A review and experimental verification of using chitosan and its derivatives as adsorbents for selected heavy metals

A literature survey on liquid-phase adsorption of selected heavy metals including Cu(II), Zn(II), Ni(II), Cd(II), Pb(II), Hg(II), and Cr(VI) on chitosan (CTS) and its derivatives was made from the viewpoint of adsorption capacity. This parameter was obtained from the Langmuir fit of isotherm data. The magnitude of adsorption capacity of heavy metals on pristine CTS was also used to discuss the mechanism of adsorption; that is, how many amino groups in CTS chains would coordinate with one heavy metal ion. Furthermore, a newly defined parameter, the approaching equilibrium factor R_L, was proposed to quantitatively indicate the favorability of the related adsorption process and to judge the correctness of adsorption capacity determined by the Langmuir equation.     

Preparation of novel activated carbons from H2SO4-pretreated corncob hulls with KOH activation for quick adsorption of dye and 4-chlorophenol

Corncob hull was immersed in 25 wt% H(2)SO(4) and was carbonized in an oven at 290 °C for 2h to obtain the char. The char was then activated for 1h at 780 °C by KOH at weight ratio of KOH/char of 2.5, 3.0, and 3.5. SEM photos of the carbons revealed that the cell wall of corncob hull was etched into thin film structure. It was shown that the adsorption isotherms of methylene blue and 4-chlorophenol on the carbons were well fitted by the Langmuir equation. Moreover, the adsorption kinetics could be satisfactorily described by the Elovich equation. The normalized standard deviations are less than 2.8%. The high fraction of adsorption amount adsorbed within 1 min to that at saturation demonstrated the advantage of the prepared activated carbons. The fraction of adsorption amount within 1 min to that at saturation (q(1)/q(mon)) for the adsorption of 4-CP is high up to 0.807. Such quick adsorption behavior was mainly attributed to the presence of the thin film structure of carbons.     

Removal of metal ions from the complexed solutions in fixed bed using a strong-acid ion exchange resin

Fixed bed removal of equimolar metal ions (Co²⁺, Ni²⁺, Mn²⁺, Sr²⁺) from aqueous solutions using a strong-acid resin was examined. The solution contained a water-soluble complexing agent including ethylenediaminetetraacetic acid, nitrilotriacetic acid, and citric acid. Experiments were performed under different solution pH and molar concentration ratios of complexing agent to the total metals. It was shown from batch studies that the equilibrium exchange of metals and the resin mainly depended on solution pH, and partly on the type of complexing agent used. A mass transfer model was proposed to describe the breakthrough curves of the resin bed, which contained two parameters (τ and k) estimated from the observed breakthrough data. The calculated breakthrough curves agreed well with the measured ones (standard deviation <6%). In fixed bed tests at low pH (=2), the type of complexing agent had little effect on the breakthrough data. For a given complexing agent, the metal with a larger overall formation constant (K_f) showed a smaller exchange capacity. For a given metal ion, the complexing agent with a larger K_f also revealed a smaller exchange capacity.     

Using sequential indicator simulation to assess the uncertainty of delineating heavy-metal contaminated soils

