A collaborative strategy for enhanced reduction of Cr(VI) by Fe(0) in the presence of oxalate under sunlight: Performance and mechanism

Nanometer-size zero-valent iron (NZVI) is an efficient reducing agent, but its surface is easily passivated with an oxide layer, leading to reaction inefficiency. In our study, oxalate (OA) was introduced into this heterogeneous system of NZVI, which could form ferrioxalate complexes with the NZVI surface-bound Fe³⁺ and dissolved Fe³⁺ in the solution. Photolysis of ferrioxalate complexes can facilitate the generation of Fe²⁺ from Fe³⁺ and CO₂^?- radical, both species have strong reduction capacity. Hence, a “photo-oxalate-Fe(0)” system through sunlight induction was established, which not only prohibited the formation of a surface passivation layer, but also displayed a synergetic mechanism of ferrioxalate photolysis to enhance reduction, exhibiting remarkably higher degradation activity (several times faster) toward the model pollutant Cr(VI) than the mechanism with NZVI alone. Factor tests suggested that both NZVI dosage and OA content markedly affected the reduction rate. Low pH was beneficial to the reduction efficiency. Moreover, recyclability experiment showed that the reduction rate decreased from 0.21706 to 0.03977 min^?1 after three cycles of reuse due to the NZVI losing reaction activity generally, but the system still maintained considerable reduction capacity. Finally, a mechanism was revealed whereby NZVI would transform to Fe oxides after the exhaustion of its reductive power, and the photolysis of ferrioxalate to promote the cycling of iron species played the predominant role in providing extra reduction ability. These features confirm that introduction of OA into Cr(VI) reduction by NZVI through sunlight induction is advantageous and promising.     

Nanoscale zero-valent iron/magnetite carbon composites for highly efficient immobilization of U(Ⅵ)

Nanoscale zerovalent iron/magnetic carbon(NZVI/MC) composites were successfully synthesized by simply calcining yellow pine and iron precursors. NZVI/MC pyrolyzed at 800°C(NZVI/MC800) had a higher percentage of NZVI and displayed better resistance to aggregation and oxidation of NZVI than samples prepared at other temperatures. The NZVI/MC800 material was applied for the elimination of U(Ⅵ) from aqueous solutions. The results suggested that the NZVI/MC800 displayed excellent adsorption capacity(203.94 mg/g)toward U(Ⅵ). The significant adsorption capacity and fast adsorption kinetics were attributed to the presence of well-dispersed NZVI, which could quickly reduce U(Ⅵ) into U(Ⅳ), trapping the guest U(Ⅳ) in the porous biocarbon matrix. The removal of U(Ⅵ) on the NZVI/MC samples was strongly affected by solution pH. The NZVI/MC samples also displayed outstanding reusability for U(Ⅵ) removal after multiple cycles. These findings indicate that NZVI/MC has great potential for remediation of wastewater containing U(Ⅵ).     

Insight into the adsorption of tetracycline onto amino and amino–Fe~(3+) gunctionalized mesoporous silica: Effect of functionalized groups

In order to study the influences of functionalized groups onto the adsorption of tetracycline,we prepared a series of amino and amino–Fe~(3+)complex mesoporous silica adsorbents with diverse content of amino and Fe~(3+)groups(named N,N-SBA15 and Fe-N,N-SBA15).The resulting mesoporous silica adsorbents were fully characterized by X-ray powder diffraction(XRD),Fourier transform infrared spectrometer(FTIR)and N_2adsorption/desorption isotherms.Furthermore,the effects of functionalized groups on the removal of TC were investigated.The results showed that the periodic ordered structure of SBA-15 was maintained after modification of amino/Fe~(3+)groups.The functionalized amino groups decreased the adsorption capacity while the coordinated Fe~(3+)increased the adsorption capacity.The adsorption kinetics of TC fitted pseudo-second-order model well and the equilibrium was achieved quickly.The adsorption isotherms fitted the Langmuir model well and with the Fe~(3+)content increased from 3.93%to 8.26%,the Q_(max)of the adsorbents increased from 102 to 188 mmol/kg.The solution p H affected the adsorption of TC onto amino complex adsorbents slightly while influenced the adsorption onto Fe-amine complex adsorbents greatly.The adsorption of TC on SBA15 and N,N-SBA15 may be related to the formation of outer-sphere surface complexes,while the adsorption of TC onto Fe-N,N-SBA15 was mainly attributed to the inner-sphere surface complexes.This study could offer potential materials that have excellent adsorption behavior for environmental remediation and suggested useful information for the preparing other adsorbents in environmental applications.     

