1,721,022 research outputs found
Polymer brushes as smart coatings for On-Chip electrochemical sensors
No full textFunctional polymer brushes have a tremendous interest for surface engineering, thanks to their stimuli-responsive behaviour, allowing applications in the fields of the development of switchable wettability/adhesion devices, controlled release devices and especially sensors.
In this work [1], silicon substrates functionalized with an alkoxysilane-type initiator were used as substrates to grow polymer brushes using SI-ARGET ATRP (Atom transfer Radical Polymerization). Different brushes compositions were obtained usingdifferent feed ratios of the two monomers (2-hydroxyethyl methacrylate (HEMA) and 2-aminoethyl methacrylate hydrochloride (AMA)). Both homopolymer (PHEMA, PAMA) andcopolymer (PHEMA-co-PAMA 80:20, PHEMA-co-PAMA 50:50) brushes were investigated. Moreover, the effect of micropatterning (achieved by remote photocatalytic lithography [2]) on the brushes properties was also determined. Every step (Figure 1) of this grafting-from procedure was studied using electrochemical techniques, in particular electrochemical impedance spectroscopy (EIS) (Figure 2), demonstrating the great potential of these techniques for the investigation of such complex systems.
The homogeneity and density of the initiator layer and of the resulting brushes, their composition and thickness,have been thoroughly investigated. Brushes with different loading of cationic groups could be differentiated through their marked reactions to an anionic redox probe (ferrocyanide). Noteworthy, the brushes were grown on silicon substrate which is an atypical electrode material due to its very poor electrochemical response. Grafted-from brushes allowed the reaction of ferrocyanide at the silicon surface, behaving as «tentacles» to capture the redox probe and keep it in proximity of the silicon surface. Micropatterning was found to significantly improve the electrochemical behavior of the system.
The obtained results pave the way to the development of on-chip electrochemical devices and microsensors. Applications for drug-delivery and microfluidics can be envisaged as well.
References
[1] G. Panzarasa, G. Soliveri, V. Pifferi, J. Mater. Chem. C 4, 2016, pp 340–347.
[2] G. Panzarasa, G. Soliveri, K. Sparnacci, S. Ardizzone, Chem. Commun. 51, 2015, pp 7313–7316.
Figure 1. Scheme of the polymer brushes grafting-from and examples of devices.
Figure 2. EIS spectra of the different devices
Functional polymer brushes for on-chip electrochemical sensors
No full textFunctional polymer brushes have a tremendous interest for surface engineering, thanks to their stimuli-responsive behaviour, allowing applications in the fields of the development of switchable wettability/adhesion devices, controlled release devices and especially sensors. In this context, standard characterization techniques (GPC and NMR) are not able to provide a deep insight in their structure due to the very small amount of polymer grafted (~0.01 mg cm-2).
In this work [1], functional, hydrophilic polymer brushes were grown using Surface-Initiated Activators Regenerated by Electron Transfer Atom Transfer Radical Polymerization (SI-ARGET ATRP) from silicon substrates which were previously functionalized with a suitable alkoxysilane-type initiator (BIB-APTES). Using different feed ratios of the two monomers employed (2-hydroxyethyl methacrylate (HEMA) and 2-aminoethyl methacrylate hydrochloride (AMA), both homopolymer (PHEMA, PAMA) and copolymer (PHEMA-co-PAMA 80:20, PHEMA-co-PAMA 50:50) brushes were obtained. Micropatterned polymer brushes were obtained using remote photocatalytic lithography [2] on the initiator monolayer.
Every step of the grafting procedure (Figure 1) was studied using electrochemical techniques, in particular electrochemical impedance spectroscopy (EIS) (Figure 2), demonstrating the power and simplicity of these techniques in investigating such systems.
The homogeneity and density of the initiator layer and of the resulting brushes, their composition and thickness and also the post-functionalization reactions have been easily investigated. Brushes with different loading of cationic groups could be differentiated through their marked reactions to an anionic redox probe. Noteworthy, the brushes were grown on silicon substrate which is an atypical electrode material due to its very poor electrochemical response. Grafted-from brushes allowed the reaction of ferrocyanide at the silicon surface, behaving as «tentacles» to capture the redox probe and keep it in proximity of the silicon surface. Micropatterning was found to improve the electrochemical behaviour of the system.
