Achieving Non-Interfacial Blocking Zinc Ion Transport Based on MOF Derived Manganese Oxides and Amorphous Carbon Hybrid Materials.

How to coordinate electron and ion transport behavior across scales and interfaces within ion battery electrodes? The exponential increase in surface area observed in nanoscale electrode materials results in an incomprehensibly vast spatial interval. Herein, to address the problems of volume expansion, dissolution of cathode material, and the charge accumulation problem existing in manganiferous materials for zinc ion batteries, metal organic framework is utilized to form the architecture of non-interfacial blocking ~10 nm Mn2O3 nanoparticles and amorphous carbon hybrid electrode materials, demonstrating a high specific capacity of 361 mAh g-1 (0.1 A g-1), and excellent cycle stability of 105 mAh g-1 after 2000 cycles under 1 A g-1. The uniform and non-separated disposition of Mn and C atoms constitutes an interconnected network with high electronic and ionic conductivity, minimizing issues like structural collapse and volume expansion of the electrode material during cycling. The cooperative insert mechanism of H+ and Zn2+ are analyzed via ex-situ XRD and in-situ Raman tests. The model battery is assembled to present practical possibilities. The results indicate that MOF-derived carbonization provides an effective strategy for exploring Mn-based electrode materials with high ion and electron transport capacity.

A novel three-dimensional porous Ag/TiO2 hybrid aerogels with high dense hot spot as effective SERS substrate for ultrasensitive detection.

This research focuses on preparing a series of new TiO2/Ag hybrid aerogels with varying TiO2 contents, and demonstrates their application as ultrasensitive SERS substrates. The synthesized TiO2/Ag hybrid aerogels exhibited excellent SERS behavior when detecting 4-Mercaptobenzoic acid (4-MBA), and the calculated SERS enhancement factor (EF) was 6.34 × 106. 3D structured aerogels can create more hot spots and adsorption sites, and multiple interband chemical transfer (CT) pathways emerged and enhanced CT efficiency because of the large number of surface oxygen vacancies of meso-TiO2 NPs. Therefore, the synergy of electromagnetic field enhancement and chemical enhancement leads to SERS enhancement. In addition, the composite SERS substrate has high sensitivity, and the detection limit of adsorbed 4-MBA probe molecules reaches 10-11 M. Furthermore, the TiO2/Ag hybrid aerogels demonstrate good reproducibility with minimal standard deviation in terms of SERS signals. In addition, even after standing for 6 months, there is almost no attenuation in the SERS signal intensity, which highlights the excellent stability of this substrate. Therefore, these highly sensitive TiO2/Ag hybrid aerogels SERS substrates have important practical value in environmental monitoring, medical inspection and food supervision.

Multifunctional Luminescent 3D Ln-MOFs with High Sensitivity for Trace Detection of Micronutrients.

The synthesis of two versatile fluorescent metal-organic frameworks (MOFs), [Eu(4-NCP)(1,4-bdc)]n·0.5H2O (1) and [Eu(4-NCP)(4,4'-bpdc)]n·0.75H2O (2) (HNCP = 2-(4-carboxyphenyl)imidazo(4,5-f)-(1,10)phenanthroline, 1,4-H2bdc = benzene-1,4-dicarboxylic acid, 4,4'-H2bpdc = 4,4'-biphenyldicarboxylic acid), was carried out using a hydrothermal method. These MOFs were characterized through various advanced technologies to determine their structural information. The results indicate that both MOFs exhibited 3D network structures with specific topologies. Furthermore, these MOFs demonstrated exceptional thermal stabilities and adsorption capabilities. Additionally, complex 2 was utilized for studying the fluorescence sensing properties of various micronutrients including metal ions, nitro aromatic compounds, and biological small molecules. Notably, complex 2 showed promising potential as a multifunctional sensor for selectively detecting Fe3+, nitrobenzene, and ascorbic acid in aqueous solutions through fluorescence quenching with low limits of detection (LODs ∼ 10-7 M) and high quenching constants (Ksv ∼ 103 M-1). Moreover, the detection mechanism of complex 2 was further investigated by using experimental methods and DFT calculations.

Atomic-scale imaging of ytterbium ions in lead halide perovskites.

