxidative coupling of benzylamine to the corresponding N‐benzyl‐1‐phenymethanimine (BPMI) in air atmosphere. The conversion of benzylamine and the selectivity to BPMI reach 97% and 99%, respectively. The catalyst shows good cyclability with the conversion of benzylamine decreasing just by 22% after being repeated six times with the well‐maintained selectivity of BPMI. The composite also exhibits excellent photo‐bactericidal ability, which greatly inhibits the reproducing of both the Gram‐positive bacteria (e.g., S. epidermidis) and Gram‐negative bacteria (e.g., E. coli).

Enhanced photoactivity and selectivity over BiOI-decorated Bi2WO6 microflower for selective oxidation of benzylamine: Role of BiOI and mechanism

The importance of developing effective and selective photocatalytic materials to realize efficient renewable energy-based organic synthetic processes, such as selective oxidation of benzylamines and its derivatives to the corresponding imines has become more apparent in recent years. Here we present the first reported BiOI/Bi2WO6 (BI/BW) microflower heterostructure as a visible-light-driven photocatalyst for such reactions. By decorating the hydrothermally prepared BW with BI via successive ionic layer adsorption and reaction (SILAR) method, benzylamine conversion is improved from 68 % to 92 % as compared to undecorated. Furthermore, selectivity to desired imine product is substantially increased from 59 % to 95 %. These outstanding performances are attributed to enhanced electron-hole separation and transfer efficiency as well as a greater preference for adsorption of benzylamine compared to the imine products and extended visible-light absorption range inherited from BI component as supported by competitive adsorption studies, ultraviolet–visible diffuse reflectance spectroscopy, and photoelectrochemical experiments. Possible mechanisms, band energy diagram, and decisive roles of O2− and h+ in the selective transformation of benzylamine were proposed based on Mott-Schottky, scavenging, and electron paramagnetic resonance radical trapping experiments. This work highlights a simple approach for improving photocatalytic activity and selectivity which are highly desirable in renewable energy-based chemical synthetic processes.

Stainless steel promoted the electrochemical oxidation of amines into imines

AbstractWe report the electrochemical oxidation of benzylamine (BA) into the imine by applying a bare stainless steel mesh (SSM) as an anode. Scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectroscopy (EDX) elemental mapping analysis confirmed that there was no corrosion on the surface of SSM after an anodic electrolysis. Based on the gas chromatography (GC) analysis and electrochemical results, it was confirmed that conversion of BA with SSM was approximately 3.3 times higher than with Pt electrode. This work suggests that the anodic electrolysis with a bare SSM could be a promising route to electrochemical oxidation of BA in the absence of oxidizing agents.

Boosting the Photocatalytic H2 Evolution and Benzylamine Oxidation using 2D/1D g-C3N4/TiO2 Nanoheterojunction.

The present research aims at the elevation of solar-to-chemical energy conversion with extortionate performance and sustainability. The nanostructured materials are revolutionizing the water splitting technology into decoupled hydrogen with simultaneous value-added organic chemical production. Yet, the bottleneck in semiconductor photocatalysis is rapid charge recombination and sluggish reaction kinetics. Herein, we demonstrate an efficient and non-noble metal-based catalyst for successful redox reaction with a theoretical modeling through density functional theory (DFT) study. Implementing this robust approach on 2D/1D ultrathin g-C3N4 nanosheets and TiO2 nanowires heterojunction, we achieved H2 production of 5.1 mmol g-1 h-1 with apparent quantum efficiency of 7.8% under visible light illumination and 93% of benzylamine conversion to N-benzylidene benzylamine in situ. The interface of 2D g-C3N4 nanosheets and 1D nanowires provide ample active sites and extends the visible light absorption with requisite band edge position for the separation of photoinduced charge carriers with superior stability. The electronic properties, band structure, and stability of the heterojunction are further investigated via DFT calculations which corroborate the experimental results and in good agreement for the enhanced activity of the heterojunction.

Tridimensional N, P-Codoped Carbon Sponges as Highly Selective Catalysts for Aerobic Oxidative Coupling of Benzylamine.

