Yu-Ming Zheng

Systematic study of synergistic and antagonistic effects on adsorption of tetracycline and copper onto a chitosan

Sorption of tetracycline and copper onto chitosan is systematically investigated in this study. The sorption of tetracycline and copper occurs rapidly in the first few hours and 90% of completed uptake occurs in the first 11-12 and 6 h, respectively. The sorption equilibrium of both contaminants is established in 24 h. The solution pH largely affects the sorption of both contaminants. The tetracycline uptake increases as pH is increased from 2.8 to 5.6, and 2.5 to 7 in the absence and the presence of copper, respectively. The presence of copper significantly improves the tetracycline adsorption likely due to the formation of cationic bridging of copper between tetracycline and chitosan. The maximum adsorption capacity and the adsorption affinity constant for tetracycline dramatically increase from 53.82 to 93.04 mmol kg(-1) and from 1.22 to 10.20 L mmol(-1) as the copper concentration is increased from 0 to 0.5 mmol L(-1). The uptake of copper increases with an increase in pH from around 3.5-6.0 in the absence and the presence of tetracycline. The presence of tetracycline decreases the copper adsorption, which may be ascribed to the competition of tetracycline with copper ions for the adsorption sites at the chitosan surface. The adsorption isothermal data of both tetracycline and copper are fit well by the Langmuir equation. The maximum adsorption capacity and adsorption affinity constant of copper ions decrease from 1856.06 to 1486.20 mmol kg(-1) and from 1.80 to 1.68 L mmol(-1) in the absence and the presence of tetracycline. FTIR and XPS studies reveal that amino, hydroxyl, and ether groups in the chitosan are involved in the adsorption of tetracycline and copper.

Improvement of metal adsorption onto chitosan/Sargassum sp. composite sorbent by an innovative ion-imprint technology

Technology for immobilization of biomass has attracted a great interest due to the high sorption capacity of biomass for sequestration of toxic metals from industrial effluents. However, the currently practiced immobilization methods normally reduce the metal sorption capacities. In this study, an innovative ion-imprint technology was developed to overcome the drawback. Copper ion was first imprinted onto the functional groups of chitosan that formed a pellet-typed sorbent through the granulation with Sargassum sp.; the imprinted copper ion was chemically detached from the sorbent, leading to the formation of a novel copper ion-imprinted chitosan/Sargassum sp. (CICS) composite adsorbent. The copper sorption on CICS was found to be highly pH-dependent and the maximum uptake capacity was achieved at pH 4.7-5.5. The adsorption isotherm study showed the maximum sorption capacity of CICS of 1.08 mmol/g, much higher than the non-imprinted chitosan/Sargassum sp. sorbent (NICS) (0.49 mmol/g). The used sorbent was reusable after being regenerated through desorption. The FTIR and XPS studies revealed that the greater sorption of heavy metal was attributed to the large number of primary amine groups available on the surfaces of the ion-imprinted chitosan and the abundant carboxyl groups on Sargassum sp. Finally, an intraparticle surface diffusion controlled model well described the sorption history of the sorbents.

Synthesis of Fe3O4/Polyacrylonitrile Composite Electrospun Nanofiber Mat for Effective Adsorption of Tetracycline.

Novel Fe3O4/polyacrylonitrile (PAN) composite nanofibers (NFs) were prepared by a simple two-step process, an electrospinning and solvothermal method. Characterization by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) demonstrated formation of a uniform nanoparticles coating (about 20 nm in thickness) on the PAN nanofiber backbone. The coating was constructed by well-crystallized cubic phase Fe3O4 nanoparticles as examined by X-ray diffraction spectroscopy (XRD). The coating doubled the specific surface area of NFs, from 8.4 to 17.8 m2 g(-1), as confirmed by nitrogen sorption isotherm analysis. To evaluate the feasibility of Fe3O4/PAN composite NFs as a potential adsorbent for antibiotic removal, batch adsorption experiments were conducted using tetracycline (TC) as the model antibiotic molecule. The results showed that Fe3O4/PAN composite NFs were effective in removing TC with no impactful loss of Fe in the pH regime of environmental interest (5-8). The adsorption of TC onto Fe3O4/PAN composite NFs better fitted the pseudo-second-order kinetics model, and the maximum adsorption capacity calculated from Langmuir isotherm model was 257.07 mg g(-1) at pH 6. The composite NFs also exhibited good regenerability over repeated adsorption/desorption cycles. Surface complexation between TC and the composite NFs contributed most to the adsorption as elucidated by X-ray photoelectron spectroscopy (XPS). This highly effective and novel adsorbent can be easily modularized and separated, promising its huge potential in drinking and wastewater treatment for antibiotic removal.

