Zhaohui Jin

Preparation of chitosan-stabilized Fe0 nanoparticles for removal of hexavalent chromium in water

Chitosan-stabilized Fe(0) nanoparticles (CTO-Fe(0)) and Fe(0) nanoparticles synthesized in ethanol-water mixed system (EW-Fe(0)) were tested for reduction of Cr(VI) in water. Fourier transform infrared (FTIR) study suggested that nitrogen and oxygen atoms are the binding sites for chitosan on iron which was accountable for the stability of Fe(0) nanoparticles. While the EW-Fe(0) ignites spontaneously when exposed to air, the CTO-Fe(0) was still in zero valence state after exposure to air over 2-month period as shown by X-ray powder diffraction patterns. Batch experiments demonstrated that the maximum Cr(VI) reduction rates for CTO-Fe(0) was about 3 times higher than EW-Fe(0). Characterizations with high-resolution X-ray photoelectron spectroscopy (HR-XPS) revealed that Cr(VI) was reduced to Cr(III) and Fe(III) was the only component present on the Fe(0) nanoparticles surface. Additionally, chitosan can inhibited the formation of Fe(III)-Cr(III) precipitation due to its high ability to chelate Fe(III) which resulted in k(obs) for CTO-Fe(0) was about 1-3 times higher than EW-Fe(0). Due to the fast reaction kinetics and good stability against oxidation in air, the chitosan-stabilized Fe(0) nanoparticles have the potential to become an effective agent for in situ subsurface environment remediation.

Kinetics of hexavalent chromium removal from water by chitosan-Fe0 nanoparticles.

Chitosan-Fe(0) nanoparticles (chitosan-Fe(0)) were prepared using nontoxic and biodegradable chitosan as a stabilizer. Batch experiments were conducted to evaluate the influences of initial Cr(VI) concentration and other factors on Cr(VI) reduction on the surface of the chitosan-Fe(0). The overall disappearance of Cr(VI) may include both physical adsorption of Cr(VI) onto the chitosan-Fe(0) surface and subsequent reduction of Cr(VI) to Cr(III). The rate of reduction of Cr(VI) to Cr(III) can be expressed by a pseudo-first-order reaction kinetics. The rate constants increase with the increase in temperature and iron loading but decrease with the increase in initial Cr(VI) concentration and pH. The apparent activation energy is found to be 33 kJ mol(-1), which is characteristic of a chemically controlled reaction. Characterization with high-resolution X-ray photoelectron spectroscopy reveals that after the reaction, relative to Cr(VI) and Fe(0), Cr(III) and Fe(III) are the predominant species on the surface of chitosan-Fe(0). Chitosan has also been found to inhibit the formation of Fe(III)-Cr(III) precipitation due to its high efficiency in chelating the Fe(III) ions. This study demonstrates that chitosan-Fe(0) has the potential to become an effective agent for in situ subsurface environment remediation.

Reactivity characteristics of poly( methyl methacrylate) coated nanoscale iron particles for trichloroethylene remediation

The unstable characteristic of nanoscale zerovalent iron (NZVI) has been a drawback in practical application, despite the expectation of an enhanced reactivity. It has been ever-increasing interests to maintain the NZVI stability in air without significant reactivity sacrifice. This study demonstrated a novel method of coating NZVI particles with poly(methyl methacrylate) (PMMA), which protected the core iron nanoparticles from oxidation in air and enhanced their dispersion stability in organic solvents. The reactivity studies on trichloroethene (TCE) reduction showed that the PMMA coated nanoscale zerovalent iron (PNZVI) particles were capable of effectively reducing TCE. The main roles of PMMA on the dechlorination reactions were confirmed to be sorption enhancement, competitive sorption and corrosion inhibition.

