A study of nano-particle based silane consolidants for Globigerina limestone

This STEPS funded study focuses on the application of hybrid and nanoparticle loaded hybrid silane consolidants for the treatment of 'Franka' type Globigerina Limestone. Consolidants act by gluing the deteriorated stone material to the underlying healthy stone (Dukes, 1972; Gutt, 1973; Alessandrini et al., 1975; Garrod, 2001). The consolidants evaluated in this work were a laboratory prepared hybrid silane based on a mixture of tetraethylorthosilicate (TEOS) and 3-(glycidoxypropyl) trimethoxysilane (GPTMS), the same hybrid consolidant loaded with silica nanoparticles and GPTMS-modified silica nanoparticles. In addition, a consolidant based on the hydrolysis product of TEOS was also tested. Prepared consolidants were applied to Globigerina Limestone test blocks by complete immersion. Untreated stone block were used as benchmarks. Following application of the consolidants, half of the treated limestone blocks were subjected to accelerated weathering. Non-weathered and weathered limestone blocks were then characterised by optical and electron microscopy and the stone colour before and after treatment with consolidants was assessed by a colorimetric technique. The pore size distribution before and after application of the different consolidant treatments was assessed by Mercury Intrusion Porosimetry. A water absorption by capillarity technique was also carried out to assess how the water uptake rate into the limestone alters with the different treatments. The mechanical properties of the consolidated limestone blocks were assessed by resistance to sodium sulfate crystallisation. Microscopy observations showed that the consolidants penetrated the stone to different extents depending on the consolidant and the method of application. The hybrid consolidant on its own led to yellowing of the limestone but the addition of nanoparticles to the hybrid (modified or not) appeared to help restore the original colour of the stone. The porosity of the limestone was only marginally affected by the different treatments but the somewhat hydrophobic nature of the consolidants led to a disruption in the capillary flow of water into the limestone.peer-reviewe

Synthesis and ageing transformations of manufactured metal oxide nanomaterials

With the increased use of manufactured nanomaterials (MNMs) and increased environmental and human exposure, "nanosafety" has become a major research objective. This field has yet to advance due to challenges in systematically linking physicochemical properties to toxicity. The aim of this work was to develop a library of comparable NMs and study their behaviour and ageing in different scenarios. A library of metal oxide NMs based on a PVP capped ceria synthesis protocol was developed and extensively characterised. The protocol was successfully modified to produce PVP capped zinc oxide and copper oxide NMs, of comparable sizes. These NMs along with commercial uncoated ceria NMs were subjected to time and temperature dependent studies. The work studied the transformations occurring on exposure to 25, 45, 65 and 80 °C temperatures for 4 weeks. Results showed increased aggregation, changes in metal valency state and decreased stability with increasing temperature and time. Finally the potential phosphate induced environmental transformation of ceria was studied for the ceria library NMs, the commercial ceria NM and a series of zirconium doped ceria NMs. Samples were exposured to pH-adjusted phosphatisation solutions. Ceria and ceria-rich samples underwent physical and chemical transformations. Furthermore the commercial ceria was exposed to a pH-adjusted phospholipid containing phosphatisation solution where no characteristic phosphate ageing transformations were observed

TEOS based consolidants for Maltese Globigerina Limestone : effect of hydroxyl conversion treatment

Lime-based consolidants are widely used in Malta where the main building material is a sedimentary limestone. Over the past few years, commercial alkoxysilane consolidants have also infiltrated the local market, yet the effects of these materials on local Globigerina Limestone is still not well documented. Whereas it is well established that alkoxysilane consolidants form strong bridges between the deteriorating surface and healthy underlying stone in sandstones, the same is not necessarily true for porous limestone. A hydroxyl conversion treatment (HCT) has been proposed to improve bonding between silica-based consolidants and limestone (Wheeler 2005). In this work, Globigerina Limestone test samples were treated respectively with a laboratory-prepared consolidant based on tetraethylorthosilicate (TEOS), and the same consolidant loaded with 35 nm silica particles. Another set of stone samples were first pre-treated with an ammonium tartrate solution known as HCT before application of TEOS and nanoparticle-loaded TEOS. The HCT converts the stone surface into calcium tartrate, offering a hydroxylated surface onto which the alkoxysilane can anchor. Ammonium tartrate was preferred to tartaric acid on grounds of conservation ethics. The effect of the surface conversion treatment was evaluated by an infra-red technique. Untreated limestone samples were employed for comparative purposes. Consolidant- stone interactions were observed at high magnification under the electron microscope. Alteration to stone colour was followed by a colorimetric technique. The physical properties of the consolidated stone were assessed by a hardness test, water absorption by capillarity and resistance to sodium sulphate crystallisation. Results showed that HCT improved the consolidation properties of the TEOS and possibly those of the alkoxysilane containing nanoparticles. The ammonium tartrate (AMT) pre-treatment was successful even though chemical formation of calcium tartrate was not favourable according to solubility equilibria. The tartrate treatment however led to some discolouration, probably resulting from mobilisation of intrinsic iron in the limestone.peer-reviewe

