Advanced electrocatalytic redox processes for environmental remediation of halogenated organic water pollutants.

Halogenated organic compounds are widespread, and decades of heavy use have resulted in global bioaccumulation and contamination of the environment, including water sources. Here, we introduce the most common halogenated organic water pollutants, their classification by type of halogen (fluorine, chlorine, or bromine), important policies and regulations, main applications, and environmental and human health risks. Remediation techniques are outlined with particular emphasis on carbon-halogen bond strengths. Aqueous advanced redox processes are discussed, highlighting mechanistic details, including electrochemical oxidations and reductions of the water-oxygen system, and thermodynamic potentials, protonation states, and lifetimes of radicals and reactive oxygen species in aqueous electrolytes at different pH conditions. The state of the art of aqueous advanced redox processes for brominated, chlorinated, and fluorinated organic compounds is presented, along with reported mechanisms for aqueous destruction of select PFAS (per- and polyfluoroalkyl substances). Future research directions for aqueous electrocatalytic destruction of organohalogens are identified, emphasizing the crucial need for developing a quantitative mechanistic understanding of degradation pathways, the improvement of analytical detection methods for organohalogens and transient species during advanced redox processes, and the development of new catalysts and processes that are globally scalable.

Analysis of the Scale of Global Human Needs and Opportunities for Sustainable Catalytic Technologies.

We analyzed the enormous scale of global human needs, their carbon footprint, and how they are connected to energy availability. We established that most challenges related to resource security and sustainability can be solved by providing distributed, affordable, and clean energy. Catalyzed chemical transformations powered by renewable electricity are emerging successor technologies that have the potential to replace fossil fuels without sacrificing the wellbeing of humans. We highlighted the technical, economic, and societal advantages and drawbacks of short- to medium-term decarbonization solutions to gauge their practicability, economic feasibility, and likelihood for widespread acceptance on a global scale. We detailed catalysis solutions that enhance sustainability, along with strategies for catalyst and process development, frontiers, challenges, and limitations, and emphasized the need for planetary stewardship. Electrocatalytic processes enable the production of solar fuels and commodity chemicals that address universal issues of the water, energy and food security nexus, clothing, the building sector, heating and cooling, transportation, information and communication technology, chemicals, consumer goods and services, and healthcare, toward providing global resource security and sustainability and enhancing environmental and social justice. Supplementary Information: The online version contains supplementary material available at 10.1007/s11244-023-01799-3.

Pulsed Laser in Liquids Made Nanomaterials for Catalysis.

Catalysis is essential to modern life and has a huge economic impact. The development of new catalysts critically depends on synthetic methods that enable the preparation of tailored nanomaterials. Pulsed laser in liquids synthesis can produce uniform, multicomponent, nonequilibrium nanomaterials with independently and precisely controlled properties, such as size, composition, morphology, defect density, and atomistic structure within the nanoparticle and at its surface. We cover the fundamentals, unique advantages, challenges, and experimental solutions of this powerful technique and review the state-of-the-art of laser-made electrocatalysts for water oxidation, oxygen reduction, hydrogen evolution, nitrogen reduction, carbon dioxide reduction, and organic oxidations, followed by laser-made nanomaterials for light-driven catalytic processes and heterogeneous catalysis of thermochemical processes. We also highlight laser-synthesized nanomaterials for which proposed catalytic applications exist. This review provides a practical guide to how the catalysis community can capitalize on pulsed laser in liquids synthesis to advance catalyst development, by leveraging the synergies of two fields of intensive research.

Site-Selective Halogenation of Polyoxovanadate Clusters: Atomically Precise Models for Electronic Effects of Anion Doping in VO2.

