Influence of the iron-oxide mass fractions of magnetic powdered activated carbon on its hexavalent chromium adsorption performance in water.

Magnetic powdered activated carbon (Mag-PAC) is an effective adsorbent to remove hexavalent chromium (Cr(VI)) from water and can be recovered for reuse. However, the tradeoff between the adsorption performance of Cr(VI) and magnetic properties of Mag-PAC remains unclear. Herein, we prepared a series of Mag-PAC adsorbents containing various iron-oxide mass fractions with FeSO4·7H2O as the precursor, using a facile wet-chemical precipitation route and conducted batch experiments to evaluate the Cr(VI) adsorption performance. Results revealed that Mag-PAC was functionalized by magnetic iron oxide comprising crystalline goethite and magnetite structures. Furthermore, its adsorption performance was highly dependent on pH and was most effective at an initial solution pH of 2. Both the sorption rate constant and Cr(VI) adsorption capacity were greatly influenced by magnetization, and they gradually decreased as the iron-oxide mass fraction increased. Among the prepared adsorbents, Mag-PAC-75 (∼32% wt iron) exhibited not only an excellent Cr(VI) adsorption performance (Langmuir adsorption capacity: 75.76 mg/g) but also effective magnetic properties (saturation magnetization: 9.66 emu/g). Coexisting anions had a negligible competitive effect on Cr(VI) removal by Mag-PAC-75 at an initial pH of 2, whereas the presence of tannic acid markedly improved the Cr(VI) elimination. The presence of trivalent chromium on the surface of Mag-PAC-75 confirmed via X-ray photoelectron spectroscopy indicated that some synergistic redox reactions may occur during the sorption process. After five regeneration cycles using NaOH, Mag-PAC-75 continued to exhibit a high Cr(VI) removal efficiency and magnetic stability. These findings indicate that optimizing the adsorption performance and magnetic properties is a key factor for realizing the practical application of Mag-PAC for Cr(VI) removal. Overall, Mag-PAC may have been a promising application prospect for Cr(VI) removal from water due to its high adsorption capacity and magnetic properties, coupled with its good reusability and magnetic stability after regeneration cycles.

Study on regeneration mechanism of composite adsorbent by Mg-MOF-74-based modified biochar.

In this paper, composite adsorbent was prepared from biochar and Mg-MOF-74 by in-situ growth method to investigate regeneration mechanism. The effects of O2 and temperature on regeneration characteristics were investigated by CO2 adsorption properties and characterization techniques, and the optimal regeneration conditions were determined. Regeneration mechanism of adsorbent was revealed by adsorption kinetics and elemental valence analysis. The related wave function parameters were calculated based on DFT to reveal the repair mechanism of the failed oxidation sites from the microscopic level. The mechanism of CO2 adsorption by the repaired oxidation sites was explored based on the regenerated adsorption configuration. It was found that the regeneration performance of the adsorbent exhibited a trend of increasing and then decreasing with the increase of O2 concentration and temperature, and the optimal regeneration conditions were determined to be 5 % O2 concentration and 200 °C. At optimal regeneration conditions, a synergistic interaction between O2 and poly-metals was generated to enhance the adsorbent polarity. O2 also reacted with the adsorbent in a redox reaction to produce new oxygen-containing functional groups and cause pore expansion, the mass transfer and diffusion was enhanced. The oxidation site adsorbed O2 to undergo electron rearrangement and release the adsorbed CO2. Due to the nature of common orbital hybridization between metals, the metals underwent conjugation and synergistic effects with O2 to form tetrahedral co-coordination structures with lower energies. The electron density and electric field effects of the system were enhanced. The former enhanced interaction with CO2 to form carbonate. The latter increased the activity of the neighboring N atom, which in turn generated a stable ring structure with carbonate, and CO2 adsorption was enhanced.

A magnetic imprinted polymer nano-adsorbent with embedded quantum dots and mesoporous carbon for the microextraction of triazine herbicides.