Debromination of decabromodiphenyl ether by organo-montmorillonite-supported nanoscale zero-valent iron：Preparation, characterization and influence factors

An organo-montmorillonite-supported nanoscale zero-valent iron material(M-NZVI) was synthesized to degrade decabromodiphenyl ether(BDE-209). The results showed that nanoscale zero-valent iron had good dispersion on organo-montmorillonite and was present as a core-shell structure with a particle size range of nanoscale iron between 30–90 nm, characterized by XRD, SEM, TEM, XRF, ICP-AES, and XPS. The results of the degradation of BDE-209 by M-NZVI showed that the efficiency of M-NZVI in removing BDE-209 was much higher than that of NZVI. The efficiency of M-NZVI in removing BDE-209 decreased as the pH and the initial dissolved oxygen content of the reaction solution increased, but increased as the proportion of water in the reaction solution increased.     

Novel synthesis of aluminum hydroxide gel-coated nano zero-valent iron and studies of its activity in flocculation-enhanced removal of tetracycline

A newly designed aluminum hydroxide gel-coated nanoscale zero-valent iron(AHG@NZVI)with enhanced activity and dispersibility of NZVI was successfully synthesized.The AHG@NZVI composite was synthesized via control of the surface AHG content.AHG@NZVI-1,AHG@NZVI-2 and AHG@NZVI-3 were prepared under centrifugal mixing speeds of 1000,2000 and 4000 r/min,respectively.The activity of AHG@NZVI was evaluated by its tetracycline(TC) removal efficiency.The effects of AHG content,pH value,reaction temperature,and presence of competitive anions on TC removal were investigated.TC could be removed by both adsorption and chemical reduction on AHG@NZVI-2(centrifugal speed 2000 r/min) in a short time with high removal efficiency(≥98.1%) at the optimal conditions.Such excellent performance can be attributed to a synergistic interaction between aluminum hydroxide gel and NZVI:(1) AHG could enhance the stability and dispersity of NZVI;(2) aluminum hydroxide gel could absorb a certain amount of TC and Fe~(2+)/Fe~(3+),which facilitated the mass transfer of TC onto the NZVI surface,resulting in acceleration of the reduction rate of TC by the AHG@NZVI composite;and(3) AHG-Fe~(2+)/Fe~(3+)could absorb a certain amount of TC by flocculation.The kinetics of TC removal by AHG@NZVI composite was found to follow a two-parameter pseudo-first-order model.The presence of competitive anions slightly inhibited the activity of AHG@NZVI systems for TC removal.Overall,this study provides a promising alternative material and environmental pollution management option for antibiotic wastewater treatment.     

Effect of Fe(Ⅲ) on the bromate reduction by humic substances in aqueous solution

Humic substances are ubiquitous redox-active organic compounds of environment.In this study,experiments were conducted to determine the reduction capacity of humic acid in the matrix of bromate and Fe(Ⅲ) solutions and the role of Fe(Ⅲ) in this redox process.The results showed that the humic acid regenerated Fe(Ⅱ) and reduced bromate abiotically.The addition of Fe(Ⅲ) could accelerate the bromate reduction rate by forming humic acid-Fe(Ⅲ) complexes.Iron species acts as electron mediator and catalyst for the bromate reduction by humic acid,in which humic acid transfers electrons to the complexed Fe(Ⅲ) to form Fe(Ⅱ),and the regenerated Fe(Ⅱ) donate the electrons to bromate.The kinetics study on bromate reduction further indicated that bromate reduction by humic acid-Fe(Ⅲ) complexes is pH dependent.The rate decreased by 2-fold with the increase in solution pH by one unit.The reduction capacity of Aldrich humic acid was observed to be lower than that of humic acid or natural organic matter of Suwanne River,indicating that such redox process is expected to occur in the environment.     

