Two-electron Reduction Process Research Articles

Structure-Property Relationships for Potential Inversion From Electron Acceptors Based on Thiophene-Fused Triptycene Quinones, 1,4-Diketones and Their Malononitrile Adducts.

The synthesis and properties of a series of 11,11,12,12-tetracyano-9,10-anthraquinodimethane (TCAQ) inspired electron acceptors based on thiophene-fused quinone and triptycene motifs is presented. This has yielded insights into structure-property relationships for establishing and modulating simultaneous two-electron reduction processes in TCAQ analogues. These new compounds were synthesised using a Friedel-Crafts acylation between triptycene and thiophene-3,4-dicarbonyl chloride. Isomeric para-quinones featuring a [c]-fused thiophene on one side and a β,β- or α,β-fused triptycene on the other were isolated alongside a thiophene-3,4-diketone which bears two triptycene fragments. Knoevenagel condensation of these products with malononitrile produced a quinoidal bis(dicyanomethylene), an oxo-dicyanomethylene and an acyclic bis(dicyanomethylene). This series of new electron accepting molecules has been studied using X-ray crystallography and the implications of their 3D structures on NMR and UV/vis absorbance spectroscopy and cyclic voltammetry results have been ascertained with conclusions underpinned by computational methods.

Synthesis, characterization, electrochemistry and spectroelectrochemistry of new non-peripherally substituted lutetium bis phthalocyanines

The synthesis, characterization, spectral, and electrochemical properties of bis-(phthalocyanine)lutetium (III) (LuPc2) bearing halogenated (F (F-LuPc2), Cl (Cl-LuPc2) and Br (Br-LuPc2)) phenoxy groups were reported for the first time. To explore the possible application of the LuPc2 complexes, their detailed redox mechanisms were determined by voltammetric and spectroelectrochemical characterizations. One of the Pc rings exhibits radical characteristics as a result of the sandwich structures of the complexes, which led to the typical one electron reduction process between 0.20 and 0.40 V and the typical one electron oxidation process between 0.60 and 0.80 V.In addition to the characteristic Pc.-Lu3+Pc2-/Pc2-Lu3+Pc2-1- reduction and Pc.-Lu3+Pc2-/Pc.-Lu3+Pc.-1+ oxidation couple of the complexes, further two-electron reduction and oxidation processes were also observed due to the simultaneous electron transfer reactions of each Pc ring at very close potentials. Moreover, at more negative potentials sequential one electron reduction waves for each Pc ring were also observed. While the Cl-LuPc2 reduced at less positive potential and more negative potential, changing Br with Cl and F alters the ease of the electron transfer reactions of the complexes. In situ spectroelectrochemical results supported these voltammetric assignments. Moreover, distinct color changes of LuPc2 in the solution observed with in situ spectroelectrochemical measurements indicated their functionality as electrochromic materials.

Novel Triangulenes: Computational Investigations of Energy Thresholds for Photocatalytic Water Splitting.

Organic materials with Inverted Singlet-Triplet (INVEST) gaps are interesting for their potential use in photocatalytic small molecule transformations such as the entirely solar-driven water splitting reaction. However, only a few INVEST emitters are thermodynamically able to split water requiring a first singlet excited dark state, S1 , above 1.27 or 1.76 eV, and absorption near solar the maximum, 2.57 eV. These requirements and the INVEST character are key for achieving a long-lived photocatalyst for water splitting. The only known INVEST emitters that conform to these criteria are large triangular boron carbon nitrides with unknown synthesis pathways. Using ADC(2), a quantum-mechanical method, we describe three triangulenes. 3 a is a cyano azacyclopenta[cd]phenalene derivative while 3 b and 3 c are cycl[3.3.3]azine derivatives. 3 b has a previously undescribed disulfide bridge. Overall, 3 a fulfills requirements for photocatalytic four-electron reduction of water while the S1 states of 3 b and 3 c are likely slightly low for the two-electron reduction process. By analyzing impacts of ligands, we find that there are guidelines describing how S1 -S5 energies and oscillator strengths, T1 energies, and ΔES1T1 gaps are affected, requiring deep-learning algorithms for which studies will be presented by us in due time. The impact of ground-state geometries, solvation effects, as well as reduced-cost ADC(2) algorithms on our findings are also discussed.

O, N Coordination-Mediated Nickel Single-Atom Catalysts for High-Efficiency Generation of H2O2.

