Photodegradation Process Research Articles

Aquatic photolysis of high-risk chemicals of emerging concern from secondary effluent mediated by sunlight irradiation for ecological safety and the enhanced methods

Natural sunlight can reduce the chemicals of emerging concern (CECs) and biological effects from the discharged domestic wastewater. But the aquatic photolysis and biotoxic variations of specific CECs detected in secondary effluent (SE) were not clear. In this study, 29 CECs were detected in the SE, and 13 medium- and high-risk CECs were identified as target chemicals based on their ecological risk assessment. To comprehensively explore the photolysis properties of the identified target chemicals, the direct and self-sensitized photodegradation of the target chemicals, even the indirect photodegradation in the mixture, were investigated and compared with these photodegradation in the SE. Of the 13 target chemicals, only five chemicals (including dichlorvos (DDVP), mefenamic acid (MEF), diphenhydramine hydrochloride (DPH), chlorpyrifos (CPF), and imidacloprid (IMI)) underwent direct and self-sensitized photodegradation processes. The removal of DDVP, MEF, and DPH was attributed to self-sensitized photodegradation, which was mainly mediated by •OH; CPF and IMI primarily relied on direct photodegradation. Synergistic and/or antagonistic actions that occurred in the mixture improved/decreased the rate constants of five photodegradable target chemicals. Meanwhile, the biotoxicities (acute toxicity and genotoxicity) of the target chemicals (including individual chemicals and the mixture) were significantly reduced, which can explain the reduction of biotoxicities from SE. For the two refractory high-risk chemicals, atrazine (ATZ) and carbendazim (MBC), algae-derived intracellular dissolved organic matter (IOM) on ATZ, and IOM and extracellular dissolved organic matter (EOM) on MBC had slightly promotion for their photodegradation; while peroxysulfate, and peroxymonosulfate served as sensitizers were activated by natural sunlight and effectively improved their photodegradation rate, and then reduced their biotoxicities. These findings will promote the development of CECs treatment technologies based on sunlight irradiation.

A Porous Geopolymer Containing Ti-Bearing Blast Furnace Slag: Synthesis, Characterization, and Adsorption-Photodegradation Studies towards Methylene Blue Removal under Visible Light Condition.

A porous geopolymer with adsorption and photocatalytic degradation functions was successfully developed by utilizing Ti-bearing blast furnace slag (TBBFS) as the raw material. The prepared porous geopolymers were characterized by X-ray diffraction, scanning electron microscope, energy dispersive spectrometer, and Fourier transform infrared spectrum. Selective crystallization, water quenching, and natural cooling methods were employed to investigate the influences of these modifications on the applicability of TBBFS as a precursor for geopolymer synthesis. Water-quenched slag with amorphous content was prone to alkali dissolution, and the resulting geopolymer exhibited the highest adsorption capacity (97.18 mg/g) for methylene blue (MB) removal. Selective crystallization at 1400 °C generated a hybrid microstructure consisting of a non-cementitious CaTiO3 crystallization phase and a cementitious amorphous fraction. The retention of CaTiO3 in the final geopolymer enables a bifunctionality in adsorption-photodegradation. Particularly, the adsorption and photodegradation processes under various conditions were investigated. The superior removal efficiency for MB could be attributed to the synergistic effects between the geopolymer matrix and CaTiO3, leading to an enhancement in the formation of hydroxyl radicals. The conversion of TBBFS into porous geopolymer offers an efficient and straightforward solution for slag utilization and dye removal.

Photocatalytic degradation of diclofenac using a novel double Z-scheme catalyst (O-g-C3N4/ZnO/TiO2@halloysite nanotubes): Degradation mechanism, identification of by-products and environmental implementation

It is challenging and expensive to synthesize multivariate composites with high photocatalytic efficiency and recyclability. Herein, a novel direct double Z-scheme O-g-C3N4/ZnO/TiO2@halloysite nanotubes (HNTs) photocatalyst was synthesized using a simple and low-cost method to degrade and mineralize diclofenac (DCF). During 50 min, O-g-C3N4/ZnO/TiO2@HNTs degraded DCF completely at pH 6.83, 10 mg/L DCF concentration, and 1.0 g/L catalyst, which was 1.66 and 2.4 times higher than ternary O-g-C3N4/ZnO/TiO2 and O-g-C3N4/HNTs/TiO2. Under the same conditions, 35.12 % of DCF was removed from urban wastewater. A negative effect of anions on the process was observed as follows: CO32− > HPO42− > Cl− > NO3−. Under the same conditions, 39.23 % of total organic carbon (TOC) was removed. Moreover, Mott-Schottky analysis and active species trapping experiments were performed to investigate the photodegradation mechanism systematically. It was observed that O2− played a minor part in the photodegradation process, while hole and OH were the more critical reactive species. Several intermediate compounds formed during the photocatalytic reaction were identified by LC-MS analysis. The results showed that a simple design and synthesis of multi-component complex catalysts presented a new insight into removing emerging pollutants from the aquatic environment and apprehending the enhanced photocatalytic mechanism.

