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Carbon dioxide is considered an inert gas that rarely participates in atmospheric chemical reactions. However, we show here that CO2 is involved in some important photo-oxidation reactions in the atmosphere through the formation of carbonate radicals (CO3∙-). This potentially active intermediate CO3∙- is routinely overlooked in atmospheric chemistry regarding its effect on sulfate formation. Present work demonstrates that SO2 uptake coefficient is enhanced by 17 times on mineral dust particles driven by CO3∙-. It can be produced through two routes over mineral dust surfaces: i) hydroxyl radical + CO32-; ii) holes (h+) + CO32-. Employing a suite of laboratory investigations of sulfate formation in the presence of carbonate radical on the model and authentic dust particles, field measurements of sulfate and (bi)carbonate ions within ambient PM, together with density functional theory (DFT) calculations for single electron transfer processes in terms of CO3∙--initiated S(IV) oxidation, a new role of carbonate radical in atmospheric chemistry is elucidated.

Bismuth-based material has been broadly studied due to their potential applications in various areas, especially used as promising photocatalysts for the removal of persistent organic pollutants (POPs) and several approaches have been adopted to tailor their features. Herein, the bismuth-based photocatalysts (BiOCl, BiPO4, BiOPO4/BiOCl) were synthesized by hydrothermal method and advanced characterization techniques (XRD, SEM, EDS elemental mapping, Raman and UV–vis DRS) were employed to analyze their morphology, crystal structure, and purity of the prepared photocatalysts. These synthesized photocatalysts offered a praiseworthy activity as compared to commercial TiO2 (P25) for the degradation of model pollutant perfluorooctanoic acid (PFOA) under 254 nm UV light. It was interesting to observe that all synthesized photocatalysts show significant degradation of PFOA and their photocatalytic activity follows the order: bismuth-based catalysts > TiO2 (P25) > without catalyst. Bismuth-based catalysts degraded the PFOA by almost 99.99% within 45 min while this degradation efficiency was 66.05% with TiO2 under the same reaction condition. Our work shows that the bismuth-based photocatalysts are promising in PFOA treatment.

Visible-light-driven photoelectrochemical (PEC) catalysis has been widely studied as a promising technique for the degradation of organic pollutants in wastewater. Herein, we report a sulfite-enhanced PEC degradation process for the degradation of organic pollutant. The degradation rate was significantly enhanced by ～30 times with the addition of 16 mM sulfite. The Electron Spin Resonance (ESR), Transient Absorption (TA) and hole scavenger studies showed that sulfite radicals ( S O 3 ⦁ - ) were the main reactive species in the reactions. The pollutant degradation pathway was studied by in-situ techniques and mass spectrometer, showing that the sulfite addition can promote the cleavage of aromatic ring C C bond and C N bond.

Summary Recently, the environmental impacts of microplastics have received extensive attention owing to their accumulation in the environment. However, developing efficient technology for the control and purification of microplastics is still a big challenge. Herein, we investigated the photocatalytic degradation of typical microplastics such as polystyrene (PS) microspheres and polyethylene (PE) over TiO2 nanoparticle films under UV light irradiation. TiO2 nanoparticle film made with Triton X-100 showed complete mineralization (98.40%) of 400-nm PS in 12 h, while degradation for varying sizes of PS was also studied. PE degradation experiment presented a high photodegradation rate after 36 h. CO2 was found as the main end product. The degradation mechanism and intermediates were studied by in situ DRIFTS and HPPI-TOFMS, showing the generation of hydroxyl, carbonyl, and carbon-hydrogen groups during the photodegradation of PS. This study provides a green and cost-efficient strategy for the control of microplastics contamination in the environment., Graphical Abstract, Highlights • Efficient degradation of microplastics under UV light by TiO2 film • Triton-based TiO2 film showed higher photocatalytic performance • The role of radical species during microplastics degradation was elucidated • Degradation mechanism and reaction intermediates were explored, Catalysis; Environmental Chemistry; Nanomaterials

Sulfite is recently found to be promising in enhancing photocatalytic pollutants degradation, and it is a byproduct from flue gas desulfuration process. Herein, 4-chlorophenol (4-CP) photodegradation was systematically investigated in a sulfite mediated system with g-C3N4 as photocatalyst. The degradation efficacy was improved by about 3 times with addition of 25 mM Na2SO3. The dominant responsible reactive oxygen species for chlorophenols remediation in the presence of sulfite included O2·-, SO3·-, and SO4·- as confirmed by radical quenching experiments and electron spin resonances technology. In-situ DRIFTs results indicated the improved cleavage of C-Cl and C-H bonds with the simultaneous formation of C O and C C bonds when bisulfite was added. Degradation intermediates such as 4-chlorocatechol, hydroquinone, and muconic acid were detected by HPLC-MS. Furthermore, the photodegradation mechanisms were discussed in the presence of sulfite. Other chlorophenols (phenol, 2-CP, 2,4-DCP, and their mixture) were also efficiently removed in the system, suggesting that sulfite could be universally applied in photocatalytic wastewater purification.

