Average Carbon Oxidation State Research Articles

Innovative RGO-bridged S-scheme CuFe2O4@Ag2S heterojunction for efficient Sun-light-driven photocatalytic disintegration of Ciprofloxacin

Antibiotics contamination in water bodies poses a significant threat to public health and the environment, necessitating advanced methods for their removal from wastewater. In response to this issue, developing a novel magnetic nanocomposite (RGO/CuFe2O4@Ag2S) as an efficient photocatalyst for the degradation of pharmaceuticals like ciprofloxacin (CIP) is of great importance. The synthesized nanocomposite underwent comprehensive characterization to elucidate its crystalline structure, chemical bonding, surface morphology, elemental composition, internal structure, optical properties, surface area, particle size distribution, and magnetic properties. Under optimized conditions (pH = 9, nanocomposite dose = 0.5 g/L, CIP concentration of 20 mg/L, and duration of 200 min), the nanocomposite demonstrated complete degradation of CIP. Moreover, post-treatment analysis revealed significant reductions in total organic carbon (TOC) and chemical oxygen demand (COD) of 70.08 % and 85.08 %, respectively, indicating extensive mineralization of the antibiotic. Mechanistic investigations revealed a unique S-scheme heterojunction in the RGO/CuFe2O4@Ag2S nanocomposite, where RGO acts as an electronic bridge between CuFe2O4 and Ag2S. This innovative architecture facilitates efficient charge separation and transfer, significantly enhancing the photocatalytic activity. Reusability tests demonstrated the robust nature of the photocatalyst, with only a modest 6 % decline in efficiency after six consecutive cycles. To further assess the system's effectiveness in real-world applications, its performance was evaluated in treating pharmaceutical wastewater. The biodegradation efficiency was quantified by measuring the Average Oxidation State (AOS) and Carbon Oxidation State (COS) of the wastewater samples before and after treatment.

Improved Characterization of Soil Organic Matter by Integrating FT-ICR MS, Liquid Chromatography Tandem Mass Spectrometry, and Molecular Networking: A Case Study of Root Litter Decay under Drought Conditions.

Understanding of how soil organic matter (SOM) chemistry is altered in a changing climate has advanced considerably; however, most SOM components remain unidentified, impeding the ability to characterize a major fraction of organic matter and predict what types of molecules, and from which sources, will persist in soil. We present a novel approach to better characterize SOM extracts by integrating information from three types of analyses, and we deploy this method to characterize decaying root-detritus soil microcosms subjected to either drought or normal conditions. To observe broad differences in composition, we employed direct infusion Fourier-transform ion cyclotron resonance mass spectrometry (DI-FT-ICR MS). We complemented this with liquid chromatography tandem mass spectrometry (LC-MS/MS) to identify components by library matching. Since libraries contain only a small fraction of SOM components, we also used fragment spectral cosine similarity scores to relate unknowns and library matches through molecular networks. This integrated approach allowed us to corroborate DI-FT-ICR MS molecular formulas using library matches, which included fungal metabolites and related polyphenolic compounds. We also inferred structures of unknowns from molecular networks and improved LC-MS/MS annotation rates from ∼5 to 35% by considering DI-FT-ICR MS molecular formula assignments. Under drought conditions, we found greater relative amounts of lignin-like vs condensed aromatic polyphenol formulas and lower average nominal oxidation state of carbon, suggesting reduced decomposition of SOM and/or microbes under stress. Our integrated approach provides a framework for enhanced annotation of SOM components that is more comprehensive than performing individual data analyses in parallel.

Novel nanostructure approach for antibiotic decomposition in a spinning disc photocatalytic reactor

Conventional wastewater treatment processes are often unable to remove antibiotics with resistant compounds and low biological degradation. The need for advanced and sustainable technologies to remove antibiotics from water sources seems essential. In this regard, the effectiveness of a spinning disc photocatalytic reactor (SDPR) equipped with a visible light-activated Fe3O4@SiO2-NH2@CuO/ZnO core–shell (FSNCZ CS) thin film photocatalyst was investigated for the decomposition of amoxicillin (AMX), a representative antibiotic. Various characterization techniques, such as TEM, FESEM, EDX, AFM, XRD, and UV–Vis-DRS, were employed to study the surface morphology, optoelectronic properties, and nanostructure of the FSNCZ CS. Key operating parameters such as irradiation time, pH, initial AMX concentration, rotational speed, and solution flow rate were fine-tuned for optimization. The results indicated that the highest AMX decomposition (98.7%) was attained under optimal conditions of 60 min of irradiation time, a rotational speed of 350 rpm, a solution flow rate of 0.9 L/min, pH of 5, and an initial AMX concentration of 20 mg/L. Moreover, during the 60 min irradiation time, more than 69.95% of chemical oxygen demand and 61.2% of total organic carbon were removed. After the photocatalytic decomposition of AMX, there is a substantial increase in the average oxidation state and carbon oxidation state in SDPR from 1.33 to 1.94 and 3.2, respectively. Active species tests confirmed that ·OH and ·O2− played a dominant role in AMX decomposition. The developed SDPR, which incorporates a reusable and robust FSNCZ CS photocatalyst, demonstrates promising potential for the decomposition of organic compounds.

