Photoinduced Conversion Research Articles

Reassessing the Photochemical Upcycling of Polystyrene Using Acridinium Salts.

Approaches aimed at deconstructing PS by photocatalytic means struggle to generate high-energy species capable of cleaving the C-H and C-C bonds of PS. We show herein that 9-mesityl-10-methylacridinium perchlorate (MA) is capable of upcycling various grades of PS susbstrates into benzoic acid (BAc) up to 40%, with small proportions of acetophenone and formic acid, under visible light (456 nm) or through solar radiation. Time-resolved emission and absorption spectroscopy evidence that a reaction with oxygen is the primary photochemical step in oxygen-saturated solutions, accounting for 77% of the photons absorbed vs. 1% for the direct reaction with PS. These results suggest a mechanism in which MA-mediated photocycling of PS to BAc occurs through the abstraction of benzylic H atoms by reactive oxygen species generated by energy or electron transfer from the excited state of MA. Addition of triplet O2 to these radicals, followed by intra- or inter-molecular hydrogen atom transfer (HAT), generates C- or O-centered radicals then undergoing β-scission or hydroperoxide fragmentation. The formation of intermediate oligomers functionalized by terminal carbonyl groups is demonstrated by both infrared analysis and mass spectrometry. These oligomers undergo further photoinduced conversion in the absence of MA, as evidenced by size exclusion chromatography analysis.

Reassessing the Photochemical Upcycling of Polystyrene Using Acridinium Salts

Approaches aimed at deconstructing PS by photocatalytic means struggle to generate high‐energy species capable of cleaving the C‐H and C‐C bonds of PS. We show herein that 9‐mesityl‐10‐methylacridinium perchlorate (MA) is capable of upcycling various grades of PS susbstrates into benzoic acid (BAc) up to 40%, with small proportions of acetophenone and formic acid, under visible light (456 nm) or through solar radiation. Time‐resolved emission and absorption spectroscopy evidence that a reaction with oxygen is the primary photochemical step in oxygen‐saturated solutions, accounting for 77% of the photons absorbed vs. 1% for the direct reaction with PS. These results suggest a mechanism in which MA‐mediated photocycling of PS to BAc occurs through the abstraction of benzylic H atoms by reactive oxygen species generated by energy or electron transfer from the excited state of MA. Addition of triplet O2 to these radicals, followed by intra‐ or inter‐molecular hydrogen atom transfer (HAT), generates C‐ or O‐centered radicals then undergoing β‐scission or hydroperoxide fragmentation. The formation of intermediate oligomers functionalized by terminal carbonyl groups is demonstrated by both infrared analysis and mass spectrometry. These oligomers undergo further photoinduced conversion in the absence of MA, as evidenced by size exclusion chromatography analysis.

Wettability of anatase TiO2 surface: Effect of niobium doping

The effect of niobium doping on the hydrophilic behavior of anatase TiO2 surface was demonstrated on a series of x-Nb-TiO2 nanocoatings with dopant concentrations in the range of 0.0 - 1.0 at.% Nb. Thin films prepared on glass substrates from sols by dip-coating were characterized by tensiometric, work function and isoelectric point measurements along with FT-IR spectroscopy in situ method. Using macroscopic and microscopic techniques, it was found that, at low doping level, it is the functionalization of the anatase surface with niobium ions that leads to a drastic change in its surface acid-base as well as electronic properties and, as a consequence, to a sharp increase in the initial surface hydrophilicity. The rearrangement in the hydroxyl‑hydrated layer with the formation of additional hydroxyl groups as a result of surface functionalization has an increased effect on wettability only at low levels of niobium inclusion, whereas with increasing dopant content the electronic factor plays a significant role on the properties of titanium dioxide, including its wettability. The kinetic dependencies of the photoinduced superhydrophilic conversion for all Nb-doped titanium dioxide surfaces were obtained and discussed in terms of proposed mechanism. Both the initial hydrophilic state and the initial rate of photoinduced hydrophilic conversion depend on the Nb concentration in titanium dioxide, while the final UV-induced superhydrophilic state is achieved for all Nb-doped TiO2 regardless of the dopant content.