Lanthanide-doped lead halide perovskites have demonstrated great potential for photoelectric applications. However, there is a long-standing controversy about the existence of lanthanide ions, e.g., whether the doping of Ln3+ is successful or not; the substituting sites of Ln3+ in lead halide perovskites are unclear. We directly identify the doped Yb3+ in CsPbCl3 perovskites by using the state-of-the-art transmission electron microscopy and three-dimensional atom probe tomography at atomic scale. Different from the previous assumptions and/or results, we evidence that Yb3+ simultaneously replace Pb2+ and occupy the lattice interstitial sites. Furthermore, we directly observe the cluster phenomenon of CsPbCl3 single crystal at near atomic scale. Density functional theory modeling further confirms and explains the mechanisms of our findings. Our findings thus provide an atomic-level understanding of the doping mechanism in perovskites and will stimulate a further thinking of the doping effect on the performance of perovskites.

Evaluation of the potential of recovering various valuable elements from a vanadiferous titanomagnetite tailing based on chemical and process mineralogical characterization.

In order to evaluate the potential of recovering various valuable elements from vanadiferous titanomagnetite tailing (VTMT), the chemical and process mineralogical characterization of VTMT were investigated in this study by various analytical techniques such as XRF, XRD, optical microscopy, SEM, EDS, and AMICS. It was found that VTMT is a coarser powder in general; about 50% of the particle size is greater than 54.30 µm. The total iron content of the VTMT was 22.40 wt.%, and its TiO2 grade is 14.45 wt.%, even higher than those found in natural ilmenite ores. The majority of iron and titanium were located in ilmenite and hematite; 62.84% of hematite and 90.27% of ilmenite were present in monomeric form. However, there is still a portion of ilmenite and hematite embedded in gangue such as anorthite, diopside, and serpentite. For the recovery of valuable fractions such as Fe and TiO2 from VTMT, a treatment process including ball milling-high-intensity magnetic separation-one roughing and three refining flotation was proposed. Finally, a concentrate with TiO2 grade of 47.31% and total Fe (TFe) grade of 35.44% was produced; TiO2 and TFe had recovery rates of 57.71% and 28.23%, respectively. The recovered product is adequate as a raw material for the production of rutile. This study provides a reference and a new research direction for the recycling and comprehensive utilization of VTMT.

Controllable preparation of Ti3C2Tx/Ag composite as SERS substrate for ultrasensitive detection of 4-nitrobenzenethiol.

Currently, metal carbonitride (MXene) has been identified as a hot research topic in the research area of surface-enhanced Raman scattering (SERS). In this study, Ti3C2Tx/Ag composite was fabricated as SERS substrate with different Ag contents. The fabricated Ti3C2Tx/Ag composites show good SERS behavior by detecting 4-Nitrobenzenethiol (4-NBT) probe molecules. Through calculation, the SERS enhancement factor (EF) of the Ti3C2Tx/Ag substrate was as high as 4.15 × 106. It is worth noting that the detection limit of 4-NBT probe molecules can be achieved ultralow concentration of 10-11 M. In this system, electromagnetic enhancement mechanism and chemical enhancement mechanism have synergistic effects on SERS phenomenon. Meanwhile, the Ti3C2Tx/Ag composite substrate exhibited good SERS reproducibility. In addition, the SERS detection signal hardly changed after 6 months of natural standing, and the substrate showed good stability. This work suggests that the Ti3C2Tx/Ag substrate could be used as a sensitivity SERS sensor for practical application, and could be applied in the field of environmental monitoring.

Electrodeposition of Bi from Choline Chloride-Malonic Acid Deep Eutectic Solvent.

Deep eutectic solvent (DES) has been widely used in the field of metal electrodeposition as an economical and environmentally friendly green solvent. Metallic bismuth films were prepared by electrodeposition from choline chloride-malonic acid (ChCl-MA) deep eutectic solvent (DES) containing BiCl3. Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy were used to study the structure of ChCl-MA-BiCl3, and the results showed that Bi(III) was in the form of [BiCl6]3- ions. The viscosity of ChCl-MA-BiCl3 ranges from 200 to 1200 mPa·s at temperatures from 363 K to 323 K. The conductivity of 0.01 M Bi(III) in ChCl-MA is 3.24 ms·cm-1 at 363 K. The electrochemical behavior and electrodeposition of Bi(III) in DES were investigated by cyclic voltammetry (CV) and chronoamperometry. The results showed that the electrodeposition reaction was a quasi-reversible reaction controlled by the diffusion and the nucleation of bismuth was a three-dimensional instantaneous nucleation. The diffusion coefficient of Bi(III) in ChCl-MA was 1.84 × 10-9 cm2·s-1. The electrodeposition product was observed by scanning electron microscopy (SEM), and the results showed that the deposition potential has a significant influence on the morphology of the bismuth film. X-ray photoelectron spectroscopy (XPS) shows that bismuth and bismuth oxides are present in the deposited film obtained by electrodeposition.