Two tridimensional N-doped porous carbon sponges (3DC-X) have been prepared by using cetyltrimethylammonium chloride (CTAC) and cetyltrimethylammonium bromide (CTAB) as soft templates and alginate to replicate the liquid crystals formed by CTA+ in water. Alginate is a filmogenic polysaccharide of natural origin having the ability to form nanometric defectless films around objects. Subsequent pyrolysis at 900 °C under an Ar flow of the resulting CTA+–polysaccharide assemblies result in 3DC-1 and 3DC-2, with the N percentages of 0.48 and 0.36 wt % for the materials resulting from CTAC and CTAB, respectively. Another four 3DC materials were obtained via pyrolysis of the adduct of phytic acid and chitosan, rendering an amorphous, N and P-codoped carbon sample (3DC-3 to 3DC-6). The six 3DC samples exhibit a large area (>650 m2 × g–1) and porosity, as determined by Ar adsorption. The catalytic activity of these materials in promoting the aerobic oxidation of benzylamine increases with the specific surface area and doping, being the largest for 3DC-4, which is able to achieve 73% benzylamine conversion to N-benzylidene benzylamine in solventless conditions at 70 °C in 5 h. Quenching studies and hot filtration tests indicate that 3DC-4 acts as a heterogeneous catalyst rather than an initiator, triggering the formation of hydroperoxyl and hydroxyl radicals as the main reactive oxygen species involved in the aerobic oxidation.

Fabrication of Type II heterojunction in ZnIn2S4@ZnO photocatalyst for efficient oxidative coupling of Benzylamine under visible light

A series of ZnxInySz was synthesized by hydrothermal method, and the corresponding ZnxInySz@ZnO composites with the internal type II heterojunctions were prepared by solvent assisted interface. It could be observed in SEM and TEM images of ZnIn2S4@ZnO that ZnIn2S4 present a petal-like sphere composed ofnanosheets with nano-fragments of ZnO attached on its surface. The results offluorescence spectra and electrochemical impedance spectroscopy indicated that theformation of type II heterojunctions within ZnIn2S4@ZnO composites significantly promotedthe separation of photocarriers. Therefore, ZnIn2S4@ZnO delivered excellent catalyticperformance for oxidative coupling of benzylamine. Under visible-light irradiation of 2 h, the conversion of benzylamine is as high as 96%, and the catalytic performance is still very steady after several cycles. It has not been reported that such a high conversion can be achieved in such a short period of time. Another advantage is that the coupling reaction does not require additional oxygen atmosphere and can be carried out in air condition, endowing this process with the feature of easier to be operated. This work provids an effective method for oxidative coupling of benzylamine through environmentally friendly way.This work provided an effective method for coupling of benzylamine environmentally friendly way.

Tuning product selectivity and visible-light-driven activity in oxidative coupling of amines to imines: A case study of BiOIxCl1−x photocatalyst

BiOCl has shown a promising photocatalytic activity in non-selective oxidation reactions, however its application in selective photocatalytic organic transformations is often limited by the strong oxidizing ability of photogenerated holes along with inefficient visible-light absorption. Herein, we showed that the poor visible-light-harvesting ability and low product selectivity of BiOCl in the selective oxidation of primary amines to corresponding imines can be alleviated by band energy level modification using a solid solution strategy. We combined an efficient visible light absorption performance of BiOI with a strong oxidizing ability of BiOCl to achieve BiOIxCl1−x solid solution catalysts with substantial improvements in imine yield. Among the BiOIxCl1−x catalysts, BiOI0.2Cl0.8 delivers the highest benzylamine conversion of ~84% with a selectivity of ~96% towards the imine, while pure BiOCl shows much lower conversion (~65%) and product selectivity (~81%). Such excellent performance could be attributed to electronic structure modifications induced by iodine atom incorporation into BiOCl structure as supported by UV–vis DRS, Mott-Schottky, and VB-XPS studies. Based on photoelectrochemical studies and material characterizations, band energy diagram of the BiOI0.2Cl0.8 is proposed and compared with that of pristine BiOCl and BiOI. Radical scavenging study, EPR spin trapping result, and Hammett plot suggest that the imine formation mechanism may occur via both 1O2- and O2•–-mediated pathways. This work highlights a rational catalyst design for which the benefits from each individual components are used to maximize photocatalytic performance toward the selective synthesis of value-added organic compounds.