Bidimensional SnSe2-Mesoporous Ordered Titania Heterostructures for Photocatalytically Activated Anti-Fingerprint Optically Transparent Layers.

The design of functional coatings for touchscreens and haptic interfaces is of paramount importance for smartphones, tablets, and computers. Among the functional properties, the ability to suppress or eliminate fingerprints from specific surfaces is one of the most critical. We produced photoactivated anti-fingerprint coatings by embedding 2D-SnSe2 nanoflakes in ordered mesoporous titania thin films. The SnSe2 nanostructures were produced by solvent-assisted sonication employing 1-Methyl-2-pyrrolidinone. The combination of SnSe2 and nanocrystalline anatase titania enables the formation of photoactivated heterostructures with an enhanced ability to remove fingerprints from their surface. These results were achieved through careful design of the heterostructure and controlled processing of the films by liquid phase deposition. The self-assembly process is unaffected by the addition of SnSe2, and the titania mesoporous films keep their three-dimensional pore organization. The coating layers show high optical transparency and a homogeneous distribution of SnSe2 within the matrix. An evaluation of photocatalytic activity was performed by observing the degradation of stearic acid and Rhodamine B layers deposited on the photoactive films as a function of radiation exposure time. FTIR and UV-Vis spectroscopies were used for the photodegradation tests. Additionally, infrared imaging was employed to assess the anti-fingerprinting property. The photodegradation process, following pseudo-first-order kinetics, shows a tremendous improvement over bare mesoporous titania films. Furthermore, exposure of the films to sunlight and UV light completely removes the fingerprints, opening the route to several self-cleaning applications.

Mechanism and Kinetics of Prothioconazole Photodegradation in Aqueous Solution.

This study investigated the effects of light source, pH value, and NO3- concentration on the photodegradation of prothioconazole in aqueous solution. The half-life (t1/2) of prothioconazole was 173.29, 21.66, and 11.18 min under xenon, ultraviolet, and high-pressure mercury lamps, respectively. At pH values of 4.0, 7.0, and 9.0 under a xenon lamp light source, the t1/2 values were 693.15, 231.05, and 99.02 min, respectively. Inorganic substance NO3- clearly promoted the photodegradation of prothioconazole, with t1/2 values of 115.53, 77.02, and 69.32 min at NO3- concentrations of 1.0, 2.0, and 5.0 mg L-1, respectively. The photodegradation products were identified as C14H15Cl2N3O, C14H16ClN3OS, C14H15Cl2N3O2S, and C14H13Cl2N3 based on calculations and the Waters compound library. Furthermore, density functional theory (DFT) calculations showed that the C-S, C-Cl, C-N, and C-O bonds of prothioconazole were the reaction sites with high absolute charge values and greater bond lengths. Finally, the photodegradation pathway of prothioconazole was concluded, and the variation in energy of the photodegradation process was attributed to the decrease in activation energy caused by light excitation. This work provides new insight into the structural modification and photochemical stability improvement of prothioconazole, which plays an important role in decreasing safety risk during application that will reduce the exposure risk in field environment.

Silver oxide-zeolite for removal of an emerging contaminant by simultaneous adsorption-photocatalytic degradation under simulated sunlight irradiation

