Preparation of Highly Efficient CoFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/Zn<Subscript>2</Subscript>SnO<Subscript>4</Subscript> Composite Photocatalyst for the Degradation of Rhodamine B Dye from Aqueous Solution

CoFe₂O₄/Zn₂SnO₄ composite was synthesized using a simple two-step process and applied as a novel-efficient photocatalyst for the rhodamine B degradation from aqueous solution. Characterization techniques such as X-ray diffraction (XRD), N₂ adsorption-desorption isotherms, scanning electron microscopy (SEM), EDS analysis, and diffuse reflectance spectroscopy were employed in order to investigate the physical and chemical properties of composite. Higher values of the specific surface area, pore volume and diameter, and a smaller band-gap energy promoted a greater catalytic activity of CoFe₂O₄/Zn₂SnO₄ composite when compared to Zn₂SnO₄. A rapid decolorization of dye solution was observed at 40 min of reaction using the CoFe₂O₄/Zn₂SnO₄ catalyst, being 2.5 times faster than the Zn₂SnO₄ alone. Therefore, the CoFe₂O₄/Zn₂SnO₄ composite shows extraordinarily high photocatalytic activity toward the degradation of rhodamine B dye from aqueous solution.     

Improved Photodegradation Efficiency of 2,4-DCP Through a Combined Q<Subscript>3</Subscript>Fe(III)-Decorated Porous g-C<Subscript>3</Subscript>N<Subscript>4</Subscript>/H<Subscript>2</Subscript>O<Subscript>2</Subscript> System

Graphitic carbon nitride (g-C₃N₄) is a photocatalyst with wide application in removal of organic pollutants. In this study, we designed a porous g-C₃N₄ (p-g-C₃N₄)/8-quinolinolato iron(III) (Q₃Fe)/H₂O₂ system to enhance the organic pollutant removal efficiency by combining photocatalysis and Fenton interaction under neutral condition. The p-g-C₃N₄ was prepared through a two-step thermal oxidation reaction. Afterwards, Q₃Fe-coupled p-g-C₃N₄ was prepared by an impregnating method. The 2,4-dichlorophenol (2,4-DCP) photodegradation ratio and decomposition rate of the p-g-C₃N₄/Q₃Fe/H₂O₂ system are approximately 5 and 18 times as high as those of individual p-g-C₃N₄ system, respectively. Besides, its degradation rate is 4.3 times as high as that in the p-g-C₃N₄/H₂O₂ system. Meanwhile, Q₃Fe/g-C₃N₄ also exhibits higher activity than individual p-g-C₃N₄ in 2,4-DCP photo-decomposing. On the basis of the results of the radical trapping experiments and the Fe(II) concentration in different systems, the synergistic effect between photocatalysis and Fenton reaction is vital for the efficient pollutant degradation. The coupled system combining p-g-C₃N₄ with Q₃Fe and H₂O₂ shows potential for efficient treatment of recalcitrant organic pollutants. The combined system in this work indicated a new idea for the decomposition of organic pollutants.     

A Stable Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/Expanded Perlite Composite Catalyst for Degradation of Rhodamine B in Heterogeneous Photo-Fenton System

A stable and efficient Fe₂O₃/expanded perlite (Fe₂O₃-Ep) composite catalyst was synthesized by a simple hydrothermal method for degradation of refractory contaminants in heterogeneous photo-Fenton system. X-ray diffraction and FT-IR analyses confirmed the presence of the Fe₂O₃ in the synthesized catalyst. The catalytic activity of the Fe₂O₃-Ep catalyst was evaluated by the degradation of rhodamine B (RhB, 5 mg/L) and metronidazole (MET, 5 mg/L) in the presence of H₂O₂ under visible light irradiation. The Fe₂O₃-Ep catalyst exhibited high efficiency for degradation of RhB at a wide pH range from 2 to 10 and showed excellent catalytic property for decomposition of MET as well. The degradation ratio of RhB was achieved 99%, and the removal ratio of COD was 62% within 90 min at the best experimental conditions (0.5 g/L of Fe₂O₃-Ep catalyst, 2 mL/L of H₂O₂). Furthermore, iron leaching of the Fe₂O₃-Ep catalyst during the catalytic degradation reaction was negligible and the catalyst still exhibited high catalytic activity and stability after five cycles. These results show that the catalyst can be used as a highly efficient heterogeneous photo-Fenton catalyst for the degradation of non-biodegradable refractory pollutants in water.     

