Visible Light-sensitized CO2 Methanation along a Relaxed Heat Available Route.

In photocatalysis, the resulted heat by the relaxation of most of incident light no longer acts as the industrially favorite driving force back to the target photo-reaction due to more or less the negative relation between photocatalytic efficiency and temperature. Here, we reported a visible light-sensitized protocol that completely reversed the negatively temperature-dependent efficiency in photo-driven CO2 methanation with saturated water vapor. Uniform Pt/N-TiO2/PDI self-assembly material decisively injects the excited electron of PDI sensitizer into N-TiO2 forming Ti-H hydride which is crucially temperature-dependent nucleophilic species to dominate CO2 methanation, rather than conventionally separated and trapped electrons on the conductor band. Meanwhile, the ternary composite lifts itself temperature from room temperature to 305.2 °C within 400s only by the failure excitation upon simulated sunlight of 2.5 W/cm2, and smoothly achieves CO2 methanation with a record number of 4.98 mmol g-1 h-1 rate, compared to less than 0.02 mmol g-1 h-1 at classic Pt/N-TiO2/UV photocatalysis without PDI sensitization. This approach can reuse ~53.9% of the relaxed heat energy from the incident light thereby allow high-intensity incident light as strong as possible within a flowing photo-reactor, opening the most likely gateways to industrialization.

Solar overall water-splitting by a spin-hybrid all-organic semiconductor.

Direct solar-to-hydrogen conversion from pure water using all-organic heterogeneous catalysts remains elusive. The challenges are twofold: (i) full-band low-frequent photons in the solar spectrum cannot be harnessed into a unified S1 excited state for water-splitting based on the common Kasha-allowed S0 → S1 excitation; (ii) the H+ → H2 evolution suffers the high overpotential on pristine organic surfaces. Here, we report an organic molecular crystal nanobelt through the self-assembly of spin-one open-shell perylene diimide diradical anions (:PDI2-) and their tautomeric spin-zero closed-shell quinoid isomers (PDI2-). The self-assembled :PDI2-/PDI2- crystal nanobelt alters the spin-dependent excitation evolution, leading to spin-allowed S0S1 → 1(TT) → T1 + T1 singlet fission under visible-light (420 nm~700 nm) and a spin-forbidden S0 → T1 transition under near-infrared (700 nm~1100 nm) within spin-hybrid chromophores. With a triplet-triplet annihilation upconversion, a newly formed S1 excited state on the diradical-quinoid hybrid induces the H+ reduction through a favorable hydrophilic diradical-mediated electron transfer, which enables simultaneous H2 and O2 production from pure water with an average apparent quantum yield over 1.5% under the visible to near-infrared solar spectrum.

Cu2+ coordination-induced in situ photo-to-heat on catalytic sites to hydrolyze ß-lactam antibiotics pollutants in waters.

For degradation of ß-lactam antibiotics pollution in waters, the strained ß-lactam ring is the most toxic and resistant moiety to biodegrade and redox-chemically treat among their functional groups. Hydrolytically opening ß-lactam ring with Lewis acid catalysts has long been recognized as a shortcut, but at room temperature, such hydrolysis is too slow to be deployed. Here, we found when Cu2+ was immobilized on imine-linked COF (covalent organic framework) (Cu2+/Py-Bpy-COF, Cu2+ load is 1.43 wt%), as-prepared composite can utilize the light irradiation (wavelength range simulated sunlight) to in situ heat anchored Cu2+ Lewis acid sites through an excellent photothermal conversion to open the ß-lactam ring followed by a desired full-decarboxylation of hydrolysates. Under 1 W/cm2 simulated sunlight, Cu2+/Py-Bpy-COF powders placed in a microfiltration membrane rapidly cause a temperature rising even to ~211.7 °C in 1 min. It can effectively hydrolyze common ß-lactam antibiotics in waters and even antibiotics concentration is as high as 1 mM and it takes less than 10 min. Such photo-heating hydrolysis rate is ~24 times as high as under dark and ~2 times as high as Cu2+ homogenous catalysis. Our strategy significantly decreases the interference from generally coexisting common organics in waters and potential toxicity concerns of residual carboxyl groups in hydrolysates and opens up an accessible way for the settlement of ß-lactam antibiotics pollutants by the only energy source available, the sunlight.

