Effect Of Photodegradation Research Articles

Photodegradation profiling of nitrendipine: evaluation of active pharmaceutical ingredient, tablets and its altered forms.

Nitrendipine (NTR) is a dihydropyridine drug, which is well-known as a photodegradable pharmaceutical. However, the photochemical reaction of NTR has not been evaluated in detail from now. In this study, we perform the photodegradation profiling of NTR for the elucidation of its photochemical behavior. NTR amounts during ultraviolet light (UV) irradiation were monitored using high performance liquid chromatography (HPLC). NTR was photodegraded almost completely within 24h along with the generation of some photoproducts. Structural determination of two NTR photoproducts were carried out by means of electrospray ionization liquid chromatography tandem mass spectrometry (LC-ESI-MS/MS). Obtained results from this study clarified one novel NTR photoproduct, a nitroso pyridine analogue, in addition to a pyridine analogue. Furthermore, photodegradation pathway of NTR was speculated based on chemical structures of NTR photoproducts to clarify its photochemical behavior. It was proposed that a singlet oxygen molecule might withdraw two hydrogen radicals resulting in the form of a pyridine analogue, and the following reduction of its nitro group might produce a nitroso pyridine analogue. Finally, we evaluated the photostability of NTR tablets and its altered forms, indicating that the change of the dosage form led to a decrease of the photostability of NTR tablets. The obtained results will be helpful for the additional research to evaluate the effect of NTR photodegradation on its own biological activities.

Photodegradation Effect on Electrical and Thermal Performance of Polyaniline‐Montmorillonite Nanocomposites

AbstractPolymer‐clay nanocomposites have attracted significant research interest for more than a decade for various applications. The structural, thermal, and electrical stability of a nanocomposite determines its durability and long‐term application under sunlight and UV photodegradation of dyes, lithium nanopolymer batteries, and petroleum pipeline corrosion protection, in addition to the effect of high temperatures, e.g., in the Sahara. In the present work, the intercalation of montmorillonite clay within the polymer structure was done by organophilization using hexadecyltrimethylammonium bromide. The obtained nanocomposite was characterized in terms of its structural, electrical, and thermal properties using Fourier transform infrared spectroscopy, the four‐pin method, and differential scanning calorimetry, respectively. The effect of photodegradation on polymer nanocomposite properties was assessed under sunlight and UV radiation under laboratory conditions. The obtained results highlighted the good barrier properties of the nanocomposite, attributed to the clay part.

Photodegradation of glyphosate in water and stimulation of by-products on algae growth

Glyphosate is the most widely used herbicide in global agricultural cultivation. However, little is known about the environmental risks associated with its migration and transformation. We conducted light irradiation experiments to study the dynamics and mechanism of photodegradation of glyphosate in ditches, ponds and lakes, and evaluated the effect of glyphosate photodegradation on algae growth through algae culture experiments. Our results showed that glyphosate in ditches, ponds and lakes could undergo photochemical degradation under sunlight irradiation with the production of phosphate, and the photodegradation rate of glyphosate in ditches could reach 86% after 96 h under sunlight irradiation. Hydroxyl radicals (•OH) was the main reactive oxygen species (ROS) for glyphosate photodegradation, and its steady-state concentrations in ditches, ponds and lakes were 6.22 × 10−17, 4.73 × 10−17, and 4.90 × 10−17 M. The fluorescence emission-excitation matrix (EEM) and other technologies further indicated that the humus components in dissolved organic matter (DOM) and nitrite were the main photosensitive substances producing •OH. In addition, the phosphate generated by glyphosate photodegradation could greatly promote the growth of Microcystis aeruginosa, thereby increasing the risk of eutrophication. Thus, glyphosate should be scientifically and reasonably applied to avoid environmental risks.

