Oxidation behavior of TiAlZrCr/(Ti,Al,Zr,Cr)N gradient films deposited by multi-arc ion plating

The two Ti-Al-Zr targets and one pure Cr target were used to prepare the TiAlZrCr/（Ti, Al, Zr, Cr）N gradient films on high speed steel （WlSCr4V） substrates by multi-arc ion plating technique. Short-term isothermal （at 600 ℃, 700 ℃, 800℃ and 900 ℃ for 4 h） and long-terra cyclic （at 700℃ and 800℃ for 100 h） high temperature oxidation behavior of the gradient films were studied. Then the oxide scales formed on the film specimens were characterized by scanning electron microscopy （SEM）, energy dispersion X-ray spectroscopy （EDS） and X-ray diffraction （XRD）. It was showed that, under short-term isothermal condition, the high temperature oxidation resistance of the gradient film was excellent up to 800 ℃ and an oxide scale comprising TiO2 was observed. On the other hand, under long-term cyclic high temDerature condition, the oxidation resistance of the gradient film was excellent at about 700 ℃.

Evaluation of the Bioavailability of Metals in Sediment from the Southern Coastal Wetland of the Qiantang Estuary by Using Diffusive Gradients in Thin Films Technique

Metal pollution has become an major issue governing the wetland ecosystem health.The southern coastal wetland of the Qiangtang Estuary are facing unusual perturbation due to rapid development along the embayment in recent decades.This study evaluated the bioavailability of metals(Cu,Pb,Cd,Cr and Zn)in the sediment of the southern coastal wetland of the Qiangtang Es-tuary using diffusive gradients in thin films(DGT)techniques and compared with several methods based on total metal content.The results showed that the contents of Cr,Pb,Cd and Cu in sediment,as detected using DGT,were considerably correlated with the exchangeable fraction and the content in Phragmites australis roots,while a weak correlation was observed for Zn.Therefore,DGT analysis could be used to evaluate the bioavailability and potential risk of Cr,Cd,Pb and Cu for P.australis.Quantitative indices,such as DGT concentration,bioaccumulation in P.australis,geoaccumulation index(Igeo)and potential ecological risk index(RI),revealed that Cd was a major potential ecological risk factor along the southern coast wetland of the Qiantang Estuary,especially in the upstream region,which is potentially more vulnerable to the anthropogenic pollution.

Evaluation of Cadmium Bioavailability in Soils Using Diffusive Gradients in Thin Film Technique and Traditional Methods

The developed technique of diffusive gradients in thin film( DGT) has been suggested as a promising tool for evaluation of cadmium( Cd) availability in soils,but there exists considerable debate on its suitability. In this study,Cd bioavailability in soils was systemically investigated by comparing this technique with seven traditional methods, including soil solution concentration and six commonly used extraction methods( HAc,EDTA,Na c,NH4Ac,CaCl2 and MgCl2). Two typical plants( wheat and maize) were examined for Cd uptake. Maize was more sensitive to increasing exposure to Cd in soils than wheat when the added amounts of Cd ranged from 3. 5 to 5. 0 mg · kg-1,accompanied by the significant decreases of shoot and root biomasses. Cd concentrations in shoots and roots of two plants increased continuously with increasing levels of Cd in soils. Cd uptake was higher in wheat than that in maize. The bioavailable concentrations of Cd measured by all methods increased nearly linearly with increasing addition of Cd in soils. Positive correlations were observed between various bioavailable indicators of Cd in soils and Cd concentrations in two plants. The extractable Cd by six chemical extractants was considerably higher for maize than for wheat,while the DGT-measured and soil solution concentrations of Cd were lower for maize than for wheat,following the same trend as plant Cd uptake. The results imply that DGT measurement can effectively predict the bioavailable levels of Cd in soil solutions and that it is an ideal tool for prediction of Cd bioavailability in soils.