Ciprofloxacin degradation in photo-Fenton and photo-catalytic processes: Degradation mechanisms and iron chelation

Ciprofloxacin(CIP)is a broad spectrum synthetic antibiotic drug of fluoroquinolones class.CIP can act as a bidentate ligand forming iron complexes during its degradation in the photoFenton process(PFP).This work investigates on PFP for the degradation of CIP to understand the formation mechanism and stability of iron complexes under ultraviolet(UV)-light illumination.A comparison was made with the UV-photocatalysis(UV/TiO_2)process where CIP doesn't form a complex.In PFP,the optimal dose of Fe~(2+)and H_2O_2were found to be 1.25 and10 mmol/L with pH of 3.5.An optimal TiO_2dose of 1.25 g/L was determined in the UV/TiO_2process.Maximum CIP removal and mineralization efficiency of 93.1%and 47.3%were obtained in PFP against 69.7%and 27.6%in the UV/TiO_2process.The mass spectra could identify seventeen intermediate products including iron-CIP complexes in PFP,and only seven intermediate products were found in the UV/TiO_2process with a majority of common products in both the processes.The proposed mechanism supported by the mass spectra bridged the routes of CIP cleavage in the PFP and UV/TiO_2process,and the decomposition pathway of Fe~(3+)-CIP chelate complexes in PFP was also elucidated.Both in PFP and UV/TiO_2processes,the target site of HO~·radical attack was the secondary-N atom present in the piperazine ring of the CIP molecule.The death of Escherichia coli bacteria was 55.7%and 66.8%in comparison to the control media after 45 min of treatment in PFP and UV/TiO_2process,respectively.     

Efficient reduction and adsorption of Cr(Ⅵ) using FeCl3-modified biochar:Synergistic roles of persistent free radicals and Fe(Ⅱ)

Transition metal iron and persistent free radicals(PFRs) both affect the redox properties of biochar, but the electron transfer relationship between them and the coupling reduction mechanism of Cr(Ⅵ) requires further investigation. To untangle the interplay between iron and PFRs in biochar and the infuences on redox properties, FeCl₃-modified rice husk biochar(FBCs) was prepared and its reduction mechanism for Cr(Ⅵ) without light was evaluated. The FBCs had higher surface positive cha...     

Biphasic reduction model for predicting the impacts of dye-bath constituents on the reduction of tris-azo dye Direct Green-1 by zero valent iron(Fe~0)

Influence of common dye-bath additives, namely sodium chloride, ammonium sulphate,urea, acetic acid and citric acid, on the reductive decolouration of Direct Green 1 dye in the presence of Fe~0 was investigated. Organic acids improved dye reduction by augmenting Fe~0 corrosion, with acetic acid performing better than citric acid. Na Cl enhanced the reduction rate by its ‘salting out' effect on the bulk solution and by Cl~-anion-mediated pitting corrosion of iron surface.(NH_4)_2SO_4induced ‘salting out' effect accompanied by enhanced iron corrosion by SO_4~(2-)anion and buffering effect of NH+4 improved the reduction rates.However, at 2 g/L(NH_4)_2SO_4concentration, complexating of SO_4~(2-)with iron oxides decreased Fe~0 reactivity. Urea severely compromised the reduction reaction, onus to its chaotropic and‘salting in' effect in solution, and due to it masking the Fe~0 surface. Decolouration obeyed biphasic reduction kinetics(R~2 0.993 in all the cases) exhibiting an initial rapid phase,when more than 95% dye reduction was observed, preceding a tedious phase. Maximum rapid phase reduction rate of 0.955/min was observed at p H 2 in the co-presence of all dye-bath constituents. The developed biphasic model reckoned the influence of each dye-bath additive on decolouration and simulated well with the experimental data obtained at p H 2.     