The obtained results pave the way to the development of on-chip electrochemical devices and microsensors. Applications for drug-delivery and microfluidics can be envisaged as well.
References
[1] G. Panzarasa, G. Soliveri, V. Pifferi, J. Mater. Chem. C 4, 2016, pp 340-347.
[2] G. Panzarasa, G. Soliveri, K. Sparnacci, S. Ardizzone, Chem. Commun. 51, 2015, pp 7313–7316
Electrochemistry provides better understanding of polymer brushes as smart coatings
No full textFunctional polymer brushes have a tremendous interest for surface engineering, thanks to their stimuli-responsive behavior, allowing applications in the field of switchable wettability/adhesion processes, controlled release and sensor development. However, surface-attached polymer brushes are very difficult to characterize with standard techniques like GPC and NMR due to the very small amount of polymer grafted (~0.01 mg cm-2). Thus, more sophisticated (and expensive) techniques, i.e. XPS, are needed in order to achieve a satisfactory knowledge of the sample under study.
In this work [1] we demonstrate how grafted-from hydrophilic polymer brushes can solve the problem of the development of on-chip electrochemical microsensors, impaired by the electrochemical inertness of native oxide-coated silicon wafer.
Silicon substrates were functionalized with the alkoxysilane-type BIB-APTES initiator. Polymer brushes with different composition were then grown by SI-ARGET ATRP with different feed ratios of the monomers 2-hydroxyethyl methacrylate (HEMA) and 2-aminoethyl methacrylate hydrochloride (AMA). Both homopolymer (PHEMA, PAMA) and copolymer (PHEMA-co-PAMA 80:20, PHEMA-co-PAMA 50:50) and micropatterned (by using remote photocatalytic lithography[2]) brushes were obtained and characterized.
Every step of the grafting procedure, from surface pretreatment to functionalization with initiator and eventually the grafted brushes, was studied using electrochemical techniques, in particular electrochemical impedance spectroscopy (EIS).
In this way, the homogeneity and density of the initiator layer and of the resulting brushes, their composition and thickness and also the post-functionalization reactions could be easily investigated. Brushes with different loading of cationic groups could be differentiated through their marked reactions to an anionic redox probe. Noteworthy, the brushes were grown on silicon substrate which is an atypical electrode material due to its very poor electrochemical response. Grafted-from brushes allowed the reaction of ferrocyanide at the silicon surface, behaving as «tentacles» to capture the redox probe and keep it in proximity of the silicon surface. Micropatterning was found to improve the electrochemical behavior of the system. Our results thus pave the way for the development of on-chip electrochemical devices and sensors. Applications for drug-delivery and microfluidics can be envisaged as well.
REFERENCES
[1] G. Panzarasa, G. Soliveri, V. Pifferi, J. Mater. Chem. C, Accepted.
[2] G. Panzarasa, G. Soliveri, K. Sparnacci, S. Ardizzone, Chem. Commun., 51, 2015, 7313–7316
Electrochemical and theoretical investigation of the silver nanoparticles/TiO2 interface: the “silver-ion electrode”
No full textA sandwich-like structure electrode of silver nanoparticles embedded in a titania (anatase polymorph) photoactive layer was prepared [1-2] and electrochemically characterized by cyclic voltammetry and electrochemical impedance spectroscopy.
In comparison with literature data on bare silver nanoparticles-modified electrodes [3-5], the new device features a pronounced electrocatalytic effect on the silver oxidation peak (Fig. a) together with a great increase in the current intensity. Plane-wave DFT calculations, performed using the VASP code, described the composite junction as a distorted bulk Ag structure, commensurate with the periodicity of the (101) face of the I41/amd TiO2 polymorph. The silver atoms close to the semiconductor were found to gain a partially positive charge, quickly decreasing with the distance from the TiO2 surface.
These joint theoretical and experimental evidences demonstrate that the device could be considered as a “positively charged silver nanoparticles-based electrode”, with positively ionized surface silver atoms protected by the titania layer, which holds a partial negative charge. This peculiar electrode structure shows interesting properties, among which self-cleaning ability, to be conveniently used for sensor applications.
References
[1] G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst, 140, (2015), 1486 – 1494.
[2] V. Pifferi, G. Soliveri, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, L. Falciola, RSC Advances, 5, (2015), 71210 – 71214.
