Polyethylenimine-Crosslinked 3-Aminopropyltriethoxysilane-Grafted Multiwall Carbon Nanotubes for Efficient Adsorption of Reactive Yellow 2 from Water.

This research intended to report amine-functionalized multiwall carbon nanotubes (MWCNTs) prepared by a simple method for efficient and rapid removal of Reactive Yellow 2 (RY2) from water. EDS analysis showed that the N content increased from 0 to 2.42% and from 2.42 to 8.66% after modification by 3-Aminopropyltriethoxysilane (APTES) and polyethylenimine (PEI), respectively. BET analysis displayed that the specific surface area, average pore size, and total pore volume were reduced from 405.22 to 176.16 m2/g, 39.67 to 6.30 nm, and 4.02 to 0.28 cm3/g, respectively. These results proved that the PEI/APTES-MWCNTs were successfully prepared. pH edge experiments indicated that pH 2 was optimal for RY2 removal. At pH 2 and 25 °C, the time required for adsorption equilibrium was 10, 15, and 180 min at initial concentrations of 50, 100, and 200 mg/L, respectively; and the maximum RY2 uptake calculated by the Langmuir model was 714.29 mg/g. Thermodynamic studies revealed that the adsorption process was spontaneous and endothermic. Moreover, 0-0.1 mol/L of NaCl showed negligible effect on RY2 removal by PEI/APTES-MWCNTs. Five adsorption/desorption cycles confirmed the good reusability of PEI/APTES-MWCNTs in RY2 removal. Overall, the PEI/APTES-MWCNTs are a potential and efficient adsorbent for reactive dye wastewater treatment.

Preparation of adsorptive polyethyleneimine/polyvinyl chloride electrospun nanofiber membrane: Characterization and application.

Landfilling and burning plastic waste, especially waste polyvinyl chloride (PVC), can produce highly toxic and carcinogenic by-products that threaten the ecosystem and human health. However, there is still a lack of proper methods for waste PVC recycling. Therefore, developing feasible ways for waste PVC recovery is urgently needed. The purpose of this study is to analyze the characteristics of PVC-based adsorptive nanofiber membranes and test their ability for the treatment of wastewater containing Cibacron Brilliant Yellow 3G-P, a widely used reactive dye. The polyethylenimine/polyvinyl chloride membrane (PEI/PVCM) was characterized by FTIR, FE-SEM, TGA, tensile analysis, water contact angle measurement, and zeta-potential analysis. The FTIR analysis confirmed that the PEI has successfully crosslinked with PVC. The FE-SEM images showed that the nanofibers constituting PEI/PVCM are compact with an average fiber diameter of 181 nm. The TGA results showed that the membrane was able to remain stable in wastewater below 150 °C. The average stress and strain of the PEI/PVCM were 7.64 ± 0.32 MPa and 934.14 ± 48.12%, respectively. The water contact angle and zeta potential analysis showed that after the introduction of PEI, the membrane converted from hydrophobic to hydrophilic, and the pHpzc was increased from 3.1 to 1.08. The pure water flux of the membrane was measured at 0.1 MPa and the result was 3013 ± 60 L/m2‧h. The wastewater purification capability of PEI/PVCM was measured at an initial dye concentration of 10 ppm and pH 4-9 at 0.1 MPa. The reusability of PEI/PVCM was verified through three adsorption-desorption cycles. The results demonstrated that the PEI/PVCM is a reusable membrane for efficient purification of wastewater containing reactive dyes over a wide pH range (pH 4-8).

Adsorption and Desorption Properties of Polyethylenimine/Polyvinyl Chloride Cross-Linked Fiber for the Treatment of Azo Dye Reactive Yellow 2.

