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The influence of biochars on the fate of herbicides in soil depends mostly on environmental factors among which the role of soil minerals is not clear. Two wood-derived biochars produced at 400 °C (BC400) and 600 °C (BC600) were treated with alumina and montmorillonite to investigate their interaction with biochars and the influence of herbicide sorption. Both minerals exhibited a pore-expanding effect that was likely relative to the removal of authigenic organic matter away from the biochars' surface. Alumina brought more remarkable pore expansion by doubling the surface area of the BC400 biochar and the mesopore area of the BC600 biochar. Consequently, more adsorption sites were accessible for herbicide molecules, which resulted in higher sorption of herbicides (acetochlor and metribuzin) to the mineral-treated biochars than to the untreated biochars. The results are useful for understanding the change of surface and sorption properties of biochars with soil applications.

The reactivity of nanoscale zerovalent iron (NZVI) on removing chlorophenols (2-chlorophenol, 2,4-dichlorophenol, 2,4,6-trichlorophenol and pentachlorophenol) was remarkably enhanced by using a hydrophobic support of organobentonite (CTMA-Bent), namely the bentonite modified with organic cetyltrimethylammonium (CTMA) cations. The complete dechlorination of chlorophenols and total conversion into phenol using this novel NZVI/CTMA-Bent combination was observed in batch experiments. The kinetic studies suggested that the reduction of chlorophenols by NZVI was accelerated due to the enhanced adsorption onto CTMA-Bent, which facilitated the mass transfer of chlorophenols from aqueous to iron surface. The enhanced reduction rate by NZVI/CTMA-Bent was positively related to the hydrophobicity of chlorophenols, and an increasing linear relationship was obtained between the relative enhancement on reaction rate constants (k2/k1) and logKow values of chlorophenols. XPS results suggested there were fewer precipitates of ferric (hydro)xides formed on the surface of NZVI/CTMA-Bent, which may also lead to the improved reactivity and repetitive usability of NZVI/CTMA-Bent on removing chlorophenols., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

A novel composite gel composed of carboxymethyl-chitosan (CM-chit) and bentonite (H-bent) was used as the carrier for encapsulating atrazine and imidacloprid to control their release in water and retard their leaching in soil. Strong interactions between CM-chit and H-bent in the composite were confirmed by FT-IR, and good dispersion of pesticides in the carrier was observed by SEM. According to the results of release experiments in water, the CM-chit/H-bent composite carrier showed double advantages of both encapsulation by the polymer and sorption by the bentonite. The time taken for 50 % of active ingredients to be released, t₅₀, was prolonged to 572 h for atrazine and 24 h for imidacloprid, respectively. The difference between the two pesticides on release behavior was related to their hydrophobicity and water solubility. Leaching experiments through a soil layer showed that this novel carrier reduced the amount of pesticides available for leaching, and would be useful for diminishing the environmental pollution of pesticides.

NZVI was supported on a pillared bentonite (Al-bent) to enhance the reactivity of NZVI and prevent its aggregation. The performance and mechanisms of the combined NZVI/Al-bent on removing hexavalent chromium (Cr(VI)) was investigated by batch and XAFS experiments. The batch investigations indicated that Cr(VI) could be almost completely removed by NZVI/Al-bent after 120 min. The efficiency was not only much higher than that by NZVI (63.0%), but also superior to the sum of NZVI reduction and Al-bent adsorption (12.4%). Besides, NZVI/Al-bent exhibited good stability and reusability, and Al-bent could reduce the amount of iron ions released into the solution. XANES results provided evidence that NZVI/Al-bent could reduce Cr(VI) entirely into Cr(III), while NZVI reduced Cr(VI) partly into Cr(III) with a trace of Cr(VI) adsorbed on the corrosion products. The structure of Cr(VI)-treated NZVI/Al-bent determined with EXAFS revealed the formation of Cr-Al/Si bond, suggesting that some insoluble Cr(III) species might be transferred to the surface of Al-bent, therefore the precipitates on iron surface could be greatly reduced. The results demonstrated that Al-bent plays a significant role in enhanced reactivity and stability of NZVI, and may shed new light on design and fabrication of supported NZVI for environmental remediation., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Nanoscale zero valent iron (NZVI) was immobilized on the organobentonite (CTMA-bent), so as to enhance the reactivity of NZVI and prevent its aggregation. This novel composite (NZVI/CTMA-Bent) was characterized by transmission electron microscope and X-ray diffraction. Good dispersion of NZVI particles on the bentonite was observed. Its performance on removing pentachlorophenol (PCP) was investigated by batch experiments. Results showed NZVI/CTMA-Bent could rapidly and completely dechlorinate PCP to phenol with an efficiency of 96.2%. It was higher than the sum (54.5%) of reduction by NZVI (31.5%) and adsorption by CTMA-Bent (23.0%) separately. The kinetic studies indicated the removal rate of PCP was positively related to the adsorption. We proposed that the adsorption of PCP by CTMA-Bent enhanced the mass transfer of PCP from aqueous to iron surface. Besides, NZVI/CTMA-Bent exhibited good stability and reusability, and CTMA-Bent could also reduce the amount of iron ions released into the solution., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