Tailored FTO/Ag/ZIF-8 structure as SERS substrate for ultrasensitive detection.

In this work, a series of F-doped SnO2/Ag/zeolite imidazole framework (FTO/Ag/ZIF-8) sandwich structure have been successfully fabricated via a magnetic sputtering method and serve as surface-enhanced Raman scattering (SERS) substrate. The magnetic sputtering time of Ag was adjusted to obtain the optimal SERS substrate. The commonly used 4-mercaptobenzoic acid (4-MBA) molecules was selected for the SERS experiment. When the sputtering time of Ag nanoparticles (NPs) was 120 s, the FTO/Ag/ZIF-8 substrate showed the maximum SERS performance. In the system, the electromagnetic mechanism (EM) and charge-transfer (CT) enhancement mechanism have synergistic effect on the SERS phenomenon. Ag NPs was used to generate electromagnetic hot spots, which was beneficial to the EM mechanism. ZIF-8 could adsorb and capture more 4-MBA probe molecules to the hotspots. At the same time, CT happened between Ag, ZIF-8, and 4-MBA probe molecules, which was attribute to the CM mechanism. The enhancement factor (EF) of the composite SERS substrate was as high as 7.67 × 106. The detection limit of the substrate can reach 10-9 M of 4-MBA probe molecules. Moreover, the SERS templates showed good stability, the SERS signals almost unchanged after naturally kept for 6 months. Besides, due to the high sensitivity and good stability of the substrates, this work might broaden the potential practical application of SERS.

V5+-Doped Potassium Ferrite as an Efficient Trifunctional Catalyst for Large-Current-Density Water Splitting and Long-Life Rechargeable Zn-Air Battery.

Developing non-noble metal catalyst with super trifunctional activities for efficient overall water splitting (OWS) and rechargeable Zn-air battery (ZAB) is urgently needed. However, catalysts with excellent oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and hydrogen evolution reaction (HER) performances are relatively few. Although metal-ionic-conductor K2Fe4O7 (KFO) can output large current densities for OER/HER even in 10.0 M KOH electrolyte, its water-splitting property still needs to be further improved. Herein, we introduced V5+ directly into KFO and synthesized the binder-free nickel foam (NF) basal V-KFO nanoparticles (labeled as V-KFO/NF). Both the theoretical analysis and actual experimental data certify that V5+ doping enhances the instinct water-splitting property of V-KFO/NF. Additionally, V-KFO/NF can directly serve as the air cathode of liquid/flexible ZABs. The assembled liquid ZAB can continue the charge-discharge cycling testing with a lower voltage gap (0.834 V) and a longer operation life (>550 h) at 10 mA cm-2. Meanwhile, the assembled flexible ZAB can drive the two-electrode water-splitting unit of V-KFO/NF and needs only 1.54 V to achieve the current density of 10 mA cm-2, which is much lower than that of KFO/NF (1.59 V). This work not only provides a novel and efficient trifunctional catalyst for a self-powered water-splitting device but also is the foundation support for other heteroatom-doped low-cost materials.

Tunable multiple light emissions of core-shell structures based on rare earth ions doped on the surfaces of organic cocrystals.

