Photodegradation Intermediates Research Articles

UV-light promoted formation of boron nitride-fullerene composite and its photodegradation performance for antibiotics under visible light irradiation

A series of C60/BN composites have been synthesized, which can efficiently photodegrade TC under visible-light irradiation. Compared with C60/BN-D6 and C60/BN-V6 synthesized under dark and visible-light irradiation, C60/BN-U6 synthesized under UV-light irradiation has the largest adsorption and photodegradation performance for TC under visible-light irradiation. FTIR and XPS characterizations suggest that C60/BN composite is most likely the charge transfer composite, in which C60 acts as electron acceptor and BN acts as electron donor. UV-light has the best promotion effect for the formation of C60/BN. The adsorption quantity of TC by C60/BN-U6 is 2.77 times higher than that of BN (131.05 mg g−1 vs. 47.27 mg g−1), being due to that C60/BN-U6 has higher surface area than BN (135.7 m2 g−1 vs. 18.8 m2 g−1). The photodegradation of C60/BN-U6 for TC follows Z-scheme heterojunction mechanism, as well as the photo-induced ·O2- and h+ are the dominant photoactive species. Quantitative structure-activity relationship (QSAR) method is applied to evaluate the toxicity of TC and its photodegradation intermediates. The photodegradation rate of C60/BN-U6 for TC is 19.19 times, 10.06 times, 5.83 times, 2.73 times and 1.84 times higher than that of TiO2 (P25), g-C3N4, BNPA, BCNPA, and BN/TiO2, respectively, implying that C60/BN-U is a good metal-free photocatalyst.

Rapid degradation of ciprofloxacin over BiOCl: Insight into the molecular structure transformation and antibacterial activity elimination

Currently, the widespread usage of antibiotics brings great challenge to sustainable water environment due to the production of drug-resistant bacteria, the rapid and effective removal of antibiotics attracts more and more attention. Herein, a BiOCl microsphere prepared by a facile hydrolysis method via controlling the EG-H2O ratio was found to have unexpected photocatalytic activity for ciprofloxacin (CIP) removal. The photodegradation rate of CIP over optimal BiOCl-20 reached 92.9% in only 3 min of simulated sunlight irradiation, and the mineralization rate was 30.8% after 60 min reaction. The antibacterial tests of CIP solution under different irradiation minutes were evaluated using Escherichia coli (E. coli) as the model bacteria. The results indicated that CIP photodegradation intermediates had also certain antimicrobial potency, which could be eliminated almost completely after 3 min irradiation, although there still had some incompletely mineralized intermediates. In view of these results, the macroscopic degradation behavior of CIP over BiOCl-20 as well as the microscopic existence state and reaction behavior of the intermediates should be clarified. A ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was employed for determination of CIP and its intermediates. Ten primary intermediates were separated and identified, and their corresponding molecular structures were elucidated. Three main photodegradation pathways were deduced, and the correlation between molecular structure transformation and antibacterial activity of CIP was established. Because of the destruction of piperazine ring and defluorination of quinolone ring, the antibacterial activity of the treated CIP solution was weakened or even eliminated. Finally, a possible photodegradation mechanism was proposed, the OVs, O2−, h+ and OH played significant roles in the CIP photodegradation. This work does have great perspective for BiOCl potential application in CIP wastewater treatment.

Photocatalytic degradation of ibuprofen and naproxen in water over NS-TiO2 coating on polycarbonate: Process modeling and intermediates identification

Nitrogen and sulfur doped TiO2 was coated on polycarbonate (NS-TiO2@PC) by simple deposition method. The coated film was characterized by field emission scanning electron microscope and atomic force microscope. The photocatalytic activity of the NS-TiO2@PC was evaluated through degradation of ibuprofen and naproxen under visible light irradiation. Optimization results showed that the maximal degradation efficiencies of 83% and 100% were achieved for ibuprofen and naproxen, respectively. In addition, the possible photodegradation intermediates were identified by liquid chromatography–mass spectrometry. This study proved that the NS-TiO2@PC had excellent stability during photodegradation of pollutants and will have practical applications for environmental remediation.

