Under Ultraviolet Irradiation Research Articles

Preparation and characterization of plasticized polyvinyl chloride composite film based on photochromic intelligent cooling

AbstractIndoor temperature adjustment to maintain a relatively comfortable living environment has resulted in different cooling strategies. Often, these strategies are energy consuming as well as energy wasting because of the complex and changing environment. Materials development to achieve intelligent adjustment of indoor temperature through efficient and energy‐saving methods is essential. Here, we present a strategy to prepare polyvinyl chloride (PVC)/photochromic powders cooling films. By adding different colors of photochromic powders to PVC substrate and utilizing their properties of changing color and light transmittance according to sunlight intensity to achieve the intelligent cooling effect. The indoor sunlight simulation test indicates that the PVC/red photochromic powders composite film possesses the best cooling performance under ultraviolet (UV) irradiation, and the maximum cooling range is about 10°C compared with the control sample, meanwhile the maximum cooling effect is only 2–3°C without UV irradiation. The PVC/red photochromic powders composite film also shows the best cooling effect (6°C) in the outdoor solar irradiation test with strong sunlight, and all films did not exhibit an obvious cooling effect under weak sunlight. Meanwhile, PVC/photochromic powders composite films also solve the shortcoming of the single color of traditional cooling films, which can better meet the demand of people for color diversity. In addition, the stable mechanical properties of PVC/photochromic powders composite films also give it great application value. Therefore, PVC/photochromic powders composite films can provide a promising energy‐saving solution for future intelligent adjustment of indoor temperature.

Photodynamic Effect of Riboflavin on Chitosan Coatings and the Application in Pork Preservation.

Riboflavin (RF) was considered to be possessed of photoactivity to generate reactive oxygen species (ROS) under ultraviolet (UV) light, which is thought to be a favorable antibacterial candidate. Herein, RF was incorporated into chitosan (CS) coatings and treated under UV with different exposure times (2, 4, and 6 h) to improve the physicochemical and antibacterial properties. The results showed that the light transmittance and antibacterial performance of chitosan coatings gradually increased with the extension of the UV irradiation time. The antibacterial ability of chitosan coatings correlated with the generation of ROS: ∙OH and H2O2, which achieved 1549.08 and 95.48 μg/g, respectively, after 6 h irradiation. Furthermore, the chitosan coatings with UV irradiation also reduced the pH value, total volatile basic nitrogen (TVB-N), ΔE, and total viable counts (TVC) and improved sensory attributes of pork. In conclusion, the UV irradiated chitosan coatings could be used as an environmentally friendly antimicrobial packaging material to effectively delay the spoilage of pork, maintain its sensory quality and prolong its shelf life.

The reuse of nano-TiO2 under different concentration of CO32– using coagulation process and its photocatalytic ability in treatment of methyl orange

• Al-based coagulants can effectively separate nano-TiO 2 . • Flocs formed by different coagulants can degrade methyl orange. • AT 2 achieved high degradation efficiency under UV irradiation. • It proposes a new perspective on recycling coagulated flocs for sewage treatment. Photocatalysis is highly efficient for the treatment of dyeing wastewater. However, the wastewater still contains a large amount of nano-TiO 2 after photocatalysis. In order to reduce the cost of nano-TiO 2 , different coagulants were used to improve the solid/liquid separation efficiency. At the same time, the reuse of flocs has raised increasing attention after coagulation. In this study, we report on the recycling of flocs for the production of AlCl 3 and TiO 2 formed flocs (AT 1 ) and Al 13 and TiO 2 formed flocs (AT 2 ) through a simple calcination process. Results indicated the flocs formation processes under different concentration of CO 3 2– were Al species distribution and coagulant dosage dependent. Without HA molecules, the reaction between Al-based coagulants and CO 3 2– are the controlling steps in the coagulation process, and Al a and Al b species had different reaction processes. The influence of HA molecules was also studied, and the HA-Al aggregates which could bridge the TiO 2 nanoparticles, and thus induce sweep flocculation. Consequently, highly enhanced aggregation rate, due to the heteroaggregation between these aggregates and TiO 2 was observed. After calcination, the AT 2 -10 and AT 2 -20 (CO 3 2– : 10, 20 mmol/L) with petal-like structures (mesoporous), relatively high specific surface areas, i.e. 83.98 m 2 /g and 78.38 m 2 /g and high photocatalytic degradation, i.e. 72.79%, 67.78% (compared to nano-TiO 2 , AT 1 -10 and AT 1 -20), were obtained. Additionally, oxygen vacancy (OV) was generated on the surface of the recycled AT 2 -10 and AT 2 -20, which display strong photocatalytic performance for the degradation of MO greater than 65%, under ultraviolet (UV) irradiation and without any sacrificial reagents. This study proposes a new perspective on recycling coagulated flocs for practical application in wastewater treatment.