[3] O. S. Ivanova, F. P. Zamborini, J. Am. Chem. Soc., 132, (2010), 70–72.
[4] G. Chang, J. Zhang, M. Oyama, K. Hirao, J. Phys. Chem. B, 109, (2005), 1204-1209.
[5] S.E. Ward Jones, F.W. Campbell, R. Baron, L. Xiao, R.G. Compton, J. Phys. Chem. C, 112, (2008), 17820–17827.
Acknowledgements
This work has been supported by Fondazione Cariplo (Milano, Italy), grant no. 2014-1285. We acknowledge the CINECA and the Regione Lombardia award under the LISA initiative (grant SURGREEN) for the availability of high performance computing resources. We also thank the Chemistry Department for funding through the Development Plan of Athenaeum grant – line B1 (UNIAGI 17777)
Self-cleaning properties of a silica/silver nanoparticles/titania sandwich sensor
No full textOne of the main challenges faced during electroanalysis of complex matrices is represented by fouling and passivation of the electrode surface, especially in the fields of biomedical and environmental trace analysis [1], where sophisticated and highly engineered sensors have to be used in order to increase sensitivity and lower detection limits. These sensors can not be cleaned by conventional mechanical or electrochemical procedures, since these methods could affect the integrity of the active layer. In order to overcome these problems, the production of highly engineered reliable and reusable devices, designed ad hoc for specific applications, which could be simply cleaned by irradiation with UV light, would be an interesting step beyond the current state of the art.
In this context, a three-layered transparent electrode, in which silver nanoparticles are embedded between a bottom silica and a top titania layer [2, 3] was designed, prepared and characterized. The device structure is meant to confer multifunctional properties for a complex biomedical challenge: the detection and quantification of catecholamine neurotransmitters. The key role of each component of the device was thoroughly investigated to demonstrate the robustness and efficiency of the final sensor. In particular, the size distribution of silver nanoparticles, the device architecture and surface homogeneity were inspected by electron microscopy. The cleaning overlayer was made of the active polymorph of titanium dioxide (anatase), as confirmed by X-ray diffraction and by model contaminants photodegradation measurements. Electrochemical techniques (cyclic voltammetry and electrochemical impedance spectroscopy) revealed that an highly ordered distribution of silver nanoparticles is the active core of the device, allowing easier electron transfer and better quantification of the analytes even in the presence of conventional interferents, e.g. ascorbic acid and uric acid in human fluids.
The high photoactivity of titania top layer allowed total recovery of the device performance in terms of sensitivity after a fast (less than 20 min) UV cleaning step, affordable with different UV-A sources. This self-cleaning property, combined with a remarkable resistance against ageing, allows to employ the sensor also in on-field and remote applications.
References
[1] C. M. Welch and R. G. Compton, Anal. Bioanal. Chem. 2006, 384, 601–619.
[2] G. Maino, D. Meroni, V. Pifferi, L. Falciola, G. Soliveri, G. Cappelletti, S. Ardizzone, J. Nanoparticle Res. 2013, 15, 2087.
[3] G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst 2015, 140, 1486
Photo-renewable engineered sensor based on silica, silver nanoparticles and titania
No full textElectrode surface passivation and fouling are important challenges in electroanalysis when using modified electrodes in complex matrices, especially in the biomedical and environmental fields [1-2].
In order to overcome such problems, the production of highly engineered ad hoc designed devices could provide really effective sensors [2]. In particular, a reliable and reusable sensor, that could be cleaned by a simple irradiation with UV or solar light, could be perfect for this purpose.
In this context, a three-layered transparent electrode, in which silver nanoparticles are embedded between a bottom silica and a top titania layer is developed [3-4]. Such structure confers to the device multifunctional properties which can be conveniently used in the detection and quantification of some neurotransmitters: dopamine, norepinephrine and serotonin.
The sensor is thoroughly investigated by structural, morphological and electrochemical characterizations in order to understand the role of each component with the aim to improve the robustness and efficiency of the electroanalytical system. In particular, the size distribution of silver nanoparticles, the device architecture and surface homogeneity are inspected by electron microscopy. As confirmed by X-ray diffraction the overlayer is made of anatase (the active polymorph of titanium dioxide), capable of photodegrading model contaminants. Furthermore, electrochemical techniques (cyclic voltammetry and electrochemical impedance spectroscopy) revealed that a highly ordered distribution of silver nanoparticles constitutes the active analytical core of the device, allowing easier electron transfer and better quantification of the analytes.
