Organic Carbon Degradation Rate Research Articles

Organic Carbon Reaction Kinetics in Bioturbated Sediments

AbstractMost organic carbon delivered to the seafloor is degraded within the bioturbated layer. Theory and empirical evidence have shown that organic carbon reactivity relates to the age of a particle. However, due to particle mixing, the age‐depth linear relation induced by sediment accretion is obfuscated. Here we combine a Lagrangian particle tracking model that resolves the age distribution of particles in the bioturbated zone and couple it to age‐dependent organic carbon degradation. Depth profiles for organic carbon concentration, reactivity and degradation rate are presented for sediments receiving low and high reactivity organic carbon in coastal, continental slope and deep‐sea environments. Our results show that a simple first‐order kinetics model suffices for well‐mixed sediments and systems receiving pre‐processed materials. A reactive continuum approach is needed for poorly mixed sediments receiving highly reactive organic carbon and for sediments below the bioturbated layer.

Synergistic oxidation of humic acid treated by H2O2/O3 activated by CuCo/C with high efficiency and wide pH range

Combination of oxidation processes are one of the most promising humic acid treatment technologies. Single oxidant or even two oxidants in advance oxidation process can hardly achieve satisfactory removal efficiency of refractory organic matter, mainly humic acid, in the treatment process of reverse osmosis concentrates from landfill leachate. To solve this problem, this study investigated the synergistic degradation of Humic acid (HA) using a Cu and Co supported on carbon catalyst (CuCo/C) in a Hydrogen peroxide (H2O2) with ozone (O3) system. The catalyst was characterized by performing SEM, XRD, BET, XPS and FTIR technologies. UV–vis spectra, 3D Excitation Emission Matrix Spectra (3D-EEM) and gas chromatography-mass spectrometry (GC–MS) were applied for exploring degradation mechanism of HA. To further understand the oxidation mechanism, electron paramagnetic resonance (EPR) was used to evaluate the generation of hydroxyl (·OH) and superoxide radicals (O2·-). As a result, CuCo/C catalyst possessed stable catalytic performance for HA degradation with a wide pH range from 5 to 8, while T = 40 °C，catalyst dosage of 2.4 g/L，O3 intake rate of 0.15 g/min and H2O2 dosage of 1.92 mL/L, the degradation rate of total organic carbon (TOC) achieved 40–46.5 mg·L−1min−1. As affirmed by the EPR, ·OH and O2·- were effectively generated with addition of the CuCo/C catalyst. Degradation performance of UV254 proved that the catalytic activity can still be maintained above 95% with removal rate of 82% after 5 cycles reuse. GC-MS shows that the oxidation products mainly consist of amide, benzoheterocyclic ring and carboxylic acid. This work promotes an effective method for degrading HA, which has the potential for satisfactory application in landfill leachate.

Quality and Biodegradation Process of Dissolved Organic Carbon in Typical Fresh-Leaf Leachate in the Wuhan Urban Forest Park

The study investigated the leaching and biodegradation of dissolved organic carbon in leaf leachates from typical fresh leaves in the Wuhan Urban Forest Park, Central China. The fresh leaf-leached dissolved organic carbon quality and biodegradability, as well as their potential determinants, were examined for 12 major tree species, including deciduous trees and shrubs. A 28-day indoor incubation was conducted at two temperature conditions of 20 °C and 30 °C. Sampling was conducted within the planned time frame for experimental measurements, and a first-order kinetic model for dissolved organic carbon degradation was fitted. The utilization of the fir tree as the predominant deciduous species and cuckoo as the primary shrubs provided advantages in increasing the carbon sequestration capacity of urban forests. There was no significant difference in the degradation rate of the leaching solution at different temperatures, but the k value of the first-order kinetic model was different. At 20 °C, the dissolved organic carbon degradation rate was positively correlated with electrical conductivity and total dissolved nitrogen, while it was negatively correlated with the humification index and ratio of dissolved organic carbon to total dissolved nitrogen. At 30 °C, the degradation rate of dissolved organic carbon showed a positive correlation with total dissolved phosphorus and total dissolved nitrogen, while it was negatively correlated with the humification index, ratio of dissolved organic carbon to total dissolved nitrogen and ratio of dissolved organic carbon to total dissolved phosphorus.

