Zhao-dong Liu

Adhesion of Escherichia coli to nano-Fe/Al oxides and its effect on the surface chemical properties of Fe/Al oxides

We investigated the adhesion of Escherichia coli to α-Fe2O3 and γ-Al2O3 and the effects of adhesion on the surface properties of the oxides in batch experiments, where we conducted potentiometric titration, zeta potential measurements, and FTIR spectroscopy. The adhesion isotherms fitted a Langmuir equation well. γ-Al2O3 had a higher adhesion capacity than α-Fe2O3 because of the higher positive charge on γ-Al2O3. The adhesion of E. coli to Fe/Al oxides decreased with increasing pH. Adhesion increased with increasing NaCl concentration, reaching its maximum at 0.05M for α-Fe2O3 and at 0.1M for γ-Al2O3, after which it decreased with further increases in NaCl concentration. Therefore, the electrostatic force plays an important role in the adhesion of E. coli to Fe/Al oxides. The zeta potential-pH curves of the binary-system fell between that for bacteria and those for Fe/Al oxides. Thus, overlapping of the diffuse layers of the electric double layers on the negatively-charged E. coli and positively-charged Fe/Al oxides reduced the effective surface charge density of the minerals and bacteria. E. coli adhesion decreased the point of zero salt effect and the isoelectric point of the Fe/Al oxides. The FTIR spectra indicated that non-electrostatic force also contributed to the interaction between E. coli and Fe/Al oxides, in addition to the electrostatic force between them.

Interactions Between Escherchia coli and the Colloids of Three Variable Charge Soils and Their Effects on Soil Surface Charge Properties

The adhesion of Escherchia coli (E. coli) to the colloids of three variable charge soils and its effect on surface charge properties and potassium adsorption of these soil colloids were investigated. The adhesion isotherms of E. coli by soil colloids can be described using the Langmuir equation. The amount of E. coli adhered by the soil colloids varied with soil type and followed the order: Ultisol from Guangxi > Oxisol from Yunnan > Ultisol from Jiangxi. The iron and aluminum oxide contents and CECs of the soils are the important factors affecting the adhesion of E. coli to soil colloids. The relatively lower iron and aluminum oxide contents and higher CEC of the Ultisol from Jiangxi led to the lower adhesion of E. coli to the soil colloids compared to the Ultisol from Guangxi and the Oxisol from Yunnan. The amount of E. coli adhered to the soil colloids decreased with increasing pH, which was consistent with the results predicted from the DLVO theory. E. coli adhesion made the zeta potential of the soil colloids more negative and reduced the isoelectric point of the soil colloids, suggesting that E. coli decreased the surface positive charge and increased negative charge of the soil colloids. In addition, E. coli adhesion increased K+ adsorption by the soil colloids. Therefore, bacterial adhesion improves the fertility of variable charge soils by increasing soil CEC because the CECs of variable charge soils are usually low.

The effects of root surface charge and nitrogen forms on the adsorption of aluminum ions by the roots of rice with different aluminum tolerances

AimOur objectives were to compare effects of root charge properties on Al adsorption by the roots of rice that differed in Al-tolerance, and to examine effects of different nitrogen forms on charge properties of rice roots and Al adsorption.MethodsStreaming potential and chemical methods were used to measure root zeta potential and investigate Al chemical forms adsorbed on the roots of rice obtained from solution culture experiments.ResultsRice roots of the Al-sensitive variety Yangdao-6 carried greater negative charge than the Al-tolerant variety Wuyunjing-7, which meant the roots of Yangdao-6 adsorbed more exchangeable and complexed Al. When both rice varieties were grown in NH4+-containing nutrient solutions, there were less functional groups and lower negative surface charge on their roots, which reduced Al adsorption compared to the rice grown in NO3− containing nutrient solutions. The decline in nutrient solution pH due to NH4+ uptake by rice roots was responsible for the reduced numbers of functional groups and the lower negative surface charge on the roots compared to the rice grown in NO3− containing solutions.ConclusionsIntegrated root surface charge, as expressed by zeta potential, played an important role in Al adsorption by the roots of rice with different Al-tolerance.