Interfacial Behavior of Giant Amphiphiles Composed of Azobenzene and Polyhedral Oligomeric Silsesquioxane.

Giant amphiphiles containing azobenzene and polyhedral oligomeric silsesquioxane (POSS) units are synthesized by linking 4,4'-azodianiline (ADA) and POSS derivatives by stepwise amidation and further modification. The synthesized giant amphiphiles are photoresponsive and show trans-cis isomerization under ultraviolet (UV) irradiation. These giant amphiphiles are spread on the air-water interface and compressed by the barrier without and under UV irradiation. By compression, the giant amphiphiles undergo a phase transition from gas (G), liquid expanded (LE), liquid condensed (LC), and solid (S) to a final collapse on the water surface. The giant amphiphiles are cis-isomer-rich under UV irradiation and are trans-isomer-rich without UV irradiation. The trans-isomers are straight-shaped, while the cis-isomers are bent, and hence, their phase transition behaviors on the water surface exhibit a distinct difference.

Multistep photochromism by using photoinduced redox reaction in tungsten oxide colloidal solution containing Cu(II) ion

Tungsten oxide is one of the most studied inorganic photochromic materials and its color changes to blue under ultraviolet (UV) irradiation. In this paper, we reported multistep photochromism from colorless and transparent to green via yellow in WO3 colloidal solution containing Cu2+ and ethylene glycol under UV irradiation. In the absence of Cu2+, absorbance at 775 nm (Abs775) due to the intervalence charge transfer (IVCT) transition between W5+ and W6+ increased with an increase in the irradiation time and the color of the colloidal solution turned blue. The Abs775 value increased with increasing the EG concentration and reached a constant level at molar ratio of [EG]/[WO3] ≥ 3.0. On the other hand, the addition of 0.61 or 1.22 mM CuCl2 to the colloidal solution increased absorption at ca. 450 nm at first and then the absorbance at 775 nm increased, changing the transparent solution to yellow and then green during the irradiation for 120 s. In the case of [Cu2+] ≥ 3.6 mM, only a small increase in the absorbance at 450 nm without IVCT transition was observed. Electron spin resonance measurements revealed that the reduction of W6+ to W5+ occurred after all Cu2+ were reduced to Cu+ under UV irradiation. Bleaching from green to colorless via yellow occurred by purging air in the colloidal solution. The multistep photochromism showed good stability in the repeated experiments. Based on the obtained data, we proposed a possible mechanism for the multistep photochromism.

Comparison of Ergosterol and Vitamin D2 in Mushrooms Agaricus bisporus and Cordyceps militaris Using Ultraviolet Irradiation Directly on Dry Powder or in Ethanol Suspension