Diffusive gradients in thin films using molecularly imprinted polymer binding gels for in situ measurements of antibiotics in urban wastewaters

Urban wastewater is one of main sources for the introduction of antibiotics into the environment.Monitoring the concentrations of antibiotics in wastewater is necessary for estimating the amount of antibiotics discharged into the environment through urban wastewater treatment systems.In this study,we report a novel diffusive gradient in thin films(DGT)method based on molecularly imprinted polymers(MIPs)for in situ measurement of two typical antibiotics,fluoroquinolones(FQs)and sulfonamides(SAs)in urban wastewater.MIPs show specific adsorption toward their templates and their structural analogs,resulting in the selective uptake of the two target antibiotics during MIP-DGT deployment.The uptake performance of the MIP-DGTs was evaluated in the laboratory and was relatively independent of solution pH(4.0-9.0),ionic strength(1-750 mmol/L),and dissolved organic matter(DOM,0-20 mg/L).MIP-DGT samplers were tested in the effluent of an urban wastewater treatment plant for field trials,where three SA(sulfamethoxazole,sulfapyridine,and trimethoprim)and one FQ(ofloxacin)antibiotics were detected,with concentrations ranging from 25.50 to 117.58 ng/L,which are consistent with the results measured by grab sampling.The total removal efficiency of the antibiotics was 80.1%by the treatment plant.This study demonstrates that MIP-DGT is an effective tool for in situ monitoring of trace antibiotics in complex urban wastewaters.

Determining cadmium bioavailability in sediment profiles using diffusive gradients in thin films

Cadmium(Cd)uptake by plants or benthic organisms largely depends on its bioavailability in sediments,so it is necessary to understand Cd bio availability for determining its ecological risks in riverine sediments.Pore water is easily disturbed during sample collection,indicating that there was a shortage of traditional methods for investigating Cd bio availability.Here,sediment cores were collected from rivers,after which sequential extraction and diffusive gradients in thin films(DGT)method were employed to determine Cd potential bio availability in the sediments and pore water.We found that Cd concentrations measured by DGT were lower than that in pore water profiles,and Cd distribution in various fractions changed remarkably.Pearson correlation analysis showed significant positive correlations between Cd concentrations measured by DGT and total Cd concentrations(r^2=0.76),exchangeable and weak acid soluble fraction(r^2=0.68),ferromanganese fraction(r^2=0.72)and bound organic matter or oxidizable fraction(r^2=0.54).However,the correlation was relatively low between Cd concentrations measured by DGT and that in pore water profiles(r^2=0.26).These results demonstrated that DGT method could provide more accurate information of Cd bio availability in sediment profiles than traditional methods.

Diffusive gradients in thin films(DGT) probe for effectively sampling of per-and polyfluoroalkyl substances in waters and sediments

The passive sampling technique, diffusive gradients in thin films(DGT) has attracted increasing interests as an in-situ sampler for organic contaminants including per-and polyfluoroalkyl substances(PFAS). However, its effectiveness has been questioned because of the small effective sampling area(3.1 cm^(2)). In this study, we developed a DGT probe for rapid sampling of eight PFAS in waters and applied it to a water-sediment system. It has a much larger sampling area(27 cm^(2)) and as a result lower method quantification limits(0.15 –0.21 ng/L for one-day deployment and 0.02 – 0.03 ng/L for one-week deployment) and much higher(by > 10 factors) sampling rate(100 m L/day) compared to the standard DGT(piston configuration). The sampler could linearly accumulate PFAS from wastewater, was sensitive enough even for a 24 hr deployment with performance comparable to grab sampling(500m L). The DGT probe provided homogeneous sampling performance along the large exposure area. The use of the probe to investigate distributions of dissolved PFAS around the sediment-water interface was demonstrated. This work, for the first time, demonstrated that the DGT probe is a promising monitoring tool for trace levels of PFAS and a research tool for studying their distribution, migration, and fate in aquatic environments including the sediment-water interface.