We report the synthesis and characterization of a monochloride-functionalized polyoxovanadate-alkoxide (POV-alkoxide) cluster, which can serve as a molecular model for halogen-doped vanadium oxide (VO2) materials that have recently attracted great interest as advanced materials for energy-saving smart window applications. Chloride-substituted variants of the Lindqvist vanadium-oxide cluster were obtained via two distinct chemical pathways: (1) direct halogenation of the isovalent parent POV-alkoxide architecture, [V6O7(OC2H5)12]-2 with AlCl3 and (2) coordination of a chloride ion to a coordinatively unsaturated vanadium center within a cluster that bears a single oxygen-atom vacancy, [V6O6(OC2H5)12]0. Notably, our direct halogenation constitutes the first example of selective, single-site halide doping of homometallic metal oxide clusters. The chloride-containing compound, [V6O6Cl(OC2H5)12]-1, was characterized by 1H NMR spectroscopy and X-ray crystallography. The electronic structure of the chloride-functionalized POV-alkoxide cluster was established by infrared, electronic absorption, and X-ray photoelectron spectroscopy and revealed formation of a site-differentiated VIII ion upon halogenation. Cyclic voltammetry was employed to assess the electrochemical response of halide doping. A comparison of the Cl-VO2 model to the fully oxygenated cluster, [V6O7(OC2H5)12]-2, provides molecular-level insights into a new proposed mechanism by which halogenation increases the carrier density in solid VO2, namely, through prompting charge separation within the material.

Driving Force Dependence of Electron Transfer from Electronically Excited [Ir(COD)(µ-Me2pz)]2 to Photo-Acid Generators.

We report the rates of electron transfer (ET) reactions of electronically excited [Ir(COD)(µ-Me2pz)]2 with onium salt photoacid generators (PAGs). The reduction potentials of the PAGs span a large electrochemical window that allows determination of the driving force dependence of the ET reactions. Rate constants of ET from electronically excited [Ir(COD)(µ-Me2pz)]2 to onium PAGs are determined by the reaction driving force until the diffusion limit in acetonitrile is reached.

Mixed-Metal Tungsten Oxide Photoanode Materials Made by Pulsed-Laser in Liquids Synthesis.

Globally scalable sunlight-driven devices that convert solar energy into storable fuels will require efficient light absorbers that are made of non-precious elements. Suitable photoanode materials are yet to be discovered. Here we utilised the timesaving nature of pulsed-laser-in-liquids synthesis and prepared a series of neat and mixed-metal tungsten oxide photoanode materials to investigate the effect of ad-metals on optical and photocurrent generation properties. We obtained sub-µm-sized materials with different colours from W, Al, Ta, or first-row transition metal targets in water or aqueous ammonium metatungstate solutions. We observed metastable polymorphs of WO3 and tungsten oxides with varying degrees of oxygen deficiency. Pulsed-laser in liquids synthesis of Ni in ammonium metatungstate solutions produce hollow spheres (with ≤6 % Ni with respect to W). Photocurrent generation in strong aqueous acid is highest in mixed-metal tungsten oxide photoanode materials with around 5 % of iron or nickel.

Complex nanomineral formation utilizing kinetic control by PLAL.

We used pulsed-laser ablation in liquids (PLAL) of Cu or Zn foil targets in water or in aqueous Cu or Zn salt solutions. PLAL in neat water generated mixtures of metal and (thermodynamically preferred) metal oxide nanomaterials, whereas the availability of select dissolved anions predictably led to the fabrication of more complex phase-pure nanominerals. PLAL of Cu foil in aqueous CuCl2 solution produced nano-paratacamite, Cu2Cl(OH)3, whereas nano-rouaite, Cu2(NO3)(OH)3, was formed in aqueous Cu(NO3)2 and NH4OH solution. Likewise, we synthesized simonkolleite, Zn5(OH)8Cl2·H2O, or layered zinc hydroxide nitrate, Zn5(OH)8(NO3)2·2H2O, nanoparticles by PLAL of Zn targets in aqueous ablation liquids with added ZnCl2 and NH4OH or Zn(NO3)2, respectively. Bimetallic zincian paratacamite resulted from PLAL of Cu foil in aqueous Cu and Zn chloride solution. Our results show that kinetic control exceeded thermodynamic product formation during nanosecond ultraviolet PLAL.

Earth-Abundant Heterogeneous Water Oxidation Catalysts.

