Saccharide-derived microporous spherical biochar prepared from hydrothermal carbonization and different pyrolysis temperatures: synthesis, characterization, and application in water treatment.

Three saccharides (glucose, sucrose, and xylose) were used as pure precursors for synthesizing spherical biochars (GB, SB, and XB), respectively. The two-stage synthesis process comprised: (1) the hydrothermal carbonization of saccharides to produce spherical hydrochar' and (2) pyrolysis of the hydrochar at different temperatures from 300°C to 1200°C. The results demonstrated that the pyrolysis temperatures insignificantly affected the spherical morphology and surface chemistry of biochar. The biochar' isoelectric point ranged from 2.64 to 3.90 (abundant oxygen-containing functionalities). The Brunauer-Emmett-Teller (BET)-specific surface areas (SBET) and total pore volumes (Vtotal) of biochar increased with the increasing pyrolysis temperatures. The highest SBET and Vtotal were obtained at a pyrolysis temperature of 900°C for GB (775 m2/g and 0.392 cm3/g), 500°C for SB (410 m2/g and 0.212 cm3/g), and 600°C for XB (426 m2/g and 0.225 cm3/g), respectively. The spherical biochar was a microporous material with approximately 71-98% micropore volume. X-ray diffraction results indicated that the biochar' structure was predominantly amorphous. The spherical biochar possessed the graphite structure when the pyrolysis temperature was higher than 600°C. The adsorption capacity of GB depended strongly on the pyrolysis temperature. The maximum Langmuir adsorption capacities ([Formula: see text]) of 900GB exhibited the following selective order: phenol (2.332 mmol/g) > Pb2+ (1.052 mmol/g) > Cu2+ (0.825 mmol/g) > methylene green 5 (0.426 mmol/g) > acid red 1 (0.076 mmol/g). This study provides a simple method to prepare spherical biochar - a new and potential adsorbent for adsorbing heavy metals and aromatic contaminants.

Application of hydrothermal method derived titanate nanotubes as adsorbents.

Titanate nanotubes (TNT) derived from alkaline hydrothermal method are characterized by high specific surface area, specific pore volume, and ion-exchange capacity. They may be a promising and important adsorbent in the environmental protection. Although their applications in the fields of lithium ion batteries, dye-sensitized solar cell, photocatalysis, catalysts support, gas and humidity sensors, and ion exchange have been intensely studied during recent years, however, the researches concerning their potential application as an adsorbent are seldom reported. In this mini-review, we first highlight the effects of hydrothermal temperature and sodium content on the microstructures of hydrothermal method derived TNT, because the morphology and microstructure of TNT are highly dependent on the preparation conditions. Effects of the alterations of microstructures induced by the variation of hydrothermal temperature and sodium content on the dyes, heavy metal ions, and organic vapors adsorption characteristics of TNT are then introduced citing recent patents.

Effects of synthesis temperature on the microstructures and basic dyes adsorption of titanate nanotubes.

The adsorption of two basic dyes (Basic Green 5 (BG5) and Basic Violet 10 (BV10)) onto titanate nanotubes (TNT) that were prepared via a hydrothermal method with different synthesis temperatures was studied to examine the potential of TNT for the removal of basic dyes from aqueous solution. Effects of synthesis temperature on the microstructures of TNT were characterized with transmission electron microscopy (TEM), X-ray diffraction (XRD), and nitrogen adsorption-desorption isotherms. For synthesis temperature greater than 160 degrees C, the microstructure of titanate might transform from nanotube into nanorod accompanying with the sharp decrease in the titanate interlayer spacing, BET surface area, and pore volume. Effects of the pore structure variation on the basic dyes adsorption of TNT were discussed. Moreover, the adsorption mechanisms of basic dyes from aqueous solution onto TNT were examined with the aid of model analyses of the adsorption equilibrium and kinetic data of BG5 and BV10. The regeneration of TNT was also briefly discussed.

Selective adsorption and partitioning of nonionic surfactants onto solids via liquid chromatograph mass spectra analysis.