Degradation of 2,4-dinitrotoluene in aqueous solution by dielectric barrier discharge plasma combined with Fe–RGO–BiVO4 nanocomposite

2,4-Dinitrotoluene (2,4-DNT) as a priority and hazardous pollutant, is widely used in industrial and military activities. In this study the synergistic effect of Fe–RGO–BiVO4 nanocomposite in a non-thermal dielectric barrier discharge plasma reactor (NTP-DBD) for degrading 2,4-DNT was evaluated. Preparation of the Fe–RGO–BiVO4 nanocomposite was done by a stepwise chemical method depositing Fe and reduced graphene oxide (RGO) on BiVO4. Field emission scanning electron microscopy (FESEM), X-ray diffraction analysis (XRD), UV–vis diffuse reflectance spectra (DRS), and energy-dispersive X-ray spectroscopy mapping (EDS-mapping) validated the satisfactory synthesis of Fe–RGO–BiVO4. To find the optimal conditions and to determine the interaction of model parameters, a central composite design (RSM-CCD) had been employed. 2,4 DNT can be completely degraded at: initial 2,4-DNT concentration of 40 mg L−1, Fe–RGO–BiVO4 dosage of 0.75 g L−1, applied voltage of 21kV, reaction time of 30 min and pH equal to 7, while the single plasma process reached a degradation efficiency of 67%. The removal efficiency of chemical oxygen demand (COD) and total organic carbon (TOC) were 90.62% and 88.02% at 30 min contact time, respectively. Results also indicated that average oxidation state (AOS) and carbon oxidation state (COS) were enhanced in the catalytic NTP-DBD process, which demonstrate the effectiveness of proposed process for facilitating biodegradability of 2,4-DNT.

Impact of organic matter on transformation during thermal remediation of pyrene-contaminated substrates

Thermal remediation (TR) is a broadly applicable technology that is effective at removing volatile and semi-volatile contaminants from soil. However, TR can be costly and inefficient in practice, with underlying removal and transformation mechanisms poorly understood. To better understand the role organic matter plays in removal, a series of experiments was performed with a humic substance, humic modified silica, and a natural soil in the presence of pyrene from 100 to 500 °C and compared to prior experiments using pure minerals. Detection of by-products confirmed that pyrene was removed by transformation in addition to volatilization. Oxidation via hydroxyl radical formation and reductive hydrogenation were both indicated as possible reaction mechanisms promoted by organic matter. Because the presence of bulk water did not impact the extent of pyrene degradation or transformation, it is hypothesized that hydroxyl radicals were produced from soil organic matter functional groups, such as carboxyl and phenol groups, and possibly bound water at elevated temperatures in dry experiments. Additionally, the average oxidation state of carbon in detected by-products increased with temperature in experiments with humic modified silica and soil but not humic substance alone, though the extent of degradation did not significantly change. This shift in oxidation state may indicate that attachment of organic matter to another surface may increase interaction between reactive species. The results of this study show that contaminant transformation in soils during TR significantly contributes to removal, even at temperatures lower than those used in traditional treatment. This information will help to guide the design and operation of TR systems, potentially reducing energy requirements and highlighting the necessity of testing for transformation by-products.

Unraveling the persistence of deep podzolized carbon: Insights from organic matter characterization