Thermo‐Enhanced Photocatalytic Activity in Aerobic Oxidative Coupling of Amines to Imines over Cu‐Doped MIL‐125‐NH2

AbstractPhotocatalytic oxidation of raw organic molecules to value‐added chemicals provides a cost‐effective and sustainable strategy in organic synthesis. In this work, a series of Cu‐doped MIL‐125‐NH2 with narrower band gaps were synthesized by a one‐pot hydrothermal method and used as photocatalysts for thermo‐enhanced aerobic oxidative coupling of amines to imines under visible light irradiation. With optimal doping content, the conversion of benzylamine over MIL‐125‐NH2/Cu2% can reach 100% at 60 °C under visible light irradiation for 8 h using molecule oxygen as oxidant. It is proved that doping MIL‐125‐NH2 with a suitable Cu content can broaden the visible light absorption range, promote the separation of photo‐induced charge carriers and improve the photocatalytic performance. Moreover, the increase of reaction temperature of the photocatalytic system promotes the performance. Free radical capture experiments and ESR tests show that holes and superoxide free radicals are the main active species. Such an excellent photocatalytic performance can be attributed to the strong light absorption and more efficient electron‐hole separation efficiency via the Cu‐doping strategy in MIL‐125‐NH2 catalysts.

Highly efficient photocatalytic dehydrogenative coupling of amines with supported platinum catalyst under the oxidant-free conditions

A highly efficient photocatalytic dehydrogenative coupling (PDC) of amines to prepare value-added imines has been developed under the mild conditions. A complete conversion of benzylamine with a 99% selectivity of N-benzylidenebenzylamine could be obtained using the 2%Pt@g-C3N4 as photocatalyst in the absence of hydrogen acceptor at room temperature. Moreover, the relationship between the physical properties of different photocatalysts and their activities has been discussed according to the characterization results of the XRD, BET, SEM, TEM, and XPS techniques. Next, the PDC of different amines have been further investigated, where ca. 70.2%–99.0% yields of corresponding imines were attained. Finally, based on the experimental results and heterogeneous catalytic principle, a possible reaction mechanism for the PDC of benzylamine is proposed.

Flowerlike BiOCl nanospheres fabricated by an in situ self-assembly strategy for efficiently enhancing photocatalysis

For semiconductor-based photocatalytic reactions, defect engineering has been proven as an efficient approach to enhance the photocatalytic performance. In this work, a synergistically PVP/EG-assisted in situ self-assembly strategy has been successfully developed for preparing flowerlike BiOCl nanospheres (NSP) assembled by ultrathin nanosheets (thickness of 3.8 nm) with abundant oxygen vacancies (OVs). During the hydrothermal process, PVP plays a template role in controlling the orientation of the crystallite growth, leading to the forming of nanosheets. Meanwhlie, ethylene glycol would induce the self-assembly of nanosheets into a loose hierarchical architecture duo to its stereo-hindrance effect. NSP achieves a twice higher photocatalytic conversion of benzylamine than BiOCl nanosheets (NST) under visible light. XPS, ESR, NH3-TPD results manifest that NSP possesses more active sites including OVs and unsaturated Bi atoms than NST, because of avoiding the accumulation of ultrathin nanosheets. In situ FTIR reveals that benzylamine molecules can be chemisorbed and activated on BiOCl interfaces via forming -N…Bi- species. The OVs can facilitate the forming of superoxide radicals (•O2−), achieving the selective photooxidation. Finally, a possible synergetic mechanism based on the interaction of reactants and catalyst interfaces was proposed to illustrate the photocatalytic process at the molecular level.

Cooperative Photocatalysis with 4-Amino-TEMPO for Selective Aerobic Oxidation of Amines over TiO2 Nanotubes.