Mesomorphism, high-contrast negative fluorosolvatochromism and photoinduced fluorescence conversion of thienylcyanostyrene-pyridinium salts

Novel thienylcyanostyrene and pyridinium-based luminescent ionic liquid crystals (ILCs) characterized with different length of N-alkyl chains (N–C3H7 and N–C8H17) and different size of counter anions (Br−, BF4−, PF6− and Tf2N−) on pyridinium moiety have been synthesized. The chemical modifications of N-alkyl chains and counter anions are easily achieved via pyridine alkylation followed with further ion exchanges, which played a key role in tuning supramolecular self-assembly of these ILCs. The compounds with shorter N–C3 alkyl chain (E-CTPC3X, X = Br−, BF4−, PF6− and Tf2N−) can self-assemble into 3D cubic phase or 2D hexagonal columnar phase depending on the size of counter anion, while the analogues with longer N–C8 alkyl chain (E-CTPC8X, X = BF4− and Tf2N−) only result smectic A phases. Moreover, the prolongation of the N-alkyl chain or enlargement of counter anion could significantly decrease the clear points of LC phases avoiding the thermal decomposition at high temperature, whereas introducing counter anions such as BF4−, PF6− that can form hydrogen bonds have stabilized the LC phases. The notable negative fluorosolvatochromism and the photoinduced fluorescence conversion with high-contrast of these ILCs were observed using UV–vis absorption and photoluminescence (PL) spectra, and was further analyzed by dynamic 1H NMR. These ILCs had been used as dopant to modify the n-Si/PEDOT:PSS heterojunction solar cells (HSCs) with 2 fold hole mobility (μhole) enhancement of the PEDOT:PSS layer.

The Role of Photo in Oxygen Evolution Reaction: A Review.

Photo enhanced oxygen evolution reaction has recently emerged as an advanced strategy with great application prospects for highly efficient energy conversion and storage. In the course of photo enhanced oxygen evolution reactions, the other works focus has predominantly centered on catalysts while inadvertently overlooking the pivotal role of photo. Consequently, this manuscript embarks upon a comprehensive review of recent advancements in photo-driven, aiming to illuminate this critical dimension. A detailed introduction to the photothermal effect, photoelectronic effect, photon-induced surface plasmon resonance, photo and heterojunction, photo-induced reversible geometric conversion, photo-induced energy barrier reduction, photo-induced chemical effect, photo-charging, and the synthesis of laser/photo-assisted catalysts, offering prospects for the development of each case is provided. A detailed introduction to the photothermal effect, photoelectronic effect, photon-induced surface plasmon resonance, photo and heterojunction, photo-induced reversible geometric conversion, photo-induced energy barrier reduction, photo-induced chemical effect, photo-charging, and the synthesis of laser/photo-assisted catalysts is provided. At the same time, the overpotential and Tafel slope of some catalysts mentioned above at 10mAcm-2 is collected, and calculated the lifting efficiency of light on them, offering prospects for the development of each case.

HONO chemistry at a suburban site during the EXPLORE-YRD campaign in 2018: formation mechanisms and impacts on O3 production

