Juan Mao

Selective recovery of Pd(II) from extremely acidic solution using ion-imprinted chitosan fiber: Adsorption performance and mechanisms.

A novel, selective and acid-resisting chitosan fiber adsorbent was prepared by the ion-imprinting technique using Pd(II) and epichlorohydrin as the template and two-step crosslinking agent, respectively. The resulting ion-imprinted chitosan fibers (IIF) were used to selectively adsorb Pd(II) under extremely acidic synthetic metal solutions. The adsorption and selectivity performances of IIF including kinetics, isotherms, pH effects, and regeneration were investigated. Pd(II) rapidly adsorbed on the IIF within 100 min, achieving the adsorption equilibrium. The isotherm results showed that the maximum Pd(II) uptake on the IIF was maintained as 324.6-326.4 mg g(-1) in solutions containing single and multiple metals, whereas the Pd(II) uptake on non-imprinted fibers (NIF) decreased from 313.7 to 235.3 mg g(-1) in solution containing multiple metals. Higher selectivity coefficients values were obtained from the adsorption on the IIF, indicating a better Pd(II) selectivity. The amine group, supposedly the predominant adsorption site for Pd(II), was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The pH value played a significant role on the mechanism of the selective adsorption in the extremely acidic conditions. Furthermore, the stabilized performance for three cycles of sorption/desorption shows a potential for further large-scale applications.

Distinguishing homogeneous-heterogeneous degradation of norfloxacin in a photochemical Fenton-like system (Fe3O4/UV/oxalate) and the interfacial reaction mechanism

This study demonstrated the efficient degradation of a typical bio-refractory antibiotic norfloxacin (NOR) in a photochemical iron oxides/oxalate system adopting magnetic catalyst (Fe3O4/UV/Ox). It was found that the in-situ generated HO was the main reactive oxygen species (ROS) but CO2- could also participate in the NOR degradation to form formylate organic intermediates. Besides, NOR would be degraded via an interesting pathway comprising an initial lag and a subsequent rapid period, where the former could be eliminated by introducing the pre-dissolution of Fe3O4 particles. Furthermore, specific comparative investigations and surface characterizations of pre-adsorbed Fe3O4 particles had evidenced that the existence of surface-bound iron-Ox complexes would be critical for the heterogeneous photochemical dissolution of Fe3O4 and effectively initiated the subsequent homogeneous-heterogeneous NOR degradation. Finally, a comprehensive distinguishing reaction mechanism was proposed including a homogeneous-heterogeneous iron cycle on the solid-water interface and a series of homogeneous radical reactions. Therein, complexation instead of photochemical reduction would be dominant during the whole dissolution process even under UV irradiation. Rapid electrons exchange would occur photochemically between FeII and FeIII in the octahedral sites, further weakening the surface Fe-O bonds and accelerating its breakaway from the bulk Fe3O4 structure. This work could distinguish the complex heterogeneous/homogeneous reactions in the photochemical in-situ chemical oxidation systems that utilize naturally abundant iron oxides and polycarboxylic acids.

Simulation and optimization of a coking wastewater biological treatment process by activated sludge models (ASM)

Applications of activated sludge models (ASM) in simulating industrial biological wastewater treatment plants (WWTPs) are still difficult due to refractory and complex components in influents as well as diversity in activated sludges. In this study, an ASM3 modeling study was conducted to simulate and optimize a practical coking wastewater treatment plant (CWTP). First, respirometric characterizations of the coking wastewater and CWTP biomasses were conducted to determine the specific kinetic and stoichiometric model parameters for the consecutive aeration-anoxic-aeration (O-A/O) biological process. All ASM3 parameters have been further estimated and calibrated, through cross validation by the model dynamic simulation procedure. Consequently, an ASM3 model was successfully established to accurately simulate the CWTP performances in removing COD and NH4-N. An optimized CWTP operation condition could be proposed reducing the operation cost from 6.2 to 5.5xa0€/m(3) wastewater. This study is expected to provide a useful reference for mathematic simulations of practical industrial WWTPs.

An insight in magnetic field enhanced zero-valent iron/H2O2 Fenton-like systems: Critical role and evolution of the pristine iron oxides layer.

This study demonstrated the synergistic degradation of 4-chlorophenol (4-CP) achieved in a magnetic field (MF) enhanced zero-valent iron (ZVI)/H2O2 Fenton-like (FL) system and revealed an interesting correlative dependence relationship between MF and the pristine iron oxides layer (FexOy) on ZVI particles. First, a comparative investigation between the FL and MF-FL systems was conducted under different experimental conditions. The MF-FL system could suppress the duration of initial lag degradation phase one order of magnitude in addition of the significant enhancement in overall 4-CP degradation. Monitoring of intermediates/products indicated that MF would just accelerate the Fenton reactions to produce hydroxyl radical more rapidly. Evolutions of simultaneously released dissolved iron species suggested that MF would not only improve mass-transfer of the initial heterogeneous reactions, but also modify the pristine ZVI surface. Characterizations of the specific prepared ZVI samples evidenced that MF would induce a special evolution mechanism of the ZVI particles surface depending on the existence of FexOy layer. It comprised of an initial rapid point dissolution of FexOy and a following pitting corrosion of the exposed Fe0 reactive sites, finally leading to appearance of a particular rugged surface topography with numerous adjacent Fe0 pits and FexOy tubercles.

