Photochemical Oxidation Research Articles

Stable isotope compositions, source apportionment and transformation processes of carbonaceous aerosols in PM10 in the urban city of Hyderabad, India

This study apportions sources of carbonaceous aerosols using isotopic characteristics of total carbon (TC) and elemental carbon (EC) in PM10 aerosols using filter-based CTO-375 method for pre-monsoon (summer), post-monsoon, and winter (2019–2021) over Hyderabad, India. Highest secondary organic carbon, SOC (primary organic carbon, POC) of 13.78 ± 10.25 (7.87 ± 2.48) μg/m3 was during post-monsoon 2020 (2019), while lowest was 8.90 ± 5.55 (4.18 ± 0.92) μg/m3 during pre-monsoon 2021 (post-monsoon 2020), respectively. Average effective carbon ratio (ECR) > 1 indicates dominance of light scattering aerosols during pre-monsoon and post-monsoon. δ13CTC and δ13CEC varied from – 28.1 to – 24.7 ‰ (avg. – 26.5 ± 0.7) and - 32.5 to – 24.6 ‰ (avg. – 27.4 ± 1.1), indicating contribution from C3 plant burning and liquid fuel combustion. Positive value of δ13COC – δ13CEC and heavier δ13CTC, along with gradual enrichment in δ13CTC and δ13CEC from December 2020 to March 2021, suggested photochemical aging of carbonaceous aerosols. Lighter δ13CTC and OC/EC > 4 for all seasons indicates dominance of biomass burning (wood and crop residue burning), photochemical oxidation and secondary organic aerosol (SOA) formation. The tropical study experiences dominance of lighter δ13CEC compared to subtropical, high latitude regions.

Economic and environmental sustainability of copper indium gallium selenide (CIGS) solar panels recycling

End-of-life management of copper indium gallium selenide (CIGS) thin-film solar photovoltaics (PV) panels is crucial due to the necessity of recycling valuable elements such as indium ($400/kg) and gallium ($618/kg), ensuring both economic viability and environmental sustainability. In this study, we analyze the private and external costs of end-of-life management for CIGS PV designed for mass-scale recycling. Our findings reveal that the private and external costs of end-of-life management range from ∼$3.5 to $4.5 and ∼$3.0 to $4.0 per m2, respectively. The chemicals utilized in the recycling process, particularly NaOH and HCl, significantly contribute to climate change, photochemical oxidant formation, particulate matter formation, and freshwater eutrophication impact categories, accounting for ∼50 % to 90 % of the impacts. Furthermore, we found the net cost of recycling by subtracting the economic benefit obtained from recovered materials from the sum of private and external costs, revealing values ranging between $4.3 and $5.7 per m2 of CIGS PV module. These findings suggest that there is room to reduce the net cost further by recovering more materials from the CIGS PV modules components.

Electrochemical radical cation aza-Wacker cyclizations.

Electrochemical or photochemical single-electron oxidation of bench-stable substrates can generate radical cations that offer unique reactivities as intermediates in various bond-formation processes. Such intermediates can potentially take part in both radical and ionic bond formation; however, the mechanisms involved are complicated and not fully understood. Herein, we report electrochemical radical cation aza-Wacker cyclizations under acidic conditions, which are expected to proceed via radical cations generated by single-electron oxidation of alkenes.

Degradation and detoxification of 6PPD-quinone in water by ultraviolet-activated peroxymonosulfate: Mechanisms, byproducts, and impact on sediment microbial community

N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone (6PPD-Q) has been identified to induce acute toxicity to multifarious aquatic organisms at exceptionally low concentrations. The ubiquity and harmful effects of 6PPD-Q emphasize the critical need for its degradation from water ecosystems. Herein, we explored the transformation of 6PPD-Q by an ultraviolet-activated peroxymonosulfate (UV/PMS) system, focusing on mechanism, products and toxicity variation. Results showed that complete degradation of 6PPD-Q was achieved when the initial ratio of PMS and 6PPD-Q was 60:1. The quenching experiments and EPR tests indicated that SO4•− and •OH radicals were primarily responsible for 6PPD-Q removal. Twenty-one degradation products were determined through high-resolution orbitrap mass spectrometry, and it was postulated that hydroxylation, oxidative cleavage, quinone decomposition, ring oxidation, as well as rearrangement and deamination were the major transformation pathways of 6PPD-Q. Toxicity prediction revealed that all identified products exhibited lower acute and chronic toxicities to fish, daphnid and green algae compared to 6PPD-Q. Exposure experiments also uncovered that 6PPD-Q considerably reduced the community diversity and altered the community assembly and functional traits of the sediment microbiome. However, we discovered that the toxicity of 6PPD-Q degradation solutions was effectively decreased, suggesting the superior detoxifying capability of the UV/PMS system for 6PPD-Q. These findings highlight the underlying detrimental impacts of 6PPD-Q on aquatic ecosystems and enrich our understanding of the photochemical oxidation behavior of 6PPD-Q.