Biocomposites based on poly(lactic acid)/Aloe Vera/Priplast. Effects of UVA radiation on the crystallization

AbstractBiocomposites based on poly(lactic acid) (PLA), Aloe Vera (AV), and Priplast (Pr), were produced with AV and Pr levels of 5% and 10%, and submitted to UVA radiation for a time interval up to 28 days. Chemical changes were investigated using Fourier transform infrared spectroscopy (FTIR) and the thermal behavior was elucidated using differential scanning calorimetry (DSC); the non‐isothermal crystallization kinetics was modeled using the Pseudo‐Avrami model. FTIR spectra evidenced the formation of chromophore groups resulting from the photodegradation, which it was less intense in biocomposites with 10% Pr. AV addition promoted the cold crystallization, whereas the crystallization rate () displayed higher values for PLA/10%AV, with slight increases in the degree of crystallinity (Xc); while Pr addition decreased the Xc and of PLA, and protected it more intensely against the photodegradation effects. Pseudo‐Avrami model presented R2 ≥ 0.9909 and a low discrepancy between experimental and theoretical data, being adequate to describe the cold crystallization of PLA biocomposites. Summing up, AV and Pr addition protect PLA against the harmful effects of photodegradation, with AV subtly interfering in the crystalline parameters while Pr provides greater amorphicity to PLA biocomposites.

Photoreactivity and phototoxicity of experimentally photodegraded hair melanosomes from individuals of different skin phototypes.

Even though melanin is commonly viewed as natural photoprotectant, the pigment demonstrates residual photoreactivity, which under certain conditions could contribute to UVA-dependent melanomagenesis. Skin melanin is constantly exposed to external stressors, including solar radiation, which could induce photodegradation of the pigment. Although photodegradation of melanin pigments was studied in synthetic models and RPE melanosomes, photochemical and photobiological effects of experimental photodegradation of human skin melanin of different chemical composition remain unknown. In this work, melanosomes isolated from hair of individuals of different skin phototypes (I-III, V) were exposed to high-intensity violet light and its impact on physical and chemical properties of the pigments were analyzed using electron paramagnetic resonance (EPR), spectrophotometry and dynamic light scattering (DLS). Photoreactivity of photodegraded melanins was examined by EPR oximetry, EPR spin-trapping and time-resolved singlet oxygen phosphorescence. Antioxidant potential of the pigments was measured using the EPR DPPH assay. Cellular effect of the exposure of melanosome-loaded HaCaT cells to UV-Vis light was determined by MTT assay, JC-10 assay, and iodometric assay. The data revealed that experimental photodegradation increased photoreactivity of natural melanins, while decreasing their antioxidant capacity. Photodegraded melanin was responsible for higher cell death, a decrease in mitochondrial membrane potential and elevated levels of lipid hydroperoxides.

Synthesis of Tungsten-Cerium Doped Titanium Oxide Nanocatalyst to Remediate Water by the Degradation of Atrazine Herbicide

Tungsten (W) and Cerium (Ce) doped nanoTitanium oxide (TiO2) nanophotocatalyst were prepared by the sol-gel method and their photodegradation effect against atrazine herbicide were investigated. The doping of the nanocatalyst took place at 50 °C within a time interval of 120 minutes. The prepared gel was dried and calcined in the oven at 350 °C for 75 minutes. The XRD result revealed that the synthesized nanocatalyst was 16.7 nm in size with a mostly monoclinic structure. With FTIR spectra, characteristic peaks of TiO2 were found at 516 cm-1, Ti-O-Ce at 1104 cm-1, and W-O with a single bond at 1609 cm-1. Scanning electron microscope analysis revealed the surface morphology of synthesized nanophotocatalyst. The photocatalytic activity of synthesized nanocatalyst was tested on the degradation of atrazine herbicide (ATZ) under visible and UV light in a batch reactor. The efficiency of nanocatalyst was compared for effective utilization. About 46.5 % of photocatalytic activity was observed without UV light irradiation within 120 minutes. The photocatalytic activity of W-Ce co-doped TiO2 to degrade atrazine further increased up to 99.1 % when the solution was irradiated under UV light. Factors like pH, time, and concentration of nanocatalyst were optimized to check the photocatalytic activity of nanocatalyst on ATZ. It was concluded that nanocatalyst showed an efficient photocatalytic degradation at pH 6 within 120 mins time interval after exposure to UV light.