The pillared bentonite prepared by intercalating poly(hydroxo Al(III)) cations into bentonite interlayers was used together with Fe(0) for removing nitrate in column experiments. The obvious synergetic effect on nitrate removal was exhibited through uniformly mixing the pillared bentonite with Fe(0). In such a mixing manner, the nitrate was 100% removed, and the removal efficiency was much higher than the simple summation of adsorption by the pillared bentonite and reduction by Fe(0). The influencing factors such as bentonite type, amount of the pillared bentonite and initial pH of nitrate solutions were investigated. In this uniform mixture, the pillared bentonite could adsorb nitrate ions, and facilitated the mass transfer of nitrate onto Fe(0) surface, then accelerated the nitrate reduction. The pillared bentonite could also act as the proton-donor, and helped to keep the complete nitrate removal for at least 10h even when the nitrate solution was fed at nearly neutral pH.

Carboxymethylcellulose (CMC) gel was used for encapsulating anionic herbicide 2,4-D for its controlled release. The slower release rate of 2,4-D in water and soil was obtained by adding in the gel formulation some modified bentonites, which were prepared by intercalating inorganic or organic cations in interlayers of Na(+)-saturated bentonite. The higher encapsulation efficiencies of 2,4-D were observed on the bentonite/CMC gel formulations due to the sorption of 2,4-D on modified bentonites. The time taken for 50% of 2,4-D to be released in water, t(50), showed a variation (8.8-19.8 h) for these gel formulations, the largest value corresponding to the formulation incorporated with hydroxy-iron intercalated bentonite that has the highest sorption capacity to 2,4-D. The gel formulations could also control the release of 2,4-D when applied to a thin soil layer and demonstrated potential to reduce leaching of such anionic herbicides in soil.

Both Fe pillared bentonite (Fe-B) and Al-Fe pillared bentonite (Al/Fe-B) were prepared and used as heterogeneous catalysts for the photo-Fenton discoloration of azo dye X-3B under UV irradiation. The catalysts were characterized by XRD, BET and TEM. The effects of solution pH, H(2)O(2) concentration, dye concentration and catalyst loading on the rate of discoloration were investigated in detail. The results indicate that the Fe-B and Al/Fe-B have high BET surface area (114.6 and 194.2 m(2)/g, respectively). Both the heterogeneous photo-Fenton processes employing the Fe-B or the Al/Fe-B as catalyst exhibit higher photo-catalytic activity compared to their corresponding homogeneous photo-Fenton process. The amount of Fe ions leached from the Al/Fe-B into the solution is much lower than that leached from the Fe-B during the reaction process.

Bentonite exfoliation liberated the interlayer surface with large area for immobilization of enzyme at high enzyme loading. Upon the electrostatic attraction between positively charged bovine pancreatic lipase (BPL), Yarrawia lipolytica lipase (YLL), trypsin and negatively charged surface of unilaminar bentonite, three nanohybrids with a stably card-like structure named as BPL-B, YLL-B and TB were facilely produced. These nanohybrids showed higher activities in hydrolysis as 115.2% (BPL-B), 154.8% (YLL-B) and 138.2% (TB) of that of the correspondingly free enzyme. Furthermore, BPL-B, YLL-B and TB retained 80%, 90% and 82% of each original activity after repeated use for 10, 12 and 8 times, respectively. The recyclable and active nanohybrids are expected to be widely applied as industrial catalysts in the future. [ABSTRACT FROM AUTHOR]