Attaching π-conjugated molecules onto TiO2 can form surface complexes that could capture visible light. However, to make these TiO2 surface complexes durable, integrating 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) or its analogues as a redox mediator with photocatalysis is the key to constructing selective chemical transformations. Herein, sodium 6,7-dihydroxynaphthalene-2-sulfonate (DHNS) was obtained by extending the π-conjugated system of catechol by adding a benzene ring and a substituent sodium sulfonate (-SO3 - Na+ ). The DHNS-TiO2 showed the best photocatalytic activity towards the blue light-induced selective aerobic oxidation of benzylamine. Compared to TEMPO, 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) could rise above 70% in conversion of benzylamine over the DHNS-TiO2 photocatalyst. Eventually, a wide range of amines could be selectively oxidized into imines with atmospheric O2 by cooperative photocatalysis of DHNS-TiO2 with 4-amino-TEMPO. Notably, superoxide (O2 •- ) is crucial in coupling the photocatalytic cycle of DHNS-TiO2 and the redox cycle of 4-amino-TEMPO. This work underscores the design of surface ligands for semiconductors and the selection of a redox mediator in visible light photocatalysis for selective chemical transformations.

Selective N-Alkylation of Amines with DMC over Biogenic Cu-Zr Bimetallic Nanoparticles.

Herein, we report the green synthesis of copper–zirconium bimetallic nanoparticles (Cu–Zr BNPs) from aqueous solutions using Azadirachta indica leaf extract as a reducing and stabilizing agent. The CuO, ZrO2 NP, and Cu–Zr BNP samples were characterized by X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy, and the morphologies of the samples were analyzed by high-resolution transmission electron microscopy (HR-TEM) with selected area electron diffraction analysis (SAED). The synthesized Cu–Zr BNPs have been employed as efficient catalysts for the selective N-methylation of aromatic and aliphatic amines with dimethyl carbonate. The effect of process conditions on the percentage conversion of benzylamine with dimethyl carbonate as a model reaction has been investigated. The Cu–Zr bimetallic nanoparticle catalytic system in a 1:2 molar ratio was able to convert amines into the corresponding N-methylated amines with a selectivity up to 91% at 180 °C in 4 h. The analysis of catalytic reusability confirmed that the reported heterogeneous catalyst can be used for five consecutive cycles without much loss in activity. Thus, the current protocol can be considered as a simpler, reproducible, and environmentally benign approach for N-methylation of amines.

Donor–Acceptor Type Conjugated Microporous Polymer as a Metal-Free Photocatalyst for Visible-Light-Driven Aerobic Oxidative Coupling of Amines

Developing cheap, highly efficient, metal-free heterogeneous photocatalysts remain a great challenge in photoredox reactions. Herein, we utilize a typical Suzuki coupling of low-cost triphenylamine derivative and 9,10-dibromoanthracene to synthesis a donor–acceptor type conjugated microporous polymer (denoted as PAA-CMP). As expected, heterogeneous PAA-CMP exhibits excellent photocatalytic performance, good functional group tolerance and satisfying recyclability in metal-free aerobic oxidative coupling of amines to imines driven by visible light, which is due to its absolute energy level positions and good physicochemical stability. More excitingly, PAA-CMP can enable the gram-scale air-oxidized photocatalytic conversion under natural sunlight irradiation, yielding the desired imine product with an isolated yield of 65% for 48 h. The current work provides a great application prospect for CMPs in low-cost and large-scale organic industrial production in the future. The prepared donor-acceptor (D-A) type conjugated microporous polymer (PAA-CMP) as a metal-free and heterogeneous photocatalyst enable the gram-scale air-oxidized photocatalytic conversion of benzylamine into N-benzylidenebenzylamine under natural sunlight irradiation, yielding the desired imine product with an isolated yield of 65%.