A zirconium based nanoparticle for significantly enhanced adsorption of arsenate: Synthesis, characterization and performance

In this study, a zirconium nanoparticle sorbent for significantly enhanced adsorption of arsenate (As(V)) was successfully synthesized. The characterization of the zirconium nanoparticle sorbent and its adsorption behavior for arsenate were investigated. The HRTEM micrographs showed that the sorbent was nanoscale with particle sizes ranging from 60 to 90nm. The thermal gravimetric and elemental analyses indicated that the sorbent had a molecular formula of Zr(2)(OH)(6)SO(4)·3H(2)O. The X-ray diffraction study revealed that the sorbent was amorphous. The potentiometric titration study demonstrated the surface charge density of the sorbent decreased with an increase in solution pH, and the pH of zero point charge of the sorbent was around 2.85. The kinetics study showed that most of the uptake took place in the first 6h, and the adsorption equilibrium was obtained within 12h. The optimal pH for As(V) adsorption was between 2.5 and 3.5. The Langmuir equation well described the adsorption isotherm; the maximum adsorption capacity of 256.4mg As/g was found at the optimal pH, better than most of sorbents available in the market. The presence of fluoride or nitrate did not obviously affect the adsorption of As(V) onto the sorbent; however, the existence of humic acid, phosphate or silicate in aqueous solution significantly reduced the uptake of As(V). The humic acid did not cause the reduction of the As(V). The FTIR and XPS spectroscopic analyses revealed that surface hydroxyl and sulfur-containing groups played important roles in the adsorption.

Organic Arsenic Adsorption onto a Magnetic Sorbent

The adsorption of organic arsenate, monomethylarsonate (MMA), onto a calcium alginate encapsulated magnetic sorbent is studied in this paper. A novel alginate encalsulated magnetic sorbent was used in the experiments on adsorption isotherm, kinetics, and pH effect. It was found that the equilibrium sorption can be attained within 25 h. Solution pH plays a key role in the removal of MMA from the solution. A greater adsorption can be achieved at pH 4 and below. The maximum sorption capacity of MMA was 8.57 mg As/g, which is slightly higher than the reported adsorbents. The interaction characteristics between the organic arsenate and magnetic sorbent were elucidated by applying FT-IR and XPS analyses. It is shown that the -COOH and Fe-O groups in the sorbent are involved in the adsorption process. The appearance of As-CH(3) and alkane C-H groups in the FT-IR spectrum reveals the binding of the organic arsenate to the sorbent. The XPS analysis indicates that reduction of organic arsenate to organic arsenite on the sorbents surface happens through solid state redox reaction via charge transport from Fe(II) and C-O species in the sorbent. The XPS results also show the disappearance of C-OH and formation of As-O. It is deduced from the spectral results that mechanisms of organic arsenate adsorption involve C-OH, As-O, and Fe-O groups with the solid state redox process.

Design and fabrication of an innovative and environmental friendly adsorbent for boron removal

Boron can pose adverse effects on human beings and plants species. It exists in various water environments and is difficult to be removed by conventional technologies. In this study, an efficient and environmental friendly sorbent was fabricated by the functionalization of a natural biopolymer, chitosan, with N-methylglucamine through atom transfer radical polymerization. The SEM and BET studies revealed that the sorbent had a rougher surface and a more porous structure than the chitosan. At the optimum neutral pH, the maximum sorption capacity was as high as 3.25 mmol/g, much higher than the commercial boron selective resins (e.g., Amberlite IRA-743) and many other synthesized sorbents. Almost 90% of boron sorption occurred within 8 h and the equilibrium was established in 12 h, which was well described by an intraparticle surface diffusion model. The presence of sodium chloride and sodium nitrate had no effect on the boron removal. The boron concentration in seawater could be reduced to less than 0.5 mg/L from 4.8 mg/L when a sorbent dosage of 1.2 g/L was used. It was therefore concluded that the sorption technology from this study could be promising for boron removal from aqueous solutions.

Preparation and characterization of zirconium-based magnetic sorbent for arsenate removal.