Porous Materials Modified with Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles for Arsenic Removal in Drinking Water

The contamination of drinking water with arsenic has been a problem in a lot of countries around the world because of its toxicological and carcinogenic effects on human health. Porous materials modified with Fe₃O₄ nanoparticles (Fe₃O₄ NPs) represent convenient removers for that contaminant. A co-precipitation method of Fe(III) and Fe(II) in alkaline media was applied to obtain Fe₃O₄ NPs. In a first stage, single nanoparticles were synthesized and stabilized with carboxylic acids. A characterization with attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Raman spectroscopy, and X-ray diffraction (XRD) confirms a magnetite-type structure. Moreover, transmission electron microscopy (TEM) and calculations from XRD data using Scherrer’s equation indicate an average particle size of 13 nm and an average crystallite size of 10 nm, both independent of the stabilizer used. Then, the co-precipitation method studied was applied to modify kaolin, bentonite, diatomite, and silica and thus prepare magnetic composites having support-magnetite weight ratios of 2:1. Among them, silica-modified material presented the best hydraulic characteristics, an important aspect for large-scale applications such as removal under gravity. This composite has the capacity to remove up to 80 and 70% for initial concentrations of 25 and 50 μg/L, respectively, representing a convenient remover for processes developed in subsequent stages or in continuous flow.     

Solar Decolorization of Methylene Blue by Magnetic MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript>-MWCNT/Ag<Subscript>3</Subscript>VO<Subscript>4</Subscript> Visible Active Photocatalyst

MgFe₂O₄-MWCNT/Ag₃VO₄ photocatalyst was prepared for benefiting the visible region of solar spectrum. Prepared catalyst was characterized by using scanning electron microscope (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDX). Photocatalytic activity was measured by methylene blue (MB) decolorization under visible light obtained from a 105-W tungsten light bulb. Dye decolorization and its kinetics were followed up by means of a UV-vis spectrophotometer. Kinetic model of decolorization was found to be compatible with first-order kinetics. The effects of pH and concentration of MB solution on the decolorization efficiency were determined. Low and high pH conditions were found to be more effective in increasing the MB decolorization yield and rate. On the other hand, due to the low transparency of concentrated MB solutions, an increase on decolorization time and a lowering in decolorization yield were encountered. Thanks to the magnetic MgFe₂O₃ nanoparticles, 96% of the catalyst could be recovered by a simple magnetic bar. It was observed that simulated wastewater containing MB was also successfully decolorized showing that visible region-sensitive MgFe₂O₄-MWCNT/Ag₃VO₄ photocatalyst can be benefited as a potential, efficient, and reusable material for the removal organic pollutants in aquatic environment.     

Changes in the system of chemical bonds in gibbsite under the impact of NH<Subscript>4</Subscript>H<Subscript>2</Subscript>PO<Subscript>4</Subscript> solutions of different concentrations

The participation of anionic aluminum hydroxo complexes in the binding of phosphate anions on the surface of gibbsite has been shown. The succession of changes in the anionic aluminum phosphate complexes under increasing concentration of phosphate solution has been studied. It has been found that aluminum polyphosphate complexes responsible for the intensive dissolution of gibbsite are formed, along with aluminum orthophosphate complexes, at phosphate solution concentrations of 1 and 2 mol P/L. The decisive role of polyphosphate (P–O–P) groups in the ligand structure of anionic complexes in the transformation of gibbsite to a phosphate mineral (ammonium taranakite) has been revealed. The role of hydrogen bonds with the participation of ligand P(O)OH groups in the formation of ammonium taranakite crystals has been discussed.     

