Photochemical System Research Articles

Dual-Wavelength Gated oxo-Diels-Alder Photoligation.

The control of chemical functionalization with orthogonal light stimuli paves the way toward manipulating materials with unprecedented spatiotemporal resolution. To reach this goal, we herein introduce a photochemical reaction system that enables two-color control of covalent ligation via an oxo-Diels–Alder cycloaddition between two separate light-responsive molecular entities: a UV-activated photocaged diene based on ortho-quinodimethanes and a carbonyl dienophile appended to a diarylethene photoswitch, whose reactivity can be modulated upon illumination with UV and visible light.

Photochemical hydrogen evolution from cobalt microperoxidase-11

A photochemical system utilizing the semisynthetic biomolecular catalyst acetylated cobalt microperoxidase-11 (CoMP11-Ac) along with [Ru(bpy)3]2+ as a photosensitizer and ascorbic acid as an electron donor is shown to generate hydrogen from water in a visible light-driven reaction. The reductive quenching pathway facilitated by photoexcited [Ru(bpy)3]2+ overcomes the high overpotential observed for CoMP11-Ac in electrocatalysis, yielding turnover numbers ranging from 606 to 2390 (2 μM – 0.1 μM CoMP11-Ac). The longevity of CoMP11-Ac in the photochemical system, sustaining catalysis for over 20 h, is in contrast to its previously reported behavior in an electrochemical system where catalysis slows after 15 min. Proton reduction turnover number and rate are highest at a neutral pH, a rare feature among cobalt catalysts in similar photochemical systems, which typically function best under acidic conditions. Incorporating biomolecular components into the design of catalysts for photochemical systems may address the need for hydrogen generation from neutral-pH water sources.

Improving removal rate and efficiency of As(V) by sulfide from strongly acidic wastewater in a modified photochemical reactor

ABSTRACT Employing ultraviolet light to enhance the removal of As(V) by sulfide (S(-II)) from strongly acidic wastewater is a potential method. However, we found the arsenic trisulfide (As2S3) and elemental sulfur (S8) particles formed in this method not only vastly hinder light transmission in the wastewater but also undergo light-induced redissolution, leading to a decrease in removal rate and efficiency of As(V). Herein, As(V) removal by sulfide from strongly acidic wastewater was performed in a modified photochemical reactor to weaken the effect of the formed particles on As(V) removal. It was found that in this study, the formed particles could be efficiently removed from the photoreactor by three operations, i.e. circulation-filtration, septum setting, and lamp sleeve cleaning. The removal of As(V) was approximately 11-fold faster than that without three operations, saving 90.9% of the reaction time and 89.4% of energy consumption. The removal efficiency of As(V) also increased through weakening the light-induced redissolution of the formed particles. This study facilitates the practical application of the UV light promoted As(V) removal technology and also provides a new method to lessen the light-blocking effect in the particle-forming photochemical reaction systems.

Significant role of iron on the fate and photodegradation of enrofloxacin

Enrofloxacin (ENR) belongs to the fluoroquinolone (FQ) antibiotics family, which are contaminants of emerging concern frequently found in effluents. Although many works studying photo-Fenton process for FQ degradation have been reported, there are no reports analysing in deep the effect of iron complexation, as well as other metals, towards FQs’ photolysis, which, evidently, also contributes in the overall degradation of the pollutant. Therefore, in this work, we report a comparative study between the photochemical fate of ENR and its complex with Fe(III) under simulated sunlight irradiation. In addition, the effect of dissolved oxygen, self-sensitization process, and H2O2 addition on the studied photochemical systems are also investigated. Results indicate that, for free and iron-complexed ENR, singlet oxygen (1O2) is generated from the interaction of its triplet state with ground state oxygen. Half-life time (t1/2) of ENR under sun simulated conditions is estimated to be around 22 min, while complexation with iron enhances its photostability, leading to a t1/2 of 2.1 h. Such finding indicates that at least the presence of iron, might notably increase the residence time of these pollutants in the environment. Eventually, only with the addition of H2O2, the FQ-iron complex is efficiently degraded due to photo-Fenton process even at circumneutral pH values due to the high stability of the formed complex. Finally, after LC/FT-ICR MS analysis, 39 photoproducts are detected, of which the 14 most abundant ones are identified. Results indicate that photoproducts formation is pH and iron dependent.