Study on the influence of active oxygen on the natural oxidation of arsenopyrite under different temperature conditions

Arsenic (As), a toxic element, contaminates farmlands, rivers, and groundwater, posing severe environmental and health risks. Notably, As-containing materials in tailings are affected by temperature variations during long-term storage, and this considerably impact the oxidation and migration of elements in arsenopyrite.This study focused on arsenopyrite and investigated the process of its oxidative dissolution and release of arsenic under different temperature conditions by using in-situ XRD, in-situ XPS and electron paramagnetic resonance spectroscopy(EPR), The role of oxygen free radicals in the oxidation of arsenopyrite was elucidated. It has been established that under high-temperature conditions As, iron (Fe), and sulfur (S) are primarily present As(V)/As(IV), Fe(III), and SO42−, respectively. The O2⋅− generated during the oxidation of As(III) by O2, OH⋅ produced by the Fe(II)/FeOH2+ reaction, and H2O2 formed via their interaction play a crucial role in the photochemical oxidation of arsenopyrite. These findings provide a theoretical basis for the formation of ferric arsenate precipitation, contributing in the adsorption and immobilisation of oxidatively released arsenic.

Assessing the Environmental and Health Impacts of Thermal Waste and Landfill-Based Waste Management

According to Presidential Regulation No. 35 of 2018, which focuses on accelerating the development of waste-to-energy projects, Denpasar City in Bali has been identified as one of the key Indonesian cities for implementing these projects. The daily waste generation in Denpasar City is estimated at 750 tons. The city's sanitation strategy outlines that 20% of this waste will be reduced at its source, while the remaining 80% is managed at the final treatment site. This study employs the Life Cycle Analysis (LCA) approach to evaluate the environmental impacts of traditional landfilling and various thermal waste treatment methods. The findings reveal that gasification (Scenario 2) has the lowest Global Warming Potential (GWP), with 779,759 kg CO2 equivalent emitted, indicating its superiority in reducing greenhouse gases. In contrast, landfilling (Scenario 1) is the least favorable, with a GWP of 2,885,770 kg CO2 equivalent and a significant cancer risk due to hexavalent chromium emissions estimated at 1,634,050 kg equivalent. These results underscore the health and environmental hazards of landfilling. Further, the study delves into each treatment scenario's impact on acidification, eutrophication, global warming potential, and photochemical oxidation.

Enhancing sustainability of urban waste management through data envelopment analysis for municipal solid waste composting in Tehran, Iran

The critical necessity of decreasing energy consumption and environmental effects is vital in various facets of urban life, particularly in urban waste management. This research aimed to evaluate the energy flow, CExD, and Life Cycle of a composting system for Municipal Solid Waste (MSW) in Tehran province, Iran. The initial phase entailed assessing the energy flow and effectiveness of the composting system, while the subsequent phase focused on enhancing energy efficiency through the application of Data Envelopment Analysis (DEA) to determine an optimal energy consumption strategy for conserving energy and reducing environmental impacts in Tehran's MSW composting system. Over a 90-day period, the analysis of energy usage revealed an energy input and output of 417.30 GJ (8500 t MSW)−1, with 227.02 GJ (8500 t MSW)−1 linked to transportation and 190.28 GJ (8500 t MSW)−1 related to composting activities. The overall energy consumption in the composting system was determined to be 6424.77 GJ (8500 t MSW)−1. By applying DEA optimization, energy savings of 14.45 GJ (8500 t MSW)−1 were accomplished in the composting process, with a significant reduction in electricity usage contributing to these savings. The environmental impact of the energy consumption patterns identified by DEA was notably lower compared to current energy practices. The most notable decrease in impact was observed in the Photochemical Oxidation category. By following the energy usage pattern recommended by DEA, the Global Warming Potential impact reduced by 500 kg CO2 eq. per 8500 t MSW. Additionally, the optimization of energy use through DEA led to a decrease in fossil energy resource depletion by around 4 GJ (8500 t MSW)−1 in the composting process.