Activated Biochar Prepared by Pomelo Peel Using H<Subscript>3</Subscript>PO<Subscript>4</Subscript> for the Adsorption of Hexavalent Chromium: Performance and Mechanism

Adsorption of hexavalent chromium (Cr(VI)) using pomelo peel activated biochar (PPAB) as a adsorbent was investigated. The characterization of the adsorbent was studied by Brunauer-Emmett-Teller (BET), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and zeta potentials analysis. The results showed that the PPAB had a high microporous structure and the existence of organic compounds such as hemicellulose, cellulose, and lignin. Various parameters including initial Cr(VI) concentration, pH, and adsorbent dosage were studied. The results indicated that the adsorption process was pH dependent and maximum adsorption capacity of Cr(VI) was 57.637 mg/g at pH 2.0 and 35 °C with PPAB dosage of 0.05 g. The adsorption kinetics fitted well to the pseudo-second-order model and the correlation coefficients were greater than 0.999. The adsorption isotherm data could be better described with the Langmuir model, suggesting the homogeneous and monolayer adsorption. Moreover, the scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), and Fourier transform infrared spectrum (FTIR) results showed that the surface of PPAB had plenty of developed pores after activation and the modification process was deemed to proceed between the O–H groups from pomelo peel and H₃PO₄ molecules. The main adsorption mechanism was attributed electrostatic interaction and ion exchange between the surface of PPAB and Cr(VI).     

Effectiveness of Air,N<Subscript>2</Subscript> (gas), Fe<Superscript>+3</Superscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> Nanoparticles on the Sonication of Less and More Hydrophobic Polycyclic Aromatic Hydrocarbons (PAHs) and Toxicity

In this study, the effects of 1 h aeration, nitrogen gas N₂(g) sparging (15 and 30 min) and increasing ferric ions (Fe⁺³) as FeSO₄ (10, 20 and 50 mg L⁻¹) and Fe₃O₄ nanoparticles (1, 2 and 4 g L⁻¹) concentrations on three less hydrophobic and three more hydrophobic polycyclic aromatic hydrocarbons (PAHs) and toxicity removals from a petrochemical industry in Izmir (Turkey) were investigated in a sonicator with a power of 650 W and an ultrasound frequency of 35 kHz; 1 h aeration increased the yields in benzo[b]fluoranthene, benzo[k]fluoranthene and benzo[a]pyrene PAHs (less hydrophobic) from 62% to 67% to around 95–97% after 150 min sonication at 60°C. However, 1 h aeration did not contribute to the yields of more hydrophobic PAHs (indeno[1,2,3-cd]pyrene, dibenz[a,h]anthracene, benzo[g,h,i]perylene). The maximum yields were obtained at acidic and alkaline pH for more and less hydrophobic PAHs, respectively, after 60 and 120 min sonication at 30°C; 30 min N₂(g) sparging, 50 mg L⁻¹ Fe⁺³ increased the yields of less hydropobic PAHs after 150 min sonication at 60°C. Two milligrams per liter of Fe₃O₄ nanoparticles increased both less (87–88%) and more (96–98%) hydrophobic PAH yields. The Daphnia magna acute toxicity test showed that the toxicity decreased significantly with an hour aeration, 30 min N₂(g) sparging, 50 mg L⁻¹ Fe⁺³ and 2 g L⁻¹ Fe₃O₄ nanoparticles at 60°C after 120 and 150 min sonications. Vibrio fischeri was found to be more resistant to the sonicated samples than D. magna. Significant correlations were found between the physicochemical properties of sonicated PAHs and acute toxicities both organisms.     