Coordination-driven discrete metallo-supramolecular assembly for rapid and selective photochemical CO2 reduction in aqueous solution.

A discrete metallo-supramolecular assembly composed of six iron(ii) cations and twelve redox-active terpyridine fragments has been developed for the highly efficient visible-light-driven reduction of CO2 to CO with a TON of 14 956 and 99.6% selectivity in the presence of an organic thermally activated delayed fluorescence (TADF) photosensitizer 4CzIPN in aqueous solution. The photochemical system proceeds rapidly with a turnover frequency (TOF) of 276 min-1. It is demonstrated that the redox-active terpyridine fragments in the assembly are reduced by the photosensitizer which could further act as an electron reservoir for CO2 reduction, resulting in the highly efficient reduction of CO2. This work shows that discrete metallo-supramolecular assemblies could be used for robust photochemical CO2 reduction.

Mapping Photochemical Reactivity Profiles on Surfaces.

Herein, we introduce a comprehensive methodology to map the reactivity of photochemical systems on surfaces. The reactivity of photoreactive groups in solution often departs from their corresponding solution absorption spectra. On surfaces, the relationship between the surface absorption spectra and reactivity remains unexplored. Thus, herein, the reactivity of an o-methylbenzaldehyde and a tetrazole, as ligation partners for maleimide functionalized polymers, was investigated when the reactive moieties are tethered to a surface. The ligation reaction of tetrazole functionalized surfaces was found to proceed rapidly leading to high grafting densities, while o-methylbenzaldehyde functionalized substrates required longer irradiation times and resulted in lower surface coverage at the same wavelength (330 nm). Critically, wavelength resolved reactivity profiles were found to closely match the surface absorption spectra, contrary to previously reported red shifts in solution for the same chromophores.

3D printing of metal-based materials for renewable energy applications

Large-scale renewable energy must overcome conversion and storage challenges before it can replace fossil fuels due to its intermittent nature. However, current sustainable energy devices still suffer from high cost, low efficiency, and poor service life problems. Recently, porous metal-based materials have been widely used as desirable cross-functional platforms for electrochemical and photochemical energy systems for their unique electrical conductivity, catalytic activity, and chemical stability. To tailor the porosity length scale, ordering, and compositions, 3D printing has been applied as a disruptive manufacturing revolution to create complex architected components by directly joining sequential layers into designed structures. This article intends to summarize cutting-edge advances of metal-based materials for renewable energy devices (e.g., fuel cells, solar cells, supercapacitors, and batteries) over the past decade.

Analytical Investigation of the Reaction‐Diffusion Waves in the Mesopause Photochemistry

AbstractThe mechanism of the generation of reaction‐diffusion waves in the mesopause region (80–90 km) has been studied analytically. These waves are the propagating phase fronts arising in the oscillations of O, O3, H, OH, and HO2 concentrations. They appear in the presence of horizontal eddy diffusion in zonal direction when mesospheric photochemistry responds subharmonically (with a period of 2 days) to diurnal variations of solar radiation. The photochemical system in the mesopause region is a nonlinear oscillator which can be roughly described by a system of two differential nonautonomous equations with power law nonlinearity which was derived in our earlier papers. To model the wave propagation, we have considered a continuous chain of oscillators with diffusion coupling and with the phase of external periodic forcing depending linearly on spatial coordinates. It was found that the reaction‐diffusion waves are caused by specific “wind” type transport appearing in the equations for the amplitudes of 2‐day photochemical oscillations of O and H concentrations due to the zonal inhomogeneity of the external forcing. The obtained expression for the wave propagation velocity fully confirmed the earlier numerical results that the magnitude of the velocity is proportional to the diffusion coefficient and the gradient of the external forcing phase. The wave propagation direction is determined by the definite phase relations specified by internal parameters of the system only.