Data-Independent Acquisition Represents a Promising Alternative for Fast Photochemical Oxidation of Proteins (FPOP) Samples Analysis.

Fast Photochemical Oxidation of Proteins (FPOP) is a protein footprinting method utilizing hydroxyl radicals to provide valuable information on the solvent-accessible surface area. The extensive number of oxidative modifications that are created by FPOP is both advantageous, leading to great spatial resolution, and challenging, increasing the complexity of data processing. The precise localization of the modification together with the appropriate reproducibility is crucial to obtain relevant structural information. In this paper, we propose a novel approach combining validated spectral libraries together with utilizing DIA data. First, the DDA data searched by FragPipe are subsequently validated using Skyline software to form a spectral library. This library is then matched against the DIA data to filter out nonrepresentative IDs. In comparison with FPOP data processing using only a search engine followed by generally applied filtration steps, the manually validated spectral library offers higher confidence in identifications and increased spatial resolution. Furthermore, the reproducibility of quantification was compared for DIA, DDA, and MS-only acquisition modes on timsTOF SCP. Comparison of coefficients of variation (CV) showed that the DIA and MS acquisition modes exhibit significantly better reproducibility in quantification (CV medians 0.1233 and 0.1494, respectively) compared to the DDA mode (CV median 0.2104).

Life Cycle Assessment of Single-Story Low-Income Housing: A Brazilian Case Study

This study aims to assess the environmental impacts of different construction systems employed in a single-story low-income housing development utilizing Life Cycle Assessment (LCA). The LCA was applied to the roof, wall, coating, and floor systems, considering the initial and recurring impacts from extraction to material replacement. Data were quantified using the CML 2001 method with OpenLCA 1.9 software. The analyzed impact categories are the potential for the depletion of abiotic resources—non-fossil (ADP); potential for the depletion of abiotic resources—fossil (ADP f); soil and water acidification potential (AP); eutrophication potential (EP); global warming potential—100 (GWP); stratospheric ozone layer depletion potential (ODP); and photochemical oxidation potential (POCP). The results highlight the impacts related to the maintenance and replacement of materials as the most significant, with walls being the system with the highest concentration of impacts, presenting the highest results among five of the seven categories. In the GWP category, the wall system resulted in 42% of total impacts (initial + recurring impacts). These findings show that the selection and definition of construction materials in the design phase can either mitigate or exacerbate environmental burdens. Therefore, this research contribution lies in pinpointing the environmental impacts of each construction system of low-income housing to support architects and engineers in addressing environmental impacts when making project decisions.

Environmental performance of Penaeus vannamei shrimp production in intensive and super-intensive biofloc systems