Vitamin D deficiency is a severe worldwide health issue. Edible mushrooms are an excellent vitamin D2 source and have gained popularity worldwide as a nutritional food. The objective of this study was to investigate the conversion efficiency of ergosterol to vitamin D2 in Agaricus bisporus and Cordyceps militaris mushrooms under ultraviolet (UV) irradiation directly through dry powder or in ethanol suspension (1:20 g/mL, solid to liquid ratio). Several parameters of UV irradiation conditions such as the material form (dry powder or dry powder in ethanol suspension), exposure time (30, 60, or 120 min), wavelength type (UV-C, UV-B, or UV-A), wavelength combination (UV-C plus UV-B, UV-C plus UV-A, UV-B plus UV-A, or UV-C plus UV-B plus UV-A), and wavelength sequence (UV-C → UV-B, UV-C → UV-A, UV-B → UV-A, or UV-C → UV-B → UV-A), were optimized. Under the optimal UV irradiation conditions (dry powder in ethanol suspension irradiated with UV-C at 40 cm for 120 min), vitamin D2 concentrations increased from not detectable to 72 μg/g (dw) in the A. bisporus dry powder and 1104 μg/g (dw) (about 15-fold increase) in the ethanol suspension. After UV irradiation, the vitamin D2 concentration increased from undetectable to 57 μg/g (dw) in the C. militaris dry powder. In contrast, UV irradiation increased the concentration to 877 μg/g (dw) (about 15-fold higher) in the ethanol suspension. Comparison of the effect of various wavelength combinations showed that UV-C irradiation is more effective than UV-A or UV-B. Furthermore, when irradiated by UV-C at a 40 cm irradiation distance in the ethanol suspension, the increase in vitamin D2 in A. bisporus and C. militaris mushrooms was time- or dose-dependent. The conversion rate of vitamin D2 was low to undetectable under dry powder irradiation, but its ergosterol loss rate was higher than in ethanol suspension irradiation. The ergosterol loss rate in dry C. militaris mushrooms was higher than in the dry A. bisporus mushroom powder. Ultraviolet irradiation in ethanol suspension could greatly increase the vitamin D2 concentration than directly on the dry powder and thus make edible mushrooms more practical as a natural vitamin D source for consumers after entirely removing the ethanol.

UV light absorbers executing synergistic effects of passivating defects and improving photostability for efficient perovskite photovoltaics

Metal halide perovskite-based solar cells (PSCs) have rapidly-increased power conversion efficiency (PCE) exceeding 25% but poor stability especially under ultraviolet (UV) light. Meanwhile, non-radiative recombination caused by diverse defects in perovskite absorbers and related interfaces is one of the major factors confining further development of PSCs. In this study, we systematically investigate the role of 2-(2-hydroxy-5-methylphenyl)benzotriazole (UVP) additive in perovskite layers. By adjusting the amount of doped UVP, the quality of perovskite absorbers is significantly improved with enlarged grains, longer lifetime and diffusion length of charge carriers. Furthermore, UVP not only reduces defects for less non-radiative recombination, but also matches energy level alignment for efficient interfacial charge extraction. X-ray photoelectron spectroscopy confirms that N-donor of UVP molecule coordinates with undercoordinated Pb2+ on the surface. Interestingly, UVP incorporated in PbI2 protects the perovskite by absorbing UV through the opening and closing of the chelating ring. Eventually, the UVP treated PSCs obtain a champion PCE of 22.46% with remarkably enhanced UV stability, retaining over 90% of initial PCE after 60 mW/cm2 strong UV irradiation for 9 h while the control maintaining only 74%. These results demonstrate a promising strategy fabricating passivated and UV-resistant perovskite materials simultaneously for efficient and stable perovskite photovoltaics.

Photochemical sensitive study of Au@CuO flower-like materials

CuO flower-like materials (FMs) were fabricated by hydrothermal method and then reduced to obtain Au@CuO FMs by in-situ reduction reaction. The performance of the Au@CuO FMs sensor was evaluated by detecting volatile and toxic gases such as ethanol, isopropanol, methanol, and formaldehyde under ultraviolet (UV) light illumination. It is found that the optimum working temperatures of the CuO FMs sensor and the Au@CuO FMs one are 240 and 100 °C respectively. The response of the Au@CuO FMs can reach 95.3–1000 ppm ethanol, being about 7 times stronger than that of the CuO FMs sensor. Moreover, the response of the Au@CuO FMs sensor to 1000 ppm ethanol increased from 95.3 to 174 under UV irradiation, nearly 2 times as large as that in dark. Accordingly, its corresponding LOD decreased from 99.8 to 78 ppb. Therefore, the Au@CuO FMs are a promising candidate to detect ethanol with excellent response and selectivity.