Surface adsorption configurations of H3PO4 modified TiO2 and its influence on the photodegradation intermediates of gaseous o-xylene

Abstract For the oxide-based photocatalysts, polyoxylic acid modification can affect their adsorption/desorption properties and further regulate photocatalytic reaction pathway, which is crucial for enhancing photocatalytic activity and selectivity. Herein, phosphoric acid modified TiO2 was synthesized by a facile impregnation-calcination method for photocatalytic degradation of gaseous o-xylene. According to FTIR, XPS, and EDS analysis, phosphoric acid was anchored on the surface of TiO2 successfully. The surface P atomic percentages for PT1 was 2.45%. The as-prepared phosphoric acid modified TiO2 (PTx) had a photocatalytic performance superior to that of commercial TiO2 and unmodified TiO2 (PT0), with increasing by 2.2 times at most. Interestingly, the phosphoric acid molecules strongly adsorbed on anatase TiO2 surface by forming H–O2C and =O–Ti5C chemical bonds according to the first principle calculations, which changed TiO2 surface properties (specific surface area and surface negative electrostatic field) and further improved adsorption and charge carrier separation and transfer, thus improving the photocatalytic activity. Additionally, according to the intermediates results, the relative abundance of intermediates shows obvious difference. Acetone was detected as the most abundant intermediates during o-xylene degradation for PT0, whereas that was o-methyl benzaldehyde for PT1, which could be ascribed to the difference of surface adsorption configuration of o-xylene. According to the temperature-programmed desorption (TPD) results, the surface modified by phosphoric acid could change the o-xylene adsorption configuration to favor its methyl oxidation (standing configuration), whereas the unmodified surface could be more favorable to the benzene ring-open reaction (lying configuration). This work will deepen the understanding of the relevance of surface modification and surface photocatalytic reaction, which also provides a feasible strategy to improve photocatalytic selectivity.

Degradation of metformin in water by TiO2–ZrO2 photocatalysis

The increasing use of pharmaceutical products also increases their release in aquatic environment. These contaminants are considered emerging pollutants, and induce adverse ecological and human health effects. The antidiabetic metformin is one example that has been detected in the aquatic environment at unusual concentrations. This fact indicates that conventional wastewater treatment is inefficient on eliminating this compound. Here we show that metformin can be effectively removed from water by photocatalysis. We found the optimised conditions for pH and concentration of catalyst on the photocatalytic process. TiO2 and TiO2–ZrO2 were successful in oxidising metformin under UV radiation following a pseudo-first order kinetics. Intermediates of metformin photodegradation appeared after photocatalytic treatment. Toxicity analysis showed that the degradation products are non-toxic to Lactuca sativa seeds.

Microwave-assisted synthesis of triple 2D g-C3N4/Bi2WO6/rGO composites for ibuprofen photodegradation: Kinetics, mechanism and toxicity evaluation of degradation products

In this study, the visible-light-driven Z-scheme g-C3N4/Bi2WO6/rGO heterojunctions with 2D/2D/2D configurations are prepared via a facile, rapid and low temperature microwave-assisted method. The physicochemical properties and morphologies of these heterostructured photocatalysts are characterized by various spectroscopies such as XRD, XPS, TEM/SEM, PL, FT-IR, UV–Visible spectroscopy and nitrogen adsorption measurements. The prepared g-C3N4/Bi2WO6/3 wt% rGO photocatalysts (incorporated with optimal 3 wt% of rGO) possess ca. 86 and 98% of ibuprofen (IBF) photodegradation under the visible light (λ > 420 nm) and solar light irradiation, respectively. The formation of well crystallized structure, morphology (nanoplates structure of Bi2WO6), higher visible light absorption and specific surface area (25.4 m2 g−1) are responsible for the superior performance of g-C3N4/Bi2WO6/3 wt% rGO. Moreover, the larger interfacial contact (identified by HRTEM) between triple 2D g-C3N4/Bi2WO6/rGO heterostructures can lead to surpassing interfacial charge carrier dynamics and reduce the combination of electron-hole pairs. IBF photodegradation intermediates and the corresponding reaction mechanisms are further investigated by using LC-MS/MS, indicating the superoxide radical (O2−) and hydroxyl radicals (OH) are involved in the photodegradation of IBF and accordingly five intermediates are produced via three possible reaction pathways. The anti-hormonal effects of IBF and the photodegraded intermediate products are also evaluated by yeast-based bioassays. The results show that the intermediate products of photodegraded IBF have lower antagonistic effect on human hormone receptors than the pristine IBF.