Shrimp farms worldwide have been responsible for a series of social and environmental issues that affect their surrounding regions. Modern aquaculture seeks to achieve sustainable growth that offers a balance between environmental, economic, and social perspectives, and new aquaculture technologies have been developed and improved in recent decades. One such innovation is the biofloc technology (BFT) system, which is considered an alternative to conventional aquaculture because it allows for aquatic organism production with minimal water exchange, high stocking densities, and the possibility of high levels of productivity. Life Cycle Assessment (LCA) is one of the most common methodologies used to compare the environmental performance of different systems, considering resource consumption and the emission of pollutants during the productive life cycle. The present study uses LCA to compare the environmental performance of Penaeus vannamei shrimp production in two BFT systems, an intensive system in a pond and a super-intensive system in a greenhouse. The Functional Unit used was 1.0 ton of shrimp (animals with an average final weight of 12 g). The boundaries of the system were defined as from the cradle to the farm gate. Input data related to the use of natural resources, energy consumption, and environmental emissions were obtained over eight cycles of intensive and super-intensive production. The following results were obtained for intensive and super-intensive systems, respectively: global warming (GWP100a) 5691.12 and 5512.42 kg CO2 eq; acidification 59.57 and 59.05 kg SO2-eq; eutrophication 25.96 and 25.80 kg PO4 eq; ozone layer depletion (OLP) 0.000319 and 0.000311 kg CFC-11 eq; human toxicity 1165.98 and 1233.33 kg 1.4-DB-eq; aquatic ecotoxicity 1344.13 and 1925.96 kg 1.4-DB eq; marine ecotoxicity 1881,643.65 and 2070,517.23 kg 1.4-DB eq; terrestrial ecotoxicity 24.26 and 33.54 kg 1.4-DB eq; photochemical oxidation 2.10 and 2.03 kg C2H4 eq; abiotic depletion 0.006487 and 0.008359 kg Sb eq; abiotic depletion of fossil fuels 35,612.80 and 34,504.39 MJ. Among the eleven evaluated impact categories, the intensive system showed better results in five categories, while the super-intensive system showed better performance in six categories. Feed (reference diet) was the most significant factor in the environmental performance of the evaluated systems. Based on these results, we conclude that feed and electricity had the most environmental impact in both systems. In general, when comparing the use of production factors and productivity between the systems, it becomes more evident that the SS is more efficient than the SI.

Comparative life cycle assessment of integrated renewable energy-based power systems

Integrated renewable-based power cycles should be employed to produce more sustainable electricity. This is a comparative life cycle assessment (LCA) of three combined power plants, encompassing: case 1 involving combined geothermal and wind, case 2 featuring combined geothermal and solar, and case 3 integrating wind and solar systems. The base case perovskite solar cell (PSC) modelling assumes a 3-year lifespan and a power conversion efficiency of 17 %. However, diverse scenarios are evaluated through a sensitivity assessment involving enhancements in lifetime and efficiency. The base case evaluation emphasizes that the phases with the most significant negative environmental effects which includes the drilling of geothermal wells, construction of wind plants, and manufacturing and installation of PSCs. The midpoint findings indicate that boosting the power conversion efficiency of PSC from 17 % to 35 % yields a notable decrease in environmental impact. Moreover, extending the lifetime from 3 to 15 years led to reduction in CO2 emissions from 0.0373 and 0.0185 kg CO2 eq/kWh to 0.026 and 0.0079 kg CO2 eq/kWh in cases 2 and 3, respectively. Assessing worst and best-case scenarios highlights significant declines in certain impact categories. In case 3, terrestrial ecotoxicity (TE), photochemical oxidant formation (POF), human toxicity (HT), marine ecotoxicity (ME), and marine eutrophication (MU) saw reductions exceeding 88 % compared to worst-case results. The environmental effects observed in cases 2 and 3 stem from toxicity and metal depletion, mainly linked to the PSC. Endpoint results revealed that when considering a PSC lifespan of 10 years or more, the detrimental ecosystem impacts of cases 2 and 3 become less severe than those of case 1. Uncertainty assessment has been done for different cases and impact categories. The study's results are also novel in which it evaluated the innovative PSC technology when integrated with other renewable resources, contrasting it with other integrated plants.

Environmental sustainability of closed-loop regeneration of NaHCO3 in CO2 utilization-driven desulfurization ash: From the perspective of integrated hybrid life cycle assessment

The closed-loop regeneration of NaHCO3 by treating sodium-based desulfurization ash (SDA) using CO2 in flue gas and ammonia by-products demonstrates an attractive perspective of low-cost sodium-based dry desulfurization (SDD) application. To push generation reuse of desulfurization ash into more practices, taking the application in coking plants as a case, this study first compares the environmental and economic performance of four scenarios of flue gas desulfurization (FGD) and desulfurization ash disposal by integrated hybrid life cycle assessment (IHLCA) with life cycle costing. Compared with process-based LCA, IHLCA captures more environmental impacts through the economic input-output (EIO) system, especially 36.40–67.89% of terrestrial ecotoxicity comes from the EIO system. Based on evaluation results of four scenarios, among the ten environmental impact categories (excluding photochemical oxidation), the SDD scenario with NaHCO3 regeneration by CO2 and ammonia (S2) is not only the most environmentally friendly route, but also has the lowest total hourly operating cost. These are mainly due to the offsetting effect of by-products replacing traditional chemicals on the total impact and avoiding landfill and raw material transportation. Furthermore, sensitivity analysis also shows that when technical parameters change, the environmental and economic performance of S2 still remains the best, except for the case when the NaHCO3 regeneration rate is 60%. The findings will be valuable for the selection and optimization of FGD in coking plants, incineration plants, and others.

