Photolysis Process Research Articles

Time-Resolved Spectroscopic Study of a Photoinduced Intramolecular Chloride Exchange Reaction of 3',5'-Dimethoxybenzoin Chloride.

Photoremovable protecting groups are of great importance due to their remote control over the liberation of diverse reactive species temporally and spatially, including biologically active compounds and functional groups. Here, an in-depth investigation on the heterolysis-solvolysis reaction mechanisms of a photoremovable protecting group, 3',5'-dimethoxybenzoin (DMB) chloride, has been accomplished. With the aid of transient absorption and time-resolved resonance Raman spectroscopies, the features of the intermediates that emerged from the photolysis process were directly observed. Elaborate optical and theoretical studies on DMB chloride have suggested a long-lived α-keto cation intermediate (0.9 ms) exists as a key intermediate, unlike the radical intermediates that are typically generated in such photocyclization reactions. After undergoing nucleophilic addition and isomerization, the intermediate species eventually leads to the formation of the final product(s).

Pharmaceutical compounds photolysis: pH influence

The operating parameters of photolytic and photocatalytic reaction processes directly affect the efficiency in the degradation of compounds. In particular, pH is a variable that needs to be considered as it exerts great influence on adsorption, absorption, solubility, among others. This study describes the application of the photolytic process, at different pHs, in the degradation of different pharmaceutical compounds. Photolytic reactions were performed with the following contaminants: acetylsalicylic acid (ASA), ibuprofen (IBP) and paracetamol (PAR). In addition, a comparison was performed using the commercial catalyst P25. The results indicated a great influence of the pH in the kinetic constant of the photodegradation and in the UV absorbance of the species. In particular, the degradation of ASA and PAR were favored with the reduction of pH, while the degradation of IBU and SA were favored by increasing. Also, the chromatograms indicated that pH may affect the by-products formed. In comparison, the photocatalysis process in the presence of P25 proved to be much more effective, but it was not possible to achieve complete mineralization of the compounds.

Surfactant-enhanced mobilization of persistent organic pollutants: Potential for soil and sediment remediation and unintended consequences.

This review aims to provide an overview of the sources and reactions of persistent organic pollutants (POPs) and surfactants in soil and sediments, the surfactant-enhanced solubilisation of POPs, and the unintended consequences of surfactant-induced remediation of soil and sediments contaminated with POPs. POPs include chemical compounds that are recalcitrant to natural degradation through photolytic, chemical, and biological processes in the environment. POPs are potentially toxic compounds mainly used in pesticides, solvents, pharmaceuticals, or industrial applications and pose a significant and persistent risk to the ecosystem and human health. Surfactants can serve as detergents, wetting and foaming compounds, emulsifiers, or dispersants, and have been used extensively to promote the solubilization of POPs and their subsequent removal from environmental matrices, including solid wastes, soil, and sediments. However, improper use of surfactants for remediation of POPs may lead to unintended consequences that include toxicity of surfactants to soil microorganisms and plants, and leaching of POPs, thereby resulting in groundwater contamination.

Optical receiver characterizations and corrections for ground-based and airborne measurements of spectral actinic flux densities