Novel Biofuel Cell Using Hydrogen Generation of Photosynthesis.

Energies based on biomaterials attract a lot of interest as next-generation energy because biomaterials are environmentally friendly materials and abundant in nature. Fuel cells are also known as the clean and important next-generation source of energy. In the present study, to develop the fuel cell based on biomaterials, a novel biofuel cell, which consists of collagen electrolyte and the hydrogen fuel generated from photochemical system II (PSII) in photosynthesis, has been fabricated, and its property has been investigated. It was found that the PSII solution, in which PSII was extracted from the thylakoid membrane using a surfactant, generates hydrogen by the irradiation of light. The typical hydrogen-generating rate is approximately 7.41 × 1014 molecules/s for the light intensity of 0.5 mW/cm2 for the PSII solution of 5 mL. The biofuel cell using the PSII solution as the fuel exhibited approximately 0.12 mW/cm2. This result indicates that the fuel cell using the collagen electrolyte and the hydrogen fuel generated from PSII solution becomes the new type of biofuel cell and will lead to the development of the next-generation energy.

Direct Grid-Based Nonadiabatic Dynamics on Machine-Learned Potential Energy Surfaces: Application to Spin-Forbidden Processes.

We have recently shown how high-accuracy wave function grid-based propagation schemes, such as the multiconfiguration time-dependent Hartree (MCTDH) method, can be combined with machine-learning (ML) descriptions of PESs to yield an "on-the-fly" direct dynamics scheme which circumvents potential energy surface (PES) prefitting. To date, our approach has been demonstrated in the ground-state dynamics and nonadiabatic spin-allowed dynamics of several molecular systems. Expanding on this successful previous work, this Article demonstrates how our ML-based quantum dynamics scheme can be adapted to model nonadiabatic dynamics for spin-forbidden processes such as intersystem crossing (ISC), opening up new possibilities for modeling chemical dynamic phenomena driven by spin-orbit coupling. After describing modifications to diabatization schemes to enable accurate and robust treatment or electronic states of different spin-multiplicity, we demonstrate our methodology in applications to modeling ISC in SO2 and thioformaldehyde, benchmarking our results against previous trajectory- and grid-based calculations. As a relatively efficient tool for modeling spin-forbidden nonadiabatic dynamics without demanding any prefitting of PESs, our overall strategy is a potentially powerful tool for modeling important photochemical systems, such as photoactivated pro-drugs and organometallic catalysts.

Enhancing Biosynthesis and Manipulating Flux in Whole Cells with Abiotic Catalysis.

Metabolic engineering uses genetic strategies to drive flux through desired pathways. Recent work with electrochemical, photochemical, and chemocatalytic setups has revealed that these systems can also expand metabolic pathways and manipulate flux in whole cells. Electrochemical systems add or remove electrons from metabolic pathways to direct flux to more- or less-reduced products. Photochemical systems act as synthetic light-harvesting complexes and yield artificial photosynthetic organisms. Biocompatible chemocatalysis increases product scope, streamlines syntheses, and yields single-flask processes to deliver products that would be challenging to synthesize through biosynthetic means alone. Here, we exclusively highlight systems that combine abiotic systems with living whole cells, taking particular note of strategies that enable the merger of these typically disparate systems.

Enhanced Photochemical Volatile Organic Compounds Release from Fatty Acids by Surface-Enriched Fe(III).