Developing self-cleaning photocatalytic TiO2 nanocomposite coatings

Photocatalytic coatings with self-cleaning properties are becoming increasingly more popular due to the increased awareness of the importance of cleaning and the associated high cost of cleaning supplies and services. This research investigated self-cleaning photocatalytic polydimethylsiloxane (PDMS)/titanium dioxide (TiO2) nanocomposite coatings and focused on selecting the optimal TiO2 phase and concentration. To date, the comparison of the different TiO2 phases as a nanocomposite coating has not been sufficiently considered. PDMS/TiO2 nanocomposite coatings with three nanomaterial (NM) samples (an anatase, rutile, and mixed phase) and three concentrations of TiO2 (0.6, 1 and 3 w/v%) were prepared, applied to glass slides by dip coating, and tested with respect to hydrophobicity, surface stability, antifogging, and photocatalytic properties. It was found that a stable hydrophobic coating with the optimal photocatalyitc performance was produced with 3 w/v% anatase TiO2.peer-reviewe

Uptake and impacts of polyvinylpyrrolidone (PVP) capped metal oxide nanoparticles on Daphnia magna:role of core composition and acquired corona

The potential long-term environmental impact of manufactured nanoparticles (NPs) remains poorly understood, in part due to the complexity of NPs themselves and the range of physico-chemical parameters that may influence their biological impacts (such as size, shape and chemistry), as well as their dynamic interactions with their environment, leading to acquisition of an eco-corona and a range of other possible transformations. A key hypothesis in nanosafety assessment is that the NP core chemistry is a primary factor controlling toxicity. This work aims to compare the uptake and impacts of 5 nm zinc oxide (ZnO) NPs which are highly soluble and cerium dioxide (CeO2) NPs which are considered to be poorly soluble, where both particles were produced using an identical protocol and capped with polyvinylpyrrolidone (PVP), on Daphnia magna (D. magna). These well-characterised NPs were developed as part of a systematic library, and were intended to allow controlled variation of one property at a time, e.g. the core composition as evaluated here. Half-maximal effective concentrations (EC50) were determined in pure medium and medium conditioned with biomolecules secreted by D. magna, as the presence of biomolecules in the environment has the ability to alter NP stability and biological effects. NPs were characterised by size and zeta potential measurements under both conditions. NP uptake concentrations and removal over 24 hours post exposure (without feeding) were determined by inductively coupled plasma – optical emission spectroscopy (ICP-OES) of the exposure and receiving media, respectively. Results showed that PVP capped ZnO NPs were more toxic than PVP capped CeO2 NPs. The NP impact and behaviour was due to physical effects with CeO2 NPs which showed signs of agglomeration while a chemical effect was apparent in the case of ZnO NPs which underwent partial dissolution in the gut following uptake.peer-reviewe

Internalization and toxicological mechanisms of uncoated and PVP-coated cerium oxide nanoparticles in the freshwater alga Chlamydomonas reinhardtii