Effect of wavelengths on photocatalytic oxidation mechanism of sulfadiazine and sulfamethoxazole in the presence of TiO2

In this paper, the effect of wavelengths on photocatalytic oxidation kinetics and mechanisms of sulfadiazine (SD) and sulfamethoxazole (SMX) in the presence of Degussa P25 TiO2 were discussed, and the influence of humic acids (HA) on the degradation process was further explored. The photocatalytic degradation process of sulfonamides antibiotics (SAs) can be characterized by the pseudo-first-order model, and the removal rates for SAs under ultraviolet (UV) light irradiation were higher than those under visible light irradiation, with the values in the order of 365 nm > 254 nm > 420 nm > 475 nm. The degradation ratios of SAs could reach over 99% within 90 min under UV irradiation, whereas the SAs removal rates were less than 70% after 120 min visible light irradiation. The superoxide radicals (·O2−) were the most important components during the SAs degradation both under UV and visible light irradiation. Due to the existence of special groups, SD mainly performed desulfurization reactions of the S-N bond cleavage and recombination, while SMX underwent ring-opening reactions because of the cleavage of the N-O bond in the isoxazole ring. HA had an inhibitory effect on the photocatalytic oxidation of SAs under UV light irradiation, but had a promotional effect under visible light irradiation. This study and the consequent results would provide a data basis and theoretical reference for the photocatalytic oxidation mechanisms of SAs in real water.

Green synthesis strategy for producing doped and undoped ZnO nanoparticles: their photocatalytic studies for industrial dye degradation.

A facile and green method for synthesizing Zinc Oxide nanoparticles (ZnO NPs) was successfully carried out using unutilized sweet lime; i.e., Citrus Limetta rind pulp (U-CLRP) extract. The structural, morphological and optical studies were elucidated to confirm the crystallinity, size, and shape of the synthesized NPs. Copper doping on ZnO NPs (CZnO NPs) was carried out to enhance the optical properties. The as-prepared and doped nanoparticle's potential for efficient degradation of a commercial dye, Methylene Blue (MB), was tested under Ultraviolet (UV) and visible light radiation. ZnO NPs showed promising results for dye degradation while an improved result was witnessed for CZnO NPs. ZnO NPs showed 74% of degradation of MB dye under UV irradiation and 57% degradation under visible light radiation. CZnO NPs presented 85 and 90% degradation in the UV and visible radiation, respectively. This green reduction method utilizing biological waste sources shows a promising path for photocatalysts to be developed economically as well as efficiently in the future. These CZnO/ ZnO NPs proved their potential for embedding them as efficient catalysts for wastewater treatment plants of textile industries.

Photochemical degradation of β-hexachlorocyclohexane in snow and ice.

Hexachlorocyclohexane (HCH), a typical organochloride pesticide, is one of the persistent organic pollutants. Despite the ban on technical grade HCH, it has been continuously observed at a steady level in the environment. The photochemical degradation of β-HCH in snow and ice under ultraviolet (UV) irradiation was investigated in this study. The effects of pH as well as common chemical components in snow on the degradation kinetics were investigated. In addition, the photodegradation products were determined and the reaction mechanism was hypothesized. The results showed that under UV irradiation, β-HCH can be photolyzed in snow and ice, with the photochemical degradation process conforming to the first-order kinetic equation. Changing the pH and adding Fe2+ had minimal effect on the photochemical degradation kinetics, while the presence of acetone, NO2-, NO3- and Fe3+ significantly inhibited the process. The addition of hydrogen peroxide slightly inhibited the photochemical degradation of β-HCH. Finally, the reaction rate, products and degradation mechanism of β-HCH in snow were compared with those in the ice phase. The photochemical degradation rate of β-HCH in snow was approximately 24 times faster than that in the ice phase. The photolysis product of β-HCH in snow was α-HCH, produced by the isomerization of β-HCH. However, in ice, in addition to α-HCH, pentachlorocyclohexene was produced by dechlorination. The results of this study are helpful in understanding the transformation of organochlorine pesticides in snow and ice, as well as in providing a theoretical basis for snow and ice pollution prevention and control.

Nitrogenated CQD decorated ZnO nanorods towards rapid photodegradation of rhodamine B: A combined experimental and theoretical approach

In this work, hybridization of nonmetal nitrogen-doped carbon dots (NCQDs) with ZnO nanorods (NRs) is utilized towards better photocatalytic degradation of rhodamine B under ultraviolet (UV) irradiation. The structural characterization is confirmed by XRD, XPS, FTIR and HRTEM measurements, while, optical properties have been investigated using UV–visible absorbance spectroscopy and photoluminescence study. The dye degradation using ZnO NR is recorded as ~69%, while the performance of ZnO/NCQD climbs up to ~90%, after nine minutes of UV irradiation. Furthermore, the reusability test suggests better stability of ZnO/NCQD than bare ZnO under photocorrosion. The cyclic voltammetry study confirms that the photoinduced electron-hole pairs originate from the heterojunction established between the interfaces of NCQD and ZnO. An insight on the photocatalytic excellence of ZnO/NCQD system is drawn from the density functional theory study. This indicates that appropriate band alignment of the heterostructure constituents is the key factor in this experimental attempt towards environment remedy.

