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- Liu, Peng
(författare)
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Adsorption behavior of heavy metal ions from aqueous medium on nanocellulose
- 2015
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this work was to explore the potential of nanocellulose, nanocellulose derivatives and nanochitin to remove metal ions from contaminated water. The above nano-polysaccharides were of interest in water purification technologies due to their high surface area and versatile surface chemistry. Silver, copper and iron are the primary metal ions targeted in the study, due to their abundance in industrial effluents. The first part of the study explored the potential of native nanocellulose and nanochitin isolated from bioresidues in removing silver ions from contaminated water. The highest Ag(I) removal for cellulose nanocrystals (CNC) was 34.4 mg/g, corresponding to 64 % removal ratio (CNC > ChNC > CNF). Wavelength dispersive X-ray analysis (WDX) and X-ray photoelectron spectroscopy (XPS) analysis confirmed the presence of silver ions on the surface of the nanocellulose and nanochitin after sorption. This study showed that the sorption performance is pH dependent and adsorption by cellulose nanocrystals was superior to cellulose nanofibers. The second part of the work focused on evaluating the surface adsorption enhancements after nanocellulose surface modifications viz. enzymatically phosphorylation and TEMPO-mediated oxidation. Both surface modifications dramatically improved the functionality and sorption capacity; a ten fold increase in Cu(II) adsorption was observed for TEMPO-mediated oxidized CNF compared to native CNF. Generally, when the mixture of metal ions were present in water the metal ion selectivity was in the order Ag(I) > Fe(III) > Cu(II), irrespective of the surface functionality of nanocellulose. Phosphorylated nanocelluloses demonstrated the capacity to reduce Cu(II) and Fe(III) concentrations in the effluent from mirror making industry to the level that meets WHO drinking water requirements. The increase in Cu(II) adsorption on TEMPO-mediated oxidized cellulose nanofibers (TOCNF) correlated both with the pH and carboxylate content and reached maximum values of 135 mg/g for highly oxidized cellulose. Furthermore, the Cu(II) could be easily recovered from the contaminated nanofibers through a washing procedure with acidic water. The adsorption capacity of TOCNF for other metal ions, such as Ni (II), Cr (III) and Zn (II), was also demonstrated. The third part of the work aimed at gaining deeper understanding of the Cu(II) sorption behavior onto TOCNF. The carboxylate groups introduced by TEMPO- oxidation on nanocellulose surface provided negatively charged sorption sites for Cu(II) ions. The metal sorption had fast kinetics (te < 20s) and increase in temperature lead to a mild decrease in Cu(II) sorption capacity. The equilibrium sorption data fitted well with Langmuir isotherms. Furthermore SEM analysis showed copper element-containing nanoparticles with a rather narrow size distribution on TOCNF, which opens up a new and a promising possibility of converting the TOCNF after Cu (II) adsorption into a variety of value-added products. TOCNF coupled with the adsorbed copper exhibited superhydrophilicity and decreased the filtration time for the TOCNF suspension after copper sorption. A linear correlation between Δ [H+] and the corresponding Δ [Cu(II)] in the solution during Cu(II) sorption was found and discussed. This work has demonstrated that nano-polysaccharides, particularly nanocellulose are highly promising biosorbents for scavenging metal ions from water and of great industrial relevance and may enable next-generation of water purification technologies.
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| 2. |
- Liu, Peng
(författare)
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Novel organic sensitizers and hole transport materials for efficient solid-state photovoltaic devices
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- State-of-art solid-state photovoltaic devices, such as solid-state dye sensitized solar cells (ssDSSCs) and perovskite solar cells have attracted significant attention due to their high efficiency and potential low-cost manufacture. However, there are still challenges that limit the application up-scaling.. One important factor that limits the efficiency of ssDSSCs is associated with the sensitizers. In this thesis, we have developed several organic sensitizers for highly efficient and stable ssDSSCs. The compatibility between sensitizers and hole transport materials has also been investigated. Novel blue colored sensitizers have been studied with aesthetic applications in mind. By co-sensitization using two complementary sensitizing dyes, the efficiency of ssDSSCs can be increased significantly.. For both PSCs and ssDSSCs, the hole transport materials (HTMs) represent one of the crucial factors for efficient charge collection as well as future cost of manufacturing. Here, we have studied organic triphenylamine based oligomers as HTMs for both ssDSSCs and PSCs. The influence of the molecular structure of the HTM building blocks on the photovoltaic performance has been studied in detail. In order to minimizing the cost of fabrication of photovoltaic devices, we have also developed sulfur-based cross-linked polymers as HTMs to replace the well-known, expensive HTM Spiro-OMeTAD. The cross-linked polymeric sulfur material work well in both ssDSSCs and PSCs with efficiencies around 2% and 10%, respectively. These results will provides important insights for the future design of inexpensive and efficient solid state photovoltaic devices.
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