Abstract. Solar actinic radiation in the ultraviolet and visible range (UV/VIS) perpetuates atmospheric photochemistry by inducing photolysis processes which form reactive radical species. Photolysis frequencies are rate constants that quantify the rates of photolysis reactions and therefore constitute important parameters for quantitative analyses. Photolysis frequencies are usually calculated from modelled or measured solar spectral actinic flux densities. Suitable measurement techniques are available, but measurement accuracy can suffer from non-ideal 2π or 4π solid-angle reception characteristics of the usually employed 2π optical receivers or receiver combinations. These imperfections, i.e. deviations from an angle-independent response, should be compensated for by corrections of the measured data. In this work, the relative angular sensitivities of four commonly used 2π quartz receivers were determined in the laboratory in a range 280–660 nm. Based on this information, the influence of the non-ideal responses on measured spectral actinic flux densities for ground-based and airborne applications was investigated for a wide range of atmospheric conditions. Spectral radiance distributions and contributions of direct, diffuse downward and diffuse upward spectral actinic flux densities were calculated with a radiative transfer model to derive the corrections. The intention was to determine the ranges of possible corrections under realistic measurement conditions and to derive simple parametrizations with reasonable uncertainties. For ground-based 2π measurements of downward spectral actinic flux densities, corrections typically range <10 % dependent on wavelength and solar zenith angle, with 2 %–8 % uncertainties covering all atmospheric conditions. Corrections for 4π airborne measurements were determined for the platforms Zeppelin NT (New Technology) and HALO (High Altitude and Long Range Research Aircraft) in altitude ranges 0.05–2 and 0.2–15 km, respectively. Total, downward and upward spectral actinic flux densities were treated separately. In addition to various atmospheric conditions, different ground albedos and small (<5∘) aircraft attitude variations were considered in the uncertainties, as well as aircraft headings with respect to the sun in the case of HALO. Corrections for total and downward spectral actinic flux densities again typically range <10 % dependent on wavelength, solar zenith angle and altitude, with 2 %–10 % uncertainties covering all atmospheric conditions for solar zenith angles below 80∘. For upward spectral actinic flux densities, corrections were more variable and significantly greater, up to about −50 % at low altitudes and low ground albedos. A parametrization for corrections and uncertainties was derived using uncorrected ratios of upward / downward spectral actinic flux densities as input, applicable independent of atmospheric conditions for a given wavelength, solar zenith angle and altitude. The use was limited to conditions with solar zenith angles <80∘ when direct sun radiation cannot strike upward- and downward-looking receivers simultaneously. Examples of research flights with the Zeppelin and HALO are discussed, as well as other approaches described in the literature.

Ultraviolet Light-Driven gaining of hydroxyl and nitrogen oxide radicals in Plasma–Treated water

Here we numerically demonstrate that photolytic processes induced by external ultraviolet (UV) sources considerably affect the chemical properties of plasma–water systems. When describing the chemical transport between surface dielectric barrier discharge (SDBD) and deionized water, the plasma is simulated using a global model, while the gas (air) and liquid (water) regions are considered in a one-dimensional space. Our simulation involving exposure of plasma-treated water (PTW) to UV shows that long-lived species in PTW are readily photolyzed and form hydroxyl radical (OH) and nitric oxide (NO) over the entire liquid region. The total OH concentration was enhanced by 11.6 times at 100 s under exposure to a conventional UV lamp, while the total NO concentration was remarkably enhanced up to 45.8 times at 300 s. The time at which the OH concentration notably increases was advanced by more than 100 s by photolytic processes. The results directly reveal that the exposure of PTW to UV is an attractive approach to selectively releasing extra OH and NO, thereby increasing the PTW reactivity and applicability. Owing to their high reactivity and oxidizing power, the short lifetime of radicals including OH and NO in PTW, which is crucial in diverse applications, has been troublesome. In this regard, our findings will provide new guidance in utilizing PTW for various applications.

Fe-TiO2 and Ag-ZnO mediated visible light photocatalysis for atenolol and acetaminophen removal – A comparative study and modeling