Water oxidation is a key chemical transformation for the conversion of solar energy into chemical fuels. Our review focuses on recent work on robust earth-abundant heterogeneous catalysts for the oxygen-evolving reaction (OER). We point out that improvements in the performance of OER catalysts will depend critically on the success of work aimed at understanding reaction barriers based on atomic-level mechanisms. We highlight the challenge of obtaining acid-stable OER catalysts, with proposals for elements that could be employed to reach this goal. We suggest that future advances in solar fuels science will be accelerated by the development of new methods for materials synthesis and characterization, along with in-depth investigations of redox mechanisms at catalytic surfaces.

Highly active mixed-metal nanosheet water oxidation catalysts made by pulsed-laser ablation in liquids.

Surfactant-free mixed-metal hydroxide water oxidation nanocatalysts were synthesized by pulsed-laser ablation in liquids. In a series of [Ni-Fe]-layered double hydroxides with intercalated nitrate and water, [Ni1-xFex(OH)2](NO3)y(OH)x-y·nH2O, higher activity was observed as the amount of Fe decreased to 22%. Addition of Ti(4+) and La(3+) ions further enhanced electrocatalysis, with a lowest overpotential of 260 mV at 10 mA cm(-2). Electrocatalytic water oxidation activity increased with the relative proportion of a 405.1 eV N 1s (XPS binding energy) species in the nanosheets.

Experimental and computational study of BODIPY dye-labeled cavitand dynamics.

Understanding the distance distribution and dynamics between moieties attached to the walls of a resorcin[4]arene cavitand, which is switchable between an expanded kite and a contracted vase form, might enable the use of this molecular system for the study of fundamental distance-dependent interactions. Toward this goal, a combined experimental and molecular dynamics (MD) simulation study on donor/acceptor borondipyrromethene (BODIPY) dye-labeled cavitands present in the vase and kite forms was performed. Direct comparison between anisotropy decays calculated from MD simulations with experimental fluorescence anisotropy data showed excellent agreement, indicating that the simulations provide an accurate representation of the dynamics of the system. Distance distributions between the BODIPY dyes were established by comparing time-resolved Förster resonance energy transfer experiments and MD simulations. Fluorescence intensity decay curves emulated on the basis of the MD trajectories showed good agreement with the experimental data, suggesting that the simulations present an accurate picture of the distance distributions and dynamics in this molecular system and provide an important tool for understanding the behavior of extended molecular systems and designing future applications.

A novel ruthenium(II)-cobaloxime supramolecular complex for photocatalytic H2 evolution: synthesis, characterisation and mechanistic studies.

We report the synthesis and characterization of novel mixed-metal binuclear ruthenium(II)-cobalt(II) photocatalysts for hydrogen evolution in acidic acetonitrile. First, 2-(2'-pyridyl)benzothiazole (pbt), 1, was reacted with RuCl(3)·xH(2)O to produce [Ru(pbt)(2)Cl(2)]·0.25CH(3)COCH(3), 2, which was then reacted with 1,10-phenanthroline-5,6-dione (phendione), 3, in order to produce [Ru(pbt)(2)(phendione)](PF(6))(2)·4H(2)O, 4. Compound 4 was then reacted with 4-pyridinecarboxaldehyde in order to produce [Ru(pbt)(2)(L-pyr)](PF(6))(2)·9.5H(2)O, 5 (where L-pyr = (4-pyridine)oxazolo[4,5-f]phenanthroline). Compound 5 was then reacted with [Co(dmgBF(2))(2)(H(2)O)(2)] (where dmgBF(2) = difluoroboryldimethylglyoximato) in order to produce the mixed-metal binuclear complex, [Ru(pbt)(2)(L-pyr)Co(dmgBF(2))(2)(H(2)O)](PF(6))(2)·11H(2)O·1.5CH(3)COCH(3), 6. [Ru(Me(2)bpy)(2)(L-pyr)Co(dmgBF(2))(2)(OH(2))](PF(6))(2), 7 (where Me(2)bpy = 1,10-phenanthroline, 4,4'-dimethyl-2,2'-bipyridine) and [Ru(phen)(2)(L-pyr)Co(dmgBF(2))(2)(OH(2))](PF(6))(2), 8 were also synthesised. All complexes were characterized by elemental analysis, ESI MS, HRMS, UV-visible absorption, (11)B, (19)F, and (59)Co NMR, ESR spectroscopy, and cyclic voltammetry, where appropriate. Photocatalytic studies carried out in acidified acetonitrile demonstrated constant hydrogen generation longer than a 42 hour period as detected by gas chromatography. Time resolved spectroscopic measurements were performed on compound 6, which proved an intramolecular electron transfer from an excited Ru(II) metal centre to the Co(II) metal centre via the bridging L-pyr ligand. This resulted in the formation of a cobalt(I)-containing species that is essential for the production of H(2) gas in the presence of H(+) ions. A proposed mechanism for the generation of hydrogen is presented.