A positively-charged pillared bentonite (Al-bent) was used as the carrier of nanoscale zerovalent iron (NZVI) particles for accelerating the reductive removal of anionic Se(VI) from water by NZVI. A synergetic effect on Se(VI) removal by this NZVI/Al-bent composite was observed, with removal efficiency (95.7%) much higher than the sum (72.0%) of NZVI reduction (62.1%) and Al-bent adsorption (9.86%). The multiple roles of Al-bent in the reaction system of Se(VI) with NZVI were comprehensively investigated using XAFS techniques, XRD analysis, kinetic studies and pH monitoring. The results indicate that the positively-charged Al-bent as a good adsorbent to anionic Se(VI) accelerated the reductive transformation of Se(VI) into less soluble Se(-II). Al-bent also acted as a pH buffering agent, and contributed to the enhanced stability and reusability of NZVI. In addition, Al-bent could transfer the insoluble reduction products away from the iron surface according to EXAFS studies. Particularly, Al-bent could activate Fe(II) ions generated in the reaction system through an appropriate bonding at pH 8.0, and provide NZVI with an extra reduction capacity. The results indicate the significance of correct matching of bentonite support to target contaminant for developing novel remediation technique based on this natural mineral. [ABSTRACT FROM AUTHOR]

BACKGROUND Nitrobenzene ( NB) is a persistent environmental pollutant difficult to degrade. The aim of this study was to accelerate the reduction of NB by immobilization of nanoscale zero-valent iron ( NZVI) on an organobentonite ( CTMA-Bent). RESULTS Batch experiments indicated that NB was almost completely reduced by the immobilized iron sample ( NZVI/ CTMA-Bent), with aniline as the dominant reduction product. While only 60% of NB was reduced by the bare NZVI, and aniline accounted for only half of the NB reduced. Kinetic studies confirmed that the reaction of NB with NZVI was accelerated through CTMA-Bent adsorption. XPS investigations suggested that the improved recycling of the NZVI/ CTMA-Bent composite is related to less ferric (hydr)oxides formed during the reaction. CONCLUSION Immobilization of NZVI on the organobentonite CTMA-Bent proved to be an effective method for quick and complete conversion of NB to biodegradable aniline. This novel method to remove recalcitrant organic pollutants may promote the industrial application of NZVI technique in environmental remediation. © 2013 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Highlights: [•] The immobilized lipase on composite bentonite shows the highest activity. [•] Hydrophobicity and enlarged catalytic interface of the supports activate lipase. [•] The immobilized lipase shows excellent storage and operational stabilities. [•] The lower K m of immobilized lipase confirmed the improved affinity for olive oil. [Copyright &y& Elsevier]

Thehydrophobic property and structure of Na-bentonite (Na-bent)were tuned by intercalation with cationic surfactants for lipase adsorption.The adsorption isotherms of lipase on Na-bent and modified bentonitesdemonstrated Langmuir-type shape, and Na-bent showed higher adsorptionefficiency than modified bentonites. The observed overlap of lipasemolecules on the support and the interactions between these moleculesunder high protein loading caused the reduction in the activity ofimmobilized lipase. The immobilized lipases on modified bentonites(Bent-DTAB-lipase, Bent-CTAB-lipase, and Bent-OTAB-lipase) exhibitedhigher catalytic activity than that on Na-bent, due to the hydrophobicallyinterfacial activation of modified bentonites toward lipase. The highestcatalytic activity and stability were observed on Bent-CTAB-lipase,resulting from the tunable hydrophilic/hydrophobic balance of thesupport’s surface, while the excessive hydrophobic propertyshowed negative influence on lipase’s catalytic performance.The immobilized lipases onto modified bentonites with hydrophobicproperty showed higher thermal stability and reusability than Na-bent-lipase. [ABSTRACT FROM AUTHOR]