Dual function of magnetic field in enhancing antibiotic wastewater treatment by an integrated photocatalysis and fluidized bed biofilm reactor (FBBR)

The integrated photocatalysis and fluidized bed biofilm reactor (FBBR) is an attractive wastewater treatment technique for managing wastewater containing antibiotics. However, the fast recombination of photoinduced charge and low microbial activity limit the degradation and mineralization efficiency for antibiotics. To address this, we attempt to introduce magnetic field (MF) to the integrated system with B-doped Bi3O4Cl as the photocatalysts to effectively improve removal and mineralization of ciprofloxacin (CIP). As a consequence, the degradation rate reaches 96% after 40 d in integrated system with MF. The biofilm inside the integrated system with MF carrier can mineralize the photocatalytic products, thereby increasing the total organic carbon (TOC) degradation rate by more than 32%. The electrochemical experiment indicates the Lorentz force generated by MF can accelerate charge separation, increasing the electron concentration. Simultaneously, the increased amounts of electrons lead to the generation of more ·OH and ·O2−. MF addition also results in increased biomass, increased biological respiratory activity, microbial community evolution and accelerated microbial metabolism, enabling more members to biodegrade photocatalytic intermediates. Therefore, applied MF is an efficient method to enhance CIP degradation and mineralization by the integrated system.

Characterization of low density polyethylene greenhouse films during the composting of rose residues

This study presents an evaluation of a potential alternative to plastic degradation in the form of organic composting. It stems from the urgent need of finding solutions to the plastic residues and focuses on the compost-based degradation of greenhouse film covers in an important rose exporter company in Ecuador. Thus, this study analyzes the physical, chemical, and biological changes of rose wastes composting, and also evaluates the stability of new and aged agricultural plastic under these conditions. Interestingly, results of compost characterization show a slow degradation rate of organic matter and total organic carbon, along with a significant increase in pH and rise of bacterial populations. However, the results demonstrate that despite these findings, composting conditions had no significant influence on plastic degradation, and while deterioration of aged plastic samples was reported in some tests, it may be the result of environmental conditions and a prolonged exposure to solar radiation. Importantly, these factors could facilitate the adhesion of microorganisms and promote plastic biodegradation. Hence, it is encouraged for future studies to analyze the ecotoxicity of plastics in the compost, as well as isolate, identify, and evaluate the possible biodegradative potential of these microorganisms as an alternative to plastic waste management.

Analysis of the degradation of m-cresol with Fe/AC in catalytic wet peroxide oxidation enhanced by swirl flow

Catalytic wet peroxide oxidation (CWPO) enhanced by swirl flow (SF-CWPO) was developed for the first time to explore the degradation of m-cresol in 3%iron/activated carbon catalysed Fenton reaction. Under the conditions of catalyst dosage of 0.6 g/L, H2O2 dosage of 1.5 mL/L, pH = 6 and reaction time of 20 min, the degradation rate of m-cresol and total organic carbon in 100 mg/L m-cresol solution reaches 81.5% and 82%, respectively. The reaction speed in the SF-CWPO system with an independently designed cyclone reactor was two times faster than the traditional CWPO systems. In addition, via liquid chromatography-mass spectrometry analysis of the degradation product, the possible degradation pathway for m-cresol was proposed. The proposed SF-CWPO can potentially be an efficient and economical method to treat organic pollutants in wastewaters.