A magnetic molecularly imprinted polymer (MMIP) adsorbent incorporating amino-functionalized magnetite nanoparticles, nitrogen-doped graphene quantum dots and mesoporous carbon (MIP@MPC@N-GQDs@Fe3O4NH2) was fabricated to extract triazine herbicides from fruit juice. The embedded magnetite nanoparticles simplified the isolation of the adsorbent from the sample solution. The N-GQDs and MPC enhanced adsorption by affinity binding with triazines. The MIP layer provided highly specific recognition sites for the selective adsorption of three target triazines. The extracted triazines were determined by high-performance liquid chromatography (HPLC) coupled with diode-array detection (DAD). The developed method exhibited linearity from 1.5 to 100.0 µg L-1 with a detection limit of 0.5 µg L-1. Recoveries from spiked fruit juice samples were in the range of 80.1- 108.4 %, with a relative standard deviation of less than 6.0 %. The developed MMIP adsorbent demonstrated good selectivity, high extraction efficiency, ease of fabrication and use, and good stability.

Constructing porous ZnFC-PA/PSF composite spheres for highly efficient Cs+ removal.

Radioisotope leaking from nuclear waste has become an intractable problem due to its gamma radiation and strong water solubility. In this work, a novel porous ZnFC-PA/PSF composite sphere was fabricated by immobilization of ferrocyanides modified zinc phytate into polysulfone (PSF) substrate for the treatment of Cs-contaminated water. The maximum adsorption capacity of ZnFC-PA/PSF was 305.38 mg/g, and the removal efficiency of Cs+ was reached 94.27% within 2 hr. The ZnFC-PA/PSF presented favorable stability with negligible dissolution loss of Zn2+ and Fe2+ (< 2%). The ZnFC-PA/PSF achieved high-selectivity towards Cs+ (Kd = 2.24×104 mL/g) even in actual geothermal water. The adsorption mechanism was inferred to be the ion-exchange between Cs+ and K+. What's more, ZnFC-PA/PSF worked well in the fixed-bed adsorption (E = 91.92%), indicating the application potential for the hazardous Cs+ removal from wastewater.

Waste treats waste: Facile fabrication of porous adsorbents from recycled PET and sodium alginate for efficient dye removal.

Dye-contaminated water and waste plastic both pose enormous threats to human health and the ecological environment, and simultaneously solving these two issues in a sustainable and resource-saving way is highly important. In this work, a sodium alginate-polyethylene terephthalate-sodium alginate (SA@PET) composite adsorbent for efficient dye removal is fabricated using wasted PET bottle and marine plant-based SA via simple and energy-efficient nonsolvent-induced phase separation (NIPS) method. Benefiting from its porous structure and the abundant binding sites, SA@PET shows an excellent methylene blue (MB) adsorption capacity of 1081 mg g-1. The Redlich-Peterson model more accurately describes the adsorption behavior, suggesting multiple adsorption mechanisms. In addition to the electrostatic attractions of SA to MB, polar interactions between the PET matrix and MB are also identified as adsorption mechanisms. It is worth mentioning that SA@PET could be recycled 7 times without a serious decrease in performance, and the trifluoroacetic acid-dichloromethane solvent involved in the NIPS process has the possibility of reuse and stepwise recovery. Finally, the discarded adsorbent could be completely degraded under mild conditions. This work provides not only a composite adsorbent with excellent cationic dye removal performance for wastewater treatment, but also an upcycling strategy for waste PET.

TiO2/Polystyrene Nanocomposite Antibacterial Material as a Hemoperfusion Adsorbent for Efficient Bilirubin Removal and Prevention of Bacterial Infection.

The use of hemoperfusion adsorbents for the removal of bilirubin in patients with liver failure has become a critical treatment. However, the insufficient clearance of bilirubin and the possibility of bacterial infection during hemoperfusion limit the application. In this work, we designed a novel antibacterial bilirubin adsorbent (PSVT) through the suspension polymerization reaction between double-bond functionalized TiO2 nanoparticles and styrene. PSVT showed an excellent bilirubin adsorption ability and antibacterial performance, ensuring efficient clearance of bilirubin in liver failure patients during hemoperfusion and preventing bacterial infection. The experimental results indicated that TiO2 was uniformly dispersed in the microspheres, which improved the mesoporous structure and increased the specific surface area. Composite adsorbent PSVT showed an exceptional bilirubin adsorption capacity, with the maximum adsorption capacity reaching 24.3 mg/g. In addition, the introduction of TiO2 endowed PSVT with excellent antibacterial ability; the ultimate antibacterial rates against Escherichia coli and Staphylococcus aureus reached 97.31 and 96.47%, respectively. In summary, PSVT served as a novel antibacterial bilirubin adsorbent with excellent bilirubin clearance capacity and antibacterial performance, providing excellent application prospects for treating liver failure patients.