In this study, the optimal conditions for the fabrication of polyethylenimine/polyvinyl chloride cross-linked fiber (PEI/PVC-CF) were determined by comparing the adsorption capacity of synthesized PEI/PVC-CFs for Reactive Yellow 2 (RY2). The PEI/PVC-CF prepared through the optimal conditions was characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) analyses. Several batch adsorption and desorption experiments were carried out to evaluate the sorption performance and reusability of PEI/PVC-CF for RY2. As a result, the adsorption of RY2 by PEI/PVC-CF was most effective at pH 2.0. A pseudo-second-order model fit better with the kinetics adsorption data. The adsorption isotherm process was described well by the Langmuir model, and the maximum dye uptake was predicted to be 820.6 mg/g at pH 2.0 and 25 °C. Thermodynamic analysis showed that the adsorption process was spontaneous and endothermic. In addition, 1.0 M NaHCO3 was an efficient eluent for the regeneration of RY2-loaded PEI/PVC-CF. Finally, the repeated adsorption-desorption experiments showed that the PEI/PVC-CF remained at high adsorption and desorption efficiencies for RY2, even in 17 cycles.

A reusable adsorbent polyethylenimine/polyvinyl chloride crosslinked fiber for Pd(II) recovery from acidic solutions.

In this study, a mixture of polyethylenimine (PEI) and polyvinyl chloride (PVC) was reacted at 80 °C for 6 h to synthesize crosslinked PEI/PVC polymer solution, which was injected to produce the PEI/PVC-crosslinked fiber (PEI/PVC-CF). PEI/PVC-CF was investigated as an adsorbent to remove and recover Pd(II) from acidic solutions. In order to examine the adsorption characteristics and usability of PEI/PVC-CF for Pd(II) recycling, several experiments such as isotherm, kinetics, desorption and reuse were conducted. The adsorption isotherms were fitted using the Langmuir and Freundlich models, respectively. The maximum adsorption capacity was estimated as 146.03 mg/g according to the Langmuir model. The kinetic experiments demonstrated that adsorbent reaches adsorption equilibrium within 60 min for initial Pd(II) concentrations of 25-100 mg/L. After adsorption, Pd(II) on PEI/PVC-CF was easily desorbed using acidified thiourea solution, and the desorption efficiency increased with the thiourea concentration. It was also demonstrated that PEI/PVC-CF can be used repeatedly for at least five cycles without reduction in adsorption capacity.

Adsorption of Ag (I) from aqueous solution by waste yeast: kinetic, equilibrium and mechanism studies.

One type of biosorbents, brewer fermentation industry waste yeast, was developed to adsorb the Ag (I) in aqueous solution. The result of FTIR analysis of waste yeast indicated that the ion exchange, chelating and reduction were the main binding mechanisms between the silver ions and the binding sites on the surface of the biomass. Furthermore, TEM, XRD and XPS results suggested that Ag(0) nanoparticles were deposited on the surface of yeast. The kinetic experiments revealed that sorption equilibrium could reach within 60 min, and the removal efficiency of Ag (I) could be still over 93 % when the initial concentration of Ag (I) was below 100 mg/L. Thermodynamic parameters of the adsorption process (ΔG, ΔH and ΔS) identified that the adsorption was a spontaneous and exothermic process. The waste yeast, playing a significant role in the adsorption of the silver ions, is useful to fast adsorb Ag (I) from low concentration.

Microfluidic fabrication of cell adhesive chitosan microtubes.

