To ascertain the effects of conventional hydrochemical components on the presence of endogenous fine loess particles (EFLPs) in groundwater over loess regions, Na+, NO3− and Cu2+, as conventional hydrochemical components, were employed in batch tests with EFLPs from a typical loess as aquifer media in Guanzhong Plain, China. The results showed that EFLPs had high zeta potential (ζ) and remained suspended over 40 h, indicating their good dispersity and potential to be suspended in groundwater. ζ was employed to replace electrostatic repulsion in the DLVO equation to determine the critical coagulation concentrations for Cu(NO3)2 and NaF as 0.1 mmol/L and 50 mmol/L for 1.1 µm D50 EFLPs, which were almost consistent with the batch test results and greater than those in the groundwater, respectively, further implying that EFLPs are likely to be suspended in groundwater. The multi-factor tests showed that the key factors including particle size, hydro-chemical component and concentration interacted with each other and their relative magnitudes varied in the test processes, where the effects of concentration strengthened while those of the component weakened. So, hydrogeochemical conditions were beneficial to the suspension of EFLPs and the benefit got strong along the groundwater flow path, which is conducive to the cotransport of EFLPs with pollutants in groundwater over loess regions.
In this study, a novel metal-pillared kaolinite (KDF) Fenton-like catalyst was prepared via a twostep procedure involving intercalating and pillaring.The characterization results indicated that the interlayer spacing, specific surface area, pore area and volume were dramatically enhanced for KDF compared with raw kaolinite, and FeOOH crystals were present in the interlayer spaces of KDF.When KDF was used to catalyze the Fenton-like reaction for nitrobenzene (NB) degradation in the presence of H 2 O 2 , more than 85% of NB was removed.The influencing factors of H 2 O 2 concentration, KDF dosage, NB initial concentration and reaction temperature as well the Fenton-like reaction mechanism were examined.The optimal conditions were determined to be: 10 mmol/L H 2 O 2 , 75 mg/L NB, and KDF dosage of 1.0 g/L.The first-order kinetic reaction rate constants at different temperatures were fitted by the Arrhenius equation and the activation energy (E a ) was calculated to be 36.34kJ/mol.The experimental results in the presence of a free radical scavenger showed that the NB degradation mechanism catalyzed by KDF was mainly due to the generation of free hydroxyl radicals.The low percentage of leaching Fe-containing active components showed that the KDF catalyst has good stability, suggesting its potential application in environmental remediation.
In this study, chitosan/polyacrylamide/poly(vinyl alcohol)/Fe/glutaraldehyde (CPPFG) copolymers, termed as CPPFG I, II, III and IV, respectively, were prepared with corresponding amounts of glutaraldehyde (GA).These copolymers were then employed to do batch experiments as a function of pH, Cr(VI) initial concentration, contact time, temperature and coexisting anions to study Cr(VI) adsorption process.Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to explore the characteristics of the adsorbents before and after loaded Cr(VI) and adsorption mechanism.The results showed that the copolymers had a fast adsorption rate and high adsorption efficiency above 99.50% which was hardly affected by initial pH values varying from 3.0 to 8.0 and the anions.The adsorption fitted Langmuir and Temkin isotherm models well.The removal of Cr(VI) followed pseudo-second-order and intraparticle diffusion kinetic models, and its rate was mainly controlled by chemical adsorption and intraparticle mass transport.The calculated thermodynamic parameters (ΔG 0 , ΔH 0 and ΔS 0 ) demonstrated that the adsorption was a spontaneous and endothermic process.The adsorption capacity and rate were strongly depended on the quantity of the available functional binding sites (i.e., -OH, -C=N and -NH), and surface morphologies with different GA cross-link densities under the studied conditions.The possible mechanism was proposed based on the data of FTIR, XPS, SEM and zeta potential.Adsorption properties comparison showed the copolymer was an alternative as adsorbent to remove Cr(VI) from natural water.
Chitosan/polyacrylamide/poly(vinyl alcohol)/Fe/glutaraldehyde (CS/PAM/PVA/Fe/GA) was reported as an adsorbent with several advantages, while some major disadvantages such as low desorption rate and poor reutilization, which formed an obstacle to its application in low-concentration Cr(VI) adsorption performance.These major disadvantages the authors speculate might be ascribed to PAM.To test the speculation correct, CS/PVA/Fe/GA was synthesized as adsorbent and then characterized using scanning electron microscopy, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.Low-concentration (5.0-30.0mg L -1 ) Cr(VI) adsorption was tested as a function of solution pH value, Cr(VI)initial concentration and adsorption time, and its primary mechanisms were explored.The results showed that, CS/PVA/Fe/GA has not only higher desorption rate and reutilization but also higher adsorption efficiency and (3.0-10.0)pH-independence compared with CS/PAM/PVA/Fe/GA; the adsorption mechanisms were also different, the complexation of the -NH 2 group with Fe(III) was especially included herein.The complexation, which was insensitive to pH, mainly contributed to the above advantages, proving our speculation correct.Thus, CS/PVA/Fe/ GA is an alternative adsorbent to remove Cr(VI) from natural water.