Granulation of hydrometallurgically synthesized spinel lithium manganese oxide using cross-linked chitosan for lithium adsorption from water.

A drastic increase in demand for electric vehicles and energy storage systems increases lithium (Li) need as a critical metal for the 21st century. Lithium manganese oxides stand out among inorganic adsorbents because of their high capacity, chemical stability, selectivity, and affordability for lithium recovery from aqueous media. This study investigates using hydrometallurgically synthesized lithium manganese oxide (Li1.6Mn1.6O4) in granular form coated with cross-linked chitosan for lithium recovery from water. Characterization methods such as SEM, FTIR, XRD, and BET reveal the successful synthesis of the composite adsorbent. Granular cross-linked chitosan-coated and delithiated lithium manganese oxide (CTS/HMO) adsorbent demonstrated optimal removal efficiency of 86 % at pH 12 with 4 g/L of adsorbent dosage. The Langmuir isotherm at 25 °C, which showed monolayer adsorption with a maximum capacity of 4.94 mg/g, a better fit for the adsorption behavior of CTS/HMO. Adsorption was endothermic and thermodynamically spontaneous. Lithium adsorption followed the pseudo-first-order kinetic model.

Optimization of two-phase synthesis of Fe-hydrochar for arsenic removal from drinking water: Effect of temperature and Fe concentration.

Arsenic-contaminated water is a global concern that demands the development of cost-effective treatments to ensure a safe drinking water supply for people worldwide. In this paper, we report the optimization of a two-phase synthesis for producing a hydrochar core from olive pomace to serve as support for the deposition of Fe-hydroxide, which is the active component in As(V) removal. The operating conditions considered were the initial concentration of Fe in solution in the hydrothermal treatment (phase I) and the temperature of Fe precipitation (phase II). The obtained samples were characterized for their elemental composition, solid yield, mineral content (Fe and K), phenol release, As(V) sorption capacity, and sorbent stability. Correlation analysis revealed that higher Fe concentrations (26.8 g/L) ensured better carbonization during hydrothermal treatment, increased arsenic removal, reduced concentrations of phenols in the final liquid, and improved stability of the sorbent composite. On the other hand, the temperature during Fe precipitation (phase II) can be maintained at lower levels (25-80 °C) since higher temperatures yielded lower adsorption capacity. Regression analysis demonstrated the significance of the main effects of the parameters on sorption capacity and provided a model for selecting operating conditions (Fe concentration and phase II temperature) to obtain composite sorbents with tailored sorption properties.

FeSx@MOF-808 composite for efficient As(III) removal from wastewater: behavior and mechanism.

Arsenic is extremely toxic to humans with water as its carrier. One challenge for arsenic control is the complete elimination of As(III) due to its high toxicity, mobility, and solubility. Herein, an active FeSx@MOF-808 composite was fabricated to enhance the As(III) removal for wastewater remediation. The FeSx@MOF-808 showed better As(III) adsorptive performance (Qe = 73.60 mg/g) compared with Fe2S3 (Qe=12.38 mg/g), MOF-808 (Qe = 27.85 mg/g), and Fe@MOF-808 (Qe=34.26 mg/g). This can be attributed to an improved porous structure provided by MOF-808 and abundant reactive sites provided by FeSx. Calculated by the Langmuir model (R2 =0.9965), the maximum adsorption capacity (Qmax) of FeSx@MOF-808 for As(III) removal at 298 K and pH = 7 was 203.28 ± 6.43 mg/g, which is beyond most of the traditional materials and MOFs. Additionally, FeSx@MOF-808 exhibited good stability in a wide pH range (1-13). Results also showed that the different Fe/S ratios (1:0-1:8) and FeSx loading amount (0.00625-0.25 mmol) have effects on the FeSx@MOF-808 performance. By kinetics studies, XPS, and DFT calculation, the mechanisms for arsenic by FeSx@MOF-808 were proposed. Multiple reaction mechanisms combine the adsorption by the MOF-808 support, the co-precipitation of iron oxides via hydroxyl (Fe-OH) groups, and most importantly, the precipitation through the break of Fe-S and the bond of As-S.

Removal of Eu3+ from simulated aqueous solutions by synthesis of a new composite adsorbent material.