Relative abundance of chemical forms of Cu(II) and Cd(II) on soybean roots as influenced by pH, cations and organic acids

Little information is available on chemical forms of heavy metals on integrate plant roots. KNO3 (1 M), 0.05M EDTA at pH6 and 0.01 M HCl were used sequentially to extract the exchangeable, complexed and precipitated forms of Cu(II) and Cd(II) from soybean roots and then to investigate chemical form distribution of Cu(II) and Cd(II) on soybean roots. Cu(II) and Cd(II) adsorbed on soybean roots were mainly exchangeable form, followed by complexed form, while their precipitated forms were very low under acidic conditions. Soybean roots had a higher adsorption affinity to Cu(II) than Cd(II), leading to higher toxic of Cu(II) than Cd(II). An increase in solution pH increased negative charge on soybean and thus increased exchangeable Cu(II) and Cd(II) on the roots. Ca2+, Mg2+ and NH4+ reduced exchangeable Cu(II) and Cd(II) levels on soybean roots and these cations showed greater effects on Cd(II) than Cu(II) due to greater adsorption affinity of the roots to Cu(II) than Cd(II). L-malic and citric acids decreased exchangeable and complexed Cu(II) on soybean roots. In conclusion, Cu(II) and Cd(II) mainly existed as exchangeable and complexed forms on soybean roots. Ca2+ and Mg2+ cations and citric and L-malic acids can potentially alleviate Cu(II) and Cd(II) toxicity to plants.

ATR–FTIR investigation of mechanisms of Bacillus subtilis adhesion onto variable- and constant-charge soil colloids

The primary objective of this study was to determine the capacity and the mechanisms of adhesion of Bacillus subtilis onto variable- and constant-charge soil colloids. The adhesion process was investigated using in situ attenuated total reflectance (ATR)-Fourier transform infrared spectroscopy (FTIR), zeta potential, and batch adhesion experiments. The maximum adhesion capacity of B. subtilis on the colloids of Oxisol, Ultisol, and Alfisol reached 699.17, 462.56, and 258.82mgg-1, respectively. B. subtilis adhesion to all three soil colloids decreased as the suspension pH increased from 3 to 8. Saturation coverage and adhesion rate constant values were calculated with the pseudo-first-order kinetics equation using the absorbance at 1548cm-1. Both values were highest for Oxisol, followed by Ultisol, and lowest for Alfisol. These observations are consistent with the surface charges of these soil colloids. A larger positive charge on variable-charge soils (Oxisol and Ultisol) increased B. subtilis adhesion relative to that of constant-charge soil (Alfisol). This is in agreement with the interaction energy between B. subtilis and soil colloids, which was calculated using the Derjaguin-Landau-Verwey-Overbeek theory. As revealed by ATR-FTIR spectroscopy, chemical bonds formed by protein, phosphate, and COOH groups on B. subtilis, as well as iron and aluminum hydroxyl groups in soil, contributed to B. subtilis adhesion to soil colloids. Therefore, chemical bond formation and electrostatic interaction are two major mechanisms of B. subtilis adhesion onto soil colloids.

Effects of Surface Charge and Functional Groups on the Adsorption and Binding Forms of Cu and Cd on Roots of indica and japonica Rice Cultivars

This work was designed to understand the mechanisms of adsorption of copper (Cu) and cadmium (Cd) on roots of indica and japonica varieties of rice. Six varieties each of indica and japonica rice were grown in hydroponics and the chemical properties of the root surface were analyzed, including surface charges and functional groups (-COO- groups) as measured by the streaming potential and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). Binding forms of heavy metals adsorbed on rice roots were identified using sequential extraction methods. In rice roots exposed to Cu and Cd solutions, Cu existed mainly in both exchangeable and complexed forms, whereas Cd existed mainly in the exchangeable form. The amounts of exchangeable Cu and Cd and total adsorbed metal cations on the roots of indica varieties were significantly greater than those on the roots of japonica varieties, and the higher negative charges and the larger number of functional groups on the roots of indica varieties were responsible for their higher adsorption capacity and greater binding strength for Cu and Cd. Surface charge and functional groups on roots play an important role in the adsorption of Cu and Cd on the rice roots.

Effects of adhesions of amorphous Fe and Al hydroxides on surface charge and adsorption of K+ and Cd2+ on rice roots

Iron (Fe) and aluminum (Al) hydroxides in variable charge soils attached to rice roots may affect surface-charge properties and subsequently the adsorption and uptake of nutrients and toxic metals by the roots. Adhesion of amorphous Fe and Al hydroxides onto rice roots and their effects on zeta potential of roots and adsorption of potassium (K+) and cadmium (Cd2+) by roots were investigated. Rice roots adsorbed more Al hydroxide than Fe hydroxide because of the greater positive charge on Al hydroxide. Adhesion of Fe and Al hydroxides decreased the negative charge on rice roots, and a greater effect of the Al hydroxide. Consequently, adhesion of Fe and Al hydroxides reduced the K+ and Cd2+ adsorption by rice roots. The results of attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and desorption of K+ and Cd2+ from rice roots indicated that physical masking by Fe and Al hydroxides and diffuse-layer overlapping between the positively-charged hydroxides and negatively-charged roots were responsible for the reduction of negative charge on roots induced by adhesion of the hydroxides. Therefore, the interaction between Fe and Al hydroxides and rice roots reduced negative charge on roots and thus inhibited their adsorption of nutrient and toxic cations.