Water molecule switching heterogeneous proton-coupled electron transfer pathway.

Figuring out the specific pathway of semiconductor-mediated proton-coupled electron transfer (PCET) driven by light is essential to solar energy conversion systems. In this work, we reveal that the amount of adsorbed water molecules determines the photo-induced PCET pathway on the TiO2 surface through systematic kinetic solvent isotope effect (KSIE) experiments. At low water content (<1.7 wt%), the photo-induced single-proton/single-electron transfer on TiO2 nanoparticles follows a stepwise PT/ET pathway with the formation of high-energy H+/D+-O[double bond, length as m-dash]C or H+/D+-O-C intermediates, resulting in an inverse KSIE (H/D) ∼0.5 with t Bu3ArO· and KSIE (H/D) ∼1 with TEMPO in methanol-d 0/d 4 systems. However, at high water content (>2 wt%), the PCET reaction follows a concerted pathway with a lower energy barrier, leading to normal KSIEs (H/D) ≥ 2 with both reagents. In situ ATR-FTIR observation and DFT calculations suggest that water molecules' existence significantly lowers the proton/electron transfer energy barrier, which coincides with our experimental observations.

Photocatalytic Oxo-Amination of Aryl Cyclopropanes through an Unusual SN2-Like Ring-Opening Pathway: Won >99% ee.

One-pot oxo-amination of unactivated cyclopropanes with safe, green dioxygen as an oxidant and low-cost amines as nitrogen sources has generated interest since this can directly result in uniform ß-located difunctional units. Formation of the three-electron cation radical followed by the nucleophilic attack of amines to open the strained ring of cyclopropanes catalyzed by classic noble-complex photocatalysts was a promising strategy. However, this ring-opening pathway could not maintain the entire second-order nucleophilic substitution (SN2) conversion, which generally led to unsatisfactory enantioselectivity (enantiomeric excess (ee) value ∼60%). Here, we demonstrate that for such a one-step oxo-amination of cyclopropanes with benign dioxygen and pyrazoles, a highly uniform inversion of configuration could be first accomplished through a TiO2 photocatalyst. This strategy features low-cost, semiheterogeneous photocatalysis and environmentally friendly reaction conditions, without using any sacrificial reagent or additive. Importantly, our protocol not only provides a relatively broad substrate scope tolerant to a certain range of substituted cyclopropanes and pyrazoles, resulting in various ß-amino ketone products (∼50 examples) with excellent conversions and yields, but also retains excellent enantioselectivity (ee value ∼99%). A concerted SN2 ring opening raised from an oxetane cation intermediate rather than a conventional three-electron cation radical prior to attaching to dioxygen was proposed.

Long-lasting photocatalytic activity of trace phosphorus-doped g-C3N4/SMSO and its application in antibacterial ceramics.

Conventional photocatalysts generate numerous active species-primarily hydroxyl radicals (•OH)-under solar light excitation to exert photocatalytic activity for especially antibacterial effects. However, the light dependence limits their competitiveness against other antimicrobial materials since they do not work at night. Herein, a P-g-C3N4/Sr2MgSi2O7:Eu2+,Dy3+ (P-g-C3N4/SMSO) composite day-night photocatalyst is synthesized, using a model methyl orange (MO) substrate, and the impacts of trace P doping and the SMSO composite on the activity of the photocatalyst in MO degradation is investigated; Its antibacterial effect against Escherichia coli and Staphylococcus aureus on ceramic surfaces is further examined. The morphology, structure, and composition of the photocatalyst are characterized by SEM, TEM, XRD, FT-IR, and UV-vis DRS. Finally, the photocatalytic mechanism is elucidated through active species capture experiments and ESR testing. P doping and the SMSO heterojunction structure reduce the width of the forbidden band of g-C3N4 and broaden its visible-light-response range. Moreover, SMSO acts as a light source to realize long-lasting photocatalytic performance of the composite, even in the dark. The photocatalytic process produces •O2-, 1O2, and h+ active species, with •O2- and 1O2 playing the dominant role-instead of •OH as previously thought.