Joint associations of air pollutants during pregnancy, infancy, and childhood with childhood persistent asthma: Nationwide database study in Japan

The joint effect of air pollutants at relatively low levels requires further investigation. Here, a database study was performed to evaluate the effects of exposure to mixtures of air pollutants during pregnancy, infancy, and childhood on childhood persistent asthma. We used the Japan Medical Data Center database, which provides access to family linkages and healthcare provider addresses, and included child-mother dyads in which the child was born between January 2010 and January 2017. The exposure of interest was ground-level air pollutants, and the primary outcome was childhood persistent asthma at 45 years of age, as defined based on outpatient and inpatient asthma disease codes and/or asthma medication dispensing claims. The weighted quantile sum (WQS) regression was used to evaluate the effects of air pollutant mixtures on 52,526 child-mother dyads from 1149 of 1907 municipalities (60.3 %) in Japan. The WQS regression models showed that with every 10th percentile increase in the WQS index, ground-level air pollutants during pregnancy, infancy, and childhood increased the risk of childhood persistent asthma by an odds ratio of 1.04 (95 % CI: 1.02–1.05; p<0.001), 1.02 (95 % CI: 1.01–1.03; p<0.001), and 1.03 (95 % CI: 1.01–1.04; p<0.001), respectively. Moreover, particulate matter with an aerodynamic diameter ≤ 2.5 µm was assigned the highest weight across all three exposure periods. Relatively high weights were assigned to suspended particulate matter and photochemical oxidants during pregnancy, carbon monoxide during infancy, and photochemical oxidants during childhood. Our study showed that a mixture of low-level air pollutants has a detrimental association with childhood persistent asthma.

Selective photochemical oxidation of sulfides by Gallium and Sulfur Co-Modified TiO2/g-C3N4 Nanocomposites as catalyst

In this study, with the objective of promoting the oxidation of sulfides, a distinctive photocatalyst was synthesized by incorporating Ga- and S-co-doped TiO2 onto graphitic carbon nitride (g-C3N4). Under visible light irradiation, the composites demonstrated enhanced photocatalytic performance in comparison to g-C3N4 and TiO2/g-C3N4. The nanocomposite catalyst displayed a remarkable enhancement in photocatalytic activity, benefiting from the creation of a Z-scheme heterojunction by combining TiO2 and g-C3N4, as well as the presence of electron trap centers, efficient photogenerated electron transfer, improved charge carrier separation, and extended optical absorption in the visible light range. To optimize the performance, the substitution contents of Ga and S (GaxSy@TiO2-g-C3N4) were varied, where the values of x and y were set at 5 % and 10 %, respectively. Notably, Based on the obtained results, it was observed that the Ga5.0S10.0@TiO2-g-C3N4 sample displayed the highest yield when subjected to visible-light irradiation, making it the most effective and optimal sample. The findings of this study offer a fresh perspective on the synergistic effect of dopant photocatalysts in the oxidation of organic compounds. This work presents a novel approach for the development of highly efficient photocatalysts capable of effectively oxidizing organic compounds.

Origins of the seasonal variability of PM2.5 sources in a rural site in Northern France