Focus on scavengers’ effects and GC-MASS analysis of photodegradation intermediates of sulfasalazine by Cu2O/CdS nanocomposite

Coupling of Cu2O and CdS nanoparticles (NPs) showed a boosted photocatalytic activity in the degradation of Sulfasalazine (SSZ) in aqueous solution. Some characterization techniques including x-ray diffraction (XRD), scanning electron microscope equipped with an energy dispersive X-ray (EDX) analyzer, Transmission electron microscope (TEM), x-ray mapping, photoluminescence spectroscopy (PL) and diffuse reflectance spectroscopy (DRS) was used for characterizing of samples. A blue shift in band gap energy was obtained for the composite concerning the single semiconductors and values of 2.42, 2.43 and 2.52 eV were obtained for the direct electronic transition of Cu2O, CdS and CdS/Cu2O samples, respectively. PL results confirmed an elongate lifetime of e/h pairs in the composite. The optimal conditions were CSSZ: 10 mg L−1, pH 5, 25 min irradiation time and 0.5 g L−1 of the Cu2O/CdS catalyst. The chemical oxygen demand (COD) showed about 82% of SSZ molecules were mineralized during the photodegradation process. The effects of scavengers showed that the photogenerated holes have a major role in SSZ degradation with respect to other reactive species. GC-Mass analysis was done for detecting the degradation intermediates formed during the photodegradation process. The initial pH of the solution was changed from 5 to about 7.5 at the end of the photodegradation process.

Rhodamine B Adsorptive Removal and Photocatalytic Degradation on MIL-53-Fe MOF/Magnetic Magnetite/Biochar Composites

MIL-53-Fe metal–organic framework (MOF) was grown using the terephthalic acid linker and FeCl3 into an already prepared, high surface area, magnetic, Douglas fir biochar/Fe3O4 (MBC) adsorbent hybrid. This resulting triphase hybrid, multifunctional, magnetically recoverable, sorptive, photocatalytic and degradative, adsorbent (MOF–MBC) was used both to remove and catalyze the photodegradation of Rhodamine B (Rh B) with or without Cr6+ present. Rh B is a widely used colorant in textile, printing and tanning industries that is also associated with deleterious health effects. Batch aqueous sorption studies were performed at various pHs, Rh B concentrations and temperatures in-order to determine the optimum adsorption pH, kinetics, thermodynamics and sorption capacity. This adsorption followed pseudo-2nd-order kinetics and exhibited a Rh B Langmuir adsorption capacity of ~ 55 mg/g at pH 6, 200 rpm agitation and 25 °C. This MOF–MBC hybrid was characterized by SEM, TEM, EDS, XRD, FT-IR, TGA, BET, Elemental Analysis and XPS. Deethylated and carboxylic compounds were identified as photodegradation intermediates. Electrostatic and π–π stacking interactions are thought to play a significant role in Rh B sorption. Hexavalent chromium (Cr6+) and Rh B often co-exist in tannery and printing waste water. Cr6+ can trigger the photo-degradation of Rh B into CO2 and H2O in the presence of both MIL-53-Fe MOF and MOF–MBC. Hence, adsorbent stripping regeneration can be minimized in real world applications. The biochar phase, aids to disperse the MOF, to minimize particle aggregation, to provide extra stability to the MOF, and serves as secondary adsorption site for heavy metal, oxy anion and organic contaminants. Large biochar particles allow reasonable flow through column beds while supporting other nanophases, which would cause large pressure drops when used alone.

Microwave-synthesized KNbO3 perovskites: photocatalytic pathway on the degradation of rhodamine B

In this work, KNbO3 perovskite nanostructures were prepared at different Nb2O5:KOH molar ratios via microwave-assisted hydrothermal synthesis. The structural and optical properties of the samples were characterized by XRD, SEM, TEM, diffuse reflectance, and photoluminescence analysis. The [1:16] sample showed an improved electron-hole separation when compared to the other synthetic pathways. Photocatalytic activities of the materials in the degradation of rhodamine B were also evaluated. The results indicate that the perovskite with the molar ratio [1:16] showed higher photocatalytic efficiency in the degradation of rhodamine B, with a 23-fold decrease in the initial concentration. Such improved performance is accounted for by its large values of specific surface area and a more efficient conversion of UV photons into effective charge carriers. Photodegradation intermediates were identified by micrOTOF-Q III liquid chromatography, which indicated a large amount of N-de-ethylated cleavage products and simple organic acids, thus demonstrating the excellent applicability potential of these KNbO3 ferroelectrics in the degradation of organic pollutants in wastewater.