The goal of this research is to separate and purify 152+154Eu generated from nuclear waste and/or research laboratories using synthesized composite material. Fourier infrared (FTIR), thermal gravimetric analysis (TGA), differential thermal analysis (DTA), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area measurements were used to characterize the composite material. On the 152+154Eu sorption process, the impacts of pH, contact time, and initial feed concentration were also examined. The best 152+154Eu removal efficiency was 86.4% achieved at pH 4.5 and 180 min. The sorption data of 152+154Eu ions were investigated using kinetic modeling and sorption isotherm models, and it was clear that the pseudo second-order kinetics and the Langmuir isotherm are the best matches for the sorption process. The produced adsorbent capacity was 11.48 mg g-1. Application study demonstrated that the removal efficiency (%) reached 92.4, 92.2 and 95.2% of 152+154Eu (carrier free) from river, tab and groundwater, respectively. According to the findings of this investigation, the proposed polymer composite is a strong candidate for recovering radioactive 152+154Eu ions from liquid waste.

Excellent performance separation of trypsin by novel ternary magnetic composite adsorbent based on betaine-urea- glycerol natural deep eutectic solvent modified MnFe2O4-MWCNTs.

The effective trypsin purification methods should be established since trypsin plays a crucial role in biosome. In this work, a novel ternary magnetic composite adsorbent (MnFe2O4-MWCNTs@B-U-G) with the features of strong specific selectivity, good adsorption effect, simple and efficient separation process, no secondary pollution brought in was prepared by integrating the superior physicochemical properties of ternary based natural deep eutectic solvent, multi-walled carbon nanotubes and MnFe2O4. The property, composition and microtopography structure of MnFe2O4-MWCNTs@B-U-G were characterized in detail. Combined with magnetic solid-phase extraction, MnFe2O4-MWCNTs@B-U-G was utilized to adsorb trypsin. Response surface methodology experiment was prepared under Box-Behnken design to optimize the adsorption conditions and the results showed that the practical maximum adsorption capacity for trypsin was 1020.1 mg g-1. Besides, the adsorption isotherms, adsorption kinetics, regeneration studies and method validation studies were investigated systematically to evaluate the established adsorption separation system. Mechanism exploration proved that electrostatic interaction, hydrogen bonding interaction and chelation interaction were the dominant forces for the high-performance adsorption of trypsin. The activity of trypsin after elution had been analyzed by UV-vis spectrophotometer and CD spectrometer with three methods, which illustrated that the enzyme activity, conformation and secondary structure of trypsin did not change significantly during the adsorption-desorption process. In addition, the proposed method was successful and practical applicability to isolation trypsin from crude bovine pancreas. As a result, due to the superiority of the MnFe2O4-MWCNTs@B-U-G, the proposed method not only exhibites high-performance adsorption of trypsin, but also provides a green and sustainable potential value in the adsorption of biomacromolecule.

Decoupling the adsorption mechanisms of arsenate at molecular level on modified cube-shaped sponge loaded superparamagnetic iron oxide nanoparticles.

In this study, a commercial cube-shaped open-celled cellulose sponge adsorbent was modified by in-situ co-precipitation of superparamagnetic iron oxide nanoparticles (SPION) and used to remove As(V) from aqueous solutions. Fe K-edge X-ray absorption spectroscopy (XAS) and TEM identified maghemite as the main iron phase of the SPION nanoparticles with an average size 13 nm. Batch adsorption experiments at 800 mg/L showed a 63% increase of adsorption capacity when loading 2.6 wt.% mass fraction of SPION in the cube-sponge. Experimental determination of the adsorption thermodynamic parameters indicated that the As(V) adsorption on the composite material is a spontaneous and exothermic process. As K-edge XAS results confirmed that the adsorption enhancement on the composite can be attributed to the nanoparticles loaded. In addition, adsorbed As(V) did not get reduced to more toxic As(III) and formed a binuclear corner-sharing complex with SPION. The advantageous cube-shape of the sponge-loaded SPION composite together with its high affinity and good adsorption capacity for As(V), good regeneration capability and the enhanced-diffusion attributed to its open-celled structure make this adsorbent a good candidate for industrial applications.

A dumbbell-shaped stir bar made from poly(3,4-ethylenedioxythiophene)-coated porous cryogel incorporating metal organic frameworks for the extraction of synthetic phenolic antioxidants in foodstuffs.