The sorption characteristics of three Triton series surfactants (Triton-100, Triton-305, and Triton-405) from aqueous solution onto four different solids with a wide range of organic matter (OM) content were studied through the liquid chromatograph mass spectrometry (LC-MS) analysis. The examined surfactant concentrations ranged from below to above the critical micelle concentration (CMC) of the selected surfactants. A parameter, Phi, defined as the ratio of the average ethylene oxide (EO) number of surfactant on the adsorbed phase to that in the aqueous solution, was used to distinguish the controlling mechanism (adsorption or partitioning) of surfactants from aqueous solution onto the solids. For solids with very low OM content, adsorption was the primary mechanism and the Phi values were found to be larger than 1.0 and might reduce to 1.0 with the increasing surfactant concentration. On the other hand, the Phi values for solids with very high content of OM were equal to or less than 1.0 and remained constant as the surfactant concentrations varied, in which partitioning was the most likely dominant mechanism. For solids with an intermediate content of OM, adsorption and partitioning mechanisms coexisted and the Phi values could be larger or less than 1.0 and decreased with the increasing surfactant concentration.

Effects of sodium content and calcination temperature on the morphology, structure and photocatalytic activity of nanotubular titanates.

Titanate nanotubes (TNT) were prepared via a hydrothermal treatment of TiO(2) powders (P25) in a 10 M NaOH solution at 150 degrees C for 24 h and subsequently washed with HCl aqueous solution of different concentrations (0.1, 0.01, and 0.001 N). Samples with different contents of remnant sodium in nanotubes were characterized, as synthesized and after heat-treatment, by transmission electron microscopy, X-ray diffraction, and nitrogen adsorption-desorption isotherms. The photocatalytic activity of TNT was evaluated by photocatalytic oxidation of basic dye (basic violet 10 (BV10)) in water solution. It was found that if the sodium was not completely exchanged with proton, the removal of sodium increased the specific surface area (and pore volume), while the thermal stability was reduced. When the sodium content of TNT was approximately 0 wt% (nearly complete proton exchange), the nanotubular structure of titanates might be destroyed. The effects of the alterations of microstructures induced by the exchange of sodium and heat-treatment on the photocatalytic activity of TNT were discussed with the variations of specific surface area, pore volume, and the amounts of anatase phase in TNT.

Application of titanate nanotubes for dyes adsorptive removal from aqueous solution.

The potential of adsorptive removal of basic dyes with titanate nanotubes (TNTs) and acid dyes with surfactant (hexadecyltrimethylammonium (HDTMA) chloride)-modified TNTs were investigated. TNTs were prepared via a hydrothermal method and subsequently washed with HCl aqueous solutions of different concentrations. The prepared TNTs were then mediated by the HDTMA ions through the cation exchange process. Effects of acid washing and HDTMA-modified process on the revolution of microstructure and surface chemistry characteristics of TNTs were characterized with XRD, nitrogen adsorption-desorption isotherms, and FTIR. The adsorption capacities of two basic dyes (two acid dyes) on TNTs (their HDTMA-modified version) at initial dye concentration of 2000 mg/L were measured. It was experimentally concluded that if the amount of Na(+) in the TNTs was not very low, the TNTs and their HDTMA-modified version might be a good adsorbent for the removal of basic and acid dyes from aqueous solution through the cation and anion exchange mechanism, respectively. The adsorption capacity for basic and acid dyes could reach 380 and 400 mg/g, respectively.

Application of MCM-41 for dyes removal from wastewater.

The adsorption of three basic dyes (Rhodamine B (RB), Crystal Violet (CV), and Methylene Green (MG)) and two acid dyes (Acid Red 1 (AR1) and Erioglaucine (EG)) onto MCM-41 was studied to examine the potential of MCM-41 for the removal of dyes from water solution. The revolution of pore structure and surface chemical characteristics of MCM-41 induced by dyes adsorption was characterized based on the analyses of XRD patterns, FTIR spectra, and nitrogen adsorption-desorption isotherms. The adsorption capacity of MCM-41 for the five dyes followed a decreasing order of RB>CV>MG>EG approximately AR1. It was experimentally concluded that if the dyes adsorption did not introduce a serious disorder on the pore structure of MCM-41 (such as RB adsorption), MCM-41 might be a good adsorbent for the removal of basic dyes from water solution. The fitness of both Langmuir and Freundlich adsorption model on describing the equilibrium isotherms of three basic dyes was examined. The suitability of both pseudo-second-order kinetic model and the intraparticle diffusion model for the description of the kinetic data was investigated, from which the adsorption mechanism was examined.