Both Fe(III) and fatty acids are ubiquitous and important species in environmental waters. Because they are amphipathic, many fatty acids are surface active and prone to enrichment at the air-water interface. Here, we report that by using nonanoic acid (NA) as a model fatty acid, coexisting Fe(III), even at concentrations as low as 1 μM, markedly enhanced the photochemical release of NA-derived volatile organic compounds (VOCs) such as octanal and octane into the air. Further studies indicated that the surface-enriched fatty acids dramatically increase the local concentration of Fe(III) at the water surface, which enables Fe(III)-mediated photochemical reactions to take place at the air-water interface, and the VOCs facilely produced by fatty acid photooxidation can then be released into the air. Moreover, the product distribution in the Fe(III)-mediated reactions was largely different from that in other photochemical systems, and a mechanism based on photochemical decarboxylation is proposed. Considering that the coexistence of fatty acids and Fe(III) in the environment is common, the enhanced photochemical release of VOCs by surface-enriched fatty acids and Fe(III) may be an important channel for the atmospheric emission of VOCs, which are known to play an essential role in the formation of ozone and secondary organic aerosols.

Combining Photodeprotection and Ligation into a Dual-Color Gated Reaction System.

We report a photochemical reaction system which requires activation by two colors of light. Specifically, a dual wavelength gated system is established by fusing the visible light mediated deprotection of a dithioacetal with the UV light activated Diels–Alder reaction of an o‐methylbenzaldehyde with n‐ethylmaleimide. Critically, both light sources are required to achieve the Diels–Alder adduct, irradiation with visible or UV light alone does not lead to the target product. The introduced dual gated photochemical system is particularly interesting for application in light driven 3D printing, where two color wavelength activated photoresists may become reality.

Comprehensive exploration of the ultraviolet degradation of polychlorinated biphenyls in different media

As one of the most important natural transformation processes, photodegradation deserves more attention and research. In the current work, we comprehensively explored the photochemical behaviors of polychlorinated biphenyls (PCBs) in n-hexane (Hex), methanol/water, and silica gel under UV-irradiation. Photodegradation rates were found to be faster in methanol/water than in Hex. All of the three photochemical systems generated sigmatropic rearrangement products. The dominant photodegradation pathways were dechlorination, dechlorination/methoxylation/hydroxylation, and hydroxylation in Hex, methanol/water, and silica gel systems, respectively. Furthermore, some new photodegradation products, such as polychlorinated biphenyl ethers, polychlorinated dibenzofurans, polychlorinated biphenylenes, and methylated polychlorinated biphenyls, are reported for the first time. These findings would provide deeper insight into the phototransformation behaviors of PCBs.

Photochemical degradation of chloramphenicol over jarosite/oxalate system: Performance and mechanism investigation

Rational selection of affordable catalyst and effective degradation process are significant for antibiotic-containing wastewater treatment. Herein, a photochemical catalytic system comprising of bio-synthesized jarosite and oxalic acid (Ox) was investigated for degradation of antibiotic chloramphenicol (CAP) under light irradiation. Benefiting from abundant reactive species including H2O2, OH, O2− produced in photochemical process, a 97.5 % removal efficiency of CAP was obtained within 40 min. Consecutive testing cycles indicated jarosite had excellent stability and reusability in photocatalytic system. Radical chain reaction induced by photosensitive Fe(III)-Ox complexes under light irradiation was suggested to be the main mechanism for CAP degradation. A few degradation intermediates were identified to propose the possible degradation pathways of CAP. Further investigation showed that the antibacterial activities of CAP solution towards Escherichia. coli ATCC 8739 and Staphylococcus. aureus ATCC 6538 were largely reduced after treatment by photochemical process. Typical operation parameters of light/jarosite/Ox system were also investigated. CAP degradation performance in actual water demonstrated the feasibility of light/jarosite/Ox process. Overall, the developed light/jarosite/Ox system possesses great potential for antibiotic-containing wastewater treatment.