A dumbbell-shaped stir bar adsorbent of MIL-101 entrapped in PVA cryogel coated with poly(3,4-ethylenedioxythiophene) was fabricated to extract synthetic phenolic antioxidants in foodstuffs. The interconnected porous of cryogel allowed the entrapment of MIL-101 and enhanced the surface areas of poly(3,4-ethylenedioxythiophene) coating which facilitated multiple adsorptions. The fabricated adsorbent was characterized and measured the adsorption capacities for synthetic phenolic antioxidants. Extraction efficiency was optimized by evaluating the effect of adsorbent compositions, extraction time, stirring speed, sample pH, desorption conditions, sample volume and ionic strength. The analysis of extracted synthetic phenolic antioxidants was carried out using high performance liquid chromatography. The developed analysis method provided a wide linear range of 0.20 - 200 µg kg-1 for butylated hydroxyanisole and 0.50 - 200 µg kg-1 for tert­butylhydroquinone and butylated hydroxytoluene. The limits of detection were between 0.05 and 0.15 µg kg-1. The developed stir bar adsorbent was utilized to extract these three synthetic phenolic antioxidants from juice, milk, infant formula and coffee creamer. Recoveries ranged from 87 to 101% with RSDs below 7%. The developed composite stir bar adsorbent was convenient to use, and good physical and chemical stability allowed efficient extraction for 12 extraction cycles.

Active Carbon/PAN composite adsorbent for uranium removal: Modeling adsorption isotherm data, thermodynamic and kinetic studies.

The aim of the present study was to produce a high capacity and steady adsorbent able to separate uranium ions resulting from the nuclear fuel cycle process at different pHs and concentrations. AC/PAN (active carbon/polyacrylonitrile) composite adsorbent was investigated in a batch system for uranium sorption as a function of pH, contact time, initial metal ion concentration, temperature and adsorbent concentration. The adsorption mechanism was described through a comparison of linear and nonlinear regression analysis. The adsorption capacity was found to be 27.47 and 28.45 mg g-1 according to the linear and non-linear regression analysis of the Langmuir isotherm, respectively. The adsorption mechanism followed to pseudo-second-order kinetics. The thermodynamic parameters (standard enthalpy (ΔH° = -23.46 kJ mol-1), entropy (ΔS° = 0.02 J mol-1 K-1), and free energy (ΔG°)) were determined and the results indicated that the adsorption system was exothermic, spontaneous and favorable.

Modification of activated carbon by MIL-53(Al) MOF to develop a composite framework adsorbent for CO2 capturing.

In this research, a novel composite is synthesized based on activated carbon and MIL-53(Al) through the solution mixing method at different MOF weight fractions, and the CO2 loading of prepared samples are measured in the batch and continuous apparatus. The structure, crystallinity, surface area, and chemical functionality of activated carbon, MIL-53(Al), and developed composite are characterized through BET, X-ray diffraction (XRD), scanning electron microscopy (SEM), and Fourier transform infrared spectroscopy (FTIR). The CO2 and N2 adsorption capacity of activated carbon, MIL-53(Al), and composites are examined in an isothermal batch reactor at the pressure range 0-110 kPa and equilibrium temperature 305 K. The adsorption isotherm of CO2 is correlated by the Langmuir and Toth models. Besides, the performance of composite is compared with MIL-53(Al) and activated carbon in a continuous packed bed at flow rate range 15-25 ml min-1 and temperature 32 °C, and the breakthrough curves are developed. The results show that increasing MOF content in the composite increases CO2 adsorption capacity, so the CO2 loading of synthesized composite containing 10%, 20%, and 30% MOF is 1.608, 1.704, and 1.792 mmol gr-1, respectively.

Promoting adsorption of organic pollutants via tailoring surface physicochemical properties of biomass-derived carbon-attapulgite.

