Duanwei Zhu

Synthesis, characterization and photocatalytic evaluation of visible light activated C-doped TiO2 nanoparticles

We have demonstrated heterogeneous photocatalytic degradation of microcystin-LR (MC-LR) by visible light activated carbon doped TiO(2) (C-TiO(2)) nanoparticles, synthesized by a modified sol-gel route based on the self-assembly technique exploiting oleic acid as a pore directing agent and carbon source. The C-TiO(2) nanoparticles crystallize in anatase phase despite the low calcination temperature of 350 °C and exhibit a highly porous structure that can be optimized by tuning the concentration of the oleic acid surfactant. The carbon modified nanomaterials exhibited enhanced absorption in the broad visible light region together with an apparent red shift in the optical absorption edge by 0.5 eV (2.69 eV), compared to the 3.18 eV of reference anatase TiO(2). Carbon species were identified by x-ray photoelectron spectroscopy analysis through the formation of both Ti-C and C-O bonds, indicative of substitution of carbon for oxygen atoms and the formation of carbonates, respectively. Electron paramagnetic resonance spectroscopy revealed the formation of two carbon related paramagnetic centers in C-TiO(2), whose intensity was markedly enhanced under visible light illumination, pointing to the formation of localized states within the anatase band gap, following carbon doping. The photocatalytic activity of C-TiO(2) nanomaterials was evaluated for the degradation of MC-LR at pH 3.0 under visible light (λ > 420 nm) irradiation. The doped materials showed a higher MC-LR degradation rate than reference TiO(2), behavior that is attributed to the incorporation of carbon into the titania lattice.

Physiological responses induced by copper bioaccumulation in Eichhornia crassipes (Mart.)

Eichhornia crassipes (Mart.) has strong ability to remove Cu2+ from copper-contaminated water. Physiological responses in E. crassipes exposed to known concentrations of Cu2+ were examined in this study, and demonstrated that E. crassipes could accumulate 314 mg kg−1 dry weight of Cu when exposed to 5 mg l−1 of Cu2+ for periods up to 14 d. However, there were marked changes in physiology of the plant commencing at Cu2+ concentrations of 1 mg l−1. Results of this study showed that E. crassipes could tolerate moderate concentrations (i.e. 0.5 mg l−1) of Cu2+, without significant changes in photosynthetic pigment concentrations, while high concentrations (i.e. 5 and 10 mg l−1) of Cu2+ resulted in substantial loss in pigment concentrations. Increases in malondiadehyde (MDA) content were also demonstrated in plant exposure to high Cu2+ concentrations. Soluble protein content increased to a level slightly higher than the control at <0.5 mg l−1 of Cu2+, but then decreased with exposure to >1 mg l−1 of Cu2+. Our results suggest that E. crassipes has a substantial capacity to accumulate copper when cultivated at moderate concentrations of Cu2+, without marked changes in its physiology. The findings indicate that E. crassipes is a promising possibility for phytoremediation of moderately Cu-contaminated water bodies.

Solid-phase photocatalytic degradation of polyethylene-goethite composite film under UV-light irradiation

A novel photodegradable polyethylene-goethite (PE-goethite) composite film was prepared by embedding the goethite into the commercial polyethylene. The degradation of PE-goethite composite films was investigated under ultraviolet light irradiation. The photodegradation activity of the PE plastic was determined by monitoring its weight loss, scanning electron microscopic (SEM) analysis and FT-IR spectroscopy. The weight of PE-goethite (1 wt%) sample steadily decreased and led to the total 16% reduction in 300 h under UV-light intensity for 1 mW/cm(2). Through SEM observation there were some cavities around the goethite powder in the composite films, but there were few changes except some surface chalking phenomenon in pure PE film. The degradation rate could be controlled by changing the concentration of goethite particles in PE plastic. The degradation of composite plastic initiated on PE-goethite interface and then extended into polymer matrix induced by the diffusion of the reactive oxygen species generated on goethite particle surface. The photocatalytic degradation mechanism of the composite films was briefly discussed.