Over a billion tons of terrestrial carbon (C) is stored in deep soils from the Southeastern Coastal Plain of the United States. While the size and extent of this pool, known as deep podzolized carbon (DPC), have been reported in recent studies, the stabilization mechanisms responsible for its persistence are unclear. The main hypothesis of DPC stabilization is that hydrology, specifically water table fluctuations in the phreatic zone, slow microbial degradation and promote C accumulation. This accounts for the characteristic properties and distribution of DPC and provides a mechanistic distinction between DPC and shallow podzolized C in the region's soils, however it has yet to be tested. We characterized the organic matter composition of the bulk and dissolved fractions of DPC using elemental analysis, solvent extraction, infrared spectroscopy, and high-resolution mass spectrometry. Consistent with past work, the majority of DPC organic matter was extractable by sodium pyrophosphate solution; the influence of metal association was also observable in the water extractable fraction of DPC with large species being preferentially removed and a low compound diversity compared to those from other horizons overlying DPC. Only water extractable species with low molecular mass (m/z < 375 Da) showed significant change in average nominal oxidation state of carbon (NOSC) values, indicative of oxygen-limitation influence on the processing of these species. Infrared spectroscopy revealed an increase in abundance of aliphatic (C-H:C-O) bonds relative to polysaccharide bonds with depth whereas aromatic (C=C:C-O) bonds decreased with depth in DPC relative to other subsurface horizons. Our work shows that DPC is significantly more refractory than overlying surface soil C, and yet slightly more labile than the subsoils above DPC. Together our results suggest that the maintenance of low redox conditions via persistent water saturation contributes to the stabilization and persistence of DPC.

Modeling and optimization of advanced oxidation treatment of dexamethasone from aquatic solutions using electro-peroxone/ultrasonic process: Application for real wastewater, electrical energy consumption and degradation pathway

Dexamethasone (DXM) is a widely used anti-inflammatory corticosteroid that is frequently detected in the water bodies due to its immense consumption and incomplete removal during wastewater treatment. The potential eco-toxicity of pharmaceutical pollutants and their insufficient removal in conventional wastewater treatments have provoked researchers to investigate and develop novel and highly efficient treatment systems. The present study aimed to develop a synergistic advanced oxidation system based on electro-peroxone coupled with ultrasonic irradiation (EP/US process) for the degradation of dexamethasone (DXM) from water medium and an EP/US process assisted with granular activated carbon (GAC) for the remediation of real pharmaceutical wastewater. The effects of various experimental parameters such as pH, operating time, US power, applied current, and supporting electrolyte (Na2SO4) were systematically investigated by using response surface methodology based on central composite design (RSM-CCD), and results established that the complete degradation of DEX was attained at pH 9, operating time 25 min, US power 300 W/L, applied current 420 mA, and supporting electrolyte 0.05 M. The results of analysis of variance and regression analysis revealed that the second-order polynomial equation is more suitable (R2 = 0.9981 and p-value = 0.0004) to predict removal efficiency and describe the oxidation process. Under optimized experimental condition, the integrated EP/US process provided synergy and lessenergyconsumption compared to individual EP and US processes. The removal efficiency of TOC and COD reached 44.2% and 70.8% after 25 min reaction and increased to 78.7 % and 94.4%, respectively, as contact time increased to 50 min. Also, average oxidation state (AOS) and carbon oxidation state (COS) values increased from 0.22 to 3.28 and 3.78, respectively. Scavenger tests disclosed that HO• radical is the predominant reactive free radical generated in the EP/US system, and LC-MS analysis indicated that different intermediates are produced during DEX decomposition. The EP/US system increased the BOD/COD ratio of real pharmaceutical wastewater from 0.27 to 0.5 during 100 min treatment time, while in the presence of GAC, the EP/US process showed better results. Overall, the present study highlights that the coupling of EP/US processes noticeably improves the DEX abatement rate from water medium, and GAC can improve the efficiency of this process for pharmaceutical wastewater treatment. The findings of the present study propose the EP/US and EP/US/GAC systems as promising efficient alternatives for treating persistentpharmaceutical wastewater.

Using a promising biomass-based biochar in photocatalytic degradation: highly impressive performance of RHB/SnO2/Fe3O4 for elimination of AO7.

The release of industrial dyes into the environment has recently increased, resulting in harmful effects on people and ecosystems. In recent years, the use of adsorbents in photocatalytic nanocomposites has attracted significant interest due to their low cost, efficiency, and eco-friendly physical and chemical characteristics. Herein, Acid Orange 7 (AO7) removal was investigated by photocatalytic degradation using Rice Rusk Biochar (RHB), Tin (IV) Oxide (SnO2), and Iron Oxide (Fe3O4) as heterogeneous nanocomposite. After the preparation of RHB, the nanocomposite was synthesized and characterized using Field Emission Scanning Electron Microscope (FESEM), X-ray Powder Diffraction (XRD), Brunauer-Emmett-Teller (BET), and Fourier-Transform Infrared Spectroscopy (FT-IR). To optimize the elimination of AO7 by the One-Factor-At-a-Time (OFAT) method, effective parameters including mixing ratio (RHB:SnO2:Fe3O4), dye concentration, solution pH, and nanocomposite dose were studied. The results showed that the removal efficiency of AO7 after 120min under the optimal mixing ratio of 1:1.5:0.6, dye concentration of 75mg/l, solution pH of 4, and nanocomposite dose of 0.7g/l was 92.37%. Moreover, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) removal rates were obtained at 82.22 and 72.22%, respectively. The Average Oxidation State (AOS) and Carbon Oxidation State (COS) of the AO7 solution were increased after the process, indicating biodegradability improvement. Various scavenger effects were studied under optimal conditions, and the results revealed that O2- and H+ reactive species play a crucial role in the photocatalytic degradation of AO7. The reusability and stability of nanocomposite were tested in several consecutive experiments, and the degradation efficiency was reduced from 92 to 79% after five consecutive cycles. It is expected that this research contributes significantly to the utilization of agricultural waste in photocatalytic nanocomposites for the degradation of environmental pollutants.