Synergistic degradation of antibiotic norfloxacin in a novel heterogeneous sonochemical Fe0/tetraphosphate Fenton-like system

In this study, synergistic degradation of antibiotic norfloxacin (NOR) was obtained in a novel sonochemical ultrasound/zero-valent iron/tetraphosphate system (US/ZVI/TPP). Compared to three common organic ligands (EDTA, EDDS, and DTPA), TPP could perform more excellently in activation of O2 to produce reactive oxidative species (ROS) and lead to efficient Fenton-like oxidative degradation of NOR in the sonochemical in situ chemical oxidation (ISCO) system. An optimized initial condition was obtained as 10mg/L NOR, 0.3mM TPP, 1g/L ZVI and initial pH 7, and the US/ZVI/TPP system would effectively degrade NOR with relative low dosage of ZVI and ligand as well as broad pH work range 3-9. It was found that three ROS (OH, O2- and H2O2) instead of OH only would participate in the NOR degradation, while the in situ generation of H2O2 during the series of Fe-TPP reactions should be more critical. Fourteen organic intermediates and four inorganic products were detected during the NOR decomposition, suggesting that two main degradation pathways would occur under OH oxidation via cleavage of the piperazine ring and defluorination of the benzene ring, respectively. Finally, an integrated reaction mechanism in the US/ZVI/TPP system was proposed including solid-liquid interfacial iron corrosion as well as bulk homogenous oxygen activation and Fenton reactions, wherein US would play mechanically and chemically promotional roles. Besides, triple-repeated treatments suggested the relative long-term re-usage of ZVI particles and low effluent dissolved iron (<0.6mg/L).

Efficient sonoelectrochemical decomposition of sulfamethoxazole adopting common Pt/graphite electrodes: The mechanism and favorable pathways

In this study, efficient degradation of sulfamethoxazole (SMX) with a high synergy factor of 14.7 was demonstrated in a sonoelectrochemical (US-EC) system adopting common Pt and graphite electrodes. It was found that the US-EC system could work effectively at broad pH range of 3-9, but would achieve good performances with appropriate electrochemical conditions at 20mA/cm2 and 0.1M Na2SO4. Both OH attacking and the anode oxidation would be responsible for the SMX degradation in the US-EC system, while the multiple promotional roles of US would be played homogenously and heterogeneously. US could not only effectively accelerate the decomposition of cathode-generated H2O2 into OH, but also lead to the enhancement in the heterogeneous reactions on the two electrodes, i.e. the cathode generation of H2O2 as well as the anode oxidation of SMX and H2O/OH-. Besides, the US-EC system would decompose SMX molecule via similar and simple pathways, by using either Na2SO4 or NaCl electrolytes. It was interesting to note that the US-EC system could successfully avoid the formation of complex chlorinated byproducts that detected in the referring EC system with NaCl. This finding would make the sonoelectrochemical processes favorable in treating practical wastewaters by alleviating the environmental impact of disinfection byproducts.

Adsorptive characteristics of the polyurethane-immobilized Corynebacterium glutamicum biosorbent for removal of Reactive Yellow 2 from aqueous solution

Polyurethane (PU) was evaluated for its possibility as an immobilization matrix for the raw biomass of Corynebacterium glutamicum. Initially, different blending ratios of the raw biomass to PU weight were tested, and the ratio of 7: 3 was identified as the optimal condition. PU-immobilized biosorbent (PUIB) with a particle size ranging from 0.425 to 0.18mm was selected for the adsorption of Reactive Yellow 2 (RY2). The uptake of RY2 on the PUIB was favorable at acidic pH, especially below 3. According to the Langmuir model, the maximum RY2 uptakes were estimated to be 104.0, 93.3, and 87.3mg/g at pH 2, 3, and 4, respectively. The pseudo-first-order and pseudo-secondorder models were applied to fit the biosorption kinetic data; the latter model fitted the data well with a high coefficient of determination (R2) and low average percentage error (ε) values. The RY2-sorbed PUIB was able to be regenerated and reused for five cycles of the adsorption and desorption processes.

Rapid decomposition of diclofenac in a magnetic field enhanced zero-valent iron/EDTA Fenton-like system

In this study, significant synergistic degradation of antibiotic diclofenac (DCF) was demonstrated in a novel magnetic field (MF) enhanced zero-valent iron (ZVI)/EDTA Fenton-like system. Five operational parameters, namely, initial ZVI loading, pH, EDTA dosage, DCF concentration and reaction temperature, were investigated for their effects on the DCF degradation. OH was identified as the predominant reactive oxygen species for DCF degradation in ZVI/EDTA systems whether in the presence or absence of MF. DCF molecule can be oxidized by OH, attacking via the hydroxylation and substituted dechlorination of the chlorinated aromatic ring, as well as by dehydration between the N atom and the acetoxyl. It could also be directly dechlorinated by ZVI reduction simultaneously. The reaction mechanism and promotional role of MF in the MF/ZVI/EDTA system were proposed. It is suggested that MF mainly alters the heterogeneous ZVI surface-bond reactions and accelerates the surface corrosion depending on the presence of pristine iron oxides layer, but MF does not change the homogeneous iron cycle and the Fenton-like reactions.