Efficient Photocatalytic Reduction of CO<Subscript>2</Subscript> Present in Seawater into Methanol over Cu/C-Co-Doped TiO<Subscript>2</Subscript> Nanocatalyst Under UV and Natural Sunlight

Photocatalytic reduction of CO₂ in seawater into chemical fuel, methanol (CH₃OH), was achieved over Cu/C-co-doped TiO₂ nanoparticles under UV and natural sunlight. Photocatalysts with different Cu loadings (0, 0.5, 1, 3, 5, and 7 wt%) were synthesized by the sol–gel method and were characterized by XRD, SEM, UV–Vis, FTIR, and XPS. Co-doping with C and Cu into TiO₂ remarkably promoted the photocatalytic production of CH₃OH. This improvement was attributed to lowering of bandgap energy, specific catalytic effect of Cu for CH₃OH formation, and the minimization of photo-generated carrier recombination. Co-doped TiO₂ with 3.0 wt% Cu was found to be the most active catalyst, giving a maximum methanol yield rate of 577 μmol g-cat^?1 h^?1 under illumination of UV light, which is 5.3-fold higher than the production rate over C-TiO₂ and 7.4 times the amount produced using Degussa P25 TiO₂. Under natural sunlight, the maximum rate of the photocatalytic production of CH₃OH using 3.0 wt% Cu/C-TiO₂ was found to be 188 μmol g-cat^?1 h^?1, which is 2.24 times higher than that of C-TiO₂, whereas, no CH₃OH was observed for P25.     

Visible-Light-Induced Photocatalytic Degradation of PAH-Contaminated Soil and Their Pathways by Fe-Doped TiO<Subscript>2</Subscript> 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.     

The effect of moisture on nitrous oxide emissions from soil and the N<Subscript>2</Subscript>O/(N<Subscript>2</Subscript>O+N<Subscript>2</Subscript>) ratio under laboratory conditions

Nitrous oxide (N₂O) contributes to greenhouse effect; however, little information on the consequences of different moisture levels on N₂O/(N₂O+N₂) ratio is available. The aim of this work was to analyze the influence of different soil moisture values and thus of redox conditions on absolute and relative emissions of N₂O and N₂ at intact soil cores from a Vertic Argiudoll. For this reason, the effect of water-filled porosity space (WFPS) values of soil cores of 40, 80,100, and 120% (the last one with a 2-cm surface water layer) was investigated. The greatest N₂O emission occurred at 80% WFPS treatment where conditions were not reductive enough to allow the complete reduction to N₂. The N₂O/(N₂O+N₂) ratio was lowest (0–0.051) under 120% WFPS and increased with decreasing soil moisture content. N₂O/(N₂O+N₂) ratio values significantly correlated with soil Eh; redox conditions seemed to control the proportion of N gases emitted as N₂O. N₂O emissions did not correlate satisfactorily with N₂O/(N₂O+N₂) ratio values, whereas they were significantly explained by the amount of total N₂O+N₂ emissions.     

Influence of Biochar Addition on the Denitrification Process and N<Subscript>2</Subscript>O Emission in Cd-Contaminated Soil

The aim of this study was to investigate the effect of biochar addition on the denitrification process and N₂O emission in Cd-contaminated soil. Four different biochars, i.e., dairy manure and rice straw pyrolyzed at 350 and 550 °C, respectively, were added into a Cd-contaminated soil and incubation experiments were conducted for 8 weeks. Results showed that Cd had an inhibitory effect on denitrifying reductase enzymes and reduced the abundance of functional genes. On the contrary, amendment with the biochars increased denitrifying enzyme activity and gene abundance, and thus, enhanced the denitrification process. Labile carbon (C) in the biochar-amended soil, which was calculated based on the two-pool exponential model, was the key factor to facilitate this process. As a less important factor, elevated soil pH by biochar addition also increased denitrifying activity as well as the nosZ abundance. Decrease of Cd bioavailability by the biochar addition was beneficial to the denitrification process. Addition of the biochars with higher amount of NO₃ ^?-N, especially the rice straw-derived biochars, increased cumulative N₂O emission by more than ten times relative to the Cd-contaminated soil. With the great amount of labile C and NO₃ ^?-N, the treatment of biochars prepared at 350 °C released the larger amount of CO₂ and N₂O than other treatments. The biochar addition could totally release the heavy metal stress and restore the Cd-contaminated soil in terms of bacterial community.     