Abstract. HONO is an important precursor for OH radicals that impact secondary-pollutant production. However, there are still large uncertainties about different HONO sources which hinder accurate predictions of HONO concentration and hence atmospheric oxidation capacity. Here HONO was measured during the EXPLORE-YRD campaign (EXPeriment on the eLucidation of the atmospheric Oxidation capacity and aerosol foRmation and their Effects in the Yangtze River Delta), along with other important parameters, enabling us to comprehensively investigate HONO variation characteristics and evaluate the relative importance of different HONO sources by using a box model. HONO showed significant variations, ranging from several tens of parts per thousand to 4.4 ppb. The average diurnal pattern of HONO / NOx showed a maximum of 0.17 around noon and resembled that of j(O1D), indicating the existence of photo-induced sources. Modeling simulations with only the default HONO source (OH + NO) largely underestimated HONO concentrations, with the modeled-averaged noontime HONO concentration an order of magnitude lower than the observed concentration. The calculated strength of the unknown HONO source (Punknown) showed a nearly symmetrical diurnal profile with a maximum of 2.5 ppb h−1 around noon. The correlation analysis and sensitivity tests showed that the photo-induced NO2 conversion on the ground was able to explain Punknown. Additional HONO sources incorporated into the box model improved the model's performance in simulating HONO concentrations. The revised box model reproduced the nighttime HONO concentration well but still underestimated the daytime HONO concentration. Further sensitivity tests indicated the underestimation of daytime HONO was not due to uncertainties of photo-induced NO2 uptake coefficients on the ground or aerosol surfaces or the enhancement factor of nitrate photolysis but was more likely due to other sources that were not considered in the model. Among the incorporated HONO sources and the default gas-phase source, photo-induced NO2 conversion on the ground dominated the modeled HONO production during the daytime, accounting for 71 % of the total, followed by NO + OH, NO2 hydrolysis on the ground surface, vehicle emissions, photo-induced NO2 conversion on the aerosol surface, nitrate photolysis and NO2 hydrolysis on the aerosol surface. NO2 hydrolysis on the ground surface was the major source of nighttime HONO, contributing 55 % of total HONO production. HONO photolysis contributed 43 % of ROx production during the daytime, followed by O3 photolysis (17 %), HCHO photolysis (14 %), ozonolysis of alkenes (12 %) and carbonyl photolysis (10 %). With observed HONO as a model constraint, the average peak of net ozone production rate increased by 88 % to 12.6 ppb h−1 compared to that without observed HONO as a model constraint, indicating HONO evidently enhanced O3 production and hence aggravated O3 pollution in summer seasons. Our study emphasized the importance of heterogeneous NO2 conversion on the ground surface in HONO production and accurate parameterization of HONO sources in predicting secondary-pollutant production.

Multiphoton induced photoreduction in BaFCl: Sm3+ nanocrystals under femtosecond laser field

Photoinduced valence state conversion in lanthanide-doped solid materials can find significant applications in areas like optical storage, opto-electronic devices and has been attracting great research efforts. Here, we experimentally demonstrate that trivalent samarium ions contained in the BaFCl nanocrystals can be efficiently reduced to divalent ones under 800 nm fs laser field. The dependences of the luminescence intensity of the photoinduced divalent ions on the femtosecond laser power, central wavelength and polarization are investigated in detail, respectively. Theoretical fits of the experimental observations indicate that a resonance-mediated (2 + 2) four-photon absorption is most probably involved in the multiphoton induced photoreduction process.

Synthetic Control over the Surface Chemistry of Blue-Emitting Perovskite Nanocrystals for Photocatalysis

Lead halide perovskite nanocrystals (NCs) are particularly suitable for light-emitting and photocatalysis applications, where their potential can be maximized by controlling the surface composition of their organic shell. In this study, the preparation of CsPbClxBr3–x NCs at room temperature in toluene is described. Three differently structured surfactants are utilized for the synthesis, each with a specific function, namely, the solubilization of the lead precursor (n-Hept4NBr), the surface passivation with halide modification (dimethyldioctadecylammonium chloride), and the protection of the surface-active sites (octanoic acid) for photocatalysis. Under these conditions, nearly monodispersed blue-emitting nanocubes are selectively obtained in a one-pot synthesis by combining specific amounts of the perovskite precursors. As supported by thermogravimetric analysis (TGA) and Fourier transform infrared (FT-IR) spectroscopy investigations, the organic shell of the obtained NCs is composed of electrostatically bound dimethyldioctadecylammonium ions, granting robustness to the corresponding NCs, and octanoic acid molecules, interacting with the nanoparticle surface through weaker secondary bonds. The obtained NCs exhibit a high photoluminescence quantum yield (PLQY = 72 ± 3%) notwithstanding multiexponential recombination dynamics of the excited state, resulting from the different passivation modes at the NC surface. Moreover, the NCs show a remarkable optical stability after exposure to high temperatures and to water contact due to the high surface density of the multifunctional organic ligands. The introduction of 4-tert-butylphenyl thiol promotes a charge transfer process at the NC/thiol interface formed upon removal of the labile ligands (octanoic acid) at the NC surface. In these conditions, the NCs are prone to the photoinduced conversion of the aromatic thiol into the corresponding disulfide without varying the optical properties of the perovskite photocatalyst upon the substrate conversion. Therefore, the obtained results cast light on the versatility of the surface engineering of lead halide perovskite NCs for efficient blue emission and photocatalysis with improved stability.