Electrochemical selective two-electron oxygen reduction shows great potential for on-site electrochemical production of hydrogen peroxide (H2O2). Herein, we demonstrated the synthesis of Ni single-atom sites coordinated by three oxygen atoms and one nitrogen atom (i.e., Ni-N1O3) supported by oxidized carbon black (OCB) by pyrolyzing nickel-(pyridine-2,5-dicarboxylate) coordination complexes. Aberration-corrected scanning transmission electron microscopy (AC-STEM) combined with X-ray absorption spectroscopy (XAS) proves the presence of atomically dispersed Ni atoms attached on OCB (labeled as Ni-SACs@OCB), in which Ni single atoms are stabilized by a N, O-mediated coordination configuration. This Ni-SACs@OCB catalyst shows high H2O2 selectivity (95%) in a range of 0.2-0.7 V undergoing a two-electron oxygen reduction process, with a kinetic current density of 2.8 mA cm-2 and a mass activity of 24 A gcat.-1 at 0.65 V (vs RHE). In practice, H-cells with Ni-SACs@OCB as catalysts displayed a high H2O2 production rate of 98.5 mmol gcat.-1 h-1 with negligible current loss during testing, suggesting the high H2O2 generation efficiency and robust stability. DFT theoretical calculations revealed that Ni single-atom sites coordinated by O, N coordination exhibit advantages in oxygen adsorption and increased reactivity toward the intermediate species, *OOH, which is beneficial to high selectivity for H2O2 production. This work provides a novel N, O-mediated four-coordinate nickel single-atom catalyst as a promising candidate for practical decentralized production of H2O2.

A thioether-decorated triazine-based covalent organic framework towards overall H2O2 photosynthesis without sacrificial agents

Covalent organic frameworks (COFs) have been rapidly applied in photocatalytic H2O2 production owing to their strong light absorption, suitable band structure, etc. However, sluggish water oxidation reaction (WOR) with low selectivity restricts the H2O2 photosynthesis efficiency of COFs. Herein, a thioether-decorated triazine-based COF (TDB-COF) was designed and developed for efficient overall H2O2 photosynthesis. TDB-COF achieves a photocatalytic H2O2 production rate of 723.5 μmol g−1 h−1 without any sacrificial agents and exhibits remarkable cyclic stability. The modification of thioether groups broadens the visible light absorption of TDB-COF and narrows its optical band gap. Such a strategy can not only effectively regulate the band structure suitable for two-electron two-steps WOR but also promote the photogenerated carriers transfer and accelerate a two-electron two-steps oxygen reduction process to generate H2O2, thus ultimately boosting the overall H2O2 photosynthesis. This work provides valuable suggestions for the development of the functional COFs towards overall H2O2 photosynthesis.

On-Site H2O2 Synthesis Using a Series of Ni(II) Furan-2-thiocarboxylate Complexes Integrated on Multi-Walled Carbon Nanotubes: Soft Donor Sites Stimulated Selective Two-Electron Oxygen Reduction

A series of Ni(II) complexes [Ni(tmeda)(fCOS)2] (1a), [Ni(2,2′-bipy)(fCOS)2] (1b), [Ni(1,10-Phen)(fCOS)2] (1c), [Ni(opda)2(fCOS)2] (2), [Ni(dppe)(fCOS)2] (3a), and [Ni(dppee)(fCOS)2] (3b) (fCOS = furan-2-thiocarboxylate) have been synthesized. All the complexes, except 1b, were characterized by single-crystal X-ray diffraction analysis and spectroscopic techniques. In the solid state, the geometry around the Ni(II) center is square planar in the cases of 3a and 3b, while the same is octahedral (with varying degrees of distortion) in all other complexes. The complexes were integrated separately on multi-walled carbon nanotubes (MWCNTs) to prepare their respective composites. Electrochemical characteristics and oxygen reduction response of all the composites were studied. All composites exhibited a two-electron oxygen reduction process. The composite of complex 2 (2@MWCNTs) having S and N donor sites shows the highest onset potential and the highest rate of oxygen reduction. Composites of complexes having P and S coordination sites (3a@MWCNTs and 3b@MWCNTs) show relatively high selectivity toward the two-electron oxygen reduction. The composites of complexes having S, N, and O coordination sites (1a@MWCNTs, 1b@MWCNTs, and 1c@MWCNTs) show moderate selectivity and activity for the two-electron oxygen reduction. 3a@MWCNTs show the optimum combination of activity and selectivity for H2O2 production. Remarkably, all the composites show high durability and may be suitable for the long-term oxygen-reduction process to synthesize H2O2.