The structural and sorptive characteristics of high-surface-area carbonaceous material (HSACM) in soils.

The structural and sorptive characteristics of the high-surface-area carbonaceous material (HSACM) isolated from soils were investigated. The HSACM contents in soils were first identified by the organic petrology method. A novel isolation method using acid demineralization, base extraction, and ZnBr(2) floatation sequential steps was developed to extract the HSACM from soil. The differences in structural and sorptive characteristics with the HSACM and the intact soil were investigated using nitrogen adsorption isotherms and trichloroethylene (TCE) sorption isotherms at low concentrations (0 to about 2 mg/L) both with and without tetrachloroethylene (PCE) as the cosolute. It was found that HSACM possesses a much higher specific surface area and pore volume as well as a smaller pore size than the original soil. Moreover, the sorption of TCE to HSACM is noticeably more nonlinear and competitive than to the original soil. A small amount of highly adsorptive HSACM is largely responsible for the nonlinear soil sorption of a single solute at very low concentrations.

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.

Scaling characteristics in ozone concentration time series (OCTS).

One-year series of hourly average ozone observations, which were obtained from urban and national park air monitoring stations at Taipei (Taiwan), were analyzed by means of descriptive statistics and fractal methods to examine the scaling structures of ozone concentrations. It was found that all ozone measurements exhibited the characteristic right-skewed frequency distribution, cyclic pattern, and long-term memory. A mono-fractal analysis was performed by transferring the ozone concentration time series (OCTS) into a useful compact form, namely, the box-dimension (D(B))-threshold (T(h)) and critical scale (C(S))-threshold (T(h)) plots. Scale invariance was found in these time series and the box dimension was shown to be a decreasing function of the threshold ozone level, implying the existence of multifractal characteristics. To test this hypothesis, the OCTS were transferred into the multifractal spectra, namely, the tau(q)-q plots. The analysis confirmed the existence of multifractal characteristics in the investigated OCTS. A simple two-scale Cantor set with unequal scales and weights was then used to fit the calculated tau(q)-q plots. This model fitted remarkably well the entire spectrum of scaling exponents for the examined OCTS. Because the existence of chaos behavior in OCTS has been reported in the literature, the possibility of a chaotic multifractal approach for OCTS characterization was discussed.

An alternative method for predicting organic solute volatilization rates under gas and liquid turbulence.

A method for predicting organic compound volatilization rates under turbulent liquid and gas conditions is developed. The reference compounds are classified according to their physico-chemical properties. The mass transfer coefficient (K(OL)) ratios for organic solutes to the reference compounds are constant for a wide range of environmental conditions, including liquid or air turbulence, or both at once. The obtained results indicate that when the environmental conditions are the same the determination of the volatilization rates is strongly dependent on the solute properties and the chemical structure. The presented method can more effectively estimate the volatilization rates of the solutes than the traditional one under various environmental conditions especially for low volatility solutes. The advantages and disadvantages of the traditional method are also discussed.

Effects of exchanged surfactant cations on the pore structure and adsorption characteristics of montmorillonite.

Ca-montmorillonite (Ca-Mont) was exchanged with two quaternary amines, tetramethylammonium (TMA) chloride and hexadecyltrimethylammonium (HDTMA) bromide, to study the surfactant ion exchange effect on the pore structure, surface characteristics, and adsorption properties of montmorillonite. The revolution of both the surface area and pore structure of montmorillonite was characterized based on classical and fractal analyses of the nitrogen isotherms as well as the XRD patterns. The change of surface characteristics was identified from FTIR patterns and zeta-potential plots. The adsorption isotherms of acid dye, Amido Naphthol Red G (AR1), were then measured to identify the effects of the ion-exchange process on the adsorption properties of montmorillonite. It was found that the exchange processes might induce an increase or decrease in the surface area, pore size, pore volume, and surface fractal dimension D of montmorillonite, depending on the size, the molecular arrangement, and the degree of hydration of the exchanged ion in the clay. On the other hand, it was also found that the hydrophobic bonding by conglomeration of large C(16) alkyl groups associated with HDTMA could cause positive charge development on the surface of montmorillonite, which was not observed for TMA-modified montmorillonite (TMM). The effects of the alteration of the surface characteristics of montmorillonites on their adsorption selectivity for acid dye were discussed.