Excited state dynamics in solid and monomeric tetracene: The roles of superradiance and exciton fission.

The excited state dynamics in polycrystalline thin films of tetracene are studied using both picosecond fluorescence and femtosecond transient absorption. The solid-state results are compared with those obtained for monomeric tetracene in dilute solution. The room temperature solid-state fluorescence decays are consistent with earlier models that take into account exciton-exciton annihilation and exciton fission but with a reduced delayed fluorescence lifetime, ranging from 20-100 ns as opposed to 2 µs or longer in single crystals. Femtosecond transient absorption measurements on the monomer in solution reveal several excited state absorption features that overlap the ground state bleach and stimulated emission signals. On longer timescales, the initially excited singlet state completely decays due to intersystem crossing, and the triplet state absorption superimposed on the bleach is observed, consistent with earlier flash photolysis experiments. In the solid-state, the transient absorption dynamics are dominated by a negative stimulated emission signal, decaying with a 9.2 ps time constant. The enhanced bleach and stimulated emission signals in the solid are attributed to a superradiant, delocalized S(1) state that rapidly fissions into triplets and can also generate a second superradiant state, most likely a crystal defect, that dominates the picosecond luminescence signal. The enhanced absorption strength of the S(0)→S(1) transition, along with the partially oriented nature of our polycrystalline films, obscures the weaker T(1)→T(N) absorption features. To confirm that triplets are the major species produced by relaxation of the initially excited state, the delayed fluorescence and ground state bleach recovery are compared. Their identical decays are consistent with triplet diffusion and recombination at trapping or defect sites. The results show that complications like exciton delocalization, the presence of luminescent defect sites, and crystallite orientation must be taken into account to fully describe the photophysical behavior of tetracene thin films. The experimental results are consistent with the traditional picture that tetracene's photodynamics are dominated by exciton fission and triplet recombination, but suggest that fission occurs within 10 ps, much more rapidly than previously believed.

Experimental and theoretical study of temperature dependent exciton delocalization and relaxation in anthracene thin films.

The spectroscopy of solid anthracene is examined both experimentally and theoretically. To avoid experimental complications such as self-absorption and polariton effects, ultrathin polycrystalline films deposited on transparent substrates are studied. To separate the contributions from different emitting species, the emission is resolved in both time and wavelength. The spectroscopic data are interpreted in terms of a three-state kinetic model, where two excited states, a high energy state 1 and a low energy state 2, both contribute to the luminescence and are kinetically coupled. Using this model, we analyze the spectral lineshape, relative quantum yield, and relaxation rates as a function of temperature. For state 1, we find that the ratio of the 0-0 vibronic peak to the 0-1 peak is enhanced by roughly a factor of 3.5 at low temperature, while the quantum yield and decay rates also increase by a similar factor. These observations are explained using a theoretical model previously developed for herringbone polyacene crystals. The early-time emission lineshape is consistent with that expected for a linear aggregate corresponding to an edge-dislocation defect. The results of experiment and theory are quantitatively compared at different temperatures in order to estimate that the singlet exciton in our polycrystalline films is delocalized over about ten molecules. Within these domains, the exciton's coherence length steadily increases as the temperature drops, until it reaches the limits of the domain, whereupon it saturates and remains constant as the temperature is lowered further. While the theoretical modeling correctly reproduces the temperature dependence of the fluorescence spectral lineshape, the decay of the singlet exciton appears to be determined by a trapping process that becomes more rapid as the temperature is lowered. This more rapid decay is consistent with accelerated trapping due to increased delocalization of the exciton at lower temperatures. These observations suggest that exciton coherence can play an important role in both radiative and nonradiative decay channels in these materials. Our results show that the spectroscopy of polyacene solids can be analyzed in a self-consistent fashion to obtain information about electronic delocalization and domain sizes.