The system presents good sensing performances, reaching low detection limits even in the presence of typical interferents such as ascorbic and uric acids. Moreover, the titania photoactive top layer allows the complete recovery of the device performance in terms of sensitivity after a fast and simple UV-A cleaning step, affordable with different UV sources. In particular, three lamps (different in terms of power and wavelength) were tested, reaching the total removal of the contaminants in 10-15 minutes [5]. This “self-cleaning” property, combined with a remarkable resistance against aging and ease of use, allows to employ the sensor also for detection in real matrixes, such as liquor and serum.
ACKNOWLEDGEMENTS
The Authors would like to thank MIUR (Ministero dell’Istruzione, dell’Università e della Ricerca) for the fundings in the framework of the PRIN 2012 Project (20128ZZS2H)
REFERENCES
[1] C.M.A. Brett, Pure Appl. Chem. 73, 2001, pp 1969–1977.
[2] C.M. Welch, R.G. Compton, Anal. Bioanal. Chem. 384, 2006, pp 601–619.
[3] G. Maino, D. Meroni, V. Pifferi, L. Falciola, G. Soliveri, G. Cappelletti, S. Ardizzone, J. Nanoparticle Res. 15, 2013, pp 2087.
[4] G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst 140, 2015, 1486-1494.
[5] V. Pifferi, G. Soliveri, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, L. Falciola, RSC Advances, 5, 2015, 71210-71214
Self-cleaning features of an innovative engineered sensor based on silica, silver nanoparticles and titania
No full textPassivation of the electrode surface and fouling are important challenges in electroanalysis during the use of modified electrodes in complex matrices, especially in the biomedical and environmental fields [1-2].
In order to overcome such problems, the production of highly engineered ad hoc designed devices could access really effective sensors [2]. In particular, a performing, reliable and reusable sensor, that could be cleaned by a simple irradiation with UV or solar light, would be perfect for this purpose.
In this context, a three-layered transparent electrode, in which silver nanoparticles are embedded between a bottom silica and a top titania layer was developed [3-4]. Such structure confers to the device multifunctional properties for a complex biomedical challenge: the detection and quantification of catecholamine neurotransmitters. The sensor was thoroughly investigated by structural, morphological and electrochemical characterizations in order to understand the role of each component with the aim to improve the robustness and efficiency of the electroanalytical system.
The overlayer was made of anatase (the active polymorph of titanium dioxide) as confirmed by X-ray diffraction and by measuring the photodegradation of model contaminants. The size distribution of silver nanoparticles, the device architecture and surface homogeneity were inspected by electron microscopy. Electrochemical techniques (cyclic voltammetry and electrochemical impedance spectroscopy) revealed that a highly ordered distribution of silver nanoparticles constitutes the active core of the device, allowing easier electron transfer and better quantification of the analytes even in the presence of conventional interferents, e.g. ascorbic and uric acid. Titania photoactive top layer allowed total recovery of the device performance in terms of sensitivity after a fast and simple UV-A cleaning step, affordable with different UV sources. This self-cleaning property, combined with a remarkable resistance against aging and ease of use, allows to employ the sensor also in on-field and remote applications.
References
1. C.M.A. Brett, Pure Appl. Chem. 73, 2001, pp 1969–1977.
2. C.M. Welch, R.G. Compton, Anal. Bioanal. Chem. 384, 2006, pp 601–619.
3. G. Maino, D. Meroni, V. Pifferi, L. Falciola, G. Soliveri, G. Cappelletti, S. Ardizzone, J. Nanoparticle Res. 15, 2013, pp 2087.
4. G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst 140, 2015, 1486-1494
Silver cations electroanalytical sensor: sensitivity and selectivity iIn the detection of neurotransmitters
No full textA composite electrode with a sandwich structure combining the properties of silver nanoparticles and a titania (anatase polymorph) photoactive layer was prepared [1-2] and electrochemically characterized by cyclic voltammetry and electrochemical impedance spectroscopy. A pronounced electrocatalytic effect was observed along with a great increase in the current intensity of the silver oxidation peak (Figure 1). Results are compared with literature data on bare silver nanoparticles [3-5].