Trace amounts of fenofibrate acid sensitize the photodegradation of bezafibrate in effluents: Mechanisms, degradation pathways, and toxicity evaluation

Effluent organic matter (EfOM), which is composed of background natural organic matter (NOM), soluble microbial degradation products, and trace amounts of organic pollutants, can play an important role in the photodegradation of emerging pollutants in the effluent. In this study, the impact of organic pollutants, using fenofibrate acid (FNFA) as a representative, on the photodegradation of emerging contaminants, using bezafibrate (BZF) as a representative, in effluents was investigated. It is found that BZF undergo fast degradation in the presence of FNFA although BZF is recalcitrant to degradation under simulated sunlight irradiation. The promotional effect of FNFA is due to the generation of singlet oxygen (1O2) and hydrated electrons (e-aq). Based on the structures of the identified intermediates, 1O2 initiated oxidation and e-aq initiated reduction reactions were the main photodegradation pathways of BZF in the effluents. The toxicity of the main photodegradation intermediates for BZF and FNFA was higher than that of the parent compounds, and the acute toxicity increased during simulated sunlight irradiation. The results demonstrated that trace amounts of organic compounds in EfOM can play an important role in sensitizing the photodegradation of some emerging pollutants in the effluent.

Photo-induced redox coupling of dissolved organic matter and iron in biochars and soil system: Enhanced mobility of arsenic

Dissolved organic matter (DOM) elucidated from biochars enhances the dissolution of iron oxides and reduction of iron. However, given that reduction mechanism of iron (Fe(III)) in the practical biochar applications for soil amendment and environmental remediation have not been fully elucidated, this study laid great emphasis on the photo-induced Fe(II) liberated from DOM-Fe(III) complexes. Thus, pyrolysis of biomass was carried out at 300 °C to maximize DOM release from biochars. Moreover, three different biomass samples (rice straw (R), granular sludge (G) from an anaerobic digester, and spent coffee grounds (C)) were chosen as carbon substrates for biochars preparation. To demonstrate the transformation of Fe(III), 1 and 5 wt% biochar was applied to the clean (S1) and arsenic-contaminated (S2) soil with/without the light. The results indicate that the light condition produces more Fe(II). The amount of Fe(II) accounts for 25.3, 28.6, and 30.7% of total iron under the light with 5 wt% GB, RB, and CB in S1, and 10.6, 13.1, and 13.8% in S2. This study demonstrates that Fe(II) is generated more under ultraviolet irradiation than visible light and dark condition. In addition, a control experiment without biochar showed that DOM plays an important role in the reduction of Fe(III). The mobility of arsenic increased under the light condition since the intermediates of DOM photo-degradation accelerates the dissolution of iron oxides and arsenic competes with DOM for the adsorption. Therefore, there was no significant correlation between the elution of arsenic and the formation of Fe(II) during the reductive dissolution of iron oxide under the light condition.

Zinc Porphyrin-Functionalized Fullerenes for the Sensitization of Titania as a Visible-Light Active Photocatalyst: River Waters and Wastewaters Remediation.

Zinc porphyrin-functionalized fullerene [C60] derivatives have been synthesized and used to prepare titania-based composites. The electrochemical properties and HOMO and LUMO levels of the photosensitizers were determined by electrochemical measurements. Raman and IR techniques were used to study chemical groups present on the titania surface. Absorption properties of the composites were measured in the solid state by diffuse reflectance UV-Vis spectra (DRS). The zeta potential and aggregate sizes were determined using dynamic light scattering (DLS) and electrophoretic light scattering (ELS) techniques. Surface areas were estimated based on Brunauer–Emmett–Teller (BET) isotherms. The photocatalytic activity of the photocatalysts was tested using two model pollutants, phenol and methylene blue. The composite with the highest photocatalytic potential (1/TiO2) was used for river and wastewater remediation. The photodegradation intermediates were identified by LC-UV/Vis-MS/MS techniques.