The existence of contaminants of emerging concern such as pharmaceuticals in the water sources become a growing concern matter because of their increased consumption, incomplete disposal, and potential impacts on living organisms. Accordingly, the removal of these bioactive compounds from the aqueous environment also becomes a vital issue and different treatment techniques have been investigated. The novelty of this work lies in the synthesis and implementation of silver oxide anchored on Y zeolite (Ag2O@Y Zeo) as an untried effective photocatalyst for the removal of emerging contaminants. Ranitidine (RANI) removal from aqueous solutions was investigated in this study by simultaneous adsorption-photodegradation induced via simulated sunlight irradiation in the presence of Ag2O@Y Zeo. Ag2O@Y Zeo was prepared by thermal treatment at 400 °C of Ag-form Y zeolite which was prepared by ion-exchange. The produced catalyst was characterized by X-ray diffraction, scanning electron microscopy, energy dispersive analysis by X-ray, Fourier transform infrared spectroscopy, nitrogen adsorption–desorption isotherms, UV–Vis diffuse reflection spectroscopy and photoluminescence spectroscopy. The simultaneous adsorption-photodegradation of RANI using Ag2O@Y Zeo was investigated at various conditions including a catalyst dose (5, 10, 30, 50, and 70 mg/ 100 mL), an initial RANI concentration (10, 20, 30, 40, and 50 mg/L), and a solution pH (3, 5, 9, and 11). According to the results, the RANI removal percentage was 97.51% obtained at Ag2O@Y Zeo dosage of 30 mg/100 mL, an initial RANI concentration of 40 mg/L, a solution pH of 7.4 and a time of 75 min. These results were attributed to the important role of the photogenerated holes and photogenerated electrons over the synthesized catalyst and their generation can be induced only in the presence of simulated sunlight. The photodegradation process of RANI by Ag2O@Y Zeo followed the pseudo-first-order kinetic model and O2°- was the main reactive species.

Advanced Oxidation Processes of Amoxicillin Based on Visible Light Active Nitrogen-Doped TiO<sub>2</sub> Photocatalyst

Environmental consequences during the COVID-19 pandemic have attracted attention due to the excessive use of antibiotics which lead to the release of the drug's residue, such as amoxicillin (AMX), into the environment. In this work, an advanced oxidation process based on a visible, active N-doped TiO2 photocatalyst was carried out to eliminate AMX. Nitrogen with different initial doping concentrations (15, 30, 45% w/w) was doped into TiO2 by the sol-gel method. The characterization technique such as XRD, FTIR, UV-SRS, and SEM-EDX revealed that nitrogen with 30% doping concentration improved the TiO2 response in the visible region, attributed to the lower band gap energy (2.97 eV). In the photodegradation processes, the TiO2-N (30%) photocatalyst possessed higher AMX degradation than undoped TiO2 for both UV and visible light irradiation. In an aqueous solution, the degradation percentage of AMX by TiO2-N (30%) was 68.5 and 84.12%, while the degradation percentage of AMX by TiO2 was 38.7 and 78.01% under visible and UV light, respectively.

Drugs Designed for Degradation in the Environment Post Use

Abstract: Accumulation of pharmaceuticals in the environment due to slow mineralization in nature is a growing pollution problem affecting organisms and animals and humans in the long run. When pharmaceuticals are antibiotics, the problem is twofold since the buildup of such compounds in the environment also fuels the development of antibiotic resistance. Building weak structures of biologically active compounds is one way of facilitating the quicker degradation of the drug in the environment after the drug has been excreted from the patient subsequently performing its function. The emergence of the process of photodegradation post-excretion of the pharmaceutical from the patient is one method that is under development, which will facilitate a quicker breakdown of the drug. Another method to enable this is hydrolysis, which is pH-dependent and involves making up of compounds that hydrolyze quicker under certain pH conditions. To enable the ongoing efforts in making pharmaceuticals to be more benign, this focused review showcases examples from research on antimicrobial agents and anticancer agents.

Novel self-propelled CuCr2O4-BiI3O9 nanojets for the efficient photodegradation of organics in wastewater: A non-genotoxic nanomaterial for water treatment

Antibiotic contamination as a result of disposal of untreated wastewater from hospitals can lead to the development of antibiotic-resistant bacteria. This study explored the photocatalytic remediation of antibiotics in water using CuCr2O4-BiI3O9 nanocomposite (NCs). The coupling of CuCr2O4 nanoflakes with BiI3O9 nanocubes resulted in formation of nano heterojunction for electron transfer pathway and displayed enhanced photodegradation of cefixime (CEF) by 98.2 % in 200 min under visible light irradiation. The NCs exhibits excellent photostability, reusability, enhanced charge carrier separation and good visible light absorption capacity than the pure nanoparticles (NPs). The scavenging experiment revealed that ●OH radical played a major role in cefixime photodegradation process. Furthermore, the NCs did not show any chromosomal abnormalities or micro nucleic formation in Allium cepa, suggesting the non-genotoxic nature of NCs. The effectiveness and non-toxic nature of the prepared nanomaterial makes it a promising technology for water remediation and can be extended to remove a wide range of toxic pollutants.

