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Title: Occlusion of nanoparticles within inorganic crystals
Author: Ning, Yin
ISNI:       0000 0004 6058 5899
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2016
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This Thesis describes the occlusion of nanoparticles (either diblock copolymer nanoparticles or polymer modified metal sols) within either CaCO3 (calcite) or ZnO (wurtzite). First, new spherical diblock copolymer nanoparticles were synthesised via reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerisation of 2-hydroxypropyl methacrylate at 70 °C and 20 % w/w solids using either poly(carboxybetaine methacrylate) or poly(proline methacrylate) as the steric stabiliser block. Both these stabilisers contain carboxylic acid groups, but poly(proline methacrylate) is anionic above pH 9.2, whereas poly(carboxybetaine methacrylate) has zwitterionic character at this pH. When calcite crystals are grown at an initial pH 9.5 in the presence of these two types of nanoparticles, it is found that the anionic poly(proline methacrylate)-stabilised particles are occluded uniformly throughout the crystals (up to 6.8 % by mass, 14.0 % by volume). In contrast, the zwitterionic poly(carboxybetaine methacrylate)-stabilised particles show no signs of occlusion into calcite crystals grown under identical conditions. The presence of carboxylic acid groups alone therefore does not guarantee efficient occlusion: overall anionic character is an additional prerequisite. Second, we demonstrate for the first time that poly(ammonium 2-sulfatoethyl methacrylate)-poly(benzyl methacrylate) diblock copolymer nanoparticles can be prepared with either high or low poly(ammonium 2-sulfatoethyl methacrylate) stabiliser surface densities using either RAFT dispersion polymerisation in a 2:1 v/v ethanol/water mixture or RAFT aqueous emulsion polymerisation, respectively. We then use these model nanoparticles to gain new insight into a key topic in materials chemistry - the occlusion of organic additives into inorganic crystals. Substantial differences are observed for the extent of occlusion of these two types of anionic nanoparticles into calcite, which serves as a suitable host crystal. A low poly(ammonium 2-sulfatoethyl methacrylate) stabiliser surface density leads to uniform nanoparticle occlusion within calcite at up to 7.5 % w/w (16 % v/v), while minimal occlusion occurs when using nanoparticles with a high poly(ammonium 2-sulfatoethyl methacrylate) stabiliser surface density. This counter-intuitive observation suggests an optimum anionic surface density is required for efficient occlusion, which provides a hitherto unexpected design rule for the incorporation of nanoparticles within crystals. Third, a series of new well-defined anionic diblock copolymer nanoparticles are synthesised by polymerisation-induced self-assembly (PISA) via RAFT aqueous emulsion polymerisation and then evaluated as crystal habit modifiers for the in situ formation of ZnO in aqueous solution. Systematic studies indicate that both the chemical nature (i.e. whether sulfate-based or carboxylate-based) and the mean degree of polymerisation (DP) of the anionic stabiliser block play vital roles in determining the crystal morphology. In particular, sulfate-functionalised nanoparticles are efficiently incorporated within the ZnO crystals whereas carboxylate-functionalised nanoparticles are excluded. Moreover, the extent of nanoparticle occlusion within the ZnO phase can be as high as 23 % by mass depending on the sulfate-based nanoparticle concentration. The optical properties, chemical composition and crystal structure of the resulting nanocomposite crystals are evaluated and an occlusion mechanism is proposed based on the observed evolution of the ZnO morphology in the presence of these sulfate-based anionic nanoparticles. Last, we describe an efficient aqueous route that enables the direct occlusion of non-ionic poly(glycerol monomethacrylate)70-stabilised gold nanoparticles (G70-AuNPs) at remarkably high levels (~20 % w/w) during the in situ growth of ZnO crystals under relatively mild conditions. Depending on the synthesis protocol, the G70-AuNPs can be (i) solely located within a central region, (ii) uniformly distributed throughout the ZnO host crystal or (iii) confined to a surface layer. The G70 stabiliser is essential for successful occlusion: its pendent cis-diol side-groups bind Zn2+ cations, which promotes nanoparticle interaction with the growing ZnO crystal surface. XPS studies indicate significant shifts in the Au4f and Zn2p binding energies, which suggests an intimate interaction between the G70-AuNPs and the host ZnO crystals. Finally, we demonstrate that occlusion of G70-AuNPs throughout the whole ZnO is beneficial for the enhanced photocatalytic decomposition of rhodamine B, which serves as a model dye.
Supervisor: Armes, S. P. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available