Exciton fission and fusion in bis(tetracene) molecules with different covalent linker structures.

Bichromophoric molecules can support two spatially separated excited states simultaneously and thus provide novel pathways for electronic state relaxation. Exciton fission, where absorption of a single photon leads to two triplet states, is a potentially useful example of such a pathway. In this paper, a detailed study of exciton fission in three novel phenylene-linked bis(tetracene) molecules is presented. Their spectroscopy is analyzed in terms of a three-state kinetic model in which the singlet excited state can fission into a triplet pair state, which in turn undergoes recombination on a time scale longer than the molecule's radiative lifetime. This model allows us to fit both the prompt and delayed fluorescence decay data quantitatively. The para-phenylene linked bis(tetracene) molecules 1,4-bis(tetracen-5-yl)benzene (1) and 4,4'-bis(tetracen-5-yl)biphenylene (2) show intramolecular exciton fission with yields of approximately 3%, whereas no delayed fluorescence is observed for tetracene or the meta-linked molecule 1,3-bis(tetracen-5-yl)benzene 3. Analysis of the temperature-dependent fluorescence dynamics yields activation energies for fission of (10.0 +/- 0.6) kJ/mol for 1 and (4.1 +/- 0.5) kJ/mol for 2, with Arrhenius prefactors of (1.48 +/- 0.04) x 10(8) s(-1) for 1 and (1.72 +/- 0.02) x 10(7) s(-1) for 2. The observed trends in activation energies are reproduced by ab initio calculations of the independently optimized singlet and triplet energies. The calculations indicate that electronic coupling between the two tetracene units is primarily through-bond, allowing differences in fission rates to be qualitatively explained in terms of the linker structure as well. Our results show that it is important to consider the effects of the linker structure on both energy relaxation and electronic coupling in bichromophoric molecules. This study provides insight into the structural and energetic factors that should be taken into account in the design of exciton fission molecules for possible solar cell applications.

Self-absorption correction for solid-state photoluminescence quantum yields obtained from integrating sphere measurements.

A new method is presented for analyzing the effects of self-absorption on photoluminescence integrating sphere quantum yield measurements. Both the observed quantum yield and luminescence spectrum are used to determine the self-absorption probability, taking into account both the initial emission and subsequent absorption and reemission processes. The analysis is experimentally validated using the model system of the laser dye perylene red dispersed in a polymer film. This approach represents an improvement over previous methods that tend to overestimate the true quantum yield, especially in cases with high sample absorbance or quantum yield values.

Hierarchical placement and associated optoelectronic impact of carbon nanotubes in polymer-fullerene solar cells.

Since their discovery, carbon nanotubes (CNTs) have been considered to be promising candidates for polymer-based solar cells, but their functional incorporation and utilization in such devices have been limited due to processing bottlenecks. Here, we demonstrate the realization of controlled placement of a single-walled CNT (SWNT) monolayer network at four different positions in polymer-fullerene bulk-heterojunction (BHJ) solar cells. SWNTs were deposited by dip-coating from a hydrophilic suspension, and a very brief, largely nondestructive argon plasma treatment of the active layer was utilized for incorporation of a SWNT layer within or above it. We demonstrate that SWNTs on the hole-collection side of the active layer lead to an increase in power conversion efficiency (PCE) of the photovoltaic devices from 4 to 4.9% (under AM 1.5 G, 1.3 suns illumination). This is the highest reported PCE for polymer-based solar cells incorporating CNTs, upon consideration of expected scaling of device parameters for 1 sun illumination. We also observe that SWNTs deposited on the top of the active layer lead to major electro-optical changes in the device functionality, including an increased fluorescence lifetime of poly-3-hexylthiophene (P3HT).