Influence of nitrogen on the primary and secondary metabolism and synthesis of flavonoids in Chrysanthemum morifolium Ramat

The effects of nitrogen (N) supply on nitrogen metabolism in leaves of Chrysanthemum morifolium Ramat. were examined in five different stages throughout the growing season. The results suggested that flavonoids content was positively related to phenylalanine ammonia-lyase activity through the whole growing stage of the plant but with a decreasing correlation coefficient for increasing nitrogen supply. There was no correlation between flavonoids and 4-coumarate coenzyme A ligase. Soluble protein content was positively correlated with phenylalanine ammonia-lyase activity because there was little competition for the phenylalanine in the leaves under low nitrogen supply. Phenylalanine ammonia-lyase activity decreased gradually with increasing nitrogen supply because of the competition for the phenylalanine in protein synthesizes. The results suggest that nitrogen nutrition plays a key role in biosynthesis of enzymes in the leaves of C. morifolium.

The structure characterization of cellulose xanthogenate derived from the straw of Eichhornia crassipes

Alkali-treated straw and cellulose xanthogenate were derived from shoot and root biomass of Eichhornia crassipes by treatment with NaOH and CS(2), respectively. The structures of the raw and modified plant materials were characterized by XRD, TGA/DTA, and FTIR. Alkali treatment increased the crystallinity of raw plant material, while the subsequent CS(2) treatment had the reverse effect. The thermal stability of the plant material was diminished by alkali treatment but was restored by subsequent CS(2) treatment. Alkali treatment removed most of the lignin and hemicellulose from the raw plant material, whereas the formation of cellulose xanthogenate introduced new C=S and O-CS-S functional groups.

Analysis of utilization technologies for Eichhornia crassipes biomass harvested after restoration of wastewater

Eichhornia crassipes (EC, water hyacinth) has gained attention due to its alarming reproductive capacity, which subsequently leads to serious ecological damage of water in many eutrophic lakes in the world. The traditional mechanical removal methods have disadvantages. They squander this valuable lignocellulosic resource. Meanwhile, there is a bottleneck for the subsequently reasonable and efficient utilization of EC biomass on a large scale after phytoremediation of polluted water using EC. As a result, the exploration of effective EC utilization technologies has become a popular research field. After years of exploration and amelioration, there have been significant breakthroughs in this research area, including the synthesis of excellent EC cellulose-derived materials, innovative bioenergy production, etc. This review organizes the research of the utilization of the EC biomass among several important fields and then analyses the advantages and disadvantages for each pathway. Finally, comprehensive EC utilization technologies are proposed as a reference.

Metal adsorption by quasi cellulose xanthogenates derived from aquatic and terrestrial plant materials

The FTIR spectra, SEM-EDXA and copper adsorption capacities of the raw plant materials, alkali-treated straws and cellulose xanthogenate derivatives of Eichhornia crassipes shoot, rape straw and corn stalk were investigated. FTIR spectra indicated that of the three plant materials, the aquatic biomass of E. crassipes shoot contained more OH and CO groups which accounted for the higher Cu(2+) adsorption capacities of the raw and alkali treated plant material. SEM-EDXA indicated the incorporation of sulphur and magnesium in the cellulose xanthogenate. The Cu(2+) adsorption capacities of the xanthogenates increased with their magnesium and sulphur contents. However more copper was adsorbed than that can be explained by exchange of copper with magnesium. Precipitation may contribute to the enhanced uptake of copper by the cellulose xanthogenate.