Environmental Applications of 3D g-C3N4-Based Hydrogel with Synergistic Effect of Adsorption and Photodegradation.

In this paper, g-C3N4-based hydrogel with a 3D network structure was synthesized via a simple and cheap reaction, using hydroxyethyl cellulose (HEC) and graphitic carbon nitride (g-C3N4) as the main materials. Electron microscope images revealed that the microstructure of g-C3N4-HEC hydrogel was rough and porous. The luxuriant scaly textures of this hydrogel were due to the uniform distribution of g-C3N4 nanoparticles. It was found that this hydrogel showed great removal ability of bisphenol A (BPA) through a synergistic effect of adsorption and photodegradation. The adsorption capacity and degradation efficiency of g-C3N4-HEC hydrogel (3%) for BPA were 8.66 mg/g and 78% under the conditions of C0 = 9.94 mg/L and pH = 7.0, which were much higher than those for the original g-C3N4 and HEC hydrogel. In addition, g-C3N4-HEC hydrogel (3%) exhibited excellent removal efficiency (98%) of BPA (C0 = 9.94 mg/L) in a dynamic adsorption and photodegradation system. Meanwhile, the mechanism of removal was investigated in depth. The superior batch and continuous removal capability of this g-C3N4-based hydrogel make it promising for environmental applications.

Photodegradation and Its Effect on Plant Litter Decomposition in Terrestrial Ecosystems: A Systematic Review

Photodegradation is an important mechanism that affects carbon and nutrient cycling; a significant amount of data has been reported previously. The present review includes the effect of a wider spectrum of solar radiation (sun light, UV, and visible light) on plant litter decay in terrestrial ecosystems. Although the positive effect of photodegradation on decomposition is most common, a substantial number of studies reports contrasting results. Litter from 148 plant species, from 41 families, have been used in photodegradation studies, representing functional groups of trees (33%), graminoids (30%), shrubs (23%), forbs (11%), and peat (1%). Although the majority of studies focused on mass loss, a growing number focuses on nutrient release. Positive effects on mass loss are most common across different climate regions and laboratory studies, whereas “positive” influence and “no effect” on nitrogen and lignin release are equally common in temperate and sub-tropical environments. This may potentially be due to other decomposition processes which increase in relevance with increasing moisture and can facilitate microbial activity, leaching, and fractioning by soil fauna. In addition to climate region, initial litter quality influences photodegradation. Field-based and laboratory experiments frequently obtain contrasting results, suggesting that the mechanisms controlling the responses are unclear and might be dependent on several interactions, and/or the differences in experimental approaches (such as UV filters), or coverage by particles. Future research should focus on interactions between different factors, and on conducting experiments that test specific relationships such as the potential interaction between photodegradation, soil moisture, microbial communities, soil fauna, and their effects on litter decomposition (both mass loss and nutrient release). Furthermore, the topic would benefit from international studies applying the same experimental approach, as has successfully been conducted in other fields.

Incorporation of ultrathin porous metal-free graphite carbon nitride nanosheets in polyvinyl chloride for efficient photodegradation

Solid-phase photocatalytic degradation of waste plastics is one of the promising approaches to solve the “white pollution” problem. In this work, a low cost, metal-free, environmentally friendly organic photocatalyst, graphite carbon nitride (g-C3N4), was used for the first time to successfully enhance the photodegradation of polyvinyl chloride (PVC) under simulated sunlight from its visible light photocatalytic capability, while its organic nature and abundant surface functional groups were beneficial for its good dispersion in plastics. It was found that the ultrathin porous g-C3N4 nanosheet synthesized from urea (the UCN sample) had much stronger photodegradation effect in PVC/g-C3N4 composite films than its thick block counterpart synthesized with melamine (the MCN sample) due to its larger specific surface area, higher pore volume, and enhanced photogenerated charge carrier separation. With the incorporation of only 1 wt% UCN sample into PVC, its mechanical properties were largely enhanced with the tensile strength increase of ∼ 45% and the elongation at break increase of ∼ 72%, and its weight loss increased ∼ 58% after 120 h irradiation in the weather resistance test chamber. ·O2- and h+ produced by the UCN sample were found as the main active species in the photocatalytic degradation of PVC to dechlorinate PVC and decompose its long-chain molecules into short-chain small molecules until its final degradation into CO2 and H2O under ideal conditions.