Theoretical DFT calculations, performed using the VASP code [6], described the composite junction as a distorted bulk Ag structure, commensurate with the periodicity of the (101) face of the I41/amd TiO2 polymorph. The silver atoms close to the semiconductor gain a partially positive charge [7], which quickly decreases with the distance from the TiO2 surface.
This joint theoretical and experimental study allows us to conclude that the device could be considered as a “silver cations electrode”, with silver ions protected by the titania layer, which holds a partial negative charge. This peculiar electrode structure can be conveniently used for sensor applications. For example, we successfully applied our device for the determination of neurotransmitters such as dopamine, norepinephrine and serotonin in simulated biological matrices (liquor, serum and urine). Our optimized analytical methodology is not only characterized by high sensitivity and low detection limits (around 0.03 μM) but also by high selectivity in the presence of high concentrations of conventional interferents (uric and ascorbic acids).
Moreover, the device shows under UV light self-cleaning properties of its titania overlayer, with complete removal of fouling, originated by the chemisorption of analytes and byproducts. Irradiating the device with UVA light, the initial sensor sensitivity was restored, making it reusable and suggesting its employment in integrated monitoring systems.
Acknowledgements
This work has been supported by MIUR (Ministero dell’Istruzione, dell’Università e della Ricerca) in the framework of the PRIN 2012 Project (20128ZZS2H).
References
[1] G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst 140, 2015, pp 1486 – 1494.
[2] V. Pifferi, G. Soliveri, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, L. Falciola, RSC Advances 5, 2015, pp 71210 – 71214.
[3] O. S. Ivanova, F. P. Zamborini, J. Am. Chem. Soc. 132, 2010, pp 70–72.
[4] G. Chang, J. Zhang, M. Oyama, K. Hirao, J. Phys. Chem. B 109, 2005, pp 1204-1209.
[5] S.E. Ward Jones, F.W. Campbell, R. Baron, L. Xiao, R.G. Compton, J. Phys. Chem. C 112, 2008, pp 17820–17827.
[6] G. Kresse, D. Joubert, Phys. Rev. B: Condens. Matter 59, 1999, pp 1758−1775.
[7] W. Tang, E. Sanville, and G. Henkelman, J. Phys. Condens. Matter 2009, 21, 084204
Photo-renewable electroanalytical sensor for neurotransmitters detection: The role of silver ion nanoparticles
No full textA sandwich-like structure electrode of silver nanoparticles embedded in a titania (anatase polymorph) photoactive layer was prepared [1-2] and electrochemically characterized by cyclic voltammetry and electrochemical impedance spectroscopy.
In comparison with literature data on bare silver nanoparticles-modified electrodes [3-5], the new device features a pronounced electrocatalytic effect on the silver oxidation peak together with a great increase in the current intensity (Figure a).
Theoretical DFT calculations, performed using the VASP code [6], described the composite junction as a distorted bulk Ag structure, commensurate with the periodicity of the (101) face of the I41/amd TiO2 polymorph. The silver atoms close to the semiconductor were found to gain a partially positive charge [7], quickly decreasing with the distance from the TiO2 surface.
These joint theoretical and experimental studies demonstrated that the device could be considered as a “charged silver nanoparticles-based electrode”, with positively ionized surface silver atoms protected by the titania layer, which holds a partial negative charge. This peculiar electrode structure was found to be of a highly convenient use for sensor applications.
As a proof-of-concept, this device performed efficiently for the determination of neurotransmitters such as dopamine, norepinephrine and serotonin in simulated biological matrices (liquor, serum and urine). Moreover, this optimized analytical methodology is not only characterized by high sensitivity and low detection limits (around 0.03 μM, which makes it appealing for clinical purposes), but also by high selectivity in the presence of high concentrations of conventional interferents (uric and ascorbic acids). Furthermore, the fouling of the electrode surface, typical which is unavoidable for this kind of analytes, could be easily overcome by irradiating the device with UVA-light, which restored the initial sensor sensitivity. This feature allows the possibility to reactivate the sensor on site, i.e. directly in solution, to yield a system capable of working in continuous, able to be used in an integrated monitoring system.
References
[1] G. Soliveri, V. Pifferi, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, K. Sparnacci, L. Falciola, Analyst 140, 2015, pp 1486 – 1494.
[2] V. Pifferi, G. Soliveri, G. Panzarasa, S. Ardizzone, G. Cappelletti, D. Meroni, L. Falciola, RSC Advances 5, 2015, pp 71210 – 71214.