Organic molecule-modified copper catalyst enables efficient electrochemical reduction of CO2-to-methane

Renewable electricity powered CO2 electroreduction to methane is promising for producing highly specific combustion fuels. However, the reduction process is severely limited by poor selectivity and chemical activity at high electrolysis reaction rates. Herein, we produce tandem electrocatalysts by combining organic small molecules (perylene-3,4,9,10-tetracarboxylic dianhydride and pentacene) with copper catalysts supported on microporous polytetra fluoroethylene with enhanced *CO protonation and weakened hydrogen evolution. Experimental results show that the tandem catalysts effectively suppress the two-electron reduction process associated with hydrogen (H2) and carbon monoxide (CO) production while inhibiting the multielectron conversion process associated with ethylene production (C2H4). As a result, the tandem catalysts enable an efficient eight-electron transfer for electrochemical reduction of CO2 and demonstrate a ∼ 50 % (±2%) Faradaic efficiency for CO2-to-methane conversion at a partial current density of 220 mA cm−2 in 1 M KHCO3 solution. Notably, the selectively of CO2-to-CH4 is 2.7 times higher than that of a copper catalyst supported on microporous polytetra fluoroethylene which is known to produce C2H4 with ∼ 50 % Faradaic efficiency. This work paves the way for tuning *CO dimerization and hydrogen evolution reaction to maximize CO2 methanation by using abundant organic molecular materials.

The synergistic effect of the adjacent dual NiNx sites to boost the oxygen reduction reaction activity for proton exchange membrane fuel cell

The investigation on the application of dual metallic sites in electro-catalysis for oxygen reduction reaction (ORR) has been given a lot of consideration. In this study, the reaction mechanisms and corresponding thermodynamic energy evolution in the dual Ni saturated coordinate with N atoms embedded in graphene have been investigated using first-principles density functional theory (DFT) calculations. The results show that the dual NiNx active sites are more stable than that of the NiN4 in view of the comparison of their formation energies. The reduction reaction of O2∗ on NiN4/G obviously promotes the two-electron reduction process due to its loosely bonded with O2. While the oxygen reduction reaction process on these dual NiNx active sites is thermally downhill, all of which promote a single site with four electron ORR process. The dual Ni atoms directly bonded catalysts (Ni2N6-ST2/G and Ni2N6-ST3/G) are in favor of the ORR mechanism through the reaction pathway of O2→O2∗→OOH∗→O∗→OH∗→H2O. However, the dual NiNx catalysts of others (Ni2N6-ST1/G and Ni2N7-ST4/G) prefer to undergo an unconventional 2OH∗ mechanism (O2→O2∗→OOH∗→2HO∗→OH∗→H2O). Moreover, it was found that the first reduction step (O2∗→OOH∗) is the thermodynamic rate-determining step (RDS) for the ORR on these catalysts. Both of Ni2N6-ST2/G and Ni2N6-ST3/G exhibit outstanding ORR activity with the on-set potentials of 0.65 V and 0.68 V, respectively. In particular, the two catalysts are able to adsorb the H2O2 and further reduce it into H2O through a two-electron pathway. Furthermore, it was found that the most stable intermediates in the oxygen reduction pathway depend on their lowest free energy at a given set of pH and applied potential. The free energy for these O-contained intermediates is linearly decreasing with the increment of applied potential. The critical potential for these O-contained intermediates is also linearly decreased with the increment of pH value.

Polydopamine/graphite sheet electrode for highly efficient electrocatalytic hydrogen peroxide generation and bisphenol A removal