Adsorption and photodegradation of tetracycline by mannose-grafted chitosan composite films: Performance, mechanism and availability

The world faces increase in water scarcity and water pollution. A combined effect of adsorption and photodegradation is potential way to remove pollutants from water. In this work, mannose grafted chitosan (CSMan) films were synthesized due to Schiff base. To improve the adsorption and photodegradation capacity of films, graphite carbon nitride-zinc oxide (gCNMZnO0.3) was introduced into a system through solvent volatilization to remove tetracycline (TC). Comfortingly, the composite films of CSMan-gCNMZnO0.3-1 displayed outstanding adsorption capacity and excellent activity of degrading organic pollutant by visible light in water. The maximum adsorption capacity of CSMan-gCNMZnO0.3-1 was 164.627 mg g−1 through surface complexation, cation exchange, electrostatic attraction, hydrogen bonding, π–π interaction and plane strengthening effect. The analysis revealed that OH and h+ were the crucial radicals in photodegradation process. Meanwhile, CSMan-gCNMZnO0.3-1 possessed superior reusability and broad applicability in five distinct types of water. The simulation experiment of silicone tube showed the combined effect had a removal ratio of 84.3 % in 120 min, and the adsorption-photodegradation efficiency was constant in operating after five continuance usages.

Bacillus thuringiensis Based Ruthenium/Nickel Co-Doped Zinc as a Green Nanocatalyst: Enhanced Photocatalytic Activity, Mechanism, and Efficient H2 Production from Sodium Borohydride Methanolysis

Today, the development of green nanocatalysts is among the popular topics due to the need for energy production and the cleaning of organic pollutants. In this approach, Bacillus thuringiensis, a bacterium, was used as a biosupport of ruthenium/nickel co-doped zinc nanoparticles (btRNZn NPs) to release hydrogen from the methanolysis of sodium borohydride (NaBH4). In addition, their photocatalytic activity was reported against Methyl Orange (MO) organic dye. This study focused on the preparation, characterization, and catalytic and photocatalytic activity of the btRNZn biocatalyst for the release of hydrogen from the methanolysis of NaBH4 and removal of MO dye. According to TEM analysis, the average size of btRNZn NPs was found to be 11.78 nm; in addition, btRNZn NPs showed a photodegradation effect of 68.2% against MO dye at 90 min, and its photocatalytic mechanism was discussed. The effects of the catalyst, substrate, and temperature in the methanolysis reaction of NaBH4 in the presence of the catalyst were investigated extensively. The reaction kinetics was calculated, and TOF, activation energy, and enthalpy energy were measured as 2497.14 h–1, 14.89 kJ/mol, and 12.35 kJ/mol, respectively. It was observed that the methanolysis process is a first-order reaction based on the amount of the catalyst and substrate. This study aimed to synthesize a nanobiocatalyst (btRNZn NPs) by a biological method, and it will be used as a great photocatalyst to prevent wastewater pollution; also, it can be an excellent catalyst to produce hydrogen from NaBH4 methanolysis. The application of btRNZn NPs in solar photocatalysis to prevent wastewater pollution and to research it for energy production through hydrogen creation are both made clear by these studies.