Air quality in rural areas results from the crossing of aged air masses transported from urban areas with local emissions dominated by agriculture and vegetation. The result is a complex mixture of primary and secondary atmospheric species, coming from varied sources and geographical areas. We implemented a methodology for deconvoluting and determining the geographical origins of the main aerosol sources impacting a typical rural area of northern France. A one-year field campaign was conducted in a rural site located between Paris and Brussels from March 2018 to February 2019. Hourly-based observations of inorganic and organic precursor gases and PM2.5 speciation were collected using on-line instrumentation. The annual PM2.5 concentrations of 12.2 ± 9.23 μg m−3 were explained by four sources extracted through positive matrix factorization analyses: combustion (40.2%), NO3-rich (26.8%), SO4-rich (18%) and mixed aged marine (15%). The combustion and SIA-rich sources drive 85 % of the yearly PM2.5 mass and variability. The combustion factor was most prominent during winter (53.3% of PM2.5 mass) due to high contributions from local and regional transport of biomass burning pollutants (winter OC/EC = 6.0; OC-to-OM factor = 2.05). In summer, it was most likely driven by secondary organic aerosol production and agricultural waste burning events (summer OC/EC = 8.6; OC-to-OM factor = 1.85). Comparing with other regional sites, we observed a strong regional background of carbonaceous particles regardless of the site typology. The SIA fraction is dominated by the NO3-rich source compared to the SO4-rich source. In spring, NO3-rich particles dominate PM2.5 (36.9%) due to intense agricultural activity. The temporal variability is driven by transport processes from the Benelux area in a North-to-South gradient of decreasing concentrations. A minor proportion of the NH4NO3 observed seems to be due to the local effects of morning dew and photochemical oxidation of NO2 in the afternoon. HNO3 appears to be the limiting factor for local NH4NO3 formation. PM2.5 toxicity in rural areas with low population densities should be not only addressed based on mass concentration, but also considering the chemical composition of particles as people from rural environments are exposed to high contributions from biomass burning sources and secondary inorganic aerosols triggered by the NH3 excess.

On-Site Determination of Soil Organic Carbon Content: A Photocatalytic Approach

This investigation presents a new approach for evaluating soil organic carbon (SOC) content in farming soils using a photocatalytic chemical oxygen demand (PeCOD) analyzer combined with geographic information system (GIS) technology for spatial analysis. Soil samples were collected at various sites throughout Canada and were analyzed using sieve analysis, followed by further SOC evaluation using three distinct techniques: loss on ignition (LOI), Walkley-Black, and PeCOD. The PeCOD system, which relies on the photochemical oxidation of organic carbon, showed an exciting correlation between its evaluations and SOC content, making it a prompt and reliable method to evaluate SOC. In this investigation, finer materials such as clayey soils (soil fractions of (&lt;50 µm)) demonstrated high SOC content compared to coarser ones (soil fractions of (&gt;75 µm)) and decreased SOC content with increased soil depth, generally below the 30 cm mark. It should be noted that this investigation revealed that other variables, such as land management practices, precipitation, and atmospheric temperature, have drastic effects on the formation and residence time of SOC. GIS georeferencing еnablеd mapping of the SOC distribution and identification of hotspot areas with high SOC content. The results of this study have implications for sustainable farming, climate change mitigation, and soil health operations by providing farmers with schemes that amplify carbon sequestration while simultaneously improving soil health.

Chemical composition, source characteristics, and hygroscopic properties of organic-enriched aerosols in the high Arctic during summer

Arctic regions are extremely sensitive to global warming. Aerosols are one of the most important short-lived climate-forcing agents affecting the Arctic climate. The present study examines the summertime chemical characteristics and potential sources of various organic and inorganic aerosols at a Norwegian Arctic site, Ny-Ålesund (79°N). The results show that organic matter (OM) accounts for 60 % of the total PM10 mass, followed by sulfate (SO42−). Water-soluble organic carbon (WSOC) contributes 62 % of OC. Photochemical processes involving diverse anthropogenic and biogenic precursor compounds are identified as the major sources of WSOC, while water-insoluble organic carbon (WIOC) aerosols are predominantly linked to primary marine emissions. Despite being a remote pristine site, the aerosols show a sign of chemical aging, evidenced by a significant chloride depletion, which was about 82 % on average during the study period. Nitrogen-containing aerosols are likely stemming from migratory seabird colonies and local dust sources around the sampling site. While biogenic, crustal, and sea salt-derived SO42- account for 37%, 8%, and 5% respectively, the remaining 50% is attributed to anthropogenic SO42-. Through chemical tracers, Pearson correlation coefficient matrix, and Hierarchical Cluster Analysis (HCA), the present study identifies soil biota (terrestrial biogenic) and marine emissions, along with their photochemical oxidation processes, as potential sources of Arctic aerosols during summer, while biomass burning and combustion-related sources have a minor contribution. The chemical closure of hygroscopicity highlights that while organics predominantly control aerosol hygroscopicity in the Arctic summer, specific inorganic components like (NH4)2SO4 can significantly increase it on certain days, affecting aerosol-cloud interactions and climate processes over the Arctic during summer. The present study highlights the high abundance of organics and their vital role in the Arctic climate during summer when natural aerosols are conquered.