Abstract: In this work, a novel combination of pillared bentonite (OH-Al-bent) with zero valent iron (ZVI) was studied in column experiments so as to enhance Cr(VI) removal efficiency and improve the longevity of Fe0-based permeable reactive barriers. The influence of mixing manner, bentonite type, initial pH and OH-Al-bent amount on the removal efficiency were evaluated. The enhanced removal was attributed to the synergetic effect between adsorption by OH-Al-bent and reduction by ZVI. The adsorption facilitated the mass transfer of Cr(VI) from aqueous to iron surface, and thus accelerated the reduction of Cr(VI) by ZVI. Additionally, the higher removal efficiency was observed under lower pH, and the complete Cr(VI) removal could last longer due to the buffering effect of OH-Al-bent. XPS analysis indicated that Cr(VI) was reduced to Cr(III), and then precipitated in the forms of Cr(III) and Fe(III) hydroxides or Cr(III)–Fe(III) hydroxides. But fewer precipitations on iron surface were detected when OH-Al-bent was combined with ZVI, which might also contribute to the extended longevity of reaction medium. [Copyright &y& Elsevier]

Abstract: The organobentonite (CTMA-Bent) was prepared from Na+-saturated bentonite (Na-Bent) by intercalation with cetyltrimethylammonium bromide (CTMA), and used as a carrier of nanoscale zero valent iron (NZVI) for the removal of atrazine. The NZVI/CTMA-Bent composite was characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM), and good dispersion of nanoscale iron particles on the carrier was observed. The removal efficiency of atrazine by this composite was compared with that by commercial iron powder and NZVI itself. For both treatments by NZVI and NZVI/CTMA-Bent, the removal efficiency increased as the pH of the solution decreased, and the removal percentage of atrazine by NZVI/CTMA-Bent reached 63.5% at initial pH=5.0 after 120min. It is not only much higher than that (26.6%) by NZVI containing the same amount of iron, but also superior to the sum (32.1%) of reduction by NZVI plus adsorption by CTMA-Bent (5.5%). Besides, the NZVI/CTMA-Bent has a good long-term stability, and the carrier CTMA-Bent could prevent the iron ions (the byproduct of dechlorination) from leaching into the solution. [ABSTRACT FROM AUTHOR]

Abstract: Inorganic–organic bentonites were prepared by co-adsorption of cetyl trimethylammonium (CTMA) ions onto bentonites intercalated by poly(hydroxo aluminum) or poly(hydroxo iron) cations. The inorganic–organic bentonites adsorbed much more anionic herbicide 2,4-D than the inorganic and organic bentonites. For bentonites modified with poly(hydroxo iron) and CTMA ions, the enhancement may be attributed not only to the van der Waals interaction between 2,4-D and the organic cations, but also to the strong bonding of 2,4-D on the inorganic cations, which was confirmed by desorption studies, XRD measurements and FTIR analysis. The inorganic–organic bentonites did not show higher adsorption of acetochlor compared to the organo-bentonite. For such a nonionic herbicide, the van der Waals interaction dominated the adsorption, and the inorganic modification did not make an obvious contribution to the adsorption. [Copyright &y& Elsevier]

The article presents a study which investigates the water sorption behavior of bentonite composite gels or carboxylmethylcellulose and their performance on controlled release of herbicide metolachlor. The study uses Fourier transform infrared (FTIR) spectroscopy to determine composite gels' formation. Results show the low water sorption capacity of composite gels as well as the water sorption process' less effect on herbicide release from the gels.

Reports on the synthesis of organobentonites. Sorption properties; Removal percentages for organobentonites to treat organic compounds from water; Isothermal sorption curves; Application in wastewater treatment.

The reductive removal of U(VI) bynanoscale zerovalent iron (NZVI) was enhanced by using Na+-saturated bentonite (Na–bent) as the support, and the mechanismfor the enhanced removal were investigated comprehensively. Underthe same experimental conditions, NZVI supported on the negativelycharged Na–bent showed much higher removal efficiency (99.2%)of cationic U(VI) than either bare NZVI (48.3%) or NZVI supportedon the positively charged bentonite (Al–bent) did. Subsequentexperimental investigations revealed the unique roles of bentoniteon enhancing the reactivity and reusability of NZVI. First, Na–bentcan buffer the pH in reaction media, besides preventing NZVI fromaggregation. Second, Na–bent promoted the mass transfer ofU(VI) from solution to NZVI surface, leading to the enhanced removalefficiency. Third, the bentonite may transfer some insoluble reductionproducts away from the iron surface according to X-ray absorptionfine structure (XAFS) study. Finally, Na–bent as the adsorbentto Fe(II) makes it more reactive with U(VI), which enhanced stoichiometricallythe reduction capacity of NZVI besides accelerating the reaction rate. [ABSTRACT FROM AUTHOR]