The advancement in industries and modern technology has been escorted by an expansion in the utilization of chemicals to obtain plastic-based products. Increased plastic production and disposal have greatly affected the environment and living organisms globally. Macro and micro-plastics have a persistent nature, and their natural degradation takes years. Transport, impact, behavior, and degradation have attracted growing research attention. However, a review study on titanium dioxide (TiO2) based photocatalytic degradation of macro and micro-plastics has not been summarized. Herein, a brief overview of the TiO2 application for macro and micro-plastics degradation has been summarized. Different preparation methods for TiO2 synthesis and its modification for plastics decomposition have been presented. The degradation efficiency and applied system limitations with future research directions are proposed. Nevertheless, the existing knowledge about the TiO2 application for macro and micro-plastics is still limited. This work provides a good reference for plastic pollution control.

Photocatalysis has been regarded as a sustainable strategy for wastewaters remediation, and sulfite addition could significantly accelerate the photocatalytic performances. However, the related mechanisms are still not well understood. Here, we for the first time found that plasmonic Bi and oxygen vacancies were in-operando generated on BiOX (X = Cl, Br, I) in the presence of sulfite under light irradiation. The oxidative degradation rate constants of 4-nitrophenol, bisphenol A, and phenol were improved by about 11.5, 4.7, and 12.2 times on BiOBr and 9.1, 1.6, and 3.1 times on BiOCl with addition of 5 mM sulfite, while the photocatalytic reduction rate of 4-nitrophenol to 4-aminophenol was promoted by approximate 31.7 times on BiOI. The results indicated that sulfite could improve the photooxidation ability of BiOBr and BiOCl and the photoreduction performance of BiOI, resulted from the improved light absorption and separation of photogenerated charge carriers. This work can provide exploratory platforms for understanding and maximizing the sulfite-assisted BiOX photocatalysis.

Despite the increased awareness of heterogeneous reaction on mineral dust, the knowledge of how the intensity of solar irradiation influences the photochemistry activity remains a crucially important part in atmospheric research. Relevant studies have not seriously discussed the photochemistry under weak sunlight during haze, and thus ignored some underlying pollution and toxicity. Here, we investigated the heterogeneous formation of nitrate and nitrite under various illumination conditions by laboratory experiments and field observations. Observed by in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), water-solvated nitrate was the main surface product, followed by other species varying with illumination condition. The growth of nitrate formation rate tends to be slow after the initial fast with increasing light intensity. For example, the geometric uptake coefficient (γgeo) under 30.5 mW/cm2 (5.72 × 10−6) has exceeded the 50 % of that under 160 mW/cm2 (1.13 × 10−5). This case can be explained by the excess NO2 adsorption under weak illumination while the excess photoinduced active species under strong irradiation. Being negatively associated with nitrate (R2 = 0.748, P

As a green adsorbent, biochar has attained progressive attention due to its advantages such as high carbon content, high surface area, stable structure, and heavy metals removal through cation exchange capacity. Biochar can be synthesized from the feedstock, agricultural, and organic waste. In this study, the activated biochar (AC) and ammonia modified biochar (NAC) were prepared from Eucalyptus waste by acid activation. The adsorption properties of pure AC and NAC were compared for aqueous Cr(VI) removal. Advanced characterization techniques such as scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) were used to examine the morphology, elemental composition, and functional groups. Several influencing factors on adsorption processes such as solution pH, adsorption dosage, contact time, and initial concentration were investigated. The ammonia modified biochar (NAC) could remove 85.67% of Cr (VI), whereas 76.73% removal rate was observed for the activated biochar (AC) at an initial concentration of 300 mg/L at pH 2.0 and 25 °C with a dosage of 0.025 g/25 mL. The pseudo-second-order kinetic and Freundlich isotherm adsorption models showed close-fitting for the activated biochar (AC) and the ammonia modified biochar (NAC) adsorption in Cr(VI) equilibrium state. Cr (VI) oxidizes nitrogen and oxygen functional groups on NAC following the conversion into Cr (III). The removal and adsorption mechanism was the coexistence of physical adsorption and chemical reduction examined by FTIR and XPS illustrating Cr(VI) removal.