Chitosan has been used as a scaffolding material in tissue engineering due to its mechanical properties and biocompatibility. With increased appreciation of the effect of micro- and nanoscale environments on cellular behavior, there is increased emphasis on generating microfabricated chitosan structures. Here we employed a microfluidic coaxial flow-focusing system to generate cell adhesive chitosan microtubes of controlled sizes by modifying the flow rates of a chitosan pre-polymer solution and phosphate buffered saline (PBS). The microtubes were extruded from a glass capillary with a 300 µm inner diameter. After ionic crosslinking with sodium tripolyphosphate (TPP), fabricated microtubes had inner and outer diameter ranges of 70-150 µm and 120-185 µm. Computational simulation validated the controlled size of microtubes and cell attachment. To enhance cell adhesiveness on the microtubes, we mixed gelatin with the chitosan pre-polymer solution. During the fabrication of microtubes, fibroblasts suspended in core PBS flow adhered to the inner surface of chitosan-gelatin microtubes. To achieve physiological pH values, we adjusted pH values of chiotsan pre-polymer solution and TPP. In particular, we were able to improve cell viability to 92 % with pH values of 5.8 and 7.4 for chitosan and TPP solution respectively. Cell culturing for three days showed that the addition of the gelatin enhanced cell spreading and proliferation inside the chitosan-gelatin microtubes. The microfluidic fabrication method for ionically crosslinked chitosan microtubes at physiological pH can be compatible with a variety of cells and used as a versatile platform for microengineered tissue engineering.

Different binding mechanisms in biosorption of reactive dyes according to their reactivity.

Various binding mechanisms for the uptake of reactive dyes by the protonated waste biomass of Corynebacterium glutamicum were investigated. As model reactive dyes, Reactive Blue 4 (RB 4), Reactive Orange 16 (RO 16) and Reactive Yellow 2 (RY 2) were used in this study. The solution pH strongly influenced the sorption capacity and the binding mechanisms of reactive dyes by C. glutamicum. At acidic pH, the electrostatic interaction was found to be a major binding mechanism. The maximum uptakes of RY 2, RO 16 and RB 4 at pH 2 were estimated to be 155.0+/-14.1, 156.6+/-6.7 and 184.9+/-16.4mg/g, respectively. Under alkaline conditions, the binding mechanisms were quite different according to the reactivity of reactive dyes. It was found that chemical bonding existed between the biomass surface and dye molecules under basic pH conditions.

Adsorption performance and mechanism in binding of Reactive Red 4 by coke waste.

The protonated coke waste was used as a new type of adsorbent for the removal of Reactive Red 4. To identify the binding sites in the protonated coke waste, the waste was potentiometrically titrated. As a result, four types of functional groups were present in the waste, which was confirmed by FT-IR analysis. Among functional groups, primary amine groups (-NH2) were likely the binding sites for anionic Reactive Red 4. It was also found that sulfonate, carboxyl and phosphonate groups played a role in electrostatic interference with the binding of dye molecules. The maximum adsorption capacities of the coke waste were 70.3+/-11.1 and 24.9+/-1.8 mg/g at pH 1 and 2, respectively. Kinetic study showed a pseudo-first-order rate of adsorption with respect to the solution. The uptake of Reactive Red 4 was not significantly affected by the high concentration of salts. These results of adsorption performance indicate the coke waste as a potentially economical adsorbent for dye removal.

The role of biomass in polyethylenimine-coated chitosan/bacterial biomass composite biosorbent fiber for removal of Ru from acetic acid waste solution.

The present study is aimed at understanding the role of bacterial biomass in functionalizing polyethylenimine (PEI)-coated bacterial biosorbent fiber (PBBF). To make PBBF, chitosan/biomass composite fiber was coated with PEI and then cross-linked by glutaraldehyde. The role of biomass in the fiber was investigated through sorption experiments and SEM, FTIR and XPS analyses with differently prepared fiber sorbents. In the case that the chitosan fiber was made without the biomass, it could not be coated with PEI. Meanwhile, the chitosan/biomass composite fiber could successfully coated with PEI and primary amine groups were significantly increased on the surface of the fiber. Therefore, the biomass should be essential to make PEI-reinforced chitosan fiber.

Biosorbents for recovery of precious metals.