Surface modifying MIL-125(Ti) by devisable poly(amino) conjugate molecule to significantly enhance its visible light photo-degradation properties

A novel core/shell nanocomposite was successfully synthesized through surface coating MIL-125(Ti) with a poly(amino) conjugate molecule (4′,4‴,4⁗′,4⁗‴-(ethene-1,1,2,2-tetrayl)tetrakis([1,1′-biphenyl]-4-amine)) by the facile one-step solvothermal method for improving the photocatalytic properties under visible light. The nanocomposite was detailed characterized through TEM, SEM, XRD, FT-IR, BET, EDS and XPS. Photoelectrochemical characterizations showed that the nanocomposites exhibited lower band gap as well as excellent migration and separation efficiency of photo-generated charges compared with the original MIL-125(Ti). The optimized nanocomposite (TNMT-2) exhibited an excellent photo-degradation effect for a representative organic contaminant tetracycline hydrochloride and the total tetracycline hydrochloride removal efficiency can reach 96.5 % under visible light illumination, and higher removal efficiency was received in practical water treatment. In addition, TNMT-2 nanocomposite showed great reusability, stability, and applicability. Furthermore, the photo-degradation mechanism and the photo-degradation pathways of tetracycline hydrochloride were investigated. The relationship between the photocatalytic properties of the nanocomposite and the structure of the organic molecular were explored, and electron-donating groups as well as large π–π conjugate structure were the two most important factors. This study indicates that by designing the molecular structures, the photocatalytic properties of Ti-based MOFs can be easily regulated and TNMT-2 nanocomposite is an effective visible light catalyst for organic pollutants with great applicable potential.

NATURAL DYE’S PHOTODEGRADATION EFFECT TOWARDS OPTICAL PROPERTIES FOR SOLAR ENERGY APPLICATIONS

Photodegradation effect to natural plant waste under solar irradiation was investigated. Five plants waste namely, Averrhoe Bilimbi, Eugenia Clavifora, Elaies Guineensis, Terminalia cattapa and Clidemia hirta were selected from all over the states. Main purpose of this research was to study the stability of natural dye in presence of sunlight radiation for future solar cell applications. FTIR and UV-Vis absorption were used to investigate the optical properties of dye. Eugenia Clavifora was clearly revealed that it took more than 10 weeks to degrade and required 64% of degradation percentage. Optical energy gap was observed at 2.04 eV before exposure, while 2.15 eV after exposure of sunlight. Efficiency of Eugenia Clavifora hybrid solar cells was leading at the highest performance of 1.33%. This clearly shows that Eugenia Clavifora can be used as a natural photosensitizer thus enhancing the efficiency of any solar cell applications.

3D printing of green and environment-friendly rGO@ZnO/GP for removal of methylene blue from wastewater

In this work, we report the fabrication of geopolymer materials containing different amounts of reduced graphene oxide loaded on zinc oxide (rGO@ZnO/GP) to be used as efficient photocatalysts for the degradation of methylene blue (MB). The synergistic effects of adsorption and photodegradation resulted in a 92.56% removal efficiency of MB within 30 min by a geopolymer containing 56%rGO@ZnO (56%rGO@ZnO/GP). The results showed that the geopolymer matrix provided a reusable carrier for rGO@ZnO, and the presence of rGO could promote the migration of photogenerated electrons and hinder the recombination of charges, thereby enhancing the photocatalytic activity. The best performing material (56%rGO@ZnO/GP) was also used to 3D print a scaffold using Direct Ink Writing technology. The 3D printed 56%rGO@ZnO/GP was also an efficient photocatalyst for the degradation of MB, and the use of a structured catalyst facilitates the recovery of the active material. This work can provide a way for preparing efficient and environmentally friendly photocatalysts.