Increases in soil CO<Subscript>2</Subscript> and N<Subscript>2</Subscript>O emissions with warming depend on plant species in restored alpine meadows of Wugong Mountain,China

Purpose

Ecosystem restorations can impact carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions which are important greenhouse gasses. Alpine meadows are degraded worldwide, but restorations are increasing. Because their soils represent large carbon (C) and nitrogen (N) pools, they may produce significant amounts of CO₂ and N₂O depending on the plant species used in restorations. In addition, warming and N deposition may impact soil CO₂ and N₂O emissions from restored meadows.

Materials and methods

We collected soils from degraded meadows and plots restored using three different plant species at Wugong Mountain (Jiangxi, China). We measured CO₂ and N₂O emissions when soils were incubated at different temperatures (15, 25 or 35 °C) and levels of N addition (control vs. 4 g m^?2) to understand their responses to warming and N deposition.

Results and discussion

Dissolved organic C was higher in restored plots (especially with Fimbristylis dichotoma) compared to non-restored bare soils, and their soil inorganic N was lower. CO₂ emission rates were increased by vegetation restorations, decreased by N deposition, and increased by warming. CO₂ emission rates were similar for the three grass species at 15 and 25 °C, but they were lower with Miscanthus floridulus at 35 °C. Soils from F. dichotoma and Carex chinensis plots had higher N₂O emissions than degraded or M. floridulus plots, especially at 25 °C.

Conclusions

These results show that the effects of restorations on soil greenhouse gas emissions depended on plant species. In addition, these differences varied with temperature suggesting that future climate should be considered when choosing plant species in restorations to predict soil CO₂ and N₂O emissions and global warming potential.

     

Different ways in which CO<Subscript>2</Subscript> can be released during the turnover of roots in soil

Here, we investigated how root age and mode of death influenced their subsequent turnover and rate of C loss from soil. Young white-coloured and older pigmented roots of Cistus monspeliensis were excised (to simulate death by mechanical severance) or frozen (to simulate death by cell rupture) and immediately buried in soil. CO₂ loss from soil was then measured over time. In a parallel experiment, the rate of CO₂ loss from severed or ruptured roots in the absence of soil was determined. Our results revealed large differences in root chemistry related to age, with young roots having a lower C:N ratio and a greater nutrient content (soluble C, N, P and K). Both root age and mode of death resulted in very different temporal patterns of C release from soil. The amount of C lost from soil followed the series: severed white roots (42.6 ± 3.3 mg C) > ruptured pigmented roots (27.7 ± 0.4 mg C) = ruptured white roots (27.1 ± 0.5 mg C) > severed pigmented roots (10.1 ± 1.0 mg C) > soil only (3.0 ± 0.2 mg C). Therefore, depending on the treatment, 7 to 41% of the total root-derived C was lost as CO₂ over the duration of the experiment. Comparison with soil-free treatments revealed that the CO₂ release from the severed roots buried in soil was not associated with microbial breakdown but caused by root-induced autophagy in an attempt to keep themselves metabolically active. Ruptured roots also induced a rapid loss of CO₂ which we ascribe to the diffusive loss of root solutes into the soil and subsequent microbial mineralization. Surprisingly, the rate of C loss from soil was greater from the severed root tips than those that were ruptured. Our results imply two distinct routes of C loss dependent on how roots die, one which bypasses the microbial community and one which flows through it.     

