Effects of cerium precursors on surface properties of mesoporous CeMnO_x catalysts for toluene combustion

Mesoporous CeMnOx composite oxides catalysts were prepared by surfactant-assisted co-precipitation method and used for the catalytic oxidation of toluene.The effect of different cerium precursors[Ce(NO3)3 and(NH4)2 Ce(NO3)6] on catalyst structure,surface properties and toluene combustion activities of mesoporous CeMnOx catalysts were investigated.The Ce(Ⅲ)MnOx catalyst prepared from Ce(NO3)3 precursor shows higher catalytic activity,with a 90% conversion temperature of 240℃,which is better than the Ce(Ⅳ)MnOx catalyst derived from[(NH4)2 Ce(NO3)6] precursor.On the basis of characterizations,it reveals that abundant surface content of Mn4+,better redox behavior and larger concentration of surface active oxygen species are responsible for the excellent catalytic performance.

Preliminary investigation of phosphorus adsorption onto two types of iron oxide-organic matter complexes

Iron oxide（FeO）coated by natural organic matter（NOM）is ubiquitous.The associations of minerals with organic matter（OM）significantly changes their surface properties and reactivity,and thus affect the environmental fate of pollutants,including nutrients（e.g.,phosphorus（P））.In this study,ferrihydrite/goethite-humic acid（FH/GE–HA）complexes were prepared and their adsorption characteristics on P at various p H and ionic strength were investigated.The results indicated that the Fe O–OM complexes showed a decreased P adsorption capacity in comparison with bare Fe O.The maximum adsorption capacity（Q（max））decreased in the order of FH（22.17 mg/g）〉FH-HA（5.43 mg/g）〉GE（4.67 mg/g）〉GE-HA（3.27 mg/g）.After coating with HA,the amorphous FH–HA complex still showed higher P adsorption than the crystalline GE–HA complex.The decreased P adsorption observed might be attributed to changes of the Fe O surface charges caused by OM association.The dependence of P adsorption on the specific surface area of adsorbents suggests that the Fe O component in the complexes is still the main contributor for the adsorption surfaces.The P adsorptions on Fe O–HA complexes decreased with increasing initial p H or decreasing initial ionic strength.A strong dependence of P adsorption on ionic strength and p H may demonstrate that outer-sphere complexes between the OM component on the surface and P possibly coexist with inner-sphere surface complexes between the Fe O component and P.Therefore,previous over-emphasis on the contributions of original minerals to P immobilization possibly over-estimates the P loading capacity of soils,especially in humic-rich areas.

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 Fe3＋ 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.

Effect of different supports on activity of Mn-Ce binary oxides catalysts for toluene combustion

The effects of support materials on catalytic performance were investigated in catalytic removal of toluene.And the Mn–Ce binary oxides as active components were supported on ZrO_(2),SiO_(2),γ-Al_(2)O_(3) and TiO_(2) support materials.Many techniques,including X-ray diffraction(XRD),Brunauer–Emmett–Teller method(BET),X-ray photoelectron spectroscopy(XPS),temperature-programmed reduction(TPR)and NH_(3)-temperature-programmed desorption(NH_(3)-TPD),were used to characterize physicochemical properties.Among the different catalysts,the MnCe/ZrO_(2) catalyst with the lowest specific surface area(39.7 m^(2)/g)shows the best catalytic activity.In terms of toluene conversion,the activity order is as follows:MnCe/ZrO_(2)>MnCe/TiO_(2)≈MnCe/SiO_(2)>MnCe/Al_(2)O_(3).The better performance of MnCe/ZrO_(2) should be attributed to the low-temperature reducibility,and abundant surface species(Mn^(4+)and lattice oxygen).And XPS and TPR results reveal that more surface abundant Mn and Ce elements generate good interaction in MnCe/ZrO_(2).The weak interaction between metal oxide and support also boosts the dispersion and complete reduction of MnCe oxides at low temperature.In addition,the in-situ DRIFTS results clarify that the carbonate species are main intermediates in MnCe/ZrO_(2) sample during surface reaction process.

Physicochemical disintegration of biochar:a potentially important process for long-term cadmium and lead sorption

Cadmium(Cd)and lead(Pb)contaminated soils that are used for food production can lead to metal bioaccumulation in the food chain and eventually affect human health.In these agroecosystems,means by which Cd and Pb bioavailability can be reduced are desperately required,with biochar as a proxy for bioavailability reductions.Molecular Cd and Pb sorption mecha-nisms within short-(0-2 years)or long-term(8-10 years)time periods following biochar application to a contaminated rice paddy soil were investigated.A combination of Fourier transform infrared spectroscopy,X-ray photoelectron spectroscopy,and soft X-ray imaging was utilized to discern potential metal sorption mechanisms.Following both short-and long-term biochar applications,soil Cd and Pb bioavailable fractions shifted partially towards metal(hydr)oxide and carbonate pre-cipitates,and partially towards biochar-organic function group associations;oxygen-containing groups,such as C=O and O-H,appeared to bind Cd and Pb.Soft X-ray imaging results suggested that heavy metals were primarily sorbed on biochar exterior surfaces,yet given time and particle disintegration,metals sorbed onto biochar interior pore walls.Findings sug-gest that biochar may play a pivotal role in reducing long-term bioavailable Cd and Pb in contaminated soils.Observations also support previous findings that suggest biochar use can lead to reduced heavy metal transfer to plants and potentially to reduced heavy metal consumption by humans.

Nutrient alterations following biochar application to a Cd-contaminated solution and soil

Biochars,when applied to contaminated solutions or soils,may sequester potentially toxic elements while releasing neces-sary plant nutrients.This purpose of this study focused on quantifying both phenomenon following wheat straw(Triticum aestivum L.)biochar application(0,5,and 15%by wt)to a Cd containing solution and a Cd-contaminated paddy soil using 240-day laboratory batch experiments.Following both experiments,solid phases were analyzed for elemental associations using a combination of wet chemical sequential extractions and synchrotron-based X-ray absorption spectroscopy(XAS).When wheat straw biochar was applied at 15%to Cd containing solutions,Cd and Zn concentrations decreased to below detection in some instances,Ca and Mg concentrations increased by up to 290%,and solution pH increased as compared to the 5%biochar application rate.Similar responses were observed when biochar was added to the Cd-contaminated paddy soil,suggesting that this particular biochar has the ability to sequester potentially toxic elements while releasing necessary plant nutrients to the soil solution.When significant,positive correlations existed between nutrient release over time,while negative correlations were present between biochar application rate,potentially toxic element sorption and pH.The latter suggests that potentially toxic elements were sorbed by a combination of organic functional groups or mineral precipitation based on whether pH was above or below~7.In support of this contention,the wet chemical sequential extraction procedure in conjunction with previously observed Cd or current Zn XAS showed that biochar application promoted the formation of layered double hydroxides,sorption to(oxy)hydroxides,and organically bound to biochar as Zn species.As a multi-functional material,biochar appears to play an important role in sequestering Cd while releasing essential plant nutrients.These findings suggest that biochar may be a‘win-win’for improving environmental quality in potentially toxic element contaminated agroecosystems.