High-contrast fluorescence modulation driven by intramolecular photocyclization and protonation of bithienylpyridine functionalized α-cyanostilbene

We report herein a light-inducible fluorescence conversion and an acidochromism based on the bithienylpyridine functionalized α-cyanostilbene luminogen (E-CTP). The thienylcyanostyrene unit in this luminogen endows E-CTP AIEE property and 365 nm light-induced fluorescence conversion with high contrast in color (Δλem = 85 nm) and strong intensity. The fluorescence conversion of this molecular system might be driven by an intramolecular photocyclization rather than the commonly occurred intermolecular photodimerization for the α-cyanostilbene system as indicated by UV, PL, TCL-MS as well as NMR spectra measurements. Due to the bithienyl-pyridine in its skeleton, the optoelectronic properties of this luminogen can also be tuned by protonation. The luminogen shows 6 fold fluorescence enhancement and 110 nm emission red-shift in solution upon addition of trifluoroacetic acid (TFA). The optical feature of the reversible recoverability for E-CTP under acid-base stimuli in film was utilized to prepare security paper. Moreover, cooperating the acidochromism with the photo-induced fluorescence conversion of E-CTP, multicolor light-painting pattern was achieved.

Manipulating fluorescence by photo-switched spin-state conversions in an iron(ii)-based SCO-MOF.

Manipulating fluorescence by photo-switched spin-state conversions is an attractive prospect for applications in smart magneto-optical materials and devices. The challenge is how to modulate the energy transfer paths of the singlet excited state by light-induced spin-state conversions. In this work, a spin crossover (SCO) FeII-based fluorophore was embedded into a metal-organic framework (MOF) to tune the energy transfer paths. Compound 1 {Fe(TPA-diPy)[Ag(CN)2]2}·2EtOH (1) has an interpenetrated Hofmann-type structure, wherein the FeII ion is coordinated by a bidentate fluorophore ligand (TPA-diPy) and four cyanide nitrogen atoms and acts as the fluorescent-SCO unit. Magnetic susceptibility measurements revealed that 1 underwent an incomplete and gradual spin crossover with T1/2 = 161 K. Photomagnetic studies confirmed photo-induced spin state conversions between the low-spin (LS) and high-spin (HS) states, where the irradiation of 532 and 808 nm laser lights converted the LS and HS states to the HS and LS states, respectively. Variable-temperature fluorescence spectra study revealed an anomalous decrease in emission intensity upon the HS → LS transition, confirming the synergetic coupling between the fluorophore and SCO units. Alternating irradiation of 532 and 808 nm laser lights resulted in reversible fluorescence intensity changes, confirming spin state-controlled fluorescence in the SCO-MOF. Photo-monitored structural analyses and UV-vis spectroscopic studies demonstrated that the photo-induced spin state conversions changed energy transfer paths from the TPA fluorophore to the metal-centered charge transfer bands, ultimately leading to the switching of fluorescence intensities. This work represents a new prototype compound showing bidirectional photo-switched fluorescence by manipulating the spin states of iron(ii).