Visible light-driven oxidation of arsenite, sulfite and thiazine dyes: A new strategy for using waste to treat waste

Recently, the advanced oxidation processes (AOPs) based on sulfate radical (SO4•⁻) using sulfite has received increasing concerns. Metal-free activation of sulfite is still in urgent demands from the perspective of cleaner production since the reported efficient systems containing sulfite has been relied on the transition metals. In this work, methylene blue (MB⁺), a well-known photosensitizer and thiazine dye contaminant, was utilized to activate sulfite for the efficient photooxidation of arsenite (As(III)) to arsenate (As(V)) under visible light (LED lamps with wavelength 640 nm) and sunlight, respectively. The initial oxidation rates of 5–40 μM As(III) are 28-fold–116-fold as that of the decolorization of 0.27 μM MB⁺ with 50 μM sulfite at pH 7.3. The maximum stoichiometric ratio MB⁺: As(III): sulfite was obtained to be 1 : 142: 247, suggesting an efficient utilization of both MB⁺ and sulfite as waste resources. The electrical energy per order (EE/O) index was calculated to be 1.83 × 10−3 kWh L−1 for the visible light-MB+-sulfite system, which is much less than those reported systems. Oxysulfur radicals (mainly peroxymonosulfate radical, SO5•⁻) produced in this photochemical system are responsible for As(III) oxidation. The other two common thiazine dyes (thionine and Azure B) are also capable of activating sulfite for As(III) oxidation due to the same chromophores. Thus the novel strategy of using waste sulfite and the thiazine dyes is promising for As(III) oxidation under sunlight, with which low-concentration wastes of thiazine dye and sulfite can be utilized to achieve the goal of cleaner production.

Effective in-situ reduction of Cr(VI) from leather wastewater by advanced reduction process based on CO2·- with visible-light photocatalyst

Advanced reduction process (ARP) has drawn an increasing interest as a new manner for removing oxidative pollutants in water. In this paper, we demonstrate the possibility of in-situ reduction of Cr(VI) by CO2·- produced from formate originally existing in leather wastewater by visible-light-driven ARP containing black TiO2 photocatalyst. The prepared black TiO2 with nanotube structure achieves remarkable enhanced the reduction rate of Cr(VI) as high as 96.2% (k = 0.0114 min−1) in the presence of formate, which is approximately 4.75 times than that of 56.3% (k = 0.0024 min−1) in the absence under 120 min visible-light irradiate at unadjusted pH. The results exhibit a distinct contrast with commercial TiO2 (P25). A series of control experiments are also performed, indicating that formate is able to convert the oxidative environment into a highly reductive one, and the formate concentration, black TiO2 dosage and pH may greatly impact on the Cr(VI) reduction rate. According to the electron spin resonance (ESR) measurement, CO2·- radicals can be directly verified as dominate radical in this system. Moreover, this system appears to be attractive for creating photochemical systems where in-situ production of CO2·- radicals may be realized by using formate. Then this in-situ ARP system will provide a new perspective for the Cr(VI) removing, which makes leather wastewater treatment much easier and more sustainable in the future.

Ab Initio Nonadiabatic Molecular Dynamics with Hole-Hole Tamm-Dancoff Approximated Density Functional Theory.

The study of photoinduced dynamics in chemical systems necessitates accurate and computationally efficient electronic structure methods, especially as the systems of interest grow larger. The linear response hole-hole Tamm-Dancoff approximated (hh-TDA) density functional theory method was recently proposed to satisfy such demands. The N-electron electronic states are obtained by means of double annihilations on a doubly anionic (N + 2)-electron reference state, allowing for the ground and excited states to be formed on the same footing and thus enabling the correct description of conical intersections. Dynamic electron correlation effects are incorporated by means of the exchange-correlation functional. The accuracy afforded by the simultaneous treatment of static and dynamic correlation in addition to the relatively low computational cost, comparable to that of time-dependent density functional theory (TDDFT), makes it a promising ab initio electronic structure method for on-the-fly generation of potential energy surfaces in nonadiabatic dynamics simulations of photochemical systems, particularly those for which the nπ* and ππ* electronic excitations are most relevant. Here, we apply the hh-TDA method to nonadiabatic dynamics simulations of prototypical photochemical processes. First, we demonstrate the ability of hh-TDA to adequately describe conical intersection geometries. We next examine its ability to describe the ultrafast excited state dynamics of photoexcited ethylene through an ab initio multiple spawning (AIMS) dynamics simulation. Finally, we present an alternative variant of the hh-TDA method, which uses orbitals from a fractional occupation number Kohn-Sham (FON-KS) calculation applied to an ensemble with N-electrons. The resulting method is termed floating occupation molecular orbital hh-TDA (FOMO-hh-TDA). This scheme allows us to combine hh-TDA with global hybrid functionals and allows us to avoid unbound valence orbitals that may result from an (N + 2)-electron self-consistent field (SCF) procedure. FOMO-hh-TDA-BHLYP faithfully reproduces the nonadiabatic dynamics of trans-azobenzene (TAB) and is used to characterize the excited state decay pathways from the first (nπ*) excited state.