Accelerated photodegradation of polystyrene by TiO2-polyaniline photocatalyst under UV radiation

Photodegradation of polystyrene (PS) was studied under ultraviolet (UV) radiation, using nano TiO2, surface modified with polyaniline (PANI). X-Ray diffractogram reveals that the crystalline structure of TiO2 remained intact in TiO2-PANI composites. The existence of strong molecular interaction between TiO2 and PANI lead to a decrease in the optical bang gap energy of TiO2 in the composites. PS loaded with TiO2-PANI composites underwent better chain scission and photo-oxidation compared to PS and PS-TiO2 composites, upon UV irradiation. TiO2-PANI composites enhanced the mechanical properties (tensile and flexural) of PS appreciably. Tensile and flexural strengths however decreased with respect to UV exposure time, proving mechanical deterioration of the polymer composites as an outcome of photodegradation. Thermal stability of the composites too decreased upon UV exposure. A decrease in the values of break down voltage as well as increase in dielectric permittivity of the composites upon UV irradiation suggests the formation of charge centers and polarisable species in the polymer matrix. All the polymer composites underwent considerable weight loss due to the formation and evolution of volatile gases, during the course of photodegradation. Suitable mechanism of degradation of PS composites was proposed based on the observed results.

In situ deposition of NiO nano particles on cotton fabric using sol–gel method- photocatalytic activation properties

In this research, NiO nanoparticles were synthesized and in-situ deposited on cotton fibers to investigate photocatalytic activity and degradation dye pollutants from wastewater. NiO NPs were prepared by the sol–gel method in two acidic and basic media with different precursors (nickel nitrate hexahydrate and nickel chloride hexahydrate) at the optimal temperature with similar concentrations. The synthesized nanoparticles were studied by powder XRD, SEM, FESEM, EDAX, VSM, UV–Vis, PL and Total Organic Carbon. The results of the X-ray diffraction pattern of NiO nanoparticles show all specimens have a simple cubic structure with upper crystallinity that was used Debye–Scherrer equation for calculation size of nanoparticles. The smallest crystallite size related to Nickel nitrate hexahydrate sample in basic medium. Scanning electron microscopy and field emission scanning electron microscope were used for studying morphological properties. Vibrating sample magnetometer analysis showed that all specimens had ferromagnetic properties. The photocatalytic activity of NiO nanoparticles deposited upon cotton fibers were investigated. Controlling the degradation of methylene blue (MB) dye under UV irradiation revealed Photocatalytic characteristics of deposited cotton fibers. The results show that, the concentration of the (MB) as a colorant exposing under ultraviolet (UV) irradiation in presence of NiO deposited cotton is diminished. The degredation of MB dye is attributed to the production of hydroxyl and superoxide radicals as oxidant species.

The Adverse Effects of TiO2 Photocatalycity on Paraloid B72 Hybrid Stone Relics Protective Coating Aging Behaviors under UV Irradiation.

The incorporation of photocatalytic nanomaterials into polymer coatings is used to protect stone relics from weathering. However, the photocatalytic nanomaterials might generate excess free radicals to degrade the polymer matrix. In this work, a certain amount of TiO2 nanoparticles were dispersed into Paraloid B72 and applied onto sandstone relics to explore the adverse effects of TiO2 nanoparticles on Paraloid B72 under ultraviolet (UV) irradiation. To fulfill this goal, the effects of TiO2 on pore formation and the structure of Paraloid B72 was studied by scanning electron microscopy (SEM). Moreover, the surface chemical composition, pore structure, surface roughness and surface wettability were explored via Fourier transform infrared (FTIR) spectroscopy, SEM, optical profilometer and water contact angle measurement under UV irradiation. Results showed that the incorporation of TiO2 nanoparticles prohibited the generation of pores in Paraloid B72 and there were no pores formed when the content of TiO2 exceeded 0.8 wt%. The water contact angle of origin Paraloid B72 and TiO2/Paraloid B72 decreased with the prolonging UV irradiation. Moreover, TiO2 nanoparticles were extracted from the matrix and the pores cannot be detected with the prolonging UV irradiation time under a higher content of TiO2. These research findings might promote the understanding of using photocatalytic nanomaterials in developing stone relics’ protective coating.

