Zhi-neng Hong

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.

Competition between bacteria and phosphate for adsorption sites on gibbsite: An in-situ ATR-FTIR spectroscopic and macroscopic study.

Sorption and desorption of phosphate (P) on Fe and Al (hydr)oxides may be affected by bacteria in soils because their ubiquitous and strong interactions. The role of Bacillus subtilis and Pseudomonas fluorescens in adsorption of P on gibbsite (γ-AlOOH) was systematically investigated under a wide range of conditions by combining in-situ attenuated total reflectance Fourier-transform infrared (ATR-FTIR) spectroscopy with batch macroscopic experiments. In-situ ATR-FTIR observations of the ternary systems (bacteria, P, and gibbsite) showed simultaneous desorption of P from, and adhesion of the bacteria to, gibbsite, indicating a competition between the two for surface sites. Batch desorption experiments showed that bacteria could mobilize the P from gibbsite into solution, and macroscopic adsorption data showed that the amount of P adsorbed on the bacteria-gibbsite complex was less than that on gibbsite alone over durations from 0h to 26h, concentrations of P from 0.1mM to 2.0mM, pH from 5 to 8, and ionic strength from 0M to 0.5M, suggesting that bacteria inhibit the adsorption of P on gibbsite. The degree of inhibition increased with the number of bacteria in the system and was significantly but non-linearly correlated with the decline in the positive charge on gibbsite induced by the bacteria. Therefore, competition for suitable sites on the surface of gibbsite between P and the bacteria and reduction in the positive charge on the surface of gibbsite induced by bacteria are proposed as two important mechanisms that inhibit P adsorption. These findings highlight the role of bacteria in regulating the availability of P to plants and its mobility in natural environments.

Mechanisms for Increasing the pH Buffering Capacity of an Acidic Ultisol by Crop Residue-Derived Biochars

The effects and underlying mechanisms of crop residue-derived biochars on the pH buffering capacity (pHbuff) of an acidic Ultisol, with low pHbuff, were investigated through indoor incubation and simulated acidification experiments. The incorporation of biochars significantly increased soil pHbuff with the magnitude of the increase dependent on acid buffering capacity of the biochar incorporated to the soil. Cation release, resulting from the protonation of carboxyl groups on biochar surfaces and the dissolution of carbonates, was the predominant mechanism responsible for the increase in soil pHbuff at pH 4.0-7.0 and accounted for >67% of the increased pHbuff. The reaction of protons with soluble silica (Si) in biochars derived from rice straw and corn stover also accounted for ∼20% of the pHbuff increase due to H3SiO4- precipitation. In conclusion, the incorporation of crop residue-derived biochars into acidic soils increased soil pHbuff with peanut stover biochar being the most effective biochar tested.

Evaluation of ferrolysis in arsenate adsorption on the paddy soil derived from an Oxisol

Iron oxides are dominant effective adsorbents for arsenate in iron oxide-rich variable charge soils. Oxisol-derived paddy soils undergo intensive ferrolysis, which results in high leaching and transformation of iron oxides. However, little information is available concerning the effect of ferrolysis on arsenate adsorption by paddy soil and parent Oxisol. In the present study, we examined the arsenate affinity of soils using arsenate adsorption/desorption isotherms, zeta potential, adsorption kinetics, pH effect and phosphate competition experiments. Results showed that ferrolysis in an alternating flooding-drying Oxisol-derived paddy soil resulted in a significant decrease of free iron oxides and increase of amorphous iron oxides in the surface and subsurface layers. There were more reactive sites exposed on amorphous than on crystalline iron oxides. Therefore, disproportionate ratios of arsenate adsorption capacities and contents of free iron oxides were observed in the studied Oxisols compared with paddy soils. The Gibbs free energy values corroborated that both electrostatic and non-electrostatic adsorption mechanisms contributed to the arsenate adsorption by bulk soils, and the kinetic adsorption data further suggested that the rate-limiting step was chemisorption. The zeta potential of soil colloids decreased after arsenate was adsorbed on the surfaces, forming inner-sphere complexes and thus transferring their negative charges to the soil particle surfaces. The adsorption/desorption isotherms showed that non-electrostatic adsorption was the main mechanism responsible for arsenate binding to the Oxisol and derived paddy soils, representing 91.42-94.65% of the adsorption capacities. Further studies revealed that arsenate adsorption was greatly inhibited by increasing suspension pH and incorporation of phosphate.

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.