Removal of methylene blue using a novel generation photocatalyst based on nano-SnO2/wild plumb kernel shell biochar composite

A series of measurement results revealed that the nano-SnO2 (n-SnO2) nanoparticles were spread uniformly on the carbon surface inside the wild plum (Prunus domestica) kernel shell biochar (WPKSB) structure. The addition of hydrothermally synthesized n-SnO2 to WPKS improved both the adsorption capacity and the photocatalytic potential of WPKSB for methylene blue (MB) removal. When the initial MB content was 5 mg/L, the n-SnO2@WPKSB composite demonstrated high MB removal efficiency under UV light via a combined effect of adsorption and photocatalysis. The n-SnO2@WPKSB composite removed 99.5 (±0.4) % of the MB from the dye-polluted water sample in 105 minutes at pH of 7.0. Because of the synergistic effect of adsorption and photodegradation, the composite was more effective at treating the aqueous MB solution than WPKSB and n-SnO2 alone. Reusability tests were run to remove MB to assess the composite structure’s chemical stability and catalytic capacity. The n-SnO2@WPKSB composite was characterized using X-ray Diffraction, Fourier Transform infrared and Scanning Electron Microscopy. This research investigates how to make metal oxide/biochar nanocomposites with exceptional adsorption and photocatalysis properties for the oxidation and removal of MB.

Effects of Photodegradation on the Optical Indices of Chromophoric Dissolved Organic Matter from Typical Sources.

Chromophoric dissolved organic matter (CDOM) plays important roles in aquatic environments, and its optical properties provide a series of indices for evaluating the source and composition of dissolved organic matter (DOM). However, little is known about the varying photodegradation of CDOM from different sources and the effects on the optical indices of DOM composition. This was studied for typical natural and anthropogenic sources (plant and leaf litter leachates, the influent and effluent of a wastewater treatment plant, and a river). The CDOM absorption (a280) showed a lower degradability for the plant leachate than other sources, mainly due to its low molecular weight and aromaticity. Four fluorescent components were identified with excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC), namely benzoic acid/monolignol-like C1, humic-like C2 and C3, and tryptophan-like C4. The plant leachate contained mainly C1, which was photodegraded moderately, while other sources had more C2 and C3 with higher photodegradability. C4 was photodegraded in most sources but was photoproduced in the leaf litter leachate. The absorption slope (S275-295) and slope ratio (SR) increased while the humification index (HIX) decreased, suggesting a decreasing molecular weight and humic content by photodegradation. This was consistent with the decreasing %C2 and %C3 but increasing %C4, which indicated preferential removal of humic-like components. The %C1, %C2, biological index (BIX), and fluorescence index (FI) were less affected by photodegradation than other indices for most sources. These results have implications for a better understanding of the photochemistry of CDOM and the applications of optical indices.

Green Assembly of Covalently Linked BiOBr/Graphene Composites for Efficient Visible Light Degradation of Dyes.

A novel high-performance BiOBr@graphene (BiOBr@G) photocatalyst with a new assembly structure had been demonstrated using a facile hydrothermal method through chemical bonding of reduced graphene oxide and structure-defined BiOBr flakes for improving charge separation and transfer performance, which were first synthesized at room temperature in immiscible solvents without corrosive acids. The prepared samples were characterized, and the BiOBr@G composite realized an efficient assembly portfolio of graphene and BiOBr flakes with defined structures, verified by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Raman and X-ray photoelectron spectroscopy (XPS), in which BiOBr flakes were covalently linked with the assembled graphene sheets through the Bi–C bond. This composite exhibited remarkable visible light absorbance and efficient photoinduced charge splitting characteristics in comparison with those of pure BiOBr, as established by DRS absorption, photoluminescence radiation, and photocurrent study. Hence, a very small amount (5 mg) of the BiOBr@G composite displayed a complete photodegradation effect on the rhodamine B dye under only 15 min of visible light excitation, which was three times faster than that of pure BiOBr and extremely superior to that of commercial P25. This was probably ascribed to the well-defined BiOBr structure itself, elevated light absorbance, and Bi–C chemical bond inducing quick charge separation and transfer in the BiOBr@G composite. Additionally, investigations on the photocatalytic mechanism displayed that the photogenerated holes in the BiOBr valence band and derivative superoxide radicals played vital roles in the photodegradation of RhB dyes, as reinforced by the electron spin resonance method, where the covalent linking of BiOBr and graphene served as an effective pathway for charge transportation.