Fundamental Flaw in the Current Construction of the TiO2 Electron Transport Layer of Perovskite Solar Cells and Its Elimination.

The top-performing perovskite solar cells (efficiency > 20%) generally rely on the use of a nanocrystal TiO2 electron transport layer (ETL). However, the efficacies and stability of the current stereotypically prepared TiO2 ETLs employing commercially available TiO2 nanocrystal paste are far from their maximum values. As revealed herein, the long-hidden reason for this discrepancy is that acidic protons (∼0.11 wt %) always remain in TiO2 ETLs after high-temperature sintering due to the decomposition of the organic proton solvent (mostly alcohol). These protons readily lead to the formation of Ti-H species upon light irradiation, which act to block the electron transfer at the perovskite/TiO2 interface. Affront this challenge, we introduced a simple deprotonation protocol by adding a small amount of strong proton acceptors (sodium ethoxide or NaOH) into the common TiO2 nanocrystal paste precursor and replicated the high-temperature sintering process, which wiped out nearly all protons in TiO2 ETLs during the sintering process. The use of deprotonated TiO2 ETLs not only promotes the PCE of both MAPbI3-based and FA0.85MA0.15PbI2.55Br0.45-based devices over 20% but also significantly improves the long-term photostability of the target devices upon 1000 h of continuous operation.

Magnetically modulated photochemical reaction pathways in anthraquinone molecules and aggregates.

The chemical reactions involving excited-state radical pairs (RPs) of parallel/anti-parallel spin configurations are sensitive to magnetic field, leading to the possibilities of magnetically controlled synthesis of chemical compounds. Here we show that the reaction of anthraquinone (AQ) in sodium dodecyl sulfate (SDS) micellar solution under UV excitation is significantly influenced by applying external field. The steady state and time-resolved spectroscopies reveal that the reaction intermediate (pairs of AQH-SDS radicals) can undergo two distinct pathways depending on whether it is spin singlet or triplet, and the field is beneficial to the conversion between spin configurations of RPs. The applied field not only affects the reaction rate constant but also changes the final products. Besides, the aggregation of AQ molecules would change the population of singlets and triplets and thus enhance magnetic field effect. This work represents a promising way of controlling chemical reaction and improving reaction selectivity via magnetic field methods.

Crucial Effect of Ti-H Species Generated in the Visible-Light-Driven Transformations: Slowed-Down Proton-Coupled Electron Transfer.

Despite the fact that proton-coupled electron transfer (PCET) has been hypothesized to play a pivotal role in the power conversion efficiency (PCE) of TiO2-based solar-energy applications, the specific relationship between the intrinsic nature of visible-light (Vis)-driven PCET reactions and limited PCE gains has not yet been well revealed. Here we studied the detailed kinetics of reactions between various alcohols and radicals (tBu3ArO•/TEMPO) on a TiO2 photocatalyst under dye-sensitization Vis irradiation versus direct ultraviolet (UV) irradiation. We found that the rates of Vis-driven reactions were much slower than those of UV-driven reactions under identical light intensity. A similar phenomenon was observed under the off-line dark-reaction conditions in which TiO2 was prereduced by alcohols. The rapid formation and difficult breakage of the stable "Ti-H" intermediate were proposed to account for the slowed-down PCET effect. This finding revealed an inherent bottleneck in Vis-driven energy conversion applications.