Effect of clay colloids on the zeta potential of Fe/Al oxide-coated quartz: a streaming potential study

PurposeThis study was conducted in order to examine the effect of colloidal particles on electrochemical properties of charged larger size materials.Materials and methodsA self-made streaming potential apparatus was used to measure the zeta potentials of Fe/Al oxide-coated quartz. The effects of colloidal particles of kaolinite and montmorillonite on the electrochemical properties of Fe/Al oxide-coated quartz were investigated through comparing the difference in zeta potential of the coated quartz in electrolyte and clay suspension.Results and discussionThe change of zeta potentials of the coated quartz, when clay suspensions flowed through, increased with the increasing concentrations of kaolinite and montmorillonite and degree of coating with Fe/Al oxides, and decreased with increased ionic strength of the suspensions. Electrostatic attraction between clay colloids and the coated quartz was the key factor influencing the interaction between the oppositely charged particles. The deposition of colloidal particles of kaolinite and montmorillonite on coated quartz and the overlapping of the diffuse layers of electrical double layers between the oppositely charged particles were responsible for the change in zeta potential of Fe/Al oxide-coated quartz. The relative contribution of the deposition of clay particles to the change in zeta potential was greater than that of the overlapping of diffuse layers.ConclusionsWhen clay suspensions flowed through the saturated sand of Fe/Al oxide-coated quartz, both overlapping of diffuse layers between charged sand and clay particles and deposition of clay particles contributed to change of zeta potential of the coated quartz.

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.

In-situ ATR-FTIR spectroscopic investigation of desorption of phosphate from haematite by bacteria

Summary Phosphate (P) fixed on F e‐ and A l‐(hydr)oxides can be released into solution by coexisting anions or molecules that have strong reactivity with the mineral surfaces. Bacteria have been shown to adhere strongly on to the (hydr)oxides through physical or chemical forces, or both. It is still unknown, however, whether bacteria can desorb P from oxides. We examined the desorption of P from haematite (α ‐ Fe2O3) by B acillus subtilis and P seudomonas fluorescens through the combined use of in‐situ attenuated total reflectance F ourier‐transform infrared (ATR‐FTIR) spectroscopy and macroscopic batch experiments. The ATR‐FTIR data of ternary bacteria– P –haematite systems indicated a release of P that was concurrent with the attachment of bacteria on to the haematite surface, giving direct and in‐situ evidence for the displacement of P by bacteria. The P ‐desorbing ability of bacteria was quantified by batch desorption experiments, and was further supported by the inhibitory role of bacteria in P adsorption on to haematite under varying concentrations of P and amounts of bacteria. I n‐situ ATR‐FTIR investigations and D erjaguin– L andau– V erwey– O verbeek (DLVO) prediction suggested that bacteria might compete for sorption sites with P through their electrostatic and chemical interactions (coordination of bacterial phosphate and carboxyl groups on the haematite surface) with the haematite surface. In addition, the bacteria reduced greatly the positive charge of haematite, and the reduction correlated non‐linearly with the decline in P adsorption. Therefore, the P ‐mobilizing ability of bacteria is probably attributed to the competition between P and bacterial surface groups and reduction in the positive charge on haematite by bacteria. These findings elucidate a potential role for bacteria in mobilizing P that is chemically adsorbed on F e‐oxides, which enhances the availability of P to plants and its mobility in natural environments. HighlightsWhether bacteria can desorb phosphate from oxides remained unknown.Bacteria enhanced desorption of phosphate from haematite and inhibited its adsorption by haematite.Electrostatic and chemical interactions might help bacteria compete with phosphate.Reduction in positive charges might also contribute to phosphate‐mobilizing ability of bacteria.

Peanut straw biochar increases the resistance of two Ultisols derived from different parent materials to acidification: A mechanism study

The mechanisms for increasing soil pH buffering capacity (pHBC) and soil resistance to acidification by peanut straw biochar were investigated by undertaking indoor incubation and simulated acidification experiments using two Ultisols derived from tertiary red sandstone and quaternary red earth. The biochar increased the pHBC and resistance of the two Ultisols to acidification. The addition of 3% biochar increased the pHBC of the two Ultisols by 76% and 25%, respectively. The increased resistance of the soils to acidification led to the inhibition to decrease in soil pH and the activation of soil Al during acidification. The protonation of carboxyl groups on the biochar surface was the main mechanism responsible for resisting acidification of the Ultisols when the pH was between 4.5 and 7.0. The higher soil pH (>6.0) after biochar application and the large number of carboxyl groups on the biochar surface were essential if biochar was to significantly increase the resistance of soils to acidification.