Heterogeneous Dynamic Behavior and Synergetic Evolution Mechanism of Internal Components and Released Gases during the Pyrolysis of Aquatic Biomass.

Evolution of gaseous contaminants from biomass pyrolysis has drawn increasing attention. However, the thermal degradation, dynamics, and synergetic evolution mechanisms during real-time biomass pyrolysis remain unclear. Herein, a novel method using thermogravimetry-Fourier transform infrared spectrometry-gas chromatography/mass spectrometry (TG-FTIR-GC/MS) combined with thermal kinetics and two-dimensional correlation spectroscopy was proposed to explore the chemical properties and temperature response mechanisms of gaseous species released during Phragmites communis (PC) and Typha angustifolia (TA) pyrolysis. The thermal degradation mechanisms of PC/TA pyrolysis were mainly associated with the sigmoidal rate and random nucleation mechanisms. The formation intensities of alcohols/ethers, phenols/esters, acids, aldehydes, and ketones were higher during low-temperature TA pyrolysis and high-temperature PC pyrolysis. The average carbon oxidation state () of gaseous species mainly ranged from -1.5 to -0.5, and the slope of most gaseous species was greater than -2.0, which was related to the reduction of aldehyde/ketone groups. Two-dimensional (2D)-TG-FTIR-COS analysis revealed that the sequential temperature response of gaseous species followed: acids → phenols, esters → aldehydes → hydrocarbons → alcohols, ethers → aromatics during PC/TA pyrolysis. The establishment of relationships between the sequential response of gases and degraded components provides an important basis for online monitoring/recovery of gaseous contaminants during biomass pyrolysis.

Ch3MS-RF: a random forest model for chemical characterization and improved quantification of unidentified atmospheric organics detected by chromatography–mass spectrometry techniques

Abstract. The chemical composition of ambient organic aerosols plays a critical role in driving their climate and health-relevant properties and holds important clues to the sources and formation mechanisms of secondary aerosol material. In most ambient atmospheric environments, this composition remains incompletely characterized, with the number of identifiable species consistently outnumbered by those that have no mass spectral matches in the literature or the National Institute of Standards and Technology/National Institutes of Health/Environmental Protection Agency (NIST/NIH/EPA) mass spectral databases, making them nearly impossible to definitively identify. This creates significant challenges in utilizing the full analytical capabilities of techniques which separate and generate spectra for complex environmental samples. In this work, we develop the use of machine learning techniques to quantify and characterize novel, or unidentifiable, organic material. This work introduces Ch3MS-RF (Chemical Characterization by Chromatography–Mass Spectrometry Random Forest Modeling), an open-source, R-based software tool, for efficient machine-learning-enabled characterization of compounds separated in chromatography–mass spectrometry applications but not identifiable by comparison to mass spectral databases. A random forest model is trained and tested on a known 130 component representative external standard to predict the response factors of novel environmental organics based on position in volatility–polarity space and mass spectrum, enabling the reproducible, efficient, and optimized quantification of novel environmental species. Quantification accuracy on a reserved 20 % test set randomly split from the external standard compound list indicates that random forest modeling significantly outperforms the commonly used methods in both precision and accuracy, with a median response factor percent error of −2 %, for modeled response factors, compared to &gt; 15 %, for typically used proxy assignment-based methods. Chemical properties modeling, evaluated on the same reserved 20 % test set and an extrapolation set of species identified in ambient organic aerosol samples collected in the Amazon rainforest, also demonstrate robust performance. Extrapolation set property prediction mean absolute errors for carbon number, oxygen to carbon ratio (O : C), average carbon oxidation state (OSc‾), and vapor pressure are 1.8, 0.15, 0.25, and 1.0 (log(atm)), respectively. Extrapolation set out-of-sample R2 for all properties modeled are above 0.75, with the exception of vapor pressure. While predictive performance for vapor pressure is less robust compared to the other chemical properties modeled, random-forest-based modeling was significantly more accurate than other commonly used methods of vapor pressure prediction, decreasing the mean vapor pressure prediction error to 0.24 (log(atm)) from 0.55 (log(atm)) (chromatography-based vapor pressure prediction) and 1.2 (log(atm)) (chemical formula-based vapor pressure prediction). The random forest model significantly advances an untargeted analysis of the full scope of chemical speciation yielded by two-dimensional gas chromatography (GCxGC-MS) techniques and can be applied to gas chromatography coupled with electron ionization mass spectrometry (GC-MS) as well. It enables the accurate estimation of key chemical properties commonly utilized in the atmospheric chemistry community, which may be used to more efficiently identify important tracers for further individual analysis and to characterize compound populations uniquely formed under specific ambient conditions.