On-the-fly nonadiabatic dynamics of caffeic acid sunscreen compound

As a widely-used sunscreen compound, the caffeic acid (CA) shows the strong UV absorption, while the photoinduced reaction mechanisms behind its photoprotection ability are not fully understood. We try to investigate the photoinduced internal conversion dynamics of CA in order to explore the photoprotection mechanism. The most stable CA isomer is selected to examine its nonadiabatic dynamics using the on-the-fly surface hopping simulations at the semi-empirical level of electronic-structure theory. The dynamics starting from different electronic states are simulated to explore the dependence of the photoinduced reaction channels on the excitation wavelengths. Several S1/S0 conical intersections, driven by the H-atom detachments and the ring deformations, have been found to be responsible for the nonadiabatic decay of the CA. The simulation results show that the branching ratios towards these intersections are modified by the light with different excitation energies. This provides the valuable information for the understanding of the photoprotection mechanism of the CA compound.

Photo-induced scandium-catalyzed biomimetic skeleton conversion of lathyrane to naturally rare eupholathone Euphorbia diterpenes.

The naturally scarce eupholathone-type euphornin E (1) was efficiently prepared from abundant lathyrane-type Euphorbia factor L1via a visible-light-induced Sc(OTf)3-catalyzed tandem process. Eupholathones 2 and 3 were also smoothly obtained by changing the reaction solvent. This route provides a convenient method for easily constructing scarce eupholathone- from lathyrane-type Euphorbia diterpenes, and confirms the biogenetic relationship between them from a chemical standpoint. Notably, compound 1 exhibited good anti-HIV activity.

Artificial photosynthesis a brief literature review

Dye Sensitized Photoelectrochemical Cells (DS-PEC) are a promising development for artificial photosynthesis. Currently however photoinduced conversion of water to hydrogen and oxygen remains limited by desorption, alternative processes and charge accumulation. This brief literature review will primarily focus on transition metal complex chromophore catalyst dyads, for water oxidation catalysis (WOC) as well as hydrogen evolution catalysis (HEC). Assessing the dyads individual charge separation, electron transfer and catalytic photoelectrochemical properties. Comparing and contrasting the techniques employed by Dye Sensitized Photoelectrochemical Cells (DS-PEC) dyads in addition to collectively evaluating their current limiting factors and suggesting potential developments for further work.

A simple solvothermal preparation of Mg-doped anatase TiO2 and its self-cleaning application

Self-cleaning materials have attracted considerable attention for their unique properties and practical applications in energy and environmental areas. Various commercial ceramic products developed based on photo-induced hydrophilic conversion of TiO2 surfaces have also been provided. However, UV light induced and metastable character of anatase TiO2 in medium/high temperature ceramic glaze limited practical applications for self-cleaning photocatalytic materials, which needs further development to improve their efficiency and utilities. In this work, Mg-doped anatase TiO2 was synthesized via a template-free and surfactant-free solvothermal method. The results indicated that MgCl2·6H2O content played key roles in the formation of anatase TiO2. Compared to TiO2-undoped sample, Mg-doped TiO2 sample showed higher photodegradation rate of 99.5 % in 80 min exposed to visible light irradiation. Owing to the introduction of the catalyst, the ceramic glaze showed super-hydrophilicity (water contact angle around 7°) and exhibited excellent stain resistance (e. g. the dried Marker ink on the glaze can immediately float once meeting water after 10 cycles). The glaze after more times recycles could restore super-hydrophilicity is irradiated by visible light for 1 h. This indicates that the introduction of Mg-doped anatase TiO2 demonstrated great practical applications for self-cleaning ceramics toward sunlight.

(Invited) Transient Absorption and Compressive Sensing for Understanding Dynamics in Photocatalytic Nanoparticles and Energy Conversion Materials