Globally, presence of pharmaceutical contaminants (PCs) in environment is a cause of concern. In this study, performance of the green synthesized nano-composites Fe-TiO2 and Ag-ZnO as visible light photocatalyst was evaluated by considering the removal of PCs viz., atenolol (ATL) and acetaminophen (ACT) spiked in treated domestic wastewater. Advanced oxidation process was performed in a batch photoreactor under visible radiation (650 nm). Removal of PCs were studied by considering four experimental factors viz., initial pH (4 to 12), initial ATL and ACT concentration (5 to 20 mg/L), visible photo catalyst concentration (500 to 1500 mg/L) and reaction time (40 to 120 min). Response surface methodology was used, regression models were developed (R2adj > 85 %), and optimization of factors was performed for the contaminant removal. It was found that, both Fe-TiO2 and Ag-ZnO performed well (ATL removal >63 %, and ACT removal >85 %) though, Fe-TiO2 had higher removal efficiency. It was found that the maximum removal of contaminants occurred when contaminant concentration was 5 mg/L, pH 8, catalyst concentration 1055 mg/L and reaction time 98 min. Characteristics of ATL and ACT photocatalytic degradation was performed and it was found that the contaminant removal was predominantly through the photocatalytic mechanism majorly due to OH oxidation pathway rather than adsorption and photolytic process. Further, the COD and TOC experiments indicated that >50 % mineralization could be achieved for both ATL and ACT, indicating that both the nanomaterial can be effectively used as a photocatalyst in the visible light radiation.

Removal of Reactive Blue 19 dye from synthetic wastewater using UV/H2O2 and UV/Cl advanced oxidation processes

AbstractThe textile and dyeing industries are among the largest water‐consuming and polluting industries in the world. The most important feature of the textile dyeing industry wastewater is its color, due to the use of colored materials. Most of these dye compounds are resistant to conventional purification methods and their biodegradation is very low through secondary purification processes, resulting in incomplete removal. Therefore, selecting the optimal method to remove these color compounds is essential. In this study, we studied the removal of an organic dye contaminant (Reactive Blue dye 19 [RB19]) using advanced oxidation processes (AOPs). For this purpose, ultraviolet (UV) mercury lamps with a wavelength of 254 nm and a voltage of W16 inside a reactor were used as an energy source. The experiments were performed in a collimated beam reactor inside a dark chamber. Two oxidizers, sodium hypochlorite (NaOCl) and hydrogen peroxide (H2O2), were used to remove RB19 from the artificial sewage stream. Removal of RB19 with a concentration of 20 mg/L with variable pH (5, 7, and 9), oxidant concentrations (5, 10, and 20 mg/L), and time (5, 10, 15, and 30 min) were investigated during the processes of photolysis, chemical oxidation (by H2O2 and NaOCl), and UV/NaOCl and UV/H2O2 AOPs. The photolysis process did not remove the RB19. The highest removal efficiencies of RB19 by chemical oxidation processes with NaOCl and H2O2, UV/NaOCl, and UV/H2O2 at optimal conditions (pH = 5, [oxidant] = 20 mg/L, RB19 = 20 mg/L, and radiation intensity of 1005 mJ/cm2) were 64.49%, 0.88%, 99.7%, and 13.31%, respectively. These results indicate that the hydroxyl radical was produced, under optimum conditions, more in the acidic medium; thus, the RB19 removal efficiency was higher in the acidic medium. The combination of UV rays with oxidants resulted in the production of more hydroxyl radicals and increased removal efficiency.

Dual-wavelength UV degradation of bisphenol A and bezafibrate in aqueous solution using excilamps (222, 282 nm) and LED (365 nm): yes or no synergy?

Dual-wavelength ultraviolet (DWUV) irradiation can lead to a synergistic effect in terms of accelerated degradation of emerging organic contaminants in aqueous media. This study compared the kinetics of single-wavelength and DWUV degradation of bisphenol A (BPA) and bezafibrate (BZF) in model aqueous solution using KrCl (222 nm), XeBr (282 nm) excilamps and LED (365 nm). Three novel dual combinations (222 + 282, 222 + 365 and 282 + 365 nm) were examined toward the potential synergy in direct photolysis and advanced oxidation processes (AOPs) using potassium persulfate and hydrogen peroxide. Kinetic comparison showed that the time- and fluence-based synergy did not occur in the dual combinations selected. Meanwhile, the single-wavelength UV treatment using KrCl excilamp was found to be highly efficient for degradation of target contaminants. At a given dosage of oxidants, the UV/S2O8 2− process exhibited higher performance than the UV/H2O2 one, attaining higher degradation rates and requiring lower UV fluences for 90% removal. This study demonstrates that the catalyst-free UV/S2O8 2− process using KrCl excilamp has a high potential for efficient removal of such organic contaminants from real waters with low turbidity.

