Motoi Machida

Adsorption of heavy metals onto activated carbons derived from polyacrylonitrile fiber

The aim of this research is to produce activated carbons derived from polyacrylonitrile (PAN) fiber and to examine their feasibility of removing heavy metals from aqueous solution. Thermogravimetric analysis was used to identify the suitable conditions for preparing oxidized fiber and coke as activated carbon precursors. Steam and CO(2) were used to activate the precursors. Activated carbons were characterized by their pore texture, elemental compositions and surface functionalities. Batch adsorption and desorption studies were carried out to determine the metal-binding ability of activated carbons. Two commercial activated carbon fibers (ACFs), i.e., A-20 and W10-W, were employed to compare the removal performance of PAN derived activated carbons. Influence of oxidation treatment of PAN fiber prior to steam activation was also explored and discussed. Results indicated that steam produced a higher surface area but a lower resultant yield as compared to CO(2). Also, precursors activated by steam showed a greater removal performance. For both activation methods, fiber displayed a better metal-binding ability than coke. A small nitrogen loss from PAN fiber as a result of oxidation treatment assisted a greater removal of Cu(II) and Pb(II), but the interaction to Cu(II) was found stronger. It is proposed that the formation of cyclized structure by oxidation treatment minimized the nitrogen loss during steam activation, hence increased the uptake performance.

Adsorption of aqueous metal ions on cattle-manure-compost based activated carbons.

The objective of this study is to examine the suitability and performance of cattle-manure-compost (CMC) based activated carbons in removing heavy metal ions from aqueous solution. The influence of ZnCl(2) activation ratios and solution pH on the removal of Cu(II) and Pb(II) were studied. Pore texture, available surface functional groups, pH of point zero charge (pH(PZC)), thermogravimetric analysis and elemental compositions were obtained to characterize the activated carbons. Batch adsorption technique was used to determine the metal-binding ability of activated carbons. The equilibrium data were characterized using Langmuir, Freundlich and Redlich-Peterson models. It was found that the uptake of aqueous metal ions by activated carbons could be well described by Langmuir equation. It is suggested that the increase of surface area and mesopore ratio as a result of increasing activation ratios favored the removal of Cu(II), while activated carbon rich in acidic groups showed selective adsorption towards Pb(II). The preferable removal of Cu(II) over Pb(II) could be due to the rich nitrogen content as well as the higher mesoporous surface area in the CMC activated carbons. The impregnated CMC activated carbons also showed a better performance for Cu(II) removal at varying solution pH than Filtrasorb 400 (F400), while a similar performance was observed for Pb(II) removal.

Cadmium(II) adsorption using functional mesoporous silica and activated carbon.

The role of surface functionality on silica and carbonaceous materials for adsorption of cadmium(II) was examined using various mesoporous silica and activated carbon. Silica surfaces were principally functionalized by mono-amino- and mercapto-groups, while carboxylic group was introduced to the activated carbons by oxidation. Functional groups on silica surface were formed using grafting and co-condensation techniques in their preparation. Mono-amino group was found more effective than di- and tri-amino groups for cadmium(II) adsorption on the grafted silica. Mono-amino groups prepared by co-condensation adsorbed cadmium(II) as much as 0.25mmol/g compared to mercapto- and carboxyl-groups which adsorbed around 0.12mmol/g, whereas Langmuir adsorption affinities were as strong as 50-60L/mmol for all of the three functions. The working pH range was wider for mercapto- and carboxyl-functions than for amino-group. Basic site could be an adsorption center for amino-functional groups while ion exchange sites were found to work for the mercapto- and carboxyl-functions to adsorb cadmium(II) from aqueous phase. Based on the experimental results, surface functional groups rather than structure of silica and carbon seemed to play a decisive role for cadmium(II) adsorption.