Establishing a high-speed electron transfer channel via CuS/MIL-Fe heterojunction catalyst for photo-Fenton degradation of acetaminophen

Active pharmaceutical pollution has become “a new force” of water pollution, and a high-efficiency process is urgently required to remove it. Herein, the CuS/MIL-Fe heterojunction catalyst with high-speed electron transfer channel is designed by adjusting the energy band and regulating the direction of electron transfer, which exhibits excellent acetaminophen (APAP) removal ability in photo-Fenton reaction. The charge transfer pathway of heterojunction is identified by X-ray photoelectron spectroscopy analysis and density functional theory (DFT) calculation, which provides the evidence of electron transfer from CuS to MIL-101(Fe) at the heterointerface. Meanwhile, kelvin probe force microscopy measurement indicates that photogenerated electrons can be easily transported through the CuS/MIL-Fe interface. The close contact interface and high charge transfer conductivity realize the synergistic effect of photo and Fenton degradation by establishing high-speed electron transfer channel. This study will open up a new insight into the application of heterojunction photo-Fenton technology in environmental remediation.

Grass species litter have varied trait response to the photodegradation and microbial decomposition in tropical savanna grasslands, South Africa

Purpose of the paper: This paper evaluated the effects of microbial and photodegradation on the ten grass species in a tropical grassland ecosystem in South Africa. Despite continuous necromass accumulation in tropical grasslands, the process that governs how the grass litter gets to the soil has often been ignored. In the absence of fire, abiotic factors and biotic factors are drivers of this process of nutrient cycling. Methods and approaches: A classical litterbag experiment was set up to simulate photodegradation (standing litter) versus microbial (soil surface) decomposition using 10 savanna types of grass from the start of the dry season until the beginning of spring. The rates of photodegradation versus microbial decomposition were compared for tropical savanna grasses and plant traits or predictors of decomposition were also investigated. Main results: The results showed that the grass litter decomposed more rapidly when exposed to the activity of soil microbes at the soil surface (k = 0.0028 ) than when held above ground (k = 0.0018) and subjected to photodegradation only. However, examination of the individual litter species revealed up to 4 fold variation between the slowest (0.0001) and fastest (0.006) decomposing species. Differences in decomposition rates were more pronounced for litter decomposed at the soil surface than held above the soil surface. Multiple linear regression analyses did not resolve clear differences between measures of litter quality as drivers of decomposition in the two treatments. Implications: Photodegradation appeared to be a rate-controlling step during the process of decomposition in tropical savanna grasslands. Therefore grasslands dominated by photodegradation-resistant grasses were likely to need fire to get rid of moribund litter, which may be the reason why mesic grasslands need to burn to recycle nutrients.

ZIF‐8‐Derived ZnO and SnO2 Form ZnO@SnO2 Composites for Enhanced Photocatalysis under Visible Light

AbstractZIF‐8 was used as a precursor and was converted to ZnO by calcining at high temperature to remove the organic functional groups therein. Then ZnO@SnO2 composites were synthesized by hydrothermal method using ZnO as the carrier. All samples were characterized by XRD, SEM, EIS, Transient photocurrent test and Mott‐schottky test. The photodegradation effects of pristine ZnO, SnO2 and ZnO@SnO2 composites on tetracycline (TC) were evaluated and the best results were obtained (ZnO@SnO2=2 : 1), which could remove 91.2 % of TC under visible light irradiation. The effects of pH, ionic strength, and TC concentration were researched in batch experiments. ZnO@SnO2=2 : 1 showed favorable photocatalytic activity and stability, including pH and resistance to ionic strength. The enhanced photocatalytic activity of the ZnO@SnO2=2 : 1 composite could be ascribed to the lower recombination probability of electron‐hole pairs in the heterojunction and the enlarged surface area for TC adsorption during photodegradation. This study provided a reference for heterojunctions with excellent photocatalytic properties.