Biosorption is a promising technology not only for the removal of heavy metals and dyes but also for the recovery of precious metals (PMs) from solution phases. The biosorptive recovery of PMs from waste solutions and secondary resources is recently getting paid attractive attention because their price is increasing or fluctuating, their available deposit is limited and maldistributed, and high-tech industries need more consumption of PMs. The biosorbents for recovery of PMs require specifications which differ from those for the treatment of wastewaters containing heavy metals and dyes. In this review, the previous works on biosorbents and biosorption for recovery of PMs were summarized. Especially, we discuss and suggest the required specifications of biosorbents for recovery of PMs and strategies to give the required properties to the biosorbents. We believe this review will provide useful information to scientists and engineers and hope to give insights into this research frontier.

Recovery of high-purity metallic Pd from Pd(II)-sorbed biosorbents by incineration.

This work reports a direct way to recover metallic palladium with high purity from Pd(II)-sorbed polyethylenimine-modified Corynebacterium glutamicum biosorbent using a combined method of biosorption and incineration. This study is focused on the incineration part which affects the purity of recovered Pd. The incineration temperature and the amount of Pd loaded on the biosorbent were considered as major factors in the incineration process, and their effects were examined. The results showed that both factors significantly affected the enhancement of the recovery efficiency and purity of the recovered Pd. SEM-EDX and XRD analyses were used to confirm that Pd phase existed in the ash. As a result, the recovered Pd was changed from PdO to zero-valent Pd as the incineration temperature was increased from 600 to 900°C. Almost 100% pure metallic Pd was recovered with recovery efficiency above 99.0% under the conditions of 900°C and 136.9 mg/g.

Binding sites and mechanisms of cadmium to the dried sewage sludge biomass.

The Cd biosorption on the dried sewage sludge biomass were experimentally evaluated and mathematically modeled at different pH values. The potentiometric titration of the biomass was well fitted by the four-site model, which consists of three-negative and one-positive sites. The main functional groups were identified through the FTIR study. The pH edge study showed that both the carboxyl and phosphonate groups played an important role in the binding of Cd. From the dynamic biosorption experiments, the H(+)/Cd(2+) exchange ratios at pH 4, 5 and 6 were estimated; thereby the binding mechanisms were established to be complexation with carboxyl and phosphonate groups. Finally, biosorption model was developed based upon the binding mechanism, which was successfully applied for predicting the isotherms and pH edges. Using the developed model equation, the contribution of each functional group on Cd binding could be predicted and visualized.

Cationic polymer-immobilized polysulfone-based fibers as high performance sorbents for Pt(IV) recovery from acidic solutions.

This work reports a novel concept for the development of a polysulfone (PS)-based fiber as a high-performance acid-tolerant adsorbent for the recovery of platinum group metals (PGMs), particularly Pt(IV), in acidic media. Polyethylenimine (PEI)-coated PS-Escherichia coli biomass composite fiber (PEI-PSBF) was prepared by spinning biomass-PS blends in water, coating with PEI and cross-linking with glutaraldehyde. The E. coli biomass on the fiber was executed as a functional group donor for binding PEI. PS fiber (PSF), PS-biomass composite fiber (PSBF), and PEI-modified PSF (PEI-PSF) were also prepared and compared with PEI-PSBF. The results of SEM and FTIR analyses revealed the presence of PEI on the surface of PEI-PSBF. Kinetic and isotherm experiments showed the negligible sorption capacity of PSF. In contrast, adsorption equilibrium on PSBF and PEI-PSBF was attained after 40 min and 6h, respectively. The maximum Pt(IV) uptake of PEI-PSBF was 6.6 times higher than that of PSBF. Pt(IV) ions were completely recovered from loaded PEI-PSBF by 0.1M thiourea in 1M HCl solution. The PEI-PSBF was also stable in 0.1M and 1M HCl solutions. The PEI-PSBF exhibited promising properties as an adsorbent for PGMs-containing acidic wastewaters.

Ruthenium recovery from acetic acid waste water through sorption with bacterial biosorbent fibers.