Biomass-derived carbon-attapulgite adsorbent was developed for organic pollutants removal. All the batch assays were performed to evaluate the effects of organic components, contact time, and initial concentration of organic pollutants on the adsorption performance of the as-prepared adsorbent. The samples were characterized via Brunauer-Emmett-Teller (BET), Fourier transform infrared (FTIR), X-ray diffractometer (XRD), and scanning electron microscopy (SEM). The results demonstrated that the acid-treated carbon-attapulgite adsorbent (H-ATP/BC) showed a large specific surface area (237 m2 g-1) and possessed abundant oxygen-containing functional groups and silicon-oxygen bonds (i.e., O-Si-O and O-Si), which provided more active sites and conduced to the adhesive of organic pollutants. Both physical adsorption and chemical adsorption were involved in the adsorption process, and competitive adsorption occurred when two or more target pollutants coexist. Especially, phenol and/or aniline with an aromatic ring were much more likely to adhere to the H-ATP/BC surface than pyridine, and the selectivity order of H-ATP/BC for these pollutants was phenol > aniline > pyridine. From the model fitting, it was observed that the adsorption data could be described well by a pseudo-second-order model and Freundlich isotherms. The theoretical maximum phenol, aniline, and pyridine adsorption capacities of the H-ATP/BC were 14.31 mg g-1, 15.21 mg g-1, and 20.74 mg g-1, respectively. Comparison among the commercial adsorbents price also illustrated that H-ATP/BC could be a promising material for efficient treatment of organic pollutants.Graphical abstract.

Novel Activated Carbon Nanofibers Composited with Cost-Effective Graphene-Based Materials for Enhanced Adsorption Performance toward Methane.

Various types of activated carbon nanofibers' (ACNFs) composites have been extensively studied and reported recently due to their extraordinary properties and applications. This study reports the fabrication and assessments of ACNFs incorporated with graphene-based materials, known as gACNFs, via simple electrospinning and subsequent physical activation process. TGA analysis proved graphene-derived rice husk ashes (GRHA)/ACNFs possess twice the carbon yield and thermally stable properties compared to other samples. Raman spectra, XRD, and FTIR analyses explained the chemical structures in all resultant gACNFs samples. The SEM and EDX results revealed the average fiber diameters of the gACNFs, ranging from 250 to 400 nm, and the successful incorporation of both GRHA and reduced graphene oxide (rGO) into the ACNFs' structures. The results revealed that ACNFs incorporated with GRHA possesses the highest specific surface area (SSA), of 384 m2/g, with high micropore volume, of 0.1580 cm3/g, which is up to 88% of the total pore volume. The GRHA/ACNF was found to be a better adsorbent for CH4 compared to pristine ACNFs and reduced graphene oxide (rGO/ACNF) as it showed sorption up to 66.40 mmol/g at 25 °C and 12 bar. The sorption capacity of the GRHA/ACNF was impressively higher than earlier reported studies on ACNFs and ACNF composites. Interestingly, the CH4 adsorption of all ACNF samples obeyed the pseudo-second-order kinetic model at low pressure (4 bar), indicating the chemisorption behaviors. However, it obeyed the pseudo-first order at higher pressures (8 and 12 bar), indicating the physisorption behaviors. These results correspond to the textural properties that describe that the high adsorption capacity of CH4 at high pressure is mainly dependent upon the specific surface area (SSA), pore size distribution, and the suitable range of pore size.

Effective removal of radioactive cesium from contaminated water by synthesized composite adsorbent and its thermal treatment for enhanced storage stability.

A composite adsorbent for the removal of radioactive cesium (137Cs) was synthesized by immobilizing potassium cobalt ferrocyanide in the micro pores of the zeolite chabazite. The synthetically optimized composite adsorbent demonstrates a rapid cesium adsorption rate under both salt-free and high-salt conditions with a high distribution coefficient of cesium (≥105 mL/g). Although both components have the same ion-exchange reaction between potassium and cesium, the reaction by ferrocyanide component was predominant, which derived hundred times higher distribution coefficient of the composite adsorbent than that of pure chabazite. A thermal stabilization process was studied for improving the storage and/or disposal stability of the spent adsorbent. The formation of a eutectic system within the spent adsorbent reduced the stabilization temperature to 1000 °C from 1200 °C. Accordingly, the leaching of cesium was remarkably reduced by the remineralization to the stable pollucite. The stable impregnation of ferrocyanide component in the chabazite pores derived the reduction of cesium volatility enabling the high temperature stabilization method. Our experimental results provide evidence that the composite adsorbent has clear advantages on the cesium removal from contaminated water and its stabilization via thermal-treatment.

Combined use of tannic acid-type organic composite adsorbents and ozone for simultaneous removal of various kinds of radionuclides in river water.