Photochemically driven shape changes of crystalline organic nanorods.

Nanorods composed of 9-tert-butylanthroate (9-TBAE) are synthesized using an Al2O3 template and solvent annealing. The rods consist of micron-scale crystalline domains, and UV light induces a [4 + 4] photodimerization that results in a uniform 15% expansion along the rod axis. This is in contrast to random 9-TBAE crystals, which disintegrate under the same conditions. Transmission electron microscopy, atomic force microscopy, and comparison of the X-ray crystal structures of the monomer and photodimer all provide evidence for a mechanism based on a crystal-to-crystal photoreaction leading to an increase in molecular volume. It is likely that the high surface-to-volume ratio in the nanorods provides a strain relief pathway that is absent in larger crystals. Preliminary attempts to reverse the reaction using shorter wavelength light to photodissociate the dimers were only partly successful. These results suggest that crystalline organic nanostructures may provide an efficient way to transform photochemical energy into mechanical motion on the nanometer scale.

Energy and charge transfer dynamics in fully decorated benzyl ether dendrimers and their disubstituted analogues.

We examine the photophysics of a series of molecules consisting of a benzthiadiazole core surrounded by a network of benzyl ether arms terminated by aminopyrene chromophores, which function as both energy and electron donors. Three classes of molecules are studied: dendrimers whose peripheries are fully decorated with aminopyrene donors (F), disubstituted dendrimers whose peripheries contain only two donors (D), and linear analogues in which a pair of benzyl ether arms link two donors to the central core (L). The electronic energy transfer (EET) and charge transfer (CT) rates are determined by fluorescence lifetime measurements on the energy donors and electron acceptors, respectively. In all three types of molecules, the EET time scales as the square root of the generation number G, consistent with the flexible nature of the benzyl ether framework. Transient anisotropy measurements confirm that donor-donor energy hopping does not play a major role in determining the EET times. The CT dynamics occur on the nanosecond time scale and lead to stretched exponential decays, probably due to conformational disorder. Measurements at 100 degrees C confirm that conformational fluctuations play a role in the CT dynamics. The average CT time increases with G in the L and D molecules but decreases for the F dendrimers. This divergent behavior as G increases is attributed to the competing effects of larger donor-acceptor distances (which lengthen the CT time) versus a larger number of donors (which shorten the average CT time). This work illustrates two important points about light-harvesting and charge-separation dendrimers. First, the use of a flexible dendrimer framework can lead to a more favorable scaling of the EET time (and thus the light-harvesting efficiency) with dendrimer size, relative to what would be expected for a fully extended dendrimer. Second, fully decorated dendrimers can compensate for the distance-dependent slowdown in CT rate as G increases by providing additional pathways for the CT reaction to occur.

The photophysical properties of chromophores at high (100 mM and above) concentrations in polymers and as neat solids.

The absorption, fluorescence, and photostability of five conjugated chromophores: perylene, 2,5,8,11-tetra-t-butyl perylene (TTBP), perylene orange (PO), perylene red (PR), and a zwitterionic Meisenheimer complex (MHC), are studied as a function of concentration in poly(methyl methacrylate) (PMMA). At 1 mM concentrations, all five molecules exhibit properties consistent with unaggregated chromophores. At higher concentrations, perylene and PO both exhibit excimer formation, while TTBP, PR, and the MHC retain their monomeric fluorescent lineshapes. In these three molecules, however, the fluorescence decay times decrease by 10% (TTBP) to 50% (MHC) at concentrations of 100 mM in PMMA. The fluorescence properties of these highly concentrated samples are sensitive to the sample preparation conditions. In the neat solid where the effective concentration is on the order of 1 M, all three molecules exhibit very fast fluorescence decays, on the order of 150 ps or less, despite the fact that they retain their basic monomeric fluorescence lineshape. In addition to the enhanced nonradiative decay at high concentrations, these three molecules also undergo a concentration-dependent photobleaching. The combined effects of intermolecular nonradiative decay channels and photobleaching appear to be a general obstacle to achieving highly concentrated dye-doped solids.