Gel electrolyte via in situ polymerization to promote durable lithium-air batteries

Aprotic lithium-air batteries(LABs)have been known as the holy grail of energy storage systems due to their extremely high energy density.However,their real-world application is still hindered by the great challenges from the Li anode side,like dendrite growth and corrosion reactions,thus a pure oxygen atmosphere is usually adopted to prolong the lifetime of LABs,which is a major obstacle to fully liberate the energy density advantages of LABs.Here,a gel polymer electrolyte has been designed through in-situ polymerization of 1,3-dioxolane(DOL)by utilizing the unique semi-open nature of LABs to protect the Li anode to conquer its shortcomings,enabling the high-performance running of LABs in the ambient air.Unlike common liquid electrolytes,the in-situ formed gel polymer electrolyte could facilitate constructing a gradient SEl film with the gradual decrease of organic components from top to bottom,preventing the Li anode from dendrite growth and air-induced corrosion reactions and thus realizing durable Li repeated plating/stripping(2000h).Benefiting from the anode protection effects of the gradient SEI film,the LABs display a long lifetime of 17o cycles,paving an avenue for practical,long-term,and high-efficiency operation of LABs.

Synergistic effect of vermiculite and submerged plants on lake sediments

The synergistic effect of vermiculite and the submerged macrophytes Vallisneria spiralis and Hydrilla verticillata on lake sediment was studied using diffusive gradients in thin films(DGT)technology.The dynamics of phosphorus(P)fractions in sediment,the labile-P and labile-S in the water-sediment continuum,and the microbial community in the rhizosphere were studied.Vermiculite effectively promoted reproduction of microorganisms in the sediments Microbial abundance in treatments containing V.spiralis with sediments containing 10%added vermiculite,and H.verticillata containing 50%added vermiculite being 1.7 and 3.5 times higher than the controls which contained no added vermiculite.Acidobacteria and Proteobacteria populations,which are both beneficial for the sediment microenvironment,were higher in treatment groups containing vermiculite.The bioavailable-P in treatment groups containing added vermiculite was lower at the sediment-water interface,with a correlating decrease of TP by between 63%and 91%in the overlying water.This suggests that vermiculite can affect the release of labile P and facilitate the assimilation of nutrients by macrophyte roots.Additionally,vermiculite can improve the Oxidation-Reduction potential and further reduce sulfide toxicity to plants.These results provide theoretical guidance and technical support for the application of vermiculite combined with submerged plants for the remediation of eutrophic lakes.

Attenuation of Metal Bioavailability in Acidic Multi-Metal Contaminated Soil Treated with Fly Ash and Steel Slag

A pot experiment was conducted with multi-metal （Pb, Cd, Cu, and Zn） contaminated acidic soil to investigate changes in available metal burden resulting from the application of industrial wastes （fly ash and steel slag）. The efficiency of amendments- induced metal stabilization was evaluated by diffusive gradients in thin films （DGT）, sequential extraction, and plant uptake. The stability of remediation was assessed by an acidification test and by chemical equilibrium modeling. Addition of fly ash （20 g kg-1） and steel slag （3 g kg-1） resulted in similar increase in soil pH. Both amendments significantly decreased the concentrations of metals measured with DGT （CDGT） and the metal uptake by Oryza sativa L. Significant correlations were found between CDGT and the concentration of a combination of metal fractions （exchangeable, bound to carbonates, and bound to Fe/Mn oxides）, unraveling the labile species that participate in the flux of metal resupply. The capability of metal resupply, as reflected by the R （ratio of CDGT to pore water metal concentration） values, significantly decreased in the amended soils. The CDGT correlated well with the plant uptake, suggesting that DGT is a good indicator for bioavailability. Acidification raised the extractable metal concentration in amended soil but the concentration did not return to the pre-amendment level. Equilibrium modeling indicated that the soil amendments induced the precipitation of several Fe, A1 and Ca minerals, which may play a positive role in metal stabilization. Chemical stabilization with alkaline amendments could be an effective and stable soil remediation strategy for attenuating metal bioavailability and reducing plant metal uptake.