Tannic acid-type organic composite adsorbents (PA316TAS, AR-01TAS, PYRTAS, WA10TAS, WA20TAS, and WA30TAS), combined with hydrolyzed and sulfonated tannic acid (TAS) and porous-type strongly basic anion-exchange resin (PA316), benzimidazole-type anion-exchange resin embedded in high-porous silica beads (AR-01), pyridine-type anion-exchange resin (PYR), acrylic-type weakly basic anion-exchange resin (WA10), or styrene-type weakly basic anion-exchange resins (WA20 and WA30) for simultaneous removal of various kinds of radionuclides in river water were successfully synthesized. The adsorption behavior of twelve kinds of simulated radionuclides (Mn, Co, Sr, Y, Ru, Rh, Sb, Te, Cs, Ba, Eu, and I (I- and IO3-)) on these composite adsorbents has been studied in real river water at room temperature. PA316TAS adsorbents showed much higher distribution coefficients (Kd) for all metal ions. TAS structure has more selective adsorption ability for Mn, Co, Sr, Y, Cs, Ba, Eu, and IO3-. On the other hand, Y, Ru, Rh, Sb, Te, Eu, I (I- and IO3-) were adsorbed on both PA316 and TAS structures. To evaluate the validity of these mechanistic expectations, the respective chemical adsorption behaviors of Mn, Co, Sr, etc. and PA316TAS adsorbent were examined in river water ranging in temperature from 278 to 333 K. As was expected, one adsorption mechanism for Mn, Co, Sr, Cs, and Ba systems and two types of adsorption mechanisms for Y, Ru, Rh, Sb, Te, Eu, I (I- and IO3-) systems were observed. On the other hand, the precipitation of Mn, Co, Y, Ru, Rh, Te, and Eu was formed by ozonation for river water, that is, ozone can transform Mn, Co, Y, Ru, Rh, Te, and Eu ions into the insoluble precipitates. Hence, one straight line for Sr, Cs, Ba systems and two types of straight lines for Sb, I (I- and IO3-) systems were obtained in river water treated with ozone. The chromatography experiments of Cs, Sr, I (I- and IO3-) were carried out to calculate their maximum adsorption capacities. The obtained maximum adsorption capacities of Cs, Sr, and I- mixed with IO3- were 1.7 × 10-4 (Cs), 1.8 × 10-3 (Cs/O3), 7.8 × 10-5 (Sr), 5.6 × 10-4 (Sr/O3), 5.4 × 10-2 (I- and IO3-), 3.1 × 10-2 (I- and IO3-/O3) mol/g - PA316TAS. It was discovered that the maximum adsorption capacities of I- and IO3- for the composite adsorbent is unprecedented high and the capacity become much greater than an order of magnitude, compared with those of previous reports. This phenomenon suggests the formation of electron-donor-acceptor (EDA) complexes or pseudo EDA complex. Based on these results, it was concluded that the combined use of tannic acid-type organic composite adsorbents and ozone made it possible to remove simultaneously and effectively various kinds of radionuclides in river water in the wide pH and temperature ranges.

Evaluation of the selective adsorption of silica-sand/anionized-starch composite for removal of dyes and Cupper(II) from their aqueous mixtures.

A silica-sand/anionized-starch composite (CMS-SS) was prepared simply. CMS-SS was used as an efficient adsorbent for removal of cationic dyes [methyl blue (MB) and crystal violet (CV)] and metal ions [cupper(II), Cu(II)] from water in respective single and binary systems. Compared with the anionized-starch without silica sand, CMS-SS shows evidently improved adsorption capacities, i.e. approximately 653.31 ± 27.30, 1246.40 ± 34.10, and 383.08 ± 13.50 mg·g-1, for MB, CV, and Cu(II), respectively, ascribed to the additional carboxyl groups. The isotherms and kinetics study indicated that the Langmuir model and the pseudo-second-order model were more suitable. The adsorption process is thus a homogeneous monolayer chemisorption. The adsorptions of these three pollutants are spontaneous and exothermal processes driven by increasing entropy. The adsorption behaviors of CMS-SS have high pH dependence, and electrostatic attraction play an important role in adsorption. Dyes showed higher affinity to CMS-SS than metal ions causing a preferential adsorption of dye over Cu(II) in their aqueous mixture. This adsorbent after saturated adsorption could be rapidly separated from water due to its enlarged density after embedded silica sand; moreover, those rapidly recovered adsorbents were tried to use as new adsorbents for removal of an anionic dye from water due to the complete changes in their surface structures after saturated adsorption.