The sedimentation, bioturbation and organic matter degradation as revealed by excess 230Th and 210Pb in the Cosmonaut Sea

Sedimentation and bioturbation (the activity of benthic organisms) play an important role in organic matter degradation. The excess 230Th and 210Pb in a sediment core were used to evaluate the sedimentation, bioturbation and organic degradation processes in the Cosmonaut Sea, East Antarctica. Our results show that the sedimentation rate estimated from excess 230Th through the Constant Flux (CF) and Constant Flux and Constant Sedimentation (CFCS) models has changed in the past 200 ka. The mass accumulation and the linear sedimentation rates vary from 0.36 to 0.76 kg m-2 ka-1 and from 0.6 to 1.3 mm ka-1, which are significantly lower than the rates in other Antarctic seas. The stage III (120–202 ka), which corresponds to Marine Isotope Stage (MIS) 6 (glacial period), had the lowest sedimentation rate, indicating less sediment input by sea ice expansion. The bioturbation coefficient estimated by excess 210Pb is as low as 0.023 ± 0.003 cm2 a-1, showing inactive benthic activities. The average C/N ratio of organic matter is 7.2 ± 0.4, which is close to that of fresh organic matter and lower than the typical value of deep-sea sediments, indicating that organic matter is less degraded. The degradation rates of organic carbon and organic nitrogen estimated by the bio-diffusion model are 0.61 ka-1 and 0.29 ka-1, respectively, which are significantly lower than previously reported values for Southern Ocean sites. Despite the low sedimentation rate, low rates of bioturbation and inefficient organic matter degradation are conducive to the preservation of organic matter in sediments of the Cosmonaut Sea.

Development of a compound microbial agent beneficial to the composting of Chinese medicinal herbal residues

This study was aimed at developing a compound microbial agent to facilitate the composting of Chinese medicinal herbal residues (CMHRs). Different microbial agents were inoculated into a mixture of CMHRs, sheep manure, and biochar and composted for 42 days. The results demonstrated that the compound microbial agent (K1 + P1 + N4) inoculated in T1 can extend the thermophilic period during composting. Compared with control check (CK), the total nutrient contents of the vaccinated groups increased by 5.45–28.54%, and T1 had the highest value. The total organic carbon degradation rate and germination index of T1 were 1.95 and 1.03 times higher than those of the control. Moreover, significant increases in the abundance and diversity of the microbial community were also found in T1. Consequently, using K1 + P1 + N4 as a microbial agent for the composting of CMHRs is recommended, and this research provides a new idea to solve the problem of waste of CMHRs.

Ag2O and NiO Decorated CuFe2O4 with Enhanced Photocatalytic Performance to Improve the Degradation Efficiency of Methylene Blue.

Dye wastewater is a serious threat to human health and life. It is an important task for researchers to treat it efficiently. Among many treatment methods, the photo-Fenton method can rapidly degrade organic pollutants. In this study, a ternary photocatalyst, Ag2O-NiO/CuFe2O4, was prepared and applied for a photo-Fenton reaction to degrade methylene blue (MB). MB had the best degradation effect when 10 mg of the catalyst were used in an 80 mL reaction system for measurement. The degradation rate of MB was up to 96.67% in 60 min with a high degradation rate constant . The total organic carbon (TOC) degradation rate was 78.64% with a TOC degradation rate constant of . Therefore, this study fully proves that Ag2O-NiO/CuFe2O4 can catalyze the photo-Fenton reaction and effectively degrade MB.

Degradation of neurotoxin β-N-methylamino-L-alanine by UV254 activated persulfate: Kinetic model and reaction pathways