Maximum energy output chemical pump configuration with an infinite-low- and a finite-high-chemical potential mass reservoirs

The chemical pumps widely exist in various chemical systems, such as mass exchangers, desalination systems, biological systems, electrochemical systems, photochemical systems, solid-state devices, fuel pumps for solar-energy conversion systems, absorption and carbon pumps for material capture systems, etc. Therefore, performance improvements of the chemical systems become an urgent and important problem, which can be solved by optimizing the cycle configurations of the chemical pumps. Based on this consideration, an isothermal endoreversible chemical pump model is built in this paper, which operates between an infinite-low- and a finite-high-chemical potential mass reservoirs. Based on finite time thermodynamic theory, two mass transfer laws, i.e., the linear law and diffusive law are considered. When the cycle work input and operating time are specified, the optimal cycle configuration with maximum energy output is gained. For the linear law, with the optimal chemical pump configuration, the chemical potentials in the finite-high-chemical potential mass reservoir and the working substance nonlinearly vary with the operating time, meanwhile their ratio stays invariant. When both the chemical potential mass reservoirs are infinite ones, the dimensionless energy pumping rate and dimensionless entropy generation rate under the optimal time decrease with the increases of coefficient of performance and exergy efficiency. For the diffusive law, the optimal cycle configuration is quite different with that gained from the linear law. For the linear or diffusive law, the optimal chemical pump configuration with infinite-chemical potential mass reservoirs is made up of two invariant chemical potential branches along with two instant invariant mass-flux branches. The gained results can offer new references for the practical chemical pump designs.

Elimination of representative fluoroquinolones, penicillins, and cephalosporins by solar photo-Fenton: degradation routes, primary transformations, degradation improvement by citric acid addition, and antimicrobial activity evolution.

This work studies the degradation of seven representative antibiotics (ciprofloxacin, norfloxacin, levofloxacin, oxacillin, cloxacillin, cefalexin, and cefadroxil) by solar photo-Fenton process. The removal of antibiotics by the individual components (i.e., light, H2O2, or Fe (II)) and the complete photochemical system (light/H2O2/Fe (II)) was initially evaluated. Then, the effect of citric acid addition to the photo-Fenton system was assessed. In the third place, the primary transformation products for two illustrative cases (ciprofloxacin and oxacillin treated by photo-Fenton) were determined. Also, photo-Fenton in the presence of citric acid was applied to remove antibiotics from a simulated hospital wastewater. It was found that the solar light component induced degradation of ciprofloxacin, norfloxacin, and levofloxacin, but the rest of the considered antibiotics were not reduced by photolysis. In turn, the photo-Fenton system showed a degrading action on all the tested antibiotics. The addition of citric acid to the system significantly increased the removal of antibiotics. Initial degradation products indicated that hydroxyl radical attacked moieties of antibiotics responsible for their antimicrobial activity. Finally, the treatment of hospital wastewater evidenced the high potentiality of photo-Fenton process for degrading antibiotics in aqueous matrices containing elevated concentrations of citric acid.