Abstract: Organobentonites were prepared from Na-bentonite (NB) by intercalation with cetyltrimethyl ammonium bromide (CTMAB), and used to support the lipase from porcine pancreas. The immobilized lipase showed higher activity in hydrolysis of olive oil than free lipase, with the highest specific activity of 347.8Ug−1 protein for lipase immobilized on bentonite-CTMAB100 (BC100-lipase). The apparent activation energy (E a) of catalysis declined from 29.25kJmol−1 for free lipase to 16.31kJmol−1 for BC100-lipase, resulting in a higher catalytic efficiency of lipase. The improvement of catalytic activity was attributed to the interfacial activation by hydrophobic microenvironment and highly scattered surface created by organobentonite, according to the structural and morphological characterizations by Fourier transform infrared spectroscopy (FTIR) and Transmission electron microscopy (TEM). The immobilized lipase showed better resistance to pH and heating inactivation in comparison to the free lipase. After the storage of 8 days, BC100-lipase retained 80.7% of initial activity, which was 2.7 times higher than the residual activity of free lipase. Particularly, BC100-lipase kept 82.5% of initial activity after 6 continuous recycles under vigorous agitation, showing the excellent stability of the immobilized lipase by adsorption. [Copyright &y& Elsevier]

Nanoscale zero valent iron (NZVI) can remove Ni(II) from wastewater through surface adsorption and then reduction into lower-toxic Ni 0 , but the reduction is often blocked by the iron oxide shell of NZVI. In this study, the negatively charged Na-saturated bentonite (Na-bent) with high adsorption capacity to Ni(II) was used to support NZVI for improving the removal and reduction of Ni(II), and the functions of Na-bent were investigated by X-ray photoelectron micro-spectroscopy (XPS), transmission electron microscope (TEM) and Fe(II) determination. The results showed that Na-bent as a carrier could enrich Ni(II) on the reaction surface, protect the surface of NZVI from oxidation, prevent the aggregation of NZVI particles, and decrease the iron oxides products on NZVI surface by pH buffering. Therefore, NZVI/Na-bent not only showed much higher removal efficiency of Ni(II) (98.5%) than the sum (48.8%) of those by bare NZVI removal (41.9%) and by Na-bent adsorption (6.9%), but also greatly enhanced the reduction efficiency of Ni(II) into Ni 0 by facilitating the electron transfer from Fe 0 core to the surface-adsorbed Ni(II). In general, the unique property of bentonites will provide effective solutions to support NZVI for enhancing the removal and transformation of various environmental contaminants. [ABSTRACT FROM AUTHOR]

The zero-valent iron permeable reactive barrier (ZVI-PRB) is a promising technology for in-situ groundwater remediation. However, its long-term performance often declined due to the blocked reactive sites by corrosion products and by interference of co-existing solutes. In order to address these issues, a pillared bentonite (Al-bent) was homogeneously mixed with ZVI for removing selenate (Se(VI)) from simulated groundwater in column experiments. The Se(VI) removal was enhanced because first Al-bent could facilitate the mass transfer of Se(VI) from solution to iron surface and accelerate Se(VI) reduction. XANES analysis indicated that Se(VI) was almost completely reduced to Se(0) and Se(-II) of less toxicity and solubility by the ZVI/Al-bent mixture, and the buffering effect of Al-bent could maintain the pH at a lower level that favored the Se(VI) removal. Besides, Al-bent could transfer the corrosion products away from iron surface, leading to the enhanced reactivity and longevity of ZVI. The inhibition on reactivity towards Se(VI) in both the single ZVI and the ZVI/Al-bent systems increased in the order of Cl − < NO 3 − < HCO 3 − < SO 4 2− , and the removal efficiency decreased with the increasing HA concentration. However, the lower decrease of Se(VI) removal in the ZVI/Al-bent system indicates its resistance to the interference of these co-existing solutes in groundwater. [ABSTRACT FROM AUTHOR]