Effect of Ag modification on TiO2 and melem/g-C3N4 composite on photocatalytic performances

Here, the comparison of two different semiconductor materials is demonstrated, TiO2 and melem/g-C3N4 composites—modified with balls of approximately 5 nm Ag nanoparticles (NPs) as photocatalysts for the degradation of the model dye acid orange 7 (AO7). The melem molecule synthesized here is one of a series of organic compounds consisting of triazine ring compounds with a structure similar to that of melam and melamine. The photodegradation process of AO7 was carried out to examine all powder materials as a potential photocatalyst. Additionally, two different lamps of wavelengths 368 nm (UV light) and 420 nm (VIS light) were applied to compare the photodegradation tests. A new synthesis route for the acquisition of Ag NPs (Ag content 0.5, 1.0 and 2.5 wt%), based on a wet and low temperature method without the use of reducing reagents was proposed. The best photocatalytic performances under UV and VIS light were obtained for both, TiO2 and melem/g-C3N4 materials (new synthesis route) modified with a very low Ag content—0.5 wt%. The photodegradation activities using UV lamp (3 h, 368 nm irradiation) for samples with 0.5 wt% of Ag: TiO2 and melem/g-C3N4, in excess of 95 and 94%, respectively, were achieved. The highest photoactive materials melem/g-C3N4 with 0.5 and 1 wt% Ag revealed 98% of activity under the VIS lamp after 3 h long irradiation. Our work demonstrates a novel, environmentally acceptable, and cost-effective chemical strategy for preparation of photocatalysts suitable for degradation of organic contaminants in wastewater treatment.

Controllable Fabrication of Zn2+ Self-Doped TiO2 Tubular Nanocomposite for Highly Efficient Water Treatment

Tailoring high-efficiency photocatalytic composites for various implementations is a major research topic. 1D TNTs-based nanomaterials show promise as a photocatalyst for the remediation of organic pigments in an aqueous solution. Despite this, TiO2 (TNTs) is only photoactive in the UV range due to its inherent restriction on absorption of light in the UV range. Herein, we provide a facile recipe to tailor the optical characteristics and photocatalytic activity of TNTs by incorporating Zn (II) ionic species via an ion-exchange approach in an aqueous solution. The inclusion of Zn (II) ions into the TNTs framework expands its absorption of light toward the visible light range, therefore TiO2 nanotubes shows the visible-light photo-performance. Activity performance on photocatalytic decontamination of RhB at ambient temperature demonstrates that Zn-TNTs offer considerable boosted catalytic performance compared with untreated tubular TiO2 during the illumination of visible light. RhB (10 mg L-1) degradation of around 95% was achieved at 120 min. Radical scavenger experiment demonstrated that when electron (e-) or holes (h+) scavengers are introduced to the photodegradation process, the assessment of decontamination efficacy decreased by 45% and 76%, respectively. This demonstrates a more efficient engagement of the photoexcited electrons over photogenerated holes in the photodegradation mechanism. Furthermore, there seems to be no significant decrease in the activity of the Zn-TNTs after five consecutive runs. As a result, the fabricated Zn-TNTs composite has a high economic potential in the energy and environmental domains.

Nd-Doped ZnO Nanostructures with Enhanced Photocatalytic Performance for Environmental Protection.

Neodymium (Nd)-doped ZnO nanostructures with different amounts of Nd were obtained by the electrospinning-calcination method. X-ray diffraction measurements indicated that the prepared nanostructures have a wurtzite structure without undesirable impurities. Nd doping changes the mean crystallite size as well the lattice strain, as proved by Williamson-Hall plots. The ZnO-based nanostructures were tested as photocatalysts for methylene blue (MB) dye and ciprofloxacin (CIP) drug pollutant degradations under visible light irradiation. Corroborating the obtained results, it was found that the reaction rate constant increased almost linearly with the mean crystallite size (from 2.235 × 10-2 to 3.482 × 10-2 min-1) with a variation in the mean crystallite size from 24.2 to 42.1 nm. Furthermore, the best catalyst sample (0.1% Nd-doped ZnO) was used to optimize the photodegradation process of ciprofloxacin, taking into account the pollutant concentration as well as the catalyst dose. The removal efficiency after 120 min was about 100%, with the rate constant of k = 5.291·10-2 min-1 (CIP) and k = 4.780·10-2 min-1 (MB) for the established optimal conditions. Considering the value of the rate constant, the half-life of the reaction (τ1/2 = ln2/k) was evaluated to be about τ1/2 =13 min for CIP and 14.5 min corresponding to MB. Several catalytic cycles were successfully performed without any loss of photocatalytic activity using these nanostructures, demonstrating that the obtained nanostructures have good stability in the leaching processes.