The fungal and bacterial biomass (selective inhibition) and the production of CO<Subscript>2</Subscript> and N<Subscript>2</Subscript>O by soddy-podzolic soils of postagrogenic biogeocenoses

In the humus horizon of soddy-podzolic soils of postagrogenic cenoses and primary forests, the contributions of the fungi and bacteria were determined by the selective inhibition of the substrate-induced respiration (SIR) by antibiotics; the basal (microbial) respiration and the net-produced nitrous oxide (N₂O) were also determined. The procedure of the SIR separation using antibiotics (cycloheximide and streptomycin) into the fungal and bacterial components was optimized. It was shown that the fungi: bacteria ratio was 1.58, 2.04, 1.55, 1.39, 2.09, and 1.86 for the cropland, fallow, and different-aged forests (20, 45, 90, and 450 years), respectively. The fungal and bacterial production of CO₂ in the primary forest soil was higher than in the cropland by 6.3 and 11.4 times, respectively. The production of N₂O in the soils of the primary and secondary (90-year-old) forests (3 and 7 ng N-N₂O/g soil per hour, respectively) was 2–13 times lower than in the postagrogenic cenoses, where low values were also found for the microbial biomass carbon (C_mic), its components (the C_mic-bacteria and C_mic-fungi), and the portion of C_mic in the organic carbon of the soil. A conclusion was drawn about the misbalance of the microbial processes in the overgrown cropland accompanied by the increased production of N₂O by the soil during its enrichment with an organic substrate (glucose).     

Nitrogen Removal and N<Subscript>2</Subscript>O Emission During Low Carbon Wastewater Treatment Using the Multiple A/O Process

With the organic carbon of acetate (SBR-A) and propionate (SBR-P), the effect of organic carbon sources on nitrogen removal and nitrous oxide (N₂O) emission in the multiple anoxic and aerobic process was investigated. The nitrogen removal percentages in SBR-A and SBR-P reactor were both 72%, and the phosphate removal percentages were 97 and 85.4%, respectively. During nitrification, both the NH₄ ⁺-N oxidation rate in the SBR-A and SBR-P had a small change without the influence of the addition of nitrite nitrogen (NO₂ ^?-N). With the addition of 10 mg/L NO₂ ^?-N, the nitrate nitrogen (NO₃ ^?-N) production rate, N₂O accumulation rate and emission factor had increased. At the same time, the N₂O emission factor of SBR-A and SBR-P reactors increased from 2.13 and 0.87% to 4.66 and 2.08%, respectively. During exogenous denitrification, when nitrite was used as electron acceptor, the N₂O emission factors were 34.1 and 8.6 times more than those of NO₃ ^?-N as electron acceptor in SBR-A and SBR-P. During endogenous denitrification with NO₂ ^?-N as electron acceptor, the accumulation rate and emission factor of N₂O were higher than those of NO₃ ^?-N as electron acceptor. High-throughput sequencing test showed that the dominant bacteria were Proteobacteria and Bacteroidetes in both reactors at the phylum level, while the main denitrification functional bacteria were Thauera sp., Zoogloea sp. and Dechloromonas sp. at the genus level.     

Visible-Light-Driven Photocatalytic N-Doped TiO<Subscript>2</Subscript> for Degradation of Bisphenol A (BPA) and Reactive Black 5 (RB5) Dye

Bisphenol A (BPA) and reactive black 5 (RB5) dye are among the most persistent and non-biodegradable contaminants in water which require an urgent need for the development of effective removal method. The ubiquitous existence of both contaminants could interfere with the human health and aquatic environmental balance. Photocatalytic process as one of advanced oxidation processes (AOPs) has shown high performance for degradation of organic compounds to the harmless materials under sensible condition. Therefore, this study aims to develop a visible-light-driven photocatalyst that can efficiently degrade BPA and RB5 present in household water. N-doped TiO₂ were successfully synthesized via simple and direct sol–gel method. The prepared TiO₂ nanoparticles were characterized by field emission scanning microscope (FE-SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Brunauere Emmette Teller (BET) analysis. The incorporation of nitrogen in TiO₂ lattice exhibited excellent optical responses to visible region as revealed by UV–Vis–NIR spectroscopy absorption capability at 400–600 nm. The photocatalytic activity of the N-doped TiO₂ nanoparticles was measured by photocatalytic degradation of BPA and RB5 in an aqueous solution under visible-light irradiations. Degradation of BPA and RB5 was 91.3% and 89.1%, respectively after 360 min illumination. The degradation of BPA and RB5 by N-doped TiO₂ was increased up to 89.8% and 88.4%, respectively under visible-light irradiation as compared to commercial TiO₂ P25. This finding clearly shows that N-doped TiO₂ exhibits excellent photocatalytic degradation of BPA and RB5 under visible irradiation, hence have a promising potential in removing various recalcitrant contaminants for water treatment to fulfill the public need to consume clean water.