Underestimation of phosphorus fraction change in the supernatant after phosphorus adsorption onto iron oxides and iron oxide–natural organic matter complexes

The phosphorus(P) fraction distribution and formation mechanism in the supernatant after P adsorption onto iron oxides and iron oxide-humic acid(HA) complexes were analyzed using the ultrafiltration method in this study.With an initial P concentration of 20 mg/L(I =0.01 mol/L and pH = 7),it was shown that the colloid(1 kDa-0.45 μm) component of P accounted for 10.6%,11.6%,6.5%,and 4.0%of remaining total P concentration in the supernatant after P adsorption onto ferrihydrite(FH),goethite(GE),ferrihydrite-humic acid complex(FH-HA),goethite-humic acid complex(GE-HA),respectively.The 1 kDa component of P was still the predominant fraction in the supernatant,and underestimated colloidal P accounted for 2.2%,55.1%,45.5%,and 38.7%of P adsorption onto the solid surface of FH,FH-HA,GE and GE-HA,respectively.Thus,the colloid P could not be neglected.Notably,it could be interpreted that Fe~(3+) hydrolysis from the adsorbents followed by the formation of colloidal hydrous ferric oxide aggregates was the main mechanism for the formation of the colloid P in the supernatant.And colloidal adsorbent particles co-existing in the supernatant were another important reason for it.Additionally,dissolve organic matter dissolved from iron oxide-HA complexes could occupy large adsorption sites of colloidal iron causing less colloid P in the supernatant.Ultimately,we believe that the findings can provide a new way to deeply interpret the geochemical cycling of P,even when considering other contaminants such as organic pollutants,heavy metal ions,and arsenate at the sediment/soil-water interface in the real environment.     

Iron-doped Mn-Ce/TiO2 catalyst for low temperature selective catalytic reduction of NO with NH3

The catalysts of iron-doped Mn-Ce/TiO 2(Fe-Mn-Ce/TiO 2) prepared by sol-gel method were investigated for low temperature selective catalytic reduction(SCR) of NO with NH 3.It was found that the NO conversion over Fe-Mn-Ce/TiO 2 was obviously improved after iron doping compared with that over Mn-Ce/TiO 2.Fe-Mn-Ce/TiO 2 with the molar ratio of Fe/Ti = 0.1 exhibited the highest activity.The results showed that 96.8% NO conversion was obtained over Fe(0.1)-Mn-Ce/TiO 2 at 180°C at a space velocity of 50,000 hr 1.Fe-Mn-Ce/TiO 2 exhibited much higher resistance to H 2 O and SO 2 than that of Mn-Ce/TiO 2.The properties of the catalysts were characterized using X-ray diffraction(XRD),N 2 adsorption,temperature programmed desorption(NH 3-TPD and NOx-TPD),and Xray photoelectron spectroscopy(XPS) techniques.BET,NH3-TPD and NOx-TPD results showed that the specific surface area and NH3 and NOx adsorption capacity of the catalysts increased with iron doping.It was known from XPS analysis that iron valence state on the surface of the catalysts were in Fe3+ state.The doping of iron enhanced the dispersion and oxidation state of Mn and Ce on the surface of the catalysts.The oxygen concentrations on the surface of the catalysts were found to increase after iron doping.Fe-Mn-Ce/TiO2 represented a promising catalyst for low temperature SCR of NO with NH3 in the presence of H2 O and SO2.     

Abiotic degradation of four phthalic acid esters in aqueous phase under natural sunlight irradiation

Abiotic degradability of four phthalic acid esters (PAEs) in the aquatic phase was evaluated over a wide pH range 5–9. The PAE solutions in glass test tubes were placed either in the dark and under the natural sunlight irradiation for evaluating the degradation rate via hydrolysis or photolysis plus hydrolysis, respectively, at ambient temperature for 140 d from autumn to winter in Osaka, Japan. The e ciency of abiotic degradation of the PAEs with relatively short alkyl chains, such as butylbenzyl phthalate (BBP) and di-nbutyl phthalate (DBP), at neutral pH was significantly lower than that in the acidic or alkaline condition. Photolysis was considered to contribute mainly to the total abiotic degradation at all pH. Neither hydrolysis nor photolysis of di-ethylhexyl phthalate (DEHP) proceeded significantly at any pH, especially hydrolysis at neutral pH was negligible. On the other hand, the degradation rate of diisononyl phthalate (DINP) catalyzed mainly by photolysis was much higher than those of the other PAEs, and was almost completely removed during the experimental period at pH 5 and 9. As a whole, according to the half-life (t1=2) obtained in the experiments, the abiotic degradability of the PAEs was in the sequence: DINP (32–140 d) > DBP (50–360 d), BBP (58–480 d) > DEHP (390–1600 d) under sunlight irradiation (via photolysis plus hydrolysis). Although the abiotic degradation rates for BBP, DBP, and DEHP are much lower than the biodegradation rates reported, the photolysis rate for DINP is comparable to its biodegradation rate in the acidic or alkaline condition.     