Photochemical Oxidation of Substrate Water Analogs and Halides by Photosystem II

AbstractPhotosystem II (PSII) is a multi‐subunit protein‐pigment complex with diverse redox‐active cofactors, which enabled the biological availability of O2 on Earth. The substrate specificity and the underlying redox chemistry of the Mn4CaO5 catalytic center are investigated using alternate substrates such as small molecules (ammonia and methanol) and halides (Cl‐, Br‐, I‐) instead of the natural substrate water. Changes in the kinetic profiles of steady‐state O2 evolution and of dichlorophenolindophenol (DCIP) photochemical reduction by PSII as well as the detection of modified sites by proteomic analysis implied the possibility of alternate substrate photooxidation. Of particular interest is the role of two chlorides bound close to the putative water channels in the native system. The mutation of D2‐K317 to alanine is believed to impair the binding of a catalytically relevant chloride, eliminating the chloride requirement for water oxidation catalysis. The efficiency of small molecule photooxidation by the OEC is enhanced by the mutated D2‐K317A PSII complex without the competition from chloride. These results provide insight into the role of bound chloride in native PSII as a filter for enhancing the selectivity of water oxidation. The design principles for PSII may be extended to new strategies for developing highly selective catalysts.

XPS analysis of molecular contamination and sp2 amorphous carbon on oxidized (100) diamond

The efficacy of oxygen (O) surface terminations on diamond is an important factor for the performance and stability for diamond-based quantum sensors and electronics. Given the wide breadth of O-termination techniques, it can be difficult to discern which method would yield the highest and most consistent O coverage. Furthermore, the interpretation of surface characterization techniques is complicated by surface morphology and purity, which if not accounted for will yield inconsistent determination of the oxygen coverage. We present a comprehensive approach to consistently prepare and analyze oxygen termination of surfaces on (100) single-crystalline diamond. We report on x-ray photoelectron spectroscopy (XPS) characterization of diamond surfaces treated with six oxidation methods that include various wet chemical oxidation techniques, photochemical oxidation with UV illumination, and steam oxidation using atomic layer deposition (ALD). Our analysis entails a rigorous XPS peak-fitting procedure for measuring the functionalization of O-terminated diamond. The findings herein have provided molecular-level insights on oxidized surfaces in (100) diamond, including the demonstration of clear correlation between the measured oxygen atomic percentage and the presence of molecular contaminants containing nitrogen, silicon, and sulfur. We also provide a comparison of the sp2 carbon content with the O1s atomic percentage and discern a correlation with the diamond samples treated with dry oxidation which eventually tapers off at a max O1s atomic percentage value of 7.09 ± 0.40%. Given these results, we conclude that the dry oxidation methods yield some of the highest oxygen amounts, with the ALD water vapor technique proving to be the cleanest technique out of all the oxidation methods explored in this work.

Photocatalytic Degradation of Naproxen: Intermediates and Total Reaction Mechanism.

Photochemical and photocatalytic oxidation of naproxen (NPX) with UV-A light and commercial TiO2 under constant flow of oxygen have been investigated. Adsorption experiments indicated that 90% of the solute remained in the solution. Combined chemical analysis of samples on the photochemical degradation indicated that NPX in an aqueous solution (20 ppm) is efficiently transformed into other species but only 18% of the reactant is mineralized into CO2 and water after three hours of reaction. Performing the photocatalytic oxidation in the presence of TiO2, more than 80% of the organic compounds are mineralized by reactive oxidation species (ROS) within four hours of reaction. Analysis of reaction mixtures by a combination of analytical techniques indicated that naproxen is transformed into several aromatic naphthalene derivatives. These latter compounds are eventually transformed into polyhydroxylated aromatic compounds that are strongly adsorbed onto the TiO2 surface and are quickly oxidized into low-molecular-weight acids by an electron transfer mechanism. Based on this and previous studies on NPX photocatalytic oxidation, a unified and complete degradation mechanism is presented.