One-step synthesis and characterization of core–shell Fe@SiO2 nanocomposite for Cr (VI) reduction

A facile one-step method was developed to fabricate mono-dispersed Fe nanoparticles (Fe NPs) coated with SiO(2) shell by aqueous reduction method combined with modified Stöber method. Borohydride was acted not only as a reductant for iron salt but also as a catalyst for hydrolysis and polycondensation reaction of tetraethylorthosilicate (TEOS), and more importantly, there was no need to use surface primer for the generation of Fe NPs and catalyst NH(4)OH for SiO(2). Both the Fe NPs agglomeration and SiO(2) shell thickness can be controlled through the synthetic conditions. Lower potassium borohydride (KBH(4)) injection speed was preferable to assemble Fe NPs. The SiO(2) shell thickness increased gradually with the increase of TEOS amount. Under the condition of TEOS amount of 0.1mL and KBH(4) injection speed of 5mL/min, 25nm single Fe NP was coated with SiO(2) shell with thickness of about 9nm. The resulting nanoporous SiO(2) shell was proved to allow reactant to reach the Fe NPs while at the same time protect them from aggregation. The reactivity characterization of the SiO(2)-coated Fe nanoparticles (Fe@SiO(2)) showed that both TEOS concentration and KBH(4) injection speed had effect on Cr (VI) degradation ability. The highest removal capacity of Fe@SiO(2) can reach 467mgCr/gFe at an initial Cr (VI) concentration of 70mg/L under pH 6.0±0.1. XPS and TEM results showed that Cr (VI) was converted to nontoxic Cr (III) and the reaction product was completely adsorbed to SiO(2) shell.

Effect of bimetallic and polymer-coated Fe nanoparticles on biological denitrification

Bimetallic nanoparticles (nano Fe-Ni, nano Fe-Cu) and coated iron nanoparticles (chitosan-Fe(0), sodium oleate-Fe(0)) were utilized to support autotrophic denitrification. In comparison to nanoscale zero-valent iron (NZVI) particles, Ni-containing nanoparticles resulted in faster nitrate removal, but generated 17% more ammonium. The nano Fe-Cu integrated system, required two days less than the unmodified NZVI integrated system to remove all the nitrate and decrease ammonium by 13%, but a large amount of nitrite remained in the system. Compared to uncoated NZVI particles, chitosan-coated nanoparticles allowed the same nitrate removal time but 23% more ammonium production. The sodium oleate-Fe(0) nanoparticles did not only decrease the generation of ammonium by 17%, but also reduced the toxicity of the nanoparticles to bacteria. Therefore, sodium oleate-Fe(0) nanoparticles may be an appropriate substitute for NZVI particles to support autotrophic denitrification provided that additional time (two days) is allowed for complete nitrate removal.

Stabilization of Fe0 nanoparticles with silica fume for enhanced transport and remediation of hexavalent chromium in water and soil

Effective in situ remediation of Cr(VI) in groundwater requires the successful delivery of reactive iron particles to the subsurface. Fe(0) nanoparticles (20-110 nm diameter) supported on silica fume were synthesized by borohydride reduction of an aqueous iron salt in the presence of a support material. The experimental result showed that attachment of Fe(0) nanoparticles on the commercial available sub-micrometer silica fume prevented them from aggregation while maintaining the particle reactivity. When the Fe(0) concentration was 0.4 g/L, 88.00% of 40 mg/L Cr(VI) was removed by silica fume-supported Fe(0) nanoparticles (SF-Fe(0) in 120 min, 22.55% higher than unsupported Fe(0). Furthermore, transport experiments confirmed that almost all unsupported Fe(0) was retained, whereas 51.50% and 38.29% of SF-Fe(0) were eluted from the vertical and horizontal sand column, respectively. Additionally, the effect of solution ionic strength on the transport ability of SF-Fe(0) was evaluated. The result showed that increase in the salt concentration led to a decrease in the mobility and also the divalent ion Ca2+ had a greater effect than that of monovalent ion Na+.

Reduction of nitrate by bimetallic Fe/Ni nanoparticles.