Efficacy and safety of early prone positioning combined with HFNC or NIV in moderate to severe ARDS: a multi-center prospective cohort study.

BACKGROUND: Previous studies suggest that prone positioning (PP) can increase PaO2/FiO2 and reduce mortality in moderate to severe acute respiratory distress syndrome (ARDS). The aim of our study was to determine whether the early use of PP combined with non-invasive ventilation (NIV) or high-flow nasal cannula (HFNC) can avoid the need for intubation in moderate to severe ARDS patients. METHODS: This prospective observational cohort study was performed in two teaching hospitals. Non-intubated moderate to severe ARDS patients were included and were placed in PP with NIV or with HFNC. The efficacy in improving oxygenation with four support methods-HFNC, HFNC+PP, NIV, NIV+PP-were evaluated by blood gas analysis. The primary outcome was the rate of intubation. RESULTS: Between January 2018 and April 2019, 20 ARDS patients were enrolled. The main causes of ARDS were pneumonia due to influenza (9 cases, 45%) and other viruses (2 cases, 10%). Ten cases were moderate ARDS and 10 cases were severe. Eleven patients avoided intubation (success group), and 9 patients were intubated (failure group). All 7 patients with a PaO2/FiO2 < 100 mmHg on NIV required intubation. PaO2/FiO2 in HFNC+PP were significantly higher in the success group than in the failure group (125 ± 41 mmHg vs 119 ± 19 mmHg, P = 0.043). PaO2/FiO2 demonstrated an upward trend in patients with all four support strategies: HFNC < HFNC+PP ≤ NIV < NIV+PP. The average duration for PP was 2 h twice daily. CONCLUSIONS: Early application of PP with HFNC, especially in patients with moderate ARDS and baseline SpO2 > 95%, may help avoid intubation. The PP was well tolerated, and the efficacy on PaO2/FiO2 of the four support strategies was HFNC < HFNC+PP ≤ NIV < NIV+PP. Severe ARDS patients were not appropriate candidates for HFNC/NIV+PP. TRIAL REGISTRATION: ChiCTR, ChiCTR1900023564. Registered 1 June 2019 (retrospectively registered).

Modification of TiO2 Nanoparticles with Organodiboron Molecules Inducing Stable Surface Ti3+ Complex.

As one of the most promising semiconductor oxide materials, titanium dioxide (TiO2) absorbs UV light but not visible light. To address this limitation, the introduction of Ti3+ defects represents a common strategy to render TiO2 visible-light responsive. Unfortunately, current hurdles in Ti3+ generation technologies impeded the widespread application of Ti3+ modified materials. Herein, we demonstrate a simple and mechanistically distinct approach to generating abundant surface-Ti3+ sites without leaving behind oxygen vacancy and sacrificing one-off electron donors. In particular, upon adsorption of organodiboron reagents onto TiO2 nanoparticles, spontaneous electron injection from the diboron-bound O2- site to adjacent Ti4+ site leads to an extremely stable blue surface Ti3+‒O-· complex. Notably, this defect generation protocol is also applicable to other semiconductor oxides including ZnO, SnO2, Nb2O5, and In2O3. Furthermore, the as-prepared photoelectronic device using this strategy affords 103-fold higher visible light response and the fabricated perovskite solar cell shows an enhanced performance.

Brönsted Catalyzed Hydrolysis of Microcystin-LR by Siderite.