Dynamic Evolution and Covariant Response Mechanism of Volatile Organic Compounds and Residual Functional Groups during the Online Pyrolysis of Coal and Biomass Fuels.

Volatile organic compound (VOC) emissions from pyrolysis of widely used biomass are expected to increase significantly under the carbon neutrality target. However, the dynamic emissions and evolution mechanism of biomass-VOCs remain unclear, hindered by complex reactions and offline measurements. Here, we propose a novel covariant evolution mechanism to interpret the emission heterogeneities, sequential temperature responses, and evolved correlations of both VOCs and residual functional groups (RFGs) during corn straw (CS), wood pellet (WP), and semibituminous coal (SBC) pyrolysis. An innovative combination of online thermogravimetric-Fourier transform infrared-gas chromatography/mass spectrometry and two dimensional-correlation spectroscopy was applied. The relative percentages of CS/WP-VOCs were higher than those of SBC-VOCs, and most VOCs tended to have relatively small carbon skeletons as the average carbon oxidation state increased. With the temperature increased from low to high during CS/WP pyrolysis, the primary sequential response of VOCs (acids → phenols/esters → alcohols/ethers/aldehydes/ketones → hydrocarbons/aromatics) corresponded to the RFG response (hydroxyl groups → -CH3/-CH2-/-CH groups → aliphatic ethers and conjugated ketones). Compared with the relative regularity for CS/WP responses, the gas-solid products from SBC pyrolysis exhibited complex temperature-dependent responses and high oxidation-induced variability. These insights provide favorable strategies for the online monitoring system to facilitate priority removal of coal and biomass fuels-VOCs.

Identifying carbon processing based on molecular differences between groundwater and water-extractable aquifer sediment dissolved organic matter in a Quaternary alluvial-lacustrine aquifer

Dissolved organic matter in groundwater (GDOM) plays an important role in many biogeochemical processes. The molecular composition of GDOM varies with the source and processing pathways, and also affects its reactivity. Sedimentary organic matter (SOM) is a key carbon source in groundwater, but its association with GDOM remains unclear. In this study, Fourier transform-ion cyclotron resonance-mass spectrometry (FT-ICR-MS) and comprehensive data analysis were used to identify the molecular characteristics of SOM and the fate of DOM in groundwater by comparing the differences between the GDOM with depth-matched water-extractable aquifer SOM (WEOM; the most bioavailable and dynamic pool of organic carbon in SOM) in a Quaternary alluvial-lacustrine aquifer with abundant SOM in Jianghan Plain, central China. The results show that WEOM is a key carbon source in groundwater as reflected by the strong correlation (rs = 0.76, P = 0.028) of the DOC content between GDOM and WEOM, and the large proportion (70.64 ± 14.09%) of common compounds present both in GDOM and WEOM. However, the molecular compositions of GDOM and WEOM are significantly different even for common compounds when considering the relative abundance. WEOM contains relatively high abundance of low molecular weight and thermodynamically more favorable components for microbial oxidation (aminosugars and carbohydrates), making WEOM an energetic carbon source for groundwater that can fuel reduction half-reactions such as iron oxide reduction. Although the hydrochemical compositions and the DOC content of groundwater are quite different, the molecular composition of GDOM is relatively similar and enriched in oxygen-poor highly unsaturated and phenolic compounds compared with WEOM. This indicates that organic matter is gradually processed into stable components with relatively medium aromaticity, low average nominal carbon oxidation state, low O/C and medium H/C; these transformations occur through adsorption to minerals and biodegradation after being mobilized from aquifer sediment into groundwater. We identified the processing pathways of GDOM based on comprehensive comparisons of molecular compositions between aquifer WEOM and GDOM, and highlight the combined influence of aquifer SOM and processing pathways on the GDOM molecular compositions in the alluvial-lacustrine aquifer with abundant aquifer SOM.