A fibrous bacterial biosorbent was developed to bind precious metal-organic complexes in batch and column processes. Polyethylenimine (PEI)-modified bacterial biosorbent fiber (PBBF) was prepared by spinning Corynebacterium glutamicum biomass-chitosan blends, coating them with PEI and cross-linking with glutaraldehyde. When an acetic acid waste solution containing 1822.9mg/L Ru was used as a model waste solution, Ru uptake by the PBBF was 16.5 times higher than that of the commercial ion exchange resin, Lewatit MonoPlus M600. The maximum amounts of Ru uptake were 110.5, 16.0 and 6.7mg/g for PBBF, raw biomass, and Lewatit MonoPlus M600, respectively. In a flow-through packed bed, PBBF exhibited the breakthrough time of 42.32h. Therefore, PBBF can be considered as an alternative sorbent for recovery of anionic metal-organic complexes from waste solutions.

Removal of 1-ethyl-3-methylimidazolium cations with bacterial biosorbents from aqueous media.

This study aims to determine whether biosorption can be used for the removal of ionic liquids (ILs), especially their cationic parts, from aqueous media. As a model IL, 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc) was used. Five types of bacterial biosorbents were prepared from fermentation wastes through chemical modification of the bacterial surface. Screening study was performed to compare the cationic [EMIM] biosorption capacity among the bacterial biosorbents, indicating that the succinated Escherichia coli biomass (SB-E) was the best biosorbent for removing [EMIM] cations. The [EMIM] biosorption performance of SB-E was evaluated in detail through various experiments. The optimal pH range for [EMIM] biosorption was from 7 to 10, and biosorption equilibrium was reached within 10 min. The maximum uptake of SB-E was also estimated to be 72.6 mg/g. Moreover, [EMIM] cations were easily desorbed from [EMIM]-sorbed SB-E by adding acetic acid.

Glutaraldehyde-crosslinked chitosan beads for sorptive separation of Au(III) and Pd(II): opening a way to design reduction-coupled selectivity-tunable sorbents for separation of precious metals.

Glutaraldehyde (GA)-crosslinked chitosan beads (GA-CS) are prepared with coagulating solution containing sodium tripolyphosphate and GA, and used for the adsorption of metals from binary-metal solution Au(III) and Pd(II). GA-CS exhibited selective sorption of Au(III) in the Au(III)-Pd(II) mixture. X-ray diffraction analyses showed that Au(III) was reduced to Au(0) following sorption, while Pd(II) was present as unreduced divalent form. Increased GA led to more selectivity toward Au(III), indicating that Au(III) selectivity is attributed to reduction-couple sorption of Au(III) with a reducing agent GA. Furthermore, a 2-step desorption process enabled selective recovery of Pd and Au using 5M HCl and 0.5M thiourea-1M HCl, respectively, leading to pure Pd(II) and Au(III)-enriched solutions. This finding may open a new way to design reduction-coupled selectivity-tunable metal sorbents by combination of redox potentials of metal ions and reducing agents.

Recovery of gold as a type of porous fiber by using biosorption followed by incineration.

This study introduces a new process for the recovery of gold in porous fiber form by the incineration of Au-loaded biosorbent fiber from gold-cyanide solutions. For the recovery of gold from such aqueous solutions, polyethylenimine (PEI)-modified bacterial biosorbent fiber (PBBF) and PEI-modified chitosan fiber (PCSF) were developed and used. The maximum uptakes of Au(I) ions were estimated as 421.1 and 251.7 mg/g at pH 5.5 for PBBF and PCSF, respectively. Au-loaded biosorbents were freeze-dried and then incinerated to oxidize their organic constituents while simultaneously obtaining reduced gold. As a result, porous metallic gold fibers were obtained with 60 µm of diameter. Scanning electron microscopic (SEM) analysis and mercury porosimetry revealed the fibers to have 60 µm of diameter and to be highly porous and hollow. The proposed process therefore offers the potential for the efficient recovery of metallic porous gold fibers using combined biosorption and incineration.