The charge transfer (CT) interactions play a vital role in tuning the luminescence of organic crystals. The enhanced energy transfer (ET) effect in rare earth (RE) ions is a significant method to achieve long-lifetime fluorescence. These studies are of great significance in the fields of photoelectric functional materials. However, the effect of CT interactions on the process of ET from the cocrystal ligand group to RE ions is unknown. In this work, we have doped Eu3+ ions, Tb3+ ions and Eu3+/Tb3+ mixed ions on the surfaces of Phen-TCNB (Phen = 1,10-phenanthroline, and TCNB = 1,2,4,5-tetracyanobenzene) to construct organic cocrystal-type core-shell structures by the epitaxial growth method. The core-shell structures exhibited multiple photoluminescence depending on the types and proportions of RE3+ ions that are doped on the surfaces of the cocrystals. Experimental and theoretical investigations prove that the ET enhancements from ligand groups to Eu3+ ions originate from appropriate energy differences between the lowest triplet states of Phen-TCNB and the lowest excited state of RE3+ ions. In contrast, the reduced Tb3+ 5D4 lifetime is caused by the energy back transfer process since the energy difference becomes small. These results reveal that the multiple luminescences of the cocrystal-type core-shell structures can be adjusted by the CT and ET, and this study provides a new strategy for developing novel optoelectronic materials.

A novel method for dearsenization from arsenic-bearing waste slag by selective chlorination and low-temperature volatilization.

Because of the widespread presence of arsenic in various smelting waste slags, it not only hinders the recycling and utilization of waste slag, but also causes serious pollution to the ecological environment. In this study, As2O3, the main form of arsenic in non-ferrous metal smelting slag, was used as the research object, and FeCl3 was used as the chlorination agent. As2O3 was selectively chlorinated to low-boiling-point AsCl3 gas which was easy to be volatilized and removed by chlorination roasting. According to the thermodynamic calculation results, the feasibility of FeCl3 as the chlorination agent for selective chlorination and low-temperature volatilization of dearsenization was analyzed. The TG-DTA diagram was analyzed by thermogravimetric experiment, and the mass change, endothermic and exothermic behaviors of the As2O3-FeCl3 system during the linear heating process were studied. The effects of roasting temperature, roasting time, and molar ratio of reactants on the chlorination-volatilization of the As2O3-FeCl3 system were investigated. The optimal chlorination roasting conditions were determined with a roasting temperature of 290-300 ℃, a roasting time of 50 min, and a reactant FeCl3/As2O3 molar ratio of 4:1. The results of this study provided a novel idea for the removal of arsenic from smelting slag and dust, but the mechanism and process conditions of chlorination still need to be further studied and optimized.

Facile fabrication of PS/Cu2S/Ag sandwich structure as SERS substrate for ultra-sensitive detection.

In this work, a serials of PS(polystyrene)/Cu2S/Ag sandwich substrates were successfully constructed using the magnetic sputtering method by adjusting the Ag sputtering time (0 min, 2 min, 4 min, 6 min, 8 min and 10 min) and used as the surface-enhanced Raman scattering (SERS) substrates. When the Ag sputtering time was 6 min, the strongest SERS signal was observed. The optimized SERS substrate has strong SERS activity on 4-mercaptobenzoic acid (4-MBA), the minimum detection limit was 10-13 M and the enhancement factor was as high as 4.7 × 107. In addition, the SERS signals were highly reproducible with small standard deviation. The SERS enhancement mechanism of the PS/Cu2S/Ag system was attributed to the synergistic effect of the chemical mechanism and the electromagnetic enhancement mechanism. This strategy has find a new way for manufacturing SERS activity sensor with high sensitivity and reproducibility.

Encapsulating silicon particles by graphitic carbon enables High-performance Lithium-ion batteries.

Silicon combines the advantages of high theoretical specific capacity, low potential and natural abundance, which exhibits great promise as an anode for lithium-ion batteries. However, the main challenges associated with Si anode are continuous volume expansion upon cycling and intrinsic low electronic conductivity, leading to sluggish reaction kinetics and rapid capacity fading. Herein we propose a novel in-situ self-catalytic strategy for the growth of highly graphitic carbon to encapsulate Si nanoparticles by chemical vapor deposition, where the magnesiothermic reduction byproducts are used as templates and catalysts for the formation of three-dimensional (3D) conductive network architecture. Benefiting from the improved electronic conductivity and significant suppression of volume expansion, the as-synthesized Si carbon composites exhibit excellent lithium storage capabilities in terms of high specific capacity (2126 mAh g-1 at 0.1 A g-1), remarkable rate capability (750 mAh g-1 at 5 A g-1), and good cycling stability over 450 cycles. Furthermore, the as-fabricated full cell (Si//Ni-rich LiNi0.815Co0.185-xAlxO2) shows high energy density of 395.1 Wh kg-1 and long-term stable cyclability. Significantly, this work demonstrates the effectiveness of in-situ self-catalysis reaction by using magnesiothermic reduction byproducts catalytically derived carbon matrix to encapsulate alloy-type anode material in giving rise to the overall energy storage performance.