Rational design 2D/2D BiOBr/CDs/g-C3N4 Z-scheme heterojunction photocatalyst with carbon dots as solid-state electron mediators for enhanced visible and NIR photocatalytic activity: Kinetics, intermediates, and mechanism insight

Rapid recombination of photogenerated carriers and narrow visible light absorption range are two main defects in graphitic carbon nitride (g-C3N4)-based photocatalysts. To address these problems, construction of Z-scheme 2D/2D BiOBr/CDs/g-C3N4 heterojunction photocatalysts with carbon dots as solid-state electron mediators has been investigated. The resultant BiOBr/CDs/g-C3N4 hybrids exhibits remarkable interfacial charge transfer abilities and a broadened solar light absorption range owing to the short charge transport distance and the up-converted photoluminescence character of CDs. Simultaneously, the enhanced specific surface area and nanosheet structure impart more active sites to BiOBr/CDs/g-C3N4 composites. As a result, BiOBr/CDs/g-C3N4 composites reveal significant enhancement in the activity of photodegradation of ciprofloxacin (CIP) and tetracycline (TC) under visible and near infrared (NIR) light irradiation. Moreover, the photodegradation efficiency of BiOBr/CDs/g-C3N4 hybrids was significantly enhanced over that of pristine BiOBr nanosheets and g-C3N4 ultrathin nanosheets. The photocatalytic mechanism is expounded according to free radical capture experiments and electron spin resonance spin-trapping tests and the photodegradation intermediates of CIP were detected by liquid chromatography–mass/mass spectrometry. Moreover, BiOBr/CDs/g-C3N4 composites show excellent photostability and reusability after four runs for CIP degradation.

In-situ fabrication of needle-shaped MIL-53(Fe) with 1T-MoS2 and study on its enhanced photocatalytic mechanism of ibuprofen

High photocatalytic hole-electron pairs separation efficiency and the wide use of inexpensive and earth-abundant materials as cocatalysts in most semiconductor-based photocatalytic systems are desired for improving the photocatalytic activity and practical application. Herein, we report a facile one-pot solvothermal approach of integrating stable metallic nonmetal materials 1T-MoS2 nanosheets with MIL-53(Fe) to form needle-shaped 1T-MoS2@MIL-53(Fe) (TSMF) composites. Interestingly, the introduction of 1T-MoS2 turns nonspecial-structured MIL-53(Fe) into needle-like structure and the BET analysis reveals that the optimal TSMF composites possess abundant coexistence of micropores and mesopores with a large surface area of 337 m2 g−1, which is about 16 folds higher than that of the pure MOFs. Meanwhile, it is remarkable that the photocatalytic rate of ibuprofen (IBP) by optimal TSMF nanocomposites has improved 7.5 and 9.4 times compared to the pristine MIL-53(Fe) and 1T-MoS2, respectively. The photocatalytic efficiency of TSMF composites enhances due to the emerging micropores, which can provide more adsorption and reaction sites. In addition, the formed compact and uniform interface contact between 1T-MoS2 sheets and MOF may dramatically accelerate the separation of the photo-induced charges, thus enhance the photocatalytic activity. We also study the photocatalytic mechanism combined the corresponding electrochemical testing and the photo-degradation intermediates identified by ion chromatography (IC) and LC–MS-MS, indicating that superoxide radicals (O2–), hydroxyl radical (OH) and electrons (e−) are the main active radicals in IBP photocatalysis and decarboxylation and hydroxylation are the main degradation pathways of IBP.

In situ growth of Ag-SnO2 quantum dots on silver phosphate for photocatalytic degradation of carbamazepine: Performance, mechanism and intermediates toxicity assessment