In this study, the degradation of β-N-methylamino -L-alanine (BMAA; a novel neurotoxin produced by cyanobacteria) in the UV254/persulfate (PS) system was investigated. The degradation of BMAA satisfied the pseudo-first-order kinetic model. Moreover, the effects of reaction parameters (PS concentration, BMAA concentration, and pH) and water matrix (natural organic matter (NOM) and some anions) were evaluated. The second-order rate constants between BMAA and SO4− or OH at pH 7 were 4.75 × 10 9 M −1·s −1 and 5.49 × 10 9 M −1·s −1, respectively, as measured by a competition kinetics experiment. The results of the steady-state kinetics model and scavenging experiments indicated that SO4− was the major radical contributing to BMAA degradation in the UV254/PS system. Moreover, pH significantly affected the degradation rate of BMAA, and the highest rate was obtained at pH 8 with a pseudo-first-order rate constant (kobs) of 1.039 min−1. However, the degradation of BMAA was inhibited in aqueous solution due to the influence of the water matrix. The kobs decreased in the presence of NOM and chloride ions (Cl−) and increased in the presence of bicarbonate (HCO3−). Given that the degradation rate of total organic carbon (TOC) was lower than that of BMAA, the transformation products and a possible degradation pathway were investigated. The C-N bond on BMAA may be attacked by radicals, and BMAA may be transformed into 2,3-diaminopropionic acid or L-alanine. Moreover, BMAA could also be converted to 2-hydroxy-3-methylamino propanoic acid through hydroxylation. Three different BMAA transformants were further oxidized to generate pyruvic acid, after which decarboxylation leads to the formation of acetic acid from pyruvate.

Adsorption and photocatalytic degradation performances of TiO2/diatomite composite for volatile organic compounds: Effects of key parameters

The TiO2/diatomite composites with excellent adsorption and photo-degradation performances were leveraged to investigate the influences of calcination temperature and operating factors on their properties. The results showed that the calcination temperature was closely bound up with the crystallization of TiO2 and the specific surface area of composite. The composite with calcination temperature of 550 °C exhibited enhanced photocatalytic owing to the high surface area and small TiO2 crystallite size. A series of dynamic degradation experiments were conducted to investigate the effect of various operating parameters on acetone and p-xylene adsorption/degradation performances of the composite. The results illustrated that when the relative humidity (0–70%), gas flow rate (1–4 L/min), and VOC concentration (10–40 ppm) were set as the low values, the high total organic carbon degradation rate could be acquired. The total organic carbon degradation rate reached to a high value when the composite dosage was 3.76 mg/cm2. With the increase of light intensity (0.48–1.33 mW/cm2), the total organic carbon degradation rate presented an upward trend and then kept stable. The absorbent-photocatalyst hybrid TiO2/diatomite composite could be the promising VOC purification materials.

Spatial heterogeneity of organic carbon cycling in sediments of the northern Yap Trench: Implications for organic carbon burial

The hadal trenches (>6000 m) are considered to be ultimate sinks of organic carbon (OC) from biosphere. However, highly spatial heterogeneity of geographic background and organic matter in different zones make significant influences on the OC cycling, and further the carbon burial. In this study, three sediment cores were drilled across the northern Yap Trench axis (9.8–9.9°N, 138.3–138.7°E). The elemental compositions, stable carbon isotopes of organic matter, mineral-specific surface area, and grain size composition were analyzed to investigate the spatial variations of organic sources, distribution, and its degradation in the northern Yap Trench. The surface sedimentary OC (SOC) contents in the northern Yap Trench increase from 0.25% at abyssal depth (4435 m) to 0.50% at hadal depth (~6674 m). Higher OC content (0.27% ± 0.08%) and sedimentation rate (5.8 cm kyr−1) occur in the station on the gradual oceanward slope (~4.2°) compared to those on the steep landward slope (~10°) (0.17% ± 0.13%, 0.52–1.8 cm kyr−1), suggesting enhanced accumulation of OC on the gradual slope. The allochthonous OC (i.e. marine phytoplankton-derived (55% ± 7%) and terrestrial (16% ± 8%)) dominates the SOC pool on the oceanward slope, whereas autochthonous microbe reworked OC contributes more than 50% in the steep landward slope, based on the evaluation of a three-end-member mixing model using δ13C composition and OC/N ratios as source markers. Correspondingly, radiocarbon age of SOC in the gradual slope is ~700 years younger than that in the steep slope with similar depth, indicating that the relatively fresh allochthonous OC is selectively deposited on the gradual slope. A multi-G degradation model demonstrates that OC degradation rates in the northern Yap Trench range from 0.00015 yr−1 to 0.00068 yr−1, which can be comparable with abyssal plain (3000–6000 m) and are lower than those of neritic environments (<1000 m). Mass accumulation model calculation shows that accumulation rate of surface OC in the northern Yap trench is ~2.7 × 10−2 g C m−2 yr−1, much lower than those from other deep ocean seafloors. This study suggests an inefficient SOC preservation within the northern Yap Trench, which might be induced by high labile marine phytoplankton-derived OC inputs and active heterotrophic microbial activity, and the results have important implications for better understanding the effects of sediment dynamics on OC cycling in hadal zones.