A multivariate modeling and experimental realization of photocatalytic system of engineered S–C3N4/ZnO hybrid for ciprofloxacin removal: Influencing factors and degradation pathways

Ciprofloxacin, a pharmaceutically active compound, is present as a micropollutant in wastewater, which cannot be removed by conventional techniques due to its recalcitrant nature. Therefore, in the present study, the photocatalytic degradation of this bio-toxic compound was demonstrated using a three-dimensional sulfur-doped graphitic-carbon nitride/zinc oxide hybrid, with enriched oxygen vacancies. The influence of various water matrices and experimental conditions on the ciprofloxacin degradation was optimized. The hybrid material showed 98.8% and 75.8% degradation efficiency under optimum experimental conditions (i.e., catalyst dose: 1 g/L; pH: 5; initial ciprofloxacin concentration: 20 mg/L; temperature: 27 °C) under ultraviolet (UV) and visible light, respectively. A neural-network-based multivariate approach was used to predict a significant model considering the experimental conditions that showed adequate statistical significance (R2: 0.992 and F-value: 8707.1). The relative significance of the experimental conditions was assessed, suggesting that the initial ciprofloxacin concentration has a more significant effect on the degradation efficiency than the other factors. The rate kinetics and reaction mechanisms for ciprofloxacin degradation were demonstrated, and the driving radicals involved were identified. A higher rate of reaction was found under UV irradiation (0.01702 min−1) than under visible light (0.00802 min−1). Superoxide radicals were identified as the main driving radicals, which caused substantial photocatalytic reactions among the hybrid and ciprofloxacin molecules. Microscopic and macroscopic analyses of the used hybrid were conducted, which confirmed the presence of higher defect concentrations, crystallinity, and interlinked stacked structure in the hybrid. Hence, the 3D hybrid can be efficiently used and reused for ciprofloxacin degradation. This advanced photocatalytic system can be widely used to remediate emerging contaminants in wastewater treatment.

Ultrasensitive Detection of Mercury Ions Under UV Illumination of MoS2 Functionalized AlGaN/GaN Transistor

In this work, the MoS2 functionalized AlGaN/GaN high-electron mobility transistor (HEMT) was utilized for the first time to detect toxic mercury (Hg2+) ions under ultraviolet (UV) illumination. The AlGaN/GaN HEMT was fabricated on the sapphire substrate, and corresponding structural and electrical properties were investigated. Subsequently, the optimization of MoS2 concentration for device functionalization was carried out by performing sensing analysis of Hg2+ ions on three devices, and it was observed that the 20 mg/mL concentration of MoS2 is optimum for the detection of Hg2+ ions. Furthermore, the detection of Hg2+ ions was performed under UV exposure, where the developed sensor showed much-improved sensitivity of $548.07~\mu \text{A}$ /ppb compared with normal light. The comparative analysis indicates the increase of three orders of magnitude in sensitivity under UV irradiation, and it is the highest sensitivity ever observed by the AlGaN/GaN HEMT sensor for Hg2+ ion detection. Moreover, the sensor also exhibits the limit of detection (LoD) of 6.14 parts per trillion (ppt) that is much lower than the World Health Organization (WHO) standard limit for Hg2+ ions in drinking water. Due to the photoexcitation process, the generation of electron–hole pairs provides more binding sites on the MoS2 surface, which results in the ultrasensitive detection of the Hg2+ ions at trace and ultratrace levels.

Understanding the Role of Silver Nanostructures and Graphene Oxide Applied as Surface Modification of TiO2 in Photocatalytic Transformations of Rhodamine B under UV and Vis Irradiation.