Electrocatalytic processes, are greatly limited by acid conditions during water/wastewater treatment, and lead to higher disposal costs. Herein, based on the principle of strong adhesion of invertebrate mussels, polydopamine with multiple functional groups was immobilized on graphite sheet electrodes for constructing the electrocatalytic system (GS-PDA), which achieved favorable stability in hydrogen peroxide (H2O2) yield and model pollutant Bisphenol A (BPA) removal at pH = 3–9. At natural pH (∼5.8), GS-PDA had a higher BPA removal efficiency with 113 % increase in degradation rate and an 1100 % increase in productivity of H2O2 than control group. O2 bubbling was the original contributor of oxidant and its two-electron reduction product (H2O2) had a significant contribution for BPA removal in GS-PDA. High pH (pH ≥ 5) increased the selectivity toward the four-electron oxygen reduction process (to H2O) in control group, while GS-PDA could inhibit this process, thus promoting the production of H2O2 from two-electron oxygen reduction process. Both hydroxyl radicals and singlet oxygen were effective in removing BPA and the former was the primary pathway. Furthermore, 18 dominant degradations were identified in GS-PDA by high resolution hybrid quadrupole time-of-flight mass spectrometer, and BPA degradation pathway was proposed. This work found a way to decrease the effects of pH on electrocatalytic purification of water and generation of H2O2, and provided a strategy for treating wastewater at neutral pH.

(Digital Presentation) Synergistic Effect of Sn and Cu Oxides for the Electrochemical Reduction of CO2 to Formic Acid

The development of an electrochemical catalyst system that converts carbon dioxide (CO2) to high-value chemicals, such as formic acid (FA) will simultaneously curb CO2 emissions to atmosphere and provide sustainable pathways to create a range of fuels at lower cost. Electrochemical conversion of CO2 to FA is a two-electron reduction process and can be carried out at ambient conditions, and the reduced product has been found wide-ranging applications in chemical industries for production of household products, and a safe liquid-phase chemical for hydrogen storage. Synergistic bimetallic electrocatalysts can improve the activity and selectivity over their monometallic counterparts by tuning the structure, morphology, and composition. At the University of Kentucky’s Institute for Decarbonization and Energy Advancement (UK IDEA), our enhanced bimetallic oxide carbon utilization (EBOCU) process uses an engineered catalyst that facilitates operating at relatively low applied potentials, and high product selectivity to produce FA. Using bimetallic tin-copper oxide containing 95 mol% of Sn and 5 mol% of Cu immobilized on mesoporous carbon xerogel and alkaline electrolyte, we observed that hydrogen evolution reaction is suppressed and the selectivity towards formate is enhanced for the cell potential from 3.6 V through 4.0 V. Notably, our electrochemical reactor is successful in converting CO2 to formate at the rate of 2 mM/h in 3 mL/min flow system. Maximum faradaic efficiency of 94% is achieved towards formate at 3.8 V, which remained above 80% even after 200 h of continuous operation.

Synthesis, substitution kinetics, DNA/BSA binding and cytotoxicity of tridentate N^E^N (E = NH, O, S) pyrazolyl palladium(II) complexes.

The pincer complexes, [Pd(L1)Cl]BF4 (PdL1), [Pd(L2)Cl]BF4 (PdL2), [Pd(L3)Cl]BF4 (PdL3), [Pd(L4)Cl]BF4 (PdL4) were prepared by reacting the corresponding ligands, 2,6-bis[(1H-pyrazol-1-yl)methyl]pyridine (L1), bis[2-(1H-pyrazol-1-yl)ethyl]amine (L2), bis[2-(1H-pyrazol-1-yl)ethyl]ether (L3), and bis[2-(1H-prazol-1-yl)ethyl]sulphide (L4) with [PdCl2(NCMe)]2 in the presence NaBF4. The solid-state structures of complexesPdL1-PdL4 confirmed a tridentate coordination mode, with one chloro ligand completing the coordination sphere to afford square-planar complexes. Chemical behaviour of the complexes in solution confirms their stability in both aqueous and DMSO stock media. The electrochemical properties of the compounds showed irreversible two-electron reduction process. Kinetic reactivity of Pd complexes with the biological nucleophiles viz, thiourea (Tu), L-methionine (L-Met) and guanosine 5'-diphosphate disodium salt (5'-GMP) followed the order: PdL2 < PdL3 < PdL4, and PdL2 < PdL1. The kinetic reactivity is subject to the electronic effects of the spectator ligand(s), and the trend was supported by the DFT computed results. The palladium complexes PdL1-PdL4 bind to calf thymus (CT-DNA) via intercalation mode. In addition, the bovine serum albumin (BSA) showed good binding affinity to the complexes. The mode of quenching mechanism of the intrinsic fluorescence of CT-DNA and BSA by the complexes was found to be static. The order of interactions of the complexes with DNA and BSA was in tandem with the rate of substitution kinetics. The complexes, however, displayed relatively low cytotoxicity (IC50 > 100µM) when tested against the human cervical adenocarcinoma (HeLa) cell line and the transformed human lung fibroblast cell line (MRC-5 SV2).