Magnetically recoverable Fe3O4@polydopamine nanocomposite as an excellent co-catalyst for Fe3+ reduction in advanced oxidation processes

Advanced oxidation processes are widely applied to removal of persistent toxic substances from wastewater by hydroxyl radicals (·OH), which is generated from hydrogen peroxide (H2O2) decomposition. However, their practical applications have been hampered by many strict conditions, such as iron sludge, rigid pH condition, large doses of hydrogen peroxide and Fe2+, etc. Herein, a magnetically recyclable Fe3O4@polydopamine (Fe3O4@PDA) core-shell nanocomposite was fabricated. As an excellent reducing agent, it can convert Fe3+ to Fe2+. Combined with the coordination of polydopamine and ferric ions, the production of iron sludge is inhibited. The minimum concentration of hydrogen peroxide (0.2 mmol/L and Fe2+ (0.18 mmol/L)) is 150-fold and 100-fold lower than that of previous reports, respectively. It also exhibits excellent degradation performance over a wide pH range from 3.0 to 9.0. Even after the tenth recycling, it still achieves over 99% degradation efficiency with the total organic carbon degradation rate of 80%, which is environmentally benign and has a large economic advantage. This discovery paves a way for extensive practical application of advanced oxidation processes, especially in environmental remediation.

Treatment of high-strength olive mill wastewater by combined Fenton-like oxidation and coagulation/flocculation

The efficiency of Fenton/Fenton-like processes on the oxidation of organic matter from real olive mill wastewater (OMW) is described. Tests were performed in lab-scale batch reactors and the influence of different operational parameters was evaluated, namely: type of iron salt, effect of pH readjustments during the reaction, reactants addition method and Fe/H2O2 mass ratio. For the Fenton-like system (Fe3+/H2O2) it was found that H2O2 consumption and consequently total organic carbon (TOC) degradation rate are significantly affected by the reagents addition method, especially in earlier stages of the reaction, although the overall extent of TOC removal is not. Results showed that the gradual addition of H2O2 along with pH readjustments during the process led to better chemical oxygen demand (COD) and total phenolic content (TPh) reduction. Operating at pH0 = 3.0, T0 = 25 °C, [Fe3+] = 1.0 g·L−1 and Fe/H2O2 = 0.04, 34.9% of TOC, 55.7% of COD and 81.4% of TPh were removed after 180 min. The same conditions were applied with the assistance of artificial radiation (photo-Fenton-like process) with slight organic matter degradation improvement (41.8% of TOC, 63.2% of COD and 83.8% of TPh removals). The catalyst’s (ferric chloride salt) ability to act as a coagulant/flocculant after the oxidative process was also checked, being reached a global reduction of 76.7% for COD and 96.4% for TPh after 1 h of sedimentation and no further pH adjustments. Moreover, the effluent’s biodegradability (BOD5:COD ratio) after the combined process improved from the initial value of 0.11 to 0.33, and toxicity against the bioluminescent Vibrio fischeri bacteria decreased from 53% to 4%, putting into evidence the possibility of coupling downstream a biological unit so that the final effluent meets legal discharge limits.