Transient absorption (TA) is a well-known tool for understanding the dynamical response of materials following the absorption of a photon. TA allows the dynamics of photoinduced energy flow and energy conversion to be monitored, along with other competing dissipative processes. With current technologies, TA can provide dynamical information over the ultraviolet, visible, near-infrared, mid-infrared, and terahertz spectral ranges, which allows the study of a concomitant range of photoinduced processes of relevance to photocatalysis. However, since TA usually involves very small changes in absorption, the approach can be quite time consuming and, as a result, signal averaging for hours is not uncommon. In addition to time limitations, long signal averages are challenging for many materials, including photocatalytic systems, because many materials degrade under long periods of laser illumination. Longer experiments also place greater demands on the stability of lasers, usually leading to the need for environmental controls, which adds cost and complexity to TA spectroscopies. Thus, there are several important reasons to increase the speed of TA as long as accuracy and sensitivity can be maintained.In this talk, I present recent efforts to dramatically decrease the time needed to perform TA through compressive sensing, whereby a smaller number of data points are randomly collected over the chosed dynamical range of the TA experiment.[1] The general principle works well when the transformation of the optical signal to another domain has a low density of TA features. Studies and applications to colloidal plasmonic nanoparticles, such as nanostructures made of refractory materials, and energy conversion materials are shown. I also present imaging efforts using femtosecond optical pulses in scattering environments where conventional imaging is difficult.[2] By utilizing enhanced second harmonic generation from high peak-power ultrashort pulses, combined with compressive sensing approaches, successful reconstruction of optical images can be undertaken.Work performed at the Center for Nanoscale Materials, a U.S. Department of Energy Office of Science User Facility, was supported by the U.S. DOE, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357. This material is based on work supported by Laboratory Directed Research and Development (LDRD) funding from Argonne National Laboratory, provided by the Director, Office of Science, of the U.S. Department of Energy under Contract No. DE-AC02-06CH11357. References Adhikari, S., Cortes, C. L., Wen X., Panuganti, S., Gosztola, D. J., Schaller, R. D., Wiederrecht, G. P., Gray, S. K., “Accelerating ultrafast spectroscopy with compressive sensing,” Phys. Rev. Appl., Vol. 15, 024032, 2021.Wen, X., Adhikari, S., Cortes, C. L., Gosztola, D. J., Gray, S. K., Wiederrecht, G. P., “Ghost imaging second harmonic generation microscopy,” Appl. Phys. Lett., Vol. 116, 191101, 2020.

Photo-induced conversion of type-II CoPc/BiOBr-NSs to S-scheme heterostructure for boosting CO2 photoreduction

With efficient charge separation, S-scheme heterostructures are very attractive for photocatalytic carbon dioxide reduction, but their construction is still facing challenge. Herein, cobalt phthalocyanine (CoPc) was combined with BiOBr nanosheets (NSs) as type-II heterostructure CoPc/BiOBr-NSs. It is more interesting that light-induced oxygen vacancies on BiOBr-NSs can convert type-II CoPc/BiOBr-NSs to S-scheme structures for CO2 reduction. The optimal CoPc/BiOBr-NSs exhibited significantly enhanced CO generation with rate of 59.9 μmol g−1 h−1 (selectivity of 90.4 %), which was 25-fold higher than that of BiOBr-NSs, and much higher than most reported photocatalysts. Photo-induced oxygen vacancies on BiOBr-NSs can generate defect states on bottom of conduction band (CB), which can trap the electrons to have a recombination with holes left on HOMO band of CoPc, boosting charge separation for efficient CO2 reduction. Moreover, the central Co2+ of CoPc can accept the excited electrons from the ligand to act as active site for CO2 reduction. This work provides a new strategy of constructing metal-complex/semiconductor S-scheme photocatalyst for boosting CO2 photoreduction.

Reversible Photoinduced Conversion of Unprecedented Norbornadiene-Based Photoswitches with Redox-Active Naphthalene Diimide Functionalities.

An unprecedented compound class of functional organic hybrids consisting of a photoswitchable norbornadiene building block and a redoxactive chromophore, namely naphthalene diimide, were designed and synthesized. Within these structures the capability of rylene chromophores to function as a redox active catalyst upon their photoexcitation was utilized to initiate the oxidative back-conversion of the in situ formed quadricyclane unit to its norbornadiene analogue. In this way successive photoexcitation at two different wavelengths enabled a controlled photoswitching between the two isomerical states of the hybrids. Beyond this prove of concept, the dependency of the reaction rate to the intramolecular distance of the two functional molecular building blocks as well as the concentration of the photoexcited sample was monitored. The experimental findings and interpretations were furthermore supported by quantum chemical investigations.