Synergistic Nanostructured MnOx/TiO2 Catalyst for Highly Selective Synthesis of Aromatic Imines

AbstractThis work reports the development of a synergistic nanostructured MnOx/TiO2 catalyst, with highly dispersed MnOx nanoparticles (4.5±1 nm) on shape‐controlled TiO2 nanotubes (8–11 nm width and 120–280 nm length), for selective synthesis of valuable aromatic imines at industrially important conditions. Pristine TiO2 nanotubes exhibited 97 % imine selectivity at a 38.3 % benzylamine conversion, whereas very low imine selectivity was obtained over commercial TiO2 materials, indicating the catalytic significance of shape‐controlled TiO2 nanotubes. The MnOx nanoparticle/TiO2 nanotube (10 wt% Mn) catalyst calcined at 400 °C showed the best activity with 95.6 % benzylamine conversion and 99.9 % imine selectivity. This catalyst exhibited good recyclability for four times and is effective for converting numerous benzylamines into higher yields of imines. The high catalytic performance of MnOx/TiO2 nanotubes was attributed to higher number of redox sites (Mn3+), high dispersion of Mn species, and shape‐controlled structure of TiO2, indicating that this catalyst could be a promising candidate for selective oxidation reactions.

Recent advances in the oxidative conversion of benzylamines

Benzylamines and their derivatives are important building blocks in the chemical, pharmaceutical and polymer industries and have a great contribution in the synthesis of a variety of N -heterocycles. Due to the basic role of N -heterocycles in the synthetic organic chemistry, especially in pharmaceutics, an increasing number of studies are devoted to the oxidative reactions of benzylamines in presence of various catalysts under different conditions in the last decade. Thus in this review, we’ve focused on the oxidative reactions of benzylamines including a brief description of the reaction mechanisms for the synthesis of N -heterocyclic compounds based on the catalytic system applied. In this respect, the related studies from 2012 to 2019, have been categorized and classified in five main sections. • The latest findings on the oxidative reactions of benzylamines. • These findings were classified based on the catalytic systems applied. • Help for designing novel bioactive compounds.

Thermo-enhanced photocatalytic oxidation of amines to imines over MIL-125-NH2@Ag@COF hybrids under visible light.

Thermo-enhanced photocatalysis combines the advantages of thermocatalysis and photocatalysis and provides a very promising approach for the selective oxidation of organic compounds to value-added chemicals. In this work, the amino group in MIL-125-NH2 first reacts with formaldehyde to form the reducing group (-NH-CH2OH), which can in situ auto reduce the introduced Ag+ ions to Ag clusters/nanoparticles in the cavities. Then the formed MIL-125-NH-CH2OH@Ag was further coated with a covalent organic framework (COF) through imine bonds to form a series of MIL-125-NH-CH2OH@Ag@COF hybrids. Oxidative coupling of amines was selected to evaluate the photocatalytic performance of these materials under visible light at set temperatures (20-60 °C). With an optimized composition, MIL-125-NH-CH2OH@Ag-0.5@COF-2 not only improves the optical properties, but also exhibits the highest conversion (almost 100%) of benzylamine under visible light at 60 °C and good stability for at least three cycles. Free radical capture experiments and electron spin resonance detection demonstrated that holes (h+), hydroxyl (˙OH) and superoxide radicals (O2˙-) were the active species. The results prove that the MIL-125-NH-CH2OH@Ag@COF hybrid possessed higher photocatalytic performance than individual MIL-125-NH2, Ag and COF on account of the efficient separation and transfer of photoinduced electrons and holes. Moreover, the promotion of the reaction temperature on the photocatalytic oxidation of amines has been reported, revealing that the conversion of benzylamine over MIL-125-NH-CH2OH@Ag-0.5@COF-2 at 60 °C is nearly twice as high as that at 20 °C under visible light irradiation. Therefore, the thermo-enhanced photocatalytic oxidation performance of the MOF@Ag@COF hybrid demonstrates the great potential of thermal energy for further improving the photocatalytic selective oxidation performance.