Nanoscale zero-valent iron/magnetite carbon composites for highly efficient immobilization of U(VI)

Nanoscale zerovalent iron/magnetic carbon (NZVI/MC) composites were successfully synthesized by simply calcining yellow pine and iron precursors. NZVI/MC pyrolyzed at 800°C (NZVI/MC800) had a higher percentage of NZVI and displayed better resistance to aggregation and oxidation of NZVI than samples prepared at other temperatures. The NZVI/MC800 material was applied for the elimination of U(VI) from aqueous solutions. The results suggested that the NZVI/MC800 displayed excellent adsorption capacity (203.94?mg/g) toward U(VI). The significant adsorption capacity and fast adsorption kinetics were attributed to the presence of well-dispersed NZVI, which could quickly reduce U(VI) into U(IV), trapping the guest U(IV) in the porous biocarbon matrix. The removal of U(VI) on the NZVI/MC samples was strongly affected by solution pH. The NZVI/MC samples also displayed outstanding reusability for U(VI) removal after multiple cycles. These findings indicate that NZVI/MC has great potential for remediation of wastewater containing U(VI).     

Metabolism of benzo[a]pyrene in peroxynitrite/Fe(III) porphyrin system

The peroxynitrite/porphyrin biomimetic system was established to investigate the effects of peroxynitrite on benzo[a]pyrene (B[a]P) metabolism. Three model systems consisting of different iron porphyrins were compared, and the results showed that the peroxynitrite/T(p-Cl)PPFeCl system was the highest catalytic efficiency in the metabolism of B[a]P. We analyzed the B[a]P metabolites produced from this system by RP-HPLC method and firstly identified the formation of nitrobenzo[a]pyrenes which are the special metabolites of B[a]P induced by peroxynitrite.     

Experimental study on Cr(Ⅵ) reduction by Pseudomonas aeruginosa

Investigation on Cr( Ⅵ ) reduction was conducted using Pseudomonas aeruginosa. The study demonstrated that the Cr(Ⅵ) canbe effectively reduced to Cr( Ⅲ ) by Pseudomonas aeruginosa. The effects of the factors affecting Cr( Ⅵ ) reduction rate including carbon source type, pH, initial Cr(Ⅵ) concentration and amount of calls inoculum were thoroughly studied. Malate was found to yield maximum biotransformation, followed by succinate and glucose, with the reduction rate of 60.86%, 43. 76% and 28.86% respectively. The optimum pH for Cr( Ⅵ ) reduction was ?.0, with reduction efficiency of 61.71 % being achieved. With the increase of initial Cr(Ⅵ) concentration,the rate of Cr(Ⅵ) reduction decreased. The reduction was inhibited strongly when the initial Cr(Ⅵ) concentration increased to 157 mg/L. As the amount of cells inoculum increased, the rate of Cr( Ⅵ ) reduction also increased. The mechanism of Cr( Ⅵ ) reduction and final products were also analysed. The results suggested that the soluble enzymes appear to be responsible for Cr (Ⅵ) reduction by Pseudomonas aeruginosa, and the reduced Cr( Ⅲ ) was not precipitated in the form of Cr(OH)3.     

Simultaneous Fe(Ⅲ) reduction and ammonia oxidation process in Anammox sludge

In recent years, there have been a number of reports on the phenomenon in which ferric iron(Fe(Ⅲ)) is reduced to ferrous iron [Fe(Ⅱ)] in anaerobic environments, accompanied by simultaneous oxidation of ammonia to NO2-, NO3-, or N2.However, studies on the relevant reaction characteristics and mechanisms are rare. Recently, in research on the effect of Fe(Ⅲ) on the activity of Anammox sludge, excess ammonia oxidization has also been found.Hence, in the present study, Fe(Ⅲ) was used to serve as the electron acceptor instead of NO2-,and the feasibility and characteristics of Anammox coupled to Fe(Ⅲ) reduction(termed Feammox) were investigated. After 160 days of cultivation, the conversion rate of ammonia in the reactor was above 80%, accompanied by the production of a large amount of NO3-and a small amount of NO2-. The total nitrogen removal rate was up to 71.8%. Furthermore,quantities of Fe(Ⅱ) were detected in the sludge fluorescence in situ hybridization(FISH) and denaturated gradient gel electrophoresis(DGGE) analyses further revealed that in the sludge, some Anammox bacteria were retained, and some microbes were enriched during the acclimatization process. We thus deduced that in Anammox sludge, Fe(Ⅲ) reduction takes place together with ammonia oxidation to NO2-and NO3-along with the Anammox process.     