Six naturally occurring minerals were employed to catalyze the hydrolysis of microcystin-LR (MC-LR) in water. After preliminary screening experiments, siderite stood out among these minerals due to its higher activity and selectivity. In comparison with kaolinite, which is known to act as a Lewis acid catalyst, siderite was found to act primarily as a Brönsted acid catalyst in the hydrolysis of MC-LR. More interestingly, we found that the presence of humic acid significantly inhibited catalytic efficiency of kaolinite, while the efficiency of siderite remained high (∼98%). Reaction intermediates detected by LC-ESI/MS were used to indicate cleavage points in the macrocyclic ring of MC-LR, and XPS was used to characterize siderite interaction with MC-LR. Detailed analysis of the in situ ATR-FTIR absorption spectra of MC-LR indicated hydrogen bonding at the siderite-water-MC-LR interface. A metastable ring, involving hydrogen bonding, between surface bicarbonate of siderite and an amide of MC-LR was proposed to explain the higher activity and selectivity toward MC-LR. Furthermore, siderite was found to reduce the toxicity of MC-LR to mice by hydrolyzing MC-LR peptide bonds. The study demonstrates the potential of siderite, an earth-abundant and biocompatible mineral, for removing MC-LR from water.

Aqueous Oxidations Started by TiO2 Photoinduced Holes Can Be a Rate-Determining Step.

In aqueous TiO2 photocatalytic hydroxylation of weakly polar aromatics, a series of inverse H/D KIEs of 0.7-0.8 were observed, which is different than the normal H/D kinetic isotope effects (KIEs) usually observed for polar aromatics. This result indicated that the oxidation started by photo-induced hvb+ can be the rate-determining step.

The Formation of Ti-H Species at Interface Is Lethal to the Efficiency of TiO2-Based Dye-Sensitized Devices.

TiO2-based dye-sensitization cycle is one of the basic strategies for the development of solar energy applications. Although the power conversion efficiency (PCE) of dye-sensitized devices has been improved through constant attempts, the intrinsically fatal factor that leads to the complete failure of the PCE of TiO2-mediated dye-sensitized devices has not yet been determined. Here, by using isotopically labeled MAS-1H NMR, ATR-FTIR spectroscopy (separate H/D and 48Ti/49Ti experiments), and ESR, we revealed that the accumulative formation of Ti-H species on the TiO2 surface is the intrinsic cause of the PCE failure of TiO2-based dye-sensitization devices. Such a Ti-H species is generated from the reduction of hydrogen ions (mostly released from dye carboxyl groups or organic electrolyte) accompanied by electron injection on the surface of TiO2, which deteriorates the PCE mainly by reducing the electrical conductivity of the TiO2 (by a maximum of ∼80%) and the hydrophilic nature of the TiO2 surface (contact angle increased).

Modulating the photocatalytic redox preferences between anatase TiO2 {001} and {101} surfaces.

It is widely believed that anatase TiO2 {001} and {101} surfaces acts as the oxidative and reductive sites in photocatalytic reactions, respectively, which is attributed to their different intrinsic surface structures. However, we demonstrate that the photocatalytic redox preferences of TiO2 {001} and {101} surfaces are determined by the adsorbate-reconstructed surface structure instead of their intrinsic surface structures, which can be modulated by surface protonation/deprotonation.

Mechanistic Studies of TiO2 Photocatalysis and Fenton Degradation of Hydrophobic Aromatic Pollutants in Water.

HO-adduct radicals have been investigated and confirmed as the common initial intermediates in TiO2 photocatalysis and Fenton degradations of water-insoluble aromatics. However, the evolution of HO-adduct radicals to phenols has not been completely clarified. When 4-d-toluene and p-xylene were degraded by TiO2 photocatalysis and Fenton reactions, respectively, a portion of the 4-deuterium or 4-CH3 group (18-100 %) at the attacked ipso position shifted to the adjacent position of the ring in the formed phenols (NIH shift; NIH is short for the National Institutes of Health, to honor the place where this phenomenon was first discovered). The results, combined with the observation of a key dienyl cationic intermediate by in situ attenuated total reflectance FTIR spectroscopy, indicate that, for the evolution of HO-adduct radicals, a mixed mechanism of both the carbocation intermediate pathway and O2 -capturing pathway occurs in both aqueous TiO2 photocatalysis and aqueous Fenton reactions.

Doping-Promoted Solar Water Oxidation on Hematite Photoanodes.