Distr ibution, risk and bioavailability of metals in sediments of Lake Yamdrok Basin on the Tibetan Plateau, China

Total contents of metals in soil and sediments on the Tibetan Plateau of China have been widely analyzed,but existing information is insufficient to effectively evaluate metal ecological risk because of a lack of metal bioavailability data.In this study,distribution,potential risk,mobility and bioavailability of metals in sediments of Lake Yamdrok Basin in Tibet of China were explored by combined use of total digestion,sequential extraction and the diffusive gradient in thin-films(DGT).Average concentrations of Cr,Ni,Cu,Zn,As,Cd and Pb in surface sediments were 31.25,30.31,22.00,45.04,31.32,0.13 and 13.39 mg/kg,respectively.Higher levels of metals were found near the inflowing rivers.Residual form was dominant in Cr,Ni,Zn,Cd and Pb,and reducible form was dominant in As and Cd.Metals in surface sediments showed a low enrichment degree overall,but Cd and As had higher ecological risk levels than the other metals.Furthermore,there was a larger average proportion of exchangeable form of As(20.4%)and Cd(9.0%)than the other metals(1.7%-3.3%),implying their higher mobility and release risk.Average DGT-labile concentrations of Cr,Ni,Cu,Zn,As,Cd and Pb were 0.5,4.5,0.7,25.1,60.0,0.22 and 1.0μg/L,respectively.The DGT-labile As was significantly correlated with extractable As forms(p<0.01),suggesting that extractable As in sediments acts as a"mobile pool"for bioavailable As.These results suggest potential risks of As and Cd,especially As,deserve further attention in Lake Yamdrok Basin.

Investigation of potential interferences on the measurement of dissolved reactive phosphate using zirconium oxide-based DGT technique

A diffusive gradients in thin films （DGT） technique based on hydrous zirconium oxide （Zr-oxide） has been recently developed for the measurement of dissolved reactive phosphate （DRP）. In this study, the detailed performance of the DGT technique is reported. Spiking experiments revealed that several orthophosphate monoester compounds contributed to the Zr-oxide DGT measurements of DRP. However, such a phenomenon is unlikely to occur during field conditions due to the low concentration of organic P in typical natural waters. The presence of Cl- （up to 106 g/L）, SO42- （up to 16 g/L）, HCO3- （up to 817 g/L）, and AsO2- and AsO 3 4 （both up to 1 mg As/L） in solutions had negligible effects on the measurement of DRP. The threshold concentrations of Cl-, SO42- and HCO3- have been increased from previous reports for the measurements of DRP using other adsorbent-based DGT techniques. The capacity for DGT measurements of DRP decreased with increasing solution pH （4.2-9.2）. The lowest capacity （95 μg P/m2 at pH 9.2） was still greater than that of other DGT techniques that are usually used for the measurement of DRP （2-12 μg P/cm2 ）. The Zr-oxide binding gel could be stored for up to 2 years without any aging effect. This period of validity was considerably longer than the ferrihydrite binding gel that is commonly used in present DGT devices （6 months）. The field application revealed that the concentrations of DRP measured in three fresh water samples using the Zr-oxide DGT technique were in agreement with those of the traditional colorimetric method.