Using chitosan-based heterogeneous catalyst for degradation of Acid Blue 25 in the effective electro-Fenton process with rotating cathodes

Herein, the capability of glutaraldehyde cross-linked magnetic chitosan nanoparticles (Fe3O4/CS/GA NPs) was investigated as a heterogeneous electro-Fenton catalyst for the degradation of Acid Blue 25. A cylindrical reactor with rotating cathodes was used for performing the electro-Fenton process. Fe3O4/CS/GA NPs were characterized by Fourier-Transform Infrared Spectroscopy (FT-IR), X-ray Powder Diffraction (XRD), Field Emission Scanning Electron Microscope (FESEM), Energy Dispersive X-Ray (EDX), and Vibrating Sample Magnetometer (VSM). According to the results, the dye removal efficiency reached 94.83% after 90 min under the optimal conditions of Fe3O4/CS/GA NPs with the iron content of 15 mmol Fe/g chitosan and concentration of 0.3 g/L, natural pH of dye (6.8), initial dye concentration of 150 mg/L, the current intensity of 0.7 A, and rotational speed of 100 rpm. Also, Chemical Oxygen Demand (COD) and Total Organic Carbon (TOC) removal reached 74.19% and 61.53% after 120 min, respectively. Average oxidation state (AOS) and carbon oxidation state (COS) values were increased after treatment, indicating that wastewater's biodegradability was improved. Moreover, the heterogeneous electro-Fenton process using optimal Fe3O4/CS/GA NPs resulted in about 16% improvement in the removal efficiency compared to the homogeneous process. The catalyst showed good reusability up to 5 cycles. The amounts of leached iron into the solution were much less than allowable amounts of the Iranian wastewater discharge standard, thus no need for secondary treatment. Furthermore, scavengers studies under the optimum conditions showed the dye degradation occurred mainly by surface-bonded hydroxyl radicals. In short, this study proved, Fe3O4/CS/GA NPs are a promising heterogeneous electro-Fenton catalyst due to their low cost, excellent stability and reusability, negligible iron leaching, environmental compatibility, and superior catalytic activity in a wide range of pH.

Internal electric field driving separation and migration of charge carriers via Z-scheme path in AgIn5S8/ZnO heterojunction for efficient decontamination of pharmaceutical pollutants

Z-scheme heterojunctions are considered as prospective photocatalysts for elimination of organic pollutants. However, the origin of enhanced oxidation ability of Z-scheme heterojunctions is not well understood, and the working mechanism based on internal electrical field is still ambiguous. Here, we report Z-scheme AgIn5S8/ZnO heterojunction with superior photocatalytic activity in degrading pharmaceutical pollutants and enhancing biodegradability of pharmaceutical wastewater. The average oxidation state (AOS) and carbon oxidation state (COS) of pharmaceutical wastewater are significantly increased from 0.42 to 1.35 and 2.94 after photocatalytic treatment of AgIn5S8/ZnO. The analysis on the origin of superior photocatalytic activity reveals that the internal electric field in AgIn5S8/ZnO heterojunction works as a driving force to facilitate efficient separation of photogenerated charge carriers via Z-scheme path, thus generating spatially separated holes and electrons with high redox ability and realizing effective elimination of pharmaceutical pollutants. This study provides deep insight into photocatalytic mechanism of Z-scheme heterojunction for efficacious elimination of organic pollutants and boosted biodegradability of pharmaceutical wastewater.

Using banana peel waste to synthesize BPAC/ZnO nanocomposite for photocatalytic degradation of Acid Blue 25: Influential parameters, mineralization, biodegradability studies

In this study, Acid Blue 25 (AB25) removal was investigated by photocatalytic degradation using banana peel activated carbon (BPAC) and zinc oxide (ZnO) nanocomposite. The nanocomposite was synthesized by the physical mixing method. The BPAC/ZnO nanocomposite was characterized by XRD, FT-IR, FESEM, EDX-mapping, and BET. The effective parameters, including nanocomposite mixing ratio (BPAC:ZnO), pH, initial dye concentration, nanocomposite concentration, aeration rate, and UV light intensity was studied on the degradation of AB25 by the OFAT method. The results indicated that the removal efficiency of AB25 was obtained 94% after 150 min at the optimum conditions of nanocomposite mixing ratio 3:7 (BPAC:ZnO), pH = 5, initial dye concentration = 150 mg L-1, nanocomposite concentration = 0.6 g L-1, aeration rate = 5 L min-1, and UV light intensity = 16 W. Also, the energy consumption at the optimum condition of parameters was obtained 631 kWh kg-1. Moreover, COD and TOC removal was obtained 78% and 61%, respectively. The average oxidation state (AOS) and carbon oxidation state (COS) of AB25 solution were increased after photocatalytic degradation, indicating biodegradability improvement. Also, under the optimum condition of parameters, the effect of scavengers on photocatalytic degradation of AB25 was examined. The results revealed that photo-generated holes and superoxide radicals played a significant role in the degradation process. The reusability of the nanocomposite was studied in several successive experiments, and the degradation efficiency declined from 94% to 82% after four cycles.