Bimetallic Fe/Ni nanoparticles were synthesized and their nitrate reduction capacity was studied. Nitrate (354 mg L−1, equal to 5.71 mmol L−1) reduction was performed using Fe/Ni nanoparticles with various Ni contents (1.0, 5.0, 10 and 20%) in an unbuffered condition. Optimum nitrate reduction rate ( ) was obtained with 5.0% nano-scale Fe/Ni, while only 25% nitrate ( ) was transformed by nano-scale Fe0 within the same reaction time, which means that these bimetallic nanoparticles are obviously more reactive than mono-metallic nano-scale Fe0. For this bimetallic system a near-neutral initial pH (6.5) is more favourable than an acidic condition (2.0 and 4.0). Relatively air-stable nano-scale Fe/Ni particles were developed by slowly aging them for 22 h and exhibited similar reactivity to freshly synthesized nano-scale Fe0. Although undesirable transformation of nitrate (91.0±0.37% ) to ammonium was observed in this study, Fe/Ni particles showed a much higher nitrate reduction rate and an optimum reduction rate at near-neutral pH, which may have important implications for nitrate-contaminated site remediation.

Reduction and immobilization of chromium(VI) by nano-scale Fe0 particles supported on reproducible PAA/PVDF membrane

A new class of nano-scale Fe0 particles (NZVI) supported on a PAA/PVDF membrane (NZVI-PAA/PVDF) were synthesized and the feasibility of using NZVI-PAA/PVDF for reductive immobilization of Cr(VI) in water was investigated through laboratory batch tests. The results showed that the Cr(VI) removal capacity of NZVI-PAA/PVDF was 181 mg Cr/g Fe at an initial Cr(VI) concentration of 20 mg L(-1) under pH 6.5 +/- 0.1. XPS results showed that Cr(VI) was converted to nontoxic Cr(III). Interfering ions exerted various degrees of impact on NZVI-PAA/PVDFs Cr(VI) removal capacity. Specifically, Ca2+ alone showed the mildest impact while the presence of ions (Mg2+ and HCO3-) exerted the greatest impact. An advantage of NZVI-PAA/PVDF is that the nano-scale Fe0 and resultant particles were combined within a PAA/PVDF membrane, which prevents secondary pollution. Moreover, a piece of PAA/PVDF membrane (4.7 cm diameter) can still support 6.51 mg of nano-scale Fe0 particles after being renewed.

Characterization of Urban Stormwater Runoff in Tianjin

Characterization of urban stormwater runoff was carried out in commercial, residential and cultural and educational zones during 2009 rainy season in Tianjin. The pH, DO, BOD5, COD, TOC, TSS, TN, TP, NH3-N, As, Pb, Zn, Cd, LAS and fecal coliforms in stormwater runoff were analyzed. The ranges of arithmetic mean concentration of COD, TSS, TN, LAS and fecal coliforms were 67-331mg/L, 134-480 mg/L, 4.00-4.69 mg/L, 1.53-11.12 mg/L, 3.03×108-6.46×109 cfu/100mL respectively, depending on the type of land using . In conclusion, COD, TSS, TN, LAS and fecal coliforms were the major runoff pollutants. The sequence of surface runoff pollution was in the following order: commercial zone > residential zone > cultural and educational zone in terms of the major pollutants. On the meantime, the results indicated that the urban non-point source pollution played an important part in the decreasing of water quality after analyzing the changes of quality in receiving waters.

Reduction of Nitrate in Groundwater with Modified Iron Nanoparticles

Nitrate reduction using laboratory synthesized Fe/Ni bimetallic nanoparticles was discussed. Nanoparticles were characterized by TEM-EDS, SEM, XRD and BET techniques. Denitriflcation of 80 mg-N/L nitrate solutions was performed with various Ni contents (1.0, 5.0, 10 and 20%) nanosized Fe/Ni particles compared with monometallic nano-scale FeO. The introduction of Ni enhances the reduction rate remarkably and 5.0% Ni loading shows the highest reactivity, for which nitrate was removed completely in 40 min when iron concentration was 1.5 g/L. Different from iron powder, Fe/Ni nanoparticles behaved the largest reaction rate under the condition of neutral solution pH without pH control. After slowly ageing 22 h, the reactivity of freshly prepared nanoscale Fe/Ni particles decreased about 10 times, but with the followed 44 h ageing, little decreasing of reactivity was observed which is equivalent to freshly synthesized nano-FeO. The effects of initial nitrate concentration and the reduction kinetics were also investigated. For Fe/Ni bimetallic nanoparticles, about 90% nitrate was transformed to ammonium, and nitrite was detected as intermediate product.