Biogeochemical mechanisms controlling phosphorus diagenesis and internal loading in a remediated hard water eutrophic embayment

Phosphorus (P) levels in eutrophic lakes with restricted external P inputs often show hysteresis resulting from sediment P diagenetic recycling. Hard water oxygenated lakes are often thought to be less susceptible to P release from sediment due to precipitation of P with calcium carbonate and P sorption on iron (Fe) oxyhydroxides in oxidized surface sediments. However, perpetuated eutrophic conditions in many hard water oxygenated lakes persist despite drastic reduction of external P inputs. What limits P sediment binding capacity and drives its release from sediments in such lakes is often less understood. Here we characterize sediment P diagenetic processes driving persistent internal loading in the Bay of Quinte, a hard water, polymictic embayment of Lake Ontario, Canada. We used a multifaceted approach, combining a comprehensive three-year study of sediment P binding forms, recent sediment stratigraphy and accumulation, high spatial resolution measurement of dissolved oxygen, redox potential and pH across the sediment-water interface and depth profiles of nutrient and metals concentrations in pore water. Despite oxygenated bottom water conditions P diffusive fluxes during summer are substantial (1–6.5 mg P/m2/day), representing as much as 50% of external P inputs. Estimated rates of benthic organic carbon degradation indicate that anaerobic organic P mineralization in anoxic sediments is the main driver of P release, which is strongly influenced by Fe reduction. Estimated rates of benthic organic carbon degradation indicate that anaerobic organic P mineralization in anoxic sediments is the main driver of P release. In surface sediment the redox sensitive P is the prevailing diagenetically reactive P phase, emphasizing strong coupling with ferric Fe. While this indicates substantial P sorption on Fe oxyhydroxides, their spare binding capacity is limited, as reducible Fe: P ratios are close to sorption limit. The calcium carbonate bound P increased with sediment depth at the expense of redox sensitive P, suggesting diagenetic sequestration into apatite with sediment burial. However, only 40% of diagenetically reactive P forms, which account for ~2/3 of the total P in surface sediment, are permanently retained during burial. Importantly, our data show that in fact significant P-flux occurs in shallow areas, with an apparent discordance with concurrent measures of long-term P release from the sediments. These results also demonstrate that short-term measures cannot be extrapolated to long-term estimates and vice versa.

Reduced Mineralization of Terrestrial OC in Anoxic Sediment Suggests Enhanced Burial Efficiency in Reservoirs Compared to Other Depositional Environments.

Freshwater reservoirs are important sites of organic carbon (OC) burial, but the extent to which reservoir OC burial is a new anthropogenic carbon sink is currently unclear. While burial of aquatic OC (by, e.g., phytoplankton) in reservoirs may count as a new C sink, the burial of terrestrial OC in reservoirs constitutes a new C sink only if the burial is more efficient in reservoirs than in other depositional environments. We carried out incubation experiments that mimicked the environmental conditions of different depositional environments along the land‐sea continuum (oxic and anoxic freshwater, oxic and anoxic seawater, oxic river bedload, and atmosphere‐exposed floodplain) to investigate whether reservoirs bury OC more efficiently compared to other depositional environments. For sediment OC predominantly of terrestrial origin, OC degradation rates were significantly lower, by a factor of 2, at anoxic freshwater and saltwater conditions compared to oxic freshwater and saltwater, river, and floodplain conditions. However, the transformation of predominantly terrestrial OC to methane was one order of magnitude higher in anoxic freshwater than at other conditions. For sediment OC predominantly of aquatic origin, OC degradation rates were uniformly high at all conditions, implying equally low burial efficiency of aquatic OC (76% C loss in 57 days). Since anoxia is more common in reservoirs than in the coastal ocean, these results suggest that reservoirs are a depositional environment in which terrestrial OC is prone to become buried at higher efficiency than in the ocean but where also the terrestrial OC most efficiently is transformed to methane.