Phosphorus removal from sediments by Potamogeton crispus:New high-resolution in-situ evidence for rhizosphere assimilation and oxidization-induced retention

Macrophytes are usually chosen for phytoremediation tools to remove P in eutrophic aquatic ecosystems,but the lack of test methods hinders the understanding of removal mechanism and application.In this study,we used the novel technologies combined of Diffusive gradients in thin films(DGT),Planar optode(PO),and Non-invasive micro-test technology(NMT)to explore P dynamics in water-sediment continuum and rhizosphere of Potamogeton crispus over time.Results of the high-resolution in situ measurement showed that labile P(LPDGT)fluxes at the surficial sediment significantly decreased from approximate 120,140,and 200 pg/(cm^(2)·sec)via 30 days incubation period to 17,40,and 56 pg/(cm2•sec)via that of 15 days.Obvious synchronous increase of LPDGT was not detected in overlying water,suggesting the intense assimilation of dissolve reactive P via root over time.PO measurement indicated that O_(2)concentration around the rhizosphere remarkably increased and radially diffused into deeper sediment until 100%saturation along with the root stretch downwards.NMT detection of roots showed the obvious O_(2)inflow into root tissue with the uppermost flux of 30 pmol/(cm2•sec)from surroundings via aerenchyma on different treatment conditions.Different from previous reports,gradually saturating O_(2)concentrations around the rhizosphere was principally driven by O_(2)penetration through interspace attributing to root stretch downward rather than root O_(2)leakage.Increased O_(2)concentrations in deep sediment over time finally induced the oxidization of labile Fe(II)into Fe(III)bound P and local P immobilization.

Mobility and sulfidization of heavy metals in sediments of a shallow eutrophic lake, Lake Taihu, China

The technique of DGT（diffusive gradients in thin films） using three diffusive gel thicknesses was applied to estimate the mobility and bioavailability of heavy metals in sediments and porewater of Lake Taihu, China. The DGT results showed significantly positive correlations between Co, Pb, Cd and Mn, and Ni and Fe concentrations in porewater. Cu and Zn showed a significantly negative correlation with Mn, due to Cu combination with carbonates and Zn derived from agricultural pollution, respectively. The rank order of average concentrations of Co, Ni and Cd at each station was DGT1.92〉DGT0.78〉 DGT0.39, suggesting stronger resupply from sediments to porewater when using thicker diffusive gels. Comparing centrifugation and DGT measurements, Co, Ni and Cd are highly labile; Mn and Fe are moderately labile; and Cu, Zn and Pb are slightly labile. The variations of AVS concentrations in sediment cores indicate that metal sulfides in deeper layers are easily diffused into surface sediments.

Using DGT to Assess Cadmium Bioavailability to Ryegrass as Influenced by Soil Properties

A generally accepted method for predicting the bioavailability and transfer of cadmium(Cd) from soil to plants has not yet been established. In this study, the diffusive gradients in thin films(DGT) and conventional extraction methods for metal fractions were used to investigate how effective these methods were at predicting Cd bioavailability to ryegrass(Lolium perenne) and to assess whether these holistic variables were independent of the soil property variables. The influences of soil properties on the predictive capabilities of the different methods were evaluated using multivariate statistics. The Cd concentrations in the shoots and roots of ryegrass correlated more closely with the effective Cd concentration measured by DGT(CE), compared with those with soil total Cd, pore water Cd, and ethylenediaminetetraacetic acid disodium salt(Na2EDTA)- and acetic acid(HOAc)-extractable Cd. When soil properties were included in a stepwise multiple linear regression, Cd transfer to L. perenne was negatively influenced by p H and positively influenced by organic matter(OM). The multivariate statistics showed that the adjusted correlation coefficients for the plots involving soil total Cd, pore water Cd, and Na2EDTA- and HOAc-extractable Cd had been significantly improved after considering the influences of soil properties, which suggested that these methods were p H and OM dependent. For CE, the relationship was p H independent or only dependent in strongly acidic soils. These results suggested that the main soil factors affecting bioavailability had the lowest impact on the DGT technique. Therefore, the DGT technique provided significant advantages over conventional methods when assessing Cd bioavailability.