Synthesis and Characterization of Mn–C–Codoped Nanoparticles and Photocatalytic Degradation of Methyl Orange Dye under Sunlight Irradiation

Novel visible-light-active Mn–C–TiO2 nanoparticles were synthesized by modified sol-gel method based on the self-assembly technique using polyoxyethylenes orbitan monooleate (Tween 80) as template and carbon precursor and manganese acetate as manganese precursor. The samples were characterized by XRD, FTIR, UV-vis diffuse reflectance, XPS, and laser particle size analysis. The XRD results showed that Mn–C–TiO2 sample exhibited anatase phase and no other crystal phase was identified. High specific surface area, small crystallite size, and small particle size distribution could be obtained by manganese and carbon codoped and Mn–C–TiO2 exhibited greater red shift in absorption edge of samples in visible region than that of C–TiO2 and pure TiO2. The photocatalytic activity of synthesized catalyst was evaluated by photocatalytic oxidation of methyl orange (MO) solution under the sunlight irradiation. The results showed that Mn–C–TiO2 nanoparticles have higher activity than other samples under sunlight, which could be attributed to the high specific surface area, smaller particle size, and lower band gap energy.

Distinguishable root plaque on root surface of Potamogeton crispus grown in two sediments with different nutrient status

The properties of plaques were different on the root surface of Potamogeton crispus planted in sediments from two different shallow lakes. Lake Tangxunhu sediment, with low pH, contained low organic matter, whereas Lake Yuehu sediment, with high pH, had high calcium deposits mixed with high organic matter. The contents of mineral elements in sediment of Lake Tangxunhu was lower than that of Lake Yuehu, except for iron (Fe) content, but the contents of mineral elements extracted by sodium dithionite–sodium citrate–sodium bicarbonate (DCB) from root plaques were higher in Lake Tangxunhu than those in Lake Yuehu, except for Fe. These element distributions on P. crispus root plaques were characterized by scanning electron microscope combined with energy-dispersive X-ray spectrometer and were consistent with the contents of mineral elements in sediment. The root plaque of P. crispus planted in Lake Tangxunhu sediment mainly contained silicon (Si) and Fe, and the content of Si was greater than Fe, which may be contributed to the formation of poly-silicic-ferric in the natural conditions. However, the root plaque of P. crispus planted in the sediment with higher calcium content of Lake Yuehu was rich in Fe, Si, phosphorus (P), and calcium (Ca). Due to oxygen secretion by plant roots, the root plaque has more Fe3(PO4)2 and a certain amount of Ca3(PO4)2. The ratio of magnesium (Mn) to Fe extracted by DCB from root plaque in Lake Tangxunhu sediment was 0.031 and 0.010 in Lake Yuehu sediment. In Lake Tangxunhu sediment, lower content of organic matter results in weak reducibility. Enhanced oxidation ability by oxygen secretion of P. crispus root could oxidize low-valent Fe and Mn into iron–manganese oxide, which leads to formation of iron–manganese plaque on the root surface. However, this case is different in Lake Yuehu sediment, where Fe and Mn can be reduced in high organic sediment and low-valent Mn can precipitate in the sediment in which pH is >8. Thus, low-valent Fe in Lake Yuehu sediment moves to the root surface of P. crispus, where it oxidizes into Fe oxide, i.e., Fe plaque.

Effect of chemical and biological degumming on the adsorption of heavy metal by cellulose xanthogenates prepared from Eichhornia crassipes

Cellulose xanthogenates, derived from the straw of Eichhornia crassipes, were prepared as adsorbents for heavy metals by CS(2) sulfonation and magnesium substitution after degumming with alkali, self-isolated A(1) strain and pectase, respectively. The effects of three degumming treatments were compared by functional groups analysis, surface morphology and surface element composition and heavy metal (Pb(2+)) adsorption studies. The results demonstrate that bio-degumming treatments by A(1) strain and pectase have weaker degumming effects than alkali treatment. However, the surface characteristics of the bio-degumming products, especially the pectase degumming product, are more beneficial to heavy metal adsorption. In comparison to that of the raw plant materials, the Pb(2+) adsorption performances of the three xanthogenates improved significantly, although no obvious differences being observed among themselves. From an environmental point of view, the two bio-degumming treatments, especially the pectase degumming treatment, are more beneficial to prepare heavy metal adsorbents than the alkali degumming treatment.