Heterotrophic metabolism of C1 and C2 low molecular weight compounds in northern Gulf of Mexico sediments: Controlling factors and implications for organic carbon degradation

Low molecular weight (LMW) compounds are key intermediates in organic matter degradation and their metabolism supports a diverse microbial community in anoxic sediments. Much remains to be learned about the metabolic pathways and turnover rates of LMW compounds as well as the factors that influence their metabolism in the environment. We studied the microbial metabolism of acetate, methanol and methylamine in sediments from Northern Gulf of Mexico to elucidate their role as energy and carbon sources for microorganisms mediating terminal metabolic processes and to constrain the importance of C1 and C2 metabolism in the sedimentary carbon cycle. In terms of carbon flow, methanogenesis was a minor process in sulfate-rich sediments; acetate and methanol were oxidized primarily by non-methanogenic heterotrophs as an energy source. A large fraction of utilized acetate (20–76%) was assimilated into biomass, suggesting that acetate was a significant biomass-building source. In situ thermodynamic calculations suggested the utilization of acetate and methanol by sulfate-reducing bacteria was more favorable than the utilization by methanogens, consistent with the observed higher oxidation rates than methanogenesis rates as well as results from inhibitor experiments employing 2-bromoethanesulfonate and molybdate. Methylamine, by contrast, was utilized for methane production (up to 100%), but its utilization was not limited to methanogens. At an organic-poor deep-sea site, elevated acetate and methanol oxidation rates in the absence of sulfate-reducing and methanogenic activity indicated that metabolism of LMW compounds was coupled to other electron accepting processes, such as denitrification. Heterotrophic carbon assimilation was an important pathway for generating biomass at this site, as evidenced by comparable rates of acetate assimilation to bicarbonate incorporation. The oxidation and assimilation rates of LMW compounds generally decreased with sediment depth, following the trend of organic carbon degradation rates. Environmental factor, such as temperature but not pressure, affected the metabolism of LMW compounds; the oxidation of acetate, methanol and methylamine exhibited distinct responses to changes in temperature. In seep sediments, the oxidation of acetate and methanol accounted for 5% and 0.9%, respectively, of the total organic carbon oxidation. Collectively, this assessment of C1 and C2 LMW compound utilization shows that these compounds serve as energetic substrates to fuel methanogens, sulfate reducers and other microbes.

Defective black Ti3+ self-doped TiO2 and reduced graphene oxide composite nanoparticles for boosting visible-light driven photocatalytic and photoelectrochemical activity

We present a facile and environmentally friendly way to successfully build partially reduced titanium dioxide nanoparticles integrated with reduced graphene oxide composite nanosheets (RGO/TiO2−x) through an environmental solvothermal method at relatively low temperature. The Ti3+ self-doping of TiO2−x is conducive to enhance its visible light absorption, and the existence of RGO as the electron receiver makes the electrons on TiO2−x transport better to its surface, effectively promoting the separation of electrons and holes. Experiments on photocatalytic degradation of methylene blue dye and phenol colorless organic pollutant by visible light demonstrate that the RGO/TiO2−x assemblies exhibit the highest photocatalytic activity, and that methylene blue solution concentration of used in the experiment is 40 mg L−1, which was more higher than the concentration (10 mg L−1) used in many of reported articles. Compared to the pure TiO2 and TiO2−x, the photodegradation efficiency of methylene blue and phenol can be increased to 100% within 120 min and 150 min under visible light. Moreover, the mineralization rates of MB, such as the total organic carbon (TOC) degradation rate, can reach to 75.7%, 86.6% and 89.4% for m-RGO/TiO2−x, respectively. And the reaction efficiency of RGO/TiO2−x is basically not much changed after 4th cycles, suggesting its excellent photocatalytic stability.