Influence of Ag size and shape in dye photodegradation using silver nanoparticle/ZnO nanohybrids and polychromatic light

In this work, we propose zinc oxide (ZnO) surface functionalization with plasmonic silver nanoparticles (AgNP) of different sizes and shapes (spheres, prisms, and rods) creating ZnO/AgNP nanohybrids. These were characterized by UV-Vis spectroscopy, X-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectroscopy, diffuse reflectance spectroscopy, and photoluminescence spectroscopy. Surface functionalization with AgNP improved photocatalyst electronic properties, its visible light absorption, and slow electron/hole recombination on the ZnO surface. Photocatalysis assays performed with a polychromatic Hg lamp degraded methyl orange, a model of persistent organic pollutant in water. A systematic study showed that the photodegradation kinetics of the nanohybrids are significantly more efficient than pure ZnO (up to 18 times) and that AgNP size and especially its shape are important in dye degradation. Mechanistic studies revealed that degradation occurred by direct dye reduction on the ZnO surface holes, ZnO electron transfer to Ag followed by •O2- formation, and direct injection of AgNP hot electrons in the ZnO conduction band. The last effect was stronger for anisotropic AgNP, which explains their high kinetic degradation rates. Therefore, the rational design in ZnO/AgNP nanohybrid engineering and a systematic approach used in this manuscript allowed a detailed description of photodegradation process that occur at ZnO/AgNP interface. Our results are not conclusive about AgNP size; on the other hand, it clearly demonstrates that anisotropic nanoparticles (as Ag rods and prims) present superior photodegradation efficiency and are promising particles for further large-scale use of solar-irradiated nanohybrids.

Iron oxide nanoparticles derived from Chlorella vulgaris extract: Characterization and crystal violet photodegradation studies

Nanoparticles were first used a century ago, but have recently gained popularity due to their ease of use, eco-friendliness, pollution-free nature, nontoxicity and low cost for wastewater treatment applications. In terms of nanoparticles preparation, green synthesis is a more convenient, economical, quick, and environmentally friendly process than traditional synthesis (i.e. chemical and mechanical) methods. The objective of this study was to synthesise iron oxide nanoparticles from iron (III) chloride using microalgae (Chlorella vulgaris) extract for photodegradation of crystal violet (CV) dye. Various characterization methods such as X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and Fourier-transform infrared spectroscopy (FTIR) were used to examine properties of the nanoparticles including its crystallinity, morphologies and sizes, and functional groups, respectively. The CV photodegradation process was carried out under different process conditions included initial CV concentration (10 mg/L – 25 mg/L), CV solution pH (5.39 – 8.98), and irradiation period (30 – 90 mins) to investigate the optimum operating conditions for the CV removal. The analysis using FESEM demonstrated that the nanoparticles exhibited irregularities and cylindrical shapes, measuring 109 nm in size. Meanwhile, the XRD analysis indicated that the iron oxide nanoparticles possessed a tetragonal crystal structure. The presence of Fe-O stretching vibrations at 486 cm-1 was confirmed by the FTIR spectrum. In terms of CV photodegradation studies, the optimum operating conditions for CV removal using iron oxide nanoparticles were determined to be at initial CV concentration of 10 mg/L, solution pH of 8.98, and an irradiation period of 90 mins, with a percentage removal of 96.21 %.

Boosting photocatalytic activity of single metal atom oxide anchored on TiO2 nanoparticles: An efficient catalyst for photodegradation of pharmaceutical pollutants

The distribution of active sites across the surface of a catalyst can help alleviate issues with mass transfer and improve atom economy. To create such a precise catalyst, this work reports the high loading of a single metal (tungsten/nickel) atom oxide anchored on the surface of TiO2 nanoparticles (WNiTiR) through a simple sonication method. According to aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), tungsten/nickel atoms are distributed uniformly over TiO2 and reduced graphene oxide (rGO). The photodegradation process was optimized by investigating the impact of different catalysts, dosage variations, and the pH of the reaction medium. Remarkably, the WNiTiR nanocomposites demonstrated increased photocatalytic activity by degrading over 97.15% of Ibuprofen (IBF) and 98.35% of Ciprofloxacin (CF) pollutants. The findings of the experiment on reactive oxygen species (ROS) showed that the predominant active species were superoxide radicals (O2•-). In addition, the WNiTiR nanocomposite displayed superior structural stability and reusability even after being put through six cycles of continuous use.