Effect of TiO2 on the Sintering Behavior of Low-Grade Vanadiferous Titanomagnetite Ore.

Low-grade vanadiferous titanomagnetite ore (LVTM) is as an important mineral resource for sintering ore manufacturing. Furthermore, TiO2 has a significant effect on the sintering process of iron ore fines. The effects of TiO2 on the metallurgical properties, microstructure, and mineral composition of LVTM sinter were investigated by sintering pot tests, X-ray diffraction (XRD), scanning electron microscopy (SEM), and mineral phase microanalysis. The results were as follows: as the TiO2 content increased from 1.75% to 4.55%, the flame front speed and productivity decreased, while the reduction degradation index (RDI) and softening properties deteriorated. In addition, the tumbler index (TI) values reached a maximum at TiO2 = 1.75%. In addition, with increasing TiO2 content, an increase in the magnetite and perovskite phase, and a decrease in calcium ferrite and hematite were found with an increase in TiO2 content. Thus, the lower the TiO2 content, the better the quality of the sinter.

High-efficiency charge transfer on SERS-active semiconducting K2Ti6O13 nanowires enables direct transition of photoinduced electrons to protein redox centers.

Photoinduced charge transfer (PICT) plays a crucial role in the chemical mechanism of surface-enhanced Raman scattering (SERS), in which small organic molecules are generally used as probes. Herein, semiconducting K2Ti6O13 nanowires (NWs) are synthesized and are found to exhibit high SERS activity probed by 4-mercaptobenzoic acid (4-MBA). Density functional theory (DFT) calculations reveal high-efficiency CT on the K2Ti6O13 nanowires. Furthermore, PICT on the K2Ti6O13 NWs is for the first time evidenced by a redox protein, cytochrome c (Cyt c). Under optimized experimental conditions, the transformation of oxidized Cyt c to its reduced state clearly verifies the electron transfer (ET) from the K2Ti6O13 nanowire to the protein. The ET mechanism is explored based on energy levels of semiconductors and molecular dynamics simulations, thus revealing the importance of energy level matching and electron tunneling from the semiconductor surface to the redox center. This study indicates a great potential of multiple-layered K2Ti6O13 NWs in the application of SERS on semiconducting materials and more importantly, it provides a new route for the rational design of protein-semiconductor interfaces for investigating electron transfer processes of redox proteins and biocatalytic reactions.

Construction of MOF-shell porous materials and performance studies in the selective adsorption and separation of benzene pollutants.

Metastable Cu2O is an attractive material for the architectural design of integrated nanomaterials. In this context, Cu2O was used as the sacrificial agent to form the core-shell structure of Cu2O@HKUST-1 by in situ growth technology. The MOFs with BOPs adsorption property were gathered together by a Cu2O etching method, and the hollow structure of the HKUST-1 shell material with fast BOP adsorption was successfully constructed. The adsorption experiments showed that the HKUST-1 shell has a good adsorption effect on nitrobenzene pollutants in wastewater. The investigation of various factors affecting the adsorption, thermodynamic and kinetic equations was carried out. The adsorption equilibrium was reached within 30 min, and the maximum adsorption capacity was 94.67 mg g-1 at 298 K. The adsorption capacity of nitrobenzene by the HKUST-1 shell is in good agreement with the Freundlich model and the second-order kinetic model. The possible mechanism of adsorption of nitrobenzene by the HKUST-1 shell was discussed. The experimental results suggested that Cu-BTC materials have potential applications for wastewater treatment involving benzene pollutants.

Significant influences of TiO2 crystal structures on NO2 and HONO emissions from the nitrates photolysis.

The emissions of NO2 and HONO from the KNO3 photolysis in the presence of TiO2 were measured using a round-shape reactor coupled to a NOx analyzer. TiO2 played important roles in the emission flux density of NO2 (RNO2) and HONO (RHONO), depending on crystal structures and mass ratios of TiO2. RNO2 and RHONO significantly decreased with increasing the rutile and anatase mass ratios from 0 to 8 and 0.5 wt.%, respectively. Nevertheless, with further increasing the anatase mass ratio to 8 wt.%, there was an increase in RNO2 and RHONO. RNO2 on KNO3/TiO2/SiO2 had positive correlation with the KNO3 mass (1-20 wt.%), irradiation intensity (80-400 W/m2) and temperature (278-308 K), while it had the maximum value at the relative humidity (RH) of 55%. RHONO on KNO3/TiO2/SiO2 slightly varied with the KNO3 mass and temperature, whereas it increased with the irradiation intensity and RH. In addition, the mechanism for NO2 and HONO emissions from the nitrates photolysis and atmospheric implications were discussed.

