Nanoparticles/polysaccharide nanocomposites for water purification

AlAhmadi, Nadiyah Saad M.

Abstract

The main objective of this study was to synthesise of nanocomposites made of nanoparticles and cellulose or cellulose derivatives for the use of these in water purification. A variety of different kinds of nanoparticles were synthesised using similar approaches. Chapters one and two contain a literature review, introduction and technical information about the instruments. Chapter three includes all the experimental methodologies that have been used in general, while more details are giving late as required. Then, five chapters are about the synthesis and characterisation of specified nanocomposites and in each of these five chapters, water remediation was attempted.

In chapter four, spherical silver nanostructures were synthesised in aqueous media and attached to cellulose paper: an environmentally porous support. The general method of synthesis was based on attaching Ag+ ions in the cellulose substrate then reducing these ions with sodium borohydride, a mild reducing agent. Different reaction conditions were investigated, for example precursors concentration and use of a stabiliser. The silver/cellulose nanocomposite was characterised with different analytical techniques. Silver nanoparticles appear as face-centred cubic (fcc) crystals of pure metallic silver. The quantity of silver nanoparticles was proportional to the concentration of silver ions in the precursor solution. Additional stabilised cellulose had a non-negligible impact: the investigations showed that its presence of them enhances the amount of silver nanoparticles immobilised in the samples. Moreover, it does not change the morphology of silver nanoparticles, although it helps keep these nanoparticles dispersed.

In chapter five, nanocomposites were fabricated by interacting dispersion of nanoparticles with a support. First, a yellow dispersion of silver nanoparticles was synthesised by a chemical reduction method. The resulting dispersion of silver nanoparticles was stabilised by electrostatic forces. Attention was focused on the effect of temperature and addition method during the reduction step. The morphology of nanoparticles was investigated by quantitative and qualitative analytical techniques. Silver nanoparticles were spherical with a size of 17 nm ± 5.6, and shown to adsorb light ~ 400 nm due to surface plasmon resonance (SPR). The colloidal silver nanoparticles were put in contact with cellulose triacetate to prepare the composites. The process of adsorption was controlled by varying the pH of the dispersion. The coverage of silver nanoparticles over a solid substrate was evaluated by ICP analysis and visual observation. pH has a great impact on the improvement of quantity of silver nanoparticles over the surface; a homogenous yellow coverage of silver nanoparticles over cellulose triacetate was obtained at higher pH. Positive antibacterial action was observed from the silver cellulose triacete nanocomposites against MRSA.

In chapter six, the electrochemical-behaviour of silver cellulose nanocomposites was investigated in relation to various parameters, i.e., the concentration of silver nanoparticles, electrolytes and concentration of electrolyte. The stripping of silver cellulose nanocomposites may depend on the size of the nanoparticles and the coverage of silver nanoparticles in the sample. Small nanoparticles showed a very sharp oxidation peak. However, polydispersed nanoparticles had slow and complex redox pattern. The peak potential varied with change in the electrolyte. The oxidation of silver nanoparticles was very sensitive to chloride ions. PXRD patterns confirmed the formation of silver chloride and silver nitrate. Silver cellulose nanocomposites have great potential in water purification.

In chapter seven, cobalt nanoparticles was prepared by two synthetic approaches. The first approach involved the preparation of aqueous dispersions of cobalt nanoparticles by reduction of metal salt using sodium borohydride. A number of procedure conditions were investigated such as the precursor’s concentration, reduction time and temperature. In the first approach, highly crystalline cobalt nanoparticles with some other compounds were produced after further decomposing. Changing temperature has an impact on the crystal structure. The second approach involved saturating the porous, absorptive substrate with an aqueous solution of cobalt salt and then reducing the metal salt using sodium borohydride or hydrogen gas to cobalt nanoparticles in situ on the substrate surface. Cellulose was used to inhibit aggregation and agglomeration of the cobalt nanoparticles. It was likely that chemical reduction using sodium borohydride formed a mixture of spherical crystal and amorphous cobalt nanoparticles. In contrast, reduction by hydrogen gas may produce spherical crystal cobalt nanoparticles Therefore, cellulose substrate and hydrogen gas have potential in green synthesis of cobalt cellulose nanocomposites. The potential for using cobalt nanoparticles in wastewater treatment and a medical setting is high as cobalt nanoparticles mainly showed good antibacterial action against all bacterial isolates tested with zone of inhibition sizes up to 15 mm.

In chapter eight, the green synthesis of copper nanoparticles and copper cellulose nanocomposites was carried out using a simple reduction method. Mixtures of copper and copper oxide nanoparticles were synthesised by reduction of copper ions using sodium borohydride, in different reaction conditio ns: concentration, atmosphere, temperature and using a stabiliser. The natural substrate cellulose was used to stabilise the nanoparticles. The physicochemical properties of copper as free nanoparticles and as copper cellulose nanocomposites were investigated. PXRD was used to identify the structure of the copper nanoparticles and show the effect of reaction condition, i.e., concentration precursor on crystal structures. PXRD patterns, TEM images and UV-VIS display the impact of cellulose on nanoparticle size, i.e., the presence of cellulose reduces the size of copper nanoparticles formed. Copper cellulose nanocomposites and copper nanoparticles had only sufficient or limited antibacterial action. Increasing the concentration of copper nanoparticles in samples may improve antibacterial activity.

Citation

AlAhmadi, N. S. M. (2014). Nanoparticles/polysaccharide nanocomposites for water purification. (Thesis). University of Hull. Retrieved from https://hull-repository.worktribe.com/output/4222805

• Thesis Type: Thesis
• Deposit Date: Feb 22, 2021
• Publicly Available Date: Feb 23, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4222805
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: Oct 1, 2014