Treatment of brackish water inland desalination brine via antiscalant removal using persulfate photolysis

The combined persulfate photolysis and chemical demineralization process effectively treated brine for additional water recovery and mineral resource recovery. This technology has the potential to enhance the sustainability of desalination plants.

Effectiveness of ultra-, nanofiltration and selected photolytic processes in removing of selected priority substances from water

Effectiveness of ultra-, nanofiltration and selected photolytic processes in removing of selected priority substances from water

Controlling the repair mechanisms of oxetanes through functional group substitution.

Intersystem crossing (ISC) plays a key role in the photolysis processes of oxetanes formed by benzophenone (BP)-like and thymine structures. In this work, we systematically explored the photophysical processes of oxetanes and ring-splitting products and investigated the effect of substituents on the repair mechanisms of oxetanes. The regioselectivity of oxetanes (head-to-head, HH and head-to-tail, HT) and the electron-donating and electron-withdrawing substituents, including CH3, OCH3 and NO2, were considered. It was found that the substituents influence the ISC rates of these compounds more by changing their spin-orbit coupling (SOC) coefficients rather than energy gaps. The SOC coefficients of HH-oxetanes are more affected by these groups than HT-oxetanes and products, and they have greater ISC rates on the whole. Besides, the insertion of substituents can alter the radiative and nonradiative decay rates, thereby transforming the photoinduced cycloreversion mechanisms of oxetanes. The ring-splitting reactions of non-substituted oxetanes could occur via two pathways of singlet and triplet manifolds. Furthermore, oxetanes with NO2 at the X site have the largest ISC rates but hardly undergo repair processes, while the introduction of electron-donating substituents can effectively promote the repair of oxetanes. The singlet ring-splitting reactions of HH-oxetanes are more inclined to occur after introducing CH3 and OCH3 at two sites. However, HT-oxeatnes with CH3 are more likely to undergo triplet repair processes and OCH3-substituted structures tend to originate cycloreversion in the singlet manifolds. Moreover, the introduction of CH3 and OCH3 at the Y site rather than the X site can more significantly accelerate the repair processes of HH-oxetanes. Contrarily, HT-oxetanes with electron-donating groups at the X site exhibit faster repair rates than those at the Y site. We hope this work can provide valuable insights into BP-like drugs and photosensitive DNA repair.

Study of the Phytoextraction and Phytodegradation of Sulfamethoxazole and Trimethoprim from Water by Limnobium laevigatum

Phytoremediation is an environmentally friendly and economical method for removing organic contaminants from water. The purpose of the present study was to use Limnobium laevigatum for the phytoremediation of water from sulfamethoxazole (SMX) and trimethoprim (TRI) residues. The experiment was conducted for 14 days, in which the loss of the pharmaceuticals in water and their concentration in plant tissues was monitored. Determination of SMX and TRI was conducted using liquid chromatography coupled with tandem mass spectrometry. The results revealed that various factors affected the removal of the contaminants from water, and their bioaccumulation coefficients were obtained. Additionally, the transformation products of SMX and TRI were identified. The observed decrease in SMX and TRI content after 14 days was 96.0% and 75.4% in water, respectively. SMX removal mainly involved photolysis and hydrolysis processes, whereas TRI was mostly absorbed by the plant. Bioaccumulation coefficients of the freeze-dried plant were in the range of 0.043-0.147 for SMX and 2.369-2.588 for TRI. Nine and six transformation products related to SMX and TRI, respectively, were identified in water and plant tissues. The detected transformation products stemmed from metabolic transformations and photolysis of the parent compounds.