Dissolved oxygen dynamic across the new-born interface of bottom water and sediment after dredging contaminated sediment

借助微氧电极测试技术对太湖贡湖湾试验区疏浚后的新生界面溶解氧动态进行一年的跟踪调研，分析溶解氧在新生微米级界面的分布特征、扩散通量以及界面附近有机质矿化速率.结果表明疏浚后半年内，溶解氧在表层沉积物的侵蚀深度增大，氧化层明显加厚.氧气在新生界面表层沉积物中呈指数下降，但衰减相对较缓.在连续一年的跟踪调查中发现，仅秋季新生界面附近溶解氧浓度明显高于对照，而在其他月份无差异.污染底泥疏浚后一个月内氧扩散通量及有机碳矿化速率下降最为明显，仅为疏浚前的13%，其他月份沉积物-水界面氧的扩散通量、氧气的消耗速率、有机碳的降解速率均有不同程度下降，疏浚后新生界面氧气交换速率下降以及由此导致的有机碳矿化过程变缓可能深刻影响界面生源要素的迁移过程.;Oxygen dynamic had been conducted a yearlong investigation to obtain oxygen distribution, oxygen diffusion flux and mineralization rate of organic matter across the new-born interface of bottom water and sediments due to dredge. The results showed that oxygen penetration depth increased with thickening oxidation layer in new-born sediments. Oxygen concentrations decreased rapidly with depth in the sediments, but relatively moderate. Below the penetration depth, the O₂ concentration inside the sediment was under the detection limit (approximation for 0). Oxygen concentration in bottom water in autumn was significantly higher in dredge treatment than those in control, however, there was not statistically significant among the three sampling during the investigation. The diffusive O₂ flux (F_O₂) and the oxygen consumption rate (R_O₂) were observed based on O₂ microprofiles, otherwise, organic carbon degradation rates (R_org) were obtained from the oxygen consumption rate based on the modified Redfield ratio (O₂/C_org=170/117) and the values also obviously decreased. Therefore, thickening oxidation layer and slowdown organic carbon degradation rates could significantly influence nutrients biogeochemical cycle after dredge.

An advanced TiO2/Fe2TiO5/Fe2O3 triple-heterojunction with enhanced and stable visible-light-driven fenton reaction for the removal of organic pollutants

The construction of catalysts with high efficiency and stability for heterogeneous Photo-Fenton reaction Heterogeneous (PFR) has been a major challenge for the degradation of organic pollutants. Here, we successfully develop an advanced TiO2/Fe2TiO5/Fe2O3 triple-heterojunction structure by using the mesoporous TiO2 spheres as the substrate via a simple ion-exchange method. The XRD and HRTEM results demonstrate the generation of Fe2TiO5 on the interface between TiO2 and Fe2O3, which can be used as a “bridge” to transfer the photo-excited electrons from TiO2 to Fe2O3. The as-prepared triple-heterojunction has abundant interphase boundaries which greatly improve the migration of photo-excited charges among different components. As a result, the prepared triple-heterojunction has a significantly enhanced PFR activity for the visible-light-driven degradation of methyl orange (MO) and colorless organic pollutant of phenol, compared with the single catalysts of Fe2O3 and TiO2, and the binary-heterojunction of TiO2/Fe2O3. Compared to the traditional Fe2O3 based PFR, the degradation rates of MO and phenol over triple-heterojunction can be increased from 4% to 87% within 10min irradiation and from 38% to 100% within 60min irradiation, respectively. And the total organic carbon (TOC) degradation rate of phenol can be up to 85%. Moreover, this advanced triple-heterojunction has a wide pH value range of application in PFR. Either at a pH of 4.0 or 7.0, it shows a much higher and more stable PFR activity for the degradation of MO than the catalysts of Fe2O3 and TiO2/Fe2O3. And the reaction rate of TiO2/Fe2TiO5/Fe2O3 almost keeps changeless even after 10th cycles, suggesting its vast application foreground in the environmental pollutant treatment.