[3] O. S. Ivanova, F. P. Zamborini, J. Am. Chem. Soc. 132, 2010, pp 70–72.
[4] G. Chang, J. Zhang, M. Oyama, K. Hirao, J. Phys. Chem. B 109, 2005, pp 1204-1209.
[5] S.E. Ward Jones, F.W. Campbell, R. Baron, L. Xiao, R.G. Compton, J. Phys. Chem. C 112, 2008, pp 17820–17827.
[6] G. Kresse, D. Joubert, Phys. Rev. B: Condens. Matter 59, 1999, pp 1758−1775.
[7] W. Tang, E. Sanville, and G. Henkelman, J. Phys. Condens. Matter 2009, 21, 084204.
Acknowledgements
This work has been supported by Fondazione Cariplo (Milano, Italy), grant no. 2014-1285. We acknowledge the CINECA and the Regione Lombardia award under the LISA initiative (grant SURGREEN) for the availability of high performance computing resources. We also thank the Chemistry Department for funding through the Development Plan of Athenaeum grant – line B1 (UNIAGI 17777)
PATTERNING AND MODULATION OF OXIDE SURFACE PROPERTIES
Full text linkMost of the topics dealt with in this thesis belong to surface science. The starting point was the fundamental understanding of phenomena at the oxide-gas interface and the effect of its modification. Such knowhow was then used to solve (or, at least, to attempt to solve) issues of critical impact in everyday life: the increasing lifetime of building materials employed in low-impact smart houses; the fouling prevention in electroanalytical sensors for neurotransmitter detection; the unspecialized laboratories accessibility to microlithography, critical to device miniaturization. These challenges might seem not related, but they actually share deep scientific and technological foundations. The physicochemical modification of oxide surfaces, the creation of organic/inorganic hybrids and the exploiting / the enhancing of semiconductor peculiar properties allowed us, starting from the foundation, the realization of proof-of-concept protocols and devices, ready for the pre-commercial development.
The Leitmotif of my research was the synthesis and the modification of titanium dioxide surfaces. TiO2 has been the main character in physico, physicochemical and material science researches of the last 50 years. Biocompatibility and low cost make it engaging for many applications. Its (near-UV active) semiconductor features, well known and abundantly investigated by the scientific community, are acquiring central interest also in many markets with the development of self cleaning coatings, windows and asphalts, anti-fogging mirrors and self-sterilizing surgery rooms and instrumentations. New generation batteries and solar cells are going to be developed as commercial prototypes. One of the biggest challenges in the titania fundamental research is the enhancement of activity in the solar spectrum. First, the most recent aspects in titania doping and promotion were touched. While, in the last twenty years, great effort has been made in the mono-atomic doping of titania and in the understanding of the influence of the dopant position in the titania lattice and its electronic behavior, the most recent literature describes the co-promotion of the material by two (or more) atoms doping. The metal/non-metal codoping seems especially promising; the synergetic effect of the two atoms in the TiO2 lattice was both theoretically and experimentally proved. In this contest, the N/Nb codoping was analyzed, investigating the effect of the atoms in the lattice from morphological (surface area, porosity and crystallographic structure) and electronic point of view (EXAFS, UV-Vis absorption and EPR analyses). N/Nb codoping was compared with N/Ta co-doped samples, synthesized by two different procedures. The photoactivity of the two sample families was tested by a model reaction (the degradation of ethanol, throughout acetaldehyde intermediate) both under UV and solar simulated irradiation.
Then, a different approach in the modification of surfaces was tested. The assembly of organic/inorganic hybrids was tested; thanks to the formation of organic mono- or multi-layers at the surface,they can tune the chemistry, the polarity and the adhesion properties of the interface. Siloxanes were used as active agents, thanks to their compatibility with oxide materials and, especially, for the ability to self-assemble at the surface to form a monolayer. Siloxanes are able to react with the -OH groups at the surface, chemisorbing and polymerizing at the interface in such a way to form a monolayer with tunable functionalities. Many different silanes were tested and their dipole momenta were related to their wettability properties. Such siloxanes chemisorb strongly both from the gas phase and the liquid phase. Their reactivity, both on smooth and rough surfaces, was tested vs the temperature of functionalization in gas phase. Many characterization techniques were adopted to understand the behavior of such molecules from a molecular point of view: magnetic (solid state NMR), microscopic (SEM, TEM, AFM), optical and electrochemical (CV and EIS). The science of adhesion and wettability was also adopted for the development of superhydrophobic coatings. Titanium dioxide particles with engineered morphology were used as the best candidate to create superhydrophobic/superhydrophilic patch-wise surfaces, exploiting their photoactivity (photolithograpy).