Hydrodynamic Impacts on the Fate of Polychlorinated Biphenyl 153 in the Marine Environment

Due to their long half-life, polychlorinated biphenyls (PCBs) tend to contaminate not only coastal areas, but they travel over long distances, eventually reaching remote areas such the Arctic. The physical and biogeochemical features of every coastal area govern the main distribution patterns of freshly introduced PCBs into the marine system. Some of these processes are determined by chemical properties of the individual PCB congener. Thus, atmospheric influx along with ad/absorption on non-living organic material, photolytical and biological degradation processes vary from one PCB congener to another. For a detailed fate analysis of individual congeners, we developed a new chemical model, based on the GOTM-ECOSMO-FABM model framework. Here, we exemplarily present results for PCB153 based on 1D simulations of four regions in the North-Baltic Sea. The study area is characterized by different hydrodynamic and biogeochemical conditions. We investigate the impact of resuspension, mixing and the biological pump, sea ice and tides on the final phasal distribution of PCB153. Different combinations of these factors lead to the development of different areas of PCB153 accumulation, with the formation of hotspot areas, and influence the total uptake and concentration of PCB153 in the water column. As a result, two major dynamics determine the fate of PCB153 in the coastal ocean: (i) Primary production leads to PCB153 being adsorbed by organic material. Partitioning to organic material and sedimentation of organic particles removes dissolved PCB153 from the surface ocean and increases atmospheric influx. (ii) Tidal-induced resuspension and mixing control the benthic–pelagic exchange of PCB153 and its distribution in the water column. Depending on the resuspension regime and stratification, sediments can become a permanent (Gotland Deep, the Baltic Sea) or seasonal sink for PCB153. In regions with seasonal stratification and high near bottom turbulence (Northern North Sea), resuspension events can lead to pronounced peaks in PCB153 concentrations and can therefore have a major impact on bioaccumulation. Under the conditions of permanent mixing and high bottom turbulence (Southern North Sea, Bothnian Bay), pollutants are hardly accumulating in sediments.

A critical review of organic pollutants in Refinery wastewater by advanced oxidation processes

Advanced oxidation processes (AOPs), for instance Ozone, Fenton process, photo Fenton, photolysis, photo-catalysis, and photolysis of hydrogen peroxide and photolysis of ozone have remained inspected widely aimed at the elimination of a wide variety of organic pollutants (OPs). AOP without UV might not attain complete elimination of a comprehensive group of OPS. When combined with UV, AOPs produce additional free radicals, consequently execution improved squalor of the OPS. This review briefly deliberates the individual AOPs and their limits in the direction of the squalor of OPS comprising diverse useful collections. It too categorizes AOPs and lengthily clarifies their efficiency aimed at the squalor of a wide variety of OPS. Underneath suitable circumstances, AOPs not solitary initiate squalor nonetheless might too principal to whole mineralization. Numerous issues can affect the competence of procedures counting the chemistry of water and the organic molecular structure for instance, the attendance of organic content in water can have an important influence. In general, these organic also change toward high redox possible radicals upon crash with additional reactive species and upsurge the rates of reaction, or might performance by way of radical scavengers and reduction the development competence

Cerium oxide: synthesis, brief characterization, and optimization of the photocatalytic activity against phenazopyridine in an aqueous solution.

Water pollution by antibiotics is a global crisis, and its risk is critically more severe due to the explosive use of these drug compounds. A critical effective removal method to diminish this risk is heterogeneous photocatalysis and optimizing the conditions to reach higher mineralization efficiency. CeO2 anoparticles (NPs) were synthesized and characterized by X-ray diffraction (XRD), UV-Vis diffuse reflection spectroscopy (DRS), and Fourier transform infrared spectroscopy (FTIR) techniques. A cubic structural crystallite phase was detected that had crystallite sizes of 17.9 and 16.7nm estimated by the Scherrer and Williamson-Hall models. A typical FTIR absorption band for the Ce-O stretching absorption has appeared at 554cm-1. Based on DRS data and the Kubelka-Munk and Tauc models, Eg values of 2.80, 3.06, 3.12, and 3.13eV were obtained for n-values of 1/2, 2, 3/2, and 3, respectively. pHpzc of CeO2 NPs was about 5.7. The direct photolysis and surface adsorption processes have no critical role in phenazopyridine (PP) removal by appearing with 2.7 and 6.7% removal efficiencies, respectively. Due to the highest photocatalytic activity of CeO2 NPs toward PP, the effects of the critical operating variable on the activity were evaluated, and the optimal conditions were as catalyst dose, 0.7g/L; pH, 6; irradiation time, 90min; and CPP, 20ppm. The Hinshelwood kinetics equation plot was y = - 6.6442 - 0.4677x (r2 = 0.9296), in which its slope as the rate constant of the photodegradation process was 0.4677min-1 (corresponding to a t1/2 value of 1.48min).