The occurrence of carbamazepine (CBZ) in environments poses a potential risk to aquatic life and exhibits growth inhibition of human embryonic cells. In this work, for the first time a series of Ag-SnO2 quantum dots (QDs)/silver phosphate (AgSn/AgP) composites were synthesized and used as photocatalysts for CBZ degradation. The obtained AgSn/AgP composites showed superior photodegradation efficiency for CBZ removal. The degradation rate constant of 10AgSn/AgP (with 10 wt% of Ag-SnO2 QDs) was almost 8.5, 5.7, 5.7, and 1.9 times as that of Ag-SnO2 QDs, Ag3PO4, Ag/Ag3PO4, and SnO2 QDs/Ag3PO4, respectively. The improved photocatalytic activity could be primarily ascribed to the improved charge separation through a collaborative effect of Ag-SnO2 QDs and Ag3PO4, and in situ photoreduced metallic silver. Electron spin resonance (ESR) measurement and radical trapping experiments suggested that holes (h+), (superoxideradical) ·O2− and (hydroxylradical) ·OH corporately participated in the decomposition of CBZ. Moreover, a reasonable mechanism for photocatalytic degradation of CBZ over 10AgSn/AgP composites was tentatively proposed. Additionally, eight degradation intermediates were determined by liquid chromatography-mass spectrometry (LC-MS). Toxicity evaluation using the Ecological Structure Activity Relationships (ECOSAR) program revealed that the toxicity of most photodegradation intermediates were much lower than that of the parent compound CBZ. This work not only provides a new technique for preparing Ag3PO4-based photocatalysts with high activity, but also demonstrates that 10AgSn/AgP could be a promising photocatalyst for treating water and wastewaters containing CBZ.

Conjugated conducting polymers PANI decorated Bi12O17Cl2 photocatalyst with extended light response range and enhanced photoactivity

In this work, PANI/Bi12O17Cl2 composites have been successfully synthesized via a simple and green strategy at room temperature. From TEM, EDS-mapping and DRS results, it can be seen that conducting polymers PANI loaded well on the Bi12O17Cl2, and extended the light-absorption region of the composite to a higher wavelength. The photocatalytic activity was evaluated by removal of CIP under visible light (λ > 420 nm). The degradation rate of the optimal ratio composite is about 2 times to that of Bi12O17Cl2. The photodegradation intermediates of CIP were identified by mass spectrometry and the toxicity of the CIP photodegraded products were investigated via a microbiological antibacterial reaction. The results indicated the low-toxicity of the degraded products. Photocurrent results showed that the high separation and transfer of the photogenerated charge carriers were implemented by the introduction of PANI into the surface of Bi12O17Cl2 material. Furthermore, long wavelength light (λ > 550 nm) degradation of CIP indicated that the PANI played as photosentizer could extend the light absorption region and thus enhance the photocatalytic ability. The reaction rate constant of optimal ratio PANI/Bi12O17Cl2 composite was 3.1 times to Bi12O17Cl2. Eventually, a possible photocatalysis mechanism was proposed.

Visible-Light-Induced Photocatalytic Degradation of PAH-Contaminated Soil and Their Pathways by Fe-Doped TiO2 Nanocatalyst

The aim of the present study was to establish the photocatalytic efficiency of Fe-doped TiO2 nanocatalysts toward polycyclic aromatic hydrocarbons (PAHs), which were phenanthrene, anthracene, and fluoranthene, contaminated soil under visible irradiation. The morphology, phase, and particle size of the prepared nanocatalyst have been studied as a first mention in literature. The photoresponse of the TiO2 extends from UV region to the visible region was proved by the diffuse reflectance spectrophotometry (DRS). The surface area is greatly increased though the Fe-doped TiO2 compared with the bare TiO2. The pH value of the media showed the beneficial to PAH absorption on the Fe-doped TiO2 under the alkaline condition due to the surface catalyst possesses much negative charge, which is increase in percentage of PAH degradation. Based on GC-MS study, the mechanism of photoactivity of the selected PAHs involves hydroxylation, ring opening, and rearrangement reactions. The main intermediates of PAH photodegradation were found to be 9-octadecanoic acid, heptadecane, octadecane, cyclohexane (1-hexadecylheptadecyl), and 15-hydroxypentadecanoic acid.

Insight into the highly efficient degradation of PAHs in water over graphene oxide/Ag3PO4 composites under visible light irradiation