Mapping the spatial distribution of soil pollutants is essential for delineating contaminated areas. Currently, geostatistical interpolation, kriging, is increasingly used to estimate pollutant concentrations in soils. The kriging-based approach, indicator kriging (IK), may be used to model the uncertainty of mapping. However, a smoothing effect is usually produced when using kriging in pollutant mapping. The detailed spatial patterns of pollutants could, therefore, be lost. The local uncertainty of mapping pollutants derived by the IK technique is referred to as the conditional cumulative distribution function (ccdf) for one specific location (i.e. single-location uncertainty). The local uncertainty information obtained by IK is not sufficient as the uncertainty of mapping at several locations simultaneously (i.e. multi-location uncertainty or spatial uncertainty) is required to assess the reliability of the delineation of contaminated areas. The simulation approach, sequential indicator simulation (SIS), which has the ability to model not only single, but also multi-location uncertainties, was used, in this study, to assess the uncertainty of the delineation of heavy metal contaminated soils. To illustrate this, a data set of Cu concentrations in soil from Taiwan was used. The results show that contour maps of Cu concentrations generated by the SIS realizations exhausted all the spatial patterns of Cu concentrations without the smoothing effect found when using the kriging method. Based on the SIS realizations, the local uncertainty of Cu concentrations at a specific location of x', refers to the probability of the Cu concentration z(x') being higher than the defined threshold level of contamination (z(c)). This can be written as Prob(SIS)[z(x')>z(c)], representing the probability of contamination. The probability map of Prob(SIS)[z(x')>z(c)] can then be used for delineating contaminated areas. In addition, the multi-location uncertainty of an area A,delineated as contaminated based on the probability map of Prob(SIS)[z(x')>z(c)], can be calculated to assess the reliability of delineation. Multi-location uncertainty refers to the probability of Cu concentrations in several locations, x'(1), x'(2), em leader, x'(m,) in the area A, being higher than the threshold (z(c)) as denoted by Prob(SIS)[z(x'(1))>z(c), z(x'(2))>z(c), em leader, andz(x'(m))>z(c)] or Prob(SIS)[z(A)>z(c)]. The multi-location uncertainty Prob(SIS)[z(A)>z(c)], obtained from the SIS, can be used to assess the reliability of delineation for regions suspected of contamination, (A), which has been delineated as contaminated. Reliance on this information facilitates the decision making process in determining which areas are contaminated and require cleanup action.     

Electrochemical decolorization of dye wastewater by surface-activated boron-doped nanocrystalline diamond electrode

Complex organics contained in dye wastewater are difficult to degrade and often require electrochemical advanced oxidation processes (EAOPs) to treat it. Surface activation of the electrode used in such treatment is an important factor determining the success of the process. The performance of boron-doped nanocrystalline diamond (BD-NCD) film electrode for decolorization of Acid Yellow (AY-36) azo dye with respect to the surface activation by electrochemical polarization was studied. Anodic polarization found to be more suitable as electrode pretreatment compared to cathodic one. After anodic polarization, the originally H-terminated surface of BD-NCD was changed into O-terminated, making it more hydrophilic. Due to the oxidation of surface functional groups and some portion of sp² carbon in the BD-NCD film during anodic polarization, the electrode was successfully being activated showing lower background current, wider potential window and considerably less surface activity compared to the non-polarized one. Consequently, electrooxidation (EO) capability of the anodically-polarized BD-NCD to degrade AY-36 dye was significantly enhanced, capable of nearly total decolorization and chemical oxygen demand (COD) removal even after several times of re-using. The BD-NCD film electrode favored acidic condition for the dye degradation; and the presence of chloride ion in the solution was found to be more advantageous than sulfate active species.     

Preparation of activated carbons from unburnt coal in bottom ash with KOH activation for liquid-phase adsorption

In this work, unburnt coal (UC) in bottom ash from coal-fired power plants was soaked in KOH solution and activated for 1 h at 780 °C. The yield of activated carbons varied from 47.8 to 54.8% when the KOH/UC weight ratio changed from 2 to 4. Pore properties of these activated carbons including the BET surface area, pore volume, pore size distribution, and pore diameter were characterized based on N₂ adsorption isotherms. It was shown that the isotherms for the adsorption of methylene blue, acid blue 74, and 4-chlorophenol from aqueous solutions on these activated carbons at 30 °C were well fitted by the Langmuir equation (correlation coefficient r² > 0.9968). The adsorption capacities of methylene blue, acid blue 74, and 4-chlorophenol were obtained to be 2.40–2.88, 0.57–1.29, and 2.34–5.62 mmol/g, respectively. Moreover, the adsorption kinetics could be suitably described by the Elovich equation.     