This work is focused on photocatalytic properties of titanium dioxide thin coatings modified with silver nanostructures (AgNSs) and graphene oxide (GO) sheets which were analyzed in processes of chemical transformations of rhodamine B (RhB) under ultraviolet (UV) or visible light (Vis) irradiation, respectively. UV-Vis spectroscopy was applied to analyze the changes in the RhB spectrum during photocatalytic processes, revealing decolorization of RhB solution under UV irradiation while the same process coexisting with the transformation of RhB to rhodamine 110 was observed under Vis irradiation. The novelty of this study is the elaboration of a methodology for determining the parameters characterizing the processes occurring under the Vis irradiation, which enables the comparison of photocatalysts’ activity. For the first time, the method for quantification of rhodamine B transformation into rhodamine 110 in the presence of a semiconductor under visible light irradiation was proposed. Photocatalysts with various surface architectures were designed. TiO2 thin coatings were obtained by the sol-gel method. GO sheets were deposited on their surface using the dip-coating method. AgNSs were photogenerated on TiO2 or grown spontaneously on GO flakes. For characterization of obtained photocatalysts, scanning electron microscopy (SEM), X-ray diffraction (XRD) and diffuse-reflectance spectroscopy (DRS) techniques were applied. The results indicate that the surface architecture of prepared coatings does not affect the main reaction path but have an influence on the reaction rates and yields of observed processes.

Specific H2S Release from Thiosulfate Promoted by UV Irradiation for Removal of Arsenic and Heavy Metals from Strongly Acidic Wastewater.

The removal of arsenic and heavy metals (HMs) from strongly acidic wastewater by hydrogen sulfide (H2S) is an efficient method. However, traditional sulfuration reagents (Na2S, FeS, CaS, etc.) rapidly release H2S under acidic conditions via spontaneous hydrolysis, leading to serious H2S pollution. Herein, a H2S release process employing thiosulfate as a sulfuration reagent was proposed to eliminate H2S pollution. We found that thiosulfate can release H2S with specificity both in the dark and under ultraviolet (UV) irradiation under acidic conditions. In the absence of arsenic/HMs, H2S is not released because the formed H2S is consumed by a thiosulfate decomposition product, sulfite, or by its photolysis. In the presence of arsenic/HMs, H2S is released because the formed H2S immediately reacts with arsenic/HMs to generate sulfide precipitates rather than being consumed. The efficiency of transforming thiosulfate to H2S under UV irradiation is 2.5-fold the efficiency in the dark, because UV irradiation promotes the transformation of "effective sulfur" in thiosulfate molecules to form H2S through the transformation of HS· and S2O3• - radicals. Moreover, more than 99.9% of arsenic/HMs were removed from strongly acidic wastewater without producing H2S pollution under UV irradiation. This thiosulfate-based H2S-specific release process solves the problem of H2S pollution under acidic conditions.

Photocatalytic inactivation of airborne bacteria in a polyurethane foam reactor loaded with a hybrid of MXene and anatase TiO2 exposing {0 0 1} facets

A hybrid of TiO2 exposing {001} facets and monolayer Ti3C2Tx nanosheet (MXene) was synthesized, characterized and used as a photocatalyst in this study. The introduction of MXene (3.4 wt%) helped to reduce the recombination of photo-induced electrons and holes, and thus enhanced the photocatalytic activity by 30%. A continuous flow-through reactor loaded with the as-prepared photocatalyst coated onto polyurethane foam was developed to inactivate airborne bacteria. The photocatalytic inactivation efficiency of airborne Escherichia coli (E. coli) achieved 3.4 lg order under ultraviolet (UV) irradiation at 254 (UV254), which was superior to that using UV254-only treatment with 2.5 lg order under the same operating condition (95% relative humidity and retention time of 4.27 s). The effect of humidity and bacteria species on inactivation performance was also investigated. The thick cell membrane could protect bacteria from photocatalytic oxidation while high humidity increased the photocatalytic inactivation efficiency by generating more reactive oxygen species. The phenomena of photo reactivation and dark repair of airborne E. coli using UV254-only treatment was observed. However, no reactivation occurred after UV photocatalytic inactivation, and even a continuous decline under visible light. These results suggested a different inactivation mechanism between UV irradiation and UV photocatalysis that the former inactivated bacteria by damaging their DNA, whereas photocatalysis physically damaged their cell structure.