Estimation of the carbon valence from its average formal oxidation state in the soil organic matter

AbstractThe wet dichromate methods for the quantification of soil organic carbon on the basis of the reductant ability of soil organic matter have been widely used and they are still nowadays. The results obtained with these methods depart from the reference dry combustion with CO2 measurement and the discrepancies are interpreted in terms of incomplete oxidation under the wet dichromate conditions. However, in the calculations accompanying the dichromate methods a carbon valence (VC) equal to four is systematically used, even though the actual VC could be different. To assess the importance that an actual VC different from four could have in the mismatch between the wet dichromate methods and the reference dry combustion, the relationship between VC and the average formal oxidation state of carbon (zC) in soil organic matter should be known. On the basis of the definition of the equivalent weight and the average formal oxidation state, it is shown that a simple linear expression of the form VC = 4 – zC relates both concepts in carbon‐hydrogen‐oxygen‐nitrogen‐phosphorus‐sulphur compounds, which are representative of soil organic matter. On the basis of this equation the actual VC in soil organic matter can be assessed, thus helping in the interpretation of soil organic carbon determinations with the wet dichromate methods and, therefore, in the comparison between the dichromate methods and the reference dry combustion.Highlights Although questioned, a carbon valence of four is always used in the wet dichromate methods for SOC. How the valence of carbon depends on its average formal oxidation had not been previously shown. Both concepts are related through a simple linear equation: VC = 4 – zC. The mismatch between the dichromate oxidation and the dry combustion will be better interpreted.

Identification and source attribution of organic compounds in ultrafine particles near Frankfurt International Airport

Abstract. Analysing the composition of ambient ultrafine particles (UFPs) is a challenging task due to the low mass and chemical complexity of small particles, yet it is a prerequisite for the identification of particle sources and the assessment of potential health risks. Here, we show the molecular characterization of UFPs, based on cascade impactor (Nano-MOUDI) samples that were collected at an air quality monitoring station near one of Europe's largest airports, in Frankfurt, Germany. At this station, particle-size-distribution measurements show an enhanced number concentration of particles smaller than 50 nm during airport operating hours. We sampled the lower UFP fraction (0.010–0.018, 0.018–0.032, 0.032–0.056 µm) when the air masses arrived from the airport. We developed an optimized filter extraction procedure using ultra-high-performance liquid chromatography (UHPLC) for compound separation and a heated electrospray ionization (HESI) source with an Orbitrap high-resolution mass spectrometer (HRMS) as a detector for organic compounds. A non-target screening detected ∼200 organic compounds in the UFP fraction with sample-to-blank ratios larger than 5. We identified the largest signals as homologous series of pentaerythritol esters (PEEs) and trimethylolpropane esters (TMPEs), which are base stocks of aircraft lubrication oils. We unambiguously attribute the majority of detected compounds to jet engine lubrication oils by matching retention times, high-resolution and accurate mass measurements, and comparing tandem mass spectrometry (MS2) fragmentation patterns between both ambient samples and commercially available jet oils. For each UFP stage, we created molecular fingerprints to visualize the complex chemical composition of the organic fraction and their average carbon oxidation state. These graphs underline the presence of the homologous series of PEEs and TMPEs and the appearance of jet oil additives (e.g. tricresyl phosphate, TCP). Targeted screening of TCP confirmed the absence of the harmful tri-ortho isomer, while we identified a thermal transformation product of TMPE-based lubrication oil (trimethylolpropane phosphate, TMP-P). Even though a quantitative determination of the identified compounds is limited, the presented method enables the qualitative detection of molecular markers for jet engine lubricants in UFPs and thus strongly improves the source apportionment of UFPs near airports.