In this study, a zirconium-based magnetic sorbent is developed by a coprecipitation technology. The characterization of the sorbent and its adsorption behavior are systematically investigated. It is shown that the sorbent has a small mean diameter of 543.7 nm, a specific surface area of 151 m(2)/g, and a pH(zpc) of 7. The sorbent has a rough surface and many pores developed on the surface. It has a molecular formula of ZrO(OH)(2) x 1.6 Fe(3)O(4) x 2.5 H(2)O, which was determined by the thermal gravimetric analysis, the elemental analysis, and the digestion experiments. The sorption equilibrium can be reached within 25 h. Better adsorption can be obtained at lower pH, and the optimal initial pH is from 2.6 to 3.3. The maximum adsorption capacity of 45.6 mg-As/g is achieved, which is much higher than many reported sorbents. FTIR spectra analysis indicates that -OH groups play an important role in the uptake. Some of the arsenate are reduced to arsenite after its adsorption onto the magnetic sorbent; the divalent iron in the sorbent may provide electrons for the reduction. A conceptual model for the adsorption of arsenate by the magnetic sorbent is proposed to illustrate the mechanism.

Self-assembly of Au nanoparticles on PMMA template as flexible, transparent, and highly active SERS substrates.

We report a simple and rapid method for fabricating a surface-enhanced Raman scattering (SERS) substrate, which offers good flexibility, excellent optical transparency, and high SERS activity. Specifically, the SERS substrate (AuNPs/PMMA film) was obtained through self-assembly of gold nanoparticles (AuNPs) on newborn poly(methyl methacrylate) (PMMA) template. The UV-vis spectroscopy analysis and scanning electron microscopy observation revealed that the gold nanoparticles were closely assembled on the flexible and transparent PMMA template. The fabricated AuNPs/PMMA film SERS substrate allowed detection of model molecule, malachite green isothiocyanate, at a concentration as low as 0.1 nM, and exhibited good reproducibility in the SERS measurement. The Raman enhancement factor (EF) of the AuNPs/PMMA film was found to be as high as (2.4 ± 0.3) × 10(7). In addition, measure of residual malachite green on fish surface was carried out, and the result indicated that the AuNPs/PMMA film had great potential in the in situ ultrasensitive detection of analyte on irregular objects.

Functionalization of Regenerated Cellulose Membrane via Surface Initiated Atom Transfer Radical Polymerization for Boron Removal from Aqueous Solution

In this study, an adsorptive membrane was prepared for efficient boron removal. Poly(glycidyl methacrylate) was grafted on the surfaces of the regenerated cellulose (RC) membrane via surface-initiated atom transfer radical polymerization, and N-methylglucamine was used to further react with epoxide rings to introduce polyhydroxyl functional groups, which served as the major binding sites for boron. The pristine and modified membranes were characterized by X-ray photoelectron spectroscopy (XPS), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), dynamic water contact angle measurement, and scanning electron microscopy. It was shown that the designed functional groups were successfully grafted onto the RC membrane, and surface modification contributed to higher boron binding capability. The optimal pH range for boron adsorption was 4-8. Under a neutral pH condition, the maximum adsorption capacity of the modified membrane was determined to be 0.75 mmol/g, which was comparable with those of commercial resins. Studies of electrolyte influence indicated the formation of inner-sphere surface complexes on the membrane surface. The ATR-FTIR and XPS analyses showed that secondary alcohol and tertiary amine groups were mainly involved in boron adsorption, and tetrahedral boron complexes were found on the membrane surface.

Application of nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, UV–Visible spectroscopy and kinetic modeling for elucidation of adsorption chemistry in uptake of tetracycline by zeolite beta

Extensive usage of tetracycline has resulted in its contamination in surface water and groundwater. The adsorption of tetracycline on zeolite beta was systematically investigated for the decontamination of the antibiotic polluted water in this study. Ninety percent of uptake by the zeolite beta occured in 0.25h, and the adsorption equilibrium was obtained within 3h, which was well described by an intraparticle diffusion model. The adsorption generally increased when pH was increased from 4.0 to 5.0, and then decreased significantly as the pH was further increased, which was caused by the pH-dependent speciation of tetracycline and surface charge of zeolite beta. Both Freundlich and Langmuir equations well described the adsorption isotherm. A thermodynamic analysis showed that the sorption process was spontaneous and endothermic. Aluminum atoms in the zeolite played a crucial role in the uptake; the adsorption increased with the increasing aluminum content in zeolite. The UV-Visible spectroscopy study showed that the spectra of tetracycline changed upon the interaction with zeolite beta, which could be ascribed to the formation of complexes of tetracycline and aluminum atoms in the zeolite surface. Nuclear magnetic resonance spectroscopy study further confirmed the participation of Al in the tetracycline adsorption. Fourier transform infrared spectroscopy studies showed that the amino functional groups in tetracycline were involved in the complexation with the zeolite surface.