Unveiling the lattice distortion and electron-donating effects in methoxy-functionalized MOF photocatalysts for H2O2 production

Semiconducting metal-organic frameworks (MOFs) are emerging photocatalysts for H2O2 production via the two-electron oxygen reduction (2e-ORR) process. Whether and how the functional groups on MOF nodes affect the 2e-ORR mechanism and performance remain largely unexplored. Herein, we report that partial replacement of formate (-COO-) by methoxy (-OMe) coordinated Zr-oxo cluster in UIO-66-NH2 significantly enhances the H2O2 production. The introduction of -OMe groups induces lattice distortion in UIO-66-NH2, resulting in the change of proton donor for the protonation of OOH* intermediate from -COOH to -NH3+ with a lowered kinetic energy barrier. The -OMe groups with electron-donating effect contribute to promoted light harvesting and charge separation. The 2e-ORR selectivity of -OMe functionalized UIO-66-NH2 is also enhanced, evidenced by rotating ring-disk electrode test and theoretical calculation. As a result, an improved photocatalytic ability is achieved with an H2O2 yield of 312.9 mM g−1 h−1, ~4.7 times higher than that of the original UIO-66-NH2.

Oxygen Vacancy-Mediated Z-Scheme Charge Transfer in a 2D/1D B-Doped g-C3N4/rGO/TiO2 Heterojunction Visible Light-Driven Photocatalyst for Simultaneous/Efficient Oxygen Reduction Reaction and Alcohol Oxidation.

Hydrogen peroxide (H2O2) is a powerful oxidant that directly or indirectly oxidizes many organic and inorganic contaminants. The photocatalytic generation of H2O2 is achieved by using a semiconductor photocatalyst in the presence of alcohol as a proton source. Herein, we have synthesized oxygen vacancy (Ov)-mediated TiO2/B-doped g-C3N4/rGO (TBCN@rGO) ternary heterostructures by a simple hydrothermal technique. Several characterization techniques were employed to explore the existence of oxygen vacancies in the crystal structure and investigate their impact on the optoelectronic properties of the catalyst. Oxygen vacancies offered additional sites for adsorbing molecular oxygen, activating alcohols, and facilitating electron migration from TBCN@rGO to the surface-adsorbed O2. The defect creation (oxygen vacancy) and Z-scheme mechanistic pathways create a suitable platform for generating H2O2 by two-electron reduction processes. The optimized catalyst showed the highest photocatalytic H2O2 evolution rate of 172 μmol/h, which is 1.9 and 2.5 times greater than that of TBCN and BCN, respectively. The photocatalytic oxidation of various lignocellulose-derived alcohols (such as furfural alcohol and vanillyl alcohol) and benzyl alcohol was also achieved. Photocatalytic activity data, physicochemical and optoelectronic features, and trapping experiments were conducted to elucidate the structure-activity relationships. The TBCN@rGO acts as a multifunctional Z-scheme photocatalyst having an oxygen vacancy, modulates surface acidity-basicity required for the adsorption and activation of the reactant molecules, and displays excellent photocatalytic performance due to the formation of a large number of active surface sites, increased electrical conductivity, improved charge transfer properties, outstanding photostability, and reusability. The present study establishes a unique strategy for improving H2O2 generation and alcohol oxidation activity and also provides insights into the significance of a surface vacancy in the semiconductor photocatalyst.

Hard template derived N, S dual heteroatom doped ordered mesoporous carbon as an efficient electrocatalyst for oxygen reduction reaction

At present, a low-cost and efficient electrocatalyst is vital to conquering the sluggish oxygen reduction reaction (ORR) in fuel cells. In particular, N and S dual heteroatom doped mesoporous carbon (NSMC) catalysts are believed to be one of the best ORR catalyst options due to the distribution of nitrogen, sulfur sites. In this work, for NSMC synthesis we employed 2D Santa barbara amorphous (SBA-15) silica as support material and L-cysteine as N and S dual precursor. The optimal loading of NSMC-0.4, reveals the high concentration of defect sites (ID/IG = 0.99), pyridinic (21.41 at. %), graphitic-N (50.27 at. %), thiophene-S (77.16 at. %) sites on MC surface resulting in an improved ORR performance. The NSMC-0.4 showed more positive onset potential of 0.78 V vs. RHE, half-wave potential of 0.68 V, current density of 2.8 mA/cm2, peroxide production of 81%, followed by two-electron reduction process and lower Rct of 10 Ω/cm2 in an alkaline electrolyte solution. However, NSMC-0.6 demonstrated the higher amount of peroxide selectivity (150%) due to the presence of a large quantity of pyrrolic-N sites. In addition, our work provide an excellent guide for the synthesis and design of NSMC for efficient peroxide production via an electrochemical synthesis route.