A graphene oxide Cookbook: Exploring chemical and colloidal properties as a function of synthesis parameters

Herein, we describe the synthesis of graphene oxide (GO) over a large range of conditions, exploring the effects of reaction temperature, reaction time, oxidant ratio, and sonication time on the chemical and colloidal properties of the product. As a function of reaction parameters, modified from Hummers’ method, GO products were characterized and described via a suite of spectroscopic, structural, and morphological techniques, including TEM, UV–vis spectroscopy, XPS, Raman spectroscopy, FTIR, and DLS. Average carbon oxidation state and the yield (upon sonication) were chosen as the two criteria to evaluate synthesized GO materials. It was observed that as reaction temperature increased, GO oxidation state and yield of the sonication step both increased. Further, increasing reaction time and oxidant ratio not only increased the oxidation state, but also had a pronounced effect on the final yield. As synthesized, GO with higher degrees of oxidization exhibited higher negative ζ-potential, slightly smaller hydrodynamic diameter, and higher critical coagulation concentration(s). Data sets collectively demonstrate that carbon oxidation state, functional group ratios, and the aggregation kinetics of GO products can be readily controlled by varying processing time and conditions with expected changes in aqueous behavior(s), including stability/aggregation.

Synthesis of Carboxylic Acid and Dimer Ester Surrogates to Constrain the Abundance and Distribution of Molecular Products in α-Pinene and β-Pinene Secondary Organic Aerosol.

Liquid chromatography/negative electrospray ionization mass spectrometry [LC/(-)ESI-MS] is routinely employed to characterize the identity and abundance of molecular products in secondary organic aerosol (SOA) derived from monoterpene oxidation. Due to a lack of authentic standards, however, commercial terpenoic acids (e.g., cis-pinonic acid) are typically used as surrogates to quantify both monomeric and dimeric SOA constituents. Here, we synthesize a series of enantiopure, pinene-derived carboxylic acid and dimer ester homologues. We find that the (-)ESI efficiencies of the dimer esters are 19-36 times higher than that of cis-pinonic acid, demonstrating that the mass contribution of dimers to monoterpene SOA has been significantly overestimated in past studies. Using the measured (-)ESI efficiencies of the carboxylic acids and dimer esters as more representative surrogates, we determine that molecular products measureable by LC/(-)ESI-MS account for only 21.8 ± 2.6% and 18.9 ± 3.2% of the mass of SOA formed from ozonolysis of α-pinene and β-pinene, respectively. The 28-36 identified monomers (C7-10H10-18O3-6) constitute 15.6-20.5% of total SOA mass, whereas only 1.3-3.3% of the SOA mass is attributable to the 46-62 identified dimers (C15-19H24-32O4-11). The distribution of identified α-pinene and β-pinene SOA molecular products is examined as a function of carbon number (nC), average carbon oxidation state , and volatility (C*). The observed order-of-magnitude difference in (-)ESI efficiency between monomers and dimers is expected to be broadly applicable to other biogenic and anthropogenic SOA systems analyzed via (-) or (+) LC/ESI-MS under various LC conditions, and demonstrates that the use of unrepresentative surrogates can lead to substantial systematic errors in quantitative LC/ESI-MS analyses of SOA.

Efficient treatment for landfill leachate through sequential electrocoagulation, electrooxidation and PMS/UV/CuFe2O4 process

Landfill leachate is well known as one of the most serious environmental problems due to the high concentrations of organic and inorganic compounds. Several methods have been reported for the treatment and detoxification of landfill leachate. However, high organic load and the presence of refractory organic pollutants resulted in inefficiency of those methods when at least applied alone. The present work recommended a sequence of processes: electrocoagulation (EC), electrooxidation (EO) and peroxymonosulfate (PMS)/UV/CuFe2O4 (sulfate radical-based advanced oxidation process, SR-AOP) for treatment of landfill leachate. A parametric evaluation was conducted for each process including pH, current densities, electrode type, catalyst loading, PMS dosage and reaction time. Al and Fe electrodes for the EC process and Pt, PbO2 and graphite for the EO process were investigated. The results showed that Fe and PbO2 were more efficient than other electrodes for EC and EO respectively. COD removal efficiencies were up to 60.0, 50.0 and 77.9% for EC, EO and SR-AOP, respectively. Removal efficiencies for the sequential process were 95.6, 90.5, 91.6 and 99.8% for COD, TOC, BOD and ammonia (NH4-N) respectively. Biodegradability was significantly enhanced according to the BOD/COD ratio and the average oxidation state of carbon (AOSC). Biodegradation test indicated that the organic matter was completely degraded by activated sludge in seven days. Phytotoxicity experiments also demonstrated a considerable reduction in phytotoxicity after each process. The results confirmed that the proposed sequence is efficient for COD removal, phytotoxicity reduction and biodegradability improvement being an acceptable treatment for landfill leachates.