Polycyclic aromatic hydrocarbons (PAHs) are associated with adverse health effects in humans, and the photocatalysis degradation is regarded as promising technology to remove contaminants from environment. Although many TiO2-based photocatalysts were reported to be active for this process, the efficiency is still quite low. In this work, graphene oxide (GO) enwrapped silver phosphate composites were found to exhibit superior activities in the photocatalytic degradation process of a variety of PAHs (naphthalene, phenanthrene and pyrene) under visible light irradiation. The optimum amount of GO was 3.0wt%. Within several minutes or even seconds’ visible light irradiation, naphthalene, phenanthrene and pyrene can be completely oxidized. Meanwhile, good photocatalytic activity was retained after six cycles run. The trapping experiments gave evidence that degradation was mediated by photogenerated holes, superoxide radicals and hydroxyl radical, different from others OH was found to play a role in the process of pyrene photoreaction. Gas chromatography-mass spectrometer (GC-MS) technique was employed to analyze photodegradation intermediates. Based on the identified intermediates, the plausible photooxidation pathways of PAHs over the surface of GO/Ag3PO4 were proposed. Ultimately, a possible synergetic mechanism associated with Ag surface plasmon resonance effect of GO/Ag3PO4 composite for PAHs photodegradation was suggested. The superior photocatalytic system for the removal of PAHs was presented and simultaneously it shed light on photodegradation of PAHs from a practical point of view.

Self-sensitized photodegradation of benzisothiazolinone by low-pressure UV-C irradiation: Kinetics, mechanisms, and the effect of media

Abstract Benzisothiazolinone (BIT) is a kind of non-oxidizing biocide widely used in reverse osmosis process for wastewater reclamation. Most BIT would reside in the RO (reverse osmosis) concentrates and show adverse effects on aquatic life when it is discharged into surface water. This study analyzed the photodegradation of BIT under UVC (254 nm) irradiation and found that UVC irradiation was as an efficient way to degrade BIT, of which the process could be well described by pseudo first order kinetics. As the results of BIT self-sensitization and light shield, the BIT photodegradation constant increased from 0.19 to 0.23 min−1 with increasing BIT concentration from 3 to 40 μM, and then followed by a decrease of the constant with further increasing BIT concentration. Radical species quenching experiments indicated that the photodegradation of BIT could be attributed to both direct and indirect photodegradation. Studies of the effects of pH suggested that non-charged state BIT (BIT0) in neutral and basic solution was much more photodegradable than protonated state BIT (BIT-H+) in acidic solution. The solution anion of HCO3− showed a slight promotion on BIT photodegradation. With the help of quadrupole time-of-flight mass spectrometry (QTOF-MS), the main intermediates of BIT photodegradation were identified. By employing the anion chromatography and HPLC tandem with triple quadrupole MS, the intermediates were quantified and the degradation pathway was proposed. This study could offer valuable suggestions for the efficient degradation of BIT and other similar emerging pollutants in wastewater reclamation and contribute to reclaimed water safety and sustainability.

Cu-α-NiMoO4 photocatalyst for degradation of Methylene blue with pathways and antibacterial performance

Abstract Cu doped α-NiMoO 4 photocatalyst has been synthesized by microwave hydrothermal method. The existence of Cu 2+ ions at lattice position of α-NiMoO 4 was observed on the basis of XRD, HRTEM, SAED, and EDS analysis. The negative zeta potential values indicate the stability of samples. Solar light driven photocatalytic degradation of Methylene blue (MB) dye in water was used to evaluate the photocatalytic performance of Cu doped α-NiMoO 4 photocatalyst. The results revealed that there is an optimum Cu (4 mol%) doping level leads to highly enhanced photocatalytic activity of Cu-α-NiMoO 4 , as compared to α-NiMoO 4 host. The experiment also suggested that active species (OH , O 2 − and h + ) play a crucial role in the scavenging system. The reduced energy band gap, oxygen vacancy, high BET surface area, and efficient separation of photogenerated electron/hole are responsible for enhancement of photocatalytic performance. MB photodegradation intermediates were identified by high resolution-quadruple time of flight electrospray ionization mass spectrometry (HR-QTOF ESI/MS) in positive ion mode and degradation pathway was proposed. Antibacterial performance was analyzed against Gram-positive (methicillin resistant Staphylococcus aureus and Bacillus Subtilis ) and Gram-negative bacteria ( Pseudomonas aeruginosa ) via well-diffusion method. The formation of larger inhibition zone by small quantity of photocatalyst powder proved the excellent antibacterial performance. The inactivation of microorganism were found in following order: B . Subtilis ˃ S . aureus ˃ P . aeruginosa . The result of our study suggested that copper doped α-NiMoO 4 photocatalyst is suitable for degradation of organic contaminates as well as effective for growth inhibition of multidrug-resistant microorganisms.