Adsorption of basic dyes onto montmorillonite.

Ca-montmorillonite (Ca-Mont) was exchanged with titanium cations and the adsorption equilibrium and kinetics of Basic Green 5 (BG5) and Basic Violet 10 (BV10) on these montmorillonites were measured to examine the ion-exchange effects on the basic dyes adsorption. The relationship between the dye adsorption and the alteration of pore structures of montmorillonite induced by ion-exchange processes was discussed. Moreover, the changes in the surface and pore structure of montmorillonites during adsorption were characterized based on classical and fractal analyses of the nitrogen adsorption isotherms as well as the XRD patterns. The decrease in BET surface area of montmorillonites after adsorption of dyes was interpreted in terms of both the coverage of some surface roughness (surface screening effect) and the inhibition of the movement of nitrogen molecule into some pores (pore blocking effect). The surface fractal dimension D was used to examine whether or not the surface screening effect exists and the pore blocking effect was examined with the changes of mean pore size before and after adsorbing basic dyes.

Effects of organic solutes properties on the volatilization processes from water solutions.

Effects of organic solutes properties, including Henry's law constant (H), molecular weight (M), molar volume at normal boiling point (Vb), and solubility (S), on the usefulness of rate estimation by reference to a reference substance (i.e., reference substance concept) and on the evaporation rate were investigated by measuring the volatilization rate constant of organic solutes under different environmental conditions, including mixing and surfactants. It was found that if benzene was used as a reference substance, the ratio of the solute rate to that of benzene (F) becomes insensitive to water mixing, whether the solute possessed high or low Henry's law constant. In the presence of surfactants, however, the F value changes sharply as the solute solubility decreases. For benzene, toluene, ethylbenzene, and xylenes (BTEX), the F values are essentially constant irrespective of the presence of other chemicals (including organic compounds, surfactants, and salinity) and of the variation in temperature. On the other hand, the volatilization rates are closely related to molecular weight (solubility) in the existence of mixing (surfactants). Three different approaches, i.e., mass-transport theory, modified Knudsen equation, and reaction rate concept, were used to evaluate the dependence of solute volatilization rates on solute properties. It was concluded that the interaction between solute properties and environmental parameters might play a key role in the volatilization process of organic solutes under different environmental conditions.

Clay-catalyzed reactions of coagulant polymers during water chlorination.

The influence of suspended clay/solid particles on organic-coagulant reactions during water chlorination was investigated by analyses of total product formation potential (TPFP) and disinfection by-product (DBP) distribution as a function of exchanged clay cation, coagulant organic polymer, and reaction time. Montmorillonite clays appeared to act as a catalytic center where the reaction between adsorbed polymer and disinfectant (chlorine) was mediated closely by the exchanged clay cation. The transition-metal cations in clays catalyzed more effectively than other cations the reactions between a coagulant polymer and chlorine, forming a large number of volatile DBPs. The relative catalytic effects of clays/solids followed the order Ti-Mont > Fe-Mont > Cu-Mont > Mn-Mont > Ca-Mont > Na-Mont > quartz > talc. The effects of coagulant polymers on TPFP follow the order nonionic polymer > anionic polymer > cationic polymer. The catalytic role of the clay cation was further confirmed by the observed inhibition in DBP formation when strong chelating agents (o-phenanthroline and ethylenediamine) were added to the clay suspension. Moreover, in the presence of clays, total DBPs increased appreciably when either the reaction time or the amount of the added clay or coagulant polymer increased. For volatile DBPs, the formation of halogenated methanes was usually time-dependent, with chloroform and dichloromethane showing the greatest dependence.