Photocatalytic degradation of phenol on different phases of TiO(2) particles in aqueous suspensions under UV irradiation

Photocatalytic degradation of phenol on different phases of TiO₂ particles was examined under 400-W UV irradiation. The effects of various operating parameters including TiO₂ dosage, solution pH (4–10), and initial phenol concentration (0.13–1.05 mM) on phenol degradation were investigated. Three forms of TiO₂ photocatalysts such as pure anatase phase, pure rutile phase, and the mixed phase were prepared by sol-gel method and followed annealing at different temperatures. The annealing temperature used were 500 °C, 700 °C and 900 °C for pure anatase phase, the mixed phase, and pure rutile phase, respectively. It was shown that pure anatase TiO₂ exhibited higher photocatalytic activity than the physical mixture of pure anatase and rutile TiO₂. Moreover, the TiO₂ particle with a specific fraction of mixed anatase and rutile phases exhibited better performance than pure anatase TiO₂. Finally, the degradation rate could be satisfactorily fitted by a pseudo-first-order kinetic model.     

Copper accumulation,translocation, and toxic effects in grapevine cuttings

Purpose  

Although the ecotoxicological effects of copper (Cu) on grapevine are of global concern due to the intensive and long-term application of Cu-based fungicides in vineyards, comparatively little is known about the phytotoxicity, accumulation, and translocation of Cu in grapevines. Therefore, this study was to conduct a hydroponic experiment to determine the influence of solution Cu concentration not only on bioaccumulation and the translocation of Cu in grapevine roots, stems, and leaves, but also on the subsequent growth inhibition of the roots.     

Adsorption of basic dyes onto MCM-41

The adsorption of two basic dyes, Basic Green 5 (BG5) and Basic Violet 10 (BV10), onto MCM-41 was studied to examine the possible effect of interactions between large adsorbates and MCM-41 on the pore structure stability of MCM-41 and the potential of MCM-41 for the removal of basic dyes from wastewater. The revolutions of surface characteristics and pore structure of MCM-41 induced by dyes adsorption were characterized based on the analyses of the nitrogen isotherms, the XRD patterns, and the FTIR spectra. It was experimentally concluded that when the effect of interactions between large dyes (such as BV10) and MCM-41 on the pore structure stability of MCM-41 was insignificant, MCM-41 might be a good adsorbent for the removal of basic dyes from wastewater. The adsorption of BV10 on MCM-41 with respect to contact time, pH, and temperature was then measured to provide more information about the adsorption characteristics of MCM-41. Both Langmuir and Freundlich adsorption models were applied to describe the equilibrium isotherms and the pseudo-second-order kinetic model was used to describe the kinetic data, from which some adsorption thermodynamic parameters were also evaluated.     

Using rank-order geostatistics for spatial interpolation of highly skewed data in a heavy-metal contaminated site

The spatial distribution of a pollutant in contaminated soils is usually highly skewed. As a result, the sample variogram often differs considerably from its regional counterpart and the geostatistical interpolation is hindered. In this study, rank-order geostatistics with standardized rank transformation was used for the spatial interpolation of pollutants with a highly skewed distribution in contaminated soils when commonly used nonlinear methods, such as logarithmic and normal-scored transformations, are not suitable. A real data set of soil Cd concentrations with great variation and high skewness in a contaminated site of Taiwan was used for illustration. The spatial dependence of ranks transformed from Cd concentrations was identified and kriging estimation was readily performed in the standardized-rank space. The estimated standardized rank was back-transformed into the concentration space using the middle point model within a standardized-rank interval of the empirical distribution function (EDF). The spatial distribution of Cd concentrations was then obtained. The probability of Cd concentration being higher than a given cutoff value also can be estimated by using the estimated distribution of standardized ranks. The contour maps of Cd concentrations and the probabilities of Cd concentrations being higher than the cutoff value can be simultaneously used for delineation of hazardous areas of contaminated soils.