Rapid Microwave-Assisted Synthesis of N/TiO2/rGO Nanoparticles for the Photocatalytic Degradation of Pharmaceuticals.

Nanocomposites comprising nitrogen-doped TiO2 and reduced graphene oxide (N/TiO2/rGO), with different rGO loading qualities, were prepared by a cost-effective microwave-assisted synthesis method. The synthesized materials were broadly characterized by Raman spectroscopy, X-ray diffraction (XRD), infrared spectroscopy (FTIR), photoelectron spectroscopy (XPS), diffuse reflectance spectroscopy (DRS), electron microscopy (SEM-EDS), and nitrogen adsorption/desorption isotherms. Anatase was the only crystalline phase observed for all synthesized materials. The rGO loading did not affect the morphological properties, but it positively influenced the photocatalytic activity of the nanocomposite materials, especially at low rGO loading. Photocatalysts were evaluated via the degradation of specific organic micropollutant (OMP) pharmaceuticals: ciprofloxacin (CIP), diclofenac (DCF), and salicylic acid (SA), under different radiation sources: ultraviolet A (UVA), solar light simulator (SLS), blue visible light (BVL) and cold visible light (CVL). CIP and SA were removed effectively via the synergy of adsorption and photocatalysis, while DCF degradation was achieved solely by photocatalysis. After implementing scavenger agents, photocatalytic degradation processes mainly depended on the specific pollutant type, while irradiation sources barely defined the photocatalytic mechanism. On the other hand, changes in irradiation intensity significantly influenced the photolysis process, while photocatalysis was slightly affected, indicating that irradiation spectra are more relevant than intensity.

Does Light Pollution Affect Nighttime Ground-Level Ozone Concentrations?

Ground-level ozone (O3) is mainly produced during daytime in the presence of ultraviolet (UV) light and later destroyed by nitrogen oxides during nighttime. However, light pollution caused by the excessive use of artificial lights may disrupt the chemistry of night-time ground-level O3 by providing enough energy to initiate nighttime ground-level O3 production. In this study, nighttime (7 p.m. to 7 a.m.) ground-level O3, nitrogen oxide (NO), and nitrogen dioxides (NO2) concentrations were observed for three years (2013, 2014, and 2015). The existence of O3 was found during nighttime, especially in urban areas with a concentration range of 8–20 ppb. The results suggested that nighttime variations of ground-level O3 concentrations were higher in urban areas than in suburban areas. The mean nighttime O3 concentration at urban sites varied, possibly because the distribution of anthropogenic lights around the urban sites is brighter than in suburban locations, as indicated by the data from the light-pollution map. This anthropogenic light has not caused the suspected nighttime photolysis processes, which directly slowed nighttime oxidation. The photochemistry rate of JNO2/k3 was supposed to be near zero because of the absence of photochemical reactions at night. However, the minimum concentration in all urban and suburban sites ranged from 2–3 ppb, indicating that O3 might also form at night, albeit not due to light pollution.