Due to the wide range of applications of cerium oxide nanoparticles (CeO2NPs), a risk assessment of their biological effects using environmentally relevant species becomes highly important. There are contradictory reports on the effects of CeO2NPs, which may be related to the use of different types of nanoparticles (NPs) and coatings. CeO2NPs may act as an oxidant causing toxicity or as an antioxidant able to scavenge free radicals. As a consequence of such complexity, the toxicological behaviour of these NPs is still poorly understood. Moreover, little is known about the internalization process of CeO2NPs in algae. There is evidence of CeO2NP-internalization by the green alga Chlamydomonas reinhardtii, but the mechanism and route of uptake are still unknown. In this study, we used uncoated and different polyvinylpyrrolidone (PVP)-coated CeO2NPs with the aim of identifying their toxicological mechanisms to C. reinhardtii and exploring their possible internalization. Our results showed that PVP coated-CeO2NPs significantly increased the formation of reactive oxygen species in exposed cells, indicating that oxidative stress is an important toxicity mechanism for these particles. Direct contact and damage of the cellular membrane was identified as the mechanism causing the toxicity of uncoated NPs. From experiments with endocytosis inhibitors, clathrin-dependent endocytosis was revealed as the main internalization route for all NPs. However, as uncoated CeO2NPs led to severe cellular membrane damage, direct passage of NPs through membrane holes could not be discarded. To our knowledge, this is the first report with evidence of direct linking between NP internalization and a specific endocytic pathway. The results presented here will help to unravel the toxicological mechanism and behaviour of CeO2NPs and provide input information for the environmental health and safety assessment of CeO2NPs.This research was supported by CTM2013-45775-C2-1,2-R and CTM2016-74927-C2-1,2-R grants from MINECO. NanoMILE (Grant Agreement no 310451 to EVJ & SMB) and the Endeavour Scholarship Scheme (Group B) (to SMB) are acknowledged.Peer reviewe

Thermal Transformations of Manufactured Nanomaterials as a Proposed Proxy for Ageing

Ageing is an important part of a manufactured nanomaterial\u27s life cycle and can be considered as a transformation over time. It is particularly relevant to nanomaterials (NMs) because they are more reactive than their bulk counterparts and therefore are likely to undergo more significant or faster transformations with time. The conditions upon exposure of a NM to the environment, e.g. temperature, humidity and redox, will all individually affect ageing, as well as time. In experimental simulations, time has to be substituted by a proxy that makes timescales more realistic. Thermal ageing accelerates the normal ageing processes of NMs and thus elevated temperatures can be used to simulate prolonged ageing, allowing access to information on the long-term effects of NM ageing within a shorter time. Similar approaches are utilised in experimental simulation of protein fibrillation, for example, where processes that naturally occur over decades are accelerated to days or hours. In this work, time and temperature dependent studies were carried out on a fully characterised library of laboratory synthesised comparable polyvinylpyrrolidone (PVP) capped NMs (with core compositions of ceria, copper oxide and zinc oxide) and a commercially available uncoated cerium dioxide NM, to assess their transformations. Specifically, physical and chemical changes were studied on NMs exposed to various temperatures (25, 45, 65 and 80 °C) for a period of 4 weeks. The size, zeta potential, agglomeration/aggregation and valence state of the NMs were studied through dynamic light scattering (DLS), zeta potential, ultra-violet visible light spectroscopy (UV-VIS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS), as a function of time. Results generally show a decrease in NM stability with increasing temperature and time. Changes in the NM size and core oxidation state were noted with increasing temperature/time. These changes varied depending on the NM core composition. Additionally the PVP capping, despite stabilising the NM dispersion, still allowed the NM core to be influenced by external factors, thus indicating likely ageing-related reduction in efficiency, though to a lesser extent than the uncapped particles. Overall the experiments recorded a complex picture of transformations as a function of time/temperature highlighting the complexity of NMs\u27 ageing

Current application of capillary electrophoresis in nanomaterial characterisation and its potential to characterise the protein and small molecule corona

Due to the increasing use and production of nanomaterials (NMs), the ability to characterise their physical/chemical properties quickly and reliably has never been so important. Proper characterisation allows a thorough understanding of the material and its stability, and is critical to establishing dose-response curves to ascertain risks to human and environmental health. Traditionally, methods such as Transmission Electron Microscopy (TEM), Field Flow Fractionation (FFF) and Dynamic Light Scattering (DLS) have been favoured for size characterisation, due to their wide-availability and well-established protocols. Capillary Electrophoresis (CE) offers a faster and more cost-effective solution for complex dispersions including polydisperse or non-spherical NMs. CE has been used to rapidly separate NMs of varying sizes, shapes, surface modifications and compositions. This review will discuss the literature surrounding the CE separation techniques, detection and NM characteristics used for the analysis of a wide range of NMs. The potential of combining CE with mass spectrometry (CE-MS) will also be explored to further expand the characterisation of NMs, including the layer of biomolecules adsorbed to the surface of NMs in biological or environmental compartments, termed the acquired biomolecule corona. CE offers the opportunity to uncover new/poorly characterised low abundance and polar protein classes due to the high ionisation efficiency of CE-MS. Furthermore, the possibility of using CE-MS to characterise the poorly researched small molecule interactions within the NM corona is discussed.peer-reviewe