Carbon/Mn3O4/SrTiO3 microsphere photocatalyst for the efficient removal of high‐concentration methylene blue from water

AbstractBACKGROUNDWith the development of the textile and dye industry, a large amount of dye wastewater has been discharged. Semiconductor photocatalysis has been widely used in the treatment of environmental pollution, so it is very important to study efficient, nontoxic and stable photocatalysts.RESULTSIn this study, a microspherical activated carbon/Mn3O4/SrTiO3 composite photocatalyst with high catalytic activity was synthesized using sol–gel and chemical precipitation methods. The photocatalyst was characterized through X‐ray diffraction, scanning and transmission electron microscopy, energy dispersive spectroscopy, X‐ray photoelectron spectroscopy, photoluminescence, Electrochemical impedance spectroscopy, electron paramagnetic resonance spectroscopy and photocurrent measurements, and the effects of the initial methylene blue (MB) concentration and pH on the catalytic performance of the photocatalyst were investigated. The results revealed that the MC/Mn3O4/SrTiO3 composite has large light absorbance, and it can effectively inhibit photoinduced electron–hole pair recombination. The catalyst exhibited high photocatalytic degradation activity, and the degradation efficiency of MB at 300 ppm and pH 7 reached 99% after 80 min of UV light irradiation. The photodegradation process conformed to the pseudo‐first‐order kinetic model. Recyclability experiments showed that MC/Mn3O4/SrTiO3 composite has high stability, and the degradation rate of MB is > 70% after three repeat uses.CONCLUSIONSThis work provides a new method for finding low‐cost, high‐performance materials that can be modified and put into industrial use. © 2023 Society of Chemical Industry (SCI).

Investigation of the simultaneous interactions of experimental variables and mechanism pathway in the photodegradation of methylene blue by binary ZnO/Cu2O photocatalyst

The pollution of water suppliers by various organic compounds, especially synthetic dyes, has been known as a critical global risk. An efficient removal technology is a heterogeneous photocatalysis based on the illumination of semiconducting materials, especially as coupled systems and on the nanoscale. This work synthesized and coupled ZnO and Cu2O nanoparticles (NPs) to enhance the photocatalytic activity due to the decreased electron/hole (e/h) pairs recombination. The pHpzc values of 8.5, 8.0, and 8.4 were estimated for ZnO, Cu2O, and Cu2O-ZnO samples. In the response surface methodology (RSM) study of methylene blue (MB) photodegradation, a significant model was confirmed based on model F-value of 55.8 > F0.05, 14, 15=3.18 and a lack-of-fit (LOF) of 2.52 < F0.05, 10, 5 =4.77. All correlation coefficients (R2 = 0.9812, the adjusted R2 = 0.9636, and the predicted R2 = 0.9109) are close to each other and unity. The optimal conditions run included pH 3, an illumination time of 45 min, and a binary catalyst dose of 0.55 g/L. In the presence of Na2CO3, ascorbic acid, Na2SO4, and NaCl, the initial degradation efficiency of 50.9% (in the absence of any scavenger) was decreased to 31.9%, respectively 36.3%, 39.7%, and 44.4%, respectively, within an irradiation time of 30 min. This order confirms the hydroxyl radicals, superoxide radicals, free electrons, and finally, the holes have relative importance in MB photodegradation process. Based on the results, a direct Z-scheme mechanism was suggested for the MB photodegradation. The direct Z-scheme is a favor to produce more hydroxyl and superoxide radicals as the main centers of MB photodegradation by the proposed system. The recovery percentages of 48, 45, 43, and 39% were obtained for the first to fourth reusing runs, respectively. The catalyst holds above 81% of its initial activity after four reusing runs, which is satisfactory.