In-situ fabrication of Cu doped dual-phase CsPbBr3–Cs4PbBr6 inorganic perovskite nanocomposites for efficient and selective photocatalytic CO2 reduction

Converting CO2 into chemical fuels with renewable energy is an appealing approach for the deployment of carbon utilization technologies. Halide perovskite nanocrystals have been considered as one of the most promising light-harvesting materials in photocatalytic applications. However, most of the perovskite-based photocatalysts facilitate a two-electron reduction process to convert into CO, hard for the eight-electron CH4 production pathways. Herein, we develop a facile in-situ transformation strategy to fabricate Cu doped dual-phase CsPbBr3–Cs4PbBr6 inorganic perovskite nanocomposites (Cu/CsPbBr3-Cs4PbBr6 NCs). Compared to the pristine CsPbBr3 nanoparticles, the Cu/CsPbBr3-Cs4PbBr6 NCs have presented 4.2-fold higher photocatalytic efficiency for CO2 reduction and 303% increased electron consumption rate, in addition, the significant enhanced selectivity for converting CO2 into CH4 up to 78.6% has also been achieved. The in-situ transformation strategy opens an avenue for rational design perovskite-based photocatalysts for efficient and stable CO2 reduction.

Sulfide Ligands in Hybrid Semiconductor-Metal Nanocrystal Photocatalysts: Improved Hole Extraction and Altered Catalysis.

Hybrid semiconductor-metal nanocrystals manifest efficient photocatalytic activity related to the metal domain promoting charge carrier separation and providing an active catalytic site. The surface properties of such nanoparticles are also of paramount importance in determining their photocatalytic activity. Addressing the combination of surface effects in catalysis on metals, with the electronic properties of hybrid nanoparticles, we examined the effect of coating CdS-Au hybrid nanoparticles with sulfide, an anion that is expected to bind strongly to both domains, on the photocatalytic functionality. Upon sulfide coating, one-electron processes - namely the oxidative production of hydroxyl radicals and the reductive production of superoxide - were increased, whereas the activity for two-electron reduction processes - H2 and hydrogen peroxide generation - was hampered. These findings indicate a double-edged sword effect for sulfide coating that on one side relieves the hole extraction bottleneck from the semiconductor segment and, on the other hand, poisons the metal domain restricting its reductive capacity for the two-electron processes requiring a chemisorption step on the metal surface. The work further demonstrates the importance of surface properties for the photocatalytic action of such hybrid nanoparticle systems.

Enhanced electrochemical advanced oxidation on boride activated carbon: The influences of boron groups

Exploring an efficient electro-catalyst is fundamentally important to enhance degradation of persistent organic pollutants during electrochemical advanced oxidation process. In this work, boride activated carbon (BAC) containing different boron group content was prepared as low-cost and efficient catalysts. BAC possessed a more positive onset potential of oxygen reduction reaction (0.458 V vs. RHE) and a faster rate of H2O2 generation (365 mg/L pH=3), compared with activated carbon (0.425 V vs. RHE, 138 mg/L pH=3). DFT calculations and XPS results revealed that -BC3 and -BC2O active groups enhanced oxygen adsorption, and small electronegativity difference between B and O facilitated the desorption of •OOH. The rate of in-situ phenol degradation (0.193 min−1) increased by an order of magnitude as compared to activated carbon (0.018 min−1), because BAC promoted the in-situ conversion of H2O2 to •OH. Therefore, it provided a theoretical base for the further application of boron catalyst in two-electron oxygen reduction process.

Metal-Free Catalysis: A Redox-Active Donor-Acceptor Conjugated Microporous Polymer for Selective Visible-Light-Driven CO2 Reduction to CH4.