Seasonal dynamics of iron and phosphorus in reservoir sediments in Eucalyptus plantation region

Background:Iron(Fe)and phosphorus(P)dynamics in sediments have direct and indirect impacts on water quality.However,the mobility of P and Fe in reservoir sediments in Eucalyptus plantation region remains unclear.This study examined P and Fe pollution in sediments in a Eucalyptus plantation region using the novel planar optode,the ZrO-Chelex DGT,and the DIFS model.Results:Direct in situ investigations showed that the levels of labile P and Fe were smaller in the Eucalyptus species-dominated sediments(X2)compared to sediments without Eucalyptus species(X1).The mean concentration of labile P and Fe decreased by 25%and 42%from X1 to X2.The decrement was insignificant(p=0.20)in the surface sediment concentration for labile P.The significant disparity for DGT-Fe(Fe^(2+))(p=0.03)observed in the surface sediments could be attributed to the Eucalyptus species’elevated organic matter(tannins)concentration at X2,which reacted and consumed labile Fe.For both regions,the maximum concentration of labile P and Fe occurred in November(autumn).The reductive decomposition of Fe/Mn oxides was recognized as the main driver for their high P efflux in July and November.Low concentration of labile P and Fe was observed in December(winter)due to the adsorption of Fe/Mn oxides.The concentration of labile Fe synchronizes uniformly with that of labile P in both sediments indicating the existence of a coupling relationship(r>0.8,p<0.01)in both regions.The positive diffusion fluxes in both regions suggested that the sediments release labile P and Fe.The fluxes of labile P and Fe in both regions were substantially higher(p<0.05)in the summer(anoxic period)than winter(aerobic period),indicating that hypoxia and redox conditions influenced the seasonal efflux of labile P and Fe.From the DIFS model,the replenishment ability of reactive P was higher during the anoxic period(R=0.7,k_(1)=79.4 day^(-1),k_(-1)=0.2 day^(-1))than the aerobic period(R=0.4,k_(1)=14.2 day^(-1),k_(-1)=0.1 day^(-1)),suggesting that oxygen inhibited the efflux of P in the sediments.Conclusion:Our results indicated that hypoxia,Eucalyptus species(organic matter(tannins)),and redox conditions influenced the seasonal mobility of sediment labile P and Fe.Our findings provided an insight into the mobility of labile P and Fe in Eucalyptus-dominated sediments and,moreover,serves as a reference for developing future studies on Eucalyptus-dominated sediments.

Wheat yield prediction by zero sink and equilibrium-type soil phosphorus tests

Diffusive gradients in thin films(DGT)measurements have been shown to outperform other phosphorus(P)tests in soils with strong P sorption,but this has not been confirmed for moderately weathered European soils.We compared the performance of DGT in predicting wheat grain yield in Swedish long-term fertility experiments with those of standard intensity(water-extractable P(P-H2O))and quantity(ammonium lactate-extractable P(P-AL))tests.A Mitscherlich-type model was used to fit wheat yield response to P application rates(0,15,30 or 35,and 45 kg P ha-1 year-1)in each individual trial replicate to estimate the maximum yield.For trials with clear plateau-type yield responses and the goodness of fit(R2)>0.75,relative yields(RYs)were calculated for each P treatment and plotted against the soil P test results(n=143).The goodness of the Mitscherlich-type fits decreased in the following order:DGT-measured P(P-DGT)(R2=0.35)>P-H2O(R2=0.18)>P-AL(R2=0.13).When excluding soils with P-AL:P-DGT≥0.1 L g-1,R2 was considerably improved to 0.55 for P-AL,0.46 for P-H2O,and 0.65 for P-DGT(n=61).At 95%of maximum yield,the upper limit of P deficiency for P-DGT was 44.8(the soils with P-AL:P-DGT<0.1 L g-1)and 61.9μg L-1(all soils),falling within the range reported for other European and Australian soils(6.0–142μg L-1).We show that in the investigated Swedish soils,DGT performed better than the quantity and intensity tests,which is attributed to its ability to capture P diffusion and resupply from the soil solid phase,similar to plant roots in the rhizosphere.