As one of the most promising materials for solar water oxidation, hematite has attracted intense research interest for four decades. Despite their desirable optical band gap, stability and other attractive features, there are great challenges for the implementation of hematite-based photoelectrochemical cells. In particular, the extremely low electron mobility leads to severe energy loss by electron hole recombination. Elemental doping, i.e., replacing lattice iron with foreign atoms, has been shown to be a practical solution. Here we review the significant progresses in metal and non-metal element doping-promoted hematite solar water oxidation, focusing on the role of dopants in adjusting carrier density, charge collection efficiency and surface water oxidation kinetics. The advantages and salient features of the different doping categories are compared and discussed.

Pivotal Role and Regulation of Proton Transfer in Water Oxidation on Hematite Photoanodes.

Hematite is a promising material for solar water splitting; however, high efficiency remains elusive because of the kinetic limitations of interfacial charge transfer. Here, we demonstrate the pivotal role of proton transfer in water oxidation on hematite photoanodes using photoelectrochemical (PEC) characterization, the H/D kinetic isotope effect (KIE), and electrochemical impedance spectroscopy (EIS). We observed a concerted proton-electron transfer (CPET) characteristic for the rate-determining interfacial hole transfer, where electron transfer (ET) from molecular water to a surface-trapped hole was accompanied by proton transfer (PT) to a solvent water molecule, demonstrating a substantial KIE (∼3.5). The temperature dependency of KIE revealed a highly flexible proton transfer channel along the hydrogen bond at the hematite/electrolyte interface. A mechanistic transition in the rate-determining step from CPET to ET occurred after OH(-) became the dominant hole acceptor. We further modified the proton-electron transfer sequence with appropriate proton acceptors (buffer bases) and achieved a greater than 4-fold increase in the PEC water oxidation efficiency on a hematite photoanode.

Activation of Water in Titanium Dioxide Photocatalysis by Formation of Surface Hydrogen Bonds: An In Situ IR Spectroscopy Study.

The hole-driving oxidation of titanium-coordinated water molecules on the surface of TiO2 is both thermodynamically and kinetically unfavorable. By avoiding the direct coordinative adsorption of water molecules to the surface Ti sites, the water can be activated to realize its oxidation. When TiO2 surface is covered by the H-bonding acceptor F, the first-layer water adsorption mode is switched from Ti coordination to a dual H-bonding adsorption on adjacent surface F sites. Detailed in situ IR spectroscopy and isotope-labeling studies reveal that the adsorbed water molecules by dual H-bonding can be oxidized to O2 even in the absence of any electron scavengers. Combined with theoretical calculations, it is proposed that the formation of the dual H-bonding structure can not only enable the hole transfer to the water molecules thermodynamically, but also facilitate kinetically the cleavage of O-H bonds by proton-coupled electron transfer process during water oxidation.

H2O-involved two-electron pathway for photooxidation of aldehydes on TiO2: an isotope labeling study.

Aldehyde pollution has been receiving increasing environmental concern recently. In this study, the photooxidation of aldehydes to carboxylates on the TiO2 surface was studied by an oxygen-isotope-labeling method. The solvent H2O was found to contribute much to the oxygen source of the formed carboxylate, which cannot be explained if the conventional O2-involved free radical chain reaction is the only mechanism for the photocatalytic oxidation of aldehydes. We also observed that, unlike in the TiO2 photocatalytic system, the aldehyde oxidation in homogeneous solutions initiated by single electron oxidant (•)OH and SO4(•-) radicals inserted a small O atom of H2O into the product acids. The detailed experiments, combined with DFT calculation, revealed the existence of a new pathway for the oxidation of aldehyde on TiO2, in which, analogous to oxidation of aldehyde by dehydrogenase, the aldehyde undergoes a hydration first and subsequently is oxidized through a two-electron transfer process. The present study highlights the multielectron characteristic of TiO2 photocatalytic oxidation and can have implications for the oxidation of aldehyde in the environment.