A novel self-cleaning functional composite coating with extraordinary anti-corrosion performance in high pressure CO2 conditions

This study demonstrates an alternative method for fabricating a novel integrated anticorrosion self-cleaning functional coating using the GO nanosheets with the TiO2–ZnO heterostructure to effectively induce charge separation and to accomplish photoinduced hydrophilic conversion. Through ultraviolet light (UV) irradiation, the PFDTMS-modified filler transformed from hydrophobic to hydrophilic, while the fluorine groups on the surface of the filler still existed. Research of EIS shows that the impedance at 0.01 Hz of 20% F/T-Z-G Polyurea coating was about 1 × 103 times higher than polyurea coatings, after 24 h of immersion in 2.8 MPa, 110 °C pure CO2 and NaCl solution. The results demonstrate that F/T-Z improves the dispersion of GO and make the polyurea matrix denser, inhibiting the diffusion of corrosive medium. Additionally, the GO and fluorine groups strengthen the shielding performance of the coating. Moreover, the TiO2–ZnO heterojunction traps H2O molecules to form hydroxyl radicals (OH•). Simultaneously, Fe2+ and Fe3+ combine with OH• to form Fe3O4, and the passivation film was formed on the surface of steel. It is believed that this hydrophilic-hydrophobic integrated functional coating will be an excellent candidate for technological applications, such as anticorrosion, self-cleaning materials and composite coatings.

Photocatalytic CO2 reduction for C2-C3 oxy-compounds on ZIF-67 derived carbon with TiO2

Excess carbon dioxide emission accompanied by gross fossil fuel consumption has worsened the global warming crisis in recent decades. Photo-induced conversion of CO2 into hydrocarbons is a potential solution to mitigate both energy and environmental problems. However, conventional photocatalysts suffer low efficiency in CO2 conversion with often C1 and/or C2 products. In this work, pyrolyzed cobalt type zeolitic imidazolate framework (ZIF-67), namely ZIF-derived carbon (ZDC) with residual Co nanoparticles and the corresponding ZDC/TiO2 composite (ZDC/T), were adopted as gas-phase CO2 reduction photocatalysts. The ZDC photocatalyst is inclined to form C2 compound (acetaldehyde), while the ZDC/T composite has high selectivity in C3 product (acetone). High pyrolysis temperature would degrade the photocatalytic performance in neat ZDC due to enhanced cobalt aggregation and nitrogen loss after breaking ZIF-67 Co-N coordination. Alternatively, the pyrolyzed ZDC/T revealed superior photocatalytic CO2 reduction performance because the Co-N bonds were found to decrease without changing Co nanoparticle size and dissociation of nitrogen notably. In conclusion, we synthesized novel photocatalysts for multi-carbon (C2-C3) products with high selectivity, and provided a plausible mechanism to illustrate the formation process of multi-carbon products during photoreduction of CO2.

Patterning a cellulose based dual-tone photoresist via deep X-ray lithography

The desire to combine properties such as ready availability, low price and biodegradability makes cellulose derivatives such as Trimethylsilyl cellulose (TMSC) an ideal precursor suited to study different applications on the abundant material, cellulose. Here we introduce a lithographic approach to pattern the cellulose derivative, TMSC, via photoinduced X-ray conversion. Thin films of this biopolymer were irradiated by means of proximity deep X-ray lithography. With increasing energy dose, we found distinct structural and chemical changes resulting in two polarity transitions and related thereto material solubility alterations. Based on this, we demonstrate that positive and negative tone structures can be obtained in one single exposure at the same energy dose. Notably, the positive tone pattern is produced when applying Isopropyl alcohol (IPA) or purified water to dissolve the exposed surface. In contrast, the negative tone structure is produced with toluene. These findings suggest TMSC as a potential dual-tone photoresist applicable in microelectronics or surface chemistry where it can be applied as a dielectric layer, a pattern template, used in microfluidics or functionalized for bioassays.