Biochar, due to its ability to remediate heavy metals and organic contaminants from polluted water is considered as an economic adsorption material. This work involved pyrolysis driven eucalyptus carbon (EC) to produce eucalyptus activated carbon (AC) through a novel mechanism of using phosphoric acid (H3PO4) and its subsequent testing for efficient adsorption of Cr (VI) from aqueous environments. Advanced characterization techniques like XRD, SEM, BET, FTIR, and XPS were employed to characterize the structure and composition of EC and AC. The AC could remove 99.76% of Cr(VI), which was higher than EC removal rate of 25.24%. The surface area of AC increased by almost 5 times 1265.56 m2/g compared to EC (253.25 m2/g). The removal rate of Cr(VI) was highly influenced by adsorption capacity, pH, adsorption time, temperature, kinetics, and isotherm. Reaction rate kinetics, isothermal, and thermodynamic analysis revealed that the adsorption curve of AC fits well with the quasi-second-order kinetic model. AC adsorption process was a spontaneous endothermic reaction limited by intraparticle diffusion and a combination of chemical and physical adsorption.

The rapid sulfate formation is a crucial factor determining the explosive growth of fine particles and the frequent occurrence of severe haze events in China. Recent field observations also show that brown carbon is one of the most critical components in aerosol particles sampled during haze episodes. To this day, there is limited knowledge that accesses the role of brown carbon in atmospheric chemistry. In fact, these carbonaceous particulate matters, mainly derived from forest fires, biomass burning, and biogenic release, can act as photosensitizers and produce varieties of active intermediates to alter oxidation capacity. Experimental results in this work provide evidence that hydroxyl radical (∙OH) stems from brown carbon proxies fulvic acid /humic acid (FA/HA) upon irradiation, leading to rapid SO2 oxidation on brown carbon particles in the atmosphere. Further correlation analyses for sulfate formation and chromophore properties of 12 model compounds demonstrate that brown carbon particles with higher aromaticity and E2/E3 (the ratio of absorbance at 254 nm to that at 365 nm) would facilitate ∙OH production and SO2 photo-oxidation. Uptake coefficient measurements and sulfate production rate estimation indicate that brown carbon could gain importance in atmospheric SO2 oxidation. A better understanding of SO2 uptake kinetics on brown carbon surfaces favors in defining new regulations to improve air quality and reduce the harmful effects of haze events on resident health and the environment.

Bisphenol A (BPA) is known as an endocrine-disrupting chemical, generally present in the environment. It has a harmful effect on aquatic lives and human health, therefore it is needful to exploit highly efficient innovative treatment methods for its removal. Herein, we report a Co-BiVO4 photoanode to activate peroxymonosulfate (PMS) for the complete removal of BPA via a photoelectrochemical (PEC) process. The Co-BiVO4 could degrade 99.16% of BPA in the presence of 2 mM PMS within 60 min, whereas the degradation rate constant is 0.08034 min−1, which was 20.86 times higher than the electrocatalytic (EC) and 5.35 times higher than the photocatalytic (PC) process. Notably, Co-BiVO4 showed significant activity toward PMS activation and BPA degradation as compared to other synthesized photocatalysts. Their photoelectrocatalytic performance followed the sequence Co-BiVO4 > Fe-BiVO4 > Ni-BiVO4 > pure-BiVO4 > without catalysts. Several influencing factors on the decomposition process, such as the effect of PMS concentration, applied potential, illumination time, initial pH, BPA concentration, Co loading, and co-existing anions were studied in detail. Radical scavenging experiment and transient absorption result showed that sulfate radicals (SO4•─) were the dominant reactive species. Moreover, a significant synergistic effect was noticed in Co-BiVO4/PEC/PMS system for BPA degradation. Degradation mechanism and reaction intermediates were studied by in-situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) and liquid chromatography-mass spectroscopy (LC-MS) presenting the enhanced bond cleavage in PEC activated PMS system. The BPA showed 92.47% and 87.27% removal in tap and river water samples after 60 min of reaction using Co-BiVO4/PMS PEC system. Our finding proposed an efficient method for wastewater treatment in an eco-friendly way.