Impact of dissolved organic matter on the photolysis of the ionizable antibiotic norfloxacin

Norfloxacin(NOR), an ionizable antibiotic frequently used in the aquaculture industry, has aroused public concern due to its persistence, bacterial resistance, and environmental ubiquity.Therefore, we investigated the photolysis of different species of NOR and the impact of a ubiquitous component of natural water — dissolved organic matter(DOM), which has a special photochemical activity and normally acts as a sensitizer or inhibiter in the photolysis of diverse organics; furthermore, scavenging experiments combined with electron paramagnetic resonance(EPR) were performed to evaluate the transformation of NOR in water. The results demonstated that NOR underwent direct photolysis and self-sensitized photolysis via hydroxyl radical(U OH) and singlet oxygen(1O2) based on the scavenging experiments. In addition, DOM was found to influence the photolysis of different NOR species, and its impact was related to the concentration of DOM and type of NOR species. Photolysis of cationic NOR was photosensitized by DOM at low concentration, while zwitterionic and anionic NOR were photoinhibited by DOM, where quenching of U OH predominated according to EPR experiments, accompanied by possible participation of excited triplet-state NOR and1O2. Photo-intermediate identification of different NOR species in solutions with/without DOM indicated that NOR underwent different photodegradation pathways including dechlorination, cleavage of the piperazine side chain and photooxidation, and DOM had little impact on the distribution but influenced the concentration evolution of photolysis intermediates. The results implied that for accurate ecological risk assessment of emerging ionizable pollutants, the impact of DOM on the environmental photochemical behavior of all dissociated species should not be ignored.     

Photolysis kinetics and influencing factors of bisphenol S in aqueous solutions

The photodegradation of bisphenol S (BPS) in aqueous solutions was studied under different conditions. Photolysis and kinetics were investigated, as were the photolysis mechanism and the influences of initial pH value, light source, and environmental substances in water. The results showed that the photolysis of BPS occurred under UV light, and the rate increased with light source intensity. The photolysis of 5.0-50.0 mg/L BPS in water followed first-order kinetics: the rate was γ= 0.0161C_BPS under a 40-W UV-lamp, and the degradation half-life was 43.1 min. Due to its absorption of light, direct photolysis of BPS was a predominant pathway for BPS but was not obviously affected by reactive oxygen species. The results confirmed that the photolysis rates of BPS in alkaline water solution were faster than those in acidic and neutral water solution because of the ionization of BPS. The photodegradation rate of BPS increased in the presence of chloride and ferric ions, while the rate was inhibited by nitrate and phosphate in aqueous solution.     

Effect of sorbed and desorbed Zn(Ⅱ) on the growth of a green alga (Chlorella pyrenoidosa)

Toxic effect of Zn(Ⅱ) on a green alga (Chlorella pyrenoidasa) in the presence of sepiolite and kaolinite was investigated.The Zn-free clays were found to have a negative impact on the growth of C.pyrenoidosa in comparison with control samples (without adding any clay or Zn(Ⅱ)).When Zn(Ⅱ) was added,the algae in the presence of clays could be better survived than the control samples,which was actually caused by a decrease in Zn(Ⅱ) concentration in the solution owing to the adsorption of Zn(Ⅱ) on the clays.When the solution system was diluted,the growth of algae could be further inhibited as compared to that in a system which had the same initial Zn(Ⅱ) concentration as in the diluted system.This in fact resulted from desorption of Zn(Ⅱ) from the zinc-contaminated clays,although the effect varied according to the different desorption capabilities of sepiolite and kaolinite.Therefore the adsorption and desorption processes of Zn(Ⅱ) played an important part in its toxicity,and adsorption and desorption of pollutants on soils/sediments should be well considered in natural eco-environmental systems before their risk of toxicity to aquatic organisms was assessed objectively.