Zeta potential of roots determined by the streaming potential method in relation to their Mn(II) sorption in 17 crops

AimTo compare the zeta potentials of roots of 17 crops measured with streaming potential method and to test feasibility of this method for different plants.MethodsIn addition to zeta potentials, surface charge and cation exchange capacity (CEC) of plant roots were measured independently. Mn(II) chemical forms sorbed on the roots were separated using sequential extraction.ResultsThere was a significant positive correlation between the zeta potential, CEC and negative charge of plant roots, indicating that the zeta potentials of plant roots as measured by streaming potential method were reliable. The roots of legumes carried greater negative charge than did non-legumes, which was responsible for more exchangeable and complexed Mn(II) sorbed on legume roots. In the infrared spectroscopy, the intensity of absorption peaks of legume roots was higher than that of non-legume roots. This indicated a higher concentration of functional groups on the roots of legumes than those of non-legumes, which was the main reason for the greater CEC and more negative zeta potential of legume roots and their higher sorption of Mn(II) when compared with non-legume crops.ConclusionsSurface charge properties of plant roots determined their sorption capacity for Mn(II) and chemical forms of Mn(II) on the roots.

Effect of Fe/Al Hydroxides on Transport and Retention of Escherichia coli in Saturated Sand Media

ABSTRACT The transport of bacteria has been investigated extensively using iron (Fe) (hydr)oxide-coated quartz. However, few studies have investigated the effects of aluminum (Al) (hydr)oxide on the transport of bacteria. In this study, column experiments were conducted to investigate the effects of Fe/Al hydroxides on the transport of Escherichia coli (E. coli) in saturated quartz sand at different pH levels, ionic strengths (IS), and ionic compositions. Fe/Al hydroxide coatings increased the positive charge of quartz, reduced the negative charge, shifted zeta potential in a positive direction, and thus enhanced the retention of E. coli on quartz. The retention of E. coli decreased with increasing pH and increased with increasing IS. These findings were consistent with the theoretical prediction of the Derjaguin, Landau, Verwey and Overbeek (DLVO) interaction energy. Calcium ions improved the retention of E. coli in the column. Since Al-hydroxide-coated quartz had a more positive charge, the retention of E. coli was higher in Al-hydroxide-coated quartz than in Fe-hydroxide-coated quartz. When compared with quartz alone, Fe/Al hydroxide coatings significantly reduced the transport of E. coli, and the inhibitory effect of Al hydroxide was greater than that of Fe hydroxide.

Streaming potential method for characterizing interaction of electrical double layers between rice roots and Fe/Al oxide-coated quartz in situ

The interaction between rice roots and Fe/Al oxide-coated quartz was investigated through zeta potential measurements and column leaching experiments in present study. The zeta potentials of rice roots, Fe/Al oxide-coated quartz, and the binary systems containing rice roots and Fe/Al oxide-coated quartz were measured by a specially constructed streaming potential apparatus. The interactions between rice roots and Fe/Al oxide-coated quartz particles were evaluated/deduced based on the differences of zeta potentials between the binary systems and the single system of rice roots. The zeta potentials of the binary systems moved in positive directions compared with that of rice roots, suggesting that there were overlapping of diffuse layers of electric double layers on positively charged Fe/Al oxide-coated quartz and negatively charged rice roots and neutralization of positive charge on Fe/Al oxide-coated quartz with negative charge on rice roots. The greater amount of positive charges on Al oxide led to the stronger interaction of Al oxide-coated quartz with rice roots and the more shift of zeta potential compared with Fe oxide. The overlapping of diffuse layers on Fe/Al oxide-coated quartz and rice roots was confirmed by column leaching experiments. The greater overlapping of diffuse layers on Al oxide and rice roots led to more simultaneous adsorptions of K+ and NO3− and greater reduction in leachate electric conductivity when the column containing Al oxide-coated quartz and rice roots was leached with KNO3 solution, compared with the columns containing rice roots and Fe oxide-coated quartz or quartz. When the KNO3 solution was replaced with deionized water to flush the columns, more K+ and NO3− were desorbed from the binary system containing Al oxide-coated quartz and rice roots than from other two binary systems, suggesting that the stronger electrostatic interaction between Al oxide and rice roots promoted the desorption of K+ and NO3− from the binary system and enhanced overlapping of diffuse layers on these oppositely charged surfaces compared with other two binary systems. In conclusion, the overlapping of diffuse layers occurred between positively charged Fe/Al oxides and rice roots, which led to neutralization of opposite charge and affected adsorption and desorption of ions onto and from the charged surfaces of Fe/Al oxides and rice roots.