One-step chemically vapor deposited hybrid 1T-MoS2/2H-MoS2 heterostructures towards methylene blue photodegradation

The photocatalytic degradation of methylene blue is a straightforward and cost-effective solution for water decontamination. Although many materials have been reported so far for this purpose, the proposed solutions inflicted high fabrication costs and low efficiencies. Here, we report on the synthesis of tetragonal (1T) and hexagonal (2H) mixed molybdenum disulfide (MoS2) heterostructures for an improved photocatalytic degradation efficiency by means of a single-step chemical vapor deposition (CVD) technique. We demonstrate that the 1T-MoS2/2H-MoS2 heterostructures exhibited a narrow bandgap ∼ 1.7 eV, and a very low reflectance (<5%) under visible-light, owing to their particular vertical micro-flower-like structure. We exfoliated the CVD-synthesised 1T-MoS2/2H-MoS2 films to assess their photodegradation properties towards the standard methylene blue dye. Our results showed that the photo-degradation rate-constant of the 1T-MoS2/2H-MoS2 heterostructures is much greater under UV excitation (i.e., 12.5 × 10−3 min−1) than under visible light illumination (i.e., 9.2 × 10−3 min−1). Our findings suggested that the intermixing of the conductive 1T-MoS2 with the semi-conducting 2H-MoS2 phases favors the photogeneration of electron-hole pairs. More importantly, it promotes a higher efficient charge transfer, which accelerates the methylene blue photodegradation process.

Facile synthesis of reusable Ag/TiO2 composites for efficient removal of antibiotic oxytetracycline under UV and solar light irradiation

BackgroundsIn this work, Ag-doped TiO2 nanomaterials (TiAgx, where x denotes the weight percentage of Ag) were prepared using a facile one-step sol-gel technique. The combination of Ag with TiO2 promises to enhance the lifetime of photogenerated electron-hole pairs and widen the photocatalytic activity in the visible light region, leading to improved photocatalytic activity. MethodsThe synthesized materials were characterized using different analyses and afterwards applied as photocatalysts to degrade oxytetracycline (OTC) in aqueous solution under ultraviolet (UV) and solar light illumination. Significant findingsThe highest photocatalysis was achieved for TiAg2 with 99.6% OTC removal after 120-min UV irradiation. Moreover, the best OTC removal under solar light irradiation was gotten for TiAg5, of which 94.1% of OTC was removed after 180 min. Reactive species of ∙O2− radicals were presented as the dominant agents in OTC oxidization; meanwhile, ∙OH and h+ contributed to the photodegradation process. The mineralization efficiency of OTC using TiAg2 reached 59.6% after 240-min UV irradiation. Furthermore, the OTC removal of TiAg2 by photocatalysis still maintained over 97% after 5 cycles.

GCN/CuFe2O4/SiO2 photocatalyst for photo-Fenton assisted degradation of organic dyes

Using a facile hydrothermal synthesis approach hybrid ferrite composites were fabricated, and characterized via FTIR, XRD, XPS, SEM with elemental mapping, TEM, BET UV–vis DRS, and PL studies. The photodegradation ability of the synthesized bare and GCN/CuFe2O4/SiO2 nanocomposites (with different wt.% of GCN) was inspected against toxic dyes viz. MO and RhB beneath visible light illumination. Photo-Fenton assisted S-scheme GCN/CuFe2O4/SiO2 nanocomposite with 10% loading of GCN ((10%)GCN/CuFe2O4/SiO2) demonstrated much-enhanced photoactivity compared to bare CuFe2O4 and GCN. Similarly, the addition of H2O2 in photocatalytic reactions has increased the production rate of .OH radicals which ultimately has increased the MO and RhB degradation rate. Photocatalytic studies also validated that all fabricated composites followed pseudo-first order kinetics. For hybrid composite with 10% loading of GCN, the MO degradation rate was found about 4.82 times and 6.14 times higher than pristine CuFe2O4 and GCN samples while for RhB, degradation rate was 5.31 times and 7.02 times greater. The enhanced photocatalytic activity was credited to the S-scheme heterostructure which extended visible light adsorption, minimized photocarriers recombination rate, and provided high redox capability of further photocatalytic reaction in heterostructure (10%)GCN/CuFe2O4/SiO2. PL and EIS analysis validated enhanced charge separation and migration in (10%)GCN/CuFe2O4/SiO2. Fabricated hybrid ferrite composite also revealed strong chemical stability even after 10 cycles. Radical trapping and ESR experiments validated that generated e−, ∙OH, h+ and ∙O2− proficiently played a main role in the photodegradation process.