Inhibition of nitrobenzene adsorption by water cluster formation at acidic oxygen functional groups on activated carbon

The inhibition effect of nitrobenzene adsorption by water clusters formed at the acidic groups on activated carbon was examined in aqueous and n-hexane solution. The activated carbon was oxidized with nitric acid to introduce CO complexes and then outgassed in helium flow at 1273 K to remove them completely without changing the structural properties of the carbon as a reference adsorbent. The amounts of acidic functional groups were determined by applying Boehm titration. A relative humidity of 95% was used to adsorb water onto the carbon surface. Strong adsorption of water onto the oxidized carbon can be observed by thermogravimetric analysis. The adsorption kinetic rate was estimated to be controlled by diffusion from the kinetic analysis. Significant decline in both capacity and kinetic rate for nitrobenzene adsorption onto the oxidized carbon was also observed in n-hexane solution by preadsorption of water to the carbon surface, whereas it was not detected for the outgassed carbons. These results might reveal that water molecules forming clusters at the CO complexes inhibited the entrance of nitrobenzene into the interparticles of the carbon.

Effect of phosphorus fluctuation caused by river water dilution in eutrophic lake on competition between blue-green alga Microcystis aeruginosa and diatom Cyclotella sp.

Tega-numa (Lake Tega) is one of the eutrophic lakes in Japan. For the improvement of water quality in Lake Tega, the North-chiba Water Conveyance Channel was constructed in 2000, which transfer water from Tone River into the lake. After 2000, the dominant species of diatoms, mainly Cyclotella sp., have been replacing blue-green algae, mainly Microcystis aeruginosa in Lake Tega. This transition of dominant species would be due to the dilution, but the detail mechanism has not been understood yet. This study examined the relationship between phosphorus fluctuation caused by river water dilution to Lake Tega and dominance of algal species, M. aeruginosa or Cyclotella sp. based on the single-species and the mixed-species culture experiments. The single-species culture experiment showed that the half-saturation constant and uptake rate of phosphorus were one order lower and seven times higher for M. aeruginosa than those for Cyclotella sp. These findings implied that M. aeruginosa would possess a potential for the growth and survival over Cyclotella sp. in the phosphorus limited condition. The superiority of M. aeruginosa was reflected in the outcome of the mixed-species culture experiment, i.e., dominance of M. aeruginosa, even phosphorus concentration was lowered to 0.01 mg-P/L. Therefore, it could be concluded that the decrease in phosphorus concentration due to the river water dilution to Lake Tega would be interpreted as a minor factor for the transition of dominant species from M. aeruginosa to Cyclotella sp.

Prediction of Microcystis Blooms Based on TN:TP Ratio and Lake Origin

We evaluated the relationship between TN:TP ratio and Microcystis growth via a database that includes worldwide lakes based on four types of lake origin (dammed, tectonic, coastal, and volcanic lakes). We used microcosm and mesocosm for the nutrient elution tests with lake water and four kinds of sediment (nontreated, MgO sprinkling treated, dissolved air flotation [DAF] treated, and combined treated sediment) in order to control TN:TP ratio and to suppress Microcystis growth. Microcystis growth was related to TN:TP ratio, with the maximum value at an optimum TN:TP ratio and the minimum values when the TN:TP ratios reached to 0 or ∞. The kurtosis of the distribution curve varied with the type of lake origin; the lowest kurtosis was found in dammed lakes, while the highest was found in volcanic lakes. The lake trophic state could affect the change in the kurtosis, providing much lower kurtosis at eutrophic lakes (dammed lakes) than that at oligotrophic lakes (volcanic lakes). The relationship between TN:TP ratio and Microcystis growth could be explained by the nutrient elution tests under controlled TN:TP ratios through the various sediment treatments. A significant suppression of Microcystis growth of 70% could be achieved when the TN:TP ratios exceeded 21. Lake origin could be regarded as an index including morphological and geographical factors, and controlling the trophic state in lakes. The origin rather than trophic state for lakes could be considered as an important factor of TN:TP influences on Microcystis growth.

Preparation of Bamboo Chars and Bamboo Activated Carbons to Remove Color and COD from Ink Wastewater.