Performance and mechanisms for tetrabromobisphenol A efficient degradation in a novel homogeneous advanced treatment based on S2O42− activated by Fe3+

Tetrabromobisphenol A (TBBPA), a representative brominated flame retardant (BFR), generally could be debrominated and degraded effectively in photolysis systems with the high energy consumption. In this study, the novel sulfate radical (SO4•-) generation resource of dithionite (S2O42−), activated by the common transition metal of Fe3+, has been applied for establishing an innovative homogeneous advance treatment system for BFR treatment in water. When coupling Fe3+ with S2O42−, TBBPA degradation efficiency could be remarkably improved from 38.7% to 93.8% with the debromination and mineralization efficiency of 83.9% and 18.5% in 60 min, respectively. The primary reactive species also have been identified as SO3•-, SO4•- and •OH responsible for TBBPA treatment and the contributions of SO4•- and •OH have been calculated as 43.8% and 28.4% for TBBPA degradation, respectively. In Fe3+/S2O42− system, TBBPA was effectively degraded in a wide initial pH range (3.0–9.0), whose activation energy was calculated as 32.01 kJ mol−1. Due to the only operation of reagents dosing, the energy consumption and cost could be decreasing significantly without any light energy input and reaction conditions (e.g., pH and dissolved oxygen) adjustment compared with the general photolysis process. Moreover, some possible degradation approaches of TBBPA also have been proposed via GC–MS including debromination, hydroxylation, methylation, and mineralization in Fe3+/S2O42− system. And these probable degradation pathways also have been confirmed with the decreased Gibbs free energy (ΔG) based on density functional theory (DFT). This study has revealed that it was promising of Fe3+/S2O42− system for BFRs degradation and detoxification efficiently through the simple operation and mild condtions.

Recent achievements in photoelectrocatalytic degradation of pesticides

This review summarizes recent advances in photoelectrocatalysis of pesticides, involving fundamentals, the preparation of photoanodes, and their application in the degradation of pesticides from distinct types of water. The effect of the chemical nature of the photoanodes to enhance the electrolysis and photolysis processes is discussed in this work. The use of different semiconductors for the degradation of pesticides was also described under different experimental conditions, all of them still at the laboratory level and under synthetic experimental conditions, which serve as the basis for real application in the short term. Outlooks and perspectives are provided and discussed. • Fundamentals of photoelectrocatalysis process. • Photocatalysts design to increase removal efficiency. • Pesticides removal through photoelectrocatalysis technology. • Outlooks for future research and developments are suggested.

An efficient process for aromatic VOCs degradation: Combination of VUV photolysis and photocatalytic oxidation in a wet scrubber

The elimination of volatile organic compounds (VOCs) via vacuum ultraviolet (VUV) photolysis is greatly limited by low removal efficiency and gaseous byproducts generation, while photocatalytic oxidation of VOCs suffers from catalytic deactivation. Herein, a coupled process of gaseous VUV photolysis with aqueous photocatalytic oxidation with P25 as the catalyst was firstly proposed for efficient aromatic VOCs removal (VUV/P25). The removal efficiency of toluene reached 86.2% in VUV/P25 process, but was only 33.6% and 58.1% in alone gaseous VUV photolysis and aqueous ultraviolet photocatalytic oxidation (UV/P25) process, respectively. Correspondingly, the outlet CO2 concentration in VUV/P25 process reached 132 ppmv. Toluene was firstly destructed by high-energy photons generated from gaseous VUV photolysis, resulting in its incomplete oxidation to form soluble intermediates including acids, aldehydes, esters. These soluble intermediates would be further degraded and mineralized into CO2 in subsequent aqueous UV/P25 process. Notably, the concentrations of intermediates in VUV/P25 were much lower than those in VUV photolysis, indicating the synergy effect of VUV photolysis and UV/P25 process. The stability tests proved that VUV/P25 process maintained an excellent toluene degradation performance and P25 did not suffer from catalytic deactivation. In addition to toluene, the VUV/P25 system also achieved the efficient and sustainable degradation of styrene and chlorobenzene, suggesting its good application prospect in industrial VOCs treatment. This study proposes an efficient and promising strategy for deep oxidation of multiple aromatic VOCs in industries.