Effects of humic acid fractions with different polarities on photodegradation of 2,4-D in aqueous environments

Four fractions(A,B,C,and D)of humic acids(HAs)were separated based on the polarity from weak to strong.UV-vis absorption and Fourier transform infrared spectroscopy(FTIR)analysis show that the fractions C and Dpossessedmore aromatic C5C content.The influences of HAs and their fractions on the photolysis were investigated by the photodegradation of 2,4-D solutions under simulated solar light irradiation.The degradation rate of 2,4-D was found to decrease in the presence of bulk HAs or their fractions especially at high HAs concentration.The fractions of strong polarity C and D retarded the degradation rate more than the fractions of weak polarity A and B.This could be attributed to the different absorption intensity of the four HAs fractions in the order of D≥C>A>B,and the stronger π-π electron donor-acceptor interactions between the strong polar fractions and 2,4-D.

Complexation of iron by salicylic acid and its effect on atrazine photodegradation in aqueous solution

The photodegradation of atrazine and the photochemical formation of Fe(Ⅱ)and H_(2)O_(2)in aqueous solutions containing salicylic acid and Fe(Ⅲ)were studied under simulated sunlight irradiation.Atrazine photolysis followed first-order reaction kinetics,and the rate constant(k)corresponding to the solution of Fe(Ⅲ)-salicylic acid complex(Fe(Ⅲ)-SA)was only 0.0153 h^(–1),roughly one eighth of the k observed in the Fe(Ⅲ)alone solution(0.115 h^(–1)).Compared with Fe(Ⅲ)solution,the presence of salicylic acid significantly enhanced the formation of Fe(Ⅱ)but greatly decreased H_(2)O_(2)generation,and their subsequent product,hydroxyl radical(%OH),was much less,accounting for the low rate of atrazine photodegradation in Fe(Ⅲ)-SA solution.The interaction of Fe(Ⅲ)with salicylic acid was analyzed using Fourier-transform infrared(FTIR)spectroscopy and UV-visible absorption,indicating that Fe(Ⅲ)-salicylic acid complex could be formed by ligand exchange between the hydrogen ions in salicylic acid and Fe(Ⅲ)ions.

Competitive adsorption and desorption of copper and lead in some soil of North China

The competitive adsorption and desorption of Pb（II） and Cu（II） ions in the soil of three sites in North China were investigated using single and binary metal solutions with 0.01 tool. L^-1 CaC12 as background electrolyte. The desorption isotherms of Pb（lI） and Cu（II） were similar to the adsorption isotherms, which can be fitted well by Freundlich equation （R2 〉 0.96）. The soil in the three sites had greater sorption capacities for Pb（II） than Cu （II）, which was affected strongly by the soil characteristics. In the binary metal solution containing 1 ： 1 molar ratio of Pb（II） and Cu（II）, the total amount of Pb（II） and Cu（lI） adsorption was affected by the simultaneous presence of the two metal ions, indicating the existence of adsorption competition between the two metal ions. Fourier transform infrared （FT-IR） spectroscopy was used to investigate the interaction between soil and metal ions, and the results revealed that the carboxyl and hydroxyl groups in the soil were the main binding sites of metal ions.

Accelerated degradation of orange G over a wide pH range in the presence of FeVO4

In this study, FeVO4 was prepared and used as Fenton-like catalyst to degrade orange G （OG） dye. The removal of OG in an aqueous solution containing 0.5 g.L l FeVO4 and 15 mmol.L ] hydrogen peroxide at pH 7.0 reached 93.2%. Similar rates were achieved at pH 5.7 （k = 0.0471 min-1） pH 7.0 （k= 0.0438 min-1）, and pH 7.7 （k = 0.0434 min-1）. The FeWO4 catalyst successfully overcomes the problem faced in the heterogeneous Fenton process, i.e., the narrow working pH range. The data for the removal of OG in FeVO4 systems containing H202 conform to the Langmuir-Hinshelwood model （R2 = 0.9988）, indicating that adsorption and surface reaction are the two basic mechanisms for OG removal in the FeVO4 H202 system. Furthermore, the irradiation of FeVO4 by visible light significantly increases the degradation rate of OG, which is attributed to the enhanced rates of the iron cycles and vanadium cycles.

Benzenesulfonic acid-grafted UIO-66 with improved hydrophobicity as a stable Brønsted acid catalyst

Hydrothermal and catalytic stability of UIO-66 MOFs with defective structures are critical aspects to be considered in their catalytic applications,especially under the conditions involving water,moisture and/or heat.Here,we report a facile strategy to introduce the macromolecular acid group to UIO-66 to improve the stability of the resulting UIO-66−PhSO3H MOF in aqueous phase catalysis.In detail,UIO-66−PhSO3H was obtained by grafting benzenesulfonic acid on the surface of the pristine UIO-66 to introduce the hydrophobicity,as well as the Brønsted acidity,then assessed using catalytic hydrolysis of cyclohexyl acetate(to cyclohexanol)in water.The introduction of hydrophobic molecules to UIO-66 could prevent the material from being attacked by hydroxyl polar molecules effectively,explaining its good structural stability during catalysis.UIO-66−PhSO3H promoted the conversion of cyclohexyl acetate at ca.87%,and its activity and textural properties were basically intact after the cyclic stability tests.The facile modification strategy can improve the hydrothermal stability of UIO-66 significantly,which can expand its catalytic applications in aqueous systems.