The core of the thesis was the synthesis, modification and application of transparent photoactive thin films. A procedure for the synthesis of smooth, transparent and photoactive TiO2 thin layers was developed, and used to produce highly applicative devices and protocols. Such synthetic strategy is highly tunable and reproducible; the obtained films are robust and active and, most of all, require simple instrumentation (sol-gel procedure), which is highly appealing for the market. The films were properly characterized both form the morphological/mechanical and photochemical point of view. Apart their transparency and their thickness, the films were highly crystalline (pure anatase phase). Such procedure was firstly designed as a proof-of-concept for self-cleaning windows, but, thanks to its versatility and the high activity of the films, it leads the path towards highly applicative procedures and devices. The smoothness and the photoactivity brought me to the field of photolithograpy, especially in the direction of microlithography. The high activity of the titania allowed the use of safe and low-energetic lamps. No collimation was required to obtain a resolution lower than 5 μm. First of all, I tested the lithography on siloxane monolayer films, as a proof-of-concept of resolution and efficiency. But siloxanes, as many other self-assembled monolayer molecules, can be the pillars for 3D fabrication. Such monolayers were used as polymerization initiators for polymer brushes. If the initiators of polymerization are patterned, patterned polymer brushes will be obtained. That was the first report of polymer-brushes lithography exploiting the photoactivity of TiO2. Remote photocatalytic lithography makes this procedure extremely versatile. Exploiting the remote photocatalysis, in principle, any material can be used as a support for patterned polymer brushes growth (provided that the initiator are able to graft the surface).
The developed protocol for the synthesis of TiO2 thin films was also used to design and engineer complex electrodes for cyclovoltammetric analyses of biological samples. Electrochemistry seems to be the best candidate for the development of an analytical option with sensitivity comparable with present analytical procedures but reduced time-per-analysis and cost. Unfortunately, catecholamines chemisorb and polymerize on metal and oxide electrodes quickly, making the device useless. Covering the electrode by a homogeneous, nano-porous thin layer of titania makes the surface photoactive. That is the first example in literature of self-cleaning nano-engineered electrodes for cyclic voltammetry. After the detection, also in simulated human serum and liquor, a fast and simple irradiation of the device, under non-hazardous UV-A lamp, degrades all the fouling on the surface without altering its features. The sensor, after each UV treatment, recovers its pristine performances, with full recovery in terms of selectivity and sensitivity. Irradiation trials were also performed directly in the analytical mixture, as a proof of concept for on-site application.
Modern era requires flexible and light materials for the building industry. Polymers are acquiring more and more interest thanks to their increasing performances and their smart properties. The drawbacks of such materials are connected to the low resistance to the UV light, the softness and the difficulties in cleaning procedure. The use of organic/inorganic hybrid, or better the coverage of plastic materials with an oxidic thin layer, can solve many of these problems, lengthening the lifetime of such materials. If the covering oxide is also photoactive, the material can be self-cleaned when exposed to solar light. That is a big chemical challenge, because of many synthetic problems. Two different approaches were tested to solve this relevant issue. On one side, the hydrophobicity of ionic liquid modified SPES (sulfonated polyether sulfone) was combined with designed morphological features to confer superhydrophobicity. On the other side, the polymeric surface was covered with a transparent titania layer active in the near UV-region, able to mineralize organic molecules chemisorbed at the surface.
Eventually, a different approach to modify oxidic (and not only) surfaces is the creation of a homogeneous layer of Ag nanoparticles by an innovative microwave procedure. That simple and accessible strategy allowed us to produce plasmonic surfaces (thanks to the dimension and the homogeneity of the Ag particles) with countless applications. The layer was shown to be a very active substrate for surface enhancement Raman spectroscopy (SERS). Thanks to the versatility of the synthetic method, all shapes and dimensions can be covered. That makes it a perfect candidate for the production of new generation of SERS sensors. The sensitivity towards molecules of environmental and biomedical interest was proved
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