Achieving more than a two-electron photochemical CO2 reduction process using a metal-free system is quite exciting and challenging, as it needs proper channeling of electrons. In the present study, we report the rational design and synthesis of a redox-active conjugated microporous polymer (CMP), TPA-PQ, by assimilating an electron donor, tris(4-ethynylphenyl)amine (TPA), with an acceptor, phenanthraquinone (PQ). The TPA-PQ shows intramolecular charge-transfer (ICT)-assisted catalytic activity for visible-light-driven photoreduction of CO2 to CH4 (yield = 32.2 mmol g-1) with an impressive rate (2.15 mmol h-1 g-1) and high selectivity (>97%). Mechanistic analysis based on experimental results, in situ DRIFTS, and computational studies reveals that the potential of TPA-PQ for catalyzing photoreduction of CO2 to CH4 was energetically driven by photoactivated ICT upon surface adsorption of CO2, wherein adjacent keto groups of PQ unit play a pivotal role. The critical role of ICT for stimulating photocatalysis is further illustrated by synthesizing another redox-active CMP (TEB-PQ), bearing triethynylbenzene (TEB) and PQ, that shows 8-fold lesser activity for photoreduction toward CO2 to CH4 (yield = 4.4 mmol g-1) as compared to TPA-PQ. The results demonstrate a novel concept for CO2 photoreduction to CH4 using an efficient, sustainable, and recyclable metal-free robust organic photocatalyst.

Boosting the oxidase-like activity of platinum nanozyme in MBTH-TOOS chromogenic system for detection of trypsin and its inhibitor

Nanozymes, as a new type of artificial enzyme, have recently become a research hotspot in the field of catalysis and biomedicine. However, the application of nanozyme is limited by catalytic activity changes of different substrates and low specificity. This work shows that citrate-capped platinum nanoparticles (Cit-PtNPs) exhibit stronger oxidase-like activity than other platinum nanozymes at different pH when 3-methyl-2-benzothiazolinonehydrazone hydrochloride (MBTH) and n-ethyl-n- (2-hydroxy-3-sulfopropyl)-m-toluidine sodium salt (TOOS) were used as chromogenic substrates. This phenomenon has important reference value for different nanozymes to choose chromogenic substrates in catalysis. In MBTH-TOOS chromogenic system, MBTH (-NH) radical is first produced during the reaction through catalytic oxidation of Cit-PtNPs, which reacts with TOOS to produce a colorless compound. The blue-purple quinoid dye was produced through the dismutation of the colorless compound. The catalytic mechanism of the oxidase-like activity of Cit-PtNPs is that two-electron reduction process and four-electron reduction process are simultaneously carried out in the catalytic process. Furthermore, to solve the problem of low specificity of metal nanozymes, protamine is designed as aggregation promoter of Cit-PtNPs and the specifichydrolysis substrate of trypsin. In this work, it can achieve one-step detection of trypsin by the boosting oxidase activity of Cit-PtNPs at pH8. The catalytic activity of Cit-PtNPs is proportional to the concentration of trypsin. The linear range for trypsin is 1.0–70.0 ngmL−1 and the limit of detection is measured to be 0.6 ngmL−1. This novel method has also been successfully applied to the detection of inhibitors and trypsin in urine samples.

Controllable synthesis of porous silver cyanamide nanocrystals with tunable morphologies for selective photocatalytic CO2 reduction into CH4

The conversion of CO2 driven by solar energy into carbon-containing fuel has huge potential applications. However, most photocatalysts can only promote the two-electron reduction process to generate CO, and it is difficult to produce eight-electron CH4, which is more valuable and can store more solar energy. Herein, we prepared porous silver cyanamide nanocrystals with tunable morphologies via a facile synthesis strategy. Compared with ball/rectangular plate (RAP) and ball/leaf-like plate (SAP), the ball/porous leaf-like plate (LAP) can provide more internal reaction microenvironment, which is not only conducive to the transport of photoinduced charge carriers, but also can expand the active sites for photocatalytic CO2 reduction. Moreover, the suitable band gap of LAP sample can capture more visible light to provide more photoinduced electron-hole pairs to participate in the reduction reaction. Consequently, the LAP sample can convert CO2 to CH4 with remarkable activity and high selectivity (nearly 100%) without cocatalyst and photosensitizer under visible light irradiation. This work provides a promising way to design new photocatalysts for various applications in solar energy conversion.