Herein, xylan-g-PMMA was synthesized by grafting poly(methyl methacrylate) (PMMA) onto xylan and characterized by FT-IR and HSQC NMR spectroscopies, and the xylan-g-PMMA/TiO2 solution was used to electrospun nanofibers at the voltage of 15 Kv, which was the first time employing xylan to electrospun nanofibers. Moreover, the electrospinning operating parameters were optimized by assessing the electrospinning process and the morphology of electrospun fibers, as follows: the mixed solvent of DMF and chloroform in a volume ratio of 5:1, an anhydroxylose unit (AXU)/MMA molar ratio lower than 1:2, the flow speed of 0.00565–0.02260 mL/min, and a receiving distance of 10–15 cm. Diameters of the electrospun fibers increased with increasing DMF content in the used solvent mixture, MMA dosage, and receiving distance. TiO2 nanoparticles were successfully dispersed in electrospun xylan-g-PMMA nanofibers and characterized by scanning electron microscopy, energy dispersive X-ray diffraction spectrum, and X-ray photoelectron spectroscopy, and their application for methylene blue (MB) degradation presented above 80% photocatalytic efficiency, showing the good potential in water treatment.
Functionalized pristine graphite nanoplatelets (fGNPs) by methanesulfonic acid/isopropyltrioleictitanate (MSA/NDZ-105) are used to fabricate fGNPs/polyphenylene sulfide (fGNPs/PPS) composites by mechanical ball milling followed by a compression molding method.
In this study, Fe(III)-cross-linked chitosan beads (Fe(III)-CBs) were synthesized and employed to explore the characteristics and primary mechanism of their hexavalent chromium (Cr(VI)) adsorption under low concentration Cr(VI) (less than 20.0 mg l −1 ) and a pH range from 2.0 to 8.0. Batch tests were conducted to determine the Cr(VI) adsorption capacity and kinetics, and the effects of pH and temperature on the adsorption under low concentration Cr(VI) and a pH range from 2.0 to 8.0. Scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy were employed to explore the characteristics of Fe(III)-CBs and their Cr(VI) adsorption mechanisms. The results show that, unlike the adsorption of other absorbents, the Cr(VI) adsorption was efficient in a wide pH range from 2.0 to 6.0, and well described by the pseudo-first-order model and the Langmuir–Freundlich isotherm model. The capacity of Cr(VI) adsorption by Fe(III)-CBs was as high as 166.3 mg g −1 under temperature 25°C and pH 6.0. The desorption test was also carried out by 0.1 mol l −1 NaOH solution for Fe(III)-CBs regeneration. It was found that Fe(III)-CBs could be re-used for five adsorption–desorption cycles without significant decrease in Cr(VI) adsorption capacity. Ion exchange was confirmed between functional groups (i.e. amino group) and Cr(VI) anions (i.e. CrO42− ). The amino-like functional groups played a key role in Cr(VI) distribution on the Fe(III)-CBs surface; Cr(VI) adsorbed on Fe(III)-CBs was partially reduced to Cr(III) with alcoholic group served as electron donor, and then formed another rate-limiting factor. So, Fe(III)-CBs has a good prospect in purifying low concentration Cr(VI) water with a pH range from 2.0 to 6.0.
Abstract Adsorption performances of one pollutant on different adsorbents likely depend on the adsorbent microstructures heavily. Hereon, zeolite, diatomite and kaolinite particles were selected as inexpensive adsorbents in this study with 2,4,6-trinitrotoluene (TNT) as an organic pollutant for the batch test to verify the effect of adsorbent microstructure on TNT adsorption performance. The results of kinetic, adsorption isothermic, and thermodynamic analyses indicated that the adsorption process of TNT on three particles is controlled by chemisorption, and that both are non-spontaneous entropic endothermic reactions, although they have their own specific adsorption capacities, equilibration times, and kinetic rates. Comprehensively analyzing the characterization data and adsorption performances of the particles shows that, the pore physical properties including the pore diameter distribution and volume obviously control the adsorption capacities, and well the pore surface chemical properties such as the functional groups affect the adsorption kinetics; the microstructure affects the performances through the synergistic effect of physical and chemical pathways and results in the special performances. Briefly, a particle has its special microstructure and then determinedly unique performance. The finding provides insights into the role of the microstructure of the particles in their performances, and significances for selecting and utilizing the adsorbents in water treatment.
'/%3e%3cuse xlink:href='%23a' transform='rotate(23.036 .093 25.536)'/%3e%3cuse xlink:href='%23a' transform='rotate(45.87 1.273 16.18)'/%3e%3cuse xlink:href='%23a' transform='rotate(69.945 .996 12.078)'/%3e%3cuse xlink:href='%23a' transform='rotate(20.66 -19.689 31.932)'/%3e%3c/svg%3e)