Utilization of PEI-modified Corynebacterium glutamicum biomass for the recovery of Pd(II) in hydrochloric solution.

A new type of biosorbent was developed for binding anionic precious metals through cross-linking waste biomass Corynebacterium glutamicum with polyethylenimine (PEI). This biomass was evaluated for the removal and recovery of palladium and compared to commercial adsorbents, such as Amberjet 4200 Cl, Lewatit Monoplus TP 214, SPC-100, and SPS-200. The kinetic experiments revealed that the sorption equilibrium was reached with 30 min for the PEI-modified biomass. The maximum uptake of the biosorbent was 176.8 mg/g, which was calculated using the Langmuir model. The Pd(II) maximum uptake exhibited the following order: Amberjet 4200 Cl>Lewatit Monoplus TP 214>PEI-modified biomass>SPC-100>SPS-200. Acidified thiourea in 1.0M HCl was used to desorb Pd(II) from all of the sorbents examined.

Surface modified bacterial biosorbent with poly(allylamine hydrochloride): Development using response surface methodology and use for recovery of hexachloroplatinate(IV) from aqueous solution.

In this study, poly(allylamine hydrochloride) (PAA/HCl) was cross-linked with fermentation bacterial waste (Escherichia coli) in order to introduce a large amount of amine groups as binding sites for potassium hexachloroplatinate(IV), as a model anionic pollutant. The sorption performance of PAA/HCl-modified E. coli was greatly affected by the dosages of PAA/HCl and crosslinker (epichlorohydrin, ECH), and by the pH of the modification reaction medium. These factors were optimized through the response surface methodology (RSM). A three-level factorial Box-Behnken design was performed, and a second-order polynomial model was successfully used to describe the effects of PAA/HCl, ECH and the pH on the Pt(IV) uptake (R(2) = 0.988). The optimal conditions that were obtained from the RSM were 0.49 g of PAA/HCl, 0.05 mL of ECH and pH 10.02, with 1.0 g of dried E. coli biomass. The biosorption isotherm and kinetics studies were carried out in order to evaluate the sorption potential of the PAA/HCl-modified E. coli that was prepared under the optimized conditions. The sorption performance of the developed bacterial biosorbent was 4.36 times greater than that of the raw E. coli. Desorption was carried out using 0.05 M acidified thiourea and the biosorbent was successfully regenerated and reused up to four cycles. Therefore, this simple and cost-effective method suggested here is a useful modification tool for the development of high performance biosorbents for the recovery of anionic precious metals.

Recovery of Pd(II) from hydrochloric solution using polyallylamine hydrochloride-modified Escherichia coli biomass.

A new type of biosorbent able to bind anionic metals was developed by cross-linking of waste biomass Escherichia coli with polyallylamine hydrochloride (PAH). The PAH-modified biomass was investigated for the removal and recovery of Pd(II), in the chloro-complex form, from aqueous solution. The performance of the PAH-modified biomass was evaluated in terms of the following parameters: the solution pH, contact time and initial metal concentration. In the pH edge experiments, the uptake of Pd(II) increased with increasing pH. Pd(II) biosorption proceeded rapidly in the first 10 min, with almost complete equilibrium being achieved within 60 min. Moreover, the isotherm data showed that the maximum uptakes of Pd(II) were 265.3mg/g at pH 3 and 212.9 mg/g at pH 2, respectively. After incineration of the Pd-loaded PAH-modified biomass, metallic palladium was recovered in the ash. X-ray photoelectron spectroscopy (XPS) results confirmed that the palladium was recovered in two valency states: zero-valent and divalent palladium (as PdO). Therefore, we concluded that PAH-modified biomass is a useful and cost-effective biosorbent for the recovery of anionic precious metals as chloro-complex solutions containing hydrochloric acid produced from metal refining processes.