Open image in new window

Graphical Abstract ?

     

Effects of O<Subscript>3</Subscript> stress on physico-chemical and biochemical properties and composition of main microbial groups of a soil cropped to soybean

Tropospheric O₃ (ozone) stress can negatively affect forest productivity and crop yields. Yet, relatively little attention has been paid to the effects of O₃ stress on belowground system. Here, a pot experiment was conducted in open top chambers to monitor the response of physico-chemical properties, main microbial groups, and potential enzyme activities of a soil cropped to soybean (Glycine max; a highly sensitive species to O₃) and exposed to background O₃ concentration (45?±?5 ppb, control) and O₃ stress (80?±?10 ppb, O₃+ and 110?±?10 ppb, O₃++) with sampling at branching, flowering, and podding stages. The growth of soybean was significantly inhibited by O₃ stress, which showed significant effects on soil microbial biomass C and pH during the whole growth of soybean at the highest concentration. The O₃++ stress significantly decreased soil pH at flowering stage, and increased soil pH at podding stage; the O₃+ stress and growth stage?×?O₃+ stress showed significant influences on the potential activities of acid phosphomonoesterase, invertase, and amylase. The O₃ stress significantly reduced the abundances of total PLFAs (phospholipid fatty acid), bacterial PLFAs, and AMF (arbuscular mycorrhizal) PLFAs at branching and podding stages. Our results suggest that the main soil microbial groups might be indirectly affected by the O₃ stress through the alteration of soil physico-chemical properties with changes in the potential enzyme activities of soil.     

Determination of root and microbial contributions to the CO<Subscript>2</Subscript> emission from soil by the substrate-induced respiration method

The contributions of root and microbial respiration to the CO₂ emission from the surface of gray forest and soddy-podzolic soils under meadow and forest vegetation were determined in field and laboratory experiments. In the field, a new modification of the substrate-induced respiration (SIR) method was applied. According to this method, the contribution of root respiration was estimated at 41–50% for meadow cenoses and 33% for forest cenoses; similar values were obtained in the course of separate incubation of roots and soil in laboratory (42–57% and 29–32%, respectively) and with the use of the laboratory version of the SIR method (35–40% and 21–31%, respectively). The analysis of difference between the values of root respiration and microbial respiration obtained by the field and laboratory methods for the same experimental plots and the comparison of advantages and disadvantages of these methods made it possible to outline the ways for the further improvement of the field version of the SIR method.     

Removal of trace and major metals by soil washing with Na<Subscript>2</Subscript>EDTA and oxalate

Background, aim, and scope  

Various metals such as cationic metals (Cu, Pb, Zn) and anionic metals (As, Cr) often coexist in real soils, and normal soil washing techniques for the removal of cationic metals with a single-washing reagent make it rather difficult to simultaneously remove all of them. Oxalate could effectively remove anionic As and EDTA could effectively remove the cationic metals, so it was possible to remove all coexisting cationic and anionic metals by washing with the combination of Na₂EDTA and oxalate. The objective of this study was to (1) discuss the possibility of removing five metals, As, Cd, Cu, Pb, and Zn, effectively from the soil by washing with Na₂EDTA-combined oxalate; (2) optimized through the consecutive washing.