Fabrication of Mo2C-QDs/C/Bi2MoO6 composite as efficient photocatalyst for aerobic oxidation of amines to imines

As an efficient but mild oxidation species, O2– generated from surface O2 and photo-excited electrons plays a key role in photocatalytic reactions. To improve photocatalytic activity, it is essential to facilitate the separation and transfer efficiency of photogenerated charge carriers. In this work, Mo2C-QDs/C, an alternative of noble metals, was used as an efficient and economical cocatalyst. It was added to Bi2MoO6 nanosheet to generate Mo2C-QDs/C/Bi2MoO6 (MCBMO) composites by a facile hydrothermal method. Under visible light irradiation, the carbon layer and the Mo2C-QDs acts as electronic conductor and electron trapping agent to promote the transfer of photogenerated electrons for enhanced generation of O2–. The MCBMO composites show boosted photocatalytic performance in the oxidative coupling of benzylamine to N-benzylbenzaldimine with excellent recyclability. Under the optimized conditions, benzylamine conversion over the optimized MCBMO-3 composite is up to 92% whereas that over pristine Bi2MoO6 is limited to 53%. The MCBMO-3 composite even outperforms Ag/Bi2MoO6 and Pt/Bi2MoO6. Based on the results of ESR and active species trapping studies, it is confirmed that O2– and h+ are indispensable in the photocatalytic reaction, and a possible reaction mechanism has been proposed.

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.

Multimetal Incorporation into 2D Conductive Metal-Organic Framework Nanowires Enabling Excellent Electrocatalytic Oxidation of Benzylamine to Benzonitrile.

As an important organic intermediate, benzonitrile (BN) is widely involved in organic synthetic chemistry and pharmaceutical and dyestuff industries. However, the exploration of a more efficient and controllable synthesis technique and the corresponding greener catalysts for the synthesis of BN still poses a great challenge. Herein, with multimetallic two-dimensional conductive metal-organic frameworks (2D cMOF) as anodic electrocatalysts, we develop a green, convenient, and highly efficient electrochemical synthesis strategy for BN. Thanks to the intrinsic 2D electrically conductive structure and the optimized the multimetallic coupling catalytic effect, the resulting multimetallic 2D cMOFs exhibit excellent benzylamine (BA) electrooxidation performance. Especially, the trimetallic 2D cMOF (NiCoFe-CAT) requires an ultralow potential of 1.29 V vs reversible hydrogen electrode (RHE) to achieve a 10 mA·cm-2 current density, which indicates the fastest reaction and the most favorable thermodynamic condition. A very high yield (0.058 mmol·mg-1·h-1) and faradic efficiency (∼87%) of benzonitrile are both achieved during the BA electrooxidation reaction at 1.45 V. The reaction mechanism investigations indicated that the various redox mediators of MII/MIII (Ni, Co, Fe) may be regarded as multimetal active species to promote BA conversion. Also, the excellent cycling durability of multimetallic 2D cMOFs further promotes their potential practical applications. These electrocatalytic performances are considered excellent and nearly surpass all other reported Ni-based inorganics or MOF-based electrocatalysts for the electrocatalytic oxidation of benzylamine.

Photocatalytic activity enhancement of g-C3N4/BiOBr in selective transformation of primary amines to imines and its reaction mechanism

Herein, the photocatalytic activity of g-C3N4/BiOBr (CB) heterojunction in the oxidative C–N coupling of benzylamine under atmospheric air using cool white LED light was reported for the first time. The CB heterojunction was prepared by two-step combustion-coprecipitation method. By tuning the weight percentage of g-C3N4, the optimal catalyst containing 10.2 wt% of g-C3N4 provided the highest benzylamine conversion of ca. 94% and the best N-benzylidenebenzylamine yield of ca. 82% within 4 h irradiation. The influences of catalyst amount, substrate concentration, light intensity and reaction temperature on photocatalytic performance were also discussed. The CB catalyst also successfully oxidized N-heterocyclic amines and secondary amines into their corresponding imines which extends the scope and potential use of this catalyst in the syntheses of other CN containing biologically active compounds. The enhanced performance of CB heterojunction was mainly ascribed to improved charge transfer and separation intrinsically derived from the staggered band energy configuration of the CB heterojunction as evidenced from photoelectrochemical, steady-state photoluminescence and time-resolved fluorescence studies. Electron paramagnetic resonance (EPR), Hammett and active species quenching results revealed the O2–-assisted mechanism with a possible carbocationic intermediate being generated. Under anaerobic condition, the reaction can also proceed probably through carbon-centered radical. Based on UV–vis, XPS and Mott-Schottky results, band energy level diagram and a plausible reaction mechanism at solid-liquid interface were also revealed.