A Zn-Ce Redox Flow Battery with Ethaline Deep Eutectic Solvent.

Compared with conventional aqueous and ionic liquid electrolytes, deep eutectic solvent (DES) are considered as electrolyte for redox flow batteries because they have a wider electrochemical window and relatively low price. In this study, CeIV /CeIII and ZnII /Zn redox couples are used as the positive and negative active materials, respectively, in an electrolyte consisting of choline chloride ethylene glycol (ethaline). The structure of CeIII in the positive electrolyte is inferred through spectrum detection. CeIV /CeIII and ZnII /Zn redox couples show a stable potential difference of 2.2 V (vs. Ag) through cyclic voltammetry. The charge and discharge performance of battery was tested at different current densities. In addition, battery performance was evaluated at different temperatures and concentrations of cerium in the electrolyte. Consequently, at a current density of 0.5 mA cm-2 at room temperature and using 1.0 m CeIII , the battery performance reaches the best coulombic efficiency of 84 %.

Heterogeneous photochemical uptake of NO2 on the soil surface as an important ground-level HONO source.

Nitrous acid (HONO) production from the heterogeneous photochemical reaction of NO2 on several Chinese soils was performed in a cylindrical reactor at atmospheric pressure. The NO2 uptake coefficient (γ) and HONO yield (YHONO) on different soils were (0.42-5.16) × 10-5 and 6.3%-69.6%, respectively. Although the photo-enhanced uptake of NO2 on different soils was observed, light could either enhance or inhibit the conversion efficiency of NO2 to HONO, depending on the properties of the soils. Soils with lower pH generally had larger γ and YHONO. Soil organics played a key role in HONO formation through the photochemical uptake of NO2 on soil surfaces. The γ showed a positive correlation with irradiation and temperature, while it exhibited a negative relationship with relative humidity (RH). YHONO inversely depended on the soil mass (0.32-3.25 mg cm-2), and it positively relied on the irradiance and RH (7%-22%). There was a maximum value for YHONO at 298 K. Based on the experimental results, HONO source strengths from heterogeneous photochemical reaction of NO2 on the soil surfaces were estimated to be 0.2-2.7 ppb h-1 for a mixing layer height of 100 m, which could account for the missing daytime HONO sources in most areas.

Photoenhanced heterogeneous reaction of O3 with humic acid: Focus on O3 uptake and changes in the composition and optical property.

Heterogeneous photochemical reaction of O3 with humic acid (HA) under simulated sunlight was performed using a flow tube reactor coupled to an O3 analyzer at ambient pressure. It was confirmed that light significantly enhanced the uptake of O3 on HA. The initial uptake coefficient (γi) and the steady-state uptake coefficient (γss) of O3 under irradiation increased by 1.6 and 3.8 times compared to those in the dark, respectively. The γi and γss on HA varied in the range of 0.76-2.77 × 10-5 and 1.50-9.55 × 10-6, respectively, which were dependent on various environmental factors including HA mass, total irradiance, initial O3 concentration, O2 content, temperature, relative humidity (RH) and HA solution pH. Both γi and γss showed linear dependence on the total irradiance (0-2.07 × 1016 photons/(cm2⋅s)) of the light source, and increased with the HA mass (0-3.2 µg/cm2), temperature (278-298 K) and HA solution pH (4.0-9.6). However, they showed negative correlations with the initial O3 concentration and O2 content. The γi remained constant in the RH range of 7%-60%, while γss exhibited the maximum value at RH = 20%. During the ozonization of HA under irradiation, some functional groups were consumed, including CH2, CH3, aromatic CC, OH, CO, COOH and COO-. HA aged by O3 exhibited a decrease in the mass absorption efficiency (MAE) and a small increase in the absorption Ångström exponent between 300 and 600 nm wavelength (AAE300,600), which was ascribed to changes in the composition of HA during the photochemical ozonization process.