Bamboo chars and bamboo activated carbons prepared by steam activation were applied for ink wastewater treatment. Bamboo char at 800 °C was the best for the removal of color and chemical oxygen demand (COD) from ink wastewater compared to bamboo chars at 300 to 700 °C due to higher surface area and mesopore volume. Bamboo activated carbon at 600 °C (S600) was the best compared to bamboo activated carbon at 800 °C (S800), although S800 had larger surface area (1108 m(2)/g) than S600 (734 m(2)/g). S600 had higher mesopore volume (0.20 cm(3)/g) than S800 (0.16 cm(3)/g) and therefore achieved higher color and COD removal. All bamboo activated carbons showed higher color and COD removal efficiency than commercial activated carbon. In addition, S600 had the superior adsorption capacity for methylene blue (0.89 mmol/g). Therefore, bamboo is a suitable material to prepare adsorbents for removal of organic pollutants.

Effect of Polarity of Activated Carbon Surface, Solvent and Adsorbate on Adsorption of Aromatic Compounds from Liquid Phase

In this study, introduction of acidic functional groups onto a carbon surface and their removal were carried out through two oxidation methods and outgassing to investigate the adsorption mechanism of aromatic compounds which have different polarity (benzene and nitrobenzene). Adsorption experiments for these aromatics in aqueous solution and n-hexane solution were conducted in order to obtain the adsorption isotherms for commercial activated carbon (BAC) as a starting material, its two types of oxidized BAC samples (OXs), and their outgassed samples at 900 °C (OGs). Adsorption and desorption kinetics of nitrobenzene for the BAC, OXs and OGs in aqueous solution were also examined. The results showed that the adsorption of benzene molecules was significantly hindered by abundant acidic functional groups in aqueous solution, whereas the adsorbed amount of nitrobenzene on OXs gradually increased as the solution concentration increased, indicating that nitrobenzene can adsorb favourably on a hydrophilic surface due to its high dipole moment, in contrast to benzene. In n-hexane solution, it was difficult for benzene to adsorb on any sample owing to the high affinity between benzene and n-hexane solvent. On the other hand, adsorbed amounts of nitrobenzene on OXs were larger than those of OGs in n-hexane solution, implying that nitrobenzene can adsorb two adsorption sites, graphene layers and surface acidic functional groups. The observed adsorption and desorption rate constants of nitrobenzene on the OXs were lower than those on the BAC due to disturbance of diffusion by the acidic functional groups.

Arsenic Adsorption by Activated Carbon with Different Amounts of Basic Sites under Different Solution pH and Coexistent Ions

The bamboo-based and bead-shaped activated carbon (BAC) were used to examine the effects of textural properties and surface chemistry, respectively, on As(V) adsorption. The relationships between solution pH, coexistent ions and/or arsenic species and As(V) adsorption by BAC were also investigated. The Langmuir and pseudo-second order kinetics models were employed to evaluate the prepared activated carbon for As(V) adsorption. The results showed that As(V) adsorption was strongly attributed to surface properties, that is, basic sites rather than textural properties. The fittings of adsorption data to the kinetics models revealed that As(V) adsorption would be governed by diffusion process rather than collision process. Among various acidity regulators (HCl, HNO3, and H2SO4), the pH adjustment by HCl induced the highest adsorption amount at pH 5.5, indicating that the inhibition effect of Cl− ion for As(V) adsorption was much less than and ions. The effective arsenic species for As(V) adsorption was , and the decrease in the adsorption amount in acidic condition would be due to the inhibition by excess of Cl− ion, while the decrease in the adsorption at pH more than 5.5 would be attributed to the increase in OH− ion or to the influence of increased hydrogen arsenate species ( ).

Enhanced lead(II) binding properties of heat-treated cattle-manure-compost-activated carbons

AbstractConsiderable concerns have been raised over the presence of lead(II) in water bodies. In this work, the performance of heat-treated cattle-manure-compost-activated carbons were investigated to remove lead(II) from aqueous solution. Activated carbons were prepared by one-step ZnCl2 activation followed by heat treatment at different temperatures. They were characterized according to BET surface area, pore size distribution, elemental analysis, pHPZC and Boehm’s titration. It was found that the increase of treatment temperature resulted in a decrease in both the BET surface area as well as the concentration of phenolic groups. However, such decreases were compensated by an increase of lead(II) by more than three times to a value of 0.110 mmol/g, and this was also true for commercial F400-activated carbon. Lead(II) adsorption onto heat-treated activated carbons could be described by Langmuir